International Journal of Hypertension

International Journal of Hypertension / 2013 / Article
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Brain RAS: Hypertension and Beyond

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Research Article | Open Access

Volume 2013 |Article ID 175428 | https://doi.org/10.1155/2013/175428

Courtney Premer, Courtney Lamondin, Ann Mitzey, Robert C. Speth, Mark S. Brownfield, "Immunohistochemical Localization of , , and Angiotensin II Receptor Subtypes in the Rat Adrenal, Pituitary, and Brain with a Perspective Commentary", International Journal of Hypertension, vol. 2013, Article ID 175428, 22 pages, 2013. https://doi.org/10.1155/2013/175428

Immunohistochemical Localization of , , and Angiotensin II Receptor Subtypes in the Rat Adrenal, Pituitary, and Brain with a Perspective Commentary

Academic Editor: Patrick Vanderheyden
Received31 Oct 2012
Revised01 Feb 2013
Accepted05 Feb 2013
Published19 Mar 2013

Abstract

Angiotensin II increases blood pressure and stimulates thirst and sodium appetite in the brain. It also stimulates secretion of aldosterone from the adrenal zona glomerulosa and epinephrine from the adrenal medulla. The rat has 3 subtypes of angiotensin II receptors: , , and AT2. mRNAs for all three subtypes occur in the adrenal and brain. To immunohistochemically differentiate these receptor subtypes, rabbits were immunized with C-terminal fragments of these subtypes to generate receptor subtype-specific antibodies. Immunofluorescence revealed and AT2 receptors in adrenal zona glomerulosa and medulla. immunofluorescence was present in the zona glomerulosa, but not the medulla. Ultrastructural immunogold labeling for the receptor in glomerulosa and medullary cells localized it to plasma membrane, endocytic vesicles, multivesicular bodies, and the nucleus. and AT2, but not , immunofluorescence was observed in the anterior pituitary. Stellate cells were positive while ovoid cells were AT2 positive. In the brain, neurons were , , and AT2 positive, but glia was only positive. Highest levels of , , and AT2 receptor immunofluorescence were in the subfornical organ, median eminence, area postrema, paraventricular nucleus, and solitary tract nucleus. These studies complement those employing different techniques to characterize Ang II receptors.

1. Introduction

The ability of angiotensins II (Ang II) and III (Ang III) to stimulate aldosterone [1, 2] and epinephrine [3] release from the adrenal gland is well established. The central nervous system and adenohypophyseal effects of these peptides are also well documented and numerous. While the effects of Ang II on the adrenal are thought to arise primarily from blood-borne Ang II, it is clear that there is a local brain angiotensinergic system as illustrated by biochemical, immunohistochemical, behavioral, physiological, and receptor binding studies [48] and reviews [911]. The anterior pituitary also appears to be subject to both blood-borne and local angiotensinergic systems, as well as receiving indirect regulatory signals from brain angiotensinergic activity [12, 13].

In mammals, there are two primary Ang II receptor subtypes, AT1 and AT2 [1419]. With the discovery of these multiple subtypes of Ang II receptors, pharmacological studies revealed that the AT1 subtype mediated both aldosterone [20] and epinephrine [21] release as well as pressor [22, 23], dipsogenic [2224], and sodium appetite [2426] responses to Ang II. The localization of AT1 receptors in the rat brain regions mediating pressor and dipsogenic actions of Ang II, such as the subfornical organ (SFO), median preoptic nucleus (MnPO), organum vasculosum of the lamina terminalis (OVLT) paraventricular nucleus of the hypothalamus (PVN), nucleus of the solitary tract (NTS), and area postrema [2729] is consistent with this role. In contrast, AT2 receptors tend to be distributed in sensory, motor, and emotional regions of the brain, for example, superior colliculus, medial geniculate nucleus, locus coeruleus, lateral septum, medial amygdala, subthalamic nucleus, and inferior olivary nucleus [2729]. It has been suggested that the medial amygdala can mediate salt appetite [30], but beyond that, the functional significance of the AT2 in the brain and the adrenal has not been established.

The subsequent discovery that rodents express two subtypes or isoforms of the AT1 receptor, and , [3133] raises the question as to which of these two subtypes may be mediating adrenal hormone release and the physiological effects of Ang II in the brain and pituitary. Pharmacological studies of the ability of angiotensins and AT1 receptor-selective antagonists to bind to the and receptor subtypes reveal little difference in their affinities for these two subtypes [3437].

PCR amplification of and mRNA in female rat adrenal, lung, vascular smooth muscle, pituitary, and brain indicated that the subtype mRNA was predominant in the lung, vascular smooth muscle, and hypothalamus, while the subtype was predominant in the adrenal, pituitary, subfornical organ, and organum vasculosum of the lamina terminalis [31, 38]. Both PCR amplification [31, 35, 3840] and in situ hybridization [39, 41, 42] have been used to compare the expression of mRNA for these two subtypes in the adrenal and brain. However, the expression of mRNA does not always correspond with the expression of the protein it encodes. For example, estrogen treatment can reduce AT1 receptor expression without altering AT1 mRNA expression presumably via posttranscriptional inhibition of mRNA translation [43]. Moreover, in neuronal tissues, the receptors may be expressed on axonal terminals distant from their perikaryal mRNA.

Studies of and mRNA expression in the adrenal indicate that the subtype mRNA is predominant in the rat adrenal [35, 38, 39, 44], but that it is absent in the adrenal medulla [4446]. Studies of and mRNA in rodent brain vary considerably along a continuum from a predominance of expression in the female rat brain [31], to a moderate predominance of in the male mouse brain [40, 42], a differential distribution of the mRNAs in a two-week-old male rat brain [45], to very low expression of mRNA in the adult male rat brain [41], and to no expression of mRNA in rat brain [47]. In comprehensive studies of the distribution of and mRNA the rat brain and pituitary [41], the mRNA was found to be highly expressed in brain regions reported to mediate cardiovascular effects of Ang II, while expression was very low in these regions. Conversely, mRNA was very high in the anterior pituitary while mRNA was low.

To determine if the distribution of , and AT2 receptor subtype protein in the rat adrenal, pituitary, and brain corresponds to the distribution of the mRNAs for these subtypes, this study uses fluorescence immunohistochemistry with antibodies directed at unique peptide fragments of each of these three subtypes to localize these receptors.

2. Materials and Methods

2.1. Antibody Preparation

Antipeptide antibodies were generated against fragments of rat , and AT2 receptors. Peptides candidates were selected by computer analysis of full length receptors retrieved from the NCBI protein database (http://www.ncbi.nlm.nih.gov/protein) and by Hopp-Woods analysis [48] for optimal antigenicity. Peptides corresponding to receptor fragments near the carboxy terminal tail of the receptor subtypes where there is a 2 amino acid difference were synthesized by solid phase peptide synthesis. For the receptor, the peptide was PSDNMSSSAKKPASC, which corresponds to amino acids 341–355 of this 359 amino acid protein. For the receptor, the peptide was SSSAKKSASFFEVE, which corresponds to amino acids 346–359 of this 359 amino acid protein. For the AT2 receptor, the peptide was CRKSSSLREMETFVS, which corresponds to amino acids 349–363 of this 363 amino acid protein (except that it contained a glutamic acid in position 358 versus an aspartic acid). The peptides were compared with the protein database (http://blast.ncbi.nlm.nih.gov/Blast.cgi) to establish the uniqueness of the peptide sequences from other known proteins.

Peptides were conjugated to keyhole limpet hemocyanin (KLH) and injected into rabbits at approximately monthly intervals for 6 months. Serum was obtained from the rabbits and affinity purified. To obtain -selective antibodies, serum from rabbits immunized with the peptide corresponding to the receptor subtype was affinity purified using chromatography resin cross-linked with the peptide. Antibodies retained by this resin were eluted with a high salt solution and the eluate was then applied to an affinity column made by cross-linking the receptor peptide antigen to chromatography resin. Antibody that was not retained by the resin was denoted as receptor selective. Antibody that was retained by both the and resins was defined as nonselective for or -receptors. A similar strategy was used to derive selective antibodies except that serum from rabbits immunized with the peptide corresponding to the receptor subtype was affinity purified using chromatography resin cross-linked with the peptide initially. Antibodies retained by the resin were subsequently applied to the resin. Antibodies retained by the , but not the resin, were classified as selective. AT2 receptor antibodies were affinity purified using chromatography resin cross-linked with the AT2 receptor peptide used to generate the antibody. Antibodies retained by the AT2 resin were eluted with high salt solution and classified as AT2 selective.

2.2. Animals

Adult male Sprague-Dawley rats (225–300 g body weight; Harlan, Sprague Dawley) were kept in an AAALAC approved vivarium (12 : 12 Light : Dark). Standard lab chow and water were available ad lib. Animals were kept in the vivarium for at least two weeks prior to use and were housed two per cage. All procedures were approved by the University of Wisconsin, School of Veterinary Medicine Animal Care Committee.

2.3. Western Immunoblotting

Fresh or frozen, whole or dissected rat adrenals ( ) were employed. A 2 mm slab was cut from the center of the adrenal and the medulla was removed by punch. The cortex was dissected away from the medulla. Tissues were homogenized in one complete mini protease inhibitor tablet (Roche, Indianapolis, IN) dissolved in 7 mL of RIPA buffer (Millipore, Billerica, MD). Lysates were sonicated for 5 minutes and cleared of debris by centrifugation at 15000 rpm for 20 minutes. Samples were normalized so as to amount of protein present via BCA assay (Thermo Scientific, Rockford, IL).

Samples were dissolved 1 : 1 in loading buffer with beta mercaptoethanol and boiled at 95°C for 4 minutes before loading. Proteins were separated via SDS-PAGE and transferred to PDVF membrane (Bio-Rad, Hercules, CA). Transfer conditions were wet (1 hour at 100 volts). Membranes were incubated for one hour in tris buffered saline containing 0.05% tween-20 (TBST), 5% powdered milk, and 1% bovine serum albumin. Blots were incubated in primary antibodies overnight at 4°C. Primary antibodies (Table 1) were diluted in TBST with 0.2% NaN3 as a preservative. Blots were incubated in secondary antibody for 45 minutes. Secondary antibody goat anti-rabbit HRP (KPL, Gaithersburg, MD) was diluted 1 : 100,000 in 20 mL TBST with 2 uL streptavidin HRP (Sigma Aldrich, St Louis, MO). Developing solutions used in this study were LumiGLO immunoblotting reagent (KPL) and Supersignal West Pico Substrate (Thermo Scientific).


RegionAT1aAT1b AT2

Neocortex
  Lamina I-II ND0+/5*1+/1*
  Lamina III-IV ND 4+/5*0+/4*
  Lamina V-VI ND 4+/4*3+/3*
Basal (Anterior) Forebrain
  Entorhinal cortex 2+/0*0+/0*5+/1*
Hippocampus
  CA11+/0*ND 4+/5*
  CA3 1+/0*ND 5+/5*
  Dentate Gyrus ND ND 2+/2*
Central Amygdala 1+/0*ND 4+/3*
Caudate nucleus 3+/1*1+/0*5+/3*
Thalamus
Medial Dorsal Thalamus 0+/0*0+/0*5+/2*
Periventricular nucleus of the thalamus 0+/0*0+/0*3+/5*
Medial Habenula 1+/0*0+/0*5+/3*
Lateral Habenula 0+/0*0+/0*0+/0*
Septal Area
  Dorsal Median preoptic nucleus2+/3*3+/4*4+/5*
  Medial Septum 0+/0*0+/0*0+/2*
  Lateral Septum 2+/1*1+/1*2+/0*
Hypothalamus
  Anterior Hypothalamic Area 2+/3*1+/1*3+/4*
  Lateral Hypothalamic Area 3+/2+4+/5*3+/0*
  Paraventricular nucleus 4+/0*5+/5*5+/3*
  Periventricular area 3+/0*2+/5 5+/0*
  Suprachiasmatic nucleus 1+/0*0+/0*2+/5*
  Arcuate nucleus 5+/4*5+/5*4+/0*
Circumventricular Organs/Pituitary
  Median Eminence 0+/2*0+/3*0+/4+
  Subfornical Organ 4+/5*0+/2*3+/5*
  Area Postrema 3+/0*4+/4*3+/4*
  Posterior Pituitary (pars nervosa) 0+/3*0+/2*ND
  Anterior Pituitary (pars distalis) 0+/0*5+/0*5+/0*
  Stellate cells0+/0*5+/0*1+/0*
  Ovoid cells0+/0*1+/0*4+/0*
Cerebellum
  Purkinje Cells 0+/0*5+/5*ND
Hindbrain
  RVLM 4+/2*2+/2*ND
  NTS 3+/4*5+/2*3+/4*

Key: +refers to neuronal cell bodies/*refers to fibers. Scored on a scale from 0 to 5. ND is not determined. No AT1a immunoreactivity was observed in glia. AT1b and AT2 immunoreactivity were observed in glia.
2.4. Tissue Preparation

Rats were deeply anesthetized with isoflurane or pentobarbital (65 mg/kg IP) and perfused intracardially with physiological flush solution (Tyrode’s solution) containing heparin and procaine followed by histological fixative (4% paraformaldehyde with 0.05% glutaraldehyde in 0.1 M sodium phosphate, pH 7.5). Brains, pituitaries, and adrenals were removed and immersion fixed at 4°C in the same solution overnight and then stored in saline until sectioning at 50 micron thickness for immunofluorescence microscopy using a Lancer vibratome.

2.5. Immunofluorescence Histochemistry

Adrenals, pituitaries, and brains from 12 rats were used for these studies. Initially all antibodies were screened at dilutions of 1 : 100 to 1 : 10,0000 in ICC buffer (PBS with 0.25% gelatin, 2% normal goat serum 0.1% thimerosal, and 0.05% neomycin) to determine working dilutions demonstrating the highest signal and lowest background signal for each tissue. Working dilutions of angiotensin II receptor antibodies were (1 : 500) primary antibody ( ) and 1 : 2000 AT2 for 18–72 hours at 4°C. Control sections were incubated with primary antibodies incubated with an excess of the antigenic peptides (20 μg/mL of antigenic peptide at the working dilution). Also antibodies were immunoprecipitated from their working dilutions by incubation with 100 μL , or AT2 affinity gels and then the supernatant was used in place of the antibody solution. Sections were then incubated with Cy3-labeled goat anti-rabbit IgG and then mounted onto poly-L-lysine slides. Slides were viewed and analyzed utilizing a Nikon Eclipse E600 epifluorescence microscope with UV illumination, and a digital camera (Spot RT, Diagnostic Products).

2.6. Immunoelectron Microscopy

Adrenals from 7 rats were used for ultrastructural immunocytochemistry ( rats for immunogold detection and rats for peroxidase. For both methods, rats were perfused as described above and postfixed for 24 hours in 4% paraformaldehyde with 0.1% glutaraldehyde, washed in PBS and vibratome sectioned at 50 micron thickness. The sections were incubated in 0.1% sodium borohydride 15 minutes, permeabilized in 0.05% triton for one hour, and blocked in either 0.5% BSAc (Aurion, Arnhem, Gelderland, The Netherlands) for one hour for immunogold detection or ICC buffer for immunoperoxidase detection prior to overnight exposure to primary antibody. The primary antibody dilution for receptors was 1 : 500 for both immunogold and immunoperoxidase.

For the immunogold method antibody-labeled receptor was detected using ultrasmall gold (Aurion, 0.8 nanometer average size) diluted 1 : 100 in phosphate buffer and incubated overnight. Tissues were then postfixed in 2.5% glutaraldehyde for 30 minutes. The immunological signal was silver intensified by incubation in R-Gent SE-EM (Aurion) for one hour. For immunoperoxidase detection antibody-bound receptor was incubated with peroxidase labeled goat anti-rabbit IgG-Fab (1 : 250 overnight in the refrigerator). Peroxidase signal was visualized by incubation in diaminobenzidine (30 mg %) and hydrogen peroxide (0.01%) for 10 minutes in 0.1 M Tris HCL, pH 7.5. Then both immunogold and immunoperoxidase sections were rinsed in 0.1 M sodium phosphate buffer, fixed with osmium, dehydrated through an alcohol series to propylene oxide, and flat embedded in EMBED 812 resin (Electron Microscopy Sciences, Hatfield, PA).

Ultrathin sections were cut and adsorbed to grids coated with Formvar film (Electron Microscopy Sciences), and contrasted with uranyl acetate and lead citrate. All samples were examined and photographed with a Philips CM 120 STEM electron microscope and a Megaview 3 SIs digital camera (Olympus, Munster, Westphalia, Germany) in combination with the software program iTEM (Olympus) at the University of Wisconsin Madison Electron Microscope Facility.

3. Results

Western blotting of protein extracts of the adrenal with the 3 antibodies revealed primary ~69, ~75, and ~71 kD bands for the , and AT2 receptors, respectively, with secondary bands of ~116, ~126, and ~119, respectively (Figure 1). This suggests that the solubilized receptor was glycosylated since the theoretical molecular weights of the deglycosylated receptors are 40759 Daltons for the , 40781 Daltons for the , and 41200 Daltons for the AT2 receptor. The secondary bands most likely represent dimerized receptors or receptor-protein complexes.

Immunofluorescent staining of the adrenal with the 3 antibodies gave differing discrete staining patterns in the adrenal. Using a working dilution of 1 : 500 , immunoreactivity was seen in both the adrenal medulla and the zona glomerulosa (Figures 2(a), 2(d), and 2(g)). The staining was primarily cytoplasmic in both regions, although in the medulla, localization to the cell membrane is apparent in some cells (Figure 2(g)). immunoreactivity was present in abundance in the zona glomerulosa of the adrenal (Figures 2(b) and 2(e)). The immunofluorescence was primarily localized to the cell membrane (Figure 2(e)). Weak immunoreactivity was also present in the zona reticulata (Figure 2(e)). immunostaining was nearly nonexistent in the medulla (Figure 2(h)).

AT2 immunoreactivity was abundantly present in both the adrenal medulla and the zona glomerulosa (Figures 2(c), 2(f), and 2(i)). The AT2 immunofluorescence was also primarily cytoplasmic although a plasma membrane localization was seen in many medullary cells (Figure 2(i)). No immunofluorescent signal was seen in any sections incubated with the antigenic peptide preadsorbed antibodies (not shown).

Immunoelectron microscopic analysis of the subcellular localization of receptors in the zona glomerulosa and medulla is shown in Figure 3. Both cell membrane and cytoplasmic labeling for receptors was seen in these cells. receptor immunogold labeling of endocytic vesicles and mature multivesicular vesicular bodies was seen in glomerulosa cells (Figures 3(b) and 3(c)) and immunoperoxidase labeling of cell membrane and newly forming endocytic vesicles was seen in medullary cells (Figure 3(e)). Intranuclear receptor immunogold staining was observed in cells of the zona glomerulosa. However, receptor-immunogold staining was not evident in mitochondria or endoplasmic reticulum of either glomerulosa or medullary cells.

immunoreactivity was observed in the pars distalis of the anterior pituitary. It was primarily localized to stellate cells, but significant numbers of ovoid cells were also immunopositive. By contrast, immunoreactivity was not observed in the pituitary (Figure 4). AT2 receptor immunoreactivity also was observed in the pars distalis of the anterior pituitary, primarily in ovoid cells. and receptor immunoreactivity was observed on nerve fibers in the posterior pituitary (Table 1). No Ang II receptor immunoreactivity was observed in the intermediate lobe of the pituitary.

In sections from the brain, neurons were immunopositive for all three receptors, but glial cells showing astrocytic (and microglial, Figure 4 center panel) characteristics were immunopositive only for . Immunoreactivity for all three angiotensin receptor subtypes was present in abundance in brain regions reported to have high angiotensin receptor density by ligand binding studies and other immunohistochemistry studies (Figures 47, Table 1). These regions include the SFO, median eminence, PVN, NTS, and area postrema (Figures 4 and 5, Table 1). In all five of these locations, we demonstrated the presence of all three receptors, although their distribution within each region was not identical (Table 1). Of note, receptor immunoreactivity was present in the magnocellular division of the PVN while AT2 receptor immunoreactivity was present in the supraoptic nucleus (SON) (Figure 5). AT2 receptors were more widely distributed than and receptors in the brain, and their immunoreactivity was found in every region in which AT1 receptor immunoreactivity was observed (Table 1). AT2 receptor immunoreactivity was found exclusively in the amygdala, piriform cortex, thalamus, and medial epithalamus (Figures 5 and 6, Table 1).

Angiotensin II receptor immunoreactivity also was found in rat brain regions generally reported to have low expression of Ang II receptors. These include neurons in the cerebral cortex ( and AT2), hippocampus ( and AT2), caudate nucleus ( and AT2), and SON (AT2) (Figure 5).

4. Discussion

4.1. Antibody Development Strategy

The results of these studies unequivocally demonstrate a differential distribution of , and AT2 receptor immunostaining. This was accomplished by precise epitope targeting within the C-terminus of each receptor, selective antipeptide affinity chromatographic purification methods, Western blotting, and tissue specificity studies in adrenal and pituitary where the distribution of these AT receptor-expressing cells has been established by in situ hybridization and receptor binding studies.

The initial identification of the two subtypes of AT1 Ang II receptors in rodents demonstrated the presence of mRNA for both the and subtype in the rat adrenals [32, 38, 49]. The AT1b was identified as the predominant AT1 receptor subtype in the rat adrenal based on mRNA expression [38, 49]. While these initial observations have been confirmed in the rat adrenal [50, 51], the is considered to be the predominant AT1 receptor subtype in all other rat tissues except the anterior pituitary based on mRNA expression [38, 52].

It is important to be able to discriminate and receptor protein expression, because their mRNAs are differentially regulated [31, 39, 49, 5254]. Furthermore, it is important to determine if the changes in mRNA expression translate into changes in expression of these receptor subtypes, because mRNA expression does not always correlate with protein expression. For example, in the kidney losartan increases receptor mRNA expression, but decreases AT1 receptor binding [55]. The existence of miRNAs for angiotensin receptors, for example, miR-155 [56] further erodes the value of mRNA levels as indicators of angiotensin receptor protein expression. Functionality of the subtypes may also differ; and can stimulate aldosterone release, while , but not , can stimulate corticosterone release in the mouse adrenal [57].

In view of the near identical pharmacological characteristics of the and receptor subtypes [3436], the only way to discriminate these two proteins is to exploit immunological differences arising from differences in their amino acid sequences. While the receptor (accession no. P25095 http://www.ncbi.nlm.nih.gov/protein/113493 (accessed 16 March 2012) and receptor (accession no. NP 112271) http://www.ncbi.nlm.nih.gov/protein/82524858NP112271 (accessed 16 March 2012) subtypes are encoded by separate genes, they are ~95% identical and are both made up of 359 amino acids [33, 38]. Thus there are only a few regions of these receptors where they differ substantially in amino acid sequence. One of these regions, near the carboxy terminus of the receptor proteins (amino acids 352 to 355), has 2 different amino acids in this 4 amino acid stretch. The closest similarities to the sequences of the AT1 antigenic peptides in the protein database (Protein Blast) http://blast.ncbi.nlm.nih.gov/Blast.cgi?PROGRAM=blastp&BLASTPROGRAMS=blastp&PAGETYPE=BlastSearch&SHOWDEFAULTS=on&LINKLOC=blasthome, accessed on February 4, 2013) were the serotonin 5 HT2b subtype with a 7 amino acid identity to the peptide fragment (score = 24.0 bits) and sestrin 1 with a 7 amino acid identity to the peptide fragment (score = 24.4 bits).

To generate an antibody to the AT2 receptor, a similar strategy was applied. A C-terminal domain peptide of 15 amino acids (resembling amino acids 349 to 363) was used as the antigen. The sequence of the AT2 receptor (accession no. P35351, http://www.ncbi.nlm.nih.gov/protein/543780 accessed on February 4, 2013) has negligible homology with either of the AT1 receptor subtypes. The closest similarity to this peptide sequence was an immunoglobulin kappa chain (AAA41415.1) with an 8 amino acid identity to the AT2 peptide fragment (score = 27.4 bits compared to 49.0 bits for the AT2 receptor).

4.2. Adrenal AT Receptor Subtype Localization

The presence of , and AT2 angiotensin receptor subtype immunoreactivity in the rat adrenal was clearly demonstrated in this study. and AT2 receptor subtype immunoreactivities were found in both the zona glomerulosa and medulla, which is consistent with receptor binding studies [37, 5861] and mRNA studies [44, 6164]. receptor was not observed in the adrenal medulla, but was present in the zona glomerulosa. This is consistent with in situ hybridization studies of the distribution of mRNA in the adrenal [39, 44, 46, 54].

Other studies of the localization of Ang II receptor subtype immunoreactivity in the adrenal have given mixed and controversial results. Paxton et al. [65] observed AT1 receptor immunoreactivity in the zona glomerulosa of the rat adrenal with an antibody prepared against amino acids 15–24 of the rat and receptor. However, they did not observe any AT1 receptor immunoreactivity in the adrenal medulla. Similarly, Lehoux et al. [66] observed AT1 immunoreactivity in the zona glomerulosa of the rat adrenal cortex, but not in the medulla using an antibody raised against amino acids 306–359 of the human AT1 receptor subtype. Of note, adrenals from rats kept on a low sodium diet displayed AT1 immunoreactivity in other cortical zones (fasciculata and reticularis). The lack of adrenomedullary staining with this human antibody suggests that it may only recognize the sequence in the rat. Giles et al. [67] observed AT1 immunoreactivity and AT1 mRNA in the zona glomerulosa of rat adrenals using an antibody directed against amino acids 350–359 of the rat subtype plus a small amount of immunoreactivity in the zona fasciculata. However, there was no mention of AT1 immunoreactivity or mRNA in the adrenal medulla.

Frei et al. [68] observed AT1 immunoreactivity in the rat adrenal cortex and medulla using a monoclonal antibody raised against amino acids 229–246 of the human AT1 receptor subtype. Yet, AT2 immunoreactivity was only observed in the rat adrenal medulla using an antibody raised against amino acids 314–330 of the human AT2 receptor subtype. On the other hand, Harada et al. [63] observed AT2 receptor immunoreactivity in immunoblots of the rat adrenal cortex, but not in the medulla using two different antibodies—one raised against amino acids 21–35 of the rat AT2 receptor and one raised against amino acids 221–363 of the human AT2 receptor. However, they did detect a low level of AT2 receptor-like immunoreactivity in the medulla using the latter antibody for immunohistochemical analysis. Conversely, Yiu et al. [69] reported AT2 immunoreactivity only in the rat adrenal medulla using an antibody directed against amino acids 341–351 of the rat AT2 subtype. Notably, they reported that this antibody failed to label brain regions known to express AT2 receptors. Reagan et al. [70] were unable to demonstrate any AT2 receptor immunoreactivity in the rat adrenal using a polyclonal antibody developed to recognize AT2 receptors in N1E-115 cells.

4.3. Subcellular Localization of AT1 Receptors

Localization of immunofluorescence for all three angiotensin receptor subtypes to the cell membrane as well as the cytoplasm in the adrenal is consistent with the behavior of other G protein coupled receptors that are functionally expressed on cell membranes but undergo receptor-mediated internalization [71]. The electron microscopic localization of immunoreactivity to putative developing endosomes still in contact with the cell membrane (Figure 3(e)) is consistent with receptor mediated endocytosis as the mechanism of angiotensin receptor internalization [72]. In addition, there is now a considerable body of evidence supporting the existence of an intracellular RAS which signals via AT1 receptors [73].

Noteworthy in our study is the nuclear localization of adrenal receptors. The ability of G protein coupled receptors to localize and signal directly to the cell nucleus is firmly established [74] and likely includes angiotensin receptors. Beginning with the electron microscopic studies localizing 3H-Ang II to myocardial cell nuclei [75], it has been suspected that Ang II receptors are present in cell nuclei. The existence of nuclear Ang II receptors was subsequently documented in isolated hepatic nuclei by Re and Parab [76] who showed that Ang II increased RNA polymerase II activity, increasing RNA synthesis. Notably, they used 4 mM dithiothreitol an inhibitor of Ang II binding to AT1 receptors [77], suggesting that the Ang II effect might be mediated by AT2 receptors. Eggena et al. [78] showed that AT1 receptor subtype binding was present in rat hepatic cell nuclei and that Ang II could specifically induce transcription of mRNA for renin and angiotensinogen in isolated rat liver nuclei. Moreover, hepatic nuclear AT1 receptor binding and functionality could be dynamically regulated by adrenalectomy and nephrectomy [79]. Re et al. [80] and Eggena et al. [79] reported that nuclear Ang II receptor binding was associated with nuclear chromatin. Of note, Re et al. [80] observed 125I-Ang II binding to nuclear chromatin in the presence of 5 mM dithiothreitol, again suggesting that 125I-Ang II may be binding to AT2 receptors [15, 77]. The relative abundance of binding within the nucleus, but not the nuclear membrane of the glomerulosa cells in this study, is consistent with localization to nuclear chromatin. AT1 receptor binding sites have also been identified in rat hepatocyte nuclear membranes by Booz et al. [81] and Tang et al. [82]. Interestingly, Tang et al. [82] determined that the majority of the AT1-like binding of Ang II in hepatocyte nuclei was bound to a soluble intranuclear protein. Licea et al. [83] demonstrated nuclear Ang II receptor binding in nuclei of rat renal cortex. Tadevosyan et al. [84] showed that Ang II could stimulate α-32P-UTP incorporation into RNA and increase NF-kappaB mRNA expression in isolated rat heart cardiomyocyte nuclei suggesting a nuclear site of action of Ang II.

Additional evidence supporting a nuclear localization of angiotensin receptors includes studies using an AT1 receptor-GFP fusion construct which translocates to the nucleus in Chinese hamster ovary cells [85] and human embryonic kidney (HEK-293) cells [86], as well as immunohistochemical studies showing colocalization of AT1 and AT2 immunoreactivity with the nuclear membrane markers nucleoporin-62 and histone-3 [84]. Moreover, the AT1 receptor contains a nuclear localization signal motif (KKFKK, 307-11) in its intracellular carboxy terminal tail [87], which promotes its translocation to the cell nucleus. Mutation of one amino acid in this motif (K307Q) in an r-GFP receptor construct prevents it from localizing to the nucleus of HEK293 cells [86]. Of note, both agonist induced [87] and agonist independent [71, 88] nuclear localization of AT1 receptors has been reported.

While there are no published reports of adrenal nuclear angiotensin receptor binding or function, Eggena et al. [78] reported preliminary data suggesting that Ang II could stimulate RNA transcription in isolated adrenal nuclei. In addition, Goodfriend and Peach [89] suggested that Ang III can act intracellularly in the zona glomerulosa to promote aldosterone production.

4.4. Pituitary AT Receptor Subtype Localization

Both and AT2 receptor immunoreactivities were present in high amounts in the anterior pituitary. As noted previously mRNA for receptors is abundant in the anterior pituitary, while mRNA is much less abundant and AT2 mRNA is not observed in the anterior pituitary [47, 90]. Autoradiography and radioligand binding studies have demonstrated a high density of Ang II receptors in the anterior pituitary [37, 9193]. This binding displays AT1 receptor characteristics, and little or no AT2 receptor binding has been observed [27, 94]. expression was highest in stellate cells, while AT2 expression was highest in ovoid cells. Both and immunoreactivity was present on nerve fibers in the posterior pituitary. The ability of Ang II to affect the release of pituitary hormones is well known [95]. There are no reports of Ang II receptor binding in the posterior pituitary of the rat, although there is one report of AT1 receptor-immunoreactivity in nerve fibers and cell bodies in the posterior pituitary [96] and one report of AT2 receptor-immunoreactivity in the posterior pituitary as well as in the vasopressinergic magnocellular division of the PVN and the SON [97]. mRNA studies indicate a predominance of the subtype in the anterior pituitary of the rat [38, 98100], with little or no and AT2 mRNA.

Many of the pituitary hormone-releasing effects of Ang II occur in the hypothalamus and those effects are discussed below. However, some of the pituitary hormone releasing of Ang II occur directly in the pituitary. Systemically administered Ang II stimulates vasopressin release from the posterior pituitary of the dog [101, 102]; however, this may not generalize to the rat. and receptors on nerve fibers in the rat posterior pituitary [96] could mediate these effects of Ang II, reminiscent of the mechanism whereby Ang II acts on sympathetic nerve terminals to stimulate norepinephrine release [103, 104].

Radioligand binding studies have revealed high levels of Ang II receptor binding in a lactotroph enriched pituitary preparation [105]. mRNA studies indicate that receptors appear most often on lactotrophs, being present on more than 50% of all lactotrophs [98]. The appearance of immunoreactivity in ovoid cells is consistent with these receptors being present on lactotrophs. It has been reported that mRNA is present in a somatotroph cell line [100]. Somatotrophs are also ovoid in shape and blood-borne Ang II can inhibit growth hormone release [106], although it has also been reported that Ang II synthesized by and released from lactotrophs can stimulate the release of growth hormone from somatotrophs, [107] suggesting that somatotrophs may have excitatory AT1 receptors and inhibitory AT2 receptors.

ACTH release from dissociated corticotrophs in the anterior pituitary is also stimulated by Ang II in vitro [108]. The stimulation decreases with supraphysiological estradiol exposure in vivo and correlates positively with reductions in Ang II receptor binding caused by in vivo supraphysiological estradiol exposure [108]. Autoradiographic studies of AT1 receptor binding in the anterior pituitary indicate that AT1 receptor binding varies with the estrous cycle and that exogenous estrogen decreases anterior pituitary AT1 receptor binding in ovariectomized rats [109]. mRNA for receptors in the anterior pituitary is also suppressed by estrogen treatment [38, 110]. The appearance of high levels of immunoreactivity in stellate cells in this study is consistent with these receptors being present on corticotrophs.

There is one report of AT2 receptor immunoreactivity in pituitary adenoma blood vessels in humans [96], leading to the hypothesis that AT2 receptors in could participate in tumor-induced angiogenesis.

4.5. Brain AT Receptor Subtype Localization

These studies describe a widespread distribution of , and AT2 receptor immunoreactivity throughout the rat brain. The receptors were expressed abundantly in a number of brain regions that constitute the cardiovascular regulatory circuits of the brain, as well as the noncardiovascular regulatory regions of the brain. There was considerable variation in the degree of expression of the receptors in different regions reminiscent of the profound differences in radioligand binding for Ang II receptors, particularly among the AT1 receptors. AT2 receptors displayed an unanticipated widespread distribution throughout the rat brain, which contrasts with their limited distribution as indicated by radioligand binding studies. While AT1 receptors are considered to play the predominant role of mediating the actions of Ang II in the brain, AT2 receptors are increasingly recognized as having an important role as physiological antagonists of AT1 receptor effects. The codistribution of AT1 and AT2 receptors in several brain regions as well as the adrenal is consistent with the concept of colocalization of these two subtypes in the same cells as counter regulators to each other at the cellular level as well as on an organismic level [111113].

The selective expression of receptors on astrocytes suggests that there is a cell-specific expression of Ang II receptor subtypes in the brain. Functional AT1 receptors are present in primary cultures of astroglia from rat brain [114], but questions have been raised as to whether this expression could reflect an altered phenotype of cultured cells not seen in situin a living brain [115]. In contrast, Füchtbauer et al. [116] observed AT1 immunoreactivity (Santa Cruz, sc-579, amino acids 306–359) in astrocytes of the outer molecular layer of the dentate gyrus of the mouse brain, but did not see AT1 immunoreactivity in the microglia. Of note, retinal astrocytes also express AT1 receptor immunoreactivity (Alomone, #AAR-011 amino acids 4–18) while amacrine cells in the rat retina display AT2 immunoreactivity (Alomone, no. AAR12, amino acids 21–35) [117]. These reports and our observations suggest that glia do express AT1 receptors and that they are of the subtype. Since astrocytes are the primary source of angiotensinogen in the brain, the receptor may play a role in regulating angiotensinogen in the brain.

The expression of receptor immunoreactivity on cells with the morphological characteristics of microglia suggests that this receptor subtype mediates the proinflammatory effects of Ang II. AT1 receptor antagonism blocks the activation of microglia in an animal model of brain inflammation [118]. Proinflammatory cytokine participation in the pressor actions of Ang II in the brain is reversible by AT1 antagonists [119, 120], suggesting that microglial AT1 receptors may play a role in blood pressure regulation as well as inflammation.

The concept of the presence of Ang II receptors in the brain was firmly established by the cross-perfusion studies of Bickerton and Buckley [121] showing that blood-borne Ang II had sympathoexcitatory effects mediated by the brain. Since that time, a multitude of methodological approaches have been used to map the distribution of Ang II receptors in the brain. Early radioligand binding studies of brain Ang II receptors [122, 123] indicated that Ang II receptors were located in regions within the blood-brain barrier, for example, cerebellum, hypothalamus, thalamus, septum, and midbrain, as well as outside the blood brain barrier. The first receptor autoradiographic study of brain Ang II receptors for blood-borne Ang II clearly demonstrated their presence in 4 circumventricular organs (CVOs): the SFO, OVLT, median eminence, and area postrema [124]. In vitro receptor autoradiographic studies of the rat brain confirmed the localization of Ang II receptors in these CVOs and revealed a widespread distribution of discrete populations of Ang II receptors in a large number of brain nuclei [93, 125]. Subsequent receptor autoradiographic studies using Ang II receptor subtype specific competing ligands indicated that both AT1 and AT2 receptors were present in the brain and were differentially distributed [27, 58]. Regions containing high densities of AT1 receptor binding include regions associated with dipsogenesis and cardiovascular regulation, for example, SFO, OVLT, MnPO, PVN, NTS, dorsal motor nucleus of the vagus, area postrema, rostral ventrolateral medulla (RVLM), as well as noncardiovascular regulatory regions, for example, pyriform cortex, subiculum, and spinal trigeminal nucleus. Generally, regions containing high densities of AT2 receptor binding are unrelated to blood pressure regulation and dipsogenesis, for example, mediodorsal thalamus, inferior olivary nucleus, medial geniculate, and subthalamic nucleus. While many regions have a strong predominance of one or the other subtype, several brain regions show both AT1 and AT2 receptor binding, for example, parabrachial nuclei, pedunculopontine tegmental nucleus, locus coeruleus, and superior colliculus [126].

Localized injection of exogenous Ang II has been used to map the distribution of brain Ang II receptors. Early studies directed at determining sites of action of Ang II assessed its behavioral and physiological effects. Subsequent studies using iontophoretic or pressure injection of Ang II via micropipettes have focused on its cellular effects. Early mapping of Ang II receptors mediating its dipsogenic effects indicated a widespread distribution in the forebrain [127]. However, a subsequent study [128] revealed that all the active sites were targeted with a cannula that traversed the anterior cerebral ventricles, and that only when Ang II leaked into the ventricles that a dipsogenic response occurred. Microinjection of Ang II into the SFO and PVN is excitatory to these neurons [129]. Microinjection of Ang II into the RVLM [130], area postrema, and NTS [131] increases blood pressure. Microinjection of Ang II into the periaqueductal gray increases blood pressure via its actions at AT1 receptors [132], while microinjection of Ang II into the superior colliculus increases blood pressure via its actions at AT2 receptors [133] consistent with radioligand binding studies indicating the presence of AT1 or AT2 receptors in these regions [27]. Lastly, the distribution of angiotensin responsive neurons has been determined using induction of fos expression as a functional marker [134].

A major controversy involves the presence or absence of Ang II receptors on vasopressinergic and oxytocinergic neurons in the SON and the magnocellular division of the PVN. Stimulation of vasopressin and oxytocin release from the posterior pituitary results from stimulation of the magnocellular neurons in the PVN and SON. In this study, all 3 Ang II receptor subtypes were highly expressed in the magnocellular divisions of the PVN. Radioligand binding studies of Ang II receptors reveal high expression of AT1 receptors in the parvocellular region of the PVN and low expression of Ang II receptors in the magnocellular division of the PVN and SON (as described in the previous section). Similarly, mRNA studies (succeeding section) have failed to demonstrate measurable Ang II receptor synthesizing capacity in these regions. However, electrophysiological studies suggest that neurons in these regions are responsive to Ang II. Nagatomo et al. [135] showed that Ang II inhibited potassium currents in SON neurons using patch clamping in brain slices. Ang II has a direct excitatory effect in the SON, which is consistent with the presence of AT1 receptors on vasopressinergic and oxytocinergic neurons [136]. The data reported herein is consistent with the presence of functional AT1 receptors in the PVN and SON.

Parvocellular PVN AT1 receptors revealed by radioligand binding and mRNA assays are well placed to stimulate CRH neurons in the PVN to release corticotrophin releasing hormone (CRH) from their nerve terminals in the median eminence into the hypothalamo-hypophyseal portal vessels to act upon corticotrophs in the anterior pituitary. In this study, all 3 Ang II receptor subtypes were highly expressed in the parvocellular division of the PVN.

The use of in situ hybridization or PCR for localization of mRNA to determine sites of synthesis of proteins has been widely used to localize Ang II receptor subtypes in the brain. Kakar et al. [31] reported a predominance of mRNA in the SFO, OVLT, and cerebellum and a predominance of in the hypothalamus by PCR. Conversely, Johren et al. [45] identified mRNA in the SFO, OVLT, PVN, cerebral cortex and hippocampus, mRNA in the cerebral cortex and hippocampus, (but not in the SFO or OVLT) and AT2 mRNA in the medial geniculate and inferior olivary nucleus. Similarly, Lenkei et al. [41] reported a predominance of mRNA expression in the SFO, OVLT, PVN, and MnPO as well as the anterior olfactory nucleus with very low mRNA expression in the SFO and PVN. Lenkei et al. [137] also reported the absence of and mRNA in the vasopressin positive neurons and GFAP positive astroglia in the SON and PVN. In the two-week-old rat brains, Jöhren and Saavedra [138] also observed mRNA in the pyriform cortex, basal amygdala and choroid plexus and mRNA in the choroid plexus. AT1 receptor binding has been reported in the choroid plexus [139] although at very low levels [140].

Brain AT2 receptor mRNA shows both similarities and differences from AT2 receptor binding in the rat brain. Noteworthy is the presence of AT2 mRNA in the red nucleus and the absence of AT2 mRNA in the locus coeruleus, lateral septum, and cerebellum [141]. These discrepancies have been interpreted as indicating that the red nucleus synthesizes AT2 receptors that are only expressed on its efferent nerve terminals that project to the inferior olivary nucleus and cerebellum, while the AT2 receptor expressing brain regions devoid of AT2 mRNA express AT2 receptors on the nerve terminals of its afferents from other brain regions. Lenkei et al. [142] observed AT2 mRNA in the red nucleus. However, they also observed AT2 mRNA in the lateral septum and locus coeruleus, as well as a much greater number of brain regions, including some traditionally AT1 predominant regions such as the NTS and spinal trigeminal nucleus. Lenkei et al. [47] also did a comprehensive in situ hybridization analysis of the rat brain receptor mRNA. Overall this is consistent with AT1 receptor binding, with a few exceptions, for example, the lack of AT1 mRNA in arcuate nucleus and median eminence, where it is postulated that the AT1 receptors occur on nerve terminals of hypothalamic neurons that synthesize dopamine or releasing hormones and release them into the hypothalamo-hypophyseal portal system to act upon endocrine cells of the anterior pituitary. There are also some brain regions that express mRNA, but not AT1 receptor binding, such as hippocampus CA1 and CA2 and some thalamic and brainstem nuclei [47]. An area of considerable cardiovascular regulatory significance is the RVLM. Chronic Ang II infusion was shown to up-regulate AT1 mRNA in the RVLM and reduce it in the SFO, suggesting that enhanced activation of the RVLM by enhanced AT1 stimulation increases sympathetic nervous system activity [143].

There are a large number of studies that have used immunohistochemistry and Western blotting to identify and localize Ang II receptor subtypes in the central nervous system. The receptor antigens are generally peptide fragments from different domains of the receptor protein, although one antibody [144] was generated from a purified AT2 receptor protein. Some antibodies target an extracellular domain near the amino terminal for example, Santa Cruz Biotechnology, SC-1173 (amino acids 15–24), the transmembrane spanning regions of the receptor, intra- and extracellular domains between the transmembrane spanning domains, the third intracellular loop (amino acids 225–237) of the AT1 receptor (Chemicon), and the intracellular carboxy terminal domain. Several of these studies have used antibodies directed against the same carboxy terminal regions of the (Abcam, AB18801), the or the (Advanced Targeting Systems, AB-N25AP, AB-N26AP, or AB-N27AP), and the AT2 receptors (Abcam, AB19134; Advanced Targeting Systems, AB-N28AP) that were used for generation of these antibodies.

Localization of AT1 receptor immunoreactivity in the brain was first done by Phillips et al., [145] using the 225–237 antibody directed to the third intracellular loop of the AT1 receptor. They showed extensive distribution of AT1 immunoreactivity in areas identified by receptor autoradiography to have Ang II receptors. Cardiovascular regulatory regions that were AT1 immunopositive included the PVN, OVLT, SFO, area postrema, NTS, RVLM, and nucleus ambiguous. AT1 immunopositive neurons were also present in the SON, and magnocellular division of the PVN, medial septal nucleus, LC, superior and inferior olivary nuclei, hypoglossal nucleus, ventral horn of the spinal cord and other regions not generally viewed as AT1 receptor targets of Ang II. Conversely, some areas reported to express Ang II receptor binding sites, for example, pyriform cortex, suprachiasmatic nucleus did not show AT1 immunoreactivity. They suggested that Ang II via AT1 receptors may have an expanded role in the CNS beyond that considered at that time.

Other studies also report the presence of AT1 receptors in the SON and/or the magnocellular division of the PVN using either an amino terminal peptide fragment directed antibody, AB18801 and AB-N27AP [146, 147] and the antibody directed against the 225–237 fragment of the AT1 receptor [148, 149]. Of note, the number of cells in the magnocellular division of the PVN expressing AT1 receptor using AB18801 was dramatically increased in rats with induced heart failure [146]. Two other studies observed an increase in total PVN AT1 receptor immunoreactivity (Abcam unspecified). In the first study, PVN AT1 immunoreactivity was increased in a rat model of heart failure [150]. In the second study, PVN AT1 immunoreactivity was increased with chronic intravenous Ang II infusion that was only partially reversed by ICV losartan infusion [151].

Using an antibody against purified AT2 receptor protein, Reagan et al. [152] immunohistochemically localized AT2 receptor immunoreactivity in the rat brain. Regions reported to have AT2 receptor binding and/or mRNA that were immunopositive included the locus coeruleus and several thalamic nuclei. Other regions reported to be AT2 expressing included the amygdala and the Purkinje cell layer of the cerebellum. In addition, AT2 immunoreactivity was present in the magnocellular division of the PVN and SON which further confirms observations in our study. However, as noted above, this antibody did not label the adrenal [70].

A series of studies have used the carboxy-terminal fragment-directed antibody to identify AT1 receptor immunoreactivity in the area postrema, NTS and RVLM at the electron microscopic level. immunoreactivity was present in neuronal cell bodies, dendrites, axon terminals, perivascular glial processes of astrocytes, fibroblasts, and vascular endothelial cells in the area postrema and dorsomedial NTS [153]. This immunoreactivity colocalized with the subunit of NADPH oxidase in neuronal cell bodies, dendrites, and putative vagal afferents in the medial NTS [154]. Dendritic processes of the medial NTS containing immunoreactivity also were positive for tyrosine hydroxylase (TH) or adjacent to TH containing axons [155]. In the TH positive neurons of the RVLM, AT1 receptor expression was greater in female rats than in male rats [156], and this increase was associated with a higher estrogen state (proestrus versus diestrus) and increased plasma membrane expression of AT1 immunoreactivity [157]. This same group has used the AT2 fragment directed antibody (AB19134) to identify AT2 receptor immunoreactivity in the PVN and NTS at the electron microscopic level [158, 159]. These studies have co-localized AT2 immunoreactivity with neuronal nitric oxide synthase (nNOS) in neuronal cell bodies and dendrites in the medial NTS [159], and with vasopressin in neuronal cell bodies and dendrites in the PVN [158]. This latter observation contrasts with the studies of Lenkei et al. [142], who did not find AT2 receptor mRNA in the PVN.

Extensive studies of AT1 and AT2 immunoreactivity in the RVLM and NTS in animal models of heart failure have been carried out by Gao, Zucker and colleagues using AT1 and AT2 antibodies, primarily SC-1173 and SC-9040 [160, 161]. AT1 receptors in the RVLM and NTS showed increased AT1 immunoreactivity, while AT2 receptors showed decreased immunoreactivity. Infusion of Ang II into the brain of rabbits to simulate a heart failure model increased AT1 receptor immunoreactivity in the RVLM [162]. Interestingly, viral transfection of AT2 receptors into the RVLM, which was documented with increased AT2 immunoreactivity, suppressed sympathetic activity in normal rats [163]. In a mouse model of hypertension, the RA mouse [164], immunoreactivity for AT1 (SC-1173) in the NTS and RVLM, was not shown to be up regulated [165].

AT1 (AB18801) and AT2 (AB19134) immunoreactivity in the substantia nigra (SN) colocalized with TH in neurons, GFAP in astrocytes and OX-6 and OX-42 in activated microglia [166168]. Using different carboxy terminal directed AT1 and AT2 antibodies for Western blotting, it was shown that estrogen treatment of ovariectomized rats, which was protective against 6-hydroxydopamine induced neurotoxicity in the SN, decreased AT1 and increased AT2 expression in the SN [166]. Of note, no change in AT1 receptor mRNA was observed [166]. These researchers also observed AT1 and AT2 immunoreactivity (Santa Cruz, SC-579 and SC-9040) in dopaminergic neurons, astrocytes and microglia in both monkey and human SN [169].

The dorsomedial hypothalamus (DMH), a brain region that exhibits high AT1 receptor density [170], also displays AT1 immunoreactivity using the AB-N27AP [147]. This brain region is associated with the cardiovascular manifestations of panic disorder and direct administration of an AT1 receptor antagonist into the DMH blocks this component of the panic disorder in an animal model of panic disorder [147].

Giles et al., [67] using the 350–359 carboxy terminal peptide directed antibody, observed strong AT1 receptor immunoreactivity in numerous brain regions including the SFO, OVLT, MnPO, the parvocellular division of the PVN, several other hypothalamic nuclei, and the NTS, corresponding well with radioligand binding and mRNA studies of the distribution of brain AT1 receptors.

4.6. Perspective on the Use of Antibodies for the Study of Angiotensin Receptors

The ambiguity associated with studies of angiotensin receptors using different methods, whether by radioligand binding, receptor autoradiography, mRNA, local application of Ang II, electrophysiology, fos induction, or by immunoreactivity, necessitates considerable stringency in the analysis and interpretation of the data. Strengths of the immunohistochemical studies reported herein are as follows: (1) there is no known peptide sequence that closely mimics those used to generate these antibodies, (2) the antibodies were affinity purified to eliminate antibodies that did not recognize the antigenic peptide, (3) antibody binding is blocked by incubation with an excess of the antigenic peptide (preadsorption control), (4) Western blots indicate that the primary bands of labeled protein have molecular weights within the range of those previously observed for glycosylated, dimerized or chaperone protein linked angiotensin receptors [68, 171175], and (5) the anatomical pattern of immunoreactivity correlates with radioligand binding for AT receptors [37, 59], agonist-induced c-fos expression [176], and the distribution of mRNA encoding the protein [44].

Weaknesses of this and other immunohistochemical approaches are as follows: (1) one cannot rule out the possibility that another protein could present an epitope similar to that recognized by these antibodies leading to a false positive, (2) there are posttranslational modifications of the receptor proteins that may mask the antigenic sites that they recognize, for example, phosphorylation of serine residues in Ang II receptors by a variety of protein kinases. The C-terminal domains chosen for generation of these antibodies contain several serines which when phosphorylated may mask the epitopes for the antibodies. AT1 receptors are phosphorylated by G protein receptor kinase GRK2 (formerly known as adrenergic receptor kinase, BARK1) leading to -arrestin binding to the intracellular domain of the AT1 receptors which may also mask the epitopes [177]. An additional post-translational modification is proteolytic cleavage of the receptor into smaller fragments following internalization. Cook et al. [178] demonstrated formation of a 54 amino acid carboxy terminal fragment of the rat receptor that translocated to the nucleus and induced apoptosis in a variety of cell types. Thus it is possible that the immunoreactivity observed herein is not that of the full length receptor. (3) Receptors undergo protein-protein interactions such as receptor dimerization or interactions with chaperone proteins which have the potential to mask the antigenic site on the receptor; (4) inability to document the loss of immunological reactivity in an animal in which the receptor protein has been eliminated, for example, receptor knockouts. A recent publication [179] using Western blotting and immunofluorescence has challenged the specificity of 6 commercially available AT1 receptor antibodies, including one previously questioned by Adams et al., [180] based upon the presence of immunoreactive material in mice in which the receptor is disrupted. The specificity of 3 AT1 receptor antibodies, Alomone Labs #AAR-011, Santa Cruz sc-1173, and Abcam 18801, has also been challenged based upon expression of immunoreactivity in and knockout mice [181]. A generalized challenge to the ability of antibodies to selectively recognize G protein-coupled receptors (GPCR) based on apparent nonspecificity of 49 GPCR antibodies to 19 different GPCRs (the AT1 and AT2 receptors were not among the 19 GPCRs) has called into question the validity of immunological identification of GPCRs [182]. However, Xue et al., [183] using the same antibody as Adams et al., [180] demonstrated knockdown of AT1 receptor immunoreactivity in the PVN. Of note, the gene disruption [184] does not eliminate the carboxy terminal coding domain of the receptor that includes the peptide sequences used to generate several of those antibodies. If this portion of the receptor is still expressed it could explain the residual presence of immunoreactive material in these knockout mice. However, the amino terminal sequence used to generate SC-1173 (amino acids 15–24) is in the deleted part; thus, it remains questionable whether the siRNA knockdown in the rat brain or the knockout of the mouse receptor gives the correct information regarding the specificity of this and other AT1 receptor antibodies.

One approach to resolve this question is to determine the identity of the protein in the band that the AT1 receptor antibodies recognize in both wild-type and AT1 receptor knockout mice. This has the potential to either (1) validate the immunological identification of AT1 receptor protein thereby calling into question the efficacy of the AT1 receptor knockout technology, (2) to discover a heretofore unknown subtype of the AT1 receptor with an mRNA sequence that somehow evaded recognition by homology cloning approaches, (3) to identify (a) non-AT1 protein(s) that colocalize(s) with AT1 receptors and display (a) sufficiently similar epitope(s) as to be recognized by a variety of AT1 receptor antibodies, (4) to discover (a) proteins with no relationship to AT1 receptors that coincidentally express the same epitope(s) as the AT1 receptor antibodies, or (5) to discover (a) novel protein(s) that has/have not yet been identified.

Until such questions are definitively answered, immunohistochemical studies, despite their known and potential limitations, can complement other types of analyses, which are also subject to a variety of differing limitations.

In conclusion, antibodies that can differentiate the 3 different angiotensin II receptor subtypes in the rat were used to immunohistochemically label angiotensin II receptor subtype-like immunoreactivity in the rat adrenal, pituitary, and brain. The pattern of staining corroborates mRNA, radioligand binding, and functional studies of adrenal and anterior pituitary angiotensin receptors. This indicates that and AT2 receptor subtypes occur in the zona glomerulosa and medulla of normal rats, the subtype occurs only in the zona glomerulosa of normal rats while the is the subtype predominantly expressed in the anterior pituitary. The localization of Ang II receptor immunoreactivity in the brain is in large part consistent with radioligand binding, mRNA, Ang II-induced fos expression, and functional studies; however, differences between these immunoreactivity observations and observations obtained from some other techniques are yet to be resolved.

Disclosure

R. C. Speth has licensed these antibodies for commercial sale to Advanced Targeting Systems, Inc., San Diego, CA, USA (92121). The immunochemical studies conducted by M. Brownfield did not benefit ImmunoStar (i.e., they do not offer these antibodies).

Acknowledgments

The authors thank Drs. Kevin Grove, Kathryn Sandberg, Julia Cook, and Richard Re for assistance and helpful suggestions in the preparation of this paper. Funding for this work was provided by The Peptide Radioiodination Service Center, Washington State University, and the University of Wisconsin with a research gift from ImmunoStar Corporation.

References

  1. J. H. Laragh, M. Angers, W. G. Kelly, and S. Lieberman, “Hypotensive agents and pressor substances. The effect of epinephrine, norepinephrine, angiotensin II, and others on the secretory rate of aldosterone in man,” The Journal of the American Medical Association, vol. 174, pp. 234–240, 1960. View at: Google Scholar
  2. J. O. Davis, P. M. Hartroft, E. O. Titus, C. C. J. Carpenter, C. R. Ayers, and H. E. Spiegel, “The role of the renin-angiotensin system in the control of aldosterone secretion,” The Journal of Clinical Investigation, vol. 41, no. 2, pp. 378–389, 1962. View at: Google Scholar
  3. W. Feldberg and G. P. Lewis, “The action of peptides on the adrenal medulla. Release of adrenaline by bradykinin and angiotensin,” The Journal of physiology, vol. 171, pp. 98–108, 1964. View at: Google Scholar
  4. D. Ganten, J. L. Minnich, P. Granger et al., “Angiotensin-forming enzyme in brain tissue,” Science, vol. 173, no. 3991, pp. 64–65, 1971. View at: Google Scholar
  5. R. L. Stornetta, C. L. Hawelu-Johnson, P. G. Guyenet, and K. R. Lynch, “Astrocytes synthesize angiotensinogen in brain,” Science, vol. 242, no. 4884, pp. 1444–1446, 1988. View at: Google Scholar
  6. R. W. Lind, L. W. Swanson, and D. Ganten, “Organization of angiotensin II immunoreactive cells and fibers in the rat central nervous system. An immunohistochemical study,” Neuroendocrinology, vol. 40, no. 1, pp. 2–24, 1985. View at: Google Scholar
  7. D. A. Booth, “Mechanism of action of norepinephrine in eliciting an eating response on injection into the rat hypothalamus,” Journal of Pharmacology and Experimental Therapeutics, vol. 160, no. 2, pp. 336–348, 1968. View at: Google Scholar
  8. I. A. Reid and D. J. Ramsay, “The effects of intracerebroventricular administration of renin on drinking and blood pressure,” Endocrinology, vol. 97, no. 3, pp. 536–542, 1975. View at: Google Scholar
  9. W. B. Severs and A. E. Daniels-Severs, “Effects of angiotensin on the central nervous system,” Pharmacological Reviews, vol. 25, no. 3, pp. 415–449, 1973. View at: Google Scholar
  10. M. I. Phillips and C. Sumners, “Angiotensin II in central nervous system physiology,” Regulatory Peptides, vol. 78, no. 1–3, pp. 1–11, 1998. View at: Publisher Site | Google Scholar
  11. J. W. Wright and J. W. Harding, “The brain renin-angiotensin system: a diversity of functions and implications for CNS diseases,” Pflügers Archiv, vol. 465, pp. 133–151, 2013. View at: Publisher Site | Google Scholar
  12. W. F. Ganong, “Blood, pituitary, and brain renin-angiotensin systems and regulation of secretion of anterior pituitary gland,” Frontiers in Neuroendocrinology, vol. 14, no. 3, pp. 233–249, 1993. View at: Publisher Site | Google Scholar
  13. E. Vila-Porcile and P. Corvol, “Angiotensinogen, prorenin, and renin are co-localized in the secretory granules of all glandular cells of the rat anterior pituitary: an immunoultrastructural study,” Journal of Histochemistry and Cytochemistry, vol. 46, no. 3, pp. 301–311, 1998. View at: Google Scholar
  14. A. T. Chiu, W. F. Herblin, D. E. McCall et al., “Identification of angiotensin II receptor subtypes,” Biochemical and Biophysical Research Communications, vol. 165, no. 1, pp. 196–203, 1989. View at: Publisher Site | Google Scholar
  15. S. Whitebread, M. Mele, B. Kamber, and M. De Gasparo, “Preliminary biochemical characterization of two angiotensin II receptor subtypes,” Biochemical and Biophysical Research Communications, vol. 163, no. 1, pp. 284–291, 1989. View at: Google Scholar
  16. T. J. Murphy, R. W. Alexander, K. K. Griendling, M. S. Runge, and K. E. Bernstein, “Isolation of a cDNA encoding the vascular type-1 angiotensin II receptor,” Nature, vol. 351, no. 6323, pp. 233–236, 1991. View at: Publisher Site | Google Scholar
  17. K. Sasaki, Y. Yamano, S. Bardhan et al., “Cloning and expression of a complementary DNA encoding a bovine adrenal angiotensin II type-1 receptor,” Nature, vol. 351, no. 6323, pp. 230–233, 1991. View at: Publisher Site | Google Scholar
  18. Y. Kambayashi, S. Bardhan, K. Takahashi et al., “Molecular cloning of a novel angiotensin II receptor isoform involved in phosphotyrosine phosphatase inhibition,” Journal of Biological Chemistry, vol. 268, no. 33, pp. 24543–24546, 1993. View at: Google Scholar
  19. M. Mukoyama, M. Nakajima, M. Horiuchi, H. Sasamura, R. E. Pratt, and V. J. Dzau, “Expression cloning of type 2 angiotensin II receptor reveals a unique class of seven-transmembrane receptors,” Journal of Biological Chemistry, vol. 268, no. 33, pp. 24539–24542, 1993. View at: Google Scholar
  20. S. P. Tofovic, A. S. Pong, and E. K. Jackson, “Effects of angiotensin subtype 1 and subtype 2 receptor antagonists in normotensive versus hypertensive rats,” Hypertension, vol. 18, no. 6, pp. 774–782, 1991. View at: Google Scholar
  21. T. Hano, M. Mizukoshi, A. Baba, N. Nakamura, and I. Nishio, “Angiotensin II subtype 1 receptor modulates epinephrine release from isolated rat adrenal gland,” Blood Pressure, Supplement, vol. 3, Supplement 5, pp. 105–108, 1994. View at: Google Scholar
  22. R. F. Kirby, R. L. Thunhorst, and A. K. Johnson, “Effects of a non-peptide angiotensin receptor antagonist on drinking and blood pressure responses to centrally administered angiotensins in the rat,” Brain Research, vol. 576, no. 2, pp. 348–350, 1992. View at: Publisher Site | Google Scholar
  23. D. C. Hogarty, E. A. Speakman, V. Puig, and M. I. Phillips, “The role of angiotensin, AT1 and AT2 receptors in the pressor, drinking and vasopressin responses to central angiotensin,” Brain Research, vol. 586, no. 2, pp. 289–294, 1992. View at: Publisher Site | Google Scholar
  24. E. Lazartigues, P. Sinnayah, G. Augoyard, C. Gharib, A. K. Johnson, and R. L. Davisson, “Enhanced water and salt intake in transgenic mice with brain-restricted overexpression of angiotensin (AT1) receptors,” American Journal of Physiology, vol. 295, no. 5, pp. R1539–R1545, 2008. View at: Publisher Site | Google Scholar
  25. D. S. A. Colombari, J. V. Menani, and A. K. Johnson, “Forebrain angiotensin type 1 receptors and parabrachial serotonin in the control of NaCl and water intake,” American Journal of Physiology, vol. 271, no. 6, pp. R1470–R1476, 1996. View at: Google Scholar
  26. L. A. A. Camargo, W. A. Saad, S. Simões, T. A. B. Santos, and W. Abrão Saad, “Interaction between paraventricular nucleus and septal area in the control of physiological responses induced by angiotensin II,” Brazilian Journal of Medical and Biological Research, vol. 35, no. 9, pp. 1017–1023, 2002. View at: Google Scholar
  27. B. P. Rowe, K. L. Grove, D. L. Saylor, and R. C. Speth, “Angiotensin II receptor subtypes in the rat brain,” European Journal of Pharmacology, vol. 186, no. 2-3, pp. 339–342, 1990. View at: Google Scholar
  28. K. Tsutsumi and J. M. Saavedra, “Quantitative autoradiography reveals different angiotensin II receptor subtypes in selected rat brain nuclei,” Journal of Neurochemistry, vol. 56, no. 1, pp. 348–351, 1991. View at: Publisher Site | Google Scholar
  29. K. Song, A. M. Allen, G. Paxinos, and F. A. O. Mendelsohn, “Angiotensin II receptor subtypes in rat brain,” Clinical and Experimental Pharmacology and Physiology, vol. 18, no. 2, pp. 93–96, 1991. View at: Google Scholar
  30. M. N. Nitabach, J. Schulkin, and A. N. Epstein, “The medial amygdala is part of a mineralocorticoid-sensitive circuit controlling NaCl intake in the rat,” Behavioural Brain Research, vol. 35, no. 2, pp. 127–134, 1989. View at: Google Scholar
  31. S. S. Kakar, K. K. Riel, and J. D. Neill, “Differential expression of angiotensin II receptor subtype mRNAs (AT-1A and AT-1B) in the brain,” Biochemical and Biophysical Research Communications, vol. 185, no. 2, pp. 688–692, 1992. View at: Publisher Site | Google Scholar
  32. N. Iwai and T. Inagami, “Identification of two subtypes in the rat type I angiotensin II receptor,” FEBS Letters, vol. 298, no. 2-3, pp. 257–260, 1992. View at: Publisher Site | Google Scholar
  33. T. S. Elton, C. C. Stephan, G. R. Taylor et al., “Isolation of two distinct type I angiotensin II receptor genes,” Biochemical and Biophysical Research Communications, vol. 184, no. 2, pp. 1067–1073, 1992. View at: Publisher Site | Google Scholar
  34. A. T. Chiu, J. Dunscomb, J. Kosierowski et al., “The ligand binding signatures of the rat AT1a, AT1b and the human AT1 receptors are essentially identical,” Biochemical and Biophysical Research Communications, vol. 197, no. 2, pp. 440–449, 1993. View at: Publisher Site | Google Scholar
  35. K. Sandberg, H. Ji, A. J. L. Clark, H. Shapira, and K. J. Catt, “Cloning and expression of a novel angiotensin II receptor subtype,” Journal of Biological Chemistry, vol. 267, no. 14, pp. 9455–9458, 1992. View at: Google Scholar
  36. Y. Tian, A. J. Baukal, K. Sandberg, K. E. Bernstein, T. Balla, and K. J. Catt, “Properties of AT1a and AT1b angiotensin receptors expressed in adrenocortical Y-1 cells,” American Journal of Physiology, vol. 270, no. 5, pp. E831–E839, 1996. View at: Google Scholar
  37. R. C. Speth, “Sarcosine1,glycine8 angiotensin II is an AT 1 angiotensin II receptor subtype selective antagonist,” Regulatory Peptides, vol. 115, no. 3, pp. 203–209, 2003. View at: Publisher Site | Google Scholar
  38. S. S. Kakar, J. C. Sellers, D. C. Devor, L. C. Musgrove, and J. D. Neill, “Angiotensin II type-1 receptor subtype cDNAs: differential tissue expression and hormonal regulation,” Biochemical and Biophysical Research Communications, vol. 183, no. 3, pp. 1090–1096, 1992. View at: Publisher Site | Google Scholar
  39. O. Jöhren, C. Golsch, A. Dendorfer, F. Qadri, W. Häuser, and P. Dominiak, “Differential expression of AT1 receptors in the pituitary and adrenal gland of SHR and WKY,” Hypertension, vol. 41, no. 4, pp. 984–990, 2003. View at: Publisher Site | Google Scholar
  40. J. M. Burson, G. Aguilera, K. W. Gross, and C. D. Sigmund, “Differential expression of angiotensin receptor 1A and 1B in mouse,” American Journal of Physiology, vol. 267, no. 2, pp. E260–E267, 1994. View at: Google Scholar
  41. Z. Lenkei, P. Corvol, and C. Llorens-Cortes, “The angiotensin receptor subtype AT1a predominates in rat forebrain areas involved in blood pressure, body fluid homeostasis and neuroendocrine control,” Molecular Brain Research, vol. 30, no. 1, pp. 53–60, 1995. View at: Publisher Site | Google Scholar
  42. Y. Chen and M. Morris, “Differentiation of brain angiotensin type 1a and 1b receptor mRNAs a specific effect of dehydration,” Hypertension, vol. 37, no. 2, pp. 692–697, 2001. View at: Google Scholar
  43. K. Krishnamurthi, J. G. Verbalis, W. Zheng, Z. Wu, L. B. Clerch, and K. Sandberg, “Estrogen regulates angiotensin AT1 receptor expression via cytosolic proteins that bind to the 5' leader sequence of the receptor mRNA,” Endocrinology, vol. 140, no. 11, pp. 5435–5438, 1999. View at: Google Scholar
  44. J. M. Gasc, S. Shanmugam, M. Sibony, and P. Corvol, “Tissue-specific expression of type 1 angiotensin II receptor subtypes: an in situ hybridization study,” Hypertension, vol. 24, no. 5, pp. 531–537, 1994. View at: Google Scholar
  45. O. Johren, T. Inagami, and J. M. Saavedra, “AT1a, AT1b, and AT2 angiotensin II receptor subtype gene expression in rat brain,” NeuroReport, vol. 6, no. 18, pp. 2549–2552, 1995. View at: Google Scholar
  46. M. Jezova, I. Armando, C. Bregonzio et al., “Angiotensin II AT1 and AT2 receptors contribute to maintain basal adrenomedullary norepinephrine synthesis and tyrosine hydroxylase transcription,” Endocrinology, vol. 144, no. 5, pp. 2092–2101, 2003. View at: Publisher Site | Google Scholar
  47. Z. Lenkei, M. Palkovits, P. Corvol, and C. Llorens-Cortès, “Expression of angiotensin type-1 (AT1) and type-2 (AT2) receptor mRNAs in the adult rat brain: a functional neuroanatomical review,” Frontiers in Neuroendocrinology, vol. 18, no. 4, pp. 383–439, 1997. View at: Publisher Site | Google Scholar
  48. T. P. Hopp and K. R. Woods, “Prediction of protein antigenic determinants from amino acid sequences,” Proceedings of the National Academy of Sciences of the United States of America, vol. 78, no. 6, pp. 3824–3828, 1981. View at: Google Scholar
  49. Y. Kitami, T. Okura, K. Marumoto, R. Wakamiya, and K. Hiwada, “Differential gene expression and regulation of type-1 angiotensin II receptor subtypes in the rat,” Biochemical and Biophysical Research Communications, vol. 188, no. 1, pp. 446–452, 1992. View at: Publisher Site | Google Scholar
  50. A. T. Chiu, J. H. Dunscomb, D. E. McCall, P. Benfield, W. Baubonis, and B. Sauer, “Characterization of angiotensin AT1a receptor isoform by its ligand binding signature,” Regulatory Peptides, vol. 44, no. 2, pp. 141–147, 1993. View at: Publisher Site | Google Scholar
  51. H. Jo, E. K. Yang, W. J. Lee, K. Y. Park, H. J. Kim, and J. S. Park, “Gene expression of central and peripheral renin-angiotensin system components upon dietary sodium intake in rats,” Regulatory Peptides, vol. 67, no. 2, pp. 115–121, 1996. View at: Publisher Site | Google Scholar
  52. C. Llorens-Cortes, B. Greenberg, H. Huang, and P. Corvol, “Tissular expression and regulation of type 1 angiotensin II receptor subtypes by quantitative reverse transcriptase-polymerase chain reaction analysis,” Hypertension, vol. 24, no. 5, pp. 538–548, 1994. View at: Google Scholar
  53. J. Qiu, S. H. Nelson, R. C. Speth, and D. H. Wang, “Regulation of adrenal angiotensin receptor subtypes: a possible mechanism for sympathectomy-induced adrenal hypertrophy,” Journal of Hypertension, vol. 17, no. 7, pp. 933–940, 1999. View at: Publisher Site | Google Scholar
  54. N. Iwai, T. Inagami, N. Ohmichi, Y. Nakamura, Y. Saeki, and M. Kinoshita, “Differential regulation of rat AT1a and AT1b receptor mRNA,” Biochemical and Biophysical Research Communications, vol. 188, no. 1, pp. 298–303, 1992. View at: Publisher Site | Google Scholar
  55. D. H. Wang, Y. Du, H. Zhao, J. P. Granger, R. C. Speth, and D. J. Dipette, “Regulation of Angiotensin type 1 receptor and its gene expression: role in renal growth,” Journal of the American Society of Nephrology, vol. 8, no. 2, pp. 193–198, 1997. View at: Google Scholar
  56. M. M. Martin, E. J. Lee, J. A. Buckenberger, T. D. Schmittgen, and T. S. Elton, “MicroRNA-155 regulates human angiotensin II type 1 receptor expression in fibroblast,” Journal of Biological Chemistry, vol. 281, no. 27, pp. 18277–18284, 2006. View at: Publisher Site | Google Scholar
  57. M. Naruse, A. Tanabe, T. Sugaya et al., “Deferential roles of angiotensin receptor subtypes in adrenocortical function in mice,” Life Sciences, vol. 63, no. 18, pp. 1593–1598, 1998. View at: Publisher Site | Google Scholar
  58. K. Song, J. Zhuo, A. M. Allen, G. Paxinos, and F. A. O. Mendelsohn, “Angiotensin II receptor subtypes in rat brain and peripheral tissues,” Cardiology, vol. 79, Supplement 1, pp. 45–54, 1991. View at: Google Scholar
  59. A. Israel, L. M. Plunkett, and J. M. Saavedra, “Quantitative autoradiographic characterization of receptors for angiotensin II and other neuropeptides in individual brain nuclei and peripheral tissues from single rats,” Cellular and Molecular Neurobiology, vol. 5, no. 3, pp. 211–222, 1985. View at: Google Scholar
  60. D. P. Healy, A. R. Maciejewski, and M. P. Printz, “Autoradiographic localization of [125I]-angiotensin II binding sites in the rat adrenal gland,” Endocrinology, vol. 116, no. 3, pp. 1221–1223, 1985. View at: Google Scholar
  61. K. G. Birukov, S. Lehoux, A. A. Birukova, R. Merval, V. A. Tkachuk, and A. Tedgui, “Increased pressure induces sustained protein kinase C-independent herbimycin A-sensitive activation of extracellular signal-related kinase 1/2 in the rabbit aorta in organ culture,” Circulation Research, vol. 81, no. 6, pp. 895–903, 1997. View at: Google Scholar
  62. R. Wakamiya, K. Kohara, and K. Hiwada, “Gene expression of the type-1 angiotensin II receptor in rat adrenal gland,” Blood Pressure, vol. 3, Supplement 5, pp. 109–112, 1994. View at: Google Scholar
  63. K. Harada, H. Matsuoka, N. Fujimoto et al., “Localization of type-2 angiotensin II receptor in adrenal gland,” Journal of Histochemistry and Cytochemistry, vol. 58, no. 7, pp. 585–593, 2010. View at: Publisher Site | Google Scholar
  64. B. Peters, S. Clausmeyer, P. Teubner et al., “Changes of AT2 receptor levels in the rat adrenal cortex and medulla induced by bilateral nephrectomy and its modulation by circulating ANG II,” Journal of Histochemistry and Cytochemistry, vol. 49, no. 5, pp. 649–656, 2001. View at: Google Scholar
  65. W. G. Paxton, M. Runge, C. Horaist, C. Cohen, R. W. Alexander, and K. E. Bernstein, “Immunohistochemical localization of rat angiotensin II AT1 receptor,” American Journal of Physiology, vol. 264, no. 6, pp. F989–F995, 1993. View at: Google Scholar
  66. J. G. Lehoux, I. M. Bird, N. Briere, D. Martel, and L. Ducharme, “Influence of dietary sodium restriction on angiotensin II receptors in rat adrenals,” Endocrinology, vol. 138, no. 12, pp. 5238–5247, 1997. View at: Google Scholar
  67. M. E. Giles, R. T. Fernley, Y. Nakamura et al., “Characterization of a specific antibody to the rat angiotensin II AT1 receptor,” Journal of Histochemistry and Cytochemistry, vol. 47, no. 4, pp. 507–515, 1999. View at: Google Scholar
  68. N. Frei, J. Weissenberger, A. G. Beck-Sickinger, M. Höfliger, J. Weis, and H. Imboden, “Immunocytochemical localization of angiotensin II receptor subtypes and angiotensin II with monoclonal antibodies in the rat adrenal gland,” Regulatory Peptides, vol. 101, no. 1–3, pp. 149–155, 2001. View at: Publisher Site | Google Scholar
  69. A. K. L. Yiu, P. F. Wong, S. Y. Yeung, S. M. Lam, S. K. S. Luk, and W. T. Cheung, “Immunohistochemical localization of type-II (AT2) angiotensin receptors with a polyclonal antibody against a peptide from the C-terminal tail,” Regulatory Peptides, vol. 70, no. 1, pp. 15–21, 1997. View at: Publisher Site | Google Scholar
  70. L. P. Reagan, R. R. Sakai, and S. J. Fluharty, “Immunological analysis of angiotensin AT2 receptors in peripheral tissues of neonatal and adult rats,” Regulatory Peptides, vol. 65, no. 2, pp. 159–164, 1996. View at: Publisher Site | Google Scholar
  71. S. S. G. Ferguson, “Evolving concepts in G protein-coupled receptor endocytosis: the role in receptor desensitization and signaling,” Pharmacological Reviews, vol. 53, no. 1, pp. 1–24, 2001. View at: Google Scholar
  72. L. Hunyady, A. J. Baukal, Z. Gáborik et al., “Differential PI 3-kinase dependence of early and late phases of recycling of the internalized AT1 angiotensin receptor,” Journal of Cell Biology, vol. 157, no. 7, pp. 1211–1222, 2002. View at: Publisher Site | Google Scholar
  73. R. Kumar, V. P. Singh, and K. M. Baker, “The intracellular renin-angiotensin system: a new paradigm,” Trends in Endocrinology and Metabolism, vol. 18, no. 5, pp. 208–214, 2007. View at: Publisher Site | Google Scholar
  74. B. Boivin, G. Vaniotis, B. G. Allen, and T. E. Hébert, “G protein-coupled receptors in and on the cell nucleus: a new signaling paradigm?” Journal of Receptors and Signal Transduction, vol. 28, no. 1-2, pp. 15–28, 2008. View at: Publisher Site | Google Scholar
  75. A. L. Robertson and P. A. Khairallah, “Angiotensin II: rapid localization in nuclei of smooth and cardiac muscle,” Science, vol. 172, no. 3988, pp. 1138–1139, 1971. View at: Google Scholar
  76. R. Re and M. Parab, “Effect of angiotensin II on RNA synthesis by isolated nuclei,” Life Sciences, vol. 34, no. 7, pp. 647–651, 1984. View at: Publisher Site | Google Scholar
  77. A. T. Chiu, D. E. McCall, T. T. Nguyen et al., “Discrimination of angiotensin II receptor subtypes by dithiothreitol,” European Journal of Pharmacology, vol. 170, no. 1-2, pp. 117–118, 1989. View at: Google Scholar
  78. P. Eggena, J. H. Zhu, K. Clegg, and J. D. Barrett, “Nuclear angiotensin receptors induce transcription of renin and angiotensinogen mRNA,” Hypertension, vol. 22, no. 4, pp. 496–501, 1993. View at: Google Scholar
  79. P. Eggena, J. H. Zhu, S. Sereevinyayut et al., “Hepatic angiotensin II nuclear receptors and transcription of growth-related factors,” Journal of Hypertension, vol. 14, no. 8, pp. 961–968, 1996. View at: Google Scholar
  80. R. N. Re, D. L. Vizard, J. Brown, and S. E. Bryan, “Angiotensin II receptors in chromatin fragments generated by micrococcal nuclease,” Biochemical and Biophysical Research Communications, vol. 119, no. 1, pp. 220–227, 1984. View at: Google Scholar
  81. G. W. Booz, K. M. Conrad, A. L. Hess, H. A. Singer, and K. M. Baker, “Angiotensin-II-binding sites on hepatocyte nuclei,” Endocrinology, vol. 130, no. 6, pp. 3641–3649, 1992. View at: Publisher Site | Google Scholar
  82. S. S. Tang, H. Rogg, R. Schumacher, and V. J. Dzau, “Characterization of nuclear angiotensin-II-binding sites in rat liver and comparison with plasma membrane receptors,” Endocrinology, vol. 131, no. 1, pp. 374–380, 1992. View at: Publisher Site | Google Scholar
  83. H. Licea, M. R. Walters, and L. G. Navar, “Renal nuclear angiotensin II receptors in normal and hypertensive rats,” Acta physiologica Hungarica, vol. 89, no. 4, pp. 427–438, 2002. View at: Google Scholar
  84. A. Tadevosyan, A. Maguy, L. R. Villeneuve et al., “Nuclear-delimited angiotensin receptor-mediated signaling regulates cardiomyocyte gene expression,” Journal of Biological Chemistry, vol. 285, no. 29, pp. 22338–22349, 2010. View at: Publisher Site | Google Scholar
  85. R. Chen, Y. V. Mukhin, M. N. Garnovskaya et al., “A functional angiotensin II receptor-GFP fusion protein: evidence for agonist-dependent nuclear translocation,” American Journal of Physiology, vol. 279, no. 3, pp. F440–F448, 2000. View at: Google Scholar
  86. T. A. Morinelli, J. R. Raymond, A. Baldys et al., “Identification of a putative nuclear localization sequence within ANG II AT1a receptor associated with nuclear activation,” American Journal of Physiology, vol. 292, no. 4, pp. C1398–C1408, 2007. View at: Publisher Site | Google Scholar
  87. D. Lu, H. Yang, G. Shaw, and M. K. Raizada, “Angiotensin II-induced nuclear targeting of the angiotensin type 1 (AT1) receptor in brain neurons,” Endocrinology, vol. 139, pp. 365–375, 1998. View at: Publisher Site | Google Scholar
  88. D. K. Lee, A. J. Lança, R. Cheng et al., “Agonist-independent nuclear localization of the apelin, angiotensin AT 1, and bradykinin B2 receptors,” Journal of Biological Chemistry, vol. 279, no. 9, pp. 7901–7908, 2004. View at: Publisher Site | Google Scholar
  89. T. L. Goodfriend and M. J. Peach, “Angiotensin III: (Des aspartic acid) angiotensin II. Evidence and speculation for its role as an important agonist in the renin angiotensin system,” Circulation Research, vol. 36, no. 6, Supplement 1, pp. 38–48, 1975. View at: Google Scholar
  90. S. Shanmugam, Z. G. Lenkei, J. M. R. Gasc, P. L. Corvol, and C. M. Llorens-Cortes, “Ontogeny of angiotensin II type 2 (AT2) receptor mRNA in the rat,” Kidney International, vol. 47, no. 4, pp. 1095–1100, 1995. View at: Google Scholar
  91. A. Israel, F. M. A. Correa, M. Niwa, and J. M. Saavedra, “Quantitative measurement of angiotensin II (A II) receptors in discrete regions of rat brain, pituitary and adrenal gland by autoradiography,” Clinical and Experimental Hypertension A, vol. 6, no. 10-11, pp. 1761–1764, 1984. View at: Google Scholar
  92. R. C. Speth, J. K. Wamsley, and D. R. Gehlert, “Angiotensin II receptor localization in the canine CNS,” Brain Research, vol. 326, no. 1, pp. 137–143, 1985. View at: Publisher Site | Google Scholar
  93. D. R. Gehlert, R. C. Speth, and J. K. Wamsley, “Distribution of [125I]angiotensin II binding sites in the rat brain: a quantitative autoradiographic study,” Neuroscience, vol. 18, no. 4, pp. 837–856, 1986. View at: Google Scholar
  94. K. Tsutsumi and J. M. Saavedra, “Angiotensin-II receptor subtypes in median eminence and basal forebrain areas involved in regulation of pituitary function,” Endocrinology, vol. 129, no. 6, pp. 3001–3008, 1991. View at: Google Scholar
  95. J. M. Saavedra, “Brain and pituitary angiotensin,” Endocrine Reviews, vol. 13, no. 2, pp. 329–380, 1992. View at: Publisher Site | Google Scholar
  96. M. Pawlikowski, “Immunohistochemical detection of angiotensin receptors AT1 and AT2 in normal rat pituitary gland, estrogen-induced rat pituitary tumor and human pituitary adenomas,” Folia Histochemica et Cytobiologica, vol. 44, no. 3, pp. 173–177, 2006. View at: Google Scholar
  97. S. G. Shelat, L. P. Reagan, J. L. King, S. J. Fluharty, and L. M. Flanagan-Cato, “Analysis of angiotensin type 2 receptors in vasopressinergic neurons and pituitary in the rat,” Regulatory Peptides, vol. 73, no. 2, pp. 103–112, 1998. View at: Publisher Site | Google Scholar
  98. Z. Lenkei, A. M. Nuyt, D. Grouselle, P. Corvol, and C. Llorens-Cortès, “Identification of endocrine cell populations expressing the AT1b subtype of angiotensin II receptors in the anterior pituitary,” Endocrinology, vol. 140, no. 1, pp. 472–477, 1999. View at: Publisher Site | Google Scholar
  99. G. L. Sanvitto, O. Jöhren, W. Häuser, and J. M. Saavedra, “Water deprivation upregulates ANG II AT1 binding and mRNA in rat subfornical organ and anterior pituitary,” American Journal of Physiology, vol. 273, no. 1, pp. E156–E163, 1997. View at: Google Scholar
  100. C. Moreau, R. Rasolojanahary, A. J. Zamora, A. Enjalbert, C. Kordon, and C. Llorens-Cortes, “Expression of angiotensin II receptor subtypes AT1a and AT1b in enriched fractions of dispersed rat pituitary cells,” Neuroendocrinology, vol. 66, no. 6, pp. 416–425, 1997. View at: Google Scholar
  101. J. P. Bonjour and R. L. Malvin, “Stimulation of ADH release by the renin-angiotensin system,” The American journal of physiology, vol. 218, no. 6, pp. 1555–1559, 1970. View at: Google Scholar
  102. V. L. Brooks, L. C. Keil, and I. A. Reid, “Role of the renin-angiotensin system in the control of vasopressin secretion in conscious dogs,” Circulation Research, vol. 58, no. 6, pp. 829–838, 1986. View at: Google Scholar
  103. B. G. Zimmerman, “Effect of acute sympathectomy on responses to angiotensin and norepinephrine,” Circulation research, vol. 11, pp. 780–787, 1962. View at: Google Scholar
  104. B. G. Zimmerman, “Adrenergic facilitation by angiotensin: does it serve a physiological function?” Clinical Science, vol. 60, no. 4, pp. 343–348, 1981. View at: Google Scholar
  105. G. Aguilera, C. L. Hyde, and K. J. Catt, “Angiotensin II receptors and prolactin release in pituitary lactotrophs,” Endocrinology, vol. 111, no. 4, pp. 1045–1050, 1982. View at: Google Scholar
  106. M. K. Steele, S. M. McCann, and A. Negro-Vilar, “Modulation by dopamine and estradiol of the central effects of angiotensin II on anterior pituitary hormone release,” Endocrinology, vol. 111, no. 3, pp. 722–729, 1982. View at: Google Scholar
  107. M. T. Bluet-Pajot, J. Epelbaum, D. Gourdji, C. Hammond, and C. Kordon, “Hypothalamic and hypophyseal regulation of growth hormone secretion,” Cellular and Molecular Neurobiology, vol. 18, no. 1, pp. 101–123, 1998. View at: Publisher Site | Google Scholar
  108. E. Spinedi, L. Herrera, and A. Chisari, “Angiotensin II (AII) and adrenocorticotropin release: modulation by estradiol of the AII biological activity and binding characteristics in anterior pituitary dispersed cells,” Endocrinology, vol. 123, no. 1, pp. 641–646, 1988. View at: Google Scholar
  109. A. Seltzer, J. E. B. Pinto, P. N. Viglione et al., “Estrogens regulate angiotensin-converting enzyme and angiotensin receptors in female rat anterior pituitary,” Neuroendocrinology, vol. 55, no. 4, pp. 460–467, 1992. View at: Google Scholar
  110. O. Johren, G. L. Sanvitto, G. Egidy, and J. M. Saavedra, “Angiotensin II AT1a receptor mRNA expression is induced by estrogen- progesterone in dopaminergic neurons of the female rat arcuate nucleus,” Journal of Neuroscience, vol. 17, no. 21, pp. 8283–8292, 1997. View at: Google Scholar
  111. T. Inagami, S. Eguchi, K. Numaguchi et al., “Cross-talk between angiotensin II receptors and the tyrosine kinases and phosphatases,” Journal of the American Society of Nephrology, vol. 10, Supplement 11, no. 1, pp. S57–S61, 1999. View at: Google Scholar
  112. C. H. Gelband, M. Zhu, D. Lu et al., “Functional interactions between neuronal AT1 and AT2 receptors,” Endocrinology, vol. 138, no. 5, pp. 2195–2198, 1997. View at: Google Scholar
  113. H. Y. Sohn, U. Raff, A. Hoffmann et al., “Differential role of angiotensin II receptor subtypes on endothelial superoxide formation,” British Journal of Pharmacology, vol. 131, no. 4, pp. 667–672, 2000. View at: Google Scholar
  114. C. Sumners, W. Tang, W. Paulding, and M. K. Raizada, “Peptide receptors in astroglia: focus on angiotensin II and atrial natriuretic peptide,” GLIA, vol. 11, no. 2, pp. 110–116, 1994. View at: Google Scholar
  115. J. M. Saavedra, “Emerging features of brain angiotensin receptors,” Regulatory Peptides, vol. 85, no. 1, pp. 31–45, 1999. View at: Publisher Site | Google Scholar
  116. L. Füchtbauer, M. Groth-Rasmussen, T. H. Holm et al., “Angiotensin II Type 1 receptor (AT1) signaling in astrocytes regulates synaptic degeneration-induced leukocyte entry to the central nervous system,” Brain, Behavior, and Immunity, vol. 25, no. 5, pp. 897–904, 2011. View at: Publisher Site | Google Scholar
  117. L. E. Downie, K. Vessey, A. Miller et al., “Neuronal and glial cell expression of angiotensin II type 1 (AT1) and type 2 (AT2) receptors in the rat retina,” Neuroscience, vol. 161, no. 1, pp. 195–213, 2009. View at: Publisher Site | Google Scholar
  118. J. Benicky, E. Sánchez-Lemus, M. Honda et al., “Angiotensin II AT1 receptor blockade ameliorates brain inflammation,” Neuropsychopharmacology, vol. 36, no. 4, pp. 857–870, 2011. View at: Publisher Site | Google Scholar
  119. P. Shi, M. K. Raizada, and C. Sumners, “Brain cytokines as neuromodulators in cardiovascular control,” Clinical and Experimental Pharmacology and Physiology, vol. 37, no. 2, pp. e52–e57, 2010. View at: Publisher Site | Google Scholar
  120. P. Shi, C. Diez-Freire, J. Y. Jun et al., “Brain microglial cytokines in neurogenic hypertension,” Hypertension, vol. 56, no. 2, pp. 297–303, 2010. View at: Publisher Site | Google Scholar
  121. R. K. Bickerton and J. P. Buckley, “Evidence for a central mechanism in angiotensin induced hypertension,” Proceedings of the Society for Experimental Biology and Medicine, vol. 106, pp. 834–836, 1961. View at: Google Scholar
  122. H. Glossmann, A. J. Baukal, and K. J. Catt, “Properties of angiotensin II receptors in the bovine and rat adrenal cortex,” Journal of Biological Chemistry, vol. 249, no. 3, pp. 825–834, 1974. View at: Google Scholar
  123. J. P. Bennett Jr. and S. H. Snyder, “Angiotensin II binding to mammalian brain membranes,” Journal of Biological Chemistry, vol. 251, no. 23, pp. 7423–7430, 1976. View at: Google Scholar
  124. M. Van Houten, E. L. Schiffrin, and J. F. E. Mann, “Radioautographic localization of specific binding sites for blood-borne angiotensin II in the rat brain,” Brain Research, vol. 186, no. 2, pp. 480–485, 1980. View at: Publisher Site | Google Scholar
  125. F. A. O. Mendelsohn, R. Quirion, J. M. Saavedra, G. Aguilera, and K. J. Catt, “Autoradiographic localization of angiotensin II receptors in rat brain,” Proceedings of the National Academy of Sciences of the United States of America, vol. 81, no. 5, pp. 1575–1579, 1984. View at: Google Scholar
  126. B. P. Rowe, D. L. Saylor, and R. C. Speth, “Analysis of angiotensin II receptor subtypes in individual rat brain nuclei,” Neuroendocrinology, vol. 55, no. 5, pp. 563–573, 1992. View at: Google Scholar
  127. A. N. Epstein, J. T. Fitzsimons, and B. J. Rolls, “Drinking induced by injection of angiotensin into the rain of the rat,” Journal of Physiology, vol. 210, no. 2, pp. 457–474, 1970. View at: Google Scholar
  128. A. K. Johnson and A. N. Epstein, “The cerebral ventricles as the avenue for the dipsogenic action of intracranial angiotensin,” Brain Research, vol. 86, no. 3, pp. 399–418, 1975. View at: Publisher Site | Google Scholar
  129. A. V. Ferguson, D. L. S. Washburn, and K. J. Latchford, “Hormonal and neurotransmitter roles for angiotensin in the regulation of central autonomic function,” Proceedings of the Society for Experimental Biology and Medicine, vol. 226, no. 2, pp. 85–96, 2001. View at: Google Scholar
  130. M. A. Fontes, O. Baltatu, S. M. Caligiorne et al., “Angiotensin peptides acting at rostral ventrolateral medulla contribute to hypertension of TGR(mREN2)27 rats,” Physiol Genomics, vol. 2, no. 3, pp. 137–142, 2000. View at: Google Scholar
  131. R. Casto and M. I. Phillips, “Cardiovascular actions of microinjections of angiotensin II in the brain stem of rats,” American Journal of Physiology, vol. 246, no. 5, Part 2, pp. R811–R816, 1984. View at: Google Scholar
  132. M. D'Amico, F. C. Di, L. Berrino, and F. Rossi, “AT1 receptors mediate pressor responses induced by angiotensin II in the periaqueductal gray area of rats,” Life Sciences, vol. 61, no. 1, pp. PL17–PL20, 1997. View at: Publisher Site | Google Scholar
  133. M. D'Amico, F. C. Di, F. Rossi, and T. D. Warner, “Role of AT2 receptors in the cardiovascular events following microinjection of angiotensin II into the superior colliculus of anaesthetised rats,” Naunyn-Schmiedeberg's Archives of Pharmacology, vol. 357, no. 2, pp. 121–125, 1998. View at: Publisher Site | Google Scholar
  134. M. J. McKinley, E. Badoer, L. Vivas, and B. J. Oldfield, “Comparison of c-fos expression in the lamina terminalis of conscious rats after intravenous or intracerebroventricular angiotensin,” Brain Research Bulletin, vol. 37, no. 2, pp. 131–137, 1995. View at: Publisher Site | Google Scholar
  135. T. Nagatomo, K. Inenaga, and H. Yamashita, “Transient outward current in adult rat supraoptic neurones with slice patch-clamp technique: inhibition by angiotensin II,” Journal of Physiology, vol. 485, no. 1, pp. 87–96, 1995. View at: Google Scholar
  136. C. W. Bourque, D. L. Voisin, and Y. Chakfe, “Stretch-inactivated cation channels: cellular targets for modulation of osmosensitivity in supraoptic neurons,” Progress in Brain Research, vol. 139, pp. 85–94, 2002. View at: Publisher Site | Google Scholar
  137. Z. Lenkei, P. Corvol, and C. Llorens-Cortes, “Comparative expression of vasopressin and angiotensin type-1 receptor mRNA in rat hypothalamic nuclei: a double in situ hybridization study,” Molecular Brain Research, vol. 34, no. 1, pp. 135–142, 1995. View at: Publisher Site | Google Scholar
  138. O. Jöhren and J. M. Saavedra, “Expression of AT1a and AT1b angiotensin II receptor messenger RNA in forebrain of 2-wk-old rats,” American Journal of Physiology, vol. 271, no. 1, pp. E104–E112, 1996. View at: Google Scholar
  139. D. R. Gehlert, S. L. Gackenheimer, and D. A. Schober, “Autoradiographic localization of subtypes of angiotensin II antagonist binding in the rat brain,” Neuroscience, vol. 44, no. 2, pp. 501–514, 1991. View at: Publisher Site | Google Scholar
  140. K. Tsutsumi and J. M. Saavedra, “Characterization and development of angiotensin II receptor subtypes (AT1 and AT2) in rat brain,” American Journal of Physiology, vol. 261, no. 1, pp. R209–R216, 1991. View at: Google Scholar
  141. O. Jöhren, T. Inagami, and J. M. Saavedra, “Localization of AT2 angiotensin II receptor gene expression in rat brain by in situ hybridization histochemistry,” Molecular Brain Research, vol. 37, no. 1-2, pp. 192–200, 1996. View at: Publisher Site | Google Scholar
  142. Z. Lenkei, M. Palkovits, P. Corvol, and C. Llorens-Cortes, “Distribution of angiotensin II type-2 receptor (AT2) mRNA expression in the adult rat brain,” Journal of Comparative Neurology, vol. 373, pp. 322–339, 1996. View at: Google Scholar
  143. F. C. Nunes and V. A. Braga, “Chronic angiotensin II infusion modulates angiotensin II type I receptor expression in the subfornical organ and the rostral ventrolateral medulla in hypertensive rats,” Journal of the Renin-Angiotensin-Aldosterone System, vol. 12, pp. 440–445, 2011. View at: Publisher Site | Google Scholar
  144. L. P. Reagan, M. Theveniau, X. D. Yang et al., “Development of polyclonal antibodies against angiotensin type 2 receptors,” Proceedings of the National Academy of Sciences of the United States of America, vol. 90, pp. 7956–7960, 1993. View at: Publisher Site | Google Scholar
  145. M. I. Phillips, L. Shen, E. M. Richards, and M. K. Raizada, “Immunohistochemical mapping of angiotensin AT1 receptors in the brain,” Regulatory Peptides, vol. 44, no. 2, pp. 95–107, 1993. View at: Publisher Site | Google Scholar
  146. S. G. Wei, Y. Yu, Z. H. Zhang, R. M. Weiss, and R. B. Felder, “Mitogen-activated protein kinases mediate upregulation of hypothalamic angiotensin II type 1 receptors in heart failure rats,” Hypertension, vol. 52, no. 4, pp. 679–686, 2008. View at: Publisher Site | Google Scholar
  147. A. Shekhar, P. L. Johnson, T. J. Sajdyk et al., “Angiotensin-II is a putative neurotransmitter in lactate-induced panic-like responses in rats with disruption of GABAergic inhibition in the dorsomedial hypothalamus,” Journal of Neuroscience, vol. 26, no. 36, pp. 9205–9215, 2006. View at: Publisher Site | Google Scholar
  148. E. Moellenhoff, A. Blume, J. Culman et al., “Effect of repetitive icv injections of ANG II on c-Fos and AT1-receptor expression in the rat brain,” American Journal of Physiology, vol. 280, no. 4, pp. R1095–R1104, 2001. View at: Google Scholar
  149. N. E. Rowland, B. H. Li, M. J. Fregly, and G. C. Smith, “Fos induced in brain of spontaneously hypertensive rats by angiotensin II and co-localization with AT-1 receptors,” Brain Research, vol. 675, no. 1-2, pp. 127–134, 1995. View at: Publisher Site | Google Scholar
  150. Y. M. Kang, Y. Ma, C. Elks, J. P. Zheng, Z. M. Yang, and J. Francis, “Cross-talk between cytokines and renin-angiotensin in hypothalamic paraventricular nucleus in heart failure: role of nuclear factor-κB,” Cardiovascular Research, vol. 79, no. 4, pp. 671–678, 2008. View at: Publisher Site | Google Scholar
  151. Y. M. Kang, Y. Ma, J. P. Zheng et al., “Brain nuclear factor-kappa B activation contributes to neurohumoral excitation in angiotensin II-induced hypertension,” Cardiovascular Research, vol. 82, no. 3, pp. 503–512, 2009. View at: Publisher Site | Google Scholar
  152. L. P. Reagan, L. M. Flanagan-Cato, D. K. Yee, L. Y. Ma, R. R. Sakai, and S. J. Fluharty, “Immunohistochemical mapping of angiotensin type 2 (AT2) receptors in rat brain,” Brain Research, vol. 662, no. 1-2, pp. 45–59, 1994. View at: Publisher Site | Google Scholar
  153. J. Huang, Y. Hara, J. Anrather, R. C. Speth, C. Iadecola, and V. M. Pickel, “Angiotensin II subtype 1A (AT1a) receptors in the rat sensory vagal complex: subcellular localization and association with endogenous angiotensin,” Neuroscience, vol. 122, no. 1, pp. 21–36, 2003. View at: Publisher Site | Google Scholar
  154. G. Wang, J. Anrather, J. Huang, R. C. Speth, V. M. Pickel, and C. Iadecola, “NADPH oxidase contributes to angiotensin II signaling in the nucleus tractus solitarius,” Journal of Neuroscience, vol. 24, no. 24, pp. 5516–5524, 2004. View at: Publisher Site | Google Scholar
  155. M. J. Glass, J. Huang, R. C. Speth, C. Iadecola, and V. M. Pickel, “Angiotensin II AT-1A receptor immunolabeling in rat medial nucleus tractus solitarius neurons: subcellular targeting and relationships with catecholamines,” Neuroscience, vol. 130, no. 3, pp. 713–723, 2005. View at: Publisher Site | Google Scholar
  156. G. Wang, T. A. Milner, R. C. Speth et al., “Sex differences in angiotensin signaling in bulbospinal neurons in the rat rostral ventrolateral medulla,” American Journal of Physiology, vol. 295, no. 4, pp. R1149–R1157, 2008. View at: Publisher Site | Google Scholar
  157. J. P. Pierce, J. Kievits, B. Graustein, R. C. Speth, C. Iadecola, and T. A. Milner, “Sex differences in the subcellular distribution of angiotensin type 1 receptors and NADPH oxidase subunits in the dendrites of C1 neurons in the rat rostral ventrolateral medulla,” Neuroscience, vol. 163, no. 1, pp. 329–338, 2009. View at: Publisher Site | Google Scholar
  158. C. G. Coleman, J. Anrather, C. Iadecola, and V. M. Pickel, “Angiotensin II type 2 receptors have a major somatodendritic distribution in vasopressin-containing neurons in the mouse hypothalamic paraventricular nucleus,” Neuroscience, vol. 163, no. 1, pp. 129–142, 2009. View at: Publisher Site | Google Scholar
  159. G. Wang, C. G. Coleman, M. J. Glass et al., “Angiotensin II type 2 receptor-coupled nitric oxide production modulates free radical availability and voltage-gated Ca2+ currents in NTS neurons,” American Journal of Physiology, vol. 302, pp. R1076–R1083, 2012. View at: Google Scholar
  160. L. Gao and I. H. Zucker, “AT2 receptor signaling and sympathetic regulation,” Current Opinion in Pharmacology, vol. 11, no. 2, pp. 124–130, 2011. View at: Publisher Site | Google Scholar
  161. I. H. Zucker, H. D. Schultz, K. P. Patel, W. Wang, and L. Gao, “Regulation of central angiotensin type 1 receptors and sympathetic outflow in heart failure,” American Journal of Physiology, vol. 297, no. 5, pp. H1557–H1566, 2009. View at: Publisher Site | Google Scholar
  162. L. Gao, W. Wang, Y. L. Li et al., “Sympathoexcitation by central ANG II: roles for AT1 receptor upregulation and NAD(P)H oxidase in RVLM,” American Journal of Physiology, vol. 288, no. 5, pp. H2271–H2279, 2005. View at: Publisher Site | Google Scholar
  163. L. Gao, W. Wang, W. Wang, H. Li, C. Sumners, and I. H. Zucker, “Effects of angiotensin type 2 receptor overexpression in the rostral ventrolateral medulla on blood pressure and urine excretion in normal rats,” Hypertension, vol. 51, no. 2, pp. 521–527, 2008. View at: Publisher Site | Google Scholar
  164. D. C. Merrill, M. W. Thompson, C. L. Carney et al., “Chronic hypertension and altered baroreflex responses in transgenic mice containing the human renin and human angiotensinogen genes,” Journal of Clinical Investigation, vol. 97, no. 4, pp. 1047–1055, 1996. View at: Google Scholar
  165. H. Xia, Y. Feng, T. D. Obr, P. J. Hickman, and E. Lazartigues, “Angiotensin II type 1 receptor-mediated reduction of angiotensin-converting enzyme 2 activity in the brain impairs baroreflex function in hypertensive mice,” Hypertension, vol. 53, no. 2, pp. 210–216, 2009. View at: Publisher Site | Google Scholar
  166. A. I. Rodriguez-Perez, R. Valenzuela, B. Villar-Cheda, M. J. Guerra, J. L. Lanciego, and J. L. Labandeira-Garcia, “Estrogen and angiotensin interaction in the substantia nigra. Relevance to postmenopausal Parkinson's disease,” Experimental Neurology, vol. 224, no. 2, pp. 517–526, 2010. View at: Publisher Site | Google Scholar
  167. J. Rodriguez-Pallares, P. Rey, J. A. Parga, A. Muñoz, M. J. Guerra, and J. L. Labandeira-Garcia, “Brain angiotensin enhances dopaminergic cell death via microglial activation and NADPH-derived ROS,” Neurobiology of Disease, vol. 31, no. 1, pp. 58–73, 2008. View at: Publisher Site | Google Scholar
  168. B. Joglar, J. Rodriguez-Pallares, A. I. Rodriguez-Perez, P. Rey, M. J. Guerra, and J. L. Labandeira-Garcia, “The inflammatory response in the MPTP model of Parkinson's disease is mediated by brain angiotensin: relevance to progression of the disease,” Journal of Neurochemistry, vol. 109, no. 2, pp. 656–669, 2009. View at: Publisher Site | Google Scholar
  169. P. Garrido-Gil, R. Valenzuela, B. Villar-Cheda, J. L. Lanciego, and J. L. Labandeira-Garcia, “Expression of angiotensinogen and receptors for angiotensin and prorenin in the monkey and human substantia nigra: an intracellular renin-angiotensin system in the nigra,” Brain Structure and Function, vol. 218, no. 2, pp. 373–388, 2012. View at: Publisher Site | Google Scholar
  170. R. C. Speth, W. T. Barry, M. S. Smith, and K. L. Grove, “A comparison of brain angiotensin II receptors during lactation and diestrus of the estrous cycle in the rat,” American Journal of Physiology, vol. 277, no. 3, pp. R904–R909, 1999. View at: Google Scholar
  171. B. Zelezna, E. M. Richards, W. Tang, D. Lu, C. Sumners, and M. K. Raizada, “Characterization of a polyclonal anti-peptide antibody to the angiotensin II type-1 (AT1) receptor,” Biochemical and Biophysical Research Communications, vol. 183, no. 2, pp. 781–788, 1992. View at: Google Scholar
  172. D. F. Guo, I. Chenier, V. Tardif, S. N. Orlov, and T. Inagami, “Type 1 angiotensin II receptor-associated protein ARAP1 binds and recycles the receptor to the plasma membrane,” Biochemical and Biophysical Research Communications, vol. 310, no. 4, pp. 1254–1265, 2003. View at: Publisher Site | Google Scholar
  173. B. Deslauriers, C. Ponce, C. Lombard, R. Larguier, J. C. Bonnafous, and J. Marie, “N-glycosylation requirements for the AT1a angiotensin II receptor delivery to the plasma membrane,” Biochemical Journal, vol. 339, Part 2, pp. 397–405, 1999. View at: Publisher Site | Google Scholar
  174. S. AbdAlla, H. Lother, and U. Quitterer, “AT1-receptor heterodimers show enhanced G-protein activation and altered receptor sequestration,” Nature, vol. 407, no. 6800, pp. 94–98, 2000. View at: Publisher Site | Google Scholar
  175. J. L. Cook, R. N. Re, D. L. DeHaro, J. M. Abadie, M. Peters, and J. Alam, “The trafficking protein GABARAP binds to and enhances plasma membrane expression and function of the angiotensin II type 1 receptor,” Circulation Research, vol. 102, no. 12, pp. 1539–1547, 2008. View at: Publisher Site | Google Scholar
  176. M. J. McKinley, E. Badoer, and B. J. Oldfield, “Intravenous angiotensin II induces Fos-immunoreactivity in circumventricular organs of the lamina terminalis,” Brain Research, vol. 594, no. 2, pp. 295–300, 1992. View at: Publisher Site | Google Scholar
  177. H. A. Rockman, K. R. Chien, D. J. U. Choi et al., “Expression of a β-adrenergic receptor kinase 1 inhibitor prevents the development of myocardial failure in gene-targeted mice,” Proceedings of the National Academy of Sciences of the United States of America, vol. 95, no. 12, pp. 7000–7005, 1998. View at: Publisher Site | Google Scholar
  178. J. L. Cook, A. Singh, D. DeHaro, J. Alam, and R. N. Re, “Expression of a naturally occurring angiotensin AT1 receptor cleavage fragment elicits caspase-activation and apoptosis,” American Journal of Physiology, vol. 301, pp. C1175–C1185, 2011. View at: Publisher Site | Google Scholar
  179. J. Benicky, R. Hafko, E. Sanchez-Lemus, G. Aguilera, and J. M. Saavedra, “Six commercially available angiotensin II AT1 receptor antibodies are non-specific,” Cellular and Molecular Neurobiology, vol. 32, pp. 1353–1365, 2012. View at: Publisher Site | Google Scholar
  180. J. M. Adams, J. J. McCarthy, and S. D. Stocker, “Excess dietary salt alters angiotensinergic regulation of neurons in the rostral ventrolateral medulla,” Hypertension, vol. 52, no. 5, pp. 932–937, 2008. View at: Publisher Site | Google Scholar
  181. M. Herrera, M. A. Sparks, A. R. Alfonso-Pecchio, and L. M. T. M. Coffman, “Lack of specificity of commercial antibodies leads to misidentification of Angiotensin type 1 receptor protein,” Hypertension, vol. 61, pp. 253–258, 2013. View at: Publisher Site | Google Scholar
  182. M. C. Michel, T. Wieland, and G. Tsujimoto, “How reliable are G-protein-coupled receptor antibodies?” Naunyn-Schmiedeberg's Archives of Pharmacology, vol. 379, no. 4, pp. 385–388, 2009. View at: Publisher Site | Google Scholar
  183. B. Xue, T. G. Beltz, Y. Yu et al., “Central interactions of aldosterone and angiotensin II in aldosterone- and angiotensin II-induced hypertension,” American Journal of Physiology, vol. 300, no. 2, pp. H555–H564, 2011. View at: Publisher Site | Google Scholar
  184. M. Ito, M. I. Oliverio, P. J. Mannon et al., “Regulation of blood pressure by the type 1A angiotensin II receptor gene,” Proceedings of the National Academy of Sciences of the United States of America, vol. 92, no. 8, pp. 3521–3525, 1995. View at: Google Scholar

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