- About this Journal
- Abstracting and Indexing
- Aims and Scope
- Article Processing Charges
- Articles in Press
- Author Guidelines
- Bibliographic Information
- Contact Information
- Editorial Board
- Editorial Workflow
- Free eTOC Alerts
- Publication Ethics
- Submit a Manuscript
- Subscription Information
- Table of Contents
Asian Journal of Neuroscience
Volume 2013 (2013), Article ID 102602, 18 pages
Renin Angiotensin System in Cognitive Function and Dementia
1Department of Biotechnology, Krishna University, Machilipatnam, Andhra Pradesh 522 001, India
2Department of Biochemistry, Kakatiya University, Vidyaranyapuri, Warangal, Andhra Pradesh 506 009, India
Received 20 July 2013; Accepted 13 August 2013
Academic Editors: Y. Kuroiwa, K. S. J. Rao, and H. Tokuno
Copyright © 2013 Vijaya Lakshmi Bodiga and Sreedhar Bodiga. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Angiotensin II represents a key molecule in hypertension and cerebrovascular pathology. By promoting inflammation and oxidative stress, enhanced Ang II levels accelerate the onset and progression of cell senescence. Sustained activation of RAS promotes end-stage organ injury associated with aging and results in cognitive impairment and dementia. The discovery of the angiotensin-converting enzyme ACE2-angiotensin (1–7)-Mas receptor axis that exerts vasodilator, antiproliferative, and antifibrotic actions opposed to those of the ACE-Ang II-AT1 receptor axis has led to the hypothesis that a decrease in the expression or activity of angiotensin (1–7) renders the systems more susceptible to the pathological actions of Ang II. Given the successful demonstration of beneficial effects of increased expression of ACE2/formation of Ang1–7/Mas receptor binding and modulation of Mas expression in animal models in containing cerebrovascular pathology in hypertensive conditions and aging, one could reasonably hope for analogous effects regarding the prevention of cognitive decline by protecting against hypertension and cerebral microvascular damage. Upregulation of ACE2 and increased balance of Ang 1–7/Ang II, along with positive modulation of Ang II signaling through AT2 receptors and Ang 1–7 signaling through Mas receptors, may be an appropriate strategy for improving cognitive function and treating dementia.
1. Cognition and Dementia
Cognition is a general term that refers to all mental processes, such as perception, thinking, memory, movement, attention, emotions, ability to understand the intentions and thoughts of other people, decision making, and self-awareness. Anecdotal evidence of age-related decline in cognitive functions is amply supported by a wealth of objective data. Mild cognitive impairment (MCI) is a widely used term to indicate a syndrome characterized by a mild memory or cognitive impairment that cannot be accounted for by any recognized medical or psychiatric conditions . The general criteria for MCI require a subjective complaint of memory loss, an objective impairment of memory function for age and education (1 or 2 SD below the mean score of the examined sample) assessed by formal neuropsychological testing, with no evidence of dementia, but preservation of intact activities of daily living and other cognitive domains . In contrast to MCI, a diagnosis of dementia is made when cognitive impairment is greater than that found in normal aging and it affects two or more cognitive domains that comprise orientation, attention, verbal linguistic capacities, visuospatial skills, calculation, executive functioning, motor control, praxia, abstraction, and judgement and the person’s ability to function. In fact, an essential condition to establish the diagnosis of dementia is that the cognitive failure must be severe enough to impair the usual social and occupational daily activities, excluding those deficits that are caused by the motor consequences of stroke. A schematic flow diagram for assessing mild cognitive impairment and dementia is shown in Figure 1. Patients with disturbances of consciousness, delirium, psychosis, serious aphasia, or sensory motor alterations that preclude correct execution of neuropsychological testing are not considered dementia deficits. Additionally, there cannot be present other cerebral or systemic pathologies that could produce a dementia syndrome, such as congestive heart failure and end-stage renal disease. The most common forms of dementia are Alzheimer’s disease (AD) and vascular dementia (VaD) due to microangiopathy, associated with poorly controlled hypertension, with respective frequencies of 70 and 15% of all forms of dementia . The term vascular dementia refers to a group of pathologies that involve cerebral damage of a vascular etiology, with the presence of focal neurological signs compatible with a diagnosis of cerebral ischemia and neuroradiological evidence of cerebral lesions arising because of multiple infarcts from the occlusion of large vessels, strategic single infarcts of the angular gyrus, thalamus, brain stem or cerebral anterior and posterior territories and ischemic lacunae of the subcortical white matter, and periventricular leukoaraiosis . A schematic flow diagram for differential assessment of dementia is given in Figure 2.
1.1. Aging and Cognition
Cognitive impairment and dementia are common interlinked disorders among elderly persons influencing the individual’s ability to function independently. Due to the aging population, the prevalence of cognitive impairment and dementia is increasing . It is also recognized that there is variability in the magnitude and rate of decline in cognitive abilities among aging individuals. A similar phenomenon exists for dementia, where individuals with similar neuropathologic burden present themselves with varying degrees of cognitive impairment. Various potentially modifiable lifestyle factors, social resource factors, and dietary factors have the capacity to modulate the cognitive function in individuals, in addition to genetic, demographic, and other health factors . In this regard, it is important to note that there is increased prevalence of cardiovascular, renal, and other malignant diseases in the aging population. More pertinent is the increase in the prevalence of hypertension, where there is a likelihood of cardiac enlargement (hypertrophy), reduction in ventricular function, and thromboembolic stroke. One of the long-term complications of hypertension is presented clinically as dementia (such as Alzheimer’s disease) or vascular dementia, associated with degenerative central nervous system (CNS) diseases. The temporal correlation between the dementia and the large cerebrovascular pathology implicates that the onset of dementia is within the three months following the diagnosis of ictus, or there is a history of abrupt onset and stepwise progression of the cognitive decline. Hypertension has been known to increase target organ complications such as cardiac enlargement, progressive hypertensive retinopathy, nephropathy, and stroke. Persistent hypertension that results in a decrease in cerebral blood flow, in addition to frequent episodes of stroke or transient ischemic attacks, is associated with vascular dementia and results in cognitive decline, a clinically gradual progression downhill . The principle effect of aging is the progressive elongation of cerebral vessels, which become more tortuous, increasing the minimal blood pressure required to maintain adequate perfusion of the white matter, thereby increasing the susceptibility to ischemia. Although the cerebral autoregulation is designed to maintain constant blood flow independent of variations in perfusion pressure, metabolic factors (the perivascular pH) and mechanical factors (variations in the tone of smooth muscle in the vascular wall) can potentially modify the autoregulation process. The compromise of autoregulation of the cerebral blood flow from systemic hypertension is of a long standing nature and is characterized by alterations in the cerebral vasculature, including vasoconstriction and increased pathological growth with proliferation of smooth muscle, decreased lumen, and decreased vascular compliance . These changes shift the cerebrovascular autoregulation towards the right, in the direction of high blood pressure . As a consequence, there is a decreased capacity of cerebral blood vessels to dilate during hypoperfusion, increasing the vulnerability to brain ischemia and stroke. The mechanisms by which high blood pressure determines a decline in the cognitive function are not completely understood, even though knowledge in this field is increasing . High blood pressure can cause different types of cerebral vascular damage, associated with an increase in atherosclerosis in the larger vessels and in the oxidative stress at the level of the vascular wall . Hypertension is the most important factor that negatively affects the modalities of cerebral aging [10, 11] and is associated with cognitive compromise in aging individuals. This observation has led to the hypothesis that hypertension is one of the factors responsible for the compromise of cognitive function in the elderly, even to the point of dementia. Thus, it is hypothesized that aging leads to hyperactivity of systemic and tissue renin-angiotensin system (RAS) and an increase in neurogenic hypertension, while evidence connecting brain RAS with Alzheimer’ disease, memory, and learning, cognitive functions is evolving . A diagrammatic sketch of the role of renin angiotensin system in inducing hypertension and in mediating cognitive impairment and dementia is shown in Figure 3.
2. Systemic and Brain Renin Angiotensin System
The renin angiotensin system (RAS) is a peptide hormone cascade that controls fluid homeostasis, blood pressure, and hormone secretion, as well as behavioral and cognitive responses through a complex enzymatic pathway generating several peptides . A schematic representation of the renin angiotensin system with key players is presented in Figure 4. Renin, a proteolytic enzyme released from the juxtaglomerular apparatus of the kidney, in response to a decrease in arterial blood pressure, acts on the inactive precursor angiotensinogen to form the decapeptide angiotensin (Ang) I. Liver is the principal site for angiotensinogen (55–60 kDa, 452 aa) synthesis and secretion; mRNA for angiotensinogen is stimulated by corticosteroids, estrogens, thyroid hormones, and angiotensin II in fat, certain regions of the central nervous system, and kidney . There is evidence within the brain of renin mRNA  and cells in the pituitary, choroid plexus, medulla oblongata, and hypothalamus are positive for renin immunoreactivity. The renin present in the cells of the choroid plexus would be positioned for release and has the ability to act on the angiotensinogen in the extracellular milieu. Renin immunoreactivity is localized in neurons, but in the medulla oblongata and subfornical organ, it has been demonstrated in glial elements as well. However, renin mRNA, as an indicator of synthesis of the protein, is predominant but not exclusive in neurons [16, 17]. Both secreted and nonsecreted forms of renin are present in the brain of rodents and humans [18, 19] and their overexpression results in a hypertensive phenotype, adding credence to the notion that brain RAS indeed exists and plays an important role in the regulation of blood pressure. The concentration of angiotensinogen in the circulation is approximately equal to the of renin (1.25 μM), and therefore, angiotensinogen availability is an important determinant of the rate of angiotensin formation . Angiotensinogen synthesis in astrocytes and its secretion into the interstitial space and cerebrospinal fluid were shown to be the major source of substrate for brain Ang II formation . It is well known that angiotensinogen is an extracellular component of cerebrospinal/interstitial fluid and constitutes one of the most abundant proteins in cerebrospinal fluid  and the production of the precursor protein is primarily glial . Overexpression of antisense to angiotensinogen behind a glial-fibrillary acidic protein (GFAP) promoter results in loss of 90% of the brain angiotensinogen . However, angiotensinogen is also found in neurons , most often in brain centers involved in cardiovascular regulation such as the subfornical organ, paraventricular nucleus, nucleus of the solitary tract, and rostroventrolateral medulla. In addition, angiotensinogen immunoreactivity is present at sites other than those associated with blood pressure (BP) and fluid and electrolyte homeostasis providing evidence that the brain RAS may serve in other capacities and is not limited to cardiovascular regulatory functions.
2.1. Formation of Ang II
The 14 amino acids at the N-terminus are the relative portion of angiotensinogen from which Ang I is derived by the active renin. Ang I, in turn, is hydrolyzed at the carboxy terminal by the action of angiotensin-converting enzyme (ACE), an ectoenzyme and a zinc metalloproteinase, to form the active octapeptide, Ang II. Expression of local Ang II was reported in the hypothalamic paraventricular nucleus (PVN), supraoptic nucleus, circumventricular organs (CVOs), and nucleus of the tractus solitarii (NTS) neuronal cell bodies . ACE mRNA was detectable in choroid plexus, caudate putamen, cerebellum, brain stem, hippocampus, and pineal gland. In addition, quantitative autoradiography established the presence of relatively high levels of ACE protein in the choroid plexus, blood vessels, subfornical organ, and organum vasculosum of the lamina terminalis and relatively low levels in the thalamus, hypothalamus, basal ganglia, and posterior pituitary gland. Most convincingly, ACE could be colocalized with renin in synaptosomal fractions of the brain . Human ACE contains 1277 amino acid residues with 2 homologous catalytic sites and a region for binding Zn2+ . Human ACE is made up of a large extracellular domain, a short intracellular carboxy-terminal domain, and a 17 amino acid hydrophobic stretch that allows the ACE to anchor to the cell membrane. ACE is widely distributed in the body, with relatively high levels in the lungs and kidneys, but is also present in the brain. Membrane ACE that has undergone proteolysis at the cell surface by a secretase is associated with the luminal surface of vascular endothelial cells and is in close contact with the circulation . Membrane-bound ACE, rather than soluble ACE, is believed to be responsible for the regional or local tissue conversion of Ang I into Ang II. This process follows first-order kinetics, since the angiotensin I levels in circulation or the interstitium are approximately six orders of magnitude below the for angiotensin I (16 M). First-order kinetics will apply even at angiotensin I levels that are 10,000-fold higher than normal. Accordingly, Ang II formation from Ang I is similar over a wide range of arterial Ang I levels. Ang II results in elevation of blood pressure by promoting vasoconstriction, upregulates renal sodium and water absorption, increases cardiac output, sympathetic tone, and arginine vasopressin release, and stimulates the sensation of thirst in the central nervous system [28, 29]. ACE, which is present in the endothelial cells of the blood vessels, has an additional effect of degrading bradykinin, an active vasodilator .
2.2. Mechanisms of Ang II Action
Ang II binds to one of the G-protein coupled receptors, termed AT1 or AT2. AT1 is the primary receptor that mediates vasoconstriction, water intake, sympathetic nervous system activation, and aldosterone, vasopressin, and endothelin secretion. Ang II also contributes to vascular smooth muscle hypertrophy, migration, proliferation, and growth, which act in concert to raise the blood pressure . In addition, AT1 receptor mediates a number of other biological actions in cardiovascular and renal tissues that include cytokine production by monocytes and macrophages, leading to inflammation, plasminogen activator inhibitor-1 (PAI-1) biosynthesis, platelet activation, aggregation, and adhesion, leading to thrombosis; collagen biosynthesis leading to fibrosis; and low-density lipoprotein transport leading to atherosclerosis. Many of these actions of Ang II have an underlying common mechanism that increases the influx of extracellular Ca2+ and mobilization of intracellular Ca2+. An increase in intracellular Ca2+ level activates acute contractile responses and also activates various cellular kinases, including mitogen-activated protein kinase (MAPK), to induce cell proliferation signaling. Ang II also generates reactive oxygen/nitrogen species, especially superoxide anion, via stimulation of NAD(P)H oxidase complex, with accompanying formation of peroxynitrite and, in the process, decreases the bioavailability of endogenous nitric oxide, an efficient vasodilator. Increased cardiac contractility, along with cardiac and vascular remodeling, and reduction in vascular compliance are widely reported effects of Ang II in vitro and in vivo. This classical axis can be called the ACE-Ang II-AT1 receptor axis. These effects of Ang II can be attenuated or partially overcome by AT1-mediated short-loop negative feedback suppression of renin biosynthesis and secretion at renal juxtaglomerular cells. In contrast, Ang II acting via AT2 induces vasodilation of both resistance and capacitance vessels, natriuresis, and inhibition of cellular proliferation and growth [32, 33]. AT2 receptors are present in brain, heart, adrenal medulla, kidney, and reproductive tissues. The AT2 receptor is involved in fetal development and control of nocturnal arterial blood pressure in rats . Both AT1 and AT2 receptors bind to Ang II with the same affinity but have contrasting effects. The relative balance between AT1 and AT2 receptor functions may be influenced by receptor expression patterns in tissues. AT1 receptors are highly expressed in the cardiovascular, renal, endocrine, and nervous systems of adults. AT2 receptor expression is quantitatively less and its tissue distribution is more limited than in AT1 receptors. Thus, the RAS plays an important role in normal cardiovascular homeostasis, and overactivity of the RAS has been implicated in the development of various cardiovascular diseases, such as hypertension, congestive heart failure, coronary ischemia, and renal insufficiency . Therefore, ACE inhibitors and angiotensin receptor blockers (ARBs) that target ACE-AngII-AT1 receptor axis are of great therapeutic benefit in the treatment of cardiovascular disease. Beneficial effects of ARBs are not only contributed by blocking AngII-AT1 receptor binding, but also by enabling AngII-AT2 receptor interactions, as the AT2 receptor stimulation seems to antagonize the signaling associated with AT1 receptor stimulation. It was long established that infusion of Ang II into the brain could increase blood pressure  and central injection of purified Ang II near the hypothalamus resulted in a drinking response [37, 38], suggesting the presence of specific receptors in brain tissue. The distribution of AT1 and AT2 receptors in brain has been well studied in rat and mouse models [39–49]. In the central nervous system, AT1 receptors are localized to areas of the brain that are exposed to blood borne Ang II, such as the circumventricular organs, including the subfornical organ, median eminence, vascular organ of the lamina terminalis, anterior pituitary, and the area of postrema in the hindbrain [47, 50]. Other regions of the hypothalamus, nucleus of the solitary tract, and ventrolateral medulla in the hindbrain also contain a high density of AT1 receptors . In line with the existence of AT1 receptors in brain, it is well documented that Ang II facilitates sympathetic transmission by enhancing the release of noradrenaline from peripheral nerve terminals as well as from the central nervous system [51, 52]. Moreover, Ang II stimulates the release of catecholamines from the adrenal medulla and aldosterone from the adrenal cortex . Ang II also exerts diverse actions on the brain by modulating drinking behavior and salt appetite, central control of blood pressure, and stimulation of pituitary hormone release and has effects on learning and memory [29, 54, 55]. Furthermore, existence of alternative pathways for Ang II formation such as chymase, cathepsin G, chymostatin-sensitive Ang II-generating enzyme (CAGE), tissue plasminogen activator, and tonin is reported [56, 57]. The main feature of this system is its distinction from the other local or tissue RAS, since it is physically separated from the endocrine RAS by the presence of the blood-brain barrier, thus preventing the diffusion of Ang II from the circulation into the brain . However, there exist several areas lacking a blood-brain barrier, called circumventricular organs (CVOs), located in the proximity of the 3rd and 4th ventricles, the vascular organ of the lamina terminalis, the subfornical organ, the median eminence, the intermediate and the posterior lobes of the hypophysis, the subcommissural organ, the pineal gland, and the area postrema [59, 60]. Most of these CVOs have fenestrated capillaries allowing molecules of large molecular weight to cross back and forth between the circulation and the cerebrospinal fluid; therefore circulating Ang II may still produce some effects inside the brain . Thus, there appears to be two closely integrated central Ang II systems, one responding to Ang II generated within the brain and stimulating receptors inside the blood-brain barrier and another with Ang II receptors in circumventricular organs and in cerebrovascular endothelial cells, responding to circulating Ang II of peripheral and/or tissue origin [62–64]. Nevertheless, the local brain RAS is thought to play a functional role in the maintenance of the BBB. Angiotensinogen, but not renin, levels in the brain appear to be relevant for this function, since a decrease in density in granular layer cells of hippocampus resulted in an impaired blood-brain barrier function which is seen in angiotensinogen-deficient mice, whereas renin-deficient mice do not show this phenotype . Other studies in knockout mice came to similar conclusions. Astrocytes of angiotensinogen knockout mice had significantly attenuated expression of glial fibrillary acidic protein and decreased laminin production in response to cold injury and ultimately incomplete reconstitution of impaired blood-brain barrier function . These data are in contrast to reports by Rose and Audus  who suggested AT1 receptor-mediated uptake and transport of Ang II at the site of the bovine blood-brain barrier. This has been questioned since there is no evidence that angiotensins cross the blood-brain barrier and penetrate noncircumventricular organ structures . Monti et al.  found functional upregulation of the AT1 receptors inside the blood-brain barrier in a transgenic rat line with specific downregulation of astroglial synthesis of angiotensinogen. The authors have found higher AT1 receptor binding in most of the regions inside the blood-brain barrier in transgenic rats compared with controls. In contrast, in the circumventricular organs investigated, AT1 receptor binding was significantly lower in transgenic rats.
2.3. Other Angiotensins
Alternatively, angiotensin III (Ang 2–8) is produced from Ang II by the actions of aminopeptidase A, a zinc metallopeptidase that cleaves the N-terminal aspartyl reside of Ang II. Further, action of aminopeptidase N on Angiotensin III results in the formation of Ang IV (Ang 3–8). Both aminopeptidases A and N are present in the rodent brain [70–72]. The AT4 receptor is defined as the high affinity binding site that selectively binds Ang IV with 1–10 nM affinity . AT4 receptors are widely distributed in the guinea pig, rat, sheep, monkey, and human brain, and the distributions are highly conserved through these species [74–78]. The receptor sites occur in high abundance in the basal nucleus of the Meynert, in the CA1 to CA3 regions of the hippocampus, and throughout the neocortex, a distribution that closely resembles cholinergic neurons and their projections and is consistent with the memory enhancing properties of the AT4 ligands. High levels of the receptors are also found in most brain regions involved in motor control. The AT4 receptor was shown to be insulin-regulated aminopeptidase (IRAP), a type II integral membrane protein belonging to the M1 family of zinc-dependent metallopeptidase .
2.4. ACE2 and Ang 1–7
To add to this complexity, an enzyme that can act upon Ang I and Ang II to produce Ang 1–9 and Ang 1–7, respectively, has been identified as a new component of the renin-angiotensin system [80–82]. This enzyme, known as ACE2, exhibits a high catalytic efficiency for the conversion of Ang II to Ang 1–7, almost 500-fold greater than that for the conversion of Ang I to Ang 1–9 . ACE2 shares 42% nucleotide sequence homology with ACE and conservation of active sites residues is an eminent feature [80, 83]. Similar to ACE, ACE2 is widely distributed in cells and tissues with high concentrations in cardiorenal and gastrointestinal tissues and limited expression in the central nervous system and lymphoid tissues [84, 85]. Low levels of ACE2 mRNA were shown in the human brain using quantitative real-time RT-PCR , while immunohistochemistry showed that ACE2 protein was restricted to endothelial and arterial smooth muscle cells of cerebral vessels . In primary cultures, ACE2 was predominantly expressed in glial cells  and neurons . Using a selective antibody, it was found that ACE2 is widespread throughout the brain, present in nuclei involved in the central regulation of cardiovascular functions like the cardiorespiratory neurons of the brainstem, as well as in noncardiovascular areas such as the motor cortex and raphe . This observation was later confirmed by Lin et al. showing the presence of ACE2 mRNA and protein in the mouse brainstem . Both ACE and ACE2 are type 1 glycoproteins with two domains, but ACE has two catalytic sites, whereas ACE2 has only one catalytic site. ACE2 is carboxymonopeptidase with a preference for hydrolysis between a proline and carboxyterminal hydrophobic or basic residues, whereas ACE cleaves two amino acids from its substrate . A more clinically important finding is that the ACE2 activity is not directly affected by ACE inhibitors . Figure 5 presents the amino acid sequences of different angiotensins produced from angiotensinogen by the action of cellular enzymes.
Consistent with the evidence that ACE2 is present in the brain, Ang 1–7 was shown to be present as an endogenous constituent of the brain, in areas including hypothalamus, medulla oblongata, and amygdale, as well as adrenal glands and plasma of normotensive rats . It is likely that the synthesis of Ang 1–7 takes place most in the extracellular space since ACE2 is a transmembrane protein with its catalytic site located outside the cell . However, because ACE2 conserves its activity even after shedding by A disintegrin and A metalloproteinase 17 (ADAM17), one can imagine that endocytosis of the secreted enzyme could lead to formation of the heptapeptide inside the cell. In line with this speculation, ACE2 enzyme was localized in the cytoplasm of neurons in the mouse brain . Interestingly, Ang 1–7 can be further metabolized into Ang 1–5 by ACE  or Ang 1–4 by neprilysiN . Ang 1–7 was shown to bind to a G-protein coupled receptor, Mas encoded by the Mas protooncogene. Mas, protein has seven hydrophobic transmembrane domains, whereas N- and C-terminal ends are hydrophilic and share strong sequence similarity with the GPCR subfamily of hormone receptor proteins . More specifically, Mas belongs to the Class A orphan GPCRs. Mas is expressed in the brain, where its mRNA has been located in the hippocampus, dentate gyrus, piriform cortex, and amygdala [96–98]. In fact, brain was the first organ where Mas was found to be highly expressed . High amounts of Mas transcripts are present in the hippocampus and cerebral cortex of rat brain . Martin et al.  could show by in situ hybridization that Mas mRNA is expressed in a subpopulation of neurons in both the adult and developing rat central nervous systemS (CNS). In the adult CNS, Mas mRNA was most abundant in hippocampal pyramidal neurons and dentate granule cells but also presented at low levels in the cortex and thalamus. Recently, Mas expression was also discovered in cardiovascular regions of the brain by western blot and immunofluorescence . Furthermore, brief seizure episodes led to a significant and transient increase in Mas mRNA in the rat hippocampus, which may contribute to anatomical and physiological plasticity associated with intense activation of hippocampal pathways . In the mouse, the distribution of Mas mRNA in the brain is comparable to the rat being highest in the hippocampus and piriform cortex as detected by in situ hybridization .
ACE2 shares 42% sequence identity with the catalytic domain of ACE. In addition, ACE2 can convert Ang II into Ang (1–7). ACE2 shows 400-fold higher substrate preference for Ang II than for Ang I . ACE2 is expressed in heart, kidney, liver, and intestine . ACE2 may play a role as negative regulator of ACE. Furthermore, ACE2 acts as a tissue-specific negative feedback regulator of the activated RAS. This action is probably mediated by Ang (1–7) and bradykinin , which is in agreement with the reduced ACE2 level in several rat models of hypertension . Deficiency of functional ACE2 resulted in severe cardiac dysfunction associated with an accumulation of cardiac Ang II . Chronic treatment with AT1 receptor antagonist induced ACE2 mRNA level in the SHR rats as well as increased Ang (1–7) level . ACE inhibitors promote Ang II antiproliferation by increasing the generation of Ang (1–7) in the vasculature . In addition, Ang 1–7 has vasodilator and antiproliferative properties [107–109]. ACE2 thus appears to have emerged to modulate pressor/mitogenic and depressor/growth inhibitory arms of the renin-angiotensin system by converting Ang II to Ang 1–7.
3. Cognitive and Behavioural Effects of Renin-Angiotensin System Components
Several studies provided convincing evidence in favor of hyperactive brain RAS in the development and maintenance of hypertension [110–114]. In normotensive models, Ang II acting on brain AT1R [111, 112] induces an increase in blood pressure mediated by enhanced sympathetic outflow [115–117] and cardiac baroreflex resetting . In spontaneous hypertensive rat (SHR), upregulation of brain RAS components (AGT, Ang-II, ACE, and AT1R) precedes and sustains the development of hypertension [112, 118–122]. Although the precise mechanisms by which Ang II triggers hypertension are not known, it seems to involve increased sympathetic vasomotor tone and altered cardiac baroreflex function .
3.1. Actions of Ang II in the Brain
Angiotensin II (Ang II), initially described as a peripheral circulating hormone regulating blood pressure and fluid homeostasis, has been recognized as a brain neuromodulator inducing fluid and salt intake and blood pressure increase . A diagrammatic view of the brain indicating Ang-II-sensitive areas is shown in Figure 6. There are two closely integrated central Ang II systems, one responding to Ang II generated in the brain and stimulating receptors inside the blood-brain barrier and another with Ang II receptors in circumventricular organs and in cerebrovascular endothelial cells, responding to circulating Ang II of peripheral origin or to locally generated Ang II, or both [62–64]. Ang II type 1 (AT1) receptors located in selective forebrain and brain stem structures mediate the classical functions of brain Ang II, including the control of the hormonal and central sympathetic systems [63, 64]. The selective localization of large numbers of AT1-receptors in sensory pathways, all limbic structures , and the endothelium of cerebral microvessels  indicated the possibility of several additional central roles for Ang II, including the regulation of the reaction to stress, brain development, neuronal migration, sensory information and motor activity, cognition, control of emotional responses, and cerebral blood flow.
The cognitive effects of Ang II, the dominant effector molecule of the RAS, are well recognised. Ang II inhibits acetylcholine release in fresh tissue slices of human temporal cortex  and rodent amygdala . Acetylcholine (Ach) is critical for communication between neurons and muscle at the neuromuscular junction, is involved in direct communication in autonomic ganglia, and has been implicated in cognitive processing, arousal, and attention in the brain . Ang II alters the sensory transmission in lateral geniculate neurons . In addition, it suppresses long-term potentiation (LTP), a measure of synaptic excitability duration that can be stimulated to last from days to months, in the hippocampus and amygdala of rats, acting through the AT1 receptor . Ang II has also been found to interfere with memory acquisition in research animals . Ang II administered in the brain disrupted an operant task in rabbits. On the other hand, it has been reported that centrally administered Ang II improves aversive memory , but using similar learning tasks, others have shown that this peptide either impairs or does not affect memory retention [132, 133]. Ang II administered to the hippocampus affects memory by the activation of AT1  or AT2 receptors . The hippocampal Ang II [135–138] and specific receptor analogues of Ang II are reported to block LTP  and selectively impair olfactory and spatial learning , indicating that LTP is related to important cognitive processes through RAS. Moreover, antagonist action at AT1 or AT2 sites may exhibit cognitive enhancing effects [141–143]. A possible role for hippocampal Ang II receptors in voluntary exercise-induced enhancement of learning and memory in rat was proposed recently . Similarly, when angiotensin II is injected directly into the dorsal neostriatum, retention of a stepdown shock avoidance response is impaired, whereas retrieval in a similar passive avoidance conditioning task improves the following intracerebroventricular administration of angiotensin II . It was also reported that Ang II exhibits both inhibitory and stimulatory effects in 8-arm radial maze and Y maze tasks . Recent studies demonstrated that Ang II modulates long-term depression (LTD) in the lateral amygdala of mice. This effect on synaptic plasticity may be dependent on AT1 receptors, since losartan blocked the Ang-II-induced effect on LTD, whereas AT2 receptors seem not to be involved. Also, the importance of L-type calcium channels in this process was demonstrated . Role of brain RAS in retention impairment was also documented . A recent report showed increased ACE activity and angiotensinogen levels in cerebrospinal fluid of patients with mild cognitive impairment and Alzheimer’s disease . Thus, several lines of evidence clearly established the contributions of renin-angiotensin system components towards modulating cognitive function.
3.2. AT1 Receptor Blockers and AT2 Receptor Agonists Affect Cognitive Function
Since AT1 receptor is a major target for antihypertensive drugs, ACE inhibitors, which reduce the conversion of Ang I to Ang II, are believed to facilitate cognitive functioning, probably by decreasing Ang II and thus removing inhibitory influence upon acetylcholine release [130, 149]. ACE inhibitors in particular, such as captopril and perindopril, which affect the central RAS, have distinct cognitive effects. In addition, preventing the formation of Ang II releases inhibition of potassium-induced exocytosis of acetylcholine, resulting in facilitation of memory consolidation and retrieval . Recent studies show that Ang II inhibitors help to preserve cognitive functions in patients with Alzheimer’s disease through a mechanism that is independent of the blood-pressure-lowering effect . Also, angiotensin-converting enzyme (ACE) inhibitors enhance conditioned avoidance and habituation memory and it has been shown that angiotensin-II-deficient mice present normal retention of spatial memory . Chronic administration of ramipril to whole-brain irradiated F344 rats prevented perirhinal cortex-dependent cognitive impairment by attenuating microglial activation in the dentate gyrus and improving neurogenesis . In an AD mouse model induced by intracerebroventricular injection of amyloid-β (Aβ) 1–40, administration of perindopril (brain penetrating ACE inhibitor) significantly inhibited hippocampal ACE activity and prevented cognitive impairment that was attributed to the suppression of microglial/astrocyte activation and attenuation of oxidative stress caused by iNOS induction and downregulation of extracellular superoxide dismutase . In contrast, neither enalapril nor imidapril (non-brain-penetrating ACE inhibitors) prevented cognitive impairment and brain injury in this AD mouse. Mice lacking AT2 receptor gene are significantly impaired in their performance in a spatial memory task and in a one-way active avoidance task .
Chronic activation of brain RAS with sustained production of angiotensin II induces cerebrovascular remodelling, promotes vascular inflammation and oxidative stress leading to endothelial dysfunction, and thereby impairs regulation of cerebral blood flow [156, 157]. It is also well known that CBF decreases with aging impairing cognitive function with the stimulation of AT1 receptor with a decrease in CBF and increase in oxidative stress. Significant reduction in the incidence and progression of Alzheimer’s disease and dementia was reported in a population aged 65 years or more with cardiovascular disease with the use of ARBs . Administration of an ARB, olmesartan, attenuated the increase in blood pressure and ameliorated cognitive decline with the enhancement of cerebral blood flow and a reduction in oxidative stress in hRN/hANG-Tg mice carrying human renin and angiotensinogen genes . Pretreatment with a low dose of olmesartan completely prevented beta-amyloid-induced vascular dysregulation and partially attenuated the impairment of hippocampal synaptic plasticity in young Alzheimer’s disease model transgenic mice (APP23 mice) with cerebrovascular dysfunction .
AT blocker, telmisartan, administered to hypertensive patients with probable Alzheimer’s disease showed increased region cerebral blood flow in the right supramarginal gyrus, superior parietal lobule, cuneus, and lingual gyrus, without any changes in cognitive function test scores . In normotensive young adults, acute administration of losartan improved performance on a task of prospective memory and reversed the detrimental effects of scopolamine in a standard lexical decision paradigm with the incorporation of a prospective memory component, highlighting the cognitive enhancing potential of losartan on compromised cognitive systems in normotensive subjects . Antihypertensive mediations targeting AT1 could therefore be successful in reducing the incidence of Alzheimer’s disease (AD) and improving cognitive function.
The importance of relative AT2 receptor stimulation during ARB treatment has been reported in terms of protection against brain damage, promoting cell differentiation and regeneration of neuronal tissue , through activation of mitogen-activated protein kinase  or nitric oxide . Direct stimulation of AT2 receptor by a newly generated agonist, compound 21 (C21), enhanced cognitive function in wild-type C57BL6 mice and an Alzheimer’s disease mouse model with intracerebroventricular injection of amyloid-β (1–40) . C21, an orally active nonpeptidergic highly selective AT2 receptor agonist, promoted cerebral blood flow and neurite outgrowth of cultured hippocampal neurons .
It has been proposed that ARBs prevent or modulate accumulation of misfolded proteins, including the amyloid (Aβ) peptide responsible for oxidative and inflammatory damage that leads to energy failure and synaptic dysfunction . The Ang II receptor antagonists, losartan and PD123177, which are selective for the AT1 and AT2 receptor subtypes, respectively, constitute important pharmacological tools for the assessment of behavioral consequences through the modulation of Ang II function [145, 168]. Several studies have shown that low doses of losartan and PD123177 improved scopolamine-impaired performance in a light/dark box habituation task. Similarly a countering effect was observed in the case of captopril and ceranopril .
3.3. Role of Ang IV and AT4 Receptors in Cognition
In addition, the activation of AT4 receptor by native Ang IV or AT4 agonists improves learning and memory . Central administration of Ang IV in rodents stimulates exploratory locomotor behaviour, enhances recall in passive avoidance situations, and facilitates memory retention . Ang IV increases potassium-evoked acetylcholine release in the hippocampus, suggesting that the brain cholinergic system may underlie, at least in part, the mechanism of this AT4 receptor-mediated memory enhancement .
3.4. Behavioural Effects of RAS Components
In addition to their cognitive effects, RAS components exert behavioural effects. A modulatory action of Ang II on anxiety has been reported, and the brain RAS may be involved in the course of affective disorders [13, 170]. ACE inhibitors, especially captopril, have mood-elevating effects in depressed patients. Dopaminergic pathways may play a role in the anxiety-modulating effects of Ang II, but additional involvement of GABAergic pathways has also been suggested, since Ang II was found to potentiate the actions of GABA.
AT1 antagonist treatment reduced anxiety and improved learning, spatial working memory, and motor performance in the aged rat [132, 134, 171, 172]. Transgenic chimera mice with human renin and angiotensinogen genes mimicking continuous activation of the brain renin-angiotensin system showed impaired cognitive function as assessed by the shuttle avoidance test. The mice were found to show a decrease in cerebral surface blood flow, increased activity of p47phox and Nox4, and an increase in oxidative stress. Administration of an angiotensin II type 1 receptor blocker, olmesartan, attenuated the increase in blood pressure and ameliorated cognitive decline with enhancement of cerebral blood flow and reduction of oxidative stress . C57BL/6J mice prepared as a model of subcortical vascular dementia by subjecting to bilateral common carotid artery stenosis with microcoil to result in chronic cerebral hypoperfusion showed significantly increased brain renin activity and angiotensinogen expression that was attributed to increased renin in activated astrocytes and microvessels and the increased angiotensinogen in activated astrocytes of the white matter. The upregulation of renin and angiotensinogen resulted in increased NADPH oxidase activity, oxidative stress, glial activation, white matter lesions, and spatial working memory deficits. Pretreatment or posttreatment of these mice with a direct renin inhibitor, aliskiren, or a superoxide scavenger, tempol, ameliorated the brain damage and working memory deficits .
3.5. Modulation of RAS Affects Cognitive Function
Furthermore, treatment with an angiotensin receptor blocker (ARB) ameliorates the cognitive impairment in mice fed a high-salt and cholesterol diet, or type 2 diabetic mice [174, 175]. ARBs were also shown to decrease BBB permeability in diabetic rats , suggesting that activation of the brain RAS is involved in the pathogenesis of cognitive impairment. On the other hand, long-term inhibition of RAS improves memory function in aged, low-salt-treated, normotensive, Dahl salt-sensitive (DSS) rats . In yet another study, DSS/hypertensive rats with leakage of brain microvessels in the hippocampus showed impaired cognitive function with a parallel increase in brain Ang II levels and a decrease in mRNA levels of tight junctions (TJs) and collagen-IV in the hippocampus, indicating disruption of BBB. Olmesartan treatment decreased brain Ang II levels, restored mRNA expression of TJs and collagen-IV, and restored the cognitive decline without altering the blood pressure . It is assumed that Ang II stimulates the production of proinflammatory cytokines and activates matrix metalloproteinases (MMPs), which are involved in TJ disruption and BBB permeability changes, leading to cognitive dysfunction [179–181]. It is important to mention that few ARBs can partially penetrate the BBB at very low concentrations and selectively inhibit central AT1 receptors that may or may not be sufficient enough to regulate brain RAS.
Ang III (2–8) binds with similar affinity to the AT1 receptor as Ang II and acts as an agonist. Therefore, it is believed that Ang III behaves similarly to Ang II in eliciting responses in brain as well as in cardiovascular tissues. Ang III appeared twice as effective as Ang II in stimulating the firing rate of certain neurons in hypothalamic paraventricular and supraoptic nuclei, ventrolateral medulla, and nucleus of the solitary tract . These studies provide evidence in favor of the pathophysiological overexpression of some of the RAS components in impairing cognitive function in experimental animal models and the beneficial effects of RAS inhibitors and blockers in ameliorating the cognitive decline.
Recently several large clinical studies [158, 183] have reported that antihypertensive drugs that modulate the RAS, that is, RAS blockers, such as angiotensin receptor blockers [ARBs] or angiotensin-converting enzyme [ACE] inhibitors, are associated with a decreased incidence of AD and reduced rates of cognitive decline in patients with mild cognitive impairment . The RAS is implicated in hypertension and adipose tissue metabolism  and has recently attracted interest because of its potential involvement in the pathogenesis of AD . The RAS exerts its effects through the generation and action of angiotensin II, which has potent vasoconstrictor, antinatriuretic, and dipsogenic properties. Angiotensin II is generated by the serial cleavage of angiotensinogen, first by renin and then by ACE. Angiotensin II exerts its well-known hypertensive effects by binding to its two receptors (AT1R and AT2R) . A potential relation between ACE and AD was first suggested by human genetic studies, which reported that an insertion/deletion polymorphism within intron 16 of the ACE gene is associated with AD . In addition to vascular systems, accumulating evidence suggests that the brain has certain components of the RAS that may have crucial roles in learning and memory processes [177, 187]. For example, ACE is upregulated in the hippocampus, frontal cortex, and caudate nucleus of patients with AD [188, 189]. In adipose tissues, angiotensin II participates in adipocyte growth, differentiation, and metabolism, thereby reducing adiponectin secretion . Treatment with RASB thus substantially increases adiponectin levels and may improve insulin sensitivity in hypertensive patients . Therefore, RASB has been recently recommended as the antihypertensive drug of choice for Japanese patients with metabolic syndrome . Because metabolic syndrome is one of the nongenetic risk factors for AD, RASB also may affect cognitive function beneficially by improving insulin resistance. In a recent retrospective study of Alzheimer’s disease patients with and without hypertension, it was reported that RAS blockers in hypertensives showed increased visceral fat accumulation, adipocytokine secretion, and improved cognitive function . In addition to endocrinological effects, direct effects of RASB on the central nervous system have been reported. RASBs decrease the production of angiotensin II, which inhibits potassium-mediated release of acetylcholine , BBB maintenance , and cell survival via AT1R and AT2R receptors . These effects of RASB on brain RAS may improve neuronal metabolic functions and, consequently, decrease cognitive impairment in patients with AD.
Targeted disruption of the Mas protooncogene led to an increased durability of LTP in the dentate gyrus, without affecting hippocampal morphology, basal synaptic transmission, or presynaptic function. The permissive influence of Mas deletion on hippocampal synaptic plasticity was paralleled by behavioral changes such as anxiety behavior [196, 197]. In addition, cell numbers in the hippocampus are not changed in Mas-KO mice compared to their WT in contrast to that in - and AT2-deficient mice . Direct effect of Ang 1–7 on limbic plasticity studies in WT and Mas-KO mice showed for the first time that Ang 1–7 enhances LTP in the hippocampus, which was abolished by Mas receptor antagonist A779, suggesting a role for Ang 1–7 in modulating learning and memory. Mas-KO mice exhibited more robust LTP than WT mice, without any change in the cell numbers and AT1 receptor density or distribution in the hippocampus . It has been demonstrated that Mas interacts with AT1 receptor and inhibits the actions of Ang II, thus being a physiological antagonist of AT1 receptor [199, 200].
The ability of angiotensin-converting enzyme (ACE) inhibitors to facilitate cognitive processes and to improve emotional feeling in patients [126, 201] may be, therefore, not only related to reduced availability of Ang II but might be also due to an increase in the level of Ang 1–7. Consequently, the pharmacological stimulation of ACE2/Ang 1–7/Mas axis could be a new promising target for the improvement of learning and memory in the older population but also in young patients with learning deficits. Brain-specific overexpression of ACE2 (neuron-targeted) effectively reversed the effects of chronic administration of Ang II, preventing neurogenic hypertension and enhancing drinking behavior in the Ang II “slow pressor” model. Infusion of a low concentration of Ang II is most effective at reaching the brain via the blood-brain barrier-deficient circumventricular organs and acting on nuclei controlling blood pressure rather than directly affecting peripheral vasculature, leading to neurogenic hypertension via increased sympathetic outflow . In this model, it was shown that the pressor response to acute Ang II essentially involved ACE2-mediated Ang II hydrolysis and AT1 receptor downregulation, further reducing Ang II downstream signaling , the reversal of neurogenic hypertension. Most importantly, blockade of Ang (1–7)/Mas receptors permitted the development of hypertension in this model, indicating that ACE2-expression-mediated decrease in neurogenic hypertension is indeed due to hydrolysis of Ang II to the form Ang(1–7), which in turn acted on Mas receptors. This is indeed supported by their observation that both Mas and AT2 receptors were upregulated by ACE2 overexpression .
Central infusion of Ang IV facilitates memory retention and retrieval in rats in passive avoidance paradigms [205, 206]. Moreover, chronic infusions of the more stable analogue of Ang IV, Nle1-Ang IV, improved performance in rats in the spatial learning task, the Morris water maze . In two rat models of memory deficit, induced by either scopolamine or bilateral perforant pathway lesion, the AT4 receptor agonists reversed the performance deficits detected in the Morris water maze paradigm [207, 208]. It was shown recently that both Ang IV and LVV-H7 dose-dependently inhibited the catalytic activity of IRAP in vitro . It was therefore proposed that the AT4 ligands, Ang IV and LVV-H7, facilitate memory and enhance learning by binding to IRAP and inhibiting its enzymatic activity.
Animal studies have demonstrated that central ACE2 overexpression exerts a potential protective effect in chronic heart failure through attenuating sympathetic outflow. SYN-hACE2[SA] mice with brain selective overexpression of ACE2 subjected to permanent coronary artery ligation exhibited only a slight decrease in mean arterial pressure compared to WT mice and showed attenuated left ventricular end-diastolic pressure, decreased urinary norepinephrine excretion, and enhanced baroreflex sensitivity. The mice also exhibited lowered AT1 receptor levels in medullary nuclei compared to WT CHF mice . In a similar study, rats with chronic heart failure showed decreased expression of ACE2, Ang 1–7 receptor, Mas, and neuronal nitric oxide synthase (NOS) within the paraventricular nucleus. Overexpression of ACE2 using an adenovirus (AdACE2) significantly improved ACE2 levels and nNOS expression and attenuated the sympathetic outflow in chronic heart failure . These data clearly suggest that ACE2 overexpression in the brain can attenuate neurogenic hypertension partially by preventing the decrease in both spontaneous barorelflex sensitivity and parasympathetic tone, which are mediated by enhanced NO release in the brain resulting from Mas and AT2 receptor upregulation .
4. Summary and Conclusions
Cognition, therefore, is a not a unitary phenomenon as it is a complex of multiple integrated neurological and behavioural activities of which renin-angiotensin system has ample documentation as a key player. The therapeutic control of cognition remains an important and complex challenge. Patients suffering from mild cognitive impairment, Alzheimer’s disease, and cognitive impairments from a host of other insults such as schizophrenia, Parkinson’s disease, and neural trauma are all potential candidates for improved therapies. Therefore, it has been argued that a compound that positively modulates RAS systemically or locally in the brain would be valuable in correcting cognitive deficiencies for which these functions were reduced. Upregulation of ACE2 and increased balance of Ang 1–7/Ang II, along with positive modulation of Ang II signaling through AT2 receptors and Ang 1–7 signaling through Mas receptors, may be an appropriate strategy for improving cognitive function and in treating dementia.
- R. C. Petersen, “Aging, mild cognitive impairment, and Alzheimer's disease,” Neurologic Clinics, vol. 18, no. 4, pp. 789–805, 2000.
- P. J. Whitehouse, C. G. Sciulli, and R. M. Mason, “Dementia drug development: use of information systems to harmonize global drug development,” Psychopharmacology Bulletin, vol. 33, no. 1, pp. 129–133, 1997.
- A. Cherubini, D. T. Lowenthal, E. Paran, P. Mecocci, L. S. Williams, and U. Senin, “Hypertension and cognitive function in the elderly,” American Journal of Therapeutics, vol. 14, no. 6, pp. 533–554, 2007.
- A. Del Parigi, F. Panza, C. Capurso, and V. Solfrizzi, “Nutritional factors, cognitive decline, and dementia,” Brain Research Bulletin, vol. 69, no. 1, pp. 1–19, 2006.
- R. Andel, T. F. Hughes, and M. Crowe, “Strategies to reduce the risk of cognitive decline and dementia,” Aging Health, vol. 1, pp. 107–116, 2005.
- F. M. Faraci and D. D. Heistad, “Regulation of large cerebral arteries and cerebral microsvascular pressure,” Circulation Research, vol. 66, no. 1, pp. 8–17, 1990.
- Y. Nishimura, T. Ito, and J. M. Saavedra, “Angiotensin II AT1 blockade normalizes cerebrovascular autoregulation and reduces cerebral ischemia in spontaneously hypertensive rats,” Stroke, vol. 31, no. 10, pp. 2478–2486, 2000.
- P. V. Vaitkevicius, J. L. Fleg, J. H. Engel et al., “Effects of age and aerobic capacity on arterial stiffness in healthy adults,” Circulation, vol. 88, no. 4 I, pp. 1456–1462, 1993.
- R. W. Alexander, “Hypertension and the pathogenesis of atherosclerosis: oxidative stress and the mediation of arterial inflammatory response: a new perspective,” Hypertension, vol. 25, no. 2, pp. 155–161, 1995.
- S. Phillips and J. Whisnant, “Hypertension and stroke,” in Hypertension: Pathophysiology, Diagnosis, and Management, J. Laragh and B. Brenner, Eds., pp. 417–431, Raven Press, New York, NY, USA, 2nd edition, 1990.
- S. Strandgaard and O. B. Paulson, “Cerebrovascular consequences of hypertension,” The Lancet, vol. 344, no. 8921, pp. 519–521, 1994.
- M. I. Phillips and E. M. De Oliveira, “Brain renin angiotensin in disease,” Journal of Molecular Medicine, vol. 86, no. 6, pp. 715–722, 2008.
- E. Savaskan, “The role of the brain renin-angiotensin system in neurodegenerative disorders,” Current Alzheimer Research, vol. 2, no. 1, pp. 29–35, 2005.
- L. A. Cassis, J. Saye, and M. J. Peach, “Location and regulation of rat angiotensinogen messenger RNA,” Hypertension, vol. 11, no. 6, pp. 591–596, 1988.
- V. J. Dzau, J. Ingelfinger, R. E. Pratt, and K. E. Ellison, “Identification of renin and angiotensinogen messenger RNA sequences in mouse and rat brains,” Hypertension, vol. 8, no. 6, pp. 544–548, 1986.
- J. L. Lavoie, M. D. Cassell, K. W. Gross, and C. D. Sigmund, “Localization of renin expressing cells in the brain, by use of a REN-eGFP transgenic model,” Physiological Genomics, vol. 16, pp. 240–246, 2004.
- J. L. Lavoie, M. D. Cassell, K. W. Gross, and C. D. Sigmund, “Adjacent expression of renin and angiotensinogen in the rostral ventrolateral medulla using a dual-reporter transgenic model,” Hypertension, vol. 43, no. 5, pp. 1116–1119, 2004.
- M. A. Lee-Kirsch, F. Gaudet, M. C. Cardoso, and K. Lindpaintner, “Distinct renin isoforms generated by tissue-specific transcription initiation and alternative splicing,” Circulation Research, vol. 84, no. 2, pp. 240–246, 1999.
- C. Fischer-Ferraro, V. E. Nahmod, D. J. Goldstein, and S. Finkielman, “Angiotensin and renin in rat and dog brain,” Journal of Experimental Medicine, vol. 133, no. 2, pp. 353–361, 1971.
- E. T. Ben-Ari and J. C. Garrison, “Regulation of angiotensinogen mRNA accumulation in rat hepatocytes,” American Journal of Physiology, vol. 255, no. 1, pp. E70–E79, 1988.
- C. F. Deschepper, J. Bouhnik, and W. F. Ganong, “Colocalization of angiotensinogen and glial fibrillary acidic protein in astrocytes in rat brain,” Brain Research, vol. 374, no. 1, pp. 195–198, 1986.
- P. Sandor and W. de Jong, “Brain peptides and catecholamines in cardiovascular regulation,” in Brain Peptides and Catecholamines in Cardiovascular Regulation, J. P. Buckley and C. M. Ferrario, Eds., p. 185, Raven Press, New York, NY, USA, 1987.
- D. I. Diz, “Approaches to establishing angiotensin II as a neurotransmitter revisited,” Hypertension, vol. 47, no. 3, pp. 334–336, 2006.
- 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.
- M. Paul, M. P. Printz, and E. Harms, “Localization of renin (EC 3.4.23) and converting enzyme (EC 220.127.116.11) in nerve endings of rat brain,” Brain Research, vol. 334, no. 2, pp. 315–324, 1985.
- K. E. Bernstein, B. M. Martin, A. S. Edwards, and E. A. Bernstein, “Mouse angiotensin-converting enzyme is a protein composed of two homologous domains,” Journal of Biological Chemistry, vol. 264, no. 20, pp. 11945–11951, 1989.
- V. Beldent, A. Michaud, C. Bonnefoy, M.-T. Chauvet, and P. Corvol, “Cell surface localization of proteolysis of human endothelial angiotensin I-converting enzyme. Effect of the amino-terminal domain in the solubilization process,” Journal of Biological Chemistry, vol. 270, no. 48, pp. 28962–28969, 1995.
- I. A. Reid, B. J. Morris, and W. F. Ganong, “The renin-angiotensin system,” Annual Review of Physiology, vol. 40, pp. 377–410, 1978.
- M. I. Phillips, “Functions of angiotensin in the central nervous system,” Annual Review of Physiology, vol. 49, pp. 413–435, 1987.
- A. Kuoppala, K. A. Lindstedt, J. Saarinen, P. T. Kovanen, and J. O. Kokkonen, “Inactivation of bradykinin by angiotensin-converting enzyme and by carboxypeptidase N in human plasma,” American Journal of Physiology, vol. 278, no. 4, pp. H1069–H1074, 2000.
- R. L. Davisson, M. I. Oliverio, T. M. Coffman, and C. D. Sigmund, “Divergent functions of angiotensin II receptor isoforms in the brain,” Journal of Clinical Investigation, vol. 106, no. 1, pp. 103–106, 2000.
- R. M. Carey, “Cardiovascular and renal regulation by the angiotensin type 2 receptor: the AT2 receptor comes of age,” Hypertension, vol. 45, no. 5, pp. 840–844, 2005.
- R. M. Carey and S. H. Padia, “Angiotensin AT2 receptors: control of renal sodium excretion and blood pressure,” Trends in Endocrinology and Metabolism, vol. 19, no. 3, pp. 84–87, 2008.
- 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.
- V. J. Dzau, “Cell biology and genetics of angiotensin in cardiovascular disease,” Journal of Hypertension, vol. 12, no. 4, supplement, pp. S3–S10, 1994.
- R. K. Bickerton and J. P. Buckley, “Evidence for a central mechanism in angiotensin induced hypertension,” in Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine, pp. 834–836, Royal Society of Medicine, New York, NY, USA, 1961.
- 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.
- D. Ganten, A. Marquez-Julio, P. Granger et al., “Renin in dog brain,” The American Journal of Physiology, vol. 221, no. 6, pp. 1733–1737, 1971.
- 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.
- O. Johren, T. Inagami, and J. M. Saavedra, “AT(1A), AT(1B), and AT2 angiotensin II receptor subtype gene expression in rat brain,” NeuroReport, vol. 6, no. 18, pp. 2549–2552, 1995.
- 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.
- 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.
- 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.
- 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.
- 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.
- N. E. Sirett, A. S. McLean, J. J. Bray, and J. I. Hubbard, “Distribution of angiotensin II receptors in rat brain,” Brain Research, vol. 122, no. 2, pp. 299–312, 1977.
- K. Song, A. M. Allen, G. Paxinos, and F. A. O. Mendelsohn, “Mapping of angiotensin II receptor subtype heterogeneity in rat brain,” Journal of Comparative Neurology, vol. 316, no. 4, pp. 467–484, 1992.
- W. Häuser, O. Jöhren, and J. M. Saavedra, “Characterization and distribution of angiotensin II receptor subtypes in the mouse brain,” European Journal of Pharmacology, vol. 348, no. 1, pp. 101–114, 1998.
- O. Jöhren, H. Imboden, W. Häuser, I. Maye, G. L. Sanvitto, and J. M. Saavedra, “Localization of angiotensin-converting enzyme, angiotensin II, angiotensin II receptor subtypes, and vasopressin in the mouse hypothalamus,” Brain Research, vol. 757, no. 2, pp. 218–227, 1997.
- 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.
- D. F. Story and J. Ziogas, “Interaction of angiotensin with noradrenergic neuroeffector transmission,” Trends in Pharmacological Sciences, vol. 8, no. 7, pp. 269–271, 1987.
- P. R. Saxena, “Interaction between the renin-angiotensin-aldosterone and sympathetic nervous systems,” Journal of Cardiovascular Pharmacology, vol. 19, no. 6, pp. S80–S88, 1992.
- G. Giacchetti, G. Opocher, R. Sarzani, A. Rappelli, and F. Mantero, “Angiotensin II and the adrenal,” Clinical and Experimental Pharmacology and Physiology, vol. 23, no. 3, supplement, pp. S119–S124, 1996.
- G. Aguilera and A. Kiss, “Regulation of the hypothalmic-pituitary-adrenal axis and vasopressin secretion: role of angiotensin II,” Advances in Experimental Medicine and Biology, vol. 396, pp. 105–112, 1996.
- J. Culman, S. Hohle, F. Qadri et al., “Angiotensin as neuromodulator/neurotransmitter in central control of body fluid and electrolyte homeostasis,” Clinical and Experimental Hypertension, vol. 17, no. 1-2, pp. 281–293, 1995.
- H. Urata, H. Nishimura, and D. Ganten, “Mechanisms of angiotensin II formation in humans,” European Heart Journal, vol. 16, pp. 79–85, 1995.
- H. Urata, H. Nishimura, D. Ganten, and K. Arakawa, “Angiotensin-converting enzyme-independent pathways of angiotensin II formation in human tissues and cardiovascular diseases,” Blood Pressure, Supplement, vol. 5, no. 2, pp. 22–28, 1996.
- P. Schelling, J. S. Hutchinson, and U. Ganten, “Impermeability of the blood cerebrospinal fluid barrier for angiotensin II in rats,” Clinical Science and Molecular Medicine, vol. 51, no. 3, supplement, pp. 399–402, 1976.
- H. M. Duvernoy and P.-Y. Risold, “The circumventricular organs: an atlas of comparative anatomy and vascularization,” Brain Research Reviews, vol. 56, no. 1, pp. 119–147, 2007.
- A. K. Johnson and P. M. Gross, “Sensory circumventricular organs and brain homeostatic pathways,” FASEB Journal, vol. 7, no. 8, pp. 678–686, 1993.
- J. B. Simpson, “The circumventricular organs and the central actions of angiotensin,” Neuroendocrinology, vol. 32, no. 4, pp. 248–256, 1981.
- J. M. Saavedra, “Brain and pituitary angiotensin,” Endocrine Reviews, vol. 13, no. 2, pp. 329–380, 1992.
- J. M. Saavedra, “Brain angiotensin II: new developments, unanswered questions and therapeutic opportunities,” Cellular and Molecular Neurobiology, vol. 25, no. 3-4, pp. 485–512, 2005.
- J. M. Saavedra, H. Ando, I. Armando et al., “Anti-stress and anti-anxiety effects of centrally acting angiotensin II AT1 receptor antagonists,” Regulatory Peptides, vol. 128, no. 3, pp. 227–238, 2005.
- K. Yanai, T. Saito, Y. Kakinuma et al., “Renin-dependent cardiovascular functions and renin-independent blood-brain barrier functions revealed by renin-deficient mice,” Journal of Biological Chemistry, vol. 275, no. 1, pp. 5–8, 2000.
- Y. Kakinuma, H. Hama, F. Sugiyama et al., “Impaired blood-brain barrier function in angiotensinogen-deficient mice,” Nature Medicine, vol. 4, no. 9, pp. 1078–1080, 1998.
- J. M. Rose and K. L. Audus, “At1 receptors mediate angiotensin II uptake and transport by bovine brain microvessel endothelial cells in primary culture,” Journal of Cardiovascular Pharmacology, vol. 33, no. 1, pp. 30–35, 1999.
- J. W. Harding, M. J. Sullivan, J. M. Hanesworth, L. L. Cushing, and J. W. Wright, “Inability of [125I]Sar1,Ile8-angiotensin II to move between the blood and cerebrospinal fluid compartments,” Journal of Neurochemistry, vol. 50, no. 2, pp. 554–557, 1988.
- J. Monti, M. Schinke, M. Böhm, D. Ganten, M. Bader, and G. Bricca, “Glial angiotensinogen regulates brain angiotensin II receptors in transgenic rats TGR(ASrAOGE),” American Journal of Physiology, vol. 280, no. 1, pp. R233–R240, 2001.
- A. Réaux, N. De Mota, S. Zini et al., “PC18, a specific aminopeptidase N inhibitor, induces vasopressin release by increasing the half-life of brain Angiotensin III,” Neuroendocrinology, vol. 69, no. 5, pp. 370–376, 1999.
- A. Reaux, M. C. Fournie-Zaluski, C. David et al., “Aminopeptidase A inhibitors as potential central antihypertensive agents,” Proceedings of the National Academy of Sciences of the United States of America, vol. 96, no. 23, pp. 13415–13420, 1999.
- S. Zini, M.-C. Fournie-Zaluski, E. Chauvel, B. P. Roques, P. Corvol, and C. Llorens-Cortes, “Identification of metabolic pathways of brain angiotensin II and III using specific aminopeptidase inhibitors: predominant role of angiotensin III in the control of vasopressin release,” Proceedings of the National Academy of Sciences of the United States of America, vol. 93, no. 21, pp. 11968–11973, 1996.
- G. N. Swanson, J. M. Hanesworth, M. F. Sardinia et al., “Discovery of a distinct binding site for angiotensin II (3–8), a putative angiotensin IV receptor,” Regulatory Peptides, vol. 40, no. 3, pp. 409–419, 1992.
- S. Y. Chai, M. A. Bastias, E. F. Clune et al., “Distribution of angiotensin IV binding sites (AT4 receptor) in the human forebrain, midbrain and pons as visualised by in vitro receptor autoradiography,” Journal of Chemical Neuroanatomy, vol. 20, no. 3-4, pp. 339–348, 2000.
- A. V. Miller-Wing, J. M. Hanesworth, M. F. Sardinia et al., “Central angiotensin IV binding sites: distribution and specificity in guinea pig brain,” Journal of Pharmacology and Experimental Therapeutics, vol. 266, no. 3, pp. 1718–1726, 1993.
- I. Moeller, S. Y. Chai, B. J. Oldfield, M. J. McKinley, D. Casley, and F. A. O. Mendelsohn, “Localization of angiotensin IV binding sites to motor and sensory neurons in the sheep spinal cord and hindbrain,” Brain Research, vol. 701, no. 1-2, pp. 301–306, 1995.
- I. Moeller, G. Paxinos, F. A. O. Mendelsohn, G. P. Aldred, D. Casley, and S. Y. Chai, “Distribution of AT4 receptors in the Macaca fascicularis brain,” Brain Research, vol. 712, no. 2, pp. 307–324, 1996.
- K. A. Roberts, L. T. Krebs, E. A. Kramar, M. J. Shaffer, J. W. Harding, and J. W. Wright, “Autoradiographic identification of brain angiotensin IV binding sites and differential c-Fos expression following intracerebroventricular injection of angiotensin II and IV in rats,” Brain Research, vol. 682, no. 1-2, pp. 13–21, 1995.
- A. L. Albiston, S. G. McDowall, D. Matsacos et al., “Evidence that the angiotensin IV (AT4) receptor is the enzyme insulin-regulated aminopeptidase,” Journal of Biological Chemistry, vol. 276, no. 52, pp. 48623–48626, 2001.
- S. R. Tipnis, N. M. Hooper, R. Hyde, E. Karran, G. Christie, and A. J. Turner, “A human homolog of angiotensin-converting enzyme: cloning and functional expression as a captopril-insensitive carboxypeptidase,” Journal of Biological Chemistry, vol. 275, no. 43, pp. 33238–33243, 2000.
- A. J. Turner, S. R. Tipnis, J. L. Guy, G. I. Rice, and N. M. Hooper, “ACEH/ACE2 is a novel mammalian metallocarboxypeptidase and a homologue of angiotensin-converting enzyme insensitive to ACE inhibitors,” Canadian Journal of Physiology and Pharmacology, vol. 80, no. 4, pp. 346–353, 2002.
- C. Vickers, P. Hales, V. Kaushik et al., “Hydrolysis of biological peptides by human angiotensin-converting enzyme-related carboxypeptidase,” Journal of Biological Chemistry, vol. 277, no. 17, pp. 14838–14843, 2002.
- M. Donoghue, F. Hsieh, E. Baronas et al., “A novel angiotensin-converting enzyme-related carboxypeptidase (ACE2) converts angiotensin I to angiotensin 1-9,” Circulation Research, vol. 87, no. 5, pp. E1–9, 2000.
- F. Gembardt, A. Sterner-Kock, H. Imboden et al., “Organ-specific distribution of ACE2 mRNA and correlating peptidase activity in rodents,” Peptides, vol. 26, no. 7, pp. 1270–1277, 2005.
- D. Harmer, M. Gilbert, R. Borman, and K. L. Clark, “Quantitative mRNA expression profiling of ACE 2, a novel homologue of angiotensin converting enzyme,” FEBS Letters, vol. 532, no. 1-2, pp. 107–110, 2002.
- I. Hamming, W. Timens, M. L. C. Bulthuis, A. T. Lely, G. J. Navis, and H. van Goor, “Tissue distribution of ACE2 protein, the functional receptor for SARS coronavirus. A first step in understanding SARS pathogenesis,” Journal of Pathology, vol. 203, no. 2, pp. 631–637, 2004.
- P. E. Gallagher, M. C. Chappell, C. M. Ferrario, and E. A. Tallant, “Distinct roles for ANG II and ANG-(1–7) in the regulation of angiotensin-converting enzyme 2 in rat astrocytes,” American Journal of Physiology, vol. 290, no. 2, pp. C420–C426, 2006.
- M. F. Doobay, L. S. Talman, T. D. Obr, X. Tian, R. L. Davisson, and E. Lazartigues, “Differential expression of neuronal ACE2 in transgenic mice with overexpression of the brain renin-angiotensin system,” American Journal of Physiology, vol. 292, no. 1, pp. R373–R381, 2007.
- Z. Lin, Y. Chen, W. Zhang, A. F. Chen, S. Lin, and M. Morris, “RNA interference shows interactions between mouse brainstem angiotensin AT1 receptors and angiotensin-converting enzyme 2,” Experimental Physiology, vol. 93, no. 5, pp. 676–684, 2008.
- W. R. Welches, K. B. Brosnihan, and C. M. Ferrario, “A comparison of the properties and enzymatic activities of three angiotensin processing enzymes: angiotensin converting enzyme, prolyl endopeptidase and neutral endopeptidase 24.11,” Life Sciences, vol. 52, no. 18, pp. 1461–1480, 1993.
- M. C. Chappell, K. B. Brosnihan, D. I. Diz, and C. M. Ferrario, “Identification of angiotensin-(1–7) in rat brain. Evidence for differential processing of angiotensin peptides,” Journal of Biological Chemistry, vol. 264, no. 28, pp. 16518–16523, 1989.
- J. L. Guy, D. W. Lambert, F. J. Warner, N. M. Hooper, and A. J. Turner, “Membrane-associated zinc peptidase families: comparing ACE and ACE2,” Biochimica et Biophysica Acta, vol. 1751, no. 1, pp. 2–8, 2005.
- M. C. Chappell, N. T. Pirro, A. Sykes, and C. M. Ferrario, “Metabolism of angiotensin-(1–7) by angiotensin-converting enzyme,” Hypertension, vol. 31, no. 1, pp. 362–367, 1998.
- A. J. Allred, D. I. Diz, C. M. Ferrario, and M. C. Chappell, “Pathways for angiotensin-(1–7) metabolism in pulmonary and renal tissues,” American Journal of Physiology, vol. 279, no. 5, pp. F841–F850, 2000.
- W. C. Probst, L. A. Snyder, D. I. Schuster, J. Brosius, and S. C. Sealfon, “Sequence alignment of the G-protein coupled receptor superfamily,” DNA and Cell Biology, vol. 11, no. 1, pp. 1–20, 1992.
- B. Bunnemann, K. Fuxe, R. Metzger et al., “Autoradiographic localization of mas proto-oncogene mRNA in adult rat brain using in situ hybridization,” Neuroscience Letters, vol. 114, no. 2, pp. 147–153, 1990.
- K. A. Martin, S. G. N. Grant, and S. Hockfield, “The mas proto-oncogene is developmentally regulated in the rat central nervous system,” Developmental Brain Research, vol. 68, no. 1, pp. 75–82, 1992.
- R. Metzger, M. Bader, T. Ludwig, C. Berberich, B. Bunnemann, and D. Ganten, “Expression of the mouse and rat mas proto-oncogene in the brain and peripheral tissues,” FEBS Letters, vol. 357, no. 1, pp. 27–32, 1995.
- D. Young, K. O'Neill, T. Jessell, and M. Wigler, “Characterization of the rat mas oncogene and its high-level expression in the hippocampus and cerebral cortex of rat brain,” Proceedings of the National Academy of Sciences of the United States of America, vol. 85, no. 14, pp. 5339–5342, 1988.
- L. K. Becker, G. M. Etelvino, T. Walther, R. A. S. Santos, and M. J. Campagnole-Santos, “Immunofluorescence localization of the receptor Mas in cardiovascular-related areas of the rat brain,” American Journal of Physiology, vol. 293, no. 3, pp. H1416–H1424, 2007.
- K. A. Martin and S. Hockfield, “Expression of the mas proto-oncogene in the rat hippocampal formation is regulated by neuronal activity,” Molecular Brain Research, vol. 19, no. 4, pp. 303–309, 1993.
- P. Pagliaro and C. Penna, “Rethinking the renin-angiotensin system and its role in cardiovascular regulation,” Cardiovascular Drugs and Therapy, vol. 19, no. 1, pp. 77–87, 2005.
- Y. Yagil and C. Yagil, “Congenics in the pathway from quantitative trait loci detection to gene identification: is that the way to go?” Journal of Hypertension, vol. 21, no. 11, pp. 2009–2011, 2003.
- M. A. Crackower, R. Sarao, G. Y. Oudit et al., “Angiotensin-converting enzyme 2 is an essential regulator of heart function,” Nature, vol. 417, no. 6891, pp. 822–828, 2002.
- M. Igase, W. B. Strawn, P. E. Gallagher, R. L. Geary, and C. M. Ferrario, “Angiotensin II at1 receptors regulate ACE2 and angiotensin-(1–7) expression in the aorta of spontaneously hypertensive rats,” American Journal of Physiology, vol. 289, no. 3, pp. H1013–H1019, 2005.
- B. Tom, A. Dendorfer, and A. H. Jan Danser, “Bradykinin, angiotensin-(1–7), and ACE inhibitors: how do they interact?” International Journal of Biochemistry and Cell Biology, vol. 35, no. 6, pp. 792–801, 2003.
- C. M. Ferrario, M. C. Chappell, E. A. Tallant, K. B. Brosnihan, and D. I. Diz, “Counterregulatory actions of angiotensin-(1–7),” Hypertension, vol. 30, no. 3, pp. 535–541, 1997.
- R. A. S. Santos, M. J. Campagnole-Santos, and S. P. Andrade, “Angiotensin-(1–7): an update,” Regulatory Peptides, vol. 91, no. 1–3, pp. 45–62, 2000.
- E. A. Tallant, D. I. Diz, and C. M. Ferrario, “Antiproliferative actions of angiotensin-(1–7) in vascular smooth muscle,” Hypertension, vol. 34, no. 4, pp. 950–957, 1999.
- J. Buggy, S. Huot, M. Pamnani, and F. Haddy, “Periventricular forebrain mechanisms for blood pressure regulation,” Federation Proceedings, vol. 43, no. 1, pp. 25–31, 1984.
- G. D. Fink, C. A. Bruner, and M. L. Mangiapane, “Area postrema is critical for angiotensin-induced hypertension in rats,” Hypertension, vol. 9, no. 4, pp. 355–361, 1987.
- J. S. Gutkind, M. Kurihara, E. Castren, and J. M. Saavedra, “Increased concentration of angiotensin II binding sites in selected brain areas of spontaneously hypertensive rats,” Journal of Hypertension, vol. 6, no. 1, pp. 79–84, 1988.
- R. Gyurko, D. Wielbo, and M. I. Phillips, “Antisense inhibition of AT1 receptor mRNA and angiotensinogen mRNA in the brain of spontaneously hypertensive rats reduces hypertension of neurogenic origin,” Regulatory Peptides, vol. 49, no. 2, pp. 167–174, 1993.
- P. Ambühl, R. Gyurko, and M. I. Phillips, “A decrease in angiotensin receptor binding in rat brain nuclei by antisense oligonucleotides to the angiotensin AT1 receptor,” Regulatory Peptides, vol. 59, no. 2, pp. 171–182, 1995.
- J. C. Falcon II, M. I. Phillips, W. E. Hoffman, and M. J. Brody, “Effects of intraventricular angiotensin II mediated by the sympathetic nervous system,” The American Journal of Physiology, vol. 235, no. 4, pp. H392–399, 1978.
- A. Blume, T. Herdegen, and T. Unger, “Angiotensin peptides and inducible transcription factors,” Journal of Molecular Medicine, vol. 77, no. 3, pp. 339–357, 1999.
- T. Unger, W. Rascher, and C. Schuster, “Central blood pressure effects of substance P and angiotensin II: role of the sympathetic nervous system and vasopressin,” European Journal of Pharmacology, vol. 71, no. 1, pp. 33–42, 1981.
- W. McDonald, C. Wickre, and S. Aumann, “The sustained antihypertensive effect of chronic cerebroventricular infusion of angiotensin antagonist in spontaneously hypertensive rats,” Endocrinology, vol. 107, no. 5, pp. 1305–1308, 1980.
- T. Okuno, S. Nagahama, M. D. Lindheimer, and S. Oparil, “Attenuation of the development of spontaneous hypertension in rats by chronic central administration of captopril,” Hypertension, vol. 5, no. 5 I, pp. 653–662, 1983.
- K. Hermann, W. McDonald, and T. Unger, “Angiotensin biosynthesis and concentrations in brain of normotensive and hypertensive rats,” Journal de Physiologie, vol. 79, no. 6, pp. 471–480, 1984.
- R. Casto and M. I. Phillips, “Angiotensin II attenuates baroreflexes at nucleus tractus solitarius of rats,” American Journal of Physiology, vol. 250, no. 2, pp. R193–R198, 1986.
- K. Tamura, S. Umemura, N. Nyui et al., “Tissue-specific regulation of angiotensinogen gene expression in spontaneously hypertensive rats,” Hypertension, vol. 27, no. 6, pp. 1216–1223, 1996.
- M. W. Chapleau and F. M. Abboud, “Neuro-Cardiovascular Regulation: from molecules to man: introduction,” Annals of the New York Academy of Sciences, vol. 940, pp. 13–22, 2001.
- 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.
- H. Ando, J. Zhou, M. Macova, H. Imboden, and J. M. Saavedra, “Angiotensin II AT1 receptor blockade reverses pathological hypertrophy and inflammation in brain microvessels of spontaneously hypertensive rats,” Stroke, vol. 35, no. 7, pp. 1726–1731, 2004.
- J. M. Barnes, N. M. Barnes, B. Costall et al., “Angiotensin II inhibits acetylcholine release from human temporal cortex: implications for cognition,” Brain Research, vol. 507, no. 2, pp. 341–343, 1990.
- O. Von Bohlen Und Halbach and D. Albrecht, “Angiotensin II inhibits long-term potentiation within the lateral nucleus of the amygdala through AT1 receptors,” Peptides, vol. 19, no. 6, pp. 1031–1036, 1998.
- A. G. Karczmar, “Brief presentation of the story and present status of studies of the vertebrate cholinergic system,” Neuropsychopharmacology, vol. 9, no. 3, pp. 181–199, 1993.
- D. Albrecht, M. Broser, H. Krüger, and M. Bader, “Effects of angiotensin II and IV on geniculate activity in nontransgenic and transgenic rats,” European Journal of Pharmacology, vol. 332, no. 1, pp. 53–63, 1997.
- J. W. Wright and J. W. Harding, “The brain RAS and Alzheimer's disease,” Experimental Neurology, vol. 223, no. 2, pp. 326–333, 2010.
- J. J. Braszko, “AT2 but not AT1 receptor antagonism abolishes angiotensin II increase of the acquisition of conditioned avoidance responses in rats,” Behavioural Brain Research, vol. 131, no. 1-2, pp. 79–86, 2002.
- D. S. Kerr, L. R. M. Bevilaqua, J. S. Bonini et al., “Angiotensin II blocks memory consolidation through an AT2 receptor-dependent mechanism,” Psychopharmacology, vol. 179, no. 3, pp. 529–535, 2005.
- W. Bild, L. Hritcu, A. Ciobica, V. Artenie, and I. Haulica, “P02-170 Comparative effects of captopril, losartan and PD123319 on the memory processes in rats,” European Psychiatry, vol. 24, p. S860, 2009.
- J. S. Bonini, L. R. Bevilaqua, C. G. Zinn et al., “Angiotensin II disrupts inhibitory avoidance memory retrieval,” Hormones and Behavior, vol. 50, no. 2, pp. 308–313, 2006.
- P. W. Landfield and S. A. Deadwyler, Long-Term Potentiation from Biophysics to Behavior, Liss, New York, NY, USA, 1988.
- G. Lynch, M. Kessler, A. Arai, and J. Larson, “The nature and causes of hippocampal long-term potentiation,” Progress in Brain Research, vol. 83, pp. 233–250, 1990.
- R. D. Traub and R. Miles, Neuronal Networks of the Hippocampus, Cambridge University Press, 1991.
- J. Storm-Mathisen, J. Zimmer, and O. P. Ottersen, “Understanding the brain through the hippocampus: preface,” Progress in Brain Research, vol. 83, pp. 1–457, 1990.
- J. W. Wright, E. A. Kramár, S. E. Meighan, and J. W. Harding, “Extracellular matrix molecules, long-term potentiation, memory consolidation and the brain angiotensin system,” Peptides, vol. 23, no. 1, pp. 221–246, 2002.
- G. Massicotte and M. Baudry, “Triggers and substrates of hippocampal synaptic plasticity,” Neuroscience and Biobehavioral Reviews, vol. 15, no. 3, pp. 415–423, 1991.
- N. M. Barnes, B. Costall, M. E. Kelly, D. A. Murphy, and R. J. Naylor, “Cognitive enhancing actions of PD 123177 detected in a mouse habituation paradigm,” NeuroReport, vol. 2, no. 6, pp. 351–353, 1991.
- N. M. Barnes, S. Champaneria, B. Costall, M. E. Kelly, D. A. Murphy, and R. J. Naylor, “Cognitive enhancing actions of DuP 753 detected in a mouse habituation paradigm,” NeuroReport, vol. 1, no. 3-4, pp. 239–242, 1990.
- N. M. Barnes, B. Costall, M. E. Kelly, D. A. Murphy, and R. J. Naylor, “Anxiolytic-like action of DuP753, a non-peptide angiotensin II receptor antagonist,” NeuroReport, vol. 1, no. 1, pp. 20–21, 1990.
- M. M. Akhavan, M. Emami-Abarghoie, B. Sadighi-Moghaddam, M. Safari, Y. Yousefi, and A. Rashidy-Pour, “Hippocampal angiotensin II receptors play an important role in mediating the effect of voluntary exercise on learning and memory in rat,” Brain Research, vol. 1232, pp. 132–138, 2008.
- O. Von Bohlen Und Halbach and D. Albrecht, “The CNS renin-angiotensin system,” Cell and Tissue Research, vol. 326, no. 2, pp. 599–616, 2006.
- J. Tchekalarova and D. Albrecht, “Angiotensin II suppresses long-term depression in the lateral amygdala of mice via L-type calcium channels,” Neuroscience Letters, vol. 415, no. 1, pp. 68–72, 2007.
- V. Raghavendra, K. Chopra, and S. K. Kulkarni, “Brain renin angiotensin system (RAS) in stress-induced analgesia and impaired retention,” Peptides, vol. 20, no. 3, pp. 335–342, 1999.
- L. Mateos, M.-A. Ismail, B. Winblad, and A. Cedazo-Mínguez, “Side-chain-oxidized oxysterols upregulate ACE2 and mas receptor in rat primary neurons,” Neurodegenerative Diseases, vol. 10, no. 1–4, pp. 313–316, 2012.
- J. Ellul, N. Archer, C. M. L. Foy et al., “The effects of commonly prescribed drugs in patients with Alzheimer's disease on the rate or deterioration,” Journal of Neurology, Neurosurgery and Psychiatry, vol. 78, no. 3, pp. 233–239, 2007.
- J. M. Barnes, N. M. Barnes, B. Costall et al., “Angiotensin-converting enzyme inhibition, angiotensin, and cognition,” Journal of Cardiovascular Pharmacology, vol. 19, no. 6, supplement, pp. S63–S71, 1992.
- K. Shah, S. U. Qureshi, M. Johnson, N. Parikh, P. E. Schulz, and M. E. Kunik, “Does use of antihypertensive drugs affect the incidence or progression of dementia? A systematic review,” American Journal Geriatric Pharmacotherapy, vol. 7, no. 5, pp. 250–261, 2009.
- T. Walther, J.-P. Voigt, A. Fukamizu, H. Fink, and M. Bader, “Learning and anxiety in angiotensin-deficient mice,” Behavioural Brain Research, vol. 100, no. 1-2, pp. 1–4, 1999.
- T. C. Lee, D. Greene-Schloesser, and V. Payne, “Chronic administration of the angiotensin-converting enzyme inhibitor, ramipril, prevents fractionated whole-brain irradiation-induced perirhinal cortex-dependent cognitive impairment,” Radiation Research, vol. 178, pp. 46–56, 2012.
- Y.-F. Dong, K. Kataoka, Y. Tokutomi et al., “Perindopril, a centrally active angiotensin-converting enzyme inhibitor, prevents cognitive impairment in mouse models of Alzheimer's disease,” FASEB Journal, vol. 25, no. 9, pp. 2911–2920, 2011.
- B. Maul, O. Von Bohlen Und Halbach, A. Becker et al., “Impaired spatial memory and altered dendritic spine morphology in angiotensin II type 2 receptor-deficient mice,” Journal of Molecular Medicine, vol. 86, no. 5, pp. 563–571, 2008.
- K. Kazama, J. Anrather, P. Zhou et al., “Angiotensin II impairs neurovascular coupling in neocortex through NADPH oxidase-derived radicals,” Circulation Research, vol. 95, no. 10, pp. 1019–1026, 2004.
- Y. Wei, A. T. Whaley-Connell, K. Chen et al., “NADPH oxidase contributes to vascular inflammation, insulin resistance, and remodeling in the transgenic (mRen2) rat,” Hypertension, vol. 50, no. 2, pp. 384–391, 2007.
- N.-C. Li, A. Lee, R. A. Whitmer et al., “Use of angiotensin receptor blockers and risk of dementia in a predominantly male population: prospective cohort analysis,” British Medical Journal, vol. 340, no. 7738, p. 141, 2010.
- S. Inaba, M. Iwai, M. Furuno et al., “Continuous activation of renin-angiotensin system impairs cognitive function in renin/angiotensinogen transgenic mice,” Hypertension, vol. 53, no. 2, pp. 356–362, 2009.
- S. Takeda, N. Sato, D. Takeuchi et al., “Angiotensin receptor blocker prevented β-amyloid-induced cognitive impairment associated with recovery of neurovascular coupling,” Hypertension, vol. 54, no. 6, pp. 1345–1352, 2009.
- K. Kume, H. Hanyu, H. Sakurai, Y. Takada, T. Onuma, and T. Iwamoto, “Effects of telmisartan on cognition and regional cerebral blood flow in hypertensive patients with Alzheimer's disease,” Geriatrics and Gerontology International, vol. 12, no. 2, pp. 207–214, 2012.
- R. Mechaeil, P. Gard, A. Jackson, and J. Rusted, “Cognitive enhancement following acute losartan in normotensive young adults,” Psychopharmacology, vol. 217, no. 1, pp. 51–60, 2011.
- K. Reinecke, R. Lucius, A. Reinecke, U. Rickert, T. Herdegen, and T. Unger, “Angiotensin II accelerates functional recovery in the rat sciatic nerve in vivo: role of the AT2 receptor and the transcription factor NF-kappaB,” The FASEB Journal, vol. 17, no. 14, pp. 2094–2096, 2003.
- L. Gendron, L. Laflamme, N. Rivard, C. Asselin, M. D. Payet, and N. Gallo-Payet, “Signals from the AT2 (angiotensin type 2) receptor of angiotensin II inhibit p21(ras) and activate MAPK (mitogen-activated protein kinase) to induce morphological neuronal differentiation in NG108-15 cells,” Molecular Endocrinology, vol. 13, no. 9, pp. 1615–1626, 1999.
- F. Côté, L. Laflamme, M. D. Payet, and N. Gallo-Payet, “Nitric oxide, a new second messenger involved in the action of angiotensin II on neuronal differentiation of NG108-15 cells,” Endocrine Research, vol. 24, no. 3-4, pp. 403–407, 1998.
- M. Mogi and M. Horiuchi, “Effect of angiotensin II type 2 receptor on stroke, cognitive impairment and neurodegenerative diseases,” Geriatrics & Gerontology International, vol. 13, no. 1, pp. 13–18, 2013.
- F. Jing, M. Mogi, A. Sakata et al., “Direct stimulation of angiotensin II type 2 receptor enhances spatial memory,” Journal of Cerebral Blood Flow and Metabolism, vol. 32, no. 2, pp. 248–255, 2012.
- L. Hritcu, W. Bild, A. Ciobica, V. Artenie, and I. Haulica, “P02-169 Behavioral changes induced by angiotensin AT1 receptors blockade in the rat brain,” European Psychiatry, vol. 24, p. S859, 2009.
- A. Chalas and E. L. Conway, “No evidence for involvement of angiotensin II in spatial learning in water maze in rats,” Behavioural Brain Research, vol. 81, no. 1-2, pp. 199–205, 1996.
- P. R. Gard, “The role of angiotensin II in cognition and behaviour,” European Journal of Pharmacology, vol. 438, no. 1-2, pp. 1–14, 2002.
- V. J. DeNoble, K. F. DeNoble, K. R. Spencer, A. T. Chiu, P. C. Wong, and P. B. M. W. M. Timmermans, “Non-peptide angiotensin II receptor antagonist and angiotensin-converting enzyme inhibitor: effect on a renin-induced deficit of a passive avoidance response in rats,” Brain Research, vol. 561, no. 2, pp. 230–235, 1991.
- K. Hellner, T. Walther, M. Schubert, and D. Albrecht, “Angiotensin-(1–7) enhances LTP in the hippocampus through the G-protein-coupled receptor Mas,” Molecular and Cellular Neuroscience, vol. 29, no. 3, pp. 427–435, 2005.
- Y.-F. Dong, K. Kataoka, K. Toyama et al., “Attenuation of brain damage and cognitive impairment by direct renin inhibition in mice with chronic cerebral hypoperfusion,” Hypertension, vol. 58, no. 4, pp. 635–642, 2011.
- M. Mogi, K. Tsukuda, J.-M. Li et al., “Inhibition of cognitive decline in mice fed a high-salt and cholesterol diet by the angiotensin receptor blocker, olmesartan,” Neuropharmacology, vol. 53, no. 8, pp. 899–905, 2007.
- K. Tsukuda, M. Mogi, J.-M. Li et al., “Amelioration of cognitive impairment in the type-2 diabetic mouse by the angiotensin II type-1 receptor blocker candesartan,” Hypertension, vol. 50, no. 6, pp. 1099–1105, 2007.
- A. S. Awad, “Role of AT1 receptors in permeability of the blood-brain barrier in diabetic hypertensive rats,” Vascular Pharmacology, vol. 45, no. 3, pp. 141–147, 2006.
- N. Hirawa, Y. Uehara, Y. Kawabata et al., “Long-term inhibition of renin-angiotensin system sustains memory function in aged Dahl rats,” Hypertension, vol. 34, no. 3, pp. 496–502, 1999.
- N. Pelisch, N. Hosomi, M. Ueno et al., “Blockade of AT1 receptors protects the blood-brain barrier and improves cognition in dahl salt-sensitive hypertensive rats,” American Journal of Hypertension, vol. 24, no. 3, pp. 362–368, 2011.
- M. A. Fleegal-Demotta, S. Doghu, and W. A. Banks, “Angiotensin II modulates BBB permeability via activation of the AT 1 receptor in brain endothelial cells,” Journal of Cerebral Blood Flow and Metabolism, vol. 29, no. 3, pp. 640–647, 2009.
- R.-W. Guo, L.-X. Yang, H. Wang, B. Liu, and L. Wang, “Angiotensin II induces matrix metalloproteinase-9 expression via a nuclear factor-kappaB-dependent pathway in vascular smooth muscle cells,” Regulatory Peptides, vol. 147, no. 1–3, pp. 37–44, 2008.
- W. Zhang, C. Smith, C. Howlett, and D. Stanimirovic, “Inflammatory activation of human brain endothelial cells by hypoxic astrocytes in vitro is mediated by IL-1β,” Journal of Cerebral Blood Flow and Metabolism, vol. 20, no. 6, pp. 967–978, 2000.
- M. J. McKinley, A. L. Albiston, A. M. Allen et al., “The brain renin-angiotensin system: location and physiological roles,” International Journal of Biochemistry and Cell Biology, vol. 35, no. 6, pp. 901–918, 2003.
- N. M. Davies, P. G. Kehoe, Y. Ben-Shlomo, and R. M. Martin, “Associations of anti-hypertensive treatments with Alzheimer's disease, vascular dementia, and other dementias,” Journal of Alzheimer's Disease, vol. 26, no. 4, pp. 699–708, 2011.
- P. G. Kehoe and G. K. Wilcock, “Is inhibition of the renin-angiotensin system a new treatment option for Alzheimer's disease?” Lancet Neurology, vol. 6, no. 4, pp. 373–378, 2007.
- A. M. Sharma, J. Janke, K. Gorzelniak, S. Engeli, and F. C. Luft, “Angiotensin blockade prevents type 2 diabetes by formation of fat cells,” Hypertension, vol. 40, no. 5, pp. 609–611, 2002.
- P. G. Kehoe, C. Russ, S. McIlroy et al., “Variation in DCP1, encoding ACE, is associated with susceptibility to Alzheimer disease,” Nature Genetics, vol. 21, no. 1, pp. 71–72, 1999.
- E. Savaskan, C. Hock, G. Olivieri et al., “Cortical alterations of angiotensin converting enzyme, angiotensin II and AT1 receptor in Alzheimer's dementia,” Neurobiology of Aging, vol. 22, no. 4, pp. 541–546, 2001.
- J. S. Miners, Z. Van Helmond, P. G. Kehoe, and S. Love, “Changes with age in the activities of β-secretase and the aβ-degrading enzymes neprilysin, insulin-degrading enzyme and angiotensin-converting enzyme,” Brain Pathology, vol. 20, no. 4, pp. 794–802, 2010.
- J. S. Miners, E. Ashby, S. Baig et al., “Angiotensin-converting enzyme levels and activity in Alzheimer's disease: differences in brain and CSF ACE and association with ACE1 genotypes,” American Journal of Translational Research, vol. 1, no. 2, pp. 163–177, 2009.
- P. Strazzullo, R. Iacone, L. Iacoviello et al., “Genetic variation in the renin-angiotensin system and abdominal adiposity in men: the olivetti prospective heart study,” Annals of Internal Medicine, vol. 138, no. 1, pp. 17–23, 2003.
- L. A. Cassis, S. B. Police, F. Yiannikouris, and S. E. Thatcher, “Local adipose tissue renin-angiotensin system,” Current Hypertension Reports, vol. 10, no. 2, pp. 93–98, 2008.
- T. Ogihara, K. Kikuchi, H. Matsuoka et al., “The Japanese Society of Hypertension Guidelines for the Management of Hypertension (JSH 2009),” Hypertension Research, vol. 32, no. 1, pp. 3–107, 2009.
- Y. Furiya, M. Ryo, M. Kawahara, T. Kiriyama, M. Morikawa, and S. Ueno, “Renin-angiotensin system blockers affect cognitive decline and serum adipocytokines in Alzheimer's disease,” Alzheimer's & Dementia, 2012.
- K. Wosik, R. Cayrol, A. Dodelet-Devillers et al., “Angiotensin II controls occludin function and is required for blood-brain barrier maintenance: relevance to multiple sclerosis,” Journal of Neuroscience, vol. 27, no. 34, pp. 9032–9042, 2007.
- H. K. Hamdi and R. Castellon, “A genetic variant of ACE increases cell survival: a new paradigm for biology and disease,” Biochemical and Biophysical Research Communications, vol. 318, no. 1, pp. 187–191, 2004.
- T. Walther, D. Balschun, J.-P. Voigt et al., “Sustained long term potentiation and anxiety in mice lacking the Mas protooncogene,” Journal of Biological Chemistry, vol. 273, no. 19, pp. 11867–11873, 1998.
- T. Walther, J.-P. Voigt, H. Fink, and M. Bader, “Sex specific behavioural alterations in Mas-deficient mice,” Behavioural Brain Research, vol. 107, no. 1-2, pp. 105–109, 2000.
- O. Von Bohlen und Halbach, T. Walther, M. Bader, and D. Albrecht, “Genetic deletion of angiotensin AT2 receptor leads to increased cell numbers in different brain structures of mice,” Regulatory Peptides, vol. 99, no. 2-3, pp. 209–216, 2001.
- E. Kostenis, G. Milligan, A. Christopoulos et al., “G-protein-coupled receptor Mas is a physiological antagonist of the angiotensin II type 1 receptor,” Circulation, vol. 111, no. 14, pp. 1806–1813, 2005.
- W. O. Sampaio, C. H. De Castro, R. A. S. Santos, E. L. Schiffrin, and R. M. Touyz, “Angiotensin-(1–7) counterregulates angiotensin II signaling in human endothelial cells,” Hypertension, vol. 50, no. 6, pp. 1093–1098, 2007.
- S. H. Croog, S. Levine, and M. A. Testa, “The effects of antihypertensive therapy on the quality of life,” New England Journal of Medicine, vol. 314, no. 26, pp. 1657–1664, 1986.
- M. C. Zimmerman, E. Lazartigues, R. V. Sharma, and R. L. Davisson, “Hypertension caused by angiotensin II infusion involves increased superoxide production in the central nervous system,” Circulation Research, vol. 95, no. 2, pp. 210–216, 2004.
- Y. Feng, X. Yue, H. Xia et al., “Angiotensin-converting enzyme 2 overexpression in the subfornical organ prevents the angiotensin II-mediated pressor and drinking responses and is associated with angiotensin II type 1 receptor downregulation,” Circulation Research, vol. 102, no. 6, pp. 729–736, 2008.
- Y. Feng, H. Xia, Y. Cai et al., “Brain-selective overexpression of human angiotensin-converting enzyme type 2 attenuates neurogenic hypertension,” Circulation Research, vol. 106, no. 2, pp. 373–382, 2010.
- J. J. Braszko, G. Kupryszewski, B. Witczuk, and K. Wisniewski, “Angiotensin II-(3–8)-hexapeptide affects motor activity, performance of passive avoidance and a conditioned avoidance response in rats,” Neuroscience, vol. 27, no. 3, pp. 777–783, 1988.
- J. W. Wright, A. V. Miller-Wing, M. J. Shaffer et al., “Angiotensin II(3–8) (ANG IV) hippocampal binding: potential role in the facilitation of memory,” Brain Research Bulletin, vol. 32, no. 5, pp. 497–502, 1993.
- E. S. Pederson, J. W. Harding, and J. W. Wright, “Attenuation of scopolamine-induced spatial learning impairments by an angiotensin IV analog,” Regulatory Peptides, vol. 74, no. 2-3, pp. 97–103, 1998.
- J. W. Wright, L. Stubley, E. S. Pederson, E. A. Kramár, J. M. Hanesworth, and J. W. Harding, “Contributions of the brain angiotensin IV-AT4 receptor subtype system to spatial learning,” Journal of Neuroscience, vol. 19, no. 10, pp. 3952–3961, 1999.
- L. Xiao, L. Gao, E. Lazartigues, and I. H. Zucker, “Brain-selective overexpression of angiotensin-converting enzyme 2 attenuates sympathetic nerve activity and enhances baroreflex function in chronic heart failure,” Hypertension, vol. 58, no. 6, pp. 1057–1065, 2011.
- H. Zheng, X. Liu, and K. P. Patel, “Angiotensin-converting enzyme 2 over expression improves central nitric oxide-mediated sympathetic outflow in chronic heart failure,” American Journal of Physiology, vol. 301, no. 6, pp. 2402–2412, 2011.