Ligand-Specific Regulation of the Endogenous Mu-Opioid Receptor by Chronic Treatment with Mu-Opioid Peptide Agonists

Table 2

Changes in [³H]DAMGO binding induced by ACHC-EM2 treatments in rat brain subcellular fractions.

Treatment	𝐾𝐷 (nM)				𝐵max (fmol/mg protein)
	SPM		MI		SPM		MI
	Control	Treated	Control	Treated	Control	Treated	Control	Treated
ACHC-EM2 acute	5.0±1.9	3.0±1.1	2.3±0.4	3.6±0.9	298±72	258±45	410±59	311±74
ACHC-EM2 chronic	2.9±1.2	1.3±0.2	4.5±2.4	2.5±0.2	291±82	286±50	333±78	462±54^∗

ACHC-EM2 was injected either acutely or chronically as described in Methods. Control animals received CSF. Subcellular fractionations of brain homogenates to obtain synaptic plasma membrane (SPM) and microsomal (MI) membranes followed by [³H]DAMGO binding was performed as outlined in Methods. Data represent the mean ± S.E.M. of at least three independent experiments performed in duplicate. Statistically significant differences due to either treatments compared to appropriate control values in each fraction were determined by Student 𝑡-test and set at ^∗𝑃<0.05.