Down-regulation of cannabinoid receptor agonist-stimulated [35S]GTP gamma S binding in synaptic plasma membrane from chronic ethanol exposed mouse.
In our previous study, we demonstrated that chronic ethanol (EtOH) exposure down-regulated the cannabinoid receptors (CB1) in mouse brain synaptic plasma membrane (SPM) (Basavarajappa et al., Brain Res. 793 (1998) 212-218). In the present study, we investigated the effect of chronic EtOH (4-day inhalation) on the CB1 agonist stimulated guanosine-5'-O-(3-[35S]thio)-triphosphate ([35S]GTP gamma S) binding in SPM from mouse. Our results indicate that the net CP55,940 stimulated [35S]GTP gamma S binding was increased with increasing concentrations of CP55,940 and GDP. This net CP55,940 (1.5 microM) stimulated [35S]GTP gamma S binding was reduced significantly (-25%) in SPM from chronic EtOH group (175 +/- 5.25%, control; 150 +/- 8.14%, EtOH; P < 0.05). This effect occurs without any significant changes on basal [35S]GTP gamma S binding (152.1 +/- 10.7 for control, 147.4 +/- 5.0 fmol/mg protein for chronic EtOH group, P > 0.05). Non-linear regression analysis of net CP55,940 stimulated [35S]GTP gamma S binding in SPM showed that the Bmax of cannabinoid stimulated binding was significantly reduced in chronic EtOH exposed mouse (Bmax = 7.58 +/- 0.22 for control; 6.42 +/- 0.20 pmol/mg protein for EtOH group; P < 0.05) without any significant changes in the G-protein affinity (Kd = 2.68 +/- 0.24 for control; 3.42 +/- 0.31 nM for EtOH group; P > 0.05). The pharmacological specificity of CP55,940 stimulated [35S]GTP gamma S binding in SPM was examined with CB1 receptor antagonist, SR141716A and these studies indicated that CP55,940 stimulated [35S]GTP gamma S binding was blocked by SR141716A with a decrease (P < 0.05) in the IC50 values in the SPM from chronic EtOH group. These results suggest that the observed down-regulation of CB1 receptors by chronic EtOH has a profound effect on desensitization of cannabinoid-activated signal transduction and possible involvement of CB1 receptors in EtOH tolerance and dependence.
Basavarajappa
B S
BS
Division of Analytical Psychopharmacology, New York State Psychiatric Institute at NKI, Orangeburg 10962, USA.
Hungund
B L
BL
D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D002908:Chronic Disease; D003511:Cyclohexanols / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000502:physiology*; D000431:Ethanol / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D051379:Mice; D010880:Piperidines / Q000494:pharmacology; D011720:Pyrazoles / Q000494:pharmacology; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000037:antagonists & inhibitors*; D000077285:Rimonabant; D013462:Sulfur Radioisotopes; D013570:Synaptic Membranes / Q000737:chemistry* / Q000378:metabolism