Cannabinoid receptor agonist‐stimulated [35S]guanosine triphosphateγs binding in the brain of C57BL/6 and DBA/2 mice

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Abstract
The two inbred strains of mice C57BL/6 (alcohol‐preferring) and DBA/2 (alcohol‐avoiding) mice have been shown to differ significantly in their preference for alcohol (EtOH). We have previously demonstrated the differences in the density and the affinity of cannabinoid (CB1) receptors in the brains of the two inbred C57BL/6 and DBA/2 mouse strains. In the present study, we investigated the CB1 receptor agonist‐stimulated guanosine‐5′‐O‐(3‐[35S]thio)‐triphosphate ([35S]GTPγS) binding in plasma membranes (PM) from C57BL/6 and DBA/2 mice. The results indicate that the net CP55,940‐stimulated [35S]GTPγS binding was increased with increasing concentrations of CB1 receptor agonists and GDP. The net CB1 receptor agonist (WIN55,212‐2 or HU‐210 or CP55,940)‐stimulated [35S]GTPγS binding was reduced significantly (–10% to –12%, P < 0.05) in PM from DBA/2 mice; no significant differences were observed in basal [35S]GTPγS binding among these strains. Nonlinear regression analysis of net CP55,940‐stimulated [35S]GTPγS binding showed that the Bmax of cannabinoid agonist‐stimulated binding was significantly reduced (–24%) in DBA/2 mice (Bmax = 12.43 ± 0.64 for C57BL/6 and 9.46 ± 0.98 pmol/mg protein for DBA/2; P < 0.05) without any significant changes in the G protein affinity. The pharmacological specificity of CP55,940‐stimulated [35S]GTPγS binding was examined with CB1 receptor antagonist SR141716A, and these studies indicated that CP55,940‐stimulated [35S]GTPγS binding was blocked by SR141716A, with a decrease in the IC50 values in the PM from the DBA/2 mouse strain. These results suggest that a signal transduction pathway(s) downstream from the CB1 receptor system may play an important role in controlling the voluntary EtOH consumption by these strains of mice. J. Neurosci. Res. 64:429–436, 2001.