ALTERED GENE EXPRESSION AND FUNCTIONAL ACTIVITY OF OPIOID RECEPTORS IN THE CEREBELLUM OF CB 1 CANNABINOID RECEPTOR KNOCKOUT MICE AFTER ACUTE TREATMENTS WITH CANNABINOIDS

Numerous studies have shown functional links between the cannabinoid and opioid systems. The goal of this study was to evaluate whether acute treatments by endogenous cannabinoid agonist, selective CB 1 or CB 2 receptor antagonists modulate the expression of μ - (MOR) and δ - (DOR) opioid receptor mRNA levels and functional activity in the cerebellum of transgenic mice deficient in the CB 1 type of cannabis receptors. We examined the effect of noladin ether (endogenous cannabinoid agonist) pretreatment on MOR and DOR mRNA expression by using reverse transcription and real-time polimerase chain reac- tion (PCR) and the ability of subsequent application of the opioid agonists to activate G-proteins, as mea- sured by [ 35 S]GTP γ S binding, in wild-type (CB 1 +/+ ) and CB 1 cannabinoid receptor deficient (CB 1 ñ/ñ , ëknockoutí, K.O.) mice. The acute administration of noladin ether markedly reduced MOR-mediated G- protein activation and caused a significant increase in the level of MOR mRNAs in the cerebella of wild- type, but not in the CB 1 ñ/ñ mice. No significant differences were observed in DOR functional activity and mRNA expression in wild-type animals. In CB 1 ñ/ñ mice the expression of DOR mRNA increased after noladin ether treatment, but no changes were found in DOR functional activity. In addition, Rimonabant (selective central cannabinoid CB 1 receptor antagonist) and SR144528 (selective peripheral cannabinoid CB 2 receptor antagonist) caused significant potentiation in MOR functional activity in the wild-type ani- mals, whereas DOR mediated G-protein activation was increased in the CB 1 ñ/ñ mice. In contrast, Rimonabant and SR144528 decreased the MOR and DOR mRNA expressions in both CB 1 +/+ and CB 1 ñ/ñ mice. Taken together, these results indicate that acute treatment with cannabinoids causes alterations in MOR and DOR mRNA expression and functional activity in the cerebella of wild-type and CB 1 knock- out mice indicating indirect interactions between these two signaling systems