Cannabinoid CB1 receptor activation, pharmacological blockade, or genetic ablation affects the function of the muscarinic auto- and heteroreceptor

Abstract

Different types of presynaptic inhibitory Gα(i/o) protein-coupled receptors usually do not act independently of each other but rather pre-activation of receptor X impairs the effect mediated via receptor Y. It is, however, unknown whether this interaction extends to the cannabinoid CB(1) receptor on cholinergic neurones and hence we studied whether its activation, pharmacological blockade, or genetic inactivation affects the function of other presynaptic inhibitory receptors. The electrically evoked acetylcholine or noradrenaline release was determined in superfused rodent tissues preincubated with (3)H-choline or (3)H-noradrenaline. The muscarinic M(2) receptor, Gα(i), and Gα(o) proteins were determined in hippocampal synaptosomes by Western blotting. Hippocampal anandamide and 2-arachidonoyl glycerol levels were determined by LC-MS/MS. The inhibitory effect of the muscarinic receptor agonist oxotremorine on acetylcholine release in hippocampal slices was increased by genetic CB(1) receptor ablation (mouse) and the CB(1) antagonist rimonabant (rat but not mouse) and decreased by a cannabinoid receptor agonist (mouse). In mouse tissues, CB(1) receptor ablation also increased the effect of a δ opioid receptor agonist on acetylcholine release in the hippocampus and the effect of oxotremorine on noradrenaline release in the vas deferens. CB(1) receptor ablation, to a very slight extent, increased Gα(o) protein levels without affecting either Gα(i) and M(2) receptor protein or the levels of anandamide and 2-arachidonoyl glycerol in the hippocampus. In conclusion, the CB(1) receptor shows an inhibitory interaction with the muscarinic and δ opioid receptor on cholinergic neurones in the rodent hippocampus and with the muscarinic receptor on noradrenergic neurones in the mouse vas deferens.