THE CB1 CANNABINOID RECEPTOR ANTAGONIST SR 141716A AFFECTS A(9) DOPAMINE NEURONAL-ACTIVITY IN THE RAT

CB1 receptors and their putative natural ligand anandamide, have been tentatively involved in the control of midbrain extrapyramidal functio n. Electrophysiological activity of dopamine neurones was measured aft er acute and repeated administration of the CB1 receptor antagonist SR 141716A (0.3-3 mg kg(-1)) in rats. Acute SR 141716A increased A(9), b ut not A(10) cell population response without affecting either their s pontaneous firing rate or apomorphine-induced rate inhibition and prev ented amphetamine-induced inhibition of A(9), but not of A(10) cell fi ring. After repeated administration SR 141716A (1 or 5 mg kg(-1)) decr eased population response of A(9) cells, which was reversed by apomorp hine. These results suggest that CB1 receptor blockade by SR 141716A i nterrupts a cannabinoid-like endogenous tone controlling extrapyramida l function.