ELECTROPHYSIOLOGICAL EFFECTS OF A CANNABINOID ON NEURAL ACTIVITY IN THE GLOBUS-PALLIDUS

The globus pallidus contains a dense distribution of cannabinoid recep tors and appears to be a site of action of cannabinoids in the product ion of catalepsy. Single unit electrophysiology was used to explore th e role of cannabinoid receptors in the globus pallidus of the rat. Int ravenous injections of the potent and selective synthetic cannabinoid rolo[1,2,3-de]-1,4-benzoxazin-6-yl](1-napthalenyl) methanone (WIN 55,2 12-2; up to 0.5 mg/kg, i.v.) inhibited the spontaneous firing of neuro ns in the globus pallidus. In a second set of experiments, WIN 55,212- 2 antagonized the inhibition of pallidal firing produced by electrical stimulation of the striatum. The pharmacological specificity of the e ffects of WIN 55,212-2 on basal and evoked activity in the globus pall idus was demonstrated by the lack of effect of the inactive enantiomer WIN 55,212-3. These results indicate that cannabinoids may produce fu nctionally opposite effects on spontaneous and evoked activity in the globus pallidus: a decrease in spontaneous firing and a decrease in th e inhibition of firing produced by the striatopallidal projection.