ROLE OF THE SUBTHALAMIC NUCLEUS IN CANNABINOID ACTIONS IN THE SUBSTANTIA-NIGRA OF THE RAT

The effect of cannabinoids on the excitatory input to the substantia n igra reticulata (SNr) from the subthalamic nucleus was explored. For t his purpose a knife cut was performed rostral to the subthalamic nucle us to isolate the subthalamic nucleus and the SNr from the striatum, a major source of cannabinoid receptors to the SNr. The data showed tha t the cannabinoid agonist WW55,212-2 blocked the increase in the firin g rate of SNr neurons induced by stimulation of the subthalamic nucleu s with bicuculline. Furthermore, the cannabinoid antagonist SR141716A antagonized the effect of the cannabinoid agonist. This study showed t hat cannabinoids regulate not only the striatonigral pathway, as previ ously reported, but also the subthalamonigral pathway. The opposite in fluences of these two inputs to the SNr, inhibitory and excitatory res pectively, suggest that endogenous cannabinoids play a major role in t he physiological regulation of the SNr.