Effects of microiontophoretically-applied morphine on the Purkinje cell in the cerebellum of the cat.

The effects of microiontophoretically-applied and pneumatically-applied morphine on the spontaneous discharge of Purkinje cells in the cerebellum of the anesthetized cat were examined. Microiontophoretic application of morphine produced both inhibitory and excitatory responses of the Purkinje cells. Pneumatic application of morphine produced similar effects to those of microiontophoresis. Both types of application of morphine induced dose-dependent responses. Excitatory responses were antagonized by naloxone (opiate antagonist), but inhibitory responses were not affected by naloxone, propranolol (beta-receptor antagonist) or methysergide (serotonin antagonist). Bicuculline and picrotoxin, GABA antagonists, abolished completely the morphine-induced inhibitory response. These results suggest that morphine-induced excitation is connected with the opiate system and that inhibition is related to the GABAergic system, in the cerebellum of the cat.