INFLUENCE OF DRUGS ON EVOKED POTENTIALS IN THE CAT CEREBELLUM: III. EFFECTS OF MORPHINE HYDROCHLORIDE (2)

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In intact cats, morphine hydrochloride (2.0 mg/kg, i.v.) depressed spontaneous discharge of the Purkinje cell in 8 of the 15 neurons tested. These effects of morphine were antagonized by naloxone hydrochloride (0.4 mg/kg, i.v.). This opiate significantly decreased the evoked potentials produced by superficial radial nerve (SR) stimulation in the molecular layer of the cerebellar cortex. Although morphine decreased the potentials evoked by SR or tooth pulp stimulation in the nucleus fastigii and nucleus interpositus, this drug hardly influenced them in the nucleus dentatus. In the decerebrated cats, morphine significantly increased the potentials evoked in the cerebellar cortices by SR stimulation. In the somatosensory area I (SSA-I) or motor area (MA)-lesioned cats, morphine decreased the cerebellar potentials evoked by SR stimulation, but increased them in the SSA-I and MA-lesioned cats. Naloxone antagonized these effects of morphine. From our results, it appears that the decreasing effects of morphine on the cerebellar potentials evoked by SR stimulation may be affected by the functions of the SSA-I and MA of the cerebral cortex and that morphine may influence the cerebellum.