EFFECT OF DELTA(9)-TETRAHYDROCANNABINOL ON CIRCLING IN RATS INDUCED BY INTRANIGRAL MUSCIMOL ADMINISTRATION

Unilateral injection of 25 ng of muscimol into the rat substantia nigr a pars reticulata induced contralateral circling. Circling induced by 25 ng of muscimol was increased by simultaneous administration of 1 mu g of Delta(9)-tetrahydrocannabinol and abolished by 10 mu g. Previous experiments have shown that Delta(9)-tetrahydrocannabinol enhances mu scimol-induced catalepsy in the globus pallidus. These results identif y another brain area in which synergism between Delta(9)-tetrahydrocan nabinol and muscimol can occur and show that Delta(9)-tetrahydrocannab inol can enhance an excitatory as well as an inhibitory GABAergic moto r effect. The data support the hypothesis that cannabinoids can facili tate transmission along central gamma-aminobutyric acid (GABA) releasi ng pathways.