Intranigral GABAergic drug effects on striatal dopamine activity.

Concentrations of striatal dopamine (DA), serotonin (5-HT) and their metabolites were measured following infusions of the GABAA receptor agonist, muscimol, or GABAA receptor antagonist, bicuculline, into the substantia nigra (SN) or areas dorsal to the SN in adult rats and 16-day-old rat pups. Results indicated that intranigral infusions of muscimol produced site-specific increases in the concentrations of striatal DA metabolites in adults, while in pups, intranigral muscimol infusions produced site-specific increases in the concentrations of striatal DA. Intranigral infusions of bicuculline had no effect on striatal DA or its metabolites in either age group. Neither GABAergic drug had any effect on striatal 5-HT or its metabolite. The data suggest that the effect of nigral GABAA agonist infusions on the activity of the nigrostriatal pathway is age-specific. The lack of opposing effects following the nigral infusion of a GABAA receptor antagonist indicates that the influences of GABAA agonists may be mediated by different mechanisms as a function of age.