The effect of muscimol on prolactin secretion in male rats

In order to further clarify the conflicting reports on the effect of gamma-aminobutyric acid (GABA) on prolactin (PRL) secretion, we have examined the effect of a potent, centrally active GABA receptor agonist, muscimol, on basal and pharmacologically elevated plasma PRL levels in male rats. Intravenous administration of muscimol, in doses from 0.5-5.0 mg/kg, produced no change in resting plasma PRL levels 15 and 30 minutes after its administration. In animals pretreated with alphamethylparatyrosine (100 mg/kg, intraperitoneally), muscimol (0.1-1.0 mg/kg, i.v.) produced significant decreases in plasma PRL concentrations. Muscimol, (5.0 mg/kg, i.p.) also significantly inhibited PRL secretion in rats pretreated with haloperidol (1.0 mg/kg, i.p.). This effect of muscimol is probably due to its ability to activate central GABA receptors.