The purpose of the present study was to examine the effects of procedures that alter impulse flow in tuberoinfundibular dopamine (DA) neurons on the metabolism of DA in the median eminence and on the secretion of prolactin from the anterior pituitary. Twenty min following the administration of gamma-butyrolactone (GBL, 1000 mg/kg, i.p.) there was a marked decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations in the median eminence and an increase in prolactin concentrations in the serum, indicating that a decrease in activity of tuberoinfundibular DA neurons is accompanied by a decrease in DA metabolism in the median eminence and a loss of tonic inhibition of pituitary prolactin secretion. Activation of tuberoinfundibular DA neurons by bilateral stimulation of the arcuate nucleus in GBL-treated rats produced a rapid increase in median eminence DOPAC concentrations and a time-dependent decrease in serum prolactin concentrations. Nomifensine (25 mg/kg, i.p., 30 min), a DA uptake inhibitor, had no effect on median eminence DOPAC concentrations in sham- or arcuate nucleus-stimulated rats, indicating that regardless of the level of activity of tuberoinfundibular neurons, very little DA is recaptured and metabolized in terminals of these neurons in the median eminence. Taken together these results reveal that alterations in impulse flow in tuberoinfundibular DA neurons are accompanied by corresponding changes in the metabolism of DA in the median eminence.