The effects of suckling on serum prolactin levels and catecholamine concentrations and turnover were examined in several discrete brain regions. Turnover rates were assessed by using the synthesis inhibitor alpha-methyltyrosine (alpha-MT) in combination with microdissection techniques for the removal of individual brain regions and sensitive radioenzymatic assays for norepinephrine (NE) and dopaime (DA). Prolactin secretion was induced by mothers experiencing 6 h of pup removal with subsequent pup replacement. Suckling or the administration of alpha-MT to mothers resulted in a marked increase in circulating titers of prolactin. A decrease in steady-state NE concentrations in the anterior hypothalamus and a decrease in steady-state DA concentrations in the ventromedial nucleus were noted in suckled mothers. The comparison of relative rates of NE depletion after alpha-MT treatment revealed a suckling-induced increase in turnover in the ventromedial nucleus and a suckling-induced decrease in turnover in the anterior hypothalamus. Neither suckling nor alpha-MT treatment produced any changes in NE or DA turnover rates in the arcuate nucleus or median eminence. These findings demonstrate that suckling-induced activation of prolactin results in changes in noradrenergic processes in the ventromedial and anterior hypothalamic nuclei. This suggests an involvement of noradrenergic systems in suckling-induced prolactin release.