The basal activity of tuberoinfundibular dopaminergic (TIDA) neurons is higher and the response of these neurons to the stimulatory actions of prolactin is greater in the female than in the male rat. In the female rat, the restraint-stress-induced increase in serum prolactin concentrations is accompanied by a concurrent decrease in the activity of TIDA neurons. The purpose of the present study was to compare these effects of restraint in male and female rats. TIDA neuronal activity was estimated by measuring the rate of dopamine (DA) synthesis (DOPA accumulation after the administration of a decarboxylase inhibitor, NSD 1015) and the rate of DA turnover (decline of DA after administration of atyrosine hydroxylase inhibitor; α-methyltyrosine) in the median eminence. Thirty minutes of restraint increased serum prolactin concentrations in both male and female rats, but a greater response was observed in the females. Restraint also decreased the rates of synthesis and turnover of DA in the median eminence of the female but not the male rat. The difference in the response of TIDA neurons in male and female rats to restraint is not the consequence of neuronal differentiation resulting from neonatal androgen exposure, because restraint also decreased the activity of TIDA neurons in androgen-sterilized female rats. The inability of restraint stress to reduce TIDA neuronal activity in the male rat appears to be the consequence of testosterone, since TIDA neurons were responsive to restraint following castration of the males. In addition, the ability of restraint stress to decrease TIDA neuronal activity was inhibited in castrated male rats by pretreatment with testosterone, and was facilitate in intact male rats by estradiol pretreatment. Neither castration nor pretreatment with estradiol or testosterone altered the responsiveness of TIDA neurons to restraint in the female rat. These results suggest that male-female differences in the response of TIDA neurons to restraint stress is a consequence of the actions of testosterone in the male rat