Effect of neonatal prolactin deficiency on prepubertal tuberoinfundibular and tuberohypophyseal dopaminergic neuronal activity.

Prolactin (PRL) is present in the milk of lactating rats and, when ingested by the pups, can pass through the gut and enter the systemic circulation. The present study tested whether a suppression of normal milk PRL intake by the pups during early postpartum period affects the subsequent level of activity of the tuberoinfundibular dopamine (TIDA) system. Maternal plasma and milk PRL levels were depressed in lactating rats by daily injections of bromocriptine. Such treatment during postpartum days 2-5, but not during postpartum days 9-12, resulted in a marked suppression of DA turnover in the median eminence (ME), and in an elevation in plasma PRL concentration in the offspring when measured at 33-35 days of age. Simultaneous infusion of ovine PRL (oPRL) by osmotic minipump reversed the effects of neonatal bromocriptine. Catecholamine turnover in the neurointermediate lobe (NIL) was unaffected by any treatment. These results suggest that the normal activity of the TIDA system, but not that of the tuberohypophyseal DA system of the rat, may be impaired by a deficiency of PRL during a critical postpartum period.