Changes in Feeding Activity, Plasma Luteinizing Hormone, and Testes Weight in Ring Doves Following Hypothalamic Injections of Prolactin

Microinjections of ovine prolactin were administered unilaterally to the ventromedial hypothalamic nucleus and the preoptic-suprachiasmatic region in adult male ring doves in an attempt to determine the site(s) at which intracranial injections of prolactin act to alter feeding behaviour and gonadotropin secretion in this species. Food intake and body weight were measured daily during a 6-day pretreatment period and the 5-day treatment period that immediately followed. During the treatment period, birds received twice daily injections (0.5 μl) of either 2.5 ng ovine prolactin or saline vehicle. An additional group of birds with cannulae in the ventromedial nucleus were given twice daily injections of 25 ng ovine prolactin. Although food consumption was unaffected by low dose prolactin treatment, birds given 25 ng prolactin injections into the ventromedial nucleus showed a significant augmentation in food intake. Injections of 25 ng prolactin into the preoptic area also increased feeding; however, the magnitude of this hyperphagic response, as expressed relative to pretreatment levels, was less than that observed following prolactin injection into the ventromedial nucleus. No differences were observed between prolactin-treated and vehicle-treated birds in either cannulation group when testes weights and plasma luteinizing hormone concentrations were compared at the end of the treatment period. However, the possibility that prolactin influenced changes in luteinizing hormone and testes weight relative to baseline values could not be assessed due to constraints imposed by the experimental paradigm used. These results suggest that prolactin-sensitive neurons in the ventromedial hypothalamic region and the preoptic area are potential sites of prolactin action in promoting hyperphagia in ring doves. However, the role of these sites in mediating prolactin-induced suppression of gonadotropin secretion in this species remains to be clarified.