Prolactin-induced parental hyperphagia in ring doves: are glucocorticoids involved?

Hyperphagia is a prominent component of the parental behavior repertoire in male and female ring doves and is necessary in order for parents to successfully provision their growing young. Although previous studies implicate both prolactin and the endogenous glucocorticoid, corticosterone, in parental hyperphagia, the functional interactions between these two hormones in regulating changes in feeding activity have not been characterized. These studies examined the possibility that prolactin's orexigenic effects are mediated through the increased secretion of corticosterone. Twice-daily intracerebroventricular (icv) injection of prolactin increased plasma corticosterone concentration in non-breeding doves of both sexes, with males exhibiting more pronounced effects than females. To further test the importance of glucocorticoid signaling in prolactin-induced feeding responses, changes in food intake were investigated in icv prolactin-treated, non-breeding doves following icv infusion of the glucocorticoid receptor antagonist RU38486 or propylene glycol vehicle. No attenuation of prolactin-induced hyperphagia was observed in either sex following co-administration of RU38486 at a dose shown previously to block dexamethasone-induced feeding in doves. These findings suggest that elevated corticosterone titers in blood may contribute to the hyperphagia observed in response to prolactin, but corticosterone signaling through a mammalian-type glucocorticoid receptor is not essential.