Effects of intracranial prolactin administration on maintenance of incubation readiness, ingestive behavior, and gonadal condition in ring doves.

Systemic administration of prolactin (PRL) reportedly maintains readiness to sit on eggs, increases body weights and liver weights, and reduces gonadal and reproductive tract tissue weights in male and female ring doves. To determine if these effects are mediated by PRL-induced changes in the central nervous system, ring doves were isolated from their mates, nests, and eggs on Day 4 of incubation and given twice-daily intracerebroventricular injections of PRL (1 microgram, 0.031 IU) or saline vehicle (2 microliter) during the next 10 days. Food and water consumption were monitored daily during treatment and tests for incubation behavior and observation of organ weight changes were conducted at the end of the period. The incidence of incubation behavior in the PRL-treated group was not significantly different from that in the control group and was significantly lower than that reported in a previous study following subcutaneous PRL injections. However, gonadal and reproductive tract tissue weights were markedly reduced and food and water consumption were significantly elevated in PRL-treated birds. Body weights and liver weights were also increased following PRL administration. In contrast, crop sac weight did not increase in the PRL treated birds, thereby indicating that the effects of icv prolactin treatment were not mediated by increased plasma PRL levels and peripheral target organ stimulation. These results suggest that PRL can act directly on the brain to inhibit gonadotropin release and to stimulate ingestive behavior but central effects of PRL alone are not sufficient to maintain incubation readiness.