Regulation of prolactin secretion in a nonphotoperiodic breeder, the zebra finch

Abstract

In avian species, high levels of prolactin (PRL) released from the anterior pituitary are associated with reproductive behaviors such as incubation and rearing of young. We studied reproduction-associated PRL levels in breeding and nonbreeding zebra finches. The general hypothesis of this dissertation was: The general pattern of PRL release in zebra finches is similar to other avian species, but differences in regulation of release can be expected due to the unique breeding environment in which these animals live. The research was divided into four parts: 1) Determining the pattern of PRL release and secretion in response to vasoactive intestinal peptide (VIP); 2) Determining PRL and growth hormone (GH) presence and distribution in the anterior pituitary; 3) Determining differences in PRL molecular weight isoforms in the anterior pituitary during different phases of reproduction; and 4) Determining the effects of dopaminergic agents and anti-VIP antibodies in regulating PRL release. Plasma PRL levels were low in nonbreeding zebra finches and high in breeding zebra finches. Males and females did not differ. Exogenous VIP raised PRL levels in nonbreeding zebra finches to a level comparable to breeding finches. The VIP-induced PRL rise occurred rapidly and had a prolonged effect. Zebra finches who were in the parental stage of reproduction showed only a slight increase in plasma PRL following VIP injection. PRL-immunoreactive (IR) cells were concentrated in the cephalic lobe and along the ventral margin of the anterior pituitary (AP) and extended into the caudal lobe in birds of all reproductive conditions. GH-IR cells were concentrated in the caudal lobe of the AP and also extended into the cephalic lobe. Zebra finches with previous reproductive experience had significantly more PRL-IR cells in the AP than inexperienced birds, regardless of