Effects of parental experience and age on expression of prolactin, vasoactive intestinal peptide and their receptors in a biparental bird, Columba livia

As animals gain parental experience, they often show more rapid and
efficient parental care responses that likely improve offspring survival
and fitness. Changes in circulating hormones that underlie reproductive
behaviors, including prolactin, have been found to correlate with parental
experience in birds and mammals. Altered responsiveness to prolactin in
key behavioral centers of the brain may also underlie the effects of
experience on parental behaviors. Further, experience may also affect
responsiveness to prolactin stimulatory hormones, such as hypothalamic
vasoactive intestinal peptide (VIP). While experience has been shown to
upregulate neural prolactin receptors and responsiveness in rodents, its
effects on prolactin receptor gene expression remain unstudied in birds.
To address this, we examined gene expression of pituitary prolactin,
hypothalamic prolactin receptors in the preoptic area, hypothalamic VIP,
and pituitary VIP receptors in both sexes of the biparental rock dove
(Columba livia) when birds were not actively nesting. As age and parental
experience are often confounded (i.e.,experienced parents tend to be older
than their inexperienced counterparts), we measured gene expression in
birds of varying combinations of age (0.6–3 years) and prior reproductive
experience (0–12 chicks raised). We found that increasing experience with
chicks correlated with lower PRLR expression in the preoptic area, and age
correlated with lower VIP expression in birds of both sexes. Pituitary PRL
and VIPR expression was not associated with parental experience or age.
These results suggest there may be persistent effects of experience and
age on neural responsiveness to, and regulation of, prolactin in birds.