Central prolactin receptor distribution and pSTAT5 activation patterns in breeding and non-breeding zebra finches...

The hormone prolactin has many diverse functions across taxa such as osmoregulation, metabolism, and reproductive behavior. In ring doves, central prolactin action is important for parental care and feeding behavior. However, there is a considerable lack of information on the distribution of the prolactin receptor (PRLR) in the avian CNS to test the hypothesis that prolactin mediates these and other functions in other birds. In order to advance this research, we collected brains from breeding and non-breeding zebra finches to map the PRLR distribution using immunohistochemistry. We found PRLRs are distributed widely across the brain, both in hypothalamic sites known to regulate parental care and feeding, but also in many non-hypothalamic sites, including the tectofugal visual pathway, song system regions, reward associated areas, and pallium. This raises the possibility that prolactin has other functions throughout the brain that are not necessarily related to feeding or parental care. In addition, we also stained brains for pSTAT5, a transcription factor which is expressed when the PRLR is activated and is used as a marker for PRLR activity. We found several notable differences in pSTAT5 activity due to the breeding state of the animal, in both directions, further supporting the hypothesis that prolactin has many diverse functions in the brain both within and outside times of breeding. Together, this study represents the first essential step to inform the design of causative studies which manipulate PRLR-expressing cells to test their role in a wide variety of behaviors and other physiological functions.