Changes in brain gonadotropin-releasing hormone- and vasoactive intestinalpolypeptide-like immunoreactivity accompanying reestablishment of photosensitivity in male dark-eyed juncos (Junco hyemalis)

In seasonally breeding, photoperiodic birds, the development of photorefrac toriness is associated with decreased brain expression of gonadotropin-rele asing hormone-like immunoreactivity (GnRH-Ii ir) and increased expression o f vasoactive intestinal polypeptide-like immunoreactivity (VIP-li ir). Diss ipation of photorefractoriness and reestablishment of photosensitivity are associated with increased GnRH-li ir brain production, but concurrent chang es in VIP-ii ir expression have not been investigated. To address this ques tion, we compared the expression of VIP-ii ir in the infundibulum (INF) of adult male dark-eyed juncos (Junco hyemalis) that were made. photorefractor y (PR) by prolonged exposure to long days with that of birds that were not photostimulated (PS), but had regained photosensitivity by exposure to shor t days for 5 (short-term-PS, ST-PS) or 13 (long-term-PS, LT-PS) consecutive months. Photosensitive males had smaller INF VIP-ii ir cell bodies than PR males, but the numbers of INF VIP-ii ir cells were independent of photoper iodic condition. Changes in infundibular VIP-li ir were correlated with cha nges in preoptic area (POA) GnRH-li expression. Specifically, photosensitiv e males had more and larger POA GnRH-li ir cells and more GnRH-li ir fibers in this region than PR males. Further, LT-PS males had more GnRH-li ir POA fibers and larger testes than ST-PS juncos. Thus, induction of photorefrac toriness is associated with increased VIP and decreased GnRH brain expressi on whereas dissipation of photorefractoriness concurs with decreased VIP an d increased GnRN brain expression. These results suggest a physiological ro le for VIP in the control of changes in GnRH expression as a function of th e photosensitive condition. (C) 2000 Academic Press.