Alterations in Hypothalamic Vasoactive Intestinal Peptide-Like Immunoreactivity Are Associated with Reproduction and Prolactin Release in the Female Turkey*

Abstract

Vasoactive intestinal peptide (VIP) has potent PRL-releasing activity, but its physiological role in the regulation of PRL release during the avian reproductive cycle is not known. We used indirect immunofluorescence to determine if changes in hypothalamic VIP are associated with the shifts in circulating PRL during the reproductive cycle of the domestic turkey. In the naturally hyperprolactinemic incubating hen, the majority of VIP immunoreactivity (VIP-IR) existed within neurons of the infundibular nuclear complex (INF) and fibers in the external layer of the median eminence. Within the INF, the numbers of VIP-IR cells increased during the cycle, paralleling increases in serum PRL. In the reproductively inactive, nonphotostimulated hen with low serum PRL, essentially no positive cells were noted, whereas the incubating hen exhibited 32.1 +/- 2.2 cells/pair of adjacent sections in the anterior INF and 59.6 +/- 2.0 cells in the posterior INF. Exposure of inactive hens to a stimulatory photoperiod resulted in a 2.6-fold increase in serum PRL with the appearance of VIP-IR cells in the INF. During laying and incubation, further increases were observed in the number of positive cells in the INF and serum PRL as well as a greater fiber density in the median eminence. To further examine the association between changes in VIP-IR and serum PRL, circulating PRL was artificially lowered by depriving incubating hens of their nests for 0, 2, 5, and 10 days. On day 2 of nest deprivation, serum PRL declined markedly to 12% of day 0 levels, with VIP-IR cell numbers at 64% and 46% in the anterior and posterior INF, respectively. By day 10, birds exhibited cell numbers in the INF averaging 20% of those observed in the day 0 incubating hens, with serum PRL at 6% of day 0 levels. The results of these studies indicate a possible causal relationship between hypothalamic VIP and changes in PRL secretion during the avian reproductive cycle, providing a basis for further research on the importance of this peptide as well as factors responsible for the modulation of its expression in hypothalamic INF neurons.

Effects of genetic polymorphisms on egg production in indigenous Noi chicken

“…The mRNA concentration of VIP varies with hens' physiological status (Mauro et al, 1989;Chaiseha et al, 1998) and VIP enhances the stability of mRNA prolactin in vivo as well. The activities that affect the VIP concentration in the body were suggested to influence the reproductive performance and hatching behavior (Caldwell et al, 1999).…”

Regulation of Prolactin Secretion by Dopamine and Vasoactive Intestinal Peptide at the Level of the Pituitary in the Turkey

“…Three genomic clones encoding D 1 -like DA receptors have been isolated from the chicken hypothalamus, named D 1 A, D 1 B, and D 1 D [32]. In the quail brain, the D 1 DA-like receptor density was shown to be low but significantly detectable in the preoptic area and other parts of the hypothalamus, such as the infundibulum [33], where abundant VIP neurons are present [34]. Prior incubation of turkey pituitary cells with the D 2 DA receptor agonist quinpirole, diminished VIP-stimulated PRL secretion and PRL mRNA abundance, suggesting the presence of D 2 DA receptors within the turkey pituitary [11].…”

Prior Experience with Photostimulation Enhances Photo-Induced Reproductive Response in Female House Finches

“…However, as VIP and prolactin play regulatory roles later in the breeding season 516 during incubation and chick rearing, it is also possible that four weeks of 517 photostimulation was not sufficient to detect significant photo-induced increases in VIP 518 or photoexperience-related differences in VIP expression. VIP-ir cell count in the INF of 519 the reproductively-experienced turkeys mentioned above, continued to increase after 10 520 days of photostimulation through egg laying, incubation and into photorefractoriness 521 (Mauro et al, 1989(Mauro et al, , 1992. Similarly, while ten days of exposure to a 16h L: 8h D 522 photoperiod was sufficient to stimulate an increase in nascent VIP mRNA in the 523 hypothalamus of female turkeys, significant increases in both steady-state cytoplasmic 524 VIP mRNA levels and VIP levels in the median eminence were not apparent until the 525 25 birds laid their first eggs (Chaiseha et al, 1998).…”

“…It is possible that the 511 four weeks of photostimulation in our study was long enough for any photoexperience-512 related differences in the timing of up-regulation of VIP expression to disappear. Only 513 two weeks of photostimulation was enough to trigger a significant increase in VIP-ir cell 514 count in the INF of turkeys in their second reproductive season (Mauro et al, 1989(Mauro et al, , 515 1992). However, as VIP and prolactin play regulatory roles later in the breeding season 516 during incubation and chick rearing, it is also possible that four weeks of 517 photostimulation was not sufficient to detect significant photo-induced increases in VIP 518 or photoexperience-related differences in VIP expression.…”

“…Although the GnRH antibody recognizes 292 both GnRH-I and -II, only GnRH-I and not GnRH-II cell bodies are present in the septo-293 preoptic area (Millam et al, 1993;van Gils et al, 1993;Sharp, 2005). Previous studies 294 have found that this region is innervated by central photoreceptors (Saldanha et al, 295 1994(Saldanha et al, 295 , 2001) and responds to photostimulation with increased fos-like immunoreactivity 296 Follett, 1995, 1997;Millam et al, 2003) Mauro et al, 1989Mauro et al, , 1992. 305…”