Photoperiod mediates the ability of serotonin to release prolactin in the turkey.
Photostimulation (PS) of turkeys increases the number of hypothalamic vasoactive intestinal peptide (VIP)-immunoreactive neurons, the number of anterior pituitary VIP binding sites, and prolactin (PRL) secretion. Serotonin (5-HT) was recently shown to stimulate PRL secretion through VIP. This study tested the hypothesis that 5-HT's ability to induce PRL secretion is mediated by reproductive status and/or photoperiod in normally cycling turkey hens. Initially, saline or 5-HT was infused into the third ventricle of nest-deprived, previously incubating (ND) hens for 60 min at rates of 0.1, 1.0, or 10 nmol/min. The results led to use of the 10 nmol/min infusion rate for the remaining 5-HT infusions. Next, 5-HT was infused into short-day (SD;6), laying (6), ND (5), and photorefractory (P/R;6) hens. Plasma PRL was elevated in all groups except for the SD hens (P < 0.05). In Experiment 3, VIP was infused into the median eminence of SD (6), laying (5), and P/R (5) hens, increasing circulating PRL levels in all three groups (P < 0.05). Finally, SD hens were photostimulated for 0, 3, or 10 days and then infused with 5-HT. Only the birds which were photostimulated for 10 days exhibited elevated plasma PRL (P < 0.05). In conclusion, PS regulates PRL secretion at the hypothalamic level and more than 3 days of PS are required for 5-HT-ergic stimulation of PRL secretion.
Pitts
G R
GR
Department of Animal Science, University of Minnesota, St. Paul 55108, USA.
Youngren
O M
OM
Phillips
R E
RE
el Halawani
M E
ME
D000818:Animals; D004305:Dose-Response Relationship, Drug; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008473:Median Eminence / Q000187:drug effects / Q000502:physiology; D017440:Photoperiod; D011388:Prolactin / Q000378:metabolism*; D012701:Serotonin / Q000008:administration & dosage / Q000494:pharmacology*; D014422:Turkeys / Q000502:physiology*; D014660:Vasoactive Intestinal Peptide / Q000008:administration & dosage / Q000494:pharmacology
D012701:Serotonin; D014660:Vasoactive Intestinal Peptide; D011388:Prolactin