Entrainment of the melatonin rhythms in early postnatal lambs and their mothers.
Although the developing sheep can produce an appropriately timed melatonin rhythm as early as 1 week after birth, it is not known whether the lamb is able to adjust its melatonin rhythm to a change in daylength. The ability of the young lamb to entrain its pattern of melatonin secretion to a new photoperiod was determined in the present study. Eight female lambs and their mothers were raised in long days (LD 16:8) beginning 2 weeks postpartum. At 7 weeks of age, the time of lights-off was advanced 8 hr, the short-day photoperiod then being LD 8:16; the time of lights-on remained unchanged. Concentrations of melatonin were measured in blood samples collected hourly on days - 1, 0, 2, 4, 6, and 13 relative to the light change. On day 0, all mothers and daughters had advanced the onset of melatonin secretion by at least 1 hr, and by day 13, 12 of 16 had completely entrained to the new photoperiod. The rate of entrainment among individuals varied; the mean rate for lambs and mothers did not differ. This study provides evidence that the melatonin-rhythm-generating system matures shortly after birth.
Wood
R I
RI
Department of Physiology, University of Michigan, Ann Arbor 48109-0404.
Claypool
L E
LE
Ebling
F J
FJ
Foster
D L
DL
D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn / Q000254:growth & development / Q000502:physiology*; D002940:Circadian Rhythm; D003624:Darkness; D005260:Female; D008027:Light; D008550:Melatonin / Q000097:blood*; D010507:Periodicity; D012756:Sheep / Q000502:physiology*; D013997:Time Factors
D008550:Melatonin