Entrainment of hamster pup circadian rhythms by prenatal melatonin injections to the mother

Abstract

A circadian pacemaker, thought to be within the suprachiasmatic nucleus (SCN) of the hypothalamus, begins to function before birth in rodents. Prenatal entrainment of the pacemaker appears to be mediated by signals regulated by the maternal SCN; ablation of the mother's SCN during gestation disrupts the normal phase of the pups' rhythms. The present paper presents an experimental approach for identifying candidate entraining signals and for testing when they are effective during development. The candidate signal examined in these experiments was the pineal gland hormone, melatonin. Female golden hamsters (Mesocricetus auratus) received SCN lesions on day 7 of gestation. During the last week of gestation, they were given two daily subcutaneous injections of oil 12 h apart. One of the injections each day contained melatonin (10, 50, or 100 micrograms). The phases of the pups' activity rhythms were measured at weaning and were found to be related to the timing of the daily injection that contained melatonin, demonstrating that the melatonin directly or indirectly set the phase of the pups' rhythms. Injections given over 4 days of gestation were found to be as effective as injections given over 7 days. Although a physiological role for melatonin as an entraining signal has not been demonstrated, the results show that exogenous, prenatal treatment can predictably set the phase of the offsprings' circadian rhythms.

Cellular Neurophysiology of the Rat Suprachiasmatic Nucleus: Electrical Properties, Neurotransmission, and Mechanisms of Synchronization

“…IA); peak activity occurred at 06:29 ± 0:26 h and then averaged in 1-h bins. Single-unit activity was circadian time (mean ± SE; n = 6; tights on from 00:00 to recorded by using glass micropipettes filled with 1 M NaCI 12:00 h circadian time), in agreement with other in vivo and (resistance = [30][31][32][33][34][35][36][37][38][39][40].…”

The Uterus Sustains Stable Biological Clock during Pregnancy

“…In mammals, maternal melatonin has a circadian pattern in its plasma concentration and is thought to convey information on the light-dark cycle to the fetus, thereby synchronizing the developing fetus's biologic clock to the 24-hour cycle (Davis and Mannion 1988;Illnerová et al 1993;Serón-Ferré et al 2007). Fetal biological clock has also been reported to be influenced by the maternal feeding schedule during pregnancy (Weaver and Reppert 1986;Ohta et al 2008).…”

Maternal Entrainment of the Developing Circadian System in the Siberian Hamster (Phodopus sungorus)

“…In fact, the potential for entrainment during the postnatal period clearly does exist in the Syrian hamster, as revealed by the synchronizing effects of timed melatonin treatments during the first postnatal week (Grosse et al, 1996). One likely explanation for this species difference may relate to litter size, which is generally smaller for Siberian hamsters (typically 4-5) (Ebling, 1994) than for Syrian hamsters (typically 6-10) (Davis and Gorski, 1988;Davis and Mannion, 1988;Grosse et al, 1996). Honma and colleagues (1987) revealed a litter size effect on the ability of a foster mother to re-entrain the phases of rat pups, in that a greater proportion of pups were synchronized to the phase of the foster mother when the litter size was small than when it was large.…”

“…Moreover, given the clearly demonstrated role for melatonin in conveying seasonal information to the developing Siberian hamster (Weaver and Reppert, 1989b;Gunduz and Stetson, 1994;Prendergast et al, 1996), this species may be an especially suitable model for investigating whether melatonin also conveys circadian information from the mother to fetus or pup. This is important because the role of melatonin in maternal entrainment is unclear in rats and Syrian hamsters, where melatonin appears to be one of several redundant signals (Reppert and Schwartz, 1986a;Davis and Mannion, 1988;Reppert, 1995).…”