[Ontogeny of circadian rhythms and the maternal role in rats: entrainment of the circadian pacemaker during the perinatal period].
Post-natal manifestation of circadian rhythms was examined in individual rats in order to clarify the manner in which pups' circadian oscillation entrained to the maternal circadian system. Ablation of the hypothalamic suprachiasmatic nucleus (SCN), a putative circadian pacemaker, completely eliminated the circadian rhythms of spontaneous locomotor activity and plasma corticosterone level in pregnant rats. However, all pups born to mothers whose SCN were lesioned at day 10 of gestation showed free-running circadian rhythms of plasma corticosterone level with similar phase angles after the 4th week of postnatal life. Strong positive correlations between the phases of circadian locomotor rhythm at the day of weaning and each free-running period (tau) were observed in blinded pups nursed under identical lighting schedule (LD). The fact suggests that the individual circadian oscillation was in phase on a certain day before the weaning. Mother-pups exchange under reversed lighting schedule (LD and DL) and nursing under 4-hourly restricted daily feeding (RF) indicated that nursing mother rat could essentially phase-set the circadian locomotor rhythm of blinded pups when the conditions during nursing were artificially modified. The weight of neonatal rats was measured every 4 hours from day 1 to day 3 and day 9 to day 10 after birth, and 4-hourly weight gains showed apparent circadian periodicity from day 2 of age. Under ad-lib feeding of mother rats, pups' weight mainly increased during daytime but the phase of weight rhythm shifted under RF corresponding to the feeding time of the mother. These findings suggest that the circadian oscillation underlying the spontaneous locomotor activity and plasma corticosterone level in rats has entrained to the maternal circadian system during fetal life, and nursing mother is capable of phase-setting the circadian oscillation of blinded pups probably through the rhythmicity of the lactation.
Department of Pedodontics, Hokkaido University School of Dentistry, Sapporo.
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Shirakawa
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001683:Biological Clocks; D001831:Body Temperature; D001835:Body Weight; D002940:Circadian Rhythm; D003345:Corticosterone / Q000097:blood; D005260:Female; D009043:Motor Activity; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013493:Suprachiasmatic Nucleus / Q000502:physiology*
D003345:Corticosterone