Maternal deprivation in neonatal period and biological rhythms

Abstract

Maternal deprivation in the neonatal period is known to induce a variety of endocrinologicaland behavioral changes in grown-up rats (Weaver et al. 2004). In particular,the responsiveness of the hypothalamus-pituitary-adrenocortical (HPA) axis tonoxious stimuli is repeatedly reported to change in adulthood. Maternal deprivationis also known to reset the circadian clock of neonatal rats in the absence of light(Viswanathan and Chandrashekaran 1985). The circadian clock located in the suprachiasmaticnucleus (SCN) entrains to light-dark cycles through the retinohypothalamictract as early as postnatal day 6 (Davis and Reppert 2001). Until this developmentalstage, the circadian clock is entrained by the periodicity of their pregnantand nursing mothers, which is called maternal entrainment (Ohta et al. 2003).Separation of newborn pups from their nursing mother for 12 h from postnatal day1 to day 6 phase-reversed the circadian rhythms in clock gene expression in theSCN in rats deprived of light.The mechanisms of the long-term effect of maternal deprivation are not well understood.Expressed symptoms are likely triggered by a lack of specific conditionsassociated with maternal nursing, which include tactile, olfactory, thermal, nutritional,and auditory stimuli (Kuhn and Schanberg 1998). In order to have better insightsinto the mechanism of maternal deprivation on the circadian clock, we examinedcertain aspects of maternal deprivation that may contribute to the long-termeffect, such as the length of deprivation in a day, the time of day of deprivation, andthe ambient temperature during deprivation. We assessed the body weight gain, thestress-induced and basal levels of plasma corticosterone in adulthood, and the circadianphases and period of locomotor activity rhythm at weaning. We further examinedthe so-called critical periods for the change in these functions.