Effects of environmental enrichment on maternal behavior of rats with early life stress / 中华行为医学与脑科学杂志

ABSTRACT

Objective To investigate the improve effects of environmental enrichment on maternal behavior in the adult female rats thatexperienced early-life stress,and to explore the molecular biological mechanism.Methods The newborn Wistar rats were divided into two groups randomly,the early life stress group and the control group.Pups from the former were separated from their mothers once per day for 4 hours from PND 2-21 (day of birth was considered PND =0),and suffered vicious stimulus during the daily 4 hours maternal separation from PND 8-21.On PND 22(weaning),pups from the early life stress group were divided into two groups12 female pups were reared singly,refered to as isolated-rearing group; another 12 were placed in a big cage that was filled with all sorts of rodents toys,refered to as enriched-rearing group; control female pups were placed in groups of 4 per cage.Mating with male rats when female pups reached PND66,then being placed in cages singly when they were detected pregnant.Maternal behavior was evaluated on the second and sixth day after delivery,and the hypothalamic OTR mRNA levels were examined by RT-PCR.Results The results of maternal behavior observation showed that the total time of retrieve and the latency of licking were significantly longer in isolated-rearing rats compared with the normal and the enriched-rearing rats (P ＜ 0.01) ; total time of licking in enriched-rearing rats was longer than the normal and the isolated-rearing rats(P＜0.01) on the sixth day after delivery;and the score of the nest building was obviously lower in isolated-rearing rats,especially on the sixth day after delivery(P ＜ 0.01).Hypothalamic OTR mRNA levels in the isolated-rearing rats showed strongly decreased compared with the normal rats(P＜0.01),but which close to normal levels in enriched-rearing rats.Conclusion Early life stress can damage some components of maternal behavior,such as retrieval,licking,nest building,but it has no obvious effect on crouching behavior; it also decreases the hypothalamic OTR mRNA levels of the adult female rats; as a kind of early environmental intervention,groups-rearing could make hypothalamic OTR mRNA levels of the female rats that subjected to early life stress restore to normal,and thus reverse the disruptions of stress in maternal behavior.