丰富环境干预对生命早期不良经历雌性大鼠母爱行为的改善作用

Effects of environmental enrichment on maternal behavior of rats with early life stress

目的观察丰富环境干预对生命早期有不良经历的雌性大鼠母爱行为的改善作用，并探讨其分子生物学机制。方法将新生大鼠随机分为生命早期应激组和对照组，生命早期应激组于出生后第2～21天给予每天与母鼠分离4h，并在第8—21d每天与母鼠分离的4h内给予恶性刺激；自第22天断奶后，将生命早期应激组仔鼠随机分为单笼饲养组和群体饲养组，对照组按雌鼠4只／笼正常饲养；饲养至第66天，将各组雌鼠分别与雄鼠合笼，怀孕后单笼饲养；分娩后第2天和第6天观察大鼠母爱行为并检测下丘脑催产素受体（OTR）mRNA表达水平。结果母爱行为观察显示：单笼饲养组雌鼠回收仔鼠总用时[第2天（1658．55±867．24）S；第6天（1517．73±674．57）s]明显长于对照组[第2天（278．38±120．46）s；第6天（205．10±81．44）s]（P〈0．01）和群体饲养组[第2天（285．45±151．14）S（P〈0．01）；第6天（504．89±197．75）s（P〈0．05）]；分娩第2天单笼饲养组雌鼠的舔仔潜伏期（541．73±287．52）s明显长于对照组（324．08±180．31）s（P〈0．05）和群体饲养组（223．13±168．72）s（P〈0．01）；分娩第2天与第6天各组雌鼠的哺乳时间比较，差异无统计学意义（P〉0．05）；单笼饲养组雌鼠的建穴质量[第2天（2．55±1．04）分；第6天（1．36±1．43）分]明显低于对照组[第2天（3．75±0．46）分，（P〈0．05）；第6天（3．00±1．00）分，（P〈0．01）]和群体饲养组[第2天（3．57±0．53）分（P〈0．05）；第6天（2．89±1．17）分伊〈0．01）]。RT—PCR结果显示：单笼饲养组雌鼠OTRmRNA表达水平（836．00±105．6）明显低于对照组（1110．60±98．41）（P〈0．01），而群体饲养组表达水平（986．20±95．40）趋于正常。结论生命早期应激使雌性大鼠的回收、舔仔、建穴行为受损（对哺乳行为无明显影响），并使雌l生大鼠成年后下丘脑OTRmRNA水平降低；群体饲养作为损伤。命早期遭受应激的大鼠下丘脑OTRmRNA水平趋于正常。

Objective To investigate the improve effects of environmental enrichment on maternal behav- ior 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 con- trol 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 groups： 12 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 hypo- thalamic 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 be- havior; it also decreases the hypothalamic OTR rnRNA levels of the adult female rats; as a kind of early environmental in-tervention,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.