早期母子分离对大鼠成年后认知功能及海马区神经型一氧化氮合酶表达的影响

摘要

目的 研究早期母子分离(maternal separation, MS)对雄性大鼠成年后认知功能与海马区神经型一氧化合酶(neural nitric oxide synthase, nNOS)表达的影响,以探讨生命早期应激(early life stress, ELS)对大鼠神经发育的影响.方法 健康SD孕鼠随机分为MS组和非母子分离(no maternal separation group, NMS)组,每组6只,MS组新生幼鼠在出生后第3~22 d,每天与母鼠分离3 h,NMS组不采取任何干预措施.饲养至10周龄时两组各取24只子代雄性大鼠,采用Morris水迷宫进行学习记忆能力测试,采用NeuN免疫荧光染色观察其海马齿状回(dentate gyrus, DG)神经元数目及分布情况,Western Blot法检测海马区nNOS、eNOS、Bax/BCL2、caspase-3及P53的含量,Ki67/DCX免疫荧光染色观察海马DG区神经元增殖、分化情况,TUNEL染色检测海马DG区神经元变性死亡情况. 结果 行为学测试提示MS组子代雄性大鼠相对于NMS组,逃逸潜伏期延长(P<0.05),目标象限停留时间和穿越平台次数减少(P<0.05). MS组子代雄性大鼠相对于NMS组,海马DG区正常及变性神经元的数目无明显变化(P＞0.05),神经元增殖减少、分化减缓、凋亡增多(P<0.05),海马区nNOS、eNOS表达减低(P<0.05),Bax/BCL2表达增高(P<0.05),caspase-3、P53表达无统计学差异(P＞0.05).结论 早期母子分离能够减少子代大鼠成年后海马区nNOS含量,影响海马DG区神经元功能,可能对神经发育有长远影响,与成年后学习、记忆能力相关的认知功能改变有关.%Objective To investigate the effect of maternal separation (MS) on cognitive function in adult male rats through the expression of neuronal nitric oxide synthase (nNOS) in hippocampus, and to reveal the roles of early life stress (ELS) on neural development in rats. Methods Healthy SD pregnant rats (n=12) were randomly divided into maternal separation group (MS group) and control group (NMS group) (n=6 for each group). The newborn rats in the MS group were separated from the mother rats for 3 h every day from postnatal day 3 to 22 whereas no intervention was taken in the NMS group. At the age of 10 weeks, Morris water maze was used to test the learning and memory abilities of two groups of offspring male rats. Neuron immunofluorescence staining was used to examine the number and distribution of neurons in dentate gyrus (DG) of two groups of offspring male rats. Western Blot method was used to detect nNOS, eNOS, Bax/BCL2, Caspase-3 and P53 levels in the hippocampus of the two groups. Ki67/DCX immunofluorescence staining were used to examine the proliferation and differentiation of neurons in the DG area of the hippocampus. TUNEL staining was used to detect the neuronal degeneration and death in the DG area of the hippocampus. Results Behavioral tests showed that the escape latency of male rats in MS group was prolonged, the target quadrant residence time and the number of platform crossing decreased (P<0.05) compared with NMS group. Compared with NMS group, the number of normal and degenerated neurons in hippocampal DG area of MS group had no significant change (P＞0.05). However, the expression of nNOS and eNOS in hippocampus was decreased (P<0.05) and the expression of Bax/BCL2 was increased (P<0.05), but the expression of caspase-3 and P53 remained unchanged (P＞0.05). In addition, Neuronal proliferation and differentiation were decreased and apoptosis was increased in MS group (P<0.05). Conclusion Repeated MS reduces the expression levels of nNOS in the hippocampus, affects the neuronal function in the DG area, and has a long-term influence on the neurodevelopment, which results in cognitive deficits related to learning and memory abilities in adult rats.