孕期脂多糖暴露对子代小鼠大脑皮层发育的影响及其微环路机制的研究

Maternal infection during pregnancy is a recognized risk factor for the occurrence of a broad spectrum of psychiatric and neurologic disorders, including schizophrenia, autism, and cerebral palsy. However, it is unclear how maternal infection can increase the risk for these disorders in offspring. In the present study, we investigate how maternal infection induces abnormal development of neocortex in offspring at the micro-circuitry level using a mouse model of prenatal infection by lipopolysaccharide (LPS). Our recent study showed that prenatal exposure to LPS increases microglia density in the cerebral cortex and differentially alters the excitability of different electrophysiological types (e-types) of layer V pyramidal neurons in the primary visual cortex of offspring. These led us to hypothesize that maternal infection selectively alters neocortical micro-circuitries properties and connectivity by activation of microglia, leading to abnormality of cortical development of offspring. To test this hypothesis, we will evaluate intrinsic excitabilities and morphologies of several types of pyramidal neurons from different cortical layers of distinct neocortical areas after prenatal exposure to LPS in young adult mice. We will also evaluate synaptic dynamics of basal synaptic transmission in different types of neuronal micro-circuitries. Furthermore, we will determine the critical involvement of microglial cells in mediating LPS-induced abnormality of functional neocortical micro-circuitry using our newly developed mice with selective deletion of microglial A2A receptor. The information derived from this proposed study will provide the neuronal and microglial mechanisms by which maternal infection can increase the risk for neuropsychiatric disorders, such as schizophrenia, autism and cerebral palsy in offspring.

孕期母体感染会导致子代精神和神经系统疾病如精神分裂症、孤独症和脑瘫的风险增加，然而相关神经机制尚不清楚。本项目以小鼠出生前暴露于脂多糖（LPS）为孕期母体感染模型，从神经微环路水平研究孕期母体感染如何导致子代大脑皮层发育异常。前期工作发现孕期LPS暴露增加子代皮层小胶质细胞的密度，差异性地改变子代视皮层V层不同电生理类型锥体神经元的兴奋性，我们推测“LPS诱导的孕期母体感染通过影响皮层小胶质细胞的活化，改变某些特定的皮层神经微环路的发育，导致子代神经发育异常”。为此，我们深入研究孕期LPS暴露对不同皮层，不同片层，不同类型锥体神经元的内在兴奋性和形态的影响，分析各种类型神经微环路的基础突触动力学，然后再利用脑内小胶质细胞腺苷A2A受体特异性敲除小鼠来改变小胶质细胞，探讨小胶质细胞是否介导了孕期LPS暴露导致的功能性皮层神经微环路异常，进一步阐释孕期母体感染导致儿童神经发育障碍的神经机制。

孕期母体感染会导致子代精神和神经系统疾病，然而相关神经机制尚不清楚。本研究以孕期脂多糖（LPS）暴露为孕期母体感染模型，用全细胞膜片钳记录和3D神经元重构技术分别研究了孕期LPS暴露后，子代小鼠V层锥体神经元（L5PC）和II层锥体神经元（L2PC）的电生理性质和形态等的改变。L5PC按照放电方式的不同分成三类，RS，IB和ROB类型。孕期高剂量LPS暴露增加子代小鼠L5PC中ROB类神经元的比例，但低剂量LPS暴露不影响L5PC中各电生理类型的组成。不同剂量的孕期LPS暴露差异性影响各电生理类型神经元的主动和被动性质，从而影响各类电生理类型神经元的可兴奋性。L5PC按照顶树突顶簇形状的不同分成两类，大顶簇锥体神经元（TTPCs）和小顶簇锥体神经元（STPCs）；孕期低剂量或者高剂量LPS暴露均不改变L5PC形态分类比例，不影响神经元胞体发育，但是差异性改变各形态类型的神经元树突空间结构。在突触传递方面，孕期LPS暴露对突触发育的影响具有剂量依赖性，当剂量较高时可以增加突触传递的效率；同时具有频率依赖性，当突触前刺激频率为10Hz时有效应，但是20Hz和40Hz时则无显著影响。L2PC按照顶树突顶簇形状的不同分成两类，L2PC_A和L2PC_B。尽管这两类L2PC类型的比例没有改变，孕期LPS暴露使L2PC_A而不是L2PC_B的基树突，以及这两种类型神经元的顶树突结构，均出现显著的重组；并且分别改变这两类L2PC的内在电生理特性，降低L2PC_A但是增加L2PC_B神经元的兴奋性。因此，孕期LPS暴露对不同片层，不同类型锥体神经元的内在兴奋性、突触和形态的影响各不相同，可以特异性改变皮层神经微环路的发育。此外，孕期LPS暴露增加子代皮层小胶质细胞的密度，而选择性敲除小胶质细胞腺苷A2A受体减少小胶质细胞数量，抑制了LPS暴露后小胶质细胞的活化，能够逆转LPS暴露后所造成的抑郁样行为，提示小胶质细胞在这一过程中起很重要的作用。本研究为阐明孕期母体感染导致儿童神经发育障碍的机理提供了一个新的视角。