Chronic Axon Hypofunction in Maternal Immune Activation Models of Neurodevelopmental Disorders

新摘要： 孕期母体感染是包括自闭症谱系障碍(ASD)在内的神经发育障碍的既定风险因素，但关于免疫侮辱如何改变发育中大脑的神经回路，从而损害行为，人们知之甚少。免疫效应的一个潜在部位是内侧前额叶皮质(MPFC)，它在神经发育异常的高级社会和认知功能受损中发挥关键作用。通过一笔探索性的R21赠款的支持，我们使用了母体免疫激活(MIA)的小鼠模型，并开发了一种基于硅探针的多通道记录系统，用于高通量的mPFC电路功能分析。使用这种方法，我们检查了母亲暴露于病毒模拟物多肌苷：多胞苷(Poly(I：C))后成年后代的mPFC，并发现mPFC的中心缺陷是第5层投射神经元输出纤维中意想不到的功能低下。特别是，第5层轴突在长时间活动期间维持输出的能力较差，其时间精确度也受到损害。MPFC的转录图谱显示细胞黏附分子L1CAM下调，L1CAM是轴突兴奋性的假定调节因子。在这里，拟议的工作将使用相同的小鼠MIA模型来确定轴突低活动在mPFC特定远程目标上的功能分支，这些目标介导ASD和相关疾病-内侧丘脑(MD)、杏仁基底外侧核(BLA)和伏隔核(NAC)的行为失调。这项建议的目标1将测试暴露于母体免疫激活(MIA)的子代是否会损害这些皮质下区域主细胞的直接招募和/或间接前馈抑制。第5层mPFC预测将专门针对病毒方法的光遗传刺激。在目标2中，我们将使用互补遗传(L1CAM拯救)或光遗传(SSFO驱动的增强兴奋性)方法来增强第5层的输出，以确定这是否恢复了L5的输出并拯救了ASD相关的缺陷。在目标3中，我们将在MIA模型和大脑皮层区域测试我们的发现的一般性。首先，我们将测试脂多糖诱导的MIA是否与Poly(I：C)对mPFC轴突功能的影响相似。接下来，我们将确定躯体感觉皮质，另一个与ASD行为有关的皮质区域，是否也显示出MIA诱导的第5层轴突功能的特定变化，如果中期MIA广泛影响处于发育关键阶段的第5层皮质神经元，可能是可以预期的。拟议中的实验结果既可以帮助解释ASD和其他神经发育障碍的发病机制，也可以确定一条可以作为恢复行为的靶点的分子途径。

New Summary: Maternal infection during pregnancy is an established risk factor for neurodevelopmental disorders, including Autism Spectrum Disorders (ASD), yet little is known about how immune insults alter neural circuitry in the developing brain and, as a result, impair behavior. One potential site for immune effects is the medial prefrontal cortex (mPFC), which plays a critical role in the higher-order social and cognitive functions compromised in disorders of altered neural development. Through the support of an exploratory R21 grant, we used a mouse model of Maternal Immune Activation (MIA) and developed a silicon probe-based multichannel recording system for high-throughput functional analysis of mPFC circuitry. Using this approach, we examined mPFC in adult offspring following maternal exposure to a viral mimetic polyinosinic:polycytidylic acid (poly(I:C)), and identified an unexpected hypofunction in the output fibers of layer 5 projection neurons as the central defect in the mPFC. In particular, layer 5 axons were less able to sustain output during prolonged activity, and their temporal precision was impaired. Transcriptomic profiling of the mPFC revealed a downregulation of the cell adhesion molecule L1cam, a putative regulator of axonal excitability. Here the proposed work will use the same mouse MIA model to determine the functional ramifications of axonal hypoactivity on specific long-range targets of the mPFC that mediate behaviors dysregulated in ASD and related disorders – mediodorsal thalamus (MD), basolateral amygdala (BLA), and nucleus accumbens (NAc). Aim 1 of this proposal will test whether direct recruitment and/or indirect feedforward inhibition of principal cells in these subcortical regions is impaired in offspring exposed to maternal immune activation (MIA). Layer 5 mPFC projections will be specifically targeted for optogenetic stimulation with viral approaches. In Aim 2, we will augment layer 5 output with complementary genetic (L1cam rescue) or optogenetic (SSFO-driven enhanced excitability) approaches to determine whether this restores L5 output and rescues ASD-related deficits. In Aim 3, we will test for generality of our findings in MIA models and cortical regions. First, we will test whether MIA induced by lipo-polysaccharide (LPS) has similar effects as poly(I:C) on mPFC axonal function. Next we will determine whether somatosensory cortex, another cortical region implicated in ASD behaviors, also shows specific MIA induced changes in layer 5 axonal function, as might be expected if midgestational MIA broadly affects layer 5 cortical neurons at a critical step in their development. The results of the proposed experiments could both help to explain pathogenesis of ASD and other neurodevelopmental disorders and identify a molecular pathway that could be targeted to restore behavior.