Project 3-Regulation of Cortical GABAergic Connectivity by NCAM

神经细胞黏附分子NCAM(11q23)通过调控在学习记忆中发挥重要作用 CMS轴突的引导。NCAM作为精神分裂症易感基因值得研究 多态与精神分裂症患者的神经认知障碍有关(CATIE)。 此外，由整个胞外区组成的可溶性NCAM片段(NCAM-EC)是 在精神分裂症患者脑中过度表达，并通过蛋白分解从正常神经元中释放出来 (胞外结构域脱落)由一种具有ADAM(去整合素和金属蛋白酶)特性的金属蛋白酶引起的。 在NCAM-EC转基因小鼠的前额叶皮质(RFC)建立了NCAM过度脱落的模型。 显示GABA能中间神经元的突触显著减少，包括调节 锥体细胞输出和同步性。NCAM-EC小鼠表现出与 神经传递缺陷，包括多动症、刻板印象、感觉门控减少和恐惧 条件反射。假设NCAM调节篮子之间的兴奋性/抑制性平衡 RFC中的中间神经元和锥体细胞以及过度脱落对NCAM的调节失调 扰乱突触连接，从而改变皮质回路和锥体细胞群的同步性 对神经认知很重要。精神分裂症患者的GABA能功能可能受损，但尚不清楚 如果GABA能功能障碍反映了皮质环路发育的改变。将确定是否有 GABA能树突/轴突分枝和突触发生的发育调节变化 正常RFC中的中间神经元和锥体神经元以及NCAM调节异常是否干扰 NCAM-EC和零突变小鼠的发育。将在开发期间评估NCAM的剥离 人脑和精神分裂症患者的尸检。皮质神经元培养将被利用 鉴定负责正常NCAM脱落的ADAM蛋白(S)，定位NCAM的裂解 并确定NCAM的脱落对神经元突起生长和分支的作用。最后， 小鼠的行为测试将评估NCAM-EC过度表达是否损害执行功能 作为工作记忆，减少伽马振荡活动，并改变焦虑中对GABA激动剂的敏感性- 比如行为和感觉运动门控。这项工作将有助于其他中心调查人员了解 GABA能中间神经元的早期分化(方案4)、迁移(方案4和5)、 并建立连接(此项目)，并将分子底物表征为异常 精神分裂症高危患者或早期患者的神经认知功能(项目1和 这些研究将阐明NCAM对GABA能皮质回路的贡献机制 与神经认知功能相关，并将探索NCAM作为精神分裂症的病理生理靶点 脆弱性。

Neural cell adhesion molecule NCAM (11q23) performs vital roles in learning and memory by regulating guidance of CMS axons. NCAM merits study as a schizophrenia vulnerability gene, as NCAM polymorphisms are associated with neurocognitive impairment in a schizophrenia population (CATIE). Moreover, a soluble NCAM fragment consisting of the entire extracellular region (NCAM-EC) is overexpressed in schizophrenic brain, and is released from normal neurons by proteolytic cleavage (ectodomain shedding) by a metalloprotease with properties of an ADAM (a disintegrin and metalloprotease). Excess NCAM shedding in the prefrontal cortex (RFC) was modeled in NCAM-EC transgenic mice, which revealed a striking decrease in synapses of GABAergic interneurons, including basket cells that regulate pyramidal cell output and synchrony. NCAM-EC mice display behavioral abnormalities associated with neurotransmission defects, including hyperlocomotion, stereotypies, decreased sensory gating and fear conditioning. It is hypothesized that NCAM regulates the excitatory/inhibitory balance between basket interneurons and pyramidal cells in the RFC, and that dysregulation of NCAM by excessive shedding perturbs synaptic connectivity, thus altering cortical circuitry and synchrony of pyramidal cell groups important for neurocognition. GABAergic function may be compromised in schizophrenia, but it is not known if GABAergic dysfunction reflects altered development of cortical circuitry. It will be determined if there are developmentally regulated changes in dendritic/axonal arborization and synaptogenesis of GABAergic interneurons and pyramidal neurons in normal RFC,and whether NCAM dysregulation interferes with development in NCAM-EC and null mutant mice. NCAM shedding will be assessed during development in post-mortem human brain and from individuals with schizophrenia. Cortical neuron cultures will be exploited to identify the ADAM protease(s) responsible for normal NCAM shedding, to localize the NCAM cleavage site, and to ascertain the role of NCAM shedding on neuronal process outgrowth and branching. Finally, behavioral testing in mice will assess whether NCAM-EC overexpression impairs executive functions such as working memory, decreases gamma oscillatory activity, and alters sensitivity to GABA agonists in anxiety- like behavior and sensorimotor gating. This work will assist other center investigators in understanding development of GABAergic interneurons from early differentiation (Project 4), migration (Projects 4 and 5), and establishment of connections (this project) and will characterize a molecular substrate for abnormal neurocognitive functions in patients who are at risk or in early stages of schizophrenia (Projects 1 and 3).These studies will illuminate a mechanism whereby NCAM contributes to GABAergic cortical circuitry relevant to neurocognitive function, and will explore NCAM as a pathophysiological target for schizophrenia vulnerability.