Project 3-Regulation of Cortical GABAergic Connectivity by NCAM

神经细胞粘附分子NCAM（11 q23）通过调节神经细胞粘附分子的表达，在学习和记忆中发挥重要作用。 CMS轴突的引导。NCAM值得作为精神分裂症易感基因进行研究 多态性与精神分裂症人群中的神经认知损害有关（CATIE）。 此外，由整个细胞外区组成的可溶性NCAM片段（NCAM-EC）是 在精神分裂症脑中过表达，并通过蛋白水解裂解从正常神经元释放 （胞外结构域脱落）。 在NCAM-EC转基因小鼠中建立了前额叶皮层（RFC）中过量NCAM脱落的模型， 结果显示，GABA能中间神经元的突触显著减少，包括调节GABA能中间神经元的篮状细胞。 锥体细胞输出和同步性。NCAM-EC小鼠表现出与以下相关的行为异常： 神经传递缺陷，包括运动过度、刻板、感觉门控减少和恐惧 条件反射假设NCAM调节篮状细胞之间的兴奋/抑制平衡， RFC中的中间神经元和锥体细胞，以及过度脱落引起的NCAM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 对神经认知很重要GABA能功能可能在精神分裂症中受损，但目前尚不清楚 GABA能功能障碍是否反映了皮层回路的发育改变。将确定是否有 GABA能神经元树突/轴突分支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失调是否干扰了 在NCAM-EC和无效突变小鼠中的发育。将在开发期间评估NCAM脱落， 以及精神分裂症患者的大脑标本。皮层神经元培养将被利用 鉴定负责正常NCAM脱落的ADAM蛋白酶，定位NCAM切割 位点，并确定NCAM脱落对神经元突起生长和分支的作用。最后， 在小鼠中的行为测试将评估NCAM-EC过表达是否损害执行功能， 作为工作记忆，减少伽马振荡活动，并改变焦虑症对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研究人员了解 GABA能中间神经元从早期分化（项目4），迁移（项目4和5）， 和建立连接（本项目），并将表征异常的分子基板 处于精神分裂症风险或早期阶段的患者的神经认知功能（项目1和 3).这些研究将阐明NCAM参与GABA能皮层回路的机制 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学靶点 易损性.

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.