Chandelier cell inputs to pyramidal neurons in schizophrenia and development

描述（由申请人提供）：精神分裂症是一种认知控制受损的神经发育障碍。这种损伤被认为至少部分是由于表达小白蛋白（PV）的吊灯细胞（ChCs）皮质GABA神经传递的改变。ChCs的轴突专门针对锥体神经元（PYR）的轴突初始段（AIS），这是动作电位产生的部位，因此ChCs可以有力地影响PYR细胞的输出和前额叶皮层（PFC）的活性。特定ChC的轴突分化，支配数百个邻近的PYR细胞，多个ChC的轴突可能会聚到单个PYR AIS上，形成一个独特的垂直方向的终端阵列，称为筒状体。在精神分裂症患者的PFC中，GABA膜转运蛋白-1 （GAT1）免疫反应性检测到的药筒密度低40%。这一发现可能反映了一种严重影响ChCs亚群的疾病过程，使得这些ChCs提供较少的轴突末端。因此，一些被这些ChC靶向的PYR AIS不能获得足够数量的ChC终端来形成可识别的药筒。这一解释得到了以下研究结果的支持：1)在精神分裂症中，约50%的PFC PV神经元缺乏可检测水平的GAD67 mRNA；2)灵长类PFC中，ChC末端含有GAD67蛋白，但GAD65蛋白含量低至不存在；3)在实验系统中，耗尽GAD67会导致终端损耗。因此，我们假设，在ChC的一个子集中，GAD67的表达明显降低，导致一些PYR AIS的神经末梢减少，从而使一些AIS不再与可识别的突触前ChC盒相关。了解精神分裂症ChC异常的发病机制需要了解ChC对PYR AIS的输入在出生后发育过程中是如何被完善的。猴子PFC的初步数据显示，ChC输入到PYR AIS的数量在儿童期明显大于成年期。这些发现表明，先前报道的正常猴子PFC青春期GAT1免疫反应性囊密度的减少是由于支配某些AIS的ChC末端数量的减少或修剪所致。我们假设在猴子PFC的青春期，PYR AIS的ChC终端输入被修剪，并且这种减少解释了先前观察到的盒密度发育变化。一项研究发现，猴子的ChC末端缺失发生在青春期，这将支持我们的解释，即我们预测的精神分裂症中每个AIS末端较少的结果反映了由于ChC与AIS连接修剪期间或之前ChC末端GAD67表达水平不足而导致的过度末端修剪。为了验证我们的假设，我们使用多标记荧光共聚焦显微镜来评估每个AIS的ChC末端数量以及精神分裂症和非人灵长类动物发育中ChC末端的相对平均GAD67蛋白水平。了解精神分裂症AIS病理的性质和AIS神经支配减少的发展轨迹，将有助于了解AIS病理在发育过程中何时出现。

DESCRIPTION (provided by applicant): Schizophrenia is a neurodevelopmental disorder in which cognitive control is impaired. This impairment is thought to be due, at least in part, to altered cortical GABA neurotransmission in parvalbumin (PV) expressing chandelier cells (ChCs). The axons of ChCs exclusively target the axon initial segment (AIS) of pyramidal neurons (PYR), the site of action potential generation, and thus ChCs can powerfully influence PYR cell output and prefrontal cortex (PFC) activity. The axon of a given ChC diverges to innervate hundreds of neighboring PYR cells, and the axons of multiple ChCs may converge onto a single PYR AIS, forming a distinctive, vertically-oriented array of terminals termed a cartridge. In PFC of subjects with schizophrenia, the density of cartridges detectable by GABA membrane transporter-1 (GAT1) immunoreactivity is 40% lower. This finding could reflect a disease process that severely affects a subpopulation of ChCs such that these ChCs furnish fewer axon terminals. As a result, some PYR AIS targeted by these ChCs do not receive a sufficient number of ChC terminals to form a recognizable cartridge. This interpretation is supported by findings showing that 1) in schizophrenia, ~50% of PFC PV neurons lack detectable levels of GAD67 mRNA; 2) in primate PFC, ChC terminals contain GAD67 protein, but low to no GAD65; and 3) in experimental systems depletion of GAD67 results in loss of terminals. Thus, we hypothesize that markedly lower GAD67 expression in a subset of ChCs results in fewer terminals innervating some PYR AIS such that some of those AIS are no longer associated with a recognizable presynaptic ChC cartridge. Understanding the pathogenesis of ChC abnormalities in schizophrenia requires knowledge of how ChC to PYR AIS inputs are refined during postnatal development. Preliminary data in monkey PFC show that the number of ChC inputs to PYR AIS is significantly greater in childhood than in adulthood. These findings suggest that the previously reported reduction in GAT1- immunoreactive cartridge density that occurs during adolescence in normal monkey PFC results from a decrease, or pruning, of the number of ChC terminals that innervate certain AIS. We hypothesize that ChC terminal inputs to PYR AIS are pruned during adolescence in monkey PFC, and that this reduction explains the prior observations of developmental changes in cartridge density. A finding that ChC terminal loss occurs during adolescence in monkeys would support the interpretation that our predicted results of fewer terminals per AIS in schizophrenia reflects excessive terminal pruning due to insufficient levels of GAD67 expression in ChC terminals during or before pruning of ChC to AIS connections. To test our hypotheses we use multi-label fluorescence confocal microscopy to assess the number of ChC terminals per AIS and relative mean GAD67 protein levels in ChC terminals in schizophrenia and across non-human primate development. Knowing the nature of the pathology at the AIS in schizophrenia and the developmental trajectory of reduced AIS innervation should provide insight into when the pathology at the AIS arises developmentally.