Cell-type specific GABA signaling is required for newborn neuron incorporation

描述（由申请人提供）： 创伤性脑损伤可以说是影响我们退伍军人的最重要的神经问题，导致诸如难治性癫痫和使人衰弱的认知缺陷等破坏性问题。虽然最初的伤害对决定最终的结果很重要，但许多问题直到几年后才显现出来。这些延迟后遗症被认为是由于病理可塑性，包括细胞死亡，轴突发芽，蛋白质表达的变化。近年来，成人神经发生的研究已成为一种有前途的方法，既提供了深入了解脑损伤的机制和潜在的治疗。移植的胚胎中间神经元已被用于改善许多神经系统疾病的动物模型中的症状，并且脑损伤后内源性神经发生被稳健地增强。然而，这些新生神经元中的许多在形态和功能上非常异常，并且实际上可能导致脑损伤后的病理变化。我们理解病理损伤后可塑性的一个关键漏洞是理解指导新生神经元如何融入正常成人回路的信号。 GABAA受体（GABARs）是指导神经元增殖、迁移和突触整合的特别重要的形态发生分子。GABAR是异五聚体蛋白复合物，通常含有2 1、2 2和单个3或4亚基蛋白。1亚基同种型（11-6）的同一性是GABAR功能的关键决定因素，能够产生GABAR动力学特性和药理学敏感性的显著差异。虽然含11的GABARs是成熟神经元中突触抑制的主要介质，但在胚胎神经元以及成人的新生神经元中存在从14到12，3到11的主要GABA能信号传导的进展，这是非常一致的发现。类似的表达程序也经常出现在成年脑损伤后已经建立的神经元中。虽然GABA通常引起抑制性反应，但在此过渡期内GABAR的激活产生去极化反应，使GABA成为一种强大的形态发生剂。去极化GABA的扰动导致异常的神经元成熟，这主要取决于细胞类型（中间神经元与主细胞）和发育阶段的问题。虽然GABAR的功能很明显依赖于亚基的组合，但神经元掺入过程中特定GABAR表达模式的意义仍然知之甚少。为了阐明特定GABAR亚基组合的作用，我们将描述GABAR亚基亚型表达的时间依赖性演变，以及主要GABAR表达的生物物理特性。最后，急性脑切片记录与事后形态学和免疫细胞化学分析将用于将GABA能信号传导的变化与细胞类型和成熟状态相关联。总体假设是，具有独特生物物理特性的特定GABAR亚基同种型的表达以细胞类型特异性方式在空间和时间上与神经元成熟锁定，以有效介导GABA能信号传导的演变作用，所述GABA能信号传导是并入功能回路所需的。我们漫长 长期目标是了解这个系统如何在脑损伤后病理重演，并利用这些信息开发特定的药物治疗方法，以预防和治疗脑损伤的慢性神经系统后遗症。

DESCRIPTION (provided by applicant): Traumatic brain injury is arguably the most significant neurological problem affecting our Veterans, leading to such devastating problems as refractory epilepsy and debilitating cognitive deficits. While the initial injury is important in determining eventual outcome, many of these problems do not manifest themselves until several years later. These delayed sequelae are thought to be due to pathological plasticity, including cell death, axonal sprouting, and changes in protein expression. Recently, the study of adult neurogenesis has emerged as a promising approach to provide both insight into the mechanisms of and potential treatment for brain injury. Transplanted embryonic interneurons have been used to ameliorate symptoms in a number of animal models of neurological disorders, and endogenous neurogenesis is robustly enhanced following brain injury. However, many of these newborn neurons are morphologically and functionally very abnormal, and may actually contribute to pathological changes following brain injury. A key hole in our understanding of pathological postinjury plasticity is an understanding o the signals directing how newborn neurons become incorporated into normal adult circuits. GABAA Receptors (GABARs) are particularly crucial morphogenic molecules directing neuronal proliferation, migration and synaptic integration. GABARs are heteropentameric protein complexes, typically containing 2 1, 2 2 and either a single 3 or 4 subunit protein. The identity o the 1 subunit isoform (11-6) is a key determinant of GABAR function, capable of producing profound differences in the kinetic properties and pharmacological sensitivity of GABARs. While 11 containing GABARs are the primary mediators of synaptic inhibition in mature neurons, there is a progression from 14 to 12,3 to 11 predominant GABAergic signaling that is an extraordinarily consistent finding in both embryonic neurons, as well as newborn neurons of the adult. A similar program of expression has also frequently encountered following already established neurons following adult brain injury. While GABA generally evokes inhibitory responses, activation of GABARs during this transitional period produces depolarizing responses, allowing GABA to serve as a powerful morphogen. Perturbations of depolarizing GABA cause aberrant neuronal maturation that depends critically on the cell type (interneuron vs principal cell) and developmental stage in question. While it is clear that GABAR function depends critically on the subunit combination, the significance of specific GABAR expression patterns during neuronal incorporation remain very poorly understood. In order to elucidate the role of specific GABAR subunit combinations, we will characterize the time-dependent evolution of GABAR subunit isoform expression, as well as the biophysical properties of the predominant GABARs being expressed. Finally acute brain slice recording with post-hoc morphological and immunocytochemical analysis will be used to correlate the changes in GABAergic signaling as a function of cell-type and maturational state. The overarching hypothesis is that the expression of specific GABAR subunit isoforms with unique biophysical properties are spatially and temporally locked with neuronal maturation in a cell-type specific manner to effectively mediate the evolving roles of GABAergic signaling required for incorporation into functional circuits. Our long term goal is to understand how this system becomes pathologically recapitulated following brain injury, and use this information to develop specific pharmacological treatments to prevent and treat the chronic neurological sequelae of brain injury.