GABA System Alterations and Fragile X Syndrome

描述(申请人提供)：脆性X综合征(FXS)是最常见的遗传性认知障碍形式，患有这种疾病的儿童通常会有额外的行为和神经问题，包括焦虑增加、自闭症倾向、多动症和癫痫。由于GABA系统在调节涉及这些行为表型的神经系统方面起着重要作用，FXS中可能存在GABA系统缺陷。虽然GABAA受体(GABAAR)的改变已经被发现，但对GABAAR亚单位改变的区域和细胞定位的了解仍然非常有限。因此，该项目的主要目标是在FXS小鼠模型中测试GABAAR特定亚单位的表达和定位在出生后发育过程中发生变化的假设，以及这些变化与功能缺陷有关，包括神经元兴奋性增加和焦虑相关行为的改变。具体目标1将利用免疫组织化学方法确定Fmr1基因敲除小鼠中缺乏脆性X智力低下蛋白(FMRP)的GABAAR的12个亚基的变化。重要的是，在野生型和Fmr1基因敲除小鼠的整个出生后早期发育过程中，将遵循12亚基的表达模式，以确定可能与FMRP功能丧失相关的早期变化，并在可能在以后的生命中变得明显的潜在代偿性变化之前。特定目标2将确定可能与Fmr1基因敲除小鼠中12亚单位表达变化有关的功能缺陷。体外电生理学研究将被用来评估齿状颗粒细胞轴突起始段的GABA能功能，在那里12个亚基通常是突出的，而含有12个亚基的GABA受体的缺失可能会影响轴突电位的产生并增加颗粒细胞的兴奋性。行为学测试将用于评估一种经典的苯二氮卓类药物的抗焦虑和镇静效果，这种药物可以随着Fmr1基因缺陷小鼠的GABAAR亚单位的变化而改变。具体目标3将确定在Fmr1基因敲除小鼠中GABAAR的4个亚基的表达和定位的变化，并确定这种变化是否反映在齿状回紧张抑制的变化及其被神经类固醇的调节中。具体目标4将确定GABAAR相关的药物治疗是否会改善Fmr1基因敲除小鼠的某些行为变化和GABAAR亚单位缺陷。这些研究将提供关于FXS小鼠模型出生后发育过程中GABAAR亚基变化的独特信息，并可能为这种疾病的新的GABAAR亚基靶向治疗提供一个框架。

DESCRIPTION (provided by applicant): Fragile X syndrome (FXS) is the most common form of inherited cognitive impairment, and children with this disorder often have additional behavioral and neurological problems, including increased anxiety, autistic tendencies, hyperactivity and epilepsy. Since the GABA system plays an important role in regulation of the neural systems involved in these behavioral phenotypes, GABA system deficits could be present in FXS. While alterations in GABAA receptors (GABAARs) have been identified, knowledge of the regional and cellular localization of changes in GABAAR subunits remains very limited. Thus, the broad goal of this project is to test the hypothesis that expression and localization of specific subunits of the GABAAR are altered during postnatal development in a mouse model of FXS and that these changes are associated with functional deficits, including increased neuronal excitability and altered anxiety- related behavior. Specific Aim 1 will identify changes in the 12 subunit of the GABAAR in Fmr1 knockout mice that lack the Fragile X mental retardation protein (FMRP), using immunohistochemical methods. Importantly, the patterns of expression of the 12 subunit will be followed throughout early postnatal development in wild-type and Fmr1 knockout mice in order to identify early changes that could be associated with loss of FMRP function and precede potential compensatory changes that may become apparent later in life. Specific Aim 2 will identify functional deficits that could be associated with altered expression of the 12 subunit in Fmr1 knockout mice. In vitro electrophysiological studies will be used to assess GABAergic function at the axon initial segment of dentate granule cells where the 12 subunit is normally prominent and where a loss of 12 subunit-containing GABAARs could influence axon potential generation and increase granule cell excitability. Behavioral tests will be used to evaluate the anxiolytic and sedative effects of a classical benzodiazepine that could be altered in response to GABAAR subunit changes in Fmr1-deficient mice. Specific Aim 3 will identify changes in the expression and localization of the 4 subunit of the GABAAR in the Fmr1 knockout mouse and determine if such changes are reflected in alterations in tonic inhibition and its modulation by neurosteroids in the dentate gyrus. Specific Aim 4 will determine if GABAAR-related pharmacological treatment will ameliorate some of the behavioral changes and GABAAR subunit deficits in Fmr1 knockout mice. These studies will provide unique information about GABAAR subunit alterations during postnatal development in a mouse model of FXS and could provide a framework for new GABAAR subunit-targeted treatments for this disorder.