GABA System Alterations and Fragile X Syndrome

描述（由申请人提供）：脆性X综合征（FXS）是遗传性认知障碍的最常见形式，患有这种疾病的儿童通常有其他行为和神经问题，包括焦虑增加，自闭症倾向，多动和癫痫。由于GABA系统在这些行为表型中涉及的神经系统的调节中起重要作用，因此FXS中可能存在GABA系统缺陷。虽然GABAA受体（GABAAR）的改变已被确定，GABAAR亚基的变化的区域和细胞定位的知识仍然非常有限。因此，该项目的广泛目标是检验以下假设：在FXS小鼠模型中，GABAAR特定亚基的表达和定位在出生后发育过程中发生改变，并且这些变化与功能缺陷相关，包括神经元兴奋性增加和焦虑相关行为改变.特异性目的1将使用免疫组织化学方法鉴定缺乏脆性X智力低下蛋白（FMRP）的Fmr1敲除小鼠中GABAAR 12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，将跟踪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，并先于可能在生命后期变得明显的潜在代偿性变化。具体目标2将确定可能与Fmr1敲除小鼠中12亚基表达改变相关的功能缺陷。体外电生理学研究将用于评估齿状颗粒细胞轴突起始段的GABA能功能，在齿状颗粒细胞轴突起始段，12亚基通常很突出，含12亚基的GABAAR缺失可能影响轴突电位生成并增加颗粒细胞兴奋性。将使用行为试验评价经典苯二氮卓类药物的抗焦虑和镇静作用，该药物可在Fmr1缺陷小鼠中对GABAAR亚基变化作出反应而改变。具体目标3将确定在Fmr1敲除小鼠中GABAAR的4亚基的表达和定位的变化，并确定这种变化是否反映在强直性抑制的改变及其在齿状回中通过神经类固醇的调节。具体目标4将确定GABAAR相关的药物治疗是否会改善Fmr1基因敲除小鼠的一些行为变化和GABAAR亚基缺陷。这些研究将提供关于FXS小鼠模型出生后发育期间GABAAR亚基改变的独特信息，并可为这种疾病的新GABAAR亚基靶向治疗提供框架。

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.