Regulation of extrasynaptic GABA-A receptors in health and disease

 描述（由申请人提供）： 抑制性神经递质GABA激活几种类型的受体，这些受体是治疗癫痫和其他神经精神疾病的治疗靶点。GABAA受体与Cl离子通道连接，并在突触处激活时产生电信号。GABAB受体是G蛋白偶联受体（GPCR），其调节细胞内信号传导途径。除了突触GABAA受体之外，存在定位于突触外位点的独特GABAA受体。这些高亲和力突触外GABAA受体被大脑中低水平的环境GABA紧张性激活。由突触外GABAA受体产生的抑制的紧张形式重要地影响细胞和网络的兴奋性。 新出现的数据表明，突触外GABAA受体在几个脑区的调节突触后GABAB受体。由于受GABAB受体影响的细胞内信号传导途径由许多GPCR共享，因此其他神经递质受体也可以调节突触外GABAA受体。该提案描述了三种假说，以调查健康和疾病中突触外GABAA受体的调节。 据推测，多种神经递质通过GPCR调节突触外GABA受体。将使用标准全细胞技术从急性海马脑切片中的齿状回颗粒细胞（DGGC）和CA 1锥体神经元记录由突触外GABAA受体产生的紧张性电流。将研究细胞内信号传导途径对紧张性电流的影响。使用选择性激动剂和拮抗剂，将确定其他GPCR（即β-肾上腺素受体、D2多巴胺受体和5-HT 2受体）对紧张性电流的影响。据预测，紧张性电流将被PKA抑制增强 (D2受体）和PKC激活（5 HT 2受体）。预计β-肾上腺素受体激活PKA会降低紧张性电流。将进行生化研究以确定细胞内信号传导途径是否通过增加GABAA受体的表面表达来增强强直电流。 自发的生理或病理生理神经活动可以产生周围GABA水平的周期性和短暂性增加。假设周围GABA的周期性增加将激活突触后GABAB受体并增强突触外GABAA受体功能。在手术前和手术期间将重复测量紧张性电流，以定期增加环境GABA。三种方法将用于产生周围GABA的瞬时增加; 1.周期性应用外源性GABA，2.刺激内源性GABA的释放（电刺激，高K+），和3.用4-AP诱发自发性发作间期放电。将证实这些程序的作用是由使用GABAB受体拮抗剂CGP 55845和含有G蛋白抑制剂（GDP-S）的移液器溶液的突触后GABAB受体活化引起的。 创伤性脑损伤（TBI）改变 海马体中GABAA受体的功能。假设GPCR在实验性TBI后调节突触外GABAA受体。我们将确定TBI对基础强直电流的影响及其通过GPCR的调节。具体地，假设DGGC的紧张性电流将被TBI增强，部分原因是GPCR的激活增加。

 DESCRIPTION (provided by applicant): The inhibitory neurotransmitter GABA activates several types of receptors that are therapeutic targets for the treatment of epilepsy and other neuropsychiatric illness. GABAA receptors are linked to a Cl ion channel and produce electrical signals when activated at synapses. GABAB receptors are G- protein coupled receptors (GPCRs) that regulate intracellular signaling pathways. In addition to synaptic GABAA receptors, there are unique GABAA receptors localized to extrasynaptic sites. These high-affinity extrasynaptic GABAA receptors are tonically activated by the low levels of ambient GABA in the brain. The tonic form of inhibition produced by extrasynaptic GABAA receptors importantly affects cellular and network excitability. Emerging data indicate that extrasynaptic GABAA receptors in several brain regions are regulated by postsynaptic GABAB receptors. Because the intracellular signaling pathways affected by GABAB receptors are shared by many GPCRs, other neurotransmitter receptors may also regulate extrasynaptic GABAA receptors. This proposal describes three hypotheses to investigate the regulation of extrasynaptic GABAA receptors in health and disease. It is hypothesized that multiple neurotransmitters acting through GPCRs regulate extrasynaptic GABA receptors. Tonic currents produced by extrasynaptic GABAA receptors will be recorded from dentate gyrus granule cells (DGGCs) and CA1 pyramidal neurons in acute hippocampal brain slices using standard whole cell techniques. The effects of intracellular signaling pathways on tonic currents will be investigated. Using selective agonists and antagonists, the effects of other GPCRs (i.e. ß- adrenoreceptors, D2 dopamine receptors, and 5-HT2 receptors) on tonic currents will be determined. It is predicted that tonic currents will be enhanced by PKA inhibition (D2 receptors) and PKC activation (5HT2 receptors). Activation of PKA by ß-adrenoreceptors is predicted to reduce tonic currents. Biochemical studies will be done to determine if intracellular signaling pathways enhance tonic currents by increasing surface expression of GABAA receptors. Spontaneous physiological or pathophysiological neural activity can produce periodic and transient increases in ambient GABA levels. It is hypothesized that periodic increases in ambient GABA will activate postsynaptic GABAB receptors and enhance extrasynaptic GABAA receptor function. Tonic currents will be repeatedly measured before and during procedures to periodically increase ambient GABA. Three approaches will be used to produce transient increases in ambient GABA; 1. periodic application of exogenous GABA, 2. stimulating release of endogenous GABA (electrical stimulation, high K+), and 3. inducing spontaneous interictal discharges with 4-AP. It will be confirmed that the effects of these procedures resulted from postsynaptic GABAB receptor activation using the GABAB receptor antagonist CGP55845 and pipette solutions containing a G protein inhibitor (GDP-ß-s). Traumatic brain injury (TBI) alters GABAA receptor function in the hippocampus. It is hypothesized that GPCRs regulate extrasynaptic GABAA receptors following experimental TBI. We will determine the effects of TBI on basal tonic currents and their regulation by GPCRs. Specifically, it is hypothesized that tonic currents of DGGCs will be enhanced by TBI, due in part to increased activation of GPCRs.