Effects of prolonged seizures on GABAA receptor function

描述（由申请人提供）：皮质神经元的电兴奋性在很大程度上受兴奋性谷氨酸能和抑制性gaba能输入的调节。该系统的失调似乎是癫痫发作的开始和传播的基础。长时间癫痫发作时，GABAA受体功能发生改变。在机体水平上，这可能与苯二氮卓类药物不敏感有关，需要大剂量巴比妥类药物来中止癫痫发作。在细胞水平上，在分离的齿状颗粒细胞上，苯二氮卓和锌对GABAA受体的调节都有衰减。虽然CA1海马神经元变得相对GABA不敏感，但颗粒细胞上GABAA受体的GABA药理学未见变化。然而，癫痫发作对GABAA受体激活/失活/脱敏的快速组分的影响尚未探讨。由于突触释放的GABA被认为仅在突触间隙中存在1-2 ms，这些GABAA受体激活的快速组分可能会深刻地改变GABA能突触后电位的形状。这些研究将利用快速给药系统研究锂/匹罗卡品诱导大鼠长时间癫痫发作后离体齿状颗粒细胞GABAA受体功能的变化。首先，确定GABA浓度响应关系。接下来，GABAA受体的快速组分动力学将使用细胞附着电压钳技术与快速给药确定。此外，单通道动力学也将在对照细胞和经历癫痫发作的动物中测量。最后，确定癫痫发作对GABAA受体变构调节剂的影响。除了具有内在的趣味性和潜在的临床用途外，这些效应的模式可能为GABAA受体功能的变化是否由于构成这些受体的亚基的重排提供重要线索。这些研究试图阐明长时间癫痫发作后GABAA受体功能的变化。这可能有助于我们进一步了解癫痫发作/流产以及正常的gaba能突触传递。

DESCRIPTION (provided by applicant): Electrical excitability of cortical neurons is regulated, in large part, by excitatory glutamatergic and inhibitory GABAergic input. Dysregulation of this system appears to underlie the initiation and propagation of seizures. With prolonged seizures, there is a change in GABAA receptor function. At an organismic level, this may be associated with benzodiazepine insensitivity, requiring high dose barbiturates to abort seizures. At a cellular level there is attenuation of both benzodiazepine and zinc modulation of GABAA receptors on isolated dentate granule cells. Although CA1 hippocampal neurons become relatively GABA insensitive, no such change in GABA pharmacology at GABAA receptors on granule cells has been seen. However, the effect of seizures on the fast components of GABAA receptor activation/deactivation/desensitization has not been explored. Since synaptically-released GABA is thought to be present in the synaptic cleft for only 1-2 ms, these fast components of GABAA receptor activation may profoundly alter the shape of GABAergic post-synaptic potentials. These studies will investigate the changes in GABAA receptor function on isolated dentate granule cells using a rapid drug delivery system following prolonged seizures induced in rats with Lithium/pilocarpine. Firstly, GABA concentration response relationships will be determined. Next, the rapid components of GABAA receptor kinetics will be determined using a cell-attached voltage clamp technique with rapid drug delivery. Furthermore, single channel kinetics will also be measured in cells from control and animals which have undergone seizures. Finally, the effect of seizures on GABAA receptor allosteric modulators will be determined. In addition to being intrinsically interesting and potentially clinically useful, the pattern of these effects may provide important clues as to whether the changes in GABAA receptor function are due to a rearrangement of the subunits making up those receptors. These studies seek to elucidate the changes in GABAA receptor function seen after prolonged seizures. This may help further our understanding of seizure initiation/abortion as well as normal GABAergic synaptic transmission.