Boychuk Jeffery A, Butler Corwin R, Smith Katalin Cs, Halmos Miklos B, Smith Bret N
Department of Physiology, University of Kentucky, Lexington, KY, United States.
Department of Cellular and Integrative Physiology, UT Health San Antonio, San Antonio, TX, United States.
Front Syst Neurosci. 2022 May 26;16:867323. doi: 10.3389/fnsys.2022.867323. eCollection 2022.
Type A GABA receptors (GABARs) are pentameric combinations of protein subunits that give rise to tonic (I) and phasic (i.e., synaptic; I) forms of inhibitory GABAR signaling in the central nervous system. Remodeling and regulation of GABAR protein subunits are implicated in a wide variety of healthy and injury-dependent states, including epilepsy. The present study undertook a detailed analysis of GABAR signaling using whole-cell patch clamp recordings from mouse dentate granule cells (DGCs) in coronal slices containing dorsal hippocampus at 1-2 or 8-13 weeks after a focal, controlled cortical impact (CCI) or sham brain injury. Zolpidem, a benzodiazepine-like positive modulator of GABARs, was used to test for changes in GABAR signaling of DGCs due to its selectivity for α subunit-containing GABARs. Electric charge transfer and statistical percent change were analyzed in order to directly compare tonic and phasic GABAR signaling and to account for zolpidem's ability to modify multiple parameters of GABAR kinetics. We observed that baseline I is preserved at both time-points tested in DGCs ipsilateral to injury (Ipsi-DGCs) compared to DGCs contralateral to injury (Contra-DGCs) or after sham injury (Sham-DGCs). Interestingly, application of zolpidem resulted in modulation of I across groups, with Ipsi-DGCs exhibiting the greatest responsiveness to zolpidem. We also report that the combination of CCI and acute application of zolpidem profoundly augments the proportion of GABAR charge transfer mediated by tonic vs. synaptic currents at both time-points tested, whereas gene expression of GABAR α, α, α, and γ subunits is unchanged at 8-13 weeks post-injury. Overall, this work highlights the shift toward elevated influence of tonic inhibition in Ipsi-DGCs, the impact of zolpidem on all components of inhibitory control of DGCs, and the sustained nature of these changes in inhibitory tone after CCI injury.
A型γ-氨基丁酸受体（GABARs）是蛋白质亚基的五聚体组合，在中枢神经系统中产生紧张性（I）和相位性（即突触性；I）形式的抑制性GABAR信号传导。GABAR蛋白亚基的重塑和调节与包括癫痫在内的多种健康和损伤依赖性状态有关。本研究使用全细胞膜片钳记录技术，对在局灶性、可控性皮质撞击（CCI）或假脑损伤后1 - 2周或8 - 13周，取自含有背侧海马的冠状切片中的小鼠齿状颗粒细胞（DGCs）的GABAR信号传导进行了详细分析。唑吡坦是一种类似苯二氮䓬的GABARs阳性调节剂，因其对含α亚基的GABARs具有选择性，故而被用于测试DGCs的GABAR信号传导变化。为了直接比较紧张性和相位性GABAR信号传导，并考虑唑吡坦改变GABAR动力学多个参数的能力，对电荷转移和统计百分比变化进行了分析。我们观察到，与损伤对侧的DGCs（Contra - DGCs）或假损伤后的DGCs（Sham - DGCs）相比，在损伤同侧的DGCs（Ipsi - DGCs）中，两个测试时间点的基线I均得以保留。有趣的是，唑吡坦的应用导致各实验组的I均受到调节，其中Ipsi - DGCs对唑吡坦表现出最大反应性。我们还报告称，CCI与急性应用唑吡坦相结合，在两个测试时间点均显著增加了由紧张性电流与突触电流介导的GABAR电荷转移比例，而在损伤后8 - 13周，GABAR α、α、α和γ亚基的基因表达未发生变化。总体而言，这项工作突出了Ipsi - DGCs中向紧张性抑制影响增强的转变、唑吡坦对DGCs抑制控制所有成分的影响，以及CCI损伤后这些抑制性音调变化的持续性。
