Shimura M, Harata N, Tamai M, Akaike N
Department of Physiology, Kyushu University Faculty of Medicine, Fukuoka, Japan.
Am J Physiol. 1996 Jun;270(6 Pt 1):C1726-34. doi: 10.1152/ajpcell.1996.270.6.C1726.
The gamma-aminobutyric acid (GABA)-induced response was investigated in acutely dissociated suprachiasmatic nucleus (SCN) neurons of 11- to 14-day-old rats, under the voltage-clamp condition of nystatin-perforated patch recording. At a holding potential of -40 mV, application of GABA induced inward currents in a concentration-dependent manner. Pentobarbital and 5 beta-pregnan-3 alpha-ol-20-one (pregnanolone) similarly induced inward currents. GABA-induced inward currents were suppressed in a concentration-dependent manner by pretreating neurons with a GABAA receptor antagonist, bicuculline. Bicuculline (3 x 10(-6) M) shifted the concentration-response curve of GABA to the left in a competitive manner. Reversal potential of the GABA response (EGABA) was -3.4 +/- 0.7 mV, close to the theoretical Cl- equilibrium potential of -4.1 mV. Pretreating SCN neurons with diazepam, pentobarbital, and pregnanolone enhanced the 3 x 10(-6) M GABA response. Diazepam (3 x 10(-8) M), pentobarbital (3 x 10(-5) M), and pregnanolone (10(-7) M) shifted the concentration-response curve of GABA to the left without changing the maximal amplitude of GABA responses. EGABA in the presence of diazepam, pentobarbital, or pregnanolone was the same as that in their absence. These results show that the GABA response in acutely dissociated SCN neurons is mediated by the GABAA receptor. Because the GABAA receptor of SCN neurons is allosterically augmented by diazepam, pentobarbital, and pregnanolone, similarly as in other regions of the central nervous system, the present study opens up ways to functionally modulate the GABAA receptors in SCN.
在制霉菌素穿孔膜片钳记录的电压钳条件下，研究了11至14日龄大鼠急性分离的视交叉上核（SCN）神经元中γ-氨基丁酸（GABA）诱导的反应。在-40 mV的钳制电位下，应用GABA以浓度依赖性方式诱导内向电流。戊巴比妥和5β-孕烷-3α-醇-20-酮（孕烷醇酮）同样诱导内向电流。用GABAA受体拮抗剂荷包牡丹碱预处理神经元后，GABA诱导的内向电流以浓度依赖性方式受到抑制。荷包牡丹碱（3×10⁻⁶ M）以竞争性方式将GABA的浓度-反应曲线向左移动。GABA反应的反转电位（EGABA）为-3.4±0.7 mV，接近理论Cl⁻平衡电位-4.1 mV。用地西泮、戊巴比妥和孕烷醇酮预处理SCN神经元可增强3×10⁻⁶ M GABA反应。地西泮（3×10⁻⁸ M）、戊巴比妥（3×10⁻⁵ M）和孕烷醇酮（10⁻⁷ M）将GABA的浓度-反应曲线向左移动，而不改变GABA反应的最大幅度。存在地西泮、戊巴比妥或孕烷醇酮时的EGABA与不存在时相同。这些结果表明，急性分离的SCN神经元中的GABA反应由GABAA受体介导。由于SCN神经元的GABAA受体与中枢神经系统其他区域一样，受到地西泮、戊巴比妥和孕烷醇酮的变构增强，本研究为在功能上调节SCN中的GABAA受体开辟了途径。
