Allosteric modulation of GABAA receptors in acutely dissociated neurons of the suprachiasmatic nucleus.

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.