A Reexamination of the Role of GABA in the Mammalian Suprachiasmatic Nucleus

Abstract Three independent electrophysiological approaches in hypothalamic slices were used to test the hypothesis that g-amino butyric acid (GABA)A receptor activation excites suprachiasmatic nucleus (SCN) neurons during the subjective day, consistent with a recent report. First, multiple-unit recordings during either the subjective day or night showed that GABA or muscimol inhibited firing activity of the SCN population in a dose-dependent manner. Second, cell-attached recordings during the subjective day demonstrated an inhibitory effect of bath- or microapplied GABA on action currents of single SCN neurons. Third, gramicidin perforated-patch recordings showed that bicuculline increased the spontaneous firing rate during the subjective day. Therefore, electro-physiological data obtained by three different experimental methods provide evidence that GABA is inhibitory rather than excitatory during the subjective day. Key words circadian, GABAA, hypothalamus, muscimol, bicucullin