Fig. 2.

GABA-mediated neuronal excitation in the SCN. (A) Example recordings of three SCN neurons adjusted to a long-day photoperiod, depicting EPSPs (marked by asterisks) and action potentials before (Left) and after (Right) the application of the GABA_A receptor blocker gabazine (10 µM, 5 min); note that gabazine eliminated the majority of the EPSPs. Dashed lines indicate the resting membrane potential before and after the treatment. (Scale bars, 20 mV, 1 s.) (B) Mean ± SEM of EPSP frequency before and after gabazine application (n = 12). **P < 0.01, Wilcoxon signed-rank test. (C) Example Ca²⁺-imaging recordings of SCN neurons adjusted to a long-day photoperiod before (left traces) and after (right traces) application of the NKCC1 antagonist bumetanide (10 µM, 5 min). Bumetanide attenuated the GABA-induced transient Ca²⁺ elevations. (Scale bars, 20 nM, 20 s.) (D) Mean ± SEM of the peak of GABA-induced Ca²⁺ transients before and after bumetanide application (n = 39). ***P < 0.001, Wilcoxon signed-rank test.