Fig. 9. Inhibiting endogenous γ-aminobutyric acid (GABA)_A alters [Ca²⁺]_i in SCN neurons.

(Top) Regional variation of gabazine-induced (10 μm) changes in baseline Ca²⁺ ratio in SCN neurons. Responses were separated into three groups: a decrease of the Ca²⁺ ratio [gabazine(Ca-), top-left]; an increase of the Ca²⁺ ratio [gabazine(Ca+), top-middle]; and a non-responsive group Ca²⁺ [gabazine(Ca0), top-right]. The position for each neuron was superimposed on a representative drawing of the SCN, with the 3^rd ventricle (3V) on the left and optic chiasm (OC) at the bottom. (Bottom left) Regional localization of individual SCN neurons with a GABA (200 μm)-induced increase in Ca²⁺ and a gabazine-induced decrease in Ca²⁺ (see Figs 5 and 8F). (Bottom middle) Regional variation of individual SCN neurons demonstrating both a GABA-induced decease and a gabazine-induced increase of [Ca²⁺]_i. (Bottom right) The mean change in the baseline Ca²⁺ ratio produced by gabazine was in an opposite direction to the Ca²⁺ response evoked by GABA. Data are the mean ± SEM of the Ca²⁺ ratio change in gabazine-responsive neurons for GABA(Ca+) (n = 125), GABA(Ca-) (n = 77) and GABA(Ca0) (n = 65) neurons (F_2,264 = 14.74, P < 0.0001, power = 1.00) by anova with Bonferroni t-tests adjusted for three comparisons, ***P < 0.0001. Note that GABA(Ca-) and GABA(Ca0) respond similarly (P = 1).