Fig. 6.

Model of day-length encoding by regulation of chloride homeostasis. (A) The GABA can introduce asymmetry in the SCN network coupling by the biased distribution of intracellular chloride, which can make GABA excitatory (Upper) or inhibitory (Lower), driven by relative activation of chloride importers (NKCC) vs. chloride exporters (KCC). (B) The GABA excitation under high intracellular chloride influences the clock gene expression cycle through excitation–transcription coupling (21) and helps organize the overall phase distribution of Bmal1 oscillations in SCN neurons, as the realistic model simulates.