Circadian Modulation of the Cl⁻ Equilibrium Potential in the Rat Suprachiasmatic Nuclei

Figure 9

Integrative model of excitatory GABA actions depending on SCN region and circadian time. (a) Dorsal day SCN neurons. High expression of NKCC1 cotransporters increases the [Cl⁻]_i. GABA_A R activation induces Cl⁻ efflux, which depolarizes the 𝐸_𝑚. Depolarized 𝐸_𝑚 increases the probability of action potentials that strengthens the SFR during the day. (b) Dorsal night. Low expression of NKCC1 decreases the [Cl⁻]_i. GABA binding induces Cl⁻ influx, which hyperpolarizes the 𝐸_𝑚. More negative 𝐸_𝑚 decreases the probability of spikes that reduces the SFR during the night. (c) Ventral day. Diminished NKCC1 expression reduces [Cl⁻]_i, and GABA_A R activation hyperpolarizes 𝐸_𝑚. Less excitability in ventral neurons decreases the probability of phase shifts. (d) Ventral night. Upregulated NKCC1 expression generates high [Cl⁻]_i that shifts the 𝐸_𝑚 close to the spike threshold. More excitability in ventral SCN neurons during the night enhances the probability of phase shifts by GABA.