Circadian modulation of membrane properties in slices of rat suprachiasmatic nucleus.

Perforated patch clamp recordings of neurons in slices of the suprachiasmatic nucleus (SCN) were made in their subjective day and night phases. The spontaneous firing rate and input resistance were significantly higher during the subjective day as compared to the subjective night. In parallel, the membrane potential of neurons recorded at daytime was significantly more depolarized than at nighttime. The day-night differences in membrane potential and input resistance were maintained when spikes and GABA(A) receptor-mediated transmission were blocked by tetrodotoxin and bicuculline, suggesting a cell-autonomous regulation of the circadian modulation of membrane properties. In conclusion, these findings suggest that at least one hyperpolarizing ionic conductance would be open at night and closed during mid-day, when spontaneous firing reaches peak levels in the SCN.