High-salt diet (HSD) increases suprachiasmatic nucleus (SCN) neuronal excitability at night. (A) Violin plots of spontaneous action potential frequencies of SCN neurons from mice fed normal salt diet (NSD) or HSD for 2 weeks, recorded during the day (Zeitgeber time [ZT] 4-8) or night (ZT 14-18). HSD significantly increased SCN firing at night (time × diet interaction, H₍₁₎ = 10.392, P = .001; NSD-night vs. HSD-night post hoc, P < .001), but had no effect during the day (P = 1.00). Solid and dotted lines indicate median and quartiles, respectively. n = 143 (NSD-day), 155 (HSD-day), 151 (NSD-night), and 155 (HSD-night) cells; 4 mice per group. (B) Representative loose-patch traces (5 s) from each group. Scale bars: 2 s, 50pA. (C) Percentage of silent (empty bars) versus spiking (filled bars) cells for each group in A and B. Three-way loglinear analysis revealed a significant increase in silent cells at night for both diets (time × spiking interaction, χ²₍₁₎ = 28.949, P < .001), as well as an increase in the proportion of spiking cells in HSD mice at both times of day (diet × spiking interaction, χ²₍₁₎ = 7.661, P = .006).