Figure 2. Fbxl3Afh mutation asymmetrically alters the daily rise and decline in membrane excitability of SCN neurons. The peak and nadir of resting membrane potential (A, B) and spontaneous firing rate (C) of vSCN neurons were delayed by the Afh mutation. In the vSCN of Fbxl3Afh/Afh (Afh/Afh) mice, the daytime progression from nadir to peak resting membrane potential slowed (∼1.4 h; A, B), whereas the decline to the nocturnal nadir was accelerated (∼1.4 h). At night, the RMP was more hyperpolarized than that of Fbxl3+/+ vSCN neurons (+/+), whereas spontaneous firing rate did not differ between the genotypes (C). Prominent asymmetry in the daily increase and decrease in RMP was seen in the FbxlAfh/Afh vSCN (B). Intergenotype comparison of the fitted spline with the GLIMMIX procedure indicated that RMP of Afh/Afh vSCN neurons differed from the RMP of +/+ SCN neurons across each ZT hour from ZT14–ZT22 (range p < 0.05–p < 0.001; A, B). Time of peak and nadir in firing rate were delayed by ∼2.0 and 0.9 h, respectively, in the Afh/Afh vSCN (C). Compared with the +/+ dSCN, time of maximal and minimal RMP were delayed by ∼1.3 and ∼2.8 h, respectively, in the Afh/Afh dSCN (D, E). However, no intergenotype differences were detected in RMP of dSCN neurons across the projected day/night cycle (D, E). The asymmetry in the daily increase and decrease in RMP seen in the Fbxl3+/+ dSCN was reversed in the dSCN of Fbxl3Afh/Afh mice (E). In the dSCN, the amplitude of the firing rate rhythm was reduced in the Fbxl3Afh/Afh compared with Fbxl3+/+ animals (0.4 vs 1.4 Hz), whereas the time of peak and nadir in firing rate of dSCN neurons showed very small genotype-related differences (F). Data in A and D are scatter plots of individual data points (Afh/Afh in red unfilled circles; +/+ in blue unfilled circles) fitted with cubic spline fits of the mean ± 95% confidence interval, whereas data in B, C, E, and F are plotted as cubic spline fits of the mean ± 95% confidence interval. B and E are the cubic splines in A and D, respectively, plotted against an expanded ordinate.