(A and C) Representative confocal images (A) of VIP neurons (red) and cFos (green) in the SCNs and (C) the number of cFos⁺ SCN VIP neurons in control and Mfn2^–/– mice at ZT7 and ZT19. Scale bars: 100 µm; insets 10 µm. (B and D) Representative confocal images (B) of VIP (red), VPAC2 (blue), and cFos (green) expression and (D) density of cFos⁺ cells in the VPAC2-expressing area in the SCN of control and Mfn2^–/– mice at ZT7 and ZT19. Analysis is of 3 sections per mice (n = 4–5 mice/group). Scale bars: 100 μm. (E) Number of cFos-expressing SCN VIP neurons and (F) density of cFos-expressing cells in the VPAC2-expressing area in the SCN of control and Mfn2^–/– mice after exposing to light for 1 hour at ZT13 (light) or stayed in the dark (no light). Analysis is of 4 sections per mice (n = 4–5 mice/group). (G) Membrane potential of SCN VIP neurons in control (n = 20) and Mfn2^–/– (n = 16) mice. (H) Ex vivo MUA recordings across the entire dorsoventral span of SCN and cross-correlation analysis between dorsal and ventral neuronal population rates in control and Mfn2^–/– mice (n = 3/group). The microphotograph and diagram depict the recording site locations in the SCN (labeling: 3V, third ventricle; OX, optic chiasm; AHC, anterior hypothalamic area central part). Kruskal-Wallis with Dunn’s test for C; 1-way ANOVA with Tukey’s test for D–F; unpaired 2-tailed t-test for G and H (right panel); Mann Whitney test for H (left panel). *P < 0.05, ***P < 0.005, and ****P < 0.0001. (See also Supplemental Table 1 for details on the statistical information for each graph.)