HFD induces a delayed increase in the number of excitatory synaptic contacts to MCH neurons. The feeding periods were staggered to age-match all groups (7 weeks old) at the time of assessment. AM1wHFD: age-matched 1-week HFD. (A) HFD feeding does not affect mEPSC amplitude in MCH neurons (one-way ANOVA, p = 0.3180). (B) HFD induces a delayed increase in mEPSC frequency (one-way ANOVA, p = 0.0029). For (A–B): n = 6–9 cells, N = 4–6 rats. ∗p < 0.05, ∗∗p < 0.01, Sidak's multiple comparison test. (C–E) Representative immunohistochemical images of the lateral hypothalamus of rats that were fed for the indicated time. The panels show an example of confocal immunofluorescence for MCH + neurons (green; C1, D1, and E1), vGluT2+ puncta (red; C2, D2, and E2), the merged confocal image containing both channels (C3, D3, and E3), and the merged binary image used for analysis (C4, D4, E4). Scale bar = 10 μm. (F) Four weeks of HFD feeding induced an increase in the number of vGluT2+ puncta apposed to the somata of MCH neurons (one-way ANOVA, p = 0.0005). For (C–F): n = 52–90 neurons from 2-4 slices per rat, N = 3–4 rats per diet condition. ∗∗∗p < 0.001, Sidak's multiple comparison test.