Fig. 1: Physiological MCH neuron Ca²⁺ activity increases in response to discrete food-predictive cues and is associated with behavioral appetitive responsivity.

a Schematic diagram depicting a viral approach to record physiological MCH neuron Ca²⁺ activity with fiber photometry in rats (n = 6). An adeno-associated virus containing an MCH promoter-driven GCaMP6s (AAV9.pMCH.GCaMP6s.hGH) is injected into the LHA and an optic fiber was implanted above the injection site. b Representative images of fluorescent reporter in MCH GCaMP6s colocalizing with MCH immunoreactive neurons (repeated and verified independently in n = 6 rats). c Schematic cartoon depicting fiber photometry recording of MCH neuron Ca²⁺ activity during the Pavlovian discrimination task (n = 8 CS+, n = 8 CS− cues). d–f Training data for Pavlovian discrimination task (data were analyzed using a one-way ANOVA with repeated measures and multiple comparisons, n = 6 rats): d Average number of licks for sucrose solution per CS+ trial, e Average latency to lick from sucrose solution per CS+ trial, and f Average number of CS+ trials with a response via licking sucrose solution. g–k Fiber photometry recording of MCH neuron Ca²⁺ activity during the test phase (data analyzed using Student’s two-tailed paired t-test, n = 6 rats, with g MCH neuron Ca²⁺ activity (z-score) time-locked to cue onset (CS+ in red and CS− in green; −15 to 25 s relative to the start of the 5 s cue [gray box]). h Heatmap of the MCH neuron Ca²⁺ activity (z-score) for each animal during each of the 5 s of CS presentation. i MCH neuron Ca²⁺ activity during cue period [gray box] (max activity during CS − activity during cue onset), **P = 0.0042, j MCH neuron Ca²⁺ activity for 5s-pre-CS, 5 s CS period and 5s-post-CS, compared between CS, **P = 0.001 and k Simple linear regression of MCH neuron Ca²⁺ activity (max activity during CS − activity during cue onset) during each CS+ trial relative to latency to lick from sucrose solution. The solid line is linear fit to data and dashed lines are 95% confidence interval error bars, R² = 0.5039, P = 1.08E-10. Data shown as mean ± SEM; Scale = 100 μm; **P < 0.01, ****P < 0.0001. Source data are provided as a Source Data file. Created with Biorender.com.