Carbachol inhibits the glutamatergic PH^Glut→ HMN input from the restricted PH region lateral to the MoXII. A, In these recordings, we restricted the expression of ChR2 in the PH region lateral to the MoXII and just at the level of the area postrema. Heatmap of AAV-DIO-ChR2-mCherry injection sites of six recorded VGlut2-IRES-Cre mice showing overlapping regions of ChR2-mCherry-expressing neurons. B, C, Photostimulation of PH^Glut input produced photo-evoked EPSCs in HMNs that were inhibited by carbachol (15 μm; mean ± SEM; n = 10; RM one-way ANOVA: F_(2,18) = 26.93, p < 0.0001; and Tukey's multiple comparison, ****p < 0.0001). Photo-evoked EPSCs were recorded at V_h = −60 mV (in gray, 30 photo-evoke EPSCs; in black, average photo-evoked EPSCs). In all of the recordings, we used 10 ms blue-light pulses, indicated by blue bars at the top of the recording traces.