Fig. 2. Enteroendocrine cells of the colon and small intestine synapse with vagal nodose neurons.

(A) Model of AG-rabies-GFP enema delivery. (B) PYY cells expressing tdTomato (top left, red) are infected by ΔG-rabies-GFP (top right, green). Overlay (bottom) shows overlap of 87.8 ± 2.4% SEM (n = 5 mice). In the absence of G glycoprotein (ΔG), AG-rabies-GFP does not spread beyond the infected PYY cell. (C) EnvA-ΔG-rabies-GFP virus enters cells via the TvA receptor and spreads by using the rabG protein within specific cells. (D) EnvA-ΔG-rabies-GFP (top right, green) infects PYY cells (top left, red) and spreads synaptically to underlying colon nerve fibers. Three-dimensional reconstruction (bottom) shows EnvA-ΔG-rabies-GFP-infected PYY cell and mono- synaptically labeled nerve fiber. (E) EnvA-ΔG-rabies-GFP enema infects colonic enteroendocrine cells and spreads onto vagal neurons in the nodose ganglion (green). (F) In additional experiments, ΔG-rabies-GFP delivered by oral gavage spreads in the intestinal lumen of CckCRE_rabG-TvA mice to label the nucleus tractus solitarius (green). This neuroepithelial circuit links the intestinal lumen with the brainstem. The inset shows the location of the nucleus tractus solitarius in the mouse brain. All scale bars, 10 μm.