Extended Data Figure 7: Vagal neurons innervating duodenal segment sense sugar.

a, Schematic of retrograde tracing experiment. Fluorescently-conjugated cholera toxin subunit B (CTB)²⁷ was injected into the proximal duodenum to back fill, and label, the cell bodies of duodenum-projecting vagal neurons (z-projection of n = 22 confocal planes from a representative ganglion, see Methods for details). The two panels below show a sample retrogradely labelled ganglion with sensory neurons (VGlut2-Cre driving the GCaMP reporter) marked in green (left) and those labelled by CTB marked by red fluorescence (right). Double-positive neurons are highlighted by the white circles. Scale bar, 100 μm. b, Representative field of a vagal imaging session showing the overlay of CTB and GCaMP. The 2 yellow circled neurons (denoted as #1 and #2) were labelled by retrogradely applied CTB in the duodenal segment, and exhibited strong responses to glucose (n = 16 ganglia from 10 mice). Scale bar, 100 μm. c, A total of 12/55 double-positive neurons responded to the 10 s glucose stimulus (see Extended Data Fig. 6d for a comparison with un-injected animals); n = 16 ganglia from 10 mice. Note the substantial enrichment in the number of responders when pre-tagged by retrograde labelling: ~20% in the duodenal tagged vs 4–5% in the whole population.