Extended Data Figure 4: Retrograde Labeling from cNST.

a, A fluorescent retrograde tracer (red RetroBeads, Lumafluor) was stereotaxically injected into the cNST to label its inputs. The nodose ganglia and dorsal root ganglia were checked for transfer of the fluorescent label after 6–7 days. The nodose ganglion (vagal neurons), but not the dorsal root ganglion (spinal neurons), was robustly labelled²³, n = 2 independent experiments. b, RetroBeads were also injected into the Cuneate nucleus, a brainstem area near but distinct from the cNST. Vagal neurons were not labelled. In contrast, note robust labelling of spinal neurons (n = 2 independent experiments). DAPI nuclear counterstain is also shown (blue). Scale bars: 200 μm (Brainstem), 50 μm (Nodose, DRG). c, Validation of TRAPing procedure. To confirm that the sugar-activated cNST neurons marked by the expression of Fos are the same as the ones labelled by Cre-recombinase in the genetic TRAPing experiments. We genetically labelled the sugar-induced TRAPed neurons with a Cre-dependent fluorescent reporter²⁴, and then performed a second cycle of sugar stimulation followed by Fos antibody labelling. d, Top row, neurons labelled by the Cre-dependent reporter after sugar TRAPing (‘Sugar-TRAP’, pseudo-coloured red) are the same as the ones labelled by Fos after a second cycle of sugar stimulation (‘Sugar-Fos’, marked in green; see Methods and text for details), >80% of Sugar-Fos are Sugar-TRAP (n = 7 animals); middle row, note that the few neurons labelled after Water-TRAP in response to water do not overlap with those labelled with Fos antibodies after sugar stimulation; bottom row, the sugar-TRAP neurons are also activated by the non-caloric sugar analogue MDG, >80% of MDG-Fos are Sugar-TRAP. Scale bar, 20 μm.