Extended Data Fig. 2: The gut-to-brain osmosensory signal depends on fluid tonicity but not osmolyte identity.

a, b, Intragastric infusion does not rapidly alter the state of the blood. a, Schematic. b, Plasma osmolality of samples collected during approximately 3–6 min after the start of the 5-min intragastric infusion (n = 9 mice per group, one-way ANOVA, Holm–Šídák correction). c–e, The gut-to-brain osmosensory signal depends on fluid tonicity but not osmolyte identity. c, Top, SFO neuron dynamics of individual mice in response to intragastric infusion of equi-osmotic concentrations of NaCl, which is absorbed into the bloodstream from the gastrointestinal tract, and mannitol, which is not absorbed (n = 4 mice). Bottom, SFO neuron dynamics of a separate cohort of individual mice in response to intragastric infusion of equiosmotic concentrations of NaCl, which does not permeate cell membranes and has high tonicity, and glucose, which does permeate cell membranes and has low tonicity (n = 5 mice). d, Left, average SFO activity during intragastric infusion of NaCl or mannitol. Right, quantification (n = 4 mice, one-way ANOVA, Holm–Šídák correction). e, Left, average SFO activity during intragastric infusion of NaCl or glucose. Right, quantification (n = 5 mice, one-way ANOVA, Holm–Šídák correction). f–h, SFO neurons encode systemic and gastrointestinal osmosensory signals additively rather than hierarchically. f, Schematic. g, Example (left) and average (right; n = 4 mice) of SFO neuron dynamics during 1.5 M NaCl intraperitoneal injection followed by intragastric infusion of water. h, Example (left) and average (right; n = 3 mice) of SFO neuron dynamics during 1.5 M NaCl intragastric infusion followed by intraperitoneal injection of water. Error bars represent mean ± s.e.m. Shaded areas in summary traces (d, e, g, h) represent mean ± s.e.m., and in example traces (g, h) represent intragastric infusion. NS, not significant, *P < 0.05, **P < 0.01.