Extended Data Fig. 8: Glucose responders are not sensing osmolarity.

Williams et al.²⁴ identified vagal neurons that indiscriminately responded to high concentrations of several stimuli delivered in very large stimulus volume for hundreds of seconds. We believe these responses, largely independent of the quality of the stimulus, are intestinal osmolarity signals. a, Shown are heat maps summarizing responses to interleaved 60-s stimuli of 500 mM glucose and 500 mM mannitol. Each row represents the average activity of a single cell during three interspersed exposures to the stimulus. Stimulus window is indicated by the dashed white lines. Of 134 neurons that responded to intestinal application of 500 mM glucose for 60 s, 101 did not exhibit statistically significant responses to mannitol (top). However, 33 (~25%) showed responses to both 500 mM glucose and 500 mM mannitol (bottom). n = 5 mice. When the intestinal stimulus consisted of a short pulse (that is, 10 s; 33 μl volume) no responses were detected to 500 mM mannitol (data not shown). b, Sample traces (three trials each) of a neuron responding to glucose (red) but not mannitol (blue). c, Sample traces (three trials each) of a neuron responding to glucose and mannitol. Scale bars indicate percentage maximal response. d, Heat maps showing responses to a 60-s stimuli of 1 M mannitol, 1 M fructose, 1 M mannose and 1 M NaCl. Note that the same cells respond indiscriminately to the various stimulus (n = 4 mice). e, The graph shows preference plots for fructose versus AceK (n = 8 mice, two-tailed paired t-test, P = 0.27). Note that fructose, a caloric sugar, does not create preference, but activates osmolarity responses. f, Williams et al.²⁴ suggest that GPR65-expressing vagal neurons function as the nutrient sensors. We generated mice in which GCaMP6s expression was targeted to GPR65-expressing vagal neurons and examined their responses to a 10-s stimulus of 500 mM glucose or osmolarity signals (that is, 1 M each of fructose, mannose and NaCl for 60 s). Shown are normalized responses of from three different mice to the four stimuli; each trace represents a different responding neuron. Note that 500 mM glucose for 10 s does not activate GPR65 neurons. By contrast, they are activated by 60-s pulse of 1 M fructose, mannose and NaCl (see also Fig. 4). g, Summary histogram of GPR65 tuning profile to 10 s 500 mM glucose, and 60 s 1 M fructose, 60 s 1 M mannose and 60 s 1 M NaCl; n = 4 mice.