Taste Coding in the Brainstem

Signals for each of the five tastes have previously been shown to be processed by distinct labeled lines from taste receptor cells (TRCs) on the tongue to the ganglion neurons that innervate them. Furthermore, different tastes have been shown to be represented by distinct neurons in the taste cortex. We recorded calcium activity using fiber photometry from genetically defined populations in the mouse rostral nucleus of the solitary tract (rNST), the first brain station receiving taste signals from the tongue. We found that Somatostatin- (Sst) expressing cells respond exclusively to bitter chemicals while Calretinin- (Calb2) expressing cells respond exclusively to sweet chemicals. Immunostaining and viral strategies demonstrated that Sst and Calb2 mark distinct neuronal populations in the rNST. We then showed that optogenetic activation of Sst and Calb2 cells elicits prototypical bitter and sweet behaviors, respectively and demonstrate that ablation of these cells strongly impairs aversion to bitter tastants and attraction to sweet tastants, respectively. These findings reveal how taste information is propagated into the brain.