Functions of gustatory afferent neuron types.

Project Summary Single-cell RNA sequencing (scRNAseq) has made unprecedented strides in discovering previously unrecognized diversity of neuronal cell types and their functions. Using scRNAseq, we showed that the mouse geniculate ganglion contains 3 molecularly distinct types of gustatory neurons that innervate taste buds, T1, T2, and T3, each with unique patterns of gene expression. In a concerted effort from two well-established laboratories, we now propose a multi-PI project to test hypotheses regarding distinct functions for each of the major types of neurons and their subtypes. Our ultimate goal is to produce an integrated molecular and functional categorization of gustatory neurons similar to what has been so powerfully effective in the auditory, visual, and somatosensory systems. We propose using a newly-optimized method for in vivo confocal Ca2+ imaging, neuron-selective fluorescent markers, and chemogenetic silencing to reveal the functions of T1 and T3 geniculate ganglion neurons. Specifically, using GCaMP-based Ca2+ imaging, we will test the hypothesis that within the cluster of T1 neurons there are subclasses that respond to distinct taste qualities whereas neurons within the T3 cluster respond to multiple, convergent tastes. We will further test the hypothesis that T1 and T3 neuronal subtypes contribute to separate central pathways serving a number of taste-dependent functions downstream of initial detection in the taste periphery. Completing the above aims will move the field of taste into a new era of molecular-functional integration. Our findings will assist electrophysiology and circuit tracing studies in taste, will shed light on the controversy over labeled lines versus combinatorial taste coding, and will bring new information on gustatory neural pathways that are so important to nutrition and ingestive behavior.