Genetic tracing of the gustatory neural pathway originating from T1R3-expressing sweet/umami taste receptor cells

Abstract

Neural pathways conveying taste information from the tongue to the brain underlie gustatory information coding and processing. To visualize the gustatory neural pathways, we established transgenic mouse lines in which a transneuronal tracer, wheat germ agglutinin (WGA), was faithfully and robustly expressed in sweet/umami taste receptor cells (TRCs) under the control of mouse T1R3 gene promoter/enhancer. WGA protein was transferred not laterally to the cells with synaptic structure, but directly to a subset of neurons in the geniculate and nodose/petrosal ganglia, and further conveyed to a subpopulation of neurons in the rostro-central region of the nucleus of the solitary tract. However, no WGA immunoreactivity was observed in more central gustatory relay nuclei even in the parabrachial nucleus. These results imply that sweet/umami information from TRCs can be directly transmitted to the gustatory neurons that innervate the sweet/umami TRCs, and this study uncovered a precise map of the sweet/umami information pathway from TRCs to the nucleus of solitary tract in the brain stem.