SPLTRAK Abstract Submission
Anatomical Underpinnings Of Broadly And Narrowly Tuned Taste Neurons
Robin Krimm
University of Louisville School of Medicine, , ,

It is unclear whether taste neurons are simply relay cells that carry a labeled-line code from specific subsets of taste receptor cells, or if there is circuitry between receptor cells and nerve fibers that transform neural responses. Nothing is known about the branching characteristics of individual taste neurons or their degree of convergence onto gustatory neurons. If taste neurons simply reflect the response characteristics of taste receptor cell types they innervate, little variation in branching characteristics between individual taste neurons would be required. To determine if this is the case, we traced the peripheral branching patterns of 96 single taste neurons, from where they enter the tongue to their terminations in the taste bud, using sparse cell genetic labeling. These neurons vary tremendously in their branching characteristics, such that individual neurons had anywhere from 1 to 20 separate branches entering between 1-7 taste buds. Cluster analysis was used to separate the neurons into 4 groups each of increasing branch complexity. Based on published EM data, the simplest taste neurons (cluster 1) should innervate approximately 4 taste receptor cells, while the most heavily branched neurons (cluster 4) would be expected to receive information from 16 or more taste receptor cells. We sought to verify this degree of convergence by asking how many labeled taste receptor cells are sufficiently proximal to a single taste neuron such that communication could occur. We found that some fibers only contact one two taste receptor cells of the same type. These neurons would be expected to have responses that directly mimic the taste receptors innervated. Alternatively, other neurons contact as many as 12 different receptor cells of multiple types. Since approximately 1 in 4 taste receptor cells responds to more than one stimulus, neurons innervating many taste receptor cells would be expected to be either broadly tuned or have complex response characteristics due to lateral enhancement and/or inhibition. Current views of gustatory neural coding must consider why some neurons innervate only a few taste receptor cells while others appear to receive heavily convergent information.