SPLTRAK Abstract Submission
Taste Neurons Vary in Degree of Converging Input from Taste Receptor Cells.
Lisa Ohman-Gault, Tao Huang, Zachary Whiddon, Robin F. Krimm
Department of Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, Louisville, KY, United States

Individual taste neurons show tremendous variation in peripheral morphology. The next step is to determine whether these morphological variations dictate variation in peripheral connectivity to taste receptor cells (TRCs). Using a whole mount immunohistochemistry to stain taste buds combined with sparse cell genetic labeling of individual chorda tympani neurons, we analyzed the proximity of individual chorda tympani nerve fibers to TRCs using the Imaris software. We examined 77 separate fiber branches entering the taste bud, of these 52% contact (come within a distance below the resolution of the light microscope) one taste receptor cell (mean = 1.4, range= 0-4) whereas 36% contact more than one and 12% form no contacts. Of the fibers contacting TRCs, 87% of fibers contact TRCs of the same type and 13% contact TRCs of multiple types. Some fibers follow along a taste receptor cell for a considerable distance (13mm, long contacts), while others do not (short contacts, 3µm). Contacts are formed by all branch order types (1st-7th order) but most frequently with 3rd order branches. Next, we traced whole neurons from the base of the tongue. Some neurons (37.5%) innervate only one taste bud, branch sparsely (3-5 branch ends), and make 1-5 contacts with 1-2 taste receptor cells of the same type. Other neurons (62.5%) branch more robustly to innervate 3-5 taste buds, with 13-27 branch ends, making 7-14 contacts with 4-13 taste receptor cells of both types. The total length of the neuron in the taste bud predicts the number of contacts made with taste receptor cells (r = 0.92). We suggest that sparsely branched neurons contacting only a few TRCs of the same type may be narrowly tuned, whereas neurons that branch robustly to innervate many taste receptor cells of different kinds may be broadly-tuned.