Tuesday, April 1, 2025
4/1/2025
Uncovering the ultrastructure and connectivity of murine fungiform taste buds - Project Summary Taste buds are the end organs of the gustatory system and allow for the detection of sweet, bitter, umami, salty, and sour stimuli. In mammals, taste buds inhabit several areas of the oral cavity, including the fungiform papillae of the anterior tongue and the circumvallate papillae of the posterior tongue. Two separate taste nerves innervate the anterior and posterior tongue; the chorda tympani branch of the facial nerve innervates the fungiform taste buds, while the glossopharyngeal nerve innervates the circumvallate taste buds. While buds from both fungiform and circumvallate tissues can detect the five established taste qualities, several lines of evidence suggest differences between anterior and posterior taste buds in both form and function (Travers et al., 1987; Ninomiya & Funakoshi, 1989; Frank 1991; Ninomiya et al., 1991; Spector & Grill 1992; Hellekant et al., 1997; St. John & Spector, 1998; Tomchik et al., 2007; Yoshida et al., 2009; Lewandowski et al., 2016). Most of the anatomical taste bud data in the literature feature only the circumvallate taste buds—this is likely due to the relative ease of isolating taste buds from the closely packed buds of the circumvallate tissue rather than the sparse buds of the fungiform tissue. The cellular composition of taste buds, detailed taste cell morphology, and patterns of connectivity between taste cells and innervating nerve fibers have been reported in circumvallate tissue (Romanov et al., 2018; Yang et al., 2020; Wilson et al., 2022). The current proposal aims to close the anatomical knowledge gap across taste fields by examining fungiform taste buds via Serial Block Face Scanning Electron Microscopy (sbfSEM). This high-resolution imaging technique can produce serial electron micrographs through entire mouse fungiform taste buds. When aligned and imported into specialized imaging software, objects in the mass of the taste bud can be manually traced and reconstructed in digital 3D space. To augment the manual segmentation process, this project will also employ machine learning techniques to identify and segment a portion of the objects of interest in the dataset. Using micrographs and the 3-D reconstructions of objects therein, this project will unveil morphological details of fungiform taste cells. It will reveal whether or not morphological subsets of the three established mature taste cells exist in fungiform taste buds, and whether or not their morphologies differ from those described in the circumvallate. By reconstructing the nerve fibers that receive synapses from fungiform taste cells, the proposed project will also reveal the “connectome” of the fungiform taste buds. Anatomical patterns of connectivity between taste cells and innervating nerve fibers underlie the taste information coding from taste bud to the central nervous system. Understanding the connectome will thus provide new insight into how fungiform taste buds communicate taste quality information to the brain, and whether their patterns of connectivity differ from those of circumvallate taste buds. By elucidating and describing the morphological details and connectome of fungiform taste buds, this project will expand our understanding of both form and function in the anterior tongue.
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