The taste bud is a small collection of 50 to 150 spindle-shaped cells that are arranged in an onion-shaped structure. Numerous small, unmyelinated nerve processes which are postsynaptic to taste cells course tortuously throughout the taste bud. We have previously observed different structural types of synapses in mouse taste buds, """"""""macular,"""""""" (small spot-shaped foci) and """"""""invaginated,"""""""" (characterized by the presence of an invagination of the presynaptic taste cell in which a process of the postsynaptic nerve fiber extends). In adult taste buds, virtually all synapses are from taste cells onto a few scattered nerve fibers present in the lower third of each bud. Our understanding of the functional nature of taste bud synapses is very limited. In this proposal, we will test the hypothesis that specific synaptic proteins known to be associated with typical neuronal synapses in the CNS are associated with morphologically identifiable synapses in taste buds of adult mice and axolotls. We will also determine whether the development of specific taste cell phenotypes is correlated with the presence of synapses. Finally, we will investigate the transient intragemmal plexus of nerve fibers that we have observed in early development. During postnatal days 1-4, a large, basal intragemmal plexus of nerve fibers is present, replete with numerous afferent and neuro- neuronal synapses. After day 4, most of the intragemmal lex and its associated synapses disappear. We will examine whether there is a relationship between this """"""""pruning"""""""" process and the development of synaptic connectivity within taste buds.
The specific aims for this project are as follows:
Aim 1. Are synapse-associated proteins present only in taste cells that have morphologically identifiable synapses? Aim 2 Is there a relationship between the expression of taste cell phenotype and the presence of morphologically identifiable synapses in adult and developing taste buds? Aim 3. What is the role of innervation in taste cell synaptogenesis?
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