Abstract
Gustatory neurons transmit chemical information from taste receptor cells, which reside in taste buds in the oral cavity, to the brain. As adult taste receptor cells are renewed at a constant rate, nerve fibers must reconnect with new taste receptor cells as they arise. Therefore, the maintenance of gustatory innervation to the taste bud is an active process. Understanding how this process is regulated is a fundamental concern of gustatory system biology. We speculated that because brain-derived neurotrophic factor (BDNF) is required for taste bud innervation during development, it might function to maintain innervation during adulthood. If so, taste buds should lose innervation when Bdnf is deleted in adult mice. To test this idea, we first removed Bdnf from all cells in adulthood using transgenic mice with inducible CreERT2 under the control of the Ubiquitin promoter. When Bdnf was removed, approximately one-half of the innervation to taste buds was lost, and taste buds became smaller because of the loss of taste bud cells. Individual taste buds varied in the amount of innervation each lost, and those that lost the most innervation also lost the most taste bud cells. We then tested the idea that that the taste bud was the source of this BDNF by reducing Bdnf levels specifically in the lingual epithelium and taste buds. Taste buds were confirmed as the source of BDNF regulating innervation. We conclude that BDNF expressed in taste receptor cells is required to maintain normal levels of innervation in adulthood.
Highlights
Taste receptor cells, which are organized into taste buds, detect the chemical content of food
Bdnf expression is reduced in adult mice with Bdnf gene deletion In the mouse taste system, brain-derived neurotrophic factor (BDNF) continues to be expressed during postnatal development and adulthood (Yee et al, 2003)
Because Bdnf is expressed in taste buds, the geniculate ganglion, and the CNS, all of which could influence taste neurons, we began by inducibly removing Bdnf from all cells using a ubiquitously express promoter
Summary
Taste receptor cells, which are organized into taste buds, detect the chemical content of food. Received August 25, 2015; accepted November 30, 2015; First published December 22, 2015. November/December 2015, 2(6) e0097-15.2015 1–20 to the brain. Gustatory neurons must continually locate and form functional connections with new adult taste receptor cells. The maintenance of innervation to the taste bud is an active process, such that nerve fibers, which fail to seek out new taste receptor cells to innervate, will be lost. Given this plasticity, some mechanism/s must be present to direct nerve fibers to innervate taste receptor cells and function to maintain innervation over time
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