The Removal of the p75 Receptor Effects Taste Bud Number and Size Without Influencing Gustatory Neurons

Neuronal targets, such as taste buds, produce protein factors called neurotrophins that regulate the development of their innervating neurons. The pan-neurotrophin receptor, p75, is one of several receptors used by neurons to interact with the neurotrophins. There is evidence that p75 is important for retrograde axonal transport of neurotrophins, specifically, brain derived neurotrophic factor (BDNF) and neurotrophic factor 4 (NT4), to the cell body. Hence, p75 may also be important to regulation and development of the taste system. Our experiment centers on the effects observed on the neurons of the geniculate ganglia, fungiform papillae, and taste buds in mice that lack p75. We hypothesized a reduction of fungiform papillae, taste buds, and neuron numbers in p75 knockout mice. Sections from the tongue and geniculate neurons of four wild type and four mutant (p75 -/-) mice were evaluated for ganglion neuron number, taste bud number, volumes, and location. The tongues were divided into five regions where the taste buds were counted. The taste bud reduction is concentrated in the ventral tip and mid-region of the tongue (p \u3c.02 and p \u3c .05, respectively). In conclusion, the effect from loss of the p75 receptor in the taste system was observed as a reduction in the number of taste buds, but an increase in the volume of those taste buds without interfering with neuron count