Expression of Nerve Growth Factor and Neurturin, and Their Receptors in Mouse Taste Buds

Nerve growth factor (NGF) and neurturin (NTN) are neurotrophic factors that affect the proliferation and survival of neurons. Using a double immunostaining method, we examined whether the taste bud cells in the circumvallate, foliate and fungiform papillae of normal mice expressed NGF, NTN, and their receptors, TrkA and GFRα2, respectively, and if so, what type of cells in the taste buds expressed them. Because NCAM is reported to be expressed in type- III cells in the taste buds, PGP9.5 in type- III and some type- II cells, and α -gustducin, in some type- II cells, we used these markers to identify the types of taste bud cells. Almost all normal taste bud cells expressed NGF, TrkA, NTN, and GFRα2. Confocal laser scanning microscopic observations after double immunostaining showed that almost all anti-NCAM-, antiPGP9.5-, or anti- α -gustducin immunoreactive cells were positive for NGF. Thus, NGF-immunoreactive cells included type- II and - III cells, and perhaps type- I cells. Almost all anti-PGP9.5-immunoreactive cells were positive for TrkA, NTN, and GFRα2, revealing that type- III cells expressed TrkA, NTN, and GFRa2 ; although other types of cells were also immunopositive for these receptors and NTN. We suppose that NGF and NTN in the taste bud cells may exert trophic actions on the taste bud cells by binding to their respective receptors, and additionally be involved in the synaptic transmission from the type- III cells to the gustatory nerves.