Changes in neurotrophin-3 messenger RNA expression patterns in the prenatal rat tongue suggest guidance of developing somatosensory nerves to their final targets

While brain-derived neurotrophic factor (BDNF) messenger RNA (mRNA) has been localized in the developing gustatory epithelium, little information is available about neurotrophin-3 (NT-3) mRNA expression pattern in the prenatal developing gustatory and lingual epithelium. In the present study, using in situ hybridization histochemistry, we report on NT-3 mRNA expression in the tongue of rats. At embryonic day (E) 13–17, NT-3 mRNA was expressed subepithelially in the periphery of the developing tongue, as well as among developing muscle. At E19, there was a shift in the expression of NT-3 mRNA. It was then expressed in the surface epithelium of the developing tongue in the developing filiform papillae and, in higher concentrations, in top-surface and fringe epithelium of the developing circumvallate papillae, and top- and lateral-surface epithelium of the developing fungiform papillae. NT-3 mRNA expression in areas rich in somatosensory innervation of the tongue, as well as its specific expression in defined regions compared with BDNF, and the decreased labeling noted from prenatal and early postnatal animals to adults indicate a specific role for NT-3 in the development of lingual somatosensory innervation, as well as for maintenance of this innervation.