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) ha s been localized in the developing gustatory epithelium, little inform ation is available about neurotrophin-3 (NT-3) mRNA expression pattern in the prenatal developing gustatory and lingual epithelium. In the p resent study, using in situ hybridization histochemistry, we report on NT-3 mRNA expression in the tongue of rats. At embryonic day (E) 13-1 7, NT-3 mRNA was expressed subepithelially in the periphery of the dev eloping 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 s urface epithelium of the developing tongue in the developing filiform papillae and, in higher concentrations, in top-surface and hinge epith elium of the developing circumvallate papillae, and top- and lateral-s urface epithelium of the developing fungiform papillae. NT-3 mRNA expr ession in areas rich in somatosensory innervation of the tongue, as we ll as its specific expression in de fined regions compared with BDNF, and the decreased labeling noted from prenatal and early postnatal ani mals to adults indicate a specific role for NT-3 in the development of lingual somatosensory innervation, as well as for maintenance of this innervation.