DIFFERENTIAL EXPRESSION OF BRAIN-DERIVED NEUROTROPHIC FACTOR AND NEUROTROPHIN-3 MESSENGER-RNA IN LINGUAL PAPILLAE AND TASTE-BUDS INDICATES ROLES IN GUSTATORY AND SOMATOSENSORY INNERVATION

Although many studies have demonstrated the dependency of taste bud fu nction and/or survival on intact innervation, relatively few have deal t with the development of taste bud innervation. Using in situ hybridi zation histochemistry, we show that brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3) mRNA are expressed in a specific patte rn in the taste buds, tongue papillae, and lingual epithelium during d evelopment and that expression persists into adulthood. BDNF mRNA is e xpressed in a fraction of the taste cells of the developing and adult taste buds in rats, showing different labeling intensities among the l abeled cells. NT3 mRNA seems to be located in areas other than those w here BDNF mRNA is expressed, mainly in the superior epithelial surface s of circumvallate papillae, the outer surface epithelium of foliate p apilae, the superior surface and the lateral epithelium of the fungifo rm papillae, and the epithelium of the filiform papillae. NT3 mRNA lab eling is also observed among muscle and connective tissue of the tongu e. The morphological appearance, expression of NT3 mRNA, and ramificat ion of nerve fibers in defined epithelial structures in the posterior wall of the anterior filiform papillae suggest the existence of a mech anosensory apparatus in these papillae. Nerve growth factor and neurot rophin 4 probes did not give rise to selective labeling in tongue, alt hough their presence cannot be totally excluded. Based on present and prior studies, we suggest that BDNF is needed during initiation and fo r maintenance of gustatory innervation of taste buds and gustatory pap illae and that NT3 is mainly needed for somatosensory innervation of t he tongue. (C) 1996 Wiley-Liss, Inc.