BRAIN-DERIVED NEUROTROPHIC FACTOR MESSENGER-RNA IS EXPRESSED IN THE DEVELOPING TASTE BUD-BEARING TONGUE PAPILLAE OF RAT

Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are expressed in many areas of the nervous system and its target tiss ues. Using in situ hybridization we have investigated the possible pre sence of NGF mRNA and BDNF mRNA in the developing fungiform and circum vallate papillae of the rat tongue. BDNF mRNA is present in the epithe lium of the developing fungiform papillae in E15, E16, and E17 rat emb ryos with peak concentration at E16. It starts to diminish after E17 a nd is almost absent at E21. There is a specific temporospatial change in the expression of BDNF mRNA in developing circumvallate papillae. I t is expressed in the epithelium of the superior and posterior surface s of the papillae at E15, E16, and E17. Already at E17 the BDNF mRNA l abeling has started to decrease in the superior epithelium. At E19 and E21, BDNF mRNA is exclusively present in the epithelium of the inner and outer walls of the trench, surrounding the papilla at the posterio r and lateral surfaces where the taste buds are located later in life. BDNF mRNA was also detected in the developing palatal taste buds. NGF mRNA was below detection level in the developing papillae. The highly localized expression of BDNF mRNA in areas where taste buds are to be formed suggests that BDNF may be one crucial factor in the formation of the epithelial innervation prior to taste bud formation. It might a lso participate in the formation and/or maintenance of the papillary a nd/or taste bud innervation apparatus. We conclude that the neurotroph in BDNF is expressed in early development of taste bud-bearing papilla e in the rat tongue in a temporally and spatially controlled manner, p resumably to act as a target-derived chemoattractant for the early ner ve fibers. (C) 1995 Wiley-Liss, Inc.