Expression of BDNF and TrkB in mouse taste buds after denervation and in circumvallate papillae during development.

Abstract

BDNF (brain-derived neurotrophic factor) is a member of the neurotrophin family which affects the proliferation and survival of neurons. Using an immunocytochemical method, we examined the expression of BDNF and its receptor, TrkB, in the taste bud cells of the circumvallate papillae of normal mice and of mice after transection of the glossopharyngeal nerves. We additionally observed the expression of BDNF and TrkB in the developing circumvallate papillae of late prenatal and early postnatal mice. In normal untreated mice, BDNF was expressed in most of the taste bud cells; TrkB was detected in the plasma membrane of taste bud cells and in the nerve fibers. Double-labeling studies showed that BDNF and NCAM (neural cell adhesion molecule) or TrkB and NCAM colocalized in some of the taste bud cells, but that most taste bud cells were immunopositive for only BDNF or TrkB. NCAM-immunoreactive cells are known to be type-III cells, which have afferent synaptic contacts with the nerve terminals. Five days after denervation, the number of taste buds and nerve fibers markedly decreased; however, the remaining taste bud cells still expressed BDNF and TrkB. By 10 days after denervation, most of the taste buds had disappeared, and there were a few TrkB-immunoreactive nerve fibers in the connective tissue core. By 4 weeks after denervation, numerous TrkB-immunoreactive nerve fibers had invaded the papillae, and a few taste buds expressing BDNF and TrkB had regenerated. At E (embryonic day) 15 during development, the circumvallate papillae appeared, and then TrkB-immunoreactive nerve fibers entered the connective tissue core, and some of these fibers further invaded among the dorsal epithelial cells of the papillae. TrkB-immunoreactive oval-shaped cells were occasionally found in the dorsal epithelium. Such TrkB-immunoreactive nerve fibers and cells were also observed at E16-18. However, BDNF was not expressed in the papillae through the late prenatal days of E15 to E18. At P (postnatal day) 0, a cluster of BDNF-and TrkB-immunoreactive cells appeared in the dorsal epithelium of the papillae, and was presumed to be primitive taste buds. We conclude that TrkB-immunoreactive nerve fibers are necessary for papillary and taste bud formation during development and for the regeneration of taste buds after denervation. BDNF in the taste bud cells may act as a neurotrophic factor for innervating sensory neurons--through TrkB receptors of the axons of those neurons, and also may exert autocrine and paracrine trophic actions on neighboring taste bud cells by binding to their TrkB receptors.

Effects of glossopharyngeal nerve section on the expression of neurotrophins and their receptors in lingual taste buds of adult mice

“…However, substantial differences exist between their study and ours in terms of colocalization and taste cell types. For example, Uchida et al (2003) report that BDNF and trkB are mainly absent from N-CAM-LIR type III taste cells, whereas we consistently find BDNF localized to type III taste cells (Yee et al, 2003). Their report is based on immunocytochemistry utilizing the same antiserum that we employ.…”

“…However, in hamsters, unlike the case in mice, taste buds do not completely disappear following denervation; hence, the expression of neurotrophins may differ between these species. For mice, Uchida et al (2003) found that trkB is present in nerve fibers following nerve transection, but did not find BDNF in nerve fibers, and the authors do not discuss NGF or its high-affinity receptor, trkA, or the proneurotrophin receptor p75 in mouse taste buds (Uchida et al, 2003). Similarly, Fan et al (2004) described the presence of p75 and NT3 in taste epithelia.…”

Expression of GDNF and GFRα1 in mouse taste bud cells

“…Both mRNA and protein of BDNF (brain-derived neurotrophic factor), another neurotrophic factor and a member of the NGF (nerve growth factor) family, were detected in taste bud cells (Nosrat et al, 1996b;Yee et al, 2003;Uchida et al, 2003). NGF and NT-3 (neurotrophin-3), also members of the NGF family, were likewise found in taste bud cells (Chou et al, 2001;Ganchrow et al, 2003).…”

Expression of Sox2 in mouse taste buds and its relation to innervation

“…The degenerated taste buds and nerve fibers disappear from the circumvallate and foliate papillae in rodents (Hosley et al 1987;Suzuki et al 1996). Concomitant with the structural loss of taste buds and nerve fibers is a loss of immunoreactivity of substances such as neural cell adhesion molecule (NCAM), brain-derived neurotrophic factor (BDNF), nerve growth factor, and glial cell line-derived neurotrophic factor normally found in taste bud cells (Takeda et al 1999(Takeda et al , 2005Uchida et al 2003;Yee et al 2005). After regenerated nerve fibers appear in the trench wall epithelium, taste buds regenerate, and the immunoreactivity of the above substances also reappears, indicating that the expression of these substances is dependent on innervation.…”