Chorda tympani nerve transection at different developmental ages produces differential effects on taste bud volume and papillae morphology in the rat

Abstract

Chorda tympani nerve transection (CTX) results in morphological changes to fungiform papillae and associated taste buds. When transection occurs during neonatal development in the rat, the effects on fungiform taste bud and papillae structure are markedly more severe than observed following a comparable surgery in the adult rat. The present study examined the potential "sensitive period" for morphological modifications to tongue epithelium following CTX. Rats received unilateral transection at 65, 30, 25, 20, 15, 10, or 5 days of age. With each descending age at the time of transection, the effects on the structural integrity of fungiform papillae were more severe. Significant losses in total number of taste buds and filiform-like papillae were observed when transection occurred 5-30 days of age. Significant reduction in the number of taste pores was indicated at every age of transection. Another group of rats received chorda tympani transection at 10, 25, or 65 days of age to determine if the time course of taste bud degeneration differed depending on the age of the rat at the time of transection. Taste bud volumes differed significantly from intact sides of the tongue at 2, 8, and 50 days post-transection after CTX at 65 days of age. Volume measurements did not differ 2 days post-transection after CTX at 10 or 25 days of age, but were significantly reduced at the other time points. Findings demonstrate a transitional period throughout development wherein fungiform papillae are highly dependent upon the chorda tympani for maintenance of morphological integrity.

Mice lacking the p75 receptor fail to acquire a normal complement of taste buds and geniculate ganglion neurons by adulthood

“…This reduction was similar to that reported previously (Fan et al, 2004). Loss of gustatory innervation during development can reduce the numbers of taste buds and fungiform papillae (Hosley et al, 1987;Nagato et al, 1995;Sollars and Bernstein, 2000;Sollars et al, 2002;Sollars, 2005). Thus, one explanation for the present findings is that neurotrophins function to maintain gustatory neurons via the p75 receptor.…”

“…This finding is consistent with a developmental role for p75. Removal of gustatory innervation during development results in the loss of both fungiform papillae and taste buds, while removal of innervation during adulthood causes taste bud loss but does not affect the fungiform papilla (Oakley et al, 1990;Nagato et al, 1995;Sollars, 2005). Quantification of fungiform taste buds over the course of development will be necessary to provide unequivocal evidence for a developmental role for p75 for fungiform papillae and taste buds.…”

Angiogenesis and Developmental Expression of Vascular Endothelial Growth Factor in Rat Lingual Papillae

“…The loop shaped vascular network is established in each subepithelial papilla by birth, and timing is very close to differentiation of the primordium of taste buds and epithelial tissues of filiform papillae, suggesting a close relationship between higher differentiation of epithelial tissues and development of the vascular system. Differentiation of taste buds was reported by several researchers, and a close relationship between development of taste buds and that of the nervous system has been demonstrated [37,38]. During early developmental stages, invasion of nerve fibers into circumvallate papillae and fungiform papillae was particularly reported at E16 [29,30,32].…”

Role of neurotrophin in the taste system following gustatory nerve injury

“…BDNF produced in taste epithelium is required for gustatory target innervation but NT-4 is not (Hoshino et al 2010;Ma et al 2009). Because nerve fibers support taste buds during postnatal development (Sollars 2005), the loss of nerve fibers results in a loss of taste bud number and size by birth in mice that lack BDNF (Mistretta et al 1999;Nosrat et al 1997;). However, NT-4 knockout mice lose very few fungiform papillae or taste buds by birth (Liebl et al 1999).…”