EFFECT OF DENERVATION ON MORPHOGENESIS OF THE RAT FUNGIFORM PAPILLA

Ln an attempt to elucidate the effects of denervation on development a nd maintenance of the structure of the fungiform papilla, unilateral n eurectomy of the chorda tympani-lingual nerve of rats was performed at day 1 and at weeks 1, 2, 3, 4, 7, and 10 after birth. Specimens were obtained at days 3, 7 and 10, weeks 2, 3, 4, 6, and 8, and months 3 an d 4 after neurectomy for examination by light and scanning electron mi croscopy. At first, the fungiform papillae were atrophic, then progres sed to forms resembling filiform papillae. When an immature fungi form papilla was denervated, it eventually changed to a papilla identical to normal filiform papillae. The elicited changes differed according t o the time of neurectomy; it was found that early neurectomy resulted in a more rapid and marked morphological change of the fungiform papil lae. The filiform-like papillae derived from the fungiform ones showed various shapes, sizes, and orientations and were rarely present on th e unoperated control side of the lingual dorsum. Sections of the filif orm-like papillae revealed that they had no taste buds. These findings suggest: (1) Morphogenesis and structural maintenance of the fungifor m papillae require the presence of the chorda tympani and/or lingual n erve. (2) Completion of differentiation and maturation differ in time among fungiform papillae. (3) Fungiform papillae may be transformed fi liform papillae induced and maintained by a neurotrophic factor or fac tors coming from the chorda tympani and/or lingual nerve. (4) Fungifor m papillae are rarely innervated contralaterally.