INNERVATION OF SINGLE FUNGIFORM TASTE BUDS DURING DEVELOPMENT IN RAT

To determine whether the innervation of taste buds changes during post natal development, the number of geniculate ganglion cells that innerv ated single fungiform taste buds were quantified in the tip- and midre gions of the tongue of adult and developing rats. There was substantia l variation in both the size of individual taste buds and number of ge niculate ganglion cells that innervated them. Importantly, taste bud m orphology and innervation were highly related. Namely, the number of l abeled geniculate ganglion cells that innervated a taste bud was highl y correlated with the size of the taste bud (r = 0.91,P<.0003): The la rger the taste bud, the more geniculate ganglion cells that innervated it. The relationship between ganglion cell number and taste bud volum e emerged during the first 40 days postnatal. Whereas there was no dif ference in the average number of ganglion cells that innervated indivi dual taste buds in rats aged 10 days postnatal through adulthood, tast e bud volumes increased progressively between 10 and 40 days postnatal , at which age taste bud volumes were similar to adults. The maturatio n of taste bud size was accompanied by the emergence of the relationsh ip between taste bud volume and number of innervating neurons. Specifi cally, there was no correlation between taste bud size and number of i nnervating geniculate ganglion cells in 10-, 20-, or 30-day-old rats, whereas taste bud size and the number of innervating ganglion cells in 40-day-old rats were positively correlated (r = .80, P<.002). Therefo re, the relationship between taste bud size and number of innervating ganglion cells develops over a prolonged postnatal period and is estab lished when taste buds grow to their adult size. J. Comp. Neurol. 398: 13-24, 1998 (C) 1998 Wiley-Liss, Inc.