Quantitative relationships between taste bud development and gustatory ganglion cells.

To determine whether patterns of taste bud innervation change during postnatal rat development, the number of geniculate ganglion cells that innervate single taste buds were quantified in adult and developing rats. While there was a large variation in numbers of ganglion cells that innervate individual taste buds, there was a high degree of organization in the system. Namely, the number of labeled geniculate ganglion cells innervating a taste bud was highly correlated with the size of the taste bud. This relationship between taste bud size and number of innervating ganglion cells develops over a prolonged postnatal period and is not established until postnatal day 40 (P40), when taste buds reach their adult size. In a second series of experiments, we sought to determine whether neural rearrangement of chorda tympani neurons is responsible for the development of this relationship by double-labeling single taste buds at different ages. We found that the number of ganglion cells innervating individual taste buds on P10 predicts the size that taste buds become by P40. This finding suggests that neural rearrangement is not responsible for establishing the relationship between taste bud size and the number of innervating ganglion cells during development. More importantly, it strongly suggests that the 'neural template' for the mature innervation pattern is determined during early postnatal development.