Journal of Neuroscience, Vol 7, 2075-2080, Copyright © 1987 by Society for Neuroscience
A sensitive period for the neural induction of taste buds
MA Hosley, SE Hughes, LL Morton and B Oakley
Taste buds mature postnatally in the vallate papilla of the rat and reach a
mean number of 610 by day 90. Although taste buds are neurotrophically
dependent, the presence of widespread bilateral innervation permits more
than 80% of the 610 vallate taste buds to survive after one IXth nerve is
removed in adults. However, after a IXth nerve is removed at 0-3 d
postpartum, about two-thirds of the vallate taste buds fail to develop. In
the present investigation, the timing of the neural induction of taste buds
was examined by unilaterally removing the IXth nerve at 12 different
postnatal ages, from 0 to 75 d. Unilateral denervation revealed the
existence of a sensitive period that is maximal from 0 to 10 d, when
unilateral or bilateral interruption of the IXth nerve profoundly impairs
the formation of taste buds. The number of taste buds that form is
nonlinearly dependent upon the number of axons; at low levels of
innervation, a doubling of the number of myelinated axons quintuples the
number of taste buds. Thus, taste axons interact synergistically. In
studying regeneration, we found that axons of both neonatal and adult IXth
nerves elongate approximately 1.8 mm/d. Taste buds were re- formed more
rapidly and a higher proportion were bilaterally innervated when
regenerating axons and the sites of former taste buds were numerous. The
proportion of bilaterally innervated taste buds could be approximated from
the likelihood of random overlap of axons from the right and left IXth
nerves. The greater ease with which taste buds are re-formed than developed
suggests that taste bud regeneration does not recapitulate taste bud
development.