Journal of Neuroscience, Vol 8, 64-72, Copyright © 1988 by Society for Neuroscience
Developmental decrease in size of peripheral receptive fields of single chorda tympani nerve fibers and relation to increasing NaCl taste sensitivity
T Nagai, CM Mistretta and RM Bradley
Department of Oral Biology, School of Dentistry, University of Michigan, Ann Arbor 48109.
During development in rats, sheep, and humans, the taste system acquires
increasing responsiveness to NaCl, compared with a variety of other salts
and chemicals. To better understand the neural basis of changes in salt
taste responses, we studied receptive field size and response properties of
single chorda tympani nerve fibers in fetal, perinatal, and postnatal
sheep. Individual fungiform papillae were stimulated electrically with 5
microA anodal current to determine the location and number of papillae in
receptive fields. Response characteristics of NH4Cl, NaCl, and KCl were
determined for the entire field. Receptive fields were dissected for later
histological reconstruction and taste bud identification. Median receptive
field size decreased during development. Field sizes in lambs were smaller
than those in younger animals. This decrease was accompanied by an increase
in the NaCl/NH4Cl response ratio of single fibers and an increase in the
proportion of fibers and associated fields that responded with higher
frequency to NaCl, compared with NH4Cl. In addition, for fibers across all
age groups, receptive field size correlated negatively with the NaCl/NH4Cl
response ratio; that is, fields most responsive to NaCl had fewer papillae
than those most responsive to NH4Cl. For all fibers, receptive field size
correlated with response frequencies to NH4Cl and KCl but not NaCl. For
NaCl-best fibers, receptive field size correlated with the response
frequencies to all 3 salts. There was no relation between number of taste
buds in a single fungiform papilla and the response frequency elicited
during electrical stimulation of the papilla.(ABSTRACT TRUNCATED AT 250
WORDS)