Morphology of chorda tympani fiber receptive fields and proposed neural rearrangements during development

The average number of fungiform papillae in receptive fields of single chorda tympani nerve fibers decreases during development in sheep, and a greater proportion of small receptive fields that are highly responsive to NaCl, compared with NH4Cl, is acquired. To learn whether there also are developmental differences in the number of taste buds within the papillae in mapped receptive fields, we studied the morphology of receptive fields and fungiform papillae, and also counted fibers in the chorda tympani nerve, in fetal, perinatal, and postnatal sheep. Whether defined as the number of fungiform papillae or as the number of taste buds within papillae, receptive fields of chorda fibers decrease developmentally. Initially, however, there is an increase, and subsequently a decrease, in the number of taste buds per field. The differences in field size cannot be attributed to developmental alterations in numbers of fungiform papillae because the total number of papillae on the tongue remains constant. The average number of taste buds per papilla, however, also increases and then decreases, and the increase in perinatal animals is accompanied by the appearance of large, multipored taste buds. Because there is a significant relation between fungiform papilla size and number of taste buds in the papilla, papilla size could be one regulating factor for taste bud number. Furthermore, the number of chorda tympani nerve fibers apparently increases up to perinatal stages and then decreases postnatally, providing another potential regulating factor for the number of taste buds.(ABSTRACT TRUNCATED AT 250 WORDS)