EXPRESSION OF THE NEURAL CELL-ADHESION MOLECULE (NCAM) AND POLYSIALICACID DURING TASTE BUD DEGENERATION AND REGENERATION

Taste receptor cells are replaced throughout life, accompanied by cont inuing synaptogenesis between newly formed taste cells and first-order gustatory fibers. The neural cell adhesion molecule (NCAM) is express ed by a subset of taste cells in adult rodents and appears on gustator y nerve fibers during development prior to differentiation of the tast e buds. We employed antibodies against the extracellular domain of the NCAM polypeptide (mAb 3F4) and against polysialic acid (PSA) residues found on embryonic forms of NCAM (mAb 5A5) to investigate the relatio nship between the expression of these molecules and the innervation of taste buds in adult rats, In unoperated rats, anti-NCAM recognized a subset of cells within the vallate taste buds and also the fibers of t he glossopharyngeal (IXth) nerve, including those innervating the gust atory epithelium. Taste bud cells did not express PSA but mAb 5A5 immu noreactivity was observed on some fibers of the IXth nerve, including a few that entered the taste buds. Bilateral crush of the IXth nerve r esulted in the loss of NCAM expression from the gustatory epithelium w ithin 8 days. As IXth nerve fibers reinnervated the epithelium, NCAM e xpression was seen first in the nerve, followed by increased expressio n in the epithelium as the taste cells differentiated from their precu rsors. PSA expression by fibers of the IXth nerve did not return to no rmal until well after the regeneration of the vallate taste buds. The present results demonstrate that taste cell expression of NCAM is depe ndent upon innervation by the IXth nerve and that NCAM expression appe ars in the nerve prior to its expression in the differentiating epithe lium during regeneration. The occurrence of a similar temporal sequenc e in the developing taste system suggests that NCAM could play a role in cell-cell interactions that are important for the differentiation o f the taste epithelium. Ongoing taste cell turnover and synaptogenesis between IXth nerve fibers and newly differentiating taste cells also requires recognition and adhesion, in which NCAM could play a role. (C ) 1994 Wiley-Liss, Inc.