Morphometric and immunocytochemical assessment of fungiform taste buds after interruption of the chorda-lingual nerve.

Unilateral interruption of the chorda-lingual nerve led to a loss of most epithelial axons and to the deterioration of fungiform taste buds in the anterior portion of the tongue of albino rats, mongolian gerbils, and golden hamsters. By three weeks after surgery the following percentages of fungiform taste buds had completely disappeared: 71% in gerbils, 28% in rats, and 26% in hamsters. Residual taste buds were classified into two groups: atrophic taste buds and taste bud remnants. Atrophic taste buds were smaller than normal and typically had no visible taste pore, although they retained the characteristic oval shape of a taste bud and numerous elongated cells. Taste bud remnants were non-oval fragments of taste buds with few elongated cells. Specific markers for elongated taste cells (monoclonal antibodies to keratin 19) confirmed that atrophic taste buds, as well as some taste bud remnants, had elongated taste cells. By 180 days after chorda-lingual nerve transection, 44% of rat fungiform taste buds had disappeared; morphometric analysis of the 311 residual taste buds established that 241 atrophic taste buds and 69 taste bud remnants were, respectively, 50% and 75% smaller than the average volume of 480 normal taste buds. The aggregate loss of gustatory tissue, calculated from the shrinkage of residual taste buds and the volume lost by the outright disappearance of many taste buds, was 88% for gerbils, 72% for rats, and 65% for hamsters. Evaluation in gerbils of the co-occurrence of taste buds and axons suggests residual taste buds were neurotrophically supported. Every gerbil fungiform papilla that lacked axons lacked a taste bud.(ABSTRACT TRUNCATED AT 250 WORDS)