Alterations in taste responses by histopathological changes of the rat tongue induced by DMBA treatment

Abstract

Temporal or acute effects on the sensations of rat tongue with treatments of DMBA (9, 10-dimethyl-1, 2-benzanthracene) known as a strong carcinogen were studied electrophysiologically. Pathological investigations of the tongue treated with DMBA were also performed. Two to 8 weeks after DMBA injection under the tongue mucosa resulted in deep defects, induration and inflammation at the injected area. Taste responses to 0.01 M HCI from chorda tympani nerve increased significantly only when the mucosa showed induration. Erosion appeared within 1 week after periodical treatments by 5% DMBA with traumatic irritation (3 times/week), that turned to ulcer within 3 or 4 weeks. Eight weeks later, it showed rough surface, and then it was covered with whitish plaque after 12 weeks. Histologically, slight dysplasia was observed in the mucosal layer under the whitish plaque. These histological observations indicated that transformation of the tongue tissue in this study may be a precancerous condition. Chorda tympani nerve responses to 0.5 M sucrose treated by 5% DMBA with traumatic irritation were irreversibly decreased in 2 weeks. This irreversible effect on sucrose response might be caused by pathological changes of the tongue surface; speculatively, DMBA might interfere with the reproduction of sucrose receptor protein on the taste cell membrane. In contrast with sucrose, the magnitude of taste responses to 0.01 M HCl applied to the ulcerous tongue increased significantly. This fact suggested that taste nerve in the mucosal layer was directly stimulated by acid solutions as a result of the increase in membrane permeability caused by the inflammation. Tactile sensitivity from the lingual nerve was reversibly diminished in erosive or ulcerous tongue area, where the nerve itself might be damaged by DMBA treatments. In conclusion, it is apparent that histological changes of the tongue caused by DMBA treatment selectively altered the taste responses.