Abstract
Gross and histopathological features of auricular chondritis in young Crj:CD(SD)IGS rats were examined. Although the rats were identified with metallic ear tags on the right pinnae, auricular chondritis was also observed on the contralateral (left) ear in some animals. Histopathologically, the lesions were characterized by granulomatous inflammation with destruction of the normal cartilaginous plate, formation of new cartilaginous nodules and osseous metaplasia. Proliferative cell nuclear antigen (PCNA) positive cells were present predominantly in chondrocytes found in the centre of the newly-formed cartilaginous nodules. The results suggest that the newly-formed cartilaginous nodules were due to interstitial proliferation of chondrocytes.