During the process of developing of the ICR-cataractous rat as an established strain, a substrain was found, which showed an early occurrence of thymus atrophy accompanied with the skin lesions. In order to make an elementary elucidation on the constitutional factors of these disorders, we observed changes in the weight and the organ/body weight ratio of thymus and histological findings of it as well as of the skin.
An accelerated process of the thymus atrophy was sho wn at the early stage of two months age in both sexes, especially in the males, being more significant after the age of three months. In regard to the histological findings, a significant atrophy of the thymus parenchyma including its cortex, was observed, being consistent with those of the organ weight or the organ/body weight ratio. At five months of age, the thymus parenchyma was completely replaced by swollen lymph nodes in some cases.
After two months of age, there appeared also the encrusted or erosive skin lesions occurring symmetrically in the cervical (including retro- or subauricular regions), the scapular and besides the dorsal regions (except the lumbar region). They could be, in part, ascribed to secondary scratching effects. However, we simultaneously observed, on the histological level, characteristic lesions such as a significant acanthosis of the epidermis especially around the hair follicles, as well as thickening of the keratohyalin zone and hyper-, para-keratosis, slight to moderate spongiosis, extension of the inflammatory infiltrate into the epidermis, inflammation of the dermal zone, hyperplasia of the sebaceous glands and perifolliculits, especially showing infiltration of mononuclear cells into the follicular region. These lesions may be regarded as a disease entity of “dennatitis” because they showed a marked similarity with the atopic or seborrheic dermatitis seen in humans. Therefore, the ICR/d-strain rat may be useful as a good disease model for elucidating the occurrence mechanisms of such dermatItis.