Spontaneous Extraskeletal Osteosarcoma in the Stomach of an Aged F344 Rat

Extraskeletal osteosarcoma is a very rare tumor in humans and animals including rats. This paper describes a case of extraskeletal osteosarcoma observed in the glandular stomach of an aged female Fischer 344 rat. Grossly, a whitish solid mass was observed at the greater curvature of the glandular stomach. Histologically, the tumor consisted of both atypical polygonal and pleomorphic spindle-shaped cells, with pleomorphic nuclei, and it contained variable amounts of osteoids and small clumps of mature bone tissue. In addition, mitotic figures were frequently observed. Neither invasion of the muscle layer or vessels in the stomach nor metastasis to distant organs was detected. There were no skeletal tumors in the body. Immunohistochemically, the tumor cells were positive for osteocalcin, osteonectin, vimentin and S-100 protein. Judging from these results, the present tumor was diagnosed as extraskeletal osteosarcoma. This is the first report of spontaneous extraskeletal osteosarcoma arising from the stomach in a rat

Ocular lesions induced in infant rats by busulfan

Although busulfan, a bifunctional alkylating agent, is known to induce cataracts in infant rats, the full nature of busulfan-induced ocular lesions has not yet been shown. In order to clarify this point, 6-day-old rats were treated with a single dose of 20 mg/kg busulfan and the ocular tissue was histopathologically and immunohistochemically examined at 1, 2, 4, 7 and 12 days after treatment (DAT). As a result, in the nuclear layer (NL) of the peripheral retina, apoptotic cells significantly increased at 1 DAT and peaked at 2 DAT when cell proliferating activity was depressed. At 4 DAT, the NL showed wavy deformation with formation of rosette-like structures, and these changes progressed prominently at 12 DAT. In addition, a significant reduction in the retinal thickness due to decreased thickness of NL or inner NL was detected at 2 and 4 DAT. On the other hand, in the germinative zone of the lens equator, apoptotic lens epithelial cells significantly increased from 2 to 7 DAT, resulting in partial loss of lens epithelial cells at 7 and 12 DAT. At 12 DAT, prominent swelling and vacuolation of lens fibers were observed in the area from the equatorial zone to the posterior pole, indicating the development of cataract. The present results strongly suggest that prominent apoptosis in component cells was the initial and essential event underlying the developpment of busulfan-induced ocular lesions in infant rats