S-100 PROTEIN AND GLIAL FIBRILLARY ACIDIC PROTEIN (GFAP) IN EXPERIMENTALLY-INDUCED AND SPONTANEOUS TUMORS OF PERIPHERAL-NERVES IN BDVI RATS- LIGHT-MICROSCOPIC AND IMMUNOHISTOCHEMICAL STUDY

Twenty-five ethylnitrosourea (ENU) induced and 24 spontaneous tumours of peripheral nerves as well as 28 spontaneous mesenchymal tumours in BDVI rats were studied by light microscopy and immunohistochemically f or the presence of S-100 protein (S-100). Early ENU induced schwannoma s representing the thickenings of nerves showed weak or negative S-10 0 immunoreactivity. S-100 positivity (both in the cytoplasm and nucleu s) was observed in all large ENU-induced tumours found in animals dyin g or killed at advanced age. Immunostaining was present in both cystic and solid areas of schwannomas. S-100 positivity was found in 20 of 2 4 spontaneous schwannomas: 14 of 20 positive tumours contained cysts. Twenty-seven schwannomas (12 ENU-induced and 15 spontaneous) were stud ied for the presence of glial fibrillar acid protein (GFAP) and 13 wer e positive (7 had cystic areas). GFAP-positivity was relatively high i n 4 tumours (3 ENU-induced and 1 spontaneous); these tumours also show ed intense S-100 reactivity. Immunoreactivity for S-100 occurred more frequently and was much more intense than that for GFAP. The incidence of spontaneous peripheral nerve tumours in BDVI males reached 4 %, cy stic schwannomas being the most frequent type. All spontaneous mesench ymal tumours except lipoma (S-100 positive) were negative for S-100 pr otein and for GFAP.