Ultrastructural findings in so-called ependymal rat tumors induced by transplacental administration of ethylnitrosourea (ENU)

Evidence for an origin of ethyl-nitrosourea-induced rat central nervous system tumors from pluripotent germinal neuroepithelium

Brain tumors induced by transplacental application of ethyl-nitrosourea (ENU) in F344 rats were immunohistochemically demonstrated to consist of undifferentiated cells, astriocyte-like cells, oligodendroglia-like cells, and two distinct types of vimentin-expressing cell groupings termed as perivascular small cell nests (PSCNs) and large cell nests (LCNs). Co-distribution of vimentin and glial fibrillary acidic protein (GFAP) was sparsely observed in the astrocyte-like cells, which suggested an immature glial phenotype. PCSNs contained cells expressing GFAP, neuron-specific enolase (NSE), beta-tubulin isotype III, and low-affinity nerve growth factor receptors (LNGFRs). LCNs contained cells showing a neuronal phenotype with expression of low- and middle-molecular mass neurofilament proteins (NF-L and -M) as well as NSE, beta-tubulin isotype III and LNGFR. Double-labelling immunohistochemistry revealed the NF-L-expression in LNGFR-positive LCN-forming cells. Oligodendroglia-like cells and their intercellular neuropil-like structures expressed beta-tubulin isotype III, synaptophysin and NSE, in addition to the expressions of vimentin and GFAP. Electron microscopically, synapse-like structures were formed between these oligodendroglia-like cells and their dendritic processes. Topographically, bidirectional cell transitions from PSCNs to astrocytes and LCNs were indicated. The present study strongly suggests that so-called ENU-induced "gliomas" originate from pluripotent germinal neuroepithelium. Furthermore, LNGFR expression may be responsible for acquisition of neuronal phenotype in these tumors.

Immunohistochemical investigations in experimentally induced tumors of the nervous system

35 tumors of brain, spinal cord and cranial and peripheral nerves were induced with ENU (ethyl-nitrosourea) in the offspring of treated BD-IX pregnant rats. 36 tumors--35 of the nervous system, one nephroblastoma--were observed in 14 rats. With these results, the number of experimental nervous system tumors of the own collection induced in BD-IX rats and classified next to the rules of human neurooncology, amounts to 2,216. All 35 tumors of the nervous system were treated by a panel of immunohistochemical reactions comprising antibodies against cytoskeleton intermediary filaments such as GFAP (glial fibrillary acid protein), neurofilament proteins, vimentin and cytokeratins and some nervous system antigens such as NSE (neuron specific enolase), MBP (myelin basic protein) and S-100 protein. In central tumors, considered to be malignant gliomas, focal reactivity against vimentin and GFAP was found. Expression of other tested markers was weak or absent. In neurinoma of trigeminal and peripheral nerves, reactivity to S-100 antigen was lacking, whilst there was strong reaction to the vimentin antigen.

Glomeruloid blood vessels in ethylnitrosourea-induced rat gliomas. Histological and immunohistochemical studies

Glomeruloid blood vessels (GBVs), a characteristic histological feature of most human malignant gliomas, were recognized with high incidence in autochthonous rat gliomas induced by transplacental administration of ethylnitrosourea. To evaluate some of the biological properties of these GBVs, we carried out a study using histological methods and immunohistochemical staining for glial fibrillary acidic protein, factor VIII-related antigen (VIII Ag) and bromodeoxyuridine (BrdUrd). Of 22 animals with large, massively growing gliomas in the CNS, GBVs including conglomerate aggregations of small blood vessels with endothelial hyperplasia and strong VIII Ag expression were observed in 13 large gliomas histologically consisting of primitive neuroepithelial neoplasms (PNN; so called ependymoma) and mixed-type gliomas in combination with astrocytoma and PNN or anaplastic astrocytoma. The anaplastic gliomas in our series were devoid of GBVs. These findings indicate that GBV formation takes place in a histological variety of experimental gliomas. Furthermore, the GBVs were frequently associated with the vasculo-mesenchymal stroma in the parent gliomas, suggesting an intimate relationship with the morphogenesis of GBVs. In addition, it was shown that the GBVs had a higher BrdUrd-labelling index than that of other blood vessels in gliomas and also that of neoplastic cells in most parent gliomas, except for anaplastic gliomas. Based on these results, the possible mechanism of GBV morphogenesis is discussed with regard to the roles of macromolecules in the induction and regulation of GBVs.

Chemical induction of brain tumors in rats by nitrosoureas: molecular biology and neuropathology

Nitrosourea-induced rat brain tumors are among the best investigated experimental systems for neuropathological, biochemical, diagnostic and therapeutic research in neurooncology. This review summarizes data concerning molecular biology, neuropathology, in vitro studies, transplantation models and antigen expression of experimental gliomas in inbred rat strains. Systemic application of nitroso-compounds, i.e., ENU and MNU, leads to the alkylation of DNA bases, which, due to a specific repair deficiency, persist in the nervous system remarkably longer than in other organs. The hypothesis is that alkylated bases cause base-mispairing and point mutations followed by uncontrolled expression of oncogenes and growth factor receptors, resulting in permanent cell proliferation. Thus, nitrosoureas are considered to be biological hazards, especially as potent endogenous and exogenous neurotoxins. Neuropathology and growth characteristics of these experimental tumors are comparable to human malignant gliomas. Similar to the human WHO grade III and IV tumors, they reveal cellular pleomorphism, elevated mitotic activity, proliferation of blood vessels, blood-brain barrier disturbances, necrosis and invasiveness. Nitrosourea-induced brain tumors have been used in investigations concerning glioma growth and regression, brain edema, glioma immunology, metabolism, regional biochemistry, and experimental therapy. The studies included conventional morphology, immunohistochemistry, -cytochemistry and -electronmicroscopy, morphometry, cell culture, hybridoma technology, tumor transplantation and regional imaging by autoradiography, bioluminescence, magnetic resonance and immunoscintigraphy.

Expression of vimentin and glial fibrillary acidic protein in ethylnitrosourea-induced rat gliomas and glioma cell lines

The expression of glial fibrillary acidic protein (GFAP) and vimentin was investigated immunohistochemically in 104 experimental gliomas induced by transplancental application of ethylnitrosourea (ENU) in CDF rats. Immunoreactivity for vimentin was prominent in many astrocytic tumor cells and especially in small glioma cells forming anaplastic medulloblastoma-like foci in many tumors. The majority of tumor cells in oligodendroglial tumors were vimentin negative, except for some of the large polymorphous oligodendrogliomas which contained intermingled vimentin positive glioma cells. GFAP immunoreactivity was detectable only in a low fraction of tumor astrocytes and in a few exceptional cases some oligodendroglial tumor cells stained positive. Immunohistochemistry with antibodies against neurofilaments and cytokeratins revealed no staining in tumor cells of ENU-induced gliomas, while all oligodendrogliomatous tumors stained positive for HNK-1. Immunocytological and immunoblot investigations of the two rat glioma cell clones RG2 and F98, which are both derived from ENU-induced gliomas, showed a prominent expression of vimentin in monolayer cultures and in syngeneic intracerebral transplantation tumors. F98 additionally demonstrated a fraction of GFAP positive cells especially in confluent cultures and in intracerebral tumors. RG2, on the other hand, exhibited virtually no GFAP immunoreactivity in culture but showed individual GFAP positive tumor cells in intracerebral tumors. Our results revealed a more precise picture of the cellular differentiation in ENU-induced rat gliomas and in two widely used glioma cell lines. They underline the heterogeneity of experimental rat gliomas which may comprise cells at different stages of differentiation towards oligodendroglial or astroglial phenotype.

Establishment and characterization of an intracerebrally transplanted tumor line, induced experimentally in the spinal cord

Transplanted tumor lines are useful to study open questions in human pathology and clinical research, particularly with the evaluation of therapeutic measures. Transplantation tumor lines derived from neoplasms in the nervous system originally induced with resorptive carcinogens are considered to be useful for these purposes. In this study observations on the histological pattern of original and intracerebrally transplanted new induced spinal cord tumors, mainly in early passages, has been investigated with the aim to improve the usefulness of the experimental model.

Morphology of early stages of ENU-induced brain tumors in rats

Tumors were induced in experimental animals in order to investigate early tumor growth with conventional histology and gliofibrillary acid protein (GFAP) demonstration with the peroxidase-antiperoxidase (PAP) method. In one experiment, the animals were killed after transplacental ENU administration, when microtumors were suspected; in the second experiment, the animals were followed up to their natural death and microtumors found at random were used for analysis. Conventional histology revealed 3 types of microtumors: growth restricted to the subventricular matrix, growth in the neighbourhood of the ventricles with obvious or probable connection to the ventricular zones and small tumors observed exclusively in the white matter. The latter tumors by conventional staining were composed of small round cells, considered to be oligodendrocytes. They did not contain GFA-protein positive cells within the tumor. The tumor in presumable and visible connection with the ventricular lining did contain GFAP-positive astrocytes. In the very small subventricular tumors, the small round cells (oligodendrocytes) were in continuous contact with the identical interfascicular glial cells, while GFAP positive astrocytes seemed to stem from the subventricular astrocytes (tanycytes, ependymoglia). The ependyma itself was always preserved. A twofold origin of these experimental tumors with probable development into one common cytological glial type is assumed.

Glial fibrillary acidic protein (GFAP) in rat brain tumors transplacentally induced by ethylnitrosourea (ENU)

The immunohistochemical distribution of glial fibrillary acidic protein (GFAP) in neoplastic lesions induced in the rat by ENU is reported. GFAP was present in hypertrophic reactive astrocytes, which were numerous in early neoplastic proliferations, in microtumors of the white matter, and in those collected at the periphery of large tumors. They were absent in cortical oligodendroglial foci and microtumors. No GFAP-positive cells were observed in hyperplasias of the white matter: astrocyte-like cells of large tumors were GFAP-negative. The significance of reactive astrocytes and the problem of the astrocytic component in transplacental ENU tumors are discussed.