Gross vascularization of experimentally induced transplanted tumors of the central and peripheral nervous system

Chemical carcinogenesis in the nervous system: past and future

The model of experimental tumors of the nervous system has greatly contributed to our understanding of growth and management of intracranial tumors, but has been somewhat neglected in the last years, because a wealth of new data concerning oncogenic action came from viral oncogenesis. These new issues led to a much better insight into human tumor induction and promotion. Yet one example of the impact of oncogenic transformation stems from the "neurooncogenic" model: the discovery of the neu oncogene and its product as a putative differentiation receptor in the cell membrane of experimental Schwann cell derived tumors. In the light of this unique finding the history of the "neurooncogenic" model and the morphological and "clinical" result of tumors produced within the model are reviewed. There is a large open field for future investigation both in basic and applied science.

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.

In vivo 31P and 2H NMR [corrected] studies of rat brain tumor pH and blood flow during acute hyperglycemia: differential effects between subcutaneous and intracerebral locations

Surface coil NMR spectroscopy was used to monitor the hyperglycemia-induced alterations in pH and blood flow in vivo in C6 gliomas implanted both subcutaneously and intracerebrally in rats. Tumor pH was calculated from the chemical shift difference between PCr and Pi in the 31P NMR spectra. Subcutaneous glioma pH decreased 0.8 units by 1 h after intraperitoneal administration of an aqueous 50% glucose solution (6 g glucose per kg body weight). In contrast, hyperglycemia failed to significantly alter the pH of intracerebral gliomas which were monitored for 90 min following administration of glucose. Tumor blood flow (TBF) was determined both pre- and post-glucose administration using deuterium NMR by monitoring the time course of D2O washout following intratumoral injection of saline D2O. Subcutaneous and intracerebral TBF were found to have an average change of -78.1% (range -47.4 to -93.3%, n = 5) and -21.1% (range +6.0 to -37.8%, n = 9), respectively. In addition, laser Doppler blood flow measurements of rat skin and subcutaneous glioma revealed a dramatic reduction in blood flow in both tissues following glucose administration. These results indicate that the effects of acute hyperglycemia are site dependent and that hyperglycemia alone is not beneficial for inducing intracellular acidosis in intracerebral tumors.

Perineurium originates from fibroblasts: demonstration in vitro with a retroviral marker

A cellular sheath, the perineurium, forms a protective barrier around fascicles of nerve fibers throughout the peripheral nervous system. In a study to determine the cellular origin of perineurium, a culture system was used in which perineurium forms after purified populations of sensory neurons, Schwann cells, and fibroblasts are recombined. Before recombination, the Schwann cells or the fibroblasts were labeled by infection with a defective recombinant retrovirus whose gene product, beta-galactosidase, is histochemically detectable in the progeny of infected cells. Perineurial cells were labeled when fibroblasts had been infected but not when Schwann cells had been infected. Thus, perineurium arises from fibroblasts in vitro and, by implication, in vivo as well.

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.

Experimental brain tumors and edema in rats. II. Tumor edema

Experimentally induced brain tumors in rats with the morphological characteristics of low differentiated gliomas were investigated with special consideration of the distribution of extravasated serum proteins within the tumor itself. Protein extravasation across tumor vessels occurs by pinocytotic vesicles which enclose serum proteins at the luminal surface of the endothelial cells. These vesicles move to the abluminal cell surface where proteins are released after fusion between vesicles and the cell membrane. Serum proteins then spread through the extracellular space from where they are taken up in tumor cells by pinocytosis. They are then transmitted to and digested by lysosomes in which acid phosphatase activity could be demonstrated. Tracer studies (human serum albumin, horseradish peroxidase) revealed that proteins reach the lysosomes 15 min after systemic application. The cellular content of tracers is variable even when systemic circulation has lasted 120 min.

The vasculature of experimental brain tumours. Part 2. A quantitative assessment of morphological abnormalities

Two groups of the morphological abnormalities of brain tumour vasculature described in the previous paper (Deane and Lantos 1981) were quantified. First, blood vessel density, endothelial hyperplasia and endothelial cytology, 3 general features of the vasculature, were assessed, giving a score according to the Microscopic Angiogenesis Grading System (Brem et al. 1972). This not only gives information about the vascular supply of tumours but also often provides a reliable index of malignancy. The system was also adapted for electron microscopy. Secondly, 3 specific features of the endothelial lining were estimated: cytoplasmic vesicle content, fenestrations and abnormal endothelial intercellular junctions, which are thought to represent possible mechanisms of increased trans-endothelial transport. It was found that cytoplasmic vesicle content was 3--6-fold greater in tumour blood vessels than in capillaries from normal brain, and may therefore play an important role in cerebral oedema. However, fenestrations and abnormal endothelial junctions were infrequently seen, and were unevenly distributed.

Evaluation of vasogenic edema in experimental brain tumors by cathodoluminescence and fluorescence microscopy

Cathodoluminescence and fluorescence microscopy have been used to study vasogenic edema in experimentally induced brain tumors in rats. Both methods are suited for the demonstration of FITC- or TRITC-coupled antiserum, and thus allow the evaluation of serum protein extravasation. Cathodoluminescence is more time consuming and laborious than fluorescence microscopy, but it has distinct advantages: Contrast enhancement improves the differentiation between certain cell types, and the higher resolution of the scanning electron microscope allows the identification of subcellular regions which cannot be recognized by conventional fluorescence microscopy.

Experimental brain tumors and edema in rats. I. Histology and cytology of tumors

In this study an experimental intracerebral tumor has been investigated with special consideration of structures, which may be involved in edema production and/or resolution. For this purpose a cloned tumor cell line (RG1 2.2) has been injected stereotactically into the brain of BD-IX rats. The tumor has some characteristics in common with low differentiated oligodendroglioma in men. A honeycomb architecture may be seen in the center of the tumor. It is built up by rounded or elongated cells, which can be impregnated in parts. In the central area, cells exhibit a voluminous digestive apparatus, composed of dictyosomes, vesicles, and some vacuoles with a membranaceous or homogeneous content. Tumor cells in the periphery show large processes and a small digestive apparatus. The sinusoidal tumor vessels are composed of an endothelium with many vesicles but no openings.

The vasculature of experimental brain tumours. Part 1. A sequential light and electron microscope study of angiogenesis

The process of vascularisation was studied in transplanted astrocytomas in BD-IX rats. The development of blood vessels was followed from the earliest signs of angiogenesis throughout tumour growth. On the basis of tumour vasculature, 3 consecutive stages of tumour growth could be distinguished; avascular, early vascular and late vascular. The tumours grew to a diameter of about 1 mm during the avascular stage after which new capillary sprouts began to penetrate the tumours. This resulted in an homogeneous vasculature of small immature capillaries up to about 5 micrometers in diameter characteristic of the early vascular growth stage. During this stage the tumours reached a diameter of about 4 mm and their vasculature consisted of capillaries similar to those seen in embryological cerebral vascularisation. During the subsequent late vascular stage of growth, continued endothelial proliferation led to an increase in blood vessel diameter up to 50 micrometers in some cases. The vessels varied in shape and size; this vascular pleomorphism and the abnormal morphological features associated with glioma vasculature were typical of the late vascular stage.

Significance of experimental models in neurooncology

Three models are induced for the production of brain tumors: Carcinogenic viruses, topically applied carcinogenic hydrocarbons and so-called resorptive carcinogens, mostly alkylating substances. The usefulness of these models for questions in human neurooncology depends upon similarity relation between model and original, i.e. the human brain tumor, both regarding the induction mode and the morphological result. In the last years the model with resorptive carcinogens has been broadly used. This model is suitable for questions concerning the mechanisms of action of carcinogenic substances and the formal pathogenesis of brain tumors. It seems less appropriate for other investigations: The growth behavior and its possible influence may be better studied with standardized tumor models. Such derived models are described in this paper and their usefulness for investigations especially concerning the chemotherapy of brain tumors is discussed.

Scanning electron microscopy of in vitro grown cells from experimentally induced neurogenic tumors

Serially transplanted neurogenic tumors of experimental origin were explanted in vitro and analyzed by scanning electron microscopy. In explants of intracerebrally transplanted gliomas, small stellate cells with branching processes were observed; in transplanted tumors of the peripheral nervous system, slender bipolar cells as well as fibroblasts emerged. The stereoscopic features were compared with the picture of conventional light microscopy. The findings are consistent with the assumption of the glial derivation of CNS-tumors induced with neurotropic alkylating carcinogens. The peripheral tumors are composed of Schwann-cell like elements and fibroblasts. The significance of the results for the cytogenetic derivation of brain tumors are discussed.