Occupational exposures and brain cancer mortality: a preliminary study of east Texas residents

The relationship between various occupational exposures and brain cancer was investigated in a case-control study using mortality data from 202 males who died in East Texas from gliomas in 1969-1978 and 238 male controls randomly selected from all deaths in East Texas in 1969-1978. Using the occupational classification scheme of the U.S. Bureau of the Census, the risk for brain cancer was significantly increased for male workers employed in the transportation, communication, and utilities industries [odds ratio (OR) = 2.26, confidence intervals (CI) = 1.18-4.32]. Further examination of this finding showed that male workers employed in occupations associated with electricity or electromagnetic (EM) fields had an elevated risk for brain cancer (OR = 3.94, CI = 1.52-10.20). In addition, there was a linear relationship between the probability of exposure to EM fields and brain cancer. Significantly elevated risk for brain cancer was also found among male workers in the trucking industry.

Intermediate filaments and anaplastic change of ENU-induced gliomass: immunohistochemical study with vimentin and astroprotein (GFAP)

To study the expression of two different subclasses of intermediate filaments in ethylnitrosourea-induced rat cerebral gliomas, the number of cells immunopositive for each subunit protein, vimentin and astroprotein (GFAP), was quantitatively analyzed. Vimentin is a subunit protein of non-specific intermediate filaments which appear transiently in immature glial cells, while astroprotein (GFAP) is a subunit protein of glial filaments, normally expressed in mature astrocytes. Although most normal astrocytes were negative for vimentin, many tumor cells showed weak to strong immunoreaction for vimentin. The expression of vimentin was more frequent and intense in anaplastic forms of gliomas than in benign forms. Accordingly, the vimentin/GFAP ratio [the number of vimentin-positive cells divided by the number of astroprotein (GFAP)-positive cells] was increased from 0.23 to 1.86, and from 0.26 to 1.85, respectively, as oligodendrogliomas and mixed gliomas become anaplastic. The present study demonstrated that the immunohistochemical study for those two subclasses of intermediate filaments can provide important informations on the cell biological nature of glial tumors.

Gliosarcoma with chromosome abnormalities in a neonate exposed to heptachlor

A neonate with a cerebral gliosarcoma was found to have chromosome abnormalities in tissue culture of the tumor, but normal karyotyping of peripheral blood. Similarities to and differences from chromosome abnormalities found in other human gliomas are noted. Unusual exposure of the child to heptachlor during prenatal development and the neonatal period suggests the need for further studies on the role of toxins in oncogenesis.

The effect of hyperosmotic blood-brain barrier disruption on blood-to-tissue transport in ENU-induced gliomas

Hyperosmotic blood-brain barrier disruption transiently increases the rate of blood-to-tissue transport of water-soluble compounds to normal brain and has been used in brain tumor patients to increase the delivery of chemotherapeutic drugs. This method remains controversial; debate concerns the extent to which it increases drug delivery to brain tumors. Ethylnitrosourea (ENU)-induced gliomas in rats have the lowest rate of blood-to-tissue transfer of the water-soluble compound alpha-aminoisobutyric acid of all experimental brain tumors studied to date. To gain further understanding about the effects of hyperosmotic blood-brain barrier disruption in brain tumors, we measured the unidirectional blood-to-tissue transfer constant of alpha-aminoisobutyric acid in ENU-induced brain tumors in rats after hyperosmotic disruption. Hyperosmotic blood-brain barrier disruption with 1.6 osmolar mannitol resulted in an averaged whole-tumor transfer constant of 0.013 +/- 0.003 (standard error) mL/(g/min), compared to a transfer constant of 0.007 +/- 0.002 mL/(g/min) for ENU-induced gliomas in the contralateral undisrupted hemisphere, a difference that was not significant. In contrast, hyperosmotic blood-brain barrier disruption produced a large and significant increase in the transfer constant of alpha-aminoisobutyric acid in tumor-free cortex (from 0.002 +/- 0.001 to 0.05 +/- 0.011 mL/[g/min]) and in tumor-free corpus callosum (from 0.001 +/- 0.003 to 0.017 +/- 0.005 mL/[g/min]). Hyperosmotic blood-brain barrier disruption does not appear to be an efficient method with which to increase the rate of delivery of water-soluble drugs to brain tumors but does result in a significant increase in the delivery rate of these drugs to normal brain tissue.

The intraneoplastic chemotherapy in a rat brain tumour model utilizing methotrexate-polymethylmethacrylate-pellets

In an experimental glioma model, using ethylnitrosourea induced and subsequently intracerebrally implanted tumours in BD-IX rats, the effectiveness of intratumoural application of methotrexate (MTX) by stereotactic implantation of polymethylmethacrylate (PMMA) pellets containing MTX, has been studied. Tumour volume 10 days after pellet implantation as well as survival rates of treated, untreated and control animals have been the criteria of the effect of treatment. Tumour volume was significantly smaller in treated compared to untreated animals. The survival rate of untreated to treated animals increased 150 and 233% respectively when compared with the control animals. Thus a positive therapeutic effect of MTX-PMMA pellet implantation in the experimental glioma could be proven. Possible consequences for the treatment of human gliomas are shortly discussed.

Promoting effect of 12-O-tetradecanoylphorbol-13-acetate on neurogenic microtumors initiated by transplacental exposure to N-ethyl-N-nitrosourea

The promoting effect of 12-O-tetradecanoylphorbol-13-acetate (TPA) on the occurrence of neurogenic microtumors in SD-JCL rats initiated transplacentally with N-ethyl-N-nitrosourea (ENU) was investigated. The treatment with TPA induced earlier occurrence of microtumors than as compared with the initiation alone. Thus, TPA has tumor-promoting activity on the formation of neurogenic microtumors in rats prenatally exposed to ENU.

Periphery of ethylnitrosourea-induced spinal gliomas in rats with special reference to the vascular structure

The histology and ultrastructure of ten spinal cord gliomas, mainly oligodendrogliomas, induced transplacentally in rat with ethylnitrosourea were studied. The characteristic feature of seven spinal tumours was distinct delineation of neoplastic tissue from the edematous surrounding zone by a ring of irregular, proliferating capillaries, among which immature capillary buds prevailed. The alterations were proliferation of endothelium with endothelial overlapping, elongation of interendothelial junctions and enhancement of pinocytotic vesicles on luminal and abluminal surfaces. The basal membranes, besides other changes, were often replaced by some floccular condensations. In the edematous zone the capillary walls were deprived of contact with glial processes. The lack of contact between astrocytic processes and vascular wall may contribute to the persistent immature state of peripheral capillaries.

Morphological and immunohistochemical evidence for the presence of subcortical target cells of N-ethyl-N-nitrosourea-induced cerebellar tumors in rats

Morphological and immunohistochemical studies of cerebellar tumor induction with neonatal administration of N-ethyl-N-nitrosourea (ENU) were conducted in four strains of rats and their hybrids, i.e., noninbred Wistar, Fischer (F344), Long-Evans, Wistar/Furth, and hybrids of Long-Evans and Wistar/Furth. Neonatal s.c. injection of 40 mg ENU/kg body weight produced 53 cerebellar tumors in 46 (8.4%) rats among 550 animals. There was no sex difference in the incidence (male = 9.6%; female = 7.0%). Histological examination showed that most of the tumors (83%) were oligodendrogliomas and the neoplastic cells were positively stained immunohistochemically with anti-Leu-7 monoclonal antibody. In examining the location of cerebellar tumors, 22 (42%) were located in the vermis, 11 (21%) in the hemisphere, 9 (17%) in the flocculus, 6 (11%) in the peduncle, and 5 (9%) in other sites. When their origins were examined in relation to their location to the internal granular layer of the cerebellum, 40 (75%) tumors were found just under the internal granular layer (subcortical region) and 9 (17%) in the white matter or cerebellar nuclei. Only 2 (4%) subependymal tumors were observed. Ontogenic study of the rat cerebellum revealed the presence of an aggregation of primitive glial cells in the subcortical region during the neonatal period, and the [3H]thymidine pulse-labeling index of these cells was 13.7%. Electron microscopic study showed the primitive nature of these cells and they reacted positively with anti-Leu-7 monoclonal antibody. These results indicate that cerebellar tumors are induced in an appreciable incidence with neonatal injection of ENU in rats and that cerebellar target cells in the subcortical region are present after ENU carcinogenesis.

Expression of c-sis and platelet-derived growth factor in in vitro-transformed glioma cells from rat brain tissue transplacentally treated with ethylnitrosourea

Long-term culturing of brain cells from neonatal BD-IX rats after transplacental treatment with N-ethyl-N-nitrosourea (ENU) results in malignantly transformed cells after a lag period of about 250 days. During culturing, the brain cells undergo a sequence of morphological changes. We examined oncogene expression in cultured cells from ENU-treated animals and found that transformed glioma cells differ from premalignant glial cells by containing high levels of c-sis transcripts. We also report that the transformed cells synthesize functional platelet-derived growth factor. Because glial cells have receptors for platelet-derived growth factor, we propose that an autocrine mechanism plays an important role in ENU-induced brain tumorigenesis.

Subcapsular renal transplantation of neurogenic tumors and tumor spheroids. A comparative study of RN6 and RG2 tumor clones after syngeneic and allogeneic transplantation

The subcapsular renal transplantation tumor model was explored to standardize the growth of rat RN6 neurinoma and RG2 glioma nitrosourea-induced clonal cell lines in syngeneic and allogeneic systems. Growth of RN6 and RG2 tumor spheroids was compared with that of solid subcutaneous tumor pieces transplanted under the renal capsule. Two morphometrical methods were applied to evaluate growth rates. Tumor specimens were examined histologically with regard to their morphology, extent of immune reactions, and development of tumor necroses. The take rate was 98%. In the syngeneic system linear progressive tumor growth was found, while in preirradiated allogeneic rats this was only the case up to 21 to 25 days post transplantation (p.t.). Strong rejection reactions in the allogeneic RN6 tumors were noted from 4 to 7 days p.t. resulting in total tumor rejection after 10 to 14 days. Both kinds of tumors, especially in the first days of growth, were characterized by strong desmoplastic reaction with rich reticulin fiber formation. However, after 10 days, in the center of RG2 subcapsular renal tumors (SRT) this kind of reaction was found only in the vicinity of tumor vessels, while RN6 SRT demonstrated reticulin fibers around tumor cells in all cases studied. The transplantation experiments revealed that the malignant RN6 and RG2 spheroids represent a suitable tool to study three-dimensional early tumor growth in both in vivo and in vitro cultures. The model of spheroid transplantation under the renal capsule is simple to handle and well reproducible. Compared with subcutaneous tumors the SRT model has advantages in early stages of tumor growth because the tumors are clearly visible grossly and can be easily submitted to adequate morphometry, indicating that this model may be suitable for experimental chemotherapy and radiotherapy studies.

Current brain tumour models with particular consideration of the transplantation techniques. Outline of literature and personal preliminary results

The most well known brain tumour models will be discussed. It is a series of animal experiments with an induced tumour and with heterologous and homologous transplantation. This work will deal especially with technical problems, which have not so far been satisfactorily resolved. With the aid of a stereotaxic operation method, the exactness of the technique of transplantation could be improved. The tumour contamination problem of the injection pathway as well as of the cerebral spinal fluid compartment is satisfactorily resolved. The authors have at their disposal a standardized cerebral glioma model in the rat in order to study the interstitial chemotherapy of brain tumours.

Effect of irradiation on ethyl nitrosourea induced neural tumours in Wistar rat

Wistar rats received 2 Gy whole body irradiation followed immediately by 10 mg/kg of ethyl nitrosourea (ENU) on the day of birth. Out of 33 rats which were given ENU alone 14 developed 22 tumours of the nervous system, out of which 15 (68.2%) were gliomas and 7 (31.8%) were Schwannomas. Out of 34 rats which were given both irradiation and ENU 12 were found to harbour 15 neural tumours out of which 14 (93.3%) were gliomas and 1 (7.1%) was a Schwannoma. The pretreatment with irradiation seems to have resulted in selective suppression of Schwannoma induction.

Cellular pharmacology of doxorubicin in sensitive and resistant rat glioblastoma cells in culture

We have studied the incorporation and cytotoxicity of doxorubicin in cultured rat C6 glioma cells grown as monolayers. Net incorporation was linear up to high extracellular concentrations of drug (10 micrograms/ml). Cytotoxicity was evaluated both by tritiated thymidine incorporation inhibition and cloning efficiency inhibition. For similar total drug exposures, cytotoxicity was very different according to the exposure time and the exposure dose; incubation with a low dose for a long time was much less cytotoxic than that performed with a high dose for a short period of time. We have obtained several clones of doxorubicin-resistant cells. As compared to the wild strain, these cells were characterized by a larger size, a slower growth, a reduced cloning efficiency and a differential sensitivity of 100-1,000 to doxorubicin. Net incorporation of doxorubicin was 5-fold reduced in these cells, due to an increased efflux of the drug. These cells provide an interesting model of doxorubicin-resistant solid tumor in culture.

The effect of dexamethasone on vascular permeability of experimental brain tumours

The vessels of experimental gliomas show an abnormally high permeability to small polar molecules, such as mannitol. To establish whether this change in vessel permeability is modified by treatment with the corticosteroid dexamethasone, the kinetics of [14C]mannitol transfer into rat astrocytomas were estimated in both steroid-and saline-treated, tumour-bearing animals. This was achieved by injecting [14C]-mannitol i.v., using a specially devised technique, so as to maintain a constant concentration of tracer in the blood plasma. In separate experiments steady levels of the tracer were maintained in the circulation from 1 to 30 min. Mean plasma and tumour radioactivity were measured, and the apparent transfer constant of mannitol across the vascular endothelium and the size of the extravascular extracellular mannitol space in the tumours were calculated. Despite a significant clinical improvement in the treated animals and adequate circulating levels of dexamethasone at the time of the permeability studies, no difference in either the apparent transfer constant for the movement of mannitol into the tumours or the fractional extracellular mannitol space was detected between these animals and the controls. With steroid treatment both tumour-bearing and non-tumour bearing animals lost weight, and in the latter there was no consistent change in routine biochemical or haematological parameters. It was concluded that under these conditions it is unlikely that clinical improvement with dexamethasone therapy was due to a non-specific reduction in tumour vessel permeability to polar substances.

[Immunohistochemical study of ethylnitrosourea-induced rat gliomas with vimentin and astroprotein (GFAP)]

Expression of two different types of intermediate filaments, vimentin filaments and glial filaments, was studied immunohistochemically in experimental rat gliomas. Although vimentin filaments are most commonly seen in mesenchymal cells, recent immunocytochemical study demonstrated that this type of filaments can be recognized also in glial cells during early cell differentiation and in tumor cells of epithelial origin. In the present communication, distribution of vimentin filaments in rat glial tumors was investigated and compared with that of glial filaments by using specific antiserum to each protein subunit, vimentin and astroprotein (GFAP). Ethylnitrosourea (50 mg/kg) was injected subcutaneously into 3 day-old Wistar rats. After four to ten months, brains of animals were removed, fixed in 95% ethanol and embedded in paraffin. Peroxidase-antiperoxidase method was carried out on 6 micron-thick sections. In normal portion of the brain, immunoreaction for vimentin was noted in ependymal cells and in vascular endothelial cells but not in astrocytes. This distribution contrasted with that of astroprotein (GFAP), which distributed in astrocytes but not in normal ependymal cells. These findings confirmed that the two antisera used in the present study do not crossreact to each other. In contrast to the absence of vimentin immunoreaction in normal astrocytes, a number of tumor cells showed positive reaction to the antiserum to vimentin. Mixed glioma with astrocytoma and oligodendroglioma had both astroprotein (GFAP)-positive and negative cells. Well developed cellular processes were noted in astroprotein (GFAP)-positive cells (astrocytoma cells). Weak immunoreaction for vimentin was noted in those cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphological maturation of tumor cells induced by ethylnitrosourea (ENU) in rat brains. II. On the tumors by administration of ENU in the mid-gestational stage

In order to clarify the relationship between cellular characteristics of rat brain tumors and the administration time of chemical carcinogens, the incidence and morphology of microtumors in the offspring of five pregnant Sprague-Dawley rats injected with ethylnitrosourea (ENU) intraperitoneally on the 11th day of gestation (Group I) were compared with those of six pregnant rats injected with ENU on the 18th day of gestation (Group II). Twenty-four microtumors and 6 macrotumors were obtained in Group I and 58 microtumors and 5 macrotumors in Group II. Histologically, the macrotumors of Group I showed a poorly differentiated pattern which corresponded to primitive spongioblastomas in comparison with those of Group II which resembled human mature oligodendrogliomas, astrocytomas or mixed gliomas. The constituent cells of the microtumors of both groups were immature and were morphologically similar to each other. Immunohistochemically, the cells of microtumors of both groups were negative for Leu 7 and glial fibrillary acidic protein. Microtumors in Group I showed more infiltrative proliferation than those in Group II and had indistinct borders. The 3H-thymidine labeling index of the constituent cells of Group I was significantly higher than that of Group II (p less than 0.001). This study revealed that the constituent cells of microtumors of Group I, in spite of being morphologically similar with those of Group II, possess a greater growth potency than the latter. This difference in growth potency is responsible for the difference in the histological maturity of the macrotumors in each group. The difference in morphological maturation of enlarged gliomas induced by ENU appears to depend on the imperceptible difference of the target cell maturation at the initiation of oncogenesis.

Morphological maturation of tumor cells induced by ethylnitrosourea (ENU) in rat brains. I. On the tumors by administration of ENU in the late gestational stage

Sequential changes in the development of ethylnitrosourea (ENU)-induced rat brain tumors were examined histologically, immunohistochemically, electron microscopically and autoradiographically. In 47 Sprague-Dawley rats transplacentally administered ENU, 95 brain tumors developed, including 76 microtumors less than 1mm in diameter. Microtumors were found mainly in the paraventricular area, but some were found in the peripheral brain tissue. They were composed of small tumor cells which had round dark nuclei and scanty cytoplasm immunohistochemically negative for Leu 7 and glial fibrillary acidic protein (GFAP). The 19 macrotumors were mature gliomas, 3 of which histologically corresponded to oligodendrogliomas and 16 to mixed gliomas. The tumor cells of the former had small round nuclei with distinct perinuclear halos and a small amount of cytoplasm positive for Leu 7. The latter were chiefly composed of polygonal cells having large round nuclei and rich cytoplasm positive for GFAP. An autoradiographic study using 3H-thymidine revealed that the labeling index of the tumor cells was high in mixed gliomas and microtumors, but low in oligodendrogliomas. It may be concluded that the constituent cells of microtumors correspond to glioblasts or migrating neuroglias, which gradually mature to form oligodendrogliomas or astrocytomas.

Cloned neoplastic cells from a chemically-induced rat glioma: immunocytochemical characterization

A cell clone--A15 A5--derived from an N-ethyl-N-nitrosourea (ENU)-induced glioma in a BDIX rat has been maintained in vitro for over 50 passages. These cells, which produce tumours when injected intracerebrally into syngeneic rats, possess several features of neoplastic astrocytes. In the present study A15 A5 cells were found to express both glial fibrillary acidic protein and glutamine synthetase, thus confirming their astrocytic nature.

Developmental behavior of N,N'-dimethylnitrosourea-induced brain gliomas and influence of a stab wound in adult rats

The developmental behavior of rat brain gliomas induced by weekly injections of N,N'-dimethylnitrosourea (DMNU) from the age of three weeks was studied. In addition, the influence of the repair process of a stab wound on tumor induction by DMNU was examined. From seven weeks after the first injection of DMNU, a loss of subependymal cells appeared along with a decrease in labeling indices in flash labeling with 3H-thymidine. From twenty weeks, gliomas began to appear. Their distribution was much denser in the vicinity of the depleted subependymal layer than in the periphery of the cerebral hemisphere, and corresponded to the distribution of labeled cells in the normal adult brain. Microtumors composed of less mature glial cells grew to histologically mature gliomas with the lapse of time. No effect of the stab wound was observed on the incidence, distribution or latency period of glioma development. From these results, it was concluded that DMNU-induced gliomas develop in close relation to cellular differentiation of target cells. It was assumed that mature gliomas are derived from less mature glial cells in the glioblastic (spongioblastic) stage or migrating neuroglias remaining in adult rat brains.

Induction of gliomas in Mongolian gerbils (Meriones unguiculatus) following neonatal administration of N-ethyl-N-nitrosourea

Mongolian gerbils (Meriones unguiculatus) were given an sc injection (40 mg/kg body wt) of N-ethyl-N-nitrosourea [(ENU) CAS: 759-73-9] on postnatal day 1 (group I) or day 29 (group II). Untreated gerbils served as controls (group III). Of 32 gerbils in group I, 10 (31%) developed a total of 14 gliomas after an observation period of 12 months, whereas no gliomas were observed in groups II and III. Seven gliomas were located in the spinal cord, 6 were in the cerebrum, and 1 was in the cerebellum. Histologically, all were oligodendrogliomas. In group II, 1 meningeal tumor (4%) was observed among 27 gerbils. ENU also induced cutaneous melanomas (22% in group I, 15% in group II, and 0% in group III), kidney hemangiomas (6% in group I, 26% in group II, and 0% in group III), and ameloblastomas of the lower jaw (6% in group I and 0% in groups II and III).

Chronic toxicity/carcinogenicity study of FD & C Blue No. 2 in rats

FD & C Blue No. 2 was fed to rats in the diet in a long-term toxicity/carcinogenicity study. The study included an in utero phase in which the compound was administered to groups of 60 male and 60 female Charles River CD albino rats at levels of 0.5, 1.0 and 2.0%. Two concurrent control groups, each containing 60 rats of each sex, received the basal diet. After random selection of the F1 animals, the long-term phase was initiated at the same dietary levels, with 70 rats of each sex in each dose group and in each of two control groups. Maximum exposure was 30 months. No consistent compound-related biologically adverse effects were noted. There were random statistically significant differences from the controls with respect to body weight, food consumption and clinical chemistry tests. Food consumption by the test groups showed a dose-related increase. This was probably due to the non-nutritive character of the colouring. A statistically significant increase in gliomas in the high-dose male rats was not found to be biologically significant, since none of the criteria for determining the neurocarcinogenic potential of chemical substances was met. The overall brain-tumour incidence in this study was within the range typical for 2-yr-old CD rats. Under the conditions of this study, FD & C Blue No. 2 did not produce evidence of any toxicity, including carcinogenicity.

Inhibitory effect of phenobarbital on the development of gliomas in WF rats treated neonatally with N-ethyl-N-nitrosourea

The present study was undertaken to evaluate the effect of phenobarbital (PB) on the development of neurogenic tumors induced in WF rats by neonatal administration of N-ethyl-N-nitrosourea (ENU; CAS: 759-73-9). Group I rats were given a single sc injection in the backs of 5 mg ENU/kg body weight within 24 hours after birth. In group II, continuous oral administration of 0.05% PB in the drinking water was commenced 4 weeks after birth. Following neonatal injection of ENU, administration of PB was commenced 4 weeks after birth in group III. Rats in group IV served as untreated controls. All groups consisted of about an equal number of both sexes of rats. The experiment was terminated when the rats were 52 weeks old. The incidence of all neurogenic tumors in both sexes combined was 11 of 26 (42%) in group I and 3 of 22 (14%) in group III (P greater than .05). The incidence of gliomas alone was 10 of 26 (38%) in group I and 2 of 22 (9%) in group III (P less than .05). When females and males were evaluated separately, the incidence of gliomas in females was 7 of 13 (54%) in group I and 1 of 12 (8.3%) in group III (P greater than .05), whereas in males, 3 of 13 (23%) in group I and 1 of 10 (10%) in group III (P greater than .05), the difference was not statistically significant. At the end of the experiment the mean serum level of PB in females (33.0 micrograms/ml) was significantly higher than that in males (19.8 micrograms/ml) (P less than .05). These data suggest an inhibitory effect of PB on the development of ENU-induced gliomas in female rats.

Prognostic role of cell morphology of animal tumors

The purpose of this presentation is to determine the prognostic role of cellular morphology in animal neoplasia. With some exceptions, cellular morphology is the single most accurate predictor of the prospective behavior of neoplasms. There is generally a positive correlation between the degree of malignancy and prognosis. The exceptions are a) morphologically malignant-appearing tumors following a benign course (e.g., canine histiocytoma, canine seminoma, equine sarcoid) and b) morphologically differentiated tumors exhibiting an unpredictable prognosis (e.g., canine pericytoma, acanthomatous epulis, myxoma, follicular thyroid cell carcinoma, etc.). Anaplasia, an important characteristic of most malignant neoplasms, may be less stable than generally assumed. Sodium butyrate may reverse it intermittently and anaplastic gliomas may loose all morphologic and cytokinetic characteristics of anaplasia following sodium butyrate exposure. Host factors, such as nerve growth factor, have similar and more lasting effects upon anaplastic cells derived from the neural crest. Such factors may act as reverse transformation agents and may represent prospective therapeutic agents for anaplastic tumors.

Correlations between the degree and type of forebrain malformations and the simultaneous neuro-oncogenic properties of ethylnitrosourea after diaplacental exposure in rats, alone and in combination with X-irradiation

Single and combined treatments were performed in rats on day 13 of gestation with either ENU or ENU subsequent to various X-irradiation doses between 0.5 and 1.5 Gy. At this time of gestation, developmental anomalies of the brain are still inducible by any of these treatments, in addition to neurocarcinogenic effects after ENU alone or in combination with X-irradiation. We looked for correlations between the degree of brain malformations still detectable in the adult animals and the simultaneous occurrence of brain tumors. These evaluations were based on a histopathological analysis regarding the type and degree of malformation residues, as well as the type and distribution pattern of the tumors (especially regarding gliomas) within the forebrain. Both after ENU and X-irradiation plus ENU-treatment, the occurrence of glioma in the offspring was positively correlated with the degree of brain dysplasia. This effect was not only restricted to the total glioma incidence but also confirmed by the higher glioma multiplicity in major dysplastic brains. Additionally, gliomas were preferentially located within the subependymal layer, which simultaneously was most severely affected by the teratogenic effects after prenatal treatment. Although forebrain dysplasia generally presents a significant predisposition for glioma inducibility, this oncogenic event is apparently strictly inversely related to a certain type of forebrain malformation, namely the occurrence of heterotopic neuronal nodules within the telencephalic roof. They emerge from "rosettes," which are typical radiation lesions occurring only after doses above 1.0 Gy. In none of the forebrains which still revealed rosette-residues in later life could a simultaneous occurrence of gliomas be observed. This explains not only the substantial decrease of glioma incidence after combined treatment with 1.0 and 1.5 Gy X-irradiation doses, but also the consistent glioma multiplicity despite the decrease of frequency.