Tumor induction by ras and myc oncogenes in fetal and neonatal brain: modulating effects of developmental stage and retroviral dose

Introduction into fetal rat brain cells of a replication-defective retroviral vector harboring v-Ha-ras and v-gag-myc rapidly causes the induction of highly malignant undifferentiated neuroectodermal tumors following transplantation into the brains of syngeneic hosts [Wiestler, et al. (1992) Cancer Res. 52: 3760–3767]. In the present study, we have investigated the modulating effect of the developmental stage of neural target cells and of the dose of the retroviral vector used in the grafting experiments. Exposure of fetal cells from embryonic day (E)12 or E14 produced a 100% incidence of malignant neuroectodermal tumors which led to the death of recipient animals after a median latency period of 32 days. A 100-fold reduction of the virus dose from 2.062×10⁶ to 2.062×10⁴ focus-forming units/ml resulted in a lower tumor incidence of 25%. Of six neural grafts exposed to v-Ha-ras and v-myc at E16, only one showed evidence of tumorigenesis (low-grade astrocytoma and hemangioma). All other transplants were morphologically normal for observation periods of 26 weeks, indicating a marked loss of transforming activity of ras and myc in more advanced stages of brain development. In retrovirus-exposed donor cells which caused the development of neural tumors in recipient rats, malignant transformation was also evident during culture in vitro, usually after 9–12 days. Oncogene complementation was also studied in the newborn rat brain. After microinjection of the retroviral vector into the brain at postnatal day (P)0, P1 and P3, 5 out of 20 animals (25%) developed a total of seven brain tumors. Histopathologically, three of these neoplasms were malignant neuroectodermal tumors which, in contrast to those induced in fetal brain transplants showed evidence of focal glial and/or neuronal differentiation. In addition, we observed one oligodendroglioma, two hemangiomas and a malignant hemangioendothelioma. These data indicate that neural precursor cells and endothelia of the rat brain represent the major target cells for the complementary action of ras and myc and that the use of target cells from later developmental stages (E16 and postnatal) leads to the induction of both primitive and more differentiated neoplasms.These studies were supported by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich (Erwin Schrödinger fellowship, JO501-MED), by the Swiss National Science Foundation and by the Cancer League of the Kanton of Zürich     

Medizinische Beurteilungskriterien zu bandscheibenbedingten Berufskrankheiten der Lendenwirbelsäule (I)

Occupational diseases Nos. 2108 and 2110 correspond to intervertebral disc-related diseases of the lumbar spine from many years of carrying or lifting heavy loads, occupations in extreme postures of full flexion or oscillation of the whole body when seated, and which compel the cessation of all activities which are or could be the cause for the origin, exacerbation or recurrence of the disease. These occupational diseases came into force at the start of 1993, but there have been considerable problems in their implementation. The present Part I of the contribution is the result of the work of an interdisciplinary study group and contains medical criteria for the assessment of possibly strain-related clinical characteristics and the evaluation of other possible causes. Part II is to be published in Volume 4/2005 and will deal with questions related to forced cessation and to the assessment of the loss of earning ability. Agreement was reached in many areas related to the assessment of occupational claims. This should allow for evidence-based decision making in the future for the occupational diseases Nos. 2108 and 2110.     

Characterization of gp 50, a major glycoprotein present in rat brain synaptic membranes, with a monoclonal antibody

Several cell lines secreting monoclonal antibodies (Mabs) against a major forebrain synaptic membrane (SM) glycoprotein, gp 50, have been raised. Western blots show that the Mabs react with a polypeptide doublet of Mrs 49 and 45 kDa. These polypeptides exist solely in a concanavalin A (Con A) binding form. Removal of the Con A receptors by digestion with endo-beta-N-acetylglucosaminidase H (endo H) lowers the Mrs of the glycoprotein doublet to 36.5 and 34 kDa. Western blots of 2D polyacrylamide gels indicate that gp 50 exists in several isoforms. Solid phase radioimmunoassay (RIA) and Western blots of brain subcellular fractions show the antigenic material to be concentrated in the SM fraction, but to be present in much lower amounts in synaptic junctions and postsynaptic densities. Gp 50 appears to be brain specific. Regional distribution studies show that it is present in all brain regions but is two-fold concentrated in cerebellum, brainstem and midbrain compared to forebrain. Immunocytochemical studies of several brain regions show that gp 50-like immunoreactivity is neuron specific and is concentrated in selected neuronal species, particularly granule cells. In both cerebellar and hippocampal granule cells gp 50-like immunoreactivity is localized in the perikarya and primary dendrites. Though immunocytochemistry did not show staining of synaptic regions this may be due to masking of the reactive epitope. The results are discussed in terms of the molecular properties of gp 50 and its subcellular localization in brain tissue.     

A case of drug-induced hematotoxicity: from in vivo to in vitro assessment

As part of the early preclinical development of a new antipsychotic compound, Wistar rats of both sexes were dosed orally for upto 7 days. At high doses, expected changes in appearance and behavior, decreases in bodyweight gain and feed intake but also a fluid and pale bone marrow (BM) were observed. Blood cell counts were normal as were clinical chemical values. BM sections showed a red cell hypoplasia. Circulating reticulocytes and erythroblasts on BM smears were decreased suggesting that the compound might have a selective toxicity for the erythroid lineage. In a mechanistic experiment, rats were dosed for 9 days and phlebotomized after 7 days of exposure to stimulate erythroid regeneration. Red-blood cell mass, reticulocytes and erythropoietin (EPO) levels were monitored before and upto 48 h after bleeding. Results showed that an EPO-mediated pathogenesis could be excluded. The effect of the drug on the formation of Colony-forming units (CFU)-E and CFU-GM was then quantitatively measured in vitro after direct exposure to the compound. In two successive assays, rat or human BM cells were incubated with the drug dissolved in the collection medium at final concentrations of 0.3×10^–7 –3×10^–5 M. In the presence of adequate growth factors, CFU-E and CFU-GM were cultured and cell proliferation was compared between treated and control groups. Our results showed an expected inhibition by the drug of the growth of erythroid progenitors associated to a similar effect on myeloid progenitors. The CFU-E and CFU-GM of both human and rat sources were totally inhibited from the concentration of 3×10^–5 M. The IC₅₀ values were consistent with rat peak plasma levels reached in vivo by the drug. Therefore, the short-term cloning assays performed on rat BM cells were sensitive indicators of the hematotoxicity of the compound and were considered as predictive for human toxicity.     

Medizinische Beurteilungskriterien zu bandscheibenbedingten Berufskrankheiten der Lendenwirbelsäule (II)

The first part of this serial paper dealt with the medical criteria used in evaluation of the clinical picture caused by physical stress and the evaluation of other candidate causes and was published in issue no. 3/2005 (pp. 711–752) of Trauma and Berufskrankheit. This follow-up paper (II) presents criteria to be used in the evaluation of whether it is necessary to give up the occupations putting the spine at risk and in estimation of the degree of disability.     

Rigid ureteroscopy: a reliable, non-aggressive technic. Apropos of 51 cases treated for ureteral lithiasis

The authors obtained 82% good results by using rigid ureteroscopy to treat a total of 55 calculi in a series of 51 patients and they propose the following therapeutic approach: calculi in the lumbar ureter are frequently difficult to reach (54% failures). There is no harm in gently trying to remove the stone by ureteroscopy which, in the event of failure, can be followed by percutaneous surgery or posterolumbar incision. Rigid ureteroscopy is easier and more reliable in the case of calculi in the iliac or pelvic ureter (7% failures) and the indications can be extended.     

Polysialylated Neural Cell Adhesion is Involved in Target-induced Morphological Differentiation of Arcuate Dopaminergic Neurons

We have previously shown that the morphological and biochemical maturation of developing rat hypothalamic dopaminergic neurons is accelerated when they are cocultivated with pituitary intermediate lobe cells, one of their targets. Only two subsets of hypothalamic dopaminergic neurons (arcuate, A12, and periventricular, A14, nuclei) may project to the pars intermedia. In order to determine whether the two populations are equally responsive to coculture conditions, we microdissected the hypothalamus of 17-day-old rat fetuses in two fragments containing cell bodies from the A12 and from the A14 regions, prepared neuronal cultures from both portions and incubated them separately with intermediate lobe cells. The presence of intermediate lobe cells increased tyrosine hydroxylase levels in both dopaminergic neuron subsets, but morphological differentiation was accelerated in dopaminergic neurons originating in the arcuate nucleus only. We then investigated whether physical contact between developing arcuate neurons and their target cells was a prerequisite of the morphological effect by interposing a semipermeable membrane between cultivated neurons and intermediate lobe cells in transwell culture dishes. The morphological effect was no longer observed under transwell coculture conditions, pointing to the involvement of membrane-bound molecules. Accordingly, the stimulating effect of coculture on arcuate dopaminergic neurons was completely abolished by the removal of polysialic acid on neural cell adhesion molecules by endoneuraminidase N treatment. Thus, maturation of A12 and A14 dopaminergic neurons exhibits differential susceptibility to intermediate lobe target cells, and polysialylated-NCAM is required for the contact-dependent effect.