An Investigation on the Persistence of Uranium Hydride during Storage of Simulant Nuclear Waste Packages.

Synchrotron X-rays have been used to study the oxidation of uranium and uranium hydride when encapsulated in grout and stored in de-ionised water for 10 months. Periodic synchrotron X-ray tomography and X-ray powder diffraction have allowed measurement and identification of the arising corrosion products and the rates of corrosion. The oxidation rates of the uranium metal and uranium hydride were slower than empirically derived rates previously reported for each reactant in an anoxic water system, but without encapsulation in grout. This was attributed to the grout acting as a physical barrier limiting the access of oxidising species to the uranium surface. Uranium hydride was observed to persist throughout the 10 month storage period and industrial consequences of this observed persistence are discussed.

Growth-promoting interactions between the murine neocortex and thalamus in organotypic co-cultures.

The aim of this study was to assess whether developing cerebral cortex produces diffusible factors that can affect the growth of thalamic cells and, if so, what the role of these factors might be during the formation of thalamocortical connections. We studied interactions between cultured organotypic explants from mice maintained in defined serum-free medium. First, we cultured explants of embryonic dorsolateral thalamus in isolation from any other tissue; after culture, these explants were viewed intact and then sectioned. We estimated the numbers of healthy and pyknotic cells before and after culture, and the rates of mitosis in the explants during culture (using bromodeoxyuridine). Based on these data, we concluded that the majority of cells in the thalamic explants survived, although significant numbers of pyknotic cells did accumulate. Thalamic explants extended either very few or no neurites when cultured alone. We then cultured explants of embryonic thalamus near to explants from other tissues. A gap was always maintained between the explants, and we measured the length and density of neurite outgrowth from each thalamic explant. Slices of embryonic cortex promoted a small but significant increase in the amount of growth from thalamic explants. Postnatal cortex stimulated much more profuse neurite outgrowth; postnatal cerebellum had less of an effect, and postnatal medulla or liver had none. We showed that there was significantly more outgrowth from thalamic explants cultured in medium that had been preconditioned with cortical slices than from thalamic explants cultured in control medium, confirming that diffusible factors were produced by the cortex. The survival and mitotic rates of thalamic cells were unaffected by co-culture with the cortex. We conclude that the developing cortex releases diffusible factors that stimulate the growth of thalamic neurites and that other regions of the brain may also release the same substance(s). The lack of a specific source of thalamic growth promoting factor(s) argues against a role for these factors in guiding thalamic axons to specific targets; indeed, we were unable to demonstrate any chemotropic guidance of thalamic axons towards cortical explants in collagen gels. Since postnatal cortex has a more potent stimulatory effect than prenatal cortex, it seems possible that, in vivo, the cortical-derived factors act mainly on thalamocortical axons that have located their targets and are in the process of arborizing and refining their connections.

Molecular characterization of an NAD-specific glutamate dehydrogenase gene inducible by L-glutamine. Antisense gene pair arrangement with L-glutamine-inducible heat shock 70-like protein gene.

The gene for an NAD-specific glutamate dehydrogenase (NAD-GDH) that is allosterically activated by NADP+ (non-substrate) was cloned, and its physical structure and nucleotide sequence was determined. The gene consists of 9 introns and 10 exons; the 10th and largest exon, which is 1863 nucleotides long, is at the 3'-end of the gene. The shortest exon of 33 base pairs is the first and is located at the 5'-end of the gene. The large exon is in perfect register along the complementary strand with a heat shock 70 (HSP)-like protein gene. The NAD-GDH gene is inducible with L-glutamine, just as the HSP 70-like protein gene (LéJohn, H.B., Cameron, L.E., Yang, B., MacBeath, G., Barker, D.S., and Williams, S.A. (1994) J. Biol. Chem. 269, 4513-4522). The phenomenon of anti-parallel coupling of two genes is named antisense gene pair. By Northern and Western blotting techniques, we obtained indirect evidence that the gene is expressed in vivo. The gene encodes a protein of M(r) 118,740 which consists of 1063 amino acid residues. The 5' and 3' borders of the gene display typical but unproven promoter motifs of CCAAT, TATAAT, and AAATAAAA polyadenylation signal bounded by a pyrimidine-rich transcription termination-type format. Restriction endonuclease site mapping of all the genomic clones isolated that carry most or all of the gene, and of the genome itself, gave hybridization patterns that are consistent with the interpretation that the organism, Achlya klebsiana, has only one form of the gene. 3'-End-labeling of a 5.2-kb XbaI DNA fragment (carrying the antisense gene pair) that was then asymmetrically cleaved to produce two single 3'-end-labeled pieces that were used as probes on L-glutamine-induced cell poly(A)+ RNA, showed that the end-labeled DNA equivalent to the HSP 70-like protein mRNA hybridized to a 3.4-kb transcript and the end-labeled DNA equivalent to the NAD-GDH mRNA hybridized to a 2.4-kb transcript.