Production of neutrons from interactions of GCR-like particles

In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations.

Antioxidants and cataract: (cataract induction in space environment and application to terrestrial aging cataract)

The effect of several antioxidants and cysteine-elevating precursor drugs (prodrugs) was tested on lens damage occurring after in vitro exposure to low levels of 60Co-gamma-irradiation, to simulate in vitro the exposure to radiation in vivo of (1) astronauts (2) jet crews (3) military radiation accident personnel. Tocopherol (100 microM), ascorbic acid (1 mM), R-alpha-lipoic acid (1 mM), and taurine (0.5 mM) protected against radiation-associated protein leakage. MTCA and ribocysteine protected lenses against opacification, LDH and protein leakage, indicating that antioxidants and prodrugs of cysteine appear to offer protection against lens damage caused by low level radiation.

Stimulus responses and amyloid precursor protein processing in DAMI megakaryocytes

Platelets, when released as anuclear cells by their precursor megakaryocytes, already carry soluble proteolytic fragments of the amyloid precursor protein (APP) within their alpha-granules and intact APP in the alpha-granule membranes. In response to activation signals elicited by physiologic stimuli such as thrombin, platelets release their granules' soluble contents and translocate granule membrane-bound proteins to the plasma membrane. Because platelets carry >90% of the circulation's APP, activated platelets have been implicated as origins of the beta-amyloid peptide fragment of APP (A beta), whose deposition in the cerebrovasculature is characteristic of Alzheimer's disease. We have therefore studied the APP contents and proteolytic processing in resting DAMI human megakaryocytic cells, along with the consequences of the activation of these cells by thrombin, comparing the results in each case to those with human platelets. Resting and PMA-differentiated DAMI cell contents were examined by Western blotting, immunoprecipitation, or metabolic labeling with sulfur 35-labeled methionine during culture, while plasma membrane-bound APP was evaluated by flow cytometry. Activation was followed by changes in cytoplasmic calcium concentration ((Ca++)in) and in membrane potential. Like platelets, DAMI cells exhibited a thrombin dose-dependent delta(Ca++)in, and membrane potential change; in contrast to the surface of a platelet, the surface of an agranular resting DAMI cell expresses granule-membrane proteins (APP and CD63) that appear on platelets only after activation. DAMI cell culture with 35S-labeled methionine confirmed that megakaryocytes synthesize large amounts of APP, of slightly higher molecular weight, and degrade their APP extensively before platelets are formed.

Unique CD8+ T cell-rich lymphoid aggregates in human uterine endometrium

Using confocal scanning laser microscopy of viable tissue sections, we have demonstrated organized lymphoid aggregates (LA), that have a unique structure, in the stratum basalis of uterine endometrium. These LA consist of a core of B cells surrounded by more numerous T cells and an outer halo of monocytes/ macrophages. The T cells in the LA were almost exclusively CD8+CD4-. These CD8+ LA, in terms of both their T cell and B cell components, were either small or absent during the early proliferative stage of the menstrual cycle, significantly larger in size at mid-cycle and during the secretory phase, and absent in post-menopausal women, suggesting that their development is hormonally influenced. This new finding of a menstrual cycle-dependent, phenotypically unique, organized immune cell structure may lead to new insights into the mechanisms by which the endometrium accepts a semiallogeneic graft while providing resistance to infectious organisms.

Dopamine, serotonin, and acid metabolites in brain regions from the developing offspring of ethanol-treated rats

Female rats were pair-fed control or ethanol liquid diets on a chronic basis prior to parturition. Six brain regions (hypothalamus, cerebellum, brain stem, cortex, corpus striatum, and hippocampus) were dissected from 19- and 35-day-old rat offspring for the determination of dopamine (DA), serotonin (5-HT), 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxyindoleacetic acid (5-HIAA), and homovanillic acid (HVA). DA, 5-HT, and the acid metabolites were separated simultaneously by reverse-phase HPLC and were quantitated using electrochemical detection. Between 19 and 35 days of age in control rats we observed an increase in the concentration of 5-HT and 5-HIAA in the corpus striatum and hippocampus and a decrease in these compounds in the cerebellum. In addition, there was a development-related decrease of 5-HIAA in the hypothalamus and an increase in the brain stem. During the same age period the concentration of dopamine increased in the hypothalamus and corpus striatum. There was also a development-related decrease in the concentration of DOPAC in the corpus striatum and an increase in the cortex as well as a decrease in HVA in the cerebellum and cortex. In comparison to age-matched control animals the 19- and 35-day-old offspring of ethanol-treated rats had a lower concentration of 5-HT and/or 5-HIAA in the cortex, cerebellum, and brainstem. In addition the 35-day-old offspring of ethanol-treated rats exhibited a decrease in DA and HVA in the cortex. The results of the present study suggest that in utero ethanol exposure affects both the serotonergic and dopaminergic systems in brain.