Selective brain responses to acute and chronic low-dose X-ray irradiation in males and females

Radiation exposure is known to have profound effects on the brain, leading to precursor cell dysfunction and debilitating cognitive declines [Nat. Med. 8 (2002) 955]. Although a plethora of data exist on the effects of high radiation doses, the effects of low-dose irradiation, such as ones received during repetitive diagnostic and therapeutic exposures, are still under-investigated [Am. J. Otolaryngol. 23 (2002) 215; Proc. Natl. Acad. Sci. USA 97 (2000) 889; Curr. Opin. Neurol. 16 (2003) 129]. Furthermore, most studies of the biological effects of ionizing radiation have been performed using a single acute dose, while clinically and environmentally relevant exposures occur predominantly under chronic/repetitive conditions. Here, we have used a mouse model to compare the effects of chronic/repetitive and acute low-dose radiation (LDR) exposure (0.5Gy) to ionizing radiation on the brain in vivo. We examined the LDR effects on p42/44 MAPK (ERK1/ERK2), CaMKII, and AKT signaling-the interconnected pathways that have been previously shown to be crucial for neuronal survival upon irradiation. We report perturbations in ERK1/2, AKT, and CREB upon acute and chronic/repetitive low-dose exposure in the hippocampus and frontal cortex of mice. These studies were paralleled by the analysis of radiation effects on neurogenesis and cellular proliferation. Repetitive exposure had a much more pronounced effect on cellular signaling and neurogenesis than acute exposure. These results suggest that studies of single acute exposures might be limited in terms of their predictive value. We also present the first evidence of sex differences in radiation-induced signaling in the hippocampus and frontal cortex. We show the role of estrogens in brain radiation responses and discuss the implications of the observed changes.     

Analysis of the nucleotide context of Arabidopsis thaliana mitochondrial mRNA editing sites

We have studied the effects of 1 mM solutions of L-amino acids on the X-ray- and heat-induced generation of hydrogen peroxide and hydroxyl radicals in phosphate buffer (5 mM, pH 7.4). Hydrogen peroxide was estimated by enhanced chemiluminescence in the luminol/p-iodophenol/peroxidase system; hydroxyl radicals were detected with a fluorescent probe coumarin-3-carboxylic acid. We demonstrate that amino acids can be grouped into three categories by their effect on X-ray-induced H₂O₂ production: those that reduce, increase, and have no influence on H₂O₂ yield. Similar amino acid effects were observed upon heating; however, the composition of respective amino acid groups was different. All amino acids lowered the X-ray-induced hydroxyl radical production, and the most effective were Cys > His > Phe = Met = Trp > > Tyr (in descending order). Hydroxyl radical generation induced by heating was inhibited by Met, His, and Phe; enhanced by Ser; and not affected by Tyr and Pro. Thus, amino acids have different effects on the production of reactive oxygen species by X-rays and heating, and some amino acids appear to be effective natural antioxidants.     

Kinetics of the rearrangement of the solvation shell of an excited fluorescent probe 4″-dimethylaminochalcone

A study was made of the processes associated with the quenching of 4″-dimethylaminochalcone (DMAC) fluorescence by proton-donor solvent (1-butanol). The kinetics of deactivation of the DMAC excited state was assessed by transient absorption spectra with a time resolution about 50 fs and by fluorescence decay with ～30-ps resolution. The following sequence of events could thus be envisaged: (i) the DMAC molecule in the ground state (prior to excitation) makes a hydrogen bond with an alcohol molecule; (ii) absorption of a light quantum causes a corresponding increase of the DMAC dipole moment; the H-bond is retained; (iii) the solvation shell formed by alcohol dipoles is reorganized in response to the raise of the DMAC dipole moment, with an energy expenditure about 24 kJ/mol and a time constant about 40 ps; the initial H-bond is still retained; (iv) processes leading to fluorescence quenching occur with an effective time constant of nearly 200 ps. Since quenching is far slower than solvate rearrangement, one can suppose that it is not a direct consequence of shell relaxation or prior H-bonding. Thus, DMAC fluorescence quenching may involve different processes observed with other aromatic molecules: H-bond rearrangement from a nonquenching to a more ‘efficient’ conformation, charge transfer between the excited molecule and alcohol, or solvent-induced out-of-plane twist of the DMAC amino group.     

Peroxidase and laccase as catalysts for removal of the phenylhydrazide protecting group under mild conditions

A new method is proposed for the removal of the phenylhydrazide protecting group by the action of peroxidase or laccase, the enzymes attributed to the class of oxidoreductases. The deblocking procedure is performed under mild oxidative conditions, i.e., aqueous solution and neutral or close to neutral pH. Such mild oxidizing agents as 1 mM H(2)O(2) and air oxygen are used for unmasking. The method is available for the deblocking of both alpha- and gamma-carboxyl groups. The enzyme-catalyzed removal of the phenylhydrazide protecting group causes no oxidative modification nor destruction of methionine or tryptophan side chains. (c) 1993 John Wiley & Sons, Inc.     

Opiate binding sites and endogenous opioids in Bufo viridis oocytes

Binding sites with high affinity for [3H]naloxone, but not for [3H]morphine and [3H] (D-Ala2, D-Leu5) enkephalin, have been found in membranes of Bufo viridis oocytes. The binding is reversible and saturable. Bound [3H]naloxone is easily displaced both by unlabeled naloxone and bremazocine, much worse by morphine and SKF 10,047; (D-Ala2, D-Leu5) enkephalin and beta-endorphin practically fail to displace [3H]naloxone. Scatchard analysis is consistent with the existence of two classes of binding sites with Kd 15 nM and 10(3) nM. The number of binding sites with high affinity for naloxone is 16 pmol/mg protein of homogenized oocytes which is 20-50-fold higher than in, toad or rat brain. Oocyte extract displaces [3H]naloxone bound with oocytes' membranes and inhibits electrically evoked contractions of the rabbit vas deferens. This inhibition is reversed by naloxone. It is suggested that compounds similar to opiate kappa-agonists exist in oocytes. It cannot be ruled out that they participate via specific receptors in the regulation of oocyte maturation and egg development.     

The absense of a definite gene-specific effect in wheat after seed treatment with exogenous DNA

Summary To reveal gene-specific genetic transformation in wheat experiments have been performed with two inheritable marker characters, namely, the complementing genes of necrosis, ne ₁ and ne ₂, and genes of awness. The awned spikes were found after treatment of seeds of awnless wheat with the DNA isolated from both awned wheat and from awnless wheat. The awned plants conserved their changed character in subsequent generations. In the experiments with necrosis genes no single example of interaction of the ne ₁ and ne ₂ genes was found, although some non specific effects (the decrease in number of germinating plants, the increase in height of plants and the length of spikes, etc) were observed.     

Transcriptome profiling reveals similarities and differences in plant responses to cadmium and lead

We analyzed the influence of salts of two heavy metals—lead and cadmium (Pb²⁺ and Cd²⁺) on plants, including plant and root size, plant genome stability as well as global genome expression. Measurement of the metal uptake showed that there was a significantly higher incorporation of Cd than of Pb, 0.6 and 0.15 uM per gram of dry weight, respectively. The analysis of the root length and plant size showed a dose dependent decrease in plants exposed to cadmium. In contrast there was little difference in the size of plants exposed to lead, although there was nearly four-fold increase of the root length. Analysis of the genome stability revealed that cadmium led to a dose dependent increase of homologous recombination whereas lead had no effect.

Analysis of the global genome expression of plants chronically exposed to 50 uM of Cd and Pb revealed 65 and 338 up- and down-regulated genes by Cd and 19 and 76 by Pb, respectively. Interestingly, half of the genes that changed their expression in Pb-treated plants also changed their expression in Cd-treated ones. The greater number of genes regulated by Cd reflects generally higher genome instability of plants as well as higher uptake as compared to Pb.     

Specific clinical, epidemiological patterns and laboratory diagnostics of enterovirus infection in the Republic of Belarus

The clinical and epidemiological patterns as well as the results of the laboratory verification of the outbreak of enterovirus infection (EVI) in Minsk during the period of summer-autumn, 2000, are presented. During this outbreak a variety of clinical forms were observed, the serous meningitis being prevalent (57.5%). Practically simultaneous occurrence of infection on the territory of all administrative districts of the city, the predominant involvement of children aged up to 14 years into the outbreak, a high proportion of simultaneous casualities in the multiple foci. A number of circulating enteroviruses (EV)--ECHO 30, ECHO 6 of three serotypes and Coxsackie B5--were simultaneously isolated from clinical material. EV of the same serotypes were isolated from tap drinking water, and neutralizing antibodies to these serotypes were often detected in the patients blood sera. Infectious EV were also present in samples of bottled water and in water reservoirs used for bathing. The routes of EV transmission and the improvement of EVI control are discussed.     

Influence of Daily Short-Term Temperature Drops on Respiration to Photosynthesis Ratio in Chilling-Sensitive Plants

Cucumber (Cucumis sativus L.), tomato (Solanum lycopersicum L.), and sweet pepper (Capsicum annuum L.) plants were subjected daily over 13 days to short-term (2 h) temperature drops to 12, 8, 4, and 1°C (DROP treatments) at the end of night periods, and effects of these chilling treatments on the ratio of dark respiration in leaves (R_d) to gross photosynthesis (A_g) were examined. The results showed that DROP treatments affected the R_d/A_g ratio in leaves: this ratio increased significantly in cucumber and tomato plants and was slightly affected in pepper plants. When the temperature drops to 12°C were applied, the increase in R_d/A_g ratio in cucumber and tomato plants was entirely due to the rise in R_d. In the case of temperature drops to 8°C and below, the increase in R_d/A_g was determined by both elevation of R_d and the concurrent decrease in Ag. In cucumber plants, the extent of Ag and R_d changes increased with the DROP severity, i.e., with lowering the temperature of DROP treatment. The inhibition of photosynthesis by DROP treatment in cucumber plants was accompanied by the diminished efficiency of light energy use for photosynthesis and by the increase in the light compensation point. The elevation in R_d/A_g ratio in cucumber plants was accompanied by the decline in growth characteristics, such as accumulation of aboveground biomass, plant height, and leaf area. It was concluded that the R/A ratio is an important indicator characterizing the adaptive potential of chilling-sensitive plant species and their response to daily short-term temperature drops.