Comparative Analysis of Behavioral Reactions and Morphological Changes in the Rat Brain After Exposure to Ionizing Radiation with Different Physical Characteristics.

The aim of this research was to study behavioral reactions and morphological changes in the brain of adult female Sprague Dawley rats after exposure to 170 MeV and 70 MeV protons and gamma radiation (60Co) at a dose of 1 Gy. The analysis of the behavioral reactions in the T-maze showed that exposure to ionizing radiation with different LETs led to an increase in number of repeated entries into the arms of the maze in the spontaneous alternation test. In the Open Field test a decrease in overall motor activity in the group of irradiated animals (70 MeV protons at the Bragg peak) was observed. A decrease in the number of standing positions was seen in all groups of irradiated animals. Morphological analysis showed the development of early amyloidosis, autolysis of the ependymal layer, an increase in the number of neurodegenerative changes in various structures of the brain, and the development of neuronal hypertrophy on the 30th day after irradiation in the cerebellum and hippocampal hilus. Exposure to protons at a dose of 1 Gy leads to the development of structural and functional disorders of the central nervous system of animals on the 30th day after irradiation. These data indicate a damage of short-term memory, a decrease in motor activity and exploratory behavior of animals. With an increase in LET, there is an increase in the number of amyloid plaques in the forebrain of rats, autolysis of the ependymal layer of the ventricles, and the development of dystrophic changes. Investigations of behavioral reactions and morphological changes in various parts of the brain of adult rats on the 30th day after influence of ionizing radiation with different physical characteristics at a dose of 1 Gy. Various negative patho-morphological and cognitive-behavioral changes observed.

Early Response of Mouse Bone Mrrow Cells to Short-Term Irradiation in a Wide Range of Doses.

Experiments on mice irradiated with γ-rays in a wide range of doses, from 0.5 to 400 cGy and the bone marrow have shown cytogenetic and cytological effects ranging from I cGy dose 24 hours after exposure to radiation. Dose-independent reduction of the number of nucleated cells in the bone marrow, normal or even elevated levels of mitotic activity, and extreme dependence of the type of chromosomal aberrations on the radiation dose with the maximum in the region of 7.5 cGy were observed in the dose range from 1 to 20 cGy. A linear dose-dependent decrease of the cell.number in the bone marrow, a decreased mitotic activity and increased number of aberrant mitosis were marked in the dose range from 20 to 400 cGy. The findings are discussed in terms of their application for explaining the mechanisms of hormesis, adaptive response, as well as the appropriateness of accounting the parameters studied for solving problems of regulation of permissible doses.

[IMMEDIATE RADIOBIOLOGICAL EFFECTS IN MICE FOLLOWING γ-IRRADIATION BY LOW DOSES].

Outbred CD-1 mice females aged 4 to 4.5-months were investigated in 21-22 hours following total γ-irradiation at 10, 25, 50, 75, 100 and 200 mGy. Loss in bone marrow karyocytes, as well as spleen and thymus mass reductions were significant in the group of animals irradiated at 50 and 200 mGy and less dramatic in mice irradiated at 75 mGy. The orientative-trying behavior reaction (OTBR) in the open field tested in 19-20 hours after exposure to 10 and 25 mGy was reliably stronger than in the group of biological control; however, emotional status (ES) in the animals that received 10 mGy dropped significantly. Mice irradiated at 50 mGy were found to weaken the grip of their front limbs. Dose levels differing in opposite radiobiological effects on the parameters under study were established. Doses in the range from 10 to 25 mGy maximized OTBR and ES, while doses of 50, 100 and 200 mGy produced high reactions of the immune and hemopoietic organs.

[Galactic heavy charged particles damaging effect on biological structures].

A concept of the radiation risk of the manned interplanetary flights is proposed and substantiated. Heavy charged particles that are a component of the galactic cosmic rays (GCR) have a high damaging effect on the biological structures as great amount of energy is deposited in heavy particle tracks. The high biological effectiveness of heavy ions is observed in their action on cell genetic structures and the whole organism, including the brain structures. The hippocampus is the part of the central nervous system that is the most sensitive to radiation--first of all, to heavy charged particles. Irradiation of animals with accelerated iron ions at doses corresponding to the real fluxes of GCR heavy nuclei, to which Mars mission crews can be exposed, leads to marked behavioral function disorders in the post-irradiation period. To evaluate the radiation risk for the interplanetary flight crews, the concept of successful mission accomplishment is introduced. In these conditions, the central nervous system structures can be the critical target of GCR heavy nuclei. Their damage can modify the higher integrative functions of the brain and cause disorders in the crew members' operator performances.

[Mathematical model of induced mutagenesis in bacteria Escherichia coli under ultraviolet irradiation].

The mathematical model of mutational process in bacteria Escherichia coli induced by ultra-violet radiation is developed. The dynamics of the basic protein complexes of the E. coli SOS-response system is investigated. The probability of mutations occurring during translesion-synthesis is estimated.

[The regularities of the induction of DNA double strand breaks and DNA repair in human lymphocytes after irradiation by accelerated heavy ions with different energy].

The regularities of the induction of DNA double strand breaks (DSB) in human lymphocytes after irradiation by different doses of accelerated lithium and carbon ions (33 and 480 MeV/nucleon, LET = 20 and 10.6 keV/microm, respectively) and gamma-rays 60Co by using of comet assay were investigated. It was shown that the dependence of DSB formation increases linearly with growing of the dose of lithium and carbon ions and gamma-rays. The biological effectiveness of carbon ions with high energy was similar with gamma-rays, lithium ions possess greater biological effectiveness in comparison with gamma-rays and value of RBE of lithium ions amount 1.6 +/- 0.1. The kinetic of DNA repair from DSB in human lymphocytes after irradiation by lithium and carbon ions and gamma-rays was studied. It is revealed that the reparation proceeds effectively with heavy ion and gamma-ray irradiation by exponential kinetics.

Cytogenetic effects of low-dose radiation with different LET in human peripheral blood lymphocytes.

Chromosome damage and the spectrum of aberrations induced by low doses of gamma-irradiation, X-rays and accelerated carbon ions (195 MeV/u, LET 16.6 keV/microm) in peripheral blood lymphocytes of four donors were studied. G0-lymphocytes were exposed to 1-100 cGy, stimulated by PHA, and analyzed for chromosome aberrations at 48 h post-irradiation by the metaphase method. A complex nonlinear dose-effect dependence was observed over the range of 1 to 50 cGy. At 1-7 cGy, the cells showed the highest radiosensitivity per unit dose (hypersensitivity, HRS), which was mainly due to chromatid-type aberration. According to the classical theory of aberration formation, chromatid-type aberrations should not be induced by irradiation of unstimulated lymphocytes. With increasing dose, the frequency of aberrations decreased significantly, and in some cases it even reached the control level. At above 50 cGy the dose-effect curves became linear. In this dose range, the frequency of chromatid aberrations remained at a low constant level, while the chromosome-type aberrations increased linearly with dose. The high yield of chromatid-type aberrations observed in our experiments at low doses confirms the idea that the molecular mechanisms which underlie the HRS phenotype may differ from the classical mechanisms of radiation-induced aberration formation. The data presented, as well as recent literature data on bystander effects and genetic instability expressed as chromatid-type aberrations on a chromosomal level, are discussed with respect to possible common mechanisms underlying all low-dose phenomena.

[Cytogenetic effects of low dose radiation with different LET in human peripheral blood lymphocytes and possible mechanisms of their realization].

The induction of chromosome damage by the exposure to low doses of gamma-(60)Co and accelerated carbon ions 12C in peripheral blood lymphocytes of different donors was investigated. The complex nonlinear dose-effect dependence at the range from 1 to 50-70 cGy was observed. At the doses of 1-5 cGy the cells show the highest radiosensitivity (hypersensitivity), mainly due to the chromatid-type aberration, which is typical to those spontaneously generated in the cell and believed not to be induced by the irradiation of unstimulated lymphocytes according to the classical theory of aberration formation. With the increasing dose the frequency of the aberrations decreases significantly, in some cases up to the control level. At the doses over 50-70 cGy the dose-effect curve becomes linear. The possible role of the oxidative stress, caused by radiation-induced increase in mitochondrial reactive oxigen species (ROS) release in the phenomenon of hypersensitivity (HS) at low doses is discussed as well as cytoprotective mechanisms causing the increased radioresistance at higher doses.

[Induction of chromosome aberrations and micronuclei in human peripheral blood lymphocytes at low dose of radiation].

The chromosome damage induced by the doses of y-irradiation 6)Co in peripheral blood lymphocytes was studied using different cytogenetic assays. Isolated lymphocytes were exposed to 0.01-1.0 Gy, stimulated by PHA, and analysed for chromosome aberrations at 48 h postirradiation by metaphase method, at 49 h--by the anaphase method, at 58 h by micronucleus assay with cytochalasin B and, additionally, micronuclei were counted at 48 h on the slides prepared for the metaphase analysis without cytochalasin B. Despite of the quantitative differences in the amount of chromosome damage revealed by different methods all of them demonstrated complex nonlinear dose dependence of the frequency of aberrant cells and aberrations. At the dose range from 0.01 Gy to 0.05-0.07 Gy the cells had the highest radiosensitivity mainly due to chromatid-type aberration induction. With dose increasing the frequency of the aberrant cells and aberrations decreased significantly (in some cases to the control level). At the doses up to 0.5-0.7 Gy the dose-effect curves have become linear with the decreased slope compare to initial one (by factor of 5 to 10 for different criteria) reflecting the higher radioresistance of cells. These data confirm the idea that the direct linear extrapolation of high dose effect to low dose range--the procedure routinelly used to estimate genetic risk of low dose irradiation--cannot be effective and may lead to underestimation of chromosome damage produced by low radiation doses. Preferences and disadvantages of used cytogenetic assays and possible mechanisms of low ionising radiation doses action were discussed.

[Induction of gene and deletion mutations by accelerated heavy charged particles in Escherichia coli cells].

The results of the induction of the point and the deletion mutations by the radiation with broad region of linear energy transfer (LET) ox Escherichia coli cells. The linear-quadratic function for point mutation induction was shown in comparison with linear dependence for deletion mutations. The relative biological effectiveness (RBE) is described as a function of LET by dependence with a local maximum. The greatest RBE coefficients for the lethal effects, gene and deletion mutation induction realize under different LET of heavy charged particles.

[Cytogenetic effects of low doses of radiation in mammalian cells: analysis of the hypersensitivity phenomenon and induced resistance]. / Tsitogeneticheskie éffekty malykh doz oblucheniia v kletkakh mlekopitaiushchikh: analiz fenomena giperchuvstvitel'nosti i indutsirovannoi rezistentnosti.

The induction of cytogenetic damage after irradiation of chinese hamster cells and human melanoma cells within a dose range 1-200 cGy was studied. The anaphase and metaphase analysis of chromosome damage and micronuclei test were applied. The hypersensitivity (HRS) at doses below 20 cGy and the increased radio-resistence at higher doses (IR) were shown with all cytogenetic critheria for both cell lines. The phenomenon of HRS/IR was reproduced in synchronic as well as in a synchronic population of chinese hamster cells. This fact shows that HRS was caused by high radiosensitivity of all cells and can not be explained by any differential sensitivity of cells in different phase of the cell cycle. So it was supposed that the increasing radio-resistence is determined by the inclusion of the inducible repair processes in all cells. This conclusion consents with the facts, that there was no evidence of HRS on dose-effect curves and that some parts of pre-existent damage was repaired after preliminary irradiation with low doses (1-20 cGy) which induce repair processes. It can be concluded that same inducible repair processes an analogous in mechanisms underlying in the base of HRS/IR phenomenon and adaptive response.

Chromosome instability of HPRT-mutant subclones induced by ionising radiation of various LET.

The induction of HPRT-mutations and survival of Chinese hamster cells (line B11ii-FAF28, clone 431) were studied after irradiation by 4He and 12C-ions of various LET (20-360 keV/micrometers), produced by the U-200 heavy ion accelerator. The RBE increases with LET up to the maximum at 100-200 keV/micrometers and then decreases. Cytogenetic analysis was performed on the HPRT-mutant subclones selected from unirradiated Chinese hamster V-79 cells and from HPRT-mutant subclones that arose after exposure to gamma-rays, 1 GeV protons and 14N-ions (LET-77 keV/micrometers), produced by the synchrophasotron and the U-400M heavy ion accelerator. Slow growing mutant subclones were observed. The cytogenetic properties of individual clones were highly heterogeneous and chromosome instability was observed in both spontaneous and radiation-induced mutants. Chromosome instability was highest among spontaneous mutants and decreased with increasing LET.

[Radiobiological research at the Joint Institute for Nuclear Research (JINR)]. / Radiobiologicheskie issledovaniia v OIAI.

The Joint Institute for Nuclear Research has the unique sources of ionizing radiation. The different radiobiological researches have been carried out at the JINR accelerators for more than forty years. They are connected not only to the solution of fundamental problems of radiation genetics but also with applied tasks of great social importance. These tasks are concerned with the improvement of targeted therapy methods for treatment of cancer diseases.

Exchange aberrations among 11 chromosomes of human lymphocytes induced by gamma-rays.

PURPOSE: To detect the frequencies of interchanges among 11 chromosomes in lymphocytes irradiated with gamma-rays and to find out whether these frequencies reflect the proximity of some of these chromosomes within the interphase nucleus. MATERIAL AND METHODS: Exchange aberrations were detected in the first mitosis after irradiation of human lymphocytes with 3 and 5 Gy gamma-rays of 60Co. Two-colour repeated FISH with two differently chemically modified probes in each hybridization was applied. The microscope stage positions of each mitosis were recorded after the first hybridization and used for the automatic scanning of images after all successive experiments. Five images were obtained for each mitosis differing in visualized pairs of chromosomes. Comparing these images, exchanges among 10 chromosomes could be detected. Painting of the p arm of chromosome 21 with the painting probe for chromosome 22 also made it possible to detect exchanges of this chromosome with other chromosomes of the selected group. RESULTS: Frequencies of exchange aberrations induced in chromosomes of the selected group as well as interchanges between many pairs of chromosomes of this group were roughly proportional to the DNA content of chromosomes. Higher frequencies of interchanges than expected according to the model of linear proportionality were found between several chromosomes involved in translocations frequent in different subtypes of leukaemia. CONCLUSIONS: Frequencies of interchanges among 11 chromosomes of human lymphocytes induced by gamma-rays do not indicate as clearly as fast neutrons the non-random arrangement of chromosomes in the cell nucleus. The interaction of a large number of chromosomes in exchange aberrations suggests that the chromatin in the territory of one chromosome is accessible for several other chromosomes.

[The effect of am umuC mutation on the induction of an SOS response in E. coli cella under the action of UV and gamma irradiation]. / Vliianie umuC-mutatsii na induktsii SOS-otveta v kletkakh E. coli pri deistvii UF- i gamma-izlucheniia.

The kinetics of the SOS induction in E. coli cells of wild type and deficient in umuC gene exposed to UV and gamma-rays were analysed. In the presence of UmuC protein SOS induction was 3-5.5 times lower and delayed for about 30 minutes after both UV and gamma rays. It was shown that decrease of the SOS induction in wild type cells irradiated by UV was due to more effective elimination of the photolesions from DNA by excision repair system. UmuCD-dependent inhibition of DNA replication was discussed as a possible mechanism allowing additional time for error-free repair.

[The dose dependence of cytogenetic damages and the adaptive response of mammalian cells under the action of ionizing radiation at low doses]. / Dozovaia zavisimost' tsitogeneticheskikh povrezhdenii i adaptivnyi otvet kletok mlekopitaiushchikh pri deistvii ioniziruiushchego izlucheniia v malykh dozakh.

The dose-effect dependence of cytogenetic damage after single dose irradiation in the dose range of 0.1-2 Gy and the adaptive response after double-dose irradiation were studied on Chinese hamster and human melanoma cells in culture. The non-linear dose dependencies were found for the induction of chromosome aberrations with decrease in cell radiosensitivity in the definite dose range. This decrease started at 10 and 20 cGy for melanoma and Chinese hamster cells respectively. The maximal adaptive response was induced at 1 cGy for melanoma cells and at 20 cGy for Chinese hamster cells. It can be supposed that the same inducible repair processes are responsible for non-linearity of dose-effect curves and induction of the adaptive response. These processes are similar in mechanisms and different in quantitative proportion for different cell types.

[Regularities of the induction of point mutation in the yeast Saccharomyces cerevisiae after exposure to gamma-radiation]. / Zakonomernosti induktsii tochkivykh mutatsii u drozhzhei Saccharomyces cerevisiae pri gamma-oblychenii.

A tester system consisting of six isogenic strains was used to study the regularities of the induction of point mutations in the yeast Saccharomyces cerevisiae after exposure to gamma-radiation. This system allowed the identification of all six possible substitutions in the Cys-22 codon of the CYC1 gene encoding iso-1-cytochrome c. The dose dependence of the frequency of these six base-pair substitutions was shown to be linear-quadratic. The pattern of base substitutions did not depend on the doses of gamma-irradiation used (from 125 to 1000 Gy) and predominantly included GC-->AT transitions and AT-->TA transversions. The possible mechanisms of gamma-ray mutagenesis leading to a nonlinear dose dependence were considered, and the spectra of mutations obtained for different yeast genes and for Escherichia coli were compared.

[Effects of low radiation doses on Chinese hamster cells]. / Deistvie malykh doz oblucheniia na kletki kitaiskogo khomiachka.

The induction of cytogenetic damages after irradiation with single dose of gamma-rays (0.1-2 Gy) have been studied. It is shown non-linear curve for the induction of chromosome aberrations, detected by anaphase method. After irradiation in S-stage of the cell cycle at dose below 0.2 Gy the cells were more radiosensitive than after irradiation with doses 0.3-2 Gy. Between the phases of high radiosensitivity and radioresistance the reversal dose-effect relation was observed. This phenomenon was not marked for the cells after irradiation in G2-stage of the cell cycle. It is possible, this results could reflect an induced radioresistance at low dose of irradiation.

A biosensor for environmental genotoxin screening based on an SOS lux assay in recombinant Escherichia coli cells.

A genetically controlled luminescent bacterial reporter assay, the SOS lux test, was developed for rapid detection of environmental genotoxins. The bioassay is based on the recombinant plasmid pPLS-1, which was constructed as a derivative of pBR322, carrying the promoterless luxCDABFE genes of Photobacterium leiognathi downstream of a truncated cda gene from ColD with a strong SOS promoter. E. coli recA+ strains containing this construction are inducible to high levels of light production in the presence of substances or agents that cause damage to the DNA of the cells. The light signal, reflecting the SOS-inducing potency, is recorded from the growing culture within 1 s, and the test results are available within 1 to 2 h. Induction of bioluminescence was demonstrated by treatment of E. coli C600(pPLS-1) with 6 genotoxic chemicals (mitomycin C, N-methyl-N'-nitro-N-nitrosoguanidine, nalidixic acid, dimethylsulfate, hydrogen peroxide, and formaldehyde) and with UV and gamma radiation. A clear dose-response relationship was established for all eight genotoxins. The sensitivity of the SOS lux test is similar to that of other bioassays for genotoxicity or mutagenicity, such as the SOS chromotest, umu test, and Ames mutatest. These results indicate that the SOS lux test is potentially useful for the in situ and continuous detection of genotoxins.