Differential organization of open field behavior in mice following acute or chronic simulated GCR exposure.

Astronauts undertaking deep space travel will receive chronic exposure to the mixed spectrum of particles that comprise Galactic Cosmic Radiation (GCR). Exposure to the different charged particles of varied fluence and energy that characterize GCR may impact neural systems that support performance on mission critical tasks. Indeed, growing evidence derived from years of terrestrial-based simulations of the space radiation environment using rodents has indicated that a variety of exposure scenarios can result in significant and long-lasting decrements to CNS functionality. Many of the behavioral tasks used to quantify radiation effects on the CNS depend on neural systems that support maintaining spatial orientation and organization of rodent open field behavior. The current study examined the effects of acute or chronic exposure to simulated GCR on the organization of open field behavior under conditions with varied access to environmental cues in male and female C57BL/6 J mice. In general, groups exhibited similar organization of open field behavior under dark and light conditions. Two exceptions were noted: the acute exposure group exhibited significantly slower and more circuitous homeward progressions relative to the chronic group under light conditions. These results demonstrate the potential of open field behavior organization to discriminate between the effects of select GCR exposure paradigms.

Systemic HDAC3 inhibition ameliorates impairments in synaptic plasticity caused by simulated galactic cosmic radiation exposure in male mice.

Deep space travel presents a number of measurable risks including exposure to a spectrum of radiations of varying qualities, termed galactic cosmic radiation (GCR) that are capable of penetrating the spacecraft, traversing through the body and impacting brain function. Using rodents, studies have reported that exposure to simulated GCR leads to cognitive impairments associated with changes in hippocampus function that can persist as long as one-year post exposure with no sign of recovery. Whether memory can be updated to incorporate new information in mice exposed to GCR is unknown. Further, mechanisms underlying long lasting impairments in cognitive function as a result of GCR exposure have yet to be defined. Here, we examined whether whole body exposure to simulated GCR using 6 ions and doses of 5 or 30 cGy interfered with the ability to update an existing memory or impact hippocampal synaptic plasticity, a cellular mechanism believed to underlie memory processes, by examining long term potentiation (LTP) in acute hippocampal slices from middle aged male mice 3.5-5 months after radiation exposure. Using a modified version of the hippocampus-dependent object location memory task developed by our lab termed "Objects in Updated Locations" (OUL) task we find that GCR exposure impaired hippocampus-dependent memory updating and hippocampal LTP 3.5-5 months after exposure. Further, we find that impairments in LTP are reversed through one-time systemic subcutaneous injection of the histone deacetylase 3 inhibitor RGFP 966 (10 mg/kg), suggesting that long lasting impairments in cognitive function may be mediated at least in part, through epigenetic mechanisms.

Effect of varying dose-per-pulse and average dose rate in X-ray beam irradiation on cultured cell survival.

Characterizing the biological effects of flattening filter-free (FFF) X-ray beams from linear accelerators is of importance, due to their increasing clinical availability. The purpose of this work is to determine whether in vitro cell survival is affected by the higher dose-per-pulse present in FFF beams in comparison with flattened X-ray beams. A Varian TrueBeam(®) linear accelerator was used to irradiate the T98G, V79-4 and U87-MG cell lines with a single fraction of 5 Gy or 10 Gy doses of X-rays. Beams with energies of 6 MegaVolt (MV), 6 MV FFF and 10 MV FFF were used, with doses-per-pulse as measured at the monitor chamber of 0.28, 0.78 and 1.31 mGy/pulse for 6 MV, 6 MV FFF and 10 MV FFF, respectively. The dose delivered to each Petri dish was verified by means of ionization chamber measurements. No statistically significant effects on survival fraction were observed for any of the cell lines considered, either as a function of dose-per-pulse, average dose rate or total dose delivered. Biological effects of higher instantaneous rates should not be excluded on the basis of in vitro experimental results such as the ones presented in this work. The next step toward an assessment of the biological impact of FFF beams will require in vivo studies.

No evidence for a low linear energy transfer adaptive response in irradiated RKO cells.

It has become increasingly evident from reports in the literature that there are many confounding factors capable of modulating radiation-induced non-targeted responses, such as the bystander effect and the adaptive response. In this paper, we examine recent data which suggest that the observation of non-targeted responses may not be universally observable for differing radiation qualities. We have conducted a study of the adaptive response following low-linear energy transfer exposures for human colon carcinoma cells and failed to observe adaption for the endpoints of clonogenic survival or micronucleus formation.

Cellular reprogramming in the F3 mouse with paternal F0 radiation history.

PURPOSE: In the mouse, paternal F0 acute irradiation of Type B spermatogonia produces biological effects in offspring, including altered signalling kinase activities and protein levels. It was hypothesized that these effects represented cellular reprogramming that would alter the response of somatic cells in these offspring to an acute ionizing radiation exposure. MATERIALS AND METHODS: Nineteen-day-old third generation (F3) CD1 mice with and without an acute 1.0 Gy paternal F0 radiation history each received an acute dose of 1.0 Gy from attenuated 137C n-rays. Kidney PKC and MAPK activities, and p53 protein levels were evaluated immediately following F3 irradiation. The same endpoints and DNA damage were evaluated in kidney-derived fibroblast primary cell cultures 3 weeks post-irradiation. RESULTS: Kidneys had significantly decreased PKC and MAPK activities and p53 protein levels related to F0 irradiation and increased PKC and MAPK activities following F3 irradiation irrespective of F0 radiation history. Kidney-derived fibroblasts had significant changes or strong trends for all selected endpoints based upon cross-interaction of F0 radiation history with F3 irradiation. Comet assays demonstrated significantly increased DNA damage in fibroblasts related to F0 irradiation and increased DNA damage following F3 irradiation. However, significantly decreased F3 irradiation damage was demonstrated based upon cross-interaction of F0 radiation. CONCLUSIONS: The data suggest that irradiation of paternal F0 Type B spermatogonia resulted in cellular reprogramming causing offspring with this radiation history to have altered responses to acute somatic n-irradiation.

Heritable effects of paternal irradiation in mice on signaling protein kinase activities in F3 offspring.

We evaluated F3 mouse offspring from paternal F0 attenuated 137Cs gamma-irradiation (1.0 Gy) for heritable effects on gene products that can modulate cell proliferation rate and that may be markers for genomic instability. The F3 generation was selected for evaluation as a stringent test for heritability of effects from paternal F0 germline irradiation. Male CD1 mice were bred 6 weeks after irradiation so that the fertilizing sperm were type B spermatogonia at the time of irradiation. The resulting F1 males were bred to CD1 females to produce F2 four-cell embryos. The F2 embryos with a radiation history were paired with 'control' CD1 four-cell embryos that were heterozygous for the neo transgene. These F2 XY-XY chimeras, consisting of cells derived from both an embryo with a paternal F0 radiation history and a control embryo, were transferred to foster mothers, raised to adulthood and bred to produce F3 offspring. F3 offspring were evaluated for hepatic activities of receptor tyrosine kinase, protein kinase C and MAP kinase and for protein levels of nuclear p53 and p21(waf1). All three protein kinase activities were altered and nuclear levels of p53 and p21(waf1) protein were higher in the group of offspring that included F3 offspring with a paternal F0 radiation history than in littermates in the neo-positive control group. To our knowledge, this is the first observation in the descendants of paternal germline irradiation of effects on signal protein kinase activities and downstream nuclear target proteins that can influence cell proliferation rates.

Impaired cell proliferation in mice that persists across at least two generations after paternal irradiation.

Irradiation of male F0 mice 6 to 7 weeks prior to mating causes significant changes in the proliferation of F1 and F2 embryonic cells. These changes are revealed as a competitive cell proliferation disadvantage in chimera assays when the affected embryo is paired with a normal embryo in an aggregation chimera. This effect has been observed previously to be transmitted to F1 embryos for absorbed doses from 0.01 to 1.0 Gy; 0.01 Gy is about 100-fold lower than detectable using conventional germline mutation assays. However, until now there has been no reported cross-generation heritability. We now report that this competitive cell proliferation disadvantage persists without degradation in the F2 generation of embryos when F0 males received 1.0 Gy from gamma irradiation 6 and 7 weeks prior to conception of F1 males.

Evidence for a parent-of-origin effect on sperm aneuploidy in mice carrying Robertsonian translocations as analyzed by fluorescence in situ hybridization.

Multi-color fluorescence in situ hybridization (FISH) was employed to investigate variations in the frequency of aneuploid spermatids produced by males derived from three separate lines of Robertsonian translocations in mice: Rb(2.8)2Lub, Rb(8.12)22Lub, and Rb(8.14)16Rma, each with one arm involving chromosome 8. The DNA probes used were specific for repetitive sequences on chromosomes 8 and X. Heterozygous males for these Robertsonian translocations produced approximately 1% of spermatids with hyperhaploid for chromosome 8. which was > 80 times higher than the frequency of sperm hyperhaploid for chromosome X within the same animals; consistent elevations in chromosome-8 sperm disomy were observed among lines. In addition, approximately 25% higher fractions of sperm aneuploidy were observed when the Robertsonian translocation was inherited from the father rather than from the mother (p = 0.009). These findings illustrate the sensitivity of the FISH procedure for detecting small differences in the hyperhaploidy in male germ cells and suggest that imprinted factors may influence sperm aneuploidy.

Three-probe fluorescence in situ hybridization to assess chromosome X, Y, and 8 aneuploidy in sperm of 14 men from two healthy groups: evidence for a paternal age effect on sperm aneuploidy.

The method of simultaneous three-chromosome fluorescence in situ hybridization (FISH) was developed using repetitive DNA sequence probes for chromosomes 8, X and Y and applied to semen of 14 men from two healthy groups who differed in their average ages (46.8 +/- 3.1 years, n = 4 v. 28.9 +/- 5.0 years, n = 10). The frequencies of disomic sperm determined by FISH compared well with frequencies obtained using the hamster-egg technique for human-sperm cytogenetics and with the frequencies of disomic and diploid sperm reported in previous FISH studies in this laboratory. The two groups of men did not differ in their baseline frequencies of sperm disomic for chromosome 8 (approximately 6.5 per 10(4) sperm), sperm with XY8 aneuploidy (approximately 9.5 per 10(4) sperm), or sperm with autodiploidy XX88 or YY88 (approximately 2 per 10(4) sperm). However, the older group had statistically higher frequencies of sperm carrying sex chromosomal disomy than the younger group (5.1 v. 2.2 per 10(4) sperm for XX8; 5.9 v. 2.0 per 10(4) sperm for YY8; P < 0.005). A recent report from this laboratory of sex-chromosomal aneuploidy in sperm of aged mice provides inter-species corroborating evidence for this preliminary finding of a paternal age effect on sperm aneuploidy in human males.