Absence of Depressive and Anxious Behavior with Genetic Dysregulation in Adult C57Bl/6J Mice after Prenatal Exposure to Ionizing Radiation.

The exposure of ionizing radiation during early gestation often leads to deleterious and even lethal effects; however, few extensive studies have been conducted on late gestational exposures. This research examined the behavior al effects of C57Bl/6J mouse offspring exposed to low dose ionizing gamma irradiation during the equivalent third trimester. Pregnant dams were randomly assigned to sham or exposed groups to either low dose or sublethal dose radiation (50, 300, or 1000 mGy) at gestational day 15. Adult offspring underwent a behavioral and genetic analysis after being raised under normal murine housing conditions. Our results indicate very little change in the behavioral tasks measuring general anxiety, social anxiety, and stress-management in animals exposed prenatally across the low dose radiation conditions. Quantitative real-time polymerase chain reactions were conducted on the cerebral cortex, hippocampus, and cerebellum of each animal; results indicate some dysregulation in markers of DNA damage, synaptic activity, reactive oxygen species (ROS) regulation, and methylation pathways in the offspring. Together, our results provide evidence in the C57Bl/6J strain, that exposure to sublethal dose radiation (<1000 mGy) during the last period of gestation leads to no observable changes in behaviour when assessed as adults, although some changes in gene expression were observed for specific brain regions. These results indicate that the level of oxidative stress occurring during late gestation for this mouse strain is not sufficient for a change in the assessed behavioral phenotype, but results in some modest dysregulation of the genetic profile of the brain.

Cardiovascular and growth outcomes of C57Bl/6J mice offspring exposed to maternal stress and ionizing radiation during pregnancy.

Purpose: Developmental programming involves an adverse intrauterine environment which can result in offspring phenotype changes following birth. The developmental programming of hypertension has been reported to possibly involve oxidative stress at the cellular level. Ionizing radiation produces oxidative stress, even at low doses, and irradiation of animals is often coupled with potential sources of maternal stress such as transportation of animals or repeated handling. Materials and methods: Pregnant C57Bl/6J mice were irradiated on gestational day 15 with 5-1000 mGy 137Cs gamma radiation. Post-natal weight, blood pressure (BP) and heart rate (HR) were measured. Radiation had minimal effects at doses ≤300 mGy, but 1000 mGy caused a significant reduction in HR in male pups and growth reduction at 16 weeks of age in both genders. The sham-irradiation protocol included repeated transportation in order to acclimate animals to transport. However, it may have resulted in programming, as sham-irradiation alone resulted in elevated BP measures compared to the offspring of animals that were never transported. Results and conclusions: Overall, there were minimal effects on cardiovascular measures or offspring weight due to irradiation except at 1000 mGy. The presence of maternal stress, a known trigger of developmental programming, may have confounded any potential irradiation effects.

Is There a Trade-Off between Radiation-Stimulated Growth and Metabolic Efficiency?

Beneficial protective effects may result from an adaptive respose to low dose radiation exposure. However, such benefits must be accompanied by some form of cost because the responsible biological mechanisms are not normally maintained in an upregulated state. It has been suggested that stimulation of adaptive response mechanisms could be metabolically costly, or that the adaptive response could come at a sacrifice to other physiological processes. We exposed developing lake whitefish embryos to a fractionated regime of gamma radiation (662 keV; 0.3 Gy min-1) to determine whether radiation-stimulated growth was accompanied by a trade-off in metabolic efficiency. Developing embryos were exposed at the eyed stage to different radiation doses delivered in four fractions, ranging from 15 mGy to 8 Gy per fraction, with a 14 day separation between dose fractions. Dry weight and standard length measurements were taken 2-5 weeks after delivery of the final radiation exposure and yolk conversion efficiency was estimated by comparing the unpreserved dry weight of the yolk to the unpreserved yolk-free dry weight of the embryos and normalizing for size-related differences in somatic maintenance. Our results show that the irradiated embryos were 8-10% heavier than the controls but yolk conversion efficiency was slightly improved. This finding demonstrates that stimulated growth in developing lake whitefish embryos is not "paid for" by a trade-off in the efficiency of yolk conversion.