Postnatal development of the rat CNS following in utero exposure to a low dose of ionizing radiation

Later Life Changes in Hippocampal Neurogenesis and Behavioral Functions After Low-Dose Prenatal Irradiation at Early Organogenesis Stage

PURPOSE

To investigate long-term changes in behavioral functions of mice after exposure to low-dose prenatal radiation at an early organogenesis stage.

METHODS AND MATERIALS

Pregnant C57BL/6J mice were irradiated (20 cGy) at postcoitus day 5.5. The male and female offspring were subjected to different behavioral assays for affective, motor, and cognitive functions at 3, 6, and 12 months of age. Behavioral functions were further correlated with the population of CA1 and CA3 pyramidal neurons and immature neurons in hippocampal dentate gyrus.

RESULTS

Prenatally exposed mice of different age groups showed a sex-specific pattern of sustained changes in behavioral functions. Male mice showed significant changes in anxiety-like phenotypes, learning, and long-term memory at age 3 months. At 6 months of age such behavioral functions were recovered to a normal level but could not be sustained at age 12 months. Female mice showed an appreciable recovery in almost all behavioral functions at 12 months. Patterns of change in learning and long-term memory were comparable to the population of CA1 and CA3 pyramidal neurons and doublecortin-positive neurons in hippocampus.

CONCLUSION

Our finding suggests that prenatal (early organogenesis stage) irradiation even at a lower dose level (20 cGy) is sufficient to cause potential changes in neurobehavioral function at later stages of life. Male mice showed relatively higher vulnerability to radiation-induced neurobehavioral changes as compared with female.

The Chernobyl accident and cognitive functioning: a study of Norwegian adolescents exposed in utero

The results of investigations on the cognitive outcomes of adolescents exposed prenatally to radiation from Chernobyl are inconsistent. In 2005 through 2006, we assessed individuals exposed prenatally (N = 84) and controls (N = 94) using a broad neuropsychological test battery. Neuropsychological performance was significantly weaker in the 84 adolescents exposed prenatally compared to the 94 controls on measures of verbal working memory, verbal memory, and executive functioning when controlling for possible confounders. Our findings add new and important support to the hypothesis that the Chernobyl accident had a specific effect on the neuropsychological functioning of those exposed prenatally.

Late effect of prenatal irradiation on the hippocampal histology and brain weight in adult mice

We studied the changes in the brain weight and hippocampal histology in adult offspring exposed to 0.25-1.5 Gy of 60Co gamma radiations during day 14 or 17 of gestation. Irradiation with 0.5-1.5 Gy produced a significant decrease in brain weight of the offspring at 6 and 12 months of age. Exposure to 1 Gy at day 14 or 17 of gestation resulted in significant decrease in the number of neurons in the CA3 and CA4 regions of hippocampus of 200 microm length, while 1.5 Gy significantly affected CA1 region also. The fetal period (13-18 days of gestation) of mouse development is an active phase of brain development involving proliferation, migration and differentiation of cerebral cortex and associated structures. The present results show that exposure at this period of mouse development to moderate doses of gamma radiation can induce permanent deficits in the brain histology, which can adversely affect the learning and memory in adults.

Prenatal protracted irradiation at very low dose rate induces severe neuronal loss in rat hippocampus and cerebellum

Prenatal irradiation is known to damage the developing brain. However, little is known about the consequences of very low dose rate prenatal protracted irradiation over several days on neuron numbers in the offspring brain, and on volumes of the corresponding brain regions. Pregnant Wistar rats were exposed either to a protracted gamma irradiation from embryonic day (E) 13 to E16 (0.7 mGy/min; total cumulative dose approximately 3 Gy) or were sham-irradiated. Thirty months old male and female offspring were then analyzed for alterations in hippocampal and cerebellar morphology. Using design-based stereology and the analysis of sets of sections systematically and randomly sampled to span the entire brain region of interest, a statistically significant decrease in numbers of hippocampal pyramidal and granule cells as well as of cerebellar Purkinje and granule cells (approximately 50%) was found in male and female irradiated offspring. The volumes of these brain regions were comparably altered. The analysis of only a "representative" section per animal yielded mostly non-significant trends. Evaluation of neuron densities showed no differences between prenatally irradiated and sham-irradiated offspring. Most importantly, very low dose rate prenatal protracted gamma irradiation did not result in the same morphologic alterations in the offspring brain as previously observed after prenatal single irradiation such as derangement of the laminar structure of pyramidal cells within the hippocampus or malformation of cerebellar lobules.

Contralateral response of macrophages and astrocytes to injury in the cerebral hemisphere of 6‐day‐old rat following prenatal gamma irradiation

Wistar pregnant rats were exposed to a single 1.0 Gy dose of gamma rays on gestational days 13, 15, 17 or 19 (E13, E15, E17 and E19, respectively). When offsprings of the irradiated females became 6-day-old, they received a mechanical injury of the cerebral hemisphere. One or 2 days after the injury, [3H]thymidine was injected and the animals were perfused. Brain sections were processed for BSI-B4 isolectin histochemistry or immunohistochemistry for glial fibrillary acidic protein (GFAP) or S-100-beta protein and subjected to autoradiography to visualise proliferating and non-proliferating macrophages or proliferating astrocytes. Significant changes in the contralateral response to injury related to the day of prenatal irradiation could be detected. The response was minimal following irradiations performed on E15 and E17. At those stages of prenatal development, the majority of cortical neurons with interhemispheric connections were formed. Therefore, irradiation-induced reduction of the neurons might minimise transfer of pathogenic stimuli to contralateral areas via degenerating nerve fibers. Consequently, the degree at which the contralateral glial response reflected reactive changes at the lesion site might also be minimal. Results of the present study do not show in detail mechanisms underlying the differences in the contralateral reactivity to injury. They, however, might be of importance to histopathological investigations using animal models of cerebral dysplasia.

Cerebellum as a target for toxic substances

The Purkinje cells and the granule cells are the most important targets in cerebellum for toxic substances. The Purkinje cells are among the largest neuron in the brain and are very sensitive to ischaemia, bilirubin, ethanol and diphenylhydantoin. The granule cells are small and seem to be sensitive to loss of intracellular glutathione. Granule cells are sensitive to methyl halides, thiophene, methyl mercury, 2-chloropropionic acid and trichlorfon. The Purkinje cells appear in the rat brain on pre-natal day 14-16, whereas the granule cells appear post-natally. Both cells are sensitive to excitotoxic chemicals and also to an effect on DNA or its repair mechanisms.

Effects of prenatal gamma-irradiation on postnatal astrogliogenesis in the hippocampal formation of rat

Female Wistar rats were exposed to a single 1.0 Gy dose of gamma radiation on gestational days 13, 15, 17 or 19 (E13, E15, E17 and E19, respectively). Their 8- and 16-day old male offsprings were injected with 3H-thymidine and sacrificed 4 h after the injection. Brain sections were immunostained for S100beta protein and subjected to autoradiography. Thereafter, the dorsal part of the hippocampal formation was examined microscopically and numbers and locations of proliferating astrocytes were recorded. Following prenatal irradiation, the intensity of astrocyte proliferation was considerably reduced, especially in the region of dentate gyrus. The reduction showed regular trend of changes being much stronger in brains irradiated on E19 than in those irradiated on E13. The changes, therefore, were related to the stage of brain development at which the irradiation was performed. A possible role of neuronal regulatory influence on the postnatal development of glial cells was discussed.

Opposite trends of changes in reactive behaviours of macrophages and astrocytes following gamma-irradiation performed at different stages of prenatal development. A study in the injured brain of 6-day-old rat

Pregnant Wistar rats were exposed to a single 1.0 Gy dose of gamma rays on gestational days 13, 15, 17 or 19 (E13s, E15s, E17s and E19s, respectively). A mechanical injury was made in the cerebral hemisphere of their 6 day-old male offsprings. The injured rats were injected with [3H] thymidine on day 1 or 2 after injury and killed 4 h after the injection. Brain sections were processed for BSI-B4 isolectin histochemistry, subjected to autoradiography and examined microscopically to record numbers of proliferating and unproliferating macrophages located within the region of injury. The total number of macrophages as well as number of their divisions were minimal in E13s then showed a regular increase in E15s and E17s, and reached its maximal level in brains irradiated on E19. The trend of changes was opposite to that showed by changes in the intensity of astrocyte proliferation [Z. Setkowicz, K. Janeczko, Effects of prenatal gamma-irradiation on the astrocyte proliferation in response to injury in the brain of 6-day-old rat, Brain Res. 803 (1998) 122-128.]. The recruitment and proliferation of macrophages and the astrocyte proliferation were regarded as reactive processes occurring under control of different regulatory mechanisms acting within the region of injury.

Effects of prenatal gamma-irradiation on the astrocyte proliferation in response to injury in the brain of 6-day-old rat

Pregnant Wistar rats were exposed to a single 1.0 Gy dose of gamma rays on gestational days 13, 15, 17 or 19 (E13, E15, E17 and E19, respectively). A mechanical injury was made in the cerebral hemisphere of their 6 day-old male offsprings. The injured rats were injected with [3H]thymidine on day 1 or 2 after injury and killed 4 h after the injection. Brain sections were immunostained for glial fibrillary acidic protein (GFAP) or S-100beta protein, subjected to autoradiography and examined microscopically to record proliferating astrocytes. The intensity of astrocyte proliferation in response to injury showed a gradual decrease from the level maximal in brains irradiated on E13 to minimal in those irradiated on E19. The changes were regarded as being related to the stage of prenatal development when irradiation of the brain was performed.

Long-term postnatal effect of prenatal irradiation on the astrocyte proliferative response to brain injury

Pregnant Wistar rats were exposed to a single 1.0 Gy dose of gamma-irradiation on gestational day 13, 15, 17 or 19. Thirty-day-old male offspring received a mechanical lesion in the left cerebral hemisphere. One, 2 or 4 days after the injury the rats were injected with [3H]thymidine and sacrificed 4 h after the injection. Thereafter, brain sections were immunostained for GFAP or S100 beta protein, subjected to autoradiography and examined microscopically to record immunopositive astrocytes labelled with [3H]thymidine. Statistically significant elevation of the reactive astrocyte proliferation was revealed on the 2nd day following injury in brains irradiated on gestational day 15. The results represent the first in vivo evidence that a low-dose prenatal gamma-irradiation can induce a long-term increase in the ability of astroglia to proliferate in response to injury.