EEG, cognitive and psychopathological abnormalities in children irradiated in utero

Epidemiological and experimental evidence for radiation-induced health effects in the progeny after exposure in utero

PURPOSE

It has been known for many decades that radiation exposure of the developing embryo or fetus may cause two fundamentally different types of severe health effects: on the one hand, radiation may interfere with the normal intrauterine development, on the other hand, radiation may induce leukemia and cancer which become manifest in childhood. A large amount of epidemiological and experimental data has recently been presented which might be used to improve our understanding of underlying mechanisms and setting radiation protection standards. Yet, ecological studies in the populations exposed to increased levels of radiation in regions contaminated by radioactivity released from reactor accidents (Chernobyl, Fukushima) do not provide solid evidence which would contribute to this aim. On the other hand, well designed experimental studies demonstrated the multifactorial mechanisms which lead to different health effects after radiation exposure in utero.

CONCLUSION

There is no convincing evidence, neither from epidemiological nor experimental data of the existence of a dose threshold for developmental defects after radiation exposure in utero. This must be taken into account in the revision of rules and regulations of radiation protection in medicine.

Cognitive effects of low dose of ionizing radiation - Lessons learned and research gaps from epidemiological and biological studies

The last decades have seen increased concern about the possible effects of low to moderate doses of ionizing radiation (IR) exposure on cognitive function. An interdisciplinary group of experts (biologists, epidemiologists, dosimetrists and clinicians) in this field gathered together in the framework of the European MELODI workshop on non-cancer effects of IR to summarise the state of knowledge on the topic and elaborate research recommendations for future studies in this area. Overall, there is evidence of cognitive effects from low IR doses both from biology and epidemiology, though a better characterization of effects and understanding of mechanisms is needed. There is a need to better describe the specific cognitive function or diseases that may be affected by radiation exposure. Such cognitive deficit characterization should consider the human life span, as effects might differ with age at exposure and at outcome assessment. Measurements of biomarkers, including imaging, will likely help our understanding on the mechanism of cognitive-related radiation induced deficit. The identification of loci of individual genetic susceptibility and the study of gene expression may help identify individuals at higher risk. The mechanisms behind the radiation induced cognitive effects are not clear and are likely to involve several biological pathways and different cell types. Well conducted research in large epidemiological cohorts and experimental studies in appropriate animal models are needed to improve the understanding of radiation-induced cognitive effects. Results may then be translated into recommendations for clinical radiation oncology and imaging decision making processes.

Reduced Midbrain Dopamine Neuron Number in the Adult Non-human Primate Brain after Fetal Radiation Exposure

Early gestation is a neurodevelopmental period that is especially vulnerable to environmental insult and one in which neurogenesis features prominently. Prenatal perturbation during early gestation has been linked to neuropsychiatric illnesses such as autism and schizophrenia, and severe environmental insult during this period can result in profound mental impairment. Midbrain dopamine neurons are generated during early gestation and play a key role in the motor, cognitive and reward circuitries implicated in neuropsychiatric disease and addiction. This study examined the impact of curtailing neurogenesis in early gestation on neuron number in the midbrain dopamine group, i.e., the substantia nigra and contiguous ventral tegmental area. Rhesus macaque monkeys were exposed in utero on embryonic days 39-41 to x-irradiation (3-4 exposures of 50 cGy over 3-7 days totalling <200 cGy) and allowed to mature to full adulthood. Stereologic cell counts of tyrosine hydroxylase-positive neurons in the midbrain dopamine group were performed in adult monkeys, as were measurements of somal size. Mean total neuron number in the irradiated monkeys was significantly reduced on average by 33% compared to that of the control group. Somal size did not differ between the groups, suggesting that the integrity of survivor populations was not impacted. Reduced midbrain dopamine neuron number in fetally irradiated, adult monkeys indicates that radiation exposure during the critical period of neurogenesis results in an enduring reduction of this population and underscores the susceptibility of early neurodevelopmental processes to irreversible damage from environmental exposures.

PSYCHOLOGICAL STATE AND TYPOLOGICAL PERSONALITY FEATURES OF CHILDREN RESIDENTS OF RADIOACTIVELY CONTAMINATED TERRITORIES IN THE REMOTE PERIOD OF CHORNOBYL СATASTROPHE

OBJECTIVE

To evaluate the psycho-emotional state of children-residents of radioactively contaminated territoriesand to characterize the typological features of their personality in the remote period of the Chornobyl catastrophe.

MATERIALS AND METHODS

Psycho-emotional status and typological personality traits were determined in 96 childrenaged 12 to 17 years, who resided in radioactively contaminated territories with a soil contamination density of 137Csabove 185 kBq/m-2, and were admitted for examination and treatment in the pediatric departments of the NRCRMclinic. Psycho-emotional state of children was determined using the test «non-existent animal», which was assessedin points on symptom complexes: anxiety, aggression and neuro-mental exhaustion. The questionnaire of A. Bassand A. Darkey was used to discriminate various aspects of the aggression symptom complex. In all children, the content of incorporated 137Cs was determined using a whole body counter.

RESULTS

The results of the evaluation of the psycho-emotional state of children - residents of radioactively contaminated territories in the remote period of the Chornobyl catastrophe according to the test «non-existent animal»showed, that the state of anxiety was registered in all 96 children (100 %); state of aggression - in 60 children(62.5 %); exhaustion - in 57 children (59.37 %). Depending on the prevalence of the one or another symptom complexes, or their combination, 5 groups of observations were formed and the personality traits of children characteristic for each group were determined. In the largest group I with the predominance of anxiety symptom complex(45,83 % of the total sample) were noted: stable tendency to perceive many life-threatening situations and environment, pessimistic assessment of one's own life perspective, constant high level of anxiety. Girls were in majorityin this group. For group II, which showed a combination of high rates of two symptom complexes - anxiety andaggression (18.75 % of the total sample), the characteristic personality traits were a constant high level of emotional tension, a tendency to perceive the environment with distrust and a sense of guilt that arouses. In group IIIof children (14.58 % of the total sample), the symptom complex of aggression with feelings of alienation, isolationand hostile attitude towards the environment prevailed. Group IV of children (16.67 % of the total sample), with thecombination of signs of exhaustion and anxiety, had poor ability to concentrate, memory and attention deficit disorders, decreased learning ability, constant fatigue and irritability, apathy, inactivity, and inertia. Group V (only 4.17 %of the total sample) was characterized by low (less than 2 points) indices of all three symptom complexes. Girls weremuch more prone to anxiety, boys were more aggressive, sometimes accompanied by anxiety. Symptom complex ofexhaustion was determined with the same frequency in both boys and girls.

CONCLUSION

Assessment of psycho-emotional sphere of children - residents of radioactively contaminated territories in the remote period of the Chornobyl catastrophe according to the «non-existent animal» test revealed in of100 % of children the presence of anxiety signs, in the vast majority - the state of aggression and exhaustion. Therewere no probable associations between the content of incorporated 137Cs (in the range from 111 to 7024 Bq) and thepeculiarities of the psycho-emotional state of children.

Low dose or low dose rate ionizing radiation-induced health effect in the human

The extensive literature review on human epidemiological studies suggests that low dose ionizing radiation (LDIR) (≤100 mSv) or low dose rate ionizing radiation (LDRIR) (<6mSv/H) exposure could induce either negative or positive health effects. These changes may depend on genetic background, age (prenatal day for embryo), sex, nature of radiation exposure, i.e., acute or chronic irradiation, radiation sources (such as atomic bomb attack, fallout from nuclear weapon test, nuclear power plant accidents, ⁶⁰Co-contaminated building, space radiation, high background radiation, medical examinations or procedures) and radionuclide components and human epidemiological experimental designs. Epidemiological and clinical studies show that LDIR or LDRIR exposure may induce cancer, congenital abnormalities, cardiovascular and cerebrovascular diseases, cognitive and other neuropsychiatric disorders, cataracts and other eye and somatic pathology (endocrine, bronchopulmonary, digestive, etc). LDIR or LDRIR exposure may also reduce mutation and cancer mortality rates. So far, the mechanisms of LDIR- or LDRIR -induced health effect are poorly understood. Further extensive studies are still needed to clarify under what circumstances, LDIR or LDRIR exposure may induce positive or negative effects, which may facilitate development of new therapeutic approaches to prevent or treat the radiation-induced human diseases or enhance radiation-induced positive health effect.

Chronic exposure of adult, postnatal and in utero rat models to low-dose 137Cesium: impact on circulating biomarkers

The presence of 137Cesium (137Cs) in the environment after nuclear accidents at Chernobyl and more recently Fukushima Daiichi raises many health issues for the surrounding populations chronically exposed through the food chain. To mimic different exposure situations, we set up a male rat model of exposure by chronic ingestion of a 137Cs concentration likely to be ingested daily by residents of contaminated areas (6500 Bq.l-1) and tested contaminations lasting 9 months for adult, neonatal and fetal rats. We tested plasma and serum biochemistry to identify disturbances in general indicators (lipids, proteins, carbohydrates and electrolytes) and in biomarkers of thyroid, heart, brain, bone, kidney, liver and testis functions. Analysis of the general indicators showed increased levels of cholesterol (+26%), HDL cholesterol (+31%), phospholipids B (+15%) and phosphorus (+100%) in the postnatal group only. Thyroid, heart, brain, bone and kidney functions showed no blood changes in any model. The liver function evaluation showed changes in total bilirubin (+67%) and alkaline phosphatase (-11%) levels, but only for the rats exposed to 137Cs intake in adulthood. Large changes in 17β-estradiol (-69%) and corticosterone (+36%) levels affected steroidogenesis, but only in the adult model. This study showed that response profiles differed according to age at exposure: lipid metabolism was most radiosensitive in the postnatal model, and steroid hormone metabolism was most radiosensitive in rats exposed in adulthood. There was no evidence of deleterious effects suggesting a potential impact on fertility or procreation.

Current Evidence for Developmental, Structural, and Functional Brain Defects following Prenatal Radiation Exposure

Ionizing radiation is omnipresent. We are continuously exposed to natural (e.g., radon and cosmic) and man-made radiation sources, including those from industry but especially from the medical sector. The increasing use of medical radiation modalities, in particular those employing low-dose radiation such as CT scans, raises concerns regarding the effects of cumulative exposure doses and the inappropriate utilization of these imaging techniques. One of the major goals in the radioprotection field is to better understand the potential health risk posed to the unborn child after radiation exposure to the pregnant mother, of which the first convincing evidence came from epidemiological studies on in utero exposed atomic bomb survivors. In the following years, animal models have proven to be an essential tool to further characterize brain developmental defects and consequent functional deficits. However, the identification of a possible dose threshold is far from complete and a sound link between early defects and persistent anomalies has not yet been established. This review provides an overview of the current knowledge on brain developmental and persistent defects resulting from in utero radiation exposure and addresses the many questions that still remain to be answered.

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.

Selective reduction of neuron number and volume of the mediodorsal nucleus of the thalamus in macaques following irradiation at early gestational ages

Neurons in the macaque brain arise from progenitors located near the cerebral ventricles in a temporally segregated manner such that lethal doses of ionizing irradiation, if administered over a discrete time interval, can deplete individual nuclei selectively. A previous study showed that neuron number in the dorsal lateral geniculate nucleus is reduced following early gestational exposure to x-irradiation (Algan and Rakic [1997] J. Comp. Neurol. 12:335-352). Here we examine whether similarly timed irradiation decreases neuron number in three associational thalamic nuclei: mediodorsal (MD), anterior, and pulvinar. Ten macaques were exposed to multiple doses of x-rays (total exposure (175-350 cGy) in early gestation (E33-E42) or midgestation (E70-E90); eight nonirradiated macaques were controls. Only the early-irradiated monkeys, not the midgestationally irradiated animals, exhibited deficits in whole-thalamic neuron (-15%) and glia numbers (-21%) compared with controls. Reduction of neuron number (-26%) and volume (-29%) was particularly pronounced in MD. In contrast, cell number and volume were not significantly decreased in the anterior or pulvinar nuclei following early gestational irradiation. Thus, reduced thalamic neuron number was associated specifically with irradiation in early gestation. Persistence of the thalamic neuronal deficit in adult animals indicates that prenatally deleted neurons had not been replenished during maturation or in adulthood. The selective reduction of MD neuron number also supports the protomap hypothesis that neurons of each thalamic nucleus originate sequentially from separate lines of neuronal stem cells (Rakic [1977a] J. Comp. Neurol. 176:23-52). The early gestationally irradiated macaque is discussed as a potentially useful model for studying the neurodevelopmental pathogenesis of schizophrenia.

Radiation, retardation and the developing brain: time is the crucial variable

BACKGROUND

Widespread radiation is a threat unique to the modern world. A recent report reveals that sub-clinical damage to human foetuses between 8 and 25 weeks of gestation can result in cognitive deficits still manifest 16-18 years after birth. These previously unrecognised, long-term effects are apparently produced by a relatively short pulse of exposure to radioactive fallout at levels that were previously thought not to be deleterious. This idea is plausible given the nature of the developmental events occurring in the brain during this period of gestation.

CONCLUSION

This exposed population should be examined for other neurological and psychiatric syndromes. If these findings are corroborated, in the event of future radiation exposures, steps should be taken to shield pregnant women who are within this window of vulnerability.

Evaluation of the effect of chronic exposure to 137Cesium on sleep–wake cycle in rats

Since the Chernobyl accident, the most significant problem for the population living in the contaminated areas is chronic exposure by ingestion of radionuclides, notably (137)Cs, a radioactive isotope of cesium. It can be found in the whole body, including the central nervous system. The present study aimed to assess the effect of (137)Cs on the central nervous system and notably on open-field activity and the electroencephalographic pattern. Rats were exposed up to 90 days to drinking water contaminated with (137)Cs at a dosage of 400 Bq kg(-1), which is similar to that ingested by the population living in contaminated territories. At this level of exposure, no significant effect was observed on open-field activity. On the other hand, at 30 days exposure, (137)Cs decreased the number of episodes of wakefulness and slow wave sleep and increased the mean duration of these stages. At 90 days exposure, the power of 0.5-4 Hz band of (137)Cs-exposed rats was increased in comparison with controls. These electrophysiological changes may be due to a regional (137)Cs accumulation in the brain stem. In conclusion, the neurocognitive effects of (137)Cs need further evaluation and central disorders of population living in contaminated territories must be considered.

Functional correlations of spatial quantitative EEG and intelligences in a nonalphabetical language group

This study investigated any functional correlations between intelligences and spatially recorded quantitative electroencephalograms (QEEGs) in a nonalphabetical language group. Participants, between 6 and 8 years old, were sampled in a teaching hospital located at the central Taiwan region. The Chinese Wechsler Intelligence Scale for Children-III (WISC-III) intelligence test and quantitative electroencephalograph recording procedures were both administrated to collect data. Intelligences were divided into two categories, verbal and performance intelligences, for statistical investigations. Statistical analyses of the noncontaminated QEEG dataset investigated the differentiability of each frequency on a single cortical region and coherence between cortical regions. Low QEEG frequencies were found to have a significant correlation with intelligences on some cortical regions. Coherence between symmetric cortical regions was found to be an important factor in predicting intelligences. Results showed the feasibility of functional brain mapping in the particular language population.

Direct and indirect effects of fetal irradiation on cortical gray and white matter volume in the macaque

BACKGROUND

Schizophrenia is associated with reductions in thalamic neuronal number and cortical gray matter volume. Exposure of nonhuman primates to x-irradiation in early gestation has previously been shown to decrease thalamic volume and neuronal number. Here we examine whether early gestational irradiation also results in cortical volume reduction.

METHODS

High-resolution, T1-weighted magnetic resonance scans were collected in adult monkeys 1) exposed to irradiation during the early gestational period (E33-E42) corresponding to thalamic neurogenesis, 2) irradiated in midgestation (E70-81) during neocortical neurogenesis, and 3) not exposed to irradiation. Cortical gray matter and white matter volumes were derived via manual segmentation; frontal and nonfrontal volumes were distinguished via sulcal landmarks.

RESULTS

Monkeys irradiated in early gestation exhibited a trend reduction in nonfrontal gray matter volume (17%) and significant reductions in white matter volume in frontal (26%) and nonfrontal (36%) lobes. Monkeys irradiated in midgestation had smaller gray (frontal: 28%; nonfrontal: 22%) and white matter (frontal: 29%; nonfrontal: 38%) volumes.

CONCLUSIONS

The cortical deficits observed in midgestationally irradiated monkeys are consistent with a reduction in cortical neuronal number. Cortical volume reductions following early gestational irradiation may be secondary to reduced thalamic neuronal number and therefore model the thalamocortical pathology of schizophrenia.