Teratogenic effects of repeated exposures to X-rays and/or ultrasound in mice

In utero exposure to ionizing radiation and metabolic regulation: perspectives for future multi- and trans-generation effects studies

PURPOSE

The radiation protection community has been particularly attentive to the risks of delayed effects on offspring from low dose or low dose-rate exposures to ionizing radiation. Despite this, the current epidemiologic studies and scientific data are still insufficient to provide the necessary evidence for improving risk assessment guidelines. This literature review aims to inform future studies on multigenerational and transgenerational effects. It primarily focuses on animal studies involving in utero exposure and discusses crucial elements for interpreting the results. These elements include in utero exposure scenarios relative to the developmental stages of the embryo/fetus, and the primary biological mechanisms responsible for transmitting heritable or hereditary effects to future generations. The review addresses several issues within the contexts of both multigenerational and transgenerational effects, with a focus on hereditary perspectives.

CONCLUSIONS

Knowledge consolidation in the field of Developmental Origins of Health and Disease (DOHaD) has led us to propose a new study strategy. This strategy aims to address the transgenerational effects of in utero exposure to low dose and low dose-rate radiation. Within this concept, there is a possibility that disruption of epigenetic programming in embryonic and fetal cells may occur. This disruption could lead to metabolic dysfunction, which in turn may cause abnormal responses to future environmental challenges, consequently increasing disease risk. Lastly, we discuss methodological limitations in our studies. These limitations are related to cohort size, follow-up time, model radiosensitivity, and analytical techniques. We propose scientific and analytical strategies for future research in this field.

Mechanical and Biological Effects of Ultrasound: A Review of Present Knowledge

Ultrasound is widely used for medical diagnosis and increasingly for therapeutic purposes. An understanding of the bio-effects of sonography is important for clinicians and scientists working in the field because permanent damage to biological tissues can occur at high levels of exposure. Here the underlying principles of thermal mechanisms and the physical interactions of ultrasound with biological tissues are reviewed. Adverse health effects derived from cellular studies, animal studies and clinical reports are reviewed to provide insight into the in vitro and in vivo bio-effects of ultrasound.

Potential teratogenic effects of ultrasound on corticogenesis: implications for autism

The phenotypic expression of autism, according to the Triple Hit Hypothesis, is determined by three factors: a developmental time window of vulnerability, genetic susceptibility, and environmental stressors. In utero exposure to thalidomide, valproic acid, and maternal infections are examples of some of the teratogenic agents which increase the risk of developing autism and define a time window of vulnerability. An additional stressor to genetically susceptible individuals during this time window of vulnerability may be prenatal ultrasound. Ultrasound enhances the genesis and differentiation of progenitor cells by activating the nitric oxide (NO) pathway and related neurotrophins. The effects of this pathway activation, however, are determined by the stage of development of the target cells, local concentrations of NO, and the position of nuclei (basal versus apical), causing consequent proliferation at some stages while driving differentiation and migration at others. Ill-timed activation or overactivation of this pathway by ultrasound may extend proliferation, increasing total cell number, and/or may trigger precipitous migration, causing maldistribution of neurons amongst cortical lamina, ganglia, white matter, and germinal zones. The rising rates of autism coincident with the increased use of ultrasound in obstetrics and its teratogenic/toxic effects on the CNS demand further research regarding a putative correlation.

Effect of diagnostic ultrasound during the fetal period on learning and memory in mice

BACKGROUND

An experiment was conducted to find out whether in utero exposure to diagnostic ultrasound leads to changes in postnatal behavior in adult mice.

METHODS

A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm(2), intensity((spatial peak-temporal peak)) (I(SPTP))=1 mW/cm(2), intensity((spatial average-temporal average)) (I(SATA))=240 mW/cm(2)) for 30 min on day 14 or 16 of gestation. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers (such as pinna detachment, eye opening and fur development) and postnatal mortality was recorded up to 6 weeks of age. The litters were subjected to behavioral tests for learning and memory at 4 months of age. Representative animals from each group were sacrificed and the hippocampal region of the brain was assayed for biogenic amines, noradrenaline, dopamine, serotonin (5-HT) and 5-HT's metabolite, 5-hydroxy indoleacetic acid (5-HIAA), in order to determine whether ultrasound exposure produced any biochemical changes in the hippocampal region of the brain. Coronal sections from the dorsal hippocampus from the representative animals from each group were processed for staining and the number of neurons was counted.

RESULTS

Neither the standard developmental markers (such as pinna detachment, eye opening and fur development) nor the postnatal mortality was affected by ultrasound exposure. However, there was a significant impairment in learning (hole board test) and memory functions (shuttle box test) in both the exposure groups. Significant reductions in the biogenic amines and the decrease in the neuronal density were found only in day 14th pc ultrasound-exposed group compared with the control animals. The 16th day exposure group is relatively resistant to ultrasound-induced impairment of brain functions.

CONCLUSIONS

The results suggest that the early fetal brain is highly susceptible to induction of neurobehavioral changes by ultrasound exposure.

Gestational stage sensitivity to ultrasound effect on postnatal growth and development of mice

BACKGROUND

An experiment was conducted to find out whether ultrasound exposure leads to changes in postnatal growth and development in the mouse.

METHODS

A total of 15 pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, 65 mW/cm2, I(SPTP) = 1 mW/cm2 Intensity(Spatial Peak-Temporal Peak), I(SATA) = 240 mW/cm2 Intensity(Spatial Average-Temporal Average)) for 30 min for a single day between days 10 and 18 of gestation (GD 10-18). Virgin female mice were placed with same age group males for mating in the ratio 2 females : 1 male and examined the next morning for the presence of vaginal plug, a sign of successful copulation. The females with vaginal plugs were separated and labeled as 0-day pregnant. Maternal vaginal temperature was also measured. A sham exposed control group of 15 pregnant mice was maintained for comparison. All exposed as well as control animals were left to complete gestation and parturition. Their offspring were used in our further studies. They were monitored during early postnatal life for standard developmental markers, postnatal mortality, body weight, body length, head length, and head width, and growth restriction was recorded up to 6 weeks of age.

RESULTS

An exposure to ultrasound induced nonsignificant deviations in the maternal vaginal temperature or developmental markers. Significant low birth weight was observed in the present study, after exposure at GD 11, 12, 14, and 16. However, 14 and 16 days postcoitus during the fetal period appears to be the most sensitive to the ultrasound effect, in view of the number of different effects as well as severity of most of the observed effects when exposed on these gestation days.

CONCLUSIONS

The results indicate that diagnostic ultrasound can induce harmful effects on mouse growth and development when given at certain critical periods of gestation.

Biological effects of high-frequency ultrasound exposure during mouse organogenesis

Little has been reported on bioeffects of high-frequency ultrasound (US) and guidelines for US use do not necessarily apply to high frequencies. Pregnant CD-1 mice were exposed to Doppler or B-mode US biomicroscopy (UBM) on embryonic day (E) 8.5 or E10.5, during organogenesis. Operating frequency was 40 MHz with a free field I(SPTA) of 11.9 W/cm(2) (Doppler) and 2.6 mW/cm(2) (B-mode), peak negative pressures of 6.61 MPa and MI of 1.05 (B-mode). Offspring were assessed weekly from 1 day postnatally to euthanasia at 6 weeks, with no significant difference in pup weight, body length or crown-rump length observed. E8.5 Doppler-exposed mice showed a small reduction in weight and length at 3 weeks and in weight at 6 weeks. E10.5 Doppler-exposed animals exhibited slight growth reduction in weeks 2 to 4, but were not significantly different at 6 weeks. Our results indicate similar exposures of mice should not cause significant adverse bioeffects.

Long-term effects of diagnostic ultrasound during fetal period on postnatal development and adult behavior of mouse

Pregnant Swiss albino mice were exposed to diagnostic levels of ultrasound (3.5 MHz, intensity 65 mW, I(SPTP) = 1 W/cm(2), I(SATA) = 240 W/cm(2)) for 10, 20 and 30 minutes on day 14 of gestation. Sham exposed controls were maintained for comparison. Fifteen pregnant mice were exposed for each group. Exposed as well as control animals were left to complete gestation and parturition. Ultrasound induced changes in maternal vaginal temperature was recorded. The changes in the physiological reflexes and postnatal mortality up to 6 weeks of age were recorded. The litters were subjected to behavioral tests for locomotor activity, learning and memory at 4 month and 1 year of age. Neither the physiological reflexes nor the postnatal mortality was affected by ultrasound exposure. However, there was a noticeable impairment in both locomotor and learning behavior even after a 10 min exposure, which further increased with increases in exposure time. Thus the present study demonstrates the neurotoxicity of diagnostic ultrasound and the high susceptibility of early fetal brain to induction of lasting detrimental changes by ultrasound exposure.

Influence of gestational age to low-level gamma irradiation on postnatal behavior in mice

The present investigation was carried out to study the effects of in utero exposure to low-level gamma radiation (0.25, 0.35, or 0.50 Gy) on the postnatal neurophysiology and neurochemistry of the mouse. Pregnant Swiss albino mice were irradiated on days 11.5, 12.5, 14.5, or 17.5 post coitus (PC) and allowed to deliver. Locomotor and exploratory activities, learning and memory functions, and emotional activities were tested at 3 months of age using behavior tests. A representative group of animals was killed and hippocampal biogenic amines, noradrenaline, dopamine, serotonin (5-HT), and 5-HT's metabolite 5-hydroxy indoleactetic acid (5-HIAA), were measured. Exposure to 0.25 Gy at any of the gestation days did not produce any significant impairment in brain functions. However, an increase in gamma irradiation to 0.50 Gy on all the gestation days produced significant impairment in locomotor (open-field test) and anxiolytic (light and dark area test) activities, learning (hole board test), memory functions (active avoidance test), and emotional activity (rearings). The late fetal period is relatively resistant to radiation-induced impairment of brain functions. Both of the organogenesis gestation days showed a higher sensitivity than the fetal gestation days studied. Even a lower dose of 0.35 Gy when exposed on the late organogenesis days 11.5 and 12.5 PC, produced significant reduction in locomotor and exploratory activities. Day 11.5 PC showed a higher sensitivity than the other PC days studied. Biogenic amines did not show significant change after any of the exposures on any of the gestation days. The results suggest a threshold between 0.25 to 0.35 Gy for postnatal neurobehavior changes.

Effect of late fetal irradiation on adult behavior of mouse: Dose-response relationship

Pregnant Swiss mice were exposed to 0.3-1.5 Gy of gamma radiation on day 17 of gestation and allowed to deliver the offspring. When the F1 mice were 6 months old, they were subjected to a number of behavioral tests. Open-field and dark-bright arena tests were conducted to study locomotor and exploratory activities. Learning and memory were tested by holeboard activity, conditioned avoidance response, and radial arm maze performance. After all the tests, 20 animals (10 males and 10 females) from each group were killed, and their brain weight was taken. The open-field and dark-bright arena tests showed a significant dose-dependent decrease in the locomotor and exploratory activities. Reduction in time spent in the dark area and higher locomotor activity in the bright area indicated a reduced aversion to bright light. But the emotional activities like rearing and grooming did not change. The learning and memory functions also showed a significant impairment, even at 0.3 Gy. The deficit in the performance in the holeboard test, conditioned avoidance response, as well as maze-learning efficiency, decreased linearly with increase in radiation dose. The brain weight showed a linear dose-dependent decrease. But the brain/body weight ratio was not significantly affected even at 1.5 Gy. These results demonstrate that exposure of a mouse on day 17 of gestation to radiation doses below 1.0 Gy can induce significant impairment in the adult brain function, without producing any notable effects on brain morphology. This study also suggests that the retardation of higher brain function by exposures during the late fetal period may have a threshold of around 0.3 Gy.