Single session high definition transcranial direct current stimulation to the cerebellum does not impact higher cognitive function

The prefrontal cortex is central to higher order cognitive function. However, the cerebellum, generally thought to be involved in motor control and learning, has also been implicated in higher order cognition. Recent work using transcranial direct current stimulation (tDCS) provides some support for right cerebellar involvement in higher order cognition, though the results are mixed, and often contradictory. Here, we used cathodal high definition tDCS (HD-tDCS) over the right cerebellum to assess the impact of HD-tDCS on modulating cognitive performance. We predicted that stimulation would result in performance decreases, which would suggest that optimal cerebellar function is necessary for cognitive performance, much like the prefrontal cortex. That is, it is not simply a structure that lends support to complete difficult tasks. While the expected cognitive behavioral effects were present, we did not find effects of stimulation. This has broad implications for cerebellar tDCS research, particularly for those who are interested in using HD-tDCS as a way of examining cerebellar function. Further implications, limitations, and future directions are discussed with particular emphasis on why null findings might be critical in developing a clear picture of the effects of tDCS on the cerebellum.

Radiofrequency electromagnetic radiation-induced behavioral changes and their possible basis

The primary objective of mobile phone technology is to achieve communication with any person at any place and time. In the modern era, it is impossible to ignore the usefulness of mobile phone technology in cases of emergency as many lives have been saved. However, the biological effects they may have on humans and other animals have been largely ignored and not been evaluated comprehensively. One of the reasons for this is the speedy uncontrollable growth of this technology which has surpassed our researching ability. Initiated with the first generation, the mobile telephony currently reaches to its fifth generation without being screened extensively for any biological effects that they may have on humans or on other animals. Mounting evidences suggest possible non-thermal biological effects of radiofrequency electromagnetic radiation (RF-EMR) on brain and behavior. Behavioral studies have particularly concentrated on the effects of RF-EMR on learning, memory, anxiety, and locomotion. The literature analysis on behavioral effects of RF-EMR demonstrates complex picture with conflicting observations. Nonetheless, numerous reports suggest a possible behavioral effect of RF-EMR. The scientific findings about this issue are presented in the current review. The possible neural and molecular mechanisms for the behavioral effects have been proposed in the light of available evidences from the literature.

iTRAQ quantitatively proteomic analysis of the hippocampus in a rat model of accumulative microwave-induced cognitive impairment

Central nervous system is sensitive and vulnerable to microwave radiation. Numerous studies have reported that microwave could damage cognitive functions, such as impairment of learning and memory ability. However, the biological effects and mechanisms of accumulative microwave radiation on cognitive functions were remained unexplored. In this study, we analyzed differential expressed proteins in rat models of microwave-induced cognitive impairment by iTRAQ high-resolution proteomic method. Rats were exposed to 2.856 GHz microwave (S band), followed by 1.5 GHz microwave exposure (L band) both at an average power density of 10 mW/cm² (SL10 group). Sham-exposed (control group), 2.856 GHz microwave-exposed (S10 group), or 1.5 GHz microwave-exposed (L10 group) rats were used as controls. Hippocampus was isolated, and total proteins were extracted at 7 days after exposure, for screening differential expressed proteins. We found that accumulative microwave exposure induced 391 differential expressed proteins, including 9 downregulated and 382 upregulated proteins. The results of GO analysis suggested that the biological processes of these proteins were related to the adhesion, translation, brain development, learning and memory, neurogenesis, and so on. The cellular components mainly focused on the extracellular exosome, membrane, and mitochondria. The molecular function contained the protein complex binding, protein binding, and ubiquitin-protein transferase activity. And, the KEGG pathways mainly included the synaptic vesicle cycle, long-term potentiation, long-term depression, glutamatergic synapse, and calcium signaling pathways. Importantly, accumulative exposure (SL10 group) caused more differential expressed proteins than single exposure (S10 group or L10 group). In conclusion, 10 mW/cm² S or L band microwave induced numerous differential expressed proteins in the hippocampus, while accumulative exposure evoked strongest responses. These proteins were closely associated with cognitive functions and were sensitive to microwave.

Light Affects Mood and Learning through Distinct Retina-Brain Pathways

Light exerts a range of powerful biological effects beyond image vision, including mood and learning regulation. While the source of photic information affecting mood and cognitive functions is well established, viz. intrinsically photosensitive retinal ganglion cells (ipRGCs), the central mediators are unknown. Here, we reveal that the direct effects of light on learning and mood utilize distinct ipRGC output streams. ipRGCs that project to the suprachiasmatic nucleus (SCN) mediate the effects of light on learning, independently of the SCN's pacemaker function. Mood regulation by light, on the other hand, requires an SCN-independent pathway linking ipRGCs to a previously unrecognized thalamic region, termed perihabenular nucleus (PHb). The PHb is integrated in a distinctive circuitry with mood-regulating centers and is both necessary and sufficient for driving the effects of light on affective behavior. Together, these results provide new insights into the neural basis required for light to influence mood and learning.

Neurochemical differences in learning and memory paradigms among rats supplemented with anthocyanin-rich blueberry diets and exposed to acute doses of 56Fe particles

The protective effects of anthocyanin-rich blueberries (BB) on brain health are well documented and are particularly important under conditions of high oxidative stress, which can lead to "accelerated aging." One such scenario is exposure to space radiation, consisting of high-energy and -charge particles (HZE), which are known to cause cognitive dysfunction and deleterious neurochemical alterations. We recently tested the behavioral and neurochemical effects of acute exposure to HZE particles such as ⁵⁶Fe, within 24-48h after exposure, and found that radiation primarily affects memory and not learning. Importantly, we observed that specific brain regions failed to upregulate antioxidant and anti-inflammatory mechanisms in response to this insult. To further examine these endogenous response mechanisms, we have supplemented young rats with diets rich in BB, which are known to contain high amounts of antioxidant-phytochemicals, prior to irradiation. Exposure to ⁵⁶Fe caused significant neurochemical changes in hippocampus and frontal cortex, the two critical regions of the brain involved in cognitive function. BB supplementation significantly attenuated protein carbonylation, which was significantly increased by exposure to ⁵⁶Fe in the hippocampus and frontal cortex. Moreover, BB supplementation significantly reduced radiation-induced elevations in NADPH-oxidoreductase-2 (NOX2) and cyclooxygenase-2 (COX-2), and upregulated nuclear factor erythroid 2-related factor 2 (Nrf2) in the hippocampus and frontal cortex. Overall results indicate that ⁵⁶Fe particles may induce their toxic effects on hippocampus and frontal cortex by reactive oxygen species (ROS) overload, which can cause alterations in the neuronal environment, eventually leading to hippocampal neuronal death and subsequent impairment of cognitive function. Blueberry supplementation provides an effective preventative measure to reduce the ROS load on the CNS in an event of acute HZE exposure.

Neurocognitive effects of proton radiation therapy in adults with low-grade glioma

To understand neurocognitive effects of proton radiation therapy (PRT) in patients with low-grade glioma, we evaluated 20 patients who received this therapy prospectively and over 5 years with a comprehensive neuropsychological battery. 20 patients were evaluated at baseline and at yearly intervals for up to 5 years with a battery of neuropsychological measures that assessed intellectual, attention, executive, visuospatial and memory functions as well as mood and functional status. We evaluated change in cognitive functioning over time. We analyzed the relationship between cognitive performance and tumor location and also examined whether patients' performance differed from that reported in a study of normative practice effects. Overall, patients exhibited stability in cognitive functioning. Tumor location played a role in performance; those with tumors in the left hemisphere versus in the right hemisphere were more impaired at baseline on verbal measures (p < .05). However, we found greater improvement in verbal memory over time in patients with left than with right hemisphere tumors (p < .05). Results of our study, the first to investigate, in depth, neurocognitive effects of PRT in adults with low-grade gliomas, are promising. We hypothesize that the conformal advantage of PRT may contribute to preservation of cognitive functioning, although larger sample sizes and a longer period of study are required. Our study also highlights the need to consider normative practice effects when studying neurocognitive functioning in response to treatment over time, and the need to utilize comprehensive neuropsychological batteries given our findings that differentiate patients with left and right hemisphere tumors.

Lack of reliability in the disruption of cognitive performance following exposure to protons

A series of three replications were run to determine the reliability with which exposure to protons produces a disruption of cognitive performance, using a novel object recognition task and operant responding on an ascending fixed-ratio task. For the first two replications, rats were exposed to head-only exposures to 1000 MeV/n protons at the NASA Space Radiation Laboratory. For the third replication, subjects were given head-only or whole-body exposures to both 1000 and 150 MeV/n protons. The results were characterized by a lack of consistency in the effects of exposure to protons on the performance of these cognitive tasks, both within and between replications. The factors that might influence the lack of consistency and the implications for exploratory class missions are discussed.

Ionising radiation immediately impairs synaptic plasticity-associated cytoskeletal signalling pathways in HT22 cells and in mouse brain: an in vitro/in vivo comparison study

Patients suffering from brain malignancies are treated with high-dose ionising radiation. However, this may lead to severe learning and memory impairment. Preventive treatments to minimise these side effects have not been possible due to the lack of knowledge of the involved signalling pathways and molecular targets. Mouse hippocampal neuronal HT22 cells were irradiated with acute gamma doses of 0.5 Gy, 1.0 Gy and 4.0 Gy. Changes in the cellular proteome were investigated by isotope-coded protein label technology and tandem mass spectrometry after 4 and 24 hours. To compare the findings with the in vivo response, male NMRI mice were irradiated on postnatal day 10 with a gamma dose of 1.0 Gy, followed by evaluation of the cellular proteome of hippocampus and cortex 24 hours post-irradiation. Analysis of the in vitro proteome showed that signalling pathways related to synaptic actin-remodelling were significantly affected at 1.0 Gy and 4.0 Gy but not at 0.5 Gy after 4 and 24 hours. We observed radiation-induced reduction of the miR-132 and Rac1 levels; miR-132 is known to regulate Rac1 activity by blocking the GTPase-activating protein p250GAP. In the irradiated hippocampus and cortex we observed alterations in the signalling pathways similar to those in vitro. The decreased expression of miR-132 and Rac1 was associated with an increase in hippocampal cofilin and phospho-cofilin. The Rac1-Cofilin pathway is involved in the modulation of synaptic actin filament formation that is necessary for correct spine and synapse morphology to enable processes of learning and memory. We suggest that acute radiation exposure leads to rapid dendritic spine and synapse morphology alterations via aberrant cytoskeletal signalling and processing and that this is associated with the immediate neurocognitive side effects observed in patients treated with ionising radiation.

[Effect of cerebral X-ray irradiation on learning and memory function in young SD rats]

OBJECTIVE

To investigate the effect of cerebral X-ray irradiation on learning and memory function in young rats.

METHODS

Fifty-four SD rats aged 35 d were randomly divided into 3 groups with 18 in each group: rats in 3-d group and 7-d group received X-ray irradiation with a dose of 28.5 mGy/d for 3 d and 7 d, respectively; rats in control group received sham X-ray irradiation. Morris water maze (MWM) was tested when animals at age of 60 d; then the animals were sacrificed and brain samples were taken. The neurodegeneration was observed by Fluro-Jade B staining; the expression of N-methyl-aspartate (NMDA) receptors subunit 2B (NR2B) and postsynaptic density protein-95 (PSD-95) in the hippocampus were analyzed by immunofluorescence and Western blot methods, respectively, and ultrastructure of CA1 region was observed with electron microscopy.

RESULTS

No significant difference in 1-4 d escape latency as shown in MWM test was noted between 3d group and control group (P>0.05); while the escape latency in 7d group was significantly longer than that in control group (P<0.01). No significant differences in lingering in the quadrant and the frequency of passing through the original platform between 3-d group and control group (P>0.05), while those in 7-d group were significantly lower than those in control group (P<0.01). Compared to control group, the number of FJB positive cells in 7-d group was increased (P<0.01); the expressions of NR2B and PSD-95 in hippocampus CA1 region were also increased (P<0.05). The ultrastructure observation in 7-d group showed that the synapse structure of some neurons was impaired.

CONCLUSION

X-ray irradiation may affect learning and memory function of young rats, which is associated with overexpression of NR2B and PSD-95 in hippocampal regions.

Effects of X-ray radiation on complex visual discrimination learning and social recognition memory in rats

The present report describes an animal model for examining the effects of radiation on a range of neurocognitive functions in rodents that are similar to a number of basic human cognitive functions. Fourteen male Long-Evans rats were trained to perform an automated intra-dimensional set shifting task that consisted of their learning a basic discrimination between two stimulus shapes followed by more complex discrimination stages (e.g., a discrimination reversal, a compound discrimination, a compound reversal, a new shape discrimination, and an intra-dimensional stimulus discrimination reversal). One group of rats was exposed to head-only X-ray radiation (2.3 Gy at a dose rate of 1.9 Gy/min), while a second group received a sham-radiation exposure using the same anesthesia protocol. The irradiated group responded less, had elevated numbers of omitted trials, increased errors, and greater response latencies compared to the sham-irradiated control group. Additionally, social odor recognition memory was tested after radiation exposure by assessing the degree to which rats explored wooden beads impregnated with either their own odors or with the odors of novel, unfamiliar rats; however, no significant effects of radiation on social odor recognition memory were observed. These data suggest that rodent tasks assessing higher-level human cognitive domains are useful in examining the effects of radiation on the CNS, and may be applicable in approximating CNS risks from radiation exposure in clinical populations receiving whole brain irradiation.

Using noninvasive brain stimulation to accelerate learning and enhance human performance

OBJECTIVE

The authors evaluate the effectiveness of noninvasive brain stimulation, in particular, transcranial direct current stimulation (tDCS), for accelerating learning and enhancing human performance on complex tasks.

BACKGROUND

Developing expertise in complex tasks typically requires extended training and practice. Neuroergonomics research has suggested new methods that can accelerate learning and boost human performance. TDCS is one such method. It involves the application of a weak DC current to the scalp and has the potential to modulate brain networks underlying the performance of a perceptual, cognitive, or motor task.

METHOD

Examples of tDCS studies of declarative and procedural learning are discussed. This mini-review focuses on studies employing complex simulations representative of surveillance and security operations, intelligence analysis, and procedural learning in complex monitoring.

RESULTS

The evidence supports the view that tDCS can accelerate learning and enhance performance in a range of complex cognitive tasks. Initial findings also suggest that such benefits can be retained over time, but additional research is needed on training schedules and transfer of training.

CONCLUSION

Noninvasive brain stimulation can accelerate skill acquisition in complex tasks and may provide an alternative or addition to other training methods.

[Effect of space flight factors simulated in ground-based experiments on the behavior, discriminant learning, and exchange of monoamines in different brain structures of rats]

Experimental treatment (long-term fractionated γ-irradiation, antiorthostatic hypodynamia, and the combination of these factors) simulating the effect of space flight in ground-based experiments rapidly restored the motor and orienting-investigative activity of animals (rats) in "open-field" tests. The study of the dynamics of discriminant learning of rats of experimental groups did not show significant differences from the control animals. It was found that the minor effect of these factors on the cognitive performance of animals correlated with slight changes in the concentration ofmonoamines in the brain structures responsible for the cognitive, emotional, and motivational functions.

Whole brain radiation-induced vascular cognitive impairment: mechanisms and implications

Mild cognitive impairment is a well-documented consequence of whole brain radiation therapy (WBRT) that affects 40-50% of long-term brain tumor survivors. The exact mechanisms for the decline in cognitive function after WBRT remain elusive and no treatment or preventative measures are available for use in the clinic. Here, we review recent findings indicating how changes in the neurovascular unit may contribute to the impairments in learning and memory. In addition to affecting neuronal development, WBRT induces profound capillary rarefaction within the hippocampus - a region of the brain important for learning and memory. Therapeutic strategies such as hypoxia, which restore the capillary density, result in the rescue of cognitive function. In addition to decreasing vascular density, WBRT impairs vasculogenesis and/or angiogenesis, which may also contribute to radiation-induced cognitive decline. Further studies aimed at uncovering the specific mechanisms underlying these WBRT-induced changes in the cerebrovasculature are essential for developing therapies to mitigate the deleterious effects of WBRT on cognitive function.

Longitudinal investigation of adaptive functioning following conformal irradiation for pediatric craniopharyngioma and low-grade glioma

PURPOSE

Children treated for brain tumors with conformal radiation therapy experience preserved cognitive outcomes. Early evidence suggests that adaptive functions or independent-living skills may be spared. This longitudinal investigation prospectively examined intellectual and adaptive functioning during the first 5 years following irradiation for childhood craniopharyngioma and low-grade glioma (LGG). The effect of visual impairment on adaptive outcomes was investigated.

METHODS AND MATERIALS

Children with craniopharyngioma (n=62) and LGG (n=77) were treated using conformal or intensity modulated radiation therapy. The median age was 8.05 years (3.21-17.64 years) and 8.09 years (2.20-19.27 years), respectively. Serial cognitive evaluations including measures of intelligence quotient (IQ) and the Vineland Adaptive Behavior Scales (VABS) were conducted at preirradiation baseline, 6 months after treatment, and annually through 5 years. Five hundred eighty-eight evaluations were completed during the follow-up period.

RESULTS

Baseline assessment revealed no deficits in IQ and VABS indices for children with craniopharyngioma, with significant (P<.05) longitudinal decline in VABS Communication and Socialization indices. Clinical factors associated with more rapid decline included females and preirradiation chemotherapy (interferon). The only change in VABS Daily Living Skills correlated with IQ change (r=0.34; P=.01) in children with craniopharyngioma. Children with LGG performed below population norms (P<.05) at baseline on VABS Communication, Daily Living Indices, and the Adaptive Behavior Composite, with significant (P<.05) longitudinal decline limited to VABS Communication. Older age at irradiation was a protective factor against longitudinal decline. Severe visual impairment did not independently correlate with poorer adaptive outcomes for either tumor group.

CONCLUSIONS

There was relative sparing of postirradiation functional outcomes over time in this sample. Baseline differences in functional abilities before the initiation of irradiation suggested that other factors influence functional outcomes above and beyond the effects of irradiation.

Learning and memory following conformal radiation therapy for pediatric craniopharyngioma and low-grade glioma

PURPOSE

The primary objective of this study was to examine whether children with low-grade glioma (LGG) or craniopharyngioma had impaired learning and memory after conformal radiation therapy (CRT). A secondary objective was to determine whether children who received chemotherapy before CRT, a treatment often used to delay radiation therapy in younger children with LGG, received any protective benefit with respect to learning.

METHODS AND MATERIALS

Learning and memory in 57 children with LGG and 44 children with craniopharyngioma were assessed with the California Verbal Learning Test-Children's Version and the Visual-Auditory Learning tests. Learning measures were administered before CRT, 6 months later, and then yearly for a total of 5 years.

RESULTS

No decline in learning scores after CRT was observed when patients were grouped by diagnosis. For children with LGG, chemotherapy before CRT did not provide a protective effect on learning. Multiple regression analyses, which accounted for age and tumor volume and location, found that children treated with chemotherapy before CRT were at greater risk of decline on learning measures than those treated with CRT alone. Variables predictive of learning and memory decline included hydrocephalus, shunt insertion, younger age at time of treatment, female gender, and pre-CRT chemotherapy.

CONCLUSIONS

This study did not reveal any impairment or decline in learning after CRT in overall aggregate learning scores. However, several important variables were found to have a significant effect on neurocognitive outcome. Specifically, chemotherapy before CRT was predictive of worse outcome on verbal learning in LGG patients. In addition, hydrocephalus and shunt insertion in craniopharyngioma were found to be predictive of worse neurocognitive outcome, suggesting a more aggressive natural history for those patients.

[Effects of 2000 μW/cm2; electromagnetic radiation on expression of immunoreactive protein and mRNA of NMDA receptor 2A subunit in rats hippocampus]

AIM

To evaluate the effects of electromagnetic irradiation of 2000 μW/cm(2); exposure on mRNA and protein expression levels of immunoreactive protein and mRNA of NMDA receptor 2A subunit in rats hippocampal, and to explore the mechanism of electromagnetic irradiation induced learning and memory impairment.

METHODS

Rats were randomly divided into normal control group, sham-radiated group, and 1 h/d, 2 h/d, and 3 h/d radiation groups. The rats in the radiation groups were fixed after microwave exposure of 2000 μW/cm(2);, then their learning and memory abilities were tested by Morris water maze experiment, the change of NR2A protein in hippocampal neurons of each group of rats were measured with immunohistochmistry and Western blot techniques, and the expression of NR2A mRNA in hippocampus were determined by RT-PCR.

RESULTS

Compared with the normal control group, each index of the sham-radiated group has no significant change (P>0.05), while the latency of rats of radiated group in Morris water maze test were significantly longer (P<0.05). In the radiation group, the hippocampal neurons of rats showing evident reduction in the ratio of NR2A positive cells, irregular, and arrayed in disorder. Moreover, the expession of NR2A protein and its mRNA in hippocampal neurons were significant decreased (P<0.05).

CONCLUSION

Electromagnetic irradiation of 2000 μW/cm(2); exposure can impair the learning and memory abilities of rats possibly through a mechanism correlated with the lower expression of NR2A protein and its mRNA in hippocampus.

Radiation biology of Caenorhabditis elegans: germ cell response, aging and behavior

The study of radiation effect in Caenorhabditis (C.) elegans has been carried out over three decades and now allow for understanding at the molecular, cellular and individual levels. This review describes the current knowledge of the biological effects of ionizing irradiation with a scope of the germ line, aging and behavior. In germ cells, ionizing radiation induces apoptosis, cell cycle arrest and DNA repair. Lots of molecules involved in these responses and functions have been identified in C. elegans, which are highly conserved throughout eukaryotes. Radiosensitivity and the effect of heavy-ion microbeam irradiation on germ cells with relationship between initiation of meiotic recombination and DNA lesions are discussed. In addition to DNA damage, ionizing radiation produces free radicals, and the free radical theory is the most popular aging theory. A first signal transduction pathway of aging has been discovered in C. elegans, and radiation-induced metabolic oxidative stress is recently noted for an inducible factor of hormetic response and genetic instability. The hormetic response in C. elegans exposed to oxidative stress is discussed with genetic pathways of aging. Moreover, C. elegans is well known as a model organism for behavior. The recent work reported the radiation effects via specific neurons on learning behavior, and radiation and hydrogen peroxide affect the locomotory rate similarly. These findings are discussed in relation to the evidence obtained with other organisms. Altogether, C. elegans may be a good "in vivo" model system in the field of radiation biology.

The effect of electromagnetic radiation in the mobile phone range on the behaviour of the rat

Electromagnetic radiation (EMR) is emitted from electromagnetic fields that surround power lines, household appliances and mobile phones. Research has shown that there are connections between EMR exposure and cancer and also that exposure to EMR may result in structural damage to neurons. In a study by Salford et al. (Environ Health Perspect 111:881-883, 2003) the authors demonstrated the presence of strongly stained areas in the brains of rats that were exposed to mobile phone EMR. These darker neurons were particularly prevalent in the hippocampal area of the brain. The aim of our study was to further investigate the effects of EMR. Since the hippocampus is involved in learning and memory and emotional states, we hypothesised that EMR will have a negative impact on the subject's mood and ability to learn. We subsequently performed behavioural, histological and biochemical tests on exposed and unexposed male and female rats to determine the effects of EMR on learning and memory, emotional states and corticosterone levels. We found no significant differences in the spatial memory test, and morphological assessment of the brain also yielded non-significant differences between the groups. However, in some exposed animals there were decreased locomotor activity, increased grooming and a tendency of increased basal corticosterone levels. These findings suggested that EMR exposure may lead to abnormal brain functioning.

Transient impairment of hippocampus-dependent learning and memory in relatively low-dose of acute radiation syndrome is associated with inhibition of hippocampal neurogenesis

Neurogenesis in the adult hippocampus, which occurs constitutively, is vulnerable to ionizing radiation. In the relatively low-dose exposure of acute radiation syndrome (ARS), the change in the adult hippocampal function is poorly understood. This study analyzed the changes in apoptotic cell death and neurogenesis in the DGs of hippocampi from adult ICR mice with single whole-body gamma-irradiation using the TUNEL method and immunohistochemical markers of neurogenesis, Ki-67 and doublecortin (DCX). In addition, the hippocampus-dependent learning and memory tasks after single whole-body gamma-irradiation were examined in order to evaluate the hippocampus-related behavioral dysfunction in the relatively low-dose exposure of ARS. The number of TUNEL-positive apoptotic nuclei in the dentate gyrus (DG) was increased 6-12 h after acute gamma-irradiation (a single dose of 0.5 to 4 Gy). In contrast, the number of Ki-67- and DCX-positive cells began to decrease significantly 6 h postirradiation, reaching its lowest level 24 h after irradiation. The level of Ki-67 and DCX immunoreactivity decreased in a dose-dependent manner within the range of irradiation applied (0-4 Gy). In passive avoidance and object recognition memory test, the mice trained 1 day after acute irradiation (2 Gy) showed significant memory deficits, compared with the sham controls. In conclusion, the pattern of the hippocampus-dependent memory dysfunction is consistent with the change in neurogenesis after acute irradiation. It is suggested that a relatively low dose of ARS in adult ICR mice is sufficiently detrimental to interrupt the functioning of the hippocampus, including learning and memory, possibly through the inhibition of neurogenesis.

Locomotion-learning behavior relationship in Caenorhabditis elegans following gamma-ray irradiation

Learning impairment following ionizing radiation (IR) exposure is an important potential risk in manned space missions. We previously reported the modulatory effects of IR on salt chemotaxis learning in Caenorhabditis elegans. However, little is known about the effects of IR on the functional relationship in the nervous system. In the present study, we investigated the effects of gamma-ray exposure on the relationship between locomotion and salt chemotaxis learning behavior. We found that effects of pre-learning irradiation on locomotion were significantly correlated with the salt chemotaxis learning performance, whereas locomotion was not directly related to chemotaxis to NaCl. On the other hand, locomotion was positively correlated with salt chemotaxis of animals which were irradiated during learning, and the correlation disappeared with increasing doses. These results suggest an indirect relationship between locomotion and salt chemotaxis learning in C. elegans, and that IR inhibits the innate relationship between locomotion and chemotaxis, which is related to salt chemotaxis learning conditioning of C. elegans.

[Experimental study of the neuroprotective properties of the melanin in embryos irradiated during antenatal development]

Daily introduction per os of the exogenous melanin in a doze of weight of 10 mg/kg pregnant female rats of line Wistar on a background continuous irradiations (dose rate of 2.6 mGy/h within 20 days of pregnancy) eliminated deficiency cognitive functions at posterity. On the basis of the received data it is concluded presence radioembryoprotective actions of melanin in the relation neuro embryotoxic effects of small dozes ionizing radiation. Taking into account small toxicity of melanin, the preparation can be perspective for practical application.

Effects of exposure to 50Hz magnetic field of 1mT on the performance of detour learning task by chicks

In the present study, we examined the effects of exposure to an extremely low-frequency magnetic field of 1 mT intensity on learning and memory in Lohmann brown domestic chicks using detour learning task. These results show that 20 h/day exposure to a low-frequency magnetic field induces a significant impairment in detour learning but 50 min/day exposure has no effect.

An animal model of functional electrical stimulation: evidence that the central nervous system modulates the consequences of training

STUDY DESIGN

Review of how spinal neurons can modulate the consequences of functional electrical stimulation (FES) in an animal model.

METHODS

Spinal effects of FES are examined in male Sprague-Dawley rats transected at the second thoracic vertebra. The rats are exposed to FES training 24-48 h after surgery. Experimental manipulations of stimulation parameters, combined with physiological and pharmacological procedures, are used to examine the potential role of spinal neurons.

RESULTS

The isolated spinal cord is inherently capable of learning the response-outcome relations imposed in FES training contingencies. Adaptive behavioral modifications are observed when an outcome (electrical stimulation) is contingent on a behavioral response. In contrast, a lack of correlation between the response and outcome in training produces a learning deficit in the spinal cord, rendering it incapable of adaptive learning for up to 48 h. The N-methyl-D-aspartic acid receptor appears to mediate both the adaptive plasticity and loss of plasticity, seen in this spinal model.

CONCLUSION

The behavioral effects observed with FES therapies are not simply due to the direct (motor) consequences of stimulation elicited by the activation of efferent motor neurons and/or selected muscles. FES training has the capacity to shape inherent spinal circuits and to produce a long-lasting behavioral modification. Further understanding of the spinal mechanisms underlying adaptive behavioral modification will be integral for establishing functional neural connections in a regenerating spinal system.

Irradiation as an experimental tool in studies of adult neurogenesis

"Loss of function" experiments have been the mainstay approach in studies seeking to determine functional roles of various brain regions in learning and memory. The hippocampal formation consists of several distinct regions that are thought to play different, yet interrelated, roles in the memory processes. Ionizing radiation offers a selective and highly flexible, relatively uninvasive method to further advance such studies. Focused applications of the radiation beam to the head under general anesthesia can selectively reduce ongoing adult neurogenesis in the dentate gyrus without causing any detectable damage to mature neurons. Further refinements of the methodology should offer many opportunities to extend our present knowledge of how and when adult neurogenesis plays a role in learning and memory.

[Relationship between millimeter wave irradiation in pregnant mice and c-Fos protein expression in hippocampus and learning and memory functions in their offsprings]

OBJECTIVE

To determine the threshold of millimeter wave irradiation for fetal injury in mice and the mechanism of decrease of learning and memory function in their offsprings and to verify whether the millimeter wave has the non-thermal effect.

METHODS

Pregnant mice were irradiated by millimeter wave with frequencies of 37.4, 42.2, 53.0 and 60.0 GHz at power densities of 1, 3, 5, 8 mW/cm(2) for two hours daily from the 6th to 15th day of their gestation. Learning and memory functions of their offsprings were tested by a Y-type electric maze. c-Fos protein expression level in hippocampus of their offsprings was determined with immunohistochemistry 0, 30, 60, 90 and 120 minutes after the offsprings were trained respectively.

RESULTS

The minimal power density of millimeter wave for the decrease in learning and memory function and decrease of c-Fos protein expression level in hippocampus of their offsprings caused by 37.4, 42.2 GHz and 53.0, 60.0 GHz was 5 and 3 mW/cm(2). Severity of injury for learning and memory in offsprings caused by irradiation increased with the power density of millimeter wave. The millimeter wave did not cause increase of the body temperature of the pregnant mice.

CONCLUSION

The threshold of millimeter wave with 37.4, 42.2 GHz, and 53.0, 60.0 GHz causing fetal injury in mice is 5 and 3 mW/cm(2) respectively. The decrease in learning and memory functions in offspring mice is related with decrease of c-Fos protein expression level in hippocampus. Millimeter wave has the non-thermal effects.

Spatial learning and long-term potentiation of mutant mice lacking D-amino-acid oxidase

We evaluated the role of D-amino-acid oxidase on spatial learning and long-term potentiation (LTP) in the hippocampus, since this enzyme metabolizes D-amino-acids, some of which enhance the N-methyl-D-aspartate receptor functions. The Morris water maze learning and the LTP in the CA1 area of the hippocampal slice were observed in wild-type mice and mutant mice lacking D-amino-acid oxidase. The mutant mice showed significantly shorter platform search times in the water maze and significantly larger hippocampal LTPs than the wild-type mice. These results suggest that the abundant D-amino-acids in the mutant mouse brain facilitate hippocampal LTP and spatial learning.

Impaired spatial learning after hypergravity exposure in rats

Most astronauts experience spatial disorientation after exposure to weightlessness, indicating that constant gravity is utilized as a stable external reference during spatial cognition. We attempted to elucidate the role of constant gravity in spatial learning using a radial arm maze test on rats housed in a hypergravity environment (HG) produced by a centrifuge device. Male Wistar rats were kept in 2G linear acceleration for 2 weeks before the spatial learning task, which lasted for 10 days. The control rats were placed close to the centrifuge device but not exposed to hypergravity. Spatial learning was evaluated by the accuracy and the re-entry rate, which were the rate of correct arm entries and the rate of entries into the arms that they had already visited, respectively. Locomotor activity was measured by number of entries per minute. The number of baits the animal took per minute was also measured. The results showed that accuracy was significantly inferior and the re-entry rate was significantly higher in the HG rats than in the controls, suggesting that animals use a constant gravity as a stable external reference in spatial learning. However, these differences disappeared at 5 days later, indicating that the HG rats learned the spatial task more rapidly than the controls. Locomotor activity was higher in the HG rats and there was no difference in number of baits per minute between the HG and control animals. In conclusion, if one sensory cue necessary for spatial cognition is disturbed by gravity change, animals can subsidize with other sensory cues such as proprioceptive and motor efference copy signals through increased locomotor activities.

How sleep affects the developmental learning of bird song

Sleep affects learning and development in humans and other animals, but the role of sleep in developmental learning has never been examined. Here we show the effects of night-sleep on song development in the zebra finch by recording and analysing the entire song ontogeny. During periods of rapid learning we observed a pronounced deterioration in song structure after night-sleep. The song regained structure after intense morning singing. Daily improvement in similarity to the tutored song occurred during the late phase of this morning recovery; little further improvement occurred thereafter. Furthermore, birds that showed stronger post-sleep deterioration during development achieved a better final imitation. The effect diminished with age. Our experiments showed that these oscillations were not a result of sleep inertia or lack of practice, indicating the possible involvement of an active process, perhaps neural song-replay during sleep. We suggest that these oscillations correspond to competing demands of plasticity and consolidation during learning, creating repeated opportunities to reshape previously learned motor skills.

TMS induced plasticity in human cortex

Repetitive transcranial magnetic stimulation (RTMS) is a novel, non-invasive and painless technique to stimulate the human brain with the intent to alter excitability or function of the stimulated cortex or its connections. This review focuses on RTMS induced changes in excitability, the potential mechanisms underlying these effects, and the usefulness of this knowledge to gain insight into mechanisms of other processes such as learning.

[Effects of different light-dark cycle on learning and memory in mice]

OBJECTIVE

To study the effect of different light-dark cycles on learning and memory in mice.

METHOD

Seventy-two ICR mice were raised under different light-dark cycles including LD 5h/5h, LD 12h/12h and LD 22h/22h for 6 weeks. The locomotor activity was recorded continuously. Morris water-maze task was used as the judging criteria for spatial learning and memory.

RESULT

The locomotor activity rhythm was consistent with the light-dark cycle. The period of light-dark cycle shorter than 24 h such as 10 h could effect on the ability of learning and memory in mice.

CONCLUSION

The short period of light-dark cycle can improve the ability of learning and memory in mice.

Facilitative effect of high frequency subthreshold repetitive transcranial magnetic stimulation on complex sequential motor learning in humans

We investigated the effect of repetitive transcranial magnetic stimulation (rTMS) applied to the motor cortex, on the motor learning of sequential finger movements. Fifteen healthy subjects were trained to perform seven sequential finger movements of the left hand. Ten Hertz or sham rTMS with a resting motor threshold of 80% was applied to each subject during the task period. Stimulation with 10Hz rTMS produced a better learning performance in terms of target score and execution time than sham stimulation. We conclude that high-frequency rTMS may modulate the excitability of the motor cortex and facilitate the sequential motor learning process in normal subjects. These findings may provide a basis for the development of therapeutic applications of rTMS in patients with impaired motor skill.

Sleep deprivation impairs hippocampus-mediated contextual learning but not amygdala-mediated cued learning in rats

Prolonged sleep deprivation results in cognitive deficits. In rats, for example, sleep deprivation impairs spatial learning and hippocampal long-term potentiation. We tested the effects of sleep deprivation on learning in a Pavlovian fear conditioning paradigm, choosing a sleep deprivation paradigm in which REM sleep was completely prevented and non-REM sleep was strongly decreased. During conditioning, rats were given footshocks, either alone or paired with a tone, and tested 24 h later for freezing responses to the conditioning context, and to the tone in a novel environment. Whereas control animals had robust contextual learning in both background and foreground contextual conditioning paradigms, 72 h of sleep deprivation before conditioning dramatically impaired both types of contextual learning (by more than 50%) without affecting cued learning. Increasing the number of footshocks did not overcome the sleep deprivation-induced deficit. The results provide behavioural evidence that REM/non-REM sleep deprivation has neuroanatomically selective actions, differentially interfering with the neural systems underlying contextual learning (i.e. the hippocampus) and cued learning (i.e. the amygdala), and support the involvement of the hippocampus in both foreground and background contextual conditioning.

[Studies on the injury effects of hippocampus induced by high power microwave radiation in rat]

OBJECTIVE

To study the changes of morphology and function in rat hippocampus induced by high power microwave (HPM) radiation.

METHODS

Fifty male Wistar rats were radiated by HPM. Then their learning and memory abilities were tested with Y maze and were sacrificed 6 h, 1 d, 3 d and 7 d after radiation. The hippocampus was taken out to study the basic pathologic changes, apoptosis and the expressions of neuron-specific enolase (NSE) and glial fibrillary acidic protein (GFAP) by means of HE staining, Nissel body staining, in situ terminal end labeling and immunohistochemistry.

RESULTS

The learning and memory abilities of rats reduced significantly after HPM radiation. HPM also resulted in rarefaction, edema and hemangiectasia of hippocampus, nervous cells degeneration and necrosis, decrease or disappearance of Nissel bodies. The injuries were more serious in field CA4 and dentate gyrus, which showed dose-effect relationship, and were progressively aggravated within 7 days. The apoptosis cells were significantly increased. NSE was increased in neurons. The NSE positive areas were also seen in the interstitial matrix and blood vessels. GFAP was increased in astrocytes, which became shorter and thicker.

CONCLUSION

HPM can damage the abilities of learning and memory and results in morphologic changes in hippocampus. The major pathologic changes are degeneration, apoptosis and necrosis of neurons and edema in interstitium. NSE and GFAP play an important role in the pathologic process.

Facilitation of visuo-motor learning by transcranial direct current stimulation of the motor and extrastriate visual areas in humans

Performance of visuo-motor tasks requires the transfer of visual data to motor performance and depends highly on visual perception and cognitive processing, mainly during the learning phase. The primary aim of this study was to determine if the human middle temporal (MT)+/V5, an extrastriate visual area that is known to mediate motion processing, and the primary motor cortex are involved in learning of visuo-motor coordination tasks. To pursue this, we increased or decreased MT+/V5, primary contralateral motor (M1) and primary visual cortex excitability by 10 min of anodal or cathodal transcranial direct current stimulation in healthy human subjects during the learning phase of a visually guided tracking task. The percentage of correct tracking movements increased significantly in the early learning phase during anodal stimulation, but only when the left V5 or M1 was stimulated. Cathodal stimulation had no significant effect. Also, stimulation of the primary visual cortex was not effective for this kind of task. Our data suggest that the areas V5 and M1 are involved in the early phase of learning of visuo-motor coordination.

Microwave effects on the nervous system

Studies have evaluated the electroencephalography (EEG) of humans and laboratory animals during and after Radiofrequency (RF) exposures. Effects of RF exposure on the blood-brain barrier (BBB) have been generally accepted for exposures that are thermalizing. Low level exposures that report alterations of the BBB remain controversial. Exposure to high levels of RF energy can damage the structure and function of the nervous system. Much research has focused on the neurochemistry of the brain and the reported effects of RF exposure. Research with isolated brain tissue has provided new results that do not seem to rely on thermal mechanisms. Studies of individuals who are reported to be sensitive to electric and magnetic fields are discussed. In this review of the literature, it is difficult to draw conclusions concerning hazards to human health. The many exposure parameters such as frequency, orientation, modulation, power density, and duration of exposure make direct comparison of many experiments difficult. At high exposure power densities, thermal effects are prevalent and can lead to adverse consequences. At lower levels of exposure biological effects may still occur but thermal mechanisms are not ruled out. It is concluded that the diverse methods and experimental designs as well as lack of replication of many seemingly important studies prevents formation of definite conclusions concerning hazardous nervous system health effects from RF exposure. The only firm conclusion that may be drawn is the potential for hazardous thermal consequences of high power RF exposure.

[Effects of 2450 MHz microwave on long-term potentiation of hippocampus and lipofuscin contents in rat brain]

OBJECTIVE

To study the mechanism of the effects of microwave on learning and memory.

METHOD

Long-term potentiation (LTP) of hippocampus induced potential and lipofuscin content in rat brain were studied. After irradiated by a 2450 MHz microwave, rats hippocampus induced potential in vivo was recorded and lipofuscin content in the brain was measured by fluorospectrophotometry.

RESULT

Continuous microwave with 10-25 mW/cm2 intensity could inhibit the amplitude of the population spike (PS) of weak and strong stimuli induced LTP with an intensity-effect relationship. At 25 mW/cm2, lipofuscin content was significantly higher than control and 10 mW/cm2 group (P<0.05).

CONCLUSION

Continuous microwave with 10-25 mW/cm2 intensity impairs learning and memory by restraining hippocampus LTP and brain lipofuscin content.

How the Shape of Pre- and Postsynaptic Signals Can Influence STDP: A Biophysical Model

Spike-timing-dependent plasticity (STDP) is described by long-term potentiation (LTP), when a presynaptic event precedes a postsynaptic event, and by long-term depression (LTD), when the temporal order is reversed. In this article, we present a biophysical model of STDP based on a differential Hebbian learning rule (ISO learning). This rule correlates presynaptically the NMDA channel conductance with the derivative of the membrane potential at the synapse as the postsynaptic signal. The model is able to reproduce the generic STDP weight change characteristic. We find that (1) The actual shape of the weight change curve strongly depends on the NMDA channel characteristics and on the shape of the membrane potential at the synapse. (2) The typical antisymmetrical STDP curve (LTD and LTP) can become similar to a standard Hebbian characteristic (LTP only) without having to change the learning rule. This occurs if the membrane depolarization has a shallow onset and is long lasting. (3) It is known that the membrane potential varies along the dendrite as a result of the active or passive backpropagation of somatic spikes or because of local dendritic processes. As a consequence, our model predicts that learning properties will be different at different locations on the dendritic tree. In conclusion, such site-specific synaptic plasticity would provide a neuron with powerful learning capabilities.

The effects of heavy particle irradiation on exploration and response to environmental change

Free radicals produced by exposure to heavy particles have been found to produce motor and cognitive behavioral toxicity effects in rats similar to those found during aging. The present research was designed to investigate the effects of exposure to 56Fe particles on the ability of male Sprague-Dawley rats to detect novel arrangements in a given environment. Using a test of spatial memory previously demonstrated to be sensitive to aging, open field activity and reaction to spatial and non-spatial changes were measured in a group that received a dose of 1.5 Gy (n=10) of 56Fe heavy particle radiation or in non-radiated controls (n=10). Animals irradiated with 1.5 Gy of 56Fe particles exhibited some age-like effects in rats tested, even though they were, for the most part, subtle. Animals took longer to enter, visited less and spent significantly less time in the middle and the center portions of the open field, independently of total frequency and duration of activity of both groups. Likewise, irradiated subjects spend significantly more time exploring novel objects placed in the open field than did controls. However, irradiated subjects did not vary from controls in their exploration patterns when objects in the open field were spatially rearranged. Thus, irradiation with a dose of 1.5 Gy of 56Fe high-energy particle radiation elicited age-like effects in general open field exploratory behavior, but did not elicit age-like effects during the spatial and non-spatial rearrangement tasks.

The effects of proton exposure on neurochemistry and behavior

Future space missions will involve long-term travel beyond the magnetic field of the Earth, where astronauts will be exposed to radiation hazards such as those that arise from galactic cosmic rays. Galactic cosmic rays are composed of protons, alpha particles, and particles of high energy and charge (HZE particles). Research by our group has shown that exposure to HZE particles, primarily 600 MeV/n and 1 GeV/n 56Fe, can produce significant alterations in brain neurochemistry and behavior. However, given that protons can make up a significant portion of the radiation spectrum, it is important to study their effects on neural functioning and on related performance. Therefore, these studies examined the effects of exposure to proton irradiation on neurochemical and behavioral endpoints, including dopaminergic functioning, amphetamine-induced conditioned taste aversion learning, and spatial learning and memory as measured by the Morris water maze. Male Sprague-Dawley rats received a dose of 0, 1.5, 3.0 or 4.0 Gy of 250 MeV protons at Loma Linda University and were tested in the different behavioral tests at various times following exposure. Results showed that there was no effect of proton irradiation at any dose on any of the endpoints measured. Therefore, there is a contrast between the insignificant effects of high dose proton exposure and the dramatic effectiveness of low dose (<0.1 Gy) exposures to 56Fe particles on both neurochemical and behavioral endpoints.

Radiation-induced cognitive dysfunction: The protective effect of ethyol in young rats

PURPOSE

To evaluate the protective learning and memory effect of Ethyol in irradiated young rats.

METHODS AND MATERIALS

One hundred twenty-eight 45-day-old Wistar rats received whole brain fractionated radiation (30 Gy), whereas 48 rats received sham irradiation. Four irradiated subgroups were defined: saline, 37.5 mg/kg, 75 mg/kg, and 150 mg/kg Ethyol. Sequential behavioral studies including one-way and two-way avoidance tasks were undertaken before and after radiation.

RESULTS

Before radiation, the performances of all groups were similar. For the one-way avoidance task, at 1, 3, and 6 months postradiation, saline-irradiated rats had a lower percentage of avoidance than sham- or Ethyol- (75 or 150 mg/kg) irradiated rats (p <or= 0.001). Nevertheless, lower percentage of avoidance (p <or= 0.001) was only seen at 1 month postradiation in saline-irradiated rats, after comparison with their preradiation values. For the two-way avoidance task, performed only after radiation, saline-irradiated rats had a lower percentage of avoidance than sham- or Ethyol- (150 or 75 mg/kg) irradiated rats at 1, 2.5, 4.5, and 7.5 months (p = 0.000). Rats treated with Ethyol did not differ from sham-irradiated rats in both avoidance tasks, except for the 37.5 mg/kg-Ethyol group which showed lower performances 6 months postradiation (p = 0.005, one-way avoidance).

CONCLUSIONS

Treatment with 75 or 150 mg/kg of Ethyol prevents radiation-induced learning and transitory memory dysfunction in young rats.

Suppression of adult neurogenesis impairs olfactory learning and memory in an adult insect

Although adult neurogenesis has now been demonstrated in many different species, the functional role of newborn neurons still remains unclear. In the house cricket, a cluster of neuroblasts, located in the main associative center of the insect brain, keeps producing new interneurons throughout the animal's life. Here we address the functional significance of adult neurogenesis by specific suppression of neuroblast proliferation using gamma irradiation of the insect's head and by examining the impact on the insect's learning ability. Forty gray irradiation performed on the first day of adult life massively suppressed neuroblasts and their progeny without inducing any noticeable side effect. We developed a new operant conditioning paradigm especially designed for crickets: the "escape paradigm." Using olfactory cues, visual cues, or both, crickets had to choose between two holes, one allowing them to escape and the other leading to a trap. Crickets lacking adult neurogenesis exhibited delayed learning when olfactory cues alone were used. Furthermore, retention 24 hr after conditioning was strongly impaired in irradiated crickets. By contrast, when visual cues instead of olfactory ones were provided, performance of irradiated insects was only slightly affected; when both olfactory and visual cues were present, their performance was not different from that of controls. From these results, it can be postulated that newborn neurons participate in the processing of olfactory information required for complex operant conditioning.

Spatial learning and memory deficits induced by exposure to iron-56-particle radiation

It has previously been shown that exposing rats to particles of high energy and charge (HZE) disrupts the functioning of the dopaminergic system and behaviors mediated by this system, such as motor performance and an amphetamine-induced conditioned taste aversion; these adverse behavioral and neuronal effects are similar to those seen in aged animals. Because cognition declines with age, spatial learning and memory were assessed in the Morris water maze 1 month after whole-body irradiation with 1.5 Gy of 1 GeV/nucleon high-energy (56)Fe particles, to test the cognitive behavioral consequences of radiation exposure. Irradiated rats demonstrated cognitive impairment compared to the control group as seen in their increased latencies to find the hidden platform, particularly on the reversal day when the platform was moved to the opposite quadrant. Also, the irradiated group used nonspatial strategies during the probe trials (swim with no platform), i.e. less time spent in the platform quadrant, fewer crossings of and less time spent in the previous platform location, and longer latencies to the previous platform location. These findings are similar to those seen in aged rats, suggesting that an increased release of reactive oxygen species may be responsible for the induction of radiation- and age-related cognitive deficits. If these decrements in behavior also occur in humans, they may impair the ability of astronauts to perform critical tasks during long-term space travel beyond the magnetosphere.

50 Hz magnetic field exposure influence on human performance and psychophysiological parameters: two double-blind experimental studies

Two double-blind studies were performed to examine magnetic field (MF) exposure effects and to determine the impact of temporal variation (continuous vs. intermittent exposure) of 100 mu T(rms) 50 Hz MF diurnal exposure on psychological and psychophysiological parameters in healthy humans. Three cephalic exposure sessions of 30-min, i.e., sham, continuous, and intermittent (15 s ON/OFF cycles) MF conditions, were involved. Each subject participated in all sessions, which were spaced at 1-wk intervals. In each session, mood ratings and performance measures were obtained before, during, or after exposure and several electrophysiological data (event-related brain potentials [ERP]) were recorded after each exposure session. These criteria were chosen to evaluate sensory functions as well as automatic and voluntary attentional processes. In experiment 1, 21 healthy male volunteers (20 to 27 years of age) were studied. Ten subjects were exposed at 13:30 h, and 11 subjects were exposed at 16:30 h. Statistically significant changes in the amplitude of ERP were observed after MF exposure in the dichotic listening task, indexing selective attention processes. Eighteen of the 21 original male volunteers took part in experiment 2, undertaken to better understand the results related to information processing involved in selective attention and control for ultradian rhythmicity. Exposure time for all the subjects was at 13:30 h. The analysis of the data again revealed significant amplitude changes of the ERP recorded in the dichotic listening task. Moreover, they demonstrated ERP latency and reaction time slowing in the oddball paradigm, a visual discrimination task after real MF exposure. These results also indicate that a low level 50 Hz MF may have a slight influence on event-related potentials and reaction time under specific circumstances of sustained attention.

Effects of prenatal low-dose beta radiation from tritiated water on learning and memory in rats and their possible mechanisms

Pregnant adult Wistar rats were randomly divided into four groups. Three of these groups were irradiated with beta rays by a single intraperitoneal injection of tritiated water ((3)H(2)O) administered on the 13th day of gestation. The doses absorbed by their offspring were estimated to be 4.6, 9.2 and 27.3 cGy. The influence of radiation on the postnatal learning ability and memory behavior and on brain development of the offspring was investigated. The number of pyramidal cells (in areas CA1, CA2, CA3 and CA4) and neurons in the hippocampus of the offspring was also measured. In addition, the Ca(++) conductance of hippocampal pyramidal cells cultured in vitro was observed. The results showed that an exposure to 4.6 cGy could prolong avoidance response time significantly and decrease the number of hippocampal pyramidal cells in the CA1 area compared to controls. An exposure to 9.2 cGy significantly decreased the establishment of conditioned reflexes and the number of hippocampal pyramidal cells in the CA3 area. This exposure also induced the degeneration and malformation of hippocampal neurons cultured in vitro, in addition to decreasing the number of hippocampal neurons observed on each culture day. A dose of 27.3 cGy significantly decreased brain and body weights and the maximum electric conductance of Ca(++) in hippocampal pyramidal neurons. In general, dose-dependent effects were observed for most of the parameters assessed in the present study. Possible mechanisms are discussed.

[Effects of low-dose tritiated water on the developing central nerve system and their mechanisms]

OBJECTIVES

To provide experimental data for evaluating tritium risk of nuclear-energy plant and instituting safety protection standard of nuclear effects of low-dose tritiated water(HTO) on the developing central nerve system.

METHODS

Pregnant adult C57BL/6J strain mice and Wistar rats were irradiated with beta-rays from HTO by a single intraperitoneal injection on the 12.5th and 13th day of gestation. The activity of HTO was (x 10(4) Bq/g. B.W) 24.09, 48.18 and 144.54, respectively. Neurobehavior and learning and memory ability were tested. Ca2+ currents of hippocampal neurons were examined by patch-clamp. Apoptosis of brain cells was detected morphologically and biochemically by DNA electrophoresis. SDS-PAGE and Western blotting were used to detect P53 protein in the cultures.

RESULTS

After irradiation with beta-rays from HTO in utero, the offspring showed hyperactivity in their young age period and then showed depression-hypoactivity in adulthood. The exposed animals had difficulties in both learning and memory retention and the developing neurons of the central nerve system showed lower Ca2+ currents, higher number of apoptosis, a typical "ladder pattern" DNA and increasing P53 protein.

CONCLUSIONS

Lower Ca2+ currents, higher number of apoptosis of brain cells and abnormal expression of P53 protein were the substance basis of the damage of central nerve system caused by tritium.

Behavioral evaluation of microwave irradiation

Establishing safe exposure levels for microwave irradiation is important since new, more powerful emitters are developed and the potential for accidental exposure is increasing. Analysis of the behavior of exposed laboratory animals has proven to be an accurate and repeatable metric for assessing the effects of microwave irradiation. Determining the specific absorption rate (SAR) at which an animal will cease an ongoing behavior has proven useful in the development of safe exposure levels for humans. Behaviors that have been used are simple tasks, and the point at which behavior changes significantly or ceases has often been referred to as "work stoppage." The tasks have been used to evaluate the overwhelming effects of heating produced by microwave irradiation. Both whole-body exposures and partial-body exposures with hotspots have been evaluated. Recent studies have suggested that microwave effects on specific cognitive aspects of behavior such as attention, learning, memory, discrimination, and time perception may occur at SAR levels far below the SARs needed to cause work stoppage. New research studies are underway to evaluate microwave-induced cognitive effects.

Differential learning impairments produced by prenatal exposure to ionizing radiation in mice

PURPOSE

To investigate the behavioural effects of prenatal irradiation on different days of gestation on the performance of two learning tasks by adult mice.

MATERIALS AND METHODS

CD1 mice were exposed in utero to 1 Gy of 250 kV X-rays on gestational days 13, 15 or 18. Other animals were sham-exposed. Male mice were tested as adults in a radial arm maze on two learning tasks considered dependent upon either spatial memory or visual associative memory.

RESULTS

Performance of the animals on the tasks was a function of the day on which exposure occurred. Compared with sham-exposed animals, exposure on day 18 produced a highly significant deficit in performance on the spatial task, and a small improvement in the visually cued task. Exposure on day 15 produced no deficit in performance on the spatial task, but a highly significant deficit in the cued task. Exposure on day 13 produced no significant deficits on either task.

CONCLUSIONS

These differential effects on performance appear to be consistent with radiation-induced insult to different memory systems within the developing mouse brain. These and further studies will help provide better estimates of the risks of radiation at different times during gestation on cognitive function in humans.