New Concerns for Neurocognitive Function during Deep Space Exposures to Chronic, Low Dose-Rate, Neutron Radiation

How the Immune System Deploys Creativity: Why We Can Learn From Astronauts and Cosmonauts

In this interdisciplinary article, we investigate the relationship between creativity and the immune system; the creative features of the immune system and how the immune system and its role in regulating homeostasis might be related to creative cognition. We argue that within a multivariate approach of creativity, the immune system is a contributing factor. New directions for research are also discussed. When astronauts and cosmonauts venture into the new and extreme environment of outer space, their immune system needs to instantly adapt and find new answers to survive biologically and psychologically. Many astronauts report interest in creative activities and therefore represent an interesting group to investigate creativity in relation with the immune system. Little is known regarding (1) how the immune system interacts with and supports creative cognition and behavior, (2) if an individual's immune system, interacting with cognition, adapts more originally to a new environment compared to another's; in other words, if there is creativity in the domain of the immune system, and (3) the creative properties and functions of the immune system itself.

Modeling space radiation induced cognitive dysfunction using targeted and non-targeted effects

Radiation-induced cognitive dysfunction is increasingly recognized as an important risk for human exploration of distant planets. Mechanistically-motivated mathematical modeling helps to interpret and quantify this phenomenon. Here we considered two general mechanisms of ionizing radiation-induced damage: targeted effects (TE), caused by traversal of cells by ionizing tracks, and non-targeted effects (NTE), caused by responses of other cells to signals released by traversed cells. We compared the performances of 18 dose response model variants based on these concepts, fitted by robust nonlinear regression to a large published data set on novel object recognition testing in rats exposed to multiple space-relevant radiation types (H, C, O, Si, Ti and Fe ions), covering wide ranges of linear energy transfer (LET) (0.22-181 keV/µm) and dose (0.001-2 Gy). The best-fitting model (based on Akaike information criterion) was an NTE + TE variant where NTE saturate at low doses (~ 0.01 Gy) and occur at all tested LETs, whereas TE depend on dose linearly with a slope that increases with LET. The importance of NTE was also found by additional analyses of the data using quantile regression and random forests. These results suggest that NTE-based radiation effects on brain function are potentially important for astronaut health and for space mission risk assessments.

Chronic Low Dose Neutron Exposure Results in Altered Neurotransmission Properties of the Hippocampus-Prefrontal Cortex Axis in Both Mice and Rats

The proposed deep space exploration to the moon and later to Mars will result in astronauts receiving significant chronic exposures to space radiation (SR). SR exposure results in multiple neurocognitive impairments. Recently, our cross-species (mouse/rat) studies reported impaired associative memory formation in both species following a chronic 6-month low dose exposure to a mixed field of neutrons (1 mGy/day for a total dose pf 18 cGy). In the present study, we report neutron exposure induced synaptic plasticity in the medial prefrontal cortex, accompanied by microglial activation and significant synaptic loss in the hippocampus. In a parallel study, neutron exposure was also found to alter fluorescence assisted single synaptosome LTP (FASS-LTP) in the hippocampus of rats, that may be related to a reduced ability to insert AMPAR into the post-synaptic membrane, which may arise from increased phosphorylation of the serine 845 residue of the GluA1 subunit. Thus, we demonstrate for the first time, that low dose chronic neutron irradiation impacts homeostatic synaptic plasticity in the hippocampal-cortical circuit in two rodent species, and that the ability to successfully encode associative recognition memory is a dynamic, multicircuit process, possibly involving compensatory changes in AMPAR density on the synaptic surface.

Progressive increase in the complexity and translatability of rodent testing to assess space-radiation induced cognitive impairment

Ground-based rodent models have established that space radiation doses (approximately those that astronauts will be exposed to on a mission to Mars) significantly impair performance in a wide range of cognitive tasks. Over the last 40 years there has been a progressive increase in both the complexity and the translatability (to humans) of the cognitive tasks investigated. This review outlines technical and conceptual advances in space radiation rodent testing approaches, along with the advances in analytical approaches, that will make data from ground based studies more amenable to probabilistic risk analysis. While great progress has been made in determining the impact of space radiation on many advanced cognitive processes, challenges remain that need to be addressed prior to commencing deep space missions. A summary of on-going attempts to address existing knowledge gaps and the critical role that rodent studies will have in establishing the impact of space radiation on even more complex (human) cognitive tasks are presented and discussed.

Human neural stem cell-derived extracellular vesicles mitigate hallmarks of Alzheimer's disease

Background

Regenerative therapies to mitigate Alzheimer’s disease (AD) neuropathology have shown very limited success. In the recent era, extracellular vesicles (EVs) derived from multipotent and pluripotent stem cells have shown considerable promise for the treatment of dementia and many neurodegenerative conditions.

Methods

Using the 5xFAD accelerated transgenic mouse model of AD, we now show the regenerative potential of human neural stem cell (hNSC)-derived EVs on the neurocognitive and neuropathologic hallmarks in the AD brain. Two- or 6-month-old 5xFAD mice received single or two intra-venous (retro-orbital vein, RO) injections of hNSC-derived EVs, respectively.

Results

RO treatment using hNSC-derived EVs restored fear extinction memory consolidation and reduced anxiety-related behaviors 4–6 weeks post-injection. EV treatment also significantly reduced dense core amyloid-beta plaque accumulation and microglial activation in both age groups. These results correlated with partial restoration of homeostatic levels of circulating pro-inflammatory cytokines in the AD mice. Importantly, EV treatment protected against synaptic loss in the AD brain that paralleled improved cognition. MiRNA analysis of the EV cargo revealed promising candidates targeting neuroinflammation and synaptic function.

Conclusions

Collectively, these data demonstrate the neuroprotective effects of systemic administration of stem cell-derived EVs for remediation of behavioral and molecular AD neuropathologies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00791-x.

Effects of Focal Ionizing Radiation of the Squid Stellate Ganglion on Synaptic and Axonal Transmission in the Giant-Fiber Pathway

Ionizing radiation is clinically used to treat neurological problems and reduce pathological levels of neural activity in the brain, but its cellular-level mechanisms are not well understood. Although spontaneous and stimulated synaptic activity has been produced in rodents by clinically and environmentally relevant doses of radiation, the effects on basic excitability properties of neurons have seldom been reported. This study examined the effects of focused ionizing radiation on synaptic transmission and action potential generation in the squid giant-fiber system, which includes the giant synapse between a secondary interneuron and the tertiary giant motor axons. Radiation of 140-300 Gy was delivered to a stellate ganglion of a living squid over several minutes, with the contralateral stellate ganglion serving as an internal control. No qualitative changes in the efficacy of synaptic transmission were noted in conjunction with stimulation of the input to the giant synapse, although in one irradiated ganglion, the refractory period increased from about 5 ms to more than 45 seconds. Small but significant changes in the action potential recorded from the giant motor axon in response to electrical stimulation were associated with an increased maximum rate of fall and a shortened action potential duration. Other action-potential parameters, including resting potential, overshoot, the maximum rate of the rise, and the refractory period were not significantly changed. Attempts to account for the observed changes in the action potential were carried through a Hodgkin-Huxley model of the action potential. This approach suggests that an increase in the maximum voltage-gated potassium conductance of about 50% mimics the action potential shortening and increased rate of fall that was experimentally observed. We propose that such an effect could result from phosphorylation of squid potassium channels.

Detrimental impacts of mixed-ion radiation on nervous system function

Galactic cosmic radiation (GCR), composed of highly energetic and fully ionized atomic nuclei, produces diverse deleterious effects on the body. In researching the neurological risks of GCR exposures, including during human spaceflight, various ground-based single-ion GCR irradiation paradigms induce differential disruptions of cellular activity and overall behavior. However, it remains less clear how irradiation comprising a mix of multiple ions, more accurately recapitulating the space GCR environment, impacts the central nervous system. We therefore examined how mixed-ion GCR irradiation (two similar 5-6 beam combinations of protons, helium, oxygen, silicon and iron ions) influenced neuronal connectivity, functional generation of activity within neural circuits and cognitive behavior in mice. In electrophysiological recordings we find that space-relevant doses of mixed-ion GCR preferentially alter hippocampal inhibitory neurotransmission and produce related disruptions in the local field potentials of hippocampal oscillations. Such underlying perturbation in hippocampal network activity correspond with perturbed learning, memory and anxiety behavior.

Consequences of space radiation on the brain and cardiovascular system

Staying longer in outer space will inevitably increase the health risks of astronauts due to the exposures to galactic cosmic rays and solar particle events. Exposure may pose a significant hazard to space flight crews not only during the mission but also later, when slow-developing adverse effects could finally become apparent. The body of literature examining ground-based outcomes in response to high-energy charged-particle radiation suggests differential effects in response to different particles and energies. Numerous animal and cellular models have repeatedly demonstrated the negative effects of high-energy charged-particle on the brain and cognitive function. However, research on the role of space radiation in potentiating cardiovascular dysfunction is still in its early stages. This review summarizes the available data from studies using ground-based animal models to evaluate the response of the brain and heart to the high-energy charged particles of GCR and SPE, addresses potential sex differences in these effects, and aims to highlight gaps in the current literature for future study.

Glia-Selective Deletion of Complement C1q Prevents Radiation-Induced Cognitive Deficits and Neuroinflammation

The adverse neurocognitive sequelae following clinical radiotherapy (RT) for central nervous system (CNS) malignancies are often long-lasting without any clinical recourse. Despite recent progress, the cellular mechanisms mediating RT-induced cognitive deficits (RICD) are poorly understood. The complement system is an immediate sensor of a disturbed inflammatory environment and a potent mediator of gliosis with a range of nonimmune functions in the CNS, including synaptic pruning, which is detrimental if dysregulated. We hypothesize that complement-mediated changes in glial cell function significantly contribute to RICD. The underlying alterations in CNS complement cascade proteins (C1q, C3), TLR4, and colabeling with glia (IBA1, GFAP) were examined using gene expression, immunofluorescence, and in silico modeling approaches in the adult mouse brain following 9 Gy cranial RT. Three-dimensional volumetric quantification showed elevated molecular signatures of gliosis at short- and long-term post-RT times. We found significant elevations in complement C1q, C3, and TLR4 post-RT accompanied by increased colabeling of astrocytes and microglia. To address the mechanism of RT-induced complement cascade activation, neuroinflammation, and cognitive dysfunction, we used a genetic approach-conditional, microglia-selective C1q (Flox) knockdown mice-to determine whether a glia-specific, upstream complement cascade contributes to RICD. C1q-Flox mice exposed to cranial RT showed no cognitive deficits compared with irradiated WT mice. Further, irradiated C1q-Flox mice were protected from RT-induced microglial activation and synaptic loss, elevation of anaphylatoxin C5a receptor, astrocytic-C3, and microglial-TLR4 expression in the brain. Our findings demonstrate for the first time a microglia-specific mechanism of RICD involving an upstream complement cascade component, C1q. SIGNIFICANCE: Clinically-relevant radiotherapy induces aberrant complement activation, leading to brain injury. Microglia-selective genetic deletion of CNS complement C1q ameliorates radiation-induced cognitive impairments, synaptic loss, and neuroinflammation, highlighting the potential for C1q as a novel therapeutic target.See related commentary by Korimerla and Wahl, p. 1635.

Sleep Fragmentation Exacerbates Executive Function Impairments Induced by Low Doses of Si Ions

Astronauts on deep space missions will be required to work autonomously and thus their ability to perform executive functions could be critical to mission success. Ground-based rodent experiments have shown that low (<25 cGy) doses of several space radiation (SR) ions impair various aspects of executive function. Translating ground-based rodent studies into tangible risk estimates for astronauts remains an enormous challenge, but should similar neurocognitive impairments occur in astronauts exposed to low-SR doses, a Numbers-Needed-to-Harm analysis (of the rodent data) predicts that approximately 30% of the astronauts could develop severe cognitive flexibility decrements. In addition to the health risks associated with SR exposure, astronauts have to contend with other stressors, of which inadequate sleep quantity and quality are considered to be major concerns. We have shown that a single session of fragmented sleep uncovered latent attentional set-shifting (ATSET) performance deficits in rats exposed to protracted neutron radiation that had no obvious defects in performance under rested wakefulness conditions. It is unclear if the exacerbating effect of sleep fragmentation (SF) only occurs in rats receiving protracted low-dose-rate-neutron radiation. In this study, we assessed whether SF also unmasks latent ATSET deficits in rats exposed to 5 cGy 600 MeV/n 28Si ions. Only sham and Si-irradiated rats that had good ATSET performance (passing every stage of the test on their first attempt) were selected for study. Sleep fragmentation selectively impaired performance in the more complex IDR, EDS and EDR stages of the ATSET test in the Si-irradiated rats. Set-shifting performance has rarely been affected by SR exposure in our studies conducted with rats tested under rested wakefulness conditions. The consistent SF-related unmasking of latent set-shifting deficits in both Si- and neutron-irradiated rats suggests that there is a unique interaction between sleep fragmentation and space radiation on the functionality of the brain regions that regulate performance in the IDR, EDS and EDR stages of ATSET. The uncovering of these latent SR-induced ATSET performance deficits in both Si- and neutron-irradiated rats suggests that the true impact of SR-induced cognitive impairment may not be fully evident in normally rested rats, and thus cognitive testing needs to be conducted under both rested wakefulness and sleep fragmentation conditions.

Noninvasive Brain Stimulation & Space Exploration: Opportunities and Challenges

As NASA prepares for longer space missions aiming for the Moon and Mars, astronauts' health and performance are becoming a central concern due to the threats associated with galactic cosmic radiation, unnatural gravity fields, and life in extreme environments. In space, the human brain undergoes functional and structural changes related to fluid shift and changes in intracranial pressure. Behavioral abnormalities, such as cognitive deficits, sleep disruption, and visuomotor difficulties, as well as psychological effects, are also an issue. We discuss opportunities and challenges of noninvasive brain stimulation (NiBS) methods - including transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES) - to support space exploration in several ways. NiBS includes safe and portable techniques already applied in a wide range of cognitive and motor domains, as well as therapeutically. NiBS could be used to enhance in-flight performance, supporting astronauts during pre-flight Earth-based training, as well as to identify biomarkers of post-flight brain changes for optimization of rehabilitation/compensatory strategies. We review these NiBS techniques and their effects on brain physiology, psychology, and cognition.

Fundamental Biological Features of Spaceflight: Advancing the Field to Enable Deep-Space Exploration

Research on astronaut health and model organisms have revealed six features of spaceflight biology that guide our current understanding of fundamental molecular changes that occur during space travel. The features include oxidative stress, DNA damage, mitochondrial dysregulation, epigenetic changes (including gene regulation), telomere length alterations, and microbiome shifts. Here we review the known hazards of human spaceflight, how spaceflight affects living systems through these six fundamental features, and the associated health risks of space exploration. We also discuss the essential issues related to the health and safety of astronauts involved in future missions, especially planned long-duration and Martian missions.

Skilled movement and posture deficits in rat string-pulling behavior following low dose space radiation (28Si) exposure

Deep space flight missions beyond the Van Allen belt have the potential to expose astronauts to space radiation which may damage the central nervous system and impair function. The proposed mission to Mars will be the longest mission-to-date and identifying mission critical tasks that are sensitive to space radiation is important for developing and evaluating the efficacy of counter measures. Fine motor control has been assessed in humans, rats, and many other species using string-pulling behavior. For example, focal cortical damage has been previously shown to disrupt the topographic (i.e., path circuity) and kinematic (i.e., moment-to-moment speed) organization of rat string-pulling behavior count to compromise task accuracy. In the current study, rats were exposed to a ground-based model of simulated space radiation (5 cGy ²⁸Silicon), and string-pulling behavior was used to assess fine motor control. Irradiated rats initially took longer to pull an unweighted string into a cage, exhibited impaired accuracy in grasping the string, and displayed postural deficits. Once rats were switched to a weighted string, some deficits lessened but postural instability remained. These results demonstrate that a single exposure to a low dose of space radiation disrupts skilled hand movements and posture, suggestive of neural impairment. This work establishes a foundation for future studies to investigate the neural structures and circuits involved in fine motor control and to examine the effectiveness of counter measures to attenuate the effects of space radiation on fine motor control.

Combined Environment Simulator for Low-Dose-Rate Radiation and Partial Gravity of Moon and Mars

Deep space exploration by humans has become more realistic, with planned returns to the Moon, travel to Mars, and beyond. Space radiation with a low dose rate would be a constant risk for space travelers. The combined effects of space radiation and partial gravity such as on the Moon and Mars are unknown. The difficulty for such research is that there are no good simulating systems on the ground to investigate these combined effects. To address this knowledge gap, we developed the Simulator of the environments on the Moon and Mars with Neutron irradiation and Gravity change (SwiNG) for in vitro experiments using disposable closed cell culture chambers. The device simulates partial gravity using a centrifuge in a three-dimensional clinostat. Six samples are exposed at once to neutrons at a low dose rate (1 mGy/day) using Californium-252 in the center of the centrifuge. The system is compact including two SwiNG devices in the incubator, one with and one without radiation source, with a cooling function. This simulator is highly convenient for ground-based biological experiments because of limited access to spaceflight experiments. SwiNG can contribute significantly to research on the combined effects of space radiation and partial gravity.

Can a comparison of clinical and deep space irradiation scenarios shed light on the radiation response of the brain?

Not surprisingly, our knowledge of the impact of radiation on the brain has evolved considerably. Decades of work have struggled with identifying the critical cellular targets in the brain, the latency of functional change and understanding how irradiation alters the balance between excitatory and inhibitory circuits. Radiation-induced cell kill following clinical fractionation paradigms pointed to both stromal and parenchymal targets but also defined an exquisite sensitivity of neurogenic populations of newly born cells in the brain. It became more and more apparent too, that acute (days) events transpiring after exposure were poorly prognostic of the late (months-years) waves of radiation injury believed to underlie neurocognitive deficits. Much of these gaps in knowledge persisted as NASA became interested in how exposure to much different radiation types, doses and dose rates that characterize the space radiation environment might impair central nervous system functionality, with possibly negative implications for deep space travel. Now emerging evidence from researchers engaged in clinical, translational and environmental radiation sciences have begun to fill these gaps and have uncovered some surprising similarities in the response of the brain to seemingly disparate exposure scenarios. This article highlights many of the commonalities between the vastly different irradiation paradigms that distinguish clinical treatments from occupational exposures in deep space.

Extracellular Vesicle-Derived miR-124 Resolves Radiation-Induced Brain Injury

Radiation-induced cognitive dysfunction (RICD) is a progressive and debilitating health issue facing patients following cranial radiotherapy to control central nervous system cancers. There has been some success treating RICD in rodents using human neural stem cell (hNSC) transplantation, but the procedure is invasive, requires immunosuppression, and could cause other complications such as teratoma formation. Extracellular vesicles (EV) are nanoscale membrane-bound structures that contain biological contents including mRNA, miRNA, proteins, and lipids that can be readily isolated from conditioned culture media. It has been previously shown that hNSC-derived EV resolves RICD following cranial irradiation using an immunocompromised rodent model. Here, we use immunocompetent wild-type mice to show that hNSC-derived EV treatment administered either intravenously via retro-orbital vein injection or via intracranial transplantation can ameliorate cognitive deficits following 9 Gy head-only irradiation. Cognitive function assessed on the novel place recognition, novel object recognition, and temporal order tasks was not only improved at early (5 weeks) but also at delayed (6 months) postirradiation times with just a single EV treatment. Improved behavioral outcomes were also associated with reduced neuroinflammation as measured by a reduction in activated microglia. To identify the mechanism of action, analysis of EV cargo implicated miRNA (miR-124) as a potential candidate in the mitigation of RICD. Furthermore, viral vector-mediated overexpression of miR-124 in the irradiated brain ameliorated RICD and reduced microglial activation. Our findings demonstrate for the first time that systemic administration of hNSC-derived EV abrogates RICD and neuroinflammation in cranially irradiated wild-type rodents through a mechanism involving miR-124. SIGNIFICANCE: Radiation-induced neurocognitive decrements in immunocompetent mice can be resolved by systemic delivery of hNSC-derived EVs involving a mechanism dependent on expression of miR-124.

Challenges to the central nervous system during human spaceflight missions to Mars

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Space Radiation Biology for "Living in Space"

Space travel has advanced significantly over the last six decades with astronauts spending up to 6 months at the International Space Station. Nonetheless, the living environment while in outer space is extremely challenging to astronauts. In particular, exposure to space radiation represents a serious potential long-term threat to the health of astronauts because the amount of radiation exposure accumulates during their time in space. Therefore, health risks associated with exposure to space radiation are an important topic in space travel, and characterizing space radiation in detail is essential for improving the safety of space missions. In the first part of this review, we provide an overview of the space radiation environment and briefly present current and future endeavors that monitor different space radiation environments. We then present research evaluating adverse biological effects caused by exposure to various space radiation environments and how these can be reduced. We especially consider the deleterious effects on cellular DNA and how cells activate DNA repair mechanisms. The latest technologies being developed, e.g., a fluorescent ubiquitination-based cell cycle indicator, to measure real-time cell cycle progression and DNA damage caused by exposure to ultraviolet radiation are presented. Progress in examining the combined effects of microgravity and radiation to animals and plants are summarized, and our current understanding of the relationship between psychological stress and radiation is presented. Finally, we provide details about protective agents and the study of organisms that are highly resistant to radiation and how their biological mechanisms may aid developing novel technologies that alleviate biological damage caused by radiation. Future research that furthers our understanding of the effects of space radiation on human health will facilitate risk-mitigating strategies to enable long-term space and planetary exploration.

Immune and Inflammatory Determinants Underlying Alzheimer's Disease Pathology

This study examines the link between peripheral immune changes in perpetuation of the Alzheimer's disease (AD) neuropathology and cognitive deficits. Our research design using human AD patients and rodent model is supported by past evidence from genomic studies. We observed an active immune response against Aβ as indicated by the increased Aβ specific IgG antibody in the serum of AD and patients with mild cognitive impairments as compared to healthy controls. A similar increase in IgG and decrease in IgM antibody against Aβ was also confirmed in the 5xFAD mouse model of AD. More importantly, we observed a negative correlation between reduced IgM levels and cognitive dysfunction that manifested as impaired memory consolidation. Strong peripheral immune activation was supported by increased activation of microglia in the brain and macrophages in the spleen of AD mice compared to wild type control littermates. Furthermore, inflammatory cytokine IL-21 that is involved in antibody class switching was elevated in the plasma of AD patients and correlated positively with the IgG antibody levels. Concurrently, an increase in IL-21 and IL-17 was observed in spleen cells from AD mice. Further investigation revealed that proportions of T follicular helper (Tfh) cells that secrete IL-21 are increased in the spleen of AD mice. In contrast to Tfh, the frequency of B1 cells that produce IgM antibodies was reduced in AD mice. Altogether, these data indicate that in AD the immune tolerance to Aβ is compromised leading to chronic immune/inflammatory responses against Aβ that are detrimental and cause neuropathology. Graphical Abstract Healthy subjects are tolerant to Aβ and usually react weakly to it resulting the in the production of IgM class of antibodies that are efficient at clearing up self-antigens such as Aβ without causing inflammation. In contrast, Alzheimer's disease patients mount a strong immune response against Aβ probably in an effort to clear up excessive Aβ. There is enhanced production of inflammatory cytokines such as IL-21 as well as an increase in Tfh cells that cause antibody class switching form IgM to IgG. The strong immune response is inefficient at clearing up Aβ and instead exacerbates inflammation that causes AD neuropathology and cognitive dysfunction.

Multi-domain cognitive assessment of male mice shows space radiation is not harmful to high-level cognition and actually improves pattern separation

Astronauts on interplanetary missions - such as to Mars - will be exposed to space radiation, a spectrum of highly-charged, fast-moving particles that includes 56Fe and 28Si. Earth-based preclinical studies show space radiation decreases rodent performance in low- and some high-level cognitive tasks. Given astronaut use of touchscreen platforms during training and space flight and given the ability of rodent touchscreen tasks to assess functional integrity of brain circuits and multiple cognitive domains in a non-aversive way, here we exposed 6-month-old C57BL/6J male mice to whole-body space radiation and subsequently assessed them on a touchscreen battery. Relative to Sham treatment, 56Fe irradiation did not overtly change performance on tasks of visual discrimination, reversal learning, rule-based, or object-spatial paired associates learning, suggesting preserved functional integrity of supporting brain circuits. Surprisingly, 56Fe irradiation improved performance on a dentate gyrus-reliant pattern separation task; irradiated mice learned faster and were more accurate than controls. Improved pattern separation performance did not appear to be touchscreen-, radiation particle-, or neurogenesis-dependent, as 56Fe and 28Si irradiation led to faster context discrimination in a non-touchscreen task and 56Fe decreased new dentate gyrus neurons relative to Sham. These data urge revisitation of the broadly-held view that space radiation is detrimental to cognition.

BRAIN AND EYE AS POTENTIAL TARGETS FOR IONIZING RADIATION IMPACT. Part І. THE CONSEQUENCES OF IRRADIATION OF THE PARTICIPANTS OF THE LIQUIDATION OF THE CHORNOBYL ACCIDENT

BACKGROUND

Exposure to ionizing radiation could affect the brain and eyes leading to cognitive and vision impairment, behavior disorders and performance decrement during professional irradiation at medical radiology, includinginterventional radiological procedures, long-term space flights, and radiation accidents.

OBJECTIVE

The objective was to analyze the current experimental, epidemiological, and clinical data on the radiation cerebro-ophthalmic effects.

MATERIALS AND METHODS

In our analytical review peer-reviewed publications via the bibliographic and scientometric bases PubMed / MEDLINE, Scopus, Web of Science, and selected papers from the library catalog of NRCRM - theleading institution in the field of studying the medical effects of ionizing radiation - were used.

RESULTS

The probable radiation-induced cerebro-ophthalmic effects in human adults comprise radiation cataracts,radiation glaucoma, radiation-induced optic neuropathy, retinopathies, angiopathies as well as specific neurocognitive deficit in the various neuropsychiatric pathology including cerebrovascular pathology and neurodegenerativediseases. Specific attention is paid to the likely stochastic nature of many of those effects. Those prenatally and inchildhood exposed are a particular target group with a higher risk for possible radiation effects and neurodegenerative diseases.

CONCLUSIONS

The experimental, clinical, epidemiological, anatomical and pathophysiological rationale for visualsystem and central nervous system (CNS) radiosensitivity is given. The necessity for further international studieswith adequate dosimetric support and the follow-up medical and biophysical monitoring of high radiation riskcohorts is justified. The first part of the study currently being published presents the results of the study of theeffects of irradiation in the participants of emergency works at the Chornobyl Nuclear Power Plant (ChNPP).

Comments on "New Concerns for Neurocognitive Function during Deep Space Exposures to Chronic, Low Dose Rate, Neutron Radiation"

Evaluations of the biological effects of space radiation must carefully consider the biological system response and the specific nature of the source term. Acharya et al. (2019) review neurocognitive function during deep space exposures to chronic, low dose rate, neutron radiation, but do not use a source term that reflects the actual space environment in terms of radiation types and their respective energies. In addition, important biological effects, including the adaptive response to the space radiation environment, are not addressed.

Sleep fragmentation exacerbates executive function impairments induced by protracted low dose rate neutron exposure

PURPOSE

Astronauts on the planned missions to Mars are expected to have to work more autonomously than on previous missions. Thus mission success may be influenced by the astronauts' ability to respond quickly to unexpected problems, processes that require several executive functions. The purpose of this study was to determine the impact that prolonged low dose and low dose rate exposure to neutrons had on two executive functions, and whether the severity and incidence of cognitive impairment was altered by sleep fragmentation.

MATERIALS AND METHODS

In this study we assessed the impact that prolonged (six month) low dose rate neutron exposure had on the ability of male Wistar rats to perform in two executive function tasks (i.e. attentional set shifting (ATSET) - a constrained cognitive flexibility task and the UCFlex assay - an unconstrained cognitive flexibility task). In recognition of the fact that astronauts also have to contend with inadequate sleep quantity and quality for much of their time in space, we determined the impact that relatively mild sleep disruption had on the ability to perform in the ATSET test in sham and neutron-irradiated rats.

RESULTS

Chronic low dose (18 cGy) and dose-rate (1 mGy/day) exposure of rats to mixed neutron and photon over the course of six months resulted in significant impairment of simple discrimination (SD) performance. Should similar effects occur in astronauts subjected to low dose rate exposure to Space Radiation, the impairment of SD performance would result in a decreased ability to identify and learn the 'rules' required to respond to a new task or situation. Analysis of the behavioral data by kernel density estimation revealed that 40% of rats had severe ATSET impairments. This value may be a best-case scenario because exposure to neutrons also adversely impacted performance in the UCFlex task. Furthermore, when the good performing rats were reevaluated after they had been subjected to sleep fragmentation, additional ATSET performance decrements were observed in the set shifting stages of the ATSET test, with only 7.4% of the neutron exposed rats able to successfully perform ATSET under normal and sleep fragmented conditions, as opposed to ∼55% of shams.

CONCLUSION

Protracted low dose and low dose rate neutron exposures impairs executive functions in a high percentage of rats that were normally rested, however further detriments in performance become evident when the rats are subjected to sleep fragmentation.

Effects of chronic exposure to a mixed field of neutrons and photons on behavioral and cognitive performance in mice

To simulate the space radiation environment astronauts are exposed to, most studies involve acute exposures but during a space mission there will be chronic (long-lasting) exposures. To address this knowledge gap, a neutron irradiator using a ²⁵²Cf (²⁵²Californium) source was used to generate a mixed field of neutrons and photons to simulate chronic, low dose rate exposures to high LET radiation. In the present study, we assessed the effects chronic neutron exposure starting at 60 days of age on behavioral and cognitive performance of BALB/c female and C3H male mice at 600 and 700 days of age as part of an opportunistic study that took advantage of the availability of neutron and sham-irradiated mice from a radiation carcinogenesis experiment. There were profound dose- and time point-dependent effects of chronic neutron exposure. At the 600-day time point, irradiated BALB/c female mice showed improved nest building at all three doses. At the 700-day, but not 600-day, time point slightly but significantly increased body weights were seen in C3H male mice exposed to 0.118 Gy. At the 600-day time point BALB/c female mice irradiated with 0.2 Gy did, like sham-irradiated, not show preferential exploration of the novel object that was seen in mice irradiated with 0.118 or 0.4 Gy. In C3H male mice exposed to 0.4 Gy and at the 600-day time point, increased measures of anxiety were observed on days 1 and 2 in the open field. Thus, different outcome measures show distinct dose-response relationships, with some anticipated to worsen performance during space missions, like increased measures of anxiety, while other anticipated to enhance performance, such as increased nest building and object recognition.

Changing the Way We Report, Interpret, and Discuss Our Results to Rebuild Trust in Our Research

eNeuro is moving forward with a new initiative asking authors to present their results with estimation statistics and not to rely solely on p values. In this editorial, I would like to introduce to you the concept of this new statistics while first discussing my evaluation of the present situation and my own experience with using statistics to interpret results, then I will propose a solution and how we will move forward in the journal. I have also included my own experience using these new statistics and provided a list of resources. This new initiative will not change what is already acceptable for statistics in the journal; it is to encourage a simple addition of using estimation statistics.