Damage traced in part to dopamine transport system injury in brain cells
Johns Hopkins scientists report that rats exposed to high-energy particles, simulating conditions astronauts would face on a long-term deep space mission, show lapses in attention and slower reaction times, even when the radiation exposure is in extremely low dose ranges.
The cognitive impairments — which affected a large subset, but far from all, of the animals — appear to be linked to protein changes in the brain, the scientists say. The findings, if found to hold true in humans, suggest it may be possible to develop a biological marker to predict sensitivity to radiation’s effects on the human brain before deployment to deep space. The study, funded by NASA’s National Space Biomedical Research Institute, is described in the April issue of the journal Radiation Research.
When astronauts are outside of the Earth’s magnetic field, spaceships provide only limited shielding from radiation exposure, explains study leader Robert D. Hienz, Ph.D., an associate professor of behavioral biology at the Johns Hopkins University School of Medicine. If they take space walks or work outside their vehicles, they will be exposed to the full effects of radiation from solar flares and intergalactic cosmic rays, he says, and since neither the moon nor Mars have a planet-wide magnetic field, astronauts will be exposed to relatively high radiation levels, even when they land on these surfaces.
But not everyone will be affected the same way, his experiments suggest. “In our radiated rats, we found that 40 to 45 percent had these attention-related deficits, while the rest were seemingly unaffected,” Hienz says. “If the same proves true in humans and we can identify those more susceptible to radiation’s effects before they are harmfully exposed, we may be able to mitigate the damage.”
If a biomarker can be identified for humans, it could have even broader implications in determining the best course of treatment for patients receiving radiotherapy for brain tumors or identifying which patients may be more at risk from radiation-based medical treatments, the investigators note.
Previous research has tested how well radiation-exposed rats do with basic learning tasks and mazes, but this new Johns Hopkins study focused on tests that closely mimic the self-tests of fitness for duty currently used by astronauts on the International Space Station prior to mission-critical events such as space walks. Similar fitness tests are also used for soldiers, airline pilots and long-haul truckers.
In one such test, an astronaut sees a blank screen on a handheld device and is instructed to tap the screen when an LED counter lights up. The normal reaction time should be less than 300 milliseconds. The rats in the experiment are similarly taught to touch a light-up key with their noses and are then tested to see how quickly they react.
To conduct the new study, rats were first trained for the tests and then taken to Brookhaven National Laboratory on Long Island in Upton, N.Y., where a collider produces the high-energy proton and heavy ion radiation particles that normally occur in space. The rats’ heads were exposed to varying levels of radiation that astronauts would normally receive during long-duration missions, while other rats were given sham exposures.
Once the rats returned to Johns Hopkins, they were tested every day for 250 days. The radiation-sensitive animals (19 of 46) all showed evidence of impairment that began at 50 to 60 days post–exposure and remained through the end of the study.
Lapses in attention occurred in 64 percent of the sensitive animals, elevations in impulsive responding occurred in 45 percent and slower reaction times occurred in 27 percent. The impairments were not dependent on radiation dose. Additionally, some of the rats didn’t recover at all from their deficits over time, while others showed some recovery over time.
The radiation-sensitive rats that received higher doses of radiation had a higher concentration of transporters for the neurotransmitter dopamine, which plays a role in vigilance and attention, says Catherine M. Davis, Ph.D., a postdoctoral fellow in the Department of Psychiatry and Behavioral Sciences and the study’s first author.
The dopamine transport system appears impaired in radiation-sensitive rats because the neurotransmitter is most likely not removed in the manner it should be for the brain to function properly, she says. Humans with genetic differences related to dopamine transport, she adds, have been shown to do worse on the type of mental fitness tests given to the astronauts and rats alike.
Davis says she wouldn’t want to see radiation-sensitive astronauts kept from future missions to the moon or Mars, but she would want those astronauts to be prepared to take special precautions to protect their brains, such as wearing extra shielding or not performing space walks.
“As with other areas of personalized medicine, we would seek to create individual treatment and prevention plans for astronauts we believe would be more susceptible to cognitive deficits from radiation exposure,” she says.
Current astronauts are not as exposed to the damaging effects of radiation, Davis says, because the International Space Station flies in an orbit low enough that the Earth’s magnetic field continues to provide protection.
While the Johns Hopkins team studies the likely effects of radiation on the brain during a deep space mission, other NASA-funded research groups are looking at the potential effects of radiation on other parts of the body and on whether it increases cancer risks.
As a reader not particularly interested in space exploration, I was surprisingly enthralled by and greatly interested in the findings elucidated by this article.
The results of experiments mentioned above are highly convincing; however, I question methodology in the experimentation, as did 14065950, with regards to the testing of cognitive responses and effects thereof on sample rats. My one concern relates to the “training” of these creatures with the expectations of them to repeat what was learnt. Taking into consideration the fact that the sample group are animals with limited understanding compared to humans, and the unpredictability of their behaviour, I question the reliability of the results obtained. The tests done on the human sample group, on the other hand, are more believable and seem substantial.
I acknowledge the importance of space exploration in universal knowledge acquisition and discovery, nonetheless, am of the firm belief that knowingly subjecting human-life to such danger and health risks in the quest thereof is unethical and agree that greater efforts should be made to protect these invaluable members of society (for example extra-protection gear) from harm, whose small steps create giant leaps for mankind.
This recent discovery could definitely influence the future of the global space industry, especially when bigger missions such as colonizing Mars are added into the equation. Since the long term effects of prolonged exposure to high-energy -particles and certain types of “space radiation” are still unknown, the newly discovered correlation between the loss in cognitive abilities and prolonged exposure in mice has opened a great door in further understanding crucial questions regarding health risks for astronauts who might have to face certain circumstances of prolonged exposure. (eg. Space walks) Research such as this is critical in establishing new methods of protecting astronauts from potential damage to their cognitive abilities on future missions in the field of deep space exploration. Is the loss of cognitive ability, due to prolonged exposures of high-energy-particles, inversely proportional to the organisms size and mass?
Food for thought: Perhaps the fact that only mice were tested, who are relatively small compared to humans, might prove that the same amount of radiation would have a much smaller effect over the same period of time in larger organisms like ourselves?
Few additional words for the – cognitive function impairment observation due to the radiation exposure – : We are evolved in this planet`s `radiation` protective environment over 3,5 billion years of evolution , sharing primitive MRCA (Most recent Common Ancestors) of all life forms along the evolutionary painful long journey from the start ; that would have never been possible if spreading phylogenetic branches of that initial MRCA was ever exposed to high levels of radiation , those radiation exposed branches –species – would have been extinct –rapidly- at no time from the surface of this planet -without any forward evolution going to no where – whether they are the representatives of most primitive life forms or the most complex advanced life forms it would have made no difference what so ever ; simply because they can not maintain -protect- their – evolutionary adaptive beneficial genetic code DNA or RNA (in case of primitive life forms like viruses ) from harmful – excessive genetic code destroying radiation- that they have gained painfully and very costly indeed over generations after generations through selections and adaptations in order to survive over millions of years on this planet .
The punch line is ; astronauts invariable are subjected cosmic radiation and harmful mutations –untold /unspoken sad truth of this matter indeed – these mutations may or may not give any clinical clue in their lifetime but if they chose to have offspring’s after their exposure ; those harmful mutations they had accumulated throughout the radiation exposure period ; may eventually manifest clinically in them in other words their -grandfather or grandmother`s testicle and ovaries –reproductive organs- radiation exposure`s side effects . There is no such thing as beneficial or neutral effect of radiation as we know well now –all radiation exposures are harmful without a single exception – in his/her life time or future generations of their offspring`s life time – who had been conceived after the radiation exposure – .
We should never take our beloved planets radiation protective shields (thick atmosphere and strong magnetic field) for granted , thicker the atmosphere and polar magnetic field better the protection , even frequent plane travel and high altitude living have inevitably higher levels of Cosmic radiation exposures as well as higher natural radioactivity certain geographic locations . Protection from ever harmful cumulative cosmic radiation exposure will be the most important and serious challenge of any life form in the future who will be attempting long space travel and living outside of our protective planet ; like Moon and Mars , they may have to live very deep underground as an effective cosmic radiation shield in order to substitute –the ever protective atmosphere and strong magnetic field of our Earth – provided that the soil radiation level at that location is low of course .