Researchers at the University of Oslo have observed the behavior of rats and have analyzed biochemical processes in their brains. The results show a clear improvement in ADHD-related behavior from supplements of omega-3 fatty acids, as well as a faster turnover of the signal substances dopamine, serotonin and glutamate in the nervous system. There are, however, clear sex differences: a better effect from omega-3 fatty acids is achieved in male rats than in female.

Unknown biology behind ADHD
Currently the psychiatric diagnosis ADHD (attention deficit hyperactivity disorder) is purely based on behavioral criteria, while the molecular genetic background for the illness is largely unknown. The new findings indicate that ADHD has a biological component and that the intake of omega-3 may influence ADHD symptoms.

“In some research environments it is controversial to suggest that ADHD has something to do with biology. But we have without a doubt found molecular changes in the brain after rats with ADHD were given omega-3,” says Ivar Walaas, professor of biochemistry.

The fact that omega-3 can reduce ADHD behavior in rats has also been indicated in previous international studies. What is unique about the study in question is a multidisciplinarity that has not previously been seen, with contributions from behavioral science in medicine as well as from psychology, nutritional science and biochemistry.

Hyperactive rats
The rats used in the study are called SHR rats—spontaneously hypertensive rats. Although this is primarily a common type of rat, random mutations in their genes have resulted in genetic damage that produces high blood pressure. It is therefore first and foremost blood-pressure researchers who have so far been interested in these rats.

However, the rats do not suffer from high blood pressure until they have reached puberty. Before that age they present totally different symptoms—namely hyperactivity, poor ability to concentrate and impulsiveness. It is exactly these three criteria that form the basis for making the ADHD diagnosis in humans. The animals also react to Ritalin, the central nervous system stimulant, in the same way as humans with ADHD: the hyperactive responses are stabilized. SHR rats are therefore increasingly used in research as a model for ADHD.

Supplements as early as the fetal stage
Researchers believe that omega-3 can have an effect from the very beginning of life. Omega-3 was therefore added to the food given to mother rats before they were impregnated, and this continued throughout their entire pregnancy and while they fed their young. The baby rats were also given omega-3 in their own food after they were separated from their mother at the age of 20 days. Another group of mother rats were given food that did not have omega-3 added, thus creating a control group of SHR offspring that had not been given these fatty acids at the fetal stage or later.

The researchers started to analyze the behavior of the offspring some days after they were separated from the mother. They studied behavior driven by reward as well as spontaneous behavior. Substantial differences were noted for both types of behavior between the rats that had been given the omega-3 supplement as fetuses and as baby rats and those that had not.

Rewards made male rats more concentrated

The reward-driven behavior was such that the rats were allowed access to a drop of water each time they pressed an illuminated button. The ADHD rats that had not been given omega-3 could not concentrate on pressing the button, whereas the rats that had been brought up on omega-3 easily managed to hold their concentration for the seconds this takes and were able to enjoy a delicious drop of water as a reward.

Surprisingly enough, it was only male rats that showed an improvement in reward-driven behavior. However, with regard to the rats’ spontaneous behavior, the same type of reduction in hyperactivity and attention difficulties was noted in both male and female rats that had been given the omega-3 supplement.

Changes in brain chemistry
Professor Walaas and his research group became involved in the study at this point in order to analyze the molecular processes in the rats’ brains.

The group analyzed the level of the chemical connections in the brain, the so-called neurotransmitters that transfer nerve impulses from one nerve cell to another. The researchers measured how much of the neurotransmitters such as dopamine, serotonin and glutamate was released and broken down within the nerve fibers. A key player in this work was Kine S. Dervola, PhD candidate, who reports clear sex differences in the turnover of the neurotransmitters—just as there had been in the reward-driven behavior.

“We saw that the turnover of dopamine and serotonin took place much faster among the male rats that had been given omega-3 than among those that had not. For serotonin the turnover ratio was three times higher, and for dopamine it was just over two and a half times higher. These effects were not observed among the female rats. When we measured the turnover of glutamate, however, we saw that both sexes showed a small increase in turnover,” Ms Dervola tells us.

Transferrable to humans?
The researchers are cautious about drawing conclusions as to whether the results can be transferred to humans.

“In the first place there is of course a difference between rats and humans, and secondly the rats are sick at the outset. Thirdly the causes of ADHD in humans are in no way mapped sufficiently well. But the end result of what takes place in the brains of both rats and humans with ADHD is hyperactivity, poor ability to concentrate and impulsiveness,” says Professor Walaas, and concludes:

“Giving priority to basic research like this will greatly increase our detailed knowledge of ADHD.”