The multidisciplinary study observed the behaviour and brain chemistry of rats with ADHD-like symptoms when supplemented with omega-3 fatty acids – finding a clear improvement in ADHD-related behaviour in addition to alterations to biochemical processes in the brain.
There are, however, clear sex differences, said the Norwegian researchers behind the study – noting that a better effect from omega-3 fatty acids is achieved in male rats than in female.
Writing in Behavioral and Brain Functions, the team – led by Professor Ivar Walaas from the University of Oslo - reveal that when compared to rats that did not receive omega-3 supplementation, those that did had a faster turnover of the signalling substances dopamine, serotonin and glutamate in the nervous system in addition to enhancing reinforcement-controlled attention and reducing lever-directed hyperactivity and impulsiveness in male rats.
"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," said Walaas.
"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,” added Kine Dervola – first author of the study. “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," she said.
The biology of ADHD?
The researchers noted that currently the psychiatric diagnosis ADHD is purely based on behavioural criteria - while the molecular genetic background for the illness is largely unknown.
However, the new findings indicate that ADHD has a biological component and that the intake of omega-3 may influence ADHD symptoms.
Indeed, they noted that many previous studies have also found that omega-3 fatty acids can reduce ADHD behaviour in rats.
What is unique about the new study in question is a multidisciplinarity that has not previously been seen, with contributions from behavioural science in medicine as well as from psychology, nutritional science and biochemistry, said Walaas and his team.
However, Walaas warned that they 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,” he said.
“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," Walaas added.
Omega-3 was 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. Baby rats were also given omega-3 in their own food after they were separated from their mother at the age of 20 days.
A second group of mother rats were given food that did not have omega-3 added, thus creating a control group.
Walaas and his team then analysed the behaviour of the offspring in the days after they were separated from the mother – studying behaviours driven by reward as well as spontaneous behaviour.
The team used SHR rats (spontaneously hypertensive rats) to study the effects of omega-3 supplementation.
They noted that the random mutations in the genes of SHR rats have resulted in genetic damage that produces high blood pressure – and that it is therefore first and foremost blood-pressure researchers who have so far been interested in these rats.
However, rats do not suffer from high blood pressure until they have reached puberty, they added. Before that age they present totally different symptoms - hyperactivity, poor ability to concentrate and impulsiveness. These symptoms are the same criteria that form the basis of ADHD diagnosis in humans, they added.
Substantial differences were found for both types of behaviour between the rats that had been given the omega-3 supplement as foetuses and as baby rats and those that had not.
Indeed Walaas and his colleagues found that rats that had not been given omega-3 could not concentrate on pressing an illuminated button that resulted in a reward, while the rats that had been brought up on omega-3 easily managed to hold their concentration for the task – and were duly rewarded with water drops.
However, they noted that it was only male rats that showed an improvement in this reward-driven behaviour.
When it came to spontaneous behaviour, similar reductions in hyperactivity and attention difficulties were found in both male and female rats that had been given the omega-3 supplement.
The Norwegian researchers then analysed levels of neurotransmitters including dopamine, serotonin and glutamate that are released and broken down within the nerve fibres.
Again, they found clear sex differences in the turnover of the neurotransmitters – with significantly enhanced dopamine and serotonin turnover ratios in the male rates, whereas females showed no change, except for an intermediate increase in serotonin catabolism.
Source: Behavioral and Brain Functions
Volume 8, Number 56, doi: 10.1186/1744-9081-8-56
“Marine omega-3 polyunsaturated fatty acids induce sex-specific changes in reinforcer-controlled behaviour and neurotransmitter metabolism in a spontaneously hypertensive rat model of ADHD”
Authors: Kine S Dervola, Bjørg Å Roberg, Grete Wøien, et al