Researchers at the University of Oslo have observed the behaviour of
rats and have analyzed biochemical processes in their brains. The
results show a clear improvement in ADHD-related behaviour 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 behavioural 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 behaviour 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 behavioural 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 behaviour of the offspring
some days after they were separated from the mother. They studied
behaviour driven by reward as well as spontaneous behaviour. Substantial
differences were noted 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.
Rewards made male rats more concentrated
The reward-driven behaviour 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 behaviour. 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 fibres. 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 behaviour.
"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."
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