|
 Brain
Differences Found in ADHD Kids: Scans find unusual levels of
certain neurotransmitters
by Amanda Gardner, HealthDay Reporter, December 5, 2003
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http://www.bridges4kids.org.
Children with
attention-deficit hyperactivity disorder (ADHD) may harbor
unusual levels of certain neurotransmitters in the frontal part
of their brains.
Researchers reporting in the December issue of the Journal of
Neuropsychiatry and Clinical Neurosciences found levels of
glutamate were increased in ADHD children while levels of GABA,
a neuro-inhibitor, were decreased.
If seeing is believing, then the research does add to the
"believability" and "reality" of this disorder, which manifests
in behavioral changes. It is considered the most common
childhood illness; on average, almost every classroom in the
United States will have one child who needs to be treated for
this disorder.
"There's such a lot of contention about ADHD and, in my opinion,
too many kids are diagnosed because they fidget," says study
author Dr. Helen Courvoisie, an assistant professor of child and
adolescent psychiatry at the Johns Hopkins Medical Institutions
in Baltimore. "What studies like mine will do is show there is a
biological basis to those kids who really have ADHD."
Dr. Bradley Peterson, a professor of pediatric neuropsychiatry
at Columbia University and New York State Psychiatric Institute
in New York City, agrees. "Historically, [seeing is believing]
has been very true for other conditions," he says. "Brain
imaging studies showed pretty major differences in brain
structure that really legitimized schizophrenia as a biological
disturbance. I think the same is true for other conditions."
Although the study is small, it is in line with previous work.
"It's one more brick in the wall," says Russell Barkley, a
professor of psychiatry at the Medical University of South
Carolina in Charleston. "It is consistent with a number of other
larger studies that have shown both structural and functional
abnormalities in ADHD children."
The frontal lobe is responsible for executive functioning, which
regulates impulse control, attention and other thought processes
that can be compromised in people with ADHD.
Here, the study authors looked at eight children aged 6 to 12
who had been diagnosed with hyperactive-type ADHD. Of the three
types of ADHD (attention-deficit, hyperactive and combined),
this one most involves a malfunction of executive function.
These children were compared to eight children without ADHD.
All of the ADHD children were taking some kind of stimulant
medication, such as Ritalin, but not for the 24 hours preceding
the scan.
All 16 children first underwent neuropsychological and IQ
testing in one session. Later, they had a type of magnetic
resonance imaging (MRI) that measured the levels of six
metabolites in the frontal part of the brain.
The results revealed that children in the ADHD group seemed to
have decreased levels of GABA, which might explain poor impulse
control, and higher levels of glutamate, which is excitatory and
can be toxic to nerve cells in high amounts. Both GABA and
glutamate are neurotransmitters, or brain chemical messengers.
The levels of the neurotransmitters were measured in relation to
each other, Barkley points out. "It's not necessarily overall
levels that were interesting," he says. "It really is the
relative proportion of chemicals."
Future studies will need to be larger and will need to "see what
kids look like both on and off medication," Courvoisie says.
Eventually, there may be implications for drug therapies.
"Certainly the hope would be that by understanding the
biological basis for these conditions, it'll provide clues as to
how better to intervene therapeutically," Peterson says. "This
particular set of findings suggests that some neurotransmitters
may be increased in concentration in the frontal lobe in
children of ADHD. We don't have good ways of manipulating those
neurotransmitters currently, but we will soon and that may be
helpful."
More information
For more on ADHD, visit the
National
Institute of Mental Health or
Children and Adults with
Attention-Deficit/Hyperactivity Disorder.
SOURCES: Helen Courvoisie, M.D., assistant professor,
division child and adolescent psychiatry, Johns Hopkins Medical
Institutions, Baltimore; Bradley Peterson, M.D., professor,
pediatric neuropsychiatry, Columbia University and New York
State Psychiatric Institute, New York City; Russell Barkley,
Ph.D., professor, psychiatry, Medical University of South
Carolina, Charleston; December 2003 Journal of Neuropsychiatry
and Clinical Neurosciences
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