Effect of ADHD Drugs on the Brain - Study Finds

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Effect of ADHD Drugs on the Brain - Study Finds

Investigating on the target areas, where ADHD drugs act, researchers have
concluded that it primarily targets the prefrontal cortex (PFC) region of
the brain rather than on accumbens and medial septum regions.

Researchers at the University of Wisconsin-Madison found how the drug
Ritalin used in treating the symptoms of attention deficit hyperactivity
disorder (ADHD), works in the brain.

But new work at the University of Wisconsin-Madison is now starting to clear
up some of the mystery. Writing in the journal Biological Psychiatry,
UW-Madison researchers report that ADHD drugs primarily target the
prefrontal cortex (PFC), a region of the brain that is associated with
attention, decision-making and an individual's expression of personality.

The finding could prove invaluable in the search for new ADHD treatments,
and comes amidst deep public concern over the widespread abuse of existing
ADHD medicines.

'There's been a lot of concern over giving a potentially addictive drug to a
child [with ADHD],' says lead author Craig Berridge, a UW-Madison professor
of psychology. 'But in order to come up with a better drug we must first
know what the existing drugs do.'

A behavioral disorder that afflicts both children and adults, ADHD is marked
by hyperactivity, impulsivity and an inability to concentrate. The National
Institute of Mental Health estimates that 2 million children in the U.S.
suffer from the condition, with between 30 to 70 percent of them continuing
to exhibit symptoms in their adult years

Despite public anxiety over the treatment of a behavioral condition with
pharmacological drugs, doctors have continued to prescribe meds like
Adderall, Ritalin and Dexedrine because - quite simply - they work better
than anything else.

ADHD drugs fall into a class of medications known as stimulants. ADHD
stimulants boost levels of two neurotransmitters, or chemical messengers in
the brain, known as dopamine and norepinephrine. Dopamine is thought to play
a role in memory formation and the onset of addictive behaviors, while
norepinephrine has been linked with arousal and attentiveness.

Berridge notes that scientists have learned little about how ADHD drugs work
because past studies have primarily examined the effects of the medicines at
high doses. High-dose stimulants can cause dramatic spikes in
neurotransmitter levels in the brain, which can in turn impair attention and
heighten the risk of developing addiction.

'It is surprising that no one was looking at low-dose [ADHD] drugs because
we know that the drugs are most effective only at low doses,' says Berridge.
'So we asked the natural question: what are these drugs doing at clinically
relevant doses?'

To answer that question, Berridge and his team monitored neurotransmitter
levels in three different brain regions thought to be targeted by ADHD
drugs: the PFC and two smaller brain areas known as the accumbens which has
been linked with processing 'rewards,' and the medial septum, which has been
implicated in arousal and movement.

Working with rats, the researchers conducted laboratory and behavioral tests
to ensure that animal drug doses were functionally equivalent to doses
prescribed in humans. Then, using a type of brain probe - a process known as
microdialysis - the UW-Madison team measured concentrations of dopamine and
norepinephrine in the three different brain areas, both in the presence and
absence of low-dose ADHD stimulants.

Under the influence of ADHD drugs, dopamine and norepinephrine levels
increased in the rats' PFC. Levels in the accumbens and medial septum,
however, remained much the same, the scientists found.

'Our work provides pretty important information on the importance of
targeting the PFC when treating ADHD,' says Berridge, 'In particular it
tells us that if we want to produce new ADHD drugs, we need to target
[neurotransmitter] transmission in the PFC.'

In the future, Berridge and his colleagues plan to look deeper within the
PFC to gain more detailed insights into how ADHD meds act on nerves to
enhance cognitive ability.

Other researchers who contributed to the study include UW-Madison co-authors
David Devilbiss, Matthew Andrzejewski, Ann Kelley, Brooke Schmeichel,
Christina Hamilton and Robert Spencer, and Yale Medical School researcher
Amy Arnsten.

(Source: Eurekalert)