Pubdate: Wed, 09 Apr 2003
Source: New Scientist (UK)
Copyright: New Scientist, RBI Limited 2003
Contact:  http://www.newscientist.com/
Details: http://www.mapinc.org/media/294
Author: Shaoni Bhattacharya
Bookmark: http://www.mapinc.org/coke.htm (Cocaine)

COCAINE ADDICTS GET A HIGH BEFORE THE HIT

Cocaine addicts may get spikes in a brain chemical associated with a high 
at the mere anticipation of a "hit", suggests a new study in rats.

US researchers found that dopamine, a neurotransmitter associated with 
pleasure, surged before rats pressed a lever to release a dose of cocaine 
and even while they were waiting for the hard drug to be delivered.

Dopamine is known to peak during addictive behaviours like drug taking, 
eating and sex, but this is the first study to demonstrate an increase 
before the actual event. The finding could help understand why recovering 
drug addicts relapse, say the researchers.

"It may be relevant with respect to human addiction because drug related 
cues and paraphernalia often result in intense carvings," says Regina 
Carelli, a psychologist at the University of North Carolina in Chapel Hill, 
and one of the team. "This craving is one of the leading causes of relapse 
and it is very important we understand the biology of this."

Dopamine might represent "both the chicken and the egg" in the events 
underlying the behaviour of addicts, says David Self, at the University of 
Texas in Dallas.

"As a rat chases its tail, drug addicts may suffer a similar vicious circle 
of priming and reward controlled by these dopamine signals," he writes in 
an commentary accompanying the Nature paper. "Therapies aimed at preventing 
one or both of these dopamine signals could be effective treatments for 
addiction."

Sub-second timescale

Scientists have suspected dopamine plays a role in drug-seeking behaviour. 
But this had not been demonstrated because until now scientists could only 
measure changes in dopamine over minutes.

"What makes our study unique is that we were actually able to measure 
dopamine on a sub-second timescale - in real time," Carelli told New Scientist.

This was possible thanks to a carbon electrode system, developed by 
Carelli's colleague Mark Wightman, that measures dopamine levels in the 
brain of the rats 10 times a second.

A strong dopamine surge was seen when the addicted rats approached a lever 
they knew would deliver a shot of cocaine. A second surge occurred when the 
rat pressed the lever prompting several audiovisual cues while it waited 
for the injection.

Carelli said the rats trained to receive cocaine in this way showed this 
increase in dopamine when exposed to the audiovisual cues alone, unlike 
rats unfamiliar with this association.

"Ideally, one approach to treating cocaine addiction in humans would be a 
drug targeted at reducing 'cue-evoked craving' for the drug," said Carelli. 
This could be used together with counseling.

Journal reference Nature (vol 422, p 615)
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