Cocaine addicts may get spikes in a brain chemical associated with a high at the mere anticipation of a 鈥渉it鈥�, 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.
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鈥淚t may be relevant with respect to human addiction because drug related cues and paraphernalia often result in intense carvings,鈥� says Regina Carelli, a psychologist at the University of North Carolina in Chapel Hill, and one of the team. 鈥淭his craving is one of the leading causes of relapse and it is very important we understand the biology of this.鈥�
Dopamine might represent 鈥渂oth the chicken and the egg鈥� in the events underlying the behaviour of addicts, says David Self, at the University of Texas in Dallas.
鈥淎s a rat chases its tail, drug addicts may suffer a similar vicious circle of priming and reward controlled by these dopamine signals,鈥� he writes in an commentary accompanying the Nature paper. 鈥淭herapies aimed at preventing one or both of these dopamine signals could be effective treatments for addiction.鈥�
Sub-second timescale
快猫短视频s 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.
鈥淲hat makes our study unique is that we were actually able to measure dopamine on a sub-second timescale 鈥� in real time,鈥� Carelli told 快猫短视频.
This was possible thanks to a carbon electrode system, developed by Carelli鈥檚 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.
鈥淚deally, one approach to treating cocaine addiction in humans would be a drug targeted at reducing 鈥榗ue-evoked craving鈥� for the drug,鈥� said Carelli. This could be used together with counseling.
Journal reference Nature (vol 422, p 615)