Predicting drug addiction
19 February 2008
A long-running debate has focused on the possible predisposition of people to drug addiction. Genetic studies are not clear-cut, and although particular types of behaviour and brain activity are seen in addiction, these could be a consequence rather than a cause of drug taking. A neat experiment in rats, however, provides strong evidence that susceptibility to addiction has a biological component.
The dopamine or 'reward' brain system is well known to be involved in addiction. It is also implicated in certain behaviours, including impulsivity - the tendency to respond prematurely without adequate reflection. Potentially, then, individual variations affecting the dopamine system could predispose to addiction through their effects on behaviour.
To test this idea, a group including Professor Trevor Robbins, Dr Jeffrey Dalley and Professor Barry Everitt in Cambridge monitored drug consumption in rats provided with access to the addictive drug cocaine. Before exposure, they measured the animals' tendency to impulsive behaviour and used brain-imaging techniques to quantify levels of particular dopamine receptors. They then looked to see which factors were associated with high drug consumption.
Since the rats had not previously been exposed to the drug, any associations would be a potential cause rather than consequence of drug taking.
The studies revealed that addiction correlated with both impulsive behaviour and low availability of dopamine receptors in key areas of the brain. A defect in dopamine receptor activity in the brain could therefore be a risk factor for drug consumption - in humans as well as rats.
Further reading
- Dalley JW et al. Nucleus accumbens D2/3 receptors predict trait impulsivity and cocaine reinforcement. Science. 2007;315(5816):1267-70.