Brain cells may be damaged for ever by cocaine abuse

Cocaine may damage the very parts of the brain that produce the high that make it pleasurable to take, researchers report today.

American scientists have found the first direct evidence that cocaine damages key cells in the brain's dopamine "pleasure centre". The finding may help explain aspects of cocaine addiction and aid the development of anti-addiction drugs.

Dopamine is a brain chemical essential for transmitting signals between brain cells, and is involved in helping us eat, feel emotions and reproduce. Low levels are associated with movement disorders such as Parkinson's disease.

Researchers from the University of Michigan and the VA Ann Arbor Healthcare System studied samples of tissue taken after death from the brains of 35 cocaine abusers and 35 non-drug abusers.

They compared the levels of dopamine andVMAT2, a protein which interacts with dopamine, and found both were significantly lower in cocaine abusers. The results are published in the American Journal of Psychiatry.

Karley Little, associate professor of psychiatry at the University of Michigan medical school, who led the study, said: "This is the clearest evidence to date that the specific neurons cocaine interacts with don't like it and are disturbed by the drug's effects.

"The questions we now face are: are the cells dormant or damaged, is the effect reversible or permanent, and is it preventable?"

The scientists said cocaine had a disruptive effect on the brain's dopamine system when it was first taken, causing it to build up in the synapses, or gaps, between the cells sending pleasure signals, which deliver the drug-induced high.

The findings confirm other research which shows that with chronic use, the brain's response to cocaine is "reset", and drug-taking for pleasure becomes drug-taking to avoid the negative feelings associated with the absence of cocaine.

The efforts of the brain to adapt to a cocaine drenched environment appear to contribute to cocaine-induced depression and other depressive disorders. Researchers have found that depressed cocaine users have more severe addiction and mental health problems than non-depressed users.

Professor Little said: "We could be seeing the result of the brain's attempt to regulate the dopamine system in response to cocaine use. But we could also be seeing real damage or death to dopamine neurons. Either way this highlights the fragility of these neurons and shows the vicious cycle that cocaine use can create."

New treatments would have to break that cycle, he said.

Dopamine neurons in the brain's pleasure centre die at a steady rate over a person's life. Severe damage is a hallmark of Parkinson's disease, causing the loss of control of movement.

Professor Little said: "As the words themselves suggest there is an intimate connection between motion and emotion. Emotion puts you in motion – they are pre-activity emotions. It is not surprising that the basal ganglia, where dopamine neurons are located, is very active in emotional states."

The vulnerable nature of dopamine neurons is important in understanding the moods and actions of normal adults as they age and lose dopamine neurons naturally, he said.