Chronic cocaine use damages neural circuits in the brain that help create the sensation of pleasure, claims a new study. This finding may explain why the rate of depression among cocaine addicts is higher than their rate in the rest of the population.
According to the author of the study, Dr. Carly Little from the University of Michigan, it is not clear whether the cocaine causes the death of the brain cells or only damages them, nor whether the effect is reversible; In any case, he says, this is bad news for cocaine addicts: "I wouldn't want to lose 10% or 20% of the nerve cells in the pleasure reward center, nor would these cells be damaged."
Little and his colleagues studied brain samples taken from postmortems of people who used large amounts of cocaine over time. The results were published in the January issue of the American Journal of Psychiatry
Steven Kish, head of the Human Brain Laboratory at the Center for Addiction and Mental Health in Toronto, said that researchers have "always considered cocaine a dangerous drug," because of its potential as an addictive and heart-damaging drug. "We have now added to the list of risks a harmful effect of cocaine on the brain, something we never expected." According to Dr. Deborah Mash, a neuroscientist at the University of Miami School of Medicine, the study reveals a "piece of the puzzle" that may explain why cocaine users are at higher risk of depression.
It is still unclear whether cocaine causes depression or whether people start using the drug because they suffer from depression. In any case, said Dr. Mash, the study raises the possibility that changes in the brain "light the fuse of depression" among cocaine users who have a tendency to suffer from it in the first place. According to her, the study also raises the possibility that the changes in the brain may cause the depression commonly observed when stopping cocaine use.
Little and his colleagues studied brain samples taken from the striatum region of the brains of 35 cocaine users and 35 non-users of similar sex and age. They measured levels of the protein VMAT2, which is found in brain cells that transmit signals between them using the neurotransmitter dopamine. Nerve cells that communicate through dopamine create neural circuits in the brain that are essential for the feeling of pleasure.
In the study it was found that the VMAT2 levels of the cocaine users were on average lower than the non-users. According to Little, this may mean that "dopamine neurons" were damaged or destroyed - a result not found in animal studies - or that they produced less VMAT2 and hence produced less dopamine.
A person whose "dopamine neurons" are damaged, or some of them have died, may find it difficult to feel pleasure and sink into depression, Little said. According to him, the next step in the research will be a comparison between the number of "dopamine neurons" in the brain samples.
The study found hints that among cocaine users suffering from severe depression, VMAT2 levels were lower compared to other users. But a statistical analysis raised the possibility that it was a coincidence.
