Repeated cocaine use damages, or even kills, the very brain cells that trigger the "high" users experience, scientists have found.The drug damages key cells in the brain's pleasure centre.The researchers say their findings could help explain the process of addiction and could even lead to the development of anti-addiction drugs.It could also improve understanding of other disorders which involve the same brain cells, such as depression.

Pleasure

Researchers from the University of Michigan Health System and the VA Ann Arbor Healthcare System looked at post-mortem brain samples from 35 cocaine users and 35 non-drug users. They examined the health of neurons, or nerve cells, which release a pleasure-signalling chemical called dopamine which interacts with cocaine. The researchers looked at dopamine levels and the amount of a protein called VMAT2 present. Levels of both were lower in cocaine users, and especially so in those who had been depressed.

Craving

Karley Little, who led the research, 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." Pleasurable feelings or sensations are triggered by the release of dopamine in the brain, helping drive people to eat, feel emotions and reproduce, as well as in drug highs. The dopamine system is involved in the urge to repeat pleasurable experiences, which scientists say could help explain addicts' cravings. The first time someone takes cocaine, it blocks the process which sends dopamine back to its home cells after it has triggered the pleasurable sensation. The chemical then builds up in the junction between the cells, sending the pleasure signals over and over again, creating the "high" cocaine users feel. The long-term effects of cocaine use could also explain users' decreased motivation, stunted emotions and difficulty weaning themselves off the drug, they said. Dopamine cells die off over a person's lifetime, and severe damage is a hallmark of Parkinson's disease causing a loss of control over movement.

The research is published in the American Journal of Psychiatry.