Dr. Karley Little, lead investigator, and colleagues studied samples of brain tissue obtained during autopsies of 35 long-term cocaine users and 35 non-users. They analyzed the tissue for dopamine and the protein VMAT2, which is found in dopamine transporters. Urine or serum samples were also analyzed for the presence of cocaine, opioids, antidepressants, and antipsychotic medications. A person close to each individual was interviewed about the individual's substance abuse, alcoholism, and symptoms of personality and mood disorders.
Researchers found that cocaine users had lower concentrations of dopamine and VMAT2 in their brains than did non-users. Additionally, cocaine users suffering from depression had lower levels of VMAT2 than those who were not depressed. Dr. Little and colleagues were uncertain whether dopamine cells had been destroyed or just dysregulated by cocaine use, and if such changes could be reversed.
This study, funded in part by the National Institute on Drug Abuse, was published in the January 2003 issue of the American Journal of Psychiatry.