Results from two recent studies may offer the promise of new approaches in fighting cocaine addiction. Blocking MCH in brain cells limits cocaine cravings In the first study, which was supported by grants from the National Institutes of Health, pharmacological researchers at the University of California-Irvine discovered a blocking hormone related to hunger that may be able to limit cravings for cocaine. Shinjae Chung and Olivier Civelli, the two UC-Irvine researchers, identified how the melanin-concentrating hormone (MCH) works along with dopamine in the brain’s pleasure center and results in the body’s addictive response to using cocaine. Dopamine, a neurotransmitter, is essential to the normal functioning of the central nervous system. In addition, Chung and Civelli found that craving for cocaine was limited by blocking MCH in those brain cells. While there is much research going on in a search for effective treatment for addiction, this study is the first that details the interaction of MCH and dopamine in cocaine addiction – and to show that occurs in the nucleus accumbens. This portion of the forebrain is believed to play a key role in feelings of pleasure and fear, and in addiction. Heightened neurotransmitter levels have been detected in the nucleus accumbens of drug addicts. The researchers, working with test mice conditioned to develop cocaine cravings, found increased amounts of MCH and dopamine in their nucleus accumbens. Subsequent to administration of compounds that block MCH proteins, the cravings for cocaine were gone. They also found that mice lacking key receptors for MCH displayed significantly fewer cravings for the drug. While further testing needs to be done, the researchers believe that efforts to target MCH could lead to new treatments to break cocaine addiction as well as addiction to other drugs such as nicotine and amphetamines. Link between intensity of dopamine secretion and drug use frequency In an article published in the May 15, 2009 issue of Biological Psychiatry, Dr. Marco Leyton, of the Montreal Neurological Institute, McGill University and the McGill University Health Center, reports on study results that link cocaine and the brain’s reward circuits as well as associate susceptibility to addiction. Cocaine triggers high levels of dopamine in the brain. Dopamine is known to play a critical role in how the brain responds to addicting drugs and to reward. The study utilized 10 non-addicted cocaine users who sniffed the drug on test day 1 and a placebo on test day 2. Blood tests were administered before and after and dopamine release in the brain was measured using PET scans. In the article, Dr. Leyton explains that the ability of cocaine to activate dopamine release varies from person to person. The results of the study, according to Dr. Leyton, seem to show that this is related to how much cocaine the individual has used in the past. The more of the drug the person has used in his or her lifetime, the more dopamine the brain will secrete during subsequent use. Results of the study point to the possibility that the intensity of the reward-circuit response is related to increased susceptibility to addiction. The relationship between dopamine and cocaine means that, in the search for treatment for cocaine addiction, target drugs using the hormone may prove fruitful. Further testing needs to be done before any such treatment will be available.
