Cocaine: Perceived as a reward by the brain?
Researchers at the MNI and the MUHC open up a new path for cocaine addiction research
Cocaine is one of the oldest drugs known to humans, and its abuse has become widespread since the end of the 19th century. At the same time, we know rather little about its effects on the human brain or the mechanisms that lead to cocaine addiction. The latest article by Dr. Marco Leyton, of the Montreal Neurological Institute (MNI), McGill University and the McGill University Health Centre, which was published in the journal Biological Psychiatry on May 15, 2009, not only demonstrates a link between cocaine and the reward circuits in the brain but also associates the susceptibility to addiction with these mechanisms.
The results of this study show that sniffing cocaine triggers high levels of dopamine secretion in a central region of the brain called the striatum. Dopamine is known to play a critical role in the brain’s response to reward as well as in its response to addictive drugs.
This study was carried out in ten non-addicted users of cocaine, all of whom sniffed cocaine on one test day and placebo powder on another. Participants underwent blood tests before and after taking the drug, and dopamine release in the brain was measured using PET scans.
“The ability of cocaine to activate dopamine release varies markedly from person to person. Our study suggests that this is related to how much of the drug the person consumed in the past,” explained Dr. Leyton. The more cocaine someone has used in his or her lifetime, the more the brain will secrete dopamine during subsequent cocaine use. “It’s possible therefore that the intensity of the reward-circuit response is related to increased susceptibility to addiction,” stated Dr. Leyton.
Although the relationship between the intensity of dopamine secretion and the frequency of drug use has been demonstrated, researchers still do not fully understand its mechanism of action. Is it the repeated stimulation of the reward circuit that leads to addiction, or is it an inherent sensitivity to addiction that leads to the increased secretion of dopamine? This question is not easy to answer, especially since other factors come into play, such as other aspects of the subject’s personal history.
Whatever the answer, the relationship between dopamine and cocaine means that this hormone could be a potential target for treatment against addiction. More research is required before treatments are available, but this study opens a new door in this direction.
This study was funded with a grant from the Canadian Institutes for Health Research. Salary support was given by the Fond de recherche en santé du Québec
Dr Marco Leyton
Dr. Marco Leyton is a researcher on mental illnesses and addiction at the Research Institute of the MUHC andthe Montreal Neurological Institute. He is also an associate professor in the Department of Psychiatry at McGill University and the recipient of a William Dawson research chair.
This study is a collaboration between several laboratories of the McGill University Health Centre and McGill University, involving : Dr Sylvia M.L. Cox, Dr Chawki Benkelfat, Dr Alain Dagher, Dr J. Scott Delaney, France Durand, Samuel A. McKenzie, Dr Theodore Kolivakis, Kevin F. Casey, Dr Marco Leyton.
The Montreal Neurological Institute (MNI) is a McGill University research and teaching institute, dedicated to the study of the nervous system and neurological diseases. Founded in 1934 by the renowned Dr. Wilder Penfield, the MNI is one of the world's largest institutes of its kind. MNI researchers are world leaders in cellular and molecular neuroscience, brain imaging, cognitive neuroscience and the study and treatment of epilepsy, multiple sclerosis and neuromuscular disorders. The MNI, with its clinical partner, the Montreal Neurological Hospital (MNH), part of the McGill University Health Centre, continues to integrate research, patient care and training, and is recognized as one of the premier neuroscience centres in the world. At the MNI, we believe in investing in the faculty, staff and students who conduct outstanding research, provide advanced, compassionate care of patients and who pave the way for the next generation of medical advances. Highly talented, motivated people are the engine that drives research - the key to progress in medical care. A new building, the North Wing Expansion, is currently under construction and will house state-of-the-art brain imaging facilities. Once the construction is completed and the new building is fully equipped, the scientific community focused on brain imaging research at the MNI will be without equivalent anywhere in the world.
The Research Institute of the McGill University Health Centre (RI MUHC) is a world-renowned biomedical and health-care hospital research centre. Located in Montreal, Quebec, the institute is the research arm of the MUHC, the university health center affiliated with the Faculty of Medicine at McGill University. The institute supports over 600 researchers, nearly 1200 graduate and post-doctoral students and operates more than 300 laboratories devoted to a broad spectrum of fundamental and clinical research. The Research Institute operates at the forefront of knowledge, innovation and technology and is inextricably linked to the clinical programs of the MUHC, ensuring that patients benefit directly from the latest research-based knowledge. The Research Institute of the MUHC is supported in part by the Fonds de la recherche en santé du Québec.For further details visit: www.muhc.ca/research.