The study, published online today in the journal Science, shows that a naturally occurring protein called brain-derived neurotrophic factor, or BDNF, acts on a part of the brain called the ventral tegmental area and switches the cells in this area from a dopamine-independent system to a dopamine-dependent system, thus causing addiction.
Researchers have known that drug addiction is a disease that disrupts the brain's dopamine response, which is involved in feelings of pleasure and reward. Chronic exposure to drugs increases levels of BDNF in the ventral tegmental area, which is where dopamine circuitry is located. The researchers gave rats who were not dependent on drugs a single injection of BDNF into the ventral tegmental area of the brain. The injection made the rats behave as if they were dependent, causing them to prefer certain smells, lighting and textures and to seek this stimulation for a "fix." The BDNF injection caused specific chemicals that normally inhibit neurons in this part of the brain to instead excite them.
"When someone chronically uses drugs, this system changes. This is the mechanism that makes you feel like you need that drug," said the lead author of the study, Hector Vargas-Perez, of the University of Toronto.
"If we can understand how the brain's circuitry changes in association with drug abuse, it could potentially suggest ways to medically counteract the effects of dependency," Scott Steffensen, a Brigham Young University neuroscientist and co-author of the study, said in a news release.
— Shari Roan
Photo: Courtesy of Advanced Cell Technology Inc.