NEW YORK, May 05 (Reuters Health) -- A month of daily exposure to moderate doses of cocaine and amphetamine triggers structural changes in the brain cells of rats, researchers report. They believe these changes may provide clues to the neurological processes governing addiction.
"These changes were still evident 1 month after the discontinuation of drug treatment," write study co-authors Dr. Terry E. Robinson of the University of Michigan in Ann Arbor, and Dr. Bryan Kolb of the University of Lethbridge in Alberta, Canada. Robinson described the findings to attendees at the Fifth Annual Wisconsin Symposium on Emotion in Madison, Wisconsin.
Addictive substances can trigger strong, permanent changes in behavior in humans and animals if used long-term. However, the effects of drug-taking on the structure of brain cells remain unclear.
In their study, Robinson and Kolb administered daily injections of either amphetamine, cocaine, or a 'placebo' saline to three groups of rats. A 'control' group of rats received no injections.
Treatment continued for four consecutive weeks. Following 24 to 25 days of no treatment, the researchers analyzed the animals' brain structures.
In an interview with Reuters Health, Robinson explained that "repeated exposure to cocaine or amphetamine changes the (structure) of neurons in the nucleus accumbens and the prefrontal cortex," two brain regions involved with memory, learning and 'reward' systems. Robinson believes these changes indicate that the brain is being "sensitized to the rewarding effects of drugs."
The authors' previous research has suggested that extended drug use also increases the number and density of dendrites -- the branch-like portions of nerve cells used to communicate with other neurons. Robinson speculated that this increased connectivity "leads to (the) excessive wanting" characteristic of addiction.
The findings are published in the May issue of the European Journal of Neuroscience.
SOURCE: European Journal of Neuroscience 1999;11:1598-1604.
