New animal research shows that stimulant drugs, such as amphetamine and cocaine, could inhibit the changes that take place in the brain as a result of life experiences. Various life experiences, such as learning, physically change the brain’s structure and affect behaviour. In the latest study, researchers from the U.S. and Canada set out to examine how drug use and life experiences interact to produce changes in certain brain cells.
  “The ability of experiences to alter brain structure is thought to be one of the primary mechanisms by which the past can influence behaviour and cognition,” said NIDA Director Dr. Nora D.Volkow.  “However, when these alterations in brain structure are produced by drugs of abuse, they may lead to the development of compulsive patterns of drug-seeking behaviours that are the hallmark of addiction.”

For the study, Dr. Bryan KoIb and his team of researchers at the University of Lethbridge in Canada and Dr. Terry Robinson and colleagues at the University of Michigan repeatedly administered amphetamine, cocaine, or saline for 20 days to individually housed rats. After 20 days, the rats were placed in a new environment for three months. Some were housed in standard laboratory cages, while others were placed in a complex environment with a variety of stimuli. At the end of three months, researchers analyzed the rats brains for changes in dendritic branching and spine density. These areas affect motivation and reward and sensory motor function. Their findings mimicked previous studies that found that amphetamine use increased dendritic branching and spine density in the nucleus accumbens and decreased spine density in the parietal cortex. However, the group of rats that had been given amphetamines and housed in the complex environment did not show the same environmental-induced structural changes in the nucleus accumbens and parietal cortex as did saline-treated animals in the complex environment. With the rats given cocaine, the researchers found that the drug blocked the environment-induced changes in the medium spiny neurons of the nucleus accumbens.

“The findings from this study indicate that at least some of the cognitive and behavioural advantages that accrue with experience may be diminished by prior exposure to psycho stimulant drugs,’ said KoIb. “This impairment of the ability of specific brain circuits to change in response to experiences may help explain some of the behavioural and cognitive deficits seen in people who are addicted to drugs.” KoIb added that additional research is needed to ‘determine whether certain experiences, such as exposure to complex or rewarding environments, can alter the ability of drugs to induce structural changes in the brain. If exposure to psycho stimulant drugs can alter the effects of subsequent experience, experience may be able to influence the later effects of drugs. It may even be possible for certain experiences to counteract the effects of psycho stimulant drugs.’
The study’s findings are published in the Aug. 25 online edition of the Proceedings of the National Academy of Sciences.