New research in monkeys suggests that, although living in an "enriched" environment can make someone less vulnerable to abusing cocaine, once started, extended drug abuse can eliminate the social advantage the abuser originally had.
However, the research also shows that prolonged abstinence from drug use can give the recovering addict another chance, and that environment again becomes a major factor influencing the success of the recovery.
Michael A. Nader, Ph.D., professor of physiology/pharmacology and of radiology at Wake Forest University Baptist Medical Center, delivered those findings today in a course for medical professionals presented by the American Society of Addiction Medicine (ASAM).
Nader said the animal research has important implications for physicians and other practitioners working with human addicts. "The most important thing that we have shown is that environmental enrichment can protect the individual from the likelihood that they'll abuse cocaine.
"There have been many studies that show that stress - the other end of that continuum - can increase the likelihood that an individual will abuse drugs. We've gone to the other side of that and shown that enrichment can actually protect the individual from drug abuse."
The ASAM course, "Addiction Across the Lifespan," was scheduled to include presentations by Paul Greengard, Ph.D., a Nobel laureate, and Nora Volkow, M.D., director of the National Institute on Drug Abuse.
Nader, one of only three animal researchers included on the program, told the group that research has focused both on behavioral patterns and on actual physiological changes in brain chemistry in animal models. He said that the animal research can verify hypotheses that can't be tested in human subjects, due to ethical considerations.
The physiological aspects have dealt with the chemistry of dopamine, a major neurotransmitter in the brain. Cocaine increases levels of dopamine, which is apparently the cause of the intense but fleeting euphoria experienced by cocaine users. Increased levels of dopamine over long-term cocaine use causes the brain to adjust by reducing the number of dopamine (D2) "receptors."
Nader said that research has shown that social "rank" in animal populations has a significant effect on whether a monkey will take cocaine. That effect has a direct correlation with the level of D2 receptors a monkey has, as measured by noninvasive brain imaging: Dominant monkeys have more D2 receptors and are less likely to abuse cocaine than the subordinate monkeys.
But, he said, the monkeys don't start out that way. It is the social environment itself that creates the difference in brain chemistry over time. Monkeys that become dominant have an enriched environment - more freedom, less fear, more grooming by other monkeys - while the subordinates live with more stress.