Simple environmental enrichment and increased social stress can both affect the level of individual drug use, according to new monkey research at Wake Forest University School of Medicine.
Previous research has shown that social rank -- whether animals are dominant or subordinate within their social groups -- can affect the amount of cocaine that monkeys will self-administer. Housed in groups of four, male cynomolgus monkeys will invariably stratify by social rank from the most dominant to the most subordinate.
Once exposed to cocaine and taught to self-administer the drug, the more subordinate animals are far more inclined to engage in the human equivalent of serious drug abuse than are the dominant animals. Research has shown differences in certain neurochemicals in the brains of the animals, both as predictors and results of the social ranking, and therefore as predictors of drug abuse.
But would additional environmental enrichment or increased stress have an effect on cocaine self-administration?
The answer is yes, according to a report April 6 by Wake Forest researcher Michael A. Nader, Ph.D., at Experimental Biology 2008 in San Diego.*
Nader and colleagues worked with a group of 24 cynomolgus macaques who were already categorized socially. For additional enrichment, the monkeys were placed in larger-than-normal cages for three days. For increased stress, they were placed next to another social group for 15 minutes, acting as an intruder to that group.
The monkeys were then given their usual choice of an intravenous cocaine mixture or food pellets.
The enrichment reduced the drug response of all the animals; however, the detrimental affect of the stress -- more drug intake, less food -- was more prominent in the subordinate monkeys.
"This is very significant for at least two reasons," said Nader, professor of physiology and pharmacology and of radiology. "First, it is a result that could be directly applied to the human situation. It suggests that a better environment could alleviate at least some of the risk that individuals will turn to drugs.
"Secondly, we are talking about very rudimentary enrichment here -- just a slightly improved living condition. Imagine what the effect could be with higher quality but easily achievable enrichment, such as interesting activities."
*The presentation was part of the scientific program of the American Society for Pharmacology and Experimental Therapeutics (ASPET). Nader's co-researchers were Paul W. Czoty, Ph.D., Nicholas R. Garrett, B.S., Michelle Icenhower, B.S., Jennifer E. Campbell, B.S., and Robert Gould, B.S., all of the Wake Forest Department of Physiology and Pharmacology.
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