Individual drug abuse can be affected by social stress as well as simple environmental enrichment, a new study in monkeys has revealed.
In previous studies, researchers have 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.
And once they are exposed to cocaine and taught to self-administer the drug, researchers found that the more subordinate animals are far more inclined to engage in the human equivalent of serious drug abuse than are the dominant animals.
Previous studies have 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.
However, the new study conducted by at researchers at Wake Forest University School of Medicine have found that environmental enrichment or increased stress also have an effect on cocaine self-administration.
Wake Forest researcher Michael A. Nader, Ph.D and colleagues worked with a group of 24 cynomolgus macaques that were already categorized socially.
For environmental enrichment, the monkeys were placed in larger-than-normal cages for three days and for increased stress, they were placed next to another social group for 15 minutes, acting as an intruder to that group.
Researchers then gave the monkeys their usual choice of an intravenous cocaine mixture or food pellets.
They found that environmental enrichment reduced the drug response of all the animals.
However, the negative 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. 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," said Nader, professor of physiology and pharmacology and of radiology.
"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," he added.
The findings were presented at a conference on Experimental Biology in San Diego.