Animal studies suggest that the use of opiate drugs, which include morphine and heroin, can leave users more vulnerable to stress, creating a vicious cycle of use and abuse.
Not only does stress trigger the drug use, but in return the drug leaves animals more vulerable to that stress, researchers at the University of New South Wales report in the current issue of Behavioral Neuroscience.
In the study, scientists injected rats with either morphine or a saline solution for 10 days. They then performed a stress test on them by gently restraining each rat for 30 minutes.
In the absence of stress, opiate-treated rats behaved the same as the other rats. But when subjected to stress, they appeared to suffer twice as much as non-drugged rodents, reports Forbes.
According to News-Medical.net, the authors say this is the first important evidence that opiate use increases subsequent vulnerability to stress - a tough knot to untie given that stress leads to drug use. The results also were first to show that the vulnerability could last at least a week, evidence that the altered response was independent of any recent effect of the opiate or of opiate withdrawal.
Co-author Gavan McNally, PhD, says, 'It appears the development of opiate dependence is the critical variable, and there are marked individual differences in humans in the development of dependence. A few days of codeine to relieve post-operative pain are unlikely to lead to the development of dependence.'
Because rodent nervous systems are so like ours, animal models allow neuroscientists to study the behavioral and brain mechanisms for drug addiction. McNally says, 'Our goal is the translation of these findings in the clinical domain.
Our data suggest that implementing treatments that are designed to reduce vulnerability to stress - such as cognitive-behavioral therapy, pharmacological approaches, or both - in opiate addicts may be therapeutically useful.'