Environmental Cues Associated with Heroin Use
May Decrease Immune Function

Scientists have long known that some drugs, such as heroin and morphine, can cause changes in the immune systems of drug abusers that make them more susceptible to infection. However, Dr. Donald Lysle and Stephanie Ijames from the University of North Carolina at Chapel Hill have now found that in rats, the environmental cues associated with drug use also may induce alterations in immunity. Their study is the first to demonstrate that cues associated with heroin use cause a reduction in the enzyme, inducible nitric oxide synthase (iNOS), which affects nitric oxide production by cells of the immune system. Nitric oxide plays a key role in the ability of immune cells to fight and kill microorganisms and tumor cells.

The researchers conditioned male rats to associate heroin administration with placement in a new environment by administering the drug to the rats as soon as they were placed in that environment. On the test day, the rats were re-exposed to the environment in the absence of heroin and then given an injection of lipopolysaccharide (LPS), which induces iNOS production by immune cells. Six hours later, the rats' spleens, lungs, and livers were analyzed for the expression of iNOS messenger ribonucleic acid (mRNA) and iNOS protein. Control groups were used to determine if any step in the conditioning process, such as the injection procedure, reexposure to the conditioning environment, or a combination of injection of heroin and exposure to the environment, contributed to alterations in iNOS production. The researchers also used an unmanipulated control group to provide a general comparison for all the control groups, as well as the experimental group.

The researchers found that exposure to the environmental cues associated with heroin administration resulted in a dramatic reduction in the expression of iNOS mRNA and iNOS protein in the conditioned rats' spleen, lung, and liver tissues.

What it means: These findings suggest that environmental cues associated with drug use may contribute to alterations in susceptibility to infection. This study, funded by the National Institute on Drug Abuse, was published in the December 2002 issue of Psychopharmacology.

NIDA NewsScan, April 9, 2003