For several years he has been seeking to understand the genetics of behavioral responses to cocaine. Hirsh and his team, which includes doctoral student Rozi Andretic and technician Sarah Chaney, use fruit flies as their genetic models for humans. Genetics researchers have long been able to manipulate genes in fruit flies for investigations of nervous system pathways. The flies used by Hirsh's team were mutated to lack certain circadian genes. These insects did not become sensitized to cocaine, a process in which repeated doses of the drug produce increasingly severe responses.
Flies containing functional circadian genes did become sensitized to cocaine.
This indicates that certain circadian genes not only play a critical role in regulating the biological clock, but they may also function in ways that allow susceptibility to drug addiction. For this study, cocaine was administered as an aerosol, and the insects'responses were closely monitored and videotaped for comparison. We may come to see drug addicts more in terms of their genes than as people who are not in control of their behavior. He published related findings in the current online issue of Current Biology , that implicate tyramine, one of the body's naturally occurring molecules, as the likely perpetrator of cocaine sensitization in fruit flies.