Researchers say that a new study demonstrating differing biochemical responses to cocaine among addicted rats supports the theory that the brains of addicts become predisposed to craving, Medical News Today reported March 17.

David Self and colleagues at the University of Texas Southwestern Medical Center found that the dopamine system in the brains of rats that strongly crave cocaine reacts differently that that in rats which are less addicted to the drug.

In the study, the rats were given cocaine, then denied the drug for three weeks. Those that were more addicted were more likely to press a level that stimulated the D2 dopamine receptor, believed to increase the craving response in the brain, and appeared to be less affected by stimulation of the D1 receptor, thought to inhibit craving.

"It's as if the cocaine-addicted animal is less easily satisfied and more easily induced to seek drugs due to alterations in these receptors," said Self.

"This work shows that there are profound alterations in the brain mechanisms that regulate motivated behavior with addiction," added Self. "It really shows that the addicted person is ill-equipped to cope because the brain is now wired to make them crave drugs more and get less satisfaction out of the drug or other life events that may be rewarding, and this study found biological changes that would explain these behavioral changes."

The research appears in the March 2006 issue of the journal Neuropsychopharmacology.