Study shows effects stayed with rats for at least 24 hours, could explain addiction Bloomberg News, May 6, 2007 PROVIDENCE, Rhode Island - The pleasure centers of a rat's brain feel the aftereffects of morphine as much as a day later, scientists say. Morphine, an addictive painkiller made from the seed pod of Asian poppies, prevents the brain from strengthening certain signals thought to be the cellular basis for memory. In the experiment, the authors found that the signals were blocked even after the drug left the animals' systems. The affected area of the brain was the ventral tegmental area, a section of the midbrain's reward system. In addition to reinforcing rewarding behaviors such as eating and having sex, this area of the brain plays a role in addiction, the researchers wrote. A single dose of morphine was enough to affect the rats for more than 24 hours. The paper, co-written by Freseshteh Nugent, Esther Penick and Kauer, was published in Nature. "This work is quite novel and contains really good ideas about how the brain helps a person get addicted to a drug," said Jose Moron-Concepcion, an assistant professor at the University of Texas Medical Branch's Pharmacology and Toxicology department in Galveston, Texas.