Understanding addiction: Using Animal Models to Answer the “Why, How, and Who”
Over the past decade, use of certain illicit drugs, including crack cocaine and methamphetamine, has shown sharp declines in the United States based on data from the Substance Abuse and Mental Health Services Administration (SAMHSA). But these encouraging data contradict other disturbing facts. Compared to 2002, use of marijuana and prescription pain relievers has jumped by approximately 20 percent and heroin use has shown an alarming 44 percent increase.
“Drug addiction persists as a major problem in the United States,” said Patricia Sue Grigson, Ph.D., professor, Department of Neural and Behavioral Sciences. “Drug use data does not reflect the devastating, long-term impact that drug addiction has on individuals and their families. This is why it is so important to continue to search for answers about why some people become addicted and others do not. Understanding and identifying risk factors for the development of addiction will lead to more effective prevention and treatment plans.”
Grigson uses an animal model to study the environmental, behavioral, and neurological underpinnings of addiction. “Humans and the rats in our studies have more in common than not,” she said. “For instance, about 17 percent of humans who try cocaine eventually become addicted; studies have shown the same percentage of rats that try cocaine also show addiction-like behavior.”
Among the numerous ongoing projects in Grigson’s laboratory are studies that examine the link between binge eating and addiction-like behaviors. “Like drug abuse, excessive food intake as occurs with binge eating has become problematic,” said Grigson. “Indeed, eating disorders and drug abuse often are seen together clinically.”
A study conducted in collaboration with the laboratory of Rebecca Corwin, Ph.D., Department of Nutritional Sciences and recently described in Behavioral Neuroscience (Puhl et al. 2011), indicates that a history of binge eating—eating large amounts of food in a short period of time—may make a person more likely to show other addiction-like behaviors, including substance abuse. In the short term, this finding may shed light on factors that promote substance abuse, addiction, and relapse—and in the long term, may help clinicians treat individuals more effectively. “If we can better understand how and why addiction develops, we stand a much better chance of predicting who will become addicted and of preventing it.”
For Grigson’s study, the researchers used rats to test whether a history of binge eating on fat would increase addiction-like behavior toward cocaine. Four groups of rats were given four different diets: normal rat chow alone; rat chow plus continuous access to an optional source of dietary fat; rat chow and one hour of access to optional dietary fat daily; and rat chow plus one hour of access to dietary fat on Mondays, Wednesdays, and Fridays. The researchers then assessed how much fat each group ate, fat-binge behaviors, and cocaine-seeking and -taking behaviors.
“Fat bingeing behaviors developed in the rats with access to fat on Mondays, Wednesdays, and Fridays—the group with the most restricted access to the optional fat,” Grigson said. “Fat bingeing was different from normal eating behavior. These rats ate a large amount of fat more rapidly than the other groups.” This phase of the study continued for six weeks and these data replicated those described in Corwin’s earlier reports.
Grigson’s research on addiction is funded by the National Institute on Drug Abuse. Other researchers with whom she collaborated on this project are Matthew D. Puhl, M.D., ’10, lead author, and now a postdoctoral fellow at McClean Hospital, Harvard University, Angie M. Cason, Ph.D., currently a postdoctoral fellow at the University Medical School of South Carolina, Francis H.E. Wojnicki, Ph.D., and Corwin, co-senior author.
– By Karen Dougherty