Endorphin system may hold the key to understanding and treating bulimia nervosa

The role of the brain's opioid receptor system - or endorphin system - may hold the key to understanding and treating bulimia nervosa, according to research reported in the Society of Nuclear Medicine's August issue of the Journal of Nuclear Medicine.

"Involvement of the opioid system may explain the addictive quality of this behavioral disorder," said Angela Guarda, M.D., assistant professor of psychiatry at Johns Hopkins School of Medicine in Baltimore, Md. The first imaging study to implicate the opioid system in bulimia nervosa shows differences in women with bulimia compared to healthy women, added J. James Frost, M.D., Ph.D., professor of radiology and neuroscience at Johns Hopkins and co-author of "Regional µ-Opioid Receptor Binding in Insular Cortex Is Decreased in Bulimia Nervosa and Correlates Inversely With Fasting Behavior." In the study, eight women with bulimia were compared to healthy women of the same age and weight. Their brains were scanned using positron emission tomography (PET) after injection with the short-acting radioactive compound carfentanil, which binds to mu-opioid receptors in the brain, explained Frost. PET is a powerful medical imaging procedure that noninvasively uses special imaging systems and radioactive tracers to produce pictures of the function and metabolism of the cells in the body. He noted, "We found that mu-opioid receptor binding in bulimic women was lower than in healthy women in the left insular cortex. The insula is involved in processing taste, as well as the anticipation and reward of eating, and has been implicated in studies of other driven behavioral disorders, including drug addiction and gambling."

Bulimia nervosa is a serious eating disorder marked by a destructive pattern of recurrent dieting, binging and vomiting to control one's weight. "Patients feel trapped by this behavioral cycle suggesting something about it is rewarding," said Guarda, "and, as with substance abuse, the course of bulimia is frequently chronic and relapsing."

Bulimia nervosa, which is 10 times more common in females than in males, affects 1–2 percent of adolescent girls and young women in the United States. Bulimia may become chronic and lead to serious health problems, including seizures, irregular heartbeat, dental erosion, swollen salivary glands, gastrointestinal irritation and electrolyte imbalances. In rare cases, it may be fatal. While the cause of bulimia nervosa is still unknown, research shows that certain brain chemicals may function abnormally in bulimia patients. This research may point to a molecular target for development of more effective treatments than those currently available. Frost indicated that medications that affect the brain's opioid receptor system and approaches to treatment for substance abuse disorders may be helpful in treating bulimia.

Frost and Guarda co-authored "Regional µ-Opioid Receptor Binding in Insular Cortex Is Decreased in Bulimia Nervosa and Correlates Inversely With Fasting Behavior" with Badreddine Bencherif, M.D., Hayden T. Ravert, Ph.D., and Robert F. Dannals, Ph.D., department of radiology, and Carlo Colantuoni, Ph.D., department of neuroscience, all at Johns Hopkins University School of Medicine, Baltimore, Md.