Dr. Lennart Mucke and colleagues at the Gladstone Institute of Neurological Disease, using a mouse model, made the discovery.

Enkephalins are part of the endogenous opioid system, which modulates learning and memory and other brain functions.

"The enkephalin pathway is an intriguing candidate for us because it is involved in many functions that are affected by Alzheimer's and other neurodegenerative diseases," said Mucke, the institute's director. "We were not sure, though, whether it contributed causally to the disease or acts as a compensatory mechanism.

"Our results indicate that the high levels of enkephalins may contribute to cognitive impairments … in AD patients," said Mucke. "Although these are early results, they are encouraging and may lead the way to a new AD therapy based on limiting enkephalin production or signaling."

The study that included William Meilandt, Gui-Qiu Yy, Jeannie Chin, Erik Roberson, Jorge Palop, Tiffany Wu and Kimberly Scearce-Levie appears in the Journal of Neuroscience.