A rat study suggests chemicals in marijuana may slow the memory loss of Alzheimer's disease, researchers say.

Added to signs that pot-smoking veterans of the 1960s and 1970s drug culture rarely develop the devastating condition, they add, the findings could point to new avenues for Alzheimer's treatment.

Researchers want to develop a drug with marijuana's beneficial properties, but without the mind-altering effects, said Gary Wenk of Ohio State University in Columbus, Ohio, one of the scientists.

The key to marijuana's benefit, he added, may be its strong effect against chronic inflammation, widely believed to be a major factor in Alzheimer's.

"Inflammation in the brain is part of aging," he said. "It happens to almost all of us... But in some cases, this inflammation gets out of hand and causes serious damage."

Treatment with a synthetic compound similar to marijuana reduced inflammation in older rats and made them "smarter," he added. "The compound substantially improved the memories of the older rats, [who] were able to hold on to key details of a specific task. Untreated older rats, on the other hand, were not."

His team presented presented its findings Oct. 18 in Atlanta at the annual meeting of the Society for Neuroscience. A similar, Spanish study published in the Journal of Neuroscience early last year found that rats injected with a cannabinoid, a synthetic version of the marijuana's active ingredient, suffered less mental decline in artificially induced Alzheimer's disease than others.

Wenk's team treated young and old rats with WIN-55212-2, or simply WIN, a synthetic drug similar to marijuana. While the compound improved memory and helped to control inflammation, it's is not a candidate for use in humans because it still contains substances that could trigger a high, Wenk added.

"We don't use marijuana in our experiments because we're trying to find a compound that isn't psychoactive," Wenk said. "And using synthetic compounds may eventually help us to separate the beneficial effects from the psychoactive effects."

The researchers inserted a small tube into the brain of each rat to periodical infuse lipopolysaccharide, a material that stimulates an immune reaction that mimics the inflammation of Alzheimer's.

Some of the rats were also treated with WIN daily for the three weeks during which infusions took place.

The animals were subjected to a memory test during the third week. They navigated a water maze that requires finding an escape platform hidden just below the surface of opaque water. The rats were given several opportunit over three days to acclimate to the water maze. On the fourth day, the researchers timed how quickly each rat found the platform.

"The maze task is sensitive to memory impairment and also to aging," Wenk said. "Old rats tend to be pretty bad at navigating the maze. It's kind of like an elderly person trying to find his way around a house that he's not familiar with."

The compound "significantly improved the older rats' memories," Wenk said. "They found the platform faster, suggesting that they were less apt to forget key information for this task. It's a pretty good prediction of how a human would respond to this drug."

Alzheimer's, a devastating, progressive degeneration of the brain estimated to affect 4 million Americans, typically starts in the 40s or 50s with memory difficulties. This tends to lead to impaired thought and speech, and eventually total helplessness.

ABOUT THE AUTHOR

Science writer Jack Lucentini is founder and editor of the World Science science news webzine. He has worked as a staff writer at three daily newspapers, and as a freelance science writer for a range of publications including The Washington Post, Discover magazine and The Scientist magazine. He earned his bachelor's degree at Oberlin College in Oberlin, Ohio in 1993.