Feb. 23, 2005 -- New clues about Alzheimer's disease have emerged from a Spanish study of marijuana. The drug's active ingredients -- cannabinoids -- help prevent brain problems seen in Alzheimer's, say the scientists.
There is no cure for Alzheimer's disease, which progressively damages brain areas involved in memory, judgment, language, and behavior. Alzheimer's disease is the most common form of mental decline, or dementia, in older adults.
The findings showed that "cannabinoids work both to prevent inflammation and to protect the brain," says researcher Maria de Ceballos in a news release. That "may set the stage for [cannabinoids'] use as a therapeutic approach for [Alzheimer's disease]."
A staff member at Madrid's Cajal Institute, de Ceballos conducted the study with colleagues from nearby Complutense University. Their results appear in the Feb. 23 edition of The Journal of Neuroscience.
Marijuana, Alzheimer's Disease, and the Human Brain
The researchers studied human brain tissue samples, some of which were from deceased Alzheimer's patients and some from normal brain tissue.
The typical features seen in the brain tissue of Alzheimer's disease are called plaques. Plaques are protein clumps that are seen outside brain cells, and they have been shown to activate inflammation seen in brain tissue of Alzheimer's disease patients.
Besides the typical plaques seen with Alzheimer's disease, the brain tissues taken from Alzheimer's patients also had many fewer cannabinoid receptors.
Significant changes in the location, expression, and function of cannabinoid receptors may play a role in Alzheimer's disease, write the researchers.
That could mean that the patients had lost the capacity to experience cannabinoids' protective effects, says the news release.
Marijuana and Alzheimer's Mental Decline
The researchers also injected rats with a protein called beta-amyloid, which gave the rats an Alzheimer's-like brain condition.
Some of the same rats were also injected with a cannabinoid. For comparison, other rats got injections of an unrelated protein along with beta-amyloid.
After two months, the rats were tested for learning, memory, and mental functions. The researchers tried to train them to find a platform in a tank of water. The rats had two minutes to find the platform. If they failed, the researchers briefly put the rats on the platform. Four times a day for five days, the rats practiced.
By the fifth day, the rats that received the cannabinoid injections were able to find the platform on their own. Those that didn't get the cannabinoid injections didn't learn to find the platform.
Another interesting result also surfaced. The cannabinoids completely prevented activation of cells that trigger inflammation. These cells gather near plaque and are believed to be involved in the development of Alzheimer's disease.
"Our results indicate that cannabinoid receptors are important in the pathology of Alzheimer's disease and that cannabinoids succeed in preventing the neurodegenerative process occurring in the disease," write the researchers in the journal.
They plan to focus future studies on a cannabinoid receptor that's unrelated to marijuana's "high," says the news release.