Scientists find marijuana reduces memory impairment

Knowing exactly how any of these compounds work in the brain can make it easier for drug designers to target specific systems with agents that will offer the most effective anti-aging benefits, said Wenk, who is also a professor of neuroscience and molecular virology, immunology and medical genetics.

"Could people smoke marijuana to prevent Alzheimer's disease if the disease is in their family? We're not saying that, but it might actually work. What we are saying is it appears that a safe, legal substance that mimics those important properties of marijuana can work on receptors in the brain to prevent memory impairments in aging. So that's really hopeful," Wenk said.

One thing is clear from the studies: Once memory impairment is evident, the treatment is not effective. Reducing inflammation and preserving or generating neurons must occur before the memory loss is obvious, Wenk said.

Marchalant led a study on old rats using the synthetic drug, called WIN-55212-2 (WIN), which is not used in humans because of its high potency to induce psychoactive effects.

The researchers used a pump under the skin to give the rats a constant dose of WIN for three weeks – a dose low enough to induce no psychoactive effects on the animals. A control group of rats received no intervention. In follow-up memory tests, in which rats were placed in a small swimming pool to determine how well they use visual cues to find a platform hidden under the surface of the water, the treated rats did better than the control rats in learning and remembering how to find the hidden platform.

"Old rats are not very good at that task. They can learn, but it takes them more time to find the platform. When we gave them the drug, it made them a little better at that task," Marchalant said.

In some rats, Marchalant combined the WIN with compounds that are known to block specific receptors, which then offers hints at which receptors WIN is activating. The results indicated the WIN lowered the rats' brain inflammation in the hippocampus by acting on what is called the TRPV1 receptor. The hippocampus is responsible for short-term memory.

With the same intervention technique, the researchers also determined that WIN acts on receptors known as CB1 and CB2, leading to the generation of new brain cells – a process known as neurogenesis. Those results led the scientists to speculate that the combination of lowered inflammation and neurogenesis is the reason the rats' memory improved after treatment with WIN.

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