Elderly rats remembered their way around a swimming pool and could find hidden resting spots after Yannick Marchalant and his colleagues at Ohio State University gave them a compound that mimics the effect of marijuana on the brain's cannabis receptors. The marijuana-like drug, known as WIN-55212-2, spurred new brain cell growth and reduced inflammation, the researchers said.
Inflammation in the brain may be linked to the development or progression of Alzheimer's, a progressive disease that destroys brain cells, disrupting the memory and cognitive capacity of some 4.5 million Americans, some scientists believe. Marchalant and his colleagues have been hunting for drugs to reduce inflammation.
''We used a low dose because we didn't want to give them a drug that tried to save their memory while we're also causing psychoactive effects,'' Marchalant said in a telephone interview yesterday. ''The dosage of WIN would be like giving one puff a day and not a whole joint.''
Marchalant and his team reported their results today at the Society for Neuroscience meeting in Washington, D.C. In the study, they first caused inflammation in the brains of young rats, which they could measure by looking at the activity of anti-inflammatory cells. Then they injected rats with WIN and saw that it reduced the activity of the inflammation-fighting cells.
Old Rats Quicker
With the older rats, they didn't need to induce inflammation because it was already present. They injected some of the old rats with WIN and had them spend time in a swimming tank.
It turned out that the rats who got hits of WIN found the hidden resting places much quicker than those who didn't. Later, the researchers dissected the rats' brains and found a reduction in inflammation and evidence that new brain cells had sprouted.
While marijuana might also promote the growth of new brain cells, it doesn't have WIN's ability to block another brain receptor that appears to cause inflammation, a key difference between the two compounds, Marchalant said. Too much pot also would overstimulate the cannabis receptors, he said.
''That's what everyone is trying to avoid,'' Marchalant said. ''If you overstimulate, you'll have a detrimental effect on memory.''
Heavy Marijuana Use Hurts
The U.S. National Institute on Drug Abuse says heavy marijuana smoking damages short-term recall and hastens age- related destruction of neurons in the brain's hippocampus responsible for memory, according to the agency's Web site.
WIN isn't a perfect compound, Marchalant said. Now that researchers know the effects on the brain they're trying to produce, and the receptors they're trying to influence, they can search for a better compound, he said.
Smoking pot, or taking WIN, once the memory loss of Alzheimer's had already begun, wouldn't help, Marchalant said.
''It's too late,'' he said. ''Patients who have been diagnosed have already lost neurons.''
A preventive strategy would need to start years earlier, he said.
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