SMOKE FOR STROKES

Cannabis, it turns out, can protect the brain from damage

TWO constituents of marijuana can help prevent the brain damage that often
follows a stroke. The discovery by researchers at the National Institutes
of Health (NIH) near Washington DC will add weight to the arguments of
doctors who think the drug should be legal for medical use.

Some patients with multiple sclerosis, glaucoma and AIDS-related wasting
already take marijuana. It also seems to help relieve the nausea suffered
by cancer patients undergoing powerful chemotherapy.

When marijuana is smoked or eaten, chemicals called cannabidiol (CBD) and
tetrahydrocannabinol (THC) enter the body. THC binds to proteins on the
surface of brain cells called cannabinoid receptors, causing the drug's
mind-altering effects. CBD doesn't bind to these proteins and is not
psychoactive.

Aidan Hampson and his NIH colleagues were interested in the normal role of
these receptors. "We didn't evolve them so that some people could enjoy
smoking pot," he says.

Hampson suspected that activating the receptors might change how cells
respond to the neurotransmitter glutamate. Damping down this response can
be crucial, since depriving neurons of oxygen, as happens in a stroke,
makes them pump out too much glutamate. This in turn boosts the production
of reactive free radicals, which can kill brain cells.

The researchers treated rat neurons with toxic levels of glutamate and then
tested THC's ability to prevent cell death. They found that extremely low
concentrations of THC protected the neurons, suggesting that the

cannabinoid receptors might indeed be involved. But to their surprise, CBD
gave exactly the same level of protection.

So if binding to the receptors wasn't crucial, how were THC and CBD
protecting the brain cells from chemical attack? The researchers wondered
if they might work like vitamins C and E, antioxidants that inactivate free
radicals by giving up electrons. They found that both CBD and THC gave up
electrons easily. In fact, they were able to protect at least 20 per cent
more neurons than either vitamin C or E at the same concentration
(Proceedings of the National Academy of Sciences, vol 95, p 8268).

Since they submitted that paper, the researchers have begun testing the
ability of CBD to prevent brain damage in rats in which they had induced
strokes. Preliminary results are promising, Hampson says.

Hampson notes that people can tolerate high doses of CBD, and because it
quickly penetrates the brain, CBD could be an ideal drug for treating strokes.

It's unclear whether the doses of CBD absorbed by smoking cannabis could
protect brain cells. But the findings will stoke the debate over the
medical use of marijuana. Those who have argued against legalisation have
pointed out that THC is available legally in a purified form called
marinol. "But now we know that CBD may also be therapeutic, so marinol
isn't a complete substitute," says Hampson.

Lester Grinspoon of the Harvard Medical School in Boston, who advocates the
medical use of marijuana, says: "Critics have insisted for a long time that
marijuana must damage the brain. Now it turns out it might actually be
neuroprotective. I'd say we've come full circle."

Checked-by: Mike Gogulski