Image caption Cannabis floods the brain with a host of chemicals which lead to changes in mood and memory

Scientists believe they are closer to understanding how taking cannabis disrupts short-term memory.

The Canadian team from Ottawa University narrowed the effect down to a particular type of brain cell called an astrocyte.

Writing in the journal Cell, they said it might be possible to block it in medicines based on cannabis.

A UK researcher said it could reveal more about natural brain chemicals.

Cannabis floods the brain with a host of chemicals which mimic one of its own subtle signalling systems, leading to pronounced changes in mood and memory.

Scientists are trying to harness the power of these chemicals, called cannabinoids, in pharmaceuticals aimed at conditions such as multiple sclerosis and chronic pain.

The doses of cannabinoid are carefully controlled to avoid the "high" feeling.

The work by the Ottawa University researchers may shed light on how one of the best known cannabinoids, THC, acts on the brain.

Memory matters

Their work suggests that, when it comes to affecting memory, THC is acting not, as might be expected, on the brain's neurons, but on a brain cell called an astrocyte.

We may find a way to deal with working memory problems in Alzheimer's. Dr Xia Zhang

They bred mice whose astrocytes could not be affected by THC, and found that their spatial memory was unaffected by the dose.

This discovery could help drug companies reduce the risk of unwanted side effects when using THC in their products, they suggested.

However, possibly more importantly, it could shed light on the brain's own chemical pathways, the "endocannabinoid" system.

Dr Xia Zhang, one of the researchers, said: "Just about any physiological function you can think of in the body, it's likely at some point endocannabinoids are involved."

Understanding how this system works could lead to ways to make it work better, he suggested.

"We may find a way to deal with working memory problems in Alzheimer's," he said.

Prof Heather Ashton, from the University of Newcastle, said that memory problems were an established feature of cannabis use, and understanding the mechanism behind them was "interesting".

She said: "When someone is taking cannabis, in some cases you find that they cannot even remember starting a sentence by the time they reach the end."

But she agreed that the practical benefits of such research might ultimately lie in a better understanding of the body's own endocannabinoid system, rather than the effects of cannabis itself.