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(Simon Hayter for The Globe and Mail/Simon Hayter for The Globe and Mail)
(Simon Hayter for The Globe and Mail/Simon Hayter for The Globe and Mail)

Pain relief without memory lapses? Marijuana study holds out hope Add to ...

At last there’s hope for medical marijuana users who have trouble staying on task after a dose of pot.

Cannabis is an effective treatment for conditions such as chronic pain, nausea, seizures, cerebral trauma and tumours. But the drug’s therapeutic potential has been limited by its side effects, including temporary impairment of working memory.

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A team of neuroscientists has discovered that memory lapses due to marijuana intoxication aren’t related solely to how neurons react to THC, the drug’s major psychoactive ingredient.

Instead, THC short-circuits working memory by interfering with passive cells, called astrocytes, long believed to exist solely to support and feed active neurons.

The findings could lead to the development of a THC-based drug that controls pain without affecting memory.

The research, published Friday in the journal Cell, is the first to show that astrocytes play a major role in spatial working memory, says co-author Xia Zhang, a neuroscientist at the University of Ottawa Institute of Mental Health Research at The Royal. In this new model, he says, “a supporting actor becomes the leading actor.”

The findings may help scientists researching spatial working memory problems in patients with conditions such as schizophrenia and Alzheimer’s, he says.

Spatial working memory is used in activities such as route finding, driving, figural reasoning (geometry) and sports (remembering and carrying out complex plays).

Dr. Zhang and researchers including Giovanni Marsicano of INSERM in Bordeaux, France, used chemicals and peptides to block spatial working memory impairment in mice and rats given injections of THC.

The peptide used to block the negative side effects of marijuana was patented by the Brain Research Institute at the University of B.C.

“Our study on both rats and mice suggests that the same mechanism underlying marijuana impairment of working memory is likely applicable to humans,” Dr. Zhang says.

The catch is that blocking the undesirable side effect would likely wipe out the euphoria associated with the drug as well, Dr. Zhang says.

Asked whether the tradeoff would be attractive to patients, he replied, “maybe, but I’m not a pot smoker.”

Follow on Twitter: @AdrianaBarton

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