Brain cell discovery has potential to change neuroscience

Ottawa researcher studied impact of marijuana on working memory

BY TOM SPEARS, THE OTTAWA CITIZENMARCH 7, 2012 

OTTAWA — Marijuana impairs the brain by acting on two types of brain cells at once, a new Ottawa study shows.

And the implication, says the lead researcher, is that there’s another side to the brain that neuroscientists hadn’t realized.

For the past century, the accepted theory was that marijuana acts on neurons to impair working memory.

Working memory is the system of holding on to information so that the brain can think about it and make decisions, without being distracted. For instance, it allows a person to drive a car, listen to the radio, think about what will happen at the end of the car ride, and watch for pedestrians all at once.

But marijuana impairs working memory, an effect that can last for a day or more after heavy pot-smoking.

At the Royal Ottawa Mental Health Centre, Xia Zhang and his team have found that there’s more to this impairment than interference with neurons.

Pot’s psychoactive chemical, THC, also acts on a second type of brain cells called astroglial cells.

“Glial cells make up 90 per cent of the brain cells,” Zhang said in an interview, “whereas neurons only make up 10 per cent.”

The various types of glial cells have always been seen as having a support role, nourishing and otherwise helping the neurons so that the neurons can do the real brain work, he said.

But his study showing that glial cells have a role in memory opens up the possibility that they are far more involved in neuron-like work than anyone had realized.

The study is published in Friday’s edition of the research journal Cell. The co-author is Giovanni Marsicano, a scientist at France’s national health research institute, INSERM.

“This is the first evidence that glial cells modulate working memory,” Zhang said. It’s “very surprising” to other researchers in the field, he said. “They don’t believe it” when they first hear of this work.

It’s likely that brain research will now broaden to explore the roles that glial cells may have in a wide variety of brain functions, he said.

Zhang is also on the faculty of the University of Ottawa.

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