A major downside of the medical use of marijuana is the drug's ill effects on working memory, the ability to transiently hold and process information for reasoning, comprehension and learning. Researchers reporting in the March 2 print issue of the Cell Press journal Cell provide new insight into the source of those memory lapses. The answer comes as quite a surprise: Marijuana's major psychoactive ingredient (THC) impairs memory independently of its direct effects on neurons. The side effects stem instead from the drug's action on astroglia, passive support cells long believed to play second fiddle to active neurons.
The findings offer important new insight into the brain and raise the possibility that marijuana's benefits for the treatment of pain, seizures and other ailments might some day be attained without hurting memory, the researchers say.
With these experiments in mice, "we have found that the starting point for this phenomenon the effect of marijuana on working memory is the astroglial cells," said Giovanni Marsicano of INSERM in France.
"This is the first direct evidence that astrocytes modulate working memory," added Xia Zhang of the University of Ottawa in Canada.
The new findings aren't the first to suggest astroglia had been given short shrift. Astroglial cells (also known as astrocytes) have been viewed as cells that support, protect and feed neurons for the last 100 to 150 years, Marsicano explained. Over the last decade, evidence has accumulated that these cells play a more active role in forging the connections from one neuron to another.
The researchers didn't set out to discover how marijuana causes its cognitive side effects. Rather, they wanted to learn why receptors that respond to both THC and signals naturally produced in the brain are found on astroglial cells. These cannabinoid type-1 (CB1R) receptors are very abundant in the brain, primarily on neurons of various types.
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