March 8, 2012

Don’t forget it! Marijuana Impairs Memory

(Ivanhoe Newswire) — Medical marijuana is often prescribed to relieve symptoms associated with numerous diseases, including arthritis, dystonia, insomnia, seizures, and Tourette's syndrome, but it comes with a cost, your memory.

Marijuana's major psychoactive ingredient (THC) impairs memory independently of its direct effects on neurons, the ability to transmit information. The side effects stem instead from the drug's action on astroglia, passive support cells long believed to play second fiddle to active neurons.

"Astroglial cells (also known as astrocytes) have been viewed as cells that support, protect and feed neurons for the last 100 to 150 years," Giovanni Marsicano of INSERM in France was quoted saying. "Over the last decade, evidence has accumulated that these cells play a more active role in forging the connections from one neuron to another."

With their experiment on mice, Marsicano and his colleagues 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.

"This is the first direct evidence that astrocytes modulate working memory," Xia Zhang of the University of Ottawa in Canada, was quoted saying.

Zhang and Marsicano now show that mice lacking CB1Rs only on astroglial cells of the brain are protected from the impairments to spatial working memory that usually follow a dose of THC. In contrast, animals lacking CB1Rs in neurons still suffer the usual lapses. Given that different cell types express different variants of CB1Rs, there might be a way to therapeutically activate the receptors on neurons while leaving the astroglial cells out.

"The study shows that one of the most common effects of cannabinoid intoxication is due to activation of astroglial CB1Rs," the researchers wrote.

The findings further suggest that "astrocytes might be playing unexpected roles in other forms of memory in addition to spatial working memory," Zhang was quoted saying.

"These findings also offer an 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 someday be attained without hurting memory," the researchers were quoted saying.

SOURCE: Cell Press Journal Cell, March, 2012