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Study shows how cannabis impairs memory

Kathleen Blanchard's picture

Researchers have uncovered how cannabis compounds impair memory. The reason is because cannabis interferes with neuronal connections in the hippocampus - an area of the brain responsible for spatial navigation and consolidation of information.

The study authors say the finding is important for optimizing medicinal use of marijuana. In the study they found THC in cannabis promotes activation of receptors that can induce long-term depression of the strength of glutamate receptors in the brain, which impairs spatial working memory.

The researcher team used mice to track receptors in the brain, finding the effect of cannabinoids in marijuana compounds. The current study specifically focused on CB1 brain receptors that are found primarily in the brain and nervous system.

The study, conducted by Giovanni Marsicano and colleagues at the Magendie Neurocentre (Inserm Research Unit 862, University of Bordeaux 2 found cannabinoids interrupt neural connections in the hippocampus region of the brain. When the compounds connect with brain receptors, signals are weakened, making it harder to perform simple tasks.

In tests performed in Petri dishes and in mice, the scientists found specific cells called astrocytes mediate CB1 receptors in the brain, which was not previously understood. THC was found to remove receptors for a compound called AMPA from the membranes of neurons that send signals throughout the brain.

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The result is decline in working memory, manifested by short-term difficulty performing common tasks like calculating, reading, writing and thinking clearly.

"The description of cannabinoid-specific action mechanisms in the hippocampus should enable optimization of the therapeutic potential of cannabinoids, which is currently limited by significant adverse effects associated with their consumption".

The study was prompted by observations in animals and humans that cannabis impairs memory. Researchers for the current finding wanted to understand what happens in the brain. The finding, say the authors, could have implications for decisions about how marijuana is used medicinally.

“It’s always difficult to extrapolate from rodents to humans,” says Marsicano, “but marijuana impairs working memory in both species, so I expect that similar mechanisms are involved.” The goal would be to find compounds derived from THC, the active ingredient in cannabis that can treat pain and other diseases without affecting memory, by targeting neurons instead of astrocytes.

“Astroglial CB1 Receptors Mediate Cannabinoid Alterations of Synaptic Plasticity and Working Memory” Jing Ha, et al.
Cell, 2 March 2012

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