An international research team has found that regularly smoking marijuana over a number of years can affect consumer’s short-term memory.
Long-term smokers may notice that they cannot temporarily hold information in their heads, like a telephone number or the name of someone they have just met.
The scientists claim that this common side effect occurs because the drug hinders a signaling mechanism between neurons and non-neuronal cells called astrocytes, reports Nature.
The research by Neuroscientists Giovanni Marsicano of the University of Bordeaux, France, and Xia Zhang of the University of Ottawa Institute of Mental Health Research examines the role of the astrocytes, which have long been considered nothing more than support cells that protect neurons.
“Our study provides compelling evidence that astrocytes control neurons and memory,” Xia Zhang said reports Nature.
“The supporting actor has become the leading actor.”
The scientists found that tetrahydrocannabinol (THC), the psychoactive ingredient of marijuana, weakens the connections between neurons in the hippocampus, a structure that is crucial for memory formation, reports Nature.
The research team came to this conclusion after injecting mice with THC and giving them a series of memory tests, such as forcing them to remember the location of an underwater platform in order to emerge from a miniature swimming pool.
“It’s probably the first time it’s been shown that astrocytes are involved in the primary event [that regulates] memory,” says Giovanni Marsicano, reports the Scientific American.
Giovanni Marsicano told Nature that understanding how the drug causes memory loss could help scientists create drugs that have the same therapeutic benefits but with fewer side effects, for example painkillers, without affecting the function of working memory.
One group of mice were genetically modified to lack CB1 receptors (tiny cellular structures normally found on both neurons and astrocytes) on astrocytes and altered another group of mice to lack these receptors on neurons, reports the Scientist.
Mice lacking CB1s on astrocytes did much better on the memory tests than mice lacking the receptors on their neurons, which suggests that marijuana impaired working memory only when it was able to bind to astrocytes.