In a new study, researchers have found that it's not only neurons in the brain that are sensitive to cannabinoids-the active chemicals in marijuana, but also cells known as astrocytes that provide neurons with support and nutrition and modulate signalling among them.
The finding, the researchers say, might help in the development of treatments for cannabinoid drug abuse.
The study was led by Marta Navarrete and Alfonso Araque, who said that as the so-called "endocannabinoids" produced by brain cells are involved in the neural machinery of pain perception and learning and memory, the findings could help in understanding those processes.
The researchers conducted their experiments with mouse brain slices in the pursuit to establish the role that cannabinoid receptors on astrocytes (which previous studies had indicated to exist) played in astrocyte function.
Receptors are proteins that rest in the membranes of cells and that are triggered by specific chemicals, like a key fitting a lock. That triggering activates a cellular response.
It was shown through the electrophysiological and imaging studies, that astrocytes do express endocannabinoid receptors that, when activated, produce a cellular response. They also found that neurons associated with the astrocytes release endocannabinoids that trigger an astrocyte response.
Lastly, the researchers also showed that this response in astrocytes can, in turn, activate neurons to release the neurotransmitter glutamate, which mediates signalling among neurons.
"These results indicate that neurons and astrocytes communicate via endocannabinoid signaling and suggest the existence of intercellular communication pathways mediated by endocannabinoid-glutamate signaling where astrocytes serve as a bridge for interneuronal communication," concluded Navarrete and Araque.
The researchers also said that their findings identify astrocytes "as cellular elements possibly involved in the physiology of cannabinoid addiction as well as potential targets for the treatment of cannabinoid-related drug abuse. Furthermore, considering the importance of the endocannabinoid-mediated intercellular signaling in numerous processes of the nervous system, such as pain perception or learning and memory, present findings indicate that astrocytes may be actively involved in relevant phenomena of brain physiology."
The findings of the study are published in the latest issue of the journal Neuron, published by Cell Press.