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  • Astrocytes reveal their role

    images51The astrocytic Ca2 + signal is essential in the exchange of infor mation between astrocytes and neurons. Cannabinoid receptors are key to brain physiology, but its expression and function in astrocytes in situ is unknown. Marta Navarrete and Alfonso Araque, Cajal Institute, have investigated the expression of cannabinoid receptors by astrocytes and its involvement in astrocyte-neuron communication.

    Immunocytochemical techniques, electrophysiology and calcium imaging in mouse hippocampal slices revealed that hippocampal astrocytes express functional cannabinoid receptors type 1 (CB1). These receptors can be activated both by synthetic agonists such as endocannabinoids from pyramidal neurons. Their activation leads to sequential stimulation of Gq/11 protein and phospholipase C which causes the release of calcium from intracellular reservoirs, which generate increases in intracellular calcium. Increased calcium serves as a signal that triggers the release of transmitter glutamate.

    Glutamate released by astrocytes activated receptors in the membrane of adjacent neurons, causing slow input currents that increase neuronal excitability. That is, the stimulation of astrocytes by endocannabinoids activate a new channel of communication between neurons, where astrocytes serve as a bridge in this communication.

    The results show that astrocytes are cellular targets of cannabinoids, and identify them as new cellular elements involved in the physiology of addiction and possible targets for the treatment of cannabinoids as drugs of abuse. Further, considering the importance of endocannabinoids in many processes of the nervous system, such as pain perception or learning and memory, these findings indicate that astrocytes are actively involved in brain function.

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