GLAST versus GFAP as astroglial marker for the subcellular study of cannabinoid CB 1 receptors in astrocytes.

The cannabinoid CB 1 receptor-mediated functions in astrocytes are highly dependent on the CB 1 receptor distribution in these glial cells relative to neuronal sites, particularly at the nearby synapses under normal or pathological conditions. However, the portrait of the CB 1 receptor distribution in astroglial compartments remains uncompleted because of the scarce CB 1 receptor expression in these cells and the limited identification of astrocytes. The glial fibrillary acidic protein (GFAP) is commonly used as astroglial marker. However, because GFAP is a cytoskeleton protein mostly restricted to the astroglial cell bodies and their main branches, it seems not ideal for the localization of CB 1 receptor distribution in astrocytes. Therefore, alternative markers to decipher the actual astroglial CB 1 receptors are required. In this work, we have compared the glutamate aspartate transporter (GLAST) versus GFAP for the CB 1 receptor localization in astrocytes. We found by immunoelectron microscopy that GLAST reveals almost three-fold astroglial area and four-fold astroglial membranes compared to GFAP. In addition, this better visualization of astrocytes was associated with the detection of 12% of the total CB 1 receptor labeling in GLAST-positive astrocytes.