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

The cannabinoid CB receptor-mediated functions in astrocytes are highly dependent on the CB 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 receptor distribution in astroglial compartments remains uncompleted because of the scarce CB 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 receptor distribution in astrocytes. Therefore, alternative markers to decipher the actual astroglial CB receptors are required. In this work, we have compared the glutamate aspartate transporter (GLAST) versus GFAP for the CB 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 receptor labeling in GLAST-positive astrocytes.