Evidence for GABAB-receptors on cultured astrocytes of rat CNS: autoradiographic binding studies.

The cellular localization of GABA-binding sites was studied in explant cultures of rat cerebellum, brain stem and spinal cord by means of autoradiography. Labelling of GABAB-sites was done with 3H(-)baclofen or 3H-GABA in presence of unlabelled bicuculline. Binding sites for these radio-ligands were found on many neurones and on a large number of astrocytes. Labelling of glial cells was usually weaker than that of neurones. Combining autoradiography with staining with anti-glial fibrillary acidic protein (GFAP) revealed that the glial cells labelled with 3H-baclofen or 3H-GABA were GFAP-positive. In contrast, when GABAA-sites were localized using 3H-GABA in presence of unlabelled baclofen, the GABAA-agonists 3H-muscimol and 3H-THIP, or the antagonist 3H-(+)-bicuculline, binding only occurred to neurones but not to astrocytes. Immunohistochemical investigations with the monoclonal antibody (bd-17) against the GABAA/benzodiazepine/chloride channel complex revealed that neurones were specifically stained whereas glial cells were immunonegative. From our observations it is suggested that astrocytes possess GABAB-receptors but there is little evidence for the existence of GABAA-sites on glial elements.