Functional expression of metabotropic GABAB receptors in primary cultures of astrocytes from rat cerebral cortex

GABAB receptor subunits are widely expressed on neurons throughout the central nervous system (CNS), at both pre- and postsynaptic sites, where they mediate the late and slow component of the inhibitory response to the major inhibitory neurotransmitter GABA. Recently, GABAB receptors have been reported to be expressed in astrocytes and microglia in the rat CNS by immunocytochemistry. However, there are few reports available for the functional characterization of GABAB receptors on astrocytes. In the present study, we therefore investigated the functional expression and characteristics of GABAB receptors in primary cultures of astrocytes from rat cerebral cortex. In the presence of 10 μM GTP, forskolin concentration-dependently increased adenylylcyclase (AC) activity in membranes prepared from rat astrocytes. The selective GABAB agonist (R)-baclofen concentration-dependently reduced forskolin-stimulated AC activity in the presence of 10 μM GTP. This effect was reversed by the selective GABAB antagonists, CGP-55845 and CGP-54626, and was completely abolished by treatment of astrocytic membranes with pertussis toxin. In addition, RT-PCR, Western blotting, and immunocytochemistry clearly showed that metabotropic GABAB receptor isoforms (GABABR1 and GABABR2) are expressed in rat cerebrocortical astrocytes. Taken collectively, these results demonstrate that functionally active metabotropic GABAB receptors are expressed in rat cerebrocortical astrocytes.