GABA B receptor subunit expression in glia.

GABA(B) receptor subunits are widely expressed on neurons throughout the CNS, at both pre- and postsynaptic sites, where they mediate the late, slow component of the inhibitory response to the major inhibitory neurotransmitter GABA. The existence of functional GABA(B) receptors on nonneuronal cells has been reported previously, although the molecular composition of these receptors has not yet been described. Here we demonstrate for the first time, using immunohistochemistry the expression of GABA(B1a), GABA(B1b), and GABA(B2) on nonneuronal cells of the rat CNS. All three principle GABA(B) receptor subunits were expressed on these cells irrespective of whether they had been cultured or found within brain tissue sections. At the ultrastructural level GABA(B) receptor subunits were expressed on astrocytic processes surrounding both symmetrical and assymetrical synapses in the CA1 subregion of the hippocampus. In addition, GABA(B1a), GABA(B1b), and GABA(B2) receptor subunits were expressed on activated microglia in culture but were not found on myelin forming oligodendrocytes in the white matter of rat spinal cord. Together these data demonstrate that the obligate subunits of functional GABA(B) receptors are expressed in astrocytes and microglia in the rat CNS.