Bergmann Glia GABA_A Receptors Concentrate on the Glial Processes That Wrap Inhibitory Synapses

Abstract

We studied the cellular and subcellular distribution of GABA_A receptors in the Bergmann glia and Purkinje cells in the molecular layer of the cerebellum by using electron microscopy postembedding immunogold techniques. Gold particles corresponding to α2 and γ1 immunoreactivity were localized in Bergmann glia processes that wrapped Purkinje cell somata, dendritic shafts, and some dendritic spines. The gold particles were mainly located on the glial plasma membrane or intracellularly but near the plasma membrane. The density of gold particles corresponding to α2 and γ1 GABA_A receptor subunits was 4.3-fold higher in the glial processes wrapping Purkinje cell somata than in the glial processes wrapping Purkinje cell dendritic spines. Moreover, the Bergmann glia GABA_A receptors were often located in close proximity to the type II GABAergic synapses made by the basket cell axons on Purkinje cell somata. These GABAergic synapses were enriched in neuronal GABA_A receptors containing α1 and β2/3 subunits. Unexpectedly, 2.8% of the Purkinje cell dendritic spines also showed immunoreactivity for the neuronal α1 or β2/3 subunits, which were located on the spine in type I synapses or extrasynaptically. Double-labeling immunogold experiments showed that ∼50% of the dendritic spines that were immunolabeled with the neuronal GABA_A receptors were wrapped by Bergmann glia processes containing glial GABA_A receptors. These results are consistent with a role of the Bergmann glial GABA_Areceptors in sensing GABAergic synaptic function.