title: Expression of the γ2-subunit distinguishes synaptic and extrasynaptic GABA(A) receptors in NG2 cells of the hippocampus.
abstract: NG2 cells are equipped with transmitter receptors and receive direct synaptic input from glutamatergic and GABAergic neurons. The functional impact of these neuron-glia synapses is still unclear. Here, we combined functional and molecular techniques to analyze properties of GABA(A) receptors in NG2 cells of the juvenile mouse hippocampus. GABA activated slowly desensitizing responses in NG2 cells, which were mimicked by muscimol and inhibited by bicuculline. To elucidate the subunit composition of the receptors we tested its pharmacological properties. Coapplication of pentobarbital, benzodiazepines, and zolpidem all significantly increased the GABA-evoked responses. The presence of small tonic currents indicated the presence of extrasynaptic GABA(A) receptors. To further analyze the subunit expression, single cell transcript analysis was performed subsequent to functional characterization of NG2 cells. The subunits α1, α2, β3, γ1, and γ2 were most abundantly expressed, matching properties resulting from pharmacological characterization. Importantly, lack of the γ2-subunit conferred a high Zn²⁺ sensitivity to the GABA(A) receptors of NG2 cells. Judging from the zolpidem sensitivity, postsynaptic GABA(A) receptors in NG2 cells contain the γ2-subunit, in contrast to extrasynaptic receptors, which were not modulated by zolpidem. To determine the effect of GABA(A) receptor activation on membrane potential, perforated patch recordings were obtained from NG2 cells. In the current-clamp mode, GABA depolarized the cells to approximately -30 mV, indicating a higher intracellular Cl⁻ concentration (∼50 mM) than previously reported. GABA-induced depolarization in NG2 cells might trigger Ca²⁺ influx through voltage-activated Ca²⁺ channels.
authors.affiliation: Institute of Cellular Neurosciences, University of Bonn, 53105 Bonn, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Passlick
authors.forename: Michael
authors.initials: M
authors.lastname: Grauer
authors.forename: Christoph
authors.initials: C
authors.lastname: Schäfer
authors.forename: Ronald
authors.initials: R
authors.lastname: Jabs
authors.forename: Gerald
authors.initials: G
authors.lastname: Seifert
authors.forename: Christian
authors.initials: C
authors.lastname: Steinhäuser
mesh_terms: D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D003975:Diazepam / Q000494:pharmacology; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009118:Muscimol / Q000494:pharmacology; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D010424:Pentobarbital / Q000494:pharmacology; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D021122:Protein Subunits; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D010424:Pentobarbital; D003975:Diazepam; D001640:Bicuculline