GABA_A receptors expressed in oligodendrocytes cultured from the neonatal rat contain a3 and g1 subunits and present differential functional and pharmacological properties

Oligodendrocytes (OLs) express functional GABA_A receptors (GABA_ARs) that are activated by GABA released at synaptic contacts with axons or by ambient GABA in extrasynaptic domains. In both instances, the receptors' molecular identity has not been fully defined. Furthermore, data on their structural diversity in different brain regions and information on age-dependent changes in their molecular composition are scant. This lack of knowledge has delayed access to a better understanding of the role of GABAergic signaling between neurons and OLs. Here, we used functional, and pharmacological analyses, as well as gene and protein expression of GABA_AR subunits, to explore the subunit combination that could explain the receptor functional profile expressed in OLs from the neonate rat. We found that GABA_AR composed of a3b2g1 subunits mimicked the characteristics of the endogenous receptor when expressed heterologously in Xenopus laevis oocytes. Either a3 or g1 subunit silencing by small interfering RNA transfection changed the GABA-response characteristics in oligodendrocyte precursor cells, indicating their participation in the endogenous receptor conformation. Thus, a3 subunit silencing shifted the mean EC₅₀ for GABA from 75.1 to 46.6 mM, whereas g1 silencing reduced the current amplitude response by 55%. We also observed that b-carbolines differentially enhance GABA responses in oligodendroglia as compared with those in neurons. These results contribute to defining the molecular and pharmacological properties of GABA_ARs in OLs. Additionally, the identification of b-carbolines as selective enhancers of GABA_ARs in OLs may help to study the role of GABAergic signaling during myelination.