Allosteric potentiation of GABA _A receptor promotes survival and maturation of oligodendroglial cells <i>in vitro</i> via Ca ²⁺ /CaMK/AKT signaling pathway

Oligodendrocytes (OLs) and their precursor cells (OPCs) express specific receptors to GABA; however, the direct functional consequences of their activation remain not fully determined. It has been shown that expression of functional GABA type A receptors (GABAARs) in OPCs and OLs is controlled by their contact with neurons. This suggests a role for GABAergic signaling in OPC-neuron dialogue establishment and their differentiation towards mature OLs. Here, OPCs (NG2 + ) isolated from rat (postnatal day 11) optic nerve, maintained in vitro, were used to directly study the functional role of the GABA signal. The oligodendroglial GABA A R activity was specifically enhanced using N-butyl-β-carboline-3-carboxylate (β-CCB), a potent positive allosteric modulator (PAM). β-CCB effects were compared with those by ganaxolone (Gx), a synthetic allopregnanolone analog and unspecific PAM of GABA A Rs. It was found that medium supplemented with one or both PAMs increased cell survival. This effect was eliminated in the presence of GABA A R antagonists, such as gabazine or bicuculline, and it was dependent on intracellular Ca2 + increase, which activated the AKT pathway through Ca2 + -calmodulin-dependent kinases (CaMKs) acting upstream. Additionally, a morphometric analysis showed that both PAMs promoted an increase in cellular complexity commonly associated with cell maturation, increasing the average cell area, number and length of branches per cell, as well as the branch point number. These direct actions on NG2 + cells would explain, at least in part, the positive effects that GABAergic signaling stimulation has on the myelination process in several experimental models, both in vivo and in vivo.