During postnatal development, myelinating oligodendrocytes derived from oligodendrocyte precursor cells, also termed NG2 cells. In the adult, NG2 cells are still largely abundant and participate in remyelination occuring as a repair process in demyelinating lesions. However, although their function as progenitors is undeniable, different findings of our laboratory support the idea that NG2 cells play other roles in the mature brain. Indeed, several physiological properties of these cells dramatically change during development of grey matter regions. First, we demonstrated that all hippocampal NG2 cells in the second postnatal week express a7 nicotinic receptors, but that the expression of these receptors is downregulated with age. Second, we showed that direct GABAergic synaptic inputs on neocortical NG2 cells are lost early in postnatal development and replaced in the adult by an extrasynaptic mode of communication, mediated solely by GABA spillover. In a more recent study, we characterized the intrinsic electrophysiological properties of NG2 cells of the somatosensory cortex. Cortical NG2 cells, recorded at different developmental stages, express high levels of voltage-gated Na1 channels, but never elicit action potential discharges. Striking developmental changes were observed in potassium channel expression. We observed that a Ba21-sensitive passive potassium current is upregulated after the second postnatal week at expenses of voltage-gated potassium currents. Pharmacological and immunocytochemistry analyses indicate that this potassium conductance is mediated by Kir4.1 channels. The properties of this conductance appear ideally suited for contributing to the regulation of extracellular potassium concentration during local neuronal activity. Indeed, low-frequency stimulation of neuronal fibers induced a Kir4.1-mediated potassium current in the mature, but not in the young somatosensory cortex. Our results point toward a new role for these cells as local regulators of extracellular potassium concentration in the adult brain.