Not long ago, glial cells were thought to have a typical linear rectification of membrane current and lack action potentials, a defining feature of neurons. But these boundaries are blurring. Oligodendrocytic precursor cells (OPCs), identified by expression of the proteoglycan NG2, appear during early postnatal life and maintain the capacity in adulthood to proliferate into oligodendrocytes producing myelin sheaths and performing myelin repair. OPCs appear to be a surprisingly excitable phenotype. They are morphologically characterized by radially projecting long and thin branches containing AMPA, NMDA and GABAergic receptors and receive direct synaptic inputs from neighbouring neurons (Lin & Bergles, 2004). Some NG2~+ OPC classes even produce fast action potentials reminiscent of neurons (Karadottir et al 2008). These findings raise the intriguing possibility that OPCs, similarly to neurons, perform intricate electrical computations. However, how synaptic currents spread along the OPC branches is not understood. In this issue of The Journal of Physiology, Chan et al. (2013) make a substantial contribution towards answering these emerging issues.
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