What’s So Exciting About Glia?

Science Signaling  01 Apr 2008:
Vol. 1, Issue 13, pp. ec116
DOI: 10.1126/stke.113ec116

Káradóttir et al. present intriguing data suggesting that, contrary to long-accepted dogma, a class of glial cells can generate action potentials. Neurons and glia constitute the two classes of cell found in neural tissue, with inability to produce action potentials a defining feature that distinguishes glia from neurons. Káradóttir et al. identified oligodendrocyte precursor glial cells (OPCs) in the white matter of cerebellar slices from young rats on the basis of their morphology and expression of the proteoglycan NG2 and the oligodendrocyte transcription factor Olig2. These NG2- and Olig2-expressing cells did not express the neuronal marker NeuN, nor did they express the astrocyte marker S100β; about half were immunoreactive for Na+ channels. Whole-cell patch clamp analysis revealed two electrophysiologically distinct classes of OPCs: One class exhibited currents mediated by voltage-gated Na+ and K+ channels and generated action potentials in response to depolarization, whereas the other (morphologically indistinguishable) class did not. The two classes of OPCs were also present in adult animals. Most of the excitable OPCs exhibited excitatory postsynaptic currents (EPSCs), inhibitory postsynaptic currents (IPSCs), or both, whereas the vast majority of the inexcitable cells did not. Pharmacological analysis indicated that EPSCs reflected glutamatergic input and that IPSCs were a response to GABA. Glutamate and the glutamate antagonist NMDA elicited larger currents in excitable OPCs than in OPCs that lacked Na+ channels, and the former were also more susceptible to ischemic death (pertinent to conditions such as stroke or spinal cord injury). Otis and Sofroniew provide thoughtful commentary and discuss the possibility that some NG2-expressing glia may have functions other than acting as OPCs.

R. Káradóttir, N. B. Hamilton, Y. Bakiri, D. Attwell, Spiking and nonspiking classes of oligodendrocyte precursor glia in CNS white matter. Nat. Neurosci. 11, 450-456 (2008). [PubMed]

T. S. Otis, M.V. Sofroniew, Glia get excited. Nat. Neurosci. 11, 379-380 (2008). [PubMed]