Expression of the NG2 chondroitin sulphate defines a subset of glial cells in the adult CNS. These NG2-glia are capable of regenerating oligodendrocytes and possibly neurons. In addition, NG2-glia are highly reactive cells that contribute to the axon growth inhibitory glial scar following CNS injury. We have examined the factors that may control the diverse functions of NG2-glia. NG2-glia form exquisite contacts with neurons at the sites of their activity, namely synapses and nodes of Ranvier. Furthermore, we show that NG2-glia are dynamic cells that respond to axonal and astroglial activity by glutamate- and ATP-evoked calcium signalling. The glutamate-mediated calcium signals were largely blocked by NBQX (100mM) and augmented by cyclothiazide (10mM), indicating a predominant role for AMPA-type glutamate receptors. We also provide evidence of NMDA-receptor mediated calcium signals in NG2-glia. The response to ATP is mediated by both P2Y and P2X receptors, and the actions of BzATP (100mM) and oxidised ATP (10mM) indicate a sinificant role for P2X7 receptors in NG2-glia. Notably, electrical stimulation of optic nerve axons or mechanical stimulation of astrocytes evokes ATP-mediated calcium signals in NG2-glia. We conclude that these signalling pathways may play diverse roles in regulating the functions of NG2-glia.

Niki Hamilton was supported by a PhD studentship from the Anatomical Society of Great Britain and Ireland