Figure 1. Hypothetical consequences of localized and synchronized release of glutamate on NG2 cells.

(A) Cartoon illustrating how synchronized release of glutamate from a localized group of axons or synapses (blue) would affect the behaviour of uniformly distributed NG2 cells (red), taking into account the known effect of glutamate on NG2 cell proliferation (upper three panels), migration/mobility (lower three panel) and differentiation (rightmost panel) (Gallo et al., 1996; Yuan et al., 1998; Gudz et al., 2006). Note that the effects of glutamate on NG2 cell proliferation and migration/mobility would synergize to lower the density of NG2 cells in the area where glutamate is synchronously released. Ultimately, this area will display lower myelination (‘grey matter area’), while the surrounding tissue will exhibit a higher density of NG2 cells and oligodendrocytes (‘white matter area’). (B) Cartoon illustrating how NG2 cells (in red) would behave in different settings where three distinct neuronal nuclei (deep blue to light blue) exhibit a high degree of internal synchronization, but different level of overall activity. Each nucleus projects towards an adjacent target area via a shared white matter tract. In the white matter tract, NG2 cells would tend to accumulate at the boundaries between the bundles of axons corresponding to each nucleus in an activity-dependent manner. In the target grey matter area, an equivalent phenomenon would occur, where NG2 would be depleted from each target area and accumulate at their boundaries in an activity-dependent manner.