Fate of neuron-glia synapses during proliferation and differentiation of NG2 cells

Abstract

Progenitor cells expressing proteoglycan NG2 (also known as oligodendrocyte precursor cells or polydendrocytes) are widespread in the grey and white matter of the CNS; they comprise 8-9% of the total cell population in adult white matter, and 2-3% of total cells in adult grey matter. NG2 cells have a complex stellate morphology, with highly branched processes that may extend more than 100 lm around the cell body. NG2 cells express a complex set of voltage-gated channels, AMPA ⁄ kainate and ⁄ or c-aminobutyric acid (GABA) A receptors, and receive glutamatergic and ⁄ or GABAergic synaptic input from neurons. In every region of the brain NG2 cells are found as proliferative cells, and the fraction of actively cycling NG2 cells is quite high in young as well as in adult animals. During development NG2 cells either differentiate into myelinating oligodendrocytes (and possibly also few astrocytes and neurons) or persist in the brain parenchyma as NG2 cells. This review highlights new findings related to the morphological and electrophysiological changes of NG2 cells, and the fate of synaptic input between neurons and NG2 cells during proliferation and differentiation of these cells in the neonatal and adult nervous system of rodents.

Neuroglial Transmission

“…While there is evidence for GABA A OPCs receive input from several glutamatergic and/or GABAergic axons, which disconnect when the OPCs develop into premyelinating oligodendrocytes (124,208,448). Such direct neuronal control of OPCs persists even in the mature brain (124).…”

“…Such direct neuronal control of OPCs persists even in the mature brain (124). It may underlie the experienceinduced changes in myelination, indicated by increased fractional anisotropy observed in the human brain by diffusion tensor magnetic resonance imaging.…”

“…Mature myelinating oligodendrocytes are formed from oligodendrocyte precursor cells (OPCs), which can be identified by their expression of the proteoglycan NG2 and are also called polydendrocytes due to their highly branched processes. OPCs are present also in the adult brain, constituting ϳ9 and ϳ3% of the total cell counts in white and grey matter, respectively, and are regulated by synaptic glutamatergic and GABAergic input (124). Like astrocytes, oligodendrocytes are able to respond to changes in the cellular and extracellular environment.…”

Neuron-NG2 Cell Synapses: Novel Functions for Regulating NG2 Cell Proliferation and Differentiation

“…Thus, the recorded current is hypothesized to be from both progeny cells. Second, morphological analysis indicated that each daughter cell has approximately half the number of glutamic acid decarboxylase 65- (GAD65-) positive putative GABAergic terminals in the parent cell [21, 88]. Altogether, these data indicated that NG2 cells are continuously kept functional; certain synaptic contacts are passed onto the resulting progenies during cell division.…”

“…Before the formation of a functional myelin sheath, NG2 cells passes through two developmental stages, namely, premyelinating oilgodendrocytes and mature oligodendrocytes [8, 95, 96]. During the process of NG2 cell differentiation, the synaptic communication between neurons and NG2 cells is rapidly lost (Figure 5) [87, 88]. The differentiation of NG2 cells is characterized by the expression of stage-specific proteins, which are finely tuned by a series of transcription factors and accompanied by the expression of specific molecular markers [8, 97–99].…”