[Abstract Title]. - Society for Neuroscience

Program#/Poster#: 242.17/I12
Topic: B.11.a. Synapses
Support: NIH/NINDS NS051509
Title: Synaptic connectivity is a universal property of NG2+ cells that is lost upon differentiation
Authors: *L. M. DE BIASE 1 , S. KANG 1 , A. NISHIYAMA 2 , D. E. BERGLES 1 ;
1 Neurosci., Johns Hopkins Sch. of Med., Baltimore, MD; 2 Physiol. and Neuorbiology, Univ. of
Connecticut, Storrs, CT
Abstract: Glial cells expressing the NG2 proteoglycan (NG2+ cells) serve as progenitors for
oligodendrocytes during development yet remain abundant in gray and white matter of the
mature CNS, suggesting that they perform additional roles. Unlike other glia, NG2+ cells form
synapses with neurons, perhaps to allow rapid, activity-dependent regulation of this ubiquitous
group of progenitors. While synaptogenesis and circuit maturation among neurons has been well
described, little is known about the developmental onset of neuron-NG2+ cell synaptic
communication, the variability of synaptic connectivity among NG2+ cells, or the changes that
occur in this form of signaling as NG2+ cells differentiate into oligodendrocytes. We used NG2-
DsRed BAC transgenic mice to study how NG2+ cell properties change during development in
the corpus callosum (CC), hippocampus (HC) and cerebellum (CB). To obtain an unbiased
assessment of neuron-NG2+ cell synaptic connectivity, we made whole-cell recordings from
NG2+ cells in acute brain slices and focally applied hypertonic solution to force fusion of primed
synaptic vesicles. Hypertonic challenge reliably induced bursts of AMPA receptor-mediated
mEPSCs that were blocked by NBQX. The number of mEPSCs evoked increased as animals
matured (P5-8: 12 ± 11; P12-15: 88 ± 51; P20-26: 55 ± 43; P40-45: 89 ± 48), paralleling the
development of neuron-neuron synapses. Although nearly all NG2+ cells exhibited voltage-gated
Na+ channel (NaV) currents (141/144 cells; NaV current density: 22 ± 1 pA/pF), the extent of
synaptic connectivity was not correlated with NaV current amplitude (P = 0.74) and NG2+ cells
did not fire action potentials in response to current injection in any brain region or developmental
time point sampled. To study how the membrane properties of NG2+ cells change as they
differentiate, we generated NG2-DsRed;NG2-CreER;Z/EG triple transgenic mice. In these mice,
tamoxifen injection induced GFP expression in NG2+ cells, yielding DsRed+GFP+ cells. As
NG2+ cells differentiated, their progeny continued to express GFP while DsRed expression was
lost as NG2 promoter activity ceased. A comparison of the physiological properties of
DsRed+GFP+, weakly DsRed+GFP+, and DsRed-GFP+ cells, revealed that NG2+ cells rapidly
lose synaptic contacts and cease expressing NaV as they began to differentiate. Our data suggest
that NG2+ cell synaptic inputs are established and refined concurrently with neuronal
synaptogenesis and that both synapses and NaV expression are maintained only prior to
differentiation into oligodendrocytes.
Disclosures: L.M. De Biase, None; A. Nishiyama, None; S. Kang, None; D.E. Bergles, None.