Figure 4.

The effects of NG2 cells on axonal outgrowth. A, B, Purified NG2 cell culture stained for NG2 (A) and astrocyte culture stained for GFAP (B). Nuclei are labeled with DAPI (blue). C–F, Examples of neurofilament (SMI31)-positive axons from P1 hippocampal neurons grown on confluent cultures of NG2 cells (C), astrocytes (D), NIH 3T3 cells (E), or directly on PLL (F). Scale bar, 24 μm. G, H, Quantification of total axonal length per neuron (G) and the length of the longest axon (H) of neurons grown on each type of substrate. NG2 cells and astrocytes promoted axonal growth of hippocampal neurons by twofold compared with NIH 3T3 cells or PLL. Means ± SEs from three independent experiments were analyzed by one-way ANOVA followed by Tukey's post test comparing all paired data sets. Groups of values with asterisks are statistically different at P < 0.001 for both G and H. I, Neurite lengths of hippocampal neurons in the inverted cocultures (I_OPC, I_Astro, I_3T3) were compared with those of hippocampal neurons contacting the non-neuronal cells (OPCs, astrocytes, NIH 3T3). In the absence of direct contact, NG2 cells did not promote axonal growth. The values for the inverted NG2 cell cultures were not statistically different from those of neurons grown on PLL or NIH 3T3 cells (ns, not significant; P > 0.05, one-way ANOVA with Tukey's post test comparing I-OPCs to PLL and NIH 3T3 cells). Data are expressed as means ± SEs.