1. Altered biological activity of peroxynitrite-modified nerve growth factor (NGF) compared to native NGF in vitro. A: Dorsal root ganglia (DRG) neurons that are neurofilament-immunoreactive by immunofluorescence at 4 DIV (upper panel) and 28 DIV (lower panel) treated with native NGF (left) or peroxynitrite-modified NGF (right), 25X, Bar = 50 μm. B, C: Peroxynitrite-modified NGF treatment caused a reduction in cell soma of DRG neurons expressed as mean cross-sectional area (μm2). B: 4 DIV (n=30, P< 0.001); C: 28 DIV (n=30, P< 0.05); there was also a marked reduction in neural processes treated at both time-points. (D) Reduction in DRG cell survival (6 fields of 0.39 mm2/condition) in peroxynitrite-modified NGF at 4 DIV (P< 0.001). At 28 DIV, there was not significant reduction in cell number between native NGF vs. peroxynitrite-modified NGF, indicating that nitrated NGF loses capacity for maintaining the survival of newly cultured DRG neurons or maintaining the phenotype of mature and fully developed DRG cultured neurons.