Effect of age and IGF-1 on axon number, density, and diameter. Quantification of histologic images reveals a significant effect of IGF-1 on (A) axons per nerve, (B) axon density (axons per mm2), and (C) average axonal diameter. Although there were differences due to age for axons per nerve and axon density, these were not statistically significant. Data are expressed as mean ± standard error *P < 0.05. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]