mRNA levels of three nerve-related genes affected by fracture in young, adult, and older rats. The first two genes were up-regulated at all three ages (0.4 week (top graph) and 2 weeks (middle graph) exceed 0 time control at P < 0.001), while the third gene was down-regulated at all three ages (0.4 week significantly less than 0 time control at P < 0.001). Rats were 6, 26 and 52 weeks of age at fracture respectively. Samples were collected at the indicated times after fracture. The 0 time samples were no-fracture controls. Each bar is the mRNA expression level for the indicated gene for the average ± SEM of three DNA microarrays in arbitrary units of fluorescence. mRNA from two rats of the same age and time after fracture were pooled for each array. Gene identifications are shown with their GenBank accession number. Axonal glycoprotein (TAG-1) is also known as contactin 2.