Figure 3. Western blotting for tissue plasminogen activator (tPA) expression in the visual cortex during post-natal development. tPA has a molecular weight corresponding to 67 kDa. The staining protocol was optimized to produce a single distinct band. Data at the top of the bands shows the tPA/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) ratio (%) at each age (mean±SD, n=10). Microdensitometry revealed that tPA is not expressed at PW1 but is present at all other ages sampled. Comparisons were made using a least significant difference (LSD) multiple comparison t-test. tPA reaches its highest expression at PW5 and then declines. Protein expression at PW3, PW7, and PW5 was significantly higher than at PW14 (p<0.05 and 0.01 respectively). The peak value at PW5 was significantly higher than that seen at PW3 and PW7 (p<0.05).