Fig. 2.

Serum IGF-I is needed for exercise-induced vessel growth in the brain. (A) Exercise induces proliferation of endothelial cells only when serum IGF-I levels are normal. (Upper) Fluorescently labeled microphotograph of a newly formed brain vessel with BrdUrd⁺ nuclei co-labeled with tomato lectin in the cytoplasm. (Lower) Exercise (E) significantly increased the number of double-labeled BrdUrd⁺/lectin⁺ cells, compared with sedentary (S) mice in the cerebellum of control littermates but not in LID mice with low serum IGF-I (^*, P < 0.05 vs. sedentary; n = 4 animals per group). (B) Vessel density in the cerebellum increases after exercise only in control mice or in LID mice treated with IGF-I, but not in LID mice treated with saline while running (^**, P < 0.01 vs. sedentary mice; ^***, P < 0.001 vs. exercised LID mice). (C) Similarly, levels of CD31, an endothelial marker, increased only in exercised control mice. The upper gel shows a representative blot of CD31. The lower gel shows protein load per lane assessed by re-blotting with anti-PI3K. The histogram shows quantitation of CD31 blots after correcting for protein load (^***, P < 0.001 vs. sedentary controls; n = 4 per group). (D) Brain levels of VEGF were not modified by exercise. The upper gel shows representative VEGF blots after 1 month of exercise. The lower gel shows the control for protein load. Quantitation is shown in the histogram (n = 4). (E) On the contrary, brain levels of HIF-1α were increased after exercise only when serum IGF-I levels are normal. The upper gel shows a representative HIF-1α blot after 1 month of exercise. The lower gel shows the PI3K control re-blot. Histograms illustrate significant increases in exercised control mice (^***, P < 0.001; n = 4).