Figure 5:

Exercise training increases endogenous opioid content in the midbrain periaqueductal gray area (PAG). A. After 5 weeks of exercise training or sedentary conditions, PAG sections from nerve-injured animals were labeled with antibodies to β-endorphin (a,b) or met-enkephalin (c,d). Images were magnified 20x. B. Densitometry was performed on 10 images from 5 animals per group. *P < 0.05 compared to spinal nerve-ligated, sedentary animals. Data shown as mean with 95% two-tailed confidence intervals.