You know that wonderful high that often follows a good workout? Many post-menopausal women don’t know it, and researchers at the University of Missouri now think they know why. A U of Missouri news release reports that the researchers believe they found a connection between lack of ovarian hormones and changes in the brain’s pleasure center, a hotspot in the brain that processes and reinforces messages related to reward, pleasure, activity and motivation for physical exercise. The researchers compared the physical activity of rats that were highly fit to rats that were less fit, studying rats’ use of running wheels set up in the cages before and after the rats had their ovaries removed. They also examined gene expression changes of dopamine receptors within the brain’s pleasure center. Here’s what they found: The high-fit rat group had more activity in the brain’s pleasure center, which correlated with greater wheel running before and after the loss of ovarian hormones. But…. the high-fit rats still saw a significant reduction in wheel running after their ovaries were removed, and that reduction in running correlated with a reduction in their dopamine signaling levels, indicating that the brain’s pleasure center could be involved.