Selective Breeding and Exercise Affect Midbrain and PAG Volume

Abstract

Inter‐specific comparative studies have shown that the size of brain structures is often correlated with behavioral propensities or capabilities. Life experiences can contribute to variation in brain‐behavior associations. For example, studies of rodents and humans have shown that environmental enrichment, exercise, and even video games can change the volume of structures within the brain, in as little as 7 days in rodents. More generally, exercise can favorably influence the brain by facilitating different neuroadaptive and neuroprotective processes that cause regions of the brain to change in size. One important region potentially influenced by exercise is the midbrain, which serves key functions in both movement and reward. Within the midbrain, an area of particular interest is the periaqueductal gray (PAG), which functions in suppressing pain and influences anxiety and fear. Another midbrain region, the red nucleus, is involved in limb motor coordination and is the site of origin for dopaminergic neurons. We investigated whether selective breeding for high voluntary exercise and/or wheel access had any significant impact on these regions. We studied 8 lines of mice: 4 selectively‐bred high runner (HR) lines and 4 non‐selected control (C) lines. 50 HR mice and 50 C mice were separated into two groups: wheel access or no wheel access for 10 weeks, beginning at weaning. After the 10 weeks, brains were dissected, sliced at 40 μm, Nissl stained, and photographed. These photographs were traced using ImageJ software to calculate the area, cell quantity, and region volume. Results from analysis of the whole midbrain volume indicate that it was not affected by wheel access but is larger in HR mice, the latter result confirming results of a previous study that used ex vivo magnetic resonance imaging of whole brains. Thus, under these conditions, a genetic history of selective breeding for high voluntary wheel running plays a greater role in affecting midbrain volume than does chronic physical exercise. Linetype and wheel access had an interactive effect on PAG volume: wheel access increased volume in C mice, but decreased it in HR mice, with no main effect of either linetype or wheel access. This result indicates an interesting relationship between selective breeding and exercise that may have implications for the modulation of pain and anxiety. Analysis of the red nucleus is in progress. Previous studies have shown that HR mice respond differently to dopamine‐targeting drugs; therefore, we hypothesize that HR mice may have evolved structural changes in this region.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.