The Effect of Selective Breeding for High Voluntary Wheel‐Running Behavior on Femoral Nutrient Canal Abundance and Size
Authors: Schwartz Nicolas Lawrence , Patel Biren A. , Garland Theodore , Horner Angela M. 
Published: June 2021

Mammalian skeletal tissue is aerobic, and has relatively high oxygen demand, presumably a result of the processes of bone modelling and remodeling. These processes are often associated with microfractures accrued from load bearing during locomotion, but they are also pivotal during bone growth and in the deposition/requisition of calcium from bone. Long bones receive blood from three sources, with the nutrient artery supplying the bulk of total blood volume in mammals (50–70%). Historically, measurement of blood flow into bones has been hindered by the compact bone surrounding the vessels. However, the size of the nutrient artery can be estimated from the dimensions of the nutrient canal, which is present long after the vascular tissue has degenerated, and so can be quantified in skeletal materials, including fossils. The literature on nutrient arteries/canals is sparse, with most studies consisting of anatomical descriptions from surgical proceedings, and only a few investigating the links between nutrient canals and physiology or behavior. Moreover, no study to date has accurately reconstructed the size and shape of the nutrient canal. The primary objective of this study was to model the nutrient canal of the femur in mice with known physiological and behavioral differences. For this study, mice from an artificial selection experiment for high voluntary wheel‐running behavior were used. Mice from the four replicate High Runner (HR) lines of the experiment are known to differ from four non‐selected Control (C) lines in both locomotor and metabolic activity, with HR mice having increased voluntary wheel‐running behavior and maximal aerobic capacity (VO2max) during forced treadmill exercise. 137 femora from adult mice (average age of approximately 7.5 months) of the 11th generation of this selection experiment were μCT scanned. Three‐dimensional virtual reconstructions of nutrient canals were measured for minimum cross‐sectional area (as an index of blood flow). Nutrient canals varied far more in number and shape than prior descriptions would indicate, regardless of genetic background (i.e., HR vs. C lines) or sex. Canals adopted non‐linear shape and pathing as they traversed from the periosteum to the medullary cavity, occasionally even branching within the cortical bone. Additionally, mice from both HR and C lines averaged more than four nutrient canals per femur, a stark contrast to the 1–2 nutrient canals described for femora from rats, pigs, and humans in prior literature. Mice from HR lines had significantly larger nutrient canal area than C lines, which was not the result of an increase in the number of nutrient canals, but rather an increase in their average size. This study demonstrates that mice with an evolutionary history of increased locomotor activity and maximal aerobic metabolic rate have a concomitant increase in the size of their nutrient canals. While the primary determinant of nutrient canal size is currently unknown, the present results bolster the use of nutrient canal size as a paleoindicator of aerobically supported levels of physical activity.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.