Department of Biology, University of California, Riverside, CA 92521, USA.
J Exp Biol. 2010 Feb 1;213(3):510-9. doi: 10.1242/jeb.029074.
Voluntary activity is a complex trait, comprising both behavioral (motivation, reward) and anatomical/physiological (ability) elements. In the present study, oxygen transport was investigated as a possible limitation to further increases in running by four replicate lines of mice that have been selectively bred for high voluntary wheel running and have reached an apparent selection limit. To increase oxygen transport capacity, erythrocyte density was elevated by the administration of an erythropoietin (EPO) analogue. Mice were given two EPO injections, two days apart, at one of two dose levels (100 or 300 microg kg(-1)). Hemoglobin concentration ([Hb]), maximal aerobic capacity during forced treadmill exercise (VO2,max) and voluntary wheel running were measured. [Hb] did not differ between high runner (HR) and non-selected control (C) lines without EPO treatment. Both doses of EPO significantly (P<0.0001) increased [Hb] as compared with sham-injected animals, with no difference in [Hb] between the 100 microg kg(-1) and 300 microg kg(-1) dose levels (overall mean of 4.5 g dl(-1) increase). EPO treatment significantly increased VO2,max by approximately 5% in both the HR and C lines, with no dosexline type interaction. However, wheel running (revolutions per day) did not increase with EPO treatment in either the HR or C lines, and in fact significantly decreased at the higher dose in both line types. These results suggest that neither [Hb] per se nor VO2,max is limiting voluntary wheel running in the HR lines. Moreover, we hypothesize that the decrease in wheel running at the higher dose of EPO may reflect direct action on the reward pathway of the brain.
自愿活动是一种复杂的特征，包括行为（动机、奖励）和解剖/生理（能力）元素。在本研究中，作为进一步增加跑步的可能限制因素，研究了氧气输送，研究对象是经过选择性繁殖的具有高自愿轮跑能力并达到明显选择极限的四个重复系小鼠。为了提高氧气输送能力，通过给予促红细胞生成素（EPO）类似物来提高红细胞密度。小鼠接受两次 EPO 注射，间隔两天，剂量水平为两种（100 或 300μg/kg）之一。血红蛋白浓度 ([Hb])、强制跑步机运动（VO2，max）和自愿轮跑时的最大有氧能力进行了测量。未经 EPO 处理时，高跑步者（HR）和非选择对照（C）系之间的 [Hb] 没有差异。与假注射动物相比，两种剂量的 EPO 均显著（P<0.0001）增加了 [Hb]，100μg/kg(-1) 和 300μg/kg(-1) 剂量水平之间 [Hb] 没有差异（总体平均增加 4.5 g dl(-1)）。EPO 处理使 HR 和 C 系的 VO2，max 分别增加了约 5%，HR 和 C 系之间没有剂量-系类型相互作用。然而，EPO 处理并未使 HR 或 C 系的轮跑（每天转数）增加，事实上，两种系类型的高剂量都显著减少。这些结果表明，无论是 [Hb] 本身还是 VO2，max 都不是 HR 系自愿轮跑的限制因素。此外，我们假设 EPO 更高剂量下轮跑减少可能反映了对大脑奖励途径的直接作用。
