Central mu-opioid receptors (MORs) modulate affective responses to physical exercise. Individuals with higher aerobic fitness report greater exercise-induced mood improvements than those with lower fitness, but the link between cardiorespiratory fitness and the MOR system remains unresolved. Here we tested whether maximal oxygen uptake (VO2peak) and physical activity level are associated with cerebral MOR availability, and whether these phenotypes predict endogenous opioid release following aerobic exercise. We studied 64 healthy lean men who performed a maximal incremental cycling test for VO2peak determination, completed a questionnaire assessing moderate-to-vigorous physical activity (MVPA, min/week), and underwent positron emission tomography with [11C]carfentanil, a specific radioligand for MOR. A subset of 24 subjects underwent additional PET scan also after a one-hour session of moderate-intensity exercise. Higher VO2peak and self-reported MVPA level were associated with larger decrease in cerebral MOR binding after aerobic exercise in ventral striatum, orbitofrontal cortex and insula. That is, higher fit and more trained individuals showed greater opioid release acutely following exercise in brain regions especially relevant for reward and cognitive processing. Higher VO2peak also associated with lower baseline BPND in the reward and pain circuits, i.e., in frontal and cingulate cortices as well as in temporal lobes and subcortically in thalamus and putamen. We conclude that higher aerobic fitness and regular exercise training may induce neuroadaptation within the MOR system which might contribute to improved emotional and behavioural responses associated with long-term exercise.

中文翻译：

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有氧健身与健康人的大脑阿片受体的可用性和激活有关

中央阿片受体（MOR）调节对体育锻炼的情感反应。有氧健身度较高的人比健身度较低的人报告的运动诱发的情绪改善更大，但心肺功能适应性与MOR系统之间的联系仍未解决。在这里，我们测试了最大摄氧量（VO2peak）和体力活动水平是否与大脑MOR的可利用性有关，以及这些表型是否可预测有氧运动后内源性阿片样物质的释放。我们研究了64位健康的瘦男人，他们进行了最大增量循环测试以测定VO2peak，完成了调查问卷，评估了中度到剧烈的身体活动（MVPA，分钟/周），并使用[11C]芬太尼（一种特定的放射性配体）进行了正电子发射断层扫描对于MOR。一小时的中等强度运动后，也有24名受试者的子集进行了额外的PET扫描。有氧运动对腹侧纹状体，眶额皮质和岛状肌组织的较高的VO2peak和自我报告的MVPA水平与大脑MOR结合的较大降低有关。也就是说，身体健康和训练有素的个体在大脑区域运动后，尤其是与奖赏和认知加工有关的急性阿片类药物释放更大。较高的VO2peak还与奖励和疼痛回路（即额叶和扣带状皮层以及颞叶以及丘脑和壳状皮层中）的基线BPND降低相关。