School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin, Ireland.
J Appl Physiol (1985). 2010 Nov;109(5):1328-36. doi: 10.1152/japplphysiol.01327.2009. Epub 2010 Sep 16.
Circadian rhythms are innate 24-h cycles in behavioral and biochemical processes that permit physiological anticipation of daily environmental changes. Elucidating the relationship between activity rhythms and circadian patterns of gene expression may contribute to improved human and equine athletic performance. Six healthy, untrained mares were studied to determine whether locomotor activity behavior and skeletal muscle gene expression reflect endogenous circadian regulation. Activity was recorded for three consecutive 48-h periods: as a group at pasture (P), and individually stabled under a light-dark (LD) cycle and in constant darkness (DD). Halter-mounted Actiwatch-L data-loggers recorded light exposure and motor activity. Analysis of mean activity (average counts/min, activity bouts/day, average bout length) and cosinor parameters (acrophase, amplitude, mesor, goodness of fit) revealed a predominantly ultradian (8.9 ± 0.7 bouts/24 h) and weakly circadian pattern of activity in all three conditions (P, LD, DD). A more robust circadian pattern was observed during LD and DD. Muscle biopsies were obtained from the middle gluteal muscles every 4 h for 24 h under DD. One-way qRT-PCR results confirmed the circadian expression (P < 0.05) of six core clock genes (Arntl, Per1, Per2, Nr1d1, Nr1d2, Dbp) and the muscle-specific transcript, Myf6. Additional genes, Ucp3, Nrip1, and Vegfa, demonstrated P values approaching significance. These findings demonstrate circadian regulation of muscle function and imply that human management regimes may strengthen, or unmask, equine circadian behavioral outputs. As exercise synchronizes circadian rhythms, our findings provide a basis for future work determining peak times for training and competing horses, to reduce injury and to achieve optimal performance.
昼夜节律是行为和生化过程中内在的 24 小时周期，使生理能够预测日常环境变化。阐明活动节律与基因表达的昼夜节律模式之间的关系，可能有助于提高人类和马的运动表现。本研究旨在确定运动行为和骨骼肌基因表达是否反映了内在的昼夜节律调节，为此选择 6 匹健康、未经训练的母马进行研究。连续 3 个 48 小时期间进行研究：作为一个组在牧场上（P），以及分别在明暗（LD）循环和持续黑暗（DD）下圈养。颈圈式 Actiwatch-L 数据记录器记录光照暴露和运动活动。平均活动（平均每分钟计数、每日活动发作、平均发作长度）和余弦参数（高峰时间、振幅、中值、拟合优度）的分析表明，在所有 3 种条件下（P、LD、DD），活动都呈现出主要的超昼夜（8.9±0.7 次/24 小时）和弱昼夜节律模式。在 LD 和 DD 期间观察到更稳健的昼夜节律模式。在 DD 下，每 4 小时从中间臀肌中采集肌肉活检 24 小时。qRT-PCR 结果证实了 6 个核心时钟基因（Arntl、Per1、Per2、Nr1d1、Nr1d2、Dbp）和肌肉特异性转录物 Myf6 的昼夜表达（P<0.05）。其他基因 Ucp3、Nrip1 和 Vegfa 的 P 值也接近显著水平。这些发现表明肌肉功能受到昼夜节律的调节，并暗示人类管理方案可能会增强或揭示马的昼夜行为输出。由于运动使昼夜节律同步，因此我们的发现为未来确定训练和比赛马匹的最佳时间提供了基础，以减少受伤并实现最佳表现。
