Circadian regulation of locomotor activity and skeletal muscle gene expression in the horse.
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.
Martin
Ann-Marie
AM
School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin, Ireland.
Elliott
Jeffrey A
JA
Duffy
Pat
P
Blake
Catriona M
CM
Ben Attia
Sarra
S
Katz
Lisa M
LM
Browne
John A
JA
Gath
Vivian
V
McGivney
Beatrice A
BA
Hill
Emmeline W
EW
Murphy
Barbara A
BA
D056044:Actigraphy / Q000295:instrumentation; D000204:Activity Cycles; D000818:Animals; D001522:Behavior, Animal; D001706:Biopsy; D056926:CLOCK Proteins / Q000235:genetics*; D002940:Circadian Rhythm / Q000235:genetics; D005260:Female; D005786:Gene Expression Regulation; D006736:Horses / Q000235:genetics / Q000502:physiology*; D006799:Housing, Animal; D009043:Motor Activity / Q000235:genetics; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D017440:Photoperiod; D020133:Reverse Transcriptase Polymerase Chain Reaction
D056926:CLOCK Proteins