Center for Respiratory Research and Rehabilitation, University of Florida, Gainesville, Florida.
Department of Physical Therapy, University of Florida, Gainesville, Florida.
Am J Physiol Regul Integr Comp Physiol. 2020 Jun 1;318(6):R1058-R1067. doi: 10.1152/ajpregu.00010.2020. Epub 2020 Apr 29.
Circadian rhythms are endogenous and entrainable daily patterns of physiology and behavior. Molecular mechanisms underlie circadian rhythms, characterized by an ~24-h pattern of gene expression of core clock genes. Although it has long been known that breathing exhibits circadian rhythms, little is known concerning clock gene expression in any element of the neuromuscular system controlling breathing. Furthermore, we know little concerning gene expression necessary for specific respiratory functions, such as phrenic motor plasticity. Thus, we tested the hypotheses that transcripts for clock genes (, , , and ) and molecules necessary for phrenic motor plasticity (, , , and ) oscillate in regions critical for phrenic/diaphragm motor function via RT-PCR. Tissues were collected from male Sprague-Dawley rats entrained to a 12-h light-dark cycle at 4 zeitgeber times (ZT; = 8 rats/group): ZT5, ZT11, ZT17, and ZT23; ZT0 = lights on. Here, we demonstrate that ) circadian clock genes (, , , and ) oscillate in regions critical for phrenic/diaphragm function, including the caudal medulla, ventral C3-C5 cervical spinal cord, and diaphragm; ) the clock protein BMAL1 is localized within CtB-labeled phrenic motor neurons; ) genes necessary for intermittent hypoxia-induced phrenic/diaphragm motor plasticity ( and ) oscillate in the caudal medulla and ventral C3-C5 spinal cord; and ) there is higher intensity of immunofluorescent BDNF protein within phrenic motor neurons at ZT23 compared with ZT11 ( = 11 rats/group). These results suggest local circadian clocks exist in the phrenic motor system and confirm the potential for local circadian regulation of neuroplasticity and other elements of the neural network controlling breathing.
昼夜节律是生理和行为的内源性和可诱导的日常模式。分子机制是昼夜节律的基础，其特征是核心时钟基因的表达呈约 24 小时模式。尽管人们早就知道呼吸具有昼夜节律，但对于控制呼吸的神经肌肉系统的任何元素中的时钟基因表达知之甚少。此外，我们对特定呼吸功能（如膈神经运动可塑性）所需的基因表达知之甚少。因此，我们通过 RT-PCR 测试了以下假设：时钟基因（、、、和）的转录本和膈神经运动可塑性所必需的分子（、、、和）在通过膈神经/膈肌运动功能的关键区域中呈振荡状态。组织取自适应 12 小时明暗循环的雄性 Sprague-Dawley 大鼠，在 4 个 Zeitgeber 时间（ZT；每组 8 只大鼠）采集：ZT5、ZT11、ZT17 和 ZT23；ZT0 = 光照。在这里，我们证明了）昼夜节律基因（、、、和）在与膈神经/膈肌功能相关的关键区域呈振荡状态，包括尾髓、颈 3-5 脊髓腹侧和膈肌；）时钟蛋白 BMAL1 位于 CtB 标记的膈神经运动神经元内；）间歇性低氧诱导的膈神经/膈肌运动可塑性所必需的基因（和）在尾髓和颈 3-5 脊髓腹侧呈振荡状态；）与 ZT11 相比，ZT23 时膈神经运动神经元内的 BDNF 蛋白免疫荧光强度更高（每组 11 只大鼠）。这些结果表明，膈神经运动系统中存在局部昼夜节律钟，并证实了局部昼夜节律调节神经可塑性和控制呼吸的神经网络其他元素的潜力。
