School of Medicine of Ribeirão Preto, Department of Physiology, University of São Paulo, Ribeirão Preto, SP, Brazil.
Paulista School of Medicine, Department of Biophysics, Federal University of São Paulo, São Paulo, Brazil.
J Physiol. 2019 Apr;597(7):1935-1956. doi: 10.1113/JP277030. Epub 2019 Feb 28.
Acute hypoxia induces active expiration in rectus abdominis (RA) muscles in conscious freely moving rats, although its overall contribution is smaller than in internal oblique (IO) muscles. Tonically active and silent RA motoneurons were identified in in vitro preparations of rat spinal cords. Sustained hypoxia (SH) increased the synaptic strength and induced morphological changes in tonically active RA motoneurons. Expiratory RA motoneurons were recorded in the in situ preparation and SH enhanced both the excitability and the synaptic transmission in those firing during the stage 2 expiration. The present study contributes to a better understanding of the mechanisms involved in SH recruitment of RA motoneurons to induce active expiration in rats.
Rectus abdominis (RA) motoneurons translate the complex respiratory brainstem inputs into effective muscle contractions. Despite their fundamental role in respiration, their functional and morphological properties are not fully understood. In the present study, we investigated for the first time the contribution of RA muscle to active expiration and characterized RA motoneurons regarding their electrical, molecular and morphological profiles in control rats and in rats submitted to sustained hypoxia (SH), which induces chronic recruitment of abdominal muscles. Electromyographic experiments in conscious freely moving control rats and SH rats showed that RA contributes to active expiration induced by acute hypoxia, although its contribution is smaller than in internal oblique muscles. in vitro whole-cell patch clamp recordings from RA motoneurons revealed two populations of cells: tonically active and silent. SH induced hyperexcitability in the tonically active cells by changing their action potential properties, and EPSCs. Three-dimensional morphological reconstructions of these cells showed that SH increased the dendritic complexity, stimulated the appearance of dendrite spines, and increased the somatic area and volume. Physiologically identified RA motoneurons, firing in two distinct phases of expiration, were recorded in the brainstem-spinal cord in situ preparation of rats. SH increased the firing frequency and EPSCs of neurons firing during stage 2 expiration. Taken together, our results show that RA motoneurons reconfigure their biophysical properties, morphology and synaptic strength to produce an appropriate expiratory drive in response to SH in rats.
急性缺氧会引起清醒自由活动大鼠腹直肌（RA）的主动呼气，尽管其总体贡献小于内斜肌（IO）。在大鼠脊髓的体外标本中鉴定出具有紧张性活动和安静性的 RA 运动神经元。持续缺氧（SH）增加了紧张性活动的 RA 运动神经元的突触强度，并诱导其形态变化。在原位标本中记录到呼气性 RA 运动神经元，SH 增强了在第 2 呼气期放电的运动神经元的兴奋性和突触传递。本研究有助于更好地理解 SH 募集 RA 运动神经元以诱导大鼠主动呼气的相关机制。
腹直肌（RA）运动神经元将复杂的脑干呼吸输入转化为有效的肌肉收缩。尽管它们在呼吸中起着至关重要的作用，但它们的功能和形态特征尚未完全了解。在本研究中，我们首次研究了 RA 肌肉对主动呼气的贡献，并在对照大鼠和接受持续缺氧（SH）的大鼠中对 RA 运动神经元的电、分子和形态特征进行了特征描述，SH 可诱导腹部肌肉的慢性募集。在清醒自由活动的对照大鼠和 SH 大鼠中进行的肌电图实验表明，RA 有助于急性缺氧诱导的主动呼气，尽管其贡献小于内斜肌。来自 RA 运动神经元的体外全细胞膜片钳记录显示存在两种细胞群体：紧张性活动和安静性。SH 通过改变其动作电位特性和 EPSC 使紧张性活动细胞产生超兴奋性。对这些细胞的三维形态重建表明，SH 增加了树突复杂性，刺激了树突棘的出现，并增加了体细胞面积和体积。在大鼠脑干-脊髓原位标本中记录到在两个呼气阶段具有不同放电模式的生理鉴定的 RA 运动神经元。SH 增加了第 2 呼气期放电神经元的放电频率和 EPSC。总之，我们的结果表明，RA 运动神经元通过改变其生物物理特性、形态和突触强度，在大鼠中对 SH 做出适当的呼气驱动反应。
