Rodrigues Karla L, Souza Juliana R, Bazilio Darlan S, de Oliveira Mauro, Moraes Melina P S, Moraes Davi J A, Machado Benedito H
Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, 14049-900, Brazil.
Exp Physiol. 2021 Mar;106(3):759-770. doi: 10.1113/EP089323. Epub 2021 Feb 6.
What is the central question of this study? Do mice submitted to sustained hypoxia present autonomic and respiratory changes similarly to rats? What is the main finding and its importance? Arterial pressure in the normal range, reduced baseline heart rate and tachypnoea were observed in behaving sustained hypoxia mice. Recordings in the in situ preparation of mice submitted to sustained hypoxia show an increase in cervical vagus nerve activity and a simultaneous reduction in thoracic sympathetic nerve activity correlated with changes in the respiratory cycle. Therefore, mice are an important model for studies on the modulation of sympathetic activity to the cardiovascular system and the vagus innervation of the upper airways due to changes in the respiratory network induced by sustained hypoxia.
Short-term sustained hypoxia (SH) in rats induces sympathetic overactivity and hypertension due to changes in sympathetic-respiratory coupling. However, there are no consistent data about the effect of SH on mice due to the different protocols of hypoxia and difficulties associated with the handling of these rodents under different experimental conditions. In situ recordings of autonomic and respiratory nerves in SH mice have not been performed yet. Herein, we evaluated the effects of SH ( = 0.1 for 24 h) on baseline mean arterial pressure (MAP), heart rate (HR), respiratory frequency (f ) and responses to chemoreflex activation in behaving SH mice. A characterization of changes in cervical vagus (cVN), thoracic sympathetic (tSN), phrenic (PN) and abdominal (AbN) nerves in SH mice using the in situ working heart-brainstem preparation was also performed. SH mice presented normal MAP, significant reduction in baseline HR, increase in baseline f , as well as increase in the magnitude of bradycardic response to chemoreflex activation. In in situ preparations, SH mice presented a reduction in PN discharge frequency, and increases in the time of expiration and incidence of late-expiratory bursts in AbN activity. Nerve recordings also indicated a significant increase in cVN activity and a significant reduction in tSN activity during expiration in SH mice. These findings make SH mice an important experimental model for better understanding how changes in the respiratory network may impact on the modulation of vagal control to the upper airways, as well as in the sympathetic activity to the cardiovascular system.
本研究的核心问题是什么？经历持续性低氧的小鼠是否会出现与大鼠类似的自主神经和呼吸变化？主要发现及其重要性是什么？在行为学实验中，经历持续性低氧的小鼠动脉血压处于正常范围，基础心率降低且呼吸急促。对经历持续性低氧的小鼠进行原位制备记录显示，颈迷走神经活动增加，同时胸交感神经活动减少，这与呼吸周期的变化相关。因此，由于持续性低氧引起的呼吸网络变化，小鼠是研究交感神经对心血管系统的调节以及上呼吸道迷走神经支配的重要模型。
大鼠短期持续性低氧（SH）由于交感神经 - 呼吸耦合的变化会导致交感神经活动亢进和高血压。然而，由于低氧方案不同以及在不同实验条件下处理这些啮齿动物存在困难，关于SH对小鼠影响的一致数据并不存在。尚未对SH小鼠的自主神经和呼吸神经进行原位记录。在此，我们评估了SH（ = 0.1，持续24小时）对行为学实验中SH小鼠的基础平均动脉压（MAP）、心率（HR）、呼吸频率（f）以及化学反射激活反应的影响。我们还使用原位工作心脏 - 脑干制备方法对SH小鼠的颈迷走神经（cVN）、胸交感神经（tSN）、膈神经（PN）和腹神经（AbN）的变化进行了表征。SH小鼠MAP正常，基础HR显著降低，基础f增加，以及对化学反射激活的心动过缓反应幅度增加。在原位制备中，SH小鼠PN放电频率降低，呼气时间增加，AbN活动中呼气后期爆发的发生率增加。神经记录还表明，SH小鼠在呼气期间cVN活动显著增加，tSN活动显著减少。这些发现使SH小鼠成为一个重要的实验模型，有助于更好地理解呼吸网络的变化如何影响对上呼吸道迷走神经控制的调节以及对心血管系统的交感神经活动。
