Marschand Rachel E, Wilson Jenna L, Burleson Mark L, Crossley Dane A, Hedrick Michael S
Developmental Integrative Biology Research Cluster, Department of Biological Sciences, University of North Texas, Denton, TX 76203, United States.
Developmental Integrative Biology Research Cluster, Department of Biological Sciences, University of North Texas, Denton, TX 76203, United States.
Respir Physiol Neurobiol. 2014 Aug 15;200:25-32. doi: 10.1016/j.resp.2014.05.006. Epub 2014 May 27.
The American alligator (Alligator mississippiensis) is a semi-aquatic diving reptile that has a periodic breathing pattern. Previous work identified pulmonary stretch receptors, that are rapidly and slowly adapting, as well as intrapulmonary chemoreceptors (IPC), sensitive to CO2, that modulate breathing patterns in alligators. The purpose of the present study was to quantify the effects of prolonged lung inflation and deflation (simulated dives) on pulmonary stretch receptors (PSR) and/or IPC discharge characteristics. The effects of airway pressure (0-20 cm H2O), hypercapnia (7% CO2), and hypoxia (5% O2) on dynamic and static responses of PSR were studied in juvenile alligators (mean mass=246 g) at 24°C. Alligators were initially anesthetized with isoflurane, cranially pithed, tracheotomized and artificially ventilated. Vagal afferent tonic and phasic activity was recorded with platinum hook electrodes. Receptor activity was a mixture of slowly adapting PSR (SAR) and rapidly adapting PSR (RAR) with varying thresholds and degrees of adaptation, without CO2 sensitivity. Receptor activity before, during and after 1 min periods of lung inflation and deflation was quantified to examine the effect of simulated breath-hold dives. Some PSR showed a change in dynamic response, exhibiting inhibition for several breaths after prolonged lung inflation. Following 1 min deflation, RAR, but not SAR, exhibited a significant potentiation of burst frequency relative to control. For SAR, the post-inflation receptor inhibition was blocked by CO2 and hypoxia; for RAR, the post-inflation inhibition was potentiated by CO2 and blocked by hypoxia. These results suggest that changes in PSR firing following prolonged inflation and deflation may promote post-dive ventilation in alligators. We hypothesize that PSR in alligators may be involved in recovery of breathing patterns and lung volume during pre- and post-diving behavior and apneic periods in diving reptiles.
美国短吻鳄（密西西比鳄）是一种半水生的潜水爬行动物，具有周期性呼吸模式。先前的研究确定了肺牵张感受器，包括快速适应和缓慢适应的，以及对二氧化碳敏感的肺内化学感受器（IPC），它们调节短吻鳄的呼吸模式。本研究的目的是量化长时间肺充气和放气（模拟潜水）对肺牵张感受器（PSR）和/或IPC放电特性的影响。在24°C下，研究了气道压力（0 - 20 cm H₂O）、高碳酸血症（7% CO₂）和低氧血症（5% O₂）对幼年短吻鳄（平均体重 = 246 g）PSR动态和静态反应的影响。短吻鳄最初用异氟烷麻醉，头部去髓，气管切开并进行人工通气。用铂钩电极记录迷走神经传入的紧张性和阶段性活动。感受器活动是具有不同阈值和适应程度的缓慢适应PSR（SAR）和快速适应PSR（RAR）的混合，对二氧化碳不敏感。对肺充气和放气1分钟期间及前后的感受器活动进行量化，以检查模拟屏气潜水的影响。一些PSR显示出动态反应的变化，在长时间肺充气后对几次呼吸表现出抑制。在放气1分钟后，RAR而非SAR相对于对照表现出爆发频率的显著增强。对于SAR，充气后感受器抑制被二氧化碳和低氧血症阻断；对于RAR，充气后抑制被二氧化碳增强并被低氧血症阻断。这些结果表明，长时间充气和放气后PSR放电的变化可能促进短吻鳄潜水后的通气。我们假设短吻鳄的PSR可能参与潜水爬行动物潜水前、潜水中和潜水后的行为及呼吸暂停期间呼吸模式和肺容量的恢复。
