St-John Walter M, Paton Julian F R, Leiter J C
Department of Physiology, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA.
Exp Physiol. 2004 Nov;89(6):727-37. doi: 10.1113/expphysiol.2004.028829. Epub 2004 Sep 13.
During eupnoea, rhythmic motor activities of the hypoglossal, vagal and phrenic nerves are linked temporally. The inspiratory discharges of the hypoglossal and vagus motor neurones commence before the onset of the phrenic burst. The vagus nerve also discharges in expiration. Upon exposure to hypocapnia or hypothermia, the hypoglossal discharge became uncoupled from that of the phrenic nerve. This uncoupling was evidenced by variable times of onset of hypoglossal discharge before or after the onset of phrenic discharge, extra bursts of hypoglossal activity in neural expiration, or complete absence of any hypoglossal discharge during a respiratory cycle. No such changes were found for vagal discharge, which remained linked to the phrenic bursts. Intracellular recordings in the hypoglossal nucleus revealed that all changes in hypoglossal discharge were due to neuronal depolarization. These results add support to the conclusion that the brainstem control of respiratory-modulated hypoglossal activity differs from control of phrenic and vagal activity. These findings have implications for any studies in which activity of the hypoglossal nerve is used as the sole index of neural inspiration. Indeed, our results establish that hypoglossal discharge alone is an equivocal index of the pattern of overall ventilatory activity and that this is accentuated by hypercapnia and hypothermia.
在平静呼吸时，舌下神经、迷走神经和膈神经的节律性运动活动在时间上相互关联。舌下神经和迷走神经运动神经元的吸气放电在膈神经爆发之前开始。迷走神经在呼气时也会放电。暴露于低碳酸血症或低温时，舌下神经放电与膈神经放电解耦。这种解耦表现为舌下神经放电在膈神经放电开始之前或之后的起始时间可变、神经呼气时舌下神经活动的额外爆发，或呼吸周期中完全没有任何舌下神经放电。迷走神经放电未发现此类变化，其仍与膈神经爆发相关联。舌下神经核的细胞内记录显示，舌下神经放电的所有变化均归因于神经元去极化。这些结果支持了脑干对呼吸调节的舌下神经活动的控制不同于对膈神经和迷走神经活动的控制这一结论。这些发现对任何将舌下神经活动用作神经吸气唯一指标的研究都有影响。事实上，我们的结果表明，仅舌下神经放电是整体通气活动模式的一个模棱两可的指标，而高碳酸血症和低温会加剧这种情况。
