延髓呼吸性神经元在呼吸暂停期间的放电变化

在向家兔颈动脉窦区注入枸橼酸钠反射性引起呼气性的呼吸暂停中,记录了128个延髓呼吸单位放电变化。一般吸气单位与膈神经放电同时停止,又同时恢复。但在延髓闩部附近的中间部及腹侧,发现约有5％的呼—吸跨时相神经元在膈神经放电停止期间呈连续的低频发放。其放电频率逐渐增高至一定水平后,转为急剧升高,同时膈神经恢复放电。由周期触发直方图显示的时相关系,可见它们放电频率骤增点早于膈神经放电的起始点,并和膈神经放电同时达到高峰频率,又同时衰减和停止放电。推测该类神经元可能与“中枢吸气性活动”(central inspiratory activity)有关。多数的呼气单位在呼吸暂停期间呈现紧张性发放,而且放电频率可高于正常的高峰频率;在膈神经放电恢复之前其放电频率又减低。而小部分的呼气单位,在膈神经放电停止时,其放电活动也受到抑制。根据呼气单位这两种不同的放电变化,推测它们在呼吸节律发生机制中可能起不同的作用.

Changes of unit-discharge of the medullary respiratoryneurons during apnea

changes of the neuronal discharge of 128 medullary respiratory units were recorded and studied during the expiratory apnea induced reflexly by Na-citrate intra-carotid sinus injection. Generally, neuronal discharges of the inspiratory units begin, stop and recover at the same time with those of the phrenic nerve.But, a few inspiratory units ( about 5 % ) near the obex show a different time course with the discharge of the phrenic nerve. They fire continuously in a low frequency while the phrenic is quiet, their firing rate increases progressively, and when approaching up to a certain level,increases abruptly and at the same time phrenic nerve begins to fire. So it seems that they act as the pacemaker of inspiration. Comparison of the cycle-triggered histograms ( CTH ) of these insp. units with these of the phrenic nerve shows clearly the above metioned phasic relationship. They started firing before the phrenic nerve, but they reached their maximal rate and then declined and stopped quite in accordance with the phrenic nerve. It is, therefore, reasonable to assume that the central inspiratory activity may originate from this kind of neurons.Most of the expiratory units show tonic discharge during the period of apnea and the rate of discharge is higher than normal, but the rate decreases just before the recovery of phrenic firing. In addition, a small portion of the expiratory units were depressed as the phrenic discharge ceased. The function of these two different kinds of neurons in the mechanism of development of respiratory rhythm is, apparently,different. The former may be involved in the mechanism of inspiratory inhibition.