Zagon A, Rocha I, Ishizuka K, Spyer K M
Department of Physiology, Royal Free and University College Medical School, London, UK.
Neuroscience. 1999;92(3):889-99. doi: 10.1016/s0306-4522(99)00041-x.
Stimulation of cervical vagal afferents inhibits central sympathetic outflows in part by inhibiting the ongoing activity of putative baroreceptive neurons in the rostral ventrolateral medulla oblongata. The aim of the present study was to examine the electrophysiological characteristics of vagal responses and their interactions with responses elicited by stimulation of the aortic nerve in neurons there. The study focused on the role of the long-lasting, late-onset vagal inhibition, which is likely to play an important role in the tonic inhibitory effects of vagal afferent stimulation. In vivo intracellular recordings were obtained from 33 neurons that received convergent inputs from aortic and vagal afferents. Sixty-four percent of these neurons exhibited a late inhibition following electrical stimulation of myelinated vagal afferents (mean onset latency of 100+/-5 ms). The average duration of late inhibition (294+/-19 ms) exceeded the duration of the cardiac cycle. As a consequence of this, sustained vagal stimulation diminished the effect of rhythmic baroreceptor inputs in neurons that exhibited late vagal inhibition. Simultaneous activation of aortic and vagal afferents significantly increased the magnitude of late inhibition, even in those neurons where stimulation of the aortic nerve alone did not elicit a response (n = 15). This suggested that the convergence between vagal and aortic afferent inputs occurred in inhibitory inteneurons antecedent to the recorded rostral ventrolateral medulla oblongata neurons. Focal stimulation of the caudal part of the nucleus of the solitary tract also elicited a late-onset inhibition in 73% of the neurons that responded to stimulation of the aortic nerve. This inhibition appeared to be similar to the late vagal inhibition, except for its shorter average onset latency (64+/-7 ms). Based on this observation, it is proposed that inhibitory inteneurons that mediate late inhibition to rostral ventrolateral medulla oblongata neurons may lie within the caudal part of the nucleus of the solitary tract. The present study established that activation of myelinated vagal afferents exerts a complex modulation over the ongoing and evoked activity of neurons that respond to stimulation of the aortic nerve. The complex interaction that occurs between aortic and vagal inputs in neurons of the rostral ventrolateral medulla may be implicated in long-term modulation of sympathetic outflows in response to changes in the activation of visceral receptors supplied by vagus afferents. The modulation elicited by late vagal inhibition may help to adjust cardiovascular outflows according to requirements set by the thoraco-abdominal visceral environment.
刺激颈迷走神经传入纤维部分地通过抑制延髓头端腹外侧部假定的压力感受神经元的持续活动来抑制中枢交感神经输出。本研究的目的是研究迷走神经反应的电生理特性，以及它们与该部位神经元中主动脉神经刺激所引发反应的相互作用。该研究聚焦于持久的、延迟出现的迷走神经抑制作用，这种抑制作用可能在迷走神经传入刺激的紧张性抑制效应中发挥重要作用。通过体内细胞内记录，从33个接受主动脉和迷走神经传入纤维汇聚输入的神经元中获取数据。这些神经元中有64%在有髓迷走神经传入纤维电刺激后表现出延迟抑制（平均起始潜伏期为100±5毫秒）。延迟抑制的平均持续时间（294±19毫秒）超过心动周期的持续时间。因此，持续的迷走神经刺激会减弱在表现出延迟迷走神经抑制的神经元中有节奏的压力感受器输入的效应。即使在那些单独刺激主动脉神经未引发反应的神经元中（n = 15），同时激活主动脉和迷走神经传入纤维也会显著增加延迟抑制的幅度。这表明迷走神经和主动脉传入纤维输入之间的汇聚发生在记录的延髓头端腹外侧部神经元之前的抑制性中间神经元中。对孤束核尾部的局部刺激也在73%对主动脉神经刺激有反应的神经元中引发了延迟出现的抑制。这种抑制似乎与延迟迷走神经抑制相似，只是其平均起始潜伏期较短（64±7毫秒）。基于这一观察结果，有人提出介导对延髓头端腹外侧部神经元延迟抑制的抑制性中间神经元可能位于孤束核尾部。本研究证实，有髓迷走神经传入纤维的激活对响应主动脉神经刺激的神经元的持续活动和诱发活动施加复杂的调制。延髓头端腹外侧部神经元中主动脉和迷走神经输入之间发生的复杂相互作用可能与响应迷走神经传入纤维所供应内脏感受器激活变化的交感神经输出的长期调制有关。延迟迷走神经抑制所引发的调制可能有助于根据胸腹内脏环境设定的需求来调整心血管输出。
