Woolley D C, McWilliam P N, Ford T W, Clarke R W
Department of Cardiovascular Studies, University of Leeds, U.K.
J Auton Nerv Syst. 1987 Dec;21(2-3):215-21. doi: 10.1016/0165-1838(87)90024-5.
The bradycardia evoked by electrical stimulation of the peripheral cut end of the rabbit vagus nerve is mediated by both myelinated and non-myelinated fibres. The purpose of this study was to assess the effects of non-myelinated fibres on heart rate in the rabbit using selective electrical stimulation techniques. In 8 rabbits selective activation of non-myelinated fibres using reversed polarity triangular shaped pulses (10 Hz, 20 s), resulted in a slowly developing fall in heart rate of 24.1 +/- 1.1 beats/min which outlasted the period of stimulation by 58.4 +/- 4.2 s. In 4 rabbits stimulation of myelinated fibres at 10 Hz for 20 s resulted in a fall in heart rate of 24.5 +/- 2.6 beats/min. On stimulation of both myelinated and non-myelinated fibres heart rate fell by 39.9 +/- 3.2 beats/min. Heart rate returned rapidly to control value following stimulation of myelinated fibres (5.6 +/- 0.5 s) but only slowly after stimulation of both myelinated and non-myelinated fibres (56.7 +/- 4.9 s). Atropine (5 mg/kg, i.v.) abolished all effects of vagal stimulation on heart rate. Hexamethonium (15 mg/kg, i.v.) abolished the effect of myelinated fibres on heart rate but did not affect the fall in heart rate produced by non-myelinated fibres. We suggest that the prolonged effects on stimulation of non-myelinated fibres may reflect the persistent action of a non-cholinergic excitatory transmitter at the cardiac parasympathetic ganglia.
电刺激兔迷走神经外周切断端所诱发的心动过缓是由有髓纤维和无髓纤维共同介导的。本研究的目的是使用选择性电刺激技术评估无髓纤维对兔心率的影响。在8只兔子中，使用反极性三角形脉冲（10 Hz，20 s）选择性激活无髓纤维，导致心率缓慢下降，下降幅度为24.1±1.1次/分钟，下降持续时间比刺激期长58.4±4.2秒。在4只兔子中，以10 Hz刺激有髓纤维20秒，导致心率下降24.5±2.6次/分钟。同时刺激有髓纤维和无髓纤维时，心率下降39.9±3.2次/分钟。刺激有髓纤维后，心率迅速恢复到对照值（5.6±0.5秒），但同时刺激有髓纤维和无髓纤维后，心率恢复缓慢（56.7±4.9秒）。阿托品（5 mg/kg，静脉注射）消除了迷走神经刺激对心率的所有影响。六甲铵（15 mg/kg，静脉注射）消除了有髓纤维对心率的影响，但不影响无髓纤维引起的心率下降。我们认为，对无髓纤维刺激的延长效应可能反映了一种非胆碱能兴奋性递质在心脏副交感神经节的持续作用。
