de Neef K J, Jansen J R, Versprille A
Circ Res. 1983 May;52(5):508-14. doi: 10.1161/01.res.52.5.508.
In the adult rabbit, both myelinated and nonmyelinated efferent fibers travel from the cervical vagus nerve to the sinoauricular node. The myelinated fibers convey the negative chronotropic effect. The influence of the nonmyelinated fibers was studied. Stimulation (4/sec) of the myelinated fibers, while the compound action potential was monitored continuously, caused a slowing of the heart rate. Subsequent activation of the non-myelinated fibers attenuated this negative chronotropic effect. Stimulation of adrenergic fibers was excluded, based on data from histochemical studies and the effects of blockade of beta- and muscarinic receptors. The lengthening of the RR interval during activation of the myelinated fibers alone was about 3.5 times larger than during activation of all fiber groups. When the conduction of the myelinated fibers was blocked (anodal block), activation of the nonmyelinated fibers did not show any effect on heart rate. It was concluded that the negative chronotropic effect is conducted via small myelinated fibers and that the nonmyelinated fibers modulate the effect of these cardiomotor fibers, without having an effect on heart rate on their own. This modulation is effected either via a presynaptic mechanism on preganglionic fibers or via an interaction with postganglionic neurons. The nonmyelinated fibers constitute a novel peripheral system to modulate heart rate.
在成年兔中，有髓鞘和无髓鞘的传出纤维都从颈迷走神经传导至窦房结。有髓鞘纤维传递负性变时效应。对无髓鞘纤维的影响进行了研究。在持续监测复合动作电位的同时，刺激（每秒4次）有髓鞘纤维会导致心率减慢。随后激活无髓鞘纤维会减弱这种负性变时效应。根据组织化学研究数据以及β受体和毒蕈碱受体阻断的效应，排除了对肾上腺素能纤维的刺激。仅激活有髓鞘纤维时RR间期的延长幅度比激活所有纤维组时大约大3.5倍。当有髓鞘纤维的传导被阻断（阳极阻滞）时，激活无髓鞘纤维对心率没有任何影响。得出的结论是，负性变时效应通过小的有髓鞘纤维传导，无髓鞘纤维调节这些心脏运动纤维的效应，但其自身对心率没有影响。这种调节要么通过节前纤维上的突触前机制实现，要么通过与节后神经元的相互作用实现。无髓鞘纤维构成了一个调节心率的新型外周系统。
