Massari V J, Johnson T A, Gatti P J
Department of Pharmacology, Howard University College of Medicine, Washington, DC 20059, USA.
Brain Res. 1995 May 15;679(2):227-40. doi: 10.1016/0006-8993(95)00227-h.
Previous data indicate that there are anatomically segregated and physiologically independent parasympathetic postganglionic vagal motoneurons on the surface of the heart which are capable of selective control of sinoatrial rate, atrioventricular conduction and atrial contractility. We have injected a retrograde tracer into the cardiac ganglion which selectively regulates atrioventricular conduction (the AV ganglion). Medullary tissues were processed for the histochemical detection of retrogradely labeled neurons by light and electron microscopic methods. Negative dromotropic retrogradely labeled cells were found in a long column in the ventrolateral nucleus ambiguus (NA-VL), which enlarged somewhat at the level of the area postrema, but reached its largest size rostral to the area postrema in an area termed the rostral ventrolateral nucleus ambiguus (rNA-VL). Three times as many cells were observed in the left rNA-VL as compared to the right (P < 0.025). Retrogradely labeled cells were also consistantly observed in the dorsal motor nucleus of the vagus (DMV). The DMV contained one third as many cells as the NA-VL. The right DMV contained twice as many cells as the left (P < 0.05). These data are consistent with physiological evidence that suggests that the left vagus nerve is dominant in the regulation of AV conduction, but that the right vagus nerve is also influential. While recording the electrocardiogram in paced and non-paced hearts, L-glutamate (GLU) was microinjected into the rNA-VL. Microinjections of GLU caused a 76% decrease in the rate of atrioventricular (AV) conduction (P < 0.05) and occasional second degree heart block, without changing heart rate. The effects of GLU were abolished by ipsilateral cervical vagotomy. These physiological data therefore support the anatomical inference that CNS neurons that are retrogradely labeled from the AV ganglion selectively exhibit negative dromotropic properties. Retrogradely labeled negative dromotropic neurons displayed a round nucleus with ample cytoplasm, abundant rough endoplasmic reticulum and the presence of distinctive somatic and dendritic spines. These neurons received synapses from afferent terminals containing small pleomorphic vesicles and large dense core vesicles. These terminals made both asymmetric and symmetric contacts with negative dromotropic dendrites and perikarya, respectively. In conclusion, the data presented indicate that there is a cardiotopic organization of ultrastructurally distinctive negative dromotropic neurons in the NA-VL. This central organization of parasympathetic preganglionic vagal motoneurons mirrors the functional organization of cardioinhibitory postganglionic neurons of the peripheral vagus nerve. These data are further discussed in comparison to a recent report on the light microscopic distribution and ultrastructural characteristics of negative chronotropic neurons in the NA-VL42.(ABSTRACT TRUNCATED AT 400 WORDS)
先前的数据表明，在心脏表面存在解剖学上分离且生理上独立的副交感神经节后迷走运动神经元，它们能够选择性地控制窦房结频率、房室传导和心房收缩力。我们已将逆行示踪剂注入选择性调节房室传导的心脏神经节（房室神经节）。通过光学和电子显微镜方法对延髓组织进行处理，以进行逆行标记神经元的组织化学检测。在腹外侧疑核（NA-VL）的一个长柱状区域中发现了负性变传导性逆行标记细胞，该区域在最后区水平略有扩大，但在最后区前方一个称为嘴侧腹外侧疑核（rNA-VL）的区域达到最大尺寸。观察到左侧rNA-VL中的细胞数量是右侧的三倍（P < 0.025）。在迷走神经背运动核（DMV）中也始终观察到逆行标记细胞。DMV中的细胞数量是NA-VL的三分之一。右侧DMV中的细胞数量是左侧的两倍（P < 0.05）。这些数据与生理学证据一致，表明左侧迷走神经在房室传导调节中占主导地位，但右侧迷走神经也有影响。在起搏和非起搏心脏记录心电图时，将L-谷氨酸（GLU）微量注射到rNA-VL中。微量注射GLU导致房室（AV）传导速率降低76%（P < 0.05），偶尔出现二度心脏传导阻滞，而心率不变。GLU的作用被同侧颈迷走神经切断术消除。因此，这些生理学数据支持解剖学推断，即从房室神经节逆行标记的中枢神经系统神经元选择性地表现出负性变传导性特性。逆行标记的负性变传导性神经元显示出圆形细胞核，细胞质丰富，粗面内质网丰富，并且存在独特的体细胞和树突棘。这些神经元接受来自含有小多形性囊泡和大致密核心囊泡的传入终末的突触。这些终末分别与负性变传导性树突和胞体形成不对称和对称接触。总之，所呈现的数据表明，在NA-VL中存在超微结构独特的负性变传导性神经元的心脏定位组织。副交感神经节前迷走运动神经元的这种中枢组织反映了外周迷走神经心脏抑制性节后神经元的功能组织。与最近一篇关于NA-VL中负性变时性神经元的光学显微镜分布和超微结构特征的报告相比，对这些数据进行了进一步讨论。（摘要截断于400字）
