Konopka L M, Merriam L A, Hardwick J C, Parsons R L
Department of Anatomy and Neurobiology, University of Vermont College of Medicine, Burlington 05405.
Can J Physiol Pharmacol. 1992;70 Suppl:S32-43. doi: 10.1139/y92-241.
Correlated histochemical, immunocytochemical, and electrophysiological experiments have been undertaken to identify putative neurotransmitter-neuromodulator substances in cells and fibers in the parasympathetic cardiac ganglion of the mudpuppy, Necturus maculosus, and to determine the action of these agents on the properties of the parasympathetic postganglionic neurons. The mudpuppy cardiac ganglion contains two neuron types: large parasympathetic postganglionic neurons and smaller intrinsic neurons initially identified as small intensely fluorescent cells. We have shown that the postganglionic neurons contain both acetylcholine and a galanin-like neuropeptide. Also, we have demonstrated that the intrinsic neurons contain a number of different biogenic amines such as dopamine and serotonin, as well as neuropeptides including a substance P-like peptide and a galanin-like peptide. The results of these studies indicate that the anatomical and histochemical organization of the mudpuppy cardiac ganglion is more complex than that seen in other amphibians and is very similar to that found in most mammalian species. Previously, we showed that galanin has actions that make it of interest as a potential inhibitory neurotransmitter in the mudpuppy cardiac ganglion. Galanin hyperpolarizes and decreases membrane excitability in most parasympathetic neurons. Here we show that galanin initiates membrane hyperpolarization by activating a voltage- and time-dependent potassium conductance. We also present the initial results of ongoing studies which indicate that calcitonin gene-related peptide can depolarize some of the parasympathetic neurons as well as evidence that serotonin initiates depolarization in many parasympathetic neurons. This serotonin-induced depolarization consists of an initial transient depolarization followed by a longer, more slowly developing depolarization. Action potential activity is stimulated during the initial period of depolarization, but depressed during the later, slow depolarization. The results of these electrophysiological experiments suggest that many of the bioactive substances that have been identified in the different cells and nerve fibers within the cardiac ganglion affect the excitability of the postganglionic neurons. In conclusion, we suggest that the results of the studies summarized in this review demonstrate that the cardiac ganglion in the mudpuppy is not simply a relay station. Rather, the cardiac ganglion has a complex organization and exhibits a diversity of physiological responses, indicating that it very likely is another site of integration for control of cardiac function.
已开展相关的组织化学、免疫细胞化学和电生理实验，以鉴定泥螈（Necturus maculosus）副交感神经心脏神经节中的细胞和纤维中假定的神经递质 - 神经调质物质，并确定这些物质对副交感神经节后神经元特性的作用。泥螈心脏神经节包含两种神经元类型：大型副交感神经节后神经元和最初被鉴定为小而强荧光细胞的较小的内在神经元。我们已经表明，节后神经元同时含有乙酰胆碱和一种甘丙肽样神经肽。此外，我们还证明，内在神经元含有多种不同的生物胺，如多巴胺和5-羟色胺，以及神经肽，包括一种P物质样肽和一种甘丙肽样肽。这些研究结果表明，泥螈心脏神经节的解剖学和组织化学结构比其他两栖动物更为复杂，与大多数哺乳动物物种中的情况非常相似。此前，我们表明甘丙肽具有一些作用，使其成为泥螈心脏神经节中一种潜在的抑制性神经递质。甘丙肽使大多数副交感神经神经元超极化并降低膜兴奋性。在此我们表明，甘丙肽通过激活一种电压和时间依赖性钾电导来引发膜超极化。我们还展示了正在进行的研究的初步结果，这些结果表明降钙素基因相关肽可使一些副交感神经神经元去极化，以及5-羟色胺在许多副交感神经神经元中引发去极化的证据。这种5-羟色胺诱导的去极化包括最初的短暂去极化，随后是更长时间、发展更缓慢的去极化。在去极化的初始阶段动作电位活动受到刺激，但在后期缓慢去极化阶段受到抑制。这些电生理实验结果表明，在心脏神经节的不同细胞和神经纤维中鉴定出的许多生物活性物质会影响节后神经元的兴奋性。总之，我们认为本综述中总结的研究结果表明，泥螈的心脏神经节不仅仅是一个中继站。相反，心脏神经节具有复杂的组织结构并表现出多种生理反应，这表明它很可能是心脏功能控制的另一个整合位点。
