查看Ch14 The Autonomic Nervous System的源代码

=== 非经典发射机可以在 ANS 的每个级别释放 ===
<b style=color:#0ae>Nonclassic transmitters can be released at each level of the ANS</b>

In the 1930s, Sir Henry Dale N14-5 first proposed that sympathetic nerves release a transmitter similar to epinephrine (now known to be norepinephrine) and parasympathetic nerves release ACh. For many years, attention was focused on these two neurotransmitters, primarily because they mediate large and fast postsynaptic responses that can be easily studied. In addition, a variety of antagonists are available to block cholinergic and adrenergic receptors and thereby permit clear characterization of the roles of these receptors in the control of visceral function. More recently, it has become evident that some neurotransmission in the ANS involves neither adrenergic nor cholinergic pathways. Moreover, many neuronal synapses use more than a single neurotransmitter. Such cotransmission is now known to be common in the ANS. As many as eight different neurotransmitters may be found within some neurons, a phenomenon known as colocalization (see Table 13-1). Thus, ACh and norepinephrine play important but not exclusive roles in autonomic control.

在 1930 年代，亨利·戴尔爵士[N14-5] 首次提出交感神经释放类似于肾上腺素的递质（现在已知是去甲肾上腺素），副交感神经释放 ACh。多年来，人们的注意力都集中在这两种神经递质上，主要是因为它们介导了易于研究的大而快速的突触后反应。此外，有多种拮抗剂可用于阻断胆碱能和肾上腺素能受体，从而可以清楚地表征这些受体在控制内脏功能中的作用。最近，很明显 ANS 中的一些神经传递既不涉及肾上腺素能通路，也不涉及胆碱能通路。此外，许多神经元突触使用不止一种神经递质。现在已知这种共传在 ANS 中很常见。在某些神经元中可能发现多达 8 种不同的神经递质，这种现象称为共定位（见表 13-1）。因此，ACh 和去甲肾上腺素在自主神经控制中起着重要但并非排他性的作用。


The distribution and function of nonadrenergic, noncholinergic (NANC) transmitters are only partially understood. However, these transmitters are found at every level of autonomic control (Table 14-3), where they can cause a wide range of postsynaptic responses. These nonclassic transmitters may cause slow synaptic potentials or may modulate the response to other inputs (as in the case of the M current) without having obvious direct effects. In other cases, nonclassic transmitters have no known effects and may be acting in ways that have not yet been determined.

非肾上腺素能、非胆碱能 （NANC） 递质的分布和功能仅部分了解。然而，这些递质存在于自主神经控制的每个水平（表 14-3），它们可以引起广泛的突触后反应。这些非经典发射器可能会导致突触电位缓慢，或者可能会调制对其他输入的响应（如 M 电流的情况），而不会产生明显的直接影响。在其他情况下，非经典递质没有已知的影响，并且可能以尚未确定的方式发挥作用。

Although colocalization of neurotransmitters is recognized as a common property of neurons, it is not clear what controls the release of each of the many neurotransmitters. In some cases, the proportion of neurotransmitters released depends on the level of neuronal activity (see pp. 327–328). For example, medullary raphé neurons project to the intermediolateral cell column in the spinal cord, where they co-release serotonin, thyrotropin-releasing hormone, and substance P onto sympathetic preganglionic neurons. The proportions of released neurotransmitters are controlled by neuronal firing frequency: at low firing rates, serotonin is released alone; at intermediate firing rates, thyrotropin-releasing hormone is also released; and at high firing rates, all three neurotransmitters are released. This frequency-dependent modulation of synaptic transmission provides a mechanism for enhancing the versatility of the ANS.

尽管神经递质的共定位被认为是神经元的共同特性，但尚不清楚是什么控制了许多神经递质中每一种的释放。在某些情况下，释放的神经递质的比例取决于神经元活动的水平（参见第 327-328 页）。例如，髓质 raphé 神经元投射到脊髓的中间外侧细胞柱，在那里它们共同释放血清素、促甲状腺激素释放激素和 P 物质到交感神经节前神经元上。释放的神经递质的比例受神经元放电频率控制：在低放电速率下，血清素单独释放;在中等放电速率下，也会释放促甲状腺激素释放激素;在高放电速率下，所有三种神经递质都被释放。这种突触传递的频率依赖性调制提供了一种增强 ANS 多功能性的机制。

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