The release of transmitters at sympathoeffector junctions is not constant, but subject to modulation by a plethora of different mechanisms. In this respect, presynaptic receptors located on the sympathetic axon terminals are of utmost importance, because they are activated by exogenous agonists and by endogenous neurotransmitters. In the latter case, the transmitters that activate the presynaptic receptors of a nerve terminal may be released either from the very same nerve ending or from a different axon terminal, and the receptors involved are auto- and heteroreceptors, respectively. In terms of their structural and functional features, receptors of sympathetic axon terminals can be categorized as either ionotropic (transmitter-gated ion channels) or metabotropic (most commonly G protein-coupled) receptors. This review summarizes results on more than 30 different metabotropic and four different ionotropic receptors that have been found to control the amount of transmitter being released from sympathetic neurons. Each of these receptors may not only stimulate, facilitate, and reduce sympathetic transmitter release, respectively, but also interact with the functions of other receptors present on the same axonal varicosity. This provides a multitude of mechanisms that regulate the amount of sympathetic transmitter output. Accordingly, a sophisticated cross-talk within and between extra- and intracellular signals is integrated at axon terminals to adapt the strength of sympathoeffector transmission to a given situation. This will not only determine the function of the sympathetic nervous system in health and disease, but also therapeutic and untoward effects of drugs that bind to the presynaptic receptors in sympathetically innervated tissues.

中文翻译：

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通过离子和代谢型突触前受体微调交感神经递质的释放。

交感神经连接点的发射器释放不是恒定的，而是受多种不同机制的调节。在这方面，位于交感神经轴突末端的突触前受体是最重要的，因为它们被外源性激动剂和内源性神经递质激活。在后一种情况下，激活神经末梢突触前受体的递质既可以从同一神经末梢释放，也可以从不同的轴突末梢释放，所涉及的受体分别是自身受体和异源受体。就它们的结构和功能特征而言，交感神经轴突末端的受体可分为离子型（发射极门控离子通道）或代谢型（最常见的是G蛋白偶联）受体。这篇综述总结了超过30种不同的代谢型和4种不同的离子型受体的结果，这些受体可控制从交感神经元释放的递质的数量。这些受体中的每一个不仅可以分别刺激，促进和减少交感递质的释放，而且还可以与存在于相同轴突静脉曲张上的其他受体的功能相互作用。这提供了调节同情发射机输出量的多种机制。因此，在轴突末端处整合了细胞外和细胞内信号之间和之间的复杂串扰，以使交感神经传递的强度适应给定的情况。这不仅会决定交感神经系统在健康和疾病中的功能，