The American lobster, Homarus americanus, cardiac neuromuscular system is controlled by the cardiac ganglion (CG), a central pattern generator consisting of four premotor and five motor neurons. Here, we show that the premotor and motor neurons can establish independent bursting patterns when decoupled by a physical ligature. We also show that mRNA encoding myosuppressin, a cardioactive neuropeptide, is produced within the CG. We thus asked whether myosuppressin modulates the decoupled premotor and motor neurons, and, if so, how this modulation might underlie the role(s) that these neurons play in myosuppressin's effects on ganglionic output. Although myosuppressin exerted dose-dependent effects on burst frequency and duration in both premotor and motor neurons in the intact CG, its effects on the ligatured ganglion were more complex, with different effects and thresholds on the two types of neurons. These data suggest that the motor neurons are more important in determining the changes in frequency of the CG elicited by low concentrations of myosuppressin, whereas the premotor neurons have a greater impact on changes elicited in burst duration. A single putative myosuppressin receptor (MSR-I) was previously described from the Homarus nervous system. We identified four additional putative MSRs (MSR-II-V) and investigated their individual distributions in the CG premotor and motor neurons using RT-PCR. Transcripts for only three receptors (MSR-II-IV) were amplified from the CG. Potential differential distributions of the receptors were observed between the premotor and motor neurons; these differences may contribute to the distinct physiological responses of the two neuron types to myosuppressin.

中文翻译：

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龙虾心脏神经节中前运动神经元和运动神经元的差异神经肽调节。

美洲龙虾, Homarus americanus, 心脏神经肌肉系统由心脏神经节 (CG) 控制，心脏神经节是一个由四个前运动神经元和五个运动神经元组成的中央模式发生器。在这里，我们展示了前运动神经元和运动神经元在通过物理结扎解耦时可以建立独立的爆发模式。我们还显示编码肌抑制素（一种心脏活性神经肽）的 mRNA 是在 CG 内产生的。因此，我们询问肌抑制素是否调节解耦的前运动神经元和运动神经元，如果是，这种调节如何成为这些神经元在肌抑制素对神经节输出的影响中所起的作用的基础。尽管肌抑制素对完整 CG 中前运动神经元和运动神经元的爆发频率和持续时间产生剂量依赖性影响，但其对结扎神经节的影响更为复杂，对两种类型的神经元具有不同的影响和阈值。这些数据表明，运动神经元在确定由低浓度肌抑制素引起的 CG 频率变化方面更为重要，而运动前神经元对爆发持续时间引起的变化有更大的影响。先前从 Homarus 神经系统中描述了一种推定的肌抑制素受体 (MSR-I)。我们确定了另外四个假定的 MSR (MSR-II-V)，并使用 RT-PCR 研究了它们在 CG 前运动神经元和运动神经元中的个体分布。从 CG 中仅扩增了三种受体 (MSR-II-IV) 的转录本。在运动前神经元和运动神经元之间观察到受体的潜在差异分布；