Leeches have four mechanosensory pressure neurons (P cells) in each midbody ganglion. Within a ganglion, P cells show complex electrical and chemical connections that vary between species. In Hirudo verbana, stimulating one P cell causes a weak depolarization followed by a strong hyperpolarization in the other P cells; however, stimulating a P cell in Erpobdella obscura produces strong depolarizations in the other P cells. In this study, we examined interactions between P cells in the American medicinal leech Macrobdella decora. Not only is Macrobdella more closely related to Hirudo than to Erpobdella, but Hirudo and Macrobdella also have very similar behavioral responses to mechanical stimulation. Despite the phylogenetic relationship and behavioral similarities between the two species, we found that intracellular stimulation of one P cell in Macrobdella causes a depolarization in the other P cells, rather than the hyperpolarization seen in Hirudo. Experiments performed in a high Mg²⁺, 0 Ca²⁺ saline solution and a high Mg²⁺, high Ca²⁺ saline solution suggest that the P cells in Macrobdella have a monosynaptic excitatory connection, a polysynaptic inhibitory connection, and a weak electrical coupling, similar to the connections between P cells in Hirudo. The difference in net response of P cells between these two species seems to be based on differences in the strengths of the chemical connections. These results demonstrate that even when behavioral patterns are conserved in closely related species, the underlying neural circuitry is not necessarily tightly constrained.

中文翻译：

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同源机械感觉神经元之间不同的突触强度。

水蛭在每个体中部神经节中有四个机械感觉压力神经元（P 细胞）。在神经节内，P 细胞显示出复杂的电和化学连接，这些连接因物种而异。在水蛭中，刺激一个 P 细胞会导致弱去极化，然后在其他 P 细胞中引起强烈的超极化；然而，刺激Erpobdella obscura 中的一个 P 细胞会在其他 P 细胞中产生强烈的去极化。在这项研究中，我们检查了美国药用水蛭Macrobdella decora 中P 细胞之间的相互作用。Macrobdella不仅与Hirudo 的关系比Erpobdella更密切，而且Hirudo和Macrobdella对机械刺激也有非常相似的行为反应。尽管这两个物种之间存在系统发育关系和行为相似性，但我们发现对Macrobdella中一个 P 细胞的细胞内刺激会导致其他 P 细胞去极化，而不是在Hirudo 中看到的超极化。在高 Mg ²⁺、0 Ca ²⁺盐溶液和高 Mg ²⁺、高 Ca ²⁺盐溶液中进行的实验表明，Macrobdella中的 P 细胞具有单突触兴奋性连接、多突触抑制性连接和弱电性连接。耦合，类似于水蛭中P 细胞之间的连接. 这两个物种之间 P 细胞净响应的差异似乎是基于化学连接强度的差异。这些结果表明，即使行为模式在密切相关的物种中是保守的，潜在的神经回路也不一定受到严格限制。