The terrestrial slug Limax has long been used as a model for the study of olfactory information processing and odor learning. Olfactory inputs from the olfactory epithelium are processed in the tentacular ganglion and then in the procerebrum. Glutamate and acetylcholine are the major neurotransmitters used in the procerebrum. Phe-Met-Arg-Phe-NH2 (FMRFamide) has been shown to be involved in the regulation of the network activity of the procerebrum. Although there are thought to be various RFamide family peptides other than FMRFamide that are potentially recognized by anti-FMRFamide antibody in the central nervous system of mollusks, identifying the entire repertoire of RFamide peptides in Limax has yet to be achieved. In the present study, we made a comprehensive search for RFamide peptide-encoding genes from the transcriptome data of Limax, and identified 12 genes. The expression maps of these RFamide genes were constructed by in situ hybridization in the cerebral ganglia including the procerebrum, and in the superior/inferior tentacles. Ten of 12 genes were expressed in the procerebrum, and nine of 12 genes were expressed in the tentacular ganglia. Gly-Ser-Leu-Phe-Arg-Phe-NH2 (GSLFRFamide), which is encoded by two different genes, LFRFamide1 (Leu-Phe-Arg-Phe-NH2–1) and LFRFamide2 (Leu-Phe-Arg-Phe-NH2–2), decreased the oscillatory frequency of the local field potential oscillation in the procerebrum when exogenously applied in vitro. We also found by immunohistochemistry that the neurons expressing pedal peptide send efferent projections from the procerebrum back to the tentacular ganglion. Our findings suggest the involvement of a far wider variety of RFamide family peptides in the olfactory information processing in Limax than previously thought.

中文翻译：

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陆生蛞蝓 Limax 嗅觉中心的射频酰胺能神经元

陆生蛞蝓 Limax 长期以来一直被用作研究嗅觉信息处理和气味学习的模型。来自嗅觉上皮的嗅觉输入在触手神经节中处理，然后在前脑中处理。谷氨酸和乙酰胆碱是前脑中使用的主要神经递质。Phe-Met-Arg-Phe-NH2 (FMRFamide) 已被证明参与调节前大脑的网络活动。尽管人们认为除 FMRFamide 之外的各种 RFamide 家族肽可能被软体动物中枢神经系统中的抗 FMRFamide 抗体识别，但尚未实现鉴定 Limax 中的整个 RFamide 肽库。在本研究中，我们从 Limax 的转录组数据中全面搜索了 RFamide 肽编码基因，并鉴定了12个基因。这些 RFamide 基因的表达图谱是通过原位杂交在包括前脑在内的大脑神经节和上/下触手中构建的。12个基因中有10个在前脑中表达，12个基因中有9个在触手神经节中表达。Gly-Ser-Leu-Phe-Arg-Phe-NH2 (GSLFRFamide)，由两个不同的基因 LFRFamide1 (Leu-Phe-Arg-Phe-NH2–1) 和 LFRFamide2 (Leu-Phe-Arg-Phe- NH2-2)，在体外外源性应用时降低了前脑局部场电位振荡的振荡频率。我们还通过免疫组织化学发现，表达踏板肽的神经元将来自前脑的传出投射发送回触手神经节。