International College of Arts and Sciences, Fukuoka Women's University, 1-1-1 Kasumigaoka, Higashi-ku, Fukuoka, 813-8529, Japan.
Kagawa School of Pharmaceutical Sciences, Tokushima Bunri University, 1314-1 Shido, Sanuki, Kagawa, 769-2193, Japan.
Peptides. 2021 Jul;141:170541. doi: 10.1016/j.peptides.2021.170541. Epub 2021 Mar 26.
The terrestrial slug Limax acquires odor-aversion memory. The procerebrum is the secondary olfactory center in the brain of Limax, and functions as the locus of the memory formation and storage. The change in the local field potential oscillation in the procerebrum reflects the information processing of the learned odor. However, it is not fully understood what factors, intrinsic or extrinsic in the procerebrum, alter the oscillatory activity and how it is regulated. In the present study, we found that FxRIamide (Phe-x-Arg-Ile-NH), which was previously identified as a myomodulatory peptide in the gastropod Fusinus ferrugineus, downregulates the oscillatory frequency of the local field potential oscillation in the procerebrum of Limax. FxRIamide peptides were encoded by two distinct transcripts, which exhibit partially overlapping expression patterns in the brain. Immunohistochemical staining revealed a scattered distribution of FxRIamide-expressing neurons in the cell mass layer of the procerebrum, in addition to the ramified innervation of FxRIamidergic neurons in the neuropile layers. Down-regulation of the oscillatory frequency of the local field potential was explained by the inhibitory effects of FxRIamide on the bursting neurons, which are the kernels of the local field potential oscillation in the procerebrum. Our study revealed the previously unidentified role of FxRIamide peptides in the network of interneurons of Limax, and these peptides may play a role in the mnemonic functions of the procerebrum.
陆地蜗牛 Limax 获得气味厌恶记忆。前脑是 Limax 大脑中的二级嗅觉中枢，是记忆形成和存储的位置。前脑局部场电位振荡的变化反映了学习气味的信息处理。然而，目前尚不完全清楚前脑内部或外部的哪些因素会改变振荡活动以及如何调节它。在本研究中，我们发现 FxRIamide（苯丙氨酸-x-精氨酸-异亮氨酸-精氨酸-NH），先前在腹足纲 Fusinus ferrugineus 中被鉴定为肌肽调节肽，可下调 Limax 前脑局部场电位振荡的振荡频率。FxRIamide 肽由两个不同的转录本编码，它们在前脑的表达模式部分重叠。免疫组织化学染色显示 FxRIamide 表达神经元在脑实质层呈散在分布，除了 FxRIamidergic 神经元在神经层的分支神经支配外。局部场电位振荡频率的下调是由 FxRIamide 对爆发神经元的抑制作用引起的，爆发神经元是前脑局部场电位振荡的核心。我们的研究揭示了 FxRIamide 肽在前脑神经元网络中以前未被识别的作用，这些肽可能在前脑的记忆功能中发挥作用。
