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Zoological Science
Abstract
Vertebrates generally possess hypophysiotropic and non-hypophysiotropic gonadotropin releasing hormone (GnRH) neurons. The terminal nerve (TN) GnRH neurons are known to belong to the non-hypophysiotropic neurons and have been suggested to modulate sexual behaviors. These neurons show spontaneous pacemaker firing activity and release neuropeptides GnRH and neuropeptide FF. Since the spontaneous firing activities of peptidergic neurons, including GnRH neurons, are believed to play important roles in the release of neuropeptides, understanding the regulatory mechanisms of these spontaneous firing activities is important. Here, we analyzed firing activities of the TN-GnRH neurons in medaka during application of acetylcholine (ACh), which is one of the essential neuromodulators in the brain. Whole cell patch clamp recording of TN-GnRH neurons demonstrated that ACh induces hyperpolarization and inhibits their pacemaker firing. Electrophysiological analysis using an antagonist for acetylcholine receptors and in situ hybridization analysis showed that firing of TN-GnRH neurons is inhibited via M2-type muscarinic acetylcholine receptor. These findings, taken together with literature from several other fish species (including teleosts and elasmobranchs), indicate that ACh may generally play an inhibitory role in modulating spontaneous activities of TN-GnRH neurons and thereby sexual behaviors in fish.
We would like to acknowledge Dr. Masaharu Hasebe for helpful discussion. We deeply thank Dr. Kana Ikegami for her help in preparing the ISH probe. We also thank Ms. Hisako Kohno, Ms. Hiroko Tsukamoto, and Ms. Miho Kyokuwa for careful animal care. We thank Dr. Hiroyuki Takeda for his support during the experiments. This work was supported by Grants-in-Aid from Japan Society for the Promotion of Science (JSPS) (Grant nos. 13J08601 and 17K15157 to C.U. and 26221104 to Y.O.).
© 2023 Zoological Society of Japan
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