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.
摘要：
脊椎动物通常具有低生理和非低生理促性腺激素释放激素（GnRH）神经元。已知终末神经（TN）GnRH神经元属于非低生理性神经元，并已被建议调节性行为。这些神经元表现出自发的起搏器放电活性并释放神经肽GnRH和神经肽FF。由于肽能神经元的自发放电活动，包括GnRH神经元,被认为在神经肽的释放中起重要作用，了解这些自发射击活动的调节机制很重要。这里,我们分析了在乙酰胆碱（ACh）的应用过程中，田鸡TN-GnRH神经元的放电活动，这是大脑中必不可少的神经调质之一。TN-GnRH神经元的全细胞膜片钳记录表明ACh诱导超极化并抑制其起搏器放电。使用拮抗剂进行乙酰胆碱受体的电生理分析和原位杂交分析显示，TN-GnRH神经元的放电受到M2型毒蕈碱乙酰胆碱受体的抑制。这些发现,与其他几种鱼类（包括硬骨鱼和松骨）的文献一起使用，表明ACh通常可能在调节TN-GnRH神经元的自发活动以及鱼类的性行为中起抑制作用。
