Umatani Chie, Oka Yoshitaka
Department of Biological Sciences, Graduate School of Science, the University of Tokyo, Tokyo, 113-0033 Japan.
Zoological Lett. 2019 Jul 22;5:23. doi: 10.1186/s40851-019-0138-y. eCollection 2019.
Gonadotropin releasing hormone (GnRH) is a hypophysiotropic hormone that is generally thought to be important for reproduction. This hormone is produced by hypothalamic GnRH neurons and stimulates the secretion of gonadotropins. On the other hand, vertebrates also have non-hypophysiotropic GnRH peptides, which are produced by extrahypothalamic GnRH neurons. They are mainly located in the terminal nerve, midbrain tegmentum, trigeminal nerve, and spinal cord (sympathetic preganglionic nerves). In vertebrates, there are typically three paralogues (, , ). GnRH-expression in the non-hypophysiotropic neurons ( or in the terminal nerve and the trigeminal nerve in the midbrain tegmentum) occurs from the early developmental stages. Recent studies have suggested that non-hypophysiotropic GnRH neurons play various functional roles. Here, we summarize their anatomical/physiological properties and discuss their possible functions, focusing on studies in vertebrates. GnRH neurons in the terminal nerve show different spontaneous firing properties during the developmental stages. These neurons in adulthood show regular pacemaker firing, and it has been suggested that these neurons show neuromodulatory function related to the regulation of behavioral motivation, etc. In addition to their recognized role in neuromodulation in adult, in juvenile fish, these neurons, which show more frequent burst firing than in adults, are suggested to have novel functions. GnRH neurons in the midbrain tegmentum show regular pacemaker firing similar to that of the adult terminal nerve and are suggested to be involved in modulations of feeding (teleosts) or nutrition-related sexual behaviors (musk shrew). GnRH neurons in the trigeminal nerve are suggested to be involved in nociception and chemosensory avoidance, although the literature on their electrophysiological properties is limited. Sympathetic preganglionic cells in the spinal cord were first reported as peptidergic modulatory neurons releasing GnRH with a putative function in coordinating interaction between vasomotor and exocrine outflow in the sympathetic nervous system. The functional role of non-hypophysiotropic GnRH neurons may thus be in the global modulation of neural circuits in a manner dependent on internal conditions or the external environment.
促性腺激素释放激素（GnRH）是一种促垂体激素，通常被认为对生殖至关重要。这种激素由下丘脑GnRH神经元产生，并刺激促性腺激素的分泌。另一方面，脊椎动物也有非促垂体GnRH肽，它们由下丘脑外GnRH神经元产生。它们主要位于终神经、中脑被盖、三叉神经和脊髓（交感神经节前神经）。在脊椎动物中，通常有三个旁系同源物（、、）。非促垂体神经元（终神经中的或中脑被盖三叉神经中的）中的GnRH表达从发育早期阶段就开始出现。最近的研究表明，非促垂体GnRH神经元发挥着多种功能作用。在这里，我们总结它们的解剖学/生理学特性，并讨论它们可能的功能，重点是脊椎动物的研究。终神经中的GnRH神经元在发育阶段表现出不同的自发放电特性。成年期这些神经元表现出规则的起搏器放电，并且有人提出这些神经元表现出与行为动机调节等相关的神经调节功能。除了在成体中公认的神经调节作用外，在幼鱼中，这些比成体更频繁爆发性放电的神经元被认为具有新的功能。中脑被盖中的GnRH神经元表现出与成年终神经相似的规则起搏器放电，并被认为参与进食调节（硬骨鱼）或营养相关性行为（麝鼩）。三叉神经中的GnRH神经元被认为参与伤害感受和化学感觉回避，尽管关于它们电生理特性的文献有限。脊髓中的交感神经节前细胞最初被报道为肽能调节神经元，释放GnRH，其假定功能是协调交感神经系统中血管运动和外分泌流出之间的相互作用。因此，非促垂体GnRH神经元的功能作用可能是以依赖于内部条件或外部环境的方式对神经回路进行全局调节。
