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 gnrh paralogues (gnrh1, gnrh2, gnrh3). GnRH-expression in the non-hypophysiotropic neurons (gnrh1 or gnrh3 in the terminal nerve and the trigeminal nerve, gnrh2 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.

中文翻译：

---

脊椎动物非促营养促性腺激素释放激素神经元的多功能

促性腺激素释放激素（GnRH）是促生理激素，通常被认为对生殖很重要。该激素由下丘脑GnRH神经元产生，并刺激促性腺激素的分泌。另一方面，脊椎动物也具有非下丘脑GnRH肽，由下丘脑GnRH神经元产生。它们主要位于末梢神经，中脑被膜，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gnrh旁系同源物（gnrh1，gnrh2，gnrh3）。非促营养神经元（末端神经和三叉神经中的gnrh1或gnrh3，中脑被盖骨中的gnrh2）中的GnRH表达从发育的早期阶段开始发生。最近的研究表明非促营养性GnRH神经元发挥各种功能作用。在这里，我们总结它们的解剖/生理特性，并讨论其可能的功能，重点是在脊椎动物中进行研究。末梢神经中的GnRH神经元在发育阶段表现出不同的自发放电特性。这些成年后的神经元表现出规律的起搏器放电，并且表明这些神经元表现出与行为动机的调节等相关的神经调节功能。除了它们在成年鱼的神经调节中的公认作用外，这些神经元还显示出比起成年人，更频繁的爆发射击被认为具有新颖的功能。中脑被膜中的GnRH神经元显示出规则的起搏器放电，类似于成人末梢神经的起搏器放电，并建议其参与进食（腰果）或与营养有关的性行为（麝香）的调节。尽管有关其电生理特性的文献有限，但建议三叉神经中的GnRH神经元参与伤害感受和化学感觉避免。脊髓中的交感神经节前细胞首先被报道为肽能调节神经元，释放GnRH，在协调交感神经系统中血管舒缩和外分泌流出之间的相互作用方面具有公认的功能。因此，非促营养性GnRH神经元的功能作用可能是取决于内部条件或外部环境，从而在神经回路的整体调节中发挥作用。