The neuroendocrine-stress axis of nonmammalian species is evolutionarily conserved, which makes them useful to serve as important model systems for elucidating the function of the vertebrate stress response. The involvement of hypothalamo-pituitary-adrenal (HPA) axis hormones in regulation of stress and reproduction is well described in different vertebrates. However, the stress response is a complex process, which appears to be controlled by a number of neurochemicals in association with hypothalamo-pituitary-interrenal (HPI) axis or independent of HPI axis in fish. In recent years, the participation of neurohormones other than HPI axis in regulation of stress and reproduction is gaining more attention. This review mainly focuses on the involvement of functional neuroanatomical systems such as the catecholaminergic neurotransmitter dopamine (DA) and opioid peptides in regulation of the stress-reproductive axis in fish. Occurrences of DA and opioid peptides like β-endorphin, enkephalins, dynorphin, and endomorphins have been demonstrated in fish brain, and diverse roles such as pain modulation, social behaviour and reproduction are implicated for these hormones. Neuroanatomical studies using retrograde tracing, immunohistochemical staining and lesion methods have demonstrated that the neurons originating in the preoptic region and the nucleus lateralis tuberis directly innervate the pituitary gland and, therefore, the hypophysiotrophic role of these hormones. In addition, heightened synthetic and secretory activity of the opioidergic and the dopaminergic neurons in hypothalamic areas of the brain during stress exposure suggest potentially intricate relationship with the stress-reproductive axis in fish. Current evidence in early vertebrates like fish provides a novel insight into the underlying neuroendocrine mechanisms as additional pathways along the stress-reproductive axis that seem to be conserved during the course of evolution.

中文翻译：

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压力——鱼的生殖轴：大脑中功能性神经解剖系统的参与

非哺乳动物物种的神经内分泌应激轴在进化上是保守的，这使得它们可用作阐明脊椎动物应激反应功能的重要模型系统。下丘脑-垂体-肾上腺 (HPA) 轴激素在调节压力和繁殖中的作用在不同的脊椎动物中得到了很好的描述。然而，应激反应是一个复杂的过程，它似乎受许多神经化学物质控制，这些神经化学物质与下丘脑 - 垂体 - 间质 (HPI) 轴相关或独立于鱼的 HPI 轴。近年来，除HPI轴以外的神经激素参与应激和生殖调节越来越受到关注。本综述主要关注功能性神经解剖系统的参与，如儿茶酚胺能神经递质多巴胺 (DA) 和阿片肽在鱼类应激-生殖轴的调节中。DA 和阿片肽如 β-内啡肽、脑啡肽、强啡肽和内吗啡肽已在鱼脑中得到证实，并且这些激素涉及多种作用，如疼痛调节、社会行为和繁殖。使用逆行追踪、免疫组织化学染色和病变方法的神经解剖学研究表明，起源于视前区和结节外侧核的神经元直接支配垂体，因此，这些激素的垂体营养作用。此外，在压力暴露期间，大脑下丘脑区域的阿片能神经元和多巴胺能神经元的合成和分泌活动增强，这表明与鱼的压力繁殖轴可能存在错综复杂的关系。目前在鱼类等早期脊椎动物中的证据提供了对潜在神经内分泌机制的新见解，这些机制是沿着压力 - 生殖轴的额外途径，在进化过程中似乎是保守的。