Enkephalins are the pentapeptides involved in pain relief and neuroendocrine responses with high affinity for delta opioid receptors in vertebrates. In the present investigation, we studied the distribution of leucine-enkephalin-immunoreactive (L-ENK-ir) neurons in the brain of the cichlid fish Oreochromis mossambicus. Application of the antisera against L-ENK revealed the presence of numerous L-ENK-ir perikarya and fibres in subdivisions of the dorsal and the ventral telencephalon, the medial olfactory tract and the nucleus entopeduncularis, whereas intensely labelled L-ENK-ir fibres were noticed in the olfactory bulb. Furthermore, the presence of L-ENK-ir cells and dense accumulations of fibres in the preoptic area and its subdivisions, the nucleus preopticus pars magnocellularis and the nucleus preopticus pars parvocellularis suggested a role for this peptide in regulation of reproduction. While intensely labelled cells and fibres were found in the nucleus lateralis tuberis pars lateralis as well as the nucleus lateralis tuberis pars medialis, some L-ENK-ir fibres were seen at the hypothalamo-hypophyseal tract indicating the possible hypophysiotrophic role for this peptide. Numerous L-ENK-ir cells and dense network of fibres were observed in the subdivisions of the nucleus recess lateralis and the pretectal area, whereas intensely labelled thick network of L-ENK- fibres were found in the ventromedial thalamic nucleus, the sub-layers of the optic tectum and the rostral spinal cord. The widespread distribution of L-ENK-immunoreactivity in the olfactory bulb, the telencephalon, the diencephalon and the mesencephalon regions of the brain as well as the spinal cord suggests the possible involvement of this peptide in the regulation of diverse functions such as neuroendocrine, antinociceptive, visual and olfactory responses in O. mossambicus.

中文翻译：

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丽鱼科鱼 Oreochromis mossambicus 脑中的亮氨酸-脑啡肽-免疫反应神经元

脑啡肽是参与镇痛和神经内分泌反应的五肽，对脊椎动物中的 delta 阿片受体具有高亲和力。在本调查中，我们研究了丽鱼科鱼 Oreochromis mossambicus 大脑中亮氨酸-脑啡肽-免疫反应 (L-ENK-ir) 神经元的分布。L-ENK 抗血清的应用揭示了在背侧和腹侧端脑、内侧嗅束和内足核的细分中存在大量 L-ENK-ir perikarya 和纤维，而强烈标记的 L-ENK-ir 纤维是在嗅球中注意到。此外，L-ENK-ir 细胞的存在和视前区及其细分中纤维的密集堆积，视前核大细胞核和视前核小细胞核表明该肽在调节生殖中起作用。虽然在结节外侧核以及外侧结节内侧核中发现了强烈标记的细胞和纤维，但在下丘脑 - 垂体束中发现了一些 L-ENK-ir 纤维，表明该肽可能具有垂体功能。在外侧核隐窝和前盖区的细分中观察到大量 L-ENK-ir 细胞和致密的纤维网络，而在丘脑腹内侧核、亚层中发现强烈标记的 L-ENK-纤维粗网络视顶盖和脊髓延髓。L-ENK 免疫反应性在嗅球、端脑、