Enkephalins are a class of opioid peptides implicated in several physiological and neuroendocrine responses in vertebrates. In this study, using immunocytochemical or immunofluorescence technique, we examined the neuroanatomical distribution of methionine enkephalin (M-ENK) immunoreactivity in the central nervous system (CNS) of the cichlid fish Oreochromis mossambicus. In the telencephalon, no M-ENK-like-immunoreactive (M-ENK-L-ir) perikarya, but sparsely distributed fibres were detected in the glomerular layer and the granule cell layer of the olfactory bulb. Although intensely labeled M-ENK-L-ir cells and fibres were found in the pallium, no M-ENK immunoreactivity was observed in the subpallium. The preoptic area showed a few M-ENK-L-ir somata and dense innervations of fibres. In the hypothalamic area, M-ENK-L-ir cells and fibres were located in magnocellular and parvocellular subdivisions of the nucleus preopticus, and medial and lateral subdivisions of the nucleus lateralis tuberis. Surrounding the recessus lateralis of the third ventricle, several intensely stained and packed M-ENK-L-ir cells and fibres were seen in dorsal, lateral and ventral subdivisions of the nucleus recessus lateralis. In the diencephalon, M-ENK immunoreactivity was restricted to the habenula, the thalamus, the pretectal area and the nucleus posterior tuberis. Dense aggregations of M-ENK-L-ir fibres were seen in the mesencephalic subdivisions, the optic tectum and the torus semicircularis, whereas a few fusiform M-ENK-L-ir cells and fibres were scattered in the midbrain tegmentum. In the rhombencephalon, different populations of ovoid or spindle shaped M-ENK-L-ir cells were observed in the secondary gustatory nucleus, the sensory trigeminal nerve nucleus, the nucleus reticularis medialis and the vagal motor nucleus, whereas bands of fibres were seen in the rostral spinal cord. Collectively, the widespread distribution of M-ENK immunoreactivity in the CNS suggests a role for this opioid peptide in regulation of neuroendocrine control of reproduction and modulation of sensorimotor functions in fish.

脑啡肽是一类与脊椎动物的几种生理和神经内分泌反应有关的阿片肽。在这项研究中，我们使用免疫细胞化学或免疫荧光技术，检查了慈鲷鱼Oreochromis mossambicus中枢神经系统 (CNS) 中蛋氨酸脑啡肽 (M-ENK) 免疫反应性的神经解剖分布。. 在端脑，未检测到 M-ENK 样免疫反应（M-ENK-L-ir）周核，但在肾小球层和嗅球的颗粒细胞层中检测到稀疏分布的纤维。虽然在苍白层中发现了强烈标记的 M-ENK-L-ir 细胞和纤维，但在下层苍白层中没有观察到 M-ENK 免疫反应性。视前区显示一些 M-ENK-L-ir 胞体和密集的纤维神经支配。在下丘脑区域，M-ENK-L-ir 细胞和纤维位于视前核的大细胞和小细胞亚部，以及外侧结节核的内侧和外侧亚部。在第三脑室的外侧隐窝周围，在外侧隐窝核的背侧、侧侧和腹侧细分中可以看到几个强烈染色和堆积的 M-ENK-L-ir 细胞和纤维。在间脑，M-ENK 免疫反应性仅限于缰核、丘脑、顶盖区和后结节核。M-ENK-L-ir 纤维密集聚集在中脑分支、视顶盖和半圆环中，而少数梭形 M-ENK-L-ir 细胞和纤维分散在中脑被盖中。在菱脑中，在次级味觉核、三叉感觉神经核、内侧网状核和迷走神经运动核中观察到不同的卵圆形或梭形M-ENK-L-ir细胞群，而在中观察到纤维条带。延髓脊髓。集体，