Both the orexin peptides produced from prepro-orexin in orexinergic neurons of the lateral hypothalamus and hypothalamic perifornical area (PFA) and serotonin coming to these hypothalamic areas from synaptic endings of serotonergic neurons of the midbrain raphe nuclei play an important role in the regulation of feeding behavior and circadian rhythms. This indicates a close relationship between the serotoninergic and orexinergic systems in the lateral hypothalamus and PFA which, however, remains poorly studied. The aim of this study was to identify immunohistochemically and quantify the 2C-subtype (5-HT2CR) and the 1B-subtype (5-HT1BR) serotonin receptors in orexinergic neurons of the hypothalamic PFA in mice and rats. An immunohistochemical reaction for orexin-A was used to identify orexinergic neurons, and the double fluorescence immunolabeling was applied to assess the colocalization of serotonin receptors and orexin-A. Using double immunolabeling, the colocalization of orexin-A and 5-HT2CR and 5-HT1BR in the hypothalamic PFA of different rodent species, such as C57Bl/6J mice and Wistar rats, was demonstrated. It was shown that all orexinergic neurons expressed both types of serotonin receptors. At the same time, only 32–35% of 5-HT2CR and 5-HT1BR were localized in the orexinergic neurons, while the remaining part of them was expressed in the other types of PFA neurons. Thus, the immunohistochemical evidence was obtained for the serotonin-mediated regulation of functional activity of orexinergic neurons in the rodent hypothalamic PFA; also it was established that these effects of serotonin can be realized via 5-HT2CR and 5-HT1BR.

中文翻译：

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5-HT2C 和 5-HT1B 5-羟色胺受体在啮齿动物下丘脑周围区域的食欲神经元中的定位

下丘脑外侧和下丘脑眶周区 (PFA) 的食欲素前体产生的食欲素前体产生的食欲素肽和从中脑中缝核的血清素能神经元突触末梢进入这些下丘脑区域的血清素在调节进食中起重要作用行为和昼夜节律。这表明外侧下丘脑和 PFA 中的 5-羟色胺能和食欲素能系统之间存在密切关系，然而，这方面的研究仍然很少。本研究的目的是通过免疫组织化学方法鉴定小鼠和大鼠下丘脑 PFA 的食欲神经元中的 2C 亚型 (5-HT2CR) 和 1B 亚型 (5-HT1BR) 血清素受体。食欲素-A 的免疫组织化学反应用于鉴定食欲素能神经元，并应用双荧光免疫标记来评估5-羟色胺受体和orexin-A 的共定位。使用双重免疫标记，证明了食欲素-A 和 5-HT2CR 和 5-HT1BR 在不同啮齿动物物种（例如 C57Bl/6J 小鼠和 Wistar 大鼠）的下丘脑 PFA 中的共定位。结果表明，所有的食欲素能神经元都表达两种类型的血清素受体。同时，只有 32-35% 的 5-HT2CR 和 5-HT1BR 位于食欲能神经元中，而其余部分则在其他类型的 PFA 神经元中表达。因此，获得了血清素介导的啮齿动物下丘脑 PFA 中食欲神经元功能活性调节的免疫组织化学证据；还确定血清素的这些作用可以通过 5-HT2CR 和 5-HT1BR 实现。