Hypocretins (Hcrt) 1 and 2 are two neuropeptides synthesized from neurons that are located in the perifornical area of the lateral hypothalamus. These neurons project diffusely throughout the central nervous system, and have been implicated in the generation and maintenance of wakefulness, as well as in critical physiological processes that occur during this behavioral state, such as motivation. The hypocretinergic projections towards the feline midbrain have not been studied before. Therefore, the aim of the present study was to analyze their relationship to the midbrain neurons, that are critically involved in the control of sleep and wakefulness. With this purpose, we examined the distribution of Hcrt1-positive fibers in the midbrain and pontomesencephalic area of the domestic cat (Felis catus), and their relationship with catecholaminergic and cholinergic neurons by means of single and double immunohistochemistry. Hcrtergic axons with distinctive varicosities and buttons were heterogeneously distributed, exhibiting different densities in distinct regions of the midbrain. High Hcrtergic fiber densities were observed in the periaqueductal gray, interpeduncular nucleus, locus coeruleus and cholinergic mesopontine regions. In addition, we studied in detail the Hcrtergic projection towards the dopaminergic nuclei of the midbrain. While very few Hcrt + fibers were observed in the substantia nigra pars compacta, the highest density of Hcrtergic fibers was found in the dopaminergic ventral periaqueductal gray area (also called A10dc area); appositions between Hcrtergic terminals and dopaminergic somata and dendrites were observed within this area. Because this dopaminergic area has been involved in the control of wakefulness, the present anatomical data provides relevant support about the role of the Hcrtergic system in the generation of this behavioral state.

中文翻译：

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猫中脑的 Hypocretin (orexin) 免疫反应性：与产生觉醒的相关性

Hypocretins (Hcrt) 1 和 2 是由位于外侧下丘脑的眶周区域的神经元合成的两种神经肽。这些神经元广泛地投射到整个中枢神经系统，并参与觉醒的产生和维持，以及在这种行为状态期间发生的关键生理过程，例如动机。以前没有研究过对猫科动物中脑的低肾上腺素能预测。因此，本研究的目的是分析它们与中脑神经元的关系，这些神经元与睡眠和觉醒的控制密切相关。为此，我们检查了家猫 (Felis catus) 中脑和桥脑中脑区域 Hcrt1 阳性纤维的分布，以及它们与儿茶酚胺能和胆碱能神经元的单一和双重免疫组织化学的关系。具有独特静脉曲张和纽扣的 Hcrtergic 轴突分布不均，在中脑的不同区域表现出不同的密度。在导水管周围灰质、脚间核、蓝斑和胆碱能中桥脑区域观察到高纤维密度。此外，我们详细研究了 Hcrtergic 对中脑多巴胺能核的投射。虽然在黑质致密部观察到很少的 Hcrt + 纤维，但在多巴胺能腹侧导水管周围灰色区域（也称为 A10dc 区域）中发现了最高密度的 Hcrtergic 纤维；在该区域内观察到 Hcrtergic 末端与多巴胺能胞体和树突之间的并置。因为这个多巴胺能区域参与了觉醒的控制，目前的解剖数据为 Hcrtergic 系统在这种行为状态的产生中的作用提供了相关支持。