College of Medicine, Ajman University, Ajman, United Arab Emirates.
Center of Medical and Bio-allied Health Sciences Research, Ajman University, Ajman, United Arab Emirates.
J Comp Neurol. 2024 Mar;532(3):e25602. doi: 10.1002/cne.25602.
The orexinergic/hypocretinergic system, while having several roles, appears to be a key link in the balance between arousal and food intake. In birds, to date, this system has only been examined anatomically in four species, all with brains smaller than 3.5 g and of limited phylogenetic range. Here, using orexin-A immunohistochemistry, we describe the distribution, morphology, and nuclear parcellation of orexinergic neurons within the hypothalami of a Congo gray and a Timneh gray parrot, a pied crow, an emu, and a common ostrich. These birds represent a broad phylogeny, with brains ranging in size from 7.85 to 26.5 g. Within the hypothalami of the species studied, the orexinergic neurons were organized in two clusters, and a densely packed paraventricular hypothalamic nucleus cluster located within the medial hypothalamus (Hyp), but not contacting the ventricle, and a more loosely packed lateral hypothalamic cluster in the lateral Hyp. Stereological analysis revealed a strong correlation, using phylogenetic generalized least squares regression analyses, between brain mass and the total number of orexinergic neurons, as well as soma parameters such as volume and area. Orexinergic axonal terminals evinced two types of boutons, larger and the smaller en passant boutons. Unlike the orexinergic system in mammals, which has several variances in cluster organization, that of the birds studied, in the present and previous studies, currently shows organizational invariance, despite the differences in brain and body mass, phylogenetic relationships, and life-histories of the species studied.
食欲素能/下丘脑分泌素能系统虽然具有多种作用，但似乎是觉醒和摄食之间平衡的关键环节。迄今为止，在鸟类中，该系统仅在四种鸟类中进行了解剖学研究，这四种鸟类的大脑均小于 3.5g，且系统的进化范围有限。在这里，我们使用食欲素-A 免疫组织化学方法，描述了刚果灰鹦鹉和提姆尼灰鹦鹉、 pied crow、鸸鹋和普通鸵鸟下丘脑内食欲素能神经元的分布、形态和核分区。这些鸟类代表了广泛的进化，大脑大小从 7.85 到 26.5g 不等。在所研究的物种的下丘脑内，食欲素能神经元组织在两个簇中，一个密集的室旁下丘脑核簇位于内侧下丘脑（Hyp）内，但不与脑室接触，另一个更松散的外侧下丘脑簇位于外侧 Hyp 内。通过使用系统发育广义最小二乘回归分析的体视学分析，发现脑质量与食欲素能神经元的总数以及体细胞参数（如体积和面积）之间存在很强的相关性。食欲素能轴突末端表现出两种类型的终末，较大的和较小的游走终末。与哺乳动物中具有多种簇组织变异性的食欲素能系统不同，在本研究和以前的研究中，鸟类的食欲素能系统目前表现出组织不变性，尽管在脑质量和身体质量、进化关系以及研究物种的生活史方面存在差异。
