School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, Johannesburg, South Africa.
J Chem Neuroanat. 2012 Jul;44(2):98-109. doi: 10.1016/j.jchemneu.2012.06.001. Epub 2012 Jun 8.
The present study describes the organization of the orexinergic (hypocretinergic) neurons in the hypothalamus of the giraffe and harbour porpoise--two members of the mammalian Order Cetartiodactyla which is comprised of the even-toed ungulates and the cetaceans as they share a monophyletic ancestry. Diencephalons from two sub-adult male giraffes and two adult male harbour porpoises were coronally sectioned and immunohistochemically stained for orexin-A. The staining revealed that the orexinergic neurons could be readily divided into two distinct neuronal types based on somal volume, area and length, these being the parvocellular and magnocellular orexin-A immunopositive (OxA+) groups. The magnocellular group could be further subdivided, on topological grounds, into three distinct clusters--a main cluster in the perifornical and lateral hypothalamus, a cluster associated with the zona incerta and a cluster associated with the optic tract. The parvocellular neurons were found in the medial hypothalamus, but could not be subdivided, rather they form a topologically amorphous cluster. The parvocellular cluster appears to be unique to the Cetartiodactyla as these neurons have not been described in other mammals to date, while the magnocellular nuclei appear to be homologous to similar nuclei described in other mammals. The overall size of both the parvocellular and magnocellular neurons (based on somal volume, area and length) were larger in the giraffe than the harbour porpoise, but the harbour porpoise had a higher number of both parvocellular and magnocellular orexinergic neurons than the giraffe despite both having a similar brain mass. The higher number of both parvocellular and magnocellular orexinergic neurons in the harbour porpoise may relate to the unusual sleep mechanisms in the cetaceans.
本研究描述了长颈鹿和港湾鼠海豚下丘脑的食欲素能（hypocretinergic）神经元的组织，这两种动物都是偶蹄目和鲸目哺乳动物的成员，它们具有单系祖先。从两只亚成体雄性长颈鹿和两只成年雄性港湾鼠海豚的大脑中脑冠状切片，并用食欲素-A 进行免疫组织化学染色。染色结果表明，根据细胞体体积、面积和长度，食欲素能神经元可以很容易地分为两种不同的神经元类型，即小细胞和大细胞食欲素-A 免疫阳性（OxA+）群。大细胞群可以根据拓扑学进一步细分为三个不同的簇——一个主要簇位于peri 穹窿和外侧下丘脑，一个簇与未定带相关，一个簇与视束相关。小细胞神经元位于下丘脑内侧，但不能再细分，而是形成一个拓扑上无定形的簇。小细胞簇似乎是偶蹄目所特有的，因为到目前为止，这些神经元尚未在其他哺乳动物中描述过，而大细胞核似乎与其他哺乳动物中描述的类似核同源。基于细胞体体积、面积和长度，长颈鹿中小细胞和大细胞神经元的总体大小大于港湾鼠海豚，但港湾鼠海豚的小细胞和大细胞食欲素能神经元数量都多于长颈鹿，尽管两者的脑质量相似。港湾鼠海豚中小细胞和大细胞食欲素能神经元数量较多可能与鲸目动物的特殊睡眠机制有关。
