Maseko Busisiwe C, Patzke Nina, Fuxe Kjell, Manger Paul R
School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, Republic of South Africa.
Brain Behav Evol. 2013;82(2):83-128. doi: 10.1159/000352004. Epub 2013 Sep 6.
The current study examined the organization of the diencephalon and brainstem of the African elephant (Loxodonta africana) - a region of the elephant brain that has not been examined for at least 50 years. The current description, employing material amenable for use with modern neuroanatomical methods, shows that, for the most part, the elephant diencephalon and brainstem are what could be considered typically mammalian, with subtle differences in proportions and topology. The variations from these previous descriptions, where they occurred, were related to four specific aspects of neural information processing: (1) the motor systems, (2) the auditory and vocalization systems, (3) the orexinergic satiety/wakefulness centre of the hypothalamus and the locus coeruleus, and (4) the potential neurogenic lining of the brainstem. For the motor systems, three specific structures exhibited interesting differences in organization - the pars compacta of the substantia nigra, the facial motor nerve nucleus, and the inferior olivary nuclear complex, all related to the timing and learning of movements and likely related to the control of the trunk. The dopaminergic neurons of the substantia nigra appear to form distinct islands separated from each other by large fibre pathways, an appearance unique to the elephant. Each island may send topologically organized projections to the striatum forming a dopaminergic innervation mosaic that may relate to trunk movements. At least five regions of the combined vocalization production and auditory/seismic reception system were specialized, including the large and distinct nucleus ellipticus of the periaqueductal grey matter, the enlarged lateral superior olivary nucleus, the novel transverse infrageniculate nucleus of the dorsal thalamus, the enlarged dorsal column nuclei and the ventral posterior inferior nucleus of the dorsal thalamus. These specializations, related to production and reception of infrasound, allow the proposal of a novel concept regarding the reception and localization of infrasonic sources. The orexinergic system of the hypothalamus displayed a medial hypothalamic parvocellular cluster of neurons in addition to the magnocellular clusters typical of mammals located in the lateral hypothalamus, and a novel medial division of the locus coeruleus was observed in the pons. These systems are related to appetitive drive and promotion of wakefulness, two aspects of elephant behaviour that appear to be inextricably linked. Lastly, we observed an extensive potential neurogenic lining of the ventricles throughout the brainstem that is present in even quite old elephants, although the function of these cells remains elusive. These observations combined demonstrate that, while much of the elephant brainstem is typically mammalian, certain aspects of the anatomy related to specialized behaviour of elephants are present and instructive in understanding elephant behaviour.
当前的研究考察了非洲象（Loxodonta africana）间脑和脑干的结构——这是大象大脑中至少50年未被研究过的区域。当前的描述采用了适用于现代神经解剖学方法的材料，结果表明，在很大程度上，大象的间脑和脑干可被认为具有典型的哺乳动物特征，只是在比例和拓扑结构上存在细微差异。与先前描述的不同之处，若有差异出现，与神经信息处理的四个特定方面有关：（1）运动系统，（2）听觉和发声系统，（3）下丘脑的食欲素能饱腹感/觉醒中枢和蓝斑，以及（4）脑干潜在的神经源性内衬。对于运动系统，三个特定结构在组织上呈现出有趣的差异——黑质致密部、面神经运动核和下橄榄核复合体，所有这些都与运动的时间和学习有关，并且可能与象鼻的控制有关。黑质的多巴胺能神经元似乎形成了由大纤维通路彼此分隔开的独特岛状结构，这是大象独有的外观。每个岛状结构可能向纹状体发送拓扑组织化的投射，形成一个可能与象鼻运动相关的多巴胺能神经支配镶嵌图。发声产生与听觉/地震接收系统的至少五个区域具有特殊性，包括导水管周围灰质中较大且独特的椭圆核、扩大的外侧上橄榄核、丘脑背侧新的横向下膝状体核、扩大的薄束核以及丘脑背侧的腹后下核。这些与次声产生和接收相关的特殊性，使得关于次声源接收和定位的新概念得以提出。下丘脑的食欲素能系统除了在外侧下丘脑有典型的哺乳动物大细胞簇外，还显示出内侧下丘脑小细胞神经元簇，并且在脑桥中观察到蓝斑的一个新的内侧部分。这些系统与食欲驱动和觉醒促进有关，而这两个方面似乎是大象行为中紧密相连的部分。最后，我们观察到整个脑干中脑室存在广泛的潜在神经源性内衬，即使在相当年老的大象中也存在，尽管这些细胞的功能仍然难以捉摸。这些观察结果共同表明，虽然大象脑干的大部分具有典型的哺乳动物特征，但与大象特殊行为相关的某些解剖学方面是存在的，并且对于理解大象行为具有指导意义。
