Reep R L, Johnson J I, Switzer R C, Welker W I
Department of Physiological Sciences, University of Florida, Gainesville.
Brain Behav Evol. 1989;34(6):365-86. doi: 10.1159/000116523.
Members of the order Sirenia are unique among mammals in being the only totally aquatic herbivores. They display correspondingly specialized physiological, behavioral and anatomical features. There have been few reports concerning sirenian neuroanatomy, and most of these have consisted of gross anatomical observations. Our interest in Sirenia stems from the desire to understand neuroanatomical specializations in the context of behavior and the effort to elucidate trends in mammalian brain evolution. The architecture of frontal regions of cerebral cortex was investigated in several brains of the Florida manatee, Trichechus manatus latirostris. Through observation of sections stained for Nissl substance or myelinated fibers, several distinct cortical areas were identified on the basis of laminar organization. These range from areas with poorly defined laminae to those having 6 well-defined layers, some of which exhibit sublayers. Two cortical areas exhibit pronounced cell clusters in layer VI, and these stain positively for acetylcholinesterase and cytochrome oxidase. We hypothesize that these clusters may be involved in perioral tactile bristle function. Certain of our findings are consistent with previous observations in the literature on the brains of dugongs. On the basis of their lamination patterns, these frontal cortical areas appear to be organized into concentric zones of allocortex, mesocortex and isocortex.
海牛目动物在哺乳动物中独具特色，是唯一完全水生的草食动物。它们相应地展现出了专门化的生理、行为和解剖学特征。关于海牛神经解剖学的报道极少，其中大多数是大体解剖学观察。我们对海牛的兴趣源于想要在行为背景下理解神经解剖学特化以及阐明哺乳动物大脑进化趋势的努力。我们研究了佛罗里达海牛（Trichechus manatus latirostris）几个大脑的大脑皮质额叶区域结构。通过观察尼氏物质染色或有髓纤维染色的切片，基于分层组织确定了几个不同的皮质区域。这些区域从分层不明确的区域到有6个明确分层的区域不等，其中一些还呈现出亚层。两个皮质区域在第VI层有明显的细胞簇，并且这些细胞簇对乙酰胆碱酯酶和细胞色素氧化酶呈阳性染色。我们推测这些细胞簇可能与口周触觉刚毛功能有关。我们的某些发现与之前关于儒艮大脑的文献观察结果一致。基于它们的分层模式，这些额叶皮质区域似乎被组织成了异皮质、中皮质和新皮质的同心区域。
