Regidor J, Divac I
Institute of Neurophysiology, School of Medicine, University of Copenhagen, Denmark.
Brain Behav Evol. 1987;30(5-6):328-41. doi: 10.1159/000118655.
Architectural characteristics of the thalamus in echidnas and rats were compared in sections stained to reveal cell bodies, myelin, acetylcholinesterase, succinate dehydrogenase and cytochrome oxidase. Numerous species differences were noticed: in general, the thalamus is architecturally more homogeneous in echidnas than in rats, especially anteriorly. In this report we emphasize the presence of a relatively large structure localized in the anteromediodorsal part of the thalamus in echidnas. This structure, previously shown to project to the frontal cortex, contains very small amounts of acetylcholinesterase and the oxidative enzymes; in this respect it resembles the mediodorsal nucleus of rats. The same properties make this formation different from the anterodorsal and anteroventral nuclei in rats, the equivalents of which could not be identified in echidnas. The anteromediodorsal region of the thalamus in echidnas consists chiefly of two cytoarchitecturally different regions: the medial, 'polymorphic' part contains relatively small, densely packed, multiform perikarya, whereas the lateral, 'monomorphic' part is characterised by larger, sparse neurons with little cytoplasm and round, large, empty-looking nuclei in which the nucleolus is clearly seen. We conclude tentatively that this brain structure of echidnas corresponds to the mediodorsal nucleus in placental species. Further studies of connections and chemical properties will be essential to determine the degree of correspondence of the presumed 'frontal lobe system' in echidnas to that in other mammals.
在对针鼹和大鼠丘脑的细胞体、髓鞘、乙酰胆碱酯酶、琥珀酸脱氢酶和细胞色素氧化酶进行染色的切片中，比较了两者的结构特征。发现了许多物种差异：一般来说，针鼹丘脑的结构比大鼠更均匀，尤其是在前部。在本报告中，我们强调在针鼹丘脑前内侧背侧部分存在一个相对较大的结构。这个结构先前已被证明投射到额叶皮质，含有极少量的乙酰胆碱酯酶和氧化酶；在这方面它类似于大鼠的背内侧核。同样的特性使这个结构不同于大鼠的前背核和前腹核，在针鼹中无法确定其对应物。针鼹丘脑的前内侧背侧区域主要由两个细胞结构不同的区域组成：内侧的“多形性”部分含有相对较小、紧密排列的多形性核周体，而外侧的“单形性”部分的特征是神经元较大、稀疏，细胞质少，细胞核圆形、大且看起来中空，其中核仁清晰可见。我们初步得出结论，针鼹的这种脑结构对应于胎盘类物种的背内侧核。进一步研究其连接和化学性质对于确定针鼹假定的“额叶系统”与其他哺乳动物的对应程度至关重要。
