Aboitiz F
Department of Experimental Morphology, Faculty of Medicine, University of Chile, Santiago, Chile.
Biol Res. 1995;28(3):187-96.
The reptilian brain is characterized by a structure that bulges into the lateral ventricle, called dorsal ventricular ridge (DVR). The DVR was originally considered to be a part of the basal ganglia, although more recent studies indicate that it may correspond to the dorsal part of the hemisphere. The anterior portion of the DVR has several connectional and functional similarities with parts of the mammalian neocortex, for which reason it has been claimed that the two structures can be considered as homologues. In this article I review the evidence supporting and refuting homology of the DVR with different telencephalic structures of mammals, concluding that it is still early to unequivocally ascribe structural correspondences between the different components in the two vertebrate classes. However, a way out of the problem is suggested by comparing the embryonic position of DVR with that of lateral cortex in the reptilian hemisphere. The lateral cortex is considered to be quite comparable in reptiles and mammals, and hence may be a good marker for the original position of the DVR. If the DVR originates dorsal to lateral cortex, it may be considered comparable to parts of the mammalian neocortex, while if it develops in its same position or ventral to it, it may not correspond to the neocortex. Early embryological work indicated that the DVR develops in the same position as the lateral cortex, but arises as a late migration wave, after cells destined to lateral cortex are generated. In other words, instead of being interposed between dorsal and lateral cortices, the DVR may originate in a position overlapping with lateral cortex. If this alternative turns out to be the case, it may imply that the DVR arose de novo, through an extension of the ancestral period of neuroblast proliferation. As a consequence, there may be no structures comparable to it in other vertebrate classes. Finally, it is also proposed that, regardless of whether the DVR and the extrastriate neocortex can or cannot be considered phylogenetic homologues, some of the integrative functions performed by them might have a common evolutionary origin, that became localized in the reptilian DVR and in the mammalian extrastriate neocortex.
爬行动物脑的特征是有一个向侧脑室突出的结构，称为背侧脑室嵴（DVR）。DVR最初被认为是基底神经节的一部分，尽管最近的研究表明它可能相当于半球的背侧部分。DVR的前部与哺乳动物新皮层的部分区域在连接和功能上有一些相似之处，因此有人认为这两个结构可以被视为同源物。在本文中，我回顾了支持和反驳DVR与哺乳动物不同端脑结构同源性的证据，得出的结论是，现在就明确确定这两个脊椎动物类群中不同组成部分之间的结构对应关系还为时过早。然而，通过比较DVR在爬行动物半球中的胚胎位置与外侧皮质的位置，可以找到解决这个问题的方法。在爬行动物和哺乳动物中，外侧皮质被认为具有相当的可比性，因此可能是DVR原始位置的一个良好标记。如果DVR起源于外侧皮质的背侧，那么它可能被认为与哺乳动物新皮层的部分区域具有可比性，而如果它在相同位置或其腹侧发育，那么它可能与新皮层不对应。早期的胚胎学研究表明，DVR在与外侧皮质相同位置发育，但在注定要形成外侧皮质的细胞产生后，作为晚期迁移波出现。换句话说，DVR可能不是位于背侧皮质和外侧皮质之间，而是起源于与外侧皮质重叠的位置。如果事实证明是这种情况，这可能意味着DVR是通过延长神经母细胞增殖的祖先时期而重新出现的。因此，在其他脊椎动物类群中可能没有与之可比的结构。最后，还提出，无论DVR和纹外新皮层是否可以被视为系统发育同源物，它们执行的一些整合功能可能有共同的进化起源，这种起源在爬行动物的DVR和哺乳动物的纹外新皮层中定位。
