Slomianka L, West M J
Department of Neurobiology, University of Aarhus, Denmark.
J Comp Neurol. 1989 Feb 22;280(4):544-52. doi: 10.1002/cne.902800405.
To investigate the structural changes in the hippocampal region (subiculum, Ammon's horn, and area dentata) associated with speciation, the volumes of homologous components of this region of the forebrain were compared in the two closely related murine rodent species, Apodemus flavicollis (yellow-necked wood mice) and A. sylvaticus (long-tailed field mice), and in two geographically separated groups of A. sylvaticus. With the exception of the mossy fiber zone, no significant differences were found in the relative sizes of the components of Ammon's horn. Significant interspecific differences were found in the deep subiculum, in the intermediate (medial perforant path) and deep (commissural-associational) zones of the molecular layer of the area dentata, and in the hilus. A significant intraspecific difference was found in the combined intermediate and superficial (medial and lateral perforant path) zone of the dentate molecular layer. Differences found in the relative size of the hilus and the mossy fiber zone of Ammon's horn were complementary in that the combined volumes of these zones, which are both terminal fields of dentate granule cells, did not differ in the species. This finding provides evidence that the distribution of the terminal field of a projection system can be altered while the size of the terminal field is maintained. Within the hippocampal region, components of Ammon's horn appear well suited for quantitative comparative studies that span taxonomic units beyond the species level. In agreement with previous quantitative studies, differences in the volumes of components of Ammon's horn found in species of different orders are more likely to reflect phylogenetic trends rather than changes resulting from specializations of the particular species used. This is not true for the subiculum and the components of the area dentata. Experimentally induced changes in the connectivity of the hippocampal region are discussed in terms of the structural changes which may be responsible for the quantitative differences observed between the two species studied here.
为了研究与物种形成相关的海马区（海马下托、海马角和齿状区）的结构变化，在前脑该区域同源成分的体积方面，对两种亲缘关系密切的鼠类啮齿动物——黄颈姬鼠（Apodemus flavicollis）和小林姬鼠（A. sylvaticus），以及地理上分隔的两组小林姬鼠进行了比较。除了苔藓纤维区外，海马角各成分的相对大小未发现显著差异。在海马下托深部、齿状区分子层的中间（内侧穿通通路）和深部（连合-联合）区以及齿状回中发现了显著的种间差异。在齿状分子层的中间和浅层（内侧和外侧穿通通路）联合区发现了显著的种内差异。在海马角的齿状回和苔藓纤维区相对大小上发现的差异是互补的，因为这两个都是齿状颗粒细胞终末场的区域的总体积在物种间没有差异。这一发现提供了证据，即投射系统终末场的分布可以改变，而终末场的大小保持不变。在海马区内，海马角的成分似乎非常适合跨越物种水平以上分类单元的定量比较研究。与之前的定量研究一致，在不同目物种中发现的海马角各成分体积差异更有可能反映系统发育趋势，而不是所研究特定物种特化导致的变化。对于海马下托和齿状区的成分来说并非如此。根据可能导致此处研究的两个物种间观察到的定量差异的结构变化，讨论了海马区连接性的实验性诱导变化。
