Aggoun-Zouaoui D, Innocenti G M
Institut d'Anatomie, Lausanne, Switzerland.
Eur J Neurosci. 1994 Dec 1;6(12):1846-63. doi: 10.1111/j.1460-9568.1994.tb00577.x.
In kittens, callosal axons originating either from medial area 17 (transient axons) or near the 17/18 border (mostly permanent axons) were labelled with anterogradely transported biocytin; they were reconstructed by computer from serial sections, and their morphologies compared at different ages. During the first and second postnatal weeks both sets of axons branched profusely in the white matter of the lateral gyrus and the number of branches increased with age. The most common type of axon ending was the growth cone; others may have been collapsing growth cones, branches in the process of elimination or early synaptic boutons. Axons from medial area 17 distributed over a broad territory, including the 17/18 border where callosal axons terminate in the adult cat, but without aiming specifically at any one area. The majority of axons and their branches terminated in the white matter or at the bottom of layer VI; exceptionally they extended further into the cortex. Most of the axons originating near the 17/18 border were different from those described above, and the difference increased with age. Although they also terminated profusely in the white matter of the lateral gyrus, most of the branches terminated near the contralateral 17/18 border; they frequently entered the grey matter up to the superficial layers and branched into it. During the third week, axons from medial area 17 were rarely found to extend beyond the corpus callosum, probably because they were in the process of being eliminated. In contrast, axons originating near the 17/18 border had increased their number of branches in the grey matter. In conclusion, during the first and second postnatal weeks axons grew and differentiated according to their origin, and this anticipated whether they would be maintained or eliminated. Neurotrophic signals, possibly from the white matter or the subplate, and growth-inhibiting signals from area 17 may be involved in this process.
在小猫中，起源于内侧17区（短暂轴突）或17/18边界附近（大多为永久轴突）的胼胝体轴突用顺行运输的生物素进行标记；通过计算机从连续切片中重建它们，并比较不同年龄时它们的形态。在出生后的第一周和第二周，两组轴突都在外侧回的白质中大量分支，且分支数量随年龄增加。最常见的轴突终末类型是生长锥；其他的可能是正在塌陷的生长锥、正在被清除过程中的分支或早期突触小体。来自内侧17区的轴突分布在广泛区域，包括成年猫胼胝体轴突终止的17/18边界，但并非专门指向任何一个区域。大多数轴突及其分支终止于白质或VI层底部；例外情况是它们进一步延伸至皮质。大多数起源于17/18边界附近的轴突与上述轴突不同，且这种差异随年龄增加。尽管它们也大量终止于外侧回的白质中，但大多数分支终止于对侧17/18边界附近；它们经常进入灰质直至表层并在其中分支。在第三周，很少发现来自内侧17区的轴突延伸至胼胝体之外，可能是因为它们正处于被清除的过程中。相比之下，起源于17/18边界附近的轴突在灰质中的分支数量增加。总之，在出生后的第一周和第二周，轴突根据其起源生长并分化，这预示着它们是否会被保留或清除。可能来自白质或板下区的神经营养信号以及来自17区的生长抑制信号可能参与了这一过程。
