Montgomery N M, Tyler C, Fite K V
Neuroscience and Behavior Program, University of Massachusetts, Amherst 01003, USA.
J Comp Neurol. 1998 Dec 14;402(2):222-37.
Light microscopic analysis of the optic nerve, chiasm, and optic tracts of Rana pipiens after the anterograde and retrograde transport of horseradish peroxidase has shown that retinal ganglion-cell axons reach the optic nerve head in chronotopically organized fascicles that form bands across the intraocular optic nerve. These bands of fascicles are divided along the midline in a "zone of reorganization" to create two full maps of the retinal surface; however, this map is discontinuous in that nasal and temporal quadrants are adjacent to one another. In the intracranial portion of the optic nerve, axons undergo another reorganization such that peripheral retinal axons shift position and become localized laterally and ventrally, whereas centrally placed axons become localized dorsally. Within this reorganization, the nerve is reconfigured into laminae of axons, and each lamina consists of age-related axons organized into two retinal maps. In the ipsilateral chiasm, axons diverge to form three central, optic tracts: the medial optic tract, the projection to the corpus geniculatum, and the basal optic root. Ipsilateral axons leave the chiasm at the same level of the chiasm as do their contralateral counterparts. The remaining axons converge in the lateral diencephalon to form a fourth fascicle, the marginal optic tract. Thus, within the optic chiasm, a sequence of positional transformations occur that result in the formation of multiple optic pathways. The various changes in axonal trajectory always coincide with changes in the orientation of cell groups that lie within the nerve and optic chiasm.
对经辣根过氧化物酶顺行和逆行运输后的牛蛙视神经、视交叉和视束进行光镜分析显示，视网膜神经节细胞轴突以时间拓扑组织的束状形式到达视神经乳头，这些束状结构在眼内视神经上形成条带。这些束状条带在“重组区”沿中线分开，以形成视网膜表面的两个完整图谱；然而，这个图谱是不连续的，因为鼻侧和颞侧象限彼此相邻。在视神经的颅内部分，轴突经历另一次重组，使得周边视网膜轴突移位并定位在外侧和腹侧，而位于中央的轴突则定位在背侧。在这次重组过程中，神经被重新配置成轴突层，每个层由与年龄相关的轴突组成，这些轴突组织成两个视网膜图谱。在同侧视交叉中，轴突发散形成三条中枢视束：内侧视束、投射到外侧膝状体的视束和基底视根。同侧轴突与对侧轴突在视交叉的同一水平离开视交叉。其余轴突在外侧间脑汇聚形成第四条束，即边缘视束。因此，在视交叉内发生了一系列位置转换，导致形成多条视觉通路。轴突轨迹的各种变化总是与神经和视交叉内细胞群方向的变化相一致。
