The organization of retinal ganglion cell (RGC) axons within the optic nerve (ON), chiasm (OCh), and tract of the frog, Rana pipiens, was examined using both light and electron microscopy. In one group of experiments, anterograde and retrograde transport of horseradish peroxidase (HRP) revealed the spatial reorganizations of RGC axons between the retina and central retinorecipient targets. Optic axons form a concentric representation or map of the retinal surface across the distal ON cross-section. Within this map, the distal ON contains two representations of the temporal and nasal retinal quadrants. Fiber reorganizations within the proximal ON result in axons from central RGCs becoming positioned within the dorsal region of the nerve and in axons of more peripheral RGC becoming localized to the ventral, anterior, and posterior margins of the nerve. As a result of this proximal ON fiber reorganization, age-related RGC axons become grouped in laminae that are aligned perpendicular to the posterodorsal-anteroventral axis of the optic projection. Axons occupying complementary positions in different retinal representations converge in a dorsal-to-ventral sequence as the projection passes through the perichiasm. Within the prechiasm, axons separate from the laminated optic projection to form four fascicles; the projection to corpus geniculatum, the projection to the neuropil of Bellonci, the basal optic root, and the marginal optic tract (MOT). In addition, electron microscopic examination of the optic fiber spectrum revealed the morphological organization of the retinofugal projection within the ON and the lateral division of the marginal optic tract (lMOT). Within the ON, myelinated and unmyelinated axons of various sizes are homogeneously distributed. Optic axons are reorganized within the MOT such that within the lMOT large myelinated optic axons become concentrated within ventromedial regions and small myelinated axons become concentrated within the dorsolateral regions. In rostral lMOT larger unmyelinated axons are also concentrated along the ventromedial regions. The morphological organization of the optic axons within lMOT, established by the reorganization of the retinofugal projection within MOT, anticipates the innervation pattern of the optic axons within the laminated, superficial layers of the optic tectum.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-2814 |
| Date | 01 January 1996 |
| Creators | Tyler, Christopher James |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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