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Changing retinal ganglion cell distribution in the frog Heleioporus eyrei
Author(s) -
Dunlop S. A.,
Beazley L. D.
Publication year - 1981
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902020208
Subject(s) - horseradish peroxidase , nissl body , biology , anatomy , cresyl violet , ganglion , retina , axon , giant retinal ganglion cells , parasol cell , staining , biophysics , optic nerve , retinal ganglion cell , neuroscience , biochemistry , genetics , enzyme
The number and distribution of retinal ganglion cells were examined in the burrowing frog Heleioporus eyrei. Retinae of midlarval tadpoles, animals at metamorphic climax, 2‐month postmetamorphic juveniles, and adults were flat‐mounted and stained with cresyl violet. The identity of retinal ganglion cells was established in the adult using retrograde transport of horseradish peroxidase applied to the optic nerve. Horseradish peroxidase‐filled cells, identified as neurons, had an axon hillock and contained Nissl substance within a pale‐staining cytoplasm. Glial cells, which never filled with horseradish peroxidase, had very dark nuclei and a thin film of cytoplasm lacking Nissl. The diameter of horseradish peroxidase‐filled neurons ranged from 7 to 16 m̈m. Cells identified as glia, which represented less than 1% of cells in the ganglion layer, were 3–8 m̈m in diameter. There were, however, a proportion (14%) of cells which did not fill with horseradish peroxidase. These small cells (5–7 m̈m diameter) had a similar appearance to the horseradish peroxidase‐filled cells and may be neuronal. The total number of ganglion cells rose almost 6‐fold, being approximately 61,000–83,000 for the tadpole, 100,000–118,000 at metamorphic climax, 170,000–184,000 in juveniles, and 454,000–495,000 in adults. Estimates for left and right sides in the same animal were within 1.9% for the tadpole, 1.6% at metamorphic climax, and 7.5% in the juvenile. Fiber counts were made by electron microscopy and were within 11% of ganglion cell estimates for the adult and within 5% for the remaining stages. Overall ganglion cell densities dropped from tadpoles to adults as retinal area increased 20‐fold. The topography of retinal ganglion cells changed at each stage. In the tadpole there was a radial anisotropy, the lowest density being in central retina. Anisotropy was still characteristically radial in animals at metamorphic climax but was less extreme since cell densities had dropped, particularly at the periphery. In contrast, the juvenile was beginning to form a visual streak with higher density patches appearing in nasal and temporal retina. The adult topography was similar, the highest densities still being in the nasal and temporal retina, but now a complete band of intermediate density extended across the horizontal axis of the eye. The transition of retinal ganglion cell topography to produce a visual streak after metamorphosis presumably reflects a change in life‐style from an aquatic, browsing tadpole to an animal which actively seeks its prey. The striking changes in retinal ganglion cell number and distribution provide an experimental model to study the continual development of the amphibian eye. The implications of this finding in terms of neuronal plasticity of connections formed within the visual centers are discussed.