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Long‐term survival of centrally projecting axons in the optic nerve of the frog following destruction of the retina
Author(s) -
Matsumoto Dan E.,
Scalia Frank
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.902020112
Subject(s) - retina , optic nerve , biology , anatomy , ganglion , tectum , axon , retinal , horseradish peroxidase , rana , axoplasmic transport , population , cell bodies , retinal ganglion cell , midbrain , central nervous system , neuroscience , medicine , biochemistry , enzyme , environmental health
A significant number of unmyelinated axons and their synaptic endings in the frog, Rana pipiens , were found to retain a normal morphology long after separation from their cell bodies. At the end of various survival periods following unilateral removal of the retina, horseradish peroxidase (HRP) was administered to the optic nerve stump by a fiber‐filling method. In frogs maintained at 20°C, unmyelinated optic nerve axons conducted HRP from the site of application in the orbit to layers A, C, and E of the contralateral optic tectum, even though their retinas had been removed up to 69 days earlier. Such fiberfilling was absent beyond 19 days in other frogs surviving at 35°C. No labeled fibers were continuous with any intracerebral neurons. The HRP was always localized intraaxonally, and the marked axons and terminals were ultrastructurally normal. Counts of surviving axons from electron micrographs of the optic nerves showed that, at 20°C, more than half of the normal complement of unmyelinated axons disappeared in the first 10 days. All the myelinated axons degenerated during the first 6 weeks survival. However, approximately 55,000 normal‐appearing unmyelinated axons (12% of the unmyelinated fiber population) persisted in the optic nerve at 10 weeks following removal of the retina. The survival rate was lower at 35°C. In other frogs, one eye was injected with 3 H‐leucine to initiate axonal transport into the retinal ganglion cell axons. That eye was removed 48 hours later. Autoradiographic analysis of brain sections of frogs surviving an additional 31 to 61 days at 20°C showed strong labeling of the optic tract and layers A, C, and E of the contralateral optic tectum. The absence of displaced ganglion cells that might exist within the optic nerve was verified by other observations. It is hypothesized that the potential shown by frog optic axons for long‐term survival in the absence of the cell‐body expresses a general property of vertebrate (and invertebrate) axons, rather than a special property of the frog optic nerve.