The optic tectum of a perciform teleost III. Electron microscopy of degenerating retino‐tectal afferents

Abstract

Abstract Axonal and terminal degeneration has been studied with the electron microscope in the optic tectum of the teleost Eugerres plumieri , at 7, 15 and 35 days after eye enucleation. The distribution of degenerating elements corresponds to that found in light microscopical studies; it is confined to myelinated axons and terminals in stratum opticum, stratum fibrosum et griseum superficiale, and stratum album centrale. No degeneration was seen in other strata. Early axonal degeneration includes increase in filaments, sometimes accompanied by axoplasmic densification, as well as formation of vacuoles and membrane bound bodies. Myelin appears normal in a large proportion of axons at seven days after eye enucleation. Degenerating terminals may show increased number of filaments as well as densification, but neither reaction is marked; they show characteristic vacuoles and membrane bound bodies. Increase in vesicle size was observed only in few degenerating terminals. At 15 days after enucleation, there is myelin breakdown, bizarre axoplasmic inclusions, and glial and perivascular cell ingestion of debris. At 35 days, no terminals are found, and various stages of axonal degeneration are present.