The fate of synaptic membranes of degenerating optic nerve terminals, and their role in the mechanism of trans-synaptic changes

Summary The fate of synaptic membranes of degenerating optic nerve terminals has been studied in the lateral geniculate nucleus of Rhesus monkey after eye enucleation. It was shown that pre-synaptic and post-synaptic membranes remain in close apposition to each other during all stages of degeneration and phagocytosis of affected terminals. As a result of this, fragments of presynaptic terminals were engulfed within glial processes, together with synaptic thickenings and parts of post-synaptic dendrites. On occasion small pieces of the degenerating terminals together with the synaptic membranes were engulfed by the post-synaptic dendrite. It is proposed that this pattern of removal of degenerating optic terminals results in injury to the post-synaptic cells, and triggers the transneuronal degeneration.