Observations on the lateral geniculate nucleus of the monkey (Macaca fascicularis) after eye removal: a light and electron microscopic study. I. Classification and degeneration of optic fibre terminals.

The morphological signs of terminal degeneration are compared at the light and electron microscopic levels in the lateral geniculate nucleus of Macaca fascicularis, from 29 hours to 10 days after eye removal. A close correlation can be found between the appearance of degenerating RLP-terminals (i.e. large terminals containing round vesicles and pale mitochondria), which display marked, unorganized neurofilamentous hyperplasia, and the club-shaped structures revealed by neurofibrillary staning. The ring-shaped entities present in silver-impregnated material closely resemble annular bundles of neurofilaments located in smaller retinal terminals within the neuropil. Various non-filamentous degenerative forms of particularly small terminals are also described. It is concluded that the clubs and rings visualized by neurofibrillary stains in the lateral geniculate nucleus of the monkey do, indeed, represent synaptic structures. The implications of this conclusion are discussed, as are possible reasons that contrary conclusions have been drawn by other investigators. It is further suggested that club and ring formation of degenerating retinal afferents may be related to Y and X axons in the optic tract, respectively.