Fine structure of synapses in the dorsal nucleus of the lateral geniculate body of normal and blinded rats

Summary Degenerating boutons, observed from 2 to 60 days after eye enucleation, displayed decreased plasma membrane density, increased axoplasmic density, and enlarged mitochondria with deformed cristae when compared with boutons from normal animals. There was also a loss of synaptic plasma membrane specialization and the boutons abnormally indented contiguous dendrites. The number and appearance of synaptic vesicles in some degenerating boutons were notably altered. Phagocytosis of boutons in most instances appeared to be accomplished by astrocytes. When degeneration was first apparent in some boutons, the subsynaptic organelle in the adjacent dendritic cytoplasm was enlarged, somewhat less dense and was associated with small granular and circular profiles. Subsynaptic organelles in experimental animals were absent from contiguities between dendrites and other cell processes, except in a few instances when only small portions of boutons remained at their synaptic sites, suggesting that the organelles disappeared when boutons had been completely phagocytized.Degenerating myelinated axons, observed from 2 to 300 days after enucleation, exhibited the same triad of features as degenerating boutons. They appeared to be phagocytized in most instances by dense glial processes, presumably oligodendrocytic, which were normally situated between the axon and its myelin sheath and were related to the inner mesaxon.This investigation was supported by U.S.P.H.S. Training Grants Nos. 2 T1 GM 202 T1 CA 505506, and 2RO 1 AM 368806.The author expresses his appreciation to Dr. A. J. Ladman for acquainting him with the techniques used in the study and to Dr. R. J. Barrnett for valuable criticism of this report. Gratitude is also extended to Mr. E. Z. Rutkowski for making the drawing.