Submicroscopic Changes of the Synapse after Nerve Section in the Acoustic Ganglion of the Guinea Pig. an Electron Microscope Study*,$

The occurrence of pathological changes in synaptic endings has been recognized in a number of disease conditions by early investigators (1-3). In cases of Friedreich's disease, Estable (4) showed that the degeneration of the presynaptic fiber is accompanied by hypertrophy, hyperargentophilia, and detachment of the neuropodia and other nerve endings, from the synaptic junctions. There is an abundant literature on the degeneration of synaptic endings after experimental section of the axon both in the peripheral and central nervous system (for references, see 5-8). The morphological changes occurring in the nerve terminals have been thoroughly studied with the light microscope in material prepared by various silver staining techniques. The alterations consist primarily of swelling and subsequent fragmentation and granulation of the endings (9, 10, 5, 11, and 12). These degenerative changes can be detected very soon after severance of the nerve fibers. In the cephalopods detectable alterations of the bouton-like nerve terminations were present 15 hours after section of the axons (9). In the central nervous system, swelling of the nerve endings has been observed as early as 24 hours after section (10, 5, 12). These changes generally precede the morphological alterations of the nerve fibers in Wallerian degeneration and are already very prominent after 48 to 72 hours. I t has also been demonstrated that the changes following nerve section differ from those that take place in the postmortem degeneration of the endings (13). In peripheral synapses regressive changes have also been studied physiologically. I t has been shown that neuromuscular transmission fails before the nerve fiber has ceased to conduct (14-15). Furthermore this failure is gradual