Enlargement of synaptic vesicles as an early sign of terminal degeneration in the rat caudate nucleus

The enlargement of synaptic vesicles in degenerating terminals which has recently been demonstrated in the pigeon retino‐tectal fibers as an early sign of secondary degeneration, is confirmed in the rat cortico‐caudate system. Enlarged synaptic vesicles appear already five hours postoperatively in endings which subsequently undergo the classical changes of Wallerian degeneration. Three categories of terminals, SS−, SL− and F‐terminals, are defined on the basis of shape and size of synaptic vesicles in the normal rat caudate nucleus. Only the first category is involved after cortical ablation, while the others remain unchanged.