Initial changes in the neuromuscular synapses of denervated rat diaphragm

Abstract

The onset of fine structural changes in the axonal terminals of the neuromuscular junction was investigated in the diaphragm of the rat over periods of 3–48 h after phrenicotomy. Changes in the axonal terminals begin as early as 3 h after the operation and are demonstrated by swelling and destruction of mitochondria, reduction in the number of synaptic vesicles and appearance of membrane whorls which envelope the degenerated mitochondria, the dense granules or synaptic vesicles. Fragmentation of the nerve terminals is noted within 6 h after the operation. Up to 12 h, the glial processes have not yet penetrated the synaptic cleft between the subneural apparatus and nerve terminal. In the subsequent 10–h, the intra-axonal changes are intensified and the axonal fragments are completely involved in and phagocytosed by the Schwann cells. At the end of the first 24 h, the Schwann cells replace the destroyed nerve terminals. Under identical experimental conditions, an exceptional variety and great differences in the degree of degenerative changes are observed. Degenerative nerve endings are established with filamentous reaction.