Degenerative changes in the frog neuromuscular junction after long durations of denervation.

Abstract

Degenerating changes after long durations of denervation have been studied in frog motor end-plate. During the 2nd month of denervation, the Schwann cell undergoes fissuration and the post-synaptic membrane displays the presence of furrows. The extent of the furrows in the post-synaptic membrane and fissuration of Schwann cell increases with increasing periods of denervation. The formation of furrows seem to be correlated with fissure formation in the Schwann cell cytoplasm. During the 4th month of denervation, at places, sequestration of postsynaptic fold from parent muscle occurs. The furrows in the postsynaptic membrane are eventually responsible for the sequestration of folds. In spite of the remarkable morphological changes at certain end-plates after long periods of denervation, the percentage of end-plates displaying spontaneous activity remains the same during this period (3-4 months) as after short periods of denervation (I2 months). This permits us to conclude that only at certain end-plate regions is the Schwann cell capable of producing acetylcholine responsible for miniature endplate potentials (min. e.p.p.s.) and this capacity is maintained until very long periods.