Endplate postsynaptic structure dependent upon muscle activity.

The influence of contractile activity on the preservation of the denervated postsynaptic region of the endplate was quantitatively assessed by electron microscopy. The extensor digitorum longus muscle of rats were denervated for 21 days. Denervated animals were divided into two groups, those receiving electrical stimulation treatment (1 h/day for 21 days) and those left untreated. The postsynaptic area of clefts and folds in endplates of type I and II muscle fibers from controls and denervated-stimulated animals were found to be comparable in size whereas the postsynaptic areas in the denervated-non-stimulated muscles were significantly reduced. The results show that electrically-induced contractile activity plays a significant role in the maintenance of the postsynaptic region of the endplate.