Tenotomy-induced motor endplate alterations in rat soleus muscle.

The effects of tenotomy on the ultrastructure of rat soleus muscle motor endplates were examined both qualitatively and quantitatively. Rat soleus muscle was studied 2 weeks following tenotomy and compared with normal littermates. The motor endplates from the tenotomized muscles were found to exhibit both degenerative and regenerative changes. Degeneration consisted of postjunctional fold breakdown, exposed junctional folds, myelin-like bodies within the sub-junctional sarcoplasm, and dense bodies within the Schwann cell cytoplasm. The regenerative changes consisted of several small nerve terminals occurring within the same primary synaptic cleft and several axons wrapped by the same Schwann cell. The results demonstrate that tenotomy induces denervation-like changes at endplates that lead to terminal sprouting within the neuromuscular junctional area and remodelling.