Characteristics of reinnervation of skeletal muscle in the rat

Both extra and intracellular fibrillation activity recorded in vivo was studied during nerve-muscle reinnervation, in control rats and in rats treated with actinomycin D. The study was performed at different times after nerve crushing. End-plate potentials (EPP's) and muscle action potentials were always present on the eleventh day after denervation. Fibrillation activity recorded extracellularly began to decrease on the twelfth day. Intracellular fibrillation activity was found in single muscle cells simultaneously with evoked EPP's muscle action potentials. In early stages of reinnervation two EPP's were recorded in a single muscle cell, thus indicating double innervation. When presynaptic action of actinomycin D was tested no changes were found in miniature end-plate potential frequency. Muscles from rats submitted to early treatment with actinomycin D did not show any delay in the onset of reinnervation. In muscles from rats submitted to late treatment, extrasynaptic sensitivity to acetylcholine was ascertained regardless of the presence of functional reinnervation. Chronic stimulation of denervated muscles, while suppressing fibrillation activity, did not interfere with reinnervation. The results reported suggest that reinnervation can take place independently of fibrillation activity as well as of extrasynaptic receptors.