An electron microscopic study of denervated motor endplates after zinc iodide-osmium impregnation

With the aid of the zinc iodide-osmium staining the disintegration and absorption of the terminal axon in motor endplates of the mouse diaphragm were studied after unilateral section of the phrenic nerve. In contrast to the specific staining of synaptic vesicles in the normal motor endplate the whole disintegrating nerve terminals show electron-dense precipitations in the denervated endplate. From the occurrence of stained vesicles in the Schwann cell 1 day after denervation and their disappearance 2 days later we conclude that the terminal axon, after its fragmentation and ingestion, is metabolized by the Schwann cell during degeneration of the motor endplate.