Motor end-plate fine structure in acrylamide dying-back neuropathy: A sequential morphometric study

Extensor digitorum longus end-plate ultrastructure was quantitatively analyzed in rats fed 300 ppm acrylamide in their diet for 10 to 90 days and in control animals. After 20 days of treatment the mean nerve terminal area was markedly enlarged due to distention by neurofilaments. Subsequently more than half of all nerve terminals disappeared, leaving behind denuded or Schwann-cell-covered postsynaptic regions. Denervation of the end- plates was subtotal; at least one nerve terminal persisted at each junction. Nerve terminals surviving after 30 days had a normal mean size and a reduced content of mitochondria and synaptic vesicles. Postsynaptic atrophy developed only after the presynaptic abnormalities were fully established. After cessation of treatment nerve terminals returned to the end- plates within 30 days but the synaptic vesicle and mitochondrial content of the terminals remained depressed even after 60 days of recovery.