Hudson_1984_Brain.Res_296_319

Ultrastructural alterations were analyzed following a single subperineural injection of batrachotoxin (BTX) into the rat peroneal nerve 10-12 mm proximal to its entrance into the extensor digitorum longus (EDL) muscle. At the injection site, most axons underwent reversible changes. Internodal segments of myelin degenerated and were phagocytized without apparent damage to the axon cylinders. Newly forming myelin sheaths were observed by 10 days after injection. Similarly, motor endplates were reversibly altered. By 18 h following injection, most nerve terminals were withdrawn from the postsynaptic elements but reinnervated original endplate regions between 7 and 10 days after injection. These observations explain earlier findings in which muscle membrane potential decreased immediately and spontaneous miniature endplate potentials (MEPPs) and evoked transmitter release were absent from 18 h to 7 days following injection. We suggest that these reversible changes were the result of an insufficient supply of neuronal materials due to BTX-induced blockade of fast axonal transport. Normal physiological function and morphology were restored after fast axonal transport recovered and sufficient quantities of appropriate materials necessary for the maintenance of the nerve terminals and muscle membrane potential were again transported distally from the nerve cell body.