Effects of acrylamide and other sulfhydryl compounds in vivo and in vitro on staining of motor nerve terminals by the zinc iodide-osmium technique.

The zinc iodide-osmium technique blackens motor nerve terminals by selectively staining synaptic vesicles. Intraperitoneal injections of acrylamide (30 mg/kg/day, 5 times each week) cause inhibition of staining by this technique so that approximately one third of the end-plates in rat sternocostalis muscle are unstained after 24 hours, and by 17 days more than 70% are unstained. This is not associated with nerve fiber degeneration. A similar inhibition of staining can also be shown after prior incubation of the sternocostalis muscle in 4 mM acrylamide in oxygenated Ringer's solution. Intraperitoneal injection of the thiol group blocker N-ethylmaleimide also causes marked inhibition of staining of motor end-plates by this method. Dithiothreitol, which prevents the oxidation of thiol groups, will partly prevent the inhibition of staining by both acrylamide and N-ethylmaleimide, when given in vivo.