A method demonstrating motor endplates for light and electron microscopy.

The cytochemical localization of acetylcholinesterase activity at motor endplates is commonly employed prior to electron microscopic examination. Methods which involve the use of thiocholine esters often lead to a loss of resolution due to the spread to surrounding tissues of an extremely dense reaction product. A method is presented in which esterase positive sites are revealed by incubation with hexazotized pararosaniline and indoxyl acetate. The osmiophilic property of the reaction product which remains localized to the synaptic cleft allows speedy identification and detailed examination of the endplate at the ultrastructural level. An application of the procedure is also described.