A histochemical study of the cholinesterase activity in the neuromuscular junction in developing chick skeletal muscles.

The development of the motor nerve ending has been studied by many investigators (TELLO, 1922, VISINTINI e LEVI-MONTALCINI, 1939; CUAJUNCO, 1942; KUPFER and KOELLE, 1951) and authors such as GEREBTZOFF (1959), MUMENTHALER and ENGEL (1961), and WAKE (1964) used the chick skeletal muscle to examine the morphogenesis of the ending. However, their studies were confined to the light microscopic observation using the histochemical cholinesterase (ChE) method as well as the silver impregnation technique. Moreover, the thiolacetic acid method used by these authors for the demonstration of the cholinesterase activity comprises some serious difficulties to obtain the clear localization of the reaction products. One of the drawbacks involved in the method is a spontaneous decomposition of substrate, thiolacetic acid, in the incubation medium, causing diffusion artefacts, and it is not unlikely that the apparent discrepancies among results obtained by these workers are based on the technical difficulties involved in the method. It is the main purpose of the present investigation to follow the morphogenesis of the motor nerve ending in the chick skeletal muscle fibers chronologically by the new copper ferrocyanide method demonstrating ChE activity (KARNOVSKY and ROOTS, 1964; KARNOVSKY, 1964), in particular in order to reevaluate the stage of an initial onset of the motor nerve ending formation in developing skeletal muscles. The enzymatic study is extended to the level of the ultrastucture with materials of a certain stage and the silver impregnation technique (SCHEFTHALER and MAYET, 1958) is also used as an ancillary method in the present study.