PHYSIOLOGICAL-CHARACTERISTICS OF IDENTIFIED MOTOR UNITS IN THE MOUSE EXTENSOR DIGITORUM LONGUS MUSCLE - AN IN-VITRO APPROACH

Physiological, histochemical, and morphometric properties of fast-twit ch single motor units were studied in mouse extensor digitorum, longus muscles in an in vitro ventral root-nerve-muscle preparation. Single motor units were functionally isolated by microdissection of the ventr al root, and the glycogen depletion technique was used to demonstrate the component muscle fibers. Monoclonal antibodies were used to identi fy their myosin heavy chain composition. The technique allows one to c orrelate physiological characteristics of single motor units with fibe r type but is less useful for morphological assessment of motor unit s ize as a result of failure to deplete glycogen from all fibers of moto r units containing fibers with high oxidative capacity.