A preparation for studying dystrophic avian muscle and neuromuscular junctions

The extensor of the second digit of the chicken wing (EDII) is a small, fast-twitch muscle susceptible to chicken muscular dystrophy and well suited for correlated studies of the morphology and physiology of identified nerve and muscle fibers. In cross section, the dystrophic EDII shows morphological abnormalities common to other well-studied dystrophic chicken muscles. However, in contrast to other dystrophic chicken muscles, living endplates can be viewed in the EDII, facilitating electrophysiological studies. A survey of electrophysiological properties of the EDII muscle in birds 5-16 weeks ex ovo revealed that compared to normal preparations, the dystrophic preparations had: (1) lower resting potentials, (2) lower miniature endplate potential frequency, (3) abortive nerve-evoked action potentials recorded extrajunctionally, and (4) multiple muscle fiber action potentials to a single depolarizing current pulse.