Distribution of motor nerve sproutings in the mouse gastrocnemius muscle after partial denervation

The distribution and frequency of motor nerve sproutings in the mouse gastrocnemius muscle were examined after a partial denervation. Terminal and nodal sproutings could be seen for a period of 7-28 days after transecting one of the two muscular nerves in the medial head. They grew out not only from the endplates and terminal nerves, but also from the preterminal nerve regions of both the intra- and extramuscular nerve. The terminal sproutings originated from endplates close to the denervated portion and subsequently they were seen farther away in the medial head. Upon regeneration of the originally transected nerve the terminal sproutings were withdrawn in the reverse sequence, i.e., first from the region farthest from the denervated area and last from the region adjacent to the denervation. The frequency of terminal sproutings was constant in the area immediately bordering the denervated portion (11-15% of the total number of endplates). In other areas more distant from the denervated portion, however, it showed a gradient which varied with the time course. The higher the frequency of terminal sproutings, the more actively each endplate produced two or three terminal sproutings without significant difference in length.