Action potentials in slow muscle fibres of the frog during regeneration of motor nerves.

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Abstract
Pyriformis muscles of Rana temporaria were denervated by crushing the sciatic nerve inside the pelvis. At different times during regeneration of the nerve, slow muscle fibers were examined for the presence of all-or-none responses. During the early period of re-innervation (35-60 days), slow muscle fibers were non-selectively re-innervated by (foreign) fast-conducting motor axons. All slow fibers during this period were able to produce full sized action potentials, with overshoot. Action potentials markedly decreased in amplitude and eventually disappeared completely between day 61-110 following denervation; during this period, slow muscle fibers were re-innervated by slowly-conducting motor axons. Functional re-innervation by slowly-conducting motor axons, in the late stages of re-innervation, was not a necessary condition for the suppression of the action potential. Slow fibers innervated by fast motor axons, and denervated slow fibers, lost the action potential simultaneously with slow fibers which were re-innervated by slowly-conducting motor axons. Apparently (small) slowly-conducting motor axons can exert a trophic influence on the slow fiber membrane, independent of their synaptic function.