Spontaneous Miniature Potentials in Denervated Coxal Muscle Fibres of the American Cockroach

1. Functional changes following denervation have been studied by intracellular recording at the neuromuscular junction of the cockroach coxal muscle. 2. Spontaneous subthreshold activity disappeared together with nerve-muscle transmission in about 2 days after nerve section at 26°C. The onset of the failure was mainly dependent on the temperature and also on the length of the transected distal stump. After complete cessation of the miniature excitatory postsynaptic potentials (MEPSPs) for about 3 weeks at 26°C, the miniature potentials resumed at a slower rate. Regeneration occurred faster when axotomy was performed by crushing the nerve rather than by sectioning. 3. Resumption of the MEPSPs was accompanied by response to nerve stimulation. However, hypertonic and hypotonic saline, and excess potassium, failed to increase the frequency of the resumed MEPSPs recorded between 15 and 45 days following denervation. 4. It is suggested that the resumed spontaneous release of transmitter may be derived from regenerating nerve terminals.