Time course of miniature currents in regenerating neuromuscular junctions of the cockroach Periplaneta americana

Miniature excitatory junctional currents in regenerating neuromuscular junctions have been recorded from the denervated leg muscle fibers of the cockroach, Periplaneta americana with an external focal electrode. Miniature currents first reappeared after 21 days after denervation at 26 degrees C. These currents occurred at a lower frequency and had a slower time course than miniature currents at normal junctions. The decay time constant of the falling phase of the earliest current was more than twice the control and the mean amplitude was less than half of the control. The decay time constant of the currents became shorter and their amplitude increased with increasing time after regeneration and approached control values at about 60 days after crushing the nerve. During regeneration of neuromuscular junctions, the falling phase of the miniature currents was always along a single exponential just as in the control. The observed change in the decay time constant of the currents suggests that the open time of the overall population of synaptic receptor-channels increases after denervation and returns to the control with time.