Transmitter release properties along regenerated nerve processes at the frog neuromuscular junction

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Reinnervation following nerve crush was examined in the frog cutaneous pectoris muscle using histological and electrophysiological techniques. Functional recovery, as monitored by miniature endplate potential (mepp) frequency and quantal content, was slower than morphological recovery. To understand this discrepancy, extracellular recording electrodes were used to determine the amount of transmitter released from localized areas of nerve terminals in both unoperated and experimental muscles. There was no increased tendency over controls for the proximal portion of a regenerated nerve process to release more quanta (spontaneous or nerve evoked) than the distal portion. Moreover, extracellular recording at the growing nerve tip showed that this portion of nerve terminal was capable of transmitter release upon nerve stimulation. These results suggest that the entire length of a regenerating nerve terminal becomes functional at early stages of reinnervation and matures at essentially the same rate.