Recently, we have demonstrated that embryonic ventral spinal cord motor neurons(ESMNs), transplanted into the distal stump of the axotomized tibial nerve, can grow into the denervated gastrocnemius muscle and form neuromuscular junctions. Our interest in study was to see whether these newly formed neuronal connections are physiologically active, and to electrophysiologically characterize the reinnervated motor units.

Three to eight weeks after transplantation rats were prepared for electrophysiological recording. Motor unit (MU) action potential and gross EMG were monitored. In eleven out of sixteen transplanted animals single unit and gross EMG were recorded after electrical stimulation of the transplant site. Total of 63 motor units were analyzed for their stimulus threshold (ST), latency and stimulus intensity, which is required to produce maximum firing.

ST intensities activating MUs were significantly higher in transplanted animals than in controls. Maximum firing of MUs occurred at less than 1.2×T in the control but greater variation was observed in the transplanted animals ranging from 1.1×T to 1.6×T. No significant differences were found in the latencies of MU's firing following stimulation. MU firing was reversibly blocked by infusion of succinylcholine.

we characterized the temporal, morphological and electrophysiological parameters of denervated skeletal muscle reinnervated by dissociated grafts of embryonic ventral spinal cord cells. MUs reinnervated by the embryonic motoneuronal transplant were physiologically active, with some properties similar to the MUs of the normal.