Evidence for direct synaptic interconnections between cat spinal alpha-motoneurons via the recurrent axon collaterals: a morphological study using intracellular injection of horseradish peroxidase.

By using intracellular injection of horseradish peroxidase into cat triceps surae alpha-motoneurons we have been able to trace the motor axons as well as the recurrent motor axon collaterals with their synaptic terminals both with the light and electron microscope. In addition to the expected projection to the 'Renshaw cell area', the triceps surae motor axon collaterals were frequently found to terminate within the motor nuclei, where at least some of the terminals made direct synaptic contact with triceps surae alpha-motoneurons.