Abstract
1. Intracellular recording of spike potentials from single motoneurons in toad's spinal cord revealed that some motoneurons were excitable from two different ventral roots (mostly IXth and Xth roots).
2. Between these two antidromic pathways, differences were found in their latent times, slopes of initial part of the spikes and liability to blockade of antidromic conduction. Same conduction velocities were found in the extraspinal part of both routes, which indicated that, in both pathways, alpha fibers were concerned.
3. Action potentials were recorded from a few fibers in one ventral root upon stimulating the other ventral root.
4. Efferent discharges were detected in a small number of ventral root fibers in response to antidromic impulses backfired through the same ventral root.
5. In order to account for these findings, seven types of correlation between two pathways were presented and their possibilities were discussed. In conclusion, the most likely neuronal configuration is a double motoneuron with dendritic liaison, though ephaptic transmission between motoneurons cannot be exclubed to a certainty.
