Primary afferent depolarization due to selective activation of propriospinal pathways

Depolarization of primary afferent terminals in the lumbosacral portion of the spinal cord evoked by selective activation of propriospinal pathways was investigated in anesthetized cats. The strongest depolarization developed as a result of activation of short (two to five segments) propriospinal pathways in the lateral funiculus; stimulation of the long propriospinal pathways of this funiculus also induced depolarization, but of lower amplitude. Stimulation of propriospinal pathways of the ventral funiculi was ineffective. Significant primary afferent depolarization developed only following the use of a series of stimuli and strong stimulation of the propriospinal pathways. Excitation of these pathways caused depolarization of afferent terminals of both cutaneous and muscular nerves, including muscular sensory fibers of group Ia, although in the latter case its intensity was low. Neuronal mechanisms involved in the generation of this depolarization and its possible functional role are dicussed.