Presynaptic depolarization of myelinated afferent fibres evoked by stimulation of cutaneous C fibres.
1. The origin of the dorsal root potential observed following a volley in cutaneous unmyelinated or C fibres (C-DRP) has been investigated by several assays.2. Measurements of the spatial decrement of the C-DRP along the dorsal roots indicate that mainly the thick myelinated primary afferent fibres contribute to this C-DRP.3. The spatial configuration of the intraspinal potential field during the course of the C-DRP is similar to that of the field correlated to the A-DRP, i.e. the DRP evoked by a volley in the A fibres of the same cutaneous nerve. It is concluded therefrom that both A- and C-DRPs signal presynaptic depolarizations of afferent fibres in the same regions of the dorsal horn.4. Intrafibre recordings reveal that C input produces primary afferent depolarization (C-PAD) mainly in cutaneous and articular afferents, but not in muscle Group Ia afferents.5. These findings and direct measurements of the interactions between A- and C-DRPs indicate that the pathways involved in A- and C-PAD exhibit convergence.6. C-DRPs were also recorded from contralateral rootlets.7. Some functional aspects of the PAD produced by an afferent volley in C fibres are discussed.
D000818:Animals; D001369:Axons / Q000502:physiology*; D002415:Cats; D004558:Electric Stimulation; D004594:Electrophysiology; D008564:Membrane Potentials; D009474:Neurons / Q000502:physiology*; D009475:Neurons, Afferent / Q000502:physiology; D012867:Skin / Q000294:innervation*; D013116:Spinal Cord / Q000502:physiology; D013126:Spinal Nerve Roots / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D013997:Time Factors