Effects of cutaneous nerve and intraspinal conditioning of C-fibre afferent terminal excitability in decerebrate spinal rats.
1. Changes in the threshold for antidromic activation of C-fibre afferent terminals in the lumbar spinal cord of the decerebrate-spinalized rat have been examined. 2. The antidromic compound action potential elicited by stimulation in the dorsal horn was recorded in a sectioned dorsal root. 3. The antidromic C wave had conduction velocities and strength-duration properties similar to that described for other unmyelinated fibres. 4. The optimal position of the stimulating electrode within the spinal cord for eliciting the antidromic C wave was found to correlate with the site of entry and termination of C-afferent fibres. 5. Local stimulation within the dorsal grey of the spinal cord was shown to produce prolonged increased excitability of the C-afferent terminals in that segment. This effect was restricted to the terminals and could not be demonstrated in the stem axons of the C fibres. 6. Cutaneous afferent conditioning volleys from the sural nerve produced marked increases in the excitability of the C-afferent terminals. This effect was present at A-fibre strength sural stimulation, with no significant alteration when C-fibre strength stimulation was used. The alteration in the threshold for antidromic stimulation produced by the sural conditioning stimuli only occurred at the C-afferent terminals and not at their axons. 7. The results are discussed in terms of presynaptic inhibition of C-fibre input at a segmental level.
D000818:Animals; D003655:Decerebrate State / Q000503:physiopathology*; D005071:Evoked Potentials; D008297:Male; D009412:Nerve Fibers / Q000502:physiology*; D009413:Nerve Fibers, Myelinated / Q000502:physiology; D009431:Neural Conduction; D009475:Neurons, Afferent / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D013126:Spinal Nerve Roots / Q000502:physiology; D013497:Sural Nerve / Q000502:physiology