Chronic peripheral nerve section diminishes the primary afferent A-fibre mediated inhibition of rat dorsal horn neurones.
The inhibitory effect of A-primary afferent activity on A- and C-evoked activity in dorsal horn convergent neurones has been investigated in the decerebrate spinal rat. A-afferent conditioning stimuli produce a powerful inhibition of the C-evoked activity in the majority of units recorded in lamina 5 but were almost without effect on the C-evoked activity in units recorded within the substantia gelatinosa (laminae 1 and 2). The ability of an A-volley to inhibit the response to a C-volley begins immediately after the arrival of the A-volley and lasts for 50-70 ms. Conditioning A-stimuli also inhibit the A-evoked activity of dorsal horn neurones, the inhibition lasting up to 125 ms. Unlike the effect of A-conditioning stimuli on C-responses, which was restricted to units in lamina 5, the A-volleys inhibited the response of both substantia gelatinosa and lamina 5 units. In rats with chronically sectioned sciatic nerves (7-14 days) both A on A and A on C inhibitions were significantly diminished in spite of intact afferent volleys and postsynaptic activity. In neurones activated by stimulation of the sectioned nerve, the A-conditioning stimuli either failed to produce an inhibition or produced a weak and shorter effect. These results are discussed in terms of the possible functional significance of A-afferent mediated inhibition.
D000818:Animals; D003213:Conditioning, Psychological / Q000502:physiology; D005071:Evoked Potentials; D009412:Nerve Fibers / Q000502:physiology; D009413:Nerve Fibers, Myelinated / Q000502:physiology*; D009433:Neural Inhibition; D010525:Peripheral Nerves / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D013116:Spinal Cord / Q000502:physiology*; D013376:Substantia Gelatinosa / Q000502:physiology