Primary afferent depolarization of C fibres in the spinal cord of the cat.

The excitability of primary afferent terminals of cutaneous C fibres was tested in the spinal cord of decerebrated cats. C fibre terminal excitability was decreased in the spinal state, and increased by conditioning volleys that activated only A fibres of another cutaneous nerve and by stimulating hair mechanically. It is suggested that C fibre input and therefore nociceptive information to the central nervous system is susceptible to presynaptic control by segmental and suprasegmental mechanisms.