Primary afferent depolarization evoked by the activity of spinal scratching generator

Abstract Fictive scratching was evoked in decerebrated and decapitated immobilized cats by mechanical stimulation of the pinna. Tubocurarine or bicuculline was applied to the dorsal surface of the upper cervical segments to facilitate the appearance of fictive scratching. Application of these drugs produced sustained depolarization of afferent terminals in lumbar segments of the spinal cord (cutaneous, 1a and 1b). The appearance of fictive scratching led to a subsequent increase of primary afferent depolarization. In the latter, 2 components—tonic and periodic synchronous with the discharges in motor nervescould be distinguished. Periodic depolarization was bilateral and synphasic in different segments of the lumbo-sarcral intumescence; it could be detected in cutaneous and 1b muscle afferent terminals only. Tonic depolarization took place in endings of all the investigated groups of fibers (cutaneous, 1a and 1b). The physiological significance and the mechanisms of modulation of primary afferent depolarization by the spinal scratching generator are discussed.