DEVELOPMENTAL ADAPTATION OF RAT NOCICEPTIVE WITHDRAWAL REFLEXES AFTERNEONATAL TENDON TRANSFER

Nociceptive withdrawal reflexes (NWRs) were studied in adult rats in w hich the movement patterns produced by single muscles had been altered by neonatal tendon transfer. NWRs evoked by cutaneous noxious mechani cal and thermal (CO2-laser) stimulation were recorded using electromyo graphy in a decerebrate spinal preparation. The sensitivity distributi on within the receptive fields of the NWRs of the extensor digitorum l ongus and the peronei muscles exhibited changes corresponding to the a ltered movement patterns. No detectable change of NWRs was found in no rmal muscles whose receptive fields overlapped that of the modified mu scle. Furthermore, NWRs of muscles that regained an essentially normal function after neonatal tendon transfer did not differ from normal. I t is proposed that a developmental experience-dependent mechanism, whi ch takes into account the hindlimb movement pattern caused by contract ion of single muscles, underlies the functionally adapted organization of adult NWRs.