NOCICEPTIVE INHIBITION OF WITHDRAWAL REFLEX RESPONSES INCREASES OVER TIME IN SPINALIZED RATS

TIME-dependent changes of nociceptive inhibition of hindlimb withdrawa l reflex (WR) pathways were investigated in acute decerebrate spinal r ats. Electromyographic recordings of WK of peroneus longus and extenso r digitorum longus muscles were made, For each muscle, both short and long latency WR evoked by subcutaneous electrical stimulation and WR e voked by noxious pinch could be inhibited by noxious CO2 laser stimula tion of a specific skin area of the ipsilateral hindlimb. The inhibito ry effects and size of the inhibitory receptive fields increased spont aneously between two- and three-fold during the first 12 h after spina lization, The functional and possible clinical significance of the str engthened nociceptive inhibitory control and mechanisms underlying the changes of this control after spinal transection are discussed.