Site-specific, inflammation-induced adaptations in withdrawal reflex pathways in the anesthetized rabbit

Transmission in spinal reflex pathways from the toes to the ankle flexor tibialis anterior (TA) and to the knee flexor semitendinosus (ST), and from the heel to the ankle extensor medial gastrocnemius (MG), has been studied during antigen-induced inflammation due to subcutaneous injection of ovalbumin at the heel or at the toes in pre-immunized, pentobarbitone-anesthetized rabbits. The ovalbumin challenge induced a mild swelling at the injection site that developed over 6 h. Inflammation at the toes facilitated both flexor reflexes evoked from the toes and inhibited MG extensor responses to stimulation at the heel, with effects usually developing within 75 min of the initial injection and persisting to the end of the 6 h post-injection recording period. When inflammation was induced at the heel, the heel-MG and toes-ST reflexes were enhanced, whereas the toes-TA reflex was inhibited. The findings support the view that long-lasting changes in reflexes evoked by noxious stimuli have evolved to enhance reflex protection of an injured site.