Sensorimotor transformation in cat nociceptive withdrawal reflex system

The withdrawal reflex system of higher vertebrates has been extensively use d as a model for spinal sensorimotor integration, nociceptive processing an d plasticity. In the rat, the nociceptive withdrawal reflex system appears to have a modular organization. Each reflex module controls a single muscle or a few synergistic muscles, and its cutaneous receptive field correspond s to the skin area withdrawn upon contraction of the effector muscle(s) whe n the limb is in the standing position. This organization principle is at o dds with the 'flexion reflex' concept postulated from cat studies. To asses s the generality of the modular organization principle we have therefore re -examined the cutaneous input to the withdrawal reflex system of the cat. T he cutaneous receptive fields of hindlimb and forelimb muscles were mapped using calibrated noxious pinch stimulation and electromyographic recording technique in barbiturate anaesthetized animals. The investigated muscles ha d specific cutaneous receptive fields that appeared to correspond to the ar ea of the skin withdrawn upon contraction of the muscle when the limb is in the standing position. The spatial organization of receptive fields in the cat was similar to that in the rat. However, differences in gain propertie s of reflexes to some anatomically equivalent muscles in the two species we re observed, possibly reflecting adaptations to the biomechanics characteri stic of the digitigrade and plantigrade stance in cats and rats, respective ly. Implications of the findings for the generality of the modular organiza tion of the withdrawal reflex system and for its adaptive properties are di scussed.