Differential effects of footpad stimulation on the monosynaptic reflex in the spinalized cat

Experiments were performed in 17 adult cats spinalized at T10-11. The effects of electrical stimulation of the central pad (CP) and toe pads (TP-2, 3, 4, 5) on the monosynaptic reflex (MR) in lumbar spinal segments were studied. The conditioning stimulation had different effects on the MRs of the various motoneurons except the posterior biceps and semitendinosus, depending on the footpad stimulated. Lateral gastrocnemius and soleus, and medial gastrocnemius (MG) MR were inhibited by footpad stimulation. The effect of TP-2 (medial footpad) stimulation on MG-MR was weak. The popliteus (Pop) and tibialis anterior muscles (TA) are inward and lateral rotators of the knee joint, respectively. Pop- and TA-MR were excited by stimulation of lateral and medial TPs, respectively. Plantaris MR was enhanced and inhibited by stimulation of the CP and TPs, respectively. There were remarkable differences in the effects of TP conditioning stimulation on the flexor digitorum longus, extensor digitorum longus, peroneus brevis and tertius, and peroneus longus-MRs, depending on the toe pads stimulated. These results suggest that afferent inputs from footpads modulate the activity of motoneurons, stabilize the foot and help maintain body balance.