Walking on a 'peg leg': extensor muscle activities and sensory feedback after distal leg denervation in cockroaches.

Previous studies in insects demonstrated that leg coordination changes following complete ablation of distal limb segments. However, normal coordination was restored when small 'peg leg' prostheses were attached to leg stumps to permit substrate contact. We have adapted this paradigm to preserve appropriate leg mass and inertia by severing all nerves and muscle tendons in the femur of the cockroach hind leg and converting the animal's own limb into a peg leg. Recordings of muscle activities and leg movements before and after denervation showed that: (1) the 'peg leg' is actively used in walking and regular bursts occur in motoneurons to leg extensor muscles; (2) driving of motoneuron activity is sufficient to produce 'fictive' bursting in a muscle whose tendon (apodeme) is cut in the ablation; and (3) similar motoneuron activities are found in walking on an oiled glass surface, when the effects of body weight and mechanical coupling are minimized. When distal segments were completely severed in these preparations, leg use and muscle bursting were disrupted but could be restored if the stumps were pressed against the substrate. These results support the hypothesis that feedback from receptors in proximal leg segments indicating forces allows for active leg use in walking.