Adaptive changes in locomotor control after partial denervation of tricepssurae muscles in the cat

1. This report concerns a test of the hypothesis that gain in the stretch r eflex pathway of cat medial gastrocnemius (MG) muscle during locomotion inc reases after denervation of its synergists, lateral gastrocnemius (LQ), sol eus (SOL) and plantaris (PL) muscles. 2. In four cats, MG, tibialis anterior (TA) and vastus lateralis (VL) muscl es were implanted with electromyogram (EMG) electrodes. The cats walked on a row of elevated pegs, some of which were spring-loaded and could be trigg ered to pop up at the moment of foot touchdown, rapidly dorsiflexing the fo ot. Pre-stretch EMG activity in MG as well as short-, medium- and long late ncy responses to the dorsiflexions were compared before and after unilatera l denervation of synergists:. 3. Short- and medium-latency responses of MG to perturbations increased in proportion to the increase in pre-stretch EMC: in the days and weeks after partial denervation. This argues against an adaptive increase in stretch re flex gain independent of centrally generated extensor drive. 4. Local anaesthesia of the skin of the paw did not significantly change th e sizes of the stretch responses of MG before or after partial denervation. 5. We conclude that pre-stretch FMG activity as well as stretch reflexes in MG: muscle increased substantially after denervation of synergistic muscle s. The data were consistent with an adaptive increase in central locomotor drive, causing more motoneuronal activity, which in turn resulted in an inc rease in the size of stretch reflexes.