title: Excitability of reciprocal and recurrent inhibitory pathways after voluntary muscle relaxation in man.
abstract: We studied the potential contribution of postsynaptic mechanisms to the depression of reflex excitability which occurs immediately after a voluntary release from tonic muscle contraction. The excitability of the Soleus (Sol) motor pool was tested at rest and after voluntary muscle relaxation. In both cases the Sol H-reflex was conditioned by a single shock to the peroneal nerve, in order to activate the Ia interneurones (INs) mediating the reciprocal inhibition via a peripheral input, or by a short-lasting voluntary contraction of the Tibialis Anterior (TA) muscle, to activate the Ia INs via a central command. Changes in excitability of Renshaw cells were also tested at rest and after release, to assess the role of recurrent inhibition in the release-induced inhibition of the Sol H-reflex. It was demonstrated that: the excitability of the INs mediating the reciprocal inhibition was only slightly enhanced in comparison with resting conditions; the H-reflex of the antagonist muscle (TA) evoked after Sol release was not consistently facilitated with respect to rest; the command to contract the TA muscle reduced the H-reflex of the Sol muscle during rest but not after Sol release; recurrent inhibition did not increase its effect in the post-release period. Such features suggest that recurrent and reciprocal post-synaptic inhibitions do not play a major role in reducing the reflex excitability of a relaxing muscle; rather, the command to release prevents the reciprocal inhibitory effect which accompanies the contraction of the antagonist muscle.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000328:Adult; D004576:Electromyography; D006181:H-Reflex; D006801:Humans; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009132:Muscles / Q000294:innervation / Q000502:physiology; D010525:Peripheral Nerves / Q000502:physiology; D012023:Reflex, Monosynaptic; D013569:Synapses / Q000502:physiology