Presynaptic and postsynaptic mechanisms underlying H-reflex changes produced by a selective voluntary contraction.
Concurrent recordings of (i) the soleus H reflex and (ii) the underlying afferent (P1) and efferent (P2) neural volleys were performed during a protracted, moderate, isometric, voluntary contraction of the soleus (S) muscle, and the subsequent release period. Besides the expected enhancement of the H reflex, muscular contraction caused a significant reduction in the corresponding central delay (as extrapolated from variations of P1-P2 interval), while the opposite trend occurred during the release phase. Control experiments, based on (a) neural blockade below the stimulation site, (b) muscle stretching at the end of the muscular contraction, (c) changes in amplitude of homonymous and heteronymous S responses, and (d) variations in effectiveness of homonymous and heteronymous conditioning volleys on the S motoneuronal pool, showed that both voluntary contraction and the subsequent release period are associated with a reduced effectiveness of la afferents, while postsynaptic motoneuronal responsiveness is significantly modified only during the actual contraction time.
Abbruzzese
M
M
Department of Neurological Sciences, University of Genoa, Italy.
Reni
L
L
Minatel
C
C
Favale
E
E
D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D004558:Electric Stimulation; D004576:Electromyography; D005528:Foot / Q000294:innervation / Q000502:physiology; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007511:Ischemia / Q000503:physiopathology; D007537:Isometric Contraction / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D009121:Muscle Denervation; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D013569:Synapses / Q000502:physiology*