Enhanced D1 and D2 Inhibitions Induced by Low-Frequency Trains of Conditioning Stimuli: Differential Effects on H- and T-Reflexes and Possible Mechanisms

Author(s)

Mezzarane, Rinaldo Andre ^{[1, 2]} ; Magalhaes, Fernando Henrique ^{[1, 3]} ; Chaud, Vitor Martins ^{[1, 4]} ; Elias, Leonardo Abdala ^{[1, 5]} ; Kohn, Andre Fabio ^[1]

Affiliation

^[1] Univ Sao Paulo, PTC, Escola Politecn, Biomed Engn Lab, Sao Paulo - Brazil

^[2] Univ Brasilia, UnB, Coll Phys Educ, Lab Signal Proc & Motor Control, Brasilia, DF - Brazil

^[3] Univ Sao Paulo, EACH, Sch Arts Sci & Humanities, Sao Paulo - Brazil

^[4] Univ Fed Triangulo Mineiro, Dept Elect Engn, Uberaba - Brazil

^[5] Univ Estadual Campinas, UNICAMP, Sch Elect & Comp Engn, Dept Biomed Engn, Campinas, SP - Brazil

• Document type: Journal article
• Source: PLoS One; v. 10, n. 3 MAR 25 2015.
• Web of Science Citations: 7

Abstract

Mechanically evoked reflexes have been postulated to be less sensitive to presynaptic inhibition (PSI) than the H-reflex. This has implications on investigations of spinal cord neurophysiology that are based on the T-reflex. Preceding studies have shown an enhanced effect of PSI on the H-reflex when a train of similar to 10 conditioning stimuli at 1 Hz was applied to the nerve of the antagonist muscle. The main questions to be addressed in the present study are if indeed T-reflexes are less sensitive to PSI and whether (and to what extent and by what possible mechanisms) the effect of low frequency conditioning, found previously for the H-reflex, can be reproduced on T-reflexes from the soleus muscle. We explored two different conditioning-to-test (C-T) intervals: 15 and 100 ms (corresponding to D1 and D2 inhibitions, respectively). Test stimuli consisted of either electrical pulses applied to the posterior tibial nerve to elicit H-reflexes or mechanical percussion to the Achilles tendon to elicit T-reflexes. The 1 Hz train of conditioning electrical stimuli delivered to the common peroneal nerve induced a stronger effect of PSI as compared to a single conditioning pulse, for both reflexes (T and H), regardless of C-T-intervals. Moreover, the conditioning train of pulses (with respect to a single conditioning pulse) was proportionally more effective for T-reflexes as compared to H-reflexes (irrespective of the C-T interval), which might be associated with the differential contingent of Ia afferents activated by mechanical and electrical test stimuli. A conceivable explanation for the enhanced PSI effect in response to a train of stimuli is the occurrence of homosynaptic depression at synapses on inhibitory interneurons interposed within the PSI pathway. The present results add to the discussion of the sensitivity of the stretch reflex pathway to PSI and its functional role. (AU)

• FAPESP's process: 10/15522-4 - Proposal of a mechanical stimulator for the study of synchronous bilateral fluctuations in reflex excitability of humans
• Grantee: Rinaldo André Mezzarane
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/10433-1 - Discharge properties of motor units from ankle extensor and flexor muscles during sinusoidal modulation of the joint torque and angle
• Grantee: Leonardo Abdala Elias
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 11/13222-6 - EVALUATION OF INHIBITORY PATHWAYS AND THE EFFECT OF ELECTRICAL NOISE STIMULATION ON PLANTAR FLEXION NEUROMUSCULAR CONTROL
• Grantee: Fernando Henrique Magalhães
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 09/15802-0 - Modelling and simulation of torque control by proprioceptive feedback through the nervous system: application to postural control
• Grantee: Leonardo Abdala Elias
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 11/17193-0 - Behavioral, brain and reflex responses to mechanical and electrical stimuli to study proprioception and the spinal cord in humans
• Grantee: André Fábio Kohn
• Support Opportunities: Regular Research Grants