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Alessandro Rossi - One of the best experts on this subject based on the ideXlab platform.
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beyond muscular effects depression of spinal Recurrent Inhibition after botulinum neurotoxin a
The Journal of Physiology, 2013Co-Authors: Veronique Marchandpauvert, Alessandro Rossi, Claire Aymard, Louissolal Giboin, Federica Dominici, Riccardo MazzocchioAbstract:Key points Botulinum neurototoxin type A (BoNT-A) is known to block central synapses after muscular injection due to retrograde transport in animal models. BoNT-A-induced changes in the human CNS activity have been attributed so far to indirect mechanisms involving peripheral afferent inputs modified after muscular injection. The question of a possible direct central action of BoNT-A in humans was further addressed by investigating the modification of spinal Recurrent Inhibition in stroke patients after BoNT-A muscular injection. Recurrent Inhibition from soleus motor axons to motoneurones supplying quadriceps was depressed after BoNT-A injection in ankle plantarflexors. BoNT-A, through retrograde transport, affects spinal synaptic transmission in humans. Abstract The natural target of the botulinum neurototoxin type A (BoNT-A) is the neuromuscular junction. When injected into a muscle, BoNT-A is internalized by motoneurone terminals where it functions as an endopeptidase, cleaving protein components of the synaptic machinery responsible for vesicle docking and exocytosis. As a result, BoNT-A induces a characteristic flaccid paralysis of the affected muscle. In animal models, BoNT-A applied in the periphery can also influence central activity via retrograde transport and transcytosis. An analogous direct central effect in humans is still debated. The present study was designed to address whether BoNT-A modifies the activity of the spinal Recurrent inhibitory pathways, when injected at muscular level, in humans. To avoid methodological bias, the Recurrent Inhibition from an injected muscle (soleus) was investigated on an untreated muscle (quadriceps), and stimulation parameters (producing Recurrent Inhibition) were monitored on a third non-injected muscle but innervated by the same nerve as the soleus (flexor digitorum brevis). The experiments were performed on 14 post-stroke patients exhibiting spasticity in ankle plantarflexors, candidates for BoNT-A. One month after BoNT-A, the level of Recurrent Inhibition was depressed. It is suggested that the depression of Recurrent Inhibition was induced by BoNT-A, injected peripherally, through axonal transport and blockade of the cholinergic synapse between motoneurone Recurrent collaterals and Renshaw cells.
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recurrence quantification analysis of surface emg detects changes in motor unit synchronization induced by Recurrent Inhibition
Experimental Brain Research, 2007Co-Authors: F Del Santo, Riccardo Mazzocchio, F Gelli, Alessandro RossiAbstract:The systemic injection of l-Acetylcarnitine (l-Ac) induces a reversible increase in Recurrent Inhibition. In addition, l-Ac potentiation of Recurrent Inhibition has been found to increase the synchronous activity of single motor units, as detected by traditional linear analysis in the time domain. This result has been recently confirmed using a nonlinear method based on the analysis of embedded determinism (%DET) extracted from the surface EMG. The present study aimed at testing the general applicability of RQA methodology, as a viable tool for assessing motor unit synchronization, by extending the analysis of surface EMG, as revealed by changes in %DET induced by l-Ac, to many upper and lower limb muscles and to muscles that are not easily studied by needle electrodes, such as the orbicularis oculi. Subjects performed brief periods of tonic contractions, alternated to periods of rests to avoid muscle fatigue. Pharmacological enhancement of Recurrent Inhibition was obtained by a short-lasting intravenous injection of l-Ac. Control experiments were performed replacingl-Ac injection with saline injection. The average %DET showed a significant increase during l-Ac injection in the deltoid, biceps brachii, extensor carpi radialis, while no effect was observed in the opponens pollicis and abductor digiti minimi for the upper limb muscles. Similarly, the average %DET showed a significant increase during l-Ac injection in the quadriceps, soleus, and tibialis anterior, while no effect was observed in the abductor hallucis for the lower limb muscles. RQA of orbicularis oculi muscle activity showed no increase in %DET during l-Ac injection in analogy to what found in the intrinsic muscles of the hand and foot, known to be devoid of Recurrent Inhibition. The presence or absence of drug-induced increase in motor unit synchronization agrees with the known distribution of Recurrent Inhibition in the various motor nuclei. The overall significance of these findings is the potential application of RQA methodology as a reliable and independent tool for generally assessing motor unit synchronization from surface EMG under strictly controlled experimental condition.
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is the human masticatory system devoid of Recurrent Inhibition
Experimental Brain Research, 2007Co-Authors: Kemal S Turker, Riccardo Mazzocchio, Alessandro Rossi, Annie Schmied, Paul F Sowman, Jeanpierre VedelAbstract:The aim of the present study was to inves- tigate the existence or otherwise of a functional Recurrent inhibitory system (Renshaw cell system) in the motoneurons that innervate human masticatory muscles. In a previous study, L-acetylcarnitine (L-Ac), a substance known to potentiate Recurrent Inhibition in humans was found to alter, in a specific way, the dis- charge variability, and the synchronous activity of motor units depending on the presence or absence of Recurrent Inhibition in the corresponding motoneuron pool. Using a similar paradigm, we have recorded the tonic discharge activity of motor unit pairs from the masseter muscle during voluntary isometric contrac- tion while subjects were undergoing continuous intra- venous saline (SAL, NaCl 0.9%) perfusion. Following a brief baseline-recording period, the subjects were given a test injection of either L-Ac or isotonic saline (SAL) in a double blind manner. The variability, synchronization, and coherence between the motor unit discharges were analysed during three successive periods: pre-injection, during injection, and post- injection, each lasting 2-3 min. Neither L-Ac nor SAL injection induced a significant change in the inter-spike interval (ISI) or the coefficient of variation of the ISIs in the motor units tested. There were also no significant changes in the pattern of synchronous activity or in the coherence, which reflects the common frequency con- tent of the unit discharges. Reminiscent of what had been observed previously with motoneurons without Recurrent Inhibition in the Abductor Digitorum Minimi muscle, the lack of effects of L-Ac injection on the firing behaviour of masseter motoneurons may suggest that classical Renshaw cell Inhibition is lacking in this motoneuron pool.
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pharmacologically induced enhancement of Recurrent Inhibition in humans effects on motoneurone discharge patterns
The Journal of Physiology, 2003Co-Authors: Benjamin Mattei, Riccardo Mazzocchio, Alessandro Rossi, Annie Schmied, Barbara Decchi, Jeanpierre VedelAbstract:The aim of the present study was to investigate the effects of spinal Recurrent Inhibition on human motoneurone discharge patterns. The tonic discharge activity of motor unit pairs was recorded in the extensor carpi radialis (ECR) and abductor digiti minimi (ADM) muscles during voluntary isometric contraction. While undergoing continuous intravenous saline (NaCl 0.9 %) perfusion, the subjects were given a short lasting injection of l-acetylcarnitine (l-Ac), which has been found to potentiate Recurrent Inhibition in humans. The variability, synchronization and coherence of the motor unit discharges were analysed during four successive test periods (lasting 2–3 min each). A significant decrease in the inter-spike interval (ISI) coefficient of variation was observed in the discharge patterns of the motor units tested in the ECR and not in the ADM, which were not accompanied by any consistent changes in the mean ISIs of the motor unit activity in either muscle. The l-Ac injection also led to a significant increase in the synchronization in half of the motor unit pairs tested in the ECR muscle (n= 29), whereas no consistent changes were observed with the ADM motor units (n= 25). However, coherence analysis failed to reveal any consistent differences in the incidence of significant values of coherence spectrum between the pre-injection and injection periods among the motor unit pairs tested with either saline or l-Ac injections, in either the ECR or ADM muscles. The contrasting effects on the variability and the synchronization of the motor unit discharges observed with ECR motoneurones known to undergo Recurrent Inhibition and with ADM motoneurones known to lack Recurrent Inhibition suggest that the drug may have specific effects which are mediated by an enhancement of the Renshaw cell activity. The decrease in the ISI variability is in line with the hypothesis that Recurrent Inhibition may contribute along with the post-spike after-hyperpolarization to limiting the influence of the synaptic noise on the firing times of steadily discharging motoneurones. The present data, which suggest that Recurrent Inhibition plays a synchronizing rather than a desynchronizing role, are in keeping with the fact that the Renshaw cells may provide an important source of common inhibitory inputs.
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effect of chemically activated fine muscle afferents on spinal Recurrent Inhibition in humans
Clinical Neurophysiology, 2003Co-Authors: Alessandro Rossi, Riccardo Mazzocchio, B DecchiAbstract:Abstract Objective : To test the hypothesis that ‘metabolites released during fatiguing muscle contractions excite group III–IV muscle nociceptive afferents, inhibiting homonymous motoneurones via Renshaw cells,’ by recording changes in Recurrent Inhibition of soleus motoneurones when high-threshold, small-diameter afferents (group III–IV fibres) from the same muscle were tonically activated. Methods : Experiments were performed in 7 healthy subjects at rest and during weak isometric voluntary contraction of the soleus muscle. Muscle nociceptive afferents were activated by local standardized injection of levo-ascorbic acid. Renshaw cells were orthodromically activated by a conditioning H reflex and the resulting Recurrent Inhibition of the soleus motoneurones was assessed by a subsequent test H reflex. An additional H reflex of the same size as the test reflex was used to assess motoneurone excitability. Results : At rest, muscle nociceptive stimulation produced transient facilitation of both test H and reference H reflexes. Under weak voluntary contraction, muscle nociceptive stimulation produced long-lasting extra-Inhibition and extra-facilitation of the test reflex and reference reflex respectively, the time course of which closely resembled that of the subjective muscle pain curve. Conclusions : Discharge of putative group III–IV muscle afferents facilitated homonymous Recurrent Inhibition. The filtering property of Recurrent Inhibition may contribute to limit motoneurone activity during muscle pain and/or adapt motoneurone firing rate to the modified contractile properties of motor units as muscle fatigue developed.
Riccardo Mazzocchio - One of the best experts on this subject based on the ideXlab platform.
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beyond muscular effects depression of spinal Recurrent Inhibition after botulinum neurotoxin a
The Journal of Physiology, 2013Co-Authors: Veronique Marchandpauvert, Alessandro Rossi, Claire Aymard, Louissolal Giboin, Federica Dominici, Riccardo MazzocchioAbstract:Key points Botulinum neurototoxin type A (BoNT-A) is known to block central synapses after muscular injection due to retrograde transport in animal models. BoNT-A-induced changes in the human CNS activity have been attributed so far to indirect mechanisms involving peripheral afferent inputs modified after muscular injection. The question of a possible direct central action of BoNT-A in humans was further addressed by investigating the modification of spinal Recurrent Inhibition in stroke patients after BoNT-A muscular injection. Recurrent Inhibition from soleus motor axons to motoneurones supplying quadriceps was depressed after BoNT-A injection in ankle plantarflexors. BoNT-A, through retrograde transport, affects spinal synaptic transmission in humans. Abstract The natural target of the botulinum neurototoxin type A (BoNT-A) is the neuromuscular junction. When injected into a muscle, BoNT-A is internalized by motoneurone terminals where it functions as an endopeptidase, cleaving protein components of the synaptic machinery responsible for vesicle docking and exocytosis. As a result, BoNT-A induces a characteristic flaccid paralysis of the affected muscle. In animal models, BoNT-A applied in the periphery can also influence central activity via retrograde transport and transcytosis. An analogous direct central effect in humans is still debated. The present study was designed to address whether BoNT-A modifies the activity of the spinal Recurrent inhibitory pathways, when injected at muscular level, in humans. To avoid methodological bias, the Recurrent Inhibition from an injected muscle (soleus) was investigated on an untreated muscle (quadriceps), and stimulation parameters (producing Recurrent Inhibition) were monitored on a third non-injected muscle but innervated by the same nerve as the soleus (flexor digitorum brevis). The experiments were performed on 14 post-stroke patients exhibiting spasticity in ankle plantarflexors, candidates for BoNT-A. One month after BoNT-A, the level of Recurrent Inhibition was depressed. It is suggested that the depression of Recurrent Inhibition was induced by BoNT-A, injected peripherally, through axonal transport and blockade of the cholinergic synapse between motoneurone Recurrent collaterals and Renshaw cells.
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recurrence quantification analysis of surface emg detects changes in motor unit synchronization induced by Recurrent Inhibition
Experimental Brain Research, 2007Co-Authors: F Del Santo, Riccardo Mazzocchio, F Gelli, Alessandro RossiAbstract:The systemic injection of l-Acetylcarnitine (l-Ac) induces a reversible increase in Recurrent Inhibition. In addition, l-Ac potentiation of Recurrent Inhibition has been found to increase the synchronous activity of single motor units, as detected by traditional linear analysis in the time domain. This result has been recently confirmed using a nonlinear method based on the analysis of embedded determinism (%DET) extracted from the surface EMG. The present study aimed at testing the general applicability of RQA methodology, as a viable tool for assessing motor unit synchronization, by extending the analysis of surface EMG, as revealed by changes in %DET induced by l-Ac, to many upper and lower limb muscles and to muscles that are not easily studied by needle electrodes, such as the orbicularis oculi. Subjects performed brief periods of tonic contractions, alternated to periods of rests to avoid muscle fatigue. Pharmacological enhancement of Recurrent Inhibition was obtained by a short-lasting intravenous injection of l-Ac. Control experiments were performed replacingl-Ac injection with saline injection. The average %DET showed a significant increase during l-Ac injection in the deltoid, biceps brachii, extensor carpi radialis, while no effect was observed in the opponens pollicis and abductor digiti minimi for the upper limb muscles. Similarly, the average %DET showed a significant increase during l-Ac injection in the quadriceps, soleus, and tibialis anterior, while no effect was observed in the abductor hallucis for the lower limb muscles. RQA of orbicularis oculi muscle activity showed no increase in %DET during l-Ac injection in analogy to what found in the intrinsic muscles of the hand and foot, known to be devoid of Recurrent Inhibition. The presence or absence of drug-induced increase in motor unit synchronization agrees with the known distribution of Recurrent Inhibition in the various motor nuclei. The overall significance of these findings is the potential application of RQA methodology as a reliable and independent tool for generally assessing motor unit synchronization from surface EMG under strictly controlled experimental condition.
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is the human masticatory system devoid of Recurrent Inhibition
Experimental Brain Research, 2007Co-Authors: Kemal S Turker, Riccardo Mazzocchio, Alessandro Rossi, Annie Schmied, Paul F Sowman, Jeanpierre VedelAbstract:The aim of the present study was to inves- tigate the existence or otherwise of a functional Recurrent inhibitory system (Renshaw cell system) in the motoneurons that innervate human masticatory muscles. In a previous study, L-acetylcarnitine (L-Ac), a substance known to potentiate Recurrent Inhibition in humans was found to alter, in a specific way, the dis- charge variability, and the synchronous activity of motor units depending on the presence or absence of Recurrent Inhibition in the corresponding motoneuron pool. Using a similar paradigm, we have recorded the tonic discharge activity of motor unit pairs from the masseter muscle during voluntary isometric contrac- tion while subjects were undergoing continuous intra- venous saline (SAL, NaCl 0.9%) perfusion. Following a brief baseline-recording period, the subjects were given a test injection of either L-Ac or isotonic saline (SAL) in a double blind manner. The variability, synchronization, and coherence between the motor unit discharges were analysed during three successive periods: pre-injection, during injection, and post- injection, each lasting 2-3 min. Neither L-Ac nor SAL injection induced a significant change in the inter-spike interval (ISI) or the coefficient of variation of the ISIs in the motor units tested. There were also no significant changes in the pattern of synchronous activity or in the coherence, which reflects the common frequency con- tent of the unit discharges. Reminiscent of what had been observed previously with motoneurons without Recurrent Inhibition in the Abductor Digitorum Minimi muscle, the lack of effects of L-Ac injection on the firing behaviour of masseter motoneurons may suggest that classical Renshaw cell Inhibition is lacking in this motoneuron pool.
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pharmacologically induced enhancement of Recurrent Inhibition in humans effects on motoneurone discharge patterns
The Journal of Physiology, 2003Co-Authors: Benjamin Mattei, Riccardo Mazzocchio, Alessandro Rossi, Annie Schmied, Barbara Decchi, Jeanpierre VedelAbstract:The aim of the present study was to investigate the effects of spinal Recurrent Inhibition on human motoneurone discharge patterns. The tonic discharge activity of motor unit pairs was recorded in the extensor carpi radialis (ECR) and abductor digiti minimi (ADM) muscles during voluntary isometric contraction. While undergoing continuous intravenous saline (NaCl 0.9 %) perfusion, the subjects were given a short lasting injection of l-acetylcarnitine (l-Ac), which has been found to potentiate Recurrent Inhibition in humans. The variability, synchronization and coherence of the motor unit discharges were analysed during four successive test periods (lasting 2–3 min each). A significant decrease in the inter-spike interval (ISI) coefficient of variation was observed in the discharge patterns of the motor units tested in the ECR and not in the ADM, which were not accompanied by any consistent changes in the mean ISIs of the motor unit activity in either muscle. The l-Ac injection also led to a significant increase in the synchronization in half of the motor unit pairs tested in the ECR muscle (n= 29), whereas no consistent changes were observed with the ADM motor units (n= 25). However, coherence analysis failed to reveal any consistent differences in the incidence of significant values of coherence spectrum between the pre-injection and injection periods among the motor unit pairs tested with either saline or l-Ac injections, in either the ECR or ADM muscles. The contrasting effects on the variability and the synchronization of the motor unit discharges observed with ECR motoneurones known to undergo Recurrent Inhibition and with ADM motoneurones known to lack Recurrent Inhibition suggest that the drug may have specific effects which are mediated by an enhancement of the Renshaw cell activity. The decrease in the ISI variability is in line with the hypothesis that Recurrent Inhibition may contribute along with the post-spike after-hyperpolarization to limiting the influence of the synaptic noise on the firing times of steadily discharging motoneurones. The present data, which suggest that Recurrent Inhibition plays a synchronizing rather than a desynchronizing role, are in keeping with the fact that the Renshaw cells may provide an important source of common inhibitory inputs.
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effect of chemically activated fine muscle afferents on spinal Recurrent Inhibition in humans
Clinical Neurophysiology, 2003Co-Authors: Alessandro Rossi, Riccardo Mazzocchio, B DecchiAbstract:Abstract Objective : To test the hypothesis that ‘metabolites released during fatiguing muscle contractions excite group III–IV muscle nociceptive afferents, inhibiting homonymous motoneurones via Renshaw cells,’ by recording changes in Recurrent Inhibition of soleus motoneurones when high-threshold, small-diameter afferents (group III–IV fibres) from the same muscle were tonically activated. Methods : Experiments were performed in 7 healthy subjects at rest and during weak isometric voluntary contraction of the soleus muscle. Muscle nociceptive afferents were activated by local standardized injection of levo-ascorbic acid. Renshaw cells were orthodromically activated by a conditioning H reflex and the resulting Recurrent Inhibition of the soleus motoneurones was assessed by a subsequent test H reflex. An additional H reflex of the same size as the test reflex was used to assess motoneurone excitability. Results : At rest, muscle nociceptive stimulation produced transient facilitation of both test H and reference H reflexes. Under weak voluntary contraction, muscle nociceptive stimulation produced long-lasting extra-Inhibition and extra-facilitation of the test reflex and reference reflex respectively, the time course of which closely resembled that of the subjective muscle pain curve. Conclusions : Discharge of putative group III–IV muscle afferents facilitated homonymous Recurrent Inhibition. The filtering property of Recurrent Inhibition may contribute to limit motoneurone activity during muscle pain and/or adapt motoneurone firing rate to the modified contractile properties of motor units as muscle fatigue developed.
J F Iles - One of the best experts on this subject based on the ideXlab platform.
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seeking functions for spinal Recurrent Inhibition
The Journal of Physiology, 2008Co-Authors: J F IlesAbstract:In this issue of The Journal of Physiology, Lamy et al. (2008) describe a rhythmic modulation of Recurrent Inhibition during walking in man. This provides some insight into the function of Recurrent Inhibition, first described by Renshaw (1941) as an Inhibition of cat motoneurones produced by antidromic stimulation of the axons of neighbouring motoneurones (homonymous action). Subsequent work, also in cats, showed that motor axon collaterals activate interneurones (the eponymous Renshaw cells) that in turn inhibit motoneurones. Actions extend to more distant muscle groups (heteronymous) and parallel the pattern of heteronymous monosynaptic excitation from muscle spindle Ia afferents. Renshaw cells receive peripheral sensory and descending inputs and have output connections to other spinal interneurones and to other Renshaw cells. So Recurrent Inhibition is more than just negative feedback from and to motoneurones and may have several functions depending upon motor context. Lamy et al. have focused on heteronymous actions (which are more widespread in man than in cats or monkeys) in the context of our unique bipedal form of walking. The knee extensor quadriceps is a source of Recurrent Inhibition to the ankle extensor and the flexor muscles soleus and tibialis anterior. But given that these ankle muscles are antagonists, how is differential activation achieved? The authors found that around heel strike and early in stance, when quadriceps is active and soleus activity is increasing, Recurrent Inhibition of soleus is weak. Conversely, later in stance, when quadriceps is active and soleus activity is declining, Recurrent Inhibition of soleus is strong. Recurrent Inhibition of tibialis anterior motoneurones was neither task nor phase dependent. The reduction in soleus Recurrent Inhibition would assist the transition from swing to stance and enhanced Inhibition later in stance would favour the transition from stance to swing by reducing reciprocal Inhibition of tibialis anterior. The origin of these changes in Recurrent Inhibition remains uncertain but activity of peripheral sensory or descending motor pathways could be involved. Two interesting possibilities are the corticospinal pathway, known to depress homonymous Recurrent Inhibition of soleus in sitting subjects (Mazzocchio et al. 1994) and the vestibulospinal pathway that depresses Recurrent Inhibition of soleus in standing stance (Iles & Pisini, 1992). It might be possible to extend such studies to heteronymous actions in walking stance. More meticulous experiments built upon the framework of human research protocols pioneered by the Paris group will likely increase our understanding of Recurrent Inhibition even further.
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task related changes of transmission in the pathway of heteronymous spinal Recurrent Inhibition from soleus to quadriceps motor neurones in man
Brain, 2000Co-Authors: J F Iles, Joanne PardoeAbstract:An H reflex conditioning technique was used to monitor the transmission of heteronymous Recurrent Inhibition from soleus to quadriceps motor neurones of the human lower limb. Inhibition declined during quadriceps muscle contraction under all conditions examined, falling to zero at around one-third of the maximum voluntary contraction. Inhibition declined during soleus muscle contraction in sitting, standing and bicycling tasks. The level of Inhibition assessed at a given (weaker than 30%) level of quadriceps contraction was reduced during postural tasks involving quadriceps and soleus co-contraction (standing and late-stance phase of walking) when compared with sitting and performing matched voluntary muscle contractions. The level of Inhibition during the mid-power stroke of a bicycling task, which also involved co-contraction of quadriceps and soleus, was greater than during matched voluntary muscle contractions while sitting. It is concluded that the pathway of heteronymous Recurrent Inhibition from soleus to quadriceps motor neurones is under at least two types of control: one related to the task, which sets the operating range, and a second which couples Inhibition to the level of muscle contraction. Multiple control pathways are consistent with the diverse effects on Recurrent Inhibition reported in subjects with upper motor neurone lesions.
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changes in transmission in the pathway of heteronymous spinal Recurrent Inhibition from soleus to quadriceps motor neurons during movement in man
Brain, 1999Co-Authors: J F Iles, Joanne PardoeAbstract:H reflexes were induced in the human quadriceps muscle by electrical stimulation of the femoral nerve. The reflexes were conditioned by prior stimulation of the inferior soleus nerve. The conditioning stimulus produced an Inhibition of long duration (>20 ms). The threshold of this Inhibition was at zero soleus motor discharge and the Inhibition scaled with soleus motor discharge. It was concluded that the Inhibition was a heteronymous Recurrent Inhibition of quadriceps motor neurons mediated by Renshaw cells which had been activated by soleus motor neuron discharge. This Recurrent Inhibition declined during voluntary tonic contraction of the quadriceps, falling to zero at around one-third of maximum voluntary contraction. Antagonist contraction and weak co-contraction of the quadriceps and its antagonists did not lead to any significant change in Recurrent Inhibition. It is concluded that motor commands descending from the brain reduce heteronymous Recurrent Inhibition during isolated quadriceps muscle contraction, but to a much lesser extent during co-contraction. No evidence was obtained for any descending facilitation of heteronymous Recurrent Inhibition.
Joanne Pardoe - One of the best experts on this subject based on the ideXlab platform.
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task related changes of transmission in the pathway of heteronymous spinal Recurrent Inhibition from soleus to quadriceps motor neurones in man
Brain, 2000Co-Authors: J F Iles, Joanne PardoeAbstract:An H reflex conditioning technique was used to monitor the transmission of heteronymous Recurrent Inhibition from soleus to quadriceps motor neurones of the human lower limb. Inhibition declined during quadriceps muscle contraction under all conditions examined, falling to zero at around one-third of the maximum voluntary contraction. Inhibition declined during soleus muscle contraction in sitting, standing and bicycling tasks. The level of Inhibition assessed at a given (weaker than 30%) level of quadriceps contraction was reduced during postural tasks involving quadriceps and soleus co-contraction (standing and late-stance phase of walking) when compared with sitting and performing matched voluntary muscle contractions. The level of Inhibition during the mid-power stroke of a bicycling task, which also involved co-contraction of quadriceps and soleus, was greater than during matched voluntary muscle contractions while sitting. It is concluded that the pathway of heteronymous Recurrent Inhibition from soleus to quadriceps motor neurones is under at least two types of control: one related to the task, which sets the operating range, and a second which couples Inhibition to the level of muscle contraction. Multiple control pathways are consistent with the diverse effects on Recurrent Inhibition reported in subjects with upper motor neurone lesions.
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changes in transmission in the pathway of heteronymous spinal Recurrent Inhibition from soleus to quadriceps motor neurons during movement in man
Brain, 1999Co-Authors: J F Iles, Joanne PardoeAbstract:H reflexes were induced in the human quadriceps muscle by electrical stimulation of the femoral nerve. The reflexes were conditioned by prior stimulation of the inferior soleus nerve. The conditioning stimulus produced an Inhibition of long duration (>20 ms). The threshold of this Inhibition was at zero soleus motor discharge and the Inhibition scaled with soleus motor discharge. It was concluded that the Inhibition was a heteronymous Recurrent Inhibition of quadriceps motor neurons mediated by Renshaw cells which had been activated by soleus motor neuron discharge. This Recurrent Inhibition declined during voluntary tonic contraction of the quadriceps, falling to zero at around one-third of maximum voluntary contraction. Antagonist contraction and weak co-contraction of the quadriceps and its antagonists did not lead to any significant change in Recurrent Inhibition. It is concluded that motor commands descending from the brain reduce heteronymous Recurrent Inhibition during isolated quadriceps muscle contraction, but to a much lesser extent during co-contraction. No evidence was obtained for any descending facilitation of heteronymous Recurrent Inhibition.
George K Kostopoulos - One of the best experts on this subject based on the ideXlab platform.
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age related changes in excitability and Recurrent Inhibition in the rat ca1 hippocampal region
European Journal of Neuroscience, 1996Co-Authors: Costas Papatheodoropoulos, George K KostopoulosAbstract:: In hippocampal slices from male Wistar rats aged 1-34 months, we recorded the synaptic field potential responses of the CA1 neurons to stimulation of Schaffer collaterals. Eight electrophysiological indexes were extracted from input/output curves and compared in 11 age groups from 1 to 30 months. Neuronal excitability presented a U-shaped curve of development with a minimum at approximately 7-8 months of age. There was a significant continuous increase in neuronal excitability, i.e. a decrease in excitatory postsynaptic potential (EPSP) producing both the threshold and half-maximal population spike from middle age (8-10 months) to senescence (30 months). Synaptic efficiency also increased in old rats to reach a maximum during senescence, i.e. both the current for threshold EPSP and that for half-maximal EPSP reached a minimum in senescence, although the earlier developmental patterns of these two indexes were non-linear. The duration of the field EPSP elicited with maximal stimulation presented an abrupt decay after the first month. Aged animals presented a relatively small maximal population spike. Recurrent Inhibition was most prominent on neuronal excitability rather than synaptic strength. Measured as the percentage change in the half-maximal EPSP and half-maximal population spike, Recurrent Inhibition was found to decrease during the first 7-10 months of life and remained small in later development.
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Age‐related Changes in Excitability and Recurrent Inhibition in the Rat CA1 Hippocampal Region
European Journal of Neuroscience, 1996Co-Authors: Costas Papatheodoropoulos, George K KostopoulosAbstract:: In hippocampal slices from male Wistar rats aged 1-34 months, we recorded the synaptic field potential responses of the CA1 neurons to stimulation of Schaffer collaterals. Eight electrophysiological indexes were extracted from input/output curves and compared in 11 age groups from 1 to 30 months. Neuronal excitability presented a U-shaped curve of development with a minimum at approximately 7-8 months of age. There was a significant continuous increase in neuronal excitability, i.e. a decrease in excitatory postsynaptic potential (EPSP) producing both the threshold and half-maximal population spike from middle age (8-10 months) to senescence (30 months). Synaptic efficiency also increased in old rats to reach a maximum during senescence, i.e. both the current for threshold EPSP and that for half-maximal EPSP reached a minimum in senescence, although the earlier developmental patterns of these two indexes were non-linear. The duration of the field EPSP elicited with maximal stimulation presented an abrupt decay after the first month. Aged animals presented a relatively small maximal population spike. Recurrent Inhibition was most prominent on neuronal excitability rather than synaptic strength. Measured as the percentage change in the half-maximal EPSP and half-maximal population spike, Recurrent Inhibition was found to decrease during the first 7-10 months of life and remained small in later development.