Short-Latency Crossed Inhibitory Responses in Extensor Muscles During Locomotion in the Cat

Frigon, Alain; Rossignol, Serge

doi:10.1152/jn.01274.2007

Cited by 35 publications

(26 citation statements)

References 48 publications

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“…Fig. 5) or the activation of crossed inhibitory pathways (Arya et al 1991; Aggelopoulos & Edgley, 1995; Aggelopoulos et al 1996; Frigon & Rossignol, 2008 c ). Crossed flexion has been reported in the cat following acute spinalization (Rossignol & Gauthier, 1980).…”

Section: Resultsmentioning

confidence: 99%

Differential modulation of crossed and uncrossed reflex pathways by clonidine in adult cats following complete spinal cord injury

Frigon

Johnson

Heckman

2012

The Journal of Physiology

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Non-technical summary Clonidine, a noradrenaline-like drug, facilitates the recovery of hindlimb walking in adult cats following a complete spinal cord injury.We show that clonidine improves operation of reflex pathways that coordinate bilateral hindlimb activity in cats after spinal cord injury. In addition, sensory signals from the periphery more easily activate the spinal network involved in producing locomotion following clonidine injection.These results show that spinal neurons that produce locomotion and coordinate bilateral activity become more excitable with clonidine.These data could help identify neurons of the spinal locomotor network and lead to a better pharmacotherapy in spinal cord-injured humans.Abstract Clonidine, an α-noradrenergic agonist, facilitates hindlimb locomotor recovery after complete spinal transection (i.e. spinalization) in adult cats. However, the mechanisms involved in clonidine-induced functional recovery are poorly understood. Sensory feedback from the legs is critical for hindlimb locomotor recovery in spinalized mammals and clonidine could alter how spinal neurons respond to peripheral inputs in adult spinalized cats. To test this hypothesis we evaluated the effect of clonidine on the responses of hindlimb muscles, primarily in the left hindlimb, evoked by stretching the left triceps surae muscles and by stimulating the right tibial and superficial peroneal nerves in eight adult decerebrate cats that were spinalized 1 month before the terminal experiment. Cats were not trained following spinalization. Clonidine had no consistent effect on responses of ipsilateral muscles evoked by triceps surae muscle stretch. However, clonidine consistently potentiated the amplitude and duration of crossed extensor responses. Moreover, following clonidine injection, stretch and tibial nerve stimulation triggered episodes of locomotor-like activity in approximately one-third of trials. Differential effects of clonidine on crossed reflexes and on ipsilateral responses to muscle stretch indicate an action at a pre-motoneuronal site. We conclude that clonidine facilitates hindlimb locomotor recovery following spinalization in untrained cats by enhancing the excitability of central pattern generating spinal neurons that also participate in crossed extensor reflex transmission.

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Section: Resultsmentioning

confidence: 99%

Differential modulation of crossed and uncrossed reflex pathways by clonidine in adult cats following complete spinal cord injury

Frigon

Johnson

Heckman

2012

The Journal of Physiology

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“…The earlier onset of responses could be due to the fact that larger responses are easier to delineate and/or that an inhibitory influence was removed. For instance, a short‐latency inhibitory pathway projects from cutaneous afferents of the foot to contralateral extensors (Edgley & Aggelopoulos, 2006; Frigon & Rossignol, 2008) and may project to several motor pools. In this scenario, spinalization reduced the efficacy of the crossed inhibitory pathways and consequently responses occurred earlier, although this requires further investigation.…”

Section: Discussionmentioning

confidence: 99%

“…automatic gain control) with the level of EMG activity (Matthews, 1986), the subtracted value was then divided by a fixed 15 ms block of blEMG in the same phase (see Fig. 1 of Frigon & Rossignol, 2008 for an example), thus giving a reflex amplitude normalized to the level of baseline locomotor activity. Inhibitory responses, in our context, can only be quantified when there is a baseline level of EMG.…”

Section: Methodsmentioning

confidence: 99%

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Adaptive changes of the locomotor pattern and cutaneous reflexes during locomotion studied in the same cats before and after spinalization

Frigon

Rossignol

2008

The Journal of Physiology

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Descending supraspinal inputs exert powerful influences on spinal reflex pathways in the legs. Removing these inputs by completely transecting the spinal cord changes the state (i.e. the configuration of the spinal circuitry) of the locomotor network and undoubtedly generates a reorganization of reflex pathways. To study changes in reflex pathways after a complete spinalization, we recorded spinal reflexes during locomotion before and after a complete transection of the spinal cord at the 13th thoracic segment in cats. We chronically implanted electrodes in three cats, to record electromyography (EMG) in several hindlimb muscles and around the left tibial (Tib) nerve at the ankle to elicit reflexes during locomotion before and after spinalization in the same cat. Control values of kinematics, EMGs and reflexes were obtained during intact locomotion for 33-60 days before spinalization. After spinalization, cats were trained 3-5 times a week on a motorized treadmill. Recordings resumed once a stable spinal locomotion was achieved (26-43 days), with consistent plantar foot placement and full hindquarter weight support without perineal stimulation. Changes in Tib nerve reflex responses after spinalization in the same cat during locomotion were found in all muscles studied and were often confined to specific phases of the step cycle. The most remarkable change was the appearance of short-latency excitatory responses in some ipsilateral ankle extensors during stance. Short-latency excitatory responses in the ipsilateral tibialis anterior were increased during stance, whereas in other flexors such as semitendinosus and sartorius, increases were mostly confined to swing. Longer-latency excitatory responses in ipsilateral flexors were absent or reduced. Responses evoked in limb muscles contralateral to stimulation were generally increased throughout the step cycle. These reflex changes after spinalization provide important clues regarding the functional reorganization of reflex pathways during spinal locomotion.

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“…Because reflex amplitude is known to scale (i.e., automatic gain control) with the level of EMG activity (Matthews 1986), the subtracted value was then divided by a fixed 15-ms block of blEMG in the same phase (for an example, see Fig. 1 of Frigon and Rossignol 2008b), thus giving a reflex amplitude normalized to the level of baseline locomotor activity. For St and TA, reflex responses evoked during swing (data points at phases 0.05 to 0.35) and those evoked during stance (data points at phases 0.45 to 0.85) were averaged together to provide an average reflex response during swing and stance, respectively.…”

Section: Tibial Nerve Stimulation and Reflexesmentioning

confidence: 99%

Locomotor and Reflex Adaptation After Partial Denervation of Ankle Extensors in Chronic Spinal Cats

Frigon¹,

Rossignol²

2008

Journal of Neurophysiology

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This work investigates the capacity of the spinal cord to generate locomotion after a complete spinal section and its ability to adapt its locomotor pattern after a peripheral nerve lesion. To study this intrinsic adaptive capacity, the left lateral gastrocnemius-soleus (LGS) nerve was sectioned in three cats that expressed a stable locomotion following a complete spinal transection. The electromyograph (EMG) of multiple hindlimb muscles and reflexes, evoked by stimulating the left tibial (Tib) nerve at the ankle, were recorded before and after denervation during treadmill locomotion. Following denervation, the mean amplitude of EMG bursts of multiple hindlimb muscles increased during locomotion, similar to what is found after an identical denervation in otherwise intact cats. Reflex changes were noted in ipsilateral flexors, such as semitendinosus and tibialis anterior, but not in the ipsilateral knee extensor vastus lateralis following denervation. The present results demonstrate that the spinal cord possesses the circuitry necessary to mediate increased EMG activity in multiple hindlimb muscles and also to produce changes in reflex pathways after a muscle denervation. The similarity of changes following LGS denervation in cats with an intact and transected spinal cord suggests that spinal mechanisms play a major role in the locomotor adaptation.

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Short-Latency Crossed Inhibitory Responses in Extensor Muscles During Locomotion in the Cat

Cited by 35 publications

References 48 publications

Differential modulation of crossed and uncrossed reflex pathways by clonidine in adult cats following complete spinal cord injury

Differential modulation of crossed and uncrossed reflex pathways by clonidine in adult cats following complete spinal cord injury

Adaptive changes of the locomotor pattern and cutaneous reflexes during locomotion studied in the same cats before and after spinalization

Locomotor and Reflex Adaptation After Partial Denervation of Ankle Extensors in Chronic Spinal Cats

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