Afferent control of central pattern generators: experimental analysis of locomotion in the decerebrate cat (original) (raw)
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Journal of Neurophysiology, 2011
Sensory feedback plays a crucial role in the control of locomotion and in the recovery of function after spinal cord injury. Investigations in reduced preparations have shown that the locomotor cycle can be modified through the activation of afferent feedback at various phases of the gait cycle. We investigated the effect of phase-dependent electrical stimulation of a cutaneous afferent nerve on the locomotor pattern of trained spinal cord-injured cats. Animals were first implanted with chronic nerve cuffs on the sural and sciatic nerves and electromyographic electrodes in different hindlimb muscles. Cats were then transected at T12 and trained daily to locomote on a treadmill. We found that electrical stimulation of the sural nerve can enhance the ongoing flexion phase, producing higher (+129%) and longer (+17.4%) swing phases of gait even at very low threshold of stimulation. Sural nerve stimulation can also terminate an ongoing extension and initiate a flexion phase. A higher pre...
Ia afferent activity during a variety of voluntary movements in the cat
The Journal of physiology, 1977
1. Implanted dorsal root electrodes were used to record discharge trains of single spindle primary afferents (Ia's) of the cat's hind limb during different types of movement.2. The length of the ipsilateral ankle extensors was continuously monitored by an implanted length gauge. Length changes occurring during active stepping were subsequently passively reproduced during brief anaesthesia.3. A comparison of the Ia responses in active and simulated step cycles revealed that moderate fusimotor drive to ankle extensor spindles probably occurred mainly, if not exclusively, during the E(1), E(2) and E(3) phases of active stepping.4. A temporal advance in the Ia response to passive stretching in the F-phase was attributed to the after-effects of fusimotor activity in the extension phases.5. Light thrust applied to the animal's back evoked a potent fusimotor response. This load compensation effect may provide an explanation for the apparently higher degree of alpha-gamma co-act...
Effects of stimulation of hindlimb flexor group II afferents during fictive locomotion in the cat
The Journal of physiology, 1995
1. This study examines the effects of electrical stimulation of hindlimb flexor nerves on the fictive locomotion pattern. Locomotion was initiated by stimulation of the mesencephalic locomotor region in the decerebrate paralysed cat and monitored by recording the electroneurogram from selected hindlimb flexor and extensor muscle nerves. Flexor nerves were stimulated using short trains (20-50 stimuli at 100 Hz) during either the flexor or the extensor phase of the fictive locomotor cycle. 2. Stimulation of tibialis anterior (TA), posterior biceps and semitendinosus (PBSt) or sartorius (Sart) nerves at 5 times threshold (T) during the flexor phase of the fictive locomotor cycle terminated on-going activity in flexor nerves and initiated activity in extensors. Thus, flexor nerve stimulation during flexion shortened the locomotor cycle by resetting to extension. The failure of lower intensity (2T) stimulation of PBSt or Sart nerves to reset the step cycle to extension suggests that grou...
Sensory integration in presynaptic inhibitory pathways during fictive locomotion in the cat
Journal of …, 2002
The aim of this study is to understand how sensory inputs of different modalities are integrated into spinal cord pathways controlling presynaptic inhibition during locomotion. Primary afferent depolarization (PAD), an estimate of presynaptic inhibition, was recorded intra-axonally in group I afferents (n ϭ 31) from seven hindlimb muscles in L 6-S 1 segments during fictive locomotion in the decerebrate cat. PADs were evoked by stimulating alternatively low-threshold afferents from a flexor nerve, a cutaneous nerve and a combination of both. The fictive step cycle was divided in five bins and PADs were averaged in each bin and their amplitude compared. PADs evoked by muscle stimuli alone showed a significant phasedependent modulation in 20/31 group I afferents. In 12/20 afferents, the cutaneous stimuli alone evoked a phase-dependent modulation of primary afferent hyperpolarization (PAH, n ϭ 9) or of PADs (n ϭ 3). Combining the two sensory modalities showed that cutaneous volleys could significantly modify the amplitude of PADs evoked by muscle stimuli in at least one part (bin) of the step cycle in 17/31 (55%) of group I afferents. The most common effect (13/17) was a decrease in the PAD amplitude by 35% on average, whereas it was increased by 17% on average in the others (4/17). Moreover, in 8/13 afferents, the PAD reduction was obtained in 4/5 bins i.e., for most of the duration of the step cycle. These effects were seen in group I afferents from all seven muscles. On the other hand, we found that different cutaneous nerves had quite different efficacy; the superficial peroneal (SP) being the most efficient (85% of trials) followed by Saphenous (60%) and caudal sural (44%) nerves. The results indicate that cutaneous interneurons may act, in part, by modulating the transmission in PAD pathways activated by group I muscle afferents. We conclude that cutaneous input, especially from the skin area on the dorsum of the paw (SP), could subtract presynaptic inhibition in some group I afferents during perturbations of stepping (e.g., hitting an obstacle) and could thus adjust the influence of proprioceptive feedback onto motoneuronal excitability.
Control of Cat Walking and Paw-Shake by a Multifunctional Central Pattern Generator
Neuromechanical Modeling of Posture and Locomotion, 2015
Central pattern generators (CPGs) are oscillatory neuronal networks controlling rhythmic motor behaviors such as swimming, walking, and breathing. Multifunctional CPGs are capable of producing multiple patterns of rhythmic activity with different periods. Here, we investigate whether two cat rhythmic motor behaviors, walking and paw-shaking, could be controlled by a single multifunctional CPG. To do this, we have created a parsimonious model of a half-center oscillator composed of two mutually inhibitory neurons. Two basic activity regimes coexist in this model: fast 10 Hz paw-shake regime and a slow 2 Hz walking regime. It is possible to switch from paw-shaking to walking with a short pulse of conductance in one neuron, and it is possible to switch from walking to paw-shaking with a longer pulse of excitatory conductance in both neurons. The paw-shake and walking rhythms generated by the CPG model were used as input to a neuromechanical model of the cat hindlimbs to simulate the corresponding rhythmic behaviors. Simulation results demonstrated that the multifunctional half-center locomotor CPG could produce movement mechanics and muscle activity patterns typical for cat walking or paw-shake responses if synaptic weights in selected spinal circuits were altered during each behavior. We propose that the selection of CPG regimes and spinal circuitry is triggered by sensory input from paw skin afferents.
The Stumbling Correction Reaction during Fictive Locomotion in the Cata
Annals of The New York Academy of Sciences, 1998
C ontact between the dorsum of a hindlimb paw and an obstacle during the swing phase of locomotion evokes a specific pattern of muscle activation in an attempt to avoid tripping. This pattern has been termed the stumbling corrective reaction 1 and consists of a cessation of activity in ankle flexor muscles and an onset of activity in knee flexors and the ankle extensor, lateral gastrocnemius. As a result of the ankle extension, the forward motion of the foot can continue and as a result of the knee flexion, the foot is raised to clear the obstacle. 1-4 Stumbling correction has been described during treadmill walking in intact, for example, and chronic spinal 2 cats and in man. 5,6 Its presence in spinal animals indicates that the response can be organized at the level of the lumbar spinal cord. Because the stumbling corrective reaction is abolished by anesthesia of the skin, 2,3 cutaneous receptors appear essential. On the other hand, because electrical stimulation of the skin does not evoke stumbling correction, 3,4 it has been suggested that participation of proprioceptors is also required for the response. The present experiments were designed to address two questions: Can the stumbling corrective reaction be evoked during fictive locomotion, and can it be evoked by cutaneous stimulation alone? Observations were obtained during fictive locomotion produced by stimulation of the midbrain in decerebrate cats following neuromuscular blockade (see reference 7 for details).The superficial peroneal (SP) nerve containing the cutaneous innervation of the dorsum of the foot was stimulated using a train of 20-40 shocks (200 Hz) at twice threshold. Rectified, integrated, electroneurogram (ENG) activity was used as a monitor of fictive locomotion and using a window discriminator, to trigger the delivery of the stimulus train during a particular part of the fictive locomotor step cycle. FIGURE 1 shows an average of 14 trials in which the SP nerve was stimulated about 200 ms after the onset of activity in the tibialis anterior (ankle flexor) nerve. The traces are aligned at the onset of stimulus delivery (vertical dashed line). Shortly after the beginning of the stimulus train there is upward deflection of the TA ENG indicating an excitation of TA, motoneurons, which is quickly followed by a reduction in TA activity to below prestimulus levels. Posterior biceps (PB) and semitendinosus (St) are activated soon after stimulus onset and a few milliseconds later, activity in lateral gastrocnemius and soleus (LGS) appears. The sequence of a sustained excitation of knee (PB and St) but not ankle (TA) flexors and the delayed excitation of ankle extensors (LGS), and the latencies of these responses are remarkably similar to those reported during treadmill locomotion in intact cats (e.g., reference 3, figure 3). Although intracellular records and accurate determination of the arrival of the volley at the spinal cord are needed to determine the minimum intraspinal latency of TA, PB, and St excitation, the 7.3-ms latency from the onset of stimulation illustrated in FIGURE 1 includes 502 a This work was supported by the Canadian MRC and the Rick Hansen Legacy Fund.
The Contribution of Cutaneous Inputs to Locomotion in the Intact and the Spinal Cata
Annals of the New York Academy of Sciences, 1998
E xperiments involving skin or cutaneous nerve stimulation during locomotion in spinal, 1 decerebrate, 2 and intact cats 3,4 have demonstrated that cutaneous inputs are involved in complex, phase-dependent reflexes that can dramatically influence the locomotor cycle. It is therefore surprising that only minor changes have been reported in the walking ability of animals following a cutaneous denervation of the hindlimbs. 5,6 We wanted to reassess, with electromyographic and video recordings, the contribution of cutaneous inputs to locomotion (treadmill and ladder) after sectioning all (two cats) or most (one cat) cutaneous nerves of the hindfeet. After adaptation to the lesion, cats were spinalized and trained to walk on the treadmill to evaluate the importance of cutaneous inputs in the expression of locomotion in completely spinal cats and also their adaptive capacities.