Candidate interneurones mediating group I disynaptic EPSPs in extensor motoneurones during fictive locomotion in the cat

Hip position and loading of limb extensors are major sensory cues for the initiation and duration of different phases during walking. Although these inputs have pathways projecting to the locomotor rhythm generator, their effects may vary in different parts of the locomotor cycle. In the present study, the plantaris (Pl), sartorius (Sart), rectus femoris (RF), and caudal gluteal (cGlu) nerves were stimulated at group I and/or group II strength during spontaneous fictive locomotion in 16 adult decerebrate cats. These nerves supply muscles that extend the ankle (Pl), flex the hip (Sart, RF), or extend the hip (cGlu). Stimuli were given at six epochs of the locomotor cycle to evaluate when they access the rhythm generator. Group I afferents from Pl nerve always reset the locomotor rhythm; stimulation during extension prolonged cycle period and extension phase duration, while stimulation during flexion terminated flexion and initiated extension. On the other hand, stimulating RF and cGlu nerves only produced significant effects on the rhythm in precise epochs, particularly during mid-flexion and/or mid- to late extension. Stimulating the Sart nerve produced complex effects on the rhythm that were not distributed evenly to all extensor motor pools. The most consistent effect was reduced flexion phase duration with stimulation during flexion, particularly at group II strength, and prolongation of the extension phase but only in late extension. That hip muscle afferents reset the rhythm in only specific epochs of the locomotor cycle suggests that the rhythm generator operates with several subdivisions to determine phase and cycle durations.

Download Full-text

Sensory Integration in Presynaptic Inhibitory Pathways During Fictive Locomotion in the Cat

Journal of Neurophysiology ◽

10.1152/jn.2002.88.1.163 ◽

2002 ◽

Vol 88 (1) ◽

pp. 163-171 ◽

Cited By ~ 21

Author(s):

Ariane Ménard ◽

Hugues Leblond ◽

Jean-Pierre Gossard

Keyword(s):

Presynaptic Inhibition ◽

Muscle Afferents ◽

Primary Afferent Depolarization ◽

Skin Area ◽

Fictive Locomotion ◽

Step Cycle ◽

Primary Afferent ◽

Decerebrate Cat ◽

Group I ◽

Group I Afferents

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 = 31) from seven hindlimb muscles in L6–S1 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 phase-dependent 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 = 9) or of PADs ( n = 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.

Download Full-text

Repetitive monosynaptic activation of motoneurones

Proceedings of the Royal Society of London Series B Biological Sciences ◽

10.1098/rspb.1951.0036 ◽

1951 ◽

Vol 138 (893) ◽

pp. 475-498 ◽

Cited By ~ 18

Keyword(s):

Repetitive Stimulation ◽

Monosynaptic Reflex ◽

Synaptic Potential ◽

Group I ◽

Excitatory Action ◽

Extensor Motoneurones ◽

Group Ii ◽

Set Up ◽

Reflex Discharge ◽

Stimulation Of

Repetitive monosynaptic activation of motoneurones has been set up by maximum repetitive stimulation of the group I afferent fibres of the nerves to various muscles. By studying the effects produced by stimuli of varying strengths and also by comparing the responses of flexor and extensor motoneurones, it has been possible to allow for complications arising from concomitant stimulation of group II and III fibres in these nerves. Motoneurone responses have been recorded either as impulses discharged along the ventral root or as synaptic potentials electrotonically transmitted thereto. The repetitive synaptic potential conforms to a standard pattern for both flexor and extensor motoneurones. With frequencies over 100/sec. there is a brief initial phase of summation, then decline to a plateau at about the height of the initial single potential. On cessation of stimulation there is an immediate decline to a positive after-potential which bears a close resemblance to that observed after repetitive stimulation of peripheral nerve. The repetitive potential is compounded of ‘diphasic’ potentials generated by each successive volley, an initial negative synaptic potential and a later positive after-potential. At high frequencies of stimulation the successive potentials show an initial rapid decline in size to a low value, e. g. to 50% at 400/sec., which is only in part attributable to a decline in the size of the volleys entering the spinal cord. Focal recording has permitted simultaneous comparison of these two declines. The excitability of the motoneurones during and after repetitive activation was tested heterosynaptically. During the synaptic potential plateau the excitability is raised, with periodic variations in phase with the successive volleys, while depression is observed during the positive after-potential. With extensor muscles the reflex discharge of impulses conforms in general with the repetitive synaptic potential curve, the initial summation giving monosynaptic reflex discharges to the first two or three volleys at high frequency. It is probable that a motoneurone fires only once in this initial burst. Subsequently, the combination of autogenetic inhibitory action of group II fibres (which may however be negligible), diminished synaptic excitatory action, and depressant action of the accumulated positive after-potentials (subsynaptic depression) may prevent all further discharge. Alternatively, after a brief quiescent interval, a small irregular discharge may be set up monosynaptically by subsequent volleys. With low frequencies of stimulation the second and subsequent volleys may all evoke reflex discharges, but they are always smaller than the initial discharge. Repetitive activation of flexor moto-neurones differs from extensors in that the autogenetic excitatory action of group II afferent fibres makes both the initial and later bursts of reflex discharge larger and more sustained.

Download Full-text

Group I disynaptic excitation of cat hindlimb flexor and bifunctional motoneurones during fictive locomotion

The Journal of Physiology ◽

10.1111/j.1469-7793.2000.t01-1-00549.x ◽

2000 ◽

Vol 525 (2) ◽

pp. 549-564 ◽

Cited By ~ 48

Author(s):

J. Quevedo ◽

B. Fedirchuk ◽

S. Gosgnach ◽

D. A. McCrea

Keyword(s):

Fictive Locomotion ◽

Group I

Download Full-text

Modulation of Oligosynaptic Cutaneous and Muscle Afferent Reflex Pathways During Fictive Locomotion and Scratching in the Cat

Journal of Neurophysiology ◽

10.1152/jn.1998.79.1.447 ◽

1998 ◽

Vol 79 (1) ◽

pp. 447-463 ◽

Cited By ~ 50

Author(s):

A. M. Degtyarenko ◽

E. S. Simon ◽

T. Norden-Krichmar ◽

R. E. Burke

Keyword(s):

Membrane Potential ◽

Central Pattern Generators ◽

Muscle Afferents ◽

Flexor Hallucis Longus ◽

Fictive Locomotion ◽

Postsynaptic Potentials ◽

Cutaneous Reflex ◽

Reflex Pathways ◽

Group I ◽

Muscle Afferent

Degtyarenko, A. M., E. S. Simon, T. Norden-Krichmar, and R. E. Burke. Modulation of oligosynaptic cutaneous and muscle afferent reflex pathways during fictive locomotion and scratching in the cat. J. Neurophysiol. 79: 447–463, 1998. We have compared state-dependent transmission through oligosynaptic (minimally disynaptic) reflex pathways from low-threshold cutaneous and muscle afferents to some flexor and extensor lumbosacral motoneurons during fictive locomotion and scratching in decerebrate unanesthetized cats. As reported in earlier work, oligosynaptic cutaneous excitatory postsynaptic potentials (EPSPs) in flexor digitorum longus (FDL) and inhibitory postsynaptic potentials (IPSPs) in extensor digitorum (EDL) longus motoneurons were enhanced markedly during the early flexion phase of fictive locomotion. We show in this paper that, in contrast, these cutaneous reflex pathways were depressed markedly during all phases of fictive scratching. On the other hand, disynaptic EPSPs produced by homonymous and synergist group I muscle afferents in flexor (tibialis anterior and EDL) motoneurons were present and strongly modulated during both fictive locomotion and scratching. During both actions, these disynaptic group I EPSPs appeared or exhibited the largest amplitude when the motoneuron membrane potential was most depolarized and the parent motor pool was active. There was an interesting exception to the simple pattern of coincident group I EPSP enhancement and motoneuron depolarization. During locomotion, disynaptic group I EPSPs in both FDL and flexor hallucis longus (FHL) motoneurons cells were facilitated during the extension phase, although FDL motoneurons were relatively hyperpolarized whereas FHL cells were depolarized. The reverse situation was found during fictive scratching; group I EPSPs were facilitated in both FDL and FHL cells during the flexion phase when FDL motoneurons were depolarized and FHL cells were relatively hyperpolarized. These observations suggest that the disynaptic EPSPs in these two motor nuclei are produced by common interneurons. Reciprocal disynaptic inhibitory pathways from group Ia muscle afferents to antagonist motoneurons were also active and subject to phase-dependent modulation during both fictive locomotion and scratching. In all but one cell tested, reciprocal disynaptic group Ia IPSPs were largest during those phases in which the motoneuron membrane potential was relatively hyperpolarized and the parent motor pool was inactive. Oligosynaptic PSPs in motoneurons produced by stimulation of the mesencephalic locomotor region (MLR) were modulated strongly during fictive locomotion but were suppressed powerfully throughout fictive scratching. Large cord dorsum potentials generated by MLR stimuli also were suppressed markedly during fictive scratching. These results allow certain inferences about the organization of interneurons in the pathways examined. They also suggest that the central pattern generators that produce fictive locomotion and scratching are organized differently.

Download Full-text

An intracellular study of muscle primary afferents during fictive locomotion in the cat

Journal of Neurophysiology ◽

10.1152/jn.1991.65.4.914 ◽

1991 ◽

Vol 65 (4) ◽

pp. 914-926 ◽

Cited By ~ 86

Author(s):

J. P. Gossard ◽

J. M. Cabelguen ◽

S. Rossignol

Keyword(s):

Muscle Spindle ◽

Vastus Lateralis ◽

Relative Size ◽

Primary Afferents ◽

Triceps Surae ◽

Resting Potential ◽

Fictive Locomotion ◽

Group I ◽

Group Ii ◽

Bifunctional Muscle

1. Presynaptic activity of identified primary afferents from flexor, extensor, and bifunctional hindlimb muscles was studied with intra-axonal recordings during fictive locomotion. Fictive locomotion appeared spontaneously in decorticate cats (n = 9), with stimulation of the mesencephalic locomotor region (n = 4), and in spinal cats injected with clonidine or nialamide and L-DOPA (n = 4). Representative flexor and extensor muscle nerves, recorded to monitor the locomotor pattern and dorsal rootlets of the sixth and seventh lumbar segments, were recorded simultaneously to monitor dorsal root potentials (DRPs). 2. From responses to muscle stretches and, in some instances, twitch contractions of the parent muscle, 75% of the single units examined were putatively identified as spindle afferents (40/53). On the basis of conduction velocity and stimulation threshold, 73% of these were further classified as group I fibers (29/40), the rest as group II fibers. 3. All units (n = 53 with resting potential more negative than -45 mV) showed fluctuations of their membrane potential (up to 1.5 mV) at the rhythm of the fictive locomotion. Subsequent averaging of these fluctuations over several cycles revealed that 89% of all units displayed a predominant wave of depolarization during the flexor phase, followed by a trough of repolarization. In 79% of the units, there was also a second, usually smaller, depolarization during the extensor phase. The relative size of each wave of depolarization could vary with different episodes of fictive locomotion in the same unit and among various afferents from the same muscle in the same experiment. 4. The firing frequency of some afferents from the ankle flexor tibialis anterior (5/16) and the bifunctional muscle posterior biceps-semitendinosus (4/15) was phasically modulated along the fictive step cycle. The maximum frequency always occurred during the flexor phase, i.e., during the largest depolarization of the unit. Because of the absence of phasic sensory input in the curarized animal, we assume that the phasic discharges were generated within the spinal cord and antidromically propagated. Phasic firing was never encountered in afferents from extensor muscles such as triceps surae (0/15) and vastus lateralis (0/4). 5. The results demonstrate that the pattern of rhythmic depolarization accompanying fictive locomotion is similar for the majority of flexor, extensor, and bifunctional group I (and possibly group II) muscle spindle primary afferents. They further indicate that there is a specific phasic modulation of antidromic firing for some flexor and bifunctional muscle spindle afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

Download Full-text