scholarly journals Direct evidence for decreased presynaptic inhibition evoked by PBSt group I muscle afferents after chronic SCI and recovery with step‐training in rats

2020 ◽  
Vol 598 (20) ◽  
pp. 4621-4642 ◽  
Author(s):  
Guillaume Caron ◽  
Jadwiga N. Bilchak ◽  
Marie‐Pascale Côté
Keyword(s):  
Presynaptic Inhibition ◽  
Direct Evidence ◽  
Muscle Afferents ◽  
Group I

Absence of effects of contralateral group I muscle afferents on presynaptic inhibition of Ia terminals in humans and cats

2012 ◽  
Vol 108 (4) ◽  
pp. 1176-1185 ◽  
Author(s):  
Rinaldo André Mezzarane ◽  
André Fabio Kohn ◽  
Erika Couto-Roldan ◽  
Lourdes Martinez ◽  
Amira Flores ◽  
...  
Keyword(s):  
Presynaptic Inhibition ◽  
Muscle Afferents ◽  
H Reflex ◽  
Triceps Surae ◽  
Reflex Response ◽  
Current View ◽  
Tendon Vibration ◽  
Vibratory Stimulus ◽  
Group I ◽  
Group I Afferents

Crossed effects from group I afferents on reflex excitability and their mechanisms of action are not yet well understood. The current view is that the influence is weak and takes place indirectly via oligosynaptic pathways. We examined possible contralateral effects from group I afferents on presynaptic inhibition of Ia terminals in humans and cats. In resting and seated human subjects the soleus (SO) H-reflex was conditioned by an electrical stimulus to the ipsilateral common peroneal nerve (CPN) to assess the level of presynaptic inhibition (PSI_control). A brief conditioning vibratory stimulus was applied to the triceps surae tendon at the contralateral side (to activate preferentially Ia muscle afferents). The amplitude of the resulting H-reflex response (PSI_conditioned) was compared to the H-reflex under PSI_control, i.e., without the vibration. The interstimulus interval between the brief vibratory stimulus and the electrical shock to the CPN was −60 to 60 ms. The H-reflex conditioned by both stimuli did not differ from that conditioned exclusively by the ipsilateral CPN stimulation. In anesthetized cats, bilateral monosynaptic reflexes (MSRs) in the left and right L7 ventral roots were recorded simultaneously. Conditioning stimulation applied to the contralateral group I posterior biceps and semitendinosus (PBSt) afferents at different time intervals (0–120 ms) did not have an effect on the ipsilateral gastrocnemius/soleus (GS) MSR. An additional experimental paradigm in the cat using contralateral tendon vibration, similar to that conducted in humans, was also performed. No significant differences between GS-MSRs conditioned by ipsilateral PBSt stimulus alone and those conditioned by both ipsilateral PBSt stimulus and contralateral tendon vibration were detected. The present results strongly suggest an absence of effects from contralateral group I fibers on the presynaptic mechanism of MSR modulation in relaxed humans and anesthetized cats.

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

2002 ◽  
Vol 88 (1) ◽  
pp. 163-171 ◽  
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.

Responses of cortical neurons (areas 3a and 4) to ramp stretch of hindlimb muscles in the baboon

1976 ◽  
Vol 39 (3) ◽  
pp. 484-500 ◽  
Author(s):  
J. Hore ◽  
J. B. Preston ◽  
P. D. Cheney
Keyword(s):  
Cortical Neurons ◽  
Muscle Length ◽  
Muscle Afferents ◽  
Muscle Stretch ◽  
Hindlimb Muscles ◽  
Group I ◽  
Hindlimb Muscle ◽  
Area 3A ◽  
Group Ii Muscle Afferents ◽  
Group Ii

1. A study was made of the response of single cortical units in areas 3a and 4 to electrical stimulation of hindlimb muscle nerves and to ramp stretch of hindlimb muscles in baboons anesthetized with chloralose.2. Stimulation of hindlimb muscle nerves revealed a group I projection primarily to area 3a but with some input into adjacent area. 4. A major group II projection was found in area 4 adjacent to area 3a. A small number of area 3a neurons receive convergence from both group I and group II muscle afferents.3a. On the basis of their response pattern to ramp stretch, units were classified into one of six categories and their cytoarchitectonic location was determined. Units in area 3a had hynamic sensitivities equivalent to that of the primary spindle afferents. Although the discharge of some area 3a neurons also reflected differences in muscle length, most area 3a neurons had low position sensitivities. One unit type in area 3a did not respond to maintained muscle stretch and signaled only velocity of stretch.4. Units in area 4 had position sensitivities equivalent to that of primary and secondary spindle afferents. Although the discharge of some area 4 units reflected different velocities of muscle stretch, these units had dynamic sensitivities similar to those of secondary spindle afferents rather than those of primary afferents. One type of unit in area 4 had no dynamic component to muscle stretch and signaled only muscle length.5. The results demonstrate that there is a transfer of dynamic and position sensitivity from spindle afferents to cortical neurons. Furthermore, data processing has occurred because some units respond only to the steady-state length of muscle, while other units encode only the dynamic phase of stretch. This behavior is different from the responses to ramp stretch of either group I or group II muscle afferents in the baboon.6. The results demonstrate that single units in cerebral cortex can encode the information transmitted to the central nervous system by muscle spindle afferents. The purpose for which this information is used remains undetermined.

Declining inhibition elicited in cat lumbar motoneurons by repetitive stimulation of group II muscle afferents

1993 ◽  
Vol 70 (5) ◽  
pp. 1805-1810 ◽  
Author(s):  
J. Lafleur ◽  
D. Zytnicki ◽  
G. Horcholle-Bossavit ◽  
L. Jami
Keyword(s):  
Muscle Afferents ◽  
Repetitive Stimulation ◽  
Excitatory Postsynaptic Potential ◽  
Constant Input ◽  
Rapid Reduction ◽  
Group I ◽  
Constant Strength ◽  
Group I Afferents ◽  
Group Ii ◽  
Stimulation Of

1. The aim of the present experiments was to verify whether group II inputs from gastrocnemius medialis (GM) muscle could elicit declining inhibitions similar to those observed during GM contractions in a variety of lumbar motoneurons of the cat spinal cord. Motoneurons were recorded intracellularly in chloralose- or pentobarbitone-anesthetized preparations during electrical stimulation of GM nerve with repetitive trains. 2. With strengths in the group I range, repetitive stimulation evoked the usual Ia excitation in homonymous motoneurons and excitatory postsynaptic potential (EPSP) amplitudes remained constant throughout the stimulation sequence. In synergic plantaris motoneurons lacking an excitatory connection with Ia afferents from GM, the same stimulation, kept at a constant strength throughout the stimulation sequence, elicited rapidly decreasing inhibitory potentials reminiscent of those evoked by GM contractions. 3. In motoneurons of pretibial flexors, quadriceps, and posterior biceps-semitendinosus, the stimulation strength required to observe declining inhibitions resembling those produced by GM contractions was 4-8 times group I threshold, engaging group II in addition to group I fibers. 4. These results show that input from GM group II plus group I afferents can elicit inhibitory effects in a variety of motoneurons. Such observations support the hypothesis that messages from spindle secondary endings and/or nonspecific muscle receptors activated during contraction might contribute to the widespread inhibition caused by GM contractions. 5. Inasmuch as constant input in group II and group I afferents evoked declining inhibitory potentials, the origin of the decline must be central, which suggests that the rapid reduction of contraction-induced inhibitions also depended on a central mechanism.

Synaptic organization of defined motor-unit types in cat tibialis anterior

1980 ◽  
Vol 43 (6) ◽  
pp. 1631-1644 ◽  
Author(s):  
R. P. Dum ◽  
T. T. Kennedy
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Muscle Afferents ◽  
Medial Gastrocnemius ◽  
Synaptic Organization ◽  
Ia Afferents ◽  
Group I ◽  
Ia Epsp ◽  
Group I Afferents ◽  
Stimulation Of

1. Synaptic potentials were recorded intracellularly in tibialis anterior (TA) motoneurons following stimulation of a descending brain stem pathway, the medial longitudinal fasciculus (MLF), and three segmental inputs, the homonymous and heteronymous group Ia afferents, the group I afferents from the antagonist, and the cutaneous and muscle afferents. Intracellular stimulation of the motoneurons was used to classify them, based on the properties of the innervated muscle units, into types FF, F(int), FR, and S (6, 16). 2. The sum of the monosynaptic EPSP amplitudes resulting from stimulation of homonymous and heteronymous group Ia afferents (summed group Ia EPSP) was inversely related to motoneuron size, as assessed by motoneuron input resistance, and was inversely related to motor-unit tetanic tension. Type-FF, -FR, and -S motoneurons showed significant differences in the mean amplitude of their summed group Ia EPSPs. 3. The amplitudes of disynaptic IPSPs resulting from stimulation of group I afferents in the antagonist muscle also showed an inverse relationship to motoneuron size. The observed relationships between motoneuron size and the monosynaptic group Ia EPSP amplitude or the disynaptic group I IPSP amplitude are compatible with the “size principle” of motor-unit recruitment (26). 4. The amplitudes of the monosynaptic EPSPs evoked in TA motoneurons by stimulation of the MLF were distributed rather randomly among all types of TA motoneurons. A slight tendency of larger monosynaptic EPSPs to occur in motoneurons with larger tetanic tensions was observed. 5. The polysynaptic effects from cutaneous and muscle afferents in sural and gastrocnemius-soleus nerves were frequently excitatory on type-FF motoneurons, but were primarily inhibitory on type-FR and -S motoneurons. Clearly, the polysynaptic cutaneous and muscle inputs and the monosynaptic MLF input onto TA motoneurons show a different pattern of synaptic organization than the group I inputs. 6. In general, the synaptic organization of the TA motor nucleus is similar to that of its extensor antagonist, medial gastrocnemius (MG) (2--5, 7, 8), when analogous neural circuits are compared. This parallel organization suggests a commonality of motor-control systems for both flexor and extensor muscles.

Sign in / Sign up

Export Citation Format

Share Document