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PubMed1978

Electrophysiological appraisal of relative segmental motoneurone pool excitability in flexor and extensor.

F responses recorded from flexor and extensor muscles were analysed in 18 normal subjects and in 16 patients with motor system abnormalities. The prominence of the F responses was evaluated quantitatively by determining the persistence--that is, the fraction of measurable F responses which actually occur after a series of supramaximal stimuli--and average amplitude of the F responses. In the normal resting state, the data are consistent with the hypothesis that the "central excitatory states" of motoneurones is greater in the antigravity muscles than in those muscles not stretched by gravity. This pattern was disrupted in eight of the 16 patients with motor system abnormalities caused by central nervous system lesions. These changes reflect a clinically testable aspect of the pathophysiology of certain motor system disorders.

Action Potentials↗
PubMed1978

Excitability relationships between lower limb myotatic arcs in spasticity.

The excitability of a lower limb myotatic reflex arc is modulated by the antecedent activation of another myotatic arc in the same limb; the changes can be represented by heteronymous excitability curves. This work compares heteronymous excitability curves in spastic and normal subjects. Eighteen patients who showed clear signs of pyramidal tract lesions at a chronic stage were studied. Three myotatic arcs of the lower limb (soleus, quadriceps, and short biceps) were activated either by mechanical percussion (T Sol-T Quad-TSBi) or by electrical stimulation of the afferent nerve (H Sol-H Quad). They were used as conditioning and test responses in six different combinations, and the results compared to those obtained previously in normal volunteers. In spastic patients, heteronymous excitability curves are more obviously modified than homonymous ones. The changes are most prominent in the thigh muscles and less marked when the soleus reflex is conditioned by activation of quadriceps and biceps femoris myotatic reflex arcs.

Adult↗
PubMed1979

Inverted knee jerk: a neglected localising sign in spinal cord disease.

Two cases are described in which inversion of the quadriceps jerk was observed. It is suggested that the finding of an inverted quadriceps jerk is evidence of a spinal cord lesion at 12, 3, 4 segmental level and has for the lumbar cord the same localising value as the inverted supinator jerk for the cervical cord.

Adult↗
PubMed1984

Cutaneous nerve stimulation and motoneuronal excitability. II: Evidence for non-segmental influences.

After stimulation of a sensory nerve, even distant motor nuclei undergo excitability changes which are evidenced by recovery curves. In all, two unequal peaks of facilitation can be identified. They appear when a given motor nucleus is tested after stimulation of various sensory nerves or when the same stimulation (of the sural nerve) is studied in various motor nuclei. The first facilitation is seen earlier in the masseter, then in the arm muscles and finally in lower limb muscles. The existence of a supraspinal centre activated by low threshold exteroceptive afferents and facilitating motor nuclei in a rostro-caudal sequence is postulated to account for certain features of the first and second peaks of facilitation.

Adolescent↗
PubMed1985

Central and peripheral causes of hyperreflexia in humans breathing 5% trimix at 650 m.

To clarify the mechanism of increased stretch reflex responsiveness in deep divers (hyperbaric hyperreflexia), comparative studies of stretch (T) and Hoffmann (H) reflexes were done on three men breathing 5% N2-0.5 bar O2-balance He at pressures up to 650 m of seawater (msw) (Atlantis IV simulated dive, F.G. Hall Laboratory, Duke Medical Center). Electromyography revealed increases at depth of up to 160% in the T reflex recruitment ratio (T reflex/Mmax) compared with surface controls. The H reflex recruitment ratio (Hmax/Mmax) did not change significantly. It is concluded that hyperbaric hyperreflexia is mainly due to increased muscle spindle sensitivity, presumably arising as a central effect on gamma-motoneuron activity. However, a purely peripheral effect of pressure on the spindle end-organ itself is not ruled out. Increases of 100-200% in muscle twitch peak force are reported and provide evidence that pressure can act directly on peripheral physiology. Postreflex clonic potentials (rebounds) during voluntary plantar flexion were significantly increased both in amplitude and number, leading to sustained clonus in one subject. In this respect, 5% N2 was less effective than 10% N2 of Atlantis III in controlling underdamping of the reflex loop. Conversely, the twitch contraction rate and clonic frequency in this study were only half as slowed compared with results from the earlier dive.

Central Nervous System↗
PubMed1987

Inhibition of skeletal muscle activity by lung expansion in the dog.

The ability of lung expansion to reflexly decrease skeletal muscle activity was tested in anesthetized dogs. In animals whose left lung was vascularly isolated but neurally intact, the left lung was inflated statically to 40 cmH2O pressure or cyclically with tidal volumes of 10, 20, or 30 ml/kg. Responses to these stimuli were compared with those of injecting 120 or 240 micrograms capsaicin into the left pulmonary artery. Skeletal muscle activity was assessed from the electromyogram (EMG) response of the left hindlimb muscles and from the monosynaptic reflex response to a periodic patellar tendon tap of the right leg (knee jerk). Static inflation and cyclic inflations above 10 ml/kg resulted in significant decreases in both EMG and knee jerk responses. The results indicate that lung expansion is capable of initiating a reflex decrease in skeletal muscle activity. Capsaicin injections caused responses that were similar to those caused by lung inflation, suggesting that at least part of this skeletal muscle reflex response to lung inflation can be attributed to the stimulation of pulmonary C-fibers that could be caused by stretch of the lung.

Animals↗
PubMed1984

Synaptic transmission from muscle afferents during fictive locomotion in the mesencephalic cat.

Modulation of synaptic potentials produced by electrical stimulation of low-threshold muscle afferents in lumbar alpha-motoneurons innervating knee and ankle muscles was studied by intracellular recording during "fictive locomotion" induced by stimulating the mesencephalic locomotor region (MLR) in paralyzed, mesencephalic cats. Averaging postsynaptic potentials in different phases of the fictive step cycle indicated that relatively little amplitude modulation occurred. In nearly half of the 38 motoneurons analyzed, there was a statistically significant tendency for excitatory postsynaptic potentials (EPSPs) to increase in amplitude during the depolarized phase of the oscillation in the membrane potential produced during fictive locomotion (locomotor-drive potential). In 8% the EPSPs decreased under the same conditions, while the rest displayed a constant amplitude during all phases of the fictive step cycle. Only three cells showed a distinct second peak in the EPSP at a latency consistent with transmission in a di- or trisynaptic pathway. Late inhibitory postsynaptic potentials (IPSPs) were also rarely observed. Thus oligosynaptic pathways from muscle afferents to the motoneuron groups studied are not prominent during the locomotor cycle in this preparation. We suggest that the marked modulation of monosynaptic reflex amplitude observed in mesencephalic cats (1) arises mainly from the effects of the locomotor-drive potential in bringing the cells closer to threshold during some phases of locomotion. Specific modulation during fictive locomotion of transmission in pathways from muscle afferents, which has been demonstrated for cutaneous pathways (28), was not observed. The implications of these results for the control of locomotion are discussed briefly.

Animals↗
PubMed1986

Differential effects of low-frequency depression, vibration-induced inhibition, and posttetanic potentiation on H-reflexes and tendon jerks in the human soleus muscle.

A comparison was made between the effects of repetition rate, muscle vibration, and tetanic stimulation of the tibial nerve on H-reflexes and tendon (T) jerks elicited in the relaxed soleus muscle of normal human. H- and T-reflexes with electromyographic (EMG) potentials of equivalent amplitude were elicited alternately in the same leg to ensure identical experimental conditions. H- and T-reflexes of identical EMG amplitude showed isometric twitch tensions of identical amplitude and time course. H- and T-reflexes were elicited at different repetition rates ranging from once every 6 s to 2/s. H-reflexes showed a significantly stronger low-frequency depression than T-reflexes. Inhibition of H- and T-reflexes was induced by 2-min vibration at 100 Hz of ankle extensors, ankle flexors, or knee flexors. Vibration of ankle extensors and flexors induced a stronger inhibition than vibration of knee flexors. In all three conditions, inhibition of H-reflexes was stronger than inhibition of T-reflexes. The difference was relatively greater during vibration of ankle extensors and flexors than during vibration of knee flexors. When tested together, the effects of low-frequency depression and vibration-induced inhibition of H- and T-reflexes were found to be independent if reflex amplitudes were expressed as a percentage of the control reflex amplitude. The cessation of vibration of ankle extensors was followed by a gradual recovery of H-reflexes from inhibition. On the contrary, T-reflexes showed a marked potentiation. Such postvibratory effects were generally not observed following vibration of ankle or knee flexors. When postvibratory effects were tested during low-frequency depression, percent postvibratory depression of H-reflexes and percent postvibratory potentiation of T-reflexes were found to be independent of the degree of low-frequency depression. Tetanic stimulation of the tibial nerve for 20 s at 200 Hz resulted in posttetanic potentiation (PTP) of H- and T-reflexes, the former being stronger than the latter. The extent of the changes in H- and T-reflex EMG amplitudes, due to changes in repetition rate, vibration, or tetanic stimulation, was generally inversely related to the intensity of the electrical or mechanical reflex stimuli. The observed discrepancies between the induced changes in H- and T-reflex amplitudes are interpreted in terms of the differences in afferent inputs between the two reflexes that were suggested by Burke and his colleagues (9-11).(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1994

Mechanical actions of heterogenic reflexes linking long toe flexors with ankle and knee extensors of the cat hindlimb.

1. To study the means whereby ankle biomechanics are represented in the interneuronal circuitry of the spinal cord we examined stretch-evoked reflex interactions between the physiological extensors flexor hallucis longus (FHL) and flexor digitorum longus (FDL) as well as their interactions with gastrocnemius (G), soleus (S), and the quadriceps group (Q) in 34 unanesthetized decerebrate cats. To evoke stretch, DC motors provided ramp-hold-release length changes to tendons detached from their bony insertions. Semiconductor myographs measured resultant muscle force response. Reflexes were examined under both quiescent (no active force generation) and activated conditions; muscle activation was achieved through either crossed-extension or flexion reflexes. 2. FHL and FDL share mutual excitatory stretch-evoked interactions under most conditions examined. These interactions depended on muscle length, were asymmetric (with FHL contributing a larger magnitude of reflex excitation onto FDL), and occurred at a latency of 16 ms. Mutual Ia synergism previously described for these two muscles provides a basis for all of the above findings. Our data demonstrate that for this muscle pair, reflex connectivities revealed at the intracellular level can be extrapolated to cover the entire motoneuron pool; further, our data directly demonstrate the net mechanical result of ensemble synaptic events. 3. FHL was found to share strong, mutually inhibitory stretch-evoked interactions with G, S, and Q. Stepwise regression statistical analyses determined that these interactions depended on recipient muscle force and donor muscle force. These reflex interactions all occurred at a latency of 28 +/- 4 (SE) ms. Further, the heterogenic inhibition between FHL/G and FHL/S was attenuated by strychnine infusion (intravenous) but unaffected by either mecamylamine, picrotoxin, or baclofen infusion (intravenous, intrathecal). Disynaptic Ib inhibition previously described among hindlimb extensors provides a basis for the above findings; our data demonstrate that under certain conditions the ensemble activity of this system can cause a dramatic decline in whole muscle force output. 4. By contrast, FDL was found to share mutually inhibitory, stretch-evoked reflex interactions with G, S, and Q that were much weaker than those observed between FHL and these same muscles. The small magnitude of inhibition observed in these interactions made it difficult to assess reflex latency or to determine the factor(s) that best predicted the heterogenic inhibition. 5. This study provides further evidence of intrinsic differences in interneuronal organization between muscles whose activity occurs in a periodic manner during locomotion ("stereotypical") and a muscle whose locomotor activity is characterized by both periodic and nonperiodic components ("facultative").(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1996

Maturation in properties of motoneurons and their segmental input in the neonatal rat.

1. The isolated neonatal rat spinal chord preparation was used to investigate the development of segmental afferent input to lumbar motoneourons during the first nine postnatal days. Motoneurons, identified with the use of antidromic stimulation of the ventral roots, were characterized electrophysiologically, and their synaptic input in response to stimulation of the homologous dorsal root was studied. 2. Motoneurons in postnatal day (P) 1-3 preparations exhibited lower rheobase and lower input conductance than those impaled in spinal cords taken from animals at P7-9. This finding is consistent with the increase in motoneuron size known to occur during this time. 3. Monosynaptic excitatory postsynaptic potentials (EPSPs) evoked at low-frequency (0.1-Hz) stimulation in high-Ca2+ saline exhibited no change in mean amplitude between P1-3 and P7-9 despite an increase in input conductance of the motoneurons, suggesting that some aspect of these synapses underwent a compensatory change. Polysynaptic EPSPs were smaller in the older animals. 4. When bursts of stimuli were delivered at higher frequencies ranging from 10 to 167 Hz, the EPSPs exhibited substantial depression. The depression of monosynaptic EPSPs was significantly less at P7-9 than at P1-3. Changing the bathing solution from a high-Ca2+ saline to a low-Ca2+/high-Mg2+ saline reduced the amplitude of the monosynaptic EPSP and made it less susceptible to depression during high-frequency stimulation. Facilitation of the evoked response, which has been observed in the adult rat, was never seen under any of these conditions. 5. Although synapses on high-rheobase motoneurons exhibited less depression than those on low-rheobase motoneurons, as anticipated from previous results in adults, the EPSPs at synapses on high-rheobase motoneurons tended to be larger in amplitude, not smaller as expected. This suggests that the specialization among synapses on motoneurons that exists in adults has not yet developed by P7-9. Instead, EPSP amplitude may be greater in motoneurons that have been growing rapidly, such as the high-rheobase motoneurons found during these stages of development. 6. Evidence is presented that the growing diversity shown in modulation behavior at the Ia afferent motoneuron synapse during the first postnatal week is determined primarily by motoneuron characteristics. It is speculated that as motoneurons grow during the immediate postnatal period, the presynaptic terminal regions of axons terminating on them become specialized to render the synapse less susceptible to depression. This specialization may be myelination of the afferent terminals or may perhaps be related to the transmitter release process itself. The adult distribution of depression develops later, presumably as the components of the monosynaptic reflex mature.

Afferent Pathways↗
PubMed1997

Stretch of quadriceps inhibits the soleus H reflex during locomotion in decerebrate cats.

Previously, it has been demonstrated that afferent signals from the quadriceps muscles can suppress H reflexes in humans during passive movements of the leg. To establish whether afferent input from quadriceps contributes to the modulation of the soleus H reflex during locomotion, the soleus H reflex was conditioned with stretches of the quadriceps muscle during bouts of spontaneous treadmill locomotion in decerebrate cats. We hypothesized that 1) in the absence of locomotion such conditioning would lead to suppression of the soleus H reflex and 2) this would be retained during periods of locomotor activity. In the absence of locomotion, slow sinusoidal stretches (0.2 Hz, 8 mm) of quadriceps cyclically modulated the amplitude of the soleus H reflex. The H reflex amplitude was least during the lengthening of the quadriceps and greatest as quadriceps shortened. Further, low-amplitude vibrations (48-78 micron) applied to the patellar tendon suppressed the reflex, indicating that the muscle spindle primaries were the receptor eliciting the effect. During bouts of locomotion, ramp stretches of quadriceps were applied during the extensor phase of the locomotor rhythm. Soleus H reflexes sampled at two points during the stance phase were reduced compared with phase-matched controls. The background level of the soleus electromyographic activity was not influenced by the applied stretches to quadriceps, either during locomotion or in the absence of locomotion. This indicates that the excitability of the soleus motoneuron pool was not influenced by the stretching of quadriceps, and that the inhibition of the soleus H reflex is due to presynaptic inhibition. We conclude that group Ia afferent feedback from quadriceps contributes to the regulation of the soleus H reflex during the stance phase of locomotion in decerebrate cats. This afferent mediated source of regulation of the H reflex, or monosynaptic stretch reflex, would allow for rapid alterations in reflex gain according to the dynamic needs of the animal. During early stance, this source of regulation might suppress the soleus stretch reflex to allow adequate yielding at the ankle and facilitate the movement of the body over the foot.

Animals↗
PubMed2001

The motor inhibitory system operating during active sleep is tonically suppressed by GABAergic mechanisms during other states.

The present study was undertaken to explore the neuronal mechanisms responsible for muscle atonia that occurs after the microinjection of bicuculline into the nucleus pontis oralis (NPO). Specifically, we wished to test the hypothesis that motoneurons are postsynaptically inhibited after the microinjection of bicuculline into the NPO and determine whether the inhibitory mechanisms are the same as those that are utilized during naturally occurring active (rapid eye movement) sleep. Accordingly, intracellular records were obtained from lumbar motoneurons in cats anesthetized with alpha-chloralose before and during bicuculline-induced motor inhibition. The microinjection of bicuculline into the NPO resulted in a sustained reduction in the amplitude of the spinal cord Ia-monosynaptic reflex. In addition, lumbar motoneurons exhibited significant changes in their electrophysiological properties [i.e., a decrease in input resistance and membrane time constant, a reduction in the amplitude of the action potential's afterhyperpolarization (AHP) and an increase in rheobase]. Discrete, large-amplitude inhibitory postsynaptic potentials (IPSPs) were also observed in high-gain recordings from lumbar motoneurons. These potentials were comparable to those that are only present during the state of naturally occurring active sleep. Furthermore, stimulation of the medullary nucleus reticularis gigantocellularis evoked a large-amplitude IPSP in lumbar motoneurons after, but never prior to, the injection of bicuculline; this reflects the pattern of motor responses that occur in conjunction with the phenomenon of "reticular response-reversal." The preceding changes in the electrophysiological properties of motoneurons, as well as the development of active sleep-specific IPSPs, indicate that lumbar motoneurons are postsynaptically inhibited following the intrapontine administration of bicuculline in a manner that is comparable to that which occurs spontaneously during the atonia of active sleep. The present results support the conclusion that the brain stem-spinal cord inhibitory system, which is responsible for motor inhibition during active sleep, can be activated by the injection of bicuculline into the NPO. These data suggest that the active sleep-dependent motor inhibitory system is under constant GABAergic inhibitory control, which is centered in the NPO. Thus during wakefulness and quiet sleep, the glycinergically mediated postsynaptic inhibition of motoneurons is prevented from occurring due to GABAergic mechanisms.

Animals↗
PubMed1974

The effects of electrical stimulation of VL and sub-VL on muscle tonus.

VL and sub-VL were electrically stimulated at 1-mm intervals and the influence on three muscles (anterior tibial muscle, gastrocnemius muscle and soleus muscle) of the contralateral limb was studied by the method of RE-EMG. The effect of VL and sub-VL stimulation was examined on ether clonus as an indicator of hyperactive muscle, especially for spasticity. The results are summarized as follows: 1. Clonus was apparently suppressed by electrical stimulation in an area (F, 10.0 mm; L, 4.0 mm; D, from +2 to -2; there was especially marked suppression of clonus by stimulation in sub-VL. 2. On electrical stimulation of the lateral third of VL, hypertonicity of anterior tibial muscle (T), hypotonicity of gastrocnemius muscle (G), and also hypotonicity of soleus muscle (S), was observed on stimulation of the middle third, T, G, S, and of the medial third, no effect was observed. 3. Electrical stimulation of the anterior part of VL showed T, G, S, and electrical stimulation of the posterior part of VL showed T, G, S.

Animals↗
PubMed1991

Changes in alpha motoneuron excitability of the soleus muscle in relation to vestibular stimulation assessed by angular acceleration in man.

Variations in spinal motoneuron excitability, tested by the monosynaptic H reflex of the soleus muscle, were studied in man in relation to angular acceleration of the body in a damped rotating chair. Clockwise and anticlockwise rotation produced similar changes on the same spinal motoneurons, consisting of a first clear-cut facilitatory phase starting at 0.4 degrees of rotation (corresponding to 156 ms) with a peak between 10 and 30 degrees, followed by a second excitatory phase between 50 and 100 degrees; then, the amplitude of the H reflex progressively recovered to its control value. Both facilitatory phases showed a significant decrease by reducing the angular velocity and acceleration. Control experiments ruled out that both the startle reaction of the subject and variations in the somatosensory input during rotation could be responsible for generating the facilitatory effects on the H reflex. The mean value of the voluntary reaction to turning sensation was 1.1 degrees, corresponding to about 335 ms. It is concluded that the changes described in motoneuron excitability could represent a vestibulospinal reflex response originating from the horizontal semicircular canals.

Acceleration↗
PubMed1978

Brainstem acetylcholine sensitive neurons activated by cutaneous impulses in cats.

In order to determine the cholinoceptive mechanism associated with cutaneous inhibition of jaw-closing and lumbar motoneurons, the area related to the inhibition produced by stimulation of the superficial radial nerve was identified by a lesion within the pontomedullary reticular formation and effects of drugs upon neurons were studied within this area. The cutaneous inhibition, as tested by the inhibition of monosynaptic reflex activity of jaw-closing and that of hindlimb spinal motoneurons was completely abolished by lesion of the medial portion of the pontomedullary reticular formation, but was little affected by lesions of the lateral portion. Intravenously administered physostigmine (0.15--0.30 mg/kg) excited 11 of 21 neurons whereas electrophoretic ACh (90 nA) excited 26 and inhibited 4 of 96 brainstem neurons located in this area. Eight of 11 physostigmine, and 4 of 26 ACh excited neurons were reticulospinal neurons with axonal conduction velocities of 20--40 m/sec. From results presented here together with those reported previously, these physostigmine sensitive and ACh excited brainstem neurons, reticulospinal and non-reticulospinal neurons, could be cholinoceptive interneurons of the polysnaptic inhibitory pathway, from the superficial radial nerve to jaw-closing and hindlimb spinal motoneurons.

Acetylcholine↗
PubMed1989

Central effects of the neurotropic mycotoxin fumitremorgin A in the rabbit (I). Effects on the spinal cord.

Effects of a potent neurotropic mycotoxin, fumitremorgin A (FTA), on the spinal cord were studied, using rabbits lightly anesthetized with urethane and chloralose. Spontaneous discharges of L7 spinal ventral roots and common peroneal nerves were increased after intravenous injection of 100-200 micrograms/kg of FTA. Their abnormal discharge pattern represented the convulsive effect of FTA. Spinal monosynaptic reflexes became irregular in amplitude, with a slight predominance of smaller reflexes. Polysynaptic reflexes were inhibited in many cases. These FTA-induced changes in ventral root discharges and spinal reflexes were abolished by spinal transection at a segment of the upper level. These results suggest that FTA may have no direct facilitatory action on spinal motoneurons and that its remarkable motor effect has its origin in the supraspinal central nervous system.

Animals↗