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Results for “Reflex, Monosynaptic”

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PubMed1994

[Extra-articular pathogenetic factors in arthritis and deformities in old age as exemplified by varus gonarthrosis].

Extraarticular, predominantly neuromuscular, factors are thought to contribute to the development of osteoarthritis. With increasing age, changed temporal dynamics of motor reflexes and reduced muscular force may affect the efficacy of neuromuscular protection of the knee joint. In three experimental studies conducted with osteoarthritis patients and healthy controls, no difference was found in monosynaptic reflex times and latencies of somatosensory evoked brain potentials. Muscular force was generally diminished in the patients, with the most prominent reduction during coxal abduction. Osteoarthritis patients had marked nociceptive hyposensitivity, but no difference was seen in fast conduction afferent systems. In an animal study with high locomotion load, interruption of articular afferent nerve fibers led to a precipitation of cartilage degeneration. It is concluded that minor extraarticular functional deficits acting over time, probably support and aggravate the development of osteoarthritic changes.

Aged↗

PubMed1981

A quantitative model of the Hoffmann reflex.

Electrical stimulation of the human posterior tibial nerve elicits two separate electromyographic responses. The shorter latency response results from electrical activation of motor axons and is termed the direct motor (M) response, while the longer latency response results from activation of stretch receptor afferents of the monosynaptic reflex arc and is termed the Hoffmann (H) reflex. At high stimulus intensities, the H reflex is either greatly reduced in size or completely extinguished, presumably by antidromic impulses elicited by stimulation of the motor nerve. In most subjects, a simple quantitative model appears to account for this extinction. In this model: (1) the M response is used to estimate the number of antidromic impulses; (2) the H reflex is used to estimate the number of orthodromic impulses which escape collision; (3) the maximum size of the M response is used to indicate the size of the motoneuron pool; and (4) it is assumed that antidromic impulses collide in a random fashion with orthodromic impulses in the motor nerve.

Electromyography↗

PubMed1985

[Excitability cycle of the soleus motor nucleus during synergistic conditioning in man].

Electrical stimulation of medial or lateral gastrocnemius nerve modulates the H reflex of the soleus muscle in a well defined sequence of inhibitory and facilitatory phases the amplitude of which depends on the strength of the conditioning stimulus. This method of investigation of the soleus monosynaptic reflex pathway avoids the disadvantages of homonymous conditioning. Discussion of our results points to the roles of Ib and Renshaw cells inhibitions in the early phases of the recovery cycle, and to the roles of reafferents, disinhibition of Renshaw cells, presynaptic inhibition and muscarinic discharge of Renshaw cells for the late phases.

Adult↗

PubMed1976

Long spinal and pyramidal actions on hindlimb motoneurons of the marsupial brush-tailed possum, Trichosurus vulpecula.

The existence of descending propriospinal reflex linkages between forelimbs and hindlimbs has been established in the brush-tailed possum (Trichosurus vulpecula). In animals under chloralose anesthesia and with intact brain stem, forelimb volleys evoked facilitation of flexor and extensor monosynaptic reflexes of both hindlimbs, more pronounced on the ipsilateral side. Powerful inhibition of briefer latency and restricted to ipsilateral flexor digitorum longus (FDL) motoneurons was also brought about by forelimb volleys; at latencies exceeding 20-30 ms, FDL inhibition was usually replaced by facilitation. Distinctness of the two long spinal actions was shown by differences in forelimb receptive fields and in threshold of the executant afferent fibers. The field for reflex inhibition was located distally in the forepaw region, that for facilitation being wider, including deep as well as superficial tissues. Threshold of afferent fibers evoking inhibition was lower than that for facilitation. The descending long spinal actions were compared with those set up by repetitive stimulation of the motor cortex contralateral to the test hindlimb reflexes. In agreement with previous work, strong facilitation of most flexor or extensor motoneurons was produced, including those of quadriceps and ankle flexors, as well as gastrocnemius and hamstring motor nuclei; inhibition consistently appeared only in the FDL motoneuron pool. Weak and inconstant inhibitory action was occasionally observed in other motor pools. Pyramidal tract section abolished the cortical inhibition of FDL, but had little effect on facilitation; both long spinal actions were unchanged. Pyramid-sparing brain stem section greatly reduced both cortical and long spinal facilitatory action, but had little or no effect on FDL inhibition from either source. Interaction experiments demonstrated facilitation of weak inhibitory actions on FDL motoneurons of forelimb and cortical stimulation when elicited together, suggesting a sharing by the two inputs of common interneuronal elements. The observation is consistent with the notion that the long propriospinal system responsible for FDL inhibition from the forepaw might provide the pathway for pyramidal inhibition of the same group of motoneurons.

Animals↗

PubMed1981

A simple in vivo method for evaluating drug action at central and peripheral synapses.

A simple in vivo method for studying spinal reflexes and neuromuscular transmission in anaesthetized mice is described. The technique utilizes electromyographic recording from muscles of both hind limbs following stimulation of the sciatic nerve in one limb. Drug effects on the neuromuscular junction, on monosynaptic reflex transmission and on crossed polysynaptic reflexes can be assessed. In addition a method for distinguishing between drugs which affect neuromuscular transmission and those which affect nerve conduction is described using their different effects on reexcitation of motoneurons. Details of data collection and analysis using a laboratory microcomputer are presented. The effects of a variety of representative compounds which have been shown to affect central and peripheral neurotransmission in other systems have been evaluated. The actions of these drugs in this system are compared with those obtained using spinal animals and more sophisticated recording techniques. The results compare favourably with those obtained using more complex methods and the technique offers a simple and inexpensive way of evaluating drug action at these synapses.

Action Potentials↗

PubMed1995

Pain effect on monosynaptic and polysynaptic reflex inhibition.

OBJECTIVE: Determine the electrophysiological effects of anterior knee pain using monosynaptic and polysynaptic reflexes. DESIGN: A pretest/posttest control group experimental design with repeated measures. SETTING: All tests were performed in a university laboratory. PARTICIPANTS: Six subjects suffering from patello-femoral dysfunction (PFD) composed the experimental group. These patients were diagnosed and referred by medical and chiropractic doctors. Six healthy subjects were recruited for the control group. INTERVENTION: Pain relief by cold application (10 minutes) on the knee. MAIN OUTCOME MEASURES: Monosynaptic reflex: H reflex of the superficial portions of the quadriceps femoris. Polysynaptic reflexes: nociceptive flexion response (NFR) of the long head of the biceps femoris. RESULTS: Cold application, producing significant pain relief (p < 0.05), did not change H-reflex amplitude (p > 0.05) for both groups and did not show modulation of the NFR. However, the PFD group showed significantly lower pain (p < 0.05) and NFR thresholds (p < 0.05) than the control group. Finally, nociceptive stimulation was applied at the sural nerve during an isometric extension of the knee (20% of maximum electromyographic contraction). After this stimulation, uni-articular extensors, especially the distal fibers of the vastus medialis, showed a longer and stronger inhibition than the bi-articular rectus femoris. CONCLUSIONS: Pain episodes do not appear to affect monosynaptic responses. NFR threshold differences found between PFD and control group could be explained by the increased excitability of the nervous system in subjects experimenting painful bouts. Functional implications of these findings are discussed.

Adult↗

PubMed1985

Relationship among recruitment order, axonal conduction velocity, and muscle-unit properties of type-identified motor units in cat plantaris muscle.

A strict interpretation of the size-principle hypothesis (37, 39-41) is that a muscle's motor units should be recruited in an ascending order according to both the size of their motoneurons and the size of their innervated muscle units (for reviews see Refs. 9, 39, 73). Studies of large mixed muscles in the cat hindlimb, however, have shown that motor axonal conduction velocity and tetanic tension, which are frequently considered indices of motoneuron and muscle-unit size, respectively, are uncorrelated in the fast-twitch (type F) motor-unit subpopulation (12, 13, 23, 24, 30, 32, 63, 71, 79). Attempting to focus on type F units, we compared the recruitment order of 42 pairs of cat plantaris (PL) motor units with both axonal conduction velocity and tetanic tension as well as with other muscle-unit properties. Single PL alpha-motor axons were functionally isolated in intact L7 ventral root filaments of decerebrate cats. Tension responses produced by stimulating each isolated motor axon were used to find the tetanic tension of the muscle unit and to classify the unit (12) as either type S (slow twitch, fatigue resistant), type FR (fast twitch, fatigue resistant), type FI (fast twitch, intermediate fatigability), or type FF (fast twitch, highly fatigable). Conduction velocity of each isolated axon was computed from measurements of axonal conduction time and length. The axon's reflex discharges were recorded from the proximal end of the cut filament and compared with the discharges of another PL axon residing in a different, previously cut filament of the same cat. The recruitment order of each motor-unit pair studied was found during reflexes elicited by homonymous muscle stretch, tendon taps, or single shocks at group I intensity to the PL nerve. If either axon of the pair failed to discharge, as often was the case with the high-threshold type F units, the monosynaptic reflex was facilitated by a 500-pps conditioning train applied proximal to a complete reversible cooling block of the PL nerve. In all 42 pairs studied, the weaker motor unit had the lower functional threshold for recruitment. Recruitment also invariably followed the order S greater than FR greater than FI greater than FF units. The motor unit of a pair with the higher resistance to fatigue thus always had the lower functional threshold. In 21 of the 22 pairs containing at least one type S motor unit, the unit with the slower-conducting motor axon had the lower functional threshold for recruitment.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2001

NMDA receptors in the spinal cord exert excitatory influences on spinal motor output in rats.

The role of NMDA receptors in the regulation of spinal motor output was studied in rats. Muscle tension of the hind limbs of decerebrate animals and spinal reflex potentials in anesthetized animals were recorded. Intrathecal injection as well as systemic or intra-4th ventricular injection of (+)-5-methyl-10-11-dihydro-5H-dibenzo[a,d]cyclohepta-5-10-imine maleate (MK-801) reduced muscle tension. Systemic MK-801 did not alter monosynaptic reflexes either in intact or spinal rats, but attenuated polysynaptic reflexes in spinal rats. Thus spinal NMDA receptors participate in spinal motor output in the presence of some specific factors such as descending facilitation and preceding segmental depolarization, which remove the Mg2+ blocking.

Animals↗

PubMed1991

Effects of tetanic stimulation on monosynaptic and dorsal root reflexes in kittens.

The effects of tetanic stimulation of peripheral afferents were examined on monosynaptic reflexes and dorsal root reflexes in kittens of various ages. Concomitantly recorded monosynaptic and dorsal root reflexes resulting from the stimulation of muscle nerves showed similar post-tetanic changes, namely, predominantly post-tetanic depression in neonates and post-tetanic potentiation in older kittens or adults. However, the changes in post-tetanic responses expressed as a percentage of control in dorsal root reflexes were much smaller than those in monosynaptic reflexes. When dorsal root reflexes originating from muscle and cutaneous afferents were compared, dorsal root reflexes from the latter behaved quite differently. For all ages, post-tetanic effects on dorsal root reflexes arising from cutaneous afferents were either insignificant or very small. The possible mechanisms underlying differences in post-tetanic effects from muscle and cutaneous afferents in adults and neonates are discussed.

Aging↗

PubMed1987

Sensitivity of spinal reflexes to TRH and 5-HT in 5,6-dihydroxytryptamine-treated rats.

Destruction of descending serotonergic nerve terminals containing thyrotropin-releasing hormone (TRH) was affected in rats by the intracisternal injection of 5,6-dihydroxytryptamine (5,6-DHT) two weeks before subsequent experiments. Although the level of TRH in the lumbar enlargement was significantly reduced in 5,6-DHT-treated rats, the effects of TRH on the monosynaptic reflex (MSR) and the polysynaptic reflex (PSR) in these rats were no different from those in control rats. MSR inhibition by 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) was attenuated by 5,6-DHT treatment although there was no obvious difference in the effects of 5-MeODMT on the PSR between 5,6-DHT-treated and control rats. In 5,6-DHT-treated rats, L-5-hydroxytryptophan (5-HTP) markedly decreased the MSR and increased the PSR although the same doses of 5-HTP did not produce any effects on either the MSR or the PSR in control rats. In control rats, after administration of imipramine or clorgyline, 5-HTP produced effects similar to those observed in 5,6-DHT-treated rats. These results suggest that the supersensitivity to 5-HTP in 5,6-DHT-treated rats is due to a lack of 5-hydroxytryptamine (5-HT) uptake into 5-HT-containing nerve terminals rather than to a change in 5-HT receptors.

5,6-Dihydroxytryptamine↗

PubMed1980

Neurophysiological effects of etomidate, a new short-acting hypnotic.

The neurophysiological effects of 0.3 mg/kg etomidate injected i.v. within 30 sec were investigated in 22 healthy volunteers, 7 of whom were premedicated with Thalamonal and fentanyl. About 30 sec after injection, a short period of delta activity (deep sleep) occurred in the EEG, successively normalizing within the next 6-8 min. EEG arousal reactions to various stimuli were blocked for several minutes. In the premedicated group neither motor hyperactivity nor monosynaptic reflex alterations were observed. In contrast, 9 out of 5 non-premedicated subjects exhibited various kinds of motor hyperactivity, consisting most often of asynchronous clonic bursts of activity in the EMG. Clonus was not related to EEG events, and could persist beyond behavioural and EEG recovery. In 12 subjects, the monosynaptic H reflex was enhanced up to 6 X of control. The plantar reflex was reinforced to a generalized withdrawal reaction, sometimes a positive Babinski sign was observed. It is assumed that clonus is generated in spinal circuits, whereas supraspinal structures may contribute to the more complex forms of motor hyperactivity.

Adult↗

PubMed1985

Electrophysiological investigation of IDPN neuropathy--initial studies.

beta,beta'-iminodipropionitrile (IDPN) causes giant axon swellings in proximal internodes of spinal motor axons and in stem processes of dorsal root ganglia neurons. The electrophysiological consequences of the swellings were investigated in cats given IDPN (50 mg/kg i.p.) weekly for 0 (control), 1 (7 days), 2 (14 days), or 5 (35 days) weeks; some additional animals were studied 15 (50 days) or 65 (100 days) days following the fifth injection. Extracellular recordings of the spinal monosynaptic reflex revealed amplitudes of efferent responses to be equally reduced at 35, 50 and 100 days. Single stimulation of dorsal roots, or soleus or medial gastrocnemius afferents often evoked doublet efferent responses which arose intraspinally. Similar repetitive responses were observed in dorsal root (afferent) input upon single stimulation of peripheral nerves. Latencies to monosynaptic responses became progressively prolonged over 100 days; spinal cord contribution to the increased latencies was maximal by 35 days. Conduction velocities in single soleus and medial gastrocnemius axons declined to 70 and 64% of normal by 50 days and to 56 and 50% of normal by 100 days respectively. Maximal recurrent inhibition was reduced 42-49% by 35 days and quantitatively similar at 50 and 100 days. Intracellular recordings from spinal motoneurons revealed that, at 35 days, action potentials could be elicited by orthodromic but not by antidromic stimulation in 14% of cells tested. This was taken as evidence of block of impulse conduction by the intervening axonal swelling upon antidromic stimulation. The possibility of abnormal electrical interactions between swollen and demyelinated intraparenchymal axons was tested by determining the number of ventral root fibers via which antidromic stimulation would elicit an action potential in the same motoneuron perikaryon. Electrical crosstalk, never seen in normal animals, varied in incidence during the evolution of the neuropathy (7-35 days), reaching a maximum of 30% at 14 days. Many motoneuron action potentials were remarkably similar to those observed in chromatolytic motoneurons, exhibiting, among other features, decreased SD thresholds and IS conduction times, reduced amplitudes and durations of afterhyperpolarization, delayed depolarizations and an enhanced propensity to fire repetitively upon single stimulation. There was no morphological evidence of chromatolysis in the motoneurons. The concept of "functional axotomy" is introduced to accommodate these findings and discussed in terms of altered dendritic excitability. Not all motoneuron types are equally compromised in the neuropathy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Amplitude modulation of the quadriceps H-reflex in the human during the early stance phase of gait.

Amplitude modulation of the quadriceps H reflex was investigated during the early part of the stance phase of gait in normal human subjects. Stability of the M wave was used to ensure constancy of the effective stimulus strength. In all subjects there was a progressive decrease in the reflex amplitude throughout the early knee flexion (yield of the knee), whereas the quadriceps EMG activity remained constant or even increased. At an equal stimulus strength and EMG level, the reflex was often larger at the onset of the stance phase of gait than during voluntary contraction, whereas it was always smaller during the knee extension following the yield of the knee. It is argued that changes in presynaptic inhibition of quadriceps Ia terminals could account for this amplitude modulation of the monosynaptic reflex during gait. The possible role of changes in the gain of the quadriceps stretch reflex during bipedal gait is discussed.

Gait↗

PubMed2005

Diurnal H-reflex variation in mice.

Mice exhibit diurnal variation in complex motor behaviors, but little is known about diurnal variation in simple spinally mediated functions. This study describes diurnal variation in the H-reflex (HR), a wholly spinal and largely monosynaptic reflex. Six mice were implanted with tibial nerve cuff electrodes and electrodes in the soleus and gastrocnemius muscles, for recording of ongoing and nerve-evoked electromyographic activity (EMG). Stimulation and recording were under computer control 24 h/day. During a 10-day recording period, HR amplitude varied throughout the day, usually being larger in the dark than in the light. This diurnal HR variation could not be attributed solely to differences in the net ongoing level of descending and segmental excitation to the spinal cord or stimulus intensity. HRs were larger in the dark than in the light even after restricting the evoked responses to subsets of trials having similar ongoing EMG and M-responses. The diurnal variation in the HR was out of phase with that reported previously for rats, but was in phase with that observed in monkeys. These data, supported by those in other species, suggest that the supraspinal control of the excitability of the HR pathway varies throughout the day in a species-specific pattern. This variation should be taken into account in experimental and clinical studies of spinal reflexes recorded at different times of day.

Animals↗

PubMed1989

Late flexion reflex in paraplegic patients. Evidence for a spinal stepping generator.

We demonstrated previously that electrical stimulation of the Flexor Reflex Afferents (FRA) induces a late flexion reflex with a central conduction time longer than 100 msec. Its latency is prolonged by increasing the intensity or the duration of the stimulation. This late reflex is therefore similar to the late flexion reflex observed in acute spinal cat with DOPA. Some findings suggest that in man the late flexion reflex could be inhibited at a premotoneuronal level by contralateral FRA stimulation. In relation to the late flexion reflex, a late contralateral facilitation of soleus monosynaptic reflex (MSR) was observed. Rhythmical activity was observed in only one patient who had an exceptional form of spinal myoclonus. This myoclonus could be modulated by FRA stimulation. These facts show that the reflex organization in paraplegic patients is similar to the one described in acute spinal cat with DOPA and therefore suggest that a spinal stepping generator could exist in humans.

Electric Stimulation↗

PubMed1998

Phasic and tonic reflexes evoked in human antagonistic wrist muscles by tendon vibration.

The electromyographic reflex responses of the voluntarily contracting wrist flexor and extensor muscles to periods of vibration-evoked enhanced, Ia-dominated afferent discharge from flexor carpi radialis (FCR) were studied in normal human subjects. Three main response phases were characterised, namely, (i) phasic 'on' responses elicited at the commencement of stimulation, (ii) tonic response levels occurring during prolonged stimulation and (iii) phasic 'off' responses elicited at the termination of stimulation. The phasic 'on' reflex responses of FCR and extensor carpi radialis (ECR) comprised, respectively, a peak of autogenetic excitation of group mean latency 18.8 ms and a trough of reciprocal inhibition of group mean latency 38.0 ms. Prolonged (2 s) trains of FCR (agonist) vibration evoked a phase of tonic reflex excitation in FCR whose mean level was significantly increased, by 20%, above pre-stimulus activity and which did not change over the 0.5-2.0 s vibration period. Progressive reduction of the duration (from 2000 ms to 100 ms) of vibration trains demonstrated that phasic disfacilitatory 'off' troughs regularly occurred, with a consistent latency (mean 24.2 ms), on withdrawal of each period of enhanced Ia-input. This indicates that the responsible excitatory reflex mechanism was operational for the entire duration of each of the vibration periods tested. The extra latency (on average 5.4 ms) of phasic 'off' relative to 'on' responses may be attributed to factors (e.g. 5-10 ms duration of unitary muscle action potentials and afterdischarge in reflex pathways) which inevitably delay the appearance of overt disfacilitatory reductions in EMG rather than the involvement of different reflex pathways. Thus, short-latency, possibly monosynaptic, reflex excitation contributed throughout the entire tonic excitatory response. Sustained FCR (antagonist) vibration produced a significant tonic reciprocal inhibitory reflex depression, by 7% pre-stimulus EMG, of ECR activity which remained steady during the 0.5-2.0 s vibration period. The absence of well-defined phasic disinhibitory 'off' responses in ECR suggests that the contribution of oligosynaptic reflex inhibitory mechanisms to the tonic suppression of activity occurring during continuing vibration is relatively small.

Adult↗

PubMed1990

Effects of the new centrally acting muscle relaxant 7-chloro-N,N,3-trimethylbenzo[b]furan-2-carboxamide on motor and central nervous systems in rats.

Effects of KW-6629 (7-chloro-N,N,3-trimethylbenzo[b]furan-2-carboxamide) were studied with special reference to the effect on motor and central nervous systems using rats. The drug effectively reduced the motor coordination (rotarod), the anemic decerebrate rigidity, the crossed extensor reflex, and the gamma-activity indirectly recorded from muscle afferent discharges without showing the direct inhibitory effect on muscle spindles. KW-6629 depressed the polysynaptic and dorsal root reflexes without showing marked effect on the monosynaptic reflex in intact spinal cord rats. KW-6629 produced high-amplitude slow wave in the cerebral cortex in electroencephalogram (EEG). KW-6629 did not reduce the EEG after-discharges and behavioral convulsion (amygdaloid kindling). KW-6629 had no effect on the neuromuscular junction. These results suggest that KW-6629 is a centrally acting muscle relaxant which has a site of action in supraspinal structures.

Animals↗

PubMed1973

Patterns of reflex excitability change after widespread cutaneous stimulation in man.

A single-shock stimulus to the skin of widespread and distant parts of the body such as the face, sites in the upper limb, trunk, buttock, and feet produced changes in amplitude of the ankle jerk. A regulated and stabilized system was used for eliciting the ankle jerk and for delivering an unvarying single-shock conditioning stimulus; 35 normal subjects were studied. The characteristics of the recovery curve of the monosynaptic reflex after stimulation at these cutaneous sites are described.

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