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PubMed2001

Excitatory actions of experimental muscle pain on early and late components of human jaw stretch reflexes.

It has recently been shown that a slow stretch evokes a short-latency (probably monosynaptic) and a long-latency (polysynaptic) reflex response in human jaw-closing muscles. The effect of nociceptive muscle input on the fusimotor system has not been investigated in detail. In order to investigate the effect of sustained muscle pain on the jaw stretch reflex, two main experiments were performed. Stretch reflex responses were evoked in the masseter and temporalis muscles by slow stretches (1-mm displacement, 40-ms ramp time) before, during and 15 min after a period of experimentally induced muscle pain. In experiment I, a dose of 1.0 M hypertonic or 154 mM isotonic (control) saline was infused in random order into the left masseter for up to 15 min (n=12). The level of excitation of the left masseter at 15% maximal voluntary contraction was controlled by visual feedback of the surface EMG (sEMG). In experiment II, a dose of 1.0 M saline was infused into the left masseter but with feedback from the sEMG of the right masseter (n=12). In a control experiment, both sEMG and intramuscular EMG (imEMG) were recorded from the left and right masseters; the feedback was from imEMG of the left masseter (n=12). The early (onset: 9--10 ms) and late (duration from 25 to 40 ms) reflex components were recorded and analysed in all experiments. Infusion of 1.0 M saline caused moderate pain (mean score on a Visual Analogue Pain Scale: 4.9--5.0 cm). The peak-to-peak amplitude of the early reflex component in the painful masseter normalized to the pre-stimulus EMG activity was significantly higher during the pain than the pre- and post-infusion conditions in all experiments. The normalized area of the late reflex component in the painful masseter was significantly larger than in the pre-infusion condition in all experiments. Isotonic saline had no significant effect on the jaw stretch reflexes. These results indicate that experimental jaw-muscle pain in humans facilitates the early as well as the late component of the jaw stretch reflex response as revealed by both sEMG and imEMG. This effect appears to be independent of the level of excitation of the muscle and not related to volume effects of the injected saline. A change in the sensitivity of the fusimotor system during muscle pain is suggested as an explanation.

Adult↗
PubMed2001

Short latency heteronymous excitatory and inhibitory reflexes between antagonist and heteronymous muscles of the human shoulder and upper limb.

The aims were (i) to investigate heteronymous excitatory and inhibitory Group Ia reflexes linking agonist/antagonist muscle pairs acting at the shoulder and elbow; clavicular pectoralis major (Pmajor) and posterior deltoid (Pdeltoid); biceps brachii (Bi) and Tri brachii (Tri), and linking muscles acting at the elbow (Bi and Tri) with muscles acting at the shoulder (Pmajor and Pdeltoid). (ii) To test the hypothesis that the excitability of the reflexes would vary between different tasks in a functionally relevant manner. The study was performed on 45 adults. Reflexes were recorded in the surface EMG when the target muscle was contracting at 10% maximum voluntary contraction. Reflexes were recorded in Bi and Tri with the elbow joint in one of three positions: 105 degrees, 80 degrees, or 55 degrees from full extension. Group Ia reflexes were evoked using a small, brief tap to the tendon of the muscle being stimulated. Reflexes were recorded by cross-correlation of the surface EMG and pseudo-random series of taps. All subjects demonstrated short latency inhibition and excitation between agonist/antagonist muscle pairs; inhibition was significantly more frequent than excitation. Excitation and inhibition occurred with equal frequency between muscle pairs acting between elbow and shoulder. Minimum central delays for excitatory reflexes were 1 ms, consistent with monosynaptic projections and for inhibitory responses were 2 ms consistent with disynaptic linkage. Later excitatory and inhibitory reflexes with central delays of up to 15 ms also occurred. The probability of evoking excitation or inhibition in Tri or Bi changed with the different elbow positions.

Adult↗
PubMed1997

Impaired modulation of tonic muscle activities and H-reflexes in the soleus muscle during standing in patients with Parkinson's disease.

The presence of postural disturbance in patients with Parkinson's disease (PD) was assessed by the displacement of the centre of foot pressure (CFP) and by changes in the amplitude of the soleus H-reflex when patients maintained an upright standing posture, followed by a forward-leaning posture. Thirteen patients and 13 age-matched normal controls (N) were studied. PD patients showed the following differences when compared to normal subjects: (1) the range of displacement of the CFP associated with forward leaning was significantly smaller (P<0.01); (2) the ratio of the increase in the soleus EMG activity to the CFP displacement (deltaEMG/deltaCFP) was larger (P<0.01), and the value of the deltaEMG/deltaCFP increased significantly in relation to the scale of clinical severity (P<0.01); and (3) the ratio of the increase in the amplitude of the soleus H-reflex to the soleus muscle EMG activity (deltaH-reflex/deltaEMG) was significantly lower in PD patients (P<0.05). The value of the deltaH-reflex/deltaEMG decreased significantly with the scale of clinical severity among the patients (P<0.05). These results suggest that the modulation of both the tonic stretch reflex and the phasic stretch reflex in the soleus muscle during standing are impaired in PD patients, and these impairments may partly cause their disability in the maintenance of a standing posture. Abnormalities in Ib inhibition and presynaptic inhibition are considered to be possible mechanisms in the disturbed modulation of the tonic stretch reflex and the phasic stretch reflex in PD patients during standing.

Adult↗
PubMed1994

Use of sacral reflex latency measurements in the evaluation of neural function of spinal cord injury patients: a comparison of neuro-urophysiological testing and urodynamic investigations.

Complete suprasacral spinal cord injury is followed by great changes in the neural control and function of the lower urinary tract. In the literature there is some controversy about the relationship between detrusor function and results of neurophysiological tests of sacral root conduction after the spinal shock phase. Therefore, we studied this relationship in a group of 73 patients with clinical as well as neurophysiological documented complete suprasacral spinal cord injury, and compared sacral reflex latency measurements (bulbocavernosus and urethro-anal reflexes) with detrusor function, documented by urodynamic investigation. A high incidence of sacral reflex latency abnormalities was found. Comparison of sacral reflex latencies with detrusor reflex activity showed a statistical significant correlation. No such relationship could be found between urodynamic characteristics of the detrusor in patients with detrusor hyperreflexia and sacral reflex latency measurements. We conclude that sacral reflex latency measurements can give an indication about the existence of reflex detrusor activity. On the other hand, these neurophysiological measurements do not provide a reliable indication of the detrusor function after complete spinal cord injury.

Adolescent↗
PubMed1989

Bulbocavernosus reflex: its validity as a diagnostic test of neurogenic impotence.

Measurement of the bulbocavernosus reflex is used widely to diagnose underlying neurogenic disorders in erectile dysfunction. A prolonged bulbocavernosus reflex latency (that is more than 45 msec.) or the absence of a reflex response of the bulbocavernosus muscles during electrical stimulation of the glans penis is considered a sign of neurological disease. Since only a few experimental studies have been performed in man related to the neurophysiological mechanism of erection, and since the results of these studies were contradictory the diagnostic validity of bulbocavernosus reflex measurement was reassessed. We determine whether men with abnormal bulbocavernosus reflex latencies have concomitant organic erectile dysfunction as confirmed by nocturnal plethysmographic and rigidity recordings. The bulbocavernosus reflex was recorded in 90 subjects and 19 had abnormal bulbocavernosus reflex latencies. Of these 19 subjects 8 had normal nocturnal erections, thus, confirming a diagnosis of psychogenic impotence. These results cast some doubts on the validity of bulbocavernosus reflex measurement for the diagnosis of organic erectile dysfunction due to a neurological disease.

Adult↗
PubMed1998

Mounting and brief noncontact exposure of males to receptive females facilitate reflexive erection in rats, even after hypogastric nerve section.

In three experiments, reflexive erection in male rats was facilitated by housing the males for 2 min with inaccessible sexually receptive females. In Experiment 1, males were sexually naive or experienced and received two reflexive erection tests, 1 week apart, immediately after the males were exposed to receptive females, to unreceptive females, or to no females (n = 8 per group). In both tests, experienced males exposed to estrous females had the shortest reflexive erection latencies; in Test 1 the differences among groups were of borderline significance (p = 0.057), but in Test 2 the differences among groups were highly reliable (p<0.01). Further analysis indicated that only experienced males exposed to receptive females were significantly different from other groups. In Experiment 2, sexually experienced males (n = 11) received four reflexive erection tests: after being with no female, and 0, 5, or 10 min after exposure to estrous females. As the interval between exposure and test increased, the males had progressively shorter erection latencies (p<0.01) and more intense glans erections (p<0.03). Experiments 1 and 2 may be viewed as demonstrating the psychogenic facilitation of reflexive erections. In Experiment 3, males underwent sham surgery (sham, n = 10) or bilateral transection of the hypogastric nerves (HgNx, n = 10), which are conventionally viewed as mediating psychogenic erection. After males mounted a receptive female for 5 min without intromission or had 2 min of non-contact exposure to receptive females, the males had shorter erection latencies (p<0.001) and more erections (p<0.02). These facilitative effects of pretest stimulation were unaffected by HgN transection. During copulation tests, HgNx males had longer ejaculation latencies (p<0.05) and lower intromission ratios (p<0.05), possible signs of impaired erectile function. However, in Experiment 4, other males were tested twice for reflexive erection and copulation after sham (n = 8) or HgNx (n = 9) surgery, and there were no significant effects of surgery on reflexive erection or copulatory behavior. Collectively, these experiments indicate (a) that brief noncontact exposure of sexually experienced males to estrous females facilitates reflexive erection, (b) that this facilitation increases for at least 10 min after the females are removed, and (c) that the hypogastric nerves do not mediate these facilitative effects. The evidence for a role for the HgN in copulation was inconclusive.

Animals↗
PubMed2003

A method for quantifying reflex responses from intra-muscular and surface electromyogram.

Measuring human reflex responses from electromyogram (EMG) traces in an accurate, repeatable and reliable way with a high degree of specificity has traditionally been a difficult task. This paper describes a new method that can be used to quantify reflex responses from both surface and intra-muscular EMG. This technique extends the classical cumulative sum (CUSUM) calculations by defining precise points for the calculation of latencies, durations and strengths to facilitate automatic reflex detection and permit the strength of a reflex to be defined in absolute units. The effect of varying the pre-stimulus time, the number of trials averaged and the amount of filtering used on the identification and classification of reflex parameters are also investigated. Furthermore, the effect of noise on these values, and how to remove it, is discussed. The new method, which is an expansion of the CUSUM analysis, is compared and contrasted with the more common threshold-crossing method in two different muscles: masseter and first dorsal interosseous (FDI), in experiments utilizing both mechanical and electrical stimulation. There are a number of advantages to using the new method; not only does the modified CUSUM method detect reflexes earlier than threshold-crossing methods but also the strength and duration are less susceptible to averaging and filtering parameters while giving a better indication of the reflex size. The data suggests that a pre-stimulus analysis period of at least 100 ms be used to correctly identify the variability inherent in EMG traces. It is also concluded that for subtle reflexes, 50 stimuli should be the minimum number used when spike trigger averaging is employed as lower numbers are associated with much greater pre-stimulus variability. Zero-phase filtering the rectified averaged EMG traces is recommended as this makes it easier to identify significant changes in the electrical activity of the muscle in question. In addition, noise estimation and removal from averaged rectified EMG recordings yields results that are a more accurate representation of the synaptic activity of the motor units in question.

Action Potentials↗
PubMed2003

Effect of mental imagery of a motor task on the Hoffmann reflex.

Research has found that mental imagery of a motor task may influence the Hoffmann reflex (H-reflex). However, this work has not examined the potential influence of background EMG (BEMG) on the H-reflex. In this study 23 adult participants (M=23.3 years, S.D.=3.2) were instructed to mentally image plantar flexion of the right foot at four intensities: 40, 60, 80 and 100% of maximum voluntary contraction (MVC) after completing practice trials of actual contractions at these intensities. Dependent measures were the BEMG activity and the peak-to-peak amplitude of the H-reflex. On each trial the peak-to-peak amplitude of the soleus H-reflex was measured in the right leg and averaged, BEMG (40 ms bin) was measured in the soleus and tibialis anterior of both legs. Following trials of plantar flexion at the target intensities participants completed 5 imagery trials at each intensity and 15 trials while performing this motor task. Five resting control trials were administered prior to and following the completion of all test trials. Administration of test trials was randomized within conditions. A main effect (P<0.05) for trial blocks was observed for H-reflex amplitude but not BEMG. The H-reflex increased linearly throughout testing, suggesting that the H-reflex was modified by the practice of imagery rather than the intensity of the imagined task.

Adult↗
PubMed1998

Role of the flocculus of the cerebellum in motor learning of the vestibulo-ocular reflex.

Structure-function studies at the systems level are an effective method for understanding the relationship of the central nervous system to behavior. Motor learning or adaptation of the vestibulo-ocular reflex is a clear example wherein this approach has been productive. During a vestibulo-ocular reflex the brain converts a head velocity signal, transduced through the vestibular semicircular canals, into an eye movement command delivered to the extraocular muscles. If the viewed target remains on the fovea of the retina, the reflex is compensatory, and its gain, eye velocity/head velocity, is one. When the image of the viewed object slips across the retina, visual acuity decreases, and the gain of the reflex, which is no longer one, is plastically adapted or adjusted until retinal stability is restored. The anatomic substrate for this plasticity thus involves brain structures in which visual-vestibular interaction can potentially occur, as well as vestibular and visual sensory and oculomotor motor structures. Further, it has been known for many years that removal of the flocculus of the cerebellum permanently precludes further vestibulo-ocular reflex adaptation, demonstrating the involvement of the cerebellum in this behavior. Maekawa and Simpson (J Neurophysiol 1973;36: 649-66) discovered that one visual input to the flocculus involved the accessory optic system and the inferior olive. Ensuing work has demonstrated that the visual signals used to adapt the vestibulo-ocular reflex are transmitted by this accessory optic system to the flocculus and subsequently to brain stem structures involved in vestibulo-ocular reflex plasticity. Presently the inclusive list of anatomic sites involved in vestibulo-ocular reflex circuitry and its adaptive plasticity is small. Our laboratory continues to believe that this behavior should be caused by interactions within this small class of neurons. By studying each class of identified neuron and its interactions with others within the list, we hope to ultimately understand the mechanisms used by the brain in the expression of this behavior.

Adaptation, Physiological↗
PubMed1998

Noradrenergic influences on the cerebellar cortex: effects on vestibular reflexes under basic and adaptive conditions.

Experiments performed either in decerebrate cats or in intact rabbits have shown that functional inactivation of the cerebellar anterior vermis or the flocculus decreased the basic gain of the vestibulospinal or the vestibulo-ocular reflex, respectively. These findings were attributed to the fact that a proportion of the vermal or floccular Purkinje cells, which are inhibitory in function, discharge out of phase with respect to the vestibulospinal or the vestibulo-ocular neurons during sinusoidal animal rotation, thus exerting a facilitatory influence on the gain of the vestibular reflexes. Intravermal injection of a beta-noradrenergic agonist slightly increased the gain of the vestibulospinal reflex, whereas the opposite result was obtained after injection of beta-antagonists. Similarly, intrafloccular injection of a beta-noradrenergic agonist slightly facilitated the gain of the vestibulo-ocular reflex in darkness (but not in light), whereas a small decrease of the reflex occurred after injection of a beta-antagonist. It was postulated that the noradrenergic system acts on Purkinje cells by enhancing their amplitude of modulation to a given labyrinth signal, thus increasing the basic gain of the vestibular reflexes. The Purkinje cells of the cerebellar anterior vermis and the flocculus also exert a prominent role on the adaptation of vestibulospinal and vestibulo-ocular reflexes, respectively. In particular, intravermal or intrafloccular injection of beta-noradrenergic antagonists decreased or suppressed the adaptive capacity of the vestibulospinal and vestibulo-ocular reflexes that always occurred during sustained out-of-phase neck-vestibular or visual-vestibular stimulation, whereas the opposite result was obtained after local injection of a beta-noradrenergic agonist. The noradrenergic innervation of the cerebellar cortex originates from the locus coeruleus complex, whose neurons respond to vestibular, neck, and visual signals. It was postulated that this structure acts through beta-adrenoceptors to increase the expression of immediate-early genes, such as c-fos and Jun-B, in the Purkinje cells during vestibular adaptation. Induction of immediate-early genes could then represent a mechanism by which impulses elicited by sustained neck-vestibular or visuovestibular stimulation are transduced into long-term biochemical changes that are required for cerebellar long-term plasticity.

Adaptation, Physiological↗
PubMed2003

Reflexes in sympathetic vasoconstrictor neurones arising from urinary bladder afferents are not amplified early after inflammation in the anaesthetised cat.

Pathophysiological processes in the viscera can lead to pain and hyperalgesia and exaggerated motility-regulating reflexes. This may be due to sensitisation of visceral afferents (peripheral sensitisation), which has repeatedly been shown to occur as a consequence of e.g. inflammation, and/or to sensitisation of dorsal horn neurones (central sensitisation), which is less well documented in the visceral domain. As an indicator of peripheral sensitisation, we previously analysed the responses of sacral spinal afferents after inflammation of the urinary bladder. Here, we studied reflexes in sympathetic vasoconstrictor neurones supplying skeletal muscle and skin elicited by bladder distension stimuli (vesico-sympathetic reflexes) before and after induction of bladder inflammation. Our aim was to test whether these vesico-sympathetic reflexes are amplified after inflammation in a way that would support a major functional role for post-inflammatory central sensitisation processes. Bladder inflammation was induced in anaesthetised cats by instillation of turpentine or mustard oil and vesico-sympathetic reflexes were studied 1 and 2 h after induction of the inflammation. Inflammation enhanced on-going activity in vasoconstrictor neurones supplying skeletal muscle (after 1 h to 187.6+/-36.8%, mean+/-SEM, P<0.01, and after 2 h to 139.1+/-12.9%, P<0.05, of baseline activity) and decreased it in most sympathetic neurones supplying skin (to 91.7+/-12.5%, P>0.05, and to 71.6+/-11.3%, P<0.05, respectively, of baseline activity). Relative to the altered baseline activity vesico-sympathetic reflexes to graded distension of the inflamed bladder were quantitatively unchanged with a tendency to be diminished. Thus, the changes in on-going sympathetic vasoconstrictor activity and the distension-evoked reflexes directly mirrored the afferent input from the inflamed urinary bladder into the spinal cord, i.e. no increase of the gain of these reflexes was observed. These results suggest that in the first 2 h of inflammation, peripheral sensitisation processes play the main role for hyperalgesia and hyperreflexia of the urinary bladder. In contrast, central sensitisation appears to be of little importance during this time period.

Action Potentials↗
PubMed1997

Age-related muscle stiffness: predominance of non-reflex factors.

This study was aimed at assessing the contribution of reflex and non-reflex factors to the muscle tone of old female Wistar rats. The hind foot of a rat was flexed or extended at the ankle joint by 25 degrees over 250 ms. The resistance of the foot to passive movements (torque, mechanomyogram), as well as the reflex electromyographic activity in the gastrocnemius and tibialis anterior muscles, were recorded simultaneously. Moreover, the impact of the blockade of the reflex activity caused by the local anesthetic lignocaine (1-2 ml of a 2% solution, injected in the vicinity of the sciatic nerve) on the muscle tone was investigated. Additionally, old rats' hind leg muscle samples were analysed using fluorescent microscopy for the expression of fibronectin, which is an early marker of connective tissue formation. It has been shown that old rats are characterized by (i) a substantially increased resistance of flexor muscle stiffness (measured during extension) and unchanged resistance of extensors (measured during flexion), (ii) the loss of a major part of the reflex electromyographic activity and (iii) the increased content of fibronectin in muscles. Moreover, it has been shown that lignocaine, which completely blocked the electromyographic reflex activity in the gastrocnemius and tibialis anterior muscles in young animals, was unable to counteract the resistance of these muscles to passive movements in old rats. The present results suggest that the muscle stiffness seen in old rats is not due to a reflex response, but depends mainly on non-reflex factors--chiefly on a large overgrowth of non-elastic connective tissue replacing degenerated active muscle fibers.

Aging↗
PubMed1999

Paradoxical inhibition of nociceptive neurons in the dorsal horn of the rat spinal cord during a nociceptive hindlimb reflex.

Nociceptive-specific and multireceptive neurons in the lumbar dorsal horn are excited by noxious stimuli applied to the hindpaw and inhibited by noxious stimuli applied to distant body regions. Given that at least a subset of these neurons are part of the circuit for nociceptive reflexes, inhibition of nociceptive-specific and multireceptive neurons should inhibit nociceptive reflexes. Unfortunately, previous attempts to test this hypothesis have been inconclusive because of methodological differences between electrophysiological and behavioral experiments. The present study overcame this problem by recording neural and reflex activity simultaneously. Rats were anesthetized with halothane and surgically prepared for single-unit recording from the lumbar dorsal horn. Hindpaw heat caused a burst of activity that reliably preceded hindpaw withdrawal in 10 nociceptive-specific and 17 multireceptive neurons. A distant noxious stimulus (tail in 50 degrees C water or ear pinch) inhibited the evoked activity of both nociceptive-specific and multireceptive neurons and simultaneously changed the topography of the hindpaw reflex from flexion to extension without altering reflex latency. The present data are consistent with previous reports of inhibition of nociceptive-specific and multireceptive neurons during application of a distant noxious stimulus. However, inhibition of nociceptive-specific and multireceptive neurons concomitant with a shift in the hindlimb reflex from flexion to extension suggests that these neurons are part of the circuit for flexor reflexes specifically. Presumably, lateral inhibition from the flexor to extensor circuit allows for the release of hindlimb extension when neurons in the flexion circuit are inhibited by a distant noxious stimulus. Such a system reduces the chance of injury by allowing for withdrawal reflexes to a single noxious stimulus and escape reactions, such as running and jumping, to multiple noxious stimuli.

Action Potentials↗
PubMed1999

Tonic adrenergic and serotonergic inhibition of a withdrawal reflex in rabbits subjected to different levels of surgical preparation.

The excitability of the heel-gastrocnemius withdrawal reflex pathway has been monitored in rabbits undergoing surgical preparation for electrophysiological experimentation under Saffan anaesthesia. Reflexes were evoked by percutaneous electrodes inserted at the heel and recorded as electromyograph signals from the ipsilateral medial gastrocnemius muscle. Two levels of surgery were carried out. The "full surgical" preparation was performed under deep Saffan anaesthesia. The trachea, carotid artery, jugular vein and intrathecal space (via a small laminectomy at L1) were cannulated, the animals were decerebrated by suction, and the left hindlimb was immobilized by screw clamps applied to the tibia and the femur. The sciatic nerve and its branches were exposed by bisection of the posterior biceps muscle and the anaesthetic was withdrawn. In the "reduced surgery" preparation, procedures were carried out with a lighter level of Saffan anaesthesia and operated tissues were infiltrated with local anaesthetic. Only the cannulations were performed in these animals. The excitability of the heel-gastrocnemius reflex declined throughout the full surgical preparation, with the median threshold increasing from 0.8 to 4.2 mA (n=19) and responses to suprathreshold stimuli reducing in size. Most of this effect was reversed after surgery was complete and anaesthesia withdrawn subsequent to decerebration. There were no significant changes in reflex excitability during the reduced surgery preparation (n = 15). Animals prepared by each of these protocols were given increasing intrathecal doses of either the selective alpha2-adrenoceptor antagonist RX 821002 (0.3 to 300 microg) or the serotonin/5-hydroxytryptamine (5-HT)1A-receptor antagonist WAY-100635 (0.01 to 30 microg). Both drugs caused significant, dose-dependent increases in reflex responses, to four to six times pre-drug control in both groups of animals. There were no differences in the effects on reflexes of either drug between the preparations. Thus, surgical preparation of decerebrated rabbits for electrophysiological recording results in depression of hindlimb withdrawal reflexes, although much of this effect did not persist beyond the completion of surgery. Tonic monoaminergic inhibition of reflexes was present to the same extent in both preparations investigated and is not therefore an epiphenomenon of the way in which the animals were prepared.

Adrenergic alpha-Antagonists↗
PubMed2002

Stretch-reflex mechanical response to varying types of previous muscle activities.

This study was designed to examine the effects of varying types of background muscle activity on the stretch-reflex mechanical response. A rapid stretch was applied to the calf muscles after an isometric (pre-ISO), shortening (pre-SHO) and lengthening contraction (pre-LEN) with several pre-contraction levels, respectively. The stretch perturbation was applied with the tibio-tarsal joint angle at 90 degrees. The ankle joint torque elicited by the stretch showed a first peak (non-reflex torque: NRT), a transient drop and a second peak (reflex torque: RT). The muscle activities before the stretch clearly influenced the stretch-reflex mechanical response. The NRT reached the largest peak with the longest duration in pre-ISO. The peak NRT increased with the pre-contraction level in pre-ISO and pre-LEN, whereas it remained unchanged in pre-SHO. The RT responded to the stretch-reflex EMG response most quickly and reached the largest peak in pre-ISO. Pre-ISO generated the mechanical response most efficiently against the size of the stretch-reflex EMG response. Pre-SHO showed lower peak RT than pre-ISO in spite of the similar size of stretch-reflex EMG response. The peak RT was closely related to the peak NRT in all conditions. Consequently, the peak RT also increased with the pre-contraction level in pre-ISO and pre-LEN, whereas it remained unchanged in pre-SHO. In conclusion, a stretch after an isometric contraction evoked a larger stretch-reflex mechanical response more efficiently than that after phasic contractions when a given effort was being maintained.

Adult↗
PubMed2003

Age comparison of H-reflex modulation with the Jendrássik maneuver and postural complexity.

OBJECTIVE: The purpose of this study was to examine modulation of the soleus Hoffmann (H)-reflex in response to the Jendrássik maneuver (JM) in standing positions in young and elderly subjects. METHODS: Seventeen elderly (mean age=72.0 years) and 23 young (mean age=23.2 years) apparently healthy subjects were examined in two separate experiments. The first experiment was conducted to compare the prone and standing position. The second experiment was conducted in the standing position with isotonic glideboard back support. The isotonic glideboard back support was inclined 30 degrees. In the standing position with back support, the knee and ankle joints were set at 0 degrees of flexion. All subjects were tested with two foot-positions: (1) with no soleus contraction on the platform (simple task) and (2) with an active calf muscle group contraction (complex task). To compare the amplitude of the H-reflex in each experiment between the control trials (relaxed) and JM trials (squeezing tennis balls), the stimulus intensity of 1.1 x motor threshold of the M-response was used for each subject in all body positions. RESULTS: To ensure experimental control, subjects did not show a difference in the amplitude of the trial M-response between the control and JM trials on any of the body positions. Also, no difference was found in the mean amplitude of the M-response between two different positions in either of the two experiments. Trial M-responses were all between 13 and 17% of M-max in the quiet standing position for the young subjects, and 17 and 21% for the elderly subjects. Results demonstrated that the JM facilitated the H-reflex in both young and elderly subjects. However, differential ability to modulate motoneuron excitability evoked by H-reflex pathways was found between the two groups. Young subjects demonstrated a significant difference in the amplitude of the H-reflex between control and JM trials in each standing position (P<0.05). The elderly subjects, in contrast, demonstrated no significant difference in the amplitude of the H-reflex between control and JM trials during normal standing. When examining standing with back support, the young subjects demonstrated a significant difference in the amplitude of the H-reflex between control and JM trials during both the simple and complex tasks (P<0.05). The elderly subjects, in contrast, demonstrated a significant difference only in the simple postural task (P<0.05). CONCLUSIONS: These results provide evidence of differential human spinal reflex modulation between young and elderly subjects. Further, these results may point towards the role of presynaptic inhibition in mediating these differences, and may lead to a more complete understanding of the different postural control strategies between young and elderly subjects.

Adult↗
PubMed2003

Trigemino-cervical-spinal reflexes in humans.

INTRODUCTION: Electrical stimulation of the supraorbital nerve (SON) induces late reflex responses in the neck muscles; these responses are hypothesised to be polysynaptic reflexes participating in a defensive withdrawal retraction of the head from facial nociceptive stimuli. Such responses may extend to the proximal muscle of the arms. OBJECTIVE: (1) to investigate reflexes in the upper limb muscles (trigemino-spinal responses, TSR) and their relationship with trigemino-cervical responses (TCR); and (2) to identify the nociceptive component of such reflexes and their functional significance. METHODS: Reflex responses were registered from the semispinalis capitis and biceps brachii muscles after electrical stimulation of the SON in 12 healthy subjects. The sensory (ST), painful (PT) and reflex thresholds, the latency and area of the responses, the effect of heterotopic painful stimulation (HTP), the recovery cycle as well as the effect of the expected and unexpected stimuli were measured. RESULTS: Stable reproducible TCR and TSR responses were identified at 2.5+/-0.4 x ST, which corresponded exactly to the PT in all the subjects. The TCR and TSR areas were markedly reduced after HTP. The recovery cycle of the TSR area was faster than that of the TCR. Repeated rhythmic stimulation failed to induce progressive reflex suppression. CONCLUSIONS: These results confirm the nociceptive nature of the TCR and indicate that the biceps brachii response (TSR) has the same nocifensive significance as the posterior neck muscle responses. TCR and TSR are mediated different polysynaptic pathways The presence of trigemino-cervical-spinal responses in our study clearly indicates that there is a reflex interaction between nociceptive trigeminal afferents and both upper and lower cervical spinal cord motoneurons.

Adult↗
PubMedDate not supplied

Reduction of acoustic reflex threshold in neonates without auditory risk.

UNLABELLED: The auditory sensitization, a tool used in the investigation of acoustic reflex, allows the decrease of acoustic reflex thresholds from a facilitating stimulus. It may be presented before or simultaneously with the elicitor tone. The thresholds after and before the facilitating stimulus are compared and it is expected to see the decreased threshold. From the study of the acoustic reflex it is possible to obtain information about the auditory pathways, such as structures of the brainstem, since the acoustic reflex pathway is related to the auditory nuclei in this site. They are also involved in auditory processing. Thus, alterations of the acoustic reflex could be related to deficits in auditory processing skills. AIM: This study aims at investigating the acoustic reflex sensitization from a high-frequency facilitating tone (6 kHz) in newborns without risk factors to hearing impairment. RESULTS: The acoustic reflex threshold decreased in males and females for all studied frequencies. CONCLUSION: A high-frequency facilitating tone presented simultaneously produced a decrease of the acoustic reflex threshold in newborns without risk factors to hearing impairment.

Acoustic Impedance Tests↗