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PubMed1985

Reflex control of dynamic muscle stiffness in a slow crustacean muscle.

The properties of a stretch reflex in the ventral superficial muscle of the hermit crab abdomen were studied in an isolated abdominal preparation to determine how the reflex affects the mechanical properties of the muscle and whether the reflex is controlling length, force, or stiffness. The reflex was elicited by stretch of hypodermal mechanoreceptors in the cuticle and resulted in the activation of excitor motoneurons to both circular and longitudinal layers of the muscle, thus stiffening the abdomen. The medial motoneuron of the longitudinal layer of the right fourth segment was selected for detailed analysis. It was tonically active and responded to stretch with a phasic burst having a latency of 100 ms. Reflex muscle tension began to increase at 130 ms and reached a peak at 300 ms. Reflex-burst frequency increased slightly with stretch amplitude. Peak force was an approximately linear function of stretch amplitude. No tonic component to the reflex was found in the medial motoneuron, in the central motoneuron (the smallest excitor to the muscle), or in the medial motoneuron studied in intact animals. The reflex-burst frequency was a function of stretch velocity, increasing between two and one-half to four times for a 10-fold increase in stretch velocity. Peak force was essentially independent of stretch velocity over this range. The reflex-burst frequency was not a function of the initial length of the muscle on the ascending limb of the length-tension relation. Active peak force (between two and three times passive peak force) was relatively constant over this range. The dynamic active stiffness (the resistance to stretch of the muscle when the nervous system was intact) was separated into two components. One component is that due to the tonic frequency of the motoneurons, the other to the reflex burst. The reflex component makes up a substantial part of the total active stiffness. Dynamic active stiffness is relatively constant under the conditions of these experiments and, when normalized, is similar to that observed in mammalian myotatic reflexes. This constancy, however, cannot be due to negative feedback control of stiffness, as in mammals. It is suggested that constant reflex stiffness arises from the combination of the low-pass filter characteristics of the muscle and the high-pass filter characteristics of the reflex over a restricted range of velocities.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
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↗
PubMed2005

The interaction of a new motor skill and an old one: H-reflex conditioning and locomotion in rats.

New and old motor skills can interfere with each other or interact in other ways. Because each skill entails a distributed pattern of activity-dependent plasticity, investigation of their interactions is facilitated by simple models. In a well characterized model of simple learning, rats and monkeys gradually change the size of the H-reflex, the electrical analog of the spinal stretch reflex. This study evaluates in normal rats the interactions of this new skill of H-reflex conditioning with the old well established skill of overground locomotion. In rats in which the soleus H-reflex elicited in the conditioning protocol (i.e., the conditioning H-reflex) had been decreased by down-conditioning, the H-reflexes elicited during the stance and swing phases of locomotion (i.e., the locomotor H-reflexes) were also smaller. Similarly, in rats in which the conditioning H-reflex had been increased by up-conditioning, the locomotor H-reflexes were also larger. Soleus H-reflex conditioning did not affect the duration, length, or right/left symmetry of the step cycle. However, the conditioned change in the stance H-reflex was positively correlated with change in the amplitude of the soleus locomotor burst, and the correlation was consistent with current estimates of the contribution of primary afferent input to the burst. Although H-reflex conditioning and locomotion did not interfere with each other, H-reflex conditioning did affect how locomotion was produced: it changed soleus burst amplitude and may have induced compensatory changes in the activity of other muscles. These results illustrate and clarify the subtlety and complexity of skill interactions. They also suggest that H-reflex conditioning might be used to improve the abnormal locomotion produced by spinal cord injury or other disorders of supraspinal control.

Animals↗
PubMed2000

Physiological and pathophysiological implications of upper airway reflexes in humans.

The upper airway is a vital part of the respiratory tract. Although the upper airway serves several functions, protection of the airway and preservation of airway patency are the most essential functions subserved by upper airway reflexes. Various types of nerve endings have been identified in and under the epithelium of the upper airway, and afferent nerve endings are the natural starting of all reflex activity. The upper airway reflexes consist of many different types of reflex responses such as sneezing, apnea, swallowing, laryngeal closure, coughing, expiration reflex, and negative pressure reflex. Although the activation of upper airway reflexes does not necessarily occur at one particular site of the respiratory tract, individual reflex response is usually considered to be highly specific for the particular respiratory site which has been affected. The upper airway reflexes are modified by many factors such as sleep, anesthesia, and background chemical ventilatory drive. Both depression and exaggeration of upper airway reflexes cause clinical problems. Depression of upper airway reflexes enhances the chance of pulmonary aspiration and compromises the maintenance of the airway, whereas exaggeration of airway reflexes such as laryngospasm and prolonged paroxysm of cough can be harmful and dangerous. In this review, various aspects of upper airway reflexes are discussed focusing on the functions of upper airway reflexes in humans and some pathophysiological problems related to clinical medicine.

Humans↗
PubMed1981

[Measurements of the acoustic reflex at variable static pressures (author's transl)].

Acoustic reflex measurements are made on thirty normal and three early stage otosclerotic ears at different static pressures in the ear canal and recorded as reflex-tympanogram at 200 Hz and 660 Hz probe-tone frequency. Acoustic reflexes were elicited contralaterally with a pure-tone stimulus at 2,000 Hz. This stimulus was chosen to avoid technical artifacts. An example of a normal acoustic reflex pattern as a function of variable static pressure is presented (Fig. 1). This record was made at 20 dB above the subjects reflex threshold, using 660 Hz probe-tone frequency. The reflex deflection of susceptance is positive up to pressures of plus or minus 50 mm H2O and then becomes negative. The reflex deflection of conductance is negative in the total range. A stiffened middle-ear system shows negative reflex deflection of both admittance components. The reflex-tympanograms (Fig. 2) show the admittance component curves as a function of variable static pressure with and without eliciting the acoustic reflex in case of a normal ear, using probe-tone frequencies of 220 Hz and 660 Hz at 10 dB and at 20 dB above the subjects reflex threshold. The reflex-tympanogram in case of an early stage otosclerotic ear shows negative reflex deflection of susceptance within the total pressure range indicating pathological stiffness (Fig. 3). The reflex related change of the dynamic properties was stimulated in a mathematical model of the middle-ear (Fig. 4). The measurements could be explained in a mathematical approach.

Audiometry↗
PubMed1993

Are H and stretch reflexes in hemiparesis reproducible and correlated with spasticity?

The measurement of spasticity has always presented a problem to clinicians and researchers alike. As yet, there is no literature addressing the reproducibility of the existing barrage of clinical evaluations of spasticity and reflex measurement. Also not clear is whether or not a systematic relationship might exist between these multiple indices of spasticity. After delineating the differences in spasticity scores and reflex functions between spastic and normal states, the aims of this study were to examine the reliability of these measurements in hemiparetic subjects, and the correlation between altered reflex functions and clinically measured spasticity. An aggregate of lower limb reflexes was compared between ten spastic hemiparetic and seven age-matched normal subjects. Lower limb reflexes examined were: (1) the ratio of maximal H reflex to M response (H/M ratio), (2) the inhibition of the H reflex during vibration (Hvib/Hctl ratio), and (3) soleus stretch reflexes (SR/M ratio). H and stretch reflex latencies were shorter (P < 0.05), and reflex amplitudes were significantly greater (H/M ratios, P < 0.05; SR/M areas, P < 0.005) in spastic subjects. While H/M ratios, Hvib/Hctl ratios, SR/M areas and SR onset angles were highly reproducible, only some physiological measurements showed consistent but non-significant relationships with clinical spasticity. The decreased reflex latencies and increased reflex responses in the hemiparetic subjects suggested that spasticity may be related to reduced reflex thresholds. The physiological measurements and clinically assessed tone were both valid and reproducible, indicating that they can be used to evaluate the long-term effects of therapeutic intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Changes in the excitability of soleus muscle short latency stretch reflexes during human hopping after 4 weeks of hopping training.

Changes in the excitability of the human triceps surae muscle short latency stretch reflexes were investigated in six male subjects before and after 4 weeks of progressive two-legged hopping training. During the measurements the subjects performed 2-Hz hopping with: preferred contact time (PCT) and short contact time. The following reflex parameters were examined before and after the training period: the soleus muscle (SOL) Hoffmann-reflex (H-reflex) at rest and during hopping, the short latency electromyogram (EMG) components of the movement induced stretch reflex (MSR) in SOL and medial gastrocnemius muscle (MG), and the EMG amplitude of the SOL and MG tendon reflexes (T-reflexes) elicited at rest. The main results can be summarized as follows: the SOL T-reflex had increased by about 28% (P < 0.05) after training while the MG T-reflex was unchanged; the SOL MSR (always evident) and the MG MSR (when observable) did not change in amplitude with training, and before training the SOL H-reflex in both hopping situations was significantly depressed to about 40% of the reference value at standing rest (P < 0.05). After training the H-reflex during PCT hopping was no longer depressed. As the value of the measured mechanical parameters (the total work rate, joint angular velocity and the ankle joint work rate) was unchanged after training in both hopping situations, the reflex changes observed could not be ascribed to changes in the movement pattern. To explain the observed changes, hypotheses of changes in the excitability of the stretch reflex caused by the training were taken into consideration and discussed.

Adult↗
PubMed2004

Paradoxical modulation of tendon tap reflex during voluntary contraction in Parkinson's disease.

OBJECTIVE: Inadequate supraspinal modulation of spinal motor control mechanisms such as alpha-gamma coactivation is supposed to cause difficulty in maintaining proper voluntary contraction in Parkinson's disease (PD). METHODS: Subjects were 42 patients with PD and 20 normal volunteers. Soleus H-reflex and tendon tap reflex (T-reflex) were recorded. The maximal reflexes (H(max) and T(max)) at rest were recorded first. Next, the stimulus intensities were fixed to obtain a reflex size of around 25% of M(max) at rest for both H- and T-reflexes, and the reflexes were recorded at rest, during tonic plantarflexion (TPF), and at the onset of plantarflexion. RESULTS: H(max) at rest was 55% and T(max) 30% in normal subjects, while they were 36 and 31%, respectively, in PD. The size ratio of T(max) and H(max) at rest in PD was larger than normal. In PD, the size of H-reflex increased with TPF as in normal subjects, but T-reflex decreased. These changes in T-reflex were correlated with the grade of rigidity, bradykinesia, and time for 10 m gait. H-reflex had no such correlations. CONCLUSIONS: T-reflex was abnormally modulated in PD especially during tonic contraction. SIGNIFICANCE: Inappropriate supraspinal modulation of the spinal reflex pathways disturbs motor performance in PD.

Aged↗
PubMed1998

Modulation of short latency stretch reflexes during human hopping.

To gain insight into central and peripheral reflex control mechanisms in moving humans we have investigated short latency stretch reflex activity in m. triceps surae during two legged hopping. The objectives were: (1) to compare movement induced short latency stretch reflexes in soleus and medial gastrocnemius (MG) muscles, (2) to determine the relationship between the size of these reflexes and the muscle spindle stretch velocities, and (3) to compare the size of the movement induced short latency stretch reflexes and the H-reflexes simultaneously. Six well-trained healthy male subjects participated and they hopped at three different work rates. Surface electromyogram (EMG) and H-reflexes were recorded during hopping. Muscle spindle length changes were estimated as the difference between estimated origin-to-insertion length changes and tendon length changes. The important findings were that during hopping: (1) movement induced short latency stretch reflexes were observed consistently in soleus, (2) the EMG amplitude of this stretch reflex was negatively correlated with the estimated peak muscle spindle stretch velocity (rs = -0.52, P < 0.02), and (3) the amplitude of the soleus H-reflex at touchdown did not change in parallel with the stretch reflex. The negative correlation observed between the stretch reflex and the estimated peak muscle spindle stretch velocity in soleus is opposite to the basic velocity sensitive behaviour of stretch reflexes mechanically elicited during resting conditions. Possible control mechanisms are discussed. Additionally, muscle spindle length changes estimated from changes in the skeletal movements (joint angles) should be inferred cautiously because of tendon compliance, especially at high tendon forces.

Adult↗
PubMed1989

The effects of voluntary contraction on the H reflex of human limb muscles.

The effects of a voluntary contraction on the H reflexes of various muscles were quantified to determine whether the reflex responses were sufficiently reproducible to be used in diagnostic studies. During a voluntary contraction, H reflexes could be recorded reliably from tibialis anterior and abductor pollicis brevis, but accurate identification of the onset of the H wave from the on-going background EMG required duplicate averages of multiple responses. During a contraction the H reflex could be obtained at lower stimulus intensities in the forearm flexor muscles than when relaxed, and a more clear separation of the H wave from the M wave was possible. The background contraction abolished the attenuation of reflex amplitude with increasing stimulus repetition rates, such that repetition rates of up to 4 Hz could be used without significant loss of reflex amplitude. There were only small and usually insignificant differences in the latency of the H reflex or its variability when elicited with the forearm muscles relaxed and when flexor carpi radialis was contracting steadily. The reflex latencies of abductor pollicis brevis, tibialis anterior and soleus were compared with F wave latencies for these muscles. The minimal F wave latencies were shorter than the H reflex latencies for abductor pollicis brevis (mean 2.2 ms) and tibialis anterior (mean 1.0 ms) but not for soleus. Comparison of the spread of F wave latencies (F max-F min) suggests that, for soleus, F waves are recorded only from the faster conducting motor units in the pool, presumably those less readily recruited in the H reflex. It was calculated that the distribution of motor conduction velocities responsible for the F waves of abductor pollicis brevis was 8.8 m.s-1. This value underestimates the likely distribution of motor conduction velocities for the thenar muscle by as much as 50%, consistent with the view that F waves rarely occur in slowly conducting motor units, the units of lowest threshold in reflex studies. It is concluded that, for many motoneuron pools, the H reflex and the F wave appear preferentially in different motoneurons, low and high threshold, respectively, and that reflex studies can provide information not available from somatosensory evoked potentials or F wave studies.

Adult↗
PubMed2005

Modulation of flexion reflex induced by hip angle changes in human spinal cord injury.

The flexion reflex can be elicited via stimulation of skin, muscle, and high-threshold afferents inducing a generalized flexion of the limb. In spinalized animal models this reflex is quite prominent and is strongly modulated by actions of hip proprioceptors. However, analogous actions on the flexion reflex in spinal cord injured (SCI) humans have not yet been examined. In this study, we investigated the effects of imposed static hip angle changes on the flexion reflex in ten motor incomplete SCI subjects when input from plantar cutaneous mechanoreceptors was also present. Flexion reflexes were elicited by low-intensity stimulation of the sural nerve at the lateral malleolus, and were recorded from the ipsilateral tibialis anterior (TA) muscle. Plantar skin stimulation was delivered through two surface electrodes placed on the metatarsals, and was initiated at different delays ranging from 3 to 90 ms. We found that non-noxious sural nerve stimulation induced two types of flexion reflexes in the TA muscle, an early, and a late response. The first was observed only in three subjects and even in these subjects, it appeared irregularly. In contrast, the second (late) flexion reflex was present uniformly in all ten subjects and was significantly modulated during hip angle changes. Flexion reflexes recorded with hip positioned at different angles were compared to the associated control reflexes recorded with hip flexed at 10 degrees. Hip flexion (30 degrees, 40 degrees) depressed the late flexion reflex, while no significant effects were observed with the hip set in neutral angle (0 degrees). Strong facilitatory effects on the late flexion reflex were observed with the hip extended to 10 degrees. Moreover, the effects of plantar skin stimulation on the flexion reflex were also found to depend on the hip angle. The results suggest that hip proprioceptors and plantar cutaneous mechanoreceptors strongly modulate flexion reflex pathways in chronic human SCI, verifying that this type of sensory afferent feedback interact with spinal interneuronal circuits that have been considered as forerunners of stepping and locomotion. The sensory consequences of this afferent input should be considered in rehabilitation programs aimed to restore movement and sensorimotor function in these patients.

Adolescent↗
PubMed2006

Simultaneous measurement of noise-activated middle-ear muscle reflex and stimulus frequency otoacoustic emissions.

Otoacoustic emissions serve as a noninvasive probe of the medial olivocochlear (MOC) reflex. Stimulus frequency otoacoustic emissions (SFOAEs) elicited by a low-level probe tone may be the optimal type of emission for studying MOC effects because at low levels, the probe itself does not elicit the MOC reflex [Guinan et al. (2003) J. Assoc. Res. Otolaryngol. 4:521]. Based on anatomical considerations, the MOC reflex activated by ipsilateral acoustic stimulation (mediated by the crossed olivocochlear bundle) is predicted to be stronger than the reflex to contralateral stimulation. Broadband noise is an effective activator of the MOC reflex; however, it is also an effective activator of the middle-ear muscle (MEM) reflex, which can make results difficult to interpret. The MEM reflex may be activated at lower levels than measured clinically, and most previous human studies have not explicitly included measurements to rule out MEM reflex contamination. The current study addressed these issues using a higher-frequency SFOAE probe tone to test for cochlear changes mediated by the MOC reflex, while simultaneously monitoring the MEM reflex using a low-frequency probe tone. Broadband notched noise was presented ipsilaterally at various levels to elicit probe-tone shifts. Measurements are reported for 15 normal-hearing subjects. With the higher-frequency probe near 1.5 kHz, only 20% of subjects showed shifts consistent with an MOC reflex in the absence of an MEM-induced shift. With the higher-frequency probe near 3.5 kHz, up to 40% of subjects showed shifts in the absence of an MEM-induced shift. However, these responses had longer time courses than expected for MOC-induced shifts, and may have been dominated by other cochlear processes, rather than MOC reflex. These results suggest caution in the interpretation of effects observed using ipsilaterally presented acoustic activators intended to excite the MOC reflex.

Adolescent↗
PubMed1985

The digastric reflex evoked by tooth-pulp stimulation in the cat and its modulation by stimuli applied to the limbs.

The digastric reflex evoked by electrical stimulation of tooth pulp in anaesthetized cats was studied together with the effects on this reflex of stimulating other parts of the body. The threshold for the digastric reflex generally lay in the range of stimulus intensities which would excite a large proportion of the pulpal afferent fibres which suggested that a large amount of central summation was required to evoke the reflex. During the course of 25/27 experiments, the threshold for the reflex increased. It was also found that repeated application of suprathreshold stimuli produced first an increase and then a decrease in the reflex response. The application of noxious but not of non-noxious mechanical conditioning stimuli to the limbs produced strong, long-lasting depressions of the digastric reflex. Electrical conditioning stimuli applied to the limbs also depressed the reflex; this depression had a latency of onset of 20-50 ms and lasted for up to 500 ms. When conditioning stimuli were applied to the saphenous nerve, the depression of the reflex occurred only when the stimuli were of an intensity sufficient to excite fibres conducting at less than 40 m X s-1; it may be assumed that some of these fibres would have been high threshold mechanoreceptors or nociceptors. These results show that noxious stimulation of anatomically remote structures can depress the activity of a population of trigeminal brainstem neurones. The opiate antagonist, naloxone, had no detectable effect on either the digastric reflex or the depression of the reflex produced by stimulating other parts of the body. The serotonin antagonists, methysergide and cinanserin, strongly depressed the digastric reflex but it was not clear whether these drugs also affected the depression of the reflex by the conditioning stimuli.

Animals↗
PubMed1991

Modulation of human short latency reflexes between standing and walking.

Inhibition of the magnitude of soleus muscle homonymous (H) reflexes occurs in humans when walking, compared to standing. The current study asked, (1) was the task modulation of Ia reflexes limited to soleus muscle, (2) was there support for attributing a presynaptic source to the inhibition in humans and (3) did an oligosynaptic short latency reflex show similar task modulation? In 3 subjects, H reflexes were evoked in vastus medialis and soleus, at 4 levels of contraction in the target muscle, with constant stimulus intensity when walking and standing. The reflex magnitudes in both muscles were significantly inhibited during the contractions for walking, compared to standing. Such inhibition also occurred in H reflexes of tibialis anterior muscle. An excitatory oligosynaptic reflex was then evoked in vastus medialis, through low intensity stimulation of the common peroneal nerve during walking and standing. The mean amplitudes of this reflex were not significantly different (P less than 0.05) between the two conditions, at any contraction level. The depression of quadriceps H reflexes, compared to the oligosynaptic reflexes through the same quadriceps motoneuronal pool in the same task, strongly suggested that the inhibition of H reflexes arose at other sites besides the motoneuronal cell body and proximal dendrites. We conclude that Ia H reflexes of various leg muscles of humans are inhibited when walking but that this does not generalize to the oligosynaptic short latency reflex between the anterior shank and thigh.

Adult↗
PubMed1988

Tonic descending inhibition of the spinal cardio-sympathetic reflex in the cat.

Electrical stimulation of the left inferior cardiac nerve elicited a two-component reflex potential (spinal and supraspinal reflexes) in the ipsilateral white ramus T3 from which recordings were made in chloralose-anaesthetised cats. Reversible interruption of all spinal pathways achieved by cooling the spinal cord at C2/C3 produced an enhancement of the spinal reflex and abolished the supraspinal reflex, the latter usually being the more prominent reflex potential prior to spinal cord block. The spinal cord block-induced increase in the amplitude of the spinal reflex was, however, less than the increase observed during stimulation of the somatic intercostal nerve T4. Recordings of the afferent volley following cardiac nerve stimulation and analysis of the stimulus-reflex response relationship in neuraxis-blocked cats indicated that the spinal reflex as determined here was activated by A delta afferent fibres. However, if stimulus strength was raised above C-fibre threshold, spinal cord block revealed in addition a late spinal reflex response. In some cases, the appearance of this late potential was accompanied by a secondary decline of the earlier spinal reflex potential, possibly indicating C-fibre-mediated afferent inhibition. Neither baroreceptor activation nor denervation had any effect on spinal reflex amplitudes. Pharmacologically, clonidine given i.v. to cats with a blocked neuraxis reduced the spinal reflex amplitudes to pre-block values, an action which could be antagonised by the subsequent administration of the alpha 2-adrenoceptor antagonist rauwolscine. When given to non-pretreated cats with intact neuraxis, however, neither rauwolscine nor its analog yohimbine were capable of inducing a persistent release from tonic inhibition. The results suggest that both purely visceral and somato-visceral reflexes are subject to tonic descending inhibition, but they do not support the hypothesis that a catecholamine is the responsible transmitter mediating this inhibition.

Adrenergic alpha-Antagonists↗
PubMed1994

The effects of intrathecal neuropeptide Y on the spinal nociceptive flexor reflex in rats with intact sciatic nerves and after peripheral axotomy.

We examined the effects of intrathecally administered neuropeptide Y on the spinal nociceptive flexor reflex in decerebrate, spinalized, unanesthetized rats with intact sciatic nerves, or 11-39 days after unilateral transection of the sciatic nerve. In rats with intact sciatic nerve, intrathecal neuropeptide Y at low doses (10 and 100 ng) caused a brief facilitation of the flexor reflex. At a dose of 300 ng, the effect of neuropeptide Y on the flexor reflex was biphasic, i.e. a brief facilitation followed by slight depression. At higher doses (1 and 10 micrograms), the effect of neuropeptide Y was mainly inhibitory, causing substantial and usually prolonged depression of the flexor reflex magnitude. The reflex depression caused by intrathecal neuropeptide Y was not reversed by the opioid antagonist naloxone or the alpha 2 adrenoceptor antagonist atipamezole. Intrathecal neuropeptide Y at doses up to 1 and 10 micrograms had no effect on reflex facilitation caused by conditioning stimulation of C-fibers, intrathecal substance P or neurokinin A. Topical application of neuropeptide Y (1 microgram/microliter) failed to influence the monosynaptic reflex in normal rats. Eleven to 16 days after peripheral axotomy, the initial excitation of the flexor reflex to intrathecal neuropeptide Y was significantly enhanced in axotomized compared with normal rats. However, the depressive effect of neuropeptide Y on the flexor reflex was unchanged. Neuropeptide Y did not influence the monosynaptic reflex in axotomized rats at this period. In experiments performed on rats in which the sciatic nerve had been transected 31-39 days previously, the facilitatory effect of neuropeptide Y on the flexor reflex remained enhanced compared with normal rats. Furthermore, the inhibitory effect of neuropeptide Y also increased as 100 ng intrathecal neuropeptide Y was able to produce reflex depression in a similar fashion as 300 ng neuropeptide Y normally and the reflex depression caused by 1 microgram neuropeptide Y was stronger and longer lasting than in normal rats. Intrathecal neuropeptide Y (100 ng-10 micrograms) in rats with intact sciatic nerves caused a moderate decrease in spinal cord dorsal surface blood flow as measured with a laser Doppler flowmeter. This effect of neuropeptide Y was unchanged in axotomized rats. The present results support previous observations that spinal application of neuropeptide Y in normal rats caused antinociception. As the depressive effect of neuropeptide Y is independent of spinal opioid and alpha 2-adrenergic systems, it may be mediated by its own receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1999

Differentiating condition-induced facilitation, inhibition and disinhibition in a complex series of reflexes in an electromyogram.

In man, the principal exteroceptive reflexes evoked by intra-oral stimulation involve the jaw-closing muscles and include inhibitory and excitatory responses [H.W. van der Glas, A. De Laat, D. van Steenberghe, Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric post-stimulus EMG complex following tapping of a tooth in man, Brain Res. 337 (1985) 117-125.]. These reflexes can be observed in electromyograms (EMGs) recorded with bipolar surface electrodes. The likelihood that these reflexes play important roles in the integrative actions of the jaw has led to interest in the physiological control mechanisms by which they may be modulated. It has been reported recently that the complex series of jaw reflexes evoked by non-painful tapping on human teeth can be modulated by the application of noxious stimulation to the hand [S.W. Cadden, H.W. van der Glas, F. Lobbezoo, A. van der Bilt, Effects of remote noxious stimulation on exteroceptive reflexes in human jaw closing muscles, Brain Res. 726 (1996) 189-197.] or by exercises which produce a change in mental state [S.W. Cadden, H.W. van der Glas, F. Lobbezoo, A. van der Bilt, The influence of attentional factors on short- and long-latency jaw reflexes in man, Arch. Oral Biol. 41 (1996) 995-998.]. The effects of remote noxious stimuli and mental exercises usually involved transient increases in electromyographic (EMG) activity around the interfaces between the successive inhibitory and excitatory reflexes. As the mechanisms underlying the tap-induced inhibitory and excitatory reflexes may show some temporal overlap [H.W. van der Glas, A. De Laat, D. van Steenberghe, Oral pressure receptors mediate a series of inhibitory and excitatory periods in the masseteric post-stimulus EMG complex following tapping of a tooth in man, Brain Res. 337 (1985) 117-125.], these condition-induced increases in EMG activity could, in the simplest hypothesis, have been due to either (i) a condition-induced inhibition of the tap-induced inhibitory influences on the motoneurones (i.e., disinhibition) and/or (ii) a condition-induced facilitation of the tap-induced excitatory influences underlying the subsequent excitatory reflexes. In the present protocol, we describe how it is possible to differentiate between these different underlying mechanisms. The method includes a regression analysis of the relationship between condition-induced changes in amplitude of a reflex and the reflex amplitude under control conditions after taking account of the effect of chance. The analysis is applied on reflex data pooled from various subjects. Although this method of data analysis is illustrated with trigeminal reflexes, it is potentially of use for other complex extracellular recordings including those in other fields of motor control (e.g., EMGs from muscles other than jaw ones).

Adult↗
PubMed1999

The pattern of reflex recovery during spinal shock.

STUDY DESIGN: A prospective descriptive study of the course of recovery of reflexes following acute spinal cord injury (SCI). OBJECTIVES: The purpose of the study was to observe the pattern of reflex recovery following acute SCI in order to determine the prognostic significance of reflexes for ambulation and their relationship to spinal shock. SETTING: A regional spinal cord injury center in Philadelphia, Pennsylvania, USA. METHODS: Fifty subjects admitted consecutively over a 9 month period and on the day of injury were observed for the following reflexes; bulbo-cavernosis (BC), delayed plantar response (DPR), cremasteric (CRM), ankle jerk (AJ), knee jerk (KJ), and normal plantar response for 5 7 days a week and 6-8 weeks duration. The 50 subjects were assessed for ambulation of 200 feet at time of discharge. MRI studies were reviewed on 13/28 complete (ASIA A) injuries. RESULTS: Thirty-five subjects (28 ASIA A, 4 ASIA B, 3 ASIA C) had a DPR of 2 days or longer duration and these subjects were not ambulatory. The fourteen subjects (12 ASIA D and 2 ASIA C), who were ambulatory, either had no DPR (11/14) or had a DPR of only 1 days duration (3/14). One subject (ASIA B) was not ambulatory and had a DRP of 1 days duration. The DPR was the first reflex to recover most often, followed by the BC, CRM in the first few days and later followed by the deep tendon reflexes (AJ & KJ) by 1-2 weeks respectively. Less than 8% of subjects had no reflexes on the day of injury and the reflexes did not follow a caudal-rostral pattern of recovery. CONCLUSIONS: Prognosis for ambulation based on reflexes early after SCI should not be linked to current descriptions of spinal shock. In fact, the view of spinal shock, based on the absence of reflexes and the recovery of reflexes in a caudal to rostral sequence, is of limited clinical utility and should be discarded. The evolution of reflexes over several days following injury may be more relevant to prognosis than the use of the term spinal shock and the presence or absence of reflexes on the day of injury.

Adult↗