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PubMedDate not supplied

Somato-vesical reflexes in chronic spinal cats.

The effects of afferent volleys in hindlimb cutaneous and muscle nerves on vesical tone and contractility and on the discharges in pelvic nerves to the bladder were measured in anesthetized CNS-intact and 2-19 months chronic spinal cats. In chronic spinal cats volleys in group III and IV fibers increased the tone of the quiet, empty bladder (excitatory somato-vesical reflex). The same volleys inhibited the slow, large, rhythmic micturition contractions of the expanded bladder (inhibitory somato-vesical reflex). In CNS intact cats single or short tetanic volleys induced a reflex discharge in pelvic vesical nerve branches with 3 distinct components. These reflexes could be observed during micturition contractions, not markedly between the contractions or when the bladder was empty and quiet. The latencies of the 3 components were 90, 320 and 770 ms, respectively. The two early components (AI- and A2-reflex) were evoked by volleys in group II and III hindlimb afferents. The late component (C-reflex) was induced by group IV volleys. In chronic spinal cats a group II and III-induced A-reflex (latency 90 ms) and a group IV-induced C-reflex (latency 340 ms) were observed. The central pathways and the physiological significance of the various somato-vesical reflexes are discussed.

Afferent Pathways↗
PubMed1986

Somatic depressor reflexes: results of specific 'depressor' afferents' excitation or an epiphenomenon of general anesthesia and certain decerebrations?

In chloralose-urethane anesthetized cats and unanesthetized decerebrate cats graded electrical stimulation of the tibial nerve A-afferents was performed and the resulting changes in the tibial nerve compound action potentials, heart rate and systemic arterial pressure were recorded. Three subgroups of the tibial nerve A delta-afferents were distinguished and their excitability, conduction velocity and relation to the circulatory reflexes were characterized. Stimulation of the same A-afferents evoked only tachycardic reflexes in high-mesencephalic unanesthetized cats while both tachy- and bradycardic reflexes developed in anesthetized brain-intact cats. The volleys of A beta-afferents elicited depressor reflexes in 50% of anesthetized cats but were ineffective in the other anesthetized brain-intact cats and in all the unanesthetized decerebrate cats. In anesthetized cats, the volleys of two low-threshold subgroups of A delta-afferents evoked only depressor reflexes and volleys of high-threshold A delta-afferents evoked both depressor and pressor reflexes in dependence on the deepness of anesthesia. In unanesthetized cats, effects of A delta-stimulation depended on the level of decerebration, being exclusively pressor when the most high-threshold A delta-fibers were stimulated in high-mesencephalic cats, both pressor and depressor when only low-threshold subgroups of A delta-fibers were stimulated in these cats, and exclusively depressor in prebulbar cats. The dependence of the direction of reflex blood pressure changes on the level of decerebration and anesthesia is incompatible with the classical concept of the so-called somatic depressor afferents. Moreover, general anesthesia is shown to suppress and invert not only excitatory effects of spinal A-afferents' volleys on sympathetic vasoconstrictor and cardioaccelerator neurones but the inhibitory effects of these afferents' signals on the vagal cardioinhibitory neurones, too. Contrary to this concept, we regard the 'somatic depressor reflexes' and accompanying bradycardia not as a result of 'specific' afferents excitation, but as an epiphenomenon of general anesthesia and certain decerebrations. This hypothesis is founded: (1) on the results of electrophysiological investigations of somato-sympathetic and somato-vagal reflexes indicating the existence of parallel excitatory and inhibitory interneuronal pathways between the spinal afferents and sympathetic and vagal neurones; and (2) on the assumption of unequal sensitivity of these pathways to certain anesthetics.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1990

Effects of habituation and classical conditioning on reflex modification.

Reflex modification is the inhibition or facilitation of a reflex by a stimulus (S1) occurring prior to a reflex-eliciting stimulus (S2). Two experiments were conducted that investigated the effects of habituation of the orienting response (OR) and classical conditioning on reflex modification of skin conductance responses (SCRs). During the first phase of Expt. 1 two groups (Group S1 and the Control group) received pre-presentations of S1 (200 Hz). Another group (Group S3) received pre-presentations of a different tone (S3, 3000 Hz). During the second phase, Groups S1 and S3 received pairings of S1 with S2 (white noise), whereas the Control group received pairings of S2 with S1. The predictions were: if the OR to S1 produces reflex modification of the response to S2, then Group S1 and the Control group will display larger SCRs on the first trial of the second phase of the experiment compared to Group S3, in which the OR to S1 will produce reflex modification. However, if conditioned diminution of the unconditioned response (UR) elicited by S1 produces reflex modification of the response to S2, then there should be no initial differences between the groups in the second phase of the experiment. The results showed that SCRs in Group S1 were significantly larger in the second phase compared to Group S3. This result favors an OR explanation of reflex modification. In Expt. 2, the effect of conditioned diminution of the UR on reflex modification was further investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1985

Reflex responses evoked in the adrenal sympathetic nerve to electrical stimulation of somatic afferent nerves in the rat.

The present study was initiated to determine the role of somatic A (myelinated) and C (unmyelinated) afferent fibers in both responses of increases and decreases in adrenal sympathetic nerve activities during repetitive mechanical pinching and brushing stimulations of the skin in anesthetized rats with central nervous system (CNS) intact. Accordingly, changes in adrenal sympathetic nerve activity resulting from repetitive and single shock electrical stimulation of various spinal afferent nerves, especially the 13th thoracic (Th13) spinal nerve and the sural nerve, were examined in urethane/chloralose-anesthetized rats. Repetitive electrical stimulation of A afferent fibers in Th13 spinal or sural nerve decreased the adrenal nerve activity similarly as brushing stimulation of skin of the lower chest or hindlimb did, while repetitive stimulation of A plus C afferent fibers of those nerves increased the adrenal nerve activity as pinching stimulation of those skins did. Single shock stimulation of spinal afferent nerves evoked various reflex components in the adrenal nerve: an initial depression of spontaneous activity (the early depression); the following reflex discharge due to activation of A afferent fibers (the A-reflex); a subsequent reflex discharge due to activation of C afferent fibers (the C-reflex); and following post-excitatory depressions. These reflexes seem to be mediated mainly via supraspinal pathways since they were abolished by spinal transection at the C1-2 level. Although the supraspinal A- and C-reflexes could be elicited from stimulation of a wide variety of spinal segmental afferent levels, the early depression was more prominent when afferents at spinal segments closer to the level of adrenal nerve outflow were excited. It is suggested that the decreased responses of the adrenal nerve during repetitive electrical stimulation of A afferent nerve fibers are attributable to summation of both the early depression and post-excitatory depression evoked by single shock stimulation, while the increased responses during repetitive stimulation of A plus C afferent fibers are attributable to summation of the C-reflex after single shock stimulation. In spinalized rats, repetitive stimulation of Th13 always increased the adrenal nerve activities regardless of whether A fibers alone or A plus C fibers were stimulated, just as brushing and pinching of the lower chest skin always increased them. The increased responses in spinal animals seem to be related to the fact that single electrical stimuli of Th13 produced A- and C-reflexes of spinal origin without clear depressions.

Adrenal Glands↗
PubMed1995

The inhibitory role of nitric oxide (NO) in the somatocardiac sympathetic C-reflex in anesthetized rats.

The role of nitric oxide (NO) in the two somatosympathetic reflex arcs, i.e. A- and C-reflexes, was examined using NO synthase (NOS) inhibitor in anesthetized rats. The A- and C-reflex components were recorded from a cardiac sympathetic efferent nerve and elicited by stimulation of myelinated A and unmyelinated C afferent fibers in the left tibial nerve. NG-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, when administered by either intrathecal (i.t.) or into the cisterna magna (i.c.m.) routes, augmented only the C-reflex in a dose-dependent manner. The effective i.t. dose of L-NAME to augment the C-reflex was approximately 1000 times the i.c.m. dose. NG-nitro-D-arginine methyl ester (D-NAME), an isomer of L-NAME, had no effect on either A- or C-reflexes, when administered i.c.m. Neither i.c.m. pre-treatment nor post-treatment with L-arginine, a NOS substrate, influenced either A- or C-reflexes, but i.c.m. pre-treatment with L-arginine abolished the facilitatory effect of L-NAME on the C-reflex. These results suggest that NO, synthesized in the brain stem, plays an inhibitory role in the central modulation of the somatocardiac sympathetic C-reflex. The possibility of movement of L-NAME to the brain stem from the spinal cord is discussed.

Anesthesia↗
PubMed1994

Operant conditioning of primate H-reflex: phases of development.

This study sought to determine whether operantly conditioned change in the primate triceps surae (TS) H-reflex develops in distinct phases. Data from 20 animals in which the TS H-reflex in one leg was trained up (i.e., HRup mode) and 18 in which it was trained down (i.e., HRdown mode) were averaged to define H-reflex behavior in trained and control legs. In HRup animals, the trained-leg H-reflex showed a large phase I increase in the first two days followed by gradual phase II increase that continued for weeks. The control-leg H-reflex appeared to show much smaller phase I and phase II increases. In HRdown animals, the trained-leg H-reflex decreased gradually over weeks, while the control-leg H-reflex appeared to increase within 2 days and did not change from then on. The initial rapid increase in the HRdown control leg suggested that two early events occurred in the HRdown trained leg: a nonspecific increase like that in the control leg and an operantly conditioned mode-specific decrease. These two effects may have obscured each other, so that H-reflex size in the HRdown trained leg did not drop rapidly in the first few days. These results improve understanding of adaptive H-reflex change as an operantly conditioned phenomenon, and provide encouragement and direction for efforts to reproduce and study the phenomenon in reduced or anesthetized preparations.

Animals↗
PubMed1995

Operantly conditioned plasticity and circadian rhythm in rat H-reflex are independent phenomena.

Recent studies indicate that rats can increase or decrease H-reflex amplitude in response to an operant conditioning paradigm. In addition, rats also display a circadian rhythm in H-reflex amplitude. As part of the development of H-reflex conditioning in the rat as a new model for defining the plasticity underlying a simple form of learning, this study examined the relationship in the rat between operantly conditioned H-reflex change and the H-reflex circadian rhythm. When H-reflex amplitude increased or decreased in response to the operant conditioning program, its circadian rhythm showed no changes in phase and minimal change in amplitude. Furthermore, animals did not alter daily performance schedule so as to use the rhythm to increase reward probability. Thus, in the rat, H-reflex operant conditioning and the H-reflex circadian rhythm appear to be independent phenomena. The circadian rhythm should not be a significant complicating factor in studies of operantly conditioned H-reflex change.

Animals↗
PubMed1988

Parametric and pharmacological studies of midbrain suppression of the hind limb flexion withdrawal reflex in the rat.

These experiments quantitatively analyzed effects of electrical midbrain stimulation on a nociceptive hind limb flexion reflex in rats anesthetized with sodium pentobarbital. We recorded the force of isometric hind limb flexion withdrawal, and related flexor electromyographic (EMG) activity, elicited by noxious heat (42-54 degrees C, 10 sec) applied to the ventral hind paw. Several hind limb flexors including biceps femoris were active during the reflex. Quantified reflex responses to identical noxious heat stimuli delivered every 2 min were constant in magnitude and were reduced or abolished during stimulation (100 msec trains at 100 Hz, 3/sec, 15-325 microA) in the midbrain periaqueductal gray (PAG) or lateral reticular formation (LRF). LRF was significantly more effective than PAG stimulation in suppressing reflex responses. The magnitude of the reflex responses increased with graded increases in the temperature of the noxious heat stimulus. The slope of the temperature-response relationship was significantly reduced during PAG stimulation, whereas it was shifted toward higher temperatures with significantly increased threshold during LRF stimulation. To investigate possible transmitters involved, we tested if PAG- or LRF-evoked reflex suppression was affected following systemic administration of the opiate antagonist naloxone, the serotonin antagonist methysergide, the noradrenergic antagonist phentolamine, or the cholinergic antagonist scopolamine. Naloxone had little effect, while methysergide and phentolamine reduced PAG- and LRF-evoked reflex suppression in about one-half of the cases. Scopolamine largely reduced PAG- and LRF-evoked reflex suppression (in 8/9 and 4/6 rats, respectively). These results indicate that the flexion reflex is under parametrically but not pharmacologically distinct inhibitory midbrain controls.

Animals↗
PubMed1984

A quantitative analysis of the spatial organization of the vestibulo-ocular reflexes in lateral- and frontal-eyed animals--II. Neuronal networks underlying vestibulo-oculomotor coordination.

The neuronal connectivity underlying the vestibulo-ocular reflexes in cat and rabbit was evaluated in the light of quantitative data of the spatial orientation on semicircular canals and extraocular muscles. Neuronal connectivity was calculated using a matrix-analysis of the sensory and motor periphery, and of the brain stem pathways connecting semicircular canals and extraocular muscles. Two cases of vestibulo-ocular reflex compensation were considered. In the first case, vestibulo-oculor reflex compensation was assumed to be isotropic, i.e. the vestibulo-ocular reflex gain is the same for all directions of rotation. In the second case, the vestibulo-oculor reflex gain was assumed to be anisotropic with the "torsional" gain smaller than the "horizontal" and "vertical" gains. The theoretical calculation predicts that besides the principal vestibulo-ocular reflex pathways (classical three-neuron-arc connectivity), several accessory connections (other than principal connections, regardless of the synapses involved) exist which are characteristic for each species. These accessory connections were compared to physiological and anatomical data. In the cat theoretical connections for an isotropic vestibulo-ocular reflex gain agree with pathways observed experimentally, of which the most characteristic are excitatory connections to the superior rectus and inhibitory connections to the inferior rectus muscle from both of the anterior canals, and a mirror image pattern of connections from the posterior canals. In the rabbit experimentally obtained data and calculated connections rarely agree. However, for an anisotropic gain we find a higher rate of coincidence between experimental and theoretical connections. Our evaluation indicates, that accessory vestibulo-ocular reflex pathways serve to compensate for the incongruence between semicircular canal and extraocular muscle planes, at least in the cat. Available experimental data suggest an important role of a special subclass of accessory pathways via axon collaterals of principal projections (three-neuron-arc nature). With certain restrictions, the presented method of calculation promises to be a useful tool for a quantitative analysis of the vestibulo-ocular reflex.

Animals↗
PubMed1991

On the role of NK-2 tachykinin receptors in the mediation of spinal reflex excitability in the rat.

The effects of intrathecal administration of neurokinin A, substance P and [Tyr5, D-Trp6,8,9 Arg10]neurokinin A-(4-10) (Men 10207), a specific NK-2 receptor antagonist, on the spinal nociceptive flexor reflex were studied in decerebrate, spinalized, unanesthetized rats. Intrathecal neurokinin A and substance P facilitate the flexor reflex in a similar manner. The reflex facilitation to intrathecal neurokinin A, but not substance P, is dose-dependently blocked by pretreatment with Men 10207. The NK-2 receptor antagonist by itself facilitates the flexor reflex with a potency about 10 times less than that of neurokinin A, indicating a partial agonistic property. Reversible depression of the flexor reflex, which is not due to nonspecific spinal blockade, is observed after 700 pmol Men 10207. Further increasing the dose of Men 10207 to 7 nmol for 20 s at an intensity that activates unmyelinated (C) fibers stimulation of peripheral nerves at 1 Hz for 20 s at an intensity that activates unmyelinated (C) fibers facilitates the ipsilateral flexor reflex. The duration of the facilitation after conditioning stimulation of the cutaneous sural nerve is several minutes and about 1 h after conditioning stimulation of the gastrocnemius muscle nerves. Pretreatment with Men 10207 (70-700 pmol) has no effect on facilitation by the sural nerve conditioning stimulation, but effectively blocks the long-term reflex facilitation to the gastrocnemius nerve stimulation. The present results indicate a distinct role for NK-2 tachykinin receptors in mediation of spinal reflex excitability in the rat. Neurokinin A may be involved in the long-term increase of spinal reflex excitability after activation of unmyelinated fibers innervating muscle.

Animals↗
PubMed1993

Evidence for a role of tachykinins as sensory transmitters in the activation of micturition reflex.

The possible involvement of tachykinin neurokinin-1 and neurokinin-2 receptors in the activation of various micturition-related reflexes was assessed by the intrathecal administration of selective neurokinin-1 or neurokinin-2 receptor antagonists at lumbosacral spinal cord level in urethane-anaesthetized rats. The effect of the glutamate N-methyl-D-aspartate receptor antagonist, 2-amino-5-phosphonovaleric acid, was also investigated for comparison. The effect of antagonists was investigated on: (i) the chemonociceptive vesicovesical reflex activated by topical application of capsaicin onto the urinary bladder; (ii) the distension-induced micturition reflex produced by transvesical filling with saline; (iii) distension-induced rhythmic bladder contractions in isovolumetric conditions (urethra-ligated rats); and (iv) the somatovesical excitatory reflex caused by noxious perineal pinching. The neurokinin-2 receptor selective antagonists MEN 10,376 and SR 48,968 were ineffective in the three models in all doses tested. Selective neurokinin-1 receptor antagonists blocked the chemonociceptive reflex produced by topical application of capsaicin with the rank order of potency (lowest effective dose in brackets): GR 82,334 (1 nmol/rat) > RP 67,580 (10 nmol/rat) > (+/-)CP 96,345 (100 nmol/rat). Unlike GR 82,334, RP 67,580 (10 nmol/rat) and (+/-)CP 96,345 (100 nmol/rat) were also effective on the distension-induced micturition reflex elicited by transvesical filling. Similarly, distension-induced rhythmic contractions were inhibited by RP 67,580 (10 nmol/rat) and (+/-)CP 96,345 (100 nmol/rat) whereas the effect of GR 82,334 was not significant. RP 68,651, the enantiomer of RP 67,580 devoid of neurokinin-1 receptor blocking activity, was inactive in both models. 2-Amino-5-phosphonovateric acid (250 nmol/rat) blocked the three types of vesicoexcitatory reflexes. Intravenous administration of (+/-)CP 96,345, RP 67,580 or 2-amino-5-phosphonovateric acid at the same doses proven effective after the intrathecal route, had no effect on distension-induced rhythmic contractions. To ascertain whether the effect of neurokinin-1 receptor antagonists or 2-amino-5-phosphonovaleric acid may be related to a blockade of tachykinins released from capsaicin-sensitive primary afferent neurons, the effect of RP 67,580 was investigated on the distension-evoked micturition reflex in capsaicin-pretreated rats. Capsaicin pretreatment (50 mg/kg, subcutaneously, four days before) increased bladder capacity. RP 67,580 was no longer effective in capsaicin-pretreated rats. In contrast, 2-amino-5-phosphonovateric acid produced a further increase in bladder capacity in capsaicin-pretreated rats. We conclude that tachykinin neurokinin-1 but not neurokinin-2 receptors are involved in the activation of vesicoexcitatory micturition-related reflexes in the rat spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1986

The acoustic middle ear muscle reflex in albino rats.

The acoustic middle ear muscle reflex was studied in albino rats anesthetized with chloralose. The best frequency of the reflex and the threshold at this frequency were on average about 3 kHz and 57 dB SPL, respectively. The threshold increased as frequency increased above, and decreased below, the best frequency at a rate of about 20 dB/octave. Above about 12 kHz, the muscular response showed instability and habituation. Thresholds were similar between stapedius and tensor tympani reflexes and between ipsilateral and contralateral reflexes. The middle ear transmission loss due to the reflex was the greatest and nearly constant below about 1 kHz, where the loss was about 18 dB at the maximal stimulation. Above this frequency the loss decreased as frequency increased up to 20 kHz. Thus the reflex, unlike that in other animals, suppressed transmission over the whole range of reflex-eliciting frequencies. The transfer function of the reflex had a well damped low-pass characteristic with a cut-off frequency of about 20 Hz. From the above characteristics of the reflex, the role of the rat's tympanic muscles in improving ultrasonic hearing under ambient noises was suggested.

Animals↗
PubMedDate not supplied

Deep tendon reflexes in premature infants.

Ten classic deep tendon reflexes (DTRs) were evaluated in 62 premature infants of greater than 27 weeks post-conceptional age. The pectoralis major was the most readily elicitable reflex in all infants (100%), regardless of maturity. Achilles, patellar, biceps, thigh adductors, and brachioradialis reflexes also were obtained in at least 98% of babies of greater than 33 weeks gestation. Among these reflexes, less mature infants (less than 33 weeks gestation) had decreased elicitation rates for patellar and biceps reflexes and overall had diminished reflex intensity when compared to older infants (33-36 weeks gestation). By order of decreasing rate, finger flexors, jaw, crossed adductors, and triceps reflexes were less frequently elicited in both groups. Equal DTRs were obtained often in healthy and previously ill infants of less than 33 weeks gestation. Head position had no apparent affect on the ability to elicit reflexes. Theophylline therapy tended to intensify the Achilles reflex and the quiet, wakeful state appeared to be the most optimal state for the elicitation of DTRs.

Gestational Age↗
PubMed1995

Primitive (developmental) reflexes, tardive dyskinesia and intellectual impairment in schizophrenia.

Primitive reflexes, also known as higher cerebral, developmental or release reflexes, are present in foetal and infant life, and are found in certain organic brain diseases. They are normally regarded as non-localising signs of cerebral immaturity or dysfunction which are uncommon in the normal population. The main aims of this study were to find out whether recent reports of an association between primitive reflexes and severity of cognitive impairment in dementia and between primitive reflexes and tardive dyskinesia in schizophrenia could be replicated in a younger population of schizophrenic patients. Forty-eight schizophrenic patients (mean age 51 years) were assessed for primitive reflexes, involuntary movements and cognitive function, and 58% exhibited at least one primitive reflex and 23% at least two. No association was found between primitive reflexes and cognitive impairment or between primitive reflexes and tardive dyskinesia. These results fail to support the hypothesis that the presence of primitive reflexes in some schizophrenic patients indicates a vulnerability to tardive dyskinesia and intellectual decline with advancing age, but long-term prospective studies would be required to test this hypothesis adequately. Nevertheless, these findings support the notion of neurodevelopmental or neurodegenerative brain disease in at least a proportion of patients with schizophrenia.

Adult↗
PubMed2004

Expansion of nociceptive withdrawal reflex receptive fields in spinal cord injured humans.

OBJECTIVE: In spinal cord injured (SCI) subjects, exaggerated withdrawal reflexes associated with a dominant flexor pattern irrespective of stimulation site have been reported. In the present study, withdrawal reflex receptive field (RRF) was determined in complete SCI subjects (N=9). METHODS: Distributed electrical stimulation was applied to the sole of the foot, and reflexes in tibialis anterior, soleus, biceps femoris, and vastus lateralis muscles were recorded together with knee and ankle movement trajectories. A group of spinally intact subjects (N=10) were included as controls. With the subjects in supine position, stimulation was applied to 10 different sites on the foot sole. Based on the tibialis anterior reflex threshold for stimulation on the mid foot sole, two stimulus intensities (1.1 times the reflex threshold and 1.4 times the reflex threshold) were used for all 10 sites. RESULTS: In SCI subjects, dorsi-flexion dominated independent of stimulus site and the tibialis anterior RRF covered the entire foot sole in contrast to a well-defined tibialis anterior receptive field at the medial, distal foot sole in the spinally intact subjects. Further, the soleus RRF also covered the entire sole in the SCI subjects. The reflexes in biceps femoris and vastus lateralis muscles were small and associated with weak knee flexion at all 10 sites in the SCI subjects and in the controls. CONCLUSIONS: The RRF of the ankle flexor and the ankle extensor muscles both covered the entire sole of the foot indicating an expansion of the RRFs following spinal cord injury. The expansion is most likely due to lack of descending inhibitory control and/or increased sensitivity of the spinal reflex loop in the SCI subjects. SIGNIFICANCE: The study improves the understanding of spinal reflex control in spinal intact and spinal cord injured subjects.

Adult↗
PubMed2005

Effects of masticatory muscle fatigue without and with experimental pain on jaw-stretch reflexes in healthy men and women.

OBJECTIVE: To examine the effects of experimentally evoked masticatory muscle fatigue, without and with experimental muscle pain, on the short-latency jaw-stretch reflex, using a randomised crossover design. METHODS: Reflexes were evoked in both the masseter and temporalis muscles in 15 men and 13 women. The study was performed in two blocks, both containing 3 experimental conditions (before, directly after, and 15 min after provocation). Provocation consisted of a fatiguing chewing test, followed by an intramuscular injection of either isotonic saline (IS; non-painful) or hypertonic saline (HS; painful). RESULTS: No significant effects of the experimental condition 'fatigue+IS' were found for any of the reflex outcome variables. For each muscle, the 'fatigue+HS' condition yielded significantly higher normalized reflex amplitudes than the other conditions. Several muscles displayed gender differences regarding both onset latency and normalized reflex amplitude. CONCLUSIONS: Experimentally evoked mild-to-moderate muscle fatigue does not modulate the human jaw-stretch reflex. On the other hand, experimental muscle pain, evoked after the performance of a fatiguing chewing test, does yield a facilitation of this reflex. The gender differences found in both onset latency and peak-to-peak amplitude stress the need to take gender into consideration in future jaw reflex studies. SIGNIFICANCE: The sensitivity of the human jaw-stretch reflex can be modulated by HS-induced muscle pain; not by muscle fatigue that is provoked by intense chewing.

Adult↗
PubMed2006

Modulations of interlimb and intralimb cutaneous reflexes during simultaneous arm and leg cycling in humans.

OBJECTIVE: We investigated to what extent intralimb and interlimb cutaneous reflexes are altered while simultaneously performing arm and leg cycling (AL cycling) under different kinematic and postural conditions. METHODS: Eleven subjects performed AL cycling under conditions in which the arm and leg crank ipsilateral to the stimulation side were moved synchronously (in-phase cycling) or asynchronously (anti-phase cycling) while sitting or standing. Cutaneous reflexes following superficial radial or superficial peroneal nerve stimulation (2.0-2.5 times radiating threshold, 5 pulses at 333 Hz) were recorded at 4 different pedal positions from 12 muscles in the upper and lower limbs. Cutaneous reflexes with a peak latency of 80-120 ms were then analyzed. RESULTS: The magnitude of interlimb and intralimb cutaneous reflexes in the arm and leg muscles was significantly modulated depending on the crank position for the relevant limb (phase-dependent modulation). A significant correlation between the magnitude of the cutaneous reflex and background EMG was observed in the majority of muscles during static contraction, but not during AL cycling (task-dependent modulation). No significant difference was found in comparisons of the magnitude of intralimb and interlimb cutaneous reflexes obtained during in- and anti-phase AL cycling. Qualitatively, the same results were obtained during AL cycling while sitting or standing. In addition, the modulation of cutaneous reflexes in arm muscles was identical among in-phase, anti-phase and isolated arm cycling. Results were the same for leg muscles. CONCLUSIONS: Cutaneous reflexes in arm muscles are little influenced by rhythmic movement of the legs and vice versa during AL cycling. It is likely that neural components that control interlimb reflexes are loosely coupled during AL cycling while sitting or standing. SIGNIFICANCE: Our results provide a better understanding of the coordination between the upper and lower limbs during rhythmic movement.

Adult↗
PubMed2006

Modulation of the withdrawal reflex during hemiplegic gait: effect of stimulation site and gait phase.

OBJECTIVE: The objective of the study was to investigate the sensitivity of the nociceptive withdrawal reflex to stimulation of different locations on the sole of the foot during hemiplegic gait. METHODS: Reflexes were evoked by cutaneous electrical stimulation of 4 locations on the sole of the foot of 7 hemiplegic and 6 age-matched healthy persons. The stimuli were delivered at heel-contact, during foot-flat, at heel-off, and during mid-swing. Reflexes were recorded from muscles of the stimulated and the contralateral leg. Ankle, knee, and hip joints angles were recorded using goniometers. RESULTS: In the hemiplegic persons, the size of tibialis anterior reflexes, and the latency of soleus reflexes were site- and phase-modulated. In both groups, the tibialis anterior reflexes were significantly smaller with stimulation to the fifth metatarsophalangeal joint and the heel compared with the first metatarsophalangeal joint and the arch of the foot. The tibialis anterior reflexes evoked at heel-off and mid-swing were larger in hemiplegic persons than in healthy persons. Reflexes in the proximal and contralateral limb muscles were not site-modulated during hemiplegic gait. The kinematic response at the ankle joint was also different in the two groups during mid-swing. CONCLUSIONS: Hemiplegic and healthy middle-aged people presented different phase-modulation of the kinematic and muscle nociceptive reflex responses evoked by stimulation delivered on the sole of the foot. SIGNIFICANCE: The results have potential application in programs to rehabilitate hemiplegic gait.

Aged↗