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At least 199 records · Page 11Linked to original sources

PubMed1990

Effects of a new analog of thyrotropin-releasing hormone, N alpha-[(S)-4-oxo-2-azetidinyl) carbonyl]-L-histidyl-L-prolinamide dehydrate (YM-14673) on spinal reflex potentials and flexor reflexes in spinalized rats.

Experiments were performed on spinalized rats, transected at the Cl level. The intravenous administration of TRH and its analog YM-14673 (N alpha-[(S)-4-oxo-2-azetidinyl) carbonyl]-L-histidyl-L-prolinamide dehydrate) produced marked increases in the amplitude of mono- and polysynaptic reflex potentials and those of the withdrawal flexor reflexes. The effects of YM-14673 were stronger and longer-lasting than those of TRH. The stimulant action of TRH and YM-14673 on the flexor reflexes was not antagonized by prazosin, chlorpromazine, haloperidol or cyproheptadine, suggesting no involvement of the release of catecholamines or serotonin in the stimulant effects of TRH and its analog. Therefore, YM-14673 may be beneficial for the treatment of several spinal motor neuron diseases.

Animals↗

PubMed2002

Modulation of trigeminal reflex excitability in migraine: effects of attention and habituation on the blink reflex.

The modulation of trigeminal reflex excitability in migraine patients was evaluated during the asymptomatic phase by studying the effects of attention, habituation and preconditioning stimulus on the R2 and R3 components of the blink reflex (BR). Fifty patients suffering from migraine without aura, 20 affected by migraine with aura and 35 sex- and age-matched controls were selected. In subgroups of migraine with-aura and without-aura patients, and normal controls, the blink reflex was elicited during different cognitive situations: (a) spontaneous mental activity; (b) stimulus anticipation; (c) recognition of target numbers. In the remaining subjects, R2 and R3 habituation was evaluated by repetitive stimulation at 1, 5, 10, 15, 20, 25 and 30 s intervals. The R2 and R3 recovery curves were also computed. A reduced R3 threshold with a normal pain threshold was found in migraine with-aura and without-aura patients; the R3 component was not significantly correlated with the pain thresholds in patients and controls. The R2 and R3 components were less influenced by the warning of the stimulus in migraine without-aura and migraine with-aura patients, in comparison with the control group. A slight increase of both R2 and R3 recovery after preconditioning stimulus was also observed in migraine patients, probably caused by a phenomenon of trigeminal hyperexcitability persisting after the last attack. The abnormal BR modulation by alerting expresses in migraine a dysfunction of adaptation capacity to environmental conditions, probably predisposing to migraine.

Adult↗

PubMed1979

Modulation of the acoustic startle reflex in humans in the absence of anticipatory changes in the middle ear reflex.

If a weak tone precedes an intense tone, then the acoustic startle eyeblink reflex elicited by the stronger stimulus is inhibited. It has been suggested that the leading stimulus gives rise to a protective middle ear reflex that attenuates the effective intensity of the second. This hypothesis was tested and disproved. In seven subjects intense tone bursts sufficient to elicit both intratympanic and eyeblink responses were presented sometimes alone and sometimes preceded at various lead times (25 to 400 msec) by a weak tone. The weak tone inhibited the amplitude of the eye blink to the strong tone, maximally at intervals of 100 to 200 msec, but was never seen to produce any of the anticipatory impedance changes that would be characteristic of middle ear reflex activity during the interval between the two stimuli.

Adolescent↗

PubMed1978

Reflex arc of the first component of the human blink reflex: a single motoneurone study.

Latency variation of consecutive responses of single orbicularis oculi motoneurones in the first component of the electrically elicited blink reflex was 2.6 times larger than that of the H reflex of the soleus muscle fibres. Some motoneurones showed bimodal latency distribution or double responses or both at an interval of about 4-5 ms. Typical first component responses were sometimes obtained by contralateral stimulation. Central conduction time in the brainstem, estimated for 15 motoneurones, was between 2.4 and 6.6 ms. It is concluded that the first component of the blink reflex is conducted through an oligosynaptic arc including one or more interneurones.

Adult↗

PubMed1979

H reflex analysis of segmental reflex excitability in flexor and extensor muscles.

In normal adults, H reflexes are commonly found only in the antigravity calf and flexor carpi radialis (FCR) muscles. However, these responses may be more widespread if agonist muscles contract. This study demonstrates that H reflexes may be found in the peroneal (P) and anterior tibialis (TA) muscles in the leg and the extensor digitorum communis (EDC) muscle in the arm on contraction of the antagonistic calf and flexor carpi radialis muscles, respectively. H reflexes were also elicited regularly in the EDC by passive extension of the wrist. The data indicate physiologic unity of comparably acting human antigravity muscles and their antagonists in both the upper and lower extremities, and imply an important functional role of group II afferent fibers in normal motor system activity.

Adult↗

PubMed1983

The reflex sympathetic dystrophy syndrome. An experimental study of sympathetic reflex control of subcutaneous blood flow in the hand.

Adrenergic sympathetic vasoconstrictor activity in subcutaneous tissue on the back of the hand was studied in 13 patients suffering from reflex sympathetic dystrophy syndrome. Subcutaneous blood flow was measured by the local 133Xe wash-out technique with simultaneous measurements on the healthy side as a control. The results indicated an increased subcutaneous blood flow in the affected hand compared with the control side. Proximal nervous blockade caused only a slight, 35% increase in subcutaneous blood flow on the affected side, whereas an increase of 122% was registered on the control side. Augmented sympathetic vasoconstrictor activity elicited by the local veno-arteriolar axon reflex mechanism or centrally elicited by head-up tilt caused an equal degree of arteriolar vasoconstriction in both hands. The results suggest that sympathetic vasomotor tone during resting conditions is reduced in the affected hand in patients with the reflex sympathetic dystrophy syndrome.

Aged↗

PubMed2006

Straining-cremasteric reflex: identification of a new reflex and its role during increased intra-abdominal pressure.

The cremasteric muscle (CM) being composed of fleshy muscle bundles constitutes the active component of the fasciomuscular tube of the spermatic cord. On contraction, the CM compresses the cord veins pushing the blood in the pampiniform plexus to the abdominal veins. The role of the CM during increased intra-abdominal pressure (IAP) could not be traced in the literature. We investigated the hypothesis that the CM contracts upon IAP increase so as to support the cord veins and prevent abdominal veins reflux into them. Thirty-two healthy male volunteers (mean age 40.2 +/- 11.2 SD years) were studied. The IAP was recorded by a manometric catheter introduced into the rectum. The CM response to straining (sudden by coughing and slow by Valsalva's maneuver) was registered by a needle electrode introduced into the muscle. The response was recorded again after individual anesthetization of the CM and rectum. The test was repeated using saline instead of lidocaine and was performed on both sides. Straining (sudden or slow sustained) effected increase of the rectal pressure and CM EMG. The more the rectal pressure was increased by straining, the more the CM EMG was increased. The CM EMG response disappeared after prolonged or repeated successive straining. The CM did not respond to straining after individual anesthetization of the rectum and CM but did respond to saline administration. The response was similar from muscles on both sides. Increased CM EMG on straining postulates a reflex relationship which we call the 'straining-cremasteric reflex' (SCR). We suggest that this reflex, which results in CM contraction, supports the spermatic cord veins against the increase of the IAP induced by straining and against the tendency of venous reflux from the abdominal veins. The SCR may prove of diagnostic significance in neurogenic disorders provided further studies are performed in this respect.

Abdomen↗

PubMed2001

Voluntary and reflex influences on the initiation of swallowing reflex in man.

The electrophysiological features of voluntarily induced and reflexive/spontaneous swallows were investigated. In normal subjects, swallows were elicited by infusing water either into the mouth (1-3 ml) or directly into the oropharyngeal region through a nasopharyngeal cannula (0.3-1 ml). For water infused orally, subjects were either requested to swallow voluntarily or instructed to resist swallowing and maintain the horizontal head position until swallowing occurred reflexively. Spontaneous saliva swallowing was investigated in patients with severe dysphagia who had a prominent clinical picture of suprabulbar palsy. Comparisons between different swallowing types were made by measuring the time interval between the onset of submental electromyographic activity (SM-EMG) and the onset of the upward movement of the larynx recorded by a movement sensor. This interval was less than 100 ms, even frequently less than 50 ms, in reflexive/spontaneous swallows, while in voluntarily induced swallows it was substantially longer. The rising time of submental muscle's excitation was also shorter in reflexive/spontaneous swallows. It was suggested that the triggering of voluntarily induced swallows commences more than 100 ms before the onset of swallowing reflex and that this mechanism is under the control of corticobulbar-pyramidal pathways. If the swallowing reflex is triggered within such a short period of time following the onset of SM-EMG, the central control by the bulbar swallowing center should be effective until the end of oropharyngeal swallowing.

Adult↗

PubMed2002

The perineorectal reflex The perineorectal reflex in health and obstructed defecation.

PURPOSE: Many females with obstructed defecation apply digital pressure on their perineum to facilitate defecation. This study investigated the impact of this maneuver on rectal tone. METHODS: Forty-five female patients with obstructed defecation were studied. Thirty-four patients (76 percent) regularly applied digital pressure on their perineum to facilitate defecation. Total colonic transit time was normal in 32 patients and prolonged in 13 patients. For comparison, 17 female controls were studied. With the subject in the left lateral position, a thin, "infinitely" compliant polyethylene bag was inserted into the rectum at 10 cm from the anal canal. Rectal tone was assessed by measuring variations in bag volume with a computer-controlled electromechanical air injection system. After an adaptation period of 15 minutes, digital pressure was applied to the anterior perineum by one of the authors (WRS). In a second recording session, the tonic response of the rectum to an evoked urge to defecate was examined. RESULTS: During the application of perineal pressure, all controls showed an increase in rectal tone (mean value, 52.8+/-19 percent). In the whole patient group, this response was significantly lower (mean value, 24.2+/-19 percent; P < 0.001). Eight of these patients (18 percent) showed no response at all. None of them applied perineal pressure. In the remaining 37 patients (72 percent), the perineorectal reflex was present but was significantly lower (mean value, 29.8+/-17 percent; P < 0.001). Thirty-four of these females (92 percent) stated that they applied perineal pressure on a regular basis to facilitate their defecation. All controls showed an increase in rectal tone during an evoked urge to defecate (mean value, 37.8+/-8 percent). In the patients, this response was significantly lower (16.7+/-6 percent). Eight of these patients showed no increase in rectal tone at all. These patients were the same patients in whom the perineorectal reflex was absent. Regarding the tonic response of the rectum to perineal pressure, no difference was found between patients with a normal colonic transit time and those with a prolonged colonic transit time. CONCLUSION: Digital pressure applied on the perineum results in an increase in rectal tone. This perineorectal reflex is present, although significantly lower, in the majority of females with obstructed defecation. This observation might explain why females with obstructed defecation frequently apply perineal pressure to facilitate defecation.

Adolescent↗

PubMed1984

Sympathetic control of sexual reflexes: peripheral 6-hydroxydopamine administration facilitates the onset of penile reflexes in male rats.

The latency to display penile reflexes was significantly reduced in male rats tested one day following treatment with 6-hydroxydopamine (6-OHDA; 75 mg/kg, administered via acute tail vein injection). Eight days following treatment the latency to the first reflex in 6-OHDA treated males did not differ significantly from saline treated control subjects. There were no significant differences in the mean number of erections or flips displayed by 6-OHDA subjects when compared to saline treated control subjects. On tests one day after 6-OHDA administration, treated subjects displayed significantly fewer cups than control subjects on the corresponding tests. Chemical sympathectomy was verified by extreme reduction of peripheral norepinephrine levels. Results of this study are consistant with those reported for spinally transected rats tested under similar conditions (that is, one day following spinal transection), and suggest sympathetic inhibition of the onset of penile reflexes.

Animals↗

PubMed2006

Functional roles of oral reflexes in chewing and biting: phase-, task- and site-dependent reflex sensitivity.

Because loading during chewing is not totally predictable and jaw-closing muscles are strong and act over short distances, feedback from oral receptors is important in the control of mastication. Information on such feedback can be obtained by studying reflexes in jaw muscle EMGs. This review will deal with the contribution of reflex mechanisms to modifying motor neuron activity during chewing, and the dependency of reflex sensitivity on motor task, phase of movement, and site of stimulation.

Bite Force↗

PubMed2000

Assessment of brainstem function in Chiari II malformation utilizing brainstem auditory evoked potentials (BAEP), blink reflex and masseter reflex.

Brainstem dysfunction was evaluated in 67 patients with myelomeningocele and Chiari II malformation using brainstem auditory evoked potentials (BAEP), blink reflex (BR) and masseter reflex (MR). Signs and symptoms related to Chiari II malformation were observed in 18 patients while 49 patients had normal brainstem findings. BAEP and BR showed a higher sensitivity of brainstem involvement than MR (BAEP=1.0, BR=0.83, MR=0.50). BR, and in particular, MR were of higher accuracy (BR=0.52, MR=0.72) than BAEP (0.39) in separating patients with brainstem signs and symptoms related to Chiari II malformation. We feel that this is due to anatomic and physiologic peculiarities of the brainstem structures mediating BR and MR. Our results suggest that brainstem reflexes can support the decision of further treatment.

Adolescent↗

PubMed2000

The clinical use of brainstem reflexes and hand-muscle reflexes.

Brainstem reflexes and hand-muscle reflexes can be elicited and recorded with routine EMG equipment. Not all these reflexes are useful in clinical neurology. But those that are - the subject of this review - exhibit distinct patterns of abnormality that have clinical diagnostic and localizing value in various diseases, including cranial neuropathies, focal lesions within the cervical cord, brainstem, and brain, movement disorders, and pain.

Adolescent↗

PubMed2001

Reflex and non-reflex elements of hypertonia in triceps surae muscles following acquired brain injury: implications for rehabilitation.

BACKGROUND: Following adult onset acquired brain injury, the triceps surae muscles tend to become shortened and exhibit increased resistance to passive lengthening; a phenomenon that has been termed 'hypertonia'. Spasticity (velocity dependent tonic reflex hyper-excitability) has traditionally been considered a major component of hypertonia. In addition, unmodulated descending excitatory influences on the alpha motorneurone pool may result in inappropriate or excessive muscle activity (dystonia). Non-reflex changes, secondary to the brain injury, and as a consequence of subsequent immobility, also take place in the passive and active elements of the muscle. These non-reflex changes affect the stiffness and extensibility of the musculo-tendinous unit. Atrophy of muscle fibres combines with collagen proliferation to produce increased muscle stiffness. This may be compounded by increased actin-myosin cross-bridge linkages, which are thought to be associated with reduced rates of cross-bridge detachment. Prolonged immobilization in a shortened position results in a loss of sarcomeres in series. Arthrogenic changes associated with disuse include remodelling of dense connective tissue and intra-articular adhesions. CONCLUSION: Decreased muscle extensibility may be exacerbated by muscle overactivity. Consideration of all of the potential factors contributing to hypertonia of the triceps surae muscle will assist clinicians to identify appropriate intervention strategies, which may facilitate better treatment outcomes.

Brain Injuries↗

PubMed2002

Prediction of the haemodynamic response to tracheal intubation: comparison of laser-Doppler skin vasomotor reflex and pulse wave reflex.

BACKGROUND: The laser-Doppler skin vasomotor reflex (SVmR) caused by tetanic stimulation of the ulnar nerve may be a test that can predict the haemodynamic response to tracheal intubation. A decrease in pulse wave amplitude (pulse wave reflex, PWR) may be an alternative index of this response. We compared the abilities of PWR and SVmR to predict the haemodynamic response to tracheal intubation and studied how alfentanil, muscle relaxation, stimulation site and stimulation pattern affected the two reflexes. METHODS: Anaesthesia was induced and maintained with 2% sevoflurane and 50% nitrous oxide in two groups of 10 ASA status 1 patients. Tetanic stimuli were applied to the flexor muscles of the forearm and the ulnar nerve before and after administration of vecuronium. The change in skin blood flow (laser-Doppler) and pulse wave amplitude (pulse oximetry) after a 5 and 10 s stimulation was measured on the opposite hand. If skin blood flow (laser-Doppler) decreased by more than 10%, a computer-controlled infusion of alfentanil was started and the target plasma concentration was increased in steps until this response was suppressed (< 10%). The trachea was intubated and arterial pressure and heart rate responses were recorded. Plasma alfentanil concentration was measured. RESULTS: When PWR and SVmR were suppressed, the haemodynamic response to tracheal intubation was reduced in 100 and 53% of patients respectively. PWR and SVmR responses decreased with increasing plasma alfentanil concentration. The SVmR response to muscle stimulation was reduced by muscle relaxants. The pulse wave response to both muscle and neural stimulation was reduced by relaxants. The responses to 5 and 10 s stimulations were similar. CONCLUSION: An absent SVmR does not predict a blunted arterial pressure or heart rate response to tracheal intubation. The PWR may be a better predictor.

Adult↗

PubMed1994

Utero-cervical inhibitory reflex. The description of a reflex and its clinical significance.

The functional relationship of the uterine corpus to the cervix was studied in 14 healthy women. The uterus was stimulated by an electro-myographic (EMG) needle electrode and the cervical pressure recorded by a balloon-tipped catheter. The test was repeated in seven women after the uterus had been anaesthetized. In the other seven patients, the response of both the uterine EMG and pressure to cervical dilatation was registered. The EMG needle electrode was then inserted into the cervix and the uterine pressure response to both stimulation and dilatation of the non-anaesthetized and anaesthetized cervix was recorded. Uterine muscle stimulation led to a cervical pressure drop from a mean of 15.8 +/- 6.6 to 5.3 +/- 2.2 cm H2O (P < 0.01). The cervical pressure did not respond to stimulation of the anaesthetized uterus. Cervical dilatation caused increase of the uterine pressure from a mean of 16.2 +/- 5.2 to 42.8 +/- 10.5 cm H2O (P < 0.01), whereas cervical stimulation effected a uterine pressure drop to a mean of 3.6 +/- 1.8 cm H2O (P < 0.01). Stimulation or dilatation of the anaesthetized cervix did not cause uterine pressure changes. The invariable cervical dilatation upon uterine stimulation suggests a reflex relationship which we have named 'utero-cervical inhibitory reflex' (UCIR). It seems that the reflex comes into action during labour and in conditions of uterine retention of blood or a dead ovum. Its impairment may interfere with cervical dilatation or lead to cervical incompetence. The UCIR could be included as an investigative tool in utero-cervical disorders.

Adult↗

PubMedDate not supplied

Conditioning the middle ear reflex at sensation levels below reflex threshold: air jet and electrical stimulation.

An ABAB functional analysis, conditioning and generalization, design was used in 3 experiments (2 were formal studies and 1 was empirical in nature) to investigate the conditionability of the middle ear reflex. The conditioned stimuli were subreflex threshold pure tones of various frequencies and intensities. The unconditioned stimulus (UCS) was an auricular air jet to the contralateral ear in the first experiment and cutaneous electrical stimulation to the ipsolateral, probe ear in the last 2 experiments. Reflexes were monitored by an otoadmittance meter, storage oscilloscope, and strip chart recorder. In the first experiment (air jet UCS), no subjects met the conditioning criterion within the maximum presentation of 400 paired trials, despite pilot evidence which indicated conditioning was feasible. In the second experiment (electrical stimulation UCS), 2 subjects met conditioning criterion; however, only one subject reconditioned and demonstrated partial generalization to other conditioned stimuli. In the third experiment (electrical stimulation UCS), one of 3 subjects who had previously been unconditionable with the air jet UCS met conditioning and reconditioning criterion and demonstrated partial generalization. Results indicate that the middle ear reflex can be conditioned to be elicited by subreflex threshold pure tones, however, results are limited.

Adult↗

PubMed2004

Effects of 3,4-methylenedioxymethamphetamine ('Ecstasy') on the jaw-opening reflex and on the alpha-adrenoceptors which regulate this reflex in the anesthetized rat.

Bruxism, principally jaw clenching, is frequently observed in users of the recreational drug 3,4-methylenedioxymethamphetamine (MDMA). It has been suggested that during bruxism a reduction of the activity of oral protective reflexes occurs. In this study we investigated the effects of intravenously administered MDMA on the digastric electromyographic responses elicited by orofacial electrical stimulation in the rat. We also assessed the effects of either the administration of a single dose (20 mg kg(-1), s.c.) or repeated doses of MDMA (same dose, twice a day, for 4 d) on the jaw-opening reflex (JOR) and on the sensitivity of the alpha(2)-adrenoceptors which, in an inhibitory way, regulate it. Increasing doses of MDMA (1-29440 micro g kg(-1)) induced an incomplete inhibition of JOR and 50% inhibition (ED(50)) at 2550 micro g kg(-1); maximal inhibition was 88%. The repeated treatment with MDMA led to an enhancement of the inhibition of JOR induced by the alpha(2)-agonist, clonidine (ED(50) was reduced by 77%), indicating an increased sensitivity of the alpha(2)-adrenoceptors. This study shows that the intravenous administration of MDMA reduces the JOR while repeated doses of the drug enhance the inhibitory noradrenergic mechanisms which regulate the reflex. The results also allow speculation that a reduction of JOR may underlie the occurrence of episodes of bruxism in MDMA users.

Adrenergic Uptake Inhibitors↗