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PubMed1988

Stabilizing gaze reflexes in the pigeon (Columba livia). I. Horizontal and vertical optokinetic eye (OKN) and head (OCR) reflexes.

A quantitative study of horizontal and vertical optokinetic nystagmus (OKN) and optocollic reflex (OCR) has been performed in the pigeon using the search-coil technique. The reflexes were analysed in response to either velocity steps or sinusoidal stimulation. Results show that: 1. In response to a velocity step stimulation, the slow phase velocity of both OKN and OCR increases gradually to reach a steady state level. When the stimulation stops in the dark, After Responses (OKAN-I, OKAR-I) occur. Time constants of the OKN charge (or OCR charge) and of the After Responses are lower for vertical than for horizontal responses. 2. In the free-head condition, both the head and the eye display a synchronized nystagmus which add their effects. However, the head reflex (OCR) accounts for about 80-90% of the entire linear gaze response (head + eye), except for the vertical steady state responses which are wholly accomplished by the head (OCR). 3. Both closed-loop and open-loop gains of steady state responses are higher for horizontal than for vertical reflexes. Vertical OCR, horizontal OKN and vertical OKN show properties of binocular integration, the response gain being higher for binocular than for monocular stimulations. By contrast, the horizontal OCR shows little binocular integration but displays a higher response gain for monocular stimulation, compared to horizontal OKN. 4. The horizontal OKN elicited by both monocular and binocular stimulation is asymmetrical, the gain being higher when the eye is driven by a temporo-nasal stimulation. In contrast, both vertical OKN and vertical OCR are practically symmetrical. 5. While both the gain of horizontal OKN and its linear range (up to 20 degrees/s) are improved when the head is free (gaze gain close to 1 up to 40 degrees/s), the vertical OKN and the vertical OCR have similar gain profiles and similar domains of linearity (up to 10 degrees/s). 6. In response to increasing the frequency of a sinusoidal stimulation at constant peak velocity, all the reflexes display a drop in gain and a strong increase of phase lag. The phase increase is greater for horizontal than for vertical reflexes. On the other hand, both gain and phase are higher for OCR than for OKN, both in the horizontal plane as well as in the vertical plane. 7. For sinusoidal stimulations, when the peak velocity (PV) is increased at a constant frequency (0.03 Hz), nonlinearities appear (drop in gain, phase increase) both for OKN and OCR.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

Sensitivity of pulmonary chemo reflexes and lung inflation reflexes to repetitive stimulation and to inhibition with lidocaine and morphine.

To study reflex responses caused by stimulation of pulmonary C-fibers and lung inflation, we used a preparation in which the left pulmonary artery and veins were ligated and cannulated and the right and left bronchi were cannulated separately in open-chest dogs. These experiments were performed to establish whether the reflex responses to injections of 150 micrograms of capsaicin through the left pulmonary circulation and inflations of this left lung to 30 cm H2O would be diminished if repeated frequently. Furthermore, the sensitivities of the reflex responses evoked by these capsaicin injections and by left lung inflations (LLI) to blockade with lidocaine or with morphine were studied. Both repeated injections of capsaicin into the left pulmonary circulation and repeated inflations of the left lung for up to 100 min produced a persistent triad of reflex responses: bradycardia, hypotension, and cessation of diaphragmatic contractions. Lidocaine injections (50 mg) into the pulmonary artery of the vascularly isolated lung abolished all reflex responses to subsequent injections of capsaicin, but only attenuated the triad of responses to subsequent left lung inflations by half. Morphine sulfate (60 mg) administered to the pulmonary vascular bed of the isolated lung reduced, but did not eliminate, the triad of reflex responses to subsequent capsaicin injections and lung inflations. The influences of morphine upon capsaicin and lung inflation responses were not abolished by naloxone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Role of positive urethrovesical feedback in vesical evacuation. The concept of a second micturition reflex: the urethrovesical reflex.

Upon feeling the urge to urinate, the urinary bladder contracts, the urethral sphincters relax and urine flows through the urethra. These actions are mediated by the micturition reflex. We investigated the hypothesis that vesical contraction is maintained by positive feedback through continuous flow of urine through the urethra, and that the cessation of urine flow aborts detrusor contraction. Normal saline was infused into the urinary bladders of 17 healthy volunteers (age 35.2 years+/-4.2(SD); ten women and seven men) at a rate of 100 ml/min. On urge, which occurred at a mean volume of 408.6 ml+/-28.7 of saline, the subject micturated while the vesical and urethral pressures during voiding were being recorded; residual urine was measured. The test was repeated after anesthetizing the urethra with xylocaine gel or, on another occasion, after applying a bland gel. On micturition, the urine was evacuated as a continuous stream without straining; no residual fluid was collected. After urethral anesthetization, the fluid came out of the urethra in multiple intermittent spurts and only with excessive straining. There was a large amount of residual fluid (184.6 ml+/-28.4). The results of bland gel application showed no significant difference ( P>0.05) from those without gel. Detrusor contraction during micturition is suggested to be maintained by positive urethrovesical feedback elicited by the continued passage of urine through the urethra. This feedback seems to be effected through the urethrovesical reflex, which produces vesical contraction on stimulation of the urethral stretch receptors. Abortion of this reflex by urethral anesthetization resulted in failure of detrusor contraction and excessive straining was needed to achieve bladder evacuation in multiple spurts. The urethrovesical reflex is thus assumed to constitute a second micturition reflex responsible for the continuation of detrusor contraction and urination. The role of this reflex in the pathogenesis of micturition disorders needs to be studied.

Adult↗

PubMed1985

The flexor reflex--influence of stimulus parameters on the reflex response.

The flexor reflex evoked in the tibialis anterior muscle by stimulation of the medial plantar nerve was investigated in 54 normal subjects. Three main reflex components were identified (excitation--inhibition-- excitation), the early excitation being composed of two subcomponents. Occasionally, a fourth (excitatory) reflex component was seen breaking through EMG inhibition. The individual reflex components were differentially susceptible to facilitatory influences which suggested transmission via a central multichannel system. Methodological experiments showed that the amplitudes and to some degree also the latencies of the individual reflex components were modified by both the parameters of the stimulus as well as by the degree of pre-innervation. However, the patterning of the reflex response was basically independent from methodological permutations.

Adult↗

PubMed1991

The cause of increased pupillary light reflex latencies in diabetic patients: the relationship between pupillary light reflex and visual evoked potential latencies.

In 42 diabetic patients the relationship between the latency of the pupillary light reflex and the pattern reversal visual evoked potential (P100) was examined. Fifty-five percent of diabetic patients had pupillary light reflex latencies above the normal range. In 19% the visual evoked potentials were prolonged when compared to the normal range. Latencies of pupillary light reflexes and VEPs showed no correlation. There was a minimal correlation between the presence of retinopathy and prolongation of both the pupillary light reflex and the visual evoked response latency (kappa coefficients respectively: 0.31, P less than 0.01 and 0.36, P less than 0.02). The presence of an increased pupillary light reflex latency was positively correlated with a reduced respiratory sinus arrhythmia (kappa coefficient: 0.58, P less than 0.0001). Increased VEP latencies showed no correlation with signs of cardiovascular autonomic neuropathy. We conclude that the afferent optic pathway can be affected in diabetic patients. However, prolongation of pupillary light reflex latency in diabetic patients is primarily due to an efferent pupillary defect and represents parasympathetic dysfunction.

Adult↗

PubMed1985

Blink reflex in patients with hemispheric cerebrovascular accident (CVA). Blink reflex in CVA.

A blink reflex consists of an early unilateral component, R1, and a late bilateral component, R2. During an acute phase of hemispheric cerebrovascular accident, R1 and R2 were abnormal in 30 and 50 of 66 patients, respectively. Paired stimuli usually corrected R1 but not R2, which was profoundly suppressed. The discrepancy between polysynaptic R2 and oligosynaptic R1 indicates a greater disfacilitation at the level of interneurons than at the motoneuron, which serves as the final common path. Abnormality of R2 occurred bilaterally with stimulation on the affected side of face and contralaterally after stimulation on the normal side in 31 patients. This finding suggests a diffuse loss of internuncial excitability, contralateral to the hemispheric lesion. Changes of R2 implicated the brainstem pathways forming the afferent and efferent arc of the reflex in 7 and 8 patients, respectively. The remaining 4 comatose patients had no R2 irrespective of stimulus sites. Clinical localization of the hemispheric lesion showed no consistent correlation with the type of blink reflex abnormalities. The CT scans revealed widely scattered changes in 29 patients with abnormal blink reflex but with a tendency to overlap in the inferior Rolandic area. This contrasted with conspicuous sparing of the inferior post-central region in 10 patients with normal blink reflex. These findings suggest the presence of crossed facilitation to this reflex from wide areas of the cortex but most prominently from the sensory representation of the face.

Acute Disease↗

PubMed1990

Levator-urethral reflex. A new reflex with clinical significance.

A preliminary study of a new reflex which I called "levator-urethral reflex" is presented. Twenty-three volunteers were studied. Two concentric needle electrodes were introduced: one in the levator ani muscle (stimulating electrode) and the other in the external urethral sphincter (recording electrode). Levator stimulation evoked external sphincter contraction in all the subjects. The anesthetized sphincter did not respond while the saline-infiltrated one responded. The mean latency of the reflex was 168 ms. The levator-urethral reflex regulates the relation between micturition and continence. Reflex external urethral sphincter contraction keeps micturition under control despite the involuntary opening of the vesical neck as a result of levator contraction. Measurement of the latency of the reflex could be an objective and accurate means of investigating micturition disorders.

Adolescent↗

PubMed1984

Spinal and supraspinal reflex pathways of cardio-cardiac sympathetic reflexes.

In anaesthetized cats recordings were made of reflex responses recorded in the inferior cardiac nerves of one side while stimulating the inferior cardiac nerves of the opposite side. Three reflex potentials were observed: an early (about 25 ms) reflex and a later (about 60 ms) reflex due to A afferent fibre excitation and a reflex with a much longer latency (about 180 ms) due to C afferent fibre excitation. Following spinal transection at C2 only the early A reflex remained and this was augmented.

Afferent Pathways↗

PubMed2005

Modulation of cutaneous reflexes in hindlimb muscles during locomotion in the freely walking rat: A model for studying cerebellar involvement in the adaptive control of reflexes during rhythmic movements.

This study aims to demonstrate stepphase-dependent modulation in the gain of cutaneously triggered reflexes in the freely locomoting rat. Electromyographic recordings of biceps femoris (mainly involved in knee flexion) and gastrocnemius (mainly involved in ankle extension) muscles were continuously monitored during locomotion and cutaneous reflexes were induced by subcutaneously placed stimulation electrodes in the lateral malleolal region. The results show that the reflex responses in both muscles during locomotion were generally reduced compared to reflexes induces in rest. For the biceps femoris reduction of reflex gain was highest during the stance phase whereas for the gastrocnemius the period of highest depression was found during the swing phase. We conclude that stepphase-dependent modulation of peripheral reflexes can be measured in freely locomoting rats and generally concur with previous studies in cat and man that this type of modulation may be functionally important for maintaining and adjusting gait. Moreover, although the mechanism of inducing and maintaining this modulation is not fully known, it is now open to experimental investigation in rodents.

Adaptation, Physiological↗

PubMedDate not supplied

The vestibulosympathetic reflex in humans: neural interactions between cardiovascular reflexes.

1. Over the past 5 years, there has been emerging evidence that the vestibular system regulates sympathetic nerve activity in humans. We have studied this issue in humans by using head-down rotation (HDR) in the prone position. 2. These studies have clearly demonstrated increases in muscle sympathetic nerve activity (MSNA) and calf vascular resistance during HDR. These responses are mediated by engagement of the otolith organs and not the semicircular canals. 3. However, differential activation of sympathetic nerve activity has been observed during HDR. Unlike MSNA, skin sympathetic nerve activity does not increase with HDR. 4. Examination of the vestibulosympathetic reflex with other cardiovascular reflexes (i.e. barorereflexes and skeletal muscle reflexes) has shown an additive interaction for MSNA. 5. The additive interaction between the baroreflexes and vestibulosympathetic reflex suggests that the vestibular system may assist in defending against orthostatic challenges in humans by elevating MSNA beyond that of the baroreflexes. 6. In addition, the further increase in MSNA via otolith stimulation during isometric handgrip, when arterial pressure is elevated markedly, indicates that the vestibulosympathetic reflex is a powerful activator of MSNA and may contribute to blood pressure and flow regulation during dynamic exercise. 7. Future studies will help evaluate the importance of the vestibulosympathetic reflex in clinical conditions associated with orthostatic hypotension.

Adrenergic Fibers↗

PubMed2004

Does spasticity result from hyperactive stretch reflexes? Preliminary findings from a stretch reflex characterization study.

PURPOSE: To characterize the stretch reflex response of the biceps brachii in stroke patients with elbow spasticity (prior to or within 15 min of treatment with botulinum toxin) and non-impaired volunteers with the aim of quantifying the stretch reflex excitability and observe the differences between the groups. METHODS: A cross-sectional study. Stretch reflexes from the biceps brachii were elicited following a controlled elbow extension. The amplitude, latency, rise time and duration, calculated from surface EMG recordings from the biceps brachii, were used to characterize the stretch reflex response. RESULTS: Seventeen non-impaired and 14 stroke patients participated. The amplitude was significantly lower in stroke patients than in non-impaired volunteers (p<0.05). The latency was significantly shorter in stroke patients than in non-impaired volunteers (p<0.05). There were no significant differences in rise time or duration (p>0.10). DISCUSSION: Reduction in the amplitude in stroke patients was unexpected suggesting the stretch reflex is not necessarily hyper-excitable in people with clinically diagnosed spasticity. Latency differences suggest decreased presynaptic inhibition and/or increased motor neurone excitability can occur following a stroke. However, carry over effects from previous botulinum toxin treatment may have confounded amplitude measurements. Further work evaluating the excitability of the stretch reflex independent of Botulinum toxin and its contribution to resistance to passive stretching is being conducted.

Adult↗

PubMed1987

Long-latency spinal reflex in man after flexor reflex afferent stimulation.

Electromyographic (EMG) flexor muscle responses evoked by electrical stimulation of ipsilateral peripheral nerves were studied in 16 patients with clinically complete spinal cord transection. Stimuli were applied either to a cutaneous nerve (sural) or to a mixed nerve (tibial) and muscle responses were recorded from tibialis anterior, biceps femoris and rectus femoris. EMG recordings after both sural and tibial nerve stimulation showed that distinct early and late ipsilateral flexor muscle responses could be elicited. This distinction was more evident for tibialis anterior. The latency of the early responses averaged approximately 100 ms with sural and 75 ms with tibial nerve stimulation. This corresponds to the latency of the flexion withdrawal reflex previously described in normal man. After sural stimulation, the early reflex appeared in biceps femoris at a threshold intensity not significantly different from that in normal man given the same stimulation parameters. Late responses appeared after a longer latency (130 ms) and at a lower threshold than the early flexor reflex. In all patients a striking feature of the late response was that its latency increased with increasing stimulus intensity, the maximum latency being as long as 450 ms. This increase also occurred with increasing duration of high intensity stimulus trains. Neither the appearance of a late response nor its latency increase could be explained by a peripheral loop due to a preceding muscle contraction (from either motor axon stimulation or motoneuronal discharge corresponding to the early flexion reflex). It was therefore concluded that both were directly elicited by the afferent volley set up by electrical stimulation. The low threshold of the late reflex corresponded to the excitation of relatively rapidly conducting afferents and its central spinal delay was more than 100 ms. The late reflexes were compared with those described by Andén et al. (1964) in the acute spinal cat injected with DOPA and were found to have similar characteristics. The mechanism for the increase in latency of the late response is discussed in relation to the interpretation of Lundberg (1979).

Adolescent↗

PubMed1997

Alfentanil blocks reflex pupillary dilation in response to noxious stimulation but does not diminish the light reflex.

BACKGROUND: Estimation of the mu-agonist opioid effect in anesthetized and paralyzed patients is often imprecise and can be obscured by concomitant administration of drugs that affect the sympathetic nervous system, such as beta-adrenergic blocking agents. As an alternative to hemodynamic measures of opioid effect, the authors tested the hypothesis that the pupillary light reflex or pupillary reflex dilation correlated with alfentanil concentrations during isoflurane anesthesia. METHODS: Six volunteers were anesthetized on 4 days with 0.8% isoflurane. Alfentanil was administered intravenously to target total plasma concentrations of 0, 25, 50, and 100 ng/ml. A 5-s tetanic electrical stimulus was applied to the skin. Pupil size and the pupillary light reflex were recorded before and after alfentanil administration, and before and for 8 min after the stimulus. RESULTS: Alfentanil exponentially impaired reflex pupillary dilation, decreasing the maximum response amplitude from 5 mm at 0 ng/ml, to 2.3 mm at 25 ng/ml, to 1.0 mm at 50 ng/ml, and finally to 0.2 mm at 100 ng/ml. In contrast, only the highest concentration of alfentanil depressed the dilation of the pupil in the first 2 s after the stimulus. Alfentanil administration had no effect on the pupillary light reflex. CONCLUSIONS: Dilation of the pupil in response to a noxious stimulus is a measure of opioid effect in isoflurane-anesthetized volunteers. In contrast, the pupillary light reflex is unaffected by alfentanil during isoflurane anesthesia. These data suggest that stimulus-induced pupillary dilation may be used to evaluate the analgesic component of a combined volatile and opioid anesthetic.

Adult↗

PubMed1992

Rectourethral reflex: description of a reflex and its clinical significance. A preliminary report.

The present communication studies the technique and clinical significance of a new reflex which I called 'rectourethral reflex'. The study comprised 29 subjects with normal anorectal and urinary functions. The procedure consisted of inflating the rectum with a balloon connected to the distal part of a catheter. The electromyographic activity of the external urethral sphincter was recorded using a concentric needle electrode inserted into the muscle. The procedure was repeated in 10 patients after muscle infiltration with Xylocaine or saline. Rectal distension evoked external urethral sphincter contraction in all the subjects. The amplitude of motor action potentials increased with increasing rectal distension. Anesthetized muscles did not respond, while saline-infiltrated muscles responded. The latency of the reflex decreased with increasing volume of rectal inflation. The reflex harmonizes the relation between defecation and micturition. It guards against involuntary micturition when the rectal detrusor is distended. Changes in amplitude and latency of the reflex may be significant in assessing rectourinary disorders. The reflex could thus be used as an investigative tool in the diagnosis of such disorders.

Adult↗

PubMedDate not supplied

Hoffmann reflex from foreleg flexor nerves in cats: lateralization, picrotoxin, strychnine, crossed flexor reflex.

Hoffmann (H) reflexes from foreleg flexor nerves were studied in cats. The right and left flexor nerves were stimulated and H reflexes were recorded from the same nerves. Paw preference was assessed by a food reaching test. Stimulation of the right median nerve elicited mono- and polysynaptic reflexes from the left ulnar nerve (crossed flexor nerve). Picrotoxin depressed, and strychnine increased H reflexes from both sides without affecting the spinal motor asymmetry. H reflexes were found to be larger on the left than the right side in right-preferent cats and vice versa in left-preferent cats. The right H-reflex recovery curve was higher than left in right-preferent cats. The inhibitory period of the recovery cycle disappeared after picrotoxin and changed to facilitation for the nonpreferred side. Strychinine caused bilateral, nearly-synchronous motoneuronal discharges from the right and left flexor nerves; the discharges originating from the left side preceded those from the right side in a right-preferent cat. These results indicate that spinal motor activity predominates on the nonpreferred side, which would be a prerequisite for postural adjustments during paw use in cats. This asymmetric motor organization in the forelegs of cats having quadrpedal locomotion seems to be similar to asymmetric motor organization in legs in humans.

Animals↗

PubMed2001

The Bezold-Jarisch reflex. A historical perspective of cardiopulmonary reflexes.

The Bezold-Jarisch reflex is an eponym for a triad of responses (apnea, bradycardia, and hypotension) following intravenous injection of veratrum alkaloids in experimental animals. The observation was first reported in 1867 by von Bezold and Hirt, and confirmed in 1938-1940 by Jarisch. The triad depends on intact vagi and is mediated through cranial nervous medullary centers controlling respiration, heart rate, and vasomotor tone. The respiratory effects are mediated through pulmonary vagal afferents and the bradycardia and vasodepression through cardiac vagal afferents. The veratrum alkaloids activate all known receptors in the carotid-aortic and cardiopulmonary areas. The cardiopulmonary receptors (baroreceptors, cough receptors, and parenchymal stretch receptors) also respond to other chemical substances: nicotine, capsaicin, venom, antihistaminics, halogenated anesthetics, diguanides, and serotonin (5-hydroxytryptamine). Derivatives of last-mentioned amine activate Type 1, 2, or 3 receptors and have potential therapeutic use. Since several types of cardiopulmonary receptors participate in the Bezold-Jarisch reflex, it has been difficult to develop a blockade to one type of receptor for therapeutic use (cough, bronchospasm, pulmonary hypertension, or coronary vasospasm). Axon reflexes influence pulmonary blood vessels, bronchial blood vessels, and bronchial smooth muscles. These intrapulmonary reflexes need further study as to how they relate to the Bezold-Jarisch reflex in health and disease. The cardiopulmonary and carotid-aortic reflexes can serve as defense mechanisms against chemical hazards that are likely to be inhaled in the workplace and in the environment.

Animals↗

PubMed1992

[Autonomic reflexes: focusing on the arterial baroreceptor-vasoconstrictor reflex].

The arterial baroreceptor-sympathetic vasoconstrictor reflex (baroreceptor reflex), among autonomic reflexes, is summarized. Arterial baroreceptor afferents terminate in the caudal part of the nucleus tractus solitarius. Excitation of the baroreceptor afferents activates neurons in the caudal ventrolateral medulla that send axonal projections to the rostral ventrolateral medulla. These neurons (CVLM neurons) then inhibit tonic activity of sympathoexcitatory reticulospinal neurons in the rostral ventrolateral medulla (RVLM neurons). Tonic activity of RVLM neurons are responsible for tonic activity of the peripheral vasoconstrictors. These two kinds of neurons are essential neuronal components for the baroreceptor reflex. Both the neurons may also participate in various vasoconstrictor reflexes, such as the somato-and viscero-sympathetic vasoconstrictor reflexes.

Autonomic Nervous System↗

PubMed2006

Blink reflex, H-reflex and nerve-conduction alterations in leprosy patients.

Peripheral nerve lesions are the most important cause of disability in leprosy patients. Electrophysiological studies are used in the diagnosis and prognosis of neuropathy. Nerve conduction is the most frequently used electrophysiological test method to detect neuropathy, although it evaluates only a part of the peripheral nervous system. Blink reflex and H-reflex are electrophysiological tests which evaluate facial and trigeminal nerve function. This study determined the frequencies of blink reflex, H-reflex and motor and sensory nerve conduction alterations in twenty five heterogeneous, clinic patients with lepromatous leprosy and a control group of 20 healthy subjects. Study results showed a decrease in motor and sensory nerve conduction in 40% and 30%, respectively. In blink reflex (BR), right R1 was altered in latency in 20% of patients, left R1 in 20%, right ipsilateral R2 in 16%, left ipsilateral R2 in 20%, and right and left contralateral R2 were altered in 32% of patients. There was an absence of H-reflex in 16% (n = 4) and prolonged latency in 4% (n = 1).

Adult↗