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At least 109 records · Page 6Linked to original sources
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↗
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↗
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↗
PubMedDate not supplied

[Effect of a dominant focus created in the center of the wink reflex on the local defense reflex in the rabbit].

The paper deals with conjugated inhibition of rabbit's defensive limb reflex at formation of a dominant focus in the center of the eye-lid reflex. In the initial period of dominant focus formation, when the dominant comes through the stage of summation reflex, electrocutaneous limb stimulation induced, along with successive summation, temporary inhibition of the forming dominant focus. The dominant focus formed in the eye-lid center did not induce conjugated inhibition of the limb defensive reflex. In the study of the influence of the eye-lid reflex on the motor defensive one it was found that formation of temporary connection of summation reflex type, led to circulatory interaction between the centers.

Animals↗
PubMed1981

[Reflex effects of cough reflex on the tracheobronchial vascular tone (author's transl)].

In a previous paper, it was shown that the cough reflex was accompanied by a slight fall of systemic arterial pressure, tracheal constriction and tracheal vasodilation. In the present study, tracheobronchial muscular and vascular tones during the cough reflex were investigated using the blood perfused canine tracheal and bronchial preparations in situ. The cough reflex was elicited with electrical stimulation of the membraneous wall mucosa of the upper trachea. In the blood perfused tracheal preparation, a close intraarterial injection of atropine or bilateral vagotomy inhibited the tracheoconstriction but had no effect on the tracheal vasodilation during the cough reflex. In the blood perfused bronchial preparation, electrical stimulation of the upper tracheal mucosa induced bronchial constriction but not bronchial vasodilation. Lung inflation with air resulted in a bronchial vasodilation and which persisted even after a close intraarterial infusion of atropine and benzonatate and after bilateral vagotomy. These findings indicate that the tracheobronchial constriction response are primary reflex effects following coughing and the tracheobronchial vasodilation responses are secondary reflex effects induced by increase in internal pressure of the respiratory tract.

Animals↗
PubMed1994

Excitability of the soleus motoneuron pool revealed by the developmental slope of the H-reflex as reflex gain.

The excitability of a motoneuron (MN) pool was evaluated by the developmental slope of H-reflexes (Hslp) evoked at a range of a stimulus intensity less than the threshold of an M-response. The Hslp has been regarded as the "reflex gain", which is the changing rate in MN excitability as a function of the increase of Ia input to an MN pool. In a comparison of two parameters used in the H-reflex technique, such as the ratio of the maximal H-reflex to the maximal M-response and the ratio of the threshold of an H-reflex to that of an M-response, the Hslp was predicted to be a reasonable parameter to evaluate motoneuronal excitability, because the Hslp is free from the effect of any collision between the H-reflex discharge and the antidromic volley drived from the occurrence of an M-response within the alpha-efferents, and the Hslp can estimate the recruitment properties of a whole MN pool. The Hslp was alleviated during dorsi-flexion and steepened during plantar-flexion, according to the inhibitory or facilitatory synaptic modifications onto soleus MNs. The developmental slope of an M-response (Mslp), which shows the recruitment property of axons of soleus MNs, was alleviated especially in plantar-flexion. In order to exclude the peripheral neuromuscular factors in evaluating substantial MN excitability, the Hslp/Mslp is proposed as a more effective parameter than the Hslp.

Adolescent↗
PubMed1993

Development of the stretch reflex in the newborn: reciprocal excitation and reflex irradiation.

The stretch reflex is a spinal cord pathway between a muscle's stretch receptors and its own motor units. This reflex is thought to play an important role in normal motor function, because it is unique as a monosynaptic pathway, and because its hyperactivity is a hallmark of many motor disorders. We previously reported a difference in the stretch reflexes in healthy newborn infants and nonambulatory individuals with cerebral palsy (CP): these reflexes are characterized by responses from the stretched muscle and from the reciprocal or antagonist muscle. We proposed the existence of a functional spinal cord pathway that connects both agonist and antagonist muscles at a single joint. We hypothesized that this "reciprocal excitation" is a functional pathway of all newborn infants, which during the normal course of development of motor skills in infants is eliminated. If the CNS is damaged at birth, as in CP, the pathway of reciprocal excitation endures and is reinforced. In the current study of newborns, we recorded stretch reflex responses from all major muscle groups of the lower limb. This "irradiation of reflexes" is a normal phenomenon of the newborn CNS. This pathway becomes suppressed during normal maturation and control of coordinated limb movements.

Achilles Tendon↗
PubMed1996

The role of the spinal cord as a reflex center for the somatically induced reflex responses of splenic sympathetic and natural killer cell activity in anesthetized rats.

Somatic afferent regulation of splenic natural killer (NK) cell activity by hindpaw pinching has been proven, in anesthetized rats, to be a reflex response whose reflex center is in the brain and efferent arc is a splenic sympathetic nerve. Using central nervous system (CNS)-intact and acutely spinalized anesthetized rats, the present study aimed to examine the possibility of whether afferent stimulation (pinching) of the skin over the abdominal segments could influence cytotoxic activity of splenic NK cells and splenic sympathetic nerve activity at the spinal segmental level. In CNS-intact rats, pinching stimulation of the skin of the abdomen with surgical clamps for 30 min did not significantly change cytotoxic activity of splenic NK cells although splenic sympathetic nerve activity increased slightly. In acutely spinalized rats the same stimulation reduced cytotoxic activity of splenic NK cells and was accompanied by an intense reflex increase in splenic sympathetic nerve activity. It is concluded that the spinal cord is capable of producing propriospinally the reflex suppression of cytotoxic activity of splenic NK cells via reflex activation of the splenic sympathetic efferent nerve following stimulation to the abdominal segments whose afferent information enters the spinal cord at the same segments or segments overlapping the splenic sympathetic outflow. A possible mechanism of inhibition of this spinal reflex by inhibitory descending pathways is discussed.

Animals↗
PubMed1997

Olfactory-corporeal reflex: description of a new reflex and its role in the erectile process.

OBJECTIVE: The dog approaches the bitch and smells the vulva. The relationship which seems to exist between a special smell in the bitch and sexual arousal in the male dog was investigated. METHODS: 12 male dogs and 25 bitches were studied. The bitches were divided into five equal groups, each representing 1 of the 5 phases of the estrous cycle. A vaginal swab that soaked in the bitches' vaginal secretions was divided into two pieces: one was sent for estradiol and progesterone determination, and the other was smelt by the male dog. The responses of the intracorporeal pressure (IP) and the electromyographic activity of the bulbo- and ischiocavernosus (BC, IC) muscles of the male dog to the smelling of bitch's vaginal odor were assessed. The pressure response was also determined 10 min and 1 h after either the nasal mucosa or the corporeal tissue was anesthetized. RESULTS: Elevated IP was recorded in 12 of 12, 10 of 12 and 8 of 12 dogs smelling vaginal swabs of bitches in metestrus (p < 0.001), estrus (p < 0.001), and diestrus (p < 0.01), respectively. No pressure response occurred when the vaginal swab was smelt while the nasal mucosa or the corporeal tissue was anesthetized. The BC and IC muscles exhibited no response to smelling of the vaginal swab of bitches in any phase of the estrous cycle. The results were reproducible. CONCLUSIONS: The study showed that the IP increased with smelling of vaginal secretions containing high progesterone levels, whereas estradiol-17 beta did not effect IP elevations. The higher the progesterone level, the greater the IP. The increased IP is not due to BC and IC muscle contraction. It is postulated that a reflex relationship exists between IP elevation and olfactory stimulation. This reflex response was reproducible and was not evoked when the two arms of the reflex were anesthetized. We call this reflex 'olfactory-corporeal reflex'. This reflex seems to prime the male dog for sexual intercourse.

Animals↗
PubMed2001

Masseter reflex and blink reflex abnormalities in Chiari II malformation.

Masseter reflex and blink reflex were evaluated in 64 patients with a myelomeningocele and Chiari II malformation. In 46 patients, no brainstem signs or symptoms were present. Brainstem dysfunction related to Chiari II malformation occurred in 18 patients. The masseter reflex was more frequently abnormal in the symptomatic than asymptomatic patients (P = 0.02). Although the blink reflex was similarly affected in the two groups of patients (P > 0.1), it was very sensitive, being abnormal in 83% of symptomatic and 65% of asymptomatic patients. Concomitant abnormality of masseter reflex and the late contralateral blink reflex component (R2c) was almost exclusively found in symptomatic patients and reached the highest significance in separating the two groups (P = 0.002).

Adolescent↗
PubMed1993

Blink reflex and the masseter inhibitory reflex in patients with dystonia.

The excitatory and inhibitory interneuronal pathways in the brainstem are tested by examining the blink reflex and the masseter inhibitory reflex, respectively. We studied the R2 component of the blink reflex and the SP2 component of the masseter inhibitory reflex and their recovery cycle in 56 patients with various forms of dystonia. In patients with cranial, cervical, and generalized dystonia, but not in patients with extracranial segmental dystonia, the recovery cycle of both reflexes was enhanced. The recovery cycle of R2 and SP2 can demonstrate subclinical changes in excitability of brainstem interneurons. The degree of enhancement of the recovery cycles did not correlate, however, with the severity of clinical facial muscle impairment. In addition, the recovery cycles correlated positively with each other, showing that excitatory as well as inhibitory interneuronal pathways in the brainstem are perturbed in dystonia. Study of the trigemino-facial and trigemino-trigeminal reflexes provides an objective tool for assessing functional abnormalities in dystonia.

Adult↗
PubMed2002

Activation of mu-opioid receptors in rat ventrolateral medulla selectively blocks baroreceptor reflexes while activation of delta opioid receptors blocks somato-sympathetic reflexes.

The effects of activation of mu and delta-opioid receptors in the rostral ventrolateral medulla (RVLM) on somato-sympathetic, baroreceptor and chemoreceptor reflexes, as well as respiratory rhythmicity in sympathetic nerves, were examined in urethane anaesthetized (1.1-1.2 g/kg) and artificially ventilated Sprague-Dawley rats. Microinjection of the delta-opioid receptor agonist [D-Pen(2,5)]-enkephalin (DPDPE; 8 mM, 50 nl) bilaterally into the RVLM potently inhibited the post-inspiratory-related burst discharges of lumbar sympathetic nerve activity (LSNA) but had only limited effects on splanchnic sympathetic nerve activity (SSNA) and phrenic nerve discharge. Injection of DPDPE into the RVLM strongly attenuated the somato-sympathetic reflex (approximately 50-80%) evoked in the lumbar sympathetic nerve and splanchnic sympathetic nerve by tibial nerve stimulation but had no effect on baroreceptor reflexes and chemoreceptor reflexes evoked by aortic nerve stimulation and brief hypoxia, respectively. Injection of the mu-opioid receptor agonist, [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]-enkephalin (DAMGO; 4 mM, 50 nl), also elicited a greater inhibition of LSNA than SSNA accompanied by an abolition of phrenic nerve discharge. Injection of DAMGO inhibited the baroreceptor reflex without significant effect on either the somato-sympathetic or the chemoreceptor reflexes. We propose that opioid peptides diminish specific excitatory and inhibitory inputs to the presympathetic neurons in RVLM via distinct presynaptic receptor subclasses.

Action Potentials↗
PubMed1988

Stabilizing gaze reflexes in the pigeon (Columba livia). II. Vestibulo-ocular (VOR) and vestibulo-collic (closed-loop VCR) reflexes.

The vestibulo-ocular reflex (VOR) and the closed-loop vestibulo-collic reflex (CL-VCR) were investigated in the pigeon. The animals, placed either in the fixed-head condition (VOR) or in the free-head condition (CL-VCR) were rotated in darkness (vestibular responses) or in the presence of visual surroundings (visuo-vestibular responses). The linear range of the reflexes were determined both in the frequency and in the velocity domains. Results show that: 1. Pigeons develop a strong VOR, which presents the same asymmetry observed with the OKN, the gain being higher when the slow-phase occurs in the T-N direction. This asymmetry persists in the light (VOR + OKN). In the free-head condition, both the eye and the head display a synchronized nystagmus whose effects are additive. The head reflex (CL-VCR) contributes about 80% of the gaze stabilization. 2. In the medium-low frequency range, the head response (CL-VCR) has a lower gain than the VOR (head-fixed), but the gain of both reflexes increases with frequency, up to about 1 at 0.6-1 Hz. The gaze response (eye + head) presents an optimal gain above 0.06 Hz. The phase lead is higher for the VOR than for the CL-VCR (40 degrees and 32 degrees respectively at 0.03 Hz), but both phases also become nul around 1 Hz. The time constants are 6.5 s for the VOR, 8.5 s for the CL-VCR and 9.6 s for the gaze response (VOR + CL-VCR). 3. While the VOR gain shows a saturation at peak stimulation velocities (PV) higher than 20 degrees/s (at 0.3 Hz), the CL-VCR gain is linear at least up to 60 degrees/s (the highest PV used). However, the phase lead declines when the PV is greater than 20 degrees/s, both for the VOR and the CL-VCR. 4. When the vestibular stimulation is delivered in the light (visuo-vestibular stimulation), there is no phase shift. The VOR gain (fixed-head) is optimal and linear over the entire frequency range, but it saturates for PV higher than 40 degrees/s. In the free-head condition, while the gaze gain is linear and close to 1 in both the frequency and the velocity domains, the head response gain (CL-VCR) remains lower especially in the low frequency and in the low velocity ranges.

Animals↗