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PubMed2005

Acute effect of amiodarone on cardiovascular reflexes of normotensive and renal hypertensive rats.

The aim of the present study was to evaluate the effect of amiodarone on mean arterial pressure (MAP), heart rate (HR), baroreflex, Bezold-Jarisch, and peripheral chemoreflex in normotensive and chronic one-kidney, one-clip (1K1C) hypertensive rats (N = 9 to 11 rats in each group). Amiodarone (50 mg/kg, iv) elicited hypotension and bradycardia in normotensive (-10 +/- 1 mmHg, -57 +/- 6 bpm) and hypertensive rats (-37 +/- 7 mmHg, -39 +/- 19 bpm). The baroreflex index (deltaHR/deltaMAP) was significantly attenuated by amiodarone in both normotensive (-0.61 +/- 0.12 vs -1.47 +/- 0.14 bpm/mmHg for reflex bradycardia and -1.15 +/- 0.19 vs -2.63 +/- 0.26 bpm/mmHg for reflex tachycardia) and hypertensive rats (-0.26 +/- 0.05 vs -0.72 +/- 0.16 bpm/mmHg for reflex bradycardia and -0.92 +/- 0.19 vs -1.51 +/- 0.19 bpm/mmHg for reflex tachycardia). The slope of linear regression from delta pulse interval/deltaMAP was attenuated for both reflex bradycardia and tachycardia in normotensive rats (-0.47 +/- 0.13 vs -0.94 +/- 0.19 ms/mmHg and -0.80 +/- 0.13 vs -1.11 +/- 0.13 ms/mmHg), but only for reflex bradycardia in hypertensive rats (-0.15 +/- 0.02 vs -0.23 +/- 0.3 ms/mmHg). In addition, the MAP and HR responses to the Bezold-Jarisch reflex were 20-30% smaller in amiodarone-treated normotensive or hypertensive rats. The bradycardic response to peripheral chemoreflex activation with intravenous potassium cyanide was also attenuated by amiodarone in both normotensive (-30 +/- 6 vs -49 +/- 8 bpm) and hypertensive rats (-34 +/- 13 vs -42 +/- 10 bpm). On the basis of the well-known electrophysiological effects of amiodarone, the sinus node might be the responsible for the attenuation of the cardiovascular reflexes found in the present study.

Amiodarone↗
PubMedDate not supplied

Grasp-reflex strength from right and left hands in relation to serum cortisol level and fetal position in human neonates.

The grasp-reflex strengths from right (R) and left (L) hands were studied in human neonates in relation to serum cortisol levels and fetal position. In males with right-ear out, there was no correlation between grasp-reflex strength from right hand and cortisol. The grasp-reflex strength from left hand significantly decreased as cortisol increased linearly in these subjects. In males with left-ear out, the grasp-reflex strengths from right and left hands were found to be negatively linearly correlated with serum cortisol level. In females with right-ear out, the grasp-reflex strength from right hand was not significantly correlated with cortisol, but grasp reflex from left hand linearly decreased as cortisol increased. In females with left-ear out, only the grasp reflex from right hand linearly increased with cortisol. Only in males with right-ear out, the R-L grasp-reflex strength linearly increased from left dominance toward right dominance. It was concluded that the stress hormone cortisol may be disadvantageous and/or advantageous for the prenatal development of the right and left brain according to fetal position; cortisol may also affect the emergence of cerebral lateralization.

Embryonic and Fetal Development↗
PubMed1999

Electrically elicited blink reflex in horses with trigeminal and facial nerve blocks.

OBJECTIVE: To reassess reference values for the components of the electrically induced blink reflex, document reference values for facial motor nerve conduction velocity, and demonstrate usefulness of the blink reflex as a diagnostic tool in peripheral facial and trigeminal nerve dysfunction in horses. ANIMALS: 10 healthy adult horses (8 males, 2 females) without neurologic abnormalities. PROCEDURE: Blink reflex tests were performed by electrical stimulation of the supraorbital nerve and facial (auriculopalpebral) nerve. Reflex and direct muscle-evoked potentials of the orbicularis oculi muscles were recorded from concentric needle electrodes inserted bilaterally in these muscles. Supraorbital and auriculopalpebral nerve blocks were performed by lidocaine hydrochloride injections. RESULTS: Supraorbital nerve stimulation elicited 2 or 3 ipsilateral and 1 contralateral reflex muscle potential in the orbicularis oculi muscles. Auriculopalpebral nerve stimulation elicited a direct and a reflex potential in the ipsilateral orbicularis oculi muscle. After left supraorbital nerve block, no responses could be elicited ipsilaterally or contralaterally upon stimulation of the blocked nerve, but bilateral responses were obtained upon stimulation of the right supraorbital nerve. After right auriculopalpebral nerve block, no responses were recorded from the right orbicularis oculi muscle upon stimulation of left or right supraorbital nerves. CONCLUSIONS AND CLINICAL RELEVANCE: Reference values for the components of the blink reflex and facial motor nerve conduction velocity will allow application of these tests to assist in the diagnosis of equine neurologic disorders involving the trigeminal and facial nerves, the brainstem, and the cranial end of the cervical segment of the spinal cord. This study reveals the usefulness of the blink reflex test in the diagnosis of peripheral trigeminal and facial nerve dysfunction in horses.

Animals↗
PubMed2003

[Contralateral electrically evoked reflex of the musculus stapedius in patients with cochlear implant].

Registration of electrically evoked reflex is widely applied in rehabilitation of patients by cochlear implantation. As a rule, visual assessment of the ipsilateral reflex is made intraoperatively for functional evaluation of surgical results. Of interest is use of contralateral electrically evoked reflex of the musculus stapedius in the course of adjustment of the speech processor. We studied the latter reflex in 20 patients with cochlear implants Cl24M and Cl22 made by 'Cochlear'. 13 patients used Sprint processors, 7 patients - Spectra ones. Zodiak impedansometer registered the reflex which was recorded in 12 patients. The threshold of the reflex registration correlated well with comfortable perception of loudness. Most of the patients evaluated threshold (for the reflex) sound perception as the sound of moderate loudness. The conclusion is made that registration and analysis of the contralateral electrically evoked reflex can assess a comfortable stimulation level in adjustment of speech processors in patients with cochlear implants.

Adolescent↗
PubMed1986

[Chronological changes in the blink reflex and MRI in a patient with lateral medullary infarction].

Recently, the brainstem pathways of bilateral late reflexes (R2) of electrically elicited blink reflex have been well established. An afferent delay or block of the late reflexes is closely related to a lesion of the lateral medullary portion. The chronological alteration of blink reflex (BR) was studied to compare with radiological abnormalities on MRI in a patient with lateral medullary infarction on the right side. A diagnosis of Wallenberg syndrome was made clinically and location of the lesion was identified in detail by MRI. The infarcted region which was well demonstrated as an increased intensity area on SE images obtained 52 days after the onset of symptoms was much smaller than that on SE as well as on IR image 21 days after the onset of symptoms. Therefore, it was concluded that more than half of the increased intensity area on the SE images obtained 21 days after the onset of symptoms recovered from the condition of being extremely damaged by ischemia on the right lateral medullary portion in this patient. On the other hand, in the initial BR 26 days after the onset of symptoms, the late reflexes (R2) were consistently absent bilaterally when the affected side (right) was stimulated and normal when the normal side (left) was stimulated. This type of BR abnormality is compatible with an afferent block of late reflexes (R2). The early reflex (R1) was normal on either side. Whereas in the second BR at 55 days after the onset of symptoms, the late reflexes turned to be normal in latency when the right side was stimulated.(ABSTRACT TRUNCATED AT 250 WORDS)

Blinking↗
PubMed1983

Three types of blink reflex evoked by supraorbital nerve, light flash and corneal stimulations.

Three types of blink reflex were evoked by 1) supraorbital nerve stimulation, 2) light flash stimulation and 3) corneal touch. The blink reflex response was recorded simultaneously for both eyes by electromyography of the orbicularis oculi muscles of the lower eyelid. After supraorbital nerve stimulation, ipsilateral early response (R1) and bilateral late responses (R2) were demonstrated. The light flash stimulation evoked the photic early and late responses. The latency times of the R1, R2 and the photic early responses were determined in 22 normal subjects. The corneal touch was exactly timed using a new device and the latency time of the corneal blink reflex was determined. The latency of the ipsilateral corneal blink reflex was significantly shorter than that of the contralateral reflex. The blink reflexes by supraorbital nerve stimulation and light flash were studied concurrently in 7 patients with neurological disorders of vascular origin. The photic reflex was disturbed by bilateral occipital lobe lesions and also by affection of the rostral midbrain. The reflexes were not affected by lesions in the medial longitudinal fasciculus but were disturbed by widespread brainstem lesions of Foville syndrome. Clinical significance of a combined use of the supraorbital nerve and light flash stimulation was emphasized.

Adult↗
PubMedDate not supplied

[Interaction of instrumental habits in the sphere of heterogeneous conditioned reflex activity].

The phenomenon of interference of one reflex with another was observed in dogs during performance of heterogeneous instrumental conditioned reflexes elicited in a stereotype order. When alimentary conditioned reflexes involving the right-leg movement, were elaborated before the defensive ones involving the left fore-leg movement, then manifestation of the second reflex was preceded by a movement with the right leg. When the elaboration of conditioned reflexes started with defensive reflexes, the opposite was observed: before performing the alimentary reflex, the dogs lifted first the left fore-leg connected with the defensive reflex, and then the right one. Inertia of the nervous mechanism underlying this phenomenon, is based on a tonic increase in the excitability of the corresponding structures.

Animals↗
PubMed1993

Effects of MK-801 on the micturition reflex in the rat--possible sites of action.

The i.v. administration of MK-801 (dizocilpine), a noncompetitive N-methyl-D-aspartate receptor antagonist, depresses reflex bladder contractions in the rat, suggesting that glutamatergic transmission may have an important role in the micturition reflex pathway. The site of action of MK-801 was analyzed in the present experiments by studying the effects of the drug in the following urethane-anesthetized preparations: 1) intact rats, 2) decerebrate rats, 3) chronic spinal rats with transection at the T6-T8 segment and 4) intact rats in which the drug was administered via an intrathecal (i.t.) catheter at the L6-S1 spinal cord segments. Reflex bladder activity was monitored by measuring intravesical pressure under isovolumetric conditions and during a cystometrogram where the bladder outlet was open and voiding occurred. MK-801 (0.001-3 mg/kg i.v.) administered to the intact rats produced a dose-dependent suppression of the amplitude of reflex bladder contractions recorded during a cystometrogram. The ED50 and dose to produce maximal inhibition were 0.36 mg/kg and 3 mg/kg i.v., respectively. Doses of 0.3 to 1 mg/kg i.v. doubled the volume threshold for inducing micturition and decreased by 80% the voided volume in the intact rats. In decerebrate rats, reflex bladder contractions were also inhibited by MK-801 (ED50 = 0.055 mg/kg i.v.); however, in chronic spinal animals, even large doses of MK-801 (3-30 mg/kg i.v.) did not inhibit reflex bladder activity. MK-801 (6-78 micrograms) administered i.t. in the intact rats produced a dose-dependent suppression of the amplitude of reflex bladder contractions (ED50 = 13 micrograms). These results suggest that the inhibition of micturition reflex by MK-801 is mediated at least in part by an action on the lumbosacral spinal cord and is dependent on an intact pathway between the brain and spinal cord.

Animals↗
PubMed1997

Videofluoroscopic evaluation of aspiration with visual examination of the gag reflex and velar movement.

The purpose of the present study was to investigate the relationship between prevalence of aspiration as determined by videofluoroscopic evaluation and prevalence of the gag reflex and velar movement as determined by direct visual examination. One hundred adult patients underwent a videofluoroscopic evaluation of aspiration with either an esophagram (n = 31), upper gastrointestinal series (n = 18), small bowel series (n = 23), or modified barium swallow procedure (n = 28), and concomitant evaluation of the gag reflex and velar movement on phonation. All studies were performed using the lateral, upright position, and all patients drank at least 5 cc of single contrast barium. Aspiration was defined as penetration of material below the level of the true vocal folds. A normal gag reflex and normal velar movement on phonation were observed in 14 of 15 (93%) patients who exhibited objective documentation of aspiration with videofluoroscopy. Conversely, 19 of 20 (95%) patients without a gag reflex were observed with videofluoroscopy to be without aspiration. Normal velar movement on phonation was observed in 99 of 100 (99%) patients. There was no significant age difference between patients with or without a gag reflex. No relationship was found between the prevalence of aspiration and the gag reflex or velar movement on phonation. It was concluded that the presence of a gag reflex does not protect against aspiration, and the absence of a gag reflex does not predict aspiration.

Adolescent↗
PubMed1989

Optimal stimulus duration for the H reflex.

Authorities advocate different stimulus durations to produce an H reflex. In order to find the optimal stimulus duration for recording H reflexes, the recruitment curves for H reflexes and M responses were studied in 10 healthy subjects. The H reflex was recorded in the upper and lower extremities, and the durations of the electrical stimulus used ranged from 0.1 to 3 msec. The amplitude of the H reflex and the relation between the H reflex and M response changed with stimulus duration. H reflexes are brought out to advantage using a stimulus duration between 0.5 and 1 msec.

Adult↗
PubMed1994

Topodiagnostic value of brain stem reflexes.

The masseter and medial pterygoid stretch reflexes, the masseter inhibitory reflexes, and the blink reflexes are useful diagnostic tools for evaluation of brain stem disorders. The structures mediating these reflexes are largely known. Characteristic changes of the normal response patterns due to various lesions have been described. Distinct reflex abnormalities indicate lesions at specific sites. Multireflex testing improves the accuracy with which localization can be made. A number of lesions suspected on clinical data may be confirmed by reflex findings only and not by imaging studies. Reflex testing can be utilized to demonstrate multiple lesions evoked by a single vascular event and evaluate dissemination of central nervous involvement in multiple sclerosis patients.

Blinking↗
PubMed2001

An investigation into mechanisms of reflex reinforcement by the Jendrassik manoeuvre.

Tendon jerk and H-reflexes are both potentiated by the Jendrassik manoeuvre, but the mechanism of potentiation remains uncertain. We investigated several possibilities in human subjects. Evidence for fusimotor activation during the Jendrassik manoeuvre was sought by recording the tendon jerk reflex as surface EMG in triceps surae after the muscles had been conditioned to leave their spindles in a slack, insensitive state. Interposing a Jendrassik manoeuvre between conditioning and the test reflex should have increased reflex amplitude by restoring spindle sensitivity, but this was not the case. In humans, a close synergist of the triceps surae is the quadriceps. A possible presynaptic disinhibitory mechanism was investigated by testing the effect of a Jendrassik manoeuvre on facilitation of the soleus H-reflex produced by a quadriceps afferent volley. The Jendrassik manoeuvre failed to increase facilitation, contrary to what would be expected if it reduced the level of tonic presynaptic inhibition; the assumption being that the inhibition acts on both homonymous and synergist afferent terminals. The Jendrassik manoeuvre did not increase the level of ongoing EMG in the soleus during a weak voluntary contraction, indicating that it does not operate by direct facilitation of motoneurones. There was found to be less potentiation of soleus tendon jerk and H-reflexes by the Jendrassik manoeuvre under conditions when spindles in the soleus were likely to have a high resting discharge rate. A remaining possibility is discussed: that the Jendrassik manoeuvre operates by modulation of oligosynaptic pathways that may contribute to the largely monosynaptic reflex response. These experiments demonstrate, with new, more sensitive methods than previously used, that neither is the fusimotor system involved in reinforcement nor are direct excitatory or presynaptic disinhibitory effects on motoneurones. While this confirms the previously prevailing view, none of the lingering uncertainties associated with the methods used now remains.

Adult↗
PubMed1995

Long-lasting conditioning of the human soleus H reflex following quadriceps tendon tap.

Percussion of the quadriceps tendon was used to test the hypothesis that knee extensor muscle spindle discharge initiates down-regulation of the gain of the soleus H reflex. Seven subjects participated. Soleus H reflex magnitude was observed for up to 15 s, following conditioning tendon taps of 60 N or 80 N force and 10 ms duration, with the knee at 60 degrees or 90 degrees of flexion. The tap elicited quadriceps stretch reflexes in four subjects, with a mean latency of 42 ms. The major component of the conditioning of the soleus H reflex was significant attenuation of magnitude by 30-90% of controls, starting as early as 36 ms post-percussion and lasting as long as 3-8 s. The attenuation of reflex magnitude was evident, whichever combination of duration and force of tap was used. Preceding and/or following this inhibition, there was mild facilitation. Static stretch of quadriceps also significantly reduced soleus H reflex magnitude. These results support the spindle receptor origin for the gain attenuation seen during movement. The time course of the gain attenuation suggests a spinal route, by which the spindle discharge of the heteronymous extensor muscles initiates presynaptic inhibition of transmission through the reflex pathway.

Adult↗
PubMed1989

Electrophysiological evidence for nicotinic and muscarinic modulation of spinal cord reflexes.

Intravenous administration of physostigmine has been found to produce dose- and time-dependent alterations of the lumbar monosynaptic and polysynaptic reflexes in spinal cats. A small dose of physostigmine (0.8 mg/kg) enhanced the monosynaptic reflex for 3 hr, while a larger dose (2.0 mg/kg) produced a pattern of initial depression which peaked at 5 min, followed by an increase which was maintained for 3 hr after injection. Both doses of physostigmine were found to produce a similar pattern of enhancement of the polysynaptic reflex. Atropine and mecamylamine antagonized the increase of the monosynaptic reflex produced by both doses of physostigmine. The initial depression of the monosynaptic reflex produced by the large dose of physostigmine was blocked by mecamylamine, but unaffected by atropine. The enhancement of the polysynaptic reflex, produced by both doses of physostigmine, was antagonized by atropine but not by mecamylamine. In addition, nicotine and oxotremorine were found to mimic the initial effects of physostigmine in the presence of the appropriate antagonist. These data show that both muscarinic and nicotinic receptors are involved differentially in the modulation of spinal reflexes and that physostigmine had an additional late effect which consistently occurred at 20 min after administration.

Animals↗
PubMed1985

Hoffmann reflex variations produced by task demand characteristics.

It has been shown that monosynaptic reflexes could be facilitated or inhibited during tasks differing in nature. The amplitude of the Hoffmann reflex (H reflex) and heart rate have been studied during the performance of two versions of a mental task and a tracking task varying in degree of difficulty. Modification of the H reflex does not depend upon the nature of the task. A slight increase in cardiac rhythm and a facilitation of H reflex during easy tasks and a marked increase in cardiac rhythm associated with inhibition of H reflex during difficult tasks were observed. The increase in H reflex would be due to an activation of the reticular formation. The inhibition of motor response can be attributed to an effortful process which develops when the tasks become difficult.

Adult↗
PubMed1990

Differential effects of the excitatory amino acid antagonists, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 3-((+-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), on spinal reflex activity in mice.

Intrathecal administration of the preferential quisqualate antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in anesthetized mice depressed Hoffmann (H)-reflexes, while flexor reflexes remained unaffected. The depressant effect of CNQX on H-reflexes was dose-dependent (range 0.1-10 nmol). The intrathecal administration of the selective N-methyl-d-aspartate (NMDA) antagonist 3-[(+-)-2-carboxypiperazin-4-yl]-propyl-1-phosphonate (CPP) reduced flexor reflexes (range 10-100 nmol) and had no effect on H-reflexes. These results suggest that H-reflexes in mice are mediated by spinal non-NMDA receptors, while flexor reflexes involve NMDA receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1990

Electrophysiological aspects of the middle ear muscle reflex in the rat: latency, rise time and effect on sound transmission.

The latency, the rise time and the influence of the acoustic reflex on sound transmission were investigated in the adult rat during ketamin anesthesia. This was done by recordings of the cochlear microphonics (CM) and electromyographic (EMG) recordings of the reflex responses of the tensor tympani muscle. The acoustic reflex was elicited by contralateral acoustic stimuli of which the intensity and frequency was varied. Ipsilaterally, the effect on sound transmission was determined by estimating the change in amplitude of the CM's of ipsilateral administered subliminal stimuli. It was shown that both the tensor tympani muscle and the stapedius muscle contribute in the reflex. The latency as well as the rise time of the reflex determined by CM recordings showed to be short (minimal values: 12 and 7 ms respectively). The mean latency of the tensor tympani muscle reflex, measured by EMG, was about 7 ms. The attenuation of 0.25-8 kHz tone bursts upto 115 dB SPL is limited to a mean maximum of 15 dB SPL. The maximal attenuation was shown to occur at 1 kHz. Frequencies above 2 kHz appeared to be the best elicitor of the middle ear muscle reflex.

Animals↗
PubMed1995

Auditory startle (audio-spinal) reaction in normal man: EMG responses and H reflex changes in antagonistic lower limb muscles.

The audiospinal reaction (ASR) to a 30 msec tone of 90 dB has been studied in 66 seated healthy volunteers. Electromyographic bursts induced in trapezius (Tra), soleus (Sol) and tibialis anterior (TA) have been looked for. Facilitation of Sol H reflex has been measured in 21 subjects in terms of delays from delivery of the sound. Among the subjects, 11 had a stable TA H reflex whose facilitation was compared to that of Sol H. Effects of selective isometric voluntary contraction of either Sol or TA were assessed both on EMG responses and H reflex facilitation. At rest, only 36% of subjects exhibited a response in Sol at a mean latency of 123 msec and 39% in TA at a latency of 119 msec. Responses were seen in antagonist muscles in 74% of subjects. Incidence in Tra was 96%. During voluntary contraction, the results were not significantly changed either in the contracted muscle or its antagonist. H reflex facilitation of both TA and Sol started 50 msec after the sound to peak after 75-125 msec and returned to baseline values after 250 msec. Extent of Sol H reflex facilitation remained similar during voluntary contraction of Sol and TA. It was observed that EMG responses were more frequent in subjects with brisk reflexes but not necessarily in those who exhibited the largest H reflex facilitation. The results are in agreement with assumptions that ASR is mediated through reticulo-spinal pathways but do not support the view that it corresponds to a flexor reaction. In addition to providing quantitative data for comparisons in pathological cases, they suggest differences in the mode of activation of motoneurones by the motor cortex and subcortical nuclei.

Acoustic Stimulation↗