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At least 1,207 records · Page 67Linked to original sources
PubMed1996

Reflex stimulation of continuously oscillatory firing alpha and gamma-motoneurons in patients with spinal cord lesion.

Single nerve-fibre action potentials (APs) were recorded extracellularly from lower human sacral nerve roots, and simultaneous single-fibre impulse patterns of alpha and gamma-motoneurons and secondary muscle spindle afferents were analysed. Identified alpha and gamma-motoneurons fired oscillatory, due to the sustained stretch reflex of the external sphincters induced by an anal catheter (and, possibly, the bladder catheter). The motoneurons and the secondary muscle spindle afferents transiently synchronized their firing upon repetitive touch, pin-prick and dimpling stimulation of the perianal skin inside the anal reflex area, by reducing the duration of their oscillation period until resetting of the oscillation cycle. In one case, the anal reflex area extended approximately 6 cm laterally from the anus. The responses to pin-prick stimulation were different from those to touch stimulation in three aspects. Firstly, the response time till the shortening of the oscillation period was longer than the oscillation period (approximately 100 ms) for pin-prick, and it was shorter for touch. Second, the response to pain stimulus was longer (shortening of several oscillation periods) and stronger than for touch stimulation. Pin-prick stimulation reduced the oscillation period to between 5 and 40 ms (mean = 18 ms), and touch stimulation to between 8 and 28 ms (mean = 15 ms). Third, transient synchronization of afferents and efferents was most pronounced for pin-prick stimulation. The shortest latency following touch was approx. 10 ms when measuring from the afferent volley running in the direction of the spinal cord, and 30 ms when measuring from the beginning of the skin touch. It is discussed that repetitive touch stimulation reinforced the sustained stretch reflex of the anal sphincter which is possible with no network reorganization (variation of the same network state) and therefore fast, whereas repetitive pin-prick stimulation replaced the sustained stretch reflex by the protection reaction of the anal sphincter (change from one network state to a different one) which made time consuming network reorganization necessary. Different sacral reflexes were analysed by studying time-related activation changes of group conduction velocities in velocity distributions. During the reflex response to stretch of the external anal sphincter, the alpha 2-motoneurons (FR) (and the secondary muscle spindle afferents) were strongly activated whereas upon eliciting the bulbocavernosus reflex (squeezing of the glans penis) the alpha 3-motoneurons (S) were mainly activated. Sacral reflexes are discussed with respect to the organization and reorganization of preformated neuronal networks, and the synchronization of oscillatory firing networks is discussed with respect to the overlapping of synfire chains.

Action Potentials↗
PubMed1997

[A case of cortical reflex positive-negative myoclonus--electrophysiological study].

An 11-year-old girl who had the positive-negative myoclonus and the history of the generalized tonic clonic seizure was electrophysiologically studied. She had no siblings with either myoclonus or epilepsy, and her intellectual level was normal. She had no other neurological deficits including ataxia, pyramidal and extrapyramidal signs. Surface EMG showed a brief increase in the EMG activity followed by the silent period associated with positive and negative myoclonus during sustained wrist extension. Giant SEP and C reflex (38.6 ms) following electric stimulation of the median nerve at the wrist were obtained in the resting condition and the silent period (about 180 ms) following C reflex was obtained during voluntary contraction. Jerk-locked back averaging of the EEG time-locked to the onset of the myoclonic discharge recorded from the right biceps muscle showed a cortical spike at the left central region preceding the myoclonus onset by 12.6 ms. The latency of C reflex in this case was very short compared with that of previously reported cortical reflex myoclonus. The estimated cortical delay between the arrival of the somatosensory volley and the motor cortex discharge responsible for the C reflex was -1.0 ms and this value was shorter than that in patients with typical cortical reflex myoclonus (mean 3.7 +/- 1.1 ms). Conditioning stimuli (C) of the right median nerve at the wrist started to facilitate the amplitude of the motor evoked potential recorded from the right abductor pollicis brevis muscle after magnetic test stimuli (T) of the left motor cortex at 20 ms of the C-T interval. This C-T interval was shorter than that (24.6 +/- 1.6 ms) in patients with the typical cortical myoclonus. These electrophysiological findings suggested the shorter reflex pathway of the cortical reflex myoclonus in this case than in typical cortical reflex myoclonus. We speculated that the myoclonus was based upon the direct sensory projection from the thalamus to the motor cortex in this case.

Child↗
PubMed2000

Ophthalmoscopic detectability of the parafoveal annular reflex in the evaluation of the optic nerve: an experimental study in rhesus monkeys.

OBJECTIVE: To evaluate whether assessment of the ophthalmoscopic visibility of the parafoveal annular reflex is helpful in the detection of optic nerve fiber and optic nerve damage. DESIGN: Experimental animal study. ANIMALS: The study was performed in rhesus monkeys, divided into four study groups, with no significant difference in ages of the animals in the various groups. Three of these groups had (1) experimental chronic high-pressure glaucoma (n = 37 monkeys), (2) experimental temporary occlusion of the central retinal artery (n = 19 monkeys), and (3) systemic atherosclerosis and arterial hypertension (n = 13 monkeys). The fourth group was the normal control group (n = 10 monkeys). METHODS: In 60-degree color fundus photographs, taken at baseline and at the end of the study, the ophthalmoscopic detectability of the parafoveal annular reflex was graded, the visibility of the retinal nerve fiber layer was assessed, and neuroretinal rim and parapapillary atrophy were measured. MAIN OUTCOME MEASURES: Ophthalmoscopic detectability of the parafoveal annular reflex; visibility of the retinal nerve fiber layer; neuroretinal rim area; size of parapapillary atrophy. RESULTS: The parafoveal annular reflex was significantly (P < 0.0001) better detectable at baseline of the study than at the end of the study. In all study groups, detectability of the parafoveal annular reflex decreased significantly (P < 0.0001) with decreasing visibility of the retinal nerve fiber layer. In the glaucoma group, parafoveal annular reflex detectability additionally decreased significantly (P < 0.001) with increasing area of beta zone of parapapillary atrophy and with decreasing neuroretinal rim area. In the normal group, the parafoveal annular reflex detectability decreased with increasing age, parallel to a loss in the visibility of the retinal nerve fiber layer. In 23 of 25 (92%) eyes with a complete loss of the visibility of the retinal nerve fiber layer at the end of the study, the parafoveal annular reflex was no longer detectable. CONCLUSIONS: The findings suggest that evaluation of the detectability of the parafoveal annular reflex in routine ophthalmoscopy is a useful additional tool in the qualitative assessment of the retinal nerve fiber layer and optic nerve.

Animals↗
PubMed1998

Endogenous angiotensin II and the reflex response to stimulation of cardiopulmonary serotonin 5HT3 receptors.

1. Angiotensin (Ang) II modulates cardiovascular baroreflexes; whether or not the peptide influences chemosensitive cardiovascular reflexes is not known. We tested the hypothesis that Ang II modulates the reflex control of sympathetic nerve activity exerted by 5-hydroxytryptamine 3 (5HT3) cardiopulmonary receptors. 2. The 5HT3 receptor agonist phenylbiguanide (PBG), infused intravenously for 15 min, elicited a sustained reflex decrease of renal sympathetic nerve activity (RSNA) but only transient (<3 min) changes of arterial blood pressure (BP) and heart rate (HR) in methohexital-anaesthesized rats. 3. Infusion of Ang II at a dose that did not affect baseline BP, HR and RSNA enhanced the PBG-evoked reflex decrease of RSNA (-54+/-5% in Ang II treated versus -33+/-6% in control rats after 15 min PBG, P<0.05, n = 6 each) in methohexital-anaesthetized rats. 4. The angiotensin converting enzyme (ACE) inhibitor lisinopril blunted the reflex responses to PBG in anaesthetized as well as conscious animals. The effect of the ACE inhibitor was abolished by concomitant infusion of Ang II. 5. The reflex response to stimulation of cardiopulmonary 5HT3 afferents was also impaired by the Ang II type 1 receptor (AT1) blocker ZD7155 but not by the type 2 (AT2) blocker PD 123319. 6. Infusion of a volume load to stimulate cardiopulmonary baroreceptors induced a gradual decrease of RSNA which was impaired by exogenous Ang II (RSNA -26+/-6% in Ang II treated versus -47+/-6% in control rats after volume load, P<0.05, n = 6 each) but unaffected by ACE inhibition. 7. The reflex control of RSNA by cardiopulmonary 5HT3 receptors is enhanced by Ang II via AT1 receptors. Thus, Ang II facilitates a chemosensitive cardiovascular reflex, in contrast to its inhibitory influences on mechanosensitive reflexes.

Anesthesia↗
PubMed1990

The effect of motor preparation on changes in h reflex amplitude during the response latency of a warned reaction time task.

Monosynaptic Hoffman reflexes (H reflexes) were recorded from the soleus muscle during the response latency of a warned reaction time (RT) task that required plantarflexion of the foot. The task was done under four conditions of predictability of the response signal (RS), created by the factorial combination of foreperiod duration (1 and 4 s) and variability (fixed and variable). RT varied systematically with RS predictability and was facilitated in conditions that favored prediction of the RS. The response latency was divided into two successive phases by the onset of reflex augmentation: a premotor phase of constant reflex amplitude and a succeeding motor phase marked by progressively increasing reflex amplitude. Reflex augmentation during the motor phase was coupled more closely to the imminent movement than to the preceding signal to respond. The duration of the premotor phase was unaffected by RS predictability, but the duration of the motor phase (like RT) was shorter when the RS was more predictable. The maximum H reflex amplitude reached during the motor phase was greater when the RS was more predictable. The tonic level of H reflex amplitude during the premotor phase was greater in conditions that made prediction of the RS difficult. A second experiment showed that this difference was present throughout the foreperiod. These results suggest that conditions that favor prediction of the RS enhance motor preparation. changes in motor preparation (which affect RT) affect the processes underlying reflex amplitudes in the premotor phase and throughout the preceding foreperiod, in conditions that make prediction of the RS difficult, appear to reflect heightened general arousal.

Journal Article↗
PubMed1994

Impaired cardiovascular reflexes precede deoxycorticosterone acetate-salt hypertension.

We hypothesized that impaired cardiopulmonary reflexes but not altered baroreceptor reflexes precede deoxycorticosterone acetate (DOCA)-salt hypertension. Uninephrectomized rats were given either DOCA and 0.9% NaCl as drinking water, 0.9% NaCl alone, or tap water. We measured mean blood pressure, heart rate, and renal sympathetic nerve activity. After 8 days, mean blood pressure was not different in DOCA-salt and control rats. Volume-sensitive cardiopulmonary reflexes were tested by intravenous volume loading with saline (10% body weight in 15 minutes), which decreased renal sympathetic nerve activity without changing mean blood pressure or heart rate. This response was blunted in DOCA-salt rats. Chemosensitive cardiopulmonary reflexes were tested by 15-minute infusions of the serotonin 5-HT3 agonist phenylbiguanide, which decreased renal sympathetic nerve activity without changing mean blood pressure or heart rate. Sustained decreases in renal sympathetic nerve activity occurred during phenylbiguanide infusion in controls but were blunted over time in DOCA-salt rats. The arterial baroreflex responses to graded infusions of methoxamine and nitroprusside were analyzed by sigmoidal curve fitting. There were no differences in gain of renal sympathetic nerve activity or heart rate between the groups. Thus, DOCA-salt rats exhibit impaired cardiopulmonary reflexes before the onset of hypertension; the volume-sensitive reflexes are more severely affected than chemosensitive reflexes. The arterial baroreceptor reflex is unaltered. The decreased sensitivity of cardiopulmonary reflexes may contribute to DOCA-salt hypertension.

Analysis of Variance↗
PubMed1998

ANP and bradycardic reflexes in hypertensive rats: influence of cardiac hypertrophy.

In previous studies we demonstrated that in normotensive rats, but not in spontaneously hypertensive rats (SHR), atrial natriuretic peptide (ANP) enhances bradycardic reflexes through an action on cardiac vagal afferent pathways. The present study aimed to determine whether cardiac hypertrophy, hypertension, or a nonreversible genetic factor accounted for the insensitivity of SHR to ANP action on cardiac reflex pathways. SHR were treated with the angiotensin-converting enzyme (ACE) inhibitor perindopril (3 mg/kg per day) for 6 weeks from 4 to 9 weeks of age (SHR-S, n=10) or for 9 weeks from 4 to 12 weeks of age (SHR-L, n=10) or were untreated (SHR, n=10) to produce differential effects on blood pressure and left ventricle/body weight ratio (LV/BW). Untreated normotensive Wistar-Kyoto rats (WKY, n=10) were also studied. At 13 weeks of age, all rats were instrumented with aortic and jugular catheters, and at 14 weeks we measured heart rate reflexes to rapid intravenous infusions of methoxamine (100 microg/kg, cardiac baroreflex) and serotonin (5 to 60 microg/kg, von Bezold-Jarisch cardiac chemosensitive reflex), with either alpha-rat ANP (150 ng/kg per minute IV) or saline vehicle (270 microL/h IV) infusion. Perindopril treatment for 6-week (SHR-S) and 9-week (SHR-L) durations maintained blood pressure at normotensive levels in both groups. SHR-S exhibited a small degree of cardiac hypertrophy (LV/BW was 8% higher than in WKY but 11% less than in untreated SHR), but LV/BW was normalized in SHR-L (to within 1% of WKY LV/BW). In WKY, ANP significantly (P<0.05) enhanced bradycardic responses to both the cardiac baroreflex (by 42+/-10%) and von Bezold-Jarisch chemosensitive reflex (by 17+/-5%) activation but had no effect in SHR. The cardiac reflex action of ANP was restored in SHR-L (ANP enhanced reflex bradycardia by 28+/-12% and 36+/-8%, baroreflex and von Bezold-Jarisch reflex, respectively; P<0.05), but SHR-S, which developed some cardiac hypertrophy, remained unresponsive to ANP. Our results suggest that the inability of ANP to sensitize cardiac vagal (nonarterial) afferents in SHR was not due to an inherited irreversible component, or the hypertension per se, but was associated with the presence of cardiac hypertrophy. A functional consequence of hypertension-induced cardiac hypertrophy may be the inhibition of the cardioprotective action of ANP through cardiac vagal reflexes.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1996

Sympathoadrenal activity in the visceral (viscerovascular) reflexes to distension of the urinary bladder.

Distension of the urinary bladder can cause reflex pressor responses, which appear to be mediated by increased sympathetic activity. We correlated the involvement of the adrenal gland (medulla) itself and adrenosympathetic nerve activities with the viscerovascular reflexes and their role in controlling the reflex response following distension of the urinary bladder. The experiments were performed in 37 chloralose anesthetized cats. It was observed that reflex rise of blood pressure was not affected by intravenous administration of propranolol, indicating that the beta-adrenoceptors (inhibitory effect) were not involved in such reflex. Phentolamine, hexamethonium and guanethidine sulfate completely prevented the reflex action, and comparison of the magnitudes of responses and this inhibitory effect suggests the participation of alpha-adrenoceptors (excitatory effect) as a result of the vasoconstriction that develops during bladder distension. In the present study, we determined that adrenalectomy significantly (p < 0.0001) altered the magnitudes of reflex response during bladder distension. The 10.4% (systolic, p < 0.001) and 10.6% (diastolic, p < 0.01) change in reflex response was mediated directly through adrenomedullary catecholamines, and the 14.8% (systolic, p < 0.001) and 23.8% (diastolic, p < 0.0001) change in vasopressor response was mediated by adrenosympathetic ganglionic activity. The single unit activity from the central cut end of the adrenal sympathetic nerve was recorded for direct evidence. An increase in electrical activity (1-3 to 7-10 spikes/s; p < 0.001) of the adrenal sympathetic nerve with the rise of blood pressure during bladder distension was observed. We concluded that, like other sympathetic nerves, the adrenal sympathetic nerve contributed to the enhancement of blood pressure during bladder distension. This result also explains the partial inhibition of reflex hypertension during bladder distension after adrenalectomy. These studies also conclude that the adrenal gland and adrenosympathetic nerve act as facilitatory modulators in maintaining catecholamine secretion under conditions of stress (urinary bladder distension).

Animals↗
PubMed2005

Effects of caffeine on the trigeminal blink reflex.

The acoustic startle and trigeminal blink reflexes share the same motor output. Since caffeine has been shown to augment the startle reflex, it was proposed that caffeine would also increase the trigeminal blink reflex. In 6 humans, the effects of caffeine (100 mg) on the trigeminal blink reflex were investigated. Reflex blinks were elicited by stimulation of the supraorbital branch of the trigeminal nerve. Following ingestion of caffeinated coffee, reflex blinks increased in amplitude and duration and occurred at a shorter latency than reflex blinks following ingestion of decaffeinated coffee. Since the blink reflex is a brainstem reflex, these results suggest that the psychomotor effects of caffeine facilitate brainstem processing.

Blinking↗
PubMed2004

Magnetic resonance imaging evidence of posterior pharynx denervation in pediatric patients with Chiari I malformation and absent gag reflex.

OBJECT: The authors hypothesized that children with preoperative Chiari I malformation and an absent gag reflex may harbor pharyngeal musculature atrophy identifiable on magnetic resonance (MR) imaging. METHODS: Thirty patients with preoperative Chiari I malformation and a functioning gag reflex, five patients with preoperative Chiari I malformation and complete absence of gag reflex, and 50 control individuals underwent radiological measurement of the posterior pharyngeal wall thickness. The thickness of the posterior pharyngeal wall in age-matched controls was significantly thinner (p < 0.0001) than that in patients with Chiari I malformation and no functioning gag reflex. Additionally, in patients with hindbrain herniation and absent gag reflex, the posterior pharyngeal wall thicknesses were comparable to or thinner than those in age-matched controls. A general decrease in the thickness of the posterior pharyngeal wall was found in control individuals who were older compared with patients with Chiari I malformation and a preserved gag reflex in whom the prevertebral soft tissues were found to increase in thickness with age. Analysis of these data showed that in children with a nonfunctioning gag reflex the prevertebral soft tissue, composed primarily of the superior constrictor muscle, is statistically thinner compared with that in age-matched controls and age-matched children with Chiari I malformation and a functioning gag reflex. The authors theorize that the discrepancy between this measurement in controls and patients with hindbrain herniation is due to the thickening of the craniocervical ligaments that is known to occur in this clinical entity. CONCLUSIONS: The finding that prevertebral soft tissue thickens with age in patients with Chiari I malformation and functioning gag reflex alone may aid in the interpretation of soft-tissue injury following cervical spine injuries in this group.

Adolescent↗
PubMed1991

Pudendal reflexes and effects of conditioning stimuli in cats.

Evaluation of pudendal reflexes and effects of pudendal branch conditioning on those reflexes was carried out in 2 studies. In the first study of pudendal reflexes, 20 adult male and female mixed-breed cats underwent surgical isolation of the anal branch, urethral branch, and distal trunk (consisting primarily of the dorsal nerve of the penis/clitoris) of the pudendal nerve. Reflexes were tested in all possible ipsilateral and contralateral test-response combinations. Latency values and effects of increasing stimulus rate on response amplitude were recorded. Reflexes were detected in all combinations, with response latencies between 6.3 and 13.0 ms. Response amplitudes were diminished at stimulus rates of 3 to 5 Hz, and responses were apparently abolished at 4 to 16 Hz, suggesting that pudendal reflexes are polysynaptic. In the second study of conditioning effects, 9 adult male and female mixed-breed cats underwent preparation similar to that for study 1. A train of conditioning stimuli was applied to branches of the pudendal nerve prior to attempting to induce reflex responses, as performed in study 1. Conditioning completely abolished reflex responses for a period of 70 to 130 ms. Reflex responses were diminished in amplitude, compared with those observed during preconditioning trials, for 180 to 300 ms after conditioning.

Anal Canal↗
PubMed1996

Premotor interneurons in generation of adaptive leg reflexes and voluntary movements in stick insects.

We investigated the role of local nonspiking interneurons involved in motor control of legs in the stick insects, Carausius morosus. In a preparation that allowed the animals to perform active leg movements such as adaptive tactile reflexes, proprioceptive reflexes, and walking, we gathered the following results. Almost all tested nonspiking interneurons that provide synaptic drive onto moto-neurons of the proximal leg muscles contribute to all of the motor programs underlying tactile reflexes and voluntary leg movements such as walking, searching, and rocking. Most of them are also involved in the generation of proprioceptive reflexes. All motor programs for coactivation, avoidance reflexes, resistance reflexes, and voluntary leg movements result from parallel pathways including nonspiking interneurons that support and others that oppose the motoneuronal activity. The contribution of a single interneuron to the different motor program is specific: it can be supporting for one motor program but opposing for the other. Even for the same motor program, for example, coactivation, the contribution of an individual interneuron can depend on the stimulus site from where the response is elicited. Our results support the idea that the different motor patterns for adaptive tactile reflexes, resistance reflexes, and voluntary leg movements emerge from a multifunctional neuronal circuit that is reorganized corresponding to the motor behavior performed. The actual motor pattern is then shaped by distributed information processing in parallel supporting and opposing pathways.

Acclimatization↗
PubMed1994

Segmental reflexes and ankle joint stiffness during co-contraction of antagonistic ankle muscles in man.

The size of soleus H-reflexes and short-latency stretch reflexes was measured at different levels of plantar flexion or co-contraction (simultaneous activation of dorsi- and plantar flexors) in seven healthy subjects. In four of seven subjects the short-latency stretch reflex was smaller during weak co-contraction than during isolated plantar flexion at matched background electromyogram (EMG) levels in the soleus muscle. In three of these four subjects the stretch reflex was larger during strong co-contraction than during plantar flexion, whereas it had the same size during the two tasks in the last subject. In the remaining subjects the stretch reflex either had the same size or was larger at all levels of co-contraction than at similar levels of plantar flexion. In contrast, the H-reflex was found to decrease with co-contraction at all contraction levels in all subjects. The decrease in the reflexes during weak co-contraction might be caused by presynaptic inhibition of Ia afferents. It is unclear why only the H-reflex decreased during strong co-contraction. The stiffness of the ankle joint was measured from the torque increment following the stretch of the plantar flexors divided by the stretch amplitude. In all subjects the total stiffness of the ankle joint was larger during strong co-contraction than during plantar flexion of similar strength. The stiffness was smaller during weak co-contraction than during weak plantar flexion in three out of seven subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

The effects of postsynaptic inhibition on the monosynaptic reflex of the cat at different levels of motoneuron pool activity.

The motoneurons to the Soleus muscle in the decerebrate cat were activated by the crossed extensor reflex, elicited by stimulation of the contralateral common peroneal (CP) nerve. Monosynaptic reflexes were obtained from the Soleus motoneuron pool by stimulation of the cut L7-S1 dorsal roots. The amplitude of the reflex increased approximately linearly with the recruitment level of the motoneuron pool. Tonic postsynaptic inhibition was induced in the Soleus motoneuron pool by repetitive antidromic stimulation of the Lateral Gastrocnemius (LG) and Medial Gastrocnemius (MG) nerves at a rate of 17-47 stimuli/s. This reduced the size of the monosynaptic reflex at rest by at least 40%. However, when the motoneurons were active, the amplitude of the monosynaptic reflex obtained during repetitive stimulation of the LG-MG nerve increased with the recruitment level along the same curve as the control reflexes. Thus, tonic postsynaptic inhibition of the motoneurons per se cannot control the amplitude of the monosynaptic reflex independently of the recruitment level of the motoneuron pool. These experimental results verify predictions from computer simulations and suggest by exclusion that presynaptic inhibition is needed to control the amplitude of the monosynaptic reflex independently of the recruitment level of the motor pool.

Action Potentials↗
PubMed1998

Reduced stretch reflex sensitivity and muscle stiffness after long-lasting stretch-shortening cycle exercise in humans.

It has been suggested that during repeated long-term stretch-shortening cycle (SSC) exercise the decreased neuromuscular function may result partly from alterations in stiffness regulation. Therefore, interaction between the short latency stretch-reflex component (M1) and muscle stiffness and their influences on muscle performance were investigated before and after long lasting SSC exercise. The test protocol included various jumps on a sledge ergometer. The interpretation of the sensitivity of the reflex was based on the measurements of the patellar reflexes and the M1 reflex components. The peak muscle stiffness was measured indirectly and calculated as a coefficient of the changes in the Achilles tendon force and the muscle length. The fatigue protocol induced a marked impairment of the neuromuscular function in maximal SSC jumps. This was demonstrated by a 14.1%-17.7% (n.s. - P < 0.001) reduction in the mean eccentric forces and a 17.3%-31.8% (n.s. - P < 0.05) reduction in the corresponding M1 area under the electromyograms. Both of these methods of assessing the short latency reflex response showed a clear deterioration in the sensitivity of the reflex after fatigue (P < 0.05-0.001). This was also the case for the eccentric peak stiffness of the soleus muscle which declined immediately after fatigue by 5.4% to 7.1% (n.s. - P < 0.05) depending on the jump condition. The results observed would suggest that the modulation of neural input to the muscle was at least partly of reflex origin from the contracting muscle, and furthermore, that the reduced muscle stiffness which accompanied the decreased reflex sensitivity could have been partly responsible for the weakened muscle performance due to impaired utilization of elastic energy.

Adult↗
PubMed1980

Preconditioning and excitability of the human orbicularis oculi reflex as a function of state.

Reflex excitability and unstimulated activity of orbicularis oculi were found to vary as a function of state but the effects of weak conditioning stimuli, preceding reflex stimulation by 30--210 msec, were independent of state. Electromyographic activity was recorded from 23 young adults: 12 subjects with eyes closed during quiet wakefulness, 3 subjects during all-night sleep, 8 subjects during an afternoon nap. Stimulation with a 50 msec, 105 dB(A) white noise burst elicited a reflex response in 92% of waking trials and 87% of trials during REM sleep, but responses occurred in only 54% of trials during NREM sleep. Further, response latency was longer and magnitude less during the NREM state. Despite the differences in reflex excitability associated with state, state did not affect the modifications of reflex activity produced by a 20 msec, 70 dB(A) conditioning tone. At all lead intervals, reflex magnitude was reduced by the weak prestimulation even though, at the shortest interval, reflex activity was initiated more rapidly. The discordant changes in reflex size and latency have been seen in previous waking studies and appear to be mediated by different mechanisms. The persistence of both effects during sleep suggests that neither effect depends on high-level central processes.

Acoustic Stimulation↗
PubMed1994

The depressant effect of GYKI 52466 on spinal reflex transmission in rats is mediated via non-NMDA and benzodiazepine receptors.

The present study examined the mechanisms by which GYKI 52466 (1-(amino-phenyl)-4-methyl-7,8-methyldioxy-5H-2,3-benzodiazepine) exerts its muscle relaxant effects. Intrathecal injection of the specific N-methyl-D-aspartate (NMDA) receptor antagonist (-)-2-amino-7-phosphonoheptanoate (AP7, 50-500 nmol) and systemic application of the benzodiazepine diazepam (0.2-5 mg/kg) dose dependently reduced the integrated area of the polysynaptic flexor reflex without affecting the monoxynaptic H-reflex. In contrast, intrathecal administration of the non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX, 0.1-10 nmol) depressed the H-reflex in a dose-dependent manner without affecting the flexor reflex. The depressant effect of GYKI 52466 on the flexor reflex was reduced by coadministration with flumazenil (5 mg/kg i.p.), an antagonist at the benzodiazepine receptor, whereas coadministration of the non-NMDA receptor agonist alpha-amino-3-hydroxy-5-tertbutyl-4-isoxazole-propionic acid (ATPA, 0.1 pmol) with GYKI 52466 attenuated the reduction of the H-reflex induced by GYKI 52466. The chosen doses of flumazenil and ATPA did not affect spinal reflex transmission when given alone. These data suggest that GYKI 52466 depresses spinal reflex transmission via an action on non-NMDA receptors and on benzodiazepine receptors.

2-Amino-5-phosphonovalerate↗
PubMed1992

Possible startle response contamination of the spinal nociceptive withdrawal reflex.

The objective of this study was to examine the possibility that the spinal nociceptive withdrawal reflex, otherwise known as the RIII reflex, is contaminated by the startle response, which is a non-pain-related supraspinal response. Startle response contamination of the RIII reflex would seriously compromise the RIIIs ability to measure spinal nociceptive processes in man, since a change in the startle response affecting EMG amplitude in the RIII latency range would be erroneously interpreted as a change in a spinal nociceptive process. EMG responses evoked by electrical stimulation of the sural nerve were recorded from the orbicularis oculi, neck, biceps, and biceps femoris muscles in 31 healthy human volunteers. The startle response was elicited under conditions often used to record the RIII reflex. Procedures are described that will completely eliminate the startle response. Comparisons between subjects that did and did not elicit a startle response revealed that the startle does not appear to significantly contaminate the biceps femoris RIII reflex, at least when performing group comparisons. There are, however, situations not dealt with in this study in which the startle might significantly contaminate the RIII reflex, such as patients with pre-existing negative emotional states, experimental procedures that induce fear and/or anxiety, and single case studies. It is important, therefore, that investigators using the RIII reflex be cognizant of the startle response and take appropriate precautions to monitor and if necessary eliminate the startle before attributing a change in the RIII reflex to a spinal nociceptive process.

Adult↗