Home About us Contact
|
Home About us Contact | ||
|
|
||
Reflex Responses (reflex + response)
Selected AbstractsOrganisation of sensitisation of hind limb withdrawal reflexes from acute noxious stimuli in the rabbitTHE JOURNAL OF PHYSIOLOGY, Issue 1 2003John Harris Spatial aspects of central sensitisation were investigated by studying the effects on three hind limb withdrawal reflexes of an acute noxious stimulus (20 % mustard oil) applied to a number of locations around the body in decerebrate and in anaesthetised rabbits. Reflex responses to electrical stimulation of the toes were recorded from the ankle flexor tibialis anterior (TA) and the knee flexor semitendinosus (ST), whereas responses to stimulation of the heel were recorded from the ankle extensor medial gastrocnemius (MG). In non-spinalised, decerebrated, pentobarbitone-sedated preparations, flexor reflexes were facilitated significantly from sites on the plantar surface of the ipsilateral foot but were either inhibited or unaffected by stimulation of sites away from this location. The heel,MG reflex was facilitated from the ipsilateral heel and was inhibited from a number of ipsilateral, contralateral and off-limb sites. In decerebrated, spinalised, pentobarbitone-sedated animals, mustard oil applied to any site on the ipsilateral hind limb enhanced both flexor reflexes, whereas the MG reflex was enhanced only after stimulation at the ipsilateral heel and was inhibited after stimulation of the toe tips or TA muscle. Mustard oil on the contralateral limb had no effect on any reflex. In rabbits anaesthetised with pentobarbitone and prepared with minimal surgical interference, the sensitisation fields for the heel,MG and toes,TA reflexes were very similar to those in non-spinal decerebrates whereas that for toes,ST was more like the pattern observed in spinalised animals. In no preparation was sensitisation or inhibition of reflexes related to the degree of motoneurone activity generated in direct response to the sensitising stimulus. This study provides for the first time a complete description of the sensitisation fields for reflexes to individual muscles. Descending controls had a marked effect on the area from which sensitisation of flexor reflexes could be obtained, as the sensitisation fields for the flexor reflexes evoked from the toes were larger in spinalised compared to decerebrated, non-spinalised animals. The intermediate sizes of sensitisation fields in anaesthetised animals suggests that the area of these fields can be dynamically controlled from the brain. On the other hand, the sensitisation field for the heel,MG reflex varied little between preparations and appears to be a function of spinal neurones. [source] Cardio-respiratory reflexes evoked by phenylbiguanide in rats involve vagal afferents which are not sensitive to capsaicinACTA PHYSIOLOGICA, Issue 1 2010A. Dutta Abstract Aim:, Stimulation of pulmonary C fibre receptors by phenylbiguanide (PBG, 5-HT3 agonist) produces hypotension, bradycardia and tachypnoea or apnoea. However, tachypnoeic or apnoeic responses are not consistent. Therefore, this study was undertaken to delineate the actions of PBG on respiration and compared with those evoked by capsaicin (TRPV1 agonist). Methods:, Blood pressure, respiratory excursions and ECG were recorded in urethane anaesthetized adult rats. The effect of PBG or capsaicin was evaluated before and after ondansetron (5-HT3 antagonist), capsazepine (TRPV1 antagonist) or bilateral vagotomy. In addition, their effect on vagal afferent activity was also evaluated. Results:, Bolus injection of PBG produced concentration-dependent (0.1,100 ,g kg,1) hypotensive and bradycardiac responses, while there was tachypnoea at lower concentrations (0.1,3 ,g kg,1) and apnoea at higher concentrations (10,100 ,g kg,1). After vagotomy or after exposure to ondansetron both tachypnoeic and apnoeic responses were abolished along with cardiovascular responses. However, capsazepine (3 mg kg,1) did not block the PBG-induced reflex responses. Capsaicin (0.1,10 ,g kg,1), on the other hand, produced a concentration-dependent apnoea, hypotension and bradycardia but tachypnoea was not observed. Ondansetron failed to block the capsaicin-induced reflex response while bilateral vagotomy abolished bradycardiac and hypotensive responses and attenuated the apnoeic response. In another series, vagal afferent activity and cardio-respiratory changes evoked by PBG were blocked by ondansetron. However, capsaicin failed to activate the PBG-sensitive vagal afferents even though cardio-respiratory alterations were observed. Conclusions:, The present observations indicate that PBG produced tachypnoea at a lower concentration and apnoea at a higher concentration involving vagal afferents which are different from those excited by capsaicin. [source] B2 kinin receptors mediate the Indian red scorpion venom-induced augmentation of visceral reflexes via the nitric oxide cyclic guanosine monophosphate pathwayACTA PHYSIOLOGICA, Issue 4 2009S. Kanoo Abstract Aim:, This study was performed to delineate the kinin (receptor)-dependent pathways in the Indian red scorpion (Mesobuthus tamulus; MBT) venom-induced pulmonary oedema as well as the augmentation of cardio-pulmonary reflexes evoked by phenyldiguanide (PDG). Methods:, In urethane-anaesthetized adult rats, the effect of venom on the PDG reflex responses (blood pressure, heart rate and respiration rate) and the pulmonary water content was ascertained using various antagonists(des- Arg, B1 receptor antagonist; Hoe 140, B2 receptor antagonist; N, -nitro- l -arginine methyl ester (l -NAME), nitric oxide (NO) synthase inhibitor; methylene blue, soluble guanylate cyclase inhibitor; and glibenclamide, K+ATP channel blocker). The effect of phosphodiesterase V inhibitor (sildenafil citrate) on the reflex response and the pulmonary water content was also examined and compared with venom-induced responses. Results:, Intravenous injection of PDG (10 ,g kg,1) evoked apnoea, bradycardia and hypotension lasting >60 s. Exposure to MBT venom (100 ,g kg,1) for 30 min augmented the PDG reflex responses by two times and increased the pulmonary water content, significantly. Hoe 140 blocked the venom-induced responses (augmentation of PDG reflex and increased pulmonary water content) whereas des-Arg did not. l -NAME, methylene blue or glibenclamide also blocked the venom-induced responses. Furthermore, sildenafil citrate (that increases cGMP levels) produced augmentation of PDG reflex response and increased the pulmonary water content as seen with venom. Conclusion:, The results indicate that venom-induced responses involve B2 kinin receptors via the NO-dependent guanylate cyclase-cGMP pathway involving K+ATP channels. [source] Modulation of the soleus H-reflex following galvanic vestibular stimulation and cutaneous stimulation in prone human subjectsMUSCLE AND NERVE, Issue 2 2009Catherine R. Lowrey MSc Abstract There is evidence to suggest that vestibular and somatosensory inputs may interact when they are processed by the central nervous system, although the nature of the individual sensory contributions to this interaction is unknown. We examined the effects of a combined vestibular and cutaneous conditioning stimulus on the motoneuron pool that supplies the soleus muscle via the Hoffman reflex (H-reflex). We applied galvanic vestibular stimulation (GVS; bipolar, binaural, 500 ms, 2.5-mA square-wave pulse) and cutaneous stimulation (medial plantar nerve; 11 ms, three-pulse train, 200 HZ) to prone human subjects and examined changes in the amplitude of the H-reflex. GVS alone caused facilitation (approximately 20%) of the H-reflex, whereas ipsilateral cutaneous stimulation alone caused a 26% inhibition. Paired GVS and cutaneous stimulation resulted in a linear summation of the individual conditioning effects. H-reflex amplitudes observed after paired conditioning with GVS and cutaneous stimulation could be predicted from the amplitudes observed with individual conditioning. These results suggest that in the prone position, when the muscles are not posturally engaged, vestibular and somatosensory information appear to sum in a linear fashion to influence the reflex response of lower limb motoneurons. Muscle Nerve 40: 213,220, 2009 [source] Supraspinal control of external anal sphincter motility: effects of vesical distension in humans and catsNEUROGASTROENTEROLOGY & MOTILITY, Issue 11 2006V. Vitton Abstract, A pontine centre located near the micturition centre controlling external anal sphincter (EAS) motility via noradrenergic neurones has been described in cats. The aim of this study was to determine (i) whether a similar centre controls EAS motility in humans and (ii) whether this centre is involved in vesico-sphincteric reflexes in cats and humans. The effects of an alpha-1-adrenoceptor antagonist (nicergoline) and those of vesical distension on the electrical activity of the EAS were studied in paraplegic and non-paraplegic volunteers. The effects of vesical distension by injecting saline at physiological levels on the responses of the EAS to pudendal nerve stimulation were investigated in intact cats and cats with nerve sections. In non-paraplegic subjects, nicergoline and vesical distension abolished the activity of the EAS. These effects were no longer observed in paraplegic patients. In cats, vesical distension inhibited the reflex response of the EAS to pudendal nerve stimulation. This vesico-sphincteric reflex, which was no longer observed in spinal animals, persisted after nicergoline injection. These findings indicate that in humans, there exists a supra-spinal centre facilitating the tonic activity of the EAS via noradrenergic neurones not involved in the inhibitory vesico-sphincteric reflex. [source] MULTIDISCIPLINARY PAIN ABSTRACTS: 20PAIN PRACTICE, Issue 1 2004Article first published online: 15 MAR 200 Trigeminocervical reflex is a brainstem reflex that is evoked by stimulating the sensory branches of the trigeminal nerve and can be recorded from the neck muscles. Electric stimulation of the supraorbital nerve evokes a reflex response (C3) and early reflex response (C1). The mean latencies of C1 and C3 of patients with parallel fibers (PFS) were compared with normal values. In healthy volunteers, C3 latency ± standard deviation was 54.17 ± 6.00 ms ipsilaterally and 51.25 ± 9.26 ms contralaterally. The difference was not significant. The C1 latency was 17.46 ± 4.89 ms. In patients with PFS, C1 latency was 13.83 ± 4.48 ms and the C3 latency was 62.70 ± 18.22 ms. The difference was not significant between the patients and healthy volunteers. Conclude in patients with PFS having neck pain, trigeminocervical connections were not influenced and some other mechanisms may be responsible for pain in these patients. [source] Phase-dependent and task-dependent modulation of stretch reflexes during rhythmical hand tasks in humansTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Ruiping Xia Phase-dependent and task-dependent modulation of reflexes has been extensively demonstrated in leg muscles during locomotory activity. In contrast, the modulation of reflex responses of hand muscles during rhythmic movement is poorly documented. The objective of this study was to determine whether comparable reflex modulation occurs in muscles controlling finger motions during rhythmic, fine-motor tasks akin to handwriting. Twelve healthy subjects performed two rhythmic tasks while reflexes were evoked by mechanical perturbations applied at various phases of each task. Electromyograms (EMGs) were recorded from four hand muscles, and reflexes were averaged during each task relative to the movement phase. Stretch reflexes in all four muscles were found to be modulated in amplitude with respect to the phase of the rhythmic tasks, and also to vary distinctly with the tasks being conducted. The extent and pattern of reflex modulation differed between muscles in the same task, and between tasks for the same muscle. Muscles with a primary role in each task showed a higher correlation between reflex response and background EMG than other muscles. The results suggest that the modulation patterns observed may reflect optimal strategies of central,peripheral interactions in controlling the performance of fine-motor tasks. As with comparable studies on locomotion, the phase-dependency of the stretch reflexes implies a dynamically fluctuating role of proprioceptive feedback in the control of the hand muscles. The clear task-dependency is also consistent with a dynamic interaction of sensory feedback and central programming, presumably adapted to facilitate the successful performance of the different fine-motor tasks. [source] 3221: Pathophysiology of dry eye syndromeACTA OPHTHALMOLOGICA, Issue 2010J HORWATH-WINTER Dry eye or dysfunctional tear syndrome is a highly prevalent disease worldwide. It is related to a pathological condition of anyone of the parts of the "ocular surface system" that involves the cornea, conjunctiva, lacrimal gland, accessory lacrimal glands, nasolacrimal duct and the lids with the meibomian glands. These are linked as a functional system by innervation, the endocrine and immune system. Endogenous or exogenous caused alterations in one or several components of the ocular surface system or its secretions result in changes of the tear film or ocular surface provoking inflammation. With time, inflammatory reactions may lead to corneal neuropathy compromising the reflex response of the lacrimal glands. Additionally a self-perpetuating vicious circle with loss of function and damage can be initiated also by an immune-modulated inflammation. [source] Cardio-respiratory reflexes evoked by phenylbiguanide in rats involve vagal afferents which are not sensitive to capsaicinACTA PHYSIOLOGICA, Issue 1 2010A. Dutta Abstract Aim:, Stimulation of pulmonary C fibre receptors by phenylbiguanide (PBG, 5-HT3 agonist) produces hypotension, bradycardia and tachypnoea or apnoea. However, tachypnoeic or apnoeic responses are not consistent. Therefore, this study was undertaken to delineate the actions of PBG on respiration and compared with those evoked by capsaicin (TRPV1 agonist). Methods:, Blood pressure, respiratory excursions and ECG were recorded in urethane anaesthetized adult rats. The effect of PBG or capsaicin was evaluated before and after ondansetron (5-HT3 antagonist), capsazepine (TRPV1 antagonist) or bilateral vagotomy. In addition, their effect on vagal afferent activity was also evaluated. Results:, Bolus injection of PBG produced concentration-dependent (0.1,100 ,g kg,1) hypotensive and bradycardiac responses, while there was tachypnoea at lower concentrations (0.1,3 ,g kg,1) and apnoea at higher concentrations (10,100 ,g kg,1). After vagotomy or after exposure to ondansetron both tachypnoeic and apnoeic responses were abolished along with cardiovascular responses. However, capsazepine (3 mg kg,1) did not block the PBG-induced reflex responses. Capsaicin (0.1,10 ,g kg,1), on the other hand, produced a concentration-dependent apnoea, hypotension and bradycardia but tachypnoea was not observed. Ondansetron failed to block the capsaicin-induced reflex response while bilateral vagotomy abolished bradycardiac and hypotensive responses and attenuated the apnoeic response. In another series, vagal afferent activity and cardio-respiratory changes evoked by PBG were blocked by ondansetron. However, capsaicin failed to activate the PBG-sensitive vagal afferents even though cardio-respiratory alterations were observed. Conclusions:, The present observations indicate that PBG produced tachypnoea at a lower concentration and apnoea at a higher concentration involving vagal afferents which are different from those excited by capsaicin. [source] B2 kinin receptors mediate the Indian red scorpion venom-induced augmentation of visceral reflexes via the nitric oxide cyclic guanosine monophosphate pathwayACTA PHYSIOLOGICA, Issue 4 2009S. Kanoo Abstract Aim:, This study was performed to delineate the kinin (receptor)-dependent pathways in the Indian red scorpion (Mesobuthus tamulus; MBT) venom-induced pulmonary oedema as well as the augmentation of cardio-pulmonary reflexes evoked by phenyldiguanide (PDG). Methods:, In urethane-anaesthetized adult rats, the effect of venom on the PDG reflex responses (blood pressure, heart rate and respiration rate) and the pulmonary water content was ascertained using various antagonists(des- Arg, B1 receptor antagonist; Hoe 140, B2 receptor antagonist; N, -nitro- l -arginine methyl ester (l -NAME), nitric oxide (NO) synthase inhibitor; methylene blue, soluble guanylate cyclase inhibitor; and glibenclamide, K+ATP channel blocker). The effect of phosphodiesterase V inhibitor (sildenafil citrate) on the reflex response and the pulmonary water content was also examined and compared with venom-induced responses. Results:, Intravenous injection of PDG (10 ,g kg,1) evoked apnoea, bradycardia and hypotension lasting >60 s. Exposure to MBT venom (100 ,g kg,1) for 30 min augmented the PDG reflex responses by two times and increased the pulmonary water content, significantly. Hoe 140 blocked the venom-induced responses (augmentation of PDG reflex and increased pulmonary water content) whereas des-Arg did not. l -NAME, methylene blue or glibenclamide also blocked the venom-induced responses. Furthermore, sildenafil citrate (that increases cGMP levels) produced augmentation of PDG reflex response and increased the pulmonary water content as seen with venom. Conclusion:, The results indicate that venom-induced responses involve B2 kinin receptors via the NO-dependent guanylate cyclase-cGMP pathway involving K+ATP channels. [source] Modulation of spinal inhibitory reflex responses to cutaneous nociceptive stimuli during upper limb movementEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 3 2008Romildo Don Abstract In the present study we investigated the probability, latency and duration of the inhibitory component of the withdrawal reflex elicited by painful electrical stimulation of the index finger in humans. The stimulus consisted of a train of high-intensity pulses. The investigation was carried out in several upper limb muscles during isometric contractions of different strengths and during a motor sequence consisting of reaching, picking up and transporting an object. We used a new algorithm to detect and characterize the inhibitory reflex. The reflex was found in all muscles except the brachioradialis at all the isometric contraction strengths, and showed a distal-to-proximal gradient of latency and duration. Conversely, during movement the reflex probability was high (> 80%) in the anterior deltoid and triceps muscles during reaching, in the extensor carpi radialis muscle during transporting of the object, and in the first interosseous muscle during both picking up and transporting of the object. This modulation of inhibitory reflex transmission in the upper limb muscles suggests that the motor response is organized in such a way as to inhibit the overall ongoing motor task by interrupting motion during reaching and by releasing the object during transporting. This pattern of modulation appears to differ markedly from that previously reported for the excitatory component of the withdrawal reflex. Study of the nociceptive inhibitory reflexes during movement offers new and more profound insights into the functional anatomical organization of the spinal interneuronal network mediating sensory,motor integration. [source] Nitric oxide regulates BDNF release from nodose ganglion neurons in a pattern-dependent and cGMP-independent mannerJOURNAL OF NEUROSCIENCE RESEARCH, Issue 6 2010Hui-ya Hsieh Abstract Activity of arterial baroreceptors is modulated by neurohumoral factors, including nitric oxide (NO), released from endothelial cells. Baroreceptor reflex responses can also be modulated by NO signaling in the brainstem nucleus tractus solitarius (NTS), the primary central target of cardiovascular afferents. Our recent studies indicate that brain-derived neurotrophic factor (BDNF) is abundantly expressed by developing and adult baroreceptor afferents in vivo, and released from cultured nodose ganglion (NG) neurons by patterns of baroreceptor activity. Using electrical field stimulation and ELISA in situ, we show that exogenous NO nearly abolishes BDNF release from newborn rat NG neurons in vitro stimulated with single pulses delivered at 6 Hz, but not 2-pulse bursts delivered at the same 6-Hz frequency, that corresponds to a rat heart rate. Application of L-NAME, a specific inhibitor of endogenous NO synthases, does not have any significant effect on activity-dependent BDNF release, but leads to upregulation of BDNF expression in an activity-dependent manner. The latter effect suggests a novel mechanism of homeostatic regulation of activity-dependent BDNF expression with endogenous NO as a key player. The exogenous NO-mediated effect does not involve the cGMP-protein kinase G (PKG) pathway, but is largely inhibited by N-ethylmaleimide and TEMPOL that are known to prevent S-nitrosylation. Together, our current data identify previously unknown mechanisms regulating BDNF availability, and point to NO as a likely regulator of BDNF at baroafferent synapses in the NTS. © 2009 Wiley-Liss, Inc. [source] Possible gender-related differences in a jaw reflex evoked by stimulation of the human lipJOURNAL OF ORAL REHABILITATION, Issue 9 2002M. F. LYONS It has been reported that the latency of the jaw jerk reflex in symptom-free human female subjects is significantly shorter than in male subjects (Kossioni et al., 1994). In the present study, we have begun to investigate whether there are any gender-related differences in other jaw reflexes. The EMG recordings were made from an active masseter muscle in 16 young adult age-matched subjects (eight male, eight female; aged 20,43 years). Inhibitory reflexes were evoked in the muscle by applying stimuli through bipolar electrodes clipped over the lower lip with the cathode placed intraorally on the oral mucosa. While the stimuli were being applied, the subjects maintained the EMG level at around 10% of maximum with the aid of visual feedback. The presence or absence of reflex responses was determined as previously described (Louca et al., 1996). Wilcoxon Rank Sum tests were used to compare the properties of the short- (,10,15 ms) and long- (,40,50 ms) latency inhibitory reflexes evoked by the stimuli in the two groups. There was no significant difference between the male and female groups in the threshold or latency of either reflex. However, the duration of the long-latency inhibition was significantly shorter in females than in males (median values: 29·0 versus 44·0 ms, P=0·015). These preliminary findings suggest that, at least in young human subjects, there is a gender-related difference in the strength but not in the presence of long-latency inhibitory jaw reflexes. [source] Excitatory synaptic potentials in spastic human motoneurons have a short rise-timeMUSCLE AND NERVE, Issue 1 2005Nina L. Suresh PhD Abstract This study assessed whether changes in size or time-course of excitatory postsynaptic potentials (EPSPs) in motoneurons innervating spastic muscle could induce a greater synaptic response, and thereby contribute to reflex hyperexcitability. We compared motor unit (MU) firing patterns elicited by tendon taps applied to both spastic and contralateral (nonspastic) biceps brachii muscle in hemiparetic stroke subjects. Based on recordings of 115 MUs, significantly shortened EPSP rise times were present on the spastic side, but with no significant differences in estimated EPSP amplitude. These changes may contribute to hyperexcitable reflex responses at short latency, but the EPSP amplitude changes appear insufficient to account for global differences in reflex excitability. Muscle Nerve, 2005 [source] Gentle dorsal root retraction and dissection can cause areflexia: Implications for intraoperative monitoring during "selective" partial dorsal rhizotomyMUSCLE AND NERVE, Issue 10 2001Eric L. Logigian MD Abstract During partial dorsal rhizotomy (PDR), intraoperative dorsal rootlet stimulation often evokes nonreflex, rather than reflex, motor responses that are due to costimulation of adjacent ventral roots. Intraoperative areflexia typically predicts that motor responses evoked by dorsal rootlet stimulation are nonreflexive. The cause of areflexia during PDR is in part due to anesthesia, but other mechanisms are likely to play a role as well. In this study of three consecutive patients undergoing lumbosacral neurosurgery, soleus H-reflexes evoked by tibial nerve stimulation at the popliteal fossa were found to suddenly decline in amplitude following retraction and gentle dissection of the S-1 dorsal root. In one areflexic patient, dorsal rootlet stimulation proximal to the main site of dissection evoked soleus H-reflexes, although they could not be evoked by tibial nerve stimulation. We conclude that the gentle retraction and dissection of dorsal rootlets that occurs during PDR can induce conduction block of reflex afferents. High-intensity dorsal rootlet stimulation distal to the site of conduction block may then evoke not reflex responses, but rather nonreflex motor responses, due to the costimulation of adjacent ventral roots. © 2001 John Wiley & Sons, Inc. Muscle Nerve 24: 1352,1358, 2001 [source] External anal sphincter responses after S3 spinal root surface electrical stimulationNEUROUROLOGY AND URODYNAMICS, Issue 7 2006Giuseppe Pelliccioni Abstract Aims The aim of this study is to present the normative data of direct and reflex motor anal sphincter responses, simultaneously evoked by S3 surface electrical stimulation. By this method, it is possible to test the functional integrity of the nervous pathways activated during sacral neuromodulation (SNM). Methods Twenty healthy subjects were studied. Motor-evoked potentials (MEPs) were recorded by concentric needle electrode from external anal sphincter (EAS). Electrical stimulation was applied by means of a bipolar surface electrode over the S3 right or left sacral foramina. Results Direct (R1) and reflex responses (R2 and R3) were found at latencies of 6.98, 25.12, and 50.31 msec, respectively. The two first responses were recorded in all the cases; the last response is steadily recorded in 17 out of 20 subjects. Conclusions Our data can serve as reference values for future study in patients with pelvic floor dysfunction. EAS responses following S3 percutaneous electrical stimulation can represent a useful aid in the selection of candidates to SNM. Neurourol. Urodynam. 25:788,791, 2006. © 2006 Wiley-Liss, Inc. [source] Mechanical and neural stretch responses of the human soleus muscle at different walking speedsTHE JOURNAL OF PHYSIOLOGY, Issue 13 2009Neil J. Cronin During human walking, a sudden trip may elicit a Ia afferent fibre mediated short latency stretch reflex. The aim of this study was to investigate soleus (SOL) muscle mechanical behaviour in response to dorsiflexion perturbations, and to relate this behaviour to short latency stretch reflex responses. Twelve healthy subjects walked on a treadmill with the left leg attached to an actuator capable of rapidly dorsiflexing the ankle joint. Ultrasound was used to measure fascicle lengths in SOL during walking, and surface electromyography (EMG) was used to record muscle activation. Dorsiflexion perturbations of 6 deg were applied during mid-stance at walking speeds of 3, 4 and 5 km h,1. At each walking speed, perturbations were delivered at three different velocities (slow: ,170 deg s,1, mid: ,230 deg s,1, fast: ,280 deg s,1). At 5 km h,1, fascicle stretch amplitude was 34,40% smaller and fascicle stretch velocity 22,28% slower than at 3 km h,1 in response to a constant amplitude perturbation, whilst stretch reflex amplitudes were unchanged. Changes in fascicle stretch parameters can be attributed to an increase in muscle stiffness at faster walking speeds. As stretch velocity is a potent stimulus to muscle spindles, a decrease in the velocity of fascicle stretch at faster walking speeds would be expected to decrease spindle afferent feedback and thus stretch reflex amplitudes, which did not occur. It is therefore postulated that other mechanisms, such as altered fusimotor drive, reduced pre-synaptic inhibition and/or increased descending excitatory input, acted to maintain motoneurone output as walking speed increased, preventing a decrease in short latency reflex amplitudes. [source] Phase-dependent and task-dependent modulation of stretch reflexes during rhythmical hand tasks in humansTHE JOURNAL OF PHYSIOLOGY, Issue 3 2005Ruiping Xia Phase-dependent and task-dependent modulation of reflexes has been extensively demonstrated in leg muscles during locomotory activity. In contrast, the modulation of reflex responses of hand muscles during rhythmic movement is poorly documented. The objective of this study was to determine whether comparable reflex modulation occurs in muscles controlling finger motions during rhythmic, fine-motor tasks akin to handwriting. Twelve healthy subjects performed two rhythmic tasks while reflexes were evoked by mechanical perturbations applied at various phases of each task. Electromyograms (EMGs) were recorded from four hand muscles, and reflexes were averaged during each task relative to the movement phase. Stretch reflexes in all four muscles were found to be modulated in amplitude with respect to the phase of the rhythmic tasks, and also to vary distinctly with the tasks being conducted. The extent and pattern of reflex modulation differed between muscles in the same task, and between tasks for the same muscle. Muscles with a primary role in each task showed a higher correlation between reflex response and background EMG than other muscles. The results suggest that the modulation patterns observed may reflect optimal strategies of central,peripheral interactions in controlling the performance of fine-motor tasks. As with comparable studies on locomotion, the phase-dependency of the stretch reflexes implies a dynamically fluctuating role of proprioceptive feedback in the control of the hand muscles. The clear task-dependency is also consistent with a dynamic interaction of sensory feedback and central programming, presumably adapted to facilitate the successful performance of the different fine-motor tasks. [source] Activated platelets contribute to stimulation of cardiac afferents during ischaemia in cats: role of 5-HT3 receptorsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2002Liang-Wu Fu Myocardial ischaemia activates blood platelets and cardiac sympathetic afferents, which mediate chest pain and cardiovascular reflex responses. We have demonstrated that activated platelets stimulate ischaemically sensitive cardiac sympathetic afferents. Platelets absorb and release 5-hydroxytryptamine (5-HT) when they are activated. In the present study we hypothesized that, by releasing 5-HT, activated platelets stimulate cardiac afferents during ischaemia through a 5-HT3 receptor mechanism. Platelet-rich plasma (PRP) and platelet-poor plasma (PPP) were obtained from cats. Activation of platelets in PRP was induced by thrombin (5 units ml,1) or collagen (2 mg kg,1). Using high-performance liquid chromatography, we observed that the concentration of 5-HT was increased significantly in suspensions of platelets activated with thrombin (PRP+thrombin, 28 ± 1.7 ,m) or collagen (PRP+collagen, 27 ± 2.5 ,m) compared with suspensions of unactivated platelets (PRP+saline, 2.3 ± 0.8 ,m) and PPP. During myocardial ischaemia and reperfusion, tirofiban, a specific inhibitor of platelet glycoprotein (GP) IIb-IIIa receptors (100 ,g kg,1, I.V., followed by 5 ,g kg,1 min,1), significantly reduced the increase in the concentration of 5-HT in cardiac venous plasma from ischaemic region. Nerve activity of single-unit cardiac afferents was recorded from the left sympathetic chain (T2-T5) in anaesthetized cats. Eighty ischaemically sensitive and seven ischaemically insensitive cardiac afferents were identified. Tirofiban reduced the ischaemia-related increase in activity of seven cardiac sympathetic afferents by 50 %. Injection of 1.5 ml of PRP+collagen or PRP+thrombin into the left atrium (LA) increased activity of 16 cardiac afferents. Tropisetron (300 ,g kg,1, I.V.), a selective 5-HT3 receptor antagonist, eliminated the afferent's responses to platelets activated with collagen or thrombin. Moreover, LA injection of 5-HT (20-40 ,g kg,1) and PBG (100 ,g kg,1), a 5-HT3 receptor agonist, stimulated nine ischaemically sensitive cardiac sympathetic afferents, significantly increasing the activity of these afferents. However, injection of ,-M-5-HT (100 ,g kg,1, LA), a 5-HT2 receptor agonist, stimulated only two of the nine ischaemically sensitive cardiac afferents, and thus did not significantly alter impulse activity of this group of afferents. Both the 5-HT1 (5-CT, 100 ,g kg,1, LA) and 5-HT4 receptor agonists (SC53116, 100 ,g kg,1, LA) did not stimulate any of the nine afferents tested. Tropisetron (300 ,g kg,1, I.V.) also eliminated the response of seven ischaemically sensitive cardiac afferents to exogenous 5-HT and attenuated the ischaemia-related increase in activity of nine cardiac sympathetic afferents by 41 %. Conversely, LA injection of 5-HT (40 ,g kg,1) did not stimulate any of seven ischaemically insensitive cardiac afferents, although this group of afferents consistently responded to bradykinin (3 ,g, LA). These data indicate that during myocardial ischaemia the activated platelets stimulate cardiac sympathetic afferents, at least in part, through a 5-HT3 receptor mechanism. [source] Control of non-adrenergic non-cholinergic reflex motor responses in circular muscle of guinea-pig small intestine by Met-enkephalinAUTONOMIC & AUTACOID PHARMACOLOGY, Issue 4 2002Chr. Ivancheva Summary 1 A triple organ bath method allowing the synchronous recording of the motor activity of the circular muscle layer belonging to the oral and anal segments of guinea-pig small intestine adjacent to an electrically stimulated middle segment was developed to study the ascending and descending reflex motor responses. 2 Electrical field stimulation (0.8 ms, 40 V, 5 Hz, 10 s) applied to the middle part of the segments elicited tetrodotoxin (1 ,m)-sensitive ascending and descending contractile responses of the nonstimulated parts, oral and anal, respectively. The ascending contraction was more pronounced as compared with the descending contraction. 3 In the presence of phentolamine (5 ,m), propranolol (5 ,m) and atropine (3 ,m) a significant decrease in the amplitude of the ascending contraction was seen and a descending relaxation, instead of a contraction was observed. 4 Met-enkephalin applied at a single concentration (0.1 ,m) or cumulatively (0.001,1 ,m) inhibited both non-adrenergic non-cholinergic (NANC) descending relaxation and ascending contraction with similar efficacy but different potency, IC50 being 5.9 ± 0.3 and 39.0 ± 4 nm, respectively. Naloxone (0.5 ,m) prevented the effects of Met-enkephalin. 5 L-NNA (0.5 mm), an inhibitor of nitric oxide synthesis, increased the ascending contraction and strongly reduced but not abolished the descending relaxation. l -Arginine (0.5 mm) restored the motor responses to the initial level in l -NNA-pretreated preparations, d -Arginine (0.5 nm) had no effects. 6 Met-enkephalin (0.1 ,m) depressed the l -NNA-dependent increase of the ascending contraction and failed to change the l -NNA-resistant part of the descending relaxation. 7 Met-enkephalin did not alter spontaneous NANC mechanical activity. SNP (1 or 10 ,m), an exogenous donor of nitric oxide, caused a concentration-dependent relaxation. The effects of SNP persisted in Met-enkephalin (0.1 ,m)-pretreated preparations. 8 NANC reflex ascending contraction and descending relaxation were synchronously induced by a local nerve stimulation indicating a functional coactivation of NANC orally projected excitatory and anally directed inhibitory pathways. Acting prejunctionally, Met-enkephalin provided a negative controlling mechanism inhibiting both ascending and descending, mainly nitric oxide mediated, reflex responses. A higher sensitivity of the descending relaxation to Met-enkephalin was observed suggesting an essential role of opioid(s) in reducing the efficacy of descending motor activity. [source] Cardiovascular reflex responses after intrathecal ,-conotoxins or dexmedetomidine in the rabbitCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 1-2 2003Duncan W Blake Summary 1.,The effects of thoracic intrathecal doses (1 µg/kg) of the ,2 -adrenoceptor agonist dexmedetomidine and ,-conotoxins MVIIA and CVID on vasoconstrictor and heart rate responses to acute central hypovolaemia were studied in seven chronically instrumented rabbits. 2.,Gradual inflation of an inferior vena cava cuff to reduce cardiac index (CI) by 8% per minute induced progressive vasoconstriction and an increase in heart rate (phase I). At approximately 40% of resting CI, there was sudden decompensation with failure of vasoconstriction and decrease in mean arterial pressure (MAP; phase II). 3.,Both intrathecal MVIIA and CVID decreased resting CI (by 20% at 3 h), but only MVIIA significantly reduced resting MAP (P = 0.003). Dexmedetomidine resulted in transient bradycardia, but no other significant change in the resting circulation. With simulated haemorrhage, the relationship between CI and vascular conductance was shifted after MVIIA (1,3 h after injection) so that there was less vasoconstriction and a reduced increase in heart rate by the end of phase I compared with other treatments (P = 0.002 and P = 0.009, respectively). One hour after injection, dexmedetomidine reduced the slope of the phase I vasoconstrictor response (P = 0.03), but did not significantly alter the end-point of the response. With failure of vasoconstriction and the onset of phase II, vascular conductance was higher after MVIIA compared with controls. Both conotoxins caused progressive failure of vasoconstriction rather than recovery during phase II (P < 0.001). 4.,Intrathecal injections of these drugs to control chronic pain may compromise cardiovascular responses to changes in central blood volume. At the single doses studied, there were significant differences between the responses to simulated haemorrhage after MVIIA or dexmedetomidine compared with CVID, with the prolonged effect after MVIIA most likely to be of clinical significance. [source] | |||||||||||||