Interaction between the Postactivation Depression of H Reflex and Long-Lasting Inhibition,Evoked by Stimulation of a Nerve to the Antagonist Muscles,in Humans

In a study on healthy humans, we examined interaction of the inhibitory influences on the H reflex recorded from the m. soleus (the respective EMG discharge, evoked by stimulation of the n. tibialis comm.). Postactivation depression of the reflex was evoked by a preceding conditioning stimulation of the same nerve, while conditioning stimulation of a nerve to the antagonist muscles (n. peroneus comm.) evoked long-lasting inhibition of the reflex, which included two consecutive waves of depression, D ₁ and D ₂. When the intensity of conditioning stimulations slightly exceeded the threshold for the development of inhibitory effects, interaction between postactivation depression and both the D ₁ and D ₂ waves demonstrated mutual facilitation of these effects. When the intensity of conditioning stimuli was increased, facilitation was changed by occlusion. We conclude that afferent impulsation, evoked by homo- and heteronymous conditioning stimulations of the peripheral nerves, converges on common interneuronal populations providing long-lasting suppression of the H reflex, which develops due to depolarization of primary afferent Ia terminals.     

Fatigue-induced modulation of the H reflex of soleus muscle in humans

We studied the effect of fatigue of the mm. gastrocnemius-soleus on the H reflex elicited by transcutaneous stimulation of n. tibialis and recorded from the m. soleus; healthy 18-to 34-year-old volunteers were tested. Fatigue was evoked by long-lasting (6 to 9 min) voluntary tonic static sole flexion of the foot (ankle extension) with a force equal to 75% of the maximum voluntary contraction (MVC). The amplitude of H reflex significantly (P < 0.001) decreased to about 60% of the initial value immediately after the period of fatiguing effort. Within 2 to 3 min, it relatively rapidly recovered and reached about 90% of the control, and this was followed by a period of slow recovery to about 96–97% of the initial value 30 min after conditioning fatigue. We suppose that the initial period of suppression of the H reflex results to a considerable extent in an increase in the intensity of presynaptic inhibition of transmission from Ia afferents due to tonic activation of high-threshold (groups III and IV) afferent fibers induced by intensive fatigue-related metabolic changes in the muscles. More long-lasting (tens of minutes) changes are related to slow reverse development of direct effects of fatigue-induced biochemical shifts in the muscle. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 426–431, September–December, 2006.     

Long-lasting H-reflex inhibition evoked by stimulation of a nerve to the antagonist muscles and vibrational stimulation of the muscle receptors in humans

In testing of healthy subjects, we studied the influence of conditioning stimulation of then.peroneus communis on the H-reflex EMG discharge recorded from them. soleus. Two waves of inhibition separated by a period of relative facilitation of the reflex were observed. The first wave,D ₁, was not longer than 50 msec. The intensity of later inhibition (D ₂ wave) within a 500 to 4000 msec time segment linearly depended on the logarithm of the interval between the conditioning and test stimuli. Extrapolation showed that the duration of this wave could be evaluated as equal to 6.3 msec, on average. We also studied the temporal course of H-reflex inhibition after conditioning vibrational stimulation of the receptors of them. tibialis ant. andm. biceps femori. Within a 500 to 4000 msec test interval, it could also be fitted with a logarithmic dependence similar to that observed after electrical stimulation of then. peroneus comm. The duration of inhibition after vibrational stimulation of them. tibialis ant. andm. biceps femori was 6.2 and 8.9 sec, respectively. Inhibition evoked by both conditioning influences was not removed after a voluntary plantar flexion of the foot. Our observations support the statement that in humans stimulation of the afferent fibers from the antagonist muscles, as well of the muscle receptors, evokes in two-neuron reflex arcs presynaptic inhibition, whose duration reaches several seconds; this phenomenon can play a significant role in the control of muscle tone in the course of muscle performance.     

Long-lasting inhibition of the soleus muscle H reflex related to realization of voluntary arm movements in humans

In healthy humans, we recorded the H reflex induced by transcutaneous stimulation of the tibial nerve (recording from the soleus muscle). In subjects in the lying position, we studied changes in the H reflex values after preceding voluntary arm movements realized with a maximum velocity after presentation of an acoustic signal. On the 200th to 300th msec after forearm flexion, long-lasting inhibition of the H reflex developed following a period of initial facilitation and reached the maximum, on average, 700 msec from the moment of the movement. Flexion of the contralateral upper limb in the elbow joint induced deeper inhibition than analogous movement of the ipsilateral arm. Long-lasting clear inhibition of the H reflex developed after arm flexion in the elbow joint but was slightly expressed after finger clenching. After inhibition reached the maximum, its time course was satisfactorily approximated by a logarithmic function of the time interval between the beginning of the conditioning voluntary movement and presentation of the test stimulus. Durations of inhibition calculated using a regression equation were equal to 6.6 sec and 8.5 sec after ipsilateral and contralateral elbow-joint flexions, respectively. Inhibition was not eliminated under conditions of tonic excitation of motoneurons of the tested muscle upon voluntary foot flexion. Long-lasting inhibition of the H reflex was also observed after electrical stimulation-induced flexions of the upper limb. The obtained data indicate that movements of the upper limb cause reflex long-lasting presynaptic inhibition of the soleus-muscle H reflex that can play a noticeable role in redistribution of the muscle tone during motor activity. Neirofiziologiya/Neurophysiology, Vol. 40, No. 3, pp. 221–227, May–June, 2008.     

Changes in the H Reflex Preceding Voluntary Movements of the Contralateral Lower Limb in Humans

In electromyographic studies on healthy subjects, we recorded the H reflex from the right m. soleus and measured changes in the magnitude of this reflex response related to voluntary movements of the contralateral lower limb performed according to a visual signal. The effects of back and plantar flexions of the contralateral foot of the tested subject in the lying and standing positions were examined. Changes in the H reflex magnitude began to be recorded 60 to 90 msec prior to voluntary movements of the contralateral limb. When the subject was in the lying position, these changes looked like facilitation of the H reflex at both types of movement of the contralateral foot. When the subject stood, facilitation preceded back flexion of the foot of this extremity, while plantar flexion was preceded by inhibition of the tested H reflex. Our results show that the pattern of preliminary changes in the muscle tone of one of the lower limbs is determined by the type of future movement of another limb and peculiarities of the support function realized by this limb.     

Effects of Long-Lasting Afferent Activation on Segmental Reflex Responses in Albino Rats,and Modifications of These Effects by Thyroxine and 4-Aminopyridine

In albino rats, we studied the effects of long-lasting tetanization of the dorsal roots of the L ₅ (homosynaptic activation) and L ₄ (heterosynaptic activation) segments on reflex discharges in the L ₅ ventral root evoked by single stimulation of the dorsal root of the same segment. Tetanization trains consisted of 5,000 stimuli applied with frequencies of 10, 50, 100, or 300 sec^–1, and their effects were tested during 10 min. There were no long-term post-tetanic potentiation (PTP) of monosynaptic responses when low frequencies of homosynaptic tetanization (10 and 50 sec^–1) were used. In the case of higher frequencies, PTP was rather clear and long-lasting. Under conditions of heterosynaptic activation, there was no PTP. Facilitation of polysynaptic responses developed at all the frequencies of homosynaptic tetanization used; when heterosynaptic tetanization was applied, such facilitation (although weaker) was also observed. In rats treated with agents increasing the excitability of spinal neuronal systems, such as thyroxine and 4-aminopyridine, tetanization of the studied inputs evoked long-term depression (LTD) of both mono- and polysynaptic components of the reflex discharges instead of PTP. Probable mechanisms of postsynaptic changes in the segmental reflex responses are discussed.     

Influence of transcutaneous electrical nerve stimulation conditions on disynaptic reciprocal Ia inhibition and presynaptic inhibition in healthy adults

This study investigated the influence of stimulus conditions of transcutaneous electrical nerve stimulation (TENS) on disynaptic reciprocal Ia inhibition (RI) and presynaptic inhibition (D1 inhibition) in healthy adults. Eight healthy participants received TENS (stimulus frequencies of 50, 100, and 200?Hz) over the deep peroneal nerve and tibialis anterior (TA) muscle in the resting condition for 30?min. At pre- and post-intervention, the RI from the TA to the soleus (SOL) and D1 inhibition of the SOL alpha motor neuron were assessed by evoked electromyography. The results showed that RI was not changed by TENS at any stimulus frequency condition. Conversely, D1 inhibition was significantly changed by TENS regardless of the stimulus frequency. The present results and previous studies pertaining to RI suggest that the resting condition might strongly influence the lack of pre- vs. post-intervention change in the RI. Regarding the D1 inhibition, the present results suggest that the effect of TENS might be caused by post-tetanic potentiation. The knowledge gained from the present study might contribute to a better understanding of fundamental studies of TENS in healthy adults and its clinical application for stroke survivors.     

吗啡对猕猴瞳孔光反应能力的影响

光照能明显改变正常人和动物瞳孔的大小,而精神疾病及药物滥用则影响人和动物瞳孔对光的反应性.因此,瞳孔对光反应异常可以用作检测精神疾病和药物滥用的指标.有关药物滥用是如何影响瞳孔对光的反应性的研究还很少.为定量地测量成瘾性药物对瞳孔光反应变化的影响,该文采用猕猴为实验对象,通过在黑暗环境中测量猕猴在吗啡给予前和吗啡给予后的不同时间段,其瞳孔直径大小以及其对光反应能力的变化情况,来系统研究吗啡是如何影响这种非自主性反射系统的.研究发现,吗啡给予降低了猕猴在黑暗环境中的扩瞳反应,并且降低了瞳孔对光反应的收缩率.该文为将瞳孔对光反应特征用作鉴定吸毒者的检测手段提供了实验依据.     

Locomotor-Like Rotation of Either Hip or Knee Inhibits Soleus H Reflexes in Humans

Human soleus H reflexes are depressed with passive movement of the leg. We investigated the limb segment origin of this inhibition. In the first experiment, H reflexes were evoked in four subjects during (1) passive pedaling movement of the test leg at 60 rpm; (2 and 3) pedaling-like flexion and extension of the hip and the knee of the test leg separately; and (4) stationary controls. In the second experiment, with the test leg stationary, the same series of movements occurred in the opposite leg. Rotation of the hip or the knee of the test leg significantly reduced mean reflex amplitudes (p > 0.01) to levels similar to those for whole-leg movement (mean H reflexes: stationary, 71%; test leg pedaling movement, 10%; knee rotation, 15%; hip rotation, 13% [all data are given as percentages of M_max]). The angle of the stationary joint did not significantly affect the results. Rotation of the contralateral hip significantly reduced mean reflex magnitudes. Rotation of the contralateral knee had a similar effect in three of the four subjects. We infer that a delimited field of receptors induces the movement conditioning of both the ipsilateral and contralateral spinal paths. It appears that somatosensory receptor discharge from movement of the hip or knee of either leg induces inhibition as the foundation for the modulation of H reflexes observed during human movement.     

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Percutaneous electrical nerve stimulation is a non-invasive method commonly used to evaluate neuromuscular function from brain to muscle (supra-spinal, spinal and peripheral levels). The present protocol describes how this method can be used to stimulate the posterior tibial nerve that activates plantar flexor muscles. Percutaneous electrical nerve stimulation consists of inducing an electrical stimulus to a motor nerve to evoke a muscular response. Direct (M-wave) and/or indirect (H-reflex) electrophysiological responses can be recorded at rest using surface electromyography. Mechanical (twitch torque) responses can be quantified with a force/torque ergometer. M-wave and twitch torque reflect neuromuscular transmission and excitation-contraction coupling, whereas H-reflex provides an index of spinal excitability. EMG activity and mechanical (superimposed twitch) responses can also be recorded during maximal voluntary contractions to evaluate voluntary activation level. Percutaneous nerve stimulation provides an assessment of neuromuscular function in humans, and is highly beneficial especially for studies evaluating neuromuscular plasticity following acute (fatigue) or chronic (training/detraining) exercise.     

声波刺激对猕猴桃愈伤组织ATP含量的影响

采用单因子实验设计,分别先固定作为交变应力的声波的频率或强度这两个参数中的一个,而改变另一个指标的值,用声波刺激木本植物中华猕猴桃(Actinidiachinensis)茎段的愈伤组织,并测定对比声波处理前后其ATP含量及变化情况。实验结果表明,声波对猕猴桃愈伤组织ATP的含量有着比较明显的增强或抑制的双重效应,适度的声场刺激将有利于提高植物的能量代谢水平,其中,最适的声波频率为1000Hz,最适声强为100dB左右 。     

Short-Term Effects of a Brief Respiratory Training on Baroreceptor Cardiac Reflex Function in Normotensive and Mild Hypertensive Subjects

Baroreceptor cardiac reflex sensitivity is reduced in hypertension and is considered a powerful prognostic factor in cardiovascular health. This study analyzes the acute effects of a brief respiratory training on baroreceptor sensitivity and on two new proposed baroreflex parameters: baroreceptor power (i.e., the percentage of cardiac beats regulated by the baroreflex) and effectiveness (i.e., the frequency in which the baroreflex responds to transient alterations in blood pressure). Twenty-two participants, 10 primary mild hypertensives and 12 normotensives, learned and practiced a respiratory pattern characterized by breathing at 6 bpm, with time of expiration being twice time of inspiration, predominantly abdominal, and with pursed lips. Baroreceptor parameters are differentiated in terms of increases (“up” sequences) or decreases (“down” sequences) in blood pressure. Irrespective of the groups, the breathing manipulation increased baroreceptor sensitivity (only in the “up” sequences), power, and effectiveness (only in the “down” sequences). These results suggest that this type of respiratory training could be used as a promising intervention to increase baroreceptor cardiac function in primary hypertension.     

光照对麻醉大鼠海马节律的影响

目的:研究光照刺激对麻醉大鼠海马节律的影响。方法:对乌拉坦麻醉大鼠,在海马中植入电极,通过神经信号放大器记录场电位。重复对大鼠进行视觉刺激,刺激10s,并给予20s的恢复期。与经典掐尾实验进行对比。结果:乌拉坦麻醉大鼠的掐尾实验能够将海马场电位从"大不规则波"(LIA)变成theta波。LIA到theta的转变通常只需1s,掐尾结束后3s后theta返回LIA。光刺激造成了在5-8s后LIA消失,光刺激撤离后4-6sLIA返回,并没有引发theta。结论:本文结果提示视觉通路与触觉通路有不同的优先级和行为特性。     

Responsiveness of the H reflex to loading and posture in patients following stroke

The objective of the research was to examine the effects of loading and posture on motoneuronal excitability of the triceps surae (TS) for patients with hemiplegia. Twelve healthy subjects and 12 patient subjects with post-stroke hemiparesis (onset period: 3–60 months) were enrolled in this study. The subjects were instructed to remain in quiet sitting with the test knee straight and three standing conditions of different superincumbent loads by shifting body weight to the test leg (10%, 50%, and 90% of body weight), while the H reflexes and M waves of the TS were measured. The results clearly indicated that H reflex amplitudes were not affected by different loading conditions in standing for both healthy subjects and patients who had a previous stroke. In addition, the H reflex amplitude in quiet standing for healthy subjects was significantly downward modulated relative to that in relaxed sitting with the test knee straight, but this posturally driven modulation was impaired in patients following stroke. Current electrophysiological findings imply that body weight as a means for rehabilitation facilitation had little immediate effect on paretic TS, and absence in postural gating of reflex excitability appeared to be an incentive for postural instability resulting from post-stroke hemiparesis.     

电刺激大鼠腓肠神经引起Aδ、 C类传入神经纤维的背根反射

在距脊髓约 15mm处切断大鼠L5背根 ,将中枢端分成 4～ 5条细束 ,电刺激腓肠神经在背根细束上记录背根反射 (dorsalrootreflex ,DRR)。共记录到DRR 5 1例 ,根据引起DRR所兴奋的腓肠神经纤维类别和DRR在背根逆向传出的纤维类别将DRR分为 5类 :Aαβ Aαβ·DRR、Aβδ Aδ·DRR、Aβδ C·DRR、Aαβδδ C·DRR和C C·DRR。结果证明 ,电刺激外周神经激活各类纤维不但能引起A类 (包括Aδ)纤维的DRR ,而且也能引起C类纤维的DRR。记录的Aδ·DRR和C·DRR为细纤维传入终末产生突触前抑制提供了客观指标 ,为DRR逆向传出冲动到达外周组织 ,释放神经肽类递质 ,调节外周效应器的功能提供了证据     

精准定位脑刺激对运动功能调控研究进展

脑刺激是神经科学研究的重要手段,传统的经颅磁刺激和经颅电刺激等脑刺激方法尽管能调控运动功能(包括减轻运动性障碍疾病的运动障碍、提高运动能力等),但存在空间分辨率低且无法刺激深部脑组织的局限性.近年来迅速发展的深部脑刺激(deep brain stimulation,DBS)、光遗传学、经颅超声刺激(transcranial ultrasound stimulation,TUS)、时间干涉(temporal interference,TI)等精准定位脑刺激方法,具有空间分辨率高、可聚焦深部脑组织等优点.本文综述了上述几种脑刺激方法的原理、特点,对运动功能调控的研究进展,以及面临的挑战和发展前景,从而为神经科学研究提供更好的研究工具,为临床实践提供更多的干预治疗手段.