The effects of transcutaneous electrical nerve stimulation on spasticity

Abstract

Transcutaneous electrical nerve stimulation (TENS) is commonly used in the treatment of chronic and acute pain with possible mechanisms of action including segmental inhibition, release of endogenous opioids, counter-irritation, nerve conduction block, and placebo. Although not frequently used in current practice, there is some evidence that TENS has an effect on spasticity in neurological conditions such as stroke, spinal cord injury, and multiple sclerosis. This paper reviews the results of studies undertaken to date, evaluating not only the effects of TENS on spasticity, but also the impact of different TENS parameters on its overall effectiveness. Recommendations based on the current evidence for the use of TENS in the treatment of spasticity are made, as well as suggestions for further study.     

Effects of transcutaneous electrical nerve stimulation on pain in patients with spinal cord injury: a randomized controlled trial

[Purpose] To investigate the effects of transcutaneous electrical nerve stimulation (TENS) on pain in patients with spinal cord injury. [Subjects and Methods] Fifty-two spinal cord injury patients with central pain were randomly allocated into two groups TENS and control with 26 subjects per group. The patients in TENS and control groups were treated with TENS and sham TENS for 20 min (three times a week) for 12 consecutive weeks, respectively. The two group’s pain was assessed using visual analog scale (VAS) and the McGill Pain Questionnaire (including pain rating index-total, pain rating index-affective, pain rating index-sensory, present pain intensity, and number of words chosen) before and after the treatment. [Results] After the intervention, we found significant differences in VAS, pain rating index-total, pain rating index-affective, pain rating index-sensory, present pain intensity, and number of words chosen between the TENS group and the control group. [Conclusion] Our results suggest that TENS effectively decreases pain in patients with spinal cord injury.Key words: Transcutaneous electrical nerve stimulation, Pain, Spinal cord injury     

Transcutaneous electrical nerve stimulation versus baclofen in spasticity: clinical and electrophysiologic comparison

OBJECTIVES: Clinical and electrophysiologic comparison of the efficacy of transcutaneous electrical nerve stimulation (TENS) and oral baclofen in the treatment of spasticity. DESIGN: Patients with spinal cord injury and spasticity were included in the study. Ten patients were assigned to oral baclofen and 11 to TENS groups. For the comparison of H-reflex variables, 20 healthy individuals were allocated to a control group. TENS was applied to the tibial nerve for 15 days at a frequency of 100 Hz. Clinical (spasm frequency scale, painful spasm scale, lower limb Ashworth score, clonus score, deep tendon reflex score, plantar stimulation response score) and electrophysiologic evaluations (H-reflex response at the highest amplitude, latency of maximum H-reflex, and ratio of H-reflex response at the highest amplitude to M response at maximum amplitude) of the lower limb and functional evaluations (functional disability score and FIM) were carried out in baclofen and TENS groups before and after treatment. Posttreatment evaluation was made 24 hrs after the 15th session in the TENS group. In addition, clinical spasticity scores and electrophysiologic variables were measured 15 mins after the first application and 15 mins after the 15th session. RESULTS: Significant improvement was detected in lower limb Ashworth score, spasm frequency scale, deep tendon reflex score, functional disability score, and FIM in the baclofen (P = 0.011, P = 0.014, P = 0.025, P = 0.004, and P = 0.005, respectively) and TENS (P = 0.020, P = 0.014, P = 0.025, P = 0.003, and P = 0.003, respectively) group after treatment. Decrease in H-reflex maximum amplitude was significant in the TENS group (P = 0.026). Most marked improvement was observed in the third evaluation, 15 mins after the 15th session, particularly in lower limb Ashworth score (P = 0.006) and H-reflex maximum amplitude (P = 0.006) in the TENS group. The percentage change in clinical, electrophysiologic, and functional variables caused by baclofen was not different from that caused by repeated applications of TENS in the short- and long-term evaluations (P > 0.05). CONCLUSION: TENS may be recommended as a supplement to medical treatment in the management of spasticity.     

TENS and FES for sensory impairment and gait dysfunction following removal of spinal cord ependymoma — a case report

Background . Sensory deficits are commonly reported following the resection of spinal cord tumours. The use of transcutaneous electrical nerve stimulation (TENS) as augmented sensory input is described in the research literature but rarely in the clinical literature. Functional electrical stimulation (FES) is used for people with motor impairments rather than sensory impairments. Method and results . This case report describes the use of TENS and FES for a patient with severe sensory loss and mild weakness in the right leg following the removal of an intramedullary spinal cord tumour. The patient was able to walk more quickly and more confidently when using TENS and FES in combination. She consistently reported greater benefits from TENS alone compared to FES alone and continued to use TENS delivered via a sock electrode at six months after surgery. Conclusion . The use of TENS as a sensory stimulus was an invaluable component of this patient's treatment, allowing her to engage in a more challenging balance and gait programme at an earlier stage in her rehabilitation. Combining FES with TENS was also useful and allowed treatment to address motor and sensory impairments concurrently during functional activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Increased release of serotonin in the spinal cord during low, but not high, frequency transcutaneous electric nerve stimulation in rats with joint inflammation

OBJECTIVE: To determine the release pattern of serotonin and noradrenaline in the spinal cord in response to transcutaneous electric nerve stimulation (TENS) delivered at low or high frequency. DESIGN: Prospective randomized allocation of 3 treatments. SETTING: Research laboratory. ANIMALS: Male Sprague-Dawley rats (weight range, 250-350 g). INTERVENTION: Knee joints of rats were inflamed with a mixture of 3% carrageenan and 3% kaolin for 24 hours prior to placement of push-pull cannulae into the dorsal horn of the spinal cord. Push-pull samples were collected in 10-minute intervals before, during, and after treatment with low-frequency TENS (4 Hz), high-frequency TENS (100 Hz), or sham TENS. TENS was applied to the inflamed knee joint for 20 minutes at sensory intensity and 100-mus pulse duration. Push-pull samples were analyzed for serotonin and noradrenaline by high performance liquid chromatography with coulemetric detection. MAIN OUTCOME MEASURES: Spinal concentrations of serotonin and noradrenaline. RESULTS: Low-frequency TENS significantly increased serotonin concentrations during and immediately after treatment. There was no change in serotonin with high-frequency TENS, nor was there a change in noradrenaline with low- or high-frequency TENS. CONCLUSIONS: Low-frequency TENS releases serotonin in the spinal cord to produce antihyperalgesia by activation of serotonin receptors.     

Deep tissue afferents, but not cutaneous afferents, mediate transcutaneous electrical nerve stimulation-Induced antihyperalgesia.

In this study we investigated the involvement of cutaneous versus knee joint afferents in the antihyperalgesia produced by transcutaneous electrical nerve stimulation (TENS) by differentially blocking primary afferents with local anesthetics. Hyperalgesia was induced in rats by inflaming one knee joint with 3% kaolin-carrageenan and assessed by measuring paw withdrawal latency to heat before and 4 hours after injection. Skin surrounding the inflamed knee joint was anesthetized using an anesthetic cream (EMLA). Low (4 Hz) or high (100 Hz) frequency TENS was then applied to the anesthetized skin. In another group, 2% lidocaine gel was injected into the inflamed knee joint, and low or high frequency TENS was applied. Control experiments were done using vehicles. In control and EMLA groups, both low and high frequency TENS completely reversed hyperalgesia. However, injection of lidocaine into the knee joint prevented antihyperalgesia produced by both low and high frequency TENS. Recordings of cord dorsum potentials showed that both low and high frequency TENS at sensory intensity activates only large diameter afferent fibers. Increasing intensity to twice the motor threshold recruits Adelta afferent fibers. Furthermore, application of EMLA cream to the skin reduces the amplitude of the cord dorsum potential by 40% to 70% for both high and low frequency TENS, confirming a loss of large diameter primary afferent input after EMLA is applied to the skin. Thus, inactivation of joint afferents, but not cutaneous afferents, prevents the antihyperalgesia effects of TENS. We conclude that large diameter primary afferent fibers from deep tissue are required and that activation of cutaneous afferents is not sufficient for TENS-induced antihyperalgesia. PERSPECTIVE: Transcutaneous electrical nerve stimulation (TENS) is an accepted clinical modality used for pain relief. It is generally believed that TENS analgesia is caused mainly by cutaneous afferent activation. In this study by differentially blocking cutaneous and deep tissue primary afferents, we show that the activation of large diameter primary afferents from deep somatic tissues, and not cutaneous afferents, are pivotal in causing TENS analgesia.     

Cholecystokinin receptors mediate tolerance to the analgesic effect of TENS in arthritic rats

Transcutaneous electrical nerve stimulation (TENS) is a treatment for pain that involves placement of electrical stimulation through the skin for pain relief. Previous work from our laboratory shows that repeated application of TENS produces analgesic tolerance by the fourth day and a concomitant cross-tolerance at spinal opioid receptors. Prior pharmacological studies show that blockade of cholecystokinin (CCK) receptors systemically and spinally prevents the development of analgesic tolerance to repeated doses of opioid agonists. We therefore hypothesized that systemic and intrathecal blockade of CCK receptors would prevent the development of analgesic tolerance to TENS, and cross-tolerance at spinal opioid receptors. In animals with knee joint inflammation (3% kaolin/carrageenan), high (100 Hz) or low frequency (4 Hz) TENS was applied daily and the mechanical withdrawal thresholds of the muscle and paw were examined. We tested thresholds before and after inflammation, and before and after TENS. Animals treated systemically, prior to TENS, with the CCK antagonist, proglumide, did not develop tolerance to repeated application of TENS on the fourth day. Spinal blockade of CCK-A or CCK-B receptors blocked the development of tolerance to high and low frequency TENS, respectively. In the same animals we show that spinal blockade of CCK-A receptors prevents cross-tolerance at spinal delta-opioid receptors that normally occurs with high frequency TENS; and blockade of CCK-B receptors prevents cross-tolerance at spinal mu-opioid receptors that normally occurs with low frequency TENS. Thus, we conclude that blockade of CCK receptors prevents the development of analgesic tolerance to repeated application of TENS in a frequency-dependent manner.     

Electrophysiological and clinical evaluation of the effects of transcutaneous electrical nerve stimulation on the spasticity in the hemiplegic stroke patients

To investigate whether transcutaneous electrical nerve stimulation (TENS) mitigates the spasticity of hemiplegic stroke patients, as assessed by electrophysiological variables, and the effects, if any, on the clinical appearance of spasticity. [Subjects and Methods] Twenty-seven subjects who had acute hemiplegia and 24 healthy people as the control group, were enrolled in this study. Some of the acute cerebrovascular disease patients could walk. Subjects who did not have spasticity, who were taking antispasticity medicine, or had a previous episode of cerebrovascular disease were excluded. The walking speed of the patients was recorded before and after TENS. EMG examinations were performed on the healthy controls and in the affected side of the patients. A 30-minute single session of TENS was applied to lower extremity. At 10 minutes after TENS, the EMG examinations were repeated. [Results] A statistically significant decrease in the spasticity variables, and increased walking speed were found post-TENS. The lower M amplitude and higher H reflex amplitude, H/M maximum amplitude ratio, H slope, and H slope/M slope ratio on the spastic side were found to be statistically significant. [Conclusion] TENS application for hemiplegic patients with spastic lower extremities due to cerebrovascular disease resulted in marked improvement in clinical scales of spasticity and significant changes in the electrophysiological variables.Key words: Hemiplegia, Spasticity, Transcutaneous electric nerve stimulation     

An investigation into the 'carry over' effect of neurostimulation in the treatment of angina pectoris

Neurostimulation, by way of transcutaneous electrical nerve stimulation (TENS) and spinal cord stimulation, improves signs and symptoms of myocardial ischaemia, with evidence (from non-randomised studies) that this effect extends beyond the period of stimulation itself ('carry-over' effect). In this randomised controlled trial, 10 patients underwent baseline treadmill-exercise-testing (TET), followed by two further tests at fortnightly intervals. TENS was compared to placebo in a randomised fashion. TENS produced a significant increase in total exercise time (399.3 vs. 364.5 s, p < 0.05) and time to maximum ST depression (374 vs. 324 s, p = 0.01) without a significant difference in the maximum degree of ST depression (2.0 vs. 2.1 mm, p = NS). Rate-pressure product at peak exercise was not significantly different (197 vs. 193, p = NS). TENS produced a nonsignificant change in time to onset of angina (352 vs. 325 s, p = 0.07). Pre-treatment with TENS produces a significant improvement in exercise tolerance and measures of ischaemia but not significant improvement in symptoms.     

Neuromodulation of thoracic intraspinal visceroreceptive transmission by electrical stimulation of spinal dorsal column and somatic afferents in rats.

Clinical studies have shown that neuromodulation therapies, such as spinal cord stimulation (SCS) and transcutaneous electrical nerve stimulation (TENS), reduce symptoms of chronic neuropathic and visceral pain. The neural mechanisms underlying SCS and TENS therapy are poorly understood. The present study was designed to compare the effects of SCS and TENS on spinal neuronal responses to noxious stimuli applied to the heart and esophagus. Direct stimulation of an intercostal nerve (ICNS) was used to simulate the effects of TENS. Extracellular potentials of left thoracic (T3) spinal neurons were recorded in pentobarbital anesthetized, paralyzed, and ventilated male rats. SCS (50 Hz, 0.2 ms, 3-5 minutes) at a clinical relevant intensity (90% of motor threshold) was applied on the C1-C2 or C8-T1 ipsilateral spinal segments. Intercostal nerve stimulation (ICNS) at T3 spinal level was performed using the same parameters as SCS. Intrapericardial injection of bradykinin (IB, 10 microg/mL, 0.2 mL, 1 minute) was used as the noxious cardiac stimulus. Noxious thoracic esophageal distension (ED, 0.4 mL, 20 seconds) was produced by water inflation of a latex balloon. C1-C2 SCS suppressed excitatory responses of 16/22 T3 spinal neurons to IB and 25/30 neurons to ED. C8-T1 SCS suppressed excitatory responses of 10/15 spinal neurons to IB and 17/23 neurons to ED. ICNS suppressed excitatory responses of 9/12 spinal neurons to IB and 17/22 neurons to ED. These data showed that SCS and ICNS modulated excitatory responses of T3 spinal neurons to noxious stimulation of the heart and esophagus. PERSPECTIVE: Neuromodulation of noxious cardiac and esophageal inputs onto thoracic spinal neurons by spinal cord and intercostal nerves stimulation observed in the present study may help account for therapeutic effects on thoracic visceral pain by activating the spinal dorsal column or somatic afferents.     

Spinal blockade of opioid receptors prevents the analgesia produced by TENS in arthritic rats

Transcutaneous electrical nerve stimulation (TENS) is commonly used for relief of pain. The literature on the clinical application of TENS is extensive. However, surprisingly few reports have addressed the neurophysiological basis for the actions of TENS. The gate control theory of pain is typically used to explain the actions of high-frequency TENS, whereas, low-frequency TENS is typically explained by release of endogenous opioids. The current study investigated the role of mu, delta, and kappa opioid receptors in antihyperalgesia produced by low- and high-frequency TENS by using an animal model of inflammation. Antagonists to mu (naloxone), delta (naltrinodole), or kappa (nor-binaltorphimine) opioid receptors were delivered to the spinal cord by microdialysis. Joint inflammation was induced by injection of kaolin and carrageenan into the knee-joint cavity. Withdrawal latency to heat was assessed before inflammation, during inflammation, after drug (or artificial cerebral spinal fluid as a control) administration, and after drug (or artificial cerebral spinal fluid) administration + TENS. Either high- (100 Hz) or low- frequency (4 Hz) TENS produced approximately 100% inhibition of hyperalgesia. Low doses of naloxone, selective for mu opioid receptors, blocked the antihyperalgesia produced by low-frequency TENS. High doses of naloxone, which also block delta and kappa opioid receptors, prevented the antihyperalgesia produced by high-frequency TENS. Spinal blockade of delta opioid receptors dose-dependently prevented the antihyperalgesia produced by high-frequency TENS. In contrast, blockade of kappa opioid receptors had no effect on the antihyperalgesia produced by either low- or high-frequency TENS. Thus, low-frequency TENS produces antihyperalgesia through mu opioid receptors and high-frequency TENS produces antihyperalgesia through delta opioid receptors in the spinal cord.     

Rehabilitation in spinal cord disorders. 3. Comprehensive management of spinal cord injury

This self-directed learning module highlights advances in the management of the person with a spinal cord deficit. Traumatic spinal cord injury is being used as the model, but the principles apply to all patients with spinal cord deficits. This article is part of the chapter on rehabilitation of spinal cord disorders for the Self-Directed Medical Knowledge Program Study Guide for practitioners and trainees in physical medicine and rehabilitation. Specifically, this section contains information regarding prehospital care, acute assessment and management, primary rehabilitation by systems, sexuality and psychosocial issues, management of pain and spasticity, functional goals, the role of functional electrical stimulation, and long-term follow-up.     

Advances in electrical nerve stimulation techniques to manage chronic pain: an overview

Pharmacologic treatments to manage chronic intractable pain have long been sought. Neuropathic pain is usually resistant to analgesics. At present, no analgesic drug totally relieves pain without producing significant unwanted side effects. Electrical stimulation can offer a degree of relief to some sufferers without risk. Transcutaneous electrical nerve stimulation (TENS) has a long clinical history. Stimulation parameters have been studied to improve the efficacy of this method. TENS is inadequate for extensive and bilateral pain, and epidural spinal cord stimulation is indicated. Dorsal column stimulation (DCS) initially was used to manage pain, but recent clinical reports show that it also can be effective in vascular disease and movement disorders. This review article reports on improvements in the electrical parameters used in neurostimulation and advances in research to overcome methodologic problems of DCS.     

Treatment of osteoarthritis of the knee with transcutaneous electrical nerve stimulation

Ten patients with pain due to osteoarthritis of the knee were treated in a double-blind cross-over study with two weeks of transcutaneous electrical nerve stimulation (TENS) and placebo. There was statistically significant pain relief by TENS and half of the patients chose to continue using TENS for pain control after the test month. However, at one year's follow-up, only two patients had sufficient benefit to continue using the device.     

Stimulation parameter optimization for functional electrical stimulation assisted gait in human spinal cord injury using response surface methodology

BACKGROUND: The aims of this study were to identify the reflex moment induced by flexion withdrawal reflex and to optimize stimulation parameters for restoring swing motion with respect to initial kinematic conditions in human with spinal cord injury. METHODS: The influence of hip position and passive movement in the reflex moment were tested in six subjects with chronic spinal cord injury. The two-dimensional dynamic models consisted of thigh, shank and foot segments were developed to compute the swing-phase response and the response surface method was also used to optimize stimulation parameters for restoration of gait by functional electrical stimulation. FINDINGS: At three different hip positions, significant linear relationship was found between the reflex moment and hip angle (P < 0.05) and hip movement also increased the reflex moment compare to isometric conditions. The hip and knee flexion velocities significantly contributed to the hip and knee flexion angle during the swing-phase (P < 0.05) and increase of initial joint velocity resulted in a decrease of the burst frequency and duration time for optimal swing motion in spinal cord injured patients. INTERPRETATION: From dynamic simulation, we concluded that optimal solutions of pulse amplitude, frequency and duration time of burst for electrical stimulation assisted gait were influenced by initial kinematic conditions at toe-off. The reflex model and the results of this study can be applied to the design and control strategies of neuroprosthetic devices using functional electrical stimulation for spinal cord injured patients.     

Effect of penile vibratory stimulation on spasticity in men with spinal cord injury

OBJECTIVE: Penile vibratory stimulation is the first treatment option for anejaculation in men with spinal cord injury. It has been postulated that it also has an antispasticity effect. The purpose of this study was to determine the effect of penile vibratory stimulation on spasticity in patients with spinal cord injury. DESIGN: Ten male patients with spinal cord injury were included in the study. They were examined at the baseline and 3, 6, 24, and 48 hrs later. After their baseline examination, they performed penile vibratory stimulation. The outcome variables were spasticity (Ashworth scale), spasm frequency, spasm severity, painful spasms, plantar stimulation response, deep tendon reflexes, clonus, and effect on function. RESULTS: Ashworth grade showed a statistically significant decrease at hour 3 and hour 6 examinations (P = 0.001 and P = 0.03, respectively, with Tukey test). The patients showed a tendency toward having less frequent and less severe spasms throughout the study; however, it did not reach to a significant level. Similarly, clonus showed a nonsignificant decrease during follow-up examinations. The other variables did not change considerably. CONCLUSIONS: Penile vibratory stimulation may contribute to the relief of the spasticity in men with spinal cord injury. In treating spasticity, all the factors that increase or decrease the tone should be considered.     

Blockade of NMDA receptors prevents analgesic tolerance to repeated transcutaneous electrical nerve stimulation (TENS) in rats.

Repeated daily application of transcutaneous electrical nerve stimulation (TENS) results in tolerance, at spinal opioid receptors, to the antihyperalgesia produced by TENS. Since N-methyl-D-aspartate (NMDA) receptor antagonists prevent analgesic tolerance to opioid agonists, we hypothesized that blockade of NMDA receptors will prevent tolerance to TENS. In rats with knee joint inflammation, TENS was applied for 20 minutes daily at high-frequency (100 Hz), low-frequency (4 Hz), or sham TENS. Rats were treated with the NMDA antagonist MK-801 (0.01 mg/kg to 0.1 mg/kg) or vehicle daily before TENS. Paw withdrawal thresholds were tested before and after inflammation and before and after TENS treatment for 4 days. On day 1, TENS reversed the decreased mechanical withdrawal threshold induced by joint inflammation. On day 4, TENS had no effect on the decreased withdrawal threshold in the group treated with vehicle, demonstrating development of tolerance. However, in the group treated with 0.1 mg/kg MK-801, TENS significantly reversed the mechanical withdrawal thresholds on day 4, demonstrating that tolerance did not develop. Vehicle-treated animals developed cross-tolerance at spinal opioid receptors. Treatment with MK-801 reversed this cross-tolerance at spinal opioid receptors. In summary, blockade of NMDA receptors prevents analgesic tolerance to daily TENS by preventing tolerance at spinal opioid receptors. PERSPECTIVE: Observed tolerance to the clinical treatment of TENS could be prevented by administration of pharmaceutical agents with NMDA receptors activity such as ketamine or dextromethorphan.     

神经肌肉电刺激股四头肌对全膝关节置换术后功能康复的影响

目的:了解神经肌肉电刺激股四头肌对全膝关节置换术(TKR)后运动功能康复的影响。方法:TKR术后患者104例,按分层随机法分为两组,治疗组52例,用神经肌肉电刺激股四头肌,要求患者随电流刺激同时进行主动伸膝;对照组52例,用经皮神经电刺激模式,两组电极分别置于膝部痛点。同时所有患者参与常规康复治疗,平均治疗(14.89±3.65)d出院。出院前行视觉模拟评分法(VAS)、膝关节活动度和膝关节损伤和骨关节炎评分量表(KOOS)评定。出院后随访平均间隔9.5月,随访时行美国膝关节协会评分(KSS)和KOOS量表评定。结果:出院时治疗组和对照组VAS评分分别为(18.11±9.66)和(16.13±4.25)、膝关节主动活动范围(AROM)分别为(103.21°±15.44°)和(99.21°±15.19°),两组的差异均无显著性(P>0.05);治疗组主动伸膝受限为(1.93°±3.47°),明显小于对照组(6.26°±4.28°),差异非常显著(P<0.01);治疗组KOOS评分为(71.52±10.97),明显高于对照组(65.02±10.26),两组差异显著(P<0.01)。随访时,两组KSS评分均达优水平,差异无显著性(P>0.05);治疗组KOOS评分(96.16±2.96)高于对照组(94.04±4.80),两组差异非常显著(P<0.01)。结论:TKR术后早期配合神经肌肉电刺激股四头肌的康复治疗,有助于早期提高伸膝装置的功能和加速功能康复。     

Spinal 5-HT(2) and 5-HT(3) receptors mediate low, but not high, frequency TENS-induced antihyperalgesia in rats

Transcutaneous electrical nerve stimulation (TENS) is a form of non-pharmacological treatment for pain. Involvement of descending inhibitory systems is implicated in TENS-induced analgesia. In the present study, the roles of spinal 5-HT and alpha(2)-adrenoceptors in TENS analgesia were investigated in rats. Hyperalgesia was induced by inflaming the knee joint with 3% kaolin-carrageenan mixture and assessed by measuring paw withdrawal latency (PWL) to heat before and 4 h after injection. The (1). alpha(2)-adrenergic antagonist yohimbine (30 microg), (2). 5-HT antagonist methysergide (5-HT(1). and 5-HT(2). 30 microg), one of the 5-HT receptor subtype antagonists, (3). NAN-190 (5-HT(1A), 15 microg), (4). ketanserin (5-HT(2A), 30 microg), (5). MDL-72222 (5-HT(3), 12 microg), or (6). vehicle was administered intrathecally prior to TENS treatment. Low (4 Hz) or high (100 Hz) frequency TENS at sensory intensity was then applied to the inflamed knee for 20 min and PWL was determined. Selectivity of the antagonists used was confirmed using respective agonists administered intrathecally. Yohimbine had no effect on the antihyperalgesia produced by low or high frequency TENS. Methysergide and MDL-72222 prevented the antihyperalgesia produced by low, but not high, frequency TENS. Ketanserin attenuated the antihyperalgesic effects of low frequency TENS whereas NAN-190 had no effect. The results from the present study show that spinal 5-HT receptors mediate low, but not high, frequency TENS-induced antihyperalgesia through activation of 5-HT(2A) and 5-HT(3) receptors in rats. Furthermore, spinal noradrenergic receptors are not involved in either low or high frequency TENS antihyperalgesia.     

Spasticity in spinal cord injured patients: 1. Short-term effects of surface electrical stimulation

Twelve spinal cord injured subjects participated in a study of the short-term effects on leg spasticity of electrical stimulation of the quadriceps. Spasticity was quantified through the use of a normalized relaxation index (R2n) obtained from the pendulum drop test both before and after measurement of isometric quadriceps torque in response to 20 minutes of cyclic electrical stimulation. Two or three baseline evaluations were made on each subject, tests being at least one day apart. By comparing the first prestimulus baseline assessment of spasticity with that obtained poststimulus, we obtained a measure of changes in spasticity brought about by fatiguing exercise. We found that spasticity significantly (p less than or equal to 0.005) decreased after stimulation. To investigate whether this change was due to electrical stimulation or was a function of the performance of the drop test itself (ie, passive range of motion of the knees), drop-to-drop variability during the pendulum drop test both before and after stimulation was assessed. A comparison was made of the R2n value of the last drop before stimulation to that of the first drop afterward, to assess the direct effect of stimulation on spasticity. Spasticity decreased significantly (p less than or equal to 0.05) during the leg ranging inherent in the drop test itself, particularly for subjects with shorter times postinjury. Spasticity also decreased significantly as a direct result of electrical stimulation. This latter change could be accounted for by an interaction of peak quadriceps torque and the initial measure of spasticity before stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)