Activin induces tactile allodynia and increases calcitonin gene-related peptide after peripheral inflammation

Calcitonin gene-related peptide (CGRP) is a sensory neuropeptide important in inflammatory pain that conveys pain information centrally and dilates blood vessels peripherally. Previous studies indicate that activin A increases CGRP-immunoreactive (IR) sensory neurons in vitro, and following wound, activin A protein increases in the skin and more neurons have detectable CGRP expression in the innervating dorsal root ganglion (DRG). These data suggest some adult sensory neurons respond to activin A or other target-derived factors with increased neuropeptide expression. This study was undertaken to test whether activin contributes to inflammatory pain and increased CGRP and to learn which neurons retained plasticity. After adjuvant-induced inflammation, activin mRNA, but not NGF or glial cell line-derived neurotrophic factor, increased in the skin. To examine which DRG neurons increased CGRP immunoreactivity, retrograde tracer-labeled cutaneous neurons were characterized after inflammation. The proportion and size of tracer-labeled DRG neurons with detectable CGRP increased after inflammation. One-third of CGRP-IR neurons that appear after inflammation also had isolectin B4 binding, suggesting that some mechanoreceptors became CGRP-IR. In contrast, the increased proportion of CGRP-IR neurons did not appear to come from RT97-IR neurons. To learn whether central projections were altered after inflammation, CGRP immunoreactivity in the protein kinase Cgamma-IR lamina IIi was quantified and found to increase. Injection of activin A protein alone caused robust tactile allodynia and increased CGRP in the DRG. Together, these data support the hypothesis that inflammation and skin changes involving activin A cause some sensory neurons to increase CGRP expression and pain responses.

Inhibition of ERK phosphorylation decreases nociceptive behaviour in monoarthritic rats

In this study we investigated the role of the activation of the extracellular signal-regulated kinases 1 and 2 (ERK) in chronic inflammatory articular nociception. Monoarthritis was induced in the left ankle of Wistar rats by injection of complete Freund's adjuvant (CFA). Movement of the inflamed joint increased ERK phosphorylation in neurones of the superficial and deep ipislateral dorsal horn laminae of L3-L5 spinal cord segments. Spinal immunoreactivity to phosphoERK was more intense in animals in which the inflammation lasted longer, 7 days or more, than in rats with less time of inflammation. PhosphoERK levels were transient, since 2h after ankle stimulation spinal immunoreaction had almost disappeared. PhosphoERK immunoreactivity was not induced by movement of ankles from non-arthritic control animals, neither in monoarthritic rats in which the inflamed ankle was not stimulated. Intrathecal administration of PD 98059, an inhibitor of ERK phosphorylation, reduced nociceptive behaviour induced by the ankle bend test in monoarthritic rats. The anti-nociceptive effect of PD 98059 was more prominent and in animals with short lasting (4 days) than in animals with longer (14 days) monoarthritis. Taken together, these findings suggest that ERK phosphorylation in spinal cord neurones plays an important role in chronic inflammatory articular pain and that its inhibition may provide significant anti-nociception.

Post-activation depression in various group I spinal pathways in humans

This investigation was designed to study the effects of post-activation depression in different spinal pathways fed by group I afferents available to investigation in human subjects. It was precipitated by a recent investigation in the cat showing that-contrary to the general assumption-post-activation depression is not a widespread phenomenon in the spinal cord. In 24 healthy subjects comparison was made between the effects of low and high-test stimulus rates on the monosynaptic Ia excitation, known to be subject to post-activation depression, and on oligosynaptic pathways fed by group I afferents. Both the amplitude of monosynaptic H reflexes and the amount of heteronymous monosynaptic Ia facilitation were significantly smaller at high than at low-test stimulus rates (1-2 s compared with 6-8 s between two consecutive stimuli). So was the amount of reciprocal Ia inhibition of tibialis anterior motoneurones. In contrast, the amount of other non-monosynaptic group I effects directed to the same motor nuclei (peroneal-induced excitation of quadriceps motoneurones, disynaptic non-reciprocal group I inhibition of flexor carpi radialis motoneurones, and D1 inhibition of flexor carpi radialis and soleus H reflexes) were enhanced at high stimulus rates. Results in humans confirm that post-activation depression depends on the type of group I afferents, and/or on the target neurones. The functional significance of the discrepancy between post-activation depression in pure Ia pathways and in other group I pathways is discussed with regard to the fusimotor-driven servo-assistance from Ia afferent discharges.

Hindlimb stepping movements in complete spinal rats induced by epidural spinal cord stimulation

The locomotor ability of the spinal cord of adult rats deprived of brain control was tested by epidural spinal cord stimulation. The studies were performed on six rats that had a complete spinal cord transection (T7-T9) and epidural electrode implantations 2-3 weeks before testing was initiated. The stimulating epidural electrodes were implanted at the T12-L6 spinal segments. Epidural electrical stimulation of the dorsal surface of the spinal cord at frequencies between 1 and 50 Hz and intensities between 1 and 10 V without any pharmacological facilitation was used. Stimulation at each of the lumbar spinal cord segments elicited some rhythmic activity in the hindlimbs. However, stimulation at most segmental levels usually evoked activity in only one leg and was maintained for short periods of time (< 10s). Bilateral hindlimb locomotor activity was evoked most often with epidural stimulation at 40-50 Hz applied at the L2 segment. A necessary condition for initiation of locomotor activity was providing a specific amount (at least 5%) of body weight support. Therefore, the rat spinal cord isolated from brain control is capable of producing bilateral stepping patterns induced most readily by epidural stimulation applied at the L2 spinal segment. Furthermore, the induced stepping patterns were dependent on sensory feedback associated with weight bearing.

Stoller afferent nerve stimulation in woman with therapy resistant over active bladder; a 1-year follow up

AIM

In this prospective observational study, we investigated the efficacy of Stoller afferent nerve stimulation (SANS) in subjects with overactive bladder who failed anticholinergic treatment.

METHODS

Thirty-five subjects with overactive bladder who failed therapy with oxybutynin participated in this study. Treatment (n = 35) was given once a week for 30 minutes for overall 10 weeks. In treatment, SANS device (Urosurge) was used. Subjects were assessed with 3-day voiding diary, SEAPI quality of life questionnaires and cystometry before therapy after completion of therapy and at one-year follow-up.

RESULTS

In 54% (n = 19) of subjects complete recovery was obtained after treatment. Urgency and SEAPI were reduced significantly whereas urine volume increased significantly (p < 0.01). Complete recovery was maintained in eight of the 19 subjects at one year.

CONCLUSIONS

SANS treatment has a short-term positive effect in patients with resistant overactive bladder. However, it was also established that efficacy was maintained at 1 year in only 23% of subjects.

Inching method in compression neuropathy of the sural nerve distal to the ankle

We present the case of a 29-year-old electric engineer with compression neuropathy of the left sural nerve due to occupational boots. Routine nerve conduction study of the sural nerve was normal. However, the sensory nerve action potential was not detected more than 3 cm distal to the lateral malleolus, although it returned to normal values after three years. Inching method of the sural nerve may be necessary for detecting compression sural neuropathy distal to the ankle.

Nerve and tendon lacerations about the foot and ankle

Nerve and tendon lacerations of the foot and ankle region are relatively common. Acute nerve and tendon injuries should be repaired with appropriate techniques at the time of initial wound exploration. Primary nerve repair may help minimize the risk of painful neuroma formation; primary tendon repair can lead to better functional results than delayed repair. Most chronic nerve injuries, except those to the tibial nerve or its major divisions, are managed by resection of a painful neuroma and burying the nerve ending in a protected area. Delayed reconstruction of tendon injuries is performed when correction of the functional deficit outweighs the morbidity of surgery.

Sensory exam with a quantitative tuning fork: rapid, sensitive and predictive of SNAP amplitude

BACKGROUND

In the standard neurologic examination, outcome measures of sensation testing are typically qualitative and subjective. The authors compared the outcome of vibratory sense evaluation using a quantitative Rydel-Seiffer 64 Hz tuning fork with qualitative vibration testing, and two other features of the neurologic evaluation, deep tendon reflexes and sensory nerve conduction studies.

METHODS

The authors studied 184 subjects, including 126 with Waldenström's macroglobulinemia and 58 controls, over the course of a weekend. Standard neurologic examinations and quantitative vibratory testing were performed. Sensory nerve action potentials (SNAP) were tested as a measure of sensory nerve function. Tests were carried out by different examiners who were blinded to the results of other testing and to clinical information other than the diagnosis of Waldenström's macroglobulinemia.

RESULTS

Quantitative vibration measurements in all body regions correlated with sural SNAP amplitudes. Quantitative vibration outcomes were more strongly related to sural SNAP results than qualitative evaluations of vibration. Quantitative vibration testing also detected a loss of sensation with increased age in all body regions tested.

CONCLUSIONS

Quantitative vibratory evaluation with Rydel-Seiffer tuning fork is rapid, has high inter- and intrarater reliability, and provides measures for evaluating changes in sensory function over time. Examinations with the quantitative tuning fork are also more sensitive and specific than qualitative vibration testing for detecting changes in sensory nerve function. Use of the quantitative tuning fork takes no more time, provides more objective information, and should replace the qualitative vibratory testing method that is now commonly used in the standard neurologic examination.

Transfer of Motor Performance in an Obstacle Avoidance Task to Different Walking Conditions

The aim of this study was to examine whether subjects who have learned a skilled locomotor task can transfer the acquired performance to conditions involving either a change in the external coordinates or in the sensory input from one leg. Subjects were trained to step over an obstacle with minimal foot clearance without visual information about either the obstacle or their legs during treadmill walking. Leg muscle activity and joint kinematics were recorded and analyzed. Acoustic signals provided feedback about foot clearance over the obstacle. After successful training, the transfer of learning between level and downhill walking and to walking with additional weight attached to the leg was examined. It was found that once subjects learned to step over the obstacle at an optimal foot clearance, they could transfer their performance within the first step over the obstacle in the new walking conditions. Closer examination of the transfer between level and downhill walking revealed no consistent kinematic strategy across subjects. To transfer the learned performance to walking with additional weight, subjects consistently and automatically increased biceps femoris muscle activation. The results are discussed in the context of emerging concepts in the neural control of walking and motor learning.

Contribution of afferent feedback to the soleus muscle activity during human locomotion

During the stance phase of the human step cycle, the ankle undergoes a natural dorsiflexion that stretches the soleus muscle. The afferent feedback resulting from this stretch enhances the locomotor drive. In this study a robotic actuator was used to slightly enhance or reduce the natural ankle dorsiflexion, in essence, mimicking the small variations in the ankle dorsiflexion movement that take place during the stance phase of the step cycle. The soleus (SOL) and tibialis anterior EMG were analyzed in response to the ankle trajectory modifications. The dorsiflexion enhancements and reductions generated gradual increments and decrements, respectively, in the ongoing SOL EMG. We exercised care to ensure that the imposed ankle movements were too slow to elicit distinct burst-like stretch reflex responses that have been investigated previously. The increased SOL EMG after the dorsiflexion enhancements was reduced when the group Ia afferents were blocked with peripheral ischemia at the thigh, and during high-frequency Achilles tendon vibration. However, neither ischemia nor tendon vibration affected the decrements in the SOL EMG during the dorsiflexion reductions. These findings give evidence of the contribution of afferent feedback to the SOL activity in an ongoing basis during the stance phase. The results suggest that mainly feedback from the group Ia pathways is responsible for the increments in the SOL EMG during the dorsiflexion enhancements. However, the decrements in the SOL activity might be mediated by different afferent mechanisms.

Optimizing the experimental design for ankle dorsiflexion fMRI

Compared to motor studies of the upper limb, few experiments have sought a relationship between blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) sensorimotor signals and the resulting lower limb output. In Experiment 1, using an fMRI simulator system, we determined the optimized experimental protocol based on two design types and four behavioral movement types during ankle dorsiflexion. Experiment 2 involved testing the BOLD sensitivity at 1.5 T during ankle movements. Subjects performed large- and small-amplitude dorsiflexion movement types using an event-related design, with the intent of contrasting spatial and temporal features of the BOLD signal. In both experiments, the subject's behavior was guided by visual biofeedback of their ankle flexion angle, using an MR-compatible fiberoptic tape. From Experiment 1, we found electromyography (EMG) difference voltage ratio of approximately 2:1 for large (40 degrees ) and small (15 degrees ) dorsiflexion, 0.13 mV and 0.07 mV, respectively. In Experimental 2, we found the peak BOLD % signal changes of 1.04% and 0.89%, for large (40 degrees ) and small (15 degrees ) dorsiflexion, respectively. In addition, graded dorsiflexion produced graded BOLD signals in the primary sensorimotor and supplementary motor areas in 10 of 12 healthy young subjects, attesting to the feasibility of lower-limb fMRI at 1.5 T. This study provides insight into the cortical network involved in dorsiflexion using an experimental paradigm that is likely to translate effectively to hemiparetic stroke subjects.

Motor skill training induces changes in the excitability of the leg cortical area in healthy humans

Training-induced changes in cortical excitability may play an important role in rehabilitation of gait ability in patients with neurological disorders. In this study, we investigated the effect of a 32-min period of motor skill, non-skill and passive training involving the ankle muscles on leg motor cortical excitability in healthy humans. Transcranial magnetic stimulation (TMS) at a range of intensities was applied to obtain a recruitment curve of the motor evoked potentials (MEPs) in the tibialis anterior (TA) muscle before and after training. We also explored the effect of training on inhibitory and facilitatory cortical circuits by using a paired-pulse TMS technique at intervals of 2.5 ms (short-interval intracortical inhibition, SICI) and 8 ms (intracortical facilitation, ICF). During motor skill training, subjects were instructed to make a cursor follow a series of target lines on a computer screen by performing voluntary ankle dorsi- and plantarflexion movements. Non-skill and passive training consisted of repeated voluntary and assisted dorsi- and plantarflexion movements, respectively. Recruitment curves increased significantly after 32 min of motor skill training but not after non-skill and passive training, suggesting that only skill motor training increases motor cortical excitability. Motor skill training was not accompanied by any changes in the recruitment curves of TA MEPs evoked by transcranial electrical stimulation, suggesting that the increased MEPs to TMS was likely caused by changes in excitability at a cortical site. SICI was decreased after 32 min of motor skill training but no changes were observed in ICF. We conclude that similar plastic changes as have previously been reported for the hand motor following motor skill training may also be observed for the leg motor area. The observed plastic changes appeared to be related to the degree of difficulty in the motor task, and may be of relevance for rehabilitation of gait disorders.

Sural nerve evoked responses in human hip and ankle muscles while standing

The objective of this study was to investigate the influence of background EMG, as manipulated by changes in limb loading, and electrical stimulus intensity on sural nerve evoked EMG responses in proximal hip (ipsilateral gluteus medius and contralateral adductor longus) and distal ankle (ipsilateral soleus) muscles during quiet standing. We studied 14 healthy subjects who were instructed to stand on a force platform and load the right leg to 20, 30, 60, and 80% body weight. Trains of stimuli were delivered to the right sural nerve at three different intensities (1.5, 2, and 3 perception threshold). Average evoked responses from each of the three muscles were obtained for each combination of body weight and stimulus intensity. Reflex responses were consistently seen in gluteus medius and soleus but not adductor longus. The responses in gluteus medius and soleus consisted of complex inhibitory and excitatory responses with the primary effect in gluteus medius being a short latency excitation (mean latency of 57 ms) and in soleus, a short latency inhibition-excitation (latencies of 47 and 58 ms, respectively). The amplitudes of the responses were influenced primarily by background EMG. The results demonstrate consistent sural nerve evoked EMG responses in both a hip (gluteus medius) and ankle (soleus) muscle. While the findings for soleus generally corroborate and extend previous studies, the responses observed for the lateral hip muscle have not been previously reported.

Short-term effects of functional electrical stimulation on motor-evoked potentials in ankle flexor and extensor muscles

Stimulating sensory afferents can increase corticospinal excitability. Intensive use of a particular part of the body can also induce reorganization of neural circuits (use-dependent plasticity) in the central nervous system (CNS). What happens in the CNS when the nerve stimulation is applied in concert with the use of particular muscle groups? The purpose of this study was to investigate short-term effects of electrical stimulation of the common peroneal (CP) nerve during walking on motor-evoked potentials (MEPs) in the ankle flexors and extensors in healthy subjects. Since the stimulation was applied during the swing phase of the step cycle when the ankle flexors are active, this is referred to as functional electrical stimulation (FES). The following questions were addressed: (1) can FES during walking increase corticospinal excitability more effectively than passively received repetitive nerve stimulation and (2) does walking itself improve the descending connection. FES was delivered using a foot drop stimulator that activates ankle dorsiflexors during the swing phase of the step cycle. MEPs in the tibialis anterior (TA) and soleus muscles were measured before, between, and after periods of walking with or without FES, using transcranial magnetic stimulation. After 30 min of walking with FES, the half-maximum peak-to-peak MEP (MEP(h)) in the TA increased in amplitude and this facilitatory effect lasted for at least 30 min. In contrast, walking had no effects on the TA MEP(h) without FES. The increase in the TA MEP(h) with FES (approximately 40%) was similar to that with repetitive CP nerve stimulation at rest. The soleus MEP(h) was also increased after walking with FES, but not without FES, which differs from the previous observation with CP nerve stimulation at rest. With FES, the TA silent period at MEP(h) was unchanged or slightly decreased, while it increased after walking without FES. Increased cortical excitability accompanied by unchanged cortical inhibition (no changes in the silent period with FES) suggests that FES did not simply increase general excitability of the cortex, but had specific effects on particular cortical neurons.

Referent configuration of the body: a global factor in the control of multiple skeletal muscles

In addition to local biomechanical and reflex factors influencing muscle activation, global factors may be used by the nervous system to control all muscles in a coherent and task-specific way. It has been hypothesized that a virtual or referent (R) configuration of the body determined by muscle recruitment thresholds specified by neural control levels is such a factor. Due to the threshold nature of the R configuration, the activity of each muscle depends on the difference between the actual (Q) and the R configuration of the body. The nervous system modifies the R configuration to produce movement. One prediction of this hypothesis is that the Q and R configurations may match each other, most likely in movements with reversals in direction, resulting in a minimum in the electromyographic (EMG) activity level of muscles involved. The depth of the minima is constrained by the degree of coactivation of opposing muscle groups. Another prediction is that EMG minima in the activity of multiple muscles may occur not only when the movement is assisted but also when it is opposed by external forces (e.g., gravity). To verify these predictions, we analyzed EMG patterns of 16-21 functionally diverse muscles of the legs, trunk, and arms during jumping and stepping in place. One EMG minimum in the activity of all muscles regularly occurred near the apex of the jump. A minimum was also observed near the point of transition of the body from flexion to extension leading to a jump. During stepping in place, the activity of muscles of each side of the body was usually minimized near the beginning and near the end of the stance phase as well as during the maximum elevation of the foot. Since EMG minima occurred not only during gravity-assisted but also gravity-opposed movement reversals, it is concluded that neural factors (such as matching between the Q and R) rather than mechanical factors are responsible for minimizing the EMG activity in these movements.

HIV-Associated Distal Sensory Polyneuropathy in the Era of Highly Active Antiretroviral Therapy

OBJECTIVES

To examine distal sensory polyneuropathy (DSP) in a highly active antiretroviral therapy era, human immunodeficiency virus (HIV)-infected cohort, to determine whether clinical manifestations are affected by demographic or other clinical variables.

PATIENTS

One hundred eighty-seven patients with HIV infection enrolled in the Manhattan HIV Brain Bank underwent baseline neurologic evaluations between January 29, 1999, and June 17, 2002. Distal sensory polyneuropathy was diagnosed if patients displayed abnormalities in 2 or more of the following: ankle reflexes or vibratory or pinprick perception. Patients were classified as symptomatic if they described pain, paresthesia, or numbness. Nonneurologic information was obtained by interview, laboratory testing, and medical chart review. Psychiatric and substance use disorders were elucidated by semistructured interview. In 36 patients, morphometric analysis was performed on autopsy-derived sural nerves.

RESULTS

Of 187 patients, 99 (53%) had DSP. Patients with neuropathy were older than those without (mean +/- SD age, 45.3 +/- 0.7 vs 41.2 +/- 0.8 years, P <.001), and DSP was significantly more common in men (58% [83/99]) than in women (37% [16/99]) (P =.02). The presence of neuropathy was not correlated with plasma viral load, decreased CD4 cell counts, or neurotoxic antiretroviral therapy. Twenty-six of 99 patients with DSP were asymptomatic. Asymptomatic neuropathy was correlated with histories of opiate and sedative abuse and dependence. Symptomatic DSP correlated with ethanol and hallucinogen syndromes, but not neurotoxic therapy. Sural nerve morphometric findings did not distinguish between patients with substance use syndromes and those without.

CONCLUSIONS

In contrast to populations before the era of highly active antiretroviral therapy, DSP in the Manhattan HIV Brain Bank cohort is not associated with increased viral load or decreased CD4 cell counts in this cross-sectional analysis. Symptoms in DSP are associated with substance use disorders, but no difference in morphologic structure is seen in nerves of patients with HIV infection with and without substance use histories. Previously reported virologic and immunologic underpinnings of DSP may be affected by highly active antiretroviral therapy. Furthermore, symptoms of DSP in substance users may be altered by central mechanisms of increased or decreased tolerance to sensory disturbance.

The integration of multiple proprioceptive information: effect of ankle tendon vibration on postural responses to platform tilt

Previous studies have looked at co-processing of multiple proprioceptive inputs but few have investigated the effect of separate dynamic and tonic predominantly proprioceptive disruptions applied concurrently at the same segment. The purpose of the present study was to investigate how simultaneous ankle tendon vibration, a tonic stimulus, with a dynamic toes-up (TU) or toes-down (TD) platform perturbation (1) affects postural stability and (2) influences the adaptation process. Sixteen normal subjects (ten male, six female, mean age 26 +/- 4.8 years) stood blindfolded on a moving platform with vibrators attached bilaterally over the Achilles tendons. Participants were tested in quiet stance (QS), and with five successive TU and TD tilts. All tests were conducted both with (QS+V, TU+V, TD+V) and without vibration. Centre of pressure (CoP) displacements and pitch angular trunk velocity were recorded. Results for QS+V showed a significant 1.02-cm backward CoP displacement (P<0.01) and a significant increase in trunk velocity (peak-to-peak amplitude, P<0.05; SD of trunk velocity, P<0.05). TU+V resulted in a non-significant increase of maximum backwards CoP displacement when compared to TU alone. In addition, no notable effect of vibration on other measures of CoP (pre-tilt position, SD and area of sway) and trunk velocity (peak-to-peak, SD and area of sway) indicates that TU+V does not introduce significantly greater instability compared to tilt alone. In the TD condition, vibration was found to be a stabilising influence, causing a significant shift of the mean pre-tilt position 0.85 cm backwards (P<0.01) and a substantial decrease in the area of forward CoP displacement (P<0.01). However, maximum forwards CoP displacement and trunk velocity measures were not significantly altered during TD+V. Furthermore, in neither TU nor TD was the time-course or pattern of adaptation disrupted by the additional application of vibration. In conclusion, although vibration significantly affects postural measures when applied in isolation, this finding does not hold when it is applied in combination with a more dynamic stimulus. Instead it seems that once postural stability has been disrupted the central nervous system can rapidly assess information from a weaker tonic input and utilise or suppress it appropriately, depending on its effect towards overall postural control. It can be concluded that postural responses to the concurrent application of different predominantly proprioceptive stimuli are dependent upon the type of stimulus and the ability of the central nervous system to rapidly assess and re-weigh available sensory inputs.

Velocity recovery cycles of C fibres innervating human skin

Velocity changes following single and double conditioning impulses were studied by microneurography in single human C fibres to provide information about axonal membrane properties. C units were identified as mechano-responsive (n = 19) or mechano-insensitive (12) nociceptors, cold-sensitive (8) or sympathetic fibres (9), and excited by single, double and triple electrical stimuli to the skin at mean rates of 0.25-2 Hz. The interval between single or paired (20 ms apart) conditioning stimuli and test stimulus was then varied between 500 and 2 ms, and recovery curves of velocity change against inter-spike interval constructed, allowing for changes in these variables with distance. All fibres exhibited an initial (4-24 ms) relative refractory phase, and a long-lasting (>500 ms) 'H2' phase of reduced velocity, attributed to activation of Na+/K+-ATPase. Mechano-responsive nociceptors exhibited an intermediate phase of either supernormality or subnormality, depending on stimulation rate. Mechano-insensitive nociceptors behaved similarly, but all were supernormal at 1 Hz. Sympathetic units exhibited only a long-lasting supernormality, while cold fibres exhibited a briefer supernormal and a late subnormal phase (H1), similar to A fibres. A pre-conditioning impulse doubled H2 and increased H1, but did not augment supernormality or the subnormality of similar time course. Like A fibre supernormality, these phenomena were explained by a passive cable model, so that they provide an estimate of membrane time constant. Nociceptor membrane time constants (median 110 ms, n = 17) were rather insensitive to membrane potential, indicating few active voltage-dependent potassium channels, whereas sympathetic time constants were longer and reduced by activity-dependent hyperpolarisation.

Erste Ergebnisse der peripheren Neuromodulation nach Stoller (SANS) bei Blasenfunktionsst�rungen

PURPOSE

The Stoller peripheral neurostimulation (SANS) is a new therapeutic procedure for bladder dysfunction.

MATERIAL AND METHODS

Each of 11 patients (8 women, 3 men) underwent 12 SANS treatment sessions.

INDICATIONS

overactive bladder (5 patients), chronic nonobstructive urinary retention (3 patients) and pelvic pain (3 patients). Median follow-up was 3 months.

RESULTS

In 2 overactive bladder patients, the number of voids was reduced by at least 50%. In one patient with chronic retention, residual urine was temporarily decreased to <100 cc. 2 pelvic pain patients reported a slight improvement. In summary, 50% of the patients demonstrated a temporary response. Only 2 overactive bladder patients reported a permanent objective and subjective improvement. No complications were observed.

CONCLUSION

As the success rate was low and the procedure is time-consuming, we recommend the SANS procedure only in selected cases. We perform SANS treatment only in patients with overactive bladder refractory to conservative treatment. Prerequisites for a successful treatment is a high patient motivation.

Reflex responses in the lower leg following landing impact on an inverting and non-inverting platform

In the lower leg, landing after a jump induces reflexes, the role of which is not well understood. This is even more so for reflexes following landing on inverting surfaces. The latter condition is of special interest since ankle inversion traumata are one of the most common injuries during sport. Most studies have investigated ankle inversions during a static standing condition. However, ankle injuries occur during more dynamic activities such as jumping. Therefore, the present study aimed at reproducing these situations but in a completely safe setting. EMG responses were recorded after landing on an inverting surface, which caused a mild ankle inversion of 25 deg of rotation (in a range sufficient to elicit reflexes but safe enough to exclude sprains). The results are compared with data from landing on a non-inverting surface to understand the effect of the inversion. In general, landing on the platform resulted in short and long latency responses (SLR and LLR) in triceps surae (soleus, gastrocnemius medialis and lateralis) and peroneal muscles (long and short peroneal) but not in the tibialis anterior muscle. Landing on the inverting platform caused significant LLRs in the peroneal muscles (which underwent the largest stretch) but not in the triceps muscles. Conversely, landing on a non-inverting platform induced larger SLRs in triceps than in the peroneal muscles. Although the peroneal LLRs thus appeared to be selectively recruited in an inverting perturbation, their role during such perturbations should be limited since the latency of these responses was about 90 ms while the inversion lasts only 42 ms. The SLRs, if present, had an onset latency of around 44 ms. In the period following the inversion, however, the responses may be important in preventing further stretch of these muscles.

Imaging of foot and ankle nerve entrapment syndromes: from well-demonstrated to unfamiliar sites

Nerve entrapment at the foot and ankle involves thin and complex anatomic structures and is underdiagnosed because clinical symptoms and electrophysiologic findings may not contribute to the diagnosis. Nerve entrapment can be secondary to acute trauma or repetitive microtrauma. The latter often results from intensive sports-related activity, inappropriate footwear, or internal foot derangement. Various lesions that occur in fibro-osseous tunnels can cause nerve compression (eg, ganglion cysts, varicosities, bone and joint abnormalities, tumors, tenosynovitis, supernumerary or hypertrophic muscles). Accurate nerve examination must be performed, particularly in patients with atypical ankle pain, to detect focal tenderness or paresthesia. Ultrasonography is useful in this setting because it yields both clinical and morphologic findings. High-resolution magnetic resonance imaging provides accurate delineation of the nervous system anatomy. Furthermore, technologic developments in the field of radiology are making it possible to obtain clearer, more accurate images. Radiologists must be aware of the main nerve entrapment syndromes at the foot and ankle and be able to perform accurate nerve examinations with different imaging modalities in patients with foot and ankle pain.

Synaptic connections from large muscle afferents to motoneurones in human lower limbs

OBJECTIVES

Our study was undertaken to investigate reciprocal inhibition in humans both from ankle flexors to extensors and from ankle extensors to flexors.

METHODS

Changes in the firing probability of single motor units in response to electrical stimulation of muscle nerves (the peristimulus time histogram technique) were used to derive the reciprocal projections of muscle spindle Ia afferents to the motoneurones of ankle muscles. Discharges of units in ankle flexors (the tibialis anterior muscle [TA]) and extensors (soleus [SOL] and medial gastrocnemius [MG] muscles) were investigated respectively after stimulation of the posterior tibial (PTN) and common peroneal (CPN) nerves (predominantly on the deep branch). In eight normal subjects aged 24 to 40 years, one motor unit per each muscle was studied.

RESULTS

CPN stimulation produced reciprocal Ia inhibition in the SOL of 5 of 7 of them and in the MG of 3 of 5, whereas PTN stimulation produced reciprocal Ia inhibition in the TA of only 2 of 6 subjects.

CONCLUSIONS

These findings suggest that at low level contraction reciprocal Ia inhibition from ankle flexors to extensors may be stronger than that from ankle extensors to flexors.

Changes in the expression of parvalbumin immunoreactivity in the lumbar spinal cord of the rat following neonatal nerve injury

Nerve injury in newborn animals results in the loss of motoneurons and dorsal root ganglion neurons and long-term changes in reflex activation of surviving motoneurons. Parvalbumin has been previously shown to be found in large-diameter primary afferent axons and interneurons in the spinal cord, and was used here to study the changes in parvalbumin-immunoreactive appositions onto identified tibialis anterior/extensor digitorum longus (TA/EDL) motoneurons, during both normal development and following neonatal nerve injury in the rat spinal cord. During normal development, there was a decrease in the number of parvalbumin-immunoreactive appositions onto TA/EDL motoneurons. Thus, at postnatal day 7 (P7), there were 72.8 +/- 17.5 (mean +/- SD) appositions per motoneuron and by P14, it had decreased to 38.8 +/- 13.2 (mean +/- SD; p > 0.05). Following neonatal nerve injury at P2, there were fewer parvalbumin-positive afferent appositions close to the TA/EDL motoneurons than normal, so that at P7, there were 53.5 +/- 17.1 (mean +/- SD), and at P14, it further decreased to 25.8 +/- 8.6 (mean +/- SD; p > 0.05). This injury-induced reduction in the number of parvalbumin-immunoreactive boutons apposing TA/EDL motoneurons may result, at least in part, from the death of dorsal root ganglion cells with the consequent loss of their central projections. The alterations in the number of parvalbumin-positive appositions close to motoneurons observed in this study may contribute to the changes in the pattern of reflex activity observed in the developing spinal cord both during normal development and following neonatal injury.

Simultaneous Hoffmann reflex measurements in multiple muscles around the ankle

Measurement of the Hoffmann reflex (H-reflex) provides an estimate of alpha motoneuron activity in the target motoneuron (MN) pool. The H-reflex has been assessed for a wide variety of reasons in neuroscience research. However, the majority of protocols have focused on the assessment of only one muscle and its corresponding motoneuron pool at any instant. Previously established protocols do not simultaneously assess reflex activity in multiple muscles elicited from a single stimulation. This new protocol allows for assessment of alpha motoneuron activity in three muscles around the ankle joint from a single stimulus to the sciatic nerve. To elicit the responses, the sciatic nerve was stimulated just prior to its bifurcation into the tibial and common peroneal nerves in the popliteal fossa. Electromyographic recording electrodes were placed on the tibialis anterior, peroneal longus, and soleus muscles. The 1-ms square wave pulse was delivered every 15 s during the recruitment curve mapping. The maximum H reflex and M waves were measured in each muscle and their ratios calculated. The measurement of these ratios simultaneously allows for assessment of the cumulative alpha motoneuron activity about the ankle at a given point in time.