Alpha-motoneuron Excitability Research Articles

Determining intracortical, corticospinal and alpha motoneurone excitability in athletes with patellar tendinopathy compared to asymptomatic controls.

Lower capacity to generate knee extension maximal voluntary force (MVF) has been observed in individuals affected with patellar tendinopathy (PT) compared to asymptomatic controls. This MVF deficit is hypothesized to emanate from alterations in corticospinal excitability (CSE). The modulation of CSE is intricately linked to the excitability levels at multiple sites, encompassing neurones within the corticospinal tract (CST), intracortical neurones within the primary motor cortex (M1), and the alpha motoneurone. The aim of this investigation was to examine the excitability of intracortical neurones, CST neurones, and the alpha motoneurone, and compare these between volleyball and basketball athletes with PT and matched asymptomatic controls. Nineteen athletes with PT and 18 asymptomatic controls participated in this cross-sectional study. Transcranial magnetic stimulation was utilized to assess CST excitability, corticospinal inhibition (silent period, and short-interval cortical inhibition). Peripheral nerve stimulation was used to evaluate lumbar spine and alpha motoneurone excitability, including the evocation of lumbar-evoked potentials and maximal compound muscle action potential (MMAX ), and CSE with central activation ratio (CAR). Knee extension MVF was also assessed. Athletes with PT exhibited longer silent period duration and greater electrical stimulator output for MMAX , as well as lower MVF, compared to asymptomatic controls (p < 0.05). These findings indicate volleyball and basketball athletes with PT exhibit reduced excitability of the alpha motoneurone or the neuromuscular junction, which may be linked to lower MVF. Subtle alterations at specific sites may represent compensatory changes to excitability aiming to maintain efferent drive to the knee extensors.

&lt;p&gt;Shock Waves as a Treatment Modality for Spasticity Reduction and Recovery Improvement in Post-Stroke Adults – Current Evidence and Qualitative Systematic Review&lt;/p&gt;

PurposeThis systematic review examines intervention studies using extracorporeal shock wave therapy (ESWT) application in post-stroke muscle spasticity with particular emphasis on the comparison of two different types of radial (rESWT) and focused shock waves (fESWT).MethodsPubMed, PEDro, Scopus, and EBSCOhost databases were systematically searched. Studies published between the years 2000 and 2019 in the impact factor journals and available in the English full-text version were eligible for inclusion. All qualified articles were classified in terms of their scientific reliability and methodological quality using the PEDro criteria. The PRISMA guidelines were followed and the registration on the PROSPERO database was done.ResultsA total of 17 articles were reviewed of a total sample of 303 patients (age: 57.87±10.45 years and duration of stroke: 40.49±25.63 months) who were treated with ESWT. Recent data confirm both a subjective (spasticity, pain, and functioning) and objective (range of motion, postural control, muscular endurance, muscle tone, and muscle elasticity) improvements for post-stroke spasticity. The mean difference showing clinical improvement was: ∆=34.45% of grade for fESWT and ∆=34.97% for rESWT that gives a slightly better effect of rESWT (∆=0.52%) for spasticity (p<0.05), and ∆=38.83% of angular degrees for fESWT and ∆=32.26% for rESWT that determines the more beneficial effect of fESWT (∆=6.57%) for range of motion (p<0.05), and ∆=18.32% for fESWT and ∆=22.27% for rESWT that gives a slightly better effect of rESWT (∆=3.95%) for alpha motor neuron excitability (p<0.05). The mean PEDro score was 4.70±2.5 points for fESWT and 5.71±2.21 points for rESWT, thus an overall quality of evidence grade of moderate (“fair” for fESWT and “good” for rESWT). Three studies in fESWT and four in rESWT obtained Sackett’s grading system’s highest Level 1 of evidence.ConclusionThe studies affirm the effectiveness of ESWT in reducing muscle spasticity and improving motor recovery after stroke.

Modified motor unit number index (MUNIX) algorithm for assessing excitability of alpha motor neuron in spasticity

ObjectiveThe understanding of the spasticity mechanism is still a problem in the literature, as its definition can be made on the basis of more than one parameter. Therefore, we studied alpha motor neuron excitability, dynamic changes based on force production, and patellar tendon (T) reflex in spasticity and healthy control groups. MethodsAlpha motor neuron excitability, force production, and patellar T reflex were evaluated through three different test protocols. Motor Unit Number Index (MUNIX) measurement was applied for understanding motor neuron pool properties in the first protocol. Voluntary force production and patellar T reflex parameters were evaluated by voluntary force production and triggering patellar T reflex. Twenty spasticity and 20 healthy volunteers participated in the study. ResultsIn the spasticity group, both MUNIX numbers and Motor Unit Size Index (MUSIX) numbers were lower than those in the control group. The results for the Ideal Case Motor Unit Count (ICMUC) parameter show that there is no significant difference between spasticity and healthy individuals for low-level contractions, whereas there is a significant difference for high-level contractions (p < 0.05). In the spasticity group, an increase was observed in the ratio of maximal voluntary force to the T reflex triggered force production (Tf/Vf). ConclusionSpasticity and healthy subjects can be distinguished easily and clearly by evaluating the changes in both kinesiological and electrophysiological findings and the decreasing threshold in the alpha motor neuron pool. SignificanceThis study shows that such combined methods, which allow the evaluation of the alpha motor neuron pool, as well as kinesiological and electrophysiological parameters, are tools that cannot be overlooked in understanding spasticity.

O121 Alpha motor neuron excitability and force generation in spasticity

Objective The aim of this study was to evaluate the motor unit number, voluntary and reflex force produced by alpha motor neuron excitability in spasticity. For this purpose, electrophysiological and dynamic measurements were taken from spasticity cases and healthy participants. Method Patient group consisted of 20 spasticity and healthy group consisted of 20 healthy individuals. The force values produced by triggering the Patella T reflex were calculated via the acceleration sensor. For calculation of the force at the Patellar Tendon during Patellar Reflex triggered force production, we used fundamental principle of leverage with acceleration sensor data. The force obtained by this measurement is defined as reflexive force. Motor unit numbers of participants were evaluated according to MUNIX algorithm. Results There were statistically significant differences between the spasticity cases and healthy control group both for motor unit number and the high level voluntary force production and the force generated by reflex triggering ( p Discussion This study shows that such combined methods, which allows the evaluation of the alpha motor neuron pool, as well as the kinesiological and electrophysiological parameters, are tools that cannot be overlooked in understanding spasticity. Conclusion Motor unit number and force generation were evaluated in spasticity and healthy individuals and statistically significance differences in these features were obtained between two groups. Significance Motor unit number of rectus femoris muscle in spasticity is measured by MUNIX algorithm. Evaluating of voluntary and reflex-generated force with motor unit number have a potential tool for investigating spasticity.

Orally Ingested Transient Receptor Potential (TRP) Channel Activators Attenuate the Intensity‐Duration of Voluntarily Induced Muscle Cramps in Humans

Transient receptor potential (TRP) ion channels in the mouth, esophagus and stomach are activated by ingestion of many naturally occurring food extracts. Recent evidence suggests that oral ingestion of TRPA1 and TRPV1 channel agonists may reflexly attenuate the intensity and/or duration of electrically induced muscle cramps in humans (Short et al., 2014, 2015; Hegarty et al., 2015), presumably by dampening alpha motor neuron excitability. To test this effect on voluntarily initiated calf muscle cramps, we conducted a randomized, double‐blinded, vehicle‐controlled crossover study. Subjects performed 3 baseline experiments in which they underwent a voluntary exercise‐induced muscle cramp protocol. From an original pool of 34 volunteers with a self‐reported history of exercise‐related muscle cramping, 6 men and 14 women (age: 22±3 yrs representing 59% of screened subjects) were able to consistently reproduce cramps voluntarily. Each of the 20 enrolled subjects subsequently participated in 2 experimental trials, one 15 min after consuming less than 3 oz. of an active (A) formulation containing a mixture of TRPA1 and TRPV1 activators derived from natural extracts and another 15 min after ingesting a vehicle control (V) in a randomized sequence. EMG leads were placed on the medial gastrocnemius, lateral gastrocnemius, soleus, and tibia. The supine subject's foot was securely strapped to an adjustable force transducer and the knee flexed to position the foot at the angle of maximum plantar flexion. As directed by the experimenter, the subject then attempted to produce a cramp by first pre‐shortening the gastrocnemius, isolating the triceps surae, and then performing a maximal voluntary static contraction (MVC). Contractions were held for 90 s or until a cramp occurred. If no cramp occurred, subjects rested for 10 min before attempting to elicit a cramp for a second time. Subjects repeated this pattern for up to 5 attempts within any given experiment; all experiments were separated by at least 1 week. EMG and force were recorded at baseline, during the static muscle contraction, and throughout the duration of the muscle cramp. There were no significant differences between active and vehicle control for pre‐cramp MVC (A: 12.4±7.0 (SD) kg, V: 12.5±7.6 kg; p=0.99), post‐cramp MVC (A: 10.1±5.6 kg, V: 10.7±6.8 kg; p=0.40), pre‐cramp contraction duration (A: 32.7±21.8 s, V: 28.3±17.2 s; p=0.16), or cramp duration (A: 13.7±11.4 s, V: 16.9±16.3 s; p=0.08). However, the integrated EMG signal, i.e., the area under the EMG intensity‐duration curve, was significantly lower (p=0.01) for A (0.51±0.38 V•s) than V (0.80±0.69 V•s). Composite subjective ratings of soreness (on a 1 to 10 rating scale) during the initial 20 min after cessation of cramping were also significantly (p=0.02) lower for the active formulation (3.4±4.6) than the vehicle control (4.0±2.2). Consistent with results from studies that have evoked leg muscle cramps using electrical stimulation, oral TRP channel activators significantly attenuated the intensity‐duration profile of voluntarily initiated muscle cramps in this sample of young adults.Support or Funding InformationFUNDING: Flex Pharma, Inc.

Effects of one session radial extracorporeal shockwave therapy on post-stroke plantarflexor spasticity: a single-blind clinical trial

Purpose To examine the effects of radial extracorporeal shockwave therapy (rESWT) on plantarflexor spasticity after stroke. Method Twelve patients with stroke were randomly included for this prospective, single-blind clinical trial. Patients received one rESWT session (0.340 mJ/mm2, 2000 shots) on plantarflexor muscle. The Modified Modified Ashworth Scale (MMAS), H-reflex tests, ankle range of motion (ROM), passive plantarflexor torque (PPFT) and timed up and go test (TUG) were measured at baseline (T0), immediately after treatment (T1) and one hour after the end of the treatment (T2). Results Patients had improved the MMAS scores for both the gastrocnemius and the soleus muscles, active and passive ROM, PPFT and TUG over time after rESWT. For the PPFT, it was greater at high velocity than at low velocity, and there was a significant three-way interaction between time, knee position (extended/flexed) and velocity (low/high). The H-reflex latency had decreased at T1, but there was no significant effect on Hmax/Mmax ratio. Conclusions The rESWT improved plantarflexor spasticity, and the effects sustained for one hour, whereas it was not effective in improving spinal excitability.Implications for RehabilitationOne session radial extracorporeal shock wave therapy (rESWT) is safe and effective in improving post stroke plantarflexor spasticity, ankle active and passive range of motion, passive torque, and walking capability.The spasticity scores improved for both the gastrocnemius and the soleus muscles and persisted one hour after rESWT.The magnitude of resistive plantarflexor passive torque in the knee extended position and high velocity was larger over time suggesting greater gastrocnemius spasticity than soleus.The rESWT had no significant effects on alpha motorneuron excitability.

Clinical Value of the Assessment of Changes in MEP Duration with Voluntary Contraction.

Transcranial magnetic stimulation (TMS) gives rise to muscle responses, known as motor evoked potentials (MEP), through activation of the motor pathways. Voluntary contraction causes facilitation of MEPs, which consists of shortening MEP latency, increasing MEP amplitude and widening MEP duration. While an increase in excitability of alpha motorneurons and the corticospinal tract can easily explain latency shortening and amplitude increase, other mechanisms have to be accounted for to explain the increase in duration. We measured the increase in duration of the MEP during contraction with respect to rest in a group of healthy volunteers and retrospectively assessed this parameter in patients who were examined in a standardized fashion during the past 5 years. We included 25 healthy subjects, 21 patients with multiple sclerosis, 33 patients with acute stroke, 5 patients with hereditary spastic paraparesis, and 5 patients with signs suggesting psychogenic paresis. We found already significant differences among groups in the MEP duration at rest, patients with MS had a significantly longer duration, and patients with stroke had significantly shorter duration, than the other two groups. The increase in MEP duration during voluntary contraction was different in patients and in healthy subjects. It was significantly shorter in MS and significantly longer in stroke patients. It was absent in the five patients with suspected psychogenic weakness. In patients with HSP, an abnormally increase in duration occurred only in leg muscles. Our results suggest that the increase in duration of the MEP during contraction may reveal the contribution of propriospinal interneurons to the activation of alpha motorneurons. This mechanism may be altered in some diseases and, therefore, the assessment proposed in this work may have clinical applicability for the differential diagnosis of weakness.

Modified Ashworth Scale and Alpha Motor Neuron Excitability Indicators of F-wave in Spastic Soleus Muscle Early after Stroke

Aims: Plantar flexor spasticity affects walking ability after stroke. Spasticity is clinically tested by modified Ashworth Scale (MAS) and it is fairly reliable. The aim of this study was to test the correlation between MAS and alpha motor neuron excitability indicators of F-wave in spastic soleus muscles early after stroke. Place and Duration of Study: Neurophysiology laboratory, Kasturba Medical College, Mangalore, India and between June 2010- August 2012. Methodology: Twenty three people with post stroke duration of 2.26 (1.18) months and MAS score > 1 on soleus muscle participated in this cross-sectional study. Modified Ashworth Scale and Fwave procedures were administered on spastic soleus muscle and the relationship was tested by Spearman’s rank correlation coefficient. Results: The correlation of MAS to persistence of F-wave was high (r=0.842; p=<0.0001), but not with latency of F-wave (r= -0.264; p=0.223). A moderate correlation was found for post stoke duration to F-wave persistence (r=0.45; p=0.013) and the relation was nonlinear with latency of Fwave (r=0.016; p=0.950). Conclusion: Modified Ashworth scale may be a tool to measure the neural aspects of soleus muscle spasticity i.e. alpha motor neuron excitability in people with early stage stroke.

F-Wave in the Upper Extremities of Patients with Primary Torsion Dystonia

We investigated characteristics of the F-waves in the upper limbs of patients suffering from primary torsion dystonia (PTD) by means of surface-electrode electromyography. Single electric stimulation was used to obtain optimum M-responses from the m. abductor pollicis brevis (median nerve) and m. abductor digiti minimi (ulnar nerve). Ten consecutive supramaximum electrical stimuli were applied to each nerve to obtain F-waves from the wrist. In general, the registered M-response latencies and amplitudes, as well as conduction velocities via all inspected nerves, demonstrated no significant deviations from the normal ranges. Nearly all investigated patients, except one, had normal F-wave minimal latencies. The mean amplitudes of F-waves from both median and ulnar nerves were higher than the average F-wave amplitudes described in the literature. The frequency of occurrence of F-waves in both median and ulnar nerves was greater than in the norm. According to our results, it can be concluded that the amplitude and, to some extent, frequency rather than the latency of F-waves are important in the studies of patients with PTD. Increased amplitudes and frequencies reveal changes in the excitability of alpha motoneurons, which could be accepted as a measure of a disturbed interneuronal balance probably caused by alterations in the suprasegmental control mechanisms related to PTD.

Cold Induced Modulation of Motoneuronal Excitability in Spastics

Background: Despite wide use of cold in controlling spasticity, scientific studies substantiating its anti-spastic effects are scarce. Current research underpin increased alpha Motoneuronal Excitability as main contributor to origin of spasticity. Clinicians and researchers, therefore, are putting emphasis on to use electrophysiological methods to measure degree of alpha Motoneuronal Excitability for spasticity evaluation. H-reflex is considered as reliable electrophysiological tool to objectively measure alpha Motoneuronal Excitability Objective: To investigate effects of ice immersion on motoneuronal excitability in spastic individuals. Methodology: Thirteen subjects with hemiplegia (Male 8, Female 5; age 53.92 ± 8.79 years) having plantar-flexor spasticity grades greater than one on Modified Ashworth Scale (MAS), participated in the study. 6 minutes of cold immersion was applied to spastic limb. H-reflexes were recorded immediately before and after application of ice immersion, peak to peak amplitude of ten H- reflexes was selected for analysis. Results: Paired ‘t’- test revealed that non-significant differences existed in pre and post H-reflex amplitude values for 6 min ice immersion (t=0.04, p≤0.05). There was inter-subject variation in response to cold as 30.77% of subjects (n=4) and 69.23% of subjects (n=9) showed increase and decrease in H-amplitude, respectively. Conclusion: Cold produces differential effect on motoneuronal excitability in spastic individuals, indicating towards complex nature of spasticity and that certain patient characteristics play a major role in determining individual response. Thus, each patient response must be determined before cold application to ascertain their appropriateness for treatment if desirable effect is to be achieved.

Acute effects of high-frequency microfocal vibratory stimulation on the H reflex of the soleus muscle. A double-blind study in healthy subjects.

This study in healthy subjects examined the effects of a system delivering focal microvibrations at high frequency (Equistasi®) on tonic vibration stimulus (TVS)-induced inhibition of the soleus muscle H reflex. Highfrequency microvibrations significantly increased the inhibitory effect of TVS on the H reflex for up to three minutes. Moreover, Equistasi® also significantly reduced alpha-motoneuron excitability, as indicated by the changes in the ratio between the maximumamplitude H reflex (Hmax reflex) and the maximumamplitude muscle response (Mmax response); this effect was due to reduction of the amplitude of the H reflex because the amplitude of muscle response remained unchanged. The present findings indicate that Equistasi® has a modulatory effect on proprioceptive reflex circuits. Therefore, Equistasi® might interfere with some mechanisms involved in both physiological and pathophysiological control of movement and of posture.

Effect of Exercise-induced Muscle Damage on Neuromuscular Function of the Quadriceps Muscle

Exercise-induced muscle injury is commonly accompanied by a reduction of muscular strength. It has been suggested that this reduction in voluntary force is attributable to "peripheral" and "central" mechanisms within the neuromuscular system. The quadriceps muscle of 15 subjects was damaged with four bouts of 25 maximal voluntary concentric-eccentric contractions at a speed of 60°/s. In a time period of 7 days, we investigated the contribution of agonist muscle activation and contractile properties (CP) to changes in isometric maximum voluntary torque (iMVT). In order to provide a comprehensive assessment, the neural drive to muscles was estimated with the interpolated twitch technique and root mean square of the EMG signal. CP were evaluated by analysing the twitch torque signal induced by single and doublet stimulation. Furthermore, we measured changes in alpha motoneuron excitability of vastus medialis at the spinal level due to muscle soreness using the H reflex technique. The iMVT was impaired at post, 24 h and 48 h, while rate of torque development and voluntary activation (VA) were only decreased immediately after the intervention. CP were impaired immediately after exercise and at 24 h. Maximal H reflex (Hmax), maximal M wave (Mmax) and the Hmax/Mmax-ratio were not affected. Sensation of muscle soreness assessment revealed impairments at 24 h, 48 h and 72 h. Data suggest that reduced VA and altered CP contribute to the force loss immediately after concentric-eccentric exercise. Thereafter, the impairment of CP seems to be mainly responsible for the reduced iMVT. In addition, there is no evidence for an association between muscle soreness and VA as well as between muscle soreness and spinal excitability.

Lateralized alpha-motoneuron excitabilities during lying and standing of healthy individuals in relation to Parkinsonian rigidity

Objectives: To elucidate mechanisms of Parkinsonian rigidity by assessing excitability of alpha-motoneurons innervating right and left soleus muscles in healthy controls and Parkinson’s disease (PD) patients with rigidities in the right, left and both legs.Methods: One group of 45 controls was recruited and 60 PD patients in three groups: rigidities, predominantly in the right, left and both legs. H-reflex (H) and muscle response (M) were recorded from right and left soleus muscles during stimulations of the posterior tibial nerve at the popliteal fossa while lying and standing. The H/M ratio was taken as an index for motoneuron excitability.Results: Mean H/M ratios were significantly different on the right and left sides, modified by postural changes in controls and PD patients. Analysis of variance showed that in healthy subjects the H/M ratio was: standing>lying (right), lying>standing (left). In right leg rigidity patients, the H/M ratio was greatest during standing, and smallest during lying. In left leg rigidity patients, the H/M ratios on the right and left sides were equally independent of posture. In controls, left H/M>right while lying, <right while standing. In right leg rigidity patients, right H/M>left, but <right in left leg rigidity patients, independent of posture. There was no side difference in patients with rigidity in both legs.Conclusions: (i) motoneuron excitability may show side and postural differences in healthy individuals and PD patients; (ii) posture may be associated with lateralized motoneuron excitability in these subjects; and (iii) Parkinsonian rigidity may have spinal motor origins.

Mechanisms of tizanidine action on spasticity.

This investigation estimated the mechanisms of tizanidine action on spasticity using a battery of neurophysiological methods. Thirty patients with old post-stroke spastic hemiparesis took part in the investigation. They were treated with tizanidine-mean daily dose 15.8 +/- 5.6 mg for a mean of 23.3 +/- 4.8 days. A questionnaire for assessment of subjective improvement after treatment used a 5-point scale. For standardization of the neurological examination 5-point scales were used to assess muscle tone, muscle force and tendon reflexes. A battery of neurophysiological methods was used to analyze different mechanisms of spasticity: for alpha motoneuron excitability--the F wave parameters; for presynaptic inhibition--the ratio of H reflex amplitudes before and after vibration of the achilles tendon (Hvibr/Hmax); for common interneuron activity--the flexor reflex parameters. Our results revealed that tizanidine reduces spastically increased muscle tone, but has no influence on muscle force, tendon reflexes, Babinski sign and ankle clonus. Tizanidine is supposed to act by increasing the presynaptic inhibition and decreasing of alpha motoneuron excitability. When spasticity has decreased presynaptic inhibition and increased motoneuron excitability, it is better to treat with tizanidine.

Role of intracortical mechanisms in the late part of the silent period to transcranial stimulation of the human motor cortex.

Transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) of the human motor cortex produce a silent period (SP) following motor evoked potentials (MEPs). The early part of the SP can be explained by decreased alpha motor neuron excitability, whereas the late part is presumably due to suprasegmental mechanisms. In order to determine the level of the suprasegmental contribution of the generation of SPs, we recorded excitatory and inhibitory responses to TMS, TES and percutaneous electrical brainstem stimulation (PBS) in the voluntarily activated first dorsal interosseous muscle of the hand. Stimulus intensities were set so that PBS and TES induced MEPs with areas equal to or larger than those of MEPs obtained with TMS. This procedure revealed that SPs were 49% and 83% shorter with TES and PBS, respectively, than with TMS. As TMS is more effective than TES or PBS in activating cortical interneurons, these findings support the idea that a significant component of the SP arises from intracortical mechanisms.

NEUROMUSCULAR CHANGES IN PATIENTS WITH TRAUMATIC DISEASE OF THE SPINAL CORD ON APPLICATION OF A BIOLOGICAL FEEDBACK

Common clinical electromyography was performed to perfect treatment technique with biological feedback (BF) and to determine the mechanism of its action. Sixty eight patients at the age of 18 to 39 years with lower thoracic and lumbar spine and spinal cord injuries were examined at a period of a fullscale picture of spinal cord disease and a period of rehabilitation. The application of BF provided the average 60.2 % growth of muscular activity amplitude due to increase in total excitability of spinal alpha-motoneurons (10 %) (of mainly small (64.8 %) and reduction of excitability of big ones) and braking influence of the central nervous system (112.5 %).

Post-Activation Potentiation

The response of muscle to volitional or electrically induced stimuli is affected by its contractile history. Fatigue is the most obvious effect of contractile history reflected by the inability of a muscle to generate an expected level of force. However, fatigue can coexist with post-activation potentiation (PAP), which serves to improve muscular performance, especially in endurance exercise and activities involving speed and power. The measured response of muscular performance following some form of contractile activity is the net balance between processes that cause fatigue and the simultaneous processes that result in potentiation. Optimal performance occurs when fatigue has subsided but the potentiated effect still exists. PAP has been demonstrated using electrically induced twitch contractions and attributed to phosphorylation of myosin regulatory light chains, which makes actin and myosin more sensitive to Ca(2+). The potentiated state has also been attributed to an increase in alpha-motoneuron excitability as reflected by changes in the H-reflex. However, the significance of PAP to functional performance has not been well established. A number of recent studies have applied the principles of PAP to short-term motor performance as well as using it as a rationale for producing long-term neuromuscular changes through complex training. Complex training is a training strategy that involves the execution of a heavy resistance exercise (HRE) prior to performing an explosive movement with similar biomechanical characteristics, referred to as a complex pair. The complex pair is then repeated for a number of sets and postulated that over time will produce long-term changes in the ability of a muscle to generate power. The results of these studies are equivocal at this time and, in fact, no training studies have actually been undertaken. The discrepancies among the results of the various studies is due in part to differences in methodology and design, with particular reference to the mode and intensity of the HRE, the length of the rest interval within and between the complex pairs, the type of explosive activity, the training history of the participants, and the nature of the dependent variables. In addition, few of the applied studies have actually included measures of twitch response or H-reflex to determine if the muscles of interest are potentiated. There is clearly more research required in order to clarify the functional significance of PAP and, in particular, the efficacy of complex training in producing long-term neuromuscular adaptations.

Focal aggregation of voltage‐gated, Kv2.1 subunit‐containing, potassium channels at synaptic sites in rat spinal motoneurones

Delayed rectifier K+ currents are involved in the control of alpha-motoneurone excitability, but the precise spatial distribution and organization of the membrane ion channels that contribute to these currents have not been defined. Voltage-activated Kv2.1 channels have properties commensurate with a contribution to delayed rectifier currents and are expressed in neurones throughout the mammalian central nervous system. A specific antibody against Kv2.1 channel subunits was used to determine the surface distribution and clustering of Kv2.1 subunit-containing channels in the cell membrane of alpha-motoneurones and other spinal cord neurones. In alpha-motoneurones, Kv2.1 immunoreactivity (-IR) was abundant in the surface membrane of the soma and large proximal dendrites, and was present also in smaller diameter distal dendrites. Plasma membrane-associated Kv2.1-IR in alpha-motoneurones was distributed in a mosaic of small irregularly shaped, and large disc-like, clusters. However, only small to medium clusters of Kv2.1-IR were observed in spinal interneurones and projection neurones, and some interneurones, including Renshaw cells, lacked demonstrable Kv2.1-IR. In alpha-motoneurones, dual immunostaining procedures revealed that the prominent disc-like domains of Kv2.1-IR are invariably apposed to presynaptic cholinergic C-terminals. Further, Kv2.1-IR colocalizes with immunoreactivity against postsynaptic muscarinic (m2) receptors at these locations. Ultrastructural examination confirmed the postsynaptic localization of Kv2.1-IR at C-terminal synapses, and revealed clusters of Kv2.1-IR at a majority of S-type, presumed excitatory, synapses. Kv2.1-IR in alpha-motoneurones is not directly associated with presumed inhibitory (F-type) synapses, nor is it present in presynaptic structures apposed to the motoneurone. Occasionally, small patches of extrasynaptic Kv2.1-IR labelling were observed in surface membrane apposed by glial processes. Voltage-gated potassium channels responsible for the delayed rectifier current, including Kv2.1, are usually assigned roles in the repolarization of the action potential. However, the strategic localization of Kv2.1 subunit-containing channels at specific postsynaptic sites suggests that this family of voltage-activated K+ channels may have additional roles and/or regulatory components.

The effect of acupuncture on alpha-motoneuron excitability.

The effect of short duration and sustained manual acupuncture on alpha-motoneuron excitability was studied using the Soleus H-reflex. The acupuncture points GB-34 and SP-9 were needled and stimulated manually. Normalised H-reflex and M-wave recruitment curves were constructed and the ratio of the slope of the ascending part of the H-reflex recruitment curve (Hslp) to the slope of the ascending part of the M-wave recruitment curve (Mslp) was used for assessing changes in alpha-motoneuron excitability. Sustained manual acupuncture caused significant reduction of alpha-motoneuron excitability, while short duration manual acupuncture had no effect. The reduction of alpha-motoneuron excitability following sustained manual acupuncture occurred fifteen minutes after cessation of acupuncture and was still present at 30 minutes. The relationship between perceived intensity of acupuncture sensation (Deqi) and changes in alpha-motoneuron excitability was also studied, but no significant correlation was found. This study indicates that manual acupuncture would be useful in clinical conditions associated with increased alpha-motoneuron excitability and that when using acupuncture for these conditions, higher intensity of perceived acupuncture sensation (Deqi) may not result in greater degree of reduction in alpha-motoneuron excitability.

Altered central nervous system processing of noxious stimuli contributes to decreased nociceptive responding in individuals at risk for hypertension

Previous evidence indicates that individuals with hypertension and those at increased risk for the disorder exhibit decreased pain perception. To test the hypothesis that attenuation of nociceptive processing in individuals at genetic risk for hypertension is related to differential central modulation of nociceptive transmission, the present study examined descending modulation, alpha-motoneuron excitability, and temporal summation of nociceptive input in young adults with and without a parental history of hypertension. Nociceptive flexion (NFR) and non-nociceptive Hoffman reflexes were assessed at rest and during performance of a mental arithmetic task. Temporal summation was assessed by examining NFR threshold in response to a series of five electrical pulses delivered at 2 Hz. Compared to participants without a parental history of hypertension, offspring of individuals with hypertension exhibited significantly higher NFR thresholds, suggesting that risk for hypertension may be associated with enhanced activation of central pain inhibition pathways.