Regeneration of starfish radial nerve cord restores animal mobility and unveils a new coelomocyte population.

The potential to regenerate a damaged body part is expressed to a different extent in animals. Echinoderms, in particular starfish, are known for their outstanding regenerating potential. Differently, humans have restricted abilities to restore organ systems being dependent on limited sources of stem cells. In particular, the potential to regenerate the central nervous system is extremely limited, explaining the lack of natural mechanisms that could overcome the development of neurodegenerative diseases and the occurrence of trauma. Therefore, understanding the molecular and cellular mechanisms of regeneration in starfish could help the development of new therapeutic approaches in humans. In this study, we tackle the problem of starfish central nervous system regeneration by examining the external and internal anatomical and behavioral traits, the dynamics of coelomocyte populations, and neuronal tissue architecture after radial nerve cord (RNC) partial ablation. We noticed that the removal of part of RNC generated several anatomic anomalies and induced behavioral modifications (injured arm could not be used anymore to lead the starfish movement). Those alterations seem to be related to defense mechanisms and protection of the wound. In particular, histology showed that tissue patterns during regeneration resemble those described in holothurians and in starfish arm tip regeneration. Flow cytometry coupled with imaging flow cytometry unveiled a new coelomocyte population during the late phase of the regeneration process. Morphotypes of these and previously characterized coelomocyte populations were described based on IFC data. Further studies of this new coelomocyte population might provide insights on their involvement in radial nerve cord regeneration.

A topographical and physiological exploration of C-tactile afferents and their response to menthol and histamine.

Unmyelinated tactile (C-tactile or CT) afferents are abundant in arm hairy skin and have been suggested to signal features of social affective touch. Here, we recorded from unmyelinated low-threshold mechanosensitive afferents in the peroneal and radial nerves. The most distal receptive fields were located on the proximal phalanx of the third finger for the superficial branch of the radial nerve and near the lateral malleolus for the peroneal nerve. We found that the physiological properties with regard to conduction velocity and mechanical threshold, as well as their tuning to brush velocity, were similar in CT units across the antebrachial (n = 27), radial (n = 8), and peroneal (n = 4) nerves. Moreover, we found that although CT afferents are readily found during microneurography of the arm nerves, they appear to be much more sparse in the lower leg compared with C-nociceptors. We continued to explore CT afferents with regard to their chemical sensitivity and found that they could not be activated by topical application to their receptive field of either the cooling agent menthol or the pruritogen histamine. In light of previous studies showing the combined effects that temperature and mechanical stimuli have on these neurons, these findings add to the growing body of research suggesting that CT afferents constitute a unique class of sensory afferents with highly specialized mechanisms for transducing gentle touch.NEW & NOTEWORHY Unmyelinated tactile (CT) afferents are abundant in arm hairy skin and are thought to signal features of social affective touch. We show that CTs are also present but are relatively sparse in the lower leg compared with C-nociceptors. CTs display similar physiological properties across the arm and leg nerves. Furthermore, CT afferents do not respond to the cooling agent menthol or the pruritogen histamine, and their mechanical response properties are not altered by these chemicals.

A novel method to measure sensory nerve conduction of the posterior antebrachial cutaneous nerve.

INTRODUCTION/AIMS: Posterior antebrachial cutaneous (PABC) nerve conduction studies could be useful for distinguishing PABC neuropathy from C7 radiculopathy. In the conventional method using an antidromic method, the sensory nerve action potential (SNAP) is sometimes followed by a large volume-conducted motor potential. In this report we describe a reliable nerve conduction study using an orthodromic method for recording SNAPs of the PABC nerve. METHODS: Thirty-six healthy volunteers participated in this study. PABC SNAPs were recorded by placing a surface-active electrode 2 cm anterior to the lateral epicondyle. The PABC nerve was stimulated 10 cm distal to the active recording electrode along a line from the recording point to the mid-dorsum of the wrist, midway between the radial and ulnar styloid processes. We also performed PABC nerve conduction studies using an antidromic method and compared the findings. RESULTS: PABC SNAPs were recorded bilaterally from all subjects. The mean peak-to-peak amplitude for SNAPs was 13.4 ± 4.8 µV. Mean maximum conduction velocity was 62.7 ± 3.9 m/s and mean negative peak conduction velocity was 51.2 ± 2.6 m/s. The mean side-to-side difference in amplitude was 22.1 ± 16.0%. The mean amplitude of SNAPs obtained by our method was 48.9% higher than that of SNAPs obtained by the conventional method (13.4 vs 9.0 µV; P < .001). In contrast to the conventional method, our method enabled SNAPs to be recorded without a volume-conducted motor potential. DISCUSSION: The higher mean amplitude of SNAPs with our method enables them to be obtained easily.

Anatomical variations of the superficial branch of the radial nerve and the dorsal branch of the ulnar nerve: A detailed electrophysiological study.

INTRODUCTION: In this study we evaluated anatomic variations of the superficial branch of the radial nerve (SBRN) and the dorsal branch of the ulnar nerve (DBUN) electrophysiologically. METHODS: Antidromic nerve conduction studies (NCS) of the SBRN and DBUN were performed on healthy individuals. To identify individual responses from the distal branches of the SBRN and DBUN, sensory nerve action potentials of each finger (lateral side/medial side) were recorded. RESULTS: NCS were performed in 50 hands of 27 healthy control subjects. The thumb and the index finger were supplied by the SBRN in all cases. The lateral and medial sides of the third finger were supplied by the SBRN in 94.0% and 74.0% of the cases, but the lateral and medial sides of the fourth finger were supplied by the SBRN in only 10.0% and 2.0% of cases. The fifth finger and the medial side of the fourth finger were always supplied by the DBUN. The lateral side of the fourth finger was supplied by the DBUN in 98.0% of cases, but the lateral and medial sides of the third finger were supplied by the DBUN in 40.0% and 70.0% of cases. Dual innervation by the SBRN and DBUN was found in 34.0% and 46.0% of the lateral and medial sides of the third finger, but in only 8.0% and 2.0% of the lateral and medial sides of the fourth finger. DISCUSSION: There are considerable anatomic variations of the SBRN and DBUN in healthy individuals.

Optimal recording electrode placement for radial motor nerve conduction study using extensor indicis muscle: Cadaver and electrophysiological studies.

INTRODUCTION/AIMS: The aim of this study was to determine the optimal combination of active (E1) and reference (E2) recording electrode placements for the radial motor nerve conduction study recording over the extensor indicis muscle using surface electrodes. METHODS: Thirty-six upper limbs from 18 fresh frozen cadavers were dissected to determine the midpoint of the extensor indicis muscle. Radial nerve conduction study was performed in 112 arms of 56 healthy subjects. Six combinations of three E1 and two E2 sites were studied. The stimulation site was 8 cm proximal to the E1 electrode. RESULTS: The optimal combination of placement sites for the E1 and E2 electrodes to provide the largest amplitude is E1 electrode at the distal 1/4 point of the forearm length and E2 electrode at the extensor indicis tendon point in the wrist. DISCUSSION: Optimal recording electrode placement may increase the accuracy and reproducibility of radial motor nerve conduction studies.

Need for early exploration of radial nerve in humeral shaft fractures with radial nerve palsy.

INTRODUCTION: Radial nerve palsy (RNP) associated with humeral shaft fracture (HSF) is the most common nerve complication in long bone fractures. There is still controversy over the need for immediate exploration of the radial nerve (RN) in HSF with RNP. The purpose of the current study was to determine which situations of HSF with RNP require early exploration of the RN. MATERIALS AND METHODS: This is a retrospective study that included 55 patients who had visited the emergency department of the current authors' hospital and had been diagnosed with HSF between March of 2005 and September of 2015. Of these 55 patients, 14 (25.4%) had been diagnosed with HSF with RNP. We reviewed the medical records of those 14 patients and their radiographs to evaluate each fracture's type, location, pattern, energy of trauma, status of RN injury, and time until recovery from RNP. RESULT: All the 14 RNP patients had suffered high-energy trauma. Three had fractures in the proximal third (21.4%), six in the middle third (42.9%), and five in the distal third (35.7%). The three patients (21.4%) with incomplete recovery of RNP all had proximal third fractures; two of these three patients had RN transection. CONCLUSION: Early exploration of the radial nerve should be considered in patients with radial nerve palsy associated with proximal third humeral shaft fracture, regardless of the fracture patterns caused by the high-energy trauma.

High frequency repetitive transcranial magnetic stimulation to the left dorsolateral prefrontal cortex modulates sensorimotor cortex function in the transition to sustained muscle pain.

Based on reciprocal connections between the dorsolateral prefrontal cortex (DLPFC) and basal-ganglia regions associated with sensorimotor cortical excitability, it was hypothesized that repetitive transcranial magnetic stimulation (rTMS) of the left DLPFC would modulate sensorimotor cortical excitability induced by muscle pain. Muscle pain was provoked by injections of nerve growth factor (end of Day-0 and Day-2) into the right extensor carpi radialis brevis (ECRB) muscle in two groups of 15 healthy participants receiving 5 daily sessions (Day-0 to Day-4) of active or sham rTMS. Muscle pain scores and pressure pain thresholds (PPTs) were collected (Day-0, Day-3, Day-5). Assessment of motor cortical excitability using TMS (mapping cortical ECRB muscle representation) and somatosensory evoked potentials (SEPs) from electrical stimulation of the right radial nerve were recorded at Day-0 and Day-5. At Day-0 versus Day-5, the sham compared to active group showed: Higher muscle pain scores and reduced PPTs (P < 0.04); decreased frontal N30 SEP (P < 0.01); increased TMS map volume (P < 0.03). These results indicate that muscle pain exerts modulatory effects on the sensorimotor cortical excitability and left DLPFC rTMS has analgesic effects and modulates pain-induced sensorimotor cortical adaptations. These findings suggest an important role of prefrontal to basal-ganglia function in sensorimotor cortical excitability and pain processing.

Sensory enhancement amplifies interlimb cutaneous reflexes in wrist extensor muscles.

Interlimb neural connections support motor tasks such as locomotion and cross-education strength training. Somatosensory pathways that can be assessed with cutaneous reflex paradigms assist in subserving these connections. Many studies show that stimulation of cutaneous nerves elicits reflexes in muscles widespread across the body and induces neural plasticity after training. Sensory enhancement, such as long-duration trains of transcutaneous stimulation, facilitates performance during rehabilitation training or fatiguing motor tasks. Performance improvements due to sensory stimulation may be caused by altered spinal and corticospinal excitability. However, how enhanced sensory input regulates the excitability of interlimb cutaneous reflex pathways has not been studied. Our purpose was to investigate the effects of sensory enhancement on interlimb cutaneous reflexes in wrist extensor muscles. Stimulation to provide sensory enhancement (2-s trains at 150 Hz to median or superficial radial nerves) or evoke cutaneous reflexes (15-ms trains at 300 Hz to superficial radial nerve) was applied in different arms while participants (n = 13) performed graded isometric wrist extension. Wrist extensor electromyography and cutaneous reflexes were measured bilaterally. We found amplified inhibitory reflexes in the arm receiving superficial radial and median nerve sensory enhancement with net reflex amplitudes decreased by 709.5% and 695.3% repetitively. This suggests sensory input alters neuronal excitabilities in the interlimb cutaneous pathways. These findings have potential application in facilitating motor function recovery through alterations in spinal cord excitability enhancing sensory input during targeted rehabilitation and sports training.NEW & NOTEWORTHY We show that sensory enhancement increases excitability in interlimb cutaneous pathways and that these effects are not influenced by descending motor drive on the contralateral side. These findings confirm the role of sensory input and cutaneous pathways in regulating interlimb movements. In targeted motor function training or rehabilitation, sensory enhancement may be applied to facilitate outcomes.

Radial Nerve F-wave reference values with surface electrodes from the anconeus muscle.

INTRODUCTION: We sought to obtain normative values for radial nerve F-wave variables, recording with surface electrodes from the anconeus muscle. METHODS: We tested 30 healthy participants (17 women, 13 men) and measured the following variables: number of F waves/40 traces (F%); minimum, maximum, and mean F-wave latency (FMIN, FMAX, FMED, respectively); F-wave chronodispersion (FCHR); interside differences of F% and FMIN (DF% and DFMIN, respectively). RESULTS: The mean F% was 41.3%; the normative values of FMIN, FMED, FMAX, and FCHR were < 21.2, <22.1, <23.3, and < 4.0 ms, respectively; and normative values of DF% and DFMIN were < 16.6% and < 1.1 ms, respectively. Height was the sole independent predictor in a regression model of FMIN, FMED, and FMAX; this explained 37%-44% of the variability. DISCUSSION: We identified a feasible and useful technique to record radial nerve F waves from the anconeus muscle and obtained normative values of F-wave variables. Muscle Nerve 59:244-246, 2019.

Age-dependent Reliability of Semmes-Weinstein and 2-Point Discrimination Tests in Children.

BACKGROUND: Objective sensory testing is a critical component of the physical examination in children as they may be unable to communicate whether or not numbness is present. The purpose of this study was to determine at what age objective sensory tests could reliably be performed. METHODS: Normal, uninjured participants aged 2 to 17 years were enrolled in the study. Monofilament and static/moving 2-point discrimination tests were performed bilaterally assessing the median, ulnar, and radial nerves. Performance scores were recorded using the monofilament size and 2-point discrimination distance. Statistical analysis was performed utilizing univariable linear regression, 1-way ANOVA, and Welch t test. RESULTS: A total of 396 hands were tested utilizing the Semmes-Weinstein monofilament and static/moving 2-point discrimination tests. For the monofilament test, 27% of 3-year-olds, 83% of 4-year-olds, and all participants 5 years of age and older were capable of performing the monofilament test. The average monofilament scores were 2.874, 2.868, and 3.043 for the ulnar, median, and radial nerves, respectively, with no correlation with advancing age present. The ulnar and median nerve distributions were more sensitive than the radial nerve distribution (P<0.001).For 2-point discrimination tests, 33% of 4-year-olds, 61% of 5-year-olds, 88% of 6-year-olds, 95% of 7- and 8-year-olds, and all participants 9 years and older were capable of performing the static/moving 2-point discrimination tests. The average static 2-point discrimination scores were 3.348, 2.806, and 9.637 mm for the ulnar, median, and radial nerves, respectively. The average moving 2-point discrimination scores were 2.977, 2.483, and 8.506 mm for the ulnar, median, and radial nerves, respectively. There was no correlation between advancing age and performance scores. Children are the most sensitive in the median, then ulnar, and then radial nerve distribution (P<0.001). Better discrimination is present between 2 moving points than static points (P<0.001). CONCLUSIONS: Objective threshold testing utilizing a monofilament can reliably be performed in the vast majority of children aged 4 years and above, whereas density testing utilizing 2-point discrimination can reliably be performed in the vast majority of children aged 6 years and above. LEVEL OF EVIDENCE: Level II.

Common Synaptic Input to Motor Neurons and Neural Drive to Targeted Reinnervated Muscles.

We compared the behavior of motor neurons innervating their physiological muscle targets with motor neurons from the same spinal segment whose axons were surgically redirected to remnant muscles (targeted muscle reinnervation). The objective was to assess whether motor neurons with nonphysiological innervation receive similar synaptic input and could be voluntary controlled as motor neurons with natural innervation. For this purpose, we acquired high-density EMG signals from the biceps brachii in 5 male transhumeral amputees who underwent targeted reinnervation of this muscle by the ulnar nerve and from the first dorsal interosseous muscle of 5 healthy individuals to investigate the natural innervation of the ulnar nerve. The same recordings were also performed from the biceps brachii muscle of additional 5 able-bodied individuals. The EMG signals were decomposed into discharges of motor unit action potentials. Motor neurons were progressively recruited for the full range of submaximal muscle activation in all conditions. Moreover, their discharge rate significantly increased from recruitment to target activation level in a similar way across the subject groups. Motor neurons across all subject groups received common synaptic input as identified by coherence analysis of their spike trains. However, the relative strength of common input in both the delta (0.5-5 Hz) and alpha (5-13 Hz) bands was significantly smaller for the surgically reinnervated motor neuron pool with respect to the corresponding physiologically innervated one. The results support the novel approach of motor neuron interfacing for prosthesis control and provide new insights into the role of afferent input on motor neuron activity.SIGNIFICANCE STATEMENT Targeted muscle reinnervation surgically redirects nerves that lost their target in the amputation into redundant muscles in the region of the stump. The study of the behavior of motor neurons following this surgery is needed for designing biologically inspired prosthetic control strategies. Moreover, targeted muscle reinnervation offers a human experimental framework for studying the control and behavior of motor neurons when changing their target innervated muscle fibers and sensory feedback. Here, we show that the control of motor neurons and their synaptic input, following reinnervation, was remarkably similar to that of the physiological innervation, although with reduced common drive at some frequencies. The results advance our knowledge on the role of sensory input in the generation of the neural drive to muscles and provide the basis for designing physiologically inspired methods for prosthesis control.

Anatomical Factors Contributing to Radial Nerve Excursion at the Brachium: A Cadaveric Study.

PURPOSE: The radial nerve appears to be more vulnerable to injury in the brachium than the median and ulnar nerves. The underlying mechanism for this increased vulnerability is not well explained. We hypothesize that the radial nerve has less excursion than the median and ulnar nerves because it is anatomically tethered by the lateral intermuscular septum (LIS) and that elbow positioning and LIS release will improve its excursion. METHODS: Eight paired fresh-frozen cadaveric upper extremity specimens were used. The radial, median, and ulnar nerves were transected at the level of the spiral groove. Nerve excursion was determined at a constant tension of 100 g from 0° to 90° of elbow flexion and repeated for the radial nerve after releasing the LIS. The cross-sectional areas of nervous and connective tissue were then determined histologically. RESULTS: Radial and median nerve excursion correlated positively with increased elbow flexion, and ulnar nerve excursion correlated negatively with increased elbow flexion. Release of the LIS significantly improved radial nerve excursion at 0°, 60°, and 90° of elbow flexion. Release of the LIS with 90° of elbow flexion increased radial nerve excursion by approximately 3 times. Histological analysis demonstrated similar mean composition of nonnervous connective tissue among the 3 nerves. CONCLUSIONS: The radial nerve is anatomically tethered in the brachium by the LIS and has limited excursion compared with the median and ulnar nerves. Radial nerve excursion improves with elbow flexion and LIS release. Flexing the elbow to 90° doubles radial nerve excursion. Releasing the LIS as well triples the excursion of the radial nerve. Histological composition was similar among the three nerves at the brachium. CLINICAL RELEVANCE: Releasing the LIS and flexing the elbow improve radial nerve excursion. These steps may be useful during humeral fracture fixation.

Comparison of Median Nerve Mechanosensitivity and Pressure Pain Threshold in Patients With Nonspecific Neck Pain and Asymptomatic Individuals.

OBJECTIVE: The purpose of this study was to investigate the presence of median nerve mechanosensitivity by comparing median nerve neurodynamic test results of patients with nonspecific neck pain (NNP) and asymptomatic individuals. METHODS: A total of 40 patients (30 women, 10 men) with NNP between the ages of 21 and 62 years (39.53 ± 10.18 years) and 38 asymptomatic individuals (23 women, 15 men) between the ages of 18 and 60 years (37.13 ± 9.64 years) participated in the study. Pressure pain threshold was assessed with digital pressure algometer, cervical joint range of motion was assessed with a universal goniometer, and median nerve mechanosensitivity was assessed with Upper Limb Neurodynamic Test 1 (ULNT1). The test step where the first sensory response was given, the location and character of the sensory response, and the final elbow extension angle were recorded during ULNT1. RESULTS: Patients with NNP had significantly decreased pressure pain threshold (P < .001), decreased range of motion of cervical flexion (P < .001), and decreased cervical lateral flexion (P = .001) compared with asymptomatic individuals, whereas no change was identified in range of motion of rotation (P = .100). In ULNT1, 45% of patients with NNP reported pain and 40% of them reported stretch. A total of 65% of asymptomatic individuals reported stretch, and 13% of them reported pain. It was identified in ULNT1 that final elbow extension angle was lower in the NNP group compared with asymptomatic individuals (P = .008). CONCLUSION: Median nerve mechanosensitivity increased, pressure pain threshold decreased, and active neck motion was limited in individuals with NNP compared with asymptomatic individuals.

Not GABA but glycine mediates segmental, propriospinal, and bulbospinal postsynaptic inhibition in adult mouse spinal forelimb motor neurons.

The general view is that both glycine (Eccles, 1964) and GABA (Curtis and Felix, 1971) evoke postsynaptic inhibition in spinal motor neurons. In newborn or juvenile animals, there are conflicting results showing postsynaptic inhibition in motor neurons by corelease of GABA and glycine (Jonas et al., 1998) or by glycine alone (Bhumbra et al., 2012). To resolve the relative contributions of GABA and glycine to postsynaptic inhibition, we performed in vivo intracellular recordings from forelimb motor neurons in adult mice. Postsynaptic potentials evoked from segmental, propriospinal, and bulbospinal systems in motor neurons were compared across four different conditions: control, after gabazine, gabazine followed by strychnine, and strychnine alone. No significant differences were observed in the proportion of IPSPs and EPSPs between control and gabazine conditions. In contrast, EPSPs but not IPSPs were recorded after adding strychnine with gabazine or administering strychnine alone, suggesting an exclusive role for glycine in postsynaptic inhibition. To test whether the injected (intraperitoneal) dose of gabazine blocked GABAergic inhibitory transmission, we evoked GABAA receptor-mediated monosynaptic IPSPs in deep cerebellar nuclei neurons by stimulation of Purkinje cell fibers. No monosynaptic IPSPs could be recorded in the presence of gabazine, showing the efficacy of gabazine treatment. Our results demonstrate that, in the intact adult mouse, the postsynaptic inhibitory effects in spinal motor neurons exerted by three different systems, intrasegmental and intersegmental as well as supraspinal, are exclusively glycinergic. These findings emphasize the importance of glycinergic postsynaptic inhibition in motor neurons and challenge the view that GABA also contributes.

The topographic specificity of muscle reinnervation predicts function.

Functional testing has assumed a progressively dominant role in validating the success of experimental nerve repair. Results obtained in one model, however, cannot predict the results in others because they reflect the coordinated interaction of several muscles across multiple joints. As a result, many combinations of topographically correct and incorrect muscle reinnervation could produce the same result. We have developed a binary model in which elbow flexors and extensors are reinnervated, and elbow flexion and extension are the functions tested. The musculocutaneous and radial nerves of Lister-Hooded rats were subjected to axonotmetic injuries that produced increasing degrees of axonal misdirection at the site of injury ranging from simple crush to transection and rotational offset of proximal and distal stumps. Elbow function was tested with a device that requires coordinated elbow extension to reach sugar pellets and flexion to return them to the mouth. After 12 weeks of regeneration, motoneurons projecting to the distal musculocutaneous nerve were retrogradely labelled with WGA-Ruby and scored regarding their location within musculocutaneous or radial motoneuron pools. The severity of axonal misdirection resulting from the initial surgery was mirrored by progressive degrees of inappropriate reinnervation of the musculocutaneous nerve by radial nerve axons. The specificity of reinnervation predicted elbow function (r = 0.72), whereas the number of motoneurons regenerating did not. This model is thus well suited to study the interaction of regeneration specificity and function across a single joint, and to produce data that can be generalized more broadly than those obtained from more complex models.

Nomogram for determining the lower normal limits for radial sensory nerve action potentials.

INTRODUCTION: In this study we aimed to determine the normal lower limits of sensory nerve action potential (SNAP) amplitude of the radial nerve by taking into account age, height, weight, and body mass index (BMI). METHODS: Three hundred thirty-four volunteers, 168 men and 166 women, were recruited. Sensory nerve conduction studies of the radial nerve were performed, and reproducible waveforms were obtained. RESULTS: The mean radial SNAP amplitude was 44.87 ± 14.58 (range 24-92) µV. SNAP amplitude had a statistically strong negative correlation with age, height, weight, and BMI of the subjects. A multiple linear correlation equation was computed, based on age and BMI of the subjects, to calculate the lower normal limits of radial SNAP and to construct the corresponding nomogram. Conclusion The lower limit of normal SNAP amplitude of the radial nerve, determined in individual subjects using the nomogram, is a useful tool for detection of polyneuropathy.

Soleus Hoffmann reflex amplitudes are specifically modulated by cutaneous inputs from the arms and opposite leg during walking but not standing.

Electrical stimulation of cutaneous nerves innervating heteronymous limbs (the arms or contralateral leg) modifies the excitability of soleus Hoffmann (H-) reflexes. The differences in the sensitivities of the H-reflex pathway to cutaneous afferents from different limbs and their modulation during the performance of motor tasks (i.e., standing and walking) are not fully understood. In the present study, we investigated changes in soleus H-reflex amplitudes induced by electrical stimulation of peripheral nerves. Selected targets for conditioning stimulation included the superficial peroneal nerve, which innervates the foot dorsum in the contralateral ankle (cSP), and the superficial radial nerve, which innervates the dorsum of the hand in the ipsilateral (iSR) or contralateral wrist (cSR). Stimulation and subsequent reflex assessment took place during the standing and early-stance phase of treadmill walking in ten healthy subjects. Cutaneous stimulation produced long-latency inhibition (conditioning-test interval of ~100 ms) of the H-reflex during the early-stance phase of walking, and the inhibition was stronger following cSP stimulation compared with iSR or cSR stimulation. In contrast, although similar conditioning stimulation significantly facilitated the H-reflex during standing, this effect remained constant irrespective of the different conditioning sites. These findings suggest that cutaneous inputs from the arms and contralateral leg had reversible effects on the H-reflex amplitudes, including inhibitions with different sensitivities during the early-stance phase of walking and facilitation during standing. Furthermore, the differential sensitivities of the H-reflex modulations were expressed only during walking when the locations of the afferent inputs were functionally relevant.

Human muscle spindle sensitivity reflects the balance of activity between antagonistic muscles.

Muscle spindles are commonly considered as stretch receptors encoding movement, but the functional consequence of their efferent control has remained unclear. The "α-γ coactivation" hypothesis states that activity in a muscle is positively related to the output of its spindle afferents. However, in addition to the above, possible reciprocal inhibition of spindle controllers entails a negative relationship between contractile activity in one muscle and spindle afferent output from its antagonist. By recording spindle afferent responses from alert humans using microneurography, I show that spindle output does reflect antagonistic muscle balance. Specifically, regardless of identical kinematic profiles across active finger movements, stretch of the loaded antagonist muscle (i.e., extensor) was accompanied by increased afferent firing rates from this muscle compared with the baseline case of no constant external load. In contrast, spindle firing rates from the stretching antagonist were lowest when the agonist muscle powering movement (i.e., flexor) acted against an additional resistive load. Stepwise regressions confirmed that instantaneous velocity, extensor, and flexor muscle activity had a significant effect on spindle afferent responses, with flexor activity having a negative effect. Therefore, the results indicate that, as consequence of their efferent control, spindle sensitivity (gain) to muscle stretch reflects the balance of activity between antagonistic muscles rather than only the activity of the spindle-bearing muscle.

Radial nerve measurements in nonsymptomatic upper extremities of Filipinos: A cross-sectional study.

INTRODUCTION: Despite reports on the association of radial nerve (RN) size and lateral epicondylalgia (LE), Filipino normative values on RN size in healthy elbows are not established. An association with upper extremity anthropometric measurements is likewise not reported. METHODS: Musculoskeletal ultrasound measurements of the RN at the level of the lateral epicondyle (RN-LE), posterior interosseous nerve at the level of the radial head and supinator (PIN-RH and PIN-sup), and superficial RN (SRN) in the elbows of healthy Filipinos were made in Manila from January-September 2011. RESULTS: A total of 198 elbows of 99 healthy participants aged 43 years (range, 33-48 years) [median(IQR)] were investigated. Men have larger PIN-RH, PIN-sup, and SRN compared with women. Arm length was associated with PIN-RH, PIN-sup, and SRN (P < 0.05). Activities and elbow circumference measurements (at 2 levels) were associated with PIN-RH. CONCLUSIONS: RN reference values can now be used for comparison in elbows with LE.

Coordination between catch connective tissue and muscles through nerves in the spine joint of the sea urchin Diadema setosum.

Echinoderms have catch connective tissues that change their stiffness as a result of nervous control. The coordination between catch connective tissue and muscles was studied in the spine joint of the sea urchin Diadema setosum. Spine joints are equipped with two kinds of effector: spine muscles and a kind of catch connective tissue, which is called the catch apparatus (CA). The former is responsible for spine movements and the latter for maintenance of spine posture. Diadema show a shadow reaction in which they wave spines when a shadow falls on them, which is a reflex involving the radial nerves. Dynamic mechanical tests were performed on the CA in a joint at which the muscles were severed so as not to interfere with the mechanical measurements. The joint was on a piece of the test that contained other spines and a radial nerve. Darkening of the preparation invoked softening of the CA and spine waving (the shadow reaction). Electrical stimulation of the radial nerve invoked a similar response. These responses were abolished after the nerve pathways from the radial nerve to spines had been cut. A touch applied to the CA stiffened it and the adjacent spines inclined toward the touched CA. A touch to the base of the adjacent spine softened the CA and the spines around the touched spine inclined towards it. The softening of the CA can be interpreted as a response that reduces the resistance of the ligaments to spine movements. Our results clearly show coordination between catch connective tissue and muscles through nerves.