Effects of neonatal capsaicin deafferentation on neuromuscular adjustments, performance, and afferent activities from adult tibialis anterior muscle during exercise

To investigate the role played by muscle afferents in the sensorimotor loops, we measured the effects of capsaicin injection in newborns on the mechano- and metabosensitive discharges and the running performance at adulthood. Female Sprague Dawley rats received a subcutaneous injection of either 50 mg/kg capsaicin or solvent (10% ethanol, 10% Tween 80 in 0.9% saline) during their second day of life. These two groups were compared with a control, untreated group. Four months later, treadmill running performance and muscle afferent (mechanosensitive and metabosensitive) activities from the tibialis anterior muscle were measured. The capsaicin-treated group demonstrated a reduced maximal exercise capacity (time to exhaustion) and a reduced response of muscle metabosensitive fibers (group III and IV nerve endings) to the examined stimuli (arterial KCl and lactic acid injections, electrically induced fatigue) compared with the sham-injected solvent and control groups. Group IV afferent responses were absent in the compound nerve action potentials evoked by peripheral nerve stimulation. The response to mechanosensitive fibers to tendon vibration was also affected in the capsaicin group compared with the control and sham-injected groups, which presented a bimodal response corresponding to the activation of muscle spindles and Golgi tendon organs. Finally, measurements of the force developed by the tibialis anterior muscle from the beginning to the end of a 3-min muscle stimulation revealed a more significant fall in the capsaicin group compared with the others. The present experiments reveal that the pharmacological alteration of muscular metabosensitive afferent resulted in drastic changes in the neuromuscular sensory encoding and in the central neural network that could accelerate failure of the task during fatigue.     

Chronic electrostimulation after nerve repair by self-anastomosis: effects on the size, the mechanical, histochemical and biochemical muscle properties

This study tests the effects of chronic electrostimulation on denervated/reinnervated skeletal muscle in producing an optimal restoration of size and mechanical and histochemical properties. We compared tibialis anterior muscles in four groups of rats: in unoperated control (C) and 10 weeks following nerve lesion with suture (LS) in the absence of electrostimulation and in the presence of muscle stimulation with either a monophasic rectangular current (LSE_m) or a biphasic modulated current (LSE_b). The main results were (1) muscle atrophy was reduced in LSE_m (−26%) while it was absent in LSE_b groups (−8%); (2) the peak twitch amplitude decreased in LS and LSE_m but not in LSE_b groups, whereas the contraction time was shorter; (3) muscle reinnervation was associated with the emergence of type IIC fibers and proportions of types I, IIA and IIB fibers recovered in the superficial portion of LSE_b muscles; (4) the ratio of oxidative to glycolytic activities decreased in the three groups with nerve injury and repair; however, this decrease was more accentuated in LSE_m groups. We conclude that muscle electrostimulation following denervation and reinnervation tends to restore size and functional and histochemical properties during reinnervation better than is seen in unstimulated muscle.     

Sural nerve stimulation and motor control of tibialis anterior muscle in spastic paresis

In patients with spastic paraparesis, increased extensor tonus can be decreased by stimulation of flexor reflex afferents. This should improve dorsiflexion of the foot and reduce the sense of effort. We therefore examined ability to maintain stable firing of a single motor unit (SMU) in tibialis anterior muscle and force of dorsiflexion in 17 normal subjects and 9 with spastic paresis, during several minutes of tonic nonpainful stimulation (20 Hz, 0.1 msec) of the sural nerve at the ankle (SNS). Subjects were asked to maintain stable SMU firing first with, then without auditory feedback of the motor unit potential. SNS was then applied for several minutes. In normal subjects, the force of dorsiflexion increased 33 +/- 26% with SNS and 2.5% +/- 5% without SNS (p less than 0.0005). Most subjects noted increased resistance to dorsiflexion during SNS that resulted in greater innervation of tibialis anterior muscle. In six abnormal subjects, the force of dorsiflexion increased 30 +/- 30% with SNS, but no increase was recorded without SNS. In normal subjects and those with spastic paresis of the legs, SNS increased innervation of tibialis anterior muscle and awareness of greater effort required to maintain constant innervation. The altered proprioception may depend on facilitation of motor neurons.     

Changes in a rat facial muscle after facial nerve injury and repair

This study describes changes in a rat facial muscle innervated by the mandibular and buccal facial nerve branches 4 months after nerve injury and repair. The following groups were studied: (A) normal controls; (B) spontaneous reinnervation by collateral or terminal sprouting; (C) reinnervation after surgical repair of the mandibular branch; and (D) chronic denervation. The normal muscle contained 1200 exclusively fast fibers, mainly myosin heavy chain (MyHC) IIB fibers. In group B, fiber number and fiber type proportions were normal. In group C, fiber number was subnormal. Diameters and proportions of MyHC IIA and hybrid fibers were above normal. The proportion of MyHC IIB fibers was subnormal. Immediate and delayed repair gave similar results with respect to the parameters examined. Group D rats underwent severe atrophic and degenerative changes. Hybrid fibers prevailed. These data suggest that spontaneous regeneration of the rat facial nerve is superior to regeneration after surgical repair and that immediacy does not give better results than moderate delay with respect to surgical repair. Long delays are shown to be detrimental.     

Regeneration of tibialis anterior muscle in rat after complete excision and reimplantation of muscle fragments

Summary 1. 35 days after excision of the anterior tibial muscle in rat and reimplantation of the piecemealed muscle a practically mature regenerate is formed.2. The regenerated muscle is, compared with normal muscle, inferior. The volume is much smaller and it is histologically characterised by a partly disorderly distribution of fibres and a clear increase in connective tissue. In spite of histological and electromyographical evidence of reinnervation the regenerated muscle does not function, probably because of extensive adhesions with the surrounding tissues.3. When less material is implanted the volume of the regenerate is smaller, the speed of regeneration and maturation is increased but the quality of the regenerate remains the sameReport on the second conference on myopathy March 18th 1971 in Janské Laznè, SSR.     

Properties of the tibialis anterior muscle after treatment with laser therapy and natural latex protein following sciatic nerve crush

Introduction: In this study we evaluated the characteristics of the tibialis anterior muscle after sciatic nerve crush and treatment with low‐level laser therapy (LLLT) or the protein from natural latex (P1). Methods: We studied the following 6 groups of male Wistar rats: control (CG); exposed nerve (EG); injured nerve (IG); injured nerve with LLLT (LG); injured nerve with P1 (PG); and injured nerve with P1 and LLLT (LPG). Results: After 4 weeks, muscle morphology showed improvement in the treated groups; after 8 weeks, the treated groups resembled controls, especially the PG. Morphometry revealed muscle fiber atrophy after nerve injury, with time‐dependent recovery. Histochemical analysis revealed increased intermediate fiber area. The PG was more similar to controls with NADH staining, whereas the LPG more closely resembled controls with SDH staining. Conclusion: Treatment using only P1 proved most efficient, revealing a negative interaction between P1 and LLLT. Muscle Nerve 52 : 869–875, 2015     

Sarcoplasmic reticulum ATPase in tibialis anterior muscle from rats with experimental myotonia

The sarcoplasmic reticulum ATPase was studied (after 3 h to 14 days) in rats treated with 2,4-dichlorophenoxyacetate to induce myotonia. It was found that ATPase decreased in the treated rats after the establishment of myotonia.     

Optimal E2 (reference) electrode placement in fibular motor nerve conduction studies recording from the tibialis anterior muscle

Introduction: In this study we aimed to determine the contribution of the E2 (reference electrode) to the compound muscle action potential (CMAP) amplitude during fibular motor recording to the tibialis anterior (TA) when E2 is placed over routine referential vs. alternative sites. Methods: The CMAP was obtained from 10 healthy subjects, using the active electrode (E1) over sites routinely used as E2 for the TA, whereas the E2 was over the contralateral knee. The same procedure was performed with the E1 over alternative E2 sites. Results: Significant electrical signal was captured over routine E2 placement sites. Among the tested alternative E2 sites, the ipsilateral patella (especially its medial aspect) was the most electrically silent. Discussion: Using alternative E2 sites with near isoelectric recordings can optimize near-field potential measurement in the fibular motor recording to the TA and represents a more accurate way of measuring nerve and muscle function. Muscle Nerve 59 :249–253, 2019     

Mapping the motor point in the human tibialis anterior muscle

ObjectivePercutaneous electrical stimulation of the motor point permits selective activation of a muscle. However, the definition and number of motor points reported for a given muscle varies. Our goal was to address these problems.MethodsThe area, location and number of motor points in human tibialis anterior were examined, using isometric dorsiflexion torque responses to electrical stimuli. Three methods were used: lowest electrical threshold, maximum muscle response, and approximate motor point.ResultsA single motor point was identified in 39/40 subjects regardless of method. The area of the site of lowest electrical threshold was smaller (median, 35 mm²) than those using the maximum muscle response (144 mm²) and approximate motor point (132 mm²). There was substantial, but not significant, between-subject variation in motor point location. Fifty three percent of motor points would have been missed if located only by reference to anatomical landmarks.ConclusionsThese results suggested that the motor point’s location cannot be determined a priori and that the identification method will affect both area and location.SignificanceIf it is important to maximally activate a single muscle in isolation, the motor point is best represented by the site producing a maximal but isolated muscle response at the lowest stimulation intensity.     

Comparative effects of ischemia and acute hypoxemia on muscle afferents from tibialis anterior in cats

Comparative effects of ischemia and acute hypoxemia (PaO₂ = 24 mm Hg) were studied in anesthetized cats on afferents from the tibialis anterior limb muscle. Metaboreceptors (groups III and IV fibers) and mechanoreceptors were identified by their activation by an intraarterial injection of lactic acid (LA) or high-frequency vibrations (HFV) applied to the extremity of the muscle tendon, respectively. Ischemia and hypoxemia exerted opposite influences on the two categories of muscle afferents: they depressed the response of mechanoreceptors to HFV, but markedly enhanced the spontaneous tonic activity of metaboreceptors. The effects of hypoxamia were delayed but slightly greater and lasted longer during the recovery period than those exerted by ischemia. The inhibitory action on mechanoreceptors exerted by a reduced oxyden supply to muscle is interpreted as a result from local acidosis. Indeed, under normoxic conditions, a LA bolus injection during the HFV test also reduced the firing rate of these receptors. © 1993 John Wiley & Sons, Inc.     

Reflex responses from the sural nerve to tibialis anterior muscle in hemiplegic patients: the relation between the responses and Babinski sign]

Stimulation of the sural nerve of healthy subjects induced short latency inhibition in the ipsilateral tibialis anterior muscle and facilitation in peroneal muscle. We examined lower limb muscle responses after stimulation of the sural nerve in 19 patients with hemiplegia caused by cerebro-vascular disease and compared them with the control responses. The sural nerve was stimulated electrically (3 or 5 square wave pulses of 0.5 ms repeated at 250 Hz) during weak tonic contraction. Stimulation was triggered to average the rectified surface electromyography (EMG) of the test muscle. Usually 100 - 200 sweeps were averaged. After stimulation, the tibialis anterior muscle on the affected side of the hemiplegic patients showed the patterns of inhibition, facilitation, and no response, whereas all responses on the unaffected side, except those of one patient, were inhibition. The peroneal muscle on both sides showed only facilitation as in the controls. Abnormal responses of the tibialis anterior muscle on the affected side were present in many patients who had the Babinski sign. Abnormal responses in the tibialis anterior muscle of the affected side may have been due to contributions by disinhibition of the flexor reflex, late-recruited motor units or both.     

Modifications of afferent activities from Tibialis anterior muscle in rat by tendon vibrations, increase of interstitial potassium or lactate concentration and electrically-induced fatigue

Although previous experiments with a partially similar objective have been described in dogs, cats and rabbits, the purpose of this study was to identify and characterize mechanosensitive and chemosensitive muscle afferents in the anaesthetized rat since it is a widely used laboratory animal. The peroneal nerve innervating the tibialis anterior muscle was studied. Measurement of conduction velocities from compound action nerve potentials evoked by peripheral nerve stimulation allowed identification of group I-II (10.79+/-1.02 m/s), group III (2.96+/-0.58 m/s) and group IV (0.46+/-0.07 m/s) afferent fibers. Computation of the different compound potential areas showed that afferents I and II arising from spindles and tendon organs represented 9.65+/-2.2%, whereas afferents III and IV arising from free nerve endings in muscle represented 90.35+/-2.2% (III, 46.66+/-2.71% and IV, 43.69+/-2.52%). Action potentials were recorded from teased nerve filaments. Mechanical tendon vibrations (10 to 90 Hz) were used to activate mechanoreceptors. Peak increase in afferent discharge (fimpulses) was measured at 50 Hz (n = 12/19 units) or 70 Hz (n = 7/19 units). Intra-arterial bolus injections of different concentrations of potassium chloride (KCl: 1 to 20 mM) or lactic acid (LA: 0.5 to 3 mM) elicited marked activation of III and IV afferents (n = 124). Enhancement of fimpulses was not proportional to the increase in [KCl] or [LA]. Activation of afferents plateaued when [KCl] was equal or greater than 5 mM while fimpulses peaked, then decreased, when [LA] was 1 mM. Muscle fatigue induced by direct electrical muscle stimulation (EIF) markedly activated group III-IV (n = 17/18) afferents (176.9+/-29.7% of control) which persisted for the 3 minutes of recovery from fatigue. Maximal fimpulses increases in response to LA (+67%) and KCl (+46.9%) injections and to EIF (+76.9%) were similar. This procedure for characterizing the functional properties of sensory nerve endings in a skeletal muscle may be used to assess further changes in sensory muscle paths in experimental rodent pathophysiological systems.     

Contralateral trigeminal nerve lesion reduces polyneuronal muscle innervation after facial nerve repair in rats

Functional recovery after facial nerve surgery is poor. Axotomized motoneurons (hyperexcitable upon intracellular current injections, but unable to discharge upon afferent stimulation) outgrow supernumerary branches which are misrouted towards improper muscles. We hypothesized that alterations in the trigeminal input to axotomized electrophysiologically silent facial motoneurons might improve specificity of reinnervation. To test this we compared, in the rat, behavioural, electrophysiological, and morphological parameters after transection and suture of the buccal facial nerve (buccal-buccal anastomosis, BBA) with those after BBA plus excision of the ipsi- or contralateral infraorbital nerve (ION). After BBA, the mystacial vibrissae dropped and remained motionless until 18-21 days post operation (days PO). After BBA plus ipsilateral ION excision, there was no recovery of vibrissae whisking at all. Following BBA plus contralateral ION excision, full restoration of whisking occurred at 7-10 days PO. Electromyography of whiskerpad muscles showed normal waveform and amplitude was also most rapidly restored after BBA plus contralateral ION excision. Neuron counts after retrograde tracing showed that the intact buccal nerve contained axons of the superior (91%) and inferior (9%) buccolabial nerves. After BBA, the superior nerve comprised 56%, the inferior 21%, and 23% of the motoneurons projected within both nerves. After BBA plus ipsilateral ION excision, misdirection worsened and values changed to 48, 39 and 13%, respectively. After BBA plus contralateral ION excision, portions improved to 69, 23 and 8%. We conclude that, by reducing the redundant axon branching, lesion of contralateral ION provides the best conditions for recovery of vibrissae rhythmical whisking after reconstructive surgery on the facial nerve.     

Modulation of H reflexes in human tibialis anterior muscle with passive movement

Significant movement-induced gain changes in H reflexes have been observed in soleus muscle following passive movement of the lower limb. Hypotheses from these concepts were tested on magnitudes of H reflexes in tonically contracted tibialis anterior. From eleven subjects at rates of 20 and 60 r.p.m. passive leg movement, statistically significant attenuation from controls and phasic modulation occurred. The results make more general the conclusions from soleus H reflexes. However, the functional effect should be much smaller, as tibialis anterior H reflexes are smaller compared to those in soleus.     

Phase-dependent modulation of cutaneous reflexes in tibialis anterior muscle during passive stepping

The purpose of this study was to determine whether the cutaneous reflex elicited in the tibialis anterior (TA) muscle would be modulated in a phase-dependent manner while human subjects were passively stepping on a treadmill (treadmill stepping) or in the air (air stepping). The passive stepping was produced by a robotic gait trainer, Lokomat. The cutaneous reflexes following electric stimulation to the distal tibial nerve were recorded at ten different phases of a step cycle under the condition of tonic dorsiflexion [10% of maximum electromyography activity (EMGmax)]. Cutaneous reflex EMG responses with peak latencies of 70-120 ms [middle latency responses (MLR)] were then analysed. The results showed that there were no visible differences in the background EMG activities at the ten phases or two passive stepping conditions. During treadmill stepping, however, the magnitude of the facilitatory reflex responses between the late stance and the early swing phase was strongly enhanced, whereas no clear modulation of the MLR during air stepping was observed. These results suggest that the load-related afferent information plays a key role in the modulation of the cutaneous reflex during human walking.     

Effects of skin cooling and warming on stretch responses of the muscle spindle primary and secondary afferent fibers from the cat's tibialis anterior

Fusimotor activation induced by thermal stimuli to the skin was investigated by recording the stretch responses of primary as well as secondary spindle afferent fibers from the tibialis anterior of the barbiturate-anesthetized, spinal cats. A standard rampand-hold stretch was repeatedly given during warming or cooling (20 to 40°C) the skin of the ipsilateral foot pads. In each response of the spindle afferent fiber to stretch, the peak (P) and static firing rates (S) were measured and the dynamic index was calculated to assess the type of fusimotor fiber influence as dynamic or static. Of 47 primary spindle afferent fibers, 22 (46%) were affected by changes in skin temperature. Cooling of the skin below a certain temperature produced a marked increase in the dynamic sensitivity of their response to stretch, and this also occurred on warming above it. Such a “critical temperature” at which a directional relationship between skin temperature and muscle spindle activity was completely altered was determined (mean ± SD: 35.10 ± 1.66°C, N = 7). However, a marked increase in static firing accompanied by a significant decrease in the dynamic index was observed at the dynamic phase of heating the skin beyond the critical temperature. None of the seven secondary afferent fibers studied showed a detectable temperature response. We conclude that the activation of primary spindle afferent fibers by thermal stimulation of the skin is to be attributed predominantly to activation of dynamic fusimotor neurons and is significant for the initiation of cold shivering.