Juvenile and adult rat neuromuscular junctions: density, distribution, and morphology

Knockdown of calpain1 in lumbar motoneurons reduces spasticity after spinal cord injury in adult rats

Spasticity, affecting ∼75% of patients with spinal cord injury (SCI), leads to hyperreflexia, muscle spasms, and cocontractions of antagonist muscles, greatly affecting their quality of life. Spasticity primarily stems from the hyperexcitability of motoneurons below the lesion, driven by an upregulation of the persistent sodium current and a downregulation of chloride extrusion. This imbalance results from the post-SCI activation of calpain1, which cleaves Nav1.6 channels and KCC2 cotransporters. Our study was focused on mitigating spasticity by specifically targeting calpain1 in spinal motoneurons. We successfully transduced lumbar motoneurons in adult rats with SCI using intrathecal administration of adeno-associated virus vector serotype 6, carrying a shRNA sequence against calpain1. This approach significantly reduced calpain1 expression in transduced motoneurons, leading to a noticeable decrease in spasticity symptoms, including hyperreflexia, muscle spasms, and cocontractions in hindlimb muscles, which are particularly evident in the second month post-SCI. In addition, this decrease, which prevented the escalation of spasticity to a severe grade, paralleled the restoration of KCC2 levels in transduced motoneurons, suggesting a reduced proteolytic activity of calpain1. These findings demonstrate that inhibiting calpain1 in motoneurons is a promising strategy for alleviating spasticity in SCI patients.

Postsynaptic cleft density changes with combined exercise protocols in an experimental model of muscular hypertrophy

The vertical ladder-based protocols contribute to the NMJ junction's adaptations, and when combined with and without load, can be potentiated. The present study aimed to investigate postsynaptic regions of the biceps brachii muscle in adult male Wistar rats submitted to different vertical ladder-based protocols (Sedentary - S; Climbing - C; Climbing with Load - LC and Combined Climbing - CC). The protocols (C, LC, CC) were performed in 24 sessions, 3 x/week, for 8 weeks. The myofibrillar ATPase analysis showed an increase in cross-sectional area (CSA) of the muscle fibers Type I in all trained Groups; Type II in C and LC and reduction in CC; Type IIx higher in all trained Groups. In the postsynaptic cleft, the stained area presents smaller in Groups C, LC, and CC; the total area showed smaller than LC and higher in C and CC. The stained and total perimeter, and dispersion showed a reduction in C, LC, and CC, higher maximum diameter in Groups C and CC, and decreased in LC. Regarding the postsynaptic cleft distribution, the stained area presented a decrease in all trained Groups. The integrated density presented higher principally in CC. The NMJ count showed an increase in all trained Groups. We concluded that the vertical ladder-based protocols combined contributed to the postsynaptic region adaptations.

Morphological Changes in the Motor Endplate and in the Belly Muscle Induced by Previous Static Stretching to the Climbing Protocol

Static stretching provides benefits to the range of motion, modulates intramuscular connective tissue, and is incorporated into warm-up exercises. In this study, we present the effects in the motor endplate and belly muscle resulting from previous static stretching to climbing training. Twenty-four adult male Wistar rats were divided into four groups (n = 6 each): Sedentary (Sed), Climbing (Clb), Static stretching (Ss), and Static stretching prior to climbing (Ssc). The animals (Clb, Ss, and Ssc groups) were subjected to a training protocol 3×/week for 8 weeks, and the Ssc group was subjected to the Ss and Clb protocols in the same session. Samples from the animals were processed for immunostaining, histochemistry, and light microscopy. The Clb group presented a higher motor endplate; the Ss group presented no changes in the motor endplate; and the Ssc group demonstrated a higher compactness. We concluded that static stretching prior to the climbing protocol maintained the density of the motor endplate and increased the compactness of the neuromuscular junction structure. Also, there was a reduction in the myofibers’ diameter (Type I and IIa), an increase in myofibrillar densities (Type I and IIx, and total), and the reorganization of the myonuclei and the interstitium.

Influence of different energy patterns on efficacy of radial shock wave therapy

BACKGROUND

One of the mechanisms of the efficacy of extracorporeal shock wave therapy (ESWT) for impaired muscle coordination of limbs is the destruction of Acetylcholine receptors (AChRs) at neuromuscular junction. The highly increased density of AChRs can change the acoustic impedance, and this change of the acoustic impedance can be the reason that radial shock wave (rESW) destroy AChRs selectively. However, the relationship between applied energy of rESWs and the therapeutic efficacy remains unclear, although some studies compared the clinical efficacy of rESWT between high- and low-energy applications. This study aimed to compare the CMAP change among different energy and pulses of rESW application.

METHODS

Male Sprauger-Dawley rats were used. A device that generates radial shock waves pneumatically, was used to apply the following six patterns of radial extracorporeal shockwaves in different energy flux densities and pulses to the right calf of each rat: 1, 8000 pulses at 0.045 mJ/mm²; 2, 4000 pulses at 0.09 mJ/mm²; 3, 2000 pulses at 0.18 mJ/mm²; 4, 4000 pulses at 0.045 mJ/mm²; 5, 2000 pulses at 0.09 mJ/mm²; 6, 1000 pulses at 0.18 mJ/mm². Left calf muscles were considered controls.

RESULTS

There was a significant reduction in CMAP amplitude between control and rESW-exposed muscles in the group applied 4000 pulses with EFD at 0.09 mJ/mm² and the group applied 2000 pulses with EFD at 0.18 mJ/mm². However, the group applied 8000 pulses with EFD at 0.045 mJ/mm² and all groups which was exposed to total 180 mJ rESW application did not show a significantly decreased CMAP amplitude compared with the untreated side.

CONCLUSIONS

Total energy and energy flux density correlate with a decrease in CMAP amplitude by rESW application. These findings could be availed by clinicians in actual clinical setting for the proper application of rESW.

Sam68 splicing regulation contributes to motor unit establishment in the postnatal skeletal muscle

Sam68 ensures the establishment of neuromuscular junctions (NMJs) and motor unit integrity by orchestrating a neuronal splicing program.

RNA-binding proteins orchestrate the composite life of RNA molecules and impact most physiological processes, thus underlying complex phenotypes. The RNA-binding protein Sam68 regulates differentiation processes by modulating splicing, polyadenylation, and stability of select transcripts. Herein, we found that Sam68^−/− mice display altered regulation of alternative splicing in the spinal cord of key target genes involved in synaptic functions. Analysis of the motor units revealed that Sam68 ablation impairs the establishment of neuromuscular junctions and causes progressive loss of motor neurons in the spinal cord. Importantly, alterations of neuromuscular junction morphology and properties in Sam68^−/− mice correlate with defects in muscle and motor unit integrity. Sam68^−/− muscles display defects in postnatal development, with manifest signs of atrophy. Furthermore, fast-twitch muscles in Sam68^−/− mice show structural features typical of slow-twitch muscles, suggesting alterations in the metabolic and functional properties of myofibers. Collectively, our data identify a key role for Sam68 in muscle development and suggest that proper establishment of motor units requires timely expression of synaptic splice variants.

Extracorporeal shock wave treatment can selectively destroy end plates in neuromuscular junctions

INTRODUCTION

This study assesses the effect of radial extracorporeal shock wave (rESW) exposure on neuromuscular transmission and neuromuscular junction (NMJ) morphology.

METHODS

We applied 2,000 rESWs at 0.18 mJ/mm² and a frequency of 15 Hz to the right calf of male rats, measured the compound muscle action potential (CMAP), and examined NMJ morphology using electron microscopy. Left calf muscles were used as controls.

RESULTS

rESW exposure significantly reduced CMAP amplitude without delayed latency in exposed muscles compared with controls. All rESW-exposed muscles exhibited NMJs with irregular end plates. Mean interjunctional fold interval was significantly increased compared with controls. However, axon terminals and muscle fibers surrounding NMJs with irregular end plates were unchanged.

DISCUSSION

This localized destruction of end plates may be caused by differences in acoustic impedance induced by the density of acetylcholine receptors. These results provide a possible mechanism for the effectiveness of rESW treatment for spasticity and dystonia. Muscle Nerve 57: 466-472, 2018.

Botulinum Toxin Treatment for Limb Spasticity in Childhood Cerebral Palsy

CP is the most common cause of chronic disability in childhood occurring in 2–2.5/1000 births. It is a severe disorder and a significant number of patients present cognitive delay and difficulty in walking. The use of botulinum toxin (BTX) has become a popular treatment for CP especially for spastic and dystonic muscles while avoiding deformity and pain. Moreover, the combination of physiotherapy, casting, orthotics and injection of BTX may delay or decrease the need for surgical intervention while reserving single-event, multi-level surgery for fixed musculotendinous contractures and bony deformities in older children. This report highlights the utility of BTX in the treatment of cerebral palsy in children. We include techniques for administration, side effects, and possible resistance as well as specific use in the upper and lower limbs muscles.

Effects of exercise on neuromuscular junction components across age: systematic review of animal experimental studies

BACKGROUND

During almost one-third of our life, maturation of the nervous system promotes strength and muscle mass increase. However, as age advances, the nervous system begins to suffer a slow and continue reduction of its functions. Neuromuscular junction (NMJ) is one of the structures of which change due to aging process. Physical training leads to significant adjustments in NMJs of young and aged animals. Nevertheless, studies that aimed to investigate this effect have, in many cases, methodological variables that may have some influence on the result. Thus, this study aimed to carry out a systematic review about the effects of exercise training on the NMJ compartments of young, adult and aged animals.

RESULTS

We searched PubMed, Google Scholar, Science Direct, Scielo and Lilacs databases for animal experimental studies that studied exercise effects on the NMJs components across age. After inclusion and exclusion criteria, we included nine articles in systematic review and two for meta-analysis (young/adult NMJ).

CONCLUSIONS

We identified that exercise training cause NMJ hypertrophy on young animals and NMJ compression on aged ones. However, many methodological issues such as age, skeletal muscle and fibers type, and type of exercise and training protocol might influence the results. Graphical abstract: Flow gram is actually to be show at results section as Fig 1.

Determination of injection site in flexor digitorum longus for effective and safe botulinum toxin injection

OBJECTIVE

To determine the optimal injection site in the flexor digitorum longus (FDL) muscle for effective botulinum toxin injection.

METHODS

Fourteen specimens from eight adult Korean cadavers were used in this study. The most proximal medial point of the tibia plateau was defined as the proximal reference point; the most distal tip of the medial malleolus was defined as the distal reference point. The distance of a line connecting the proximal and distal reference points was defined as the reference length. The X-coordinate was the distance from the proximal reference point to the intramuscular motor endpoint (IME), or motor entry point (MEP) on the reference line, and the Y-coordinate was the distance from the nearest point from MEP on the medial border of the tibia to the MEP. IME and MEP distances from the proximal reference point were evaluated using the raw value and the X-coordinate to reference length ratio was determined as a percentage.

RESULTS

The majority of IMEs were located within 30%-60% of the reference length from the proximal reference point. The majority of the MEPs were located within 40%-60% of the reference length from the proximal reference point.

CONCLUSION

We recommend the anatomical site for a botulinum toxin injection in the FDL to be within a region 30%-60% of the reference length from the proximal reference point.

The rat Digit Abduction Score (DAS) assay: a physiological model for assessing botulinum neurotoxin-induced skeletal muscle paralysis

Botulinum neurotoxins (BoNT) are approved for a number of therapeutic indications, including blepharospasm, cervical dystonia and hyperhidrosis, and have also shown efficacy in a variety of pain disorders. The potency of any given BoNT preparation can be routinely assessed by using the Digit Abduction Score (DAS) assay, which measures the local muscle weakening efficacy of BoNT following injection into mouse hindlimb muscle. While most studies have employed mice to assess BoNT efficacy in the DAS, few have utilized rats. In this study, we applied the DAS assay to a rat model and compared the potency of IM-BOTOX(®) (onabotulinumtoxinA) injections between two separate hind limb muscles, gastrocnemius and tibialis anterior (TA). The results demonstrated that the DAS assay can be performed on rats with similar criteria and parameters as for mice. Moreover in the rat, BoNT can be injected into either the gastrocnemius or TA muscle to elicit similar DAS scoring responses. Interestingly, onabotulinumtoxinA potency in the rat DAS was ∼3-fold higher following TA injections than gastrocnemius injections. Additionally, our data showed that the durational kinetics of onabotulinumtoxinA in the rat DAS are approximately twice as long as in the mouse DAS. These results position the rat DAS as a more flexible model for examining the mechanisms of BoNT diffusion and muscle paralysis, while mouse DAS can be used for physiological screening of BoNT because of the potential for higher throughput. Overall, these data confirm the utility of the DAS assay for characterizing the physiological potency of BoNT and related compounds.

Off label use of botulinum toxin in children under two years of age: a systematic review

The treatment of children with cerebral palsy with Botulinum Toxin is considered safe and effective, but is only approved for children older than two years of age. The effect of BoNT-A injection on juvenile skeletal muscle especially on neuromuscular junction density, distribution and morphology is poorly delineated and concerns of irreversible damage to the motor endplates especially in young children exist. In contrast, earlier treatment could be appropriate to improve the attainment of motor milestones and general motor development. This review systematically analyzes the evidence regarding this hypothesis. A database search, including PubMed and Medline databases, was performed and all randomized controlled trials (RCTs) comparing the efficacy of Botulinum Toxin in children younger than two years were identified. Two authors independently extracted the data and the methods of all identified trials were assessed. Three RCTs met the inclusion criteria. The results of the analysis revealed an improvement in spasticity of the upper and lower extremities as well as in the range of motion in the joints of the lower limbs. However, evidence of an improvement of general motor development could not be found, as the assessment of this area was not completely specified for this patient group. Based on available evidence it can not be concluded that Botulinum Toxin treatment in children younger than two years improves the achievement of motor milestones. However, there is evidence for the reduction of spasticity, avoiding contractures and delaying surgery. Due to some limitations, the results of this review should be cautiously interpreted. More studies, long-term follow up independent high-quality RCTs with effectiveness analyses are needed.

Off label use of botulinum toxin in children under two years of age: a systematic review

The treatment of children with cerebral palsy with Botulinum Toxin is considered safe and effective, but is only approved for children older than two years of age. The effect of BoNT-A injection on juvenile skeletal muscle especially on neuromuscular junction density, distribution and morphology is poorly delineated and concerns of irreversible damage to the motor endplates especially in young children exist. In contrast, earlier treatment could be appropriate to improve the attainment of motor milestones and general motor development. This review systematically analyzes the evidence regarding this hypothesis. A database search, including PubMed and Medline databases, was performed and all randomized controlled trials (RCTs) comparing the efficacy of Botulinum Toxin in children younger than two years were identified. Two authors independently extracted the data and the methods of all identified trials were assessed. Three RCTs met the inclusion criteria. The results of the analysis revealed an improvement in spasticity of the upper and lower extremities as well as in the range of motion in the joints of the lower limbs. However, evidence of an improvement of general motor development could not be found, as the assessment of this area was not completely specified for this patient group. Based on available evidence it can not be concluded that Botulinum Toxin treatment in children younger than two years improves the achievement of motor milestones. However, there is evidence for the reduction of spasticity, avoiding contractures and delaying surgery. Due to some limitations, the results of this review should be cautiously interpreted. More studies, long-term follow up independent high-quality RCTs with effectiveness analyses are needed.

Degeneration and recovery of the neuromuscular junction after application of extracorporeal shock wave therapy

It is known that free nerve endings are degenerated after application of shock waves. We therefore hypothesized that the application of shock waves to muscle induces dysfunction of neuromuscular transmission at neuromuscular junctions. We investigated changes in neuromuscular transmission in response to shock wave application. Sprague-Dawley rats were used in this study. Two thousand shock waves at an energy flux density of 0.18 mJ/mm(2) were applied to their right calf muscles. Neuromuscular junctions of gastrocnemius muscles were evaluated using rhodamine-α-bungarotoxin on the day of treatment (n  =  5). Amplitude and latency of compound muscle action potentials were measured on the day of treatment and 1, 2, 4, 6, and 8 weeks after treatment (n  =  10, each group). Degenerated acetylcholine receptors existed in all treated muscles. Although the action potential amplitude on the treated side was significantly less than on the control side from the day of treatment (25.1 ± 7.8 vs. 34.5 ± 9.1, p  =  0.012) to 6 weeks (27.9 ± 7.2 vs. 34.5 ± 7.2, p  =  0.037), there was no significant difference at 8 weeks. There was no significant difference in transmission latency between the groups. The application of shock waves to muscle induced a transient dysfunction of nerve conduction at neuromuscular junctions.

Association of transforming growth factor β-1 (TGFB1) regulatory region polymorphisms with myasthenia gravis-related ophthalmoparesis

We investigated the association of an ophthalmoplegic complication developing in African myasthenia gravis (MG) subjects with polymorphisms in the regulatory region of TGFB1. We found significant associations with several putative functional single nucleotide polymorphisms (SNPs) (including two novel SNPs) that potentially alter transcription factor binding. Our data support a hypothesis that altered TGFB1 regulation may predispose individuals who harbour these SNPs to developing ophthalmoplegia as a result of increased TGF-β1 driven myofibrosis as a consequence to complement-mediated damage.

Dose- and volume dependent-response to intramuscular injection of botulinum neurotoxin-A optimizes muscle force decrement in mice

Botulinum neurotoxin-A (BoNTA) is a potent neurotoxin used to alter muscle tone to manage spasticity and to provide tendon bioprotection; however, the appropriate dose and injection volume to administer is not defined. Male mice (n = 120) received BoNTA injections into one gastrocnemius with either a constant volume (10 µl) with a variable dose (1, 3, 6 U/kg) or a constant dose (3 U/kg) in a variable volume (2.5, 5, 10, 20, 30 µl). Electromyographic (EMG) examination, muscle force generation (MFG), and wet muscle mass were measured in the ipsilateral and contralateral limbs at 1, 2, 4, or 12 weeks post-injection. MFG and EMG responses decreased to approximately 40% of contralateral after a 1 U/kg injection and 0% of contralateral by 3 and 6 U/kg injection at 1 week after injection. Neuromuscular blockade was greatest with a 10 µl injection volume. MFG, EMG examination, and wet muscle mass reached contralateral values 12 weeks after injection for all injection doses and volumes tested. Effective injection doses and volumes were identified for producing full and partial neuromuscular blockade in the mouse gastrocnemius. These findings have important clinical implications in the intramuscular administration of BoNTA to manage muscle tone.

Localization of the motor endplate zone in human skeletal muscles of the lower limb: anatomical guidelines for injection with botulinum toxin

AIM

Botulinum toxin gives a local tone reduction by blocking neurotransmission at the motor endplate (MEP). The importance of using MEP-targeted injections is demonstrated in animal models and in a clinical human study. The goal of this review is to present the available data on the localization of the MEP zone of frequently injected muscles of the lower limb and to compare this with current practice.

METHOD

Current knowledge on the localization of the MEP zone is based on some older histological studies, and for some of the more frequently injected muscles also on more recent anatomical dissection.

RESULTS

We find that for some muscles the MEP zone can be more precisely demarcated, and for many other muscles that its location is somewhat different than the currently injected areas in clinical practice. Optimal injection sites are presented for gastrocnemius, soleus, tibialis posterior, semitendinosus, semimembranosus, gracilis, biceps femoris, rectus femoris, adductor longus, brevis and magnus, and psoas muscles.

INTERPRETATION

We propose optimal injection sites in relation to external anatomical landmarks for the frequently injected muscles of the human lower limb to facilitate the efficiency of botulinum toxin injections.

Localization of motor nerve branches of the human psoas muscle

Endplate-targeted botulinum toxin injections can achieve optimal neuromuscular blockade. The goal of this study was to identify the motor endplate (MEP) zone in the human psoas muscle through dissection. In 24 human cadaver psoas muscles the nerve branches and their intramuscular course were followed by stereoscopic microscopic dissection as far as their terminal ramifications. From the lumbar plexus, an average of 3.7 (range 2-7) nerve branches enter the psoas muscle. The proximal and distal limit of the MEP-zone are situated at about 30% and 70%, respectively, of the distance between the twelfth thoracic vertebra (Th12) and the passing of the psoas under the inguinal ligament. In reference to the sacral promontory (P), these limits are respectively from 50% of the Th12-P distance to 20% of the P-pubis distance. This study of the MEP zone of the human psoas muscle can allow the clinician to inject BTX-A close to its site of action.

Identification of neuromuscular junctions by correlative confocal and transmission electron microscopy

The physiological processes regulating neuromuscular transmission are highly dependent on the structural features of the motor neuron and motor endplate, and detailing the structure of neuromuscular junctions (NMJs) in muscle biopsies is a powerful method for research and diagnostics. The observation of NMJ ultrastructure, however, is complicated by the difficulty in locating NMJs for analysis by electron microscopy. Consequently, a correlative confocal-transmission electron microscopy method was developed. Fixed muscle samples were cryo-protected in sucrose, sectioned on a cryostat, and stained with fluorescent alpha-bungarotoxin for confocal microscopy. Sections containing junctions were mapped and then processed for transmission electron microscopy (TEM). Cryostat sections allowed large expanses of muscle tissue to be rapidly screened and enabled specific junctions to be targeted for TEM. The morphology of the junctions was well preserved with all essential features of the pre- and postsynaptic elements readily identifiable without freeze damage. Unlike NMJ correlative methods using histochemical stains and DAB photo-oxidation, no electron dense precipitate was deposited over the NMJ, enabling an unobstructed view of the pre- and postsynaptic structures.

Effects of Botox and Neuronox on muscle force generation in mice

The current study determined the dose-response relationship for inhibition of muscle force of two commercially available botulinum neurotoxin type-A (BoNTA) preparations (Botox and Neuronox) in a murine model and characterized the time course of recovery from the toxin-induced muscle paralysis. The effect of freezing reconstituted toxin on toxin potency was also determined. The gastrocnemius muscles in male CD-1 mice were injected with either saline or BoNTA (0.3-3.0 U/kg), and muscle force generation was examined following stimulation of the tibial nerve (single twitch and 15-200 Hz tetany). Botox and Neuronox produced nearly equivalent decrements in muscle force (30%-90%) at 4 days after toxin injection. At 28 days after injection (1 U/kg), muscle force had recovered from the effects of both toxin preparations. Maintaining reconstituted toxin at -80 degrees C for up to 5 months did not result in significant loss of toxin activity. The results of this study suggest that Botox and Neuronox produce equivalent responses in a murine model, and, in contrast to other models, muscle recovery is rapid with doses of toxin that produce less than maximal decrements in muscle force.

Influence of unilateral masseter muscle atrophy on craniofacial morphology in growing rabbits

PURPOSE

The purpose of the study was to evaluate whether the induction of unilateral masticatory muscle dysfunction can alter the skeletal growth patterns.

MATERIALS AND METHODS

Twenty-one white male New Zealand rabbits (4 weeks old) were divided into 3 groups of 7 subjects: group 1 served as the control to study normal craniofacial growth. In groups 2 and 3, rabbits were injected with 5 units and 15 units of Botulinum toxin A (BTXA) into the right masseter muscle, respectively. The effect of a neuromuscular blockade of masseteric activity on craniofacial growth was evaluated with 3 samples of serial computed tomography (CT) scans with a slice thickness of 0.625 mm, taken at 4 weeks (base line), 8 weeks (endpoint of prepubertal craniofacial growth), and 24 weeks (after pubertal growth).

RESULTS

The ipsilateral mandibular ramus height, zygomatic arch length, and masseteric length did not develop as much as those of the contralateral side after pubertal growth. At age 24 weeks, the masseter muscle volume asymmetry index reached -13.8% (group 2), -18.4% (group 3), and -1.6% for the control group. The ipsilateral side of the hemimandible showed less bone volume after 8 weeks but it showed partially recovered symmetry at 24 weeks. The maxillomandibular incisor midline and transverse molar discrepancies were not evident in any of the groups.

CONCLUSIONS

The BTXA injection can be an effective method in inducing site-specific muscular hypofunctions so that masticatory muscle-craniofacial bone interaction can be investigated efficiently. The result showed that the unilateral atrophy of the masseter muscle in the growing subjects influenced the morphology of the local skeletal sites. This did not, however, result ultimately in mandibular midline asymmetry or right-left asymmetry in hemimandibular volume after growth. The results imply that alterations in specific masticatory muscle function can be compensated by the growth of other structural components.

Neuromuscular recovery after distraction osteogenesis at different frequencies in a rabbit model

The muscle and nerve responses to stresses applied during distraction osteogenesis have not been clearly defined. This study hypothesized that distraction resulting in 30% lengthening decreases muscle force generation of the lengthened muscle and increasing the frequency of distraction attenuates the decrease of force generation accompanying lengthening. This study investigated the effects of different distraction frequencies on neuromuscular recovery in a rabbit model. Animals were assigned into group 1 (low-frequency distraction) and group 2 (high-frequency distraction). Distraction was continued until a 30% increase in the original tibial length was achieved. After consolidation of the osteotomy, knee and ankle range of motion, muscle force generation, and neuromuscular junction parameters were evaluated. Lengthening of 30% resulted in significantly decreased range of motion compared with the control leg (P < 0.05). Lengthening of 30% also substantially decreased force generation of the peroneus longus muscle. However, force generation of the peroneus longus muscle in the high-frequency group was 70.5% +/- 6.5% of the control side, significantly higher than that in the low-frequency distraction group (49.7% +/- 4.8% of the control side, P < 0.05). There was no statistical difference between the 2 groups in neuromuscular junction morphology, although an abnormal shape of the postsynaptic neuromuscular junction was observed after distraction. The use of a high-frequency distraction technique during limb lengthening may result in a reduction in impairment of knee and ankle range of motion and improved muscle function compared with that observed with the use of low-frequency distraction. Repeated microtrauma to the soft tissues associated with high-frequency distraction may facilitate the regenerative capacity of the soft tissues and result in an improved outcome of muscle and nerve function.

Pharmacology of botulinum toxin: differences between type A preparations

Different types of botulinum neurotoxin (BoNT) block different proteins of the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) protein complex within cholinergic nerve terminals, producing blockade of cholinergic neuromuscular and autonomic synapses. Animal studies indicate the longest duration of action for BoNT type A (BoNTA) followed by types B, F, and E. Diffusion to adjacent and remote muscles may be related to protein composition, dilutions, volume, target muscle selection, and injection technique. A review of head-to-head, randomized, controlled trials of BoNTA preparations (Botox and Dysport) suggests that Dysport tends to have higher efficacy, longer duration, and higher frequency of adverse effects. Conversion factors between the preparations varied, however, and remain controversial. In clinical settings, a Botox:Dysport conversion ratio of 1:3 may be appropriate. Animal studies suggest a conversion ratio of 1:2.5-3. When therapeutic effects between these preparations are attempting to be equalized, Dysport seems to produce more adverse effects. In mice, Botox appears to have a better safety margin than Dysport and BoNTB. In rats, diffusion margins are similar for Botox and Dysport. Jitter derived from stimulation single-fiber EMG of injected and remote muscles show no differences between Botox and Dysport. Atrophy of extrafusal muscle fibers of injected and remote muscles do not differ between the BoNTA preparations.

Motor points for neuromuscular blockade of the adductor muscle group

We sought to identify the motor nerve points for the adductor muscle group, relate them to specific surface anatomy markings, and define the points in terms of percentage distances along an anatomic reference line. We dissected four muscles in each of 20 legs from 15 skeletally mature, formalin-preserved cadavers. Multiple motor branches occurred in 21 of the 80 muscles dissected, but in only four limbs were they observed for more than one muscle in the group. Motor points (defined as the entry point of the motor branch into the muscle) were identified for each muscle along a reference line from the symphysis pubis to the medial joint line at the distal extent of the medial femoral condyle. The mean motor points and 95% confidence limits were as follows: adductor longus, 31% +/- 1.1%; adductor brevis, 22% +/- 1.8%; adductor magnus, 38% +/- 2.5%; and gracilis, 44% +/- 3.1%. Identification of these motor points facilitates accurate placement of neuromuscular blocking agents, such as botulinum toxin, and may lead to increased clinical efficacy of the block with a reduction in local or systemic side effects.

Development of the neuromuscular junction in extraocular muscles of white Leghorn chicks

Relatively little is known about the development of the neuromuscular junction of extraocular muscles (EOMs). In recent years, chicks have been increasingly used as a developmental model in ophthalmological research. To utilize this model system for understanding the development and plasticity of the extraocular motor system, we investigated the structural changes that occur at the developing neuromuscular junction in the chick between embryonic day 14 (E14) and posthatch day 2 (P2). Axons and nerve terminals were visualized with fluorescent neurofilament antibodies and motor endplates with rhodamine-conjugated alpha-bungarotoxin. Nerve fibers and endplates were colabeled within the same tissue samples. Motor endplates (density, length, width, and area) were measured and numbers of axons per neuromuscular junction were counted using confocal and conventional microscopy. In P2 chicks, densities of motor endplates were significantly greater in the superior oblique muscle when compared with the superior rectus and lateral gastrocnemius muscle. EOMs showed a two- to threefold larger area of motor endplate size as compared to gastrocnemius muscle. Motor endplate size also differed among EOMs with the superior oblique muscle having endplates with a larger area than those of the superior rectus muscle. The period of synapse elimination was similar between EOM and gastrocnemius muscle. Synapse elimination began at about E18 and was completed by P2. By describing the normal morphological changes in developing EOMs, this study provides a baseline for future work to elucidate underlying molecular mechanisms that regulate EOM innervation and strength.

Gene expression of nAChR, SNAP-25 and GAP-43 in skeletal muscles following botulinum toxin A injection: a study in rats

PURPOSE

Botulinum toxin A (BoNT-A) is used to manage spasticity in cerebral palsy. BoNT-A cleaves SNAP-25 protein, blocking acetylcholine release and weakening the muscle. Nicotinic acetylcholine receptors (nAChR) including alpha, beta, delta, gamma, and epsilon subunits, and GAP-43 protein are associated with functional recovery of neuromuscular junctions (NMJ) following BoNT-A. To better understand the mechanism behind this functional recovery, this study attempted to (1) document changes in NMJ morphometry following BoNT-A, and (2) determine the gene expression of nAChR subunits, SNAP-25, and GAP-43 protein.

METHODS

In this rat study (46 rats), 6 units/kg body weight of BoNT-A was injected into the gastrocnimus. NMJ morphometry and the time course of gene expression of nAChR subunits, SNAP-25, and GAP-43 were evaluated up to 1year post-injection.

RESULTS

NMJ morphometry: gutter depth was reduced vs. the control side at two months, and normalizing by 6 months following BoNT. nAChR alpha mRNA and gamma mRNA increased by 3 days, peaked at 7 days and returned to control levels; delta mRNA peaked at 3 days. Epsilon mRNA peaked by 7 days. SNAP-25 mRNA increased from 60 to 90 days, returning to control levels by 6 months. GAP-43 mRNA was unchanged.

CONCLUSIONS

Specific nAChR subunit mRNA expression up-regulates and then returns to normal within two weeks, preceding changes in NMJ morphometry. Although GAP-43 participates in nerve sprouting, no increase of GAP-43 mRNA occurred following BoNT-A. Delayed up-regulation of SNAP-25 mRNA might be associated with muscle functional recovery.

A novel endogenous erythropoietin mediated pathway prevents axonal degeneration

Clinically relevant peripheral neuropathies (such as diabetic and human immunodeficiency virus sensory neuropathies) are characterized by distal axonal degeneration, rather than neuronal death. Here, we describe a novel, endogenous pathway that prevents axonal degeneration. We show that in response to axonal injury, periaxonal Schwann cells release erythropoietin (EPO), which via EPO receptor binding on neurons, prevents axonal degeneration. We demonstrate that the relevant axonal injury signal that stimulates EPO production from surrounding glial cells is nitric oxide. In addition, we show that this endogenous pathway can be therapeutically exploited by administering exogenous EPO. In an animal model of distal axonopathy, systemic EPO administration prevents axonal degeneration, and this is associated with a reduction in limb weakness and neuropathic pain behavior. Our in vivo and in vitro data suggest that EPO prevents axonal degeneration and therefore may be therapeutically useful in a wide variety of human neurological diseases characterized by axonopathy.

Time Course of Recovery of Juvenile Skeletal Muscle After Botulinum Toxin A Injection

OBJECTIVE

To study the effects of neuromuscular blockade using botulinum toxin A on juvenile muscles at a dosage of 6 units/kg body weight in a rat model.

DESIGN

A total of 34 male Sprague-Dawley rats (1-mo old) were used. A small incision was made along the posterior aspect of the left hind leg with the exposure of the gastrocnemius. Botulinum toxin A was injected at a dosage of 6 units/kg body weight in the medial and lateral heads of the muscle. An equivalent volume of saline were injected into the right gastrocnemius (control). Motor evoked action potentials, muscle force generation, and muscle mass and neuromuscular junction morphometry were analyzed at different time intervals up to 1 yr after toxin injection.

RESULTS

During the 1-2 wks after botulinum toxin A injection, muscle mass, electrophysiologic variables, and muscle force generation were significantly reduced but returned to nearly normal at 6 mos postinjection. In the study group, neuromuscular junction gutter depth became significantly shallower 2 mos after injection, then normalized at 1 yr. There was a nonsignificant trend toward larger neuromuscular junctions from the gastrocnemius injected with botulinum toxin A.

CONCLUSION

Our findings provide scientific evidence to support the clinical situation in which the interinjection interval of 3-6 mos of botulinum toxin A at a similar dosage is used.

Targeting the Neuromuscular Junction in Skeletal Muscles

Botulinum neurotoxins selectively weaken skeletal muscle by presynaptic blockade of vesicles containing the neurotransmitter acetylcholine. Because the location of the neuromuscular junction (found in motor endplates) is most highly concentrated in a band within the midbelly of the muscle, injection of botulinum neurotoxins are hypothesized to be more potent when specifically targeted toward the motor endplate zones. Few studies have attempted to describe the distribution of motor endplate zones in skeletal muscles, and scant experimental data exist that directly tests this hypothesis. In this article, a rationale is presented for motor endplate targeting within specific limb muscles with respect to botulinum neurotoxin therapy.

Clinical usefulness of botulinum toxin in the lower extremity

As the literature that pertains to botulinum toxin expands, the scope of treatment options broadens. Although initial uses of botulinum toxin focused around the head and neck, there are many uses for the toxin in the area of the foot and ankle; more possibilities are under investigation every day. We review the uses and techniques for botulinum toxin in the foot and ankle and present results of botulinum toxin treatment in 10 idiopathic toe walkers.