Inward particle transport driven by biased endplate in a cylindrical magnetized plasma

The inward particle transport is associated with the formation of peaked density profiles,which contributes to improve the fusion rate and the realization of steady-state discharge.The active control of inward particle transport is considered as one of the most critical issues of magnetic confinement fusion.Recently,it is realized preliminarily by adding a biased endplate in the Peking University Plasma Test(PPT)device.The results reveal that the inward particle flux increases with the bias voltage of the endplate.It is also found that the profile of radial electric field(Er)shear is flattened by the increased bias voltage.Radial velocity fluctuations affect the inward particle more than density fluctuations,and the frequency of the dominant mode driving inward particle flux increases with the biased voltage applied to the endplate.The experimental results in the PPT device provide a method to actively control the inward particle flux using a biased endplate and enrich the understanding of the relationship between E_(r)×B shear and turbulence transport.

Endplate role in the degenerative disc disease:A brief review

The degenerative disease of the intervertebral disc is nowadays an important health problem,which has still not been understood and solved adequately.The vertebral endplate is regarded as one of the vital elements in the structure of the intervertebral disc.Its constituent cells,the chondrocytes in the endplate,may also be involved in the process of the intervertebral disc degeneration and their role is central both under physiological and pathological conditions.They main functions include a role in homeostasis of the extracellular environment of the intervertebral disc,metabolic support and nutrition of the discal nucleus and annulus beneath and the preservation of the extracellular matrix.Therefore,it is understandable that the cells in the endplate have been in the centre of research from several viewpoints,such as development,degeneration and growth,reparation and remodelling,as well as treatment strategies.In this article,we briefly review the importance of vertebral endplate,which are often overlooked,in the intervertebral disc degeneration.

Basic fibroblast growth factor attenuates the degeneration of injured spinal cord motor endplates

The distal end of the spinal cord and neuromuscular junction may develop secondary degeneration and damage following spinal cord injury because of the loss of neural connections. In this study, a rat model of spinal cord injury, established using a modified Allen＇s method, was injected with basic fibroblast growth factor solution via subarachnoid catheter. After injection, rats with spinal cord injury displayed higher scores on the Basso, Beattie and Bresnahan locomotor scale. Motor function was also well recovered and hematoxylin-eosin staining showed that spinal glial scar hyperplasia was not apparent. Additionally, anterior tibial muscle fibers slowly, but progressively, atrophied. Immu- nohistochemical staining showed that the absorbance values of calcitonin gene related peptide and acetylcholinesterase in anterior tibial muscle and spinal cord were similar, and injection of basic fi- broblast growth factor increased this absorbance. Results showed that after spinal cord injury, the distal motor neurons and motor endplate degenerated. Changes in calcitonin gene related peptide and acetylcholinesterase in the spinal cord anterior horn motor neurons and motor endplate then occurred that were consistent with this regeneration. Our findings indicate that basic fibroblast growth factor can protect the endplate through gene related peptide and acetylcholinesterase cord. attenuating the decreased expression of calcitonin n anterior horn motor neurons of the injured spinal

The impact of endplate fracture on postoperative vertebral height loss and kyphotic deformity during treatment of osteoporotic vertebral compression fractures with balloon kyphoplasty

This retrospective study investigated the impact of endplate fracture on postoperative vertebral height loss and kyphotic deformity in 144 patients with osteoporotic vertebral compression fracture （OVCF）, who received balloon kyphoplasty. Patients were divided into four groups： Group 1 had no superior endplate fracture, Group 2 had fractures on the anterior portion of the superior endplate, Group 3 had fractures on the posterior portion of the superior endplate, and Group 4 had complete superior endplate fractures. Anterior and middle vertebral body height, vertebral compression ratio, vertebral height loss rate, and kyphosis Cobb angle of each patient were measured and visual analogue scale （VAS） and Oswestry disability index （ODI） scores were recorded. The anterior vertebral height and kyphosis deformity of all groups significantly improved after the surgery, whereas substantial anterior vertebral height loss and increased Cobb angle were observed in all patients at the last follow-up. Although the vertebral height loss rate and the Cobb angle in Group 2, 3 and 4 were larger compared with Group 1 at the last follow-up, only the vertebral height loss rate in Group 4 and the increase in the Cobb angle in Group 2 and 4 were statistically different from those in Group 1. The VAS and ODI scores in all groups measured after the surgery and at the last follow-up were significantly lower compared with preoperative scores, but there was no significant difference among these groups. Balloon kyphoplasty significantly improved vertebral fracture height and kyphosis. Vertebral height loss and increased kyphotic deformity were observed in OVCF patients with endplate fractures after the surgery. Postoperative aggravation of kyphosis was observed in Group 2. Furthermore, severe vertebral height loss and increased kyphotic deformity were confirmed in Group 4 after the surgery. Our results suggested that postoperative vertebral height loss and aggravation of kyphosis may be associated with biomechanical changes in the vertebral body caused by endplate fracture. Therefore, surgery should not only restore compressed vertebral body height and correct kyphosis, but also correct the deformity of endplate to achieve an effective treatment of OVCF patients with endplate fracture.

Effect of osteoporosis and intervertebral disc degeneration on endplate cartilage injury in rats

Objective:To investigate the effect of osteoporosis and intervertebral disc degeneration on the endplate cartilage injury in rats.Methods:A total of 48 female Sprague Dawley rats(3 months)were randomly divided into Groups A,B,C and D with 12 rats in each group.Osteoporosis and intervertebral disc degeneration composite model,simple degeneration model and simple osteoporosis model were prepared in Groups A,B and C respectively.After modeling,four rats of each group at 12th.18th and 24th week were sacrificed,Intervertebral height of cervical vertebra C6/C7 was measured.Micro-CT was used to image the endplate of cephalic and caudal cartilage at C6/C7 intervertebral disc.Abraded area rate of C6 caudal and C7 cephalic cartilage endplate was calculated,and then C6/C7 intervertebral disc was routinely embedded and sectioned.stained with safranin O to observe histological changes microscopically.Results:At 12,18 and24 weeks,intervertebral disc height of C6/C7 were(0.58±0.09)mm,(0.53±0.04)mm and(0.04±0.06)mm in Group A rats,(0.55±0.05)mm,(0.52±0.07)mm and(0.07±0.05)mm in Group B rats.At 24th week.intervertebral disc height of Group A rats was significantly lower than that of Group B rats(P<0.05);intervertebral disc height of Groups A and B rats at each time point were significantly lower than that of Groups C and D(P<0.05).There was no significantly statistical difference of intervertebral disc height between Groups C and D(P>0.05).At 12 and 18 weeks,the abraded rate of C6 caudal and C7 cephalic cartilage endplate in Group A rats were significantly higher than that in Groups B.C and D rats(P<0.05);the abraded rate in Group B was significantly higher than that in Groups C and D(P>0.05).Microscopic observation of CT showed that ventral defects in C6caudal or C7 cephalic cartilage endplate in Groups A and B appeared after 12 weeks of modeling;obvious cracks were found in front of the C6 and C7 vertebral body,and cartilage defect shown the trend of"repairing"at 18 and 24 weeks after modeling.Conclusions:Intervertebral disc degeneration and osteoporosis can cause damage to the cartilage endplate.Co-existence of these two factors can induce more serious damage to the endplate.which has possitive correlation with intervertebral disc degeneration.Osteoporosis plays a certain role in intervertebral disc degeneration process,and accelerates the degeneration of intervertebral disc in a specific time window.

Effects of delayed repair of peripheral nerve injury on the spatial distribution of motor endplates in target muscle

Motor endplates(MEPs) are important sites of information exchange between motor neurons and skeletal muscle, and are distributed in an organized pattern of lamellae in the muscle. Delayed repair of peripheral nerve injury typically results in unsatisfactory functional recovery because of MEP degeneration. In this study, the mouse tibial nerve was transected and repaired with a biodegradable chitin conduit, immediately following or 1 or 3 months after the injury. Fluorescent α-bungarotoxin was injected to label MEPs. Tissue optical clearing combined with light-sheet microscopy revealed that MEPs were distributed in an organized pattern of lamellae in skeletal muscle after delayed repair for 1 and 3 months. However, the total number of MEPs, the number of MEPs per lamellar cluster, and the maturation of single MEPs in gastrocnemius muscle gradually decreased with increasing denervation time. These findings suggest that delayed repair can restore the spatial distribution of MEPs, but it has an adverse effect on the homogeneity of MEPs in the lamellar clusters and the total number of MEPs in the target muscle. The study procedures were approved by the Animal Ethics Committee of the Peking University People's Hospital(approval No. 2019 PHC015) on April 8, 2019.

Stability of motor endplates is greater in the biceps than in the interossei in a rat model of obstetric brachial plexus palsy

The time window for repair of the lower trunk is shorter than that of the upper trunk in patients with obstetric brachial plexus palsy. The denervated intrinsic muscles of the hand become irreversibly atrophic much faster than the denervated biceps. However, it is unclear whether the motor endplates of the denervated interosseous muscles degenerate more rapidly than those of the denervated biceps. In this study, we used a rat model of obstetric brachial plexus palsy of the right upper limb. C5–6 was lacerated distal to the intervertebral foramina, with concurrent avulsion of C7–8 and T1, with the left upper limb used as the control. Bilateral interossei and biceps were collected at 5 and 7 weeks. Immunofluorescence was used to assess the morphology of the motor endplates. Real-time quantitative polymerase chain reaction and western blot assay were used to assess mRNA and protein expression levels of acetylcholine receptor subunits(α, β and δ), rapsyn and β-catenin. Immunofluorescence microscopy showed that motor endplates in the denervated interossei were fragmented, while those in the denervated biceps were morphologically intact with little fragmentation. The number and area of motor endplates, relative to the control side, were significantly lower in the denervated interossei compared with the denervated biceps. mRNA and protein expression levels of acetylcholine receptor subunits(α, β and δ) were significantly lower, whereas β-catenin protein expression was higher, in the denervated interossei compared with the denervated biceps. The protein expression of rapsyn was higher in the denervated biceps than in the denervated interossei at 7 weeks. Our findings demonstrate that motor endplates of interossei are destabilized, whereas those of the biceps remain stable, in the rat model of obstetric brachial plexus palsy. All procedures were approved by the Experimental Animal Ethics Committee of Fudan University, China(approval No. DF-187) in January 2016.

The Endplate Morphology Changes with Change in Biomechanical Environment Following Discectomy

Bone is a dynamic structure and is known to respond to changes in the load over time, in accordance with Wolff’s law. It states that the bone changes its shape and internal architecture in response to stresses acting on it [1]. Therefore, any structural changes in the spine may lead to bone remodeling due to changes in the optimal stress pattern. The changes in apparent density and thickness of the endplates following discectomy of varying amounts were analyzed. The study design coupled a bone remodeling algorithm based on strain energy density theory of adaptive remodeling with an experimentally validated 3D ligamentous finite element model of the spine. The apparent density and thickness of the index level endplates decreased above and below the region of discectomy. On the other hand, these parameters showed increases at the remaining regions of the endplate. There were no correlations between the amount of nucleus removed and the average percentage changes in apparent density and thickness of endplate above and below the discectomy region. However, the average percentage changes in apparent density and thickness at endplate in the other region increased with increase in amount of nucleus removed. These predictions are in agreement with the clinical observations [2-6].

Biomechanical analysis of bone mesoscopic structure and mechanical properties of vertebral endplates of degenerated intervertebral discs in rabbits

In previous studies of disc degeneration,the structural and mechanical properties of the endplate were often neglected.In this paper,the station legislation was used to construct an animal model of minor trauma disc degeneration,and the mechanism of disc degeneration was further investigated by observing the changes of mesoscopic structure and developing the mechanical properties of endplate bone.Twenty-eight 6-month-old Japanese white rabbits were divided into two groups:control group and experimental group.An animal model of intervertebral disc degeneration was established by upright experiment in the experimental group.The bone mesoscopic structures in different areas of each endplate were observed by histological and imaging methods,and the mechanical properties of the endplates were measured by indentation method.The two groups of data were compared by one-way ANOVA.After the experimental animals stood for 17 weeks,The experimental group showed the characteristics of early disc degeneration.The microstructure of the degenerative group showed that the end plate mineralization degree was higher,the bone mass was larger,and the number and thickness of bone trabeculae were larger.The results of indentation test showed that the mechanical properties of the degeneration group were enhanced,and the lower endplate was obviously enhanced.We successfully established a model of human disc degeneration with non invasive trauma and more consistent with the process of human disc degeneration through the standing experiment.In the experimental group,the internal structure of the endplate was dense and pore distance was reduced.The change of bone mesoscopic structure further affects the endplate,resulting in the enhancement of the mechanical properties of the endplate after intervertebral disc degeneration.The reduction of the pore distance and the narrowing of the internal channel structure of the endplate also hinder the nutrition supply of the intervertebral disc,which may be the key reason affecting the degeneration of the intervertebral disc.A biomechanical method for investigating the mechanism of intervertebral disc degeneration can be provided in this paper.

Biomechanical effects of bone cement volume on the endplates of augmented vertebral body： a three-dimensional finite element analysis

Background Previous studies have suggested that percutaneous vertebroplasty might alter vertebral stress transfer,leading to adjacent vertebral failure.However,no three-dimensional finite element study so far accounted for the stress distributions on different cement volumes.The purpose of this study was to evaluate the stress distributions on the endplate under different loading conditions after augmentation with various volumes of bone cement.Methods L2-L3 motion segment data were obtained from CT scans of the lumbar spine from a cadaver of a young man who had no abnormal findings on roentgenograms.Three-dimensional model of L2-L3 was established using Mimics software,and finite element model of L2-L3 functional spinal unit （FSU） was established using Ansys10.0 software.For simulating percutaneous vertebral augmentation,polymethylmethacrylate （PMMA） was deposited into the bipedicle of the L2 vertebra.The percentage of PMMA volume varied between 15％ and 30％.The stress distributions on the endplate of the augmented vertebral body were calculated under three different loading conditions.Results In general,the stress level monotonically increased with bone cement volume.Under each loading condition,the stress change on the L2 superior and inferior endplates in three kinds of finite element models shows monotonic increase.Compared with the stress-increasing region of the endplate,the central part of the L2 endplate was subject to the greatest stress under three kinds of loading conditions,especially on the superior endplate and under flexion.Conclusions The finite element models of FSU are useful to optimize the planning for vertebroplasty.The bone cement volume might have an influence on the endplate of the augmentation,especially the superior endplate.It should be noted that the optimization of bone cement volume is patient specific; the volume of the bone cement should be based on the size,body mineral density,and stiffness of the vertebrae of individual patients.

Effect of pcDNA3.1-vascular endothelial growth factor 165 recombined vector on vascular buds in rabbit vertebral cartilage endplate

Background This study aimed to investigate the effect of pcDNA3.1-vascular endothelial growth factor （VEGF）165 vector on vertebral cartilage endplate vascular buds and intervertebral discs. Methods Rabbits were randomly assigned to the control and experimental groups with 10 in each. In the experimental group, we anesthetized the rabbits and exposed the front vertebral body. Using the mark of the longitudinal ossature of the front vertebral body of the lumbar vertebrae, we advanced a needle at the central point of the front fourth and fifth lumbar intervertebral discs and injected 20 pl pcDNA3.1-VEGF165. Similarly, in the control group, we injected 20 IJl pcDNA3.1. At 4 and 8 weeks post-injection, we examined the changes of the vertebral cartilage endplate using X-ray radiograph, histology, and scanning electron microscopy. Results The vertebral cartilage endplate calcification and degeneration in the experimental group were less than those in the control group at 8 weeks post-operation. The average number and diameter of vascular buds obviously increased in the experimental group at 4 and 8 weeks post-operation. The number of vascular buds and the diameter in the region of the inner annulus increased when compared to those in the area near the nucleus pulposus. Conclusions The pcDNA3.1-VEGF165 plasmid can increase the average number and diameter of vascular buds and decelerate intervertebral disc degeneration.

JNK phosphorylation promotes degeneration of cervical endplate chondrocytes through down-regulation of the expression of ANK in humans

Background C-Jun N-terminal kinase （JNK） signaling pathway and ankylosis gene （ANK） play a critical role in endplate chondrocytes degeneration. The purpose of this study was to investigate whether the expression levels of ANK was associated with the activation of JNK. Methods Cartilage endplates of 49 patients were divided into the control group （n=19） and the experimental group （n=30）. The patients in the control group were graded 0 and those in the experimental group were graded I-III according to Miller＇s classification. Endplate chondrocytes were isolated by enzyme digestion and cultured in vitro. The inverted phase contrast microscope, teluidine blue staining, HE staining, real time RT-PCR, and MTT were used to observe morphological appearances, biological characteristics, and growth curve of endplate chondrocytes from the cartilage endplate of the two groups. Real time RT-PCR and Western blotting were used to analyze the mRNA and protein expression levels of associated factors in the degeneration process in the cultured endplate chondrocytes with or without subjected SP600125. Results The expression levels of type II collagen, aggrecan, and ANK in endplate chondrocytes of experimental group were lower than that of control group and phosphorylation level of JNK in the experimental group which was higher than that in the control group. Application of JNK phosphorylation inhibitor to degeneration chondrocytes resulted in a marked decrease in the phosphorylation level of JNK and a significant increase in the expression levels of type II collagen, aggrecan, and ANK.Conclusion The degeneration of the human cervical endplate chondrocytes might be promoted by JNK phosphorylation by down-regulating the expression of ANK

Radiological features of traumatic vertebral endplate fracture:an analysis of 194 cases with 263 vertebral fractures

Background:The importance of identifying osteoporotic vertebral endplate or/and cortex fracture(ECF),which primarily includes endplate fracture(EPF)and vertebral anterior cortex buckling,has been recognized.However,some old traumatic ECFs with healing process in the elderly may be mistaken as osteoporotic.This study analyzes the radiological features of traumatic EPF.Methods:This was a retrospective analysis of 194 spine trauma patients with 263 vertebral fractures(mean age:42.11±9.82 years,118 males and 76 females).All patients had traumatic EPF identified by X-ray/CT/MRI.Results:The involved vertebra was mostly L1(29.7%),followed by T12 and L2.Except EPFs involved both superior and inferior endplates(12.6%),only 1.9%involved inferior endplate alone,with the majority involved superior endplate.If each endplate was divided into five segments of equal lengths(from anterior to posterior:a1,a2,m,p2,p1),the most depressed point of superior EPFs was mostly at segment-a2(approximately 45%),followed by segment-a1(approximately 20%)or segment-m(approximately 20%),and very rarely at segment-p1.The upper 1/3 of anterior vertebral wall was more likely to fracture,followed by middle 1/3 of anterior wall.For posterior vertebral wall fracture,68.5%broke the bony wall surrounding the basivertebral vain.58.6%,30.0%,and 11.4%of vertebral fractures had<1/5,1/5-1/3,and>1/3 vertebral body height loss.As the extent of vertebral height loss increased,the chance of having both superior and inferior EPFs also increased;however,the chance of having inferior EPF alone did not increase.Conclusion:Traumatic EPF features are characterized,which may help the differentiation of traumatic and osteoporotic EPFs.

Pathophysiology, diagnosis, and treatment of discogenic low back pain

Discogenic low back pain is a serious medical and social problem, and accounts for 26%-42% of the patients with chronic low back pain. Recent studies found that the pathologic features of discs obtained from the patients with discogenic low back pain were the formation of the zones of vascularized granulation tissue, with extensive innervation in fissures extending from the outer part of the annulus into the nucleus pulposus. Studies suggested that the degeneration of the painful disc might originate from the injury and subsequent repair of annulus fibrosus. Growth factors such as basic fibroblast growth factor, transforming growth factor β1, and connective tissue growth factor, macrophages and mast cells might play a key role in the repair of the injured annulus fibrosus and subsequent disc degeneration. Although there exist controversies about the role of discography as a diagnostic test, provocation discography still is the only available means by which to identify a painful disc. A recent study has classified discogenic low back pain into two types that were annular disruption-induced low back pain and internal endplate disruption-induced low back pain, which have been fully supported by clinical and theoretical bases. Current treatment options for discogenic back pain range from medicinal anti-inflammation strategy to invasive procedures including spine fusion and recently spinal arthroplasty. However, these treatments are limited to relieving symptoms, with no attempt to restore the disc's structure. Recently, there has been a growing interest in developing strategies that aim to repair or regenerate the degenerated disc biologically.

The anatomical,electrophysiological and histological observations of muscle contraction units in rabbits:a new perspective on nerve injury and regeneration

In the conventional view a muscle is composed of intermediate structures before its further division into microscopic muscle fibers.Our experiments in mice have confirmed this intermediate structure is composed of the lamella cluster formed by motor endplates,the innervating nerve branches and the corresponding muscle fibers,which can be viewed as an independent structural and functional unit.In this study,we verified the presence of these muscle construction units in rabbits.The results showed that the muscular branch of the femoral nerve sent out 4–6 nerve branches into the quadriceps and the tibial nerve sent out 4–7 nerve branches into the gastrocnemius.When each nerve branch of the femoral nerve was stimulated from the most lateral to the medial,the contraction of the lateral muscle,intermediate muscle and medial muscle of the quadriceps could be induced by electrically stimulating at least one nerve branch.When stimulating each nerve branch of the tibial nerve from the lateral to the medial,the muscle contraction of the lateral muscle 1,lateral muscle 2,lateral muscle 3 and medial muscle of the gastrocnemius could be induced by electrically stimulating at least one nerve branch.Electrical stimulation of each nerve branch resulted in different electromyographical waves recorded in different muscle subgroups.Hematoxylin-eosin staining showed most of the nerve branches around the neuromuscular junctions consisted of one individual neural tract,a few consisted of two or more neural tracts.The muscles of the lower limb in the rabbit can be subdivided into different muscle subgroups,each innervated by different nerve branches,thereby allowing much more complex muscle activities than traditionally stated.Together,the nerve branches and the innervated muscle subgroups can be viewed as an independent structural and functional unit.This study was approved by the Animal Ethics Committee of Peking University People’s Hospital(approval No.2019 PHE027)on October 20,2019.

CHARACTERISTIC OF FACIAL MUSCLE AND EFFERENT NERVE ON PHYSIOLOGY AND ANATOMY

Objective.To study the speciality of orbicularis oculi muscles, nerves and oris muscles, nerves and mechanism of difference of faclal muscular injury in facial paralysis deeply.Methods. The conductive velocity of the efferent nerves of orbicularis oculi and oris muscles of the health human beings and guinea pigs is measured with electromyogram (EMG) apparatus.Results. The conductive velocity of orbicularis oculi nerve is quicker and oris muscles are controlled by facial nerves on both sides. Measuring the threshold of Strength-Duration (S-D) curves of the motor point of orbicularis oculi and oris muscles shows the threshold of the former is lower. Measuring the diameter of orbicularis oculi and oris nerve fibers on the guinea pigs and rabbits shows the diameter of orbicularis oculi nerve fiber is bigger. The area of secondary synapse space of orbicularis oculi motor end plate is larger than that of oris under scanning electromicroscope.Conclusions. Orbicularis oculi muscles,orbicularis oculi nerves and oris muscles,oris nerves all have their own characteristic on physiology and anatomy. It elucidated the mechanism that orbicularis oculi muscle is easy to be injuried.

Methodology and cohort profile for the Hangzhou Lumbar Spine Study: a study focusing on back health in a Chinese population

Back pain is a worldwide health problem, adding a tremendous burden to modern societies. However, little information on back health is available in China, even though a quarter of the world＇s population is Chinese. To enhance knowledge in this area, we designed and initiated the Hangzhou Lumbar Spine Study, which is a cross-sectional study of a general sample of mainland Chinese with focusing on disc degeneration, Modic changes, endplate lesions, and back pain. The study consists of a structured questionnaire to measure back pain history and lifetime exposure to suspected risk factors, magnetic resonance imaging of the lumbar spine, bone mineral density study of the spine and hip, and DNA sample analysis. Here we briefly introduce the study methodology, report the test-retest reliability of the questionnaire, and describe the cohort profile to date. Since May 2014, 301 randomly selected subjects（male/female, 122/179; mean age, 51.0 years; range, 20–87 years） have been recruited. Tests-retests of the questionnaire, completed by 40 participants, revealed good reliability. To our knowledge, the Hangzhou Lumbar Spine Study is the first population-based epidemiological study conducted to characterize lumbar spinal phenotypes and back pain, their interaction, and their associations with lifetime environmental exposure, in mainland Chinese. Epidemiological information obtained from a reliable questionnaire, magnetic resonance（MR） imaging data, dual energy X-ray absorptiometry（DXA） measurements, and DNA analysis may serve as a valuable reference for future studies on back health, particularly for mainland Chinese.

Effects of Muscle Electrical Activity on the Transmission of Developing Neuromuscular Junction

Miniature endplate potentials (MEPPS) caused by the spontaneous release of ACh from the growth cone of cholinergic neurons, are recorded by the whole-cell patch-clamp technique on a large number of 1-day cultured myoballs which have contact neurites of co-cultured neurons. Both muscle cell and neuron are dissociated from the 1-day-old (about stage 20) Xenopus embryo. Frequency and/or amplitude of MEPPs can obviously increase after the repetitive high-level depolarization caused by the stimuli on muscle cells. No detectable changes of single ACh receptor channel property are observed by using the single-channel recording technique. These results suggest that the mechanism of the increase of MEPPs after electrical activity of postsynaptic muscle cells probably involve some alteration of presynaptic membrane.