Action Potential Conduction Velocity Research Articles

Ex-vivo systems for neuromodulation: A comparison of ex-vivo and in-vivo large animal nerve electrophysiology

BackgroundLittle research exists on extending ex-vivo systems to large animal nerves, and to the best of our knowledge, there has yet to be a study comparing these against in-vivo data. This paper details the first ex-vivo system for large animal peripheral nerves to be compared with in-vivo results. New MethodDetailed ex-vivo and in-vivo closed-loop neuromodulation experiments were conducted on pig ulnar nerves. Temperatures from 20 °C to 37 °C were evaluated for the ex-vivo system. The data were analysed in the time and velocity domains, and a regression analysis established how evoked compound action potential amplitude and modal conduction velocity (CV) varied with temperature and time after explantation. Main resultsPig ulnar nerves were sustained ex-vivo up to 5 h post-explantation. CV distributions of ex-vivo and in-vivo data were compared, showing closer correspondence at 37 °C. Regression analysis results also demonstrated that modal CV and time since explantation were negatively correlated, whereas modal CV and temperature were positively correlated. Comparison with Existing MethodsPrevious ex-vivo systems were primarily aimed at small animal nerves, and we are not aware of an ex-vivo system to be directly compared with in-vivo data. This new approach provides a route to understand how ex-vivo systems for large animal nerves can be developed and compared with in-vivo data. ConclusionThe proposed ex-vivo system results were compared with those seen in-vivo, providing new insights into large animal nerve activity post-explantation. Such a system is crucial for complementing in-vivo experiments, maximising collected experimental data, and accelerating neural interface development.

Evaluation of novel open-source software for cardiac optical mapping

KairoSight-3.0 is a recently released Python-based, open-source software for cardiac optical mapping analysis. Addressing challenges in high-resolution electrophysiological data analysis, KairoSight-3.0 facilitates comprehensive studies of cardiac conduction and excitation-contraction coupling. We compared its performance with ElectroMap, focusing on action potential duration and conduction velocity measurements in mouse heart models subjected to ischaemia and flecainide treatment. Our findings reveal that while both software are effective, inherent methodological differences impact measurement outcomes. KairoSight-3.0's robust analysis capabilities make it a valuable tool in cardiac research. Additionally, future directions for KairoSight-3.0 and other mapping analysis tools are explored. Statement of importanceOpen-source methods for analysis of cardiac optical mapping are vital tools in electrophysiological research. Our work directly evaluates the latest version of KarioSight, recently published in JMCC plus, with ElectroMap, an established and widely used tool. Our results show both software are effective in analysis of changes in both conduction and repolarisation. Considering the new features of KairoSight-3.0 and python implementation, our study importantly demonstrates the effectiveness of the software, highlights potential discrepancies between it and ElectroMap, and provides a perspective on future directions for KairoSight-3.0 and other software.

Effect of High-intensity Laser Therapy on Carpal Tunnel Syndrome Patients: A Systematic Review and Meta-analysis.

To provide a strong foundation for the use of high-intensity laser therapy (HILT) in carpel tunnel syndrome (CTS,) we conducted a systematic review and meta-analysis to investigate the outcomes of short- and long-term follow-up studies. Systematic review and meta-analysis. Sample sizes of included studies ranged from 16 to 98 patients (total N = 308). Overall, a significant difference between the treatment and control groups were found across majority of the measures. Studies using a four-week follow-up period, however, only found significantly greater benefits for HILT in visual analogue scale (VAS) compared to placebo (p = 0.0191), Transcutaneous electrical nerve stimulation (TENS) (p = 0.0026), and low-intensity laser therapy-20 J/cm2 (p < 0.0002), and exercise (p < 0.0001). For improvement in VAS score over a long treatment period, HILT was also preferred over control group (p < 0.0071). Insufficient evidence exists to determine effect of HILT on nerve conduction examinations. The only statistically significant differences observed in examinations were in relation to sensory nerve action potential (p = 0.0083) and sensory nerve conduction velocity (SNCV) (p = 0.0468). Moderate evidence exists regarding efficacy of HILT compared to placebo, HILT + wrist splint, and exercise in a short period of follow-up time but evidence on long-term follow-up is limited.

Development of myelination and axon diameter for fast and precise action potential conductance.

Axons of globular bushy cells in the cochlear nucleus convey hyper-accurate signals to the superior olivary complex, the initial site of binaural processing via comparably thick axons and the calyx of the Held synapse. Bushy cell fibers involved in hyper-accurate binaural processing of low-frequency sounds are known to have an unusual internode length-to-axon caliber ratio (L/d) correlating with higher conduction velocity and superior temporal precision of action potentials. How the L/d-ratio develops and what determines this unusual myelination pattern is unclear. Here we describe a gradual developmental transition from very simple to complex, mature nodes of Ranvier on globular bushy cell axons during a 2-week period starting at postnatal day P6/7. The molecular composition of nodes matured successively along the axons from somata to synaptic terminals with morphologically and molecularly mature nodes appearing almost exclusively after hearing onset. Internodal distances are initially coherent with the canonical L/d-ratio of ~100. Several days after hearing onset, however, an over-proportional increase in axon caliber occurs in cells signaling low-frequency sounds which alters their L/d ratio to ~60. Hence, oligodendrocytes initially myelinating axons according to their transient axon caliber but a subsequent differential axon thickening after hearing onset results in the unusual myelination pattern.

Sural nerve involvement in patients with acute inflammatory demyelinating polyneuropathy variant of Guillain-Barre syndrome with sural sparing at initial presentation

Introduction: Neurophysiological testing is a valuable tool in the diagnosis of Guillain-Barre syndrome (GBS). Sural sparing is a usual feature of acute inflammatory demyelinating polyneuropathy (AIDP) type GBS. However, sural involvement has been reported in later stages of GBS. It is important to identify patterns of sural nerve involvement to differentiate GBS from its mimickers and to stage the disease. This research aimed to detect the pattern of sural nerve involvement in AIDP-GBS cases with normal electrophysiological responses in the sural nerve at the beginning.Objectives: To determine the location and timing of sural nerve involvement in AIDP-GBS.Methods: This prospective follow up study included diagnosed cases of AIDP-GBS with preserved bilateral sural responses. Nerve conduction and somatosensory evoked potentials (SSEP) were done on admission and weekly thereafter for four consecutive weeks. The last evaluation was done four weeks after the fourth study.Results: All patients (100%) showed normal distal sural responses over the initial four weeks of follow up. They continued to remain normal up to eight weeks in eight patients (53.3%). Two patients had gradual prolongation of their sural SSEP on consecutive studies. One of them had gradual reduction of sural sensory nerve action potential and nerve conduction velocity along with the prolongation of sural SSEP latencies. The difference of SSEP latency increments in the left sural nerve of these two patients was statistically significant (p&lt;0.05). The right sural SSEP latency difference was not significant.Conclusion: Sparing of the distal sural sensory response was demonstrated in 100% of AIDP-GBS cases during the first four weeks of follow up. More than 50% of the cohort demonstrated preserved sural sensory responses for eight weeks from the initial presentation. Two out of fifteen patients showed statistically significant proximal sural sensory pathway involvement with increasing SSEP latencies. This finding suggests that in some patients, the sural sensory pathway may get affected at its proximal segments or at the central nervous system before the distal nerve is affected.

Filtering property of myelinated internode can change neural information representability and might trigger a compensatory action during demyelination

In this paper, for the first time, we showed that an Internode Segment (INS) of a myelinated axon acts as a lowpass filter, and its filter characteristics depend on the number of myelin turns. Consequently, we showed how the representability of a neural signal could be altered with myelin loss in pathological conditions involving demyelinating diseases. Contrary to the traditionally held viewpoint that myelin geometry of an INS is optimised for maximising Conduction Velocity (CV) of Action Potential (AP), our theory provides an alternative viewpoint that myelin geometry of an INS is optimised for maximizing representability of the stimuli a fibre is meant to carry. Subsequently, we show that this new viewpoint could explain hitherto unexplained experimentally observed phenomena such as, shortening of INS length during demyelination and remyelination, and non-uniform distribution of INS in the central nervous system fibres and associated changes in diameter of nodes of ranvier along an axon. Finally, our theory indicates that a compensatory action could take place during demyelination up to a certain number of loss of myelin turns to preserve the neural signal representability by simultaneous linear scaling of the length of an INS and the inner radius of the fibre.

Unraveling the pathogenesis of novel ANKRD1 missense mutation causing familial dilated cardiomyopathy using human-induced pluripotent stem cells derived cardiomyocytes

Abstract Introduction Familial dilated cardiomyopathy(f-DCM) can be caused by mutations in 30 different genes encoding sarcomeric, cytoskeletal, mechanotransducers and transcription factors. One of the genes ANKRD1 encode Cardiac ankyrin repeat protein (CARP) which is involved in the mechanosensory unit located on the I-band of the sarcomere. Here we demonstrate a novel mutation in ANKRD1 gene causing f-DCM, and the usage of human-induced pluripotent(hiPSC) technology unraveling the pathogenesis of the disease. Purpose of the study: 1) Establishing patient specific hiPSC-derived cardiomyocytes from a family harboring a mutation in ANKRD1 gene causing f-DCM; 2) Phenotypical assessment of the morphological and ultrastructural properties of the diseased cells upon CARP activation; 3) Functional assessment of the 3 component of excitation-contraction coupling at the single-cell and tissue level. Methods and Results Patient-specific hiPSC were generated from a family harboring missense mutation in the ANKRD1 gene, with a substitution of the amino acid arginine to cysteine at position 182 of the Cardiac ankyrin repeat protein (CARP). ANKRD1-mut hiPSC were differentiated into cardiomyocytes and later matured using hormonal treatment. Morphological assessment using immunofluorescence(IF) techniques revealed that ANKRD1-mut hiPSC-CMs demonstrate an attenuated response to hypertrophy (upon Angiotensin-2 and Phenylephrine treatment). In addition ANKRD1-mut hiPSC-CMs displayed a higher cellular death rate upon increasing substrate stiffness and starvation. Electrophysiological assessment of the ANKRD1-mut cardiac tissues exhibit no alternations in action potential durations and conduction velocities while assessment of calcium transients demonstrated slower kinetics. In addition forces were quantified at the single-cell and tissue level , and demonstrated reduced active tension values and abnormal post-extrasystolic potentiation, while only single-cell experiments have demonstrated decreased passive tensions. These phenotypical alternations might be attributed to decreased nuclear translocation of CARP upon phenylephrine treatment as detected in IF experiments. Conclusion Novel mutation in ANKRD1 were found and validated to be causing f-DCM, by revealing phenotypical alternation using hiPSC-CM technology. Increased cellular death rate and impaired nuclear translocation of CARP might be the underlying causes of the morphological and contractile abnormalities detected in-vitro, leading to systolic dysfunction in the affected family.

The effect of polyneuropathy severity on nerve conduction and pain syndrome in patients with type 2 diabetes

Background. The article examines the relationship between nerve conduction indicators and polyneuropathy severity in patients with type 2 diabetes. The influence of polyneuropathy severity on nerve conduction was studied, as well as the effect of insulin therapy on these indicators. Objective: to determine the influence of polyneuropathy severity and the need for additional insulin administration in patients with type 2 diabetes on nerve conduction indicators and the development of pain syndrome. Materials and methods. Eighty patients with type 2 diabetes were examined, 49 men and 31 women. All of them underwent general clinical and biochemical laboratory tests to evaluate the hematopoietic system, li-ver, kidneys, fat and carbohydrate metabolism. The need for insulin therapy was assessed by the C-peptide level. To verify the diagnosis of diabetic polyneuropathy, complaints, clinical and instrumental examination data were evaluated. The main indicators of nerve conduction were taken into account when determining polyneuritis disorders, namely: рeroneal motor nerve conduction velocity, sensory nerve action potential of the sural nerve, sensory nerve conduction velocity of the sural nerve. Results. A dependence of nerve conduction on polyneuropathy severity was revealed, рeroneal motor nerve conduction velocity was the lowest in the group with severe polyneuropathy. A correlation was also found between the levels of sensory indicators (sensory nerve action potential and sensory nerve conduction velocity) and polyneuropathy severity, nerve conduction velocity decreases with an increase in the latter. The influence of polyneuropathy severity on the painful or painless form has been found. Among patients with severe polyneuropathy, the painful form was observed more often. No relationship was found between the need for insulin therapy and the painful or painless form of polyneuropathy. Conclusions. Indicators of nerve conduction depend on polyneuropathy severity. The presence and severity of pain syndrome directly depends on polyneuropathy severity. The need for additional insulin administration affects sensory indicators but has no effect on the development of the painful form of polyneuropathy.

Yüzme Egzersizinin Siyatik Sinir Hasarı Sonrasında Elektrofizyolojik Parametreler Üzerindeki İyileştirici Etkisi

The sciatic nerve damage can cause symptoms such as loss of muscle strength and pain as a result of trauma to the nerve due to pressure, stretching or cutting, as well as lifelong disability. Despite the increasing knowledge about sciatic nerve regeneration mechanisms, full functional recovery is still insufficient. It is well known that exercise improves overall health. The current study aimed to reveal the therapeutic effects of swimming exercises using electrophysiological methods in rats with experimental sciatic nerve injury. Eighteen male Wistar Albino rats were used in this study. The subjects were randomly divided into three groups (n=6): 1-Control (C), 2-Intact Exercise (IntE), 3-Operated Exercise (OpE) groups. Sciatic nerve injury was performed by inducing experimental damage to the left hind extremity sciatic nerve of rats. Swimming exercise was applied for 45 minutes a day, five days a week (25°C) for four weeks. The level of regeneration was evaluated by taking motor function test-sciatic function index and EMG recording performed at the beginning of the experiment (day 0), after nerve damage (day 3), and at the end of the experiment (day 35). It was determined that sciatic function index, amplitude of motor and sensory nerves, peak-peak amplitude, percentage of compound muscle action potential, motor and sensory nerve conduction velocities, which decreased after sciatic nerve injury, increased with swimming exercise (p

Chronic diastolic stretch unmasks conduction defects in an in vitro model of arrhythmogenic cardiomyopathy.

We seek to elucidate the precise nature of mechanical loading that precipitates conduction deficits in a concealed-phase model of arrhythmogenic cardiomyopathy (ACM). ACM is a progressive disorder often resulting from mutations in desmosomal proteins. Exercise has been shown to worsen disease progression and unmask arrhythmia vulnerability, yet the underlying pathomechanisms may depend on the type and intensity of exercise. Because exercise causes myriad changes to multiple inter-dependent hemodynamic parameters, it is difficult to isolate its effects to specific changes in mechanical load. Here, we use engineered heart tissues (EHTs) with iPSC-derived cardiomyocytes expressing R451G desmoplakin, an ACM-linked mutation, which results in a functionally null model of desmoplakin (DSP). We also use a novel bioreactor to independently perturb tissue strain at different time points during the cardiac cycle. We culture EHTs under three strain regimes: normal physiological shortening; increased diastolic stretch, simulating high preload; and isometric culture, simulating high afterload. DSPR451G EHTs that have been cultured isometrically undergo adaptation, with no change in action potential parameters, conduction velocity, or contractile function, a phenotype confirmed by global proteomic analysis. However, when DSPR451G EHTs are subjected to increased diastolic stretch, they exhibit concomitant reductions in conduction velocity and the expression of connexin-43. These effects are rescued by inhibition of both lysosome activity and ERK signaling. Our results indicate that the response of DSPR451G EHTs to mechanical stimuli depends on the strain and the timing of the applied stimulus, with increased diastolic stretch unmasking conduction deficits in a concealed-phase model of ACM.

Trunk extensor muscle endurance and its relationship to action potential conduction velocity and spectral parameters estimated using high-density electromyography

Trunk extensor muscle fatigue typically manifests as a decline in spectral content of surface electromyography. However, previous research on the relationship of this decline with trunk extensor muscle endurance have shown inconsistent results. The decline of spectral content mainly reflects the decrease in average motor unit action potential conduction velocity (CV). We evaluated whether the rate of change in CV, as well as two approaches employing the change in spectral content, are related to trunk extensor muscle endurance. Fourteen healthy male participants without a low-back pain history performed a non-strictly controlled static forward trunk bending trial until exhaustion while standing. For 13 participants, physiologically plausible CV estimates were obtained from high-density surface electromyography bilaterally from T6 to L5. Laterally between L1 and L2, the linear rate of CV change was strongly correlated to endurance time (R2 = 0.79), whereas analyses involving the linear rate of change in spectral measures showed a lower (R2 = 0.38) or no correlation. For medial electrode locations, estimating CV and its relationship with endurance time was less successful, while the linear rate of change in spectral measures correlated moderately to endurance time (R2 = 0.44; R2 = 0.56). This study provides guidance on monitoring trunk extensor muscle fatigue development using electromyography.

Nerve conduction studies through landmark based recording and effects of hand length

As per existing guidelines, the distance between stimulator and recording electrodes in nerve conduction studies (NCS) should be the same (fixed) in all the subjects, i.e., it should not be based on anatomical landmarks. However, there are no studies comparing fixed distance recordings with landmark based NCS. We postulated that hand length can influence the NCS parameters in fixed distance recordings and this can be nullified using landmark based recordings. To test this theory, we performed NCS in 48 normal subjects as per standard guidelines (standard protocol) and then compared it to NCS with ulnar styloid as the landmark (modified protocol). NCS were performed on median and ulnar nerves of the right upper limb. Three motor NCS parameters including distal latency, compound muscle action potential (CMAP) amplitudes and nerve conduction velocities were measured. Sensory nerve action potential (SNAP) amplitudes and conduction velocities were the two sensory parameters measured. On analysis, ulnar motor conduction velocity was the only parameter affected by hand length in both standard and modified protocols. Modified protocol did not have any additional advantage to the standard protocol advised by NDTF. We conclude that the NDTF guidelines are therefore reasonable when considering the effects of hand length. Possible reasons for this result including anatomical and anthropometric explanations are discussed.

A Novel Quantitative Electrocardiography Strategy Reveals the Electroinhibitory Effect of Tamoxifen on the Mouse Heart.

Tamoxifen, a selective estrogen receptor modulator, was initially used to treat cancer in women and more recently to induce conditional gene editing in rodent hearts. However, little is known about the baseline biological effects of tamoxifen on the myocardium. In order to clarify the short-term effects of tamoxifen on cardiac electrophysiology of myocardium, we applied a single-chest-lead quantitative method and analyzed the short-term electrocardiographic phenotypes induced by tamoxifen in the heart of adult female mice. We found that tamoxifen prolonged the PP interval and caused a decreased heartbeat, and further induced atrioventricular block by gradually prolonging the PR interval. Further correlation analysis suggested that tamoxifen had a synergistic and dose-independent inhibition on the time course of the PP interval and PR interval. This prolongation of the critical time course may represent a tamoxifen-specific ECG excitatory-inhibitory mechanism, leading to a reduction in the number of supraventricular action potentials and thus bradycardia. Segmental reconstructions showed that tamoxifen induced a decrease in the conduction velocity of action potentials throughout the atria and parts of the ventricles, resulting in a flattening of the P wave and R wave. In addition, we detected the previously reported prolongation of the QT interval, which may be due to a prolonged duration of the ventricular repolarizing T wave rather than the depolarizing QRS complex. Our study highlights that tamoxifen can produce patterning alternations in the cardiac conduction system, including the formation of inhibitory electrical signals with reduced conduction velocity, implying its involvement in the regulation of myocardial ion transport and the mediation of arrhythmias. A Novel Quantitative Electrocardiography Strategy Reveals the Electroinhibitory Effect of Tamoxifen on the Mouse Heart（Figure 9）. A working model of tamoxifen producing acute electrical disturbances in the myocardium. SN, sinus node; AVN, atrioventricular node; RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle.

The interactive effects of age and sex on the neuro-cardiovascular responses during fatiguing rhythmic handgrip exercise.

The impact of age on exercise pressor responses is equivocal, likely because of sex-specific neuro-cardiovascular changes with age. However, assessments of the interactive effects of age and sex on muscle sympathetic nerve activity (MSNA) responses to exercise are lacking. We tested the hypothesis that older females would exhibit exaggerated increases in blood pressure (BP) and MSNA discharge patterns during handgrip exercise compared with similarly aged males and young adults. Twenty-five young (25 (2) years; mean (SD)) males (YM; n=12) and females (YF; n=13) and 23 older (71 (5) years) males (OM; n=11) and females (OF; n=12) underwent assessments of BP, total peripheral resistance (TPR; Modelflow) and MSNA action potential (AP) discharge patterns (microneurography) during incremental rhythmic handgrip exercise and post-exercise circulatory occlusion (PECO). OM demonstrated larger ∆BP and ∆TPR from baseline than YM (both P < 0.001) despite smaller increases in ∆APs/burst (OM: 0.4 (3) vs. YM: 5 (3) spikes/burst, P < 0.001) and ∆AP clusters/burst (OM: 0.1 (1) vs. YM: 1.8 (1) clusters/burst, P < 0.001) during exercise. Testosterone was lower in OM than YM (P < 0.001) and was inversely related to ∆BP but positively related to ∆AP clusters/burst in males (both P=0.03). Conversely, YF and OF demonstrated similar ∆BP and ∆AP discharge during exercise (range: P=0.75-0.96). Age and sex did not impact haemodynamics or AP discharge during PECO (range: P=0.08-0.94). Altogether, age-related changes in neuro-cardiovascular reactivity exist in males but not females during fatiguing exercise and seem to be related to testosterone. This sex-specific impact of age underscores the importance of considering biological sex when assessing age-related changes in neuro-cardiovascular control during exercise. KEY POINTS: Older males have the largest increase in blood pressure despite having the smallest increases in sympathetic vasomotor outflow during rhythmic handgrip exercise. Young males demonstrate greater increases in sympathetic action potential (AP) discharge compared with young females during rhythmic handgrip exercise. Older adults (regardless of sex) demonstrate smaller increases in muscle sympathetic nerve activity (MSNA) burst amplitude and total AP clusters compared with young adults during exercise, as well as smaller increases in integrated MSNA burst frequency, incidence and total MSNA activity during post-exercise circulatory occlusion (i.e. independent effect of age). Males, but not females (regardless of age), reflexively modify AP conduction velocity during exercise. Our results indicate that age and sex independently and interactively impact the neural and cardiovascular homeostatic adjustments to fatiguing small muscle mass exercise.

PO-01-180 MECHANISMS OF PULMONARY ARTERIAL HYPERTENSION-INDUCED ATRIAL FIBRILLATION IN THE RIGHT HEART: INSIGHTS FROM MULTI-SCALE MODELS OF THE HUMAN ATRIA

Pulmonary arterial hypertension (PAH) is one of the common conditions primarily affecting the right heart and promoting atrial fibrillation (AF), but the mechanisms are poorly understood. This study aimed to use multi-scale atrial models to investigate mechanisms by which right atrial (RA) remodeling facilitates and perpetuates atrial arrhythmias. We have developed single-cell-to-tissue-level computer models to mimic control and disease conditions by incorporating the most recent experimental data on PAH-induced electrical and structural remodeling (Hiram et al., JACC, 2019). The effects of PAH-induced remodeling in both RA and left atria (LA) on action potential duration (APD), calcium transient (CaT), conduction velocity (CV), and dynamics of re-entrant excitation waves were assessed using the multi-scale computer models. Our computer simulation results suggested that at the single cell level, although PAH-induced remodeling prolonged action potential (ΔAPD: 49.6 ms in the RA vs. 41.6 ms in the LA) and increased calcium transient (ΔCaT: 7.5e-2 μM in the RA vs. 0.9e-3 μM in the LA), heterogeneous remodeling increased susceptibility to afterdepolarizations only in the RA (Fig. A). At the tissue level, dramatically reduced CV (ΔCV: -0.5 m/s in the RA vs. -0.05 m/s in the LA) abbreviated wavelength inthe RA but not inthe LA. In addition, afterdepolarizations in the RA increased repolarization dispersion and promoted unidirectional conduction block (Fig B). Finally, the upregulated fibrosis increased the chance of breakdown of excitation waves and sustained reentries in in the RA (Fig C). These results demonstrated that PAH-induced AF is mainly in RA not LA, due to a higher degree of cardiac remodeling. RA remodeling increases arrhythmias risk due to elevated susceptibility to afterdepolarizations, reduced wavelength, increased repolarization heterogeneity and upregulation of fibrosis, which together facilitate initiation and maintenance of re-entrant circuits in the right heart.

Feedback contributions to excitation-contraction coupling in native functioning striated muscle.

Skeletal and cardiac muscle excitation-contraction coupling commences with Nav1.4/Nav1.5-mediated, surface and transverse (T-) tubular, action potential generation. This initiates feedforward, allosteric or Ca2+-mediated, T-sarcoplasmic reticular (SR) junctional, voltage sensor-Cav1.1/Cav1.2 and ryanodine receptor-RyR1/RyR2 interaction. We review recent structural, physiological and translational studies on possible feedback actions of the resulting SR Ca2+ release on Nav1.4/Nav1.5 function in native muscle. Finite-element modelling predicted potentially regulatory T-SR junctional [Ca2+]TSR domains. Nav1.4/Nav1.5, III-IV linker and C-terminal domain structures included Ca2+ and/or calmodulin-binding sites whose mutations corresponded to specific clinical conditions. Loose-patch-clamped native murine skeletal muscle fibres and cardiomyocytes showed reduced Na+ currents (INa) following SR Ca2+ release induced by the Epac and direct RyR1/RyR2 activators, 8-(4-chlorophenylthio)adenosine-3',5'-cyclic monophosphate and caffeine, abrogated by the RyR inhibitor dantrolene. Conversely, dantrolene and the Ca2+-ATPase inhibitor cyclopiazonic acid increased INa. Experimental, catecholaminergic polymorphic ventricular tachycardic RyR2-P2328S and metabolically deficient Pgc1β-/- cardiomyocytes also showed reduced INa accompanying [Ca2+]i abnormalities rescued by dantrolene- and flecainide-mediated RyR block. Finally, hydroxychloroquine challenge implicated action potential (AP) prolongation in slowing AP conduction through modifying Ca2+ transients. The corresponding tissue/organ preparations each showed pro-arrhythmic, slowed AP upstrokes and conduction velocities. We finally extend discussion of possible Ca2+-mediated effects to further, Ca2+, K+ and Cl-, channel types. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Metabolic implications of axonal demyelination and its consequences for synchronized network activity: An in silico and in vitro study.

Myelination enhances the conduction velocity of action potentials (AP) and increases energy efficiency. Thick myelin sheaths are typically found on large-distance axonal connections or in fast-spiking interneurons, which are critical for synchronizing neuronal networks during gamma-band oscillations. Loss of myelin sheath is associated with multiple alterations in axonal architecture leading to impaired AP propagation. While numerous studies are devoted to the effects of demyelination on conduction velocity, the metabolic effects and the consequences for network synchronization have not been investigated. Here we present a unifying computational model for electrophysiology and metabolism of the myelinated axon. The computational model suggested that demyelination not only decreases the AP speed but AP propagation in demyelinated axons requires compensatory processes like mitochondrial mass increase and a switch from saltatory to continuous propagation to rescue axon functionality at the cost of reduced AP propagation speed and increased energy expenditure. Indeed, these predictions were proven to be true in a culture model of demyelination where the pharmacologically-induced loss of myelin was associated with increased oxygen consumption rates, and a significant broadening of bandwidth as well as a decrease in the power of gamma oscillations.

Small Molecule Positive Modulator of Hepatocyte Growth Factor (HGF)/MET, ATH-1105, Improves Function and Reduces Disease Biomarkers in a TDP-43 Mouse Model of Amyotrophic Lateral Sclerosis (P8-8.007)

<h3>Objective:</h3> Evaluate the preclinical efficacy of the small molecule positive modulator of hepatocyte growth factor (HGF)/MET, ATH-1105, in a mouse model of amyotrophic lateral sclerosis (ALS). <h3>Background:</h3> Activation of the MET receptor by HGF promotes neuroprotective, neurotrophic, and anti-inflammatory mechanisms. Small molecule positive modulators of HGF/MET, including ATH-1105, have been developed to explore the therapeutic potential of this target. ALS is characterized by progressive motor neuron degeneration and demyelination, accompanied by systemic inflammation and pathological aggregation of TAR DNA-binding protein 43 (TDP-43) in 97% of patients. We hypothesized that treatment with ATH-1105 would be beneficial in a TDP-43 mouse model of ALS. <h3>Design/Methods:</h3> ATH-1105 at 10 or 20 mg/kg was orally administered daily to male Prp-TDP43_A315T mice (n=10/group) for two months. At baseline and after one and two months of treatment, we conducted a battery of motor behavior tests, and assessed sciatic nerve health by compound muscle action potential (CMAP) and nerve conduction velocity (NCV) measurements. Plasma biomarkers of inflammation (IL-6, TNF-α) and neurodegeneration (neurofilament light chain [NfL]) were interrogated after one and two months of treatment. Sciatic nerves were stained for quantification of axonal and myelin parameters as well as phospho-TDP-43 aggregation at study termination. <h3>Results:</h3> The deterioration of motor function in TDP-43 animals was significantly mitigated in a dose-dependent manner after treatment with ATH-1105, and significant functional improvement of sciatic nerve conduction was observed. Additionally, plasma levels of all biomarkers assessed were significantly decreased, indicating reduced systemic inflammation and neurodegeneration in treated TDP-43 mice. Sciatic nerve histology revealed a protection of motor axon numbers and myelination, as well as a reduction in axonal phospho-TDP-43 aggregation by ATH-1105. <h3>Conclusions:</h3> ATH-1105 was found to be protective across a multitude of functional and structural measures of ALS disease progression. These findings support the continued development of this small molecule positive modulator of HGF/MET for ALS. <b>Disclosure:</b> Mrs. Kleist has received personal compensation for serving as an employee of Athira Pharma. Mrs. Kleist has received personal compensation for serving as an employee of Alpine Immune Sciences. Mrs. Kleist has stock in Athira Pharma. Mrs. Kleist has stock in Alpine Immune Sciences. Dr. Berthiaume has received personal compensation for serving as an employee of Athira Pharma. Dr. Berthiaume has stock in Athira Pharma. An immediate family member of Dr. Berthiaume has stock in Athira Pharma. Dr. Johnston has received personal compensation for serving as an employee of Athira Pharma, Inc. Dr. Johnston has stock in Athira Pharma, Inc. An immediate family member of Dr. Johnston has stock in Athira Pharma, Inc. Dr. Johnston has received intellectual property interests from a discovery or technology relating to health care. Dr. Reda has received personal compensation for serving as an employee of Athira Pharma, Inc. . Dr. Reda has stock in Athira Pharma, Inc. . Dr. Moebius has received personal compensation in the range of $100,000-$499,999 for serving as an officer or member of the Board of Directors for Athira Pharma, Inc.. Dr. Moebius has stock in Athira Pharma, Inc.. Dr. Church has received personal compensation for serving as an employee of Athira Pharma. Dr. Church has stock in Athira Pharma. Dr. Church has received intellectual property interests from a discovery or technology relating to health care.

The effects of melatonin in the treatment of acute brachial plexus compression injury in rats.

Brachial plexus injury (BPI) is one of the most destructive peripheral nerve injuries and there is still a lack of effective treatment. This study was conducted to evaluate the effects of melatonin in the treatment of acute brachial plexus compression injury in rats using histopathological, histomorphometric, immunohistochemical and electrophysiological methods. Forty-eight adult male Sprague Dawley rats were randomly allocated into three groups: sham, melatonin and vehicle groups. The brachial plexus compression injury model was performed by a vascular clamp. Melatonin group received intraperitoneal injection of melatonin at doses of 10 mg/kg for 21 days after crush injury. The conduction velocity and amplitude of compound muscle action potential (CAMP) in the regenerated nerve, and nerve histomorphometry, as well as levels of myelin protein zero (P0) protein of the crush region were assessed. Compared with the vehicle group, the melatonin group which reported significant increased CMAP conduction velocity and amplitude also showed thicker myelin sheath and lower levels of P0 protein. Our results suggest that melatonin effectively promotes nerve regeneration and improves the function of damaged nerves. Melatonin treatment is a promising strategy for the treatment of acute brachial plexus compression injury.

Comparative analysis of the cardiomyocyte differentiation potential of induced pluripotent stem cells reprogrammed from human atrial or ventricular fibroblasts.

Background: We had shown that cardiomyocytes (CMs) were more efficiently differentiated from human induced pluripotent stem cells (hiPSCs) when the hiPSCs were reprogrammed from cardiac fibroblasts rather than dermal fibroblasts or blood mononuclear cells. Here, we continued to investigate the relationship between somatic-cell lineage and hiPSC-CM production by comparing the yield and functional properties of CMs differentiated from iPSCs reprogrammed from human atrial or ventricular cardiac fibroblasts (AiPSC or ViPSC, respectively). Methods: Atrial and ventricular heart tissues were obtained from the same patient, reprogrammed into AiPSCs or ViPSCs, and then differentiated into CMs (AiPSC-CMs or ViPSC-CMs, respectively) via established protocols. Results: The time-course of expression for pluripotency genes (OCT4, NANOG, and SOX2), the early mesodermal marker Brachyury, the cardiac mesodermal markers MESP1 and Gata4, and the cardiovascular progenitor-cell transcription factor NKX2.5 were broadly similar in AiPSC-CMs and ViPSC-CMs during the differentiation protocol. Flow-cytometry analyses of cardiac troponin T expression also indicated that purity of the two differentiated hiPSC-CM populations (AiPSC-CMs: 88.23% ± 4.69%, ViPSC-CMs: 90.25% ± 4.99%) was equivalent. While the field-potential durations were significantly longer in ViPSC-CMs than in AiPSC-CMs, measurements of action potential duration, beat period, spike amplitude, conduction velocity, and peak calcium-transient amplitude did not differ significantly between the two hiPSC-CM populations. Yet, our cardiac-origin iPSC-CM showed higher ADP and conduction velocity than previously reported iPSC-CM derived from non-cardiac tissues. Transcriptomic data comparing iPSC and iPSC-CMs showed similar gene expression profiles between AiPSC-CMs and ViPSC-CMs with significant differences when compared to iPSC-CM derived from other tissues. This analysis also pointed to several genes involved in electrophysiology processes responsible for the physiological differences observed between cardiac and non-cardiac-derived cardiomyocytes. Conclusion: AiPSC and ViPSC were differentiated into CMs with equal efficiency. Detected differences in electrophysiological properties, calcium handling activity, and transcription profiles between cardiac and non-cardiac derived cardiomyocytes demonstrated that 1) tissue of origin matters to generate a better-featured iPSC-CMs, 2) the sublocation within the cardiac tissue has marginal effects on the differentiation process.