Assessing drug safety by identifying the axis of arrhythmia in cardiomyocyte electrophysiology

Many classes of drugs can induce fatal cardiac arrhythmias by disrupting the electrophysiology of cardiomyocytes. Safety guidelines thus require all new drugs to be assessed for pro-arrhythmic risk prior to conducting human trials. The standard safety protocols primarily focus on drug blockade of the delayed-rectifier potassium current (IKr). Yet the risk is better assessed using four key ion currents (IKr, ICaL, INaL, IKs). We simulated 100,000 phenotypically diverse cardiomyocytes to identify the underlying relationship between the blockade of those currents and the emergence of ectopic beats in the action potential. We call that relationship the axis of arrhythmia. It serves as a yardstick for quantifying the arrhythmogenic risk of any drug from its profile of multi-channel block alone. We tested it on 109 drugs and found that it predicted the clinical risk labels with an accuracy of 88.1-90.8%. Pharmacologists can use our method to assess the safety of novel drugs without resorting to animal testing or unwieldy computer simulations.

Neutrophils as major drivers of increased atherosclerosis in a murine model of chronic colitis

Background

Recent findings showed a higher risk of premature atherosclerosis and cardiovascular events in patients with inflammatory bowel disease (IBD) especially during acute flare of the chronic disease. The underlying mechanisms remain to be defined since traditional risk factors such as hypercholesterinemia are not present in these patients.

Purpose

The present study aimed to unravel the underlying pathomechanisms of enhanced atherogenesis and -progression in a murine model of colitis.

Methods

Chronic colitis was induced in male Apolipoprotein E-deficient mice (Apoe−/−) using dextran sodium sulphate (DSS) in drinking water for 2,3 or 5 cycles, while the control group received regular drinking water. Each cycle consisted of 6 days DSS application and two weeks of recovery. Aortic atherosclerotic plaque burden was determined by en face Oil Red O staining and immune cell subsets were analysed by flow cytometry in the circulation, the bone marrow, and the aorta. Neutrophil depletion was performed via i.p injection of a Ly6G-depleting antibody or respective isotype control. Bone marrow-derived neutrophils were further analysed by transcriptome analysis.

Results

Similar to IBD patients, mice with chronic colitis exhibited an increased aortic plaque burden after 15 weeks of treatment despite the absence of classical risk factors. Over time, both circulating and aortic neutrophils showed an oscillatory detection pattern with the first significant increase after the 2nd DSS administration whereby the second increase after the 3rd DSS cycle was even stronger. Also, pro-inflammatory cytokines were elevated in the plasma and specifically G-CSF showed the same oscillatory pattern with increased plasma level already after the 2nd DSS administration and an even stronger increase after the 3rd thereby pointing towards alterations in bone marrow hematopoiesis. In line, flow cytometric analyses confirmed a greater rise of hematopoietic stem and even myeloid progenitor cells compared with the 2nd DSS application in IBD mice after 3rd treatment. scRNA-Seq analysis of progenitor cells revealed changes in cell differentiation towards neutrophils and upregulation of proinflammatory genes in isolated neutrophils of DSS-treated mice. These neutrophils showed also a more adhesive phenotype revealed by increased mRNA expression of Glg1 and Selplg. Accordingly, also Sele mRNA was increased in the aorta. The reduction of circulating neutrophils by an anti-Ly6G antibody during the acute phases of colitis reduced the aortic plaque burden compared to isotype treaded mice.

Conclusion

The current findings suggest detrimental effects of chronic colitis on atherogenesis and -progression in Apoe−/− mice via increased differentiation of myeloid cells into neutrophils and the promotion of a more adhesive and proinflammatory phenotype. These modified neutrophils may act as initiators of atherogenesis by promoting the invasion of immune cells into the aortic wall.

Funding Acknowledgement

Type of funding sources: None.

Pathophysiological metabolic changes associated with disease modify the proarrhythmic risk profile of drugs with potential to prolong repolarisation

BACKGROUND AND PURPOSE

Hydroxychloroquine, chloroquine and azithromycin are three drugs that were proposed to treat COVID-19. While concern already existed around their proarrhythmic potential there is little data regarding how altered physiological states encountered in patients such as febrile state, electrolyte imbalances or acidosis might change their risk profiles.

EXPERIMENTAL APPROACH

Potency of hERG block was measured using high-throughput electrophysiology in the presence of variable environmental factors. These potencies informed simulations to predict population risk profiles. Effects on cardiac repolarisation were verified in human induced pluripotent stem cell-derived cardiomyocytes from multiple individuals.

KEY RESULTS

Chloroquine and hydroxychloroquine blocked hERG with IC₅₀ of 1.47±0.07 μM and 3.78±0.17 μM respectively, indicating proarrhythmic risk at concentrations effective against SARS-CoV-2 in vitro. Hypokalaemia and hypermagnesemia increased potency of chloroquine and hydroxychloroquine, indicating increased proarrhythmic risk. Acidosis significantly reduced potency of all drugs, whereas increased temperature decreased potency of chloroquine and hydroxychloroquine against hERG but increased potency for azithromycin. In silico simulations demonstrated that proarrhythmic risk was increased by female sex, hypokalaemia and heart failure, and identified specific genetic backgrounds associated with emergence of arrhythmia.

CONCLUSION AND IMPLICATIONS

Our study demonstrates how proarrhythmic risk can be exacerbated by metabolic changes and pre-existing disease. More broadly, the study acts as a blueprint for how high-throughput in vitro screening, combined with in silico simulations can help guide both preclinical screening and clinical management of patients in relation to drugs with potential to prolong repolarisation.

POS0318 CLINICAL PHENOTYPE IN SCLERODERMA PATIENTS WITH ANTI-TOPOISOMERASE I POSITIVITY AND LIMITED CUTANEOUS FORM: DATA FROM THE EUSTAR DATABASE

Background:

There is renewed interest in the role of autoantibodies to predict outcomes in systemic sclerosis (SSc). Among the newly identified subsets, patients with limited cutaneous form (lcSSc) but anti-topoisomerase I antibodies (Scl70) positivity draw particular attention, and namely, assessing the risk of developing interstitial lung disease (ILD) —the main cause of death in SSc—to improve the management of Scl70-lcSSc patients.

Objectives:

We aimed to characterize patients with Scl70-lcSSc in the large multicenter European Scleroderma Trial and Research (EUSTAR) cohort.

Methods:

The EUSTAR database was locked in July 2019. We included all patients fulfilling 1980 ACR and/or 2013 ACR/EULAR criteria for SSc, with disease duration at database entry ≤3 yrs and known and stable skin form during the first 3 yrs. Patients with lcSSc were compared: Scl70-lcSSc (target group) vs. ACA-lcSSc and ANA-lcSSc (Step 1); and Scl70-lcSSc vs. Scl70-dcSSc (Step 2). In the ANA subgroup we included ANA+ patients with negative SSc-specific antibodies (Scl70, ACA, RNA polymerase III). In each step, we performed 5 generalized mixed models (GMM) for the risk of the new onset of ILD (defined by imaging), primary myocardial involvement (PMI), pulmonary hypertension (PH), “any severe” (ILD+PMI+PH+scleroderma renal crisis) and all-cause-mortality. An additional GMM assessed the risk of forced vital capacity (FVC) decline ≥10% vs. FVC value at ILD onset. Each GMM was adjusted for age, sex and confounders.

Results:

Overall, 1285 SSc patients were included: 1068 (83%) females, 860 (67%) lcSSc and 425 (33%) dcSSc. Among patients with lcSSc, 537 (62%) had ACA+, 194 (23%) Scl70+ and 129 (15%) ANA+; 425 patients had dcSSc and Scl70+. Median follow-up was similar in all 4 groups: 7.2 to 8.1 yrs.

Step 1: At baseline, Scl70-lcSSc patients had significantly shorter time from Raynaud’s phenomenon (RP) to SSc onset, higher mRSS (5.8±4.8 vs. 4.3±4, p=0.001), and higher rate of articular and muscular involvement vs. ACA-lcSSc patients (Figure 1). No differences were found between Scl70-lcSSc and ANA-lcSSc comparing the aforementioned variables. ILD was more frequent in Scl70-lcSSc (46%) than in ACA-lcSSc (10%) and ANA-lcSSc (25%), as well as restrictive lung disease. GMM showed that Scl70-lcSSc carries a higher risk of ILD than both ACA-lcSSc (HR 4.55, 95%CI 3.23-6.67) and ANA-lcSSc (HR 2.17, 95%CI 1.39-3.45), with a rate of FVC decline ≥10% over time similar to the other limited forms. In Scl70-lcSSc patients the risk of “any severe” organ involvement was similar to ANA-lcSSc and higher than ACA-lcSSc (HR 1.89, 95%CI 1.40-2.50). In particular, Scl70-lcSSc shows a risk of PMI similar to ANA-lcSSc and lower than ACA-lcSSc; no differences regarding PH risk. The mortality risk in patients with Scl70-lcSSc was similar to the other limited forms’.

Step 2: At baseline, time from RP to SSc onset was longer in patients with Scl70-lcSSc, with less frequent joint synovitis and tendon friction rubs vs. patients with Scl70-dcSSc. Conversely, the frequency of muscular, cardiac and pulmonary involvement was similar. The risk of ILD in Scl70-lcSSc patients was similar to Scl70-dcSSc, with a lower risk of FVC decline ≥10% over time. The risk of “any severe” involvement (HR 0.66, 95%CI 0.49-0.83), PMI and PH was lower and the mortality risk tended to be lower (HR 0.57, 95%CI 0.33-1.01, p=0.053) vs. Scl70-dcSSc.

Conclusion:

In our large multicenter EUSTAR cohort one quarter of lcSSc patients were Scl70+. We show a ranking for major organ involvement within lcSSc: Scl70 the most severe, ANA+ intermediate and ACA the milder form. Scl70-dcSSc patients present the most severe phenotype, and Scl70 positivity, more than the cutaneous subset, is strongly predictive of ILD, whereas other variables may influence progression. These results may provide new insight to improve the management of Scl70-lcSSc patients.

Disclosure of Interests:

Elisabetta Zanatta: None declared, Dörte Huscher: None declared, Paolo Airò: None declared, Alexandra Balbir-Gurman: None declared, Elise Siegert: None declared, Augusta Ortolan: None declared, Marco Matucci-Cerinic: None declared, Franco Cozzi: None declared, Gabriela Riemekasten: None declared, Anna-Maria Hoffmann-Vold: None declared, Oliver Distler Speakers bureau: has/had consultancy relationship and/or has received research funding in the area of potential treatments for systemic sclerosis and its complications from (last three years): Abbvie, Acceleron Pharma, Amgen, AnaMar, Arxx Therapeutics, Baecon Discovery, Blade Therapeutics, Bayer, Boehringer Ingelheim, ChemomAb, Corbus Pharmaceuticals, CSL Behring, Galapagos NV, Glenmark Pharmaceuticals, GSK, Horizon (Curzion) Pharmaceuticals, Inventiva, iQvia, Italfarmaco, iQone, Kymera Therapeutics, Lilly, Medac, Medscape, Mitsubishi Tanabe Pharma, MSD, Novartis, Pfizer, Roche, Sanofi, Serodapharm, Topadur, Target Bioscience and UCB. Patent issued “mir-29 for the treatment of systemic sclerosis” (US8247389, EP2331143)., Consultant of: has/had consultancy relationship and/or has received research funding in the area of potential treatments for systemic sclerosis and its complications from (last three years): Abbvie, Acceleron Pharma, Amgen, AnaMar, Arxx Therapeutics, Baecon Discovery, Blade Therapeutics, Bayer, Boehringer Ingelheim, ChemomAb, Corbus Pharmaceuticals, CSL Behring, Galapagos NV, Glenmark Pharmaceuticals, GSK, Horizon (Curzion) Pharmaceuticals, Inventiva, iQvia, Italfarmaco, iQone, Kymera Therapeutics, Lilly, Medac, Medscape, Mitsubishi Tanabe Pharma, MSD, Novartis, Pfizer, Roche, Sanofi, Serodapharm, Topadur, Target Bioscience and UCB. Patent issued “mir-29 for the treatment of systemic sclerosis” (US8247389, EP2331143)., Grant/research support from: Kymera Therapeutics, Mitsubishi Tanabe, Armando Gabrielli: None declared, Stefan Heitmann: None declared, Nicolas Hunzelmann: None declared, Carlomaurizio Montecucco: None declared, Jadranka Morovic-Vergles: None declared, Camillo Ribi: None declared, Andrea Doria: None declared, Yannick Allanore: None declared

Arrhythmogenic effects of ultra-long and bistable cardiac action potentials

Contemporary accounts of the initiation of cardiac arrhythmias typically rely on after-depolarizations as the trigger for reentrant activity. The after-depolarizations are usually triggered by calcium entry or spontaneous release within the cells of the myocardium or the conduction system. Here we propose an alternative mechanism whereby arrhythmias are triggered autonomously by cardiac cells that fail to repolarize after a normal heartbeat. We investigated the proposal by representing the heart as an excitable medium of FitzHugh-Nagumo cells where a proportion of cells were capable of remaining depolarized indefinitely. As such, those cells exhibit bistable membrane dynamics. We found that heterogeneous media can tolerate a surprisingly large number of bistable cells and still support normal rhythmic activity. Yet there is a critical limit beyond which the medium is persistently arrhythmogenic. Numerical analysis revealed that the critical threshold for arrhythmogenesis depends on both the strength of the coupling between cells and the extent to which the abnormal cells resist repolarization. Moreover, arrhythmogenesis was found to emerge preferentially at tissue boundaries where cells naturally have fewer neighbors to influence their behavior. These findings may explain why atrial fibrillation typically originates from tissue boundaries such as the cuff of the pulmonary vein.

Cardiac fibrillation is a medical condition where normal heart function is compromised as electrical activity becomes disordered. How fibrillation arises spontaneously is not fully understood. It is generally thought to be triggered by premature depolarization of the cardiac action potential in one or more cells. Those premature beats, known as after-depolarizations, subsequently initiate a self-sustaining rotor in the otherwise normal heart tissue. In this study, we propose an alternative mechanism whereby arrhythmias are initiated by cardiac cells that fail to repolarize of their own accord but still operate normally when embedded in functional heart tissue. We find that such cells can act as focal ectopic sources under appropriate conditions of inter-cellular coupling. Moreover, those cells are more prone to initiating arrhythmia when they are located on natural tissue boundaries. This may explain why atrial fibrillation typically originates from the site where the pulmonary vein attaches to the wall of the heart.

Co-expression of calcium and hERG potassium channels reduces the incidence of proarrhythmic events

AIMS

Cardiac electrical activity is extraordinarily robust. However, when it goes wrong it can have fatal consequences. Electrical activity in the heart is controlled by the carefully orchestrated activity of more than a dozen different ion conductances. While there is considerable variability in cardiac ion channel expression levels between individuals, studies in rodents have indicated that there are modules of ion channels whose expression co-vary. The aim of this study was to investigate whether meta-analytic co-expression analysis of large-scale gene expression datasets could identify modules of co-expressed cardiac ion channel genes in human hearts that are of functional importance.

METHODS AND RESULTS

Meta-analysis of 3653 public human RNA-seq datasets identified a strong correlation between expression of CACNA1C (L-type calcium current, ICaL) and KCNH2 (rapid delayed rectifier K+ current, IKr), which was also observed in human adult heart tissue samples. In silico modelling suggested that co-expression of CACNA1C and KCNH2 would limit the variability in action potential duration seen with variations in expression of ion channel genes and reduce susceptibility to early afterdepolarizations, a surrogate marker for proarrhythmia. We also found that levels of KCNH2 and CACNA1C expression are correlated in human-induced pluripotent stem cell-derived cardiac myocytes and the levels of CACNA1C and KCNH2 expression were inversely correlated with the magnitude of changes in repolarization duration following inhibition of IKr.

CONCLUSION

Meta-analytic approaches of multiple independent human gene expression datasets can be used to identify gene modules that are important for regulating heart function. Specifically, we have verified that there is co-expression of CACNA1C and KCNH2 ion channel genes in human heart tissue, and in silico analyses suggest that CACNA1C-KCNH2 co-expression increases the robustness of cardiac electrical activity.

Direction-selective motion discrimination by traveling waves in visual cortex

The majority of neurons in primary visual cortex respond selectively to bars of light that have a specific orientation and move in a specific direction. The spatial and temporal responses of such neurons are non-separable. How neurons accomplish that computational feat without resort to explicit time delays is unknown. We propose a novel neural mechanism whereby visual cortex computes non-separable responses by generating endogenous traveling waves of neural activity that resonate with the space-time signature of the visual stimulus. The spatiotemporal characteristics of the response are defined by the local topology of excitatory and inhibitory lateral connections in the cortex. We simulated the interaction between endogenous traveling waves and the visual stimulus using spatially distributed populations of excitatory and inhibitory neurons with Wilson-Cowan dynamics and inhibitory-surround coupling. Our model reliably detected visual gratings that moved with a given speed and direction provided that we incorporated neural competition to suppress false motion signals in the opposite direction. The findings suggest that endogenous traveling waves in visual cortex can impart direction-selectivity on neural responses without resort to explicit time delays. They also suggest a functional role for motion opponency in eliminating false motion signals.

It is well established that the so-called ‘simple cells’ of the primary visual cortex respond preferentially to oriented bars of light that move across the visual field with a particular speed and direction. The spatiotemporal responses of such neurons are said to be non-separable because they cannot be constructed from independent spatial and temporal neural mechanisms. Contemporary theories of how neurons compute non-separable responses typically rely on finely tuned transmission delays between signals from disparate regions of the visual field. However the existence of such delays is controversial. We propose an alternative neural mechanism for computing non-separable responses that does not require transmission delays. It instead relies on the predisposition of the cortical tissue to spontaneously generate spatiotemporal waves of neural activity that travel with a particular speed and direction. We propose that the endogenous wave activity resonates with the visual stimulus to elicit direction-selective neural responses to visual motion. We demonstrate the principle in computer models and show that competition between opposing neurons robustly enhances their ability to discriminate between visual gratings that move in opposite directions.

Effects of a partially perforated flooring system on animal-based welfare indicators in broiler housing

Alternative flooring designs in broiler housing have been the subject of intensive research. Research comparing different floor types with a focus on animal-based welfare indicators might be of special interest to meet the animal's needs. This case-control study investigated the effect of a partially perforated vs. a littered flooring system on health- and behavior-based welfare indicators of fast-growing Ross 308 broilers. Furthermore, production performance was assessed. The experimental barn was partially (50%) equipped with a perforated floor directly underneath the feeders and water lines accessible by perforated ramps. Conventional wood shavings were used in the control barn, as usual in practice. There were 4 fattening periods (repetitions) of 31 to 32 D performed with 500 animals per barn (final density of 39 kg m-2). Beside the flooring system, management conditions were identical. Health- and behavior-based welfare indicators were assessed weekly. Production performance indicators were measured continuously during animal control. During the avoidance distance test, animals were less fearful on day 21 (P = 0.010) and tended to be less fearful on day 28 (P = 0.083) in the barn with the partially perforated flooring system compared to the littered control barn. More animals around the novel object were also assessed in the barn with the partially perforated flooring system during the novel object test on day 1 (P < 0.001) and a tendency was found on day 28 (P = 0.064). Results showed that the partially perforated flooring system had a positive influence on foot pad dermatitis from day 14 (all P ≤ 0.007) and hock burn on day 28 (P < 0.001). With regard to the production performance, animals showed no differences in final body weight for both floor types. In this study, the partially perforated flooring system had a positive effect on animal health and behavior as indicated by welfare indicators without a reduction in production performance.

Putting the "dynamic" back into dynamic functional connectivity

The study of fluctuations in time-resolved functional connectivity is a topic of substantial current interest. As the term "dynamic functional connectivity" implies, such fluctuations are believed to arise from dynamics in the neuronal systems generating these signals. While considerable activity currently attends to methodological and statistical issues regarding dynamic functional connectivity, less attention has been paid toward its candidate causes. Here, we review candidate scenarios for dynamic (functional) connectivity that arise in dynamical systems with two or more subsystems; generalized synchronization, itinerancy (a form of metastability), and multistability. Each of these scenarios arises under different configurations of local dynamics and intersystem coupling: We show how they generate time series data with nonlinear and/or nonstationary multivariate statistics. The key issue is that time series generated by coupled nonlinear systems contain a richer temporal structure than matched multivariate (linear) stochastic processes. In turn, this temporal structure yields many of the phenomena proposed as important to large-scale communication and computation in the brain, such as phase-amplitude coupling, complexity, and flexibility. The code for simulating these dynamics is available in a freeware software platform, the Brain Dynamics Toolbox.

Optogenetic Stimulation Shifts the Excitability of Cerebral Cortex from Type I to Type II: Oscillation Onset and Wave Propagation

Constant optogenetic stimulation targeting both pyramidal cells and inhibitory interneurons has recently been shown to elicit propagating waves of gamma-band (40–80 Hz) oscillations in the local field potential of non-human primate motor cortex. The oscillations emerge with non-zero frequency and small amplitude—the hallmark of a type II excitable medium—yet they also propagate far beyond the stimulation site in the manner of a type I excitable medium. How can neural tissue exhibit both type I and type II excitability? We investigated the apparent contradiction by modeling the cortex as a Wilson-Cowan neural field in which optogenetic stimulation was represented by an external current source. In the absence of any external current, the model operated as a type I excitable medium that supported propagating waves of gamma oscillations similar to those observed in vivo. Applying an external current to the population of inhibitory neurons transformed the model into a type II excitable medium. The findings suggest that cortical tissue normally operates as a type I excitable medium but it is locally transformed into a type II medium by optogenetic stimulation which predominantly targets inhibitory neurons. The proposed mechanism accounts for the graded emergence of gamma oscillations at the stimulation site while retaining propagating waves of gamma oscillations in the non-stimulated tissue. It also predicts that gamma waves can be emitted on every second cycle of a 100 Hz oscillation. That prediction was subsequently confirmed by re-analysis of the neurophysiological data. The model thus offers a theoretical account of how optogenetic stimulation alters the excitability of cortical neural fields.

Optogenetic stimulation is increasingly used as a surrogate for endogenous activity to probe neural dynamics. Our model shows that optogenetic stimulation which predominantly recruits inhibitory neurons can dramatically alter the neural dynamics from type I excitability (integrators) to type II excitability (resonators). We claim that this phenomenon explains the seemingly paradoxical co-existence of propagating waves (a hallmark of type I excitability) and the onset of oscillations with small amplitude (a hallmark of type II excitability) observed in macaque motor cortex. The model provides a theoretical account of how optogenetic stimulation alters the excitability of neural tissue. As such, it predicts that propagating gamma waves can also emerge from 100 Hz oscillations at the site of the optogenetic stimulation. This prediction was confirmed by a subsequent analysis of previously published neurophysiological data.

Sensory dynamics of visual hallucinations in the normal population

Hallucinations occur in both normal and clinical populations. Due to their unpredictability and complexity, the mechanisms underlying hallucinations remain largely untested. Here we show that visual hallucinations can be induced in the normal population by visual flicker, limited to an annulus that constricts content complexity to simple moving grey blobs, allowing objective mechanistic investigation. Hallucination strength peaked at ~11 Hz flicker and was dependent on cortical processing. Hallucinated motion speed increased with flicker rate, when mapped onto visual cortex it was independent of eccentricity, underwent local sensory adaptation and showed the same bistable and mnemonic dynamics as sensory perception. A neural field model with motion selectivity provides a mechanism for both hallucinations and perception. Our results demonstrate that hallucinations can be studied objectively, and they share multiple mechanisms with sensory perception. We anticipate that this assay will be critical to test theories of human consciousness and clinical models of hallucination.

Synchrony, waves and ripple in spatially coupled Kuramoto oscillators with Mexican hat connectivity

Spatiotemporal waves of synchronized activity are known to arise in oscillatory neural networks with lateral inhibitory coupling. How such patterns respond to dynamic changes in coupling strength is largely unexplored. The present study uses analysis and simulation to investigate the evolution of wave patterns when the strength of lateral inhibition is varied dynamically. Neural synchronization was modeled by a spatial ring of Kuramoto oscillators with Mexican hat lateral coupling. Broad bands of coexisting stable wave solutions were observed at all levels of inhibition. The stability of these waves was formally analyzed in both the infinite ring and the finite ring. The broad range of multi-stability predicted hysteresis in transitions between neighboring wave solutions when inhibition is slowly varied. Numerical simulation confirmed the predicted transitions when inhibition was ramped down from a high initial value. However, non-wave solutions emerged from the uniform solution when inhibition was ramped upward from zero. These solutions correspond to spatially periodic deviations of phase that we call ripple states. Numerical continuation showed that stable ripple states emerge from synchrony via a supercritical pitchfork bifurcation. The normal form of this bifurcation was derived analytically, and its predictions compared against the numerical results. Ripple states were also found to bifurcate from wave solutions, but these were locally unstable. Simulation also confirmed the existence of hysteresis and ripple states in two spatial dimensions. Our findings show that spatial synchronization patterns can remain structurally stable despite substantial changes in network connectivity.

A dendritic mechanism for decoding traveling waves: principles and applications to motor cortex

Traveling waves of neuronal oscillations have been observed in many cortical regions, including the motor and sensory cortex. Such waves are often modulated in a task-dependent fashion although their precise functional role remains a matter of debate. Here we conjecture that the cortex can utilize the direction and wavelength of traveling waves to encode information. We present a novel neural mechanism by which such information may be decoded by the spatial arrangement of receptors within the dendritic receptor field. In particular, we show how the density distributions of excitatory and inhibitory receptors can combine to act as a spatial filter of wave patterns. The proposed dendritic mechanism ensures that the neuron selectively responds to specific wave patterns, thus constituting a neural basis of pattern decoding. We validate this proposal in the descending motor system, where we model the large receptor fields of the pyramidal tract neurons — the principle outputs of the motor cortex — decoding motor commands encoded in the direction of traveling wave patterns in motor cortex. We use an existing model of field oscillations in motor cortex to investigate how the topology of the pyramidal cell receptor field acts to tune the cells responses to specific oscillatory wave patterns, even when those patterns are highly degraded. The model replicates key findings of the descending motor system during simple motor tasks, including variable interspike intervals and weak corticospinal coherence. By additionally showing how the nature of the wave patterns can be controlled by modulating the topology of local intra-cortical connections, we hence propose a novel integrated neuronal model of encoding and decoding motor commands.

Physiological studies in humans and monkeys have revealed spatially organized waves of neuronal activity that propagate across the cortex during sensory or behavioral tasks. However the functional role of such waves remains elusive. In the present study, we use numerical simulation to investigate whether wave patterns may serve as a basis for neural coding in cortex. Specifically, we propose a theoretical dendritic mechanism which permits neurons to respond selectively to the morphological properties of waves. In this proposal, the arrangement of excitatory and inhibitory receptors within the dendritic receptor field constitutes a spatial filter of the incoming wave patterns. The proposed mechanism allows the neuron to discriminate waves based on wavelength and orientation, thereby providing a basis for neural decoding. We explore this concept in the context of the descending motor system where the pyramidal tract neurons of motor cortex monosynaptically innervate motor neurons in the spinal cord. Pyramidal tract neurons have broad dendritic fields which make them ideal candidates for spatial filters of waves in motor cortex. Our model demonstrates how wave patterns in motor cortex can be transformed into a descending motor drive which replicates some fundamental oscillatory properties of human motor physiology.

A computational role for bistability and traveling waves in motor cortex

Adaptive changes in behavior require rapid changes in brain states yet the brain must also remain stable. We investigated two neural mechanisms for evoking rapid transitions between spatiotemporal synchronization patterns of beta oscillations (13–30 Hz) in motor cortex. Cortex was modeled as a sheet of neural oscillators that were spatially coupled using a center-surround connection topology. Manipulating the inhibitory surround was found to evoke reliable transitions between synchronous oscillation patterns and traveling waves. These transitions modulated the simulated local field potential in agreement with physiological observations in humans. Intermediate levels of surround inhibition were also found to produce bistable coupling topologies that supported both waves and synchrony. State-dependent perturbation between bistable states produced very rapid transitions but were less reliable. We surmise that motor cortex may thus employ state-dependent computation to achieve very rapid changes between bistable motor states when the demand for speed exceeds the demand for accuracy.

Muscle co-contraction modulates damping and joint stability in a three-link biomechanical limb

Computational models of neuromotor control require forward models of limb movement that can replicate the natural relationships between muscle activation and joint dynamics without the burdens of excessive anatomical detail. We present a model of a three-link biomechanical limb that emphasizes the dynamics of limb movement within a simplified two-dimensional framework. Muscle co-contraction effects were incorporated into the model by flanking each joint with a pair of antagonist muscles that may be activated independently. Muscle co-contraction is known to alter the damping and stiffness of limb joints without altering net joint torque. Idealized muscle actuators were implemented using the Voigt muscle model which incorporates the parallel elasticity of muscle and tendon but omits series elasticity. The natural force-length-velocity relationships of contractile muscle tissue were incorporated into the actuators using ideal mathematical forms. Numerical stability analysis confirmed that co-contraction of these simplified actuators increased damping in the biomechanical limb consistent with observations of human motor control. Dynamic changes in joint stiffness were excluded by the omission of series elasticity. The analysis also revealed the unexpected finding that distinct stable (bistable) equilibrium positions can co-exist under identical levels of muscle co-contraction. We map the conditions under which bistability arises and prove analytically that monostability (equifinality) is guaranteed when the antagonist muscles are identical. Lastly we verify these analytic findings in the full biomechanical limb model.

Generative models of cortical oscillations: neurobiological implications of the kuramoto model

Understanding the fundamental mechanisms governing fluctuating oscillations in large-scale cortical circuits is a crucial prelude to a proper knowledge of their role in both adaptive and pathological cortical processes. Neuroscience research in this area has much to gain from understanding the Kuramoto model, a mathematical model that speaks to the very nature of coupled oscillating processes, and which has elucidated the core mechanisms of a range of biological and physical phenomena. In this paper, we provide a brief introduction to the Kuramoto model in its original, rather abstract, form and then focus on modifications that increase its neurobiological plausibility by incorporating topological properties of local cortical connectivity. The extended model elicits elaborate spatial patterns of synchronous oscillations that exhibit persistent dynamical instabilities reminiscent of cortical activity. We review how the Kuramoto model may be recast from an ordinary differential equation to a population level description using the nonlinear Fokker–Planck equation. We argue that such formulations are able to provide a mechanistic and unifying explanation of oscillatory phenomena in the human cortex, such as fluctuating beta oscillations, and their relationship to basic computational processes including multistability, criticality, and information capacity.

Characteristics of joint involvement and relationships with systemic inflammation in systemic sclerosis: results from the EULAR Scleroderma Trial and Research Group (EUSTAR) database

OBJECTIVE

To determine the prevalence of and independent factors associated with joint involvement in a large population of patients with systemic sclerosis (SSc).

METHODS

This study was cross-sectional, based on data collected on patients included in the European League Against Rheumatism (EULAR) Scleroderma Trials and Research (EUSTAR) registry. We queried this database to extract data regarding global evaluation of patients with SSc and the presence of any clinical articular involvement: synovitis (tender and swollen joints), tendon friction rubs (rubbing sensation detected as the tendon was moved), and joint contracture (stiffness of the joints that decreased their range of motion). Overall joint involvement was defined by the occurrence of synovitis and/or joint contracture and/or tendon friction rubs.

RESULTS

We recruited 7286 patients with SSc; their mean age was 56 +/- 14 years, disease duration 10 +/- 9 years, and 4210 (58%) had a limited cutaneous disease subset. Frequencies of synovitis, tendon friction rubs, and joint contractures were 16%, 11%, and 31%, respectively. Synovitis, tendon friction rubs, and joint contracture were more prevalent in patients with the diffuse cutaneous subset and were associated together and with severe vascular, muscular, renal, and interstitial lung involvement. Moreover, synovitis had the highest strength of association with elevated acute-phase reactants taken as the dependent variable.

CONCLUSION

Our results highlight the striking level of articular involvement in SSc, as evaluated by systematic examination in a large cohort of patients with SSc. Our data also show that synovitis, joint contracture, and tendon friction rubs are associated with a more severe disease and with systemic inflammation.

[Laboratory changes in anorexia nervosa]

To correctly diagnose a patient with anorexia nervosa, medical history according to DSM-IV or ICD-10 criteria and the physical examination is essential. Furthermore, it is useful for a physician to have knowledge regarding typical alteration in laboratory parameters of anorectic patients to realize diagnostical hints. Typical laboratory changes, although not exclusively seen in anorexia nervosa, include hyponatremia, hypokalemia, hypochloremia, liver enzyme elevation, and low red and white blood cell count. The hormones leptin, neuropeptide Y (NPY), triiodothyronine (T3), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and oestrogen are usually below the normal range, whereas ghrelin, pancreatic polypeptide (PP), tumor necrosis factor-alpha (TNF-alpha) and cortisol levels are reported to be typically elevated.

[Myositides]

Idiopathic inflammatory myopathies (IIM) are diseases that are potentially amenable to immunomodulatory therapy. The challenge for the neuropathologist consists in distinguishing these myopathies from secondary inflammatory myopathies, especially in the context of some muscular dystrophies and metabolic diseases that may also show inflammatory infiltrates. There are generalized IIMs (dermatomyositis, polymyositis, sporadic inclusion body myositis) and focal ones (e.g., proliferative myositis, macrophagic myofasciitis). This review provides diagnostic criteria for each of these and includes pathogenetic mechanisms where available.

Immunohistological characterization of leukocytes in the lungs of healthy mice and after bacterial intratracheal infection

Leukocytes in the peripheral lung parenchyma of mice have not been characterized histologically during bacterial infection. The aim of this study was to investigate (a) the immunohistological characteristics of healthy murine lungs and (b) the cell kinetics during acute inflammation. BALB/c and MF1 mice were examined; as well as transgenic mice with the gene defect of cystic fibrosis (CF) in the airways as an animal model for this disease. MF1 mice served as controls for the transgenic animals. Lavaged and perfused lungs were snap frozen. B and T lymphocytes, CD4+ and CD8+ cells, dendritic cells, neutrophils and a subset of macrophages were enumerated on cryostat lung sections. The lung tissue and bronchoalveolar lavage (BAL) of BALB/c mice, infected intratracheally with Haemophilus influenzae type b (Hib), were studied at different time points after infection. In the lungs of healthy mice, including CF mice, the largest population was that of T cells, CD4+ cells being always more frequent than CD8+ cells. During acute inflammation the number of neutrophils in the lung parenchyma and BAL increased strongly within the first hours after bacterial instillation and reached baseline levels within one week. This study provides a semi-quantitative analysis of immunocompetent cells in normal and infected murine lung tissue. Differences in cell numbers are found between different strains. Moreover, the cellular reaction during Hib infection in mouse lungs is dominated by neutrophils, as expected in a primary immune response. In uninfected CF mice the numbers and distribution of immune cells in the lung tissue are normal, indicating that the cellular defense is adequate.