Action Potential Generation Research Articles

Spatial heterogeneity in myelin sheathing impacts signaling reliability and susceptibility to injury.

Axons in the mammalian brain show significant diversity in myelination motifs, displaying spatial heterogeneity in sheathing along individual axons and across brain regions. However, its impact on neural signaling and susceptibility to injury remains poorly understood. To address this, we leveraged cable theory and developed model axons replicating the myelin sheath distributions observed experimentally in different regions of the mouse central nervous system. We examined how the spatial arrangement of myelin affects propagation and predisposition to conduction failure in axons with cortical versus callosal myelination motifs. Our results indicate that regional differences inmyelination significantly influence conduction timing and signaling reliability. Sensitivity of action potential propagation to the specific positioning, lengths, and ordering of myelinated and exposed segments reveals non-linear and path-dependent conduction. Furthermore, myelination motifs impact signaling vulnerability to demyelination, with callosal motifs being particularly sensitive to myelin changes. These findings highlight the crucial role of myelinating glia in brain function and disease.Significance Statement This study highlights the importance of spatial heterogeneity of myelin sheathing in shaping nerve axonal conduction. Using model axons that faithfully replicate myelin distributions observed in the mouse central nervous system, our results revealed the impact of myelin patterns on the timing and reliability of neural signaling. Contrary to the conventional view in which uniform and equally spaced myelin segments imply linear conduction, our findings show that axonal conduction is a path-dependent, non-linear process influenced by the specific distribution of myelinated and unmyelinated segments. Membrane potential propagation along model axons in the corpus callosum was found to be more vulnerable to myelin changes compared to those in the cortex, especially post-myelin injury, emphasizing the role of sheath locations in both health and disease.

Biophysical modeling and experimental analysis of the dynamics of C. elegans body-wall muscle cells.

This study combines experimental techniques and mathematical modeling to investigate the dynamics of C. elegans body-wall muscle cells. Specifically, by conducting voltage clamp and mutant experiments, we identify key ion channels, particularly the L-type voltage-gated calcium channel (EGL-19) and potassium channels (SHK-1, SLO-2), which are crucial for generating action potentials. We develop Hodgkin-Huxley-based models for these channels and integrate them to capture the cells' electrical activity. To ensure the model accurately reflects cellular responses under depolarizing currents, we develop a parallel simulation-based inference method for determining the model's free parameters. This method performs rapid parallel sampling across high-dimensional parameter spaces, fitting the model to the responses of muscle cells to specific stimuli and yielding accurate parameter estimates. We validate our model by comparing its predictions against cellular responses to various current stimuli in experiments and show that our approach effectively determines suitable parameters for accurately modeling the dynamics in mutant cases. Additionally, we discover an optimal response frequency in body-wall muscle cells, which corresponds to a burst firing mode rather than regular firing mode. Our work provides the first experimentally constrained and biophysically detailed muscle cell model of C. elegans, and our analytical framework combined with robust and efficient parametric estimation method can be extended to model construction in other species.

Caliber of zebrafish touch-sensory axons is dynamic in vivo.

Cell shape is crucial to cell function, particularly in neurons. The cross-sectional diameter, also known as caliber, of axons and dendrites is an important parameter of neuron shape, best appreciated for its influence on the speed of action potential propagation. Many studies of axon caliber focus on cell-wide regulation and assume that caliber is static. Here, we have characterized local variation and dynamics of axon caliber in vivo using the peripheral axons of zebrafish touch-sensing neurons at embryonic stages, prior to sex determination. To obtain absolute measurements of caliber in vivo, we paired sparse membrane labeling with super-resolution microscopy of neurons in live fish. We observed that axon segments had varicose or "pearled" morphologies, and thus vary in caliber along their length, consistent with reports from mammalian systems. Sister axon segments originating from the most proximal branch point in the axon arbor had average calibers that were uncorrelated with each other. Axon caliber also tapered across the branch point. Varicosities and caliber, overall, were dynamic on the timescale of minutes, and dynamicity changed over the course of development. By measuring the caliber of axons adjacent to dividing epithelial cells, we found that skin cell division is one aspect of the cellular microenvironment that may drive local differences and dynamics in axon caliber. Our findings support the possibility that spatial and temporal variation in axon caliber could significantly influence neuronal physiology.

Bioinspired Nanofluidic Circuits with Integrating Excitatory and Inhibitory Synapses.

Brain neural networks intricately integrate excitatory and inhibitory synaptic potentials to modulate the generation or suppression of action potentials, laying the foundation for neuronal computation. Although bioinspired nanofluidic systems have replicated some synaptic functions, complete integration of postsynaptic potentials remains unachieved. In this work, the developed ion concentration gradient nanofluidic memristor (ICGNM) modulates memristive effects through ion concentration gradient adjustments and exhibits synaptic plasticity phenomena, including paired-pulse facilitation, paired-pulse depression, and spike-rate-dependent plasticity. Furthermore, by incorporation of ICGNMs as the memristive elements into the classic Hodgkin-Huxley model, the action potential generation is replicated. In addition to simulating nanofluidic spiking, these ICGNMs are also employed in a bioinspired nanofluidic circuit to simulate the integration of excitatory and inhibitory synaptic signals, which is highly analogous to the signal integration in actual neural circuits. This work represents a new step toward ionic computing in solution with bioinspired nanofluidic circuits.

Power spectral analysis of voltage-gated channels in neurons

This article develops a fundamental insight into the behavior of neuronal membranes, focusing on their responses to stimuli measured with power spectra in the frequency domain. It explores the use of linear and nonlinear (quadratic sinusoidal analysis) approaches to characterize neuronal function. It further delves into the random theory of internal noise of biological neurons and the use of stochastic Markov models to investigate these fluctuations. The text also discusses the origin of conductance noise and compares different power spectra for interpreting this noise. Importantly, it introduces a novel sequential chemical state model, named p2, which is more general than the Hodgkin–Huxley formulation, so that the probability for an ion channel to be open does not imply exponentiation. In particular, it is demonstrated that the p2 (without exponentiation) and n4 (with exponentiation) models can produce similar neuronal responses. A striking relationship is also shown between fluctuation and quadratic power spectra, suggesting that voltage-dependent random mechanisms can have a significant impact on deterministic nonlinear responses, themselves known to have a crucial role in the generation of action potentials in biological neural networks.

Isoform-specific N-linked glycosylation of NaV channel α-subunits alters β-subunit binding sites.

Voltage-gated sodium channel α-subunits (NaV1.1-1.9) initiate and propagate action potentials in neurons and myocytes. The NaV β-subunits (β1-4) have been shown to modulate α-subunit properties. Homo-oligomerization of β-subunits on neighboring or opposing plasma membranes has been suggested to facilitate cis or trans interactions, respectively. The interactions between several NaV channel isoforms and β-subunits have been determined using cryogenic electron microscopy (cryo-EM). Interestingly, the NaV cryo-EM structures reveal the presence of N-linked glycosylation sites. However, only the first glycan moieties are typically resolved at each site due to the flexibility of mature glycan trees. Thus, existing cryo-EM structures may risk de-emphasizing the structural implications of glycans on the NaV channels. Herein, molecular modeling and all-atom molecular dynamics simulations were applied to investigate the conformational landscape of N-linked glycans on NaV channel surfaces. The simulations revealed that negatively charged sialic acid residues of two glycan sites may interact with voltage-sensing domains. Notably, two NaV1.5 isoform-specific glycans extensively cover the α-subunit region that, in other NaV channel α-subunit isoforms, corresponds to the binding site for the β1- (and likely β3-) subunit immunoglobulin (Ig) domain. NaV1.8 contains a unique N-linked glycosylation site that likely prevents its interaction with the β2 and β4-subunit Ig-domain. These isoform-specific glycans may have evolved to facilitate specific functional interactions, for example, by redirecting β-subunit Ig-domains outward to permit cis or trans supraclustering within specialized cellular compartments such as the cardiomyocyte perinexal space. Further experimental work is necessary to validate these predictions.

Iconography of abnormal non-neuronal cells in pediatric focal cortical dysplasia type IIb and tuberous sclerosis complex.

Once believed to be the culprits of epileptogenic activity, the functional properties of balloon/giant cells (BC/GC), commonly found in some malformations of cortical development including focal cortical dysplasia type IIb (FCDIIb) and tuberous sclerosis complex (TSC), are beginning to be unraveled. These abnormal cells emerge during early brain development as a result of a hyperactive mTOR pathway and may express both neuronal and glial markers. A paradigm shift occurred when our group demonstrated that BC/GC in pediatric cases of FCDIIb and TSC are unable to generate action potentials and lack synaptic inputs. Hence, their role in epileptogenesis remained obscure. In this review, we provide a detailed characterization of abnormal non-neuronal cells including BC/GC, intermediate cells, and dysmorphic/reactive astrocytes found in FCDIIb and TSC cases, with special emphasis on electrophysiological and morphological assessments. Regardless of pathology, the electrophysiological properties of abnormal cells appear more glial-like, while others appear more neuronal-like. Their morphology also differs in terms of somatic size, shape, and dendritic elaboration. A common feature of these types of non-neuronal cells is their inability to generate action potentials. Thus, despite their distinct properties and etiologies, they share a common functional feature. We hypothesize that, although the exact role of abnormal non-neuronal cells in FCDIIb and TSC remains mysterious, it can be suggested that cells displaying more glial-like properties function in a similar way as astrocytes do, i.e., to buffer K+ ions and neurotransmitters, while those with more neuronal properties, may represent a metabolic burden due to high energy demands but inability to receive or transmit electric signals. In addition, due to the heterogeneity of these cells, a new classification scheme based on morphological, electrophysiological, and gene/protein expression in FCDIIb and TSC cases seems warranted.

Multiple gating processes associated with the distal end of the S6 segment of domain II in the Nav channels.

Voltage-gated sodium (Nav) channels are transmembrane proteins that play crucial roles in the initiation and propagation of action potentials (APs) in excitable tissues such as the heart, muscles, and nerves. The distal ends of the four domain S6 segments of Nav channels contain hydrophobic residues, which form an intracellular gate. This gate allows Nav channels to control ion flux in excitable cells by opening and closing. However, the mechanism of the distal end of Domain II (DII) S6 segment in channel gating remains unclear. In this study, using whole-cell patch clamp recording, we systematically investigated the biophysical characteristics of various mutants L811 site (located at the distal end of the DII S6 segment) of Nav1.9 and the corresponding L796P mutant of Nav1.4. We found that the mutations significantly shifted the activation and inactivation curves, slowed the fast inactivation, accelerated the slow inactivation and use-dependent slow inactivation, and L811P altered the ion selectivity of the channel. Therefore, our findings suggest that the distal end of the DII S6 segment in Nav channels plays a pivotal role in regulating multiple gating processes.

Lipids shape brain function through ion channel and receptor modulations: physiological mechanisms and clinical perspectives.

Lipids represent the most abundant molecular type in the brain, with a fat content of ∼60% of the dry brain weight in humans. Despite this fact, little attention has been paid to circumscribe the dynamic role of lipids in brain function and disease. Membrane lipids such as cholesterol, phosphoinositide, sphingolipids, arachidonic acid, and endocannabinoids finely regulate both synaptic receptors and ion channels that ensure critical neural functions. After a brief introduction on brain lipids and their respective properties, we review here their role in regulating synaptic function and ion channel activity, action potential propagation, neuronal development, and functional plasticity and their contribution in the development of neurological and neuropsychiatric diseases. We also provide possible directions for future research on lipid function in brain plasticity and diseases.

Silver bismuth sulfide quantum dot‐based bioelectronics for light‐mediated neuronal stimulation

Aims/Purpose: Nanomaterial based bioelectronics have been effectively developed as optoelectronic bio‐interfaces for neural stimulation and can be fabricated from diverse substances to adapt to cellular environments. In this study, we employed silver bismuth sulfide (AgBiS2) quantum dot (QD)‐based neural interfaces stimulated by near‐infrared light.Methods: Primary neuron isolation and culture on AgBiS2 QD based photovoltaic device and indium tin oxide (ITO) control device was performed. Cell viability was assessed by CTG, MTT, Live/Dead assay and LDH leakage assays. Cellular stress with light stimulation was assessed by measuring intracellular reactive oxygen species. Cell specific biomarkers, NeuN, beta‐III Tubulin and F‐actin, were examined by immunofluorescence staining to demonstrate short‐ and long‐term morphological changes and neural network improvements. Number of neuron count and neurite length measurement were analyzed to compare groups. Under light stimulation (λ = 780 nm), neural dynamics and electrophysiological activity were examined through intracellular calcium flow and patch clamp.Results: Throughout the 14‐day culture period, neurons remained healthy and viable, preserving their characteristics and forming extensive networks with neurite outgrowth on both the device and ITO. Light stimulation was found to have no adverse effects on viability or intracellular stress levels. The device demonstrated successful photostimulation of neurons with calcium release and generating action potential under 780 nm light illumination which is validating its potential to be used as optoelectronic bio‐interfaces for neural applications.Conclusions: Our study holds high potential for the development of QD‐based retinal prosthesis, enabling near infrared light‐controlled activation in vision related diseases.Funding Information: This study was funded by the European Union (ERC, MESHOPTO, 101045289).References Balamur R, Oh JT, Karatum O, Wang Y, Onal A, Kaleli HN, Pehlivan C, Şahin A, Hasanreisoglu M, Konstantatos G, Nizamoglu S. Capacitive and Efficient Near‐Infrared Stimulation of Neurons via an Ultrathin AgBiS2 Nanocrystal Layer. ACS Applied Materials & Interfaces. 2024 May 29

Silver bismuth sulfide quantum dot‐based bioelectronics for light‐mediated neuronal stimulation

Aims/Purpose: Nanomaterial based bioelectronics have been effectively developed as optoelectronic bio‐interfaces for neural stimulation and can be fabricated from diverse substances to adapt to cellular environments. In this study, we employed silver bismuth sulfide (AgBiS2) quantum dot (QD)‐based neural interfaces stimulated by near‐infrared light.Methods: Primary neuron isolation and culture on AgBiS2 QD based photovoltaic device and indium tin oxide (ITO) control device was performed. Cell viability was assessed by CTG, MTT, Live/Dead assay and LDH leakage assays. Cellular stress with light stimulation was assessed by measuring intracellular reactive oxygen species. Cell specific biomarkers, NeuN, beta‐III Tubulin and F‐actin, were examined by immunofluorescence staining to demonstrate short‐ and long‐term morphological changes and neural network improvements. Number of neuron count and neurite length measurement were analyzed to compare groups. Under light stimulation (λ = 780 nm), neural dynamics and electrophysiological activity were examined through intracellular calcium flow and patch clamp.Results: Throughout the 14‐day culture period, neurons remained healthy and viable, preserving their characteristics and forming extensive networks with neurite outgrowth on both the device and ITO. Light stimulation was found to have no adverse effects on viability or intracellular stress levels. The device demonstrated successful photostimulation of neurons with calcium release and generating action potential under 780 nm light illumination which is validating its potential to be used as optoelectronic bio‐interfaces for neural applications.Conclusions: Our study holds high potential for the development of QD‐based retinal prosthesis, enabling near infrared light‐controlled activation in vision related diseases.Funding Information: This study was funded by the European Union (ERC, MESHOPTO, 101045289).References Balamur R, Oh JT, Karatum O, Wang Y, Onal A, Kaleli HN, Pehlivan C, Şahin A, Hasanreisoglu M, Konstantatos G, Nizamoglu S. Capacitive and Efficient Near‐Infrared Stimulation of Neurons via an Ultrathin AgBiS2 Nanocrystal Layer. ACS Applied Materials & Interfaces. 2024 May 29

Pinning of reaction–diffusion travelling waves in one-dimensional annular geometry

We analyse the complex dynamics arising in a one-dimensional bistable advection–reaction–diffusion equation on a bounded annular domain, along with its simplest nontrivial approximation in terms of a Fourier expansion. We investigate the pinning of travelling waves produced by spatial anisotropies and suggest possible biological implications in the context of cardiac action potential propagation failure due to acute ischemia.

Simulation Study of Envelope Wave Electrical Nerve Stimulation Based on a Real Head Model.

In recent years, the modulation of brain neural activity by applied electromagnetic fields has become a hot spot in neuroscience research. Transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS) are two common non-invasive neuromodulation techniques. However, conventional tACS has limited stimulation effects in the deeper parts of the brain. In this study, a method of low and medium frequency envelope wave neurostimulation is proposed, and its effectiveness and safety are evaluated by simulation and human experiment. First, we built a real head model from head MRI image data and used the finite element method to calculate the current distribution of the envelope wave in the brain. Then, a single-compartment neuron model was constructed in NEURON software to simulate the action potential generation of neurons under different frequencies of electrical stimulation. Finally, a human experiment was conducted to investigate the threshold of human perception of envelope wave electrical stimulation. The results show that envelope wave can both increase the depth of stimulation and induce neurons to generate effective action potentials. In envelope wave electrical stimulation, the optimal modulating wave frequency was 50 Hz, and the carrier frequency was 2 kHz-3 kHz. This method is expected to play an important role in the non-invasive treatment of neurological and psychiatric disorders.

Rare dysfunctional SCN2A variants are associated with malformation of cortical development.

SCN2A encodes the voltage-gated sodium (Na+) channel α subunit NaV1.2, which is important for the generation and forward and back propagation of action potentials in neurons. Genetic variants in SCN2A are associated with a spectrum of neurodevelopmental disorders. However, the mechanisms whereby variation in SCN2A leads to disease remains incompletely understood, and the full spectrum of SCN2A-related disorders may not be fully delineated. Here, we identified seven de novo heterozygous variants in SCN2A in eight individuals with developmental and epileptic encephalopathy (DEE) accompanied by prominent malformation of cortical development (MCD). We characterized the electrophysiological properties of Na + currents in human embryonic kidney (HEK) cells transfected with the adult (A) or neonatal (N) isoform of wild-type (WT) and variant NaV1.2 using manual and automated whole-cell voltage clamp recording. The neonatal isoforms of all SCN2A variants studied exhibit gain of function (GoF) with a large depolarized shift in steady-state inactivation, creating a markedly enhanced window current common across all four variants tested. Computational modeling demonstrated that expression of the NaV1.2-p.Met1770Leu-N variant in a developing neocortical pyramidal neuron results in hyperexcitability. These results support expansion of the clinical spectrum of SCN2A-related disorders and the association of genetic variation in SCN2A with MCD, which suggests previously undescribed roles for SCN2A in fetal brain development.

Structural and functional alterations of neurons derived from sporadic Alzheimer’s disease hiPSCs are associated with downregulation of the LIMK1-cofilin axis

BackgroundAlzheimer's Disease (AD) is a neurodegenerative disorder characterized by the accumulation of pathological proteins and synaptic dysfunction. This study aims to investigate the molecular and functional differences between human induced pluripotent stem cells (hiPSCs) derived from patients with sporadic AD (sAD) and age-matched controls (healthy subjects, HS), focusing on their neuronal differentiation and synaptic properties in order to better understand the cellular and molecular mechanisms underlying AD pathology.MethodsSkin fibroblasts from sAD patients (n = 5) and HS subjects (n = 5) were reprogrammed into hiPSCs using non-integrating Sendai virus vectors. Through karyotyping, we assessed pluripotency markers (OCT4, SOX2, TRA-1–60) and genomic integrity. Neuronal differentiation was evaluated by immunostaining for MAP2 and NEUN. Electrophysiological properties were measured using whole-cell patch-clamp, while protein expression of Aβ, phosphorylated tau, Synapsin-1, Synaptophysin, PSD95, and GluA1 was quantified by western blot. We then focused on PAK1-LIMK1-Cofilin signaling, which plays a key role in regulating synaptic structure and function, both of which are disrupted in neurodegenerative diseases such as AD.ResultssAD and HS hiPSCs displayed similar stemness features and genomic stability. However, they differed in neuronal differentiation and function. sAD-derived neurons (sAD-hNs) displayed increased levels of AD-related proteins, including Aβ and phosphorylated tau. Electrophysiological analyses revealed that while both sAD- and HS-hNs generated action potentials, sAD-hNs exhibited decreased spontaneous synaptic activity. Significant reductions in the expression of synaptic proteins such as Synapsin-1, Synaptophysin, PSD95, and GluA1 were found in sAD-hNs, which are also characterized by reduced neurite length, indicating impaired differentiation. Notably, sAD-hNs demonstrated a marked reduction in LIMK1 phosphorylation, which could be the underlying cause for the changes in cytoskeletal dynamics that we found, leading to the morphological and functional modifications observed in sAD-hNs. To further investigate the involvement of the LIMK1 pathway in the morphological and functional changes observed in sAD neurons, we conducted perturbation experiments using the specific LIMK1 inhibitor, BMS-5. Neurons obtained from healthy subjects treated with the inhibitor showed similar morphological changes to those observed in sAD neurons, confirming that LIMK1 activity is crucial for maintaining normal neuronal structure. Furthermore, administration of the inhibitor to sAD neurons did not exacerbate the morphological alterations, suggesting that LIMK1 activity is already compromised in these cells.ConclusionOur findings demonstrate that although sAD- and HS-hiPSCs are similar in their stemness and genomic stability, sAD-hNs exhibit distinct functional and structural anomalies mirroring AD pathology. These anomalies include synaptic dysfunction, altered cytoskeletal organization, and accumulation of AD-related proteins. Our study underscores the usefulness of hiPSCs in modeling AD and provides insights into the disease's molecular underpinnings, thus highlighting potential therapeutic targets.

In Search of Transcriptomic Correlates of Neuronal Firing-Rate Adaptation across Subtypes, Regions and Species: A Patch-seq Analysis.

Can the transcriptomic profile of a neuron predict its physiological properties? Using a Patch-seq dataset of the primary visual cortex, we addressed this question by focusing on spike rate adaptation (SRA), a well-known phenomenon that depends on small conductance calcium (Ca)-dependent potassium (SK) channels. We first show that in parvalbumin-expressing (PV) and somatostatin-expressing (SST) interneurons (INs), expression levels of genes encoding the ion channels underlying action potential generation are correlated with the half-width (HW) of spikes. Surprisingly, the SK encoding gene is not correlated with the degree of SRA (dAdap). Instead, genes that encode proteins upstream from the SK current are correlated with dAdap, a finding validated by a different dataset from the mouse's primary motor cortex that includes pyramidal cells and interneurons, as well as physiological datasets from multiple regions of macaque monkeys. Finally, we construct a minimal model to reproduce observed heterogeneity across cells, with testable predictions.

TRPC6 is a mechanosensitive channel essential for ultrasound neuromodulation in the mammalian brain

Ultrasound neuromodulation has become an innovative technology that enables noninvasive intervention in mammalian brain circuits with high spatiotemporal precision. Despite the expanding utility of ultrasound neuromodulation in the neuroscience research field and clinical applications, the molecular and cellular mechanisms by which ultrasound impacts neural activity in the brain are still largely unknown. Here, we report that transient receptor potential canonical 6 (TRPC6), a mechanosensitive nonselective cation channel, is essential for ultrasound neuromodulation of mammalian neurons in vitro and in vivo. We first demonstrated that ultrasound irradiation elicited rapid and robust Ca2+ transients mediated via extracellular Ca2+ influx in cultured mouse cortical and hippocampal neurons. Ultrasound-induced neuronal responses were massively diminished by blocking either the generation of action potential or synaptic transmission. Importantly, both pharmacological inhibition and genetic deficiency of TRPC6 almost completely abolished neuronal responses to ultrasound. Furthermore, we found that intracerebroventricular administration of a TRPC6 blocker significantly attenuated the number of neuronal firings in the cerebral cortex evoked by transcranial ultrasound irradiation in mice. Our findings indicate that TRPC6 is an indispensable molecule of ultrasound neuromodulation in intact mammalian brains, providing fundamental understanding of biophysical molecular mechanisms of ultrasound neuromodulation as well as insight into its future feasibility in neuroscience and translational research in humans.

An overview of drug-induced sodium channel blockade and changes in cardiac conduction: Implications for drug safety.

The human voltage-gated sodium channel Nav1.5 (hNav1.5/SCN5A) plays a critical role in the initiation and propagation of action potentials in cardiac myocytes, and its modulation by various drugs has significant implications for cardiac safety. Drug-dependent block of Nav1.5 current (INa) can lead to significant alterations in cardiac electrophysiology, potentially resulting in conduction slowing and an increased risk of proarrhythmic events. This review aims to provide a comprehensive overview of the mechanisms by which various pharmacological agents interact with Nav1.5, focusing on the molecular determinants of drug binding and the resultant electrophysiological effects. We discuss the structural features of Nav1.5 that influence drug affinity and specificity. Special attention is given to the concept of state-dependent block, where drug binding is influenced by the conformational state of the channel, and its relevance to therapeutic efficacy and safety. The review also examines the clinical implications of INa block, highlighting case studies of drugs that have been associated with adverse cardiac events, and how the Vaughan-Williams Classification system has been employed to qualify "unsafe" sodium channel block. Furthermore, we explore the methodologies currently used to assess INa block in nonclinical and clinical settings, with the hope of providing a weight of evidence approach including in silico modeling, invitro electrophysiological assays and invivo cardiac safety studies for mitigating proarrhythmic risk early in drug discovery. This review underscores the importance of understanding Nav1.5 pharmacology in the context of drug development and cardiac risk assessment.

Differential energetic profile of signal processing in central vestibular neurons.

Energetic aspects of neuronal activity have become a major focus of interest given the fact that the brain among all organs dominates the oxygen consumption. At variance with the importance of neuroenergetics, the knowledge about how electrical activity and metabolism is correlated in defined neuronal populations is still rather scarce. We have estimated the ATP consumption in the two physiologically well characterized populations of frog central vestibular neurons, with tonic and phasic firing patterns, respectively. These two distinct groups of neurons jointly process head/body movements detected by semicircular canal and otolith organs in the inner ear. The ATP consumption for maintenance of the resting membrane potential (Vr) and postsynaptic action potential (AP) generation was calculated based on the wealth of previously reported morpho-physiological features of these two neuronal types. Accordingly, tonic vestibular neurons require less ATP across the physiological activity range for these major processes, than phasic vestibular neurons, despite the considerably higher firing rates of the former subtype. However, since both neuronal subtypes are indispensable for the encoding and processing of the entire head/body motion dynamics, the higher energy demand of phasic neurons represents an obvious and necessary price to pay. Although phasic and tonic neurons form the respective core elements of the frequency-tuned vestibular pathways, both cellular components are cross-linked through feedforward and feedback side loops. The prominent influence of inhibitory tonic neurons in shaping the highly transient firing pattern of phasic neurons is cost-intensive and contributes to energy consumption for electrical activity in addition to the already extensive energy costs of signal processing by the very leaky phasic vestibular neurons. Despite the sparse production of action potentials by phasic vestibular neurons, the computation by this neuronal type dominates the ATP expense for processing head/body movements, which might have contributed to the late evolutionary arrival of this central neuronal element, dedicated to the encoding of highly dynamic motion profiles.

Design of intelligent Bayesian regularized deep cascaded NARX neurostructure for predictive analysis of FitzHugh-Nagumo bioelectrical model in neuronal cell membrane

The electrophysiological modelling paradigm unravels the complex oscillatory and excitable behaviors inherent to neural dynamics, with the FitzHugh-Nagumo model—rooted in the reductionist abstraction of Hodgkin-Huxley formalism—providing a quintessential framework for exploring the underpinnings of action potential propagation and diverse phase plane dynamics characterizing excitable membranes. The objective of this study is to present the novel intelligent computing-based Bayesian regularized multilayered deep dual cascaded nonlinear autoregressive exogenous neurostructure to model and predict the intricate dynamics of FitzHugh-Nagumo model. The numerical treatment of the FitzHugh-Nagumo (FHN) model is handled with a modified Adams-Bashforth-Moulton predictor–corrector method for three sundry scenarios encompassing the oscillatory, excitable, and bistable dynamics. These simulated temporal sequences are arbitrarily divided into training and test sets for Deep Cascaded NARX neural networks, with backpropagated refinement using the Bayesian regularization technique (DC-NARX-BR). This novel strategy is verified across reference numerical outcomes with the help of diversified evaluation metrics including mean squared error convergence plots, error histogram analysis, error regression metrics, input-error cross-correlation, and error autocorrelation plots. Comparative analysis charts present the efficacious use of the DC-NARX intelligent computing paradigm with absolute errors ranging from 10-05 to 10-12. Predictive intelligence of the step ahead DC-NARX-BR strategy is observed for the intricate FHN model dynamics with marginal deviances from realized behavior. These diminutive errors can be comprehended by the low MSE losses in the range 10-02–10-05. Exhaustive experimentational averages validate the robustness of DC-NARX intelligent computing paradigm for the correct integration with the complex bioelectrical phenomena occurring within a neuronal cell membrane.