Graphene‐Based Oscillators for Biomimetic Neuro‐Interfaces

Hysteresis observed in the current-voltage curves of both electronic and ionic devices is a phenomenon where the curve's shape is altered on the basis of the measurement speed. This effect is driven by internal processes that introduce a time delay in the response to an external stimulus, leading to measurements being dependent on the history of the past disturbances. This hysteresis effect has posed challenges, particularly in solution-processed photovoltaic devices such as halide perovskite solar cells, where it significantly complicates the evaluation of performance quality. In other devices, such as memristors and organic electrochemical transistors for neuromorphic applications, hysteresis is an inherent aspect of their functionality, facilitating transitions between different conductivity states. Natural and artificial ionically conducting channels also exhibit pronounced hysteresis, a crucial component for generating action potentials in neurons. In this study, we aim to categorize various forms of hysteresis by identifying shared elements among diverse physical, chemical, and biological conducting systems. Our method involves examining hysteresis from multiple angles, using simplified models that capture essential response types. We analyze system behavior using techniques such as linear sweep voltammetry and impedance spectroscopy and transient currents resulting from small voltage steps. Our investigation reveals two primary hysteresis types based on how current responds to rapid sweep rates: capacitive hysteresis and inductive hysteresis. These terms correspond to the dominant component in the equivalent circuit, determining the transient time response. Remarkably, these concepts provide insights into vastly different systems, spanning solar cells, capacitors, transistors, electrofluidic nanopores, and protein ion channels. The consistency in electrical responses across the different cases enables the identification of the primary cause of hysteresis. We also elucidate the frequency dependence of hysteresis and the stepwise responses of solar cells, illustrating how fundamental relaxations contribute to the overall surplus or deficit of current during extensive voltage sweeps that define the current-voltage curve. Published by the American Physical Society 2024

The immune system is one of the most important organs, discriminating “self” from “nonself” and protecting “self” from invasion by pathogens or from abnormal “self”. The organs of the peripheral immune system are the thymus, spleen, and lymph nodes. The available cells of the immune system include T cells, B cells, and natural killer (NK) cells. Immune responses are typically divided into two components: cellular immunity and hormonal activity by soluble substances such as cytokines. There is increasing evidence of communication among the immune system, the central nervous system (CNS), and the endocrine system at various levels (Jankovic 1994; Dunn 1995). Numerous studies have been published since the 1970s regarding the association between psychological phenomena and immune function. This area of these investigations is now characterized as “psychoneuroimmunology” (Irwin 1995), although there is not sufficient evidence to support interactions between psychological phenomena and immune function. Here we consider the pathophysiology of mood disorders in regard to immune function and demonstrate the importance of intracellular calcium (Ca2+) signaling as a possible factor that associates immune function with psychological phenomena.

Single neurons of rat spinal ganglia were investigated in adult rats using a voltage clamping technique and intracellular microelectrodes. Removing sodium ions from the extracellular medium and adding tetraethylammonium to it enabled the calcium component of action potentials to be recorded. It was found that progressive selective suppression of this component takes place during extracellular recording, indicating a decrease in calcium conductivity, while sodium and potassium levels are maintained. It is suggested that this disturbance is caused by excessive influx of calcium, strontium, or barium ions into the cell. The calcium component of action potentials was also found to depend on stimulation rate; this dependence differed where calcium ions were replaced by strontium or barium ions. A possible connection between this effect and the process of voltage-dependent inactivation of calcium channels is discussed.

Intracellular calcium signaling is a universal language source shared by the most part of biological entities inside cells that, all together, give rise to physiological and functional anatomical units, the organ. Although preferentially recognized as signaling between cell life and death processes, in the heart it assumes additional relevance considered the importance of calcium cycling coupled to ATP consumption in excitation-contraction coupling. The concerted action of a plethora of exchangers, channels and pumps inward and outward calcium fluxes where needed, to convert energy and electric impulses in muscle contraction. All this without realizing it, thousands of times, every day. An improper function of those proteins (i.e., variation in expression, mutations onset, dysregulated channeling, differential protein-protein interactions) being part of this signaling network triggers a short circuit with severe acute and chronic pathological consequences reported as arrhythmias, cardiac remodeling, heart failure, reperfusion injury and cardiomyopathies. By acting with chemical, peptide-based and pharmacological modulators of these players, a correction of calcium homeostasis can be achieved accompanied by an amelioration of clinical symptoms.This review will focus on all those defects in calcium homeostasis which occur in the most common cardiac diseases, including myocardial infarction, arrhythmia, hypertrophy, heart failure and cardiomyopathies. This part will be introduced by the state of the art on the proteins involved in calcium homeostasis in cardiomyocytes and followed by the therapeutic treatments that to date, are able to target them and to revert the pathological phenotype.

Calcium ions (Ca2+) play a fundamental role in a variety of physiological functions in many cell types by acting as a secondary messenger. Variation of intracellular Ca2+ concentration ([Ca2+]i) is often observed when the cell is stimulated. However, it is a challenging task to automatically quantify intracellular [Ca2+]i in a population of cells. In this study, we present a workflow including specific algorithms for the automated intracellular calcium signal analysis using high-content, time-lapse cellular images. The experimental validations indicate the effectiveness of the proposed workflow and algorithms. We applied the workflow to analyze the intracellular calcium signals induced by different concentrations of H2O2 in the cell lines transfected by presenilin-1 (PS-1) that is known to be closely related to the familial Alzheimer's disease (FAD). The analysis results imply an important role of mutant PS-1, but not normal human PS-1 and mutant human amyloid precursor protein (APP), in enhancing intracellular calcium signaling induced by H2O2.

Mesenchymal stem cells (MSCs) are a promising cell source for tissue-engineered connective tissue repair strategies. Additionally, increasing evidence confirms the role of the mechanical environment in maintaining tissue homeostasis, with calcium signaling implicated as a mediator in mechanotransduction pathways. Spontaneous intracellular calcium signaling was observed in a subset of MSCs embedded within 4% alginate hydrogel constructs, measured by a Ca2+ indicator fluo-4 in conjunction with confocal laser-scanning microscopy. By the use of pair-wise analysis, it was shown that distinct populations of MSCs up-regulated and down-regulated the frequency of calcium transients with the application of a 20% static uniaxial compressive strain of 20 min duration, delivered after a 20 min unstrained period. Calcium transients in control specimens were monitored throughout two unstrained 20 min periods. These values were statistically significant (p<0.05) by chi 2 test of independence. This dual-response indicator highlights the heterogeneous nature of MSC populations, which may have important implications for their successful use in cell therapies.

Extracellular hydrodynamic forces may be transmitted to the interior of cells through the alteration of integrin conformation and affinity. Integrin activation regulates leukocyte recruitment, cell activation, and transmigration. The cellular and molecular mechanisms for integrin activation are not precisely known, although intracellular calcium signaling is involved. Flow cytometry offers a versatile way to study intracellular calcium signaling in real-time. We report a novel method to generate defined shear by using a miniature Couette. Testing involved measuring shear-induced intracellular calcium signals of human monoblastoid U937 cells in suspension. The Couette was connected externally to a flow cytometer and pressurized at 6 PSI (4.1 N/m(2) ). Cells were subjected to a well-defined shear between 0 and 1,000 s(-1) and delivered continuously within 10 s to a FACScan at 1 μl/s. Intracellular calcium levels and the percentage of cells activated increased as shear increased in duration and intensity.

To examine the role of AMP-activated protein kinase (AMPK) in muscle glucose transport, we generated muscle-specific transgenic mice (TG) carrying cDNAs of inactive alpha2 (alpha2i TG) and alpha1 (alpha1i TG) catalytic subunits. Extensor digitorum longus (EDL) muscles from wild type and TG mice were isolated and subjected to a series of in vitro incubation experiments. In alpha2i TG mice basal alpha2 activity was barely detectable, whereas basal alpha1 activity was only partially reduced. Known AMPK stimuli including 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR), rotenone (a Complex I inhibitor), dinitrophenol (a mitochondrial uncoupler), muscle contraction, and sorbitol (producing hyperosmolar shock) did not increase AMPK alpha2 activity in alpha2i TG mice, whereas alpha1 activation was attenuated by only 30-50%. Glucose transport was measured in vitro using isolated EDL muscles from alpha2i TG mice. AICAR- and rotenone-stimulated glucose transport was fully inhibited in alpha2i TG mice; however, the lack of AMPK alpha2 activity had no effect on contraction- or sorbitol-induced glucose transport. Similar to these observations in vitro, contraction-stimulated glucose transport, assessed in vivo by 2-deoxy-d-[(3)H]glucose incorporation into EDL, tibialis anterior, and gastrocnemius muscles, was normal in alpha2i TG mice. Thus, AMPK alpha2 activation is essential for some, but not all, insulin-independent glucose transport. Muscle contraction- and hyperosmolarity-induced glucose transport may be regulated by a redundant mechanism in which AMPK alpha2 is one of multiple signaling pathways.

Measuring the dynamic relationship between neuromodulators, such as dopamine, and neuronal action potentials is imperative to understand how these fundamental modes of neural signaling interact to mediate behavior. We developed methods to measure concurrently dopamine and extracellular action potentials (i.e., spikes) in monkeys. Standard fast-scan cyclic voltammetric (FSCV) electrochemical (EChem) and electrophysiological (EPhys) recording systems are combined and used to collect spike and dopamine signals, respectively, from an array of carbon fiber (CF) sensors implanted in the monkey striatum. FSCV requires the application of small voltages at the implanted sensors to measure redox currents generated from target molecules, such as dopamine. These applied voltages create artifacts at neighboring EPhys measurement sensors which may lead to misclassification of these signals as physiological spikes. Therefore, simple automated temporal interpolation algorithms were designed to remove these artifacts and enable accurate spike extraction. We validated these methods using simulated artifacts and demonstrated an average spike recovery rate of 84.5%. We identified and discriminated cell type-specific units in the monkey striatum that were shown to correlate to specific behavioral task parameters related to reward size and eye movement direction. Synchronously recorded spike and dopamine signals displayed contrasting relations to the task variables, suggesting a complex relationship between these two modes of neural signaling. Future application of our methods will help advance our understanding of the interactions between neuromodulator signaling and neuronal activity, to elucidate more detailed mechanisms of neural circuitry and plasticity mediating behaviors in health and in disease.

GCaMP3-Derived Genetically Encoded Probes as Rapid Intracellular Signals for Calcium Dynamics

We have come a long way since Alan Tuning first proposed the Artificial Intelligence (AI) in modern computers in 1950s enabling them to response like a human brain under certain conditions. But in order to perform various machine-learning operations such as image or speech recognition, huge datasets need to be processed leading to massive power consumption. Hence for the practical implementation and progress of AI with energy efficiency there is a pressing need of new class of memory devices which can mimic the performance of human brain at equivalent low energy. The focus of my PhD project is to develop such memory element by controlled incorporation of metal ions into the insulating layer in Metal Oxide Semiconductor (MOS) transistor which can be an innovative solution for muti-level (Analog; for reference, Binary system represents two levels), non-volatile (stored data retained even after power is off), Neuromorphic (mimics human brain response) memory device. Here I have reported controlled incorporation of lithium ions in an additional deposited insulating polymer layer in a metal-oxide-semiconductor capacitor and have shown that lithium ions motion in this layer can be controlled externally which enables it to modify the conductivity of the device, overall making it a promising candidate for the new generation memory element. Successfully integrating this with present silicon-based integrated circuits can lead to a breakthrough in AI in the future.

Close intra-arterial infusion of the appetite regulating peptide orexin-A stimulates bicarbonate secretion from the duodenal mucosa. The aim of the present study was to elucidate the ability of orexin-A to induce intracellular calcium signaling in acutely isolated duodenal enterocytes. Freshly isolated clusters of enterocytes, obtained from rat duodenal mucosa or human duodenal biopsies, were loaded with fura 2-AM and mounted in a perfusion chamber. Cryptlike enterocytes were selected (caged), and changes in intracellular calcium concentration ([Ca2+]i) were evaluated by fluorescence imaging. Total RNA was extracted from pellets of enterocytes and reverse transcribed to cDNA, and expression of orexin receptors 1 and 2 (OX1R and OX2R) was measured by quantitative real-time PCR. Orexin-A at all concentrations tested (1-100 nM) increased [Ca2+]i in enterocytes isolated from continuously fed rats, and the OX1R-antagonist SB-334867 (10 nM) attenuated the response. The primary [Ca2+]i response was a slow increase to a sustained plateau persisting after orexin-A removal, and a similar response was observed in enterocytes from human biopsies. In contrast to orexin-A, the OX2R agonist (Ala11,D-Leu15)-orexin-B (1-10 nM) did not induce calcium signaling. There were no significant [Ca2+]i responses in enterocytes from animals food deprived overnight, and overnight fasting decreased (P<0.01) enterocyte OX1R as well as OX2R mRNA. Induction of intracellular calcium signaling in isolated duodenal enterocytes is thus mediated primarily by OX1R receptors. Short (overnight) food deprivation markedly depresses receptor expression and inhibits orexin-A induced increases in [Ca2+]i. Studies of enterocyte signaling and intestinal secretion requires particular evaluation regarding feeding status.

Mutations in the two presenilin genes (PS1, PS2) account for the majority of early-onset familial Alzheimer's disease (FAD) cases. Converging evidence from a variety of experimental systems, including fibroblasts from FAD patients and transgenic animals, indicates that PS1 mutations modulate intracellular calcium signaling pathways. Despite the potential relevance of these changes to the pathogenesis of FAD, a comparable effect for PS2 has not yet been demonstrated experimentally. We examined the effects of wild-type PS2, and both of the identified FAD mutations in PS2, on intracellular calcium signaling in Xenopus oocytes. Inositol 1,4, 5-trisphosphate (IP(3))-evoked calcium signals were significantly potentiated in cells expressing either of the PS2 mutations relative to wild-type PS2-expressing cells and controls. Decay rates of calcium signals were also significantly accelerated in mutant PS2-expressing cells in a manner dependent upon IP(3) concentration. The finding that mutations in both PS1 and PS2 modulate intracellular calcium signaling suggests that these disturbances may represent a common pathogenic mechanism of presenilin-associated FAD.

Post-mortem muscle proteome of crossbred bulls and steers: Relationships with carcass and meat quality

Mitochondria play a critical role in regulating cellular processes including ATP production, intracellular calcium signaling and generation of reactive oxidative species (ROS). Neurons rely on mitochondrial function to perform a range of complex processes, and mitochondrial dysfunctions have been shown to have an impact in pathologies of the nervous system. Yet, neurons contain a finite number of mitochondria, and their location is known to change in response to a number of factors including age and cellular activity, thereby impacting neuronal response. In this paper, we introduce a novel computational model of mitochondria motility that focuses on their movements along the axon. We describe the biological processes involved and the main parameters of the model. We use the model to investigate how some of these parameters affect the ability of mitochondria to position themselves in regions of high energy demand. Finally, we discuss the significance of our work and its downstream applications in further understanding pathologies of the nervous system such as Alzheimer's disease, and help identify potential novel therapeutic targets.