Cortical Network Synchrony Under Applied Electrical Field in vitro

Unveiling the impact of low-frequency electrical stimulation on network synchronization and learning behavior in cultured hippocampal neural networks

Understanding the dynamics of neural networks and their response to external stimuli is crucial for unraveling the mechanisms associated with learning processes. In this study, we hypothesized that electrical stimulation (ES) would lead to significant alterations in the activity patterns of hippocampal neuronal networks and investigated the effects of low-frequency ES on hippocampal neuronal populations using the microelectrode arrays (MEAs). Our findings revealed significant alterations in the activity of hippocampal neuronal networks following low-frequency ES trainings. Post-stimulation, the neural activity exhibited an organized burst firing pattern characterized by increased spike and burst firings, increased synchronization, and enhanced learning behaviors. Analysis of peri-stimulus time histograms (PSTHs) further revealed that low-frequency ES (1Hz) significantly enhanced neural plasticity, thereby facilitating the learning process of cultured neurons, whereas high-frequency ES (>10Hz) impeded this process. Moreover, we observed a substantial increase in correlations and connectivity within neuronal networks following ES trainings. These alterations in network properties indicated enhanced synaptic plasticity and emphasized the positive impact of low-frequency ES on hippocampal neural activities, contributing to the brain's capacity for learning and memory.

The interplay of intracellular calcium and zinc ions in response to electric field stimulation in primary rat cortical neurons in vitro

Recent pharmacological studies demonstrate a role for zinc (Zn²⁺) in shaping intracellular calcium (Ca²⁺) dynamics and vice versa in excitable cells including neurons and cardiomyocytes. Herein, we sought to examine the dynamic of intracellular release of Ca²⁺ and Zn²⁺ upon modifying excitability of primary rat cortical neurons using electric field stimulation (EFS) in vitro. We show that exposure to EFS with an intensity of 7.69 V/cm induces transient membrane hyperpolarization together with transient elevations in the cytosolic levels of Ca²⁺ and Zn²⁺ ions. The EFS-induced hyperpolarization was inhibited by prior treatment of cells with the K⁺ channel opener diazoxide. Chemical hyperpolarization had no apparent effect on either Ca²⁺ or Zn²⁺. The source of EFS-induced rise in Ca²⁺ and Zn²⁺ seemed to be intracellular, and that the dynamic inferred of an interplay between Ca²⁺ and Zn²⁺ ions, whereby the removal of extracellular Ca²⁺ augmented the release of intracellular Ca²⁺ and Zn²⁺ and caused a stronger and more sustained hyperpolarization. We demonstrate that Zn²⁺ is released from intracellular vesicles located in the soma, with major co-localizations in the lysosomes and endoplasmic reticulum. These studies further support the use of EFS as a tool to interrogate the kinetics of intracellular ions in response to changing membrane potential in vitro.

Ultra-Sharp Nanowire Arrays Natively Permeate, Record, and Stimulate Intracellular Activity in Neuronal and Cardiac Networks

We report innovative scalable, vertical, ultra-sharp nanowire arrays that are individually addressable to enable long-term, native recordings of intracellular potentials. Stable amplitudes of intracellular potentials from 3D tissue-like networks of neurons and cardiomyocytes are obtained. Individual electrical addressability is necessary for high-fidelity intracellular electrophysiological recordings. This study paves the way toward predictive, high-throughput, and low-cost electrophysiological drug screening platforms.

Functional maturation of human neural stem cells in a 3D bioengineered brain model enriched with fetal brain-derived matrix

Brain extracellular matrix (ECM) is often overlooked in vitro brain tissue models, despite its instructive roles during development. Using developmental stage-sourced brain ECM in reproducible 3D bioengineered culture systems, we demonstrate enhanced functional differentiation of human induced neural stem cells (hiNSCs) into healthy neurons and astrocytes. Particularly, fetal brain tissue-derived ECM supported long-term maintenance of differentiated neurons, demonstrated by morphology, gene expression and secretome profiling. Astrocytes were evident within the second month of differentiation, and reactive astrogliosis was inhibited in brain ECM-enriched cultures when compared to unsupplemented cultures. Functional maturation of the differentiated hiNSCs within fetal ECM-enriched cultures was confirmed by calcium signaling and spectral/cluster analysis. Additionally, the study identified native biochemical cues in decellularized ECM with notable comparisons between fetal and adult brain-derived ECMs. The development of novel brain-specific biomaterials for generating mature in vitro brain models provides an important path forward for interrogation of neuron-glia interactions.

Connectomics of Morphogenetically Engineered Neurons as a Predictor of Functional Integration in the Ischemic Brain

Recent advances in cell reprogramming technologies enable the in vitro generation of theoretically unlimited numbers of cells, including cells of neural lineage and specific neuronal subtypes from human, including patient-specific, somatic cells. Similarly, as demonstrated in recent animal studies, by applying morphogenetic neuroengineering principles in situ, it is possible to reprogram resident brain cells to the desired phenotype. These developments open new exciting possibilities for cell replacement therapy in stroke, albeit not without caveats. Main challenges include the successful integration of engineered cells in the ischemic brain to promote functional restoration as well as the fact that the underlying mechanisms of action are not fully understood. In this review, we aim to provide new insights to the above in the context of connectomics of morphogenetically engineered neural networks. Specifically, we discuss the relevance of combining advanced interdisciplinary approaches to: validate the functionality of engineered neurons by studying their self-organizing behavior into neural networks as well as responses to stroke-related pathology in vitro; derive structural and functional connectomes from these networks in healthy and perturbed conditions; and identify and extract key elements regulating neural network dynamics, which might predict the behavior of grafted engineered neurons post-transplantation in the stroke-injured brain.