Self-Organized Synchronous Calcium Transients in a Cultured Human Neural Network Derived from Cerebral Organoids

Functional Neural Networks in Human Brain Organoids

Human brain organoids are 3-dimensional brain-like tissues derived from human pluripotent stem cells and hold promising potential for modeling neurological, psychiatric, and developmental disorders. While the molecular and cellular aspects of human brain organoids have been intensively studied, their functional properties such as organoid neural networks (ONNs) are largely understudied. Here, we summarize recent research advances in understanding, characterization, and application of functional ONNs in human brain organoids. We first discuss the formation of ONNs and follow up with characterization strategies including microelectrode array (MEA) technology and calcium imaging. Moreover, we highlight recent studies utilizing ONNs to investigate neurological diseases such as Rett syndrome and Alzheimer's disease. Finally, we provide our perspectives on the future challenges and opportunities for using ONNs in basic research and translational applications.

Standardizing a method for functional assessment of neural networks in brain organoids

During the last decade brain organoids have emerged as an attractive model system, allowing stem cells to be differentiated into complex 3D models, recapitulating many aspects of human brain development. Whilst many studies have analysed anatomical and cytoarchitectural characteristics of organoids, their functional characterisation has been limited, and highly variable between studies. Standardised, consistent methods for recording functional activity are critical to providing a functional understanding of neuronal networks at the synaptic and network level that can yield useful information about functional network phenotypes in disease and healthy states. In this study we outline a detailed methodology for calcium imaging and Multi-Electrode Array (MEA) recordings in brain organoids. To illustrate the utility of these functional interrogation techniques in uncovering induced differences in neural network activity we applied various stimulating media protocols. We demonstrate overlapping information from the two modalities, with comparable numbers of active cells in the four treatment groups and an increase in synchronous behaviour in BrainPhys treated groups. Further development of analysis pipelines to reveal network level changes in brain organoids will enrich our understanding of network formation and perturbation in these structures, and aid in the future development of drugs that target neurological disorders at the network level.

A comprehensive review of electrophysiological techniques in amyotrophic lateral sclerosis research

Amyotrophic lateral sclerosis (ALS), a devastating neurodegenerative disease, is characterized by progressive motor neuron degeneration, leading to widespread weakness and respiratory failure. While a variety of mechanisms have been proposed as causes of this disease, a full understanding remains elusive. Electrophysiological alterations, including increased motor axon excitability, likely play an important role in disease progression. There remains a critical need for non-animal disease models that can integrate electrophysiological tools to better understand underlying mechanisms, track disease progression, and evaluate potential therapeutic interventions. This review explores the integration of electrophysiological technologies with ALS disease models. It covers cellular and clinical electrophysiological tools and their applications in ALS research. Additionally, we examine conventional animal models and highlight advancements in humanized models and 3D organoid technologies. By bridging the gap between these models, we aim to enhance our understanding of ALS pathogenesis and facilitate the development of new therapeutic strategies.

Microinstrumentation for Brain Organoids

Brain organoids are three-dimensional aggregates of self-organized differentiated stem cells that mimic the structure and function of human brain regions. Organoids bridge the gaps between conventional drug screening models such as planar mammalian cell culture, animal studies, and clinical trials. They can revolutionize the fields of developmental biology, neuroscience, toxicology, and computer engineering. Conventional microinstrumentation for conventional cellular engineering, such as planar microfluidic chips; microelectrode arrays (MEAs); and optical, magnetic, and acoustic techniques, has limitations when applied to three-dimensional (3D) organoids, primarily due to their limits with inherently two-dimensional geometry and interfacing. Hence, there is an urgent need to develop new instrumentation compatible with live cell culture techniques and with scalable 3D formats relevant to organoids. This review discusses conventional planar approaches and emerging 3D microinstrumentation necessary for advanced organoid-machine interfaces. Specifically, this article surveys recently developed microinstrumentation, including 3D printed and curved microfluidics, 3D and fast-scan optical techniques, buckling and self-folding MEAs, 3D interfaces for electrochemical measurements, and 3D spatially controllable magnetic and acoustic technologies relevant to two-way information transfer with brain organoids. This article highlights key challenges that must be addressed for robust organoid culture and reliable 3D spatiotemporal information transfer.

Gnao1 is a molecular switch that regulates the Rho signaling pathway in differentiating neurons

GNAO1 encodes G protein subunit alpha O1 (Gαo). Pathogenic variations in GNAO1 cause developmental delay, intractable seizures, and progressive involuntary movements from early infancy. Because the functional role of GNAO1 in the developing brain remains unclear, therapeutic strategies are still unestablished for patients presenting with GNAO1-associated encephalopathy. We herein report that siRNA-mediated depletion of Gnao1 perturbs the expression of transcripts associated with Rho GTPase signaling in Neuro2a cells. Consistently, siRNA treatment hampered neurite outgrowth and extension. Growth cone formation was markedly disrupted in monolayer neurons differentiated from iPSCs from a patient with a pathogenic variant of Gαo (p.G203R). This variant disabled neuro-spherical assembly, acquisition of the organized structure, and polarized signals of phospho-MLC2 in cortical organoids from the patient's iPSCs. We confirmed that the Rho kinase inhibitor Y27632 restored these morphological phenotypes. Thus, Gαo determines the self-organizing process of the developing brain by regulating the Rho-associated pathway. These data suggest that Rho GTPase pathway might be an alternative target of therapy for patients with GNAO1-associated encephalopathy.

Electrophysiological insights with brain organoid models: a brief review

Brain organoid is a three-dimensional (3D) tissue derived from stem cells such as induced pluripotent stem cells (iPSCs) embryonic stem cells (ESCs) that reflect real human brain structure. It replicates the complexity and development of the human brain, enabling studies of the human brain in vitro. With emerging technologies, its application is various, including disease modeling and drug screening. A variety of experimental methods have been used to study structural and molecular characteristics of brain organoids. However, electrophysiological analysis is necessary to understand their functional characteristics and complexity. Although electrophysiological approaches have rapidly advanced for monolayered cells, there are some limitations in studying electrophysiological and neural network characteristics due to the lack of 3D characteristics. Herein, electrophysiological measurement and analytical methods related to neural complexity and 3D characteristics of brain organoids are reviewed. Overall, electrophysiological understanding of brain organoids allows us to overcome limitations of monolayer in vitro cell culture models, providing deep insights into the neural network complex of the real human brain and new ways of disease modeling. [BMB Reports 2024; 57(7): 311-317].

Three dimensional and four dimensional live imaging to study mechanisms of progressive neurodegeneration

Neurodegenerative diseases are complex and progressive, posing challenges to their study and understanding. Recent advances in microscopy imaging technologies have enabled the exploration of neurons in three spatial dimensions (3D) over time (4D). When applied to 3D cultures, tissues, or animals, these technologies can provide valuable insights into the dynamic and spatial nature of neurodegenerative diseases. This review focuses on the use of imaging techniques and neurodegenerative disease models to study neurodegeneration in 4D. Imaging techniques such as confocal microscopy, two-photon microscopy, miniscope imaging, light sheet microscopy, and robotic microscopy offer powerful tools to visualize and analyze neuronal changes over time in 3D tissue. Application of these technologies to in vitro models of neurodegeneration such as mouse organotypic culture systems and human organoid models provide versatile platforms to study neurodegeneration in a physiologically relevant context. Additionally, use of 4D imaging in vivo, including in mouse and zebrafish models of neurodegenerative diseases, allows for the investigation of early dysfunction and behavioral changes associated with neurodegeneration. We propose that these studies have the power to overcome the limitations of two-dimensional monolayer neuronal cultures and pave the way for improved understanding of the dynamics of neurodegenerative diseases and the development of effective therapeutic strategies.

Rigor and reproducibility in human brain organoid research: Where we are and where we need to go

Human brain organoid models have emerged as a promising tool for studying human brain development and function. These models preserve human genetics and recapitulate some aspects of human brain development, while facilitating manipulation in an in vitro setting. Despite their potential to transform biology and medicine, concerns persist about their fidelity. To fully harness their potential, it is imperative to establish reliable analytic methods, ensuring rigor and reproducibility. Here, we review current analytical platforms used to characterize human forebrain cortical organoids, highlight challenges, and propose recommendations for future studies to achieve greater precision and uniformity across laboratories.

Three-dimensional liquid metal-based neuro-interfaces for human hippocampal organoids

Human hippocampal organoids (hHOs) derived from human induced pluripotent stem cells (hiPSCs) have emerged as promising models for investigating neurodegenerative disorders, such as schizophrenia and Alzheimer's disease. However, obtaining the electrical information of these free-floating organoids in a noninvasive manner remains a challenge using commercial multi-electrode arrays (MEAs). The three-dimensional (3D) MEAs developed recently acquired only a few neural signals due to limited channel numbers. Here, we report a hippocampal cyborg organoid (cyb-organoid) platform coupling a liquid metal-polymer conductor (MPC)-based mesh neuro-interface with hHOs. The mesh MPC (mMPC) integrates 128-channel multielectrode arrays distributed on a small surface area (~2*2 mm). Stretchability (up to 500%) and flexibility of the mMPC enable its attachment to hHOs. Furthermore, we show that under Wnt3a and SHH activator induction, hHOs produce HOPX+ and PAX6+ progenitors and ZBTB20+PROX1+ dentate gyrus (DG) granule neurons. The transcriptomic signatures of hHOs reveal high similarity to the developing human hippocampus. We successfully detect neural activities from hHOs via the mMPC from this cyb-organoid. Compared with traditional planar devices, our non-invasive coupling offers an adaptor for recording neural signals from 3D models.

Cortical brain organoid slices (cBOS) for the study of human neural cells in minimal networks

Brain organoids derived from human pluripotent stem cells are a promising tool for studying human neurodevelopment and related disorders. Here, we generated long-term cultures of cortical brain organoid slices (cBOS) grown at the air-liquid interphase from regionalized cortical organoids. We show that cBOS host mature neurons and astrocytes organized in complex architecture. Whole-cell patch-clamp demonstrated subthreshold synaptic inputs and action potential firing of neurons. Spontaneous intracellular calcium signals turned into synchronous large-scale oscillations upon combined disinhibition of NMDA receptors and blocking of GABAA receptors. Brief metabolic inhibition to mimic transient energy restriction in the ischemic brain induced reversible intracellular calcium loading of cBOS. Moreover, metabolic inhibition induced a reversible decline in neuronal ATP as revealed by ATeam1.03YEMK. Overall, cBOS provide a powerful platform to assess morphological and functional aspects of human neural cells in intact minimal networks and to address the pathways that drive cellular damage during brain ischemia.

GABAergic interneuron diversity and organization are crucial for the generation of human-specific functional neural networks in cerebral organoids

This mini review investigates the importance of GABAergic interneurons for the network function of human-induced pluripotent stem cells (hiPSC)-derived brain organoids. The presented evidence suggests that the abundance, diversity and three-dimensional cortical organization of GABAergic interneurons are the primary elements responsible for the creation of synchronous neuronal firing patterns. Without intricate inhibition, coupled oscillatory patterns cannot reach a sufficient complexity to transfer spatiotemporal information constituting physiological network function. Furthermore, human-specific brain network function seems to be mediated by a more complex and interconnected inhibitory structure that remains developmentally flexible for a longer period when compared to rodents. This suggests that several characteristics of human brain networks cannot be captured by rodent models, emphasizing the need for model systems like organoids that adequately mimic physiological human brain function in vitro.

AI-organoid integrated systems for biomedical studies and applications

In this review, we explore the growing role of artificial intelligence (AI) in advancing the biomedical applications of human pluripotent stem cell (hPSC)-derived organoids. Stem cell-derived organoids, these miniature organ replicas, have become essential tools for disease modeling, drug discovery, and regenerative medicine. However, analyzing the vast and intricate datasets generated from these organoids can be inefficient and error-prone. AI techniques offer a promising solution to efficiently extract insights and make predictions from diverse data types generated from microscopy images, transcriptomics, metabolomics, and proteomics. This review offers a brief overview of organoid characterization and fundamental concepts in AI while focusing on a comprehensive exploration of AI applications in organoid-based disease modeling and drug evaluation. It provides insights into the future possibilities of AI in enhancing the quality control of organoid fabrication, label-free organoid recognition, and three-dimensional image reconstruction of complex organoid structures. This review presents the challenges and potential solutions in AI-organoid integration, focusing on the establishment of reliable AI model decision-making processes and the standardization of organoid research.

Asteroid impact: the potential of astrocytes to modulate human neural networks within organoids

Astrocytes are a vital cellular component of the central nervous system that impact neuronal function in both healthy and pathological states. This includes intercellular signals to neurons and non-neuronal cells during development, maturation, and aging that can modulate neural network formation, plasticity, and maintenance. Recently, human pluripotent stem cell-derived neural aggregate cultures, known as neurospheres or organoids, have emerged as improved experimental platforms for basic and pre-clinical neuroscience compared to traditional approaches. Here, we summarize the potential capability of using organoids to further understand the mechanistic role of astrocytes upon neural networks, including the production of extracellular matrix components and reactive signaling cues. Additionally, we discuss the application of organoid models to investigate the astrocyte-dependent aspects of neuropathological diseases and to test astrocyte-inspired technologies. We examine the shortcomings of organoid-based experimental platforms and plausible improvements made possible by cutting-edge neuroengineering technologies. These advancements are expected to enable the development of improved diagnostic strategies and high-throughput translational applications regarding neuroregeneration.

Spatiotemporal analysis of 3D human iPSC-derived neural networks using a 3D multi-electrode array

While there is a growing appreciation of three-dimensional (3D) neural tissues (i.e., hydrogel-based, organoids, and spheroids), shown to improve cellular health and network activity to mirror brain-like activity in vivo, functional assessment using current electrophysiology techniques (e.g., planar multi-electrode arrays or patch clamp) has been technically challenging and limited to surface measurements at the bottom or top of the 3D tissue. As next-generation MEAs, specifically 3D MEAs, are being developed to increase the spatial precision across all three dimensions (X, Y, Z), development of improved computational analytical tools to discern region-specific changes within the Z dimension of the 3D tissue is needed. In the present study, we introduce a novel computational analytical pipeline to analyze 3D neural network activity recorded from a "bottom-up" 3D MEA integrated with a 3D hydrogel-based tissue containing human iPSC-derived neurons and primary astrocytes. Over a period of ~6.5 weeks, we describe the development and maturation of 3D neural activity (i.e., features of spiking and bursting activity) within cross sections of the 3D tissue, based on the vertical position of the electrode on the 3D MEA probe, in addition to network activity (identified using synchrony analysis) within and between cross sections. Then, using the sequential addition of postsynaptic receptor antagonists, bicuculline (BIC), 2-amino-5-phosphonovaleric acid (AP-5), and 6-cyano-5-nitroquinoxaline-2,3-dione (CNQX), we demonstrate that networks within and between cross sections of the 3D hydrogel-based tissue show a preference for GABA and/or glutamate synaptic transmission, suggesting differences in the network composition throughout the neural tissue. The ability to monitor the functional dynamics of the entire 3D reconstructed neural tissue is a critical bottleneck; here we demonstrate a computational pipeline that can be implemented in studies to better interpret network activity within an engineered 3D neural tissue and have a better understanding of the modeled organ tissue.

Theoretical Neurobiology of Consciousness Applied to Human Cerebral Organoids

Organoids and specifically human cerebral organoids (HCOs) are one of the most relevant novelties in the field of biomedical research. Grown either from embryonic or induced pluripotent stem cells, HCOs can be used as in vitro three-dimensional models, mimicking the developmental process and organization of the developing human brain. Based on that, and despite their current limitations, it cannot be assumed that they will never at any stage of development manifest some rudimentary form of consciousness. In the absence of behavioral indicators of consciousness, the theoretical neurobiology of consciousness being applied to unresponsive brain-injured patients can be considered with respect to HCOs. In clinical neurology, it is difficult to discern a capacity for consciousness in unresponsive brain-injured patients who provide no behavioral indicators of consciousness. In such scenarios, a validated neurobiological theory of consciousness, which tells us what the neural mechanisms of consciousness are, could be used to identify a capacity for consciousness. Like the unresponsive patients that provide a diagnostic difficulty for neurologists, HCOs provide no behavioral indicators of consciousness. Therefore, this article discusses how three prominent neurobiological theories of consciousness apply to human cerebral organoids. From the perspective of the Temporal Circuit Hypothesis, the Global Neuronal Workspace Theory, and the Integrated Information Theory, we discuss what neuronal structures and functions might indicate that cerebral organoids have a neurobiological capacity to be conscious.

Generation of mouse hippocampal brain organoids from primary embryonic neural stem cells

Here we present a protocol to generate standardized cerebral organoids with hippocampal regional specification using morphogen WNT3a. We describe steps for isolating mouse embryonic (E14.5) neural stem cells from the brain subgranular zone, preparing organoids samples for immunofluorescence, calcium imaging, and metabolic profiling. This protocol can be used to generate mouse brain organoids for developmental studies, modeling disease, and drug screening. Organoids can be obtained in one month, thus providing a rapid tool for high-throughput data validation. For complete details on the use and execution of this protocol, please refer to Ciarpella et al. "Murine cerebral organoids develop network of functional neurons and hippocampal brain region identity".1.

Peptide-Assembled Single-Chain Atomic Crystal Enhances Pluripotent Stem Cell Differentiation to Neurons

Nanomaterials hybridized with biological components have widespread applications. among many candidates, peptides are attractive in that their peptide sequences can self-assemble with the surface of target materials with high specificity without perturbing the intrinsic properties of nanomaterials. Here, a 1D hybrid nanomaterial was developed through self-assembly of a designed peptide. A hexagonal coiled-coil motif geometrically matched to the diameter of the inorganic nanomaterial was fabricated, whose hydrophobic surface was wrapped along the axis of the hydrophobic core of the coiled coil. Our morphological and spectroscopic analyses revealed rod-shaped, homogeneous peptide-inorganic nanomaterial complexes. Culturing embryonic stem cells on surfaces coated with this peptide-assembled single-chain atomic crystal increased the growth and adhesion of the embryonic stem cells. The hybridized nanomaterial also served as an ECM for brain organoids, accelerating the maturation of neurons. New methods to fabricate hybrid materials through peptide assembly can be applied.

Protruding cantilever microelectrode array to monitor the inner electrical activity of cerebral organoids

Stem cell-derived cerebral organoids are artificially grown miniature organ-like structures mimicking embryonic brain architecture. They are composed of multiple neural cell types with 3D cell layer organization exhibiting local field potential. Measuring the extracellular electrical activity by means of conventional planar microelectrode arrays is particularly challenging due to the 3D architecture of organoids. In order to monitor the intra-organoid electrical activity of thick spheroid-shaped samples, we developed long protruding microelectrode arrays able to penetrate the inner regions of cerebral organoids to measure the local potential of neurons within the organoids. A new microfabrication process has been developed which, thanks to the relaxation of internal stresses of a stack of materials deposited over a sacrificial layer, allows one to build a protruding cantilever microelectrode array placed at the apex of beams which rise vertically, over two hundred microns. These slender beams inserted deeply into the organoids give access to the recording of local field potential from neurons buried inside the organoid. This novel device shall provide valuable tools to study neural functions in greater detail.

A beginner's guide on the use of brain organoids for neuroscientists: a systematic review

BACKGROUND

The first human brain organoid protocol was presented in the beginning of the previous decade, and since then, the field witnessed the development of many new brain region-specific models, and subsequent protocol adaptations and modifications. The vast amount of data available on brain organoid technology may be overwhelming for scientists new to the field and consequently decrease its accessibility. Here, we aimed at providing a practical guide for new researchers in the field by systematically reviewing human brain organoid publications.

METHODS

Articles published between 2010 and 2020 were selected and categorised for brain organoid applications. Those describing neurodevelopmental studies or protocols for novel organoid models were further analysed for culture duration of the brain organoids, protocol comparisons of key aspects of organoid generation, and performed functional characterisation assays. We then summarised the approaches taken for different models and analysed the application of small molecules and growth factors used to achieve organoid regionalisation. Finally, we analysed articles for organoid cell type compositions, the reported time points per cell type, and for immunofluorescence markers used to characterise different cell types.

RESULTS

Calcium imaging and patch clamp analysis were the most frequently used neuronal activity assays in brain organoids. Neural activity was shown in all analysed models, yet network activity was age, model, and assay dependent. Induction of dorsal forebrain organoids was primarily achieved through combined (dual) SMAD and Wnt signalling inhibition. Ventral forebrain organoid induction was performed with dual SMAD and Wnt signalling inhibition, together with additional activation of the Shh pathway. Cerebral organoids and dorsal forebrain model presented the most cell types between days 35 and 60. At 84 days, dorsal forebrain organoids contain astrocytes and potentially oligodendrocytes. Immunofluorescence analysis showed cell type-specific application of non-exclusive markers for multiple cell types.

CONCLUSIONS

We provide an easily accessible overview of human brain organoid cultures, which may help those working with brain organoids to define their choice of model, culture time, functional assay, differentiation, and characterisation strategies.

Biosensors integrated 3D organoid/organ-on-a-chip system: A real-time biomechanical, biophysical, and biochemical monitoring and characterization

As a full-fidelity simulation of human cells, tissues, organs, and even systems at the microscopic scale, Organ-on-a-Chip (OOC) has significant ethical advantages and development potential compared to animal experiments. The need for the design of new drug high-throughput screening platforms and the mechanistic study of human tissues/organs under pathological conditions, the evolving advances in 3D cell biology and engineering, etc., have promoted the updating of technologies in this field, such as the iteration of chip materials and 3D printing, which in turn facilitate the connection of complex multi-organs-on-chips for simulation and the further development of technology-composite new drug high-throughput screening platforms. As the most critical part of organ-on-a-chip design and practical application, verifying the success of organ model modeling, i.e., evaluating various biochemical and physical parameters in OOC devices, is crucial. Therefore, this paper provides a logical and comprehensive review and discussion of the advances in organ-on-a-chip detection and evaluation technologies from a broad perspective, covering the directions of tissue engineering scaffolds, microenvironment, single/multi-organ function, and stimulus-based evaluation, and provides a more comprehensive review of the progress in the significant organ-on-a-chip research areas in the physiological state.

Consciousness in a Rotor? Science and Ethics of Potentially Conscious Human Cerebral Organoids

Human cerebral organoids are three-dimensional biological cultures grown in the laboratory to mimic as closely as possible the cellular composition, structure, and function of the corresponding organ, the brain. For now, cerebral organoids lack blood vessels and other characteristics of the human brain, but are also capable of having coordinated electrical activity. They have been usefully employed for the study of several diseases and the development of the nervous system in unprecedented ways. Research on human cerebral organoids is proceeding at a very fast pace and their complexity is bound to improve. This raises the question of whether cerebral organoids will also be able to develop the unique feature of the human brain, consciousness. If this is the case, some ethical issues would arise. In this article, we discuss the necessary neural correlates and constraints for the emergence of consciousness according to some of the most debated neuroscientific theories. Based on this, we consider what the moral status of a potentially conscious brain organoid might be, in light of ethical and ontological arguments. We conclude by proposing a precautionary principle and some leads for further investigation. In particular, we consider the outcomes of some very recent experiments as entities of a potential new kind.

Human cerebral organoids: the ethical stance of scientists

BACKGROUND

Human cerebral organoids (HCOs) offer unprecedented opportunities to study the human brain in vitro, but they also raise important ethical concerns. Here we report the first systematic analysis of scientists' stance within the ethical debate.

METHOD

Twenty-one in-depth semi-structured interviews were analyzed through a constant comparative method to highlight how the ethical concerns filter in the laboratory.

RESULTS

The results suggest that the potential emergence of consciousness is not yet seen with concern. However, there are some features of HCO research that need to be better accounted for. Communication to the public, the use of terms such as "mini-brains", and informed consent appear to be the most pressing concerns of the scientific community. Nonetheless, respondents generally showed a positive attitude toward the ethical discussion, recognizing its value and the necessity of constant ethical scrutiny over scientific advancements.

CONCLUSIONS

This research paves the way for a better-informed dialogue between scientists and ethicists, highlighting the issues to be addressed whenever scholars of different backgrounds and interests meet.

Modeling the marmoset brain using embryonic stem cell-derived cerebral assembloids

Studying the non-human primate (NHP) brain is required for the translation of rodent research to humans, but remains a challenge for molecular, cellular, and circuit-level analyses in the NHP brain due to the lack of in vitro NHP brain system. Here, we report an in vitro NHP cerebral model using marmoset (Callithrix jacchus) embryonic stem cell-derived cerebral assembloids (CAs) that recapitulate inhibitory neuron migration and cortical network activity. Cortical organoids (COs) and ganglionic eminence organoids (GEOs) were induced from cjESCs and fused to generate CAs. GEO cells expressing the inhibitory neuron marker LHX6 migrated toward the cortical side of CAs. COs developed their spontaneous neural activity from a synchronized pattern to an unsynchronized pattern as COs matured. CAs containing excitatory and inhibitory neurons showed mature neural activity with an unsynchronized pattern. The CAs represent a powerful in vitro model for studying excitatory and inhibitory neuron interactions, cortical dynamics, and their dysfunction. The marmoset assembloid system will provide an in vitro platform for the NHP neurobiology and facilitate translation into humans in neuroscience research, regenerative medicine, and drug discovery.

On the Legal Status of Human Cerebral Organoids: Lessons from Animal Law

This paper will ask whether the legal status presently afforded to nonhuman animals ought to influence regulatory debates concerning human cerebral organoids. The New York Courts recently refused to grant a writ of habeas corpus to Happy the Elephant as she was property rather than a legal person while at the same time accepting that she is a moral patient deserving of rights protection. An undesirable situation has therefore arisen in which the law holds a being with moral status to be incapable of benefitting from legal redress due to their legal status as property.The author argues that this is something that we ought to avoid when designing the regulatory framework which will govern the use of human cerebral organoids. Yet, a difference exists in that, whereas the judges already accept Happy is a moral patient, there is presently no consensus around the moral status of organoids. This paper will consider whether human cerebral organoids have passed the moral threshold of sentience. If they have, or are close to doing so, regulators ought to consider their legal status in advance so as to ensure that adequate limitations are placed on this usage so as to avoid unethical practices.

Advancing preclinical models of psychiatric disorders with human brain organoid cultures

Psychiatric disorders are often distinguished from neurological disorders in that the former do not have characteristic lesions or findings from cerebrospinal fluid, electroencephalograms (EEGs), or brain imaging, and furthermore do not have commonly recognized convergent mechanisms. Psychiatric disorders commonly involve clinical diagnosis of phenotypic behavioral disturbances of mood and psychosis, often with a poorly understood contribution of environmental factors. As such, psychiatric disease has been challenging to model preclinically for mechanistic understanding and pharmaceutical development. This review compares commonly used animal paradigms of preclinical testing with evolving techniques of induced pluripotent cell culture with a focus on emerging three-dimensional models. Advances in complexity of 3D cultures, recapitulating electrical activity in utero, and disease modeling of psychosis, mood, and environmentally induced disorders are reviewed. Insights from these rapidly expanding technologies are discussed as they pertain to the utility of human organoid and other models in finding novel research directions, validating pharmaceutical action, and recapitulating human disease.

Human embryonic stem cell-derived cerebral organoids for treatment of mild traumatic brain injury in a mouse model

OBJECTIVE

There are no effective treatments for relieving neuronal dysfunction after mild traumatic brain injury (TBI). Here, we evaluated therapeutic efficacy of human embryonic stem cell-derived cerebral organoids (hCOs) in a mild TBI model, in terms of repair of damaged cortical regions, neurogenesis, and improved cognitive function.

METHODS

Male C57BL/6 J mice were randomly divided into sham-operated, mild TBI, and mild TBI with hCO groups. hCOs cultured at 8 weeks were used for transplantation. Mice were sacrificed at 7 and 14 days after transplantation followed by immunofluorescence staining, cytokine profile microarray, and novel object recognition test.

RESULTS

8W-hCOs transplantation significantly reduced neuronal cell death, recovered microvessel density, and promoted neurogenesis in the ipsilateral subventricular zone and dentate gyrus of hippocampus after mild TBI. In addition, increased angiogenesis into the engrafted hCOs was observed. Microarray results of hCOs revealed neuronal differentiation potential and higher expression of early brain development proteins associated with neurogenesis, angiogenesis and extracellular matrix remodeling. Ultimately, 8W-hCO transplantation resulted in reconstruction of damaged cortex and improvement in cognitive function after mild TBI.

CONCLUSION

hCO transplantation may be feasible for treating mild TBI-related neuronal dysfunction via reconstruction of damaged cortex and neurogenesis in the hippocampus.

In vitro neurons learn and exhibit sentience when embodied in a simulated game-world

Integrating neurons into digital systems may enable performance infeasible with silicon alone. Here, we develop DishBrain, a system that harnesses the inherent adaptive computation of neurons in a structured environment. In vitro neural networks from human or rodent origins are integrated with in silico computing via a high-density multielectrode array. Through electrophysiological stimulation and recording, cultures are embedded in a simulated game-world, mimicking the arcade game "Pong." Applying implications from the theory of active inference via the free energy principle, we find apparent learning within five minutes of real-time gameplay not observed in control conditions. Further experiments demonstrate the importance of closed-loop structured feedback in eliciting learning over time. Cultures display the ability to self-organize activity in a goal-directed manner in response to sparse sensory information about the consequences of their actions, which we term synthetic biological intelligence. Future applications may provide further insights into the cellular correlates of intelligence.

A minimal-complexity light-sheet microscope maps network activity in 3D neuronal systems

In vitro systems mimicking brain regions, brain organoids, are revolutionizing the neuroscience field. However, characterization of their electrical activity has remained a challenge as it requires readout at millisecond timescale in 3D at single-neuron resolution. While custom-built microscopes used with genetically encoded sensors are now opening this door, a full 3D characterization of organoid neural activity has not been performed yet, limited by the combined complexity of the optical and the biological system. Here, we introduce an accessible minimalistic light-sheet microscope to the neuroscience community. Designed as an add-on to a standard inverted microscope it can be assembled within one day. In contrast to existing simplistic setups, our platform is suited to record volumetric calcium traces. We successfully extracted 4D calcium traces at high temporal resolution by using a lightweight piezo stage to allow for 5 Hz volumetric scanning combined with a processing pipeline for true 3D neuronal trace segmentation. As a proof of principle, we created a 3D connectivity map of a stem cell derived neuron spheroid by imaging its activity. Our fast, low complexity setup empowers researchers to study the formation of neuronal networks in vitro for fundamental and neurodegeneration research.

Motor neuron-derived induced pluripotent stem cells as a drug screening platform for amyotrophic lateral sclerosis

The development of cell culture models that recapitulate the etiology and features of nervous system diseases is central to the discovery of new drugs and their translation onto therapies. Neuronal tissues are inaccessible due to skeletal constraints and the invasiveness of the procedure to obtain them. Thus, the emergence of induced pluripotent stem cell (iPSC) technology offers the opportunity to model different neuronal pathologies. Our focus centers on iPSCs derived from amyotrophic lateral sclerosis (ALS) patients, whose pathology remains in urgent need of new drugs and treatment. In this sense, we aim to revise the process to obtain motor neurons derived iPSCs (iPSC-MNs) from patients with ALS as a drug screening model, review current 3D-models and offer a perspective on bioinformatics as a powerful tool that can aid in the progress of finding new pharmacological treatments.

Functional neuronal circuitry and oscillatory dynamics in human brain organoids

Human brain organoids replicate much of the cellular diversity and developmental anatomy of the human brain. However, the physiology of neuronal circuits within organoids remains under-explored. With high-density CMOS microelectrode arrays and shank electrodes, we captured spontaneous extracellular activity from brain organoids derived from human induced pluripotent stem cells. We inferred functional connectivity from spike timing, revealing a large number of weak connections within a skeleton of significantly fewer strong connections. A benzodiazepine increased the uniformity of firing patterns and decreased the relative fraction of weakly connected edges. Our analysis of the local field potential demonstrate that brain organoids contain neuronal assemblies of sufficient size and functional connectivity to co-activate and generate field potentials from their collective transmembrane currents that phase-lock to spiking activity. These results point to the potential of brain organoids for the study of neuropsychiatric diseases, drug action, and the effects of external stimuli upon neuronal networks.

Automatic differentiation of human induced pluripotent stem cells toward synchronous neural networks on an arrayed monolayer of nanofiber membrane

Automatic differentiation of human-induced pluripotent stem cells (hiPSCs) facilitates the generation of cortical neural networks and studies of brain functions. Here, we present a method of directed differentiation of hiPSCs with a substrate made of a honeycomb microframe and a monolayer of crosslinked gelatin nanofibers in the form of an array of nanofiber membranes. Neural precursor cells (NPCs) were firstly derived from hiPSCs and then placed on the nanofiber membranes for automatically controlled neural differentiation over a long period. Due to the strong modulation of the substrate stiffness and permeability, most cells were found in the center area of the honeycomb compartments, giving rise to regular and inter-connected cortical neural clusters. More importantly, the neural activities of the clusters were synchronized proving the reliability of the method. Our results showed that the self-organization, as well as the neural activities of differentiating neural cells, were more efficient in the nanofiber membrane compared to the types of the substrate such as glass and nanofiber-covered glass. In addition to the inherent advantages such as manpower saving and fewer risks of contamination and human error, automatic differentiation avoided undesired shaking which might have critical effects on the formation of synchronous neural clusters. STATEMENT OF SIGNIFICANCE: : Synchronization of cortical neural activities is essential for information processing and human cognition. By automated differentiation of human induced pluripotent stem cells on arrayed monolayer of nanofiber membrane, synchronous neural clusters could be formed. Such an approach would allow creating a variety of neural networks with regular and interconnected clusters for systematic studies of human cortical functions.

Functional imaging of brain organoids using high-density microelectrode arrays

ABSTRACT

Studies have provided evidence that human cerebral organoids (hCOs) recapitulate fundamental milestones of early brain development, but many important questions regarding their functionality and electrophysiological properties persist. High-density microelectrode arrays (HD-MEAs) represent an attractive analysis platform to perform functional studies of neuronal networks at the cellular and network scale. Here, we use HD-MEAs to derive large-scale electrophysiological recordings from sliced hCOs. We record the activity of hCO slices over several weeks and probe observed neuronal dynamics pharmacologically. Moreover, we present results on how the obtained recordings can be spike-sorted and subsequently studied across scales. For example, we show how to track single neurons across several days on the HD-MEA and how to infer axonal action potential velocities. We also infer putative functional connectivity from hCO recordings. The introduced methodology will contribute to a better understanding of developing neuronal networks in brain organoids and provide new means for their functional characterization.

IMPACT STATEMENT

Human cerebral organoids (hCOs) represent an attractive in vitro model system to study key physiological mechanisms underlying early neuronal network formation in tissue with healthy or disease-related genetic backgrounds. Despite remarkable advances in the generation of brain organoids, knowledge on the functionality of their neuronal circuits is still scarce. Here, we used complementary metal-oxide-semiconductor (CMOS)-based high-density microelectrode arrays (HD-MEAs) to perform large-scale recordings from sliced hCOs over several weeks and quantified their activity across scales. Using single-cell and network metrics, we were able to probe aspects of hCO neurophysiology that are more difficult to obtain with other techniques, such as patch clamping (lower yield) and calcium imaging (lower temporal resolution). These metrics included, for example, extracellular action potential (AP) waveform features and axonal AP velocity at the cellular level, as well as functional connectivity at the network level. Analysis was enabled by the large sensing area and the high spatiotemporal resolution provided by HD-MEAs, which allowed recordings from hundreds of neurons and spike sorting of their activity. Our results demonstrate that HD-MEAs provide a multi-purpose platform for the functional characterization of hCOs, which will be key in improving our understanding of this model system and assessing its relevance for translational research.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43577-022-00282-w.

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Generation of Interconnected Neural Clusters in Multiscale Scaffolds from Human-Induced Pluripotent Stem Cells

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Lipopolysaccharide-induced neuroinflammation disrupts functional connectivity and community structure in primary cortical microtissues

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