Light activation of channelrhodopsin-2 in excitable cells of Caenorhabditis elegans triggers rapid behavioral responses

Unravelling the Brain Resilience Following Stroke: From injury to rewiring of the brain through pathway activation, drug targets, and therapeutic interventions

Synaptic plasticity is a neuron's intrinsic ability to make new connections throughout life. The morphology and function of synapses are highly susceptible to any pathological condition. Ischemic stroke is a cerebrovascular event that affects various brain regions, resulting in the loss of neural networks. Stroke can alter both structural and functional plasticity of synapses, leading to long-term functional disability. Upon ischemic insult, numerous glutamate-mediated synaptic destruction pathways and glial-mediated phagocytic activity are triggered, resulting in excessive synapse loss, altering synaptic plasticity. The conventional stroke therapies to improve synaptic plasticity are still limited and ineffectual, leading to sub-optimal recovery in patients. Therefore, promoting synaptic plasticity to ameliorate sensory-motor function may be a promising strategy for long-term recovery in stroke patients. Here, we review the involvement of different molecular pathways of glutamate and glia-mediated synapse loss, current pharmacological targets, and the emerging novel approaches to improve synaptic plasticity and sensory-motor impairment post-stroke.

Flower/FLWR-1 regulates neuronal activity via the plasma membrane Ca2+ ATPase to promote recycling of synaptic vesicles

The Flower protein was suggested to couple the fusion of synaptic vesicles (SVs) to their recycling in different model organisms. It is supposed to trigger activity-dependent bulk endocytosis by conducting Ca2+ at endocytic sites. However, this mode of action is debated. Here, we investigated the role of the Caenorhabditis elegans homologue FLWR-1 in neurotransmission. Our results confirm that FLWR-1 facilitates the recycling of SVs at the neuromuscular junction (NMJ). Ultrastructural analysis of synaptic boutons after hyperstimulation revealed an accumulation of large endocytic structures in flwr-1 mutants. These findings do not support a role of FLWR-1 in the formation of bulk endosomes but rather a function in their breakdown. Unexpectedly, the loss of FLWR-1 led to increased neuronal Ca2+ levels in axon terminals during stimulation, particularly in GABAergic motor neurons, causing excitation-inhibition imbalance. We found that this increased NMJ transmission might be caused by deregulation of MCA-3, the nematode orthologue of the plasma membrane Ca2+ ATPase (PMCA). In vivo molecular interactions indicated that FLWR-1 may be a positive regulator of the PMCA and might influence its recycling through modification of plasma membrane levels of phosphatidylinositol-4,5-bisphosphate (PI(4,5)P2).

Neuromodulation in Small Animal fMRI

The integration of functional magnetic resonance imaging (fMRI) with advanced neuroscience technologies in experimental small animal models offers a unique path to interrogate the causal relationships between regional brain activity and brain-wide network measures-a goal challenging to accomplish in human subjects. This review traces the historical development of the neuromodulation techniques commonly used in rodents, such as electrical deep brain stimulation, optogenetics, and chemogenetics, and focuses on their application with fMRI. We discuss their advantageousness roles in uncovering the signaling architecture within the brain and the methodological considerations necessary when conducting these experiments. By presenting several rodent-based case studies, we aim to demonstrate the potential of the multimodal neuromodulation approach in shedding light on neurovascular coupling, the neural basis of brain network functions, and their connections to behaviors. Key findings highlight the cell-type and circuit-specific modulation of brain-wide activity patterns and their behavioral correlates. We also discuss several future directions and feature the use of mediation and moderation analytical models beyond the intuitive evoked response mapping, to better leverage the rich information available in fMRI data with neuromodulation. Using fMRI alongside neuromodulation techniques provide insights into the mesoscopic (relating to the intermediate scale between single neurons and large-scale brain networks) and macroscopic fMRI measures that correlate with specific neuronal events. This integration bridges the gap between different scales of neuroscience research, facilitating the exploration and testing of novel therapeutic strategies aimed at altering network-mediated behaviors. In conclusion, the combination of fMRI with neuromodulation techniques provides crucial insights into mesoscopic and macroscopic brain dynamics, advancing our understanding of brain function in health and disease. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 1.

Optogenetic engineering for ion channel modulation

Optogenetics, which integrates photonics and genetic engineering to control protein activity and cellular processes, has transformed biomedical research. Its precise spatiotemporal control, minimal invasiveness, and tunable reversibility have spurred its widespread adoption in both basic and clinical research. Optogenetic techniques have been applied to partially restore vision in blind patients and are being actively explored as innovative treatments for neurological, psychiatric, cardiac, and immunological disorders. Microbial channelrhodopsins (ChRs) allow precise manipulation of neuronal and cardiac activities, while vertebrate rhodopsins offer unique opportunities for ion channel modulation through G-protein-coupled receptor (GPCR) pathways. Plant-derived photoswitchable domains can also be engineered into ion channels to confer photosensitivity. This review summarizes the latest progress in engineering genetically encoded light-sensitive ion channel actuators and modulators (GELICAMs) with diverse ion selectivity and spectral sensitivity. We further discuss the potential applications and challenges of these tools in advancing biomedical research and therapeutic interventions.

Advances in Optogenetics and Thermogenetics for Control of Non-Neuronal Cells and Tissues in Biomedical Research

Optogenetics and chemogenetics are relatively new biomedical technologies that emerged 20 years ago and have been evolving rapidly since then. This has been made possible by the combined use of genetic engineering, optics, and electrophysiology. With the development of optogenetics and thermogenetics, the molecular tools for cellular control are continuously being optimized, studied, and modified, expanding both their applications and their biomedical uses. The most notable changes have occurred in the basic life sciences, especially in neurobiology and the activation of neurons to control behavior. Currently, these methods of activation have gone far beyond neurobiology and are being used in cardiovascular research, for potential cancer therapy, to control metabolism, etc. In this review, we provide brief information on the types of molecular tools for optogenetic and thermogenetic methods─microbial rhodopsins and proteins of the TRP superfamily─and also consider their applications in the field of activation of non-neuronal tissues and mammalian cells. We also consider the potential of these technologies and the prospects for the use of optogenetics and thermogenetics in biomedical research.

Combined Mutational and Spectroscopic Study on the Calcium-Related Kinetic Effects on the VirChR1 Photocycle

The viral rhodopsin 1 subfamily consists of microbial rhodopsins, such as VirChR1, with a light-gated cation channeling functionality, which is inhibited by calcium. For VirChR1, S14, E54, and N225 have been proposed as key residues for calcium binding. They form a highly conserved SEN-triad in channelrhodopsins near the functionally important central gate. Here, we present a time-resolved UV/vis spectroscopic study on the VirChR1 variants S14A, E54A, and N225A in a calcium-dependent manner. Comparison with the calcium-associated effects observed for the wild type shed light on the role of the respective residues for the calcium interaction. While S14A shows less pronounced, yet similar, signals, indicative of a reduced calcium affinity, E54A exhibits nearly calcium-independent photocycle kinetics, highlighting its crucial role for calcium binding. The N225A variant shows altered photocycle kinetics, in both the absence and presence of calcium, demonstrating its critical role in the formation of the functionally important central gate in VirChR1.

Optimal Neuromuscular Performance Requires Motor Neuron Phosphagen Kinases

Phosphagen systems are crucial for muscle bioenergetics - rapidly regenerating ATP to support the high metabolic demands of intense musculoskeletal activity. However, their roles in motor neurons that drive muscle contraction have received little attention. Here, we knocked down expression of the primary phosphagen kinase [Arginine Kinase 1; ArgK1] in Drosophila larval motor neurons and assessed the impact on presynaptic energy metabolism and neurotransmission in situ . Fluorescent metabolic probes showed a deficit in presynaptic energy metabolism and some glycolytic compensation. Glycolytic compensation was revealed through a faster elevation in lactate at high firing frequencies, and the accumulation of pyruvate subsequent to firing. Our performance assays included two tests of endurance: enforced cycles of presynaptic calcium pumping, and, separately, enforced body-wall contractions for extended periods. Neither test of endurance revealed deficits when ArgK1 was knocked down. The only performance deficits were detected at firing frequencies that approached, or exceeded, twice the firing frequencies recorded during fictive locomotion, where both electrophysiology and SynaptopHluorin imaging showed an inability to sustain neurotransmitter release. Our computational modeling of presynaptic bioenergetics indicates that the phosphagen system's contribution to motor neuron performance is likely through the removal of ADP in microdomains close to sites of ATP hydrolysis, rather than the provision of a deeper reservoir of ATP. Taken together, these data demonstrate that, as in muscle fibers, motor neurons rely on phosphagen systems during activity that imposes intense energetic demands.

Electrophysiologically calibrated optogenetic stimulation of dentate granule cells mitigates dendritic spine loss in denervated organotypic entorhino-hippocampal slice cultures

Organotypic slice cultures (OTCs) are versatile tools for studying long-term structure-function relationships of neurons within a defined network (e.g. hippocampus). We developed a method for repeated experimenter-controlled activation of hippocampal granule cells (GCs) in OTCs within the incubator. After several days of contact-free photonic stimulation, we were able to ameliorate entorhinal denervation-induced structural damage in GCs. To achieve this outcome, we had to calibrate the intensity and duration of optogenetic (light) pulses using whole-cell electrophysiological recordings and multi-cell calcium imaging. Our findings showed that ChR2-expressing cells generated action potentials (APs) or calcium transients in response to illumination but were otherwise functionally indistinguishable from non-transduced GCs within the same neural circuit. However, the threshold for AP firing in single GCs varied based on the stimulus light intensity and the expression levels of ChR2. This information allowed us to calibrate light intensity for chronic stimulations. Denervated GCs exhibited significant spine loss four days post-denervation, but this detrimental effect was mitigated when AP firing was induced at a physiological GC bursting rate. Phototoxic damage caused by chronic light exposure was significantly reduced if illuminated with longer wavelength and by adding antioxidants to the culture medium. Our study presents a versatile approach for concurrent non-invasive manipulation and observation of neural circuit activity and remodeling in vitro.

Optogenetic calcium modulation in astrocytes enhances post-stroke recovery in chronic capsular infarct

Stroke is caused by disruption of cerebral blood flow, leading to neuronal death and dysfunction in the interconnected areas, which results in a wide range of severe symptoms depending on the specific brain regions affected. While previous studies have primarily focused on direct modulation of neuronal activity for post-stroke treatment, accumulating evidence suggests that astrocytes may play a critical role in post-stroke progression and could serve as a potential therapeutic target for recovery. In this study, we investigate the effects of selective modulation of astrocytic calcium signals on chronic stroke using OptoSTIM1, an optogenetic tool that activates endogenous calcium channels. In contrast to channelrhodopsin-2 (ChR2), OptoSTIM1 robustly elevates astrocytic calcium levels, sustaining the increase for over 10 min upon a single activation. The calcium elevation in astrocytes in the ipsilesional sensory-parietal cortex leads to remarkable recovery from post-stroke impairment. Thus, manipulating intracellular calcium levels in astrocytes holds promise as a potential therapeutic strategy for improving recovery following a stroke.

Abraham Patchornik: The Contemporary Relevance of His Work for Chemistry and Biology

Abraham Patchornik was born in 1926 in Ness Ziona, a town in Palestine founded by his great-grandfather Reuben Lehrer in 1883. He started to study chemistry as an undergraduate at the Hebrew University. However, this was interrupted by the war, and he completed his studies in various locations in West Jerusalem. From 1952 to 1956 Patchornik completed his PhD at the (new) Weizmann Institute of Science with Ephraim Katchalski. After a postdoc at the NIH, he returned to the Weizmann in 1958, when he joined the Department of Biophysics. In 1972-1979, he became chairman of the new Department of Organic Chemistry at the Weizmann, and his own research was geared toward applying creative chemistry to solve biological problems. Patchornik passed away in his hometown of Ness Ziona in 2014. Patchornik was a conceptual leader in peptide and polymer chemistry. Given the importance of selective functional group protection for the construction of oligomeric molecules, he became interested in using "nonstandard", orthogonal chemistry for this purpose, i.e. photosensitive protecting groups (PPGs) in place of thermal reactions. It was R.B. Woodward who suggested this strategy to Patchornik in 1965, while Patchornik was on sabbatical leave at Harvard. However, it was not until Patchornik returned to the Weizmann that this idea of a versatile PPG to enable multistep synthesis was realized. Here, we provide an account of the early photosensitive protecting groups that Patchornik and co-workers developed, and the immense impact they have had on various fields. In particular, we survey the use of PPGs in live cell physiology (i.e., caged compounds), and the development of gene chips via light-directed solid-phase synthesis. Further, we highlight recent work applying new PPGs for "photochemical delivery" of drugs, otherwise termed photopharmacology. Finally, we discuss the relationship between caged compounds and how contemporary neuroscience uses genetically encoded chromophores to control cell function.

Monitoring and modulating cardiac bioelectricity: from Einthoven to end-user

In 2024, we celebrate the 100th anniversary of Willem Einthoven receiving the Nobel Prize for his discovery of the mechanism of the electrocardiogram (ECG). Building on Einthoven's legacy, electrocardiography allows the monitoring of cardiac bioelectricity through solutions to the so-called forward and inverse problems. These solutions link local cardiac electrical signals with the morphology of the ECG, offering a reversible connection between the heart's electrical activity and its representation on the body surface. Inspired by Einthoven's work, researchers have explored the transition from monitoring to modulation of bioelectrical activity in the heart for the development of new anti-arrhythmic strategies, e.g. via optogenetics. In this review, we demonstrate the lasting influence that Einthoven has on our understanding of cardiac electrophysiology in general, and the diagnosis and treatment of cardiac arrhythmias in particular.

Overexpression of enhanced yellow fluorescent protein fused with Channelrhodopsin-2 causes contractile dysfunction in skeletal muscle

Skeletal muscle activation using optogenetics has emerged as a promising technique for inducing noninvasive muscle contraction and assessing muscle function both in vivo and in vitro. Transgenic mice overexpressing the optogenetic fusion protein, Channelrhodopsin 2-EYFP (ChR2-EYFP) in skeletal muscle are widely used; however, overexpression of fluorescent proteins can negatively impact the functionality of activable tissues. In this study, we characterized the contractile properties of ChR2-EYFP skeletal muscle and introduced the ChR2-only mouse model that expresses light-responsive ChR2 without the fluorescent EYFP in their skeletal muscles. We found a significant reduction in the contractile ability of ChR2-EYFP muscles compared with ChR2-only and WT mice, observed under both electrical and optogenetic stimulation paradigms. Bulk RNAseq identified the downregulation of genes associated with transmembrane transport and metabolism in ChR2-EYFP muscle, while the ChR2-only muscle did not demonstrate any notable deviations from WT muscle. The RNAseq results were further corroborated by a reduced protein-level expression of ion channel-related HCN2 in ChR2-EYFP muscles and gluconeogenesis-modulating FBP2 in both ChR2-EYFP and ChR2-only muscles. Overall, this study reveals an intrinsic skeletal dysfunction in the widely used ChR2-EYFP mice model and underscores the importance of considering alternative optogenetic models, such as the ChR2-only, for future research in skeletal muscle optogenetics.

An inhibitory acetylcholine receptor gates context-dependent mechanosensory processing in C. elegans

An animal's current behavior influences its response to sensory stimuli, but the molecular and circuit-level mechanisms of this context-dependent decision-making are not well understood. Caenorhabditis elegans are less likely to respond to a mechanosensory stimulus by reversing if the stimuli is received while the animal turns. Inhibitory feedback from turning associated neurons are needed for this gating. But until now, it has remained unknown precisely where in the circuit gating occurs and which specific neurons and receptors receive inhibition from the turning circuitry. Here, we use genetic manipulations, single-cell rescue experiments, and high-throughput closed-loop optogenetic perturbations during behavior to reveal the specific neuron and receptor responsible for receiving inhibition and altering sensorimotor processing. Our measurements show that an inhibitory acetylcholine-gated chloride channel comprising LGC-47 and ACC-1 expressed in neuron type RIM disrupts mechanosensory evoked reversals during turns, presumably in response to inhibitory signals from turning-associated neuron SAA.

Impact of background input on memory consolidation

Memory consolidation involves repeated replay of new information by the hippocampus, which transfers memories to the neocortex for long-term storage. This occurs mainly during slow wave sleep, a phase characterized in the cortex by low cholinergic tone and low afferent input. High cholinergic tone has been shown to hamper memory consolidation, probably mediated by reduced network excitability (the ease of activity propagation in a network). We used cortical neuronal networks on multi electrode arrays to investigate whether low background input contributes to memory consolidation. Networks received focal electrical stimuli to memorize, with or without background afferent input (global optogenetic stimulation). Background stimulation hampered memory formation and consolidation, confirming the importance of low background input. Moreover, it lowered network excitability, similar to high cholinergic tone. These findings suggest that high network excitability is a critical feature of slow wave sleep that facilitates memory consolidation.

Local stimulation of pyramidal neurons in deep cortical layers of anesthetized rats enhances cortical visual information processing

In the primary visual cortex area V1 activation of inhibitory interneurons, which provide negative feedback for excitatory pyramidal neurons, can improve visual response reliability and orientation selectivity. Moreover, optogenetic activation of one class of interneurons, parvalbumin (PV) positive cells, reduces the receptive field (RF) width. These data suggest that in V1 the negative feedback improves visual information processing. However, according to information theory, noise can limit information content in a signal, and to the best of our knowledge, in V1 signal-to-noise ratio (SNR) has never been estimated following either pyramidal or inhibitory neuron activation. Therefore, we optogenetically activated pyramidal or PV neurons in the deep layers of cortical area V1 and measured the SNR and RF area in nearby pyramidal neurons. Activation of pyramidal or PV neurons increased the SNR by 267% and 318%, respectively, and reduced the RF area to 60.1% and 77.5%, respectively, of that of the control. A simple integrate-and-fire neuron model demonstrated that an improved SNR and a reduced RF area can increase the amount of information encoded by neurons. We conclude that in V1 activation of pyramidal neurons improves visual information processing since the location of the visual stimulus can be pinpointed more accurately (via a reduced RF area), and more information is encoded by neurons (due to increased SNR).

Combined-electrical optogenetic stimulation but not channelrhodopsin kinetics improves the fidelity of high rate stimulation in the auditory pathway in mice

Novel stimulation methods are needed to overcome the limitations of contemporary cochlear implants. Optogenetics is a technique that confers light sensitivity to neurons via the genetic introduction of light-sensitive ion channels. By controlling neural activity with light, auditory neurons can be activated with higher spatial precision. Understanding the behaviour of opsins at high stimulation rates is an important step towards their translation. To elucidate this, we compared the temporal characteristics of auditory nerve and inferior colliculus responses to optogenetic, electrical, and combined optogenetic-electrical stimulation in virally transduced mice expressing one of two channelrhodopsins, ChR2-H134R or ChIEF, at stimulation rates up to 400 pulses per second (pps). At 100 pps, optogenetic responses in ChIEF mice demonstrated higher fidelity, less change in latency, and greater response stability compared to responses in ChR2-H134R mice, but not at higher rates. Combined stimulation improved the response characteristics in both cohorts at 400 pps, although there was no consistent facilitation of electrical responses. Despite these results, day-long stimulation (up to 13 h) led to severe and non-recoverable deterioration of the optogenetic responses. The results of this study have significant implications for the translation of optogenetic-only and combined stimulation techniques for hearing loss.

Characterization of the tail current of Channelrhodopsin-2 variants

Our study focused on specific ChR2 variants, particularly those with the Step function Opsins (SFO) mutation at the D156-C128 gate. These are widely used in optogenetics due to their heightened sensitivity to light and bi-stable prolonged activation. However, in some ChR2 variants, specifically D156 mutants, a tail current occurs when continuous light exposure is stopped. We specifically examined the D156H-T159S ChR2 variant, which demonstrated a tail current that was somewhat responsive to light and voltage, with a single-channel current of around 9fA, similar to wt-ChR2 as determined by stationary noise analysis. To further investigate, we used nonstationary noise analysis in cell-attached patching mode, which revealed that the tail current's single-channel current falls within the same range as the peak current, albeit with mild contamination from adaptation and desensitization. This finding strongly supports the notion that a portion of the ChR2 molecules open or re-open at the end of illumination, leading to further membrane depolarization.

An activity-regulated transcriptional program directly drives synaptogenesis

Although the molecular composition and architecture of synapses have been widely explored, much less is known about what genetic programs directly activate synaptic gene expression and how they are modulated. Here, using Caenorhabditis elegans dopaminergic neurons, we reveal that EGL-43/MECOM and FOS-1/FOS control an activity-dependent synaptogenesis program. Loss of either factor severely reduces presynaptic protein expression. Both factors bind directly to promoters of synaptic genes and act together with CUT homeobox transcription factors to activate transcription. egl-43 and fos-1 mutually promote each other's expression, and increasing the binding affinity of FOS-1 to the egl-43 locus results in increased presynaptic protein expression and synaptic function. EGL-43 regulates the expression of multiple transcription factors, including activity-regulated factors and developmental factors that define multiple aspects of dopaminergic identity. Together, we describe a robust genetic program underlying activity-regulated synapse formation during development.

Dual color optogenetic tool enables heart arrest, bradycardic, and tachycardic pacing in Drosophila melanogaster

In order to facilitate cardiovascular research to develop non-invasive optical heart pacing methods, we have generated a double-transgenic Drosophila melanogaster (fruit fly) model suitable for optogenetic pacing. We created a fly stock with both excitatory H134R-ChR2 and inhibitory eNpHR2.0 opsin transgenes. Opsins were expressed in the fly heart using the Hand-GAL4 driver. Here we describe Hand > H134R-ChR2; eNpHR2.0 model characterization including bi-directional heart control (activation and inhibition) upon illumination of light with distinct wavelengths. Optical control and real-time visualization of the heart function were achieved non-invasively using an integrated light stimulation and optical coherence microscopy (OCM) system. OCM produced high-speed and high-resolution imaging; simultaneously, the heart function was modulated by blue (470 nm) or red (617 nm) light pulses causing tachycardia, bradycardia and restorable cardiac arrest episodes in the same animal. The irradiance power levels and illumination schedules were optimized to achieve successful non-invasive bi-directional heart pacing in Drosophila larvae and pupae.

Optogenetic induction of mechanical muscle stress identifies myosin regulatory ubiquitin ligase NHL-1 in C. elegans

Mechanical stress during muscle contraction is a constant threat to proteome integrity. However, there is a lack of experimental systems to identify critical proteostasis regulators under mechanical stress conditions. Here, we present the transgenic Caenorhabditis elegans model OptIMMuS (Optogenetic Induction of Mechanical Muscle Stress) to study changes in the proteostasis network associated with mechanical forces. Repeated blue light exposure of a muscle-expressed Chlamydomonas rheinhardii channelrhodopsin-2 variant results in sustained muscle contraction and mechanical stress. Using OptIMMuS, combined with proximity labeling and mass spectrometry, we identify regulators that cooperate with the myosin-directed chaperone UNC-45 in muscle proteostasis. One of these is the TRIM E3 ligase NHL-1, which interacts with UNC-45 and muscle myosin in genetic epistasis and co-immunoprecipitation experiments. We provide evidence that the ubiquitylation activity of NHL-1 regulates myosin levels and functionality under mechanical stress. In the future, OptIMMuS will help to identify muscle-specific proteostasis regulators of therapeutic relevance.

Bridging model and experiment in systems neuroscience with Cleo: the Closed-Loop, Electrophysiology, and Optophysiology simulation testbed

Systems neuroscience has experienced an explosion of new tools for reading and writing neural activity, enabling exciting new experiments such as all-optical or closed-loop control that effect powerful causal interventions. At the same time, improved computational models are capable of reproducing behavior and neural activity with increasing fidelity. Unfortunately, these advances have drastically increased the complexity of integrating different lines of research, resulting in the missed opportunities and untapped potential of suboptimal experiments. Experiment simulation can help bridge this gap, allowing model and experiment to better inform each other by providing a low-cost testbed for experiment design, model validation, and methods engineering. Specifically, this can be achieved by incorporating the simulation of the experimental interface into our models, but no existing tool integrates optogenetics, two-photon calcium imaging, electrode recording, and flexible closed-loop processing with neural population simulations. To address this need, we have developed Cleo: the Closed-Loop, Electrophysiology, and Optophysiology experiment simulation testbed. Cleo is a Python package enabling injection of recording and stimulation devices as well as closed-loop control with realistic latency into a Brian spiking neural network model. It is the only publicly available tool currently supporting two-photon and multi-opsin/wavelength optogenetics. To facilitate adoption and extension by the community, Cleo is open-source, modular, tested, and documented, and can export results to various data formats. Here we describe the design and features of Cleo, validate output of individual components and integrated experiments, and demonstrate its utility for advancing optogenetic techniques in prospective experiments using previously published systems neuroscience models.

In vivo photocontrol of orexin receptors with a nanomolar light-regulated analogue of orexin-B

Orexinergic neurons are critically involved in regulating arousal, wakefulness, and appetite. Their dysfunction has been associated with sleeping disorders, and non-peptide drugs are currently being developed to treat insomnia and narcolepsy. Yet, no light-regulated agents are available to reversibly control their activity. To meet this need, a photoswitchable peptide analogue of the endogenous neuroexcitatory peptide orexin-B was designed, synthesized, and tested in vitro and in vivo. This compound - photorexin - is the first photo-reversible ligand reported for orexin receptors. It allows dynamic control of activity in vitro (including almost the same efficacy as orexin-B, high nanomolar potency, and subtype selectivity to human OX2 receptors) and in vivo in zebrafish larvae by direct application in water. Photorexin induces dose- and light-dependent changes in locomotion and a reduction in the successive induction reflex that is associated with sleep behavior. Molecular dynamics calculations indicate that trans and cis photorexin adopt similar bent conformations and that the only discriminant between their structures and activities is the positioning of the N-terminus. This, in the case of the more active trans isomer, points towards the OX2 N-terminus and extra-cellular loop 2, a region of the receptor known to be involved in ligand binding and recognition consistent with a "message-address" system. Thus, our approach could be extended to several important families of endogenous peptides, such as endothelins, nociceptin, and dynorphins among others, that bind to their cognate receptors through a similar mechanism: a "message" domain involved in receptor activation and signal transduction, and an "address" sequence for receptor occupation and improved binding affinity.

Information Transmission through Biotic-Abiotic Interfaces to Restore or Enhance Human Function

Advancements in reliable information transfer across biotic-abiotic interfaces have enabled the restoration of lost human function. For example, communication between neuronal cells and electrical devices restores the ability to walk to a tetraplegic patient and vision to patients blinded by retinal disease. These impactful medical achievements are aided by tailored biotic-abiotic interfaces that maximize information transfer fidelity by considering the physical properties of the underlying biological and synthetic components. This Review develops a modular framework to define and describe the engineering of biotic and abiotic components as well as the design of interfaces to facilitate biotic-abiotic information transfer using light or electricity. Delineating the properties of the biotic, interface, and abiotic components that enable communication can serve as a guide for future research in this highly interdisciplinary field. Application of synthetic biology to engineer light-sensitive proteins has facilitated the control of neural signaling and the restoration of rudimentary vision after retinal blindness. Electrophysiological methodologies that use brain-computer interfaces and stimulating implants to bypass spinal column injuries have led to the rehabilitation of limb movement and walking ability. Cellular interfacing methodologies and on-chip learning capability have been made possible by organic transistors that mimic the information processing capacity of neurons. The collaboration of molecular biologists, material scientists, and electrical engineers in the emerging field of biotic-abiotic interfacing will lead to the development of prosthetics capable of responding to thought and experiencing touch sensation via direct integration into the human nervous system. Further interdisciplinary research will improve electrical and optical interfacing technologies for the restoration of vision, offering greater visual acuity and potentially color vision in the near future.

Glial KCNQ K+ channels control neuronal output by regulating GABA release from glia in C. elegans

KCNQs are voltage-gated K+ channels that control neuronal excitability and are mutated in epilepsy and autism spectrum disorder (ASD). KCNQs have been extensively studied in neurons, but their function in glia is unknown. Using voltage, calcium, and GABA imaging, optogenetics, and behavioral assays, we show here for the first time in Caenorhabditis elegans (C. elegans) that glial KCNQ channels control neuronal excitability by mediating GABA release from glia via regulation of the function of L-type voltage-gated Ca2+ channels. Further, we show that human KCNQ channels have the same role when expressed in nematode glia, underscoring conservation of function across species. Finally, we show that pathogenic loss-of-function and gain-of-function human KCNQ2 mutations alter glia-to-neuron GABA signaling in distinct ways and that the KCNQ channel opener retigabine exerts rescuing effects. This work identifies glial KCNQ channels as key regulators of neuronal excitability via control of GABA release from glia.

Calcium-Sensitive Microbial Rhodopsin VirChR1: A Femtosecond to Second Photocycle Study

Viral rhodopsins are light-gated cation channels representing a novel class of microbial rhodopsins. For viral rhodopsin 1 subfamily members VirChR1 and OLPVR1, channel activity is abolished above a certain calcium concentration. Here we present a calcium-dependent spectroscopic analysis of VirChR1 on the femtosecond to second time scale. Unlike channelrhodopsin-2, VirChR1 possesses two intermediate states P1 and P2 on the ultrafast time scale, similar to J and K in ion-pumping rhodopsins. Subsequently, we observe multifaceted photocycle kinetics with up to seven intermediate states. Calcium predominantly affects the last photocycle steps, including the appearance of additional intermediates P6Ca and P7 representing the blocked channel. Furthermore, the photocycle of the counterion variant D80N is drastically altered, yielding intermediates with different spectra and kinetics compared to those of the wt. These findings demonstrate the central role of the counterion within the defined reaction sequence of microbial rhodopsins that ultimately defines the protein function.

C. elegans: a prominent platform for modeling and drug screening in neurological disorders

INTRODUCTION

Human neurodevelopmental and neurodegenerative diseases (NDevDs and NDegDs, respectively) encompass a broad spectrum of disorders affecting the nervous system with an increasing incidence. In this context, the nematode C. elegans, has emerged as a benchmark model for biological research, especially in the field of neuroscience.

AREAS COVERED

The authors highlight the numerous advantages of this tiny worm as a model for exploring nervous system pathologies and as a platform for drug discovery. There is a particular focus given to describing the existing models of C. elegans for the study of NDevDs and NDegDs. Specifically, the authors underscore their strong applicability in preclinical drug development. Furthermore, they place particular emphasis on detailing the common techniques employed to explore the nervous system in both healthy and diseased states.

EXPERT OPINION

Drug discovery constitutes a long and expensive process. The incorporation of invertebrate models, such as C. elegans, stands as an exemplary strategy for mitigating costs and expediting timelines. The utilization of C. elegans as a platform to replicate nervous system pathologies and conduct high-throughput automated assays in the initial phases of drug discovery is pivotal for rendering therapeutic options more attainable and cost-effective.

What do the mushroom bodies do for the insect brain? Twenty-five years of progress

In 1998, a special edition of Learning & Memory was published with a discrete focus of synthesizing the state of the field to provide an overview of the function of the insect mushroom body. While molecular neuroscience and optical imaging of larger brain areas were advancing, understanding the basic functioning of neuronal circuits, particularly in the context of the mushroom body, was rudimentary. In the past 25 years, technological innovations have allowed researchers to map and understand the in vivo function of the neuronal circuits of the mushroom body system, making it an ideal model for investigating the circuit basis of sensory encoding, memory formation, and behavioral decisions. Collaborative efforts within the community have played a crucial role, leading to an interactive connectome of the mushroom body and accessible genetic tools for studying mushroom body circuit function. Looking ahead, continued technological innovation and collaborative efforts are likely to further advance our understanding of the mushroom body and its role in behavior and cognition, providing insights that generalize to other brain structures and species.

Optogenetics in taste research: A decade of enlightenment

The electrophysiological function of the tongue involves complicated activities in taste sense, producing the perceptions of salty, sweet, bitter, and sour. However, therapies and prevention of taste loss arising from dysfunction in electrophysiological activity require further fundamental research. Optogenetics has revolutionized neuroscience and brought the study of sensory system to a higher level in taste. The year 2022 marks a decade of developments of optogenetics in taste since this technology was adopted from neuroscience and applied to the taste research. This review summarizes a decade of advances that define near-term translation with optogenetic tools, and newly-discovered mechanisms with the applications of these tools. The main limitations and opportunities for optogenetics in taste research are also discussed.

The influence of internal pressure and neuromuscular agents on C. elegans biomechanics: an empirical and multi-compartmental in silico modelling study

The function of a specific tissue and its biomechanics are interdependent, with pathologies or ageing often being intertwined with structural decline. The biomechanics of Caenorhabditis elegans, a model organism widely used in pharmacological and ageing research, has been established as biomarker for healthy ageing. However, the properties of the constituent tissues, and their contribution to the overall mechanical characteristics of the organism, remain relatively unknown. In this study we investigated the biomechanics of healthy C. elegans cuticle, muscle tissue, and pseudocoelom using a combination of indentation experiments and in silico modelling. We performed stiffness measurements using an atomic force microscope. To approximate the nematode's cylindrical body we used a novel three-compartment nonlinear finite element model, enabling us to analyse of how changes in the elasticity of individual compartments affect the bulk stiffness. We then fine-tuned the parameters of the model to match the simulation force-indentation output to the experimental data. To test the finite element model, we modified distinct compartments experimentally. Our in silico results, in agreement with previous studies, suggest that hyperosmotic shock reduces stiffness by decreasing the internal pressure. Unexpectedly, treatment with the neuromuscular agent aldicarb, traditionally associated with muscle contraction, reduced stiffness by decreasing the internal pressure. Furthermore, our finite element model can offer insights into how drugs, mutations, or processes such as ageing target individual tissues.

Selective induction of programmed cell death using synthetic biology tools

Regulated cell death (RCD) controls the removal of dispensable, infected or malignant cells, and is thus essential for development, homeostasis and immunity of multicellular organisms. Over the last years different forms of RCD have been described (among them apoptosis, necroptosis, pyroptosis and ferroptosis), and the cellular signaling pathways that control their induction and execution have been characterized at the molecular level. It has also become apparent that different forms of RCD differ in their capacity to elicit inflammation or an immune response, and that RCD pathways show a remarkable plasticity. Biochemical and genetic studies revealed that inhibition of a given pathway often results in the activation of back-up cell death mechanisms, highlighting close interconnectivity based on shared signaling components and the assembly of multivalent signaling platforms that can initiate different forms of RCD. Due to this interconnectivity and the pleiotropic effects of 'classical' cell death inducers, it is challenging to study RCD pathways in isolation. This has led to the development of tools based on synthetic biology that allow the targeted induction of RCD using chemogenetic or optogenetic methods. Here we discuss recent advances in the development of such toolset, highlighting their advantages and limitations, and their application for the study of RCD in cells and animals.

A consistent map in the medial entorhinal cortex supports spatial memory

The medial entorhinal cortex (MEC) is hypothesized to function as a cognitive map for memory-guided navigation. How this map develops during learning and influences memory remains unclear. By imaging MEC calcium dynamics while mice successfully learned a novel virtual environment over ten days, we discovered that the dynamics gradually became more spatially consistent and then stabilized. Additionally, grid cells in the MEC not only exhibited improved spatial tuning consistency, but also maintained stable phase relationships, suggesting a network mechanism involving synaptic plasticity and rigid recurrent connectivity to shape grid cell activity during learning. Increased c-Fos expression in the MEC in novel environments further supports the induction of synaptic plasticity. Unsuccessful learning lacked these activity features, indicating that a consistent map is specific for effective spatial memory. Finally, optogenetically disrupting spatial consistency of the map impaired memory-guided navigation in a well-learned environment. Thus, we demonstrate that the establishment of a spatially consistent MEC map across learning both correlates with, and is necessary for, successful spatial memory.

Optical mapping and optogenetics in cardiac electrophysiology research and therapy: a state-of-the-art review

State-of-the-art innovations in optical cardiac electrophysiology are significantly enhancing cardiac research. A potential leap into patient care is now on the horizon. Optical mapping, using fluorescent probes and high-speed cameras, offers detailed insights into cardiac activity and arrhythmias by analysing electrical signals, calcium dynamics, and metabolism. Optogenetics utilizes light-sensitive ion channels and pumps to realize contactless, cell-selective cardiac actuation for modelling arrhythmia, restoring sinus rhythm, and probing complex cell-cell interactions. The merging of optogenetics and optical mapping techniques for 'all-optical' electrophysiology marks a significant step forward. This combination allows for the contactless actuation and sensing of cardiac electrophysiology, offering unprecedented spatial-temporal resolution and control. Recent studies have performed all-optical imaging ex vivo and achieved reliable optogenetic pacing in vivo, narrowing the gap for clinical use. Progress in optical electrophysiology continues at pace. Advances in motion tracking methods are removing the necessity of motion uncoupling, a key limitation of optical mapping. Innovations in optoelectronics, including miniaturized, biocompatible illumination and circuitry, are enabling the creation of implantable cardiac pacemakers and defibrillators with optoelectrical closed-loop systems. Computational modelling and machine learning are emerging as pivotal tools in enhancing optical techniques, offering new avenues for analysing complex data and optimizing therapeutic strategies. However, key challenges remain including opsin delivery, real-time data processing, longevity, and chronic effects of optoelectronic devices. This review provides a comprehensive overview of recent advances in optical mapping and optogenetics and outlines the promising future of optics in reshaping cardiac electrophysiology and therapeutic strategies.

Optogenetics: Illuminating the Future of Hearing Restoration and Understanding Auditory Perception

Hearing loss is a prevalent sensory impairment significantly affecting communication and quality of life. Traditional approaches for hearing restoration, such as cochlear implants, have limitations in frequency resolution and spatial selectivity. Optogenetics, an emerging field utilizing light-sensitive proteins, offers a promising avenue for addressing these limitations and revolutionizing hearing rehabilitation. This review explores the methods of introducing Channelrhodopsin- 2 (ChR2), a key light-sensitive protein, into cochlear cells to enable optogenetic stimulation. Viral- mediated gene delivery is a widely employed technique in optogenetics. Selecting a suitable viral vector, such as adeno-associated viruses (AAV), is crucial in efficient gene delivery to cochlear cells. The ChR2 gene is inserted into the viral vector through molecular cloning techniques, and the resulting viral vector is introduced into cochlear cells via direct injection or round window membrane delivery. This allows for the expression of ChR2 and subsequent light sensitivity in targeted cells. Alternatively, direct cell transfection offers a non-viral approach for ChR2 delivery. The ChR2 gene is cloned into a plasmid vector, which is then combined with transfection agents like liposomes or nanoparticles. This mixture is applied to cochlear cells, facilitating the entry of the plasmid DNA into the target cells and enabling ChR2 expression. Optogenetic stimulation using ChR2 allows for precise and selective activation of specific neurons in response to light, potentially overcoming the limitations of current auditory prostheses. Moreover, optogenetics has broader implications in understanding the neural circuits involved in auditory processing and behavior. The combination of optogenetics and gene delivery techniques provides a promising avenue for improving hearing restoration strategies, offering the potential for enhanced frequency resolution, spatial selectivity, and improved auditory perception.

Ethics and regulation of neuronal optogenetics in the European Union

Neuronal optogenetics is a technique to control the activity of neurons with light. This is achieved by artificial expression of light-sensitive ion channels in the target cells. By optogenetic methods, cells that are naturally light-insensitive can be made photosensitive and addressable by illumination and precisely controllable in time and space. So far, optogenetics has primarily been a basic research tool to better understand the brain. However, initial studies are already investigating the possibility of using optogenetics in humans for future therapeutic approaches for neuronal based diseases such as Parkinson's disease, epilepsy, or to promote stroke recovery. In addition, optogenetic methods have already been successfully applied to a human in an experimental setting. Neuronal optogenetics also raises ethical and legal issues, e.g., in relation to, animal experiments, and its application in humans. Additional ethical and legal questions may arise when optogenetic methods are investigated on cerebral organoids. Thus, for the successful translation of optogenetics from basic research to medical practice, the ethical and legal questions of this technology must also be answered, because open ethical and legal questions can hamper the translation. The paper provides an overview of the ethical and legal issues raised by neuronal optogenetics. In addition, considering the technical prerequisites for translation, the paper shows consistent approaches to address these open questions. The paper also aims to support the interdisciplinary dialogue between scientists and physicians on the one hand, and ethicists and lawyers on the other, to enable an interdisciplinary coordinated realization of neuronal optogenetics.

Cardiac optogenetics: shining light on signaling pathways

In the early 2000s, the field of neuroscience experienced a groundbreaking transformation with the advent of optogenetics. This innovative technique harnesses the properties of naturally occurring and genetically engineered rhodopsins to confer light sensitivity upon target cells. The remarkable spatiotemporal precision offered by optogenetics has provided researchers with unprecedented opportunities to dissect cellular physiology, leading to an entirely new level of investigation. Initially revolutionizing neuroscience, optogenetics quickly piqued the interest of the wider scientific community, and optogenetic applications were expanded to cardiovascular research. Over the past decade, researchers have employed various optical tools to observe, regulate, and steer the membrane potential of excitable cells in the heart. Despite these advancements, achieving control over specific signaling pathways within the heart has remained an elusive goal. Here, we review the optogenetic tools suitable to control cardiac signaling pathways with a focus on GPCR signaling, and delineate potential applications for studying these pathways, both in healthy and diseased hearts. By shedding light on these exciting developments, we hope to contribute to the ongoing progress in basic cardiac research to facilitate the discovery of novel therapeutic possibilities for treating cardiovascular pathologies.

A micro-LED array based platform for spatio-temporal optogenetic control of various cardiac models

Optogenetics relies on dynamic spatial and temporal control of light to address emerging fundamental and therapeutic questions in cardiac research. In this work, a compact micro-LED array, consisting of 16 × 16 pixels, is incorporated in a widefield fluorescence microscope for controlled light stimulation. We describe the optical design of the system that allows the micro-LED array to fully cover the field of view regardless of the imaging objective used. Various multicellular cardiac models are used in the experiments such as channelrhodopsin-2 expressing aggregates of cardiomyocytes, termed cardiac bodies, and bioartificial cardiac tissues derived from human induced pluripotent stem cells. The pacing efficiencies of the cardiac bodies and bioartificial cardiac tissues were characterized as a function of illumination time, number of switched-on pixels and frequency of stimulation. To demonstrate dynamic stimulation, steering of calcium waves in HL-1 cell monolayer expressing channelrhodopsin-2 was performed by applying different configurations of patterned light. This work shows that micro-LED arrays are powerful light sources for optogenetic control of contraction and calcium waves in cardiac monolayers, multicellular bodies as well as three-dimensional artificial cardiac tissues.

Optical Approaches for Investigating Neuromodulation and G Protein-Coupled Receptor Signaling

Despite the fact that roughly 40% of all US Food and Drug Administration (FDA)-approved pharmacological therapeutics target G protein-coupled receptors (GPCRs), there remains a gap in our understanding of the physiologic and functional role of these receptors at the systems level. Although heterologous expression systems and in vitro assays have revealed a tremendous amount about GPCR signaling cascades, how these cascades interact across cell types, tissues, and organ systems remains obscure. Classic behavioral pharmacology experiments lack both the temporal and spatial resolution to resolve these long-standing issues. Over the past half century, there has been a concerted effort toward the development of optical tools for understanding GPCR signaling. From initial ligand uncaging approaches to more recent development of optogenetic techniques, these strategies have allowed researchers to probe longstanding questions in GPCR pharmacology both in vivo and in vitro. These tools have been employed across biologic systems and have allowed for interrogation of everything from specific intramolecular events to pharmacology at the systems level in a spatiotemporally specific manner. In this review, we present a historical perspective on the motivation behind and development of a variety of optical toolkits that have been generated to probe GPCR signaling. Here we highlight how these tools have been used in vivo to uncover the functional role of distinct populations of GPCRs and their signaling cascades at a systems level. SIGNIFICANCE STATEMENT: G protein-coupled receptors (GPCRs) remain one of the most targeted classes of proteins for pharmaceutical intervention, yet we still have a limited understanding of how their unique signaling cascades effect physiology and behavior at the systems level. In this review, we discuss a vast array of optical techniques that have been devised to probe GPCR signaling both in vitro and in vivo.

Optogenetic control of neural activity: The biophysics of microbial rhodopsins in neuroscience

Optogenetics, the use of microbial rhodopsins to make the electrical activity of targeted neurons controllable by light, has swept through neuroscience, enabling thousands of scientists to study how specific neuron types contribute to behaviors and pathologies, and how they might serve as novel therapeutic targets. By activating a set of neurons, one can probe what functions they can initiate or sustain, and by silencing a set of neurons, one can probe the functions they are necessary for. We here review the biophysics of these molecules, asking why they became so useful in neuroscience for the study of brain circuitry. We review the history of the field, including early thinking, early experiments, applications of optogenetics, pre-optogenetics targeted neural control tools, and the history of discovering and characterizing microbial rhodopsins. We then review the biophysical attributes of rhodopsins that make them so useful to neuroscience - their classes and structure, their photocycles, their photocurrent magnitudes and kinetics, their action spectra, and their ion selectivity. Our hope is to convey to the reader how specific biophysical properties of these molecules made them especially useful to neuroscientists for a difficult problem - the control of high-speed electrical activity, with great precision and ease, in the brain.

Assessing the Role of R120 in the Gating of CrChR2 by Time-Resolved Spectroscopy from Femtoseconds to Seconds

The light-gated ion channel channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2) is the most frequently used optogenetic tool in neurosciences. However, the precise molecular mechanism of the channel opening and the correlation among retinal isomerization, the photocycle, and the channel activity of the protein are missing. Here, we present electrophysiological and spectroscopic investigations on the R120H variant of CrChR2. R120 is a key residue in an extended network linking the retinal chromophore to several gates of the ion channel. We show that despite the deficient channel activity, the photocycle of the variant is intact. In a comparative study for R120H and the wild type, we resolve the vibrational changes in the spectral range of the retinal and amide I bands across the time range from femtoseconds to seconds. Analysis of the amide I mode reveals a significant impairment of the ultrafast protein response after retinal excitation. We conclude that channel opening in CrChR2 is prepared immediately after retinal excitation. Additionally, chromophore isomerization is essential for both photocycle and channel activities, although both processes can occur independently.

A consistent map in the medial entorhinal cortex supports spatial memory

The medial entorhinal cortex (MEC) is hypothesized to function as a cognitive map for memory-guided navigation. How this map develops during learning and influences memory remains unclear. By imaging MEC calcium dynamics while mice successfully learned a novel virtual environment over ten days, we discovered that the dynamics gradually became more spatially consistent and then stabilized. Additionally, grid cells in the MEC not only exhibited improved spatial tuning consistency, but also maintained stable phase relationships, suggesting a network mechanism involving synaptic plasticity and rigid recurrent connectivity to shape grid cell activity during learning. Increased c-Fos expression in the MEC in novel environments further supports the induction of synaptic plasticity. Unsuccessful learning lacked these activity features, indicating that a consistent map is specific for effective spatial memory. Finally, optogenetically disrupting spatial consistency of the map impaired memory-guided navigation in a well-learned environment. Thus, we demonstrate that the establishment of a spatially consistent MEC map across learning both correlates with, and is necessary for, successful spatial memory.

Advances in In Vitro Models of Neuromuscular Junction: Focusing on Organ-on-a-Chip, Organoids, and Biohybrid Robotics

The neuromuscular junction (NMJ) is a peripheral synaptic connection between presynaptic motor neurons and postsynaptic skeletal muscle fibers that enables muscle contraction and voluntary motor movement. Many traumatic, neurodegenerative, and neuroimmunological diseases are classically believed to mainly affect either the neuronal or the muscle side of the NMJ, and treatment options are lacking. Recent advances in novel techniques have helped develop in vitro physiological and pathophysiological models of the NMJ as well as enable precise control and evaluation of its functions. This paper reviews the recent developments in in vitro NMJ models with 2D or 3D cultures, from organ-on-a-chip and organoids to biohybrid robotics. Related derivative techniques are introduced for functional analysis of the NMJ, such as the patch-clamp technique, microelectrode arrays, calcium imaging, and stimulus methods, particularly optogenetic-mediated light stimulation, microelectrode-mediated electrical stimulation, and biochemical stimulation. Finally, the applications of the in vitro NMJ models as disease models or for drug screening related to suitable neuromuscular diseases are summarized and their future development trends and challenges are discussed.

Channelrhodopsins: From Phototaxis to Optogenetics

Channelrhodopsins stand out among other retinal proteins because of their capacity to generate passive ionic currents following photoactivation. Owing to that, channelrhodopsins are widely used in neuroscience and cardiology as instruments for optogenetic manipulation of the activity of excitable cells. Photocurrents generated by channelrhodopsins were first discovered in the cells of green algae in the 1970s. In this review we describe this discovery and discuss the current state of research in the field.

Structural basis for ion selectivity in potassium-selective channelrhodopsins

KCR channelrhodopsins (K+-selective light-gated ion channels) have received attention as potential inhibitory optogenetic tools but more broadly pose a fundamental mystery regarding how their K+ selectivity is achieved. Here, we present 2.5-2.7 Å cryo-electron microscopy structures of HcKCR1 and HcKCR2 and of a structure-guided mutant with enhanced K+ selectivity. Structural, electrophysiological, computational, spectroscopic, and biochemical analyses reveal a distinctive mechanism for K+ selectivity; rather than forming the symmetrical filter of canonical K+ channels achieving both selectivity and dehydration, instead, three extracellular-vestibule residues within each monomer form a flexible asymmetric selectivity gate, while a distinct dehydration pathway extends intracellularly. Structural comparisons reveal a retinal-binding pocket that induces retinal rotation (accounting for HcKCR1/HcKCR2 spectral differences), and design of corresponding KCR variants with increased K+ selectivity (KALI-1/KALI-2) provides key advantages for optogenetic inhibition in vitro and in vivo. Thus, discovery of a mechanism for ion-channel K+ selectivity also provides a framework for next-generation optogenetics.

Optical EUS Activation to Relax Sensitized Micturition Response

This study aims to activate the external urethral sphincter (EUS), which plays a critical role in micturition control, through optogenetics and to determine its potential contribution to the stabilization of sensitized micturition activity. The viral vector (AAV2/8-CMV-hChR2(H134R)-EGFP) is utilized to introduce light-gated ion channels (hChR2/H134R) into the EUS of wild-type C57BL/6 mice. Following the induction of sensitized micturition activity using weak acetic acid (0.1%) in anesthetized mice, optical stimulation of the EUS muscle tissue expressing channel rhodopsin is performed using a 473 nm laser light delivered through optical fibers, and the resulting changes in muscle activation and micturition activity are examined. Through EMG (electromyography) measurements, it is confirmed that optical stimulation electrically activates the EUS muscle in mice. Analysis of micturition activity using cystometry reveals a 70.58% decrease in the micturition period and a 70.27% decrease in the voiding volume due to sensitized voiding. However, with optical stimulation, the micturition period recovers to 101.49%, and the voiding volume recovered to 100.22%. Stimulation of the EUS using optogenetics can alleviate sensitized micturition activity and holds potential for application in conjunction with other micturition control methods.

The physiological response during optogenetic-based cardiac pacing in awake freely moving mice

There are several methods to control a heart rate, such as electrical stimulation and drug administration. However, these methods may be invasive or affect other organs. Recently, an optogenetic-based cardiac pacing method has enabled us to stimulate the cardiac muscle in non-contact. In many previous studies, the pacing was applied ex vivo or in anesthetized animals. Therefore, the physiologic response of animals during optogenetic pacing remains unclear. Here, we established a method of optogenetic-based cardiac pacing in awake, freely moving mice and simultaneously measured electrocardiogram, blood pressure, and respiration. As a result, light-induced myocardial contraction produces blood flow and indirectly affects the respiration rhythm. Additionally, light illumination enabled heart rate recovery in bradycardic mice. These findings may be employed for further research that relates a heartbeat state to animal behavior. Together, this method may drive the development of less invasive pacemakers without pacing leads.

Optical and pharmacological manipulation of hypoglossal motor nucleus identifies differential effects of taltirelin on sleeping tonic motor activity and responsiveness

Pharyngeal muscle activity and responsiveness are key pathophysiological traits in human obstructive sleep apnea (OSA) and strong contributors to improvements with pharmacotherapy. The thyrotropin-releasing hormone (TRH) analog taltirelin is of high pre-clinical interest given its neuronal-stimulant properties, minimal endocrine activity, tongue muscle activation following microperfusion into the hypoglossal motor nucleus (HMN) or systemic delivery, and high TRH receptor expression at the HMN compared to rest of the brain. Here we test the hypothesis that taltirelin increases HMN activity and/or responsivity to excitatory stimuli applied across sleep-wake states in-vivo. To target hypoglossal motoneurons with simultaneous pharmacological and optical stimuli we used customized "opto-dialysis" probes and chronically implanted them in mice expressing a light sensitive cation channel exclusively on cholinergic neurons (ChAT-ChR2, n = 12) and wild-type mice lacking the opsin (n = 10). Both optical stimuli applied across a range of powers (P < 0.001) and microperfusion of taltirelin into the HMN (P < 0.020) increased tongue motor activity in sleeping ChAT-ChR2 mice. Notably, taltirelin increased tonic background tongue motor activity (P < 0.001) but not responsivity to excitatory optical stimuli across sleep-wake states (P > 0.098). This differential effect on tonic motor activity versus responsivity informs human studies of the potential beneficial effects of taltirelin on pharyngeal motor control and OSA pharmacotherapy.

Optogenetics for controlling seizure circuits for translational approaches

The advent of optogenetic tools has had a profound impact on modern neuroscience research, revolutionizing our understanding of the brain. These tools offer a remarkable ability to precisely manipulate specific groups of neurons with an unprecedented level of temporal precision, on the order of milliseconds. This breakthrough has significantly advanced our knowledge of various physiological and pathophysiological processes in the brain. Within the realm of epilepsy research, optogenetic tools have played a crucial role in investigating the contributions of different neuronal populations to the generation of seizures and hyperexcitability. By selectively activating or inhibiting specific neurons using optogenetics, researchers have been able to elucidate the underlying mechanisms and identify key players involved in epileptic activity. Moreover, optogenetic techniques have also been explored as innovative therapeutic strategies for treating epilepsy. These strategies aim to halt seizure progression and alleviate symptoms by utilizing the precise control offered by optogenetics. The application of optogenetic tools has provided valuable insights into the intricate workings of the brain during epileptic episodes. For instance, researchers have discovered how distinct interneuron populations contribute to the initiation of seizures (ictogenesis). They have also revealed how remote circuits in regions such as the cerebellum, septum, or raphe nuclei can interact with hyperexcitable networks in the hippocampus. Additionally, studies have demonstrated the potential of closed-loop systems, where optogenetics is combined with real-time monitoring, to enable precise, on-demand control of seizure activity. Despite the immense promise demonstrated by optogenetic approaches, it is important to acknowledge that many of these techniques are still in the early stages of development and have yet to reach potential clinical applications. The transition from experimental research to practical clinical use poses numerous challenges. In this review, we aim to introduce optogenetic tools, provide a comprehensive survey of their application in epilepsy research, and critically discuss their current potential and limitations in achieving successful clinical implementation for the treatment of human epilepsy. By addressing these crucial aspects, we hope to foster a deeper understanding of the current state and future prospects of optogenetics in epilepsy treatment.

Characterizing a standardized BioPart for PVQ-specific expression in C. elegans

Synthetic biology relies on standardized biological parts (BioParts), and we aim to identify cell-specific promoters for every class of neuron in C. elegans . Here, we characterize a short BioPart (P nlp-17 , 300 bp) for PVQ-specific expression. P nlp-17 ::mScarlet showed bright, persistent, and specific expression in hermaphrodite and male PVQ neurons from multicopy arrays and single-copy insertions starting from the comma stage. We generated standardized P nlp-17 cloning vectors with gfp and mScarlet compatible with single-copy or array expression for PVQ-specific transgene expression or identification. To facilitate gene synthesis, we have incorporated P nlp-17 as a standard BioPart in our online transgene design tool (www.wormbuilder.org/transgenebuilder).

Dissection of insular cortex layer 5 reveals two sublayers with opposing modulatory roles in appetitive drinking behavior

The insular cortex (insula) is known to play a modulatory role in feeding and drinking. Previous studies have revealed anterior-posterior differences of subcortical projections and roles for the insula, yet the anatomical and functional heterogeneity among the cortical layers remains poorly understood. Here, we show that layer 5 of the mouse dysgranular insula has two distinct neuronal subpopulations along the entire anterior-posterior axis: The L5a population, expressing NECAB1, projects bilaterally to the lateral and capsular divisions of the central amygdala, and the L5b population, expressing CTIP2, projects ipsilaterally to the parasubthalamic nucleus and the medial division of the central amygdala. Optogenetically activating L5a and L5b neuronal populations in thirsty male mice led to suppressed and facilitated water spout licking, respectively, without avoidance against or preference for the spout paired with the opto-stimulation. Our results suggest sublayer-specific bidirectional modulatory roles of insula layer 5 in the motivational aspect of appetitive behavior.

Combined optogenetic and electrical stimulation of the sciatic nerve for selective control of sensory fibers

Introduction

Electrical stimulation offers a drug-free alternative for the treatment of many neurological conditions, such as chronic pain. However, it is not easy to selectively activate afferent or efferent fibers of mixed nerves, nor their functional subtypes. Optogenetics overcomes these issues by controlling activity selectively in genetically modified fibers, however the reliability of responses to light are poor compared to electrical stimulation and the high intensities of light required present considerable translational challenges. In this study we employed a combined protocol of optical and electrical stimulation to the sciatic nerve in an optogenetic mouse model to allow for better selectivity, efficiency, and safety to overcome fundamental limitations of electrical-only and optical-only stimulation.

Methods

The sciatic nerve was surgically exposed in anesthetized mice (n = 12) expressing the ChR2-H134R opsin via the parvalbumin promoter. A custom-made peripheral nerve cuff electrode and a 452 nm laser-coupled optical fiber were used to elicit neural activity utilizing optical-only, electrical-only, or combined stimulation. Activation thresholds for the individual and combined responses were measured.

Results

Optically evoked responses had a conduction velocity of 34.3 m/s, consistent with ChR2-H134R expression in proprioceptive and low-threshold mechanoreceptor (Aα/Aβ) fibers which was also confirmed via immunohistochemical methods. Combined stimulation, utilizing a 1 ms near-threshold light pulse followed by an electrical pulse 0.5 ms later, approximately halved the electrical threshold for activation (p = 0.006, n = 5) and resulted in a 5.5 dB increase in the Aα/Aβ hybrid response amplitude compared to the electrical-only response at equivalent electrical levels (p = 0.003, n = 6). As a result, there was a 3.25 dB increase in the therapeutic stimulation window between the Aα/Aβ fiber and myogenic thresholds (p = 0.008, n = 4).

Discussion

The results demonstrate that light can be used to prime the optogenetically modified neural population to reside near threshold, thereby selectively reducing the electrical threshold for neural activation in these fibers. This reduces the amount of light needed for activation for increased safety and reduces potential off-target effects by only stimulating the fibers of interest. Since Aα/Aβ fibers are potential targets for neuromodulation in chronic pain conditions, these findings could be used to develop effective strategies to selectively manipulate pain transmission pathways in the periphery.