Pushing the frontiers: tools for monitoring neurotransmitters and neuromodulators

State of the art indicators for imaging purinergic dynamics in vitro and in vivo

Purinergic neurotransmission, a dynamic signaling system using adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine (ADO), uridine diphosphate (UDP), and others, plays a crucial role in brain function. Purinergic signaling is involved in regulating synaptic communication to influence sleep and neuroprotection; malfunction of purinergic signaling contributes to various neurological disorders like pain, epilepsy, and depression. Effective detection methods are crucial for a comprehensive understanding of the multifaceted roles of purinergic signaling in the brain. This review sheds light on advancements in fluorescent indicators, a powerful toolkit for visualizing purinergic activities in living animals. We explore the diverse applications of these indicators in studying purinergic transmission both in health and in diseases. Despite their current strengths, we emphasize the need for continuous development of fluorescent indicators to achieve an even more comprehensive, specific, and quantitative detection of purinergic signaling.

Voltage imaging reveals circuit computations in the raphe underlying serotonin-mediated motor vigor learning

As animals adapt to new situations, neuromodulation is a potent way to alter behavior, yet mechanisms by which neuromodulatory nuclei compute during behavior are underexplored. The serotonergic raphe supports motor learning in larval zebrafish by visually detecting distance traveled during swims, encoding action effectiveness, and modulating motor vigor. We tracked the raphe's input-output computations at millisecond timescales using voltage and neurotransmitter imaging and found that swimming opens a gate for visual input to cause spiking in serotonergic neurons, enabling the encoding of action outcomes and filtering out learning-irrelevant visual signals. Specifically, swim commands initially inhibited serotonergic neurons via γ-aminobutyric acid (GABA). Immediately after, membrane voltage increased via post-inhibitory rebound, allowing swim-induced visual motion to evoke firing through glutamate, triggering serotonin release to modulate future motor vigor. Ablating local GABAergic neurons impaired raphe coding and motor learning. Thus, serotonergic neuromodulation arises from action-outcome coincidence detection within the raphe.

Coding principles of dopaminergic transmission modes

Dopaminergic neurons influence diverse behaviors with varied firing patterns, yet the precise mechanisms remain unclear. We introduce a multiplexed genetically encoded sensor-based imaging and voltammetry method to simultaneously record synaptic, perisynaptic, and extrasynaptic dopaminergic transmission at mouse central neurons. Using this method alongside a genetically encoded sensor-based image analysis program, we found that heterogeneous dopaminergic firing patterns create various transmission modes, encoding frequency, number, and synchrony of firing pulses using neurotransmitter quantity, releasing synapse count, and synaptic and/or volume transmission. Under both tonic and low-frequency phasic activities, transporters effectively reuptake dopamine at perisynaptic sites, confining dopamine within synaptic clefts to mediate synaptic transmission. In contrast, under high-frequency, particularly synchronized firing activity or transporter inhibition, released dopamine may overwhelm transporters, escaping from synaptic clefts via one to three outlet channels, triggering volume transmission. Our study illuminates a collaborative mechanism of synaptic enclosures, properties, and transporters that defines the coding principles of activity pattern-dependent dopaminergic transmission modes.

A Chemistry-Informed Generative Deep Learning Approach for Enhancing Voltammetric Neurochemical Sensing in Living Mouse Brain

Exploring the time-resolved dynamics of neurochemicals is essential for deciphering neuronal functions, intercellular communication, and neurophysiological or pathological mechanisms. However, the complex interplay among neurochemicals between neurocytes, coupled with extensive chemical signal crosstalk, puts simultaneous sensing of multiple neurochemicals into a longstanding challenge. Herein, we report a chemistry-informed generative neural network (CIGNN) model to separate the Faradaic and the non-Faradaic components from voltammetric currents, minimizing their mutual interference and enhancing quantitative accuracy. With the assistance of generative deep learning, we successfully establish a new platform for in vivo neurochemical sensing, which is validated by simultaneously monitoring the dynamics of dopamine (DA), ascorbic acid (AA), and ionic strength in a neuroinflammation mouse model. We observe that the stimulation with KCl solution triggers a significant enhancement of AA efflux on the model mice (300 ± 50 μM) compared with that from the control mice (170 ± 20 μM), as well as a significant decrease of ion influx (55 ± 7 mM) compared with that from the control mice (120 ± 16 mM), while not evoking a significant change in the DA release from the model mice (2.8 ± 0.3 μM) versus that from the control mice (3.0 ± 0.5 μM). This work provides a robust tool for studying multineurochemical signaling and elucidating the molecular mechanisms underlying various brain activities.

Population imaging of enterochromaffin cell activity reveals regulation by somatostatin

Sensory enteroendocrine cells in the intestinal epithelium detect and relay information about the luminal environment to other cells within and outside the gut. Serotonergic enterochromaffin (EC) cells are a subset of enteroendocrine cells that detect noxious stimuli within the gut lumen, such as chemical irritants and microbial byproducts, and transduce this information to sensory nerve fibers to elicit defensive responses such as nausea and visceral pain. While much has recently been learned about the pharmacological and biophysical characteristics of EC cells, a more broadscale investigation of their properties has been hindered by their relatively low prevalence and sparse anatomical distribution within the gut epithelium. Here, we introduce a method for large-scale parallel analysis of individual EC cell activity within a physiologically relevant epithelial context. Using this approach, we identify somatostatin-28 as a potent inhibitor of both basal and stimulus-evoked serotonin release from EC cells and delineate the signaling pathway that underlies this modulatory response. Our analysis suggests that targeting this inhibitory signaling pathway may offer therapeutic avenues for treating gastrointestinal disorders associated with EC cell function and dysregulated serotonin signaling. Together with the ongoing development of specific biosensors, this platform provides a template for the efficient characterization of other rare sensory cell types and their pharmacological modulators.

Hydrogen peroxide in midbrain sleep neurons regulates sleep homeostasis

Sleep could protect animals from oxidative damage, yet the dynamic interplay between the redox state and sleep homeostasis remains unclear. Here, we show that acute sleep deprivation (SD) in mice caused a general increase in brain oxidation, particularly in sleep-promoting regions. In vivo imaging of intracellular hydrogen peroxide (H2O2) real-time dynamics revealed that in nigra sleep neurons, the increase in cytosolic but not mitochondrial H2O2 reflects sleep debt and tracks spontaneous wakefulness by positively correlating with wake duration. By controllably manipulating intraneuronal H2O2, we discovered that H2O2 elevation is required for compensatory sleep and causally promotes sleep initiation, at least partly dependent on transient receptor potential melastatin 2 (TRPM2) channel. However, excessive H2O2 induced brain inflammation and sleep fragmentation. Together, our study demonstrates intraneuronal H2O2 as a crucial signaling molecule that translates brain redox imbalance into sleep drive and underscores the significance of oxidative eustress in sleep homeostasis.

Multi-Frequency Interpolation X-talk Removal Algorithm: Enabling Combinations of Concurrent Optogenetics and Lock-in Amplification Fiber Photometry via Removal of Optogenetic Stimulation Crosstalk

Simultaneous fiber photometry and optogenetics is a powerful emerging technique for precisely studying the interactions of neuronal brain networks. However, spectral overlap between photometry and optogenetic components has severely limited the application of an all-optical approach. Due to spectral overlap, light from optogenetic stimulation saturates the photosensor and occludes photometry fluorescence, which is especially problematic in physically smaller model organism brains like mice. Here, we demonstrate the multi-frequency interpolation X-talk removal algorithm (MuFIX or μFIX) for recovering crosstalk-contaminated photometry responses recorded with lock-in amplification. μFIX exploits multifrequency lock-in amplification by modeling the remaining uncontaminated data to interpolate across crosstalk-affected segments (R2 ≈ 1.0); we found that this approach accurately recovers the original photometry response after demodulation (Pearson's r ≈ 1.0). When applied to crosstalk-contaminated data, μFIX recovered a photometry response closely resembling the dynamics of noncrosstalk photometry recorded simultaneously. Upon further verification using simulated and empirical data, we demonstrated that μFIX reproduces any signal that underwent simulated crosstalk contamination (r ≈ 1.0). We believe adopting μFIX will enable experimental designs using simultaneous fiber photometry and optogenetics that were previously not feasible due to crosstalk.

A comprehensive review of neurotransmitter modulation via artificial intelligence: A new frontier in personalized neurobiochemistry

The deployment of artificial intelligence (AI) is revolutionizing neuropharmacology and drug development, allowing the modulation of neurotransmitter systems at the personal level. This review focuses on the neuropharmacology and regulation of neurotransmitters using predictive modeling, closed-loop neuromodulation, and precision drug design. The fusion of AI with applications such as machine learning, deep-learning, and even computational modeling allows for the real-time tracking and enhancement of biological processes within the body. An exemplary application of AI is the use of DeepMind's AlphaFold to design new GABA reuptake inhibitors for epilepsy and anxiety. Likewise, Benevolent AI and IBM Watson have fast-tracked drug repositioning for neurodegenerative conditions. Furthermore, we identified new serotonin reuptake inhibitors for depression through AI screening. In addition, the application of Deep Brain Stimulation (DBS) settings using AI for patients with Parkinson's disease and for patients with major depressive disorder (MDD) using reinforcement learning-based transcranial magnetic stimulation (TMS) leads to better treatment. This review highlights other challenges including algorithm bias, ethical concerns, and limited clinical validation. Their proposal to incorporate AI with optogenetics, CRISPR, neuroprosthesis, and other advanced technologies fosters further exploration and refinement of precision neurotherapeutic approaches. By bridging computational neuroscience with clinical applications, AI has the potential to revolutionize neuropharmacology and improve patient-specific treatment strategies. We addressed critical challenges, such as algorithmic bias and ethical concerns, by proposing bias auditing, diverse datasets, explainable AI, and regulatory frameworks as practical solutions to ensure equitable and transparent AI applications in neurotransmitter modulation.

Bioengineered nanomaterials for dynamic diagnostics in vivo

In vivo diagnostics obtains real-time physiological information directly from the site of interest in a patient's body, providing more accurate disease diagnosis compared with ex vivo diagnostics. Particularly, in vivo dynamic diagnostics allows the continuous monitoring of physiological signals over a period of time, offering deeper insights into disease pathogenesis and progression. However, achieving in situ dynamic diagnostics in deep tissues presents challenges related to energy and signal penetration as well as dynamic monitoring. Bioengineered nanomaterials serve as an ideal platform for in vivo dynamic diagnostics, leveraging energy conversion and biofunctionalization to enable continuous acquisition of physiological information across temporal and spatial scales. In this review, with reference to the studies from the last five years, we summarize the fundamental components that are essential for dynamic diagnosis in vivo. Firstly, an input energy source with high tissue penetration is needed, such as near-infrared (NIR) light, X-rays, magnetic field and ultrasound. Secondly, a nanomaterial class that is responsive to such an energy source to provide a readable output signal is chosen. Thirdly, bioengineered nanoprobes are designed to exhibit spatial, temporal or spatiotemporal changes in the output signal. Finally, different methods are used to analyse the output signal of nanoprobes, such as detecting changes in optical, radiation, magnetic and ultrasound signals. This review also discusses the obstacles and potential solutions for advancing these bioengineered nanomaterials toward clinical translational applications.

Integrating endocannabinoid signaling, CCK interneurons, and hippocampal circuit dynamics in behaving animals

The brain's endocannabinoid signaling system modulates a diverse range of physiological phenomena and is also involved in various psychiatric and neurological disorders. The basic components of the molecular machinery underlying endocannabinoid-mediated synaptic signaling have been known for decades. However, limitations associated with the short-lived nature of endocannabinoid lipid signals had made it challenging to determine the spatiotemporal specificity and dynamics of endocannabinoid signaling in vivo. Here, we discuss how novel technologies have recently enabled unprecedented insights into endocannabinoid signaling taking place at specific synapses in behaving animals. In this review, we primarily focus on cannabinoid-sensitive inhibition in the hippocampus in relation to place cell properties to illustrate the potential of these novel methodologies. In addition, we highlight implications of these approaches and insights for the unraveling of cannabinoid regulation of synapses in vivo in other brain circuits in both health and disease.

Atypical plume-like events contribute to glutamate accumulation in metabolic stress conditions

Neural glutamate homeostasis is important for health and disease. Ischemic conditions, like stroke, cause imbalances in glutamate release and uptake due to energy depletion and depolarization. We here used the glutamate sensor SF-iGluSnFR(A184V) to probe how chemical ischemia affects the extracellular glutamate dynamics in slice cultures from mouse cortex. SF-iGluSnFR imaging showed spontaneous glutamate release indicating synchronous network activity, similar to calcium imaging with GCaMP6f. Glutamate imaging further revealed local, atypically large, and long-lasting plume-like release events. Plumes occurred with low frequency, independent of network activity, and persisted in tetrodotoxin (TTX). Blocking glutamate uptake with TFB-TBOA favored plumes, whereas blocking ionotropic glutamate receptors (iGluRs) suppressed plumes. During chemical ischemia plumes became more pronounced, overly abundant and contributed to large-scale glutamate accumulation. Similar plumes were previously observed in cortical spreading depression and migraine models, and they may thus be a more general consequence of glutamate uptake dysfunctions in neurological and neurodegenerative diseases.

The rhythm of sequential behavioral transitions: Neuromodulatory dynamics and male sexual behavior

In this issue of Neuron, Miyasaka et al.1 demonstrate that the sequential transitions of male sexual behaviors are orchestrated by dual rhythms of dopamine and acetylcholine signaling generated in the ventral shell of the nucleus accumbens.

An Off-On Fluorescent Probe Reveals Spatiotemporal Signaling of Opioid Receptors In Vivo for Pain Control

Interrogation of the function of neuronal receptors and how they are involved in disease intervention requires spatiotemporally precise imaging in live animal brains. Most activatable fluorescent probes can realize imaging of enzyme biomarkers but face challenges in generating an amplified fluorescence signal on GPCRs. Here, we present the visualization of μ opioid receptor (μOR) activity in zebrafish larvae using P5N3, an antagonist-conjugated pyridinium dye that enables a 25-fold fluorescence increase upon binding in the orthosteric pocket of μOR. This turn-on fluorescence is attributed to the synergistic effects of restricted movement of the pyridinium moiety and its hydrogen bond interactions with amino acid residues in the receptor binding domain, as elucidated by DFT calculations. We observed behaviorally correlated μOR activity in whole-brain recordings of wild-type zebrafish during acetic-acid-induced nociception and identified sinomenine-mediated attenuation with both spatiotemporal and pharmacological precision, highlighting the involvement of the optic tectum region. We propose that leveraging spatiotemporal mapping of μOR binding patterns using the turn-on molecular probe in freely behaving larval zebrafish holds significant promise as an in vivo tool for advancing translational pain research and accelerating the discovery of analgesic drugs.

Stabilized carbon coating on microelectrodes for scalable and interoperable neurotransmitter sensing

Real-time monitoring of neurotransmitters is essential in driving basic neuroscience understandings and creating treatments for various brain disorders. However, current neurotransmitter sensing devices are highly limited in their spatiotemporal resolution and ability to integrate with neuronal recording. Here, we introduce a unique carbon coating approach to achieve high-performance voltammetry electrodes with extraordinary scalability and interoperability. Surprisingly, we discovered that mild annealing drastically improves the electrochemical stability of graphene-based carbon coating, enabling the transformation of conventional neuroelectrodes into fast-scan-cyclic-voltammetry-stable carbon sensors. We successfully validated sub-second detection of nanomolar dopamine in vivo using carbon-coated microelectrodes (CCMs) in rodents and demonstrated arrays of one hundred CCMs with high yield and uniformity. Furthermore, we developed a dual-modal neural probe that integrates the CCM with electrophysiological recording sites, allowing us to demonstrate that dopamine fluctuation in the ventral striatum of awake rats strongly correlates with the high gamma power in the brain with sub-second-level precision. Together, these advances pave the way for spatiotemporally scalable and multiplexed brain interfacing, with also broad applicability in electrochemical-related diagnostic and interventional approaches.

Environmentally relevant concentrations lithium exposure induces neurotoxicity in yellowstripe goby (Mugilogobius chulae): Responses of BDNF/AKT/FoxOs in regulating glutamate excitotoxicity and mitochondrial function

The wide application of lithium in green energy and clinical psychiatry results in ubiquitous occurrence of lithium in aquatic environments. However, researches on the toxicity of lithium are largely confined to acute and/or high-dose scenarios, with insufficient data on its impacts on non-target organisms at environmental levels. The present study investigated the neurotoxicological effects of environmentally relevant concentrations of lithium exposure on yellowstripe goby (Mugilogobius chulae) and the related molecular response mechanisms. The results showed that lithium exposure significantly inhibited the expression of the target protein GSK-3β in the brain of M. chulae, and induced a series of harmful events including oxidative stress, glutamate accumulation, and even behavioral alteration. The organism mitigated the excitotoxic effects of glutamate accumulation by down-regulating ionotropic glutamate receptors. At the same time, the organism met the energy supply and alleviated oxidative stress by altering mitochondrial function. Notably, the stress regulators FoxOs and sestrins both modulated synaptic sensitivities to enhance the neural signaling and altered the energy metabolism pattern to alleviate energy crisis, all of which were important for maintaining neuronal survival and organismal homeostasis. In conclusion, lithium exposure induced glutamate excitability and led to a series of toxic events. Meanwhile, FoxOs played an important role in neural signaling and homeostatic regulation of energy metabolism in brain. This study furthered the comprehension of the neurotoxic impacts of lithium on aquatic organisms, elucidated the associated molecular mechanisms, and underscored the environmental risks posed by increasing lithium contamination.

Illuminating the impact of stress: In vivo approaches to track stress-related neural adaptations

Stressful experiences can affect both daily life and long-term health outcomes in a variety of ways. Acute challenges may be adaptive, promoting arousal and enhancing memory and cognitive function. Importantly, however, chronic stress dysregulates the body's physiological regulatory mechanisms consisting of complex hormone interactions throughout the peripheral and central nervous systems. This disrupted signaling consequently alters the balance of synapse formation, maturation and pruning, processes which regulate neural communication, plasticity, learning, cognitive flexibility and adaptive behaviors - hallmarks of a healthy, functional brain. The chronically stressed brain state, therefore, is one which may be uniquely vulnerable. To understand the development of this state, how it is sustained and how behavior and neural function are transiently or indelibly impacted by it, we can turn to a number of advanced approaches in animal models which offer unprecedented insights. This has been the aim of my recent work within the field and the goal of my new independent research program. To achieve this, I have employed methods to uncover how key brain circuits integrate information to support motivated behaviors, how stress impacts their ability to perform this process and how best to operationalize behavioral readouts. Here I present an overview of research contributions that I find most meaningful for advancing our understanding of the impact of stress and propose new avenues which will guide my own framework to address the salient outstanding questions within the field.

Effects of Social Housing on Electrically Stimulated Dopamine Release in the Nucleus Accumbens Core and Shell in Female and Male Rats

Dopamine (DA) is a neurotransmitter that is important in the reward system and increased DA release is associated with rewarding properties of drugs. Highly addictive stimulants like methamphetamine (METH) increase DA release and block reuptake, causing the DA to stay in the synapse longer, enhancing its effects. Because the misuse of METH is increasing in the United States, it is important to investigate ways to protect against this highly addictive stimulant. Recent studies have shown that social support can be a protective factor against METH self-administration in females, but not males. Other studies using microdialysis have shown that socially housed females have lower DA release in the nucleus accumbens (NAc) compared to single housed females after treatment with METH. Additionally, researchers have shown that there are sex differences in stimulated DA release. The present study investigates whether social housing affects stimulated DA release after METH treatment. DA release in the NAc core and shell of socially housed and individually housed rats was measured using fast scan cyclic voltammetry (FSCV) with a chronic 16-channel carbon fiber electrode in the NAc. A stimulating electrode was aimed at the ventral tegmental area (VTA) to induce DA release in the NAc. The results showed that social housing enhances electrically stimulated DA release in males and that there was greater DA release in NAc core than shell in single males, but no difference in socially housed males. In females, social housing also enhanced ES DA release. In single females there was greater ES DA release in shell than in core. Additionally, in single housed females there was greater ES DA release over time, while the socially housed females had high ES DA release that remained stable over time. These results suggest that social housing protects females from sensitization, making single females more vulnerable to the addictive properties of METH.

Coding principles and mechanisms of serotonergic transmission modes

Serotonin-mediated intercellular communication has been implicated in myriad human behaviors and diseases, yet how serotonin communicates and how the communication is regulated remain unclear due to limitations of available monitoring tools. Here, we report a method multiplexing genetically encoded sensor-based imaging and fast-scan cyclic voltammetry, enabling simultaneous recordings of synaptic, perisynaptic, proximate and distal extrasynaptic serotonergic transmission. Employing this method alongside a genetically encoded sensor-based image analysis program (GESIAP), we discovered that heterogeneous firing patterns of serotonergic neurons create various transmission modes in the mouse raphe nucleus and amygdala, encoding information of firing pulse frequency, number, and synchrony using neurotransmitter quantity, releasing synapse count, and synaptic and/or volume transmission. During tonic and low-frequency phasic activities, serotonin is confined within synaptic clefts due to efficient retrieval by perisynaptic transporters, mediating synaptic transmission modes. Conversely, during high-frequency, especially synchronized phasic activities, or when transporter inhibition, serotonin may surpass transporter capacity, and escape synaptic clefts through 1‒3 outlet channels, leading to volume transmission modes. Our results elucidate a mechanism of how channeled synaptic enclosures, synaptic properties, and transporters collaborate to define the coding principles of activity pattern-dependent serotonergic transmission modes.

Layer-specific control of inhibition by NDNF interneurons

Neuronal processing of external sensory input is shaped by internally generated top-down information. In the neocortex, top-down projections primarily target layer 1, which contains NDNF (neuron-derived neurotrophic factor)-expressing interneurons and the dendrites of pyramidal cells. Here, we investigate the hypothesis that NDNF interneurons shape cortical computations in an unconventional, layer-specific way, by exerting presynaptic inhibition on synapses in layer 1 while leaving synapses in deeper layers unaffected. We first confirm experimentally that in the auditory cortex, synapses from somatostatin-expressing (SOM) onto NDNF neurons are indeed modulated by ambient Gamma-aminobutyric acid (GABA). Shifting to a computational model, we then show that this mechanism introduces a distinct mutual inhibition motif between NDNF interneurons and the synaptic outputs of SOM interneurons. This motif can control inhibition in a layer-specific way and introduces competition between NDNF and SOM interneurons for dendritic inhibition onto pyramidal cells on different timescales. NDNF interneurons can thereby control cortical information flow by redistributing dendritic inhibition from fast to slow timescales and by gating different sources of dendritic inhibition.

Glia-like taste cells mediate an intercellular mode of peripheral sweet adaptation

The sense of taste generally shows diminishing sensitivity to prolonged sweet stimuli, referred to as sweet adaptation. Yet, its mechanistic landscape remains incomplete. Here, we report that glia-like type I cells provide a distinct mode of sweet adaptation via intercellular crosstalk with chemosensory type II cells. Using the microfluidic-based intravital tongue imaging system, we found that sweet adaptation is facilitated along the synaptic transduction from type II cells to gustatory afferent nerves, while type I cells display temporally delayed and prolonged activities. We identified that type I cells receive purinergic input from adjacent type II cells via P2RY2 and provide inhibitory feedback to the synaptic transduction of sweet taste. Aligning with our cellular-level findings, purinergic activation of type I cells attenuated sweet licking behavior, and P2RY2 knockout mice showed decelerated adaptation behavior. Our study highlights a veiled intercellular mode of sweet adaptation, potentially contributing to the efficient encoding of prolonged sweetness.

Live imaging of paracrine signaling: Advances in visualization and tracking techniques

Live imaging techniques have revolutionized our understanding of paracrine signaling, a crucial form of cell-to-cell communication in biological processes. This review examines recent advances in visualizing and tracking paracrine factors through four key stages: secretion from producing cells, diffusion through extracellular space, binding to target cells, and activation of intracellular signaling within target cells. Paracrine factor secretion can be directly visualized by fluorescent protein tagging to ligand, or indirectly by visualizing the cleavage of the transmembrane pro-ligands or plasma membrane fusion of endosomes comprising the paracrine factors. Diffusion of paracrine factors has been studied using techniques such as fluorescence correlation spectroscopy (FCS), fluorescence recovery after photobleaching (FRAP), fluorescence decay after photoactivation (FDAP), and single-molecule tracking. Binding of paracrine factors to target cells has been visualized through various biosensors, including GPCR-activation-based (GRAB) sensors and Förster resonance energy transfer (FRET) probes for receptor tyrosine kinases. Finally, activation of intracellular signaling is monitored within the target cells by biosensors for second messengers, transcription factors, and so on. In addition to the imaging tools, the review also highlights emerging optogenetic and chemogenetic tools for triggering the release of paracrine factors, which is essential for associating the paracrine factor secretion to biological outcomes during the bioimaging of paracrine factor signaling.Key words: paracrine signaling, live imaging, biosensors, optogenetics, chemogenetics.

In vivo multiplex imaging of dynamic neurochemical networks with designed far-red dopamine sensors

Neurochemical signals like dopamine (DA) play a crucial role in a variety of brain functions through intricate interactions with other neuromodulators and intracellular signaling pathways. However, studying these complex networks has been hindered by the challenge of detecting multiple neurochemicals in vivo simultaneously. To overcome this limitation, we developed a single-protein chemigenetic DA sensor, HaloDA1.0, which combines a cpHaloTag-chemical dye approach with the G protein-coupled receptor activation-based (GRAB) strategy, providing high sensitivity for DA, sub-second response kinetics, and an extensive spectral range from far-red to near-infrared. When used together with existing green and red fluorescent neuromodulator sensors, Ca2+ indicators, cAMP sensors, and optogenetic tools, HaloDA1.0 provides high versatility for multiplex imaging in cultured neurons, brain slices, and behaving animals, facilitating in-depth studies of dynamic neurochemical networks.

Enhancing striatal acetylcholine facilitates dopamine release and striatal output in parkinsonian mice

BACKGROUND

L-DOPA has been considered the first-line therapy for treating Parkinson's disease (PD) via restoring striatal dopamine (DA) to normalize the activity of local spiny projection neurons (SPNs) in the direct (dSPNs) pathway and the indirect (iSPNs) pathway. While the changes in striatal acetylcholine (ACh) induced by increasing DA have been extensively discussed, their validity remains controversial. Inhibition of striatal cholinergic signaling attenuates PD motor deficits. Interestingly, enhancing striatal ACh triggers local DA release, suggesting the pro-kinetic effects of ACh in movement control. Here, we investigated the in-vivo dynamics of ACh in the dorsolateral striatum (DLS) of the 6-OHDA-lesioned mouse model after L-DOPA administration, as well as its underlying mechanism, and to explore its modulatory role and mechanism in parkinsonian symptoms.

RESULTS

Using in vivo fiber photometry recordings with genetically encoded fluorescent DA or ACh indicator, we found L-DOPA selectively decreased DLS ACh levels in parkinsonian conditions. DA inhibited ACh release via dopamine D2 receptors and dSPNs-mediated activation of type-A γ-aminobutyric acid receptors on cholinergic interneurons. Restoring DLS ACh levels during L-DOPA treatment induced additional DA release by activating nicotinic acetylcholine receptors, thereby promoting the activity of dSPNs and iSPNs. Enhancing DLS ACh facilitated L-DOPA-induced turning behavior but not dyskinesia in parkinsonian mice.

CONCLUSIONS

Our results demonstrated that enhancing striatal ACh facilitated the effect of L-DOPA by modulating DA tone. It may challenge the classical hypothesis of a purely competitive interaction between dopaminergic and cholinergic neuromodulation in improving PD motor deficits. Modulating ACh levels within the dopaminergic system may improve striatal DA availability in PD patients.

Innervation density governs crosstalk of GPCR-based norepinephrine and dopamine sensors

GPCR-based fluorescent sensors are widely used to correlate neuromodulatory signaling with brain function. While experiments in transfected cells often reveal selectivity for individual neurotransmitters, sensor specificity in the brain frequently remains uncertain. Pursuing experiments in brain slices and in vivo, we find that norepinephrine and dopamine cross-activate the respective sensors. Non-specific activation occurred when innervation of the cross-reacting transmitter was high, and silencing of specific innervation was indispensable for interpreting sensor fluorescence.

Volumetric voltage imaging of neuronal populations in the mouse brain by confocal light-field microscopy

Voltage imaging measures neuronal activity directly and holds promise for understanding information processing within individual neurons and across populations. However, imaging voltage over large neuronal populations has been challenging owing to the simultaneous requirements of high imaging speed and signal-to-noise ratio, large volume coverage and low photobleaching rate. Here, to overcome this challenge, we developed a confocal light-field microscope that surpassed the traditional limits in speed and noise performance by incorporating a speed-enhanced camera, a fast and robust scanning mechanism, laser-speckle-noise elimination and optimized light efficiency. With this method, we achieved simultaneous recording from more than 300 spiking neurons within an 800-µm-diameter and 180-µm-thick volume in the mouse cortex, for more than 20 min. By integrating the spatial and voltage activity profiles, we have mapped three-dimensional neural coordination patterns in awake mouse brains. Our method is robust for routine application in volumetric voltage imaging.

Identifying dysfunctional cell types and circuits in animal models for psychiatric disorders with calcium imaging

A central goal of neuroscience is to understand how the brain transforms external stimuli and internal bodily signals into patterns of activity that underlie cognition, emotional states, and behavior. Understanding how these patterns of activity may be disrupted in mental illness is crucial for developing novel therapeutics. It is well appreciated that psychiatric disorders are complex, circuit-based disorders that arise from dysfunctional activity patterns generated in discrete cell types and their connections. Recent advances in large-scale, cell-type specific calcium imaging approaches have shed new light on the cellular, circuit, and network-level dysfunction in animal models for psychiatric disorders. Here, we highlight a series of recent findings over the last ~10 years from in vivo calcium imaging studies that show how aberrant patterns of activity in discrete cell types and circuits may underlie behavioral deficits in animal models for several psychiatric disorders, including depression, anxiety, autism spectrum disorders, and schizophrenia. These advances in calcium imaging in pre-clinical models demonstrate the power of cell-type-specific imaging tools in understanding the underlying dysfunction in cell types, activity patterns, and neural circuits that may contribute to disease and provide new blueprints for developing more targeted therapeutics and treatment strategies.

Mechanisms of neuromodulatory volume transmission

A wealth of neuromodulatory transmitters regulate synaptic circuits in the brain. Their mode of signaling, often called volume transmission, differs from classical synaptic transmission in important ways. In synaptic transmission, vesicles rapidly fuse in response to action potentials and release their transmitter content. The transmitters are then sensed by nearby receptors on select target cells with minimal delay. Signal transmission is restricted to synaptic contacts and typically occurs within ~1 ms. Volume transmission doesn't rely on synaptic contact sites and is the main mode of monoamines and neuropeptides, important neuromodulators in the brain. It is less precise than synaptic transmission, and the underlying molecular mechanisms and spatiotemporal scales are often not well understood. Here, we review literature on mechanisms of volume transmission and raise scientific questions that should be addressed in the years ahead. We define five domains by which volume transmission systems can differ from synaptic transmission and from one another. These domains are (1) innervation patterns and firing properties, (2) transmitter synthesis and loading into different types of vesicles, (3) architecture and distribution of release sites, (4) transmitter diffusion, degradation, and reuptake, and (5) receptor types and their positioning on target cells. We discuss these five domains for dopamine, a well-studied monoamine, and then compare the literature on dopamine with that on norepinephrine and serotonin. We include assessments of neuropeptide signaling and of central acetylcholine transmission. Through this review, we provide a molecular and cellular framework for volume transmission. This mechanistic knowledge is essential to define how neuromodulatory systems control behavior in health and disease and to understand how they are modulated by medical treatments and by drugs of abuse.

In-Depth Chemical Analysis of the Brain Extracellular Space Using In Vivo Microdialysis with Liquid Chromatography-Tandem Mass Spectrometry

Metabolomic analysis of samples acquired in vivo from the brain extracellular space by microdialysis sampling can provide insights into chemical underpinnings of a given brain state and how it changes over time. Small sample volumes and low physiological concentrations have limited the identification of compounds from this compartment, so at present, we have scant knowledge of its composition. As a result, most in vivo measurements have limited depth of analysis. Here, we describe an approach to (1) identify hundreds of compounds in brain dialysate and (2) routinely detect many of these compounds in 5 μL microdialysis samples to enable deep monitoring of brain chemistry in time-resolved studies. Dialysate samples collected over 12 h were concentrated 10-fold and then analyzed using liquid chromatography with iterative tandem mass spectrometry (LC-MS/MS). Using this approach on dialysate from the rat striatum with both reversed-phase and hydrophilic interaction liquid chromatography yielded 479 unique compound identifications. 60% of the identified compounds could be detected in 5 μL of dialysate without further concentration using a single 20 min LC-MS analysis, showing that once identified, most compounds can be detected using small sample volumes and shorter analysis times compatible with routine in vivo monitoring. To detect more neurochemicals, LC-MS analysis of dialysate derivatized with light and isotopically labeled benzoyl chloride was employed. 872 nondegenerate benzoylated features were detected with this approach, including most small-molecule neurotransmitters and several metabolites involved in dopamine metabolism. This strategy allows deeper annotation of the brain extracellular space than previously possible and provides a launching point for defining the chemistry underlying brain states.

Metal-Organic Framework Nanofluidic Synapse

Chemical synapse completes the signaling through neurotransmitter-mediated ion flux, the emulation of which has been a long-standing obstacle in neuromorphic exploration. Here, we report metal-organic framework (MOF) nanofluidic synapses in which conjugated MOFs with abundant ionic storage sites underlie the ionic hysteresis and simultaneously serve as catalase mimetics that sensitively respond to neurotransmitter glutamate (Glu). Various neurosynaptic patterns with adaptable weights are realized via Glu-mediated chemical/ionic coupling. In particular, nonlinear Hebbian and anti-Hebbian learning in millisecond time ranges are achieved, akin to those of chemical synapses. Reversible biochemical in-memory encoding via enzymatic Glu clearance is also accomplished. Such results are prerequisites for highly bionic electrolytic computers.

Mapping multi-regional functional connectivity of astrocyte-neuronal networks during behaviors

Significance

Diverse behaviors rely on coordinated activity and multi-regional functional connectivity within astrocyte-neuronal networks. However, current techniques for simultaneously measuring astrocytic and neuronal activities across multiple brain regions during behaviors remain limited.

Aim

We propose a multi-fiber solution that can simultaneously record activities of astrocyte-neuronal networks across multiple regions during behaviors.

Approach

We employed cell-specific dual-color genetically encoded calcium indicators (GECIs) and multi-fiber photometry to simultaneously measure astrocytic and neuronal Ca2+ transients across multiple brain regions in freely behaving animals.

Results

Our findings demonstrate that both movements and sensory stimuli induce synchronized and highly correlated Ca2+ transients in astrocytes and neurons of freely behaving mice. In addition, we recorded astrocytic and neuronal Ca2+ transients from multiple brain regions during mouse behaviors. Our observations reveal heightened synchronization of astrocytic and neuronal Ca2+ transients across different brain regions during movements or sensory stimuli, indicating enhanced functional connectivity within brain-wide astrocyte-neuronal networks.

Conclusions

Multi-fiber photometry, combined with cell-specific dual-color GECIs, represents a powerful approach for investigating astrocytic and neuronal activities across different brain regions during behaviors. This technique serves as a versatile tool for analyzing the multi-regional functional connectivity map of astrocyte-neuronal networks associated with specific behaviors.

Inflammation-free electrochemical in vivo sensing of dopamine with atomic-level engineered antioxidative single-atom catalyst

Electrochemical methods with tissue-implantable microelectrodes provide an excellent platform for real-time monitoring the neurochemical dynamics in vivo due to their superior spatiotemporal resolution and high selectivity and sensitivity. Nevertheless, electrode implantation inevitably damages the brain tissue, upregulates reactive oxygen species level, and triggers neuroinflammatory response, resulting in unreliable quantification of neurochemical events. Herein, we report a multifunctional sensing platform for inflammation-free in vivo analysis with atomic-level engineered Fe single-atom catalyst that functions as both single-atom nanozyme with antioxidative activity and electrode material for dopamine oxidation. Through high-temperature pyrolysis and catalytic performance screening, we fabricate a series of Fe single-atom nanozymes with different coordination configurations and find that the Fe single-atom nanozyme with FeN4 exhibits the highest activity toward mimicking catalase and superoxide dismutase as well as eliminating hydroxyl radical, while also featuring high electrode reactivity toward dopamine oxidation. These dual functions endow the single-atom nanozyme-based sensor with anti-inflammatory capabilities, enabling accurate dopamine sensing in living male rat brain. This study provides an avenue for designing inflammation-free electrochemical sensing platforms with atomic-precision engineered single-atom catalysts.

Presynaptic sensor and silencer of peptidergic transmission reveal neuropeptides as primary transmitters in pontine fear circuit

Neurons produce and release neuropeptides to communicate with one another. Despite their importance in brain function, circuit-based mechanisms of peptidergic transmission are poorly understood, primarily due to the lack of tools for monitoring and manipulating neuropeptide release in vivo. Here, we report the development of two genetically encoded tools for investigating peptidergic transmission in behaving mice: a genetically encoded large dense core vesicle (LDCV) sensor that detects presynaptic neuropeptide release and a genetically encoded silencer that specifically degrades neuropeptides inside LDCVs. Using these tools, we show that neuropeptides, not glutamate, encode the unconditioned stimulus in the parabrachial-to-amygdalar threat pathway during Pavlovian threat learning. We also show that neuropeptides play important roles in encoding positive valence and suppressing conditioned threat response in the amygdala-to-parabrachial endogenous opioidergic circuit. These results show that our sensor and silencer for presynaptic peptidergic transmission are reliable tools to investigate neuropeptidergic systems in awake, behaving animals.

General In Situ Engineering of Carbon-Based Materials on Carbon Fiber for In Vivo Neurochemical Sensing

Developing real-time, dynamic, and in situ analytical methods with high spatial and temporal resolutions is crucial for exploring biochemical processes in the brain. Although in vivo electrochemical methods based on carbon fiber (CF) microelectrodes are effective in monitoring neurochemical dynamics during physiological and pathological processes, complex post modification hinders large-scale productions and widespread neuroscience applications. Herein, we develop a general strategy for the in situ engineering of carbon-based materials to mass-produce functional CFs by introducing polydopamine to anchor zeolitic imidazolate frameworks as precursors, followed by one-step pyrolysis. This strategy demonstrates exceptional universality and design flexibility, overcoming complex post-modification procedures and avoiding the delamination of the modification layer. This simplifies the fabrication and integration of functional CF-based microelectrodes. Moreover, we design highly stable and selective H+, O2, and ascorbate microsensors and monitor the influence of CO2 exposure on the O2 content of the cerebral tissue during physiological and ischemia-reperfusion pathological processes.

Unlocking opioid neuropeptide dynamics with genetically encoded biosensors

Neuropeptides are ubiquitous in the nervous system. Research into neuropeptides has been limited by a lack of experimental tools that allow for the precise dissection of their complex and diverse dynamics in a circuit-specific manner. Opioid peptides modulate pain, reward and aversion and as such have high clinical relevance. To illuminate the spatiotemporal dynamics of endogenous opioid signaling in the brain, we developed a class of genetically encoded fluorescence sensors based on kappa, delta and mu opioid receptors: κLight, δLight and µLight, respectively. We characterized the pharmacological profiles of these sensors in mammalian cells and in dissociated neurons. We used κLight to identify electrical stimulation parameters that trigger endogenous opioid release and the spatiotemporal scale of dynorphin volume transmission in brain slices. Using in vivo fiber photometry in mice, we demonstrated the utility of these sensors in detecting optogenetically driven opioid release and observed differential opioid release dynamics in response to fearful and rewarding conditions.

Fiber photometry-based investigation of brain function and dysfunction

Fiber photometry is an optical method to monitor fluorescent signals using a fiber optic cannula. Over the past two decades, together with the development of various genetically encoded biosensors, it has been applied to investigate various types of activity in the central nervous system. This includes not only type-specific neuronal population activity, but also non-neuronal activity and neurotransmitter/neuropeptide signals in awake, freely behaving animals. In this perspective, we summarize the recent development of this technique. After describing common technical pitfalls, we discuss future directions of this powerful approach for investigating brain function and dysfunction.

Surface-Enhanced Raman Scattering Nanosensing and Imaging in Neuroscience

Monitoring neurochemicals and imaging the molecular content of brain tissues in vitro, ex vivo, and in vivo is essential for enhancing our understanding of neurochemistry and the causes of brain disorders. This review explores the potential applications of surface-enhanced Raman scattering (SERS) nanosensors in neurosciences, where their adoption could lead to significant progress in the field. These applications encompass detecting neurotransmitters or brain disorders biomarkers in biofluids with SERS nanosensors, and imaging normal and pathological brain tissues with SERS labeling. Specific studies highlighting in vitro, ex vivo, and in vivo analysis of brain disorders using fit-for-purpose SERS nanosensors will be detailed, with an emphasis on the ability of SERS to detect clinically pertinent levels of neurochemicals. Recent advancements in designing SERS-active nanomaterials, improving experimentation in biofluids, and increasing the usage of machine learning for interpreting SERS spectra will also be discussed. Furthermore, we will address the tagging of tissues presenting pathologies with nanoparticles for SERS imaging, a burgeoning domain of neuroscience that has been demonstrated to be effective in guiding tumor removal during brain surgery. The review also explores future research applications for SERS nanosensors in neuroscience, including monitoring neurochemistry in vivo with greater penetration using surface-enhanced spatially offset Raman scattering (SESORS), near-infrared lasers, and 2-photon techniques. The article concludes by discussing the potential of SERS for investigating the effectiveness of therapies for brain disorders and for integrating conventional neurochemistry techniques with SERS sensing.

Ngfr+ cholinergic projection from SI/nBM to mPFC selectively regulates temporal order recognition memory

Acetylcholine regulates various cognitive functions through broad cholinergic innervation. However, specific cholinergic subpopulations, circuits and molecular mechanisms underlying recognition memory remain largely unknown. Here we show that Ngfr+ cholinergic neurons in the substantia innominate (SI)/nucleus basalis of Meynert (nBM)-medial prefrontal cortex (mPFC) circuit selectively underlies recency judgements. Loss of nerve growth factor receptor (Ngfr-/- mice) reduced the excitability of cholinergic neurons in the SI/nBM-mPFC circuit but not in the medial septum (MS)-hippocampus pathway, and impaired temporal order memory but not novel object and object location recognition. Expression of Ngfr in Ngfr-/- SI/nBM restored defected temporal order memory. Fiber photometry revealed that acetylcholine release in mPFC not only predicted object encounters but also mediated recency judgments of objects, and such acetylcholine release was absent in Ngfr-/- mPFC. Chemogenetic and optogenetic inhibition of SI/nBM projection to mPFC in ChAT-Cre mice diminished mPFC acetylcholine release and deteriorated temporal order recognition. Impaired cholinergic activity led to a depolarizing shift of GABAergic inputs to mPFC pyramidal neurons, due to disturbed KCC2-mediated chloride gradients. Finally, potentiation of acetylcholine signaling upregulated KCC2 levels, restored GABAergic driving force and rescued temporal order recognition deficits in Ngfr-/- mice. Thus, NGFR-dependent SI/nBM-mPFC cholinergic circuit underlies temporal order recognition memory.

Imaging Neurotransmitters with Small-Molecule Fluorescent Probes

Neurotransmitters play a crucial role in regulating communication between neurons within the brain and central nervous system. Thus, imaging neurotransmitters has become a high priority in neuroscience. This minireview focuses on recent advancements in the development of fluorescent small-molecule fluorescent probes for neurotransmitter imaging and applications of these probes in neuroscience. Innovative approaches for probe design are highlighted as well as attributes which are necessary for practical utility, with a view to inspiring new probe development capable of visualizing neurotransmitters.

Learning, Fast and Slow: Single- and Many-Shot Learning in the Hippocampus

The hippocampus is critical for memory and spatial navigation. The ability to map novel environments, as well as more abstract conceptual relationships, is fundamental to the cognitive flexibility that humans and other animals require to survive in a dynamic world. In this review, we survey recent advances in our understanding of how this flexibility is implemented anatomically and functionally by hippocampal circuitry, during both active exploration (online) and rest (offline). We discuss the advantages and limitations of spike timing-dependent plasticity and the more recently discovered behavioral timescale synaptic plasticity in supporting distinct learning modes in the hippocampus. Finally, we suggest complementary roles for these plasticity types in explaining many-shot and single-shot learning in the hippocampus and discuss how these rules could work together to support the learning of cognitive maps.

Sex Differences in Dopamine Release in Nucleus Accumbens and Dorsal Striatum Determined by Chronic Fast-Scan Cyclic Voltammetry: Effects of Social Housing and Repeated Stimulation

We investigated sex differences in dopamine (DA) release in the nucleus accumbens (NAc) and dorsolateral striatum (DLS) using a chronic 16-channel carbon fiber electrode and fast-scan cyclic voltammetry (FSCV). Electrical stimulation-induced (ES; 60 Hz) DA release was recorded in the NAc of single- or pair-housed male and female rats. When core (NAcC) and shell (NAcS) were recorded simultaneously, there was greater ES DA release in NAcC of pair-housed females compared with single females and males. Housing did not affect ES NAc DA release in males. In contrast, there was significantly more ES DA release from the DLS of female rats than male rats. This was true prior to and after treatment with methamphetamine. Furthermore, in castrated (CAST) males and ovariectomized (OVX) females, there were no sex differences in ES DA release from the DLS, demonstrating the hormone dependence of this sex difference. However, in the DLS of both intact and gonadectomized rats, DA reuptake was slower in females than that in males. Finally, DA release following ES of the medial forebrain bundle at 60 Hz was studied over 4 weeks. ES DA release increased over time for both CAST males and OVX females, demonstrating sensitization. Using this novel 16-channel chronic FSCV electrode, we found sex differences in the effects of social housing in the NAcS, sex differences in DA release from intact rats in DLS, and sex differences in DA reuptake in DLS of intake and gonadectomized rats, and we report sensitization of ES-induced DA release in DLS in vivo.

A chemogenetic approach for dopamine imaging with tunable sensitivity

Genetically-encoded dopamine (DA) sensors enable high-resolution imaging of DA release, but their ability to detect a wide range of extracellular DA levels, especially tonic versus phasic DA release, is limited by their intrinsic affinity. Here we show that a human-selective dopamine receptor positive allosteric modulator (PAM) can be used to boost sensor affinity on-demand. The PAM enhances DA detection sensitivity across experimental preparations (in vitro, ex vivo and in vivo) via one-photon or two-photon imaging. In vivo photometry-based detection of optogenetically-evoked DA release revealed that DETQ administration produces a stable 31 minutes window of potentiation without effects on animal behavior. The use of the PAM revealed region-specific and metabolic state-dependent differences in tonic DA levels and enhanced single-trial detection of behavior-evoked phasic DA release in cortex and striatum. Our chemogenetic strategy can potently and flexibly tune DA imaging sensitivity and reveal multi-modal (tonic/phasic) DA signaling across preparations and imaging approaches.

Development of a genetically encoded sensor for probing endogenous nociceptin opioid peptide release

Nociceptin/orphanin-FQ (N/OFQ) is a recently appreciated critical opioid peptide with key regulatory functions in several central behavioral processes including motivation, stress, feeding, and sleep. The functional relevance of N/OFQ action in the mammalian brain remains unclear due to a lack of high-resolution approaches to detect this neuropeptide with appropriate spatial and temporal resolution. Here we develop and characterize NOPLight, a genetically encoded sensor that sensitively reports changes in endogenous N/OFQ release. We characterized the affinity, pharmacological profile, spectral properties, kinetics, ligand selectivity, and potential interaction with intracellular signal transducers of NOPLight in vitro. Its functionality was established in acute brain slices by exogeneous N/OFQ application and chemogenetic induction of endogenous N/OFQ release from PNOC neurons. In vivo studies with fibre photometry enabled direct recording of NOPLight binding to exogenous N/OFQ receptor ligands, as well as detection of endogenous N/OFQ release within the paranigral ventral tegmental area (pnVTA) during natural behaviors and chemogenetic activation of PNOC neurons. In summary, we show here that NOPLight can be used to detect N/OFQ opioid peptide signal dynamics in tissue and freely behaving animals.

Sedative and hypnotic effects of the saponins from a traditional edible plant Liriope spicata Lour. in PCPA-induced insomnia mice

ETHNOPHARMACOLOGICAL RELEVANCE

Liriope spicata Lour., a species listed in the catalogue of 'Medicinal and Edible Homologous Species', is traditionally used for the treatment of fatigue, restlessness, insomnia and constipation.

AIM OF THE STUDY

This study is aimed to evaluate the sedative and hypnotic effect of the saponins from a natural plant L. spicata Lour. in vivo.

MATERIALS AND METHODS

The total saponin (LSTS) and purified saponin (LSPS) were extracted from L. spicata, followed by a thorough analysis of their major components using the HPLC-MS. Subsequently, the therapeutic efficacy of LSTS and LSPS was evaluated by the improvement of anxiety and depression behaviors of the PCPA-induced mice.

RESULTS

LSTS and LSPS exhibited similar saponin compositions but differ in their composition ratios, with liriopesides-type saponins accounting for a larger proportion in LSTS. Studies demonstrated that both LSTS and LSPS can extend sleep duration and immobility time, while reducing sleep latency in PCPA-induced mice. However, there was no significant difference in weight change among the various mice groups. Elisa results indicated that the LSTS and LSPS could decrease levels of NE, DA, IL-6, and elevate the levels of 5-HT, NO, PGD2 and TNF-α in mice plasma. LSTS enhanced the expression of neurotransmitter receptors, while LSPS exhibited a more pronounced effect in regulating the expression of inflammatory factors. In conclusion, the saponins derived from L. spicata might hold promise as ingredients for developing health foods with sedative and hypnotic effects, potentially related to the modulation of serotonergic and GABAAergic neuron expression, as well as immunomodulatory process.

Interaction of acetylcholine and oxytocin neuromodulation in the hippocampus

A postulated role of subcortical neuromodulators is to control brain states. Mechanisms by which different neuromodulators compete or cooperate at various temporal scales remain an open question. We investigated the interaction of acetylcholine (ACh) and oxytocin (OXT) at slow and fast timescales during various brain states. Although these neuromodulators fluctuated in parallel during NREM packets, transitions from NREM to REM were characterized by a surge of ACh but a continued decrease of OXT. OXT signaling lagged behind ACh. High ACh was correlated with population synchrony and gamma oscillations during active waking, whereas minimum ACh predicts sharp-wave ripples (SPW-Rs). Optogenetic control of ACh and OXT neurons confirmed the active role of these neuromodulators in the observed correlations. Synchronous hippocampal activity consistently reduced OXT activity, whereas inactivation of the lateral septum-hypothalamus path attenuated this effect. Our findings demonstrate how cooperative actions of these neuromodulators allow target circuits to perform specific functions.

Circadian-independent light regulation of mammalian metabolism

The daily light-dark cycle is a key zeitgeber (time cue) for entraining an organism's biological clock, whereby light sensing by retinal photoreceptors, particularly intrinsically photosensitive retinal ganglion cells, stimulates the suprachiasmatic nucleus of the hypothalamus, a central pacemaker that in turn orchestrates the rhythm of peripheral metabolic activities. Non-rhythmic effects of light on metabolism have also been long known, and their transduction mechanisms are only beginning to unfold. Here, we summarize emerging evidence that, in mammals, light exposure or deprivation profoundly affects glucose homeostasis, thermogenesis and other metabolic activities in a clock-independent manner. Such light regulation could involve melanopsin-based, intrinsically photosensitive retinal ganglion cell-initiated brain circuits via the suprachiasmatic nucleus of the hypothalamus and other nuclei, or direct stimulation of opsins expressed in the hypothalamus, adipose tissue, blood vessels and skin to regulate sympathetic tone, lipolysis, glucose uptake, mitochondrial activation, thermogenesis, food intake, blood pressure and melanogenesis. These photic signalling events may coordinate with circadian-based mechanisms to maintain metabolic homeostasis, with dysregulation of this system underlying metabolic diseases caused by aberrant light exposure, such as environmental night light and shift work.

Electrochemical detection of glutamate and histamine using redox-labeled stimuli-responsive polymer as a synthetic target receptor

Glutamate (Glu) and histamine (His) are two major neurotransmitters that play many critical roles in brain physiological functions and neurological disorders. Therefore, specific and sensitive monitoring of Glu and His is essential in the diagnosis and treatment of various mental health and neurodegenerative disorders. Both being non-electroactive species, direct electrochemical detection of Glu and His has been challenging. Herein, we report a stimuli-responsive polymer-based biosensor for the electrochemical detection of Glu and His. The polymer-based target receptors consist of a linear chain stimuli-responsive templated polymer hybrid that is labeled with an osmium-based redox-active reporter molecules to elicit conformation-dependent electrochemical responses. The polymers are then attached to a gold electrode to implement an electrochemical sensor. The cyclic voltammetry (CV) and square-wave voltammetry (SWV) results confirmed the polymers' conformational changes due to the specific target (i.e., Glu and His) recognition and the corresponding electrochemical detection capabilities. The voltammetry results indicate that this biosensor can be used as a 'signal-on' and 'signal-off' sensors for the detection of Glu and His concentrations, respectively. The developed biosensor also showed excellent regeneration capability by fully recovering the initial current signal after rinsing with deionized water. To further validate the polymer's utility as a target bioreceptor, the surface plasmon resonance (SPR) technique was used to characterize the binding affinity between the designed polymers and the target chemical. The SPR results exhibited the equilibrium dissociation constants (KD) of 2.40 μM and 1.54 μM for the polymer-Glu and polymer-His interactions, respectively. The results obtained this work strongly suggest that the proposed sensing technology could potentially be used as a platform for monitoring non-electroactive neurochemicals from animal models.

Aptamer-Based Potentiometric Sensor Enables Highly Selective and Neurocompatible Neurochemical Sensing in Rat Brain

Selective and nondisruptive in vivo neurochemical monitoring within the central nervous system has long been a challenging endeavor. We introduce a new sensing approach that integrates neurocompatible galvanic redox potentiometry (GRP) with customizable phosphorothioate aptamers to specifically probe dopamine (DA) dynamics in live rat brains. The aptamer-functionalized GRP (aptGRP) sensor demonstrates nanomolar sensitivity and over a 10-fold selectivity for DA, even amidst physiological levels of major interfering species. Notably, conventional sensors without the aptamer modification exhibit negligible reactivity to DA concentrations exceeding 20 μM. Critically, the aptGRP sensor operates without altering neuronal activity, thereby permitting real-time, concurrent recordings of both DA flux and electrical signaling in vivo. This breakthrough establishes aptGRP as a viable and promising framework for the development of high-fidelity sensors, offering novel insights into neurotransmission dynamics in a live setting.

Development of a genetically encoded sensor for probing endogenous nociceptin opioid peptide release

Nociceptin/orphanin-FQ (N/OFQ) is a recently appreciated critical opioid peptide with key regulatory functions in several central behavioral processes including motivation, stress, feeding, and sleep. The functional relevance of N/OFQ action in the mammalian brain remains unclear due to a lack of high-resolution approaches to detect this neuropeptide with appropriate spatial and temporal resolution. Here we develop and characterize NOPLight, a genetically encoded sensor that sensitively reports changes in endogenous N/OFQ release. We characterized the affinity, pharmacological profile, spectral properties, kinetics, ligand selectivity, and potential interaction with intracellular signal transducers of NOPLight in vitro. Its functionality was established in acute brain slices by exogeneous N/OFQ application and chemogenetic induction of endogenous N/OFQ release from PNOC neurons. In vivo studies with fibre photometry enabled direct recording of NOPLight binding to exogenous N/OFQ receptor ligands, as well as detection of endogenous N/OFQ release within the paranigral ventral tegmental area (pnVTA) during natural behaviors and chemogenetic activation of PNOC neurons. In summary, we show here that NOPLight can be used to detect N/OFQ opioid peptide signal dynamics in tissue and freely behaving animals.

Multifunctional and Flexible Neural Probe with Thermally Drawn Fibers for Bidirectional Synaptic Probing in the Brain

Synapses in the brain utilize two distinct communication mechanisms: chemical and electrical. For a comprehensive investigation of neural circuitry, neural interfaces should be capable of both monitoring and stimulating these types of physiological interactions. However, previously developed interfaces for neurotransmitter monitoring have been limited in interaction modality due to constraints in device size, fabrication techniques, and the usage of flexible materials. To address this obstacle, we propose a multifunctional and flexible fiber probe fabricated through the microwire codrawing thermal drawing process, which enables the high-density integration of functional components with various materials such as polymers, metals, and carbon fibers. The fiber enables real-time monitoring of transient dopamine release in vivo, real-time stimulation of cell-specific neuronal populations via optogenetic stimulation, single-unit electrophysiology of individual neurons localized to the tip of the neural probe, and chemical stimulation via drug delivery. This fiber will improve the accessibility and functionality of bidirectional interrogation of neurochemical mechanisms in implantable neural probes.