A brainstem circuit amplifies aversion.

Dynamic gain control of aversive signals enables adaptive behavioral responses. Although the role of amygdalar circuits in aversive processing is well established, the neural pathway for amplifying aversion remains elusive. Here, we show that the brainstem circuit linking the interpeduncular nucleus (IPN) with the nucleus incertus (NI) amplifies aversion and promotes avoidant behaviors. IPN GABA neurons are activated by aversive stimuli and their predicting cues, with their response intensity closely tracking aversive values. Activating these neurons does not trigger aversive behavior on its own but rather amplifies responses to aversive stimuli, whereas their ablation or inhibition suppresses such responses. Detailed circuit dissection revealed anatomically distinct subgroups within the IPN GABA neuron population, highlighting the NI-projecting subgroup as the modulator of aversiveness related to fear and opioid withdrawal. These findings unveil the IPN-NI circuit as an aversion amplifier and suggest potential targets for interventions against affective disorders and opioid relapse.

Fiber photometry in neuroscience research: principles, applications, and future directions.

In recent years, fluorescent sensors are enjoying a surge of popularity in the field of neuroscience. Through the development of novel genetically encoded sensors as well as improved methods of detection and analysis, fluorescent sensing has risen as a new major technique in neuroscience alongside molecular, electrophysiological, and imaging methods, opening up new avenues for research. Combined with multiphoton microscopy and fiber photometry, these sensors offer unique advantages in terms of cellular specificity, access to multiple targets - from calcium dynamics to neurotransmitter release to intracellular processes - as well as high capability for in vivo interrogation of neurobiological mechanisms underpinning behavior. Here, we provide a brief overview of the method, present examples of its integration with other tools in recent studies ranging from cellular to systems neuroscience, and discuss some of its principles and limitations, with the aim of introducing new potential users to this rapidly developing and potent technique.

Altered activity of mPFC pyramidal neurons and parvalbumin-expressing interneurons during social interactions in a Mecp2 mouse model for Rett syndrome.

Social memory impairments in Mecp2 knockout (KO) mice result from altered neuronal activity in the monosynaptic projection from the ventral hippocampus (vHIP) to the medial prefrontal cortex (mPFC). The hippocampal network is hyperactive in this model for Rett syndrome, and such atypically heightened neuronal activity propagates to the mPFC through this monosynaptic projection, resulting in altered mPFC network activity and social memory deficits. However, the underlying mechanism of cellular dysfunction within this projection between vHIP pyramidal neurons (PYR) and mPFC PYRs and parvalbumin interneurons (PV-IN) resulting in social memory impairments in Mecp2 KO mice has yet to be elucidated. We confirmed social memory (but not sociability) deficits in Mecp2 KO mice using a new 4-chamber social memory arena, designed to minimize the impact of the tethering to optical fibers required for simultaneous in vivo fiber photometry of Ca2+-sensor signals during social interactions. mPFC PYRs of wildtype (WT) mice showed increases in Ca2+ signal amplitude during explorations of a novel toy mouse and interactions with both familiar and novel mice, while PYRs of Mecp2 KO mice showed smaller Ca2+ signals during interactions only with live mice. On the other hand, mPFC PV-INs of Mecp2 KO mice showed larger Ca2+ signals during interactions with a familiar cage-mate compared to those signals in PYRs, a difference absent in the WT mice. These observations suggest atypically heightened inhibition and impaired excitation in the mPFC network of Mecp2 KO mice during social interactions, potentially driving their deficit in social memory.

Astrocytes in the Ventral Hippocampus Bidirectionally Regulate Innate and Stress-Induced Anxiety-Like Behaviors in Male Mice.

The mechanisms of anxiety disorders, the most common mental illness, remain incompletely characterized. The ventral hippocampus (vHPC) is critical for the expression of anxiety. However, current studies primarily focus on vHPC neurons, leaving the role for vHPC astrocytes in anxiety largely unexplored. Here, genetically encoded Ca2+ indicator GCaMP6m and in vivo fiber photometry calcium imaging are used to label vHPC astrocytes and monitor their activity, respectively, genetic and chemogenetic approaches to inhibit and activate vHPC astrocytes, respectively, patch-clamp recordings to measure glutamate currents, and behavioral assays to assess anxiety-like behaviors. It is found that vHPC astrocytic activity is increased in anxiogenic environments and by 3-d subacute restraint stress (SRS), a well-validated mouse model of anxiety disorders. Genetic inhibition of vHPC astrocytes exerts anxiolytic effects on both innate and SRS-induced anxiety-related behaviors, whereas hM3Dq-mediated chemogenetic or SRS-induced activation of vHPC astrocytes enhances anxiety-like behaviors, which are reversed by intra-vHPC application of the ionotropic glutamate N-methyl-d-aspartate receptor antagonists. Furthermore, intra-vHPC or systemic application of the N-methyl-d-aspartate receptor antagonist memantine, a U.S. FDA-approved drug for Alzheimer's disease, fully rescues SRS-induced anxiety-like behaviors. The findings highlight vHPC astrocytes as critical regulators of stress and anxiety and as potential therapeutic targets for anxiety and anxiety-related disorders.

Amygdala and Cortex Relationships during Learning of a Sensory Discrimination Task.

During learning of a sensory discrimination task, the cortical and subcortical regions display complex spatiotemporal dynamics. During learning, both the amygdala and cortex link stimulus information to its appropriate association, for example, a reward. In addition, both structures are also related to nonsensory parameters such as body movements and licking during the reward period. However, the emergence of the cortico-amygdala relationships during learning is largely unknown. To study this, we combined wide-field cortical imaging with fiber photometry to simultaneously record cortico-amygdala population dynamics as male mice learn a whisker-dependent go/no-go task. We were able to simultaneously record neuronal populations from the posterior cortex and either the basolateral amygdala (BLA) or central/medial amygdala (CEM). Prior to learning, the somatosensory and associative cortex responded during sensation, while amygdala areas did not show significant responses. As mice became experts, amygdala responses emerged early during the sensation period, increasing in the CEM, while decreasing in the BLA. Interestingly, amygdala and cortical responses were associated with task-related body movement, displaying significant responses ∼200 ms before movement initiation which led to licking for the reward. A correlation analysis between the cortex and amygdala revealed negative and positive correlation with the BLA and CEM, respectively, only in the expert case. These results imply that learning induces an involvement of the cortex and amygdala which may aid to link sensory stimuli with appropriate associations.

Optimized ultrasound neuromodulation for non-invasive control of behavior and physiology.

Focused ultrasound can non-invasively modulate neural activity, but whether effective stimulation parameters generalize across brain regions and cell types remains unknown. We used focused ultrasound coupled with fiber photometry to identify optimal neuromodulation parameters for four different arousal centers of the brain in an effort to yield overt changes in behavior. Applying coordinate descent, we found that optimal parameters for excitation or inhibition are highly distinct, the effects of which are generally conserved across brain regions and cell types. Optimized stimulations induced clear, target-specific behavioral effects, whereas non-optimized protocols of equivalent energy resulted in substantially less or no change in behavior. These outcomes were independent of auditory confounds and, contrary to expectation, accompanied by a cyclooxygenase-dependent and prolonged reduction in local blood flow and temperature with brain-region-specific scaling. These findings demonstrate that carefully tuned and targeted ultrasound can exhibit powerful effects on complex behavior and physiology.

Serotonergic input from the dorsal raphe nucleus shapes learning-associated odor responses in the olfactory bulb.

AIM: Neural activity in the olfactory bulb (OB) can represent odor information during different brain and behavioral states. For example, the odor responses of mitral/tufted (M/T) cells in the OB change during learning of odor-discrimination tasks and, at the network level, beta power increases and the high gamma (HG) power decreases during odor presentation in such tasks. However, the neural mechanisms underlying these observations remain poorly understood. Here, we investigate whether serotonergic modulation from the dorsal raphe nucleus (DRN) to the OB is involved in shaping activity during the learning process in a go/no-go task in mice. METHODS: Fiber photometry was used to record the population activity of DRN serotonergic neurons during a go/no-go task. In vivo electrophysiology was used to record neural activity (single units and local field potentials) in the OB during the go/no-go task. Real-time place preference (RTPP) and intracranial light administration in a specific subarea (iClass) tests were used to assess the ability of mice to encoding reward information. RESULTS: Odor-evoked population activity in serotonergic neurons in the DRN was shaped during the learning process in a go/no-go task. In the OB, neural activity from oscillations to single cells showed complex, learning-associated changes and ability to encode information during an odor discrimination task. However, these properties were not observed after ablation of DRN serotonergic neurons. CONCLUSION: The activity of neural networks and single cells in the OB, and their ability to encode information about odor value, are shaped by serotonergic projections from the DRN.

Identifying behavioral links to neural dynamics of multifiber photometry recordings in a mouse social behavior network.

Objective.Distributed hypothalamic-midbrain neural circuits help orchestrate complex behavioral responses during social interactions. Given rapid advances in optical imaging, it is a fundamental question how population-averaged neural activity measured by multi-fiber photometry (MFP) for calcium fluorescence signals correlates with social behaviors is a fundamental question. This paper aims to investigate the correspondence between MFP data and social behaviors.Approach:We propose a state-space analysis framework to characterize mouse MFP data based on dynamic latent variable models, which include a continuous-state linear dynamical system and a discrete-state hidden semi-Markov model. We validate these models on extensive MFP recordings during aggressive and mating behaviors in male-male and male-female interactions, respectively.Main results:Our results show that these models are capable of capturing both temporal behavioral structure and associated neural states, and produce interpretable latent states. Our approach is also validated in computer simulations in the presence of known ground truth.Significance:Overall, these analysis approaches provide a state-space framework to examine neural dynamics underlying social behaviors and reveals mechanistic insights into the relevant networks.

Development and Application of a Mitochondrial Genetically Encoded Voltage Indicator in Narcosis.

Mitochondrial membrane potential (MMP) plays a crucial role in the function of cells and organelles, involving various cellular physiological processes, including energy production, formation of reactive oxygen species (ROS), unfolded protein stress, and cell survival. Currently, there is a lack of genetically encoded fluorescence indicators (GEVIs) for MMP. In our screening of various GEVIs for their potential monitoring MMP, the Accelerated Sensor of Action Potentials (ASAP) demonstrated optimal performance in targeting mitochondria and sensitivity to depolarization in multiple cell types. However, mitochondrial ASAPs also displayed sensitivity to ROS in cardiomyocytes. Therefore, two ASAP mutants resistant to ROS were generated. A double mutant ASAP3-ST exhibited the highest voltage sensitivity but weaker fluorescence. Overall, four GEVIs capable of targeting mitochondria were obtained and named mitochondrial potential indicators 1-4 (MPI-1-4). In vivo, fiber photometry experiments utilizing MPI-2 revealed a mitochondrial depolarization during isoflurane-induced narcosis in the M2 cortex.

Serotonin modulates infraslow oscillation in the dentate gyrus during Non-REM sleep.

Synchronous neuronal activity is organized into neuronal oscillations with various frequency and time domains across different brain areas and brain states. For example, hippocampal theta, gamma and sharp wave oscillations are critical for memory formation and communication between hippocampal subareas and the cortex. In this study, we investigated the neuronal activity of the dentate gyrus (DG) with electrophysiological and optical imaging tools during sleep-wake cycles. We found that the activity of major glutamatergic cell populations in the DG is organized into in-fraslow oscillations (0.01 - 0.03 Hz) during NREM sleep. Although the DG is considered a sparsely active network during wakefulness, we found that 50% of granule cells and about 25% of mossy cells exhibit increased activity during NREM sleep. Further experiments revealed that the infraslow oscillation in the DG is modulated by rhythmic serotonin release during sleep, which oscillates at the same frequency but in an opposite phase. Genetic manipulation of 5-HT receptors revealed that this neuromodulatory regulation is mediated by 5-HT1a receptors and the knockdown of these receptors leads to memory impairment. Together, our results provide novel mechanistic insights into how the 5-HT system can influence hippocampal activity patterns during sleep.

Fiber-based Probes for Electrophysiology, Photometry, Optical and Electrical Stimulation, Drug Delivery, and Fast-Scan Cyclic Voltammetry In Vivo.

Recording and modulation of neuronal activity enables the study of brain function in health and disease. While translational neuroscience relies on electrical recording and modulation techniques, mechanistic studies in rodent models leverage genetic precision of optical methods, such as optogenetics and imaging of fluorescent indicators. In addition to electrical signal transduction, neurons produce and receive diverse chemical signals which motivate tools to probe and modulate neurochemistry. Although the past decade has delivered a wealth of technologies for electrophysiology, optogenetics, chemical sensing, and optical recording, combining these modalities within a single platform remains challenging. This work leverages materials selection and convergence fiber drawing to permit neural recording, electrical stimulation, optogenetics, fiber photometry, drug and gene delivery, and voltammetric recording of neurotransmitters within individual fibers. Composed of polymers and non-magnetic carbon-based conductors, these fibers are compatible with magnetic resonance imaging, enabling concurrent stimulation and whole-brain monitoring. Their utility is demonstrated in studies of the mesolimbic reward pathway by simultaneously interfacing with the ventral tegmental area and nucleus accumbens in mice and characterizing the neurophysiological effects of a stimulant drug. This study highlights the potential of these fibers to probe electrical, optical, and chemical signaling across multiple brain regions in both mechanistic and translational studies.

Distinguishing motion artifacts during optical fiber-based in-vivo hemodynamics recordings from brain regions of freely moving rodents.

Significance: Motion artifacts in the signals recorded during optical fiber-based measurements can lead to misinterpretation of data. In this work, we address this problem during in-vivo rodent experiments and develop a motion artifacts correction (MAC) algorithm for single-fiber system (SFS) hemodynamics measurements from the brains of rodents. Aim: (i) To distinguish the effect of motion artifacts in the SFS signals. (ii) Develop a MAC algorithm by combining information from the experiments and simulations and validate it. Approach: Monte-Carlo (MC) simulations were performed across 450 to 790 nm to identify wavelengths where the reflectance is least sensitive to blood absorption-based changes. This wavelength region is then used to develop a quantitative metric to measure motion artifacts, termed the dissimilarity metric (DM). We used MC simulations to mimic artifacts seen during experiments. Further, we developed a mathematical model describing light intensity at various optical interfaces. Finally, an MAC algorithm was formulated and validated using simulation and experimental data. Results: We found that the 670 to 680 nm wavelength region is relatively less sensitive to blood absorption. The standard deviation of DM (σDM) can measure the relative magnitude of motion artifacts in the SFS signals. The artifacts cause rapid shifts in the reflectance data that can be modeled as transmission changes in the optical lightpath. The changes observed during the experiment were found to be in agreement to those obtained from MC simulations. The mathematical model developed to model transmission changes to represent motion artifacts was extended to an MAC algorithm. The MAC algorithm was validated using simulations and experimental data. Conclusions: We distinguished motion artifacts from SFS signals during in vivo hemodynamic monitoring experiments. From simulation and experimental data, we showed that motion artifacts can be modeled as transmission changes. The developed MAC algorithm was shown to minimize artifactual variations in both simulation and experimental data.

Astrocyte switch to the hyperactive mode.

Increasing pieces of evidence have suggested that astrocyte function has a strong influence on neuronal activity and plasticity, both in physiological and pathophysiological situations. In epilepsy, astrocytes have been shown to respond to epileptic neuronal seizures; however, whether they can act as a trigger for seizures has not been determined. Here, using the copper implantation method, spontaneous neuronal hyperactivity episodes were reliably induced during the week following implantation. With near 24-h continuous recording for over 1 week of the local field potential with in vivo electrophysiology and astrocyte cytosolic Ca2+ with the fiber photometry method, spontaneous occurrences of seizure episodes were captured. Approximately 1 day after the implantation, isolated aberrant astrocyte Ca2+ events were often observed before they were accompanied by neuronal hyperactivity, suggesting the role of astrocytes in epileptogenesis. Within a single developed episode, astrocyte Ca2+ increase preceded the neuronal hyperactivity by ~20 s, suggesting that actions originating from astrocytes could be the trigger for the occurrence of epileptic seizures. Astrocyte-specific stimulation by channelrhodopsin-2 or deep-brain direct current stimulation was capable of inducing neuronal hyperactivity. Injection of an astrocyte-specific metabolic inhibitor, fluorocitrate, was able to significantly reduce the magnitude of spontaneously occurring neuronal hyperactivity. These results suggest that astrocytes have a role in triggering individual seizures and the reciprocal astrocyte-neuron interactions likely amplify and exacerbate seizures. Therefore, future epilepsy treatment could be targeted at astrocytes to achieve epilepsy control.

Locus Ceruleus Dynamics Are Suppressed during Licking and Enhanced Postlicking Independent of Taste Novelty.

Attending to salient sensory attributes of food, such as tastes that are new, displeasing, or unexpected, allows the procurement of nutrients without food poisoning. Exposure to new tastes is known to increase norepinephrine (NE) release in taste processing forebrain areas, yet the central source for this release is unknown. Locus ceruleus norepinephrine neurons (LC-NE) emerge as a candidate in signaling salient information about taste, as other salient sensory stimuli (e.g., visual, auditory, somatosensation) are known to activate LC neurons. To determine if LC neurons are sensitive to features of taste novelty, we used fiber photometry to record LC-NE activity in water-restricted mice that voluntarily licked either novel or familiar substances of differential palatability (saccharine, citric acid). We observed that LC-NE activity was suppressed during lick bursts and transiently activated upon the termination of licking and that these dynamics were independent of the familiarity of the substance consumed. We next recorded LC dynamics during brief and unexpected consumption of tastants and found no increase in LC-NE activity, despite their responsiveness to visual and auditory stimuli, revealing selectivity in LC's responses to salient sensory information. Our findings suggest that LC activity during licking is not influenced by taste novelty, implicating a possible role for non-LC noradrenergic nuclei in signaling critical information about taste.

Combined Experiments with in Vivo Fiber Photometry and Behavior Tests Can Facilitate the Measurement of Neuronal Activity in the Primary Somatosensory Cortex and Hyperalgesia in an Inflammatory Pain Mice Model.

The pain matrix, which includes several brain regions that respond to pain sensation, contribute to the development of chronic pain. Thus, it is essential to understand the mechanism of causing chronic pain in the pain matrix such as anterior cingulate (ACC), or primary somatosensory (S1) cortex. Recently, combined experiment with the behavior tests and in vivo calcium imaging using fiber photometry revealed the interaction between the neuronal function in deep brain regions of the pain matrix including ACC and the phenotype of chronic pain. However, it remains unclear whether this combined experiment can identify the interaction between neuronal activity in S1, which receive pain sensation, and pain behaviors such as hyperalgesia or allodynia. In this study, to examine whether the interaction between change of neuronal activity in S1 and hyperalgesia in hind paw before and after causing inflammatory pain was detected from same animal, the combined experiment of in vivo fiber photometry system and von Frey hairs test was applied. This combined experiment detected that amplitude of calcium responses in S1 neurons increased and the mechanical threshold of hind paw decreased from same animals which have an inflammatory pain. Moreover, we found that the values between amplitude of calcium responses and mechanical thresholds were shifted to negative correlation after causing inflammatory pain. Thus, the combined experiment with fiber photometry and the behavior tests has a possibility that can simultaneously consider the interaction between neuronal activity in pain matrix and pain induced behaviors and the effects of analgesics or pain treatments.

Insula→Amygdala and Insula→Thalamus Pathways Are Involved in Comorbid Chronic Pain and Depression-Like Behavior in Mice.

The comorbidity of chronic pain and depression poses tremendous challenges for the treatment of either one because they exacerbate each other with unknown mechanisms. As the posterior insular cortex (PIC) integrates multiple somatosensory and emotional information and is implicated in either chronic pain or depression, we hypothesize that the PIC and its projections may contribute to the pathophysiology of comorbid chronic pain and depression. We show that PIC neurons were readily activated by mechanical, thermal, aversive, and stressful and appetitive stimulation in naive and neuropathic pain male mice subjected to spared nerve injury (SNI). Optogenetic activation of PIC neurons induced hyperalgesia and conditioned place aversion in naive mice, whereas inhibition of these neurons led to analgesia, conditioned place preference (CPP), and antidepressant effect in both naive and SNI mice. Combining neuronal tracing, optogenetics, and electrophysiological techniques, we found that the monosynaptic glutamatergic projections from the PIC to the basolateral amygdala (BLA) and the ventromedial nucleus (VM) of the thalamus mimicked PIC neurons in pain modulation in naive mice; in SNI mice, both projections were enhanced accompanied by hyperactivity of PIC, BLA, and VM neurons and inhibition of these projections led to analgesia, CPP, and antidepressant-like effect. The present study suggests that potentiation of the PIC→BLA and PIC→VM projections may be important pathophysiological bases for hyperalgesia and depression-like behavior in neuropathic pain and reversing the potentiation may be a promising therapeutic strategy for comorbid chronic pain and depression.

Recording the brain in vivo: emerging technologies for the exploration of mental health conditions.

Standfirst Mounting interest in mental health conditions over the last two decades has been coupled with the increasing sophistication of techniques to study the brain in vivo. [Formula: see text].

Orbitofrontal and Prelimbic Cortices Serve Complementary Roles in Adapting Reward Seeking to Learned Anxiety.

BACKGROUND: Anxiety is a common symptom of several mental health disorders and adversely affects motivated behaviors. Anxiety can emerge from associating risk of future harm while engaged in goal-guided actions. Using a recently developed behavioral paradigm to model this aspect of anxiety, we investigated the role of 2 cortical subregions, the prelimbic medial frontal cortex (PL) and lateral orbitofrontal cortex (lOFC), which have been implicated in anxiety and outcome expectation, in flexible representation of actions associated with harm risk. METHODS: A seek-take reward-guided instrumental task design was used to train animals (N = 8) to associate the seek action with a variable risk of punishment. After learning, animals underwent extinction training for this association. Fiber photometry was used to measure and compare neuronal activity in the PL and lOFC during learning and extinction. RESULTS: Animals increased action suppression in response to punishment contingencies. This increase dissipated after extinction training. These behavioral changes were associated with region-specific changes in neuronal activity. PL neuronal activity preferentially adapted to the threat of punishment, whereas lOFC activity adapted to safe aspects of the task. Moreover, correlated activity between these regions was suppressed during actions associated with harm risk, suggesting that these regions may guide behavior independently under anxiety. CONCLUSIONS: These findings suggest that the PL and lOFC serve distinct but complementary roles in the representation of learned anxiety. This dissociation may provide a mechanism to explain how overlapping cortical systems are implicated in reward-guided action execution during anxiety.

Engram reactivation mimics cellular signatures of fear.

Engrams, or the physical substrate of memory, recruit heterogeneous cell types. Targeted reactivation of neurons processing discrete memories drives the behavioral expression of memory, though the underlying landscape of recruited cells and their real-time responses remain elusive. To understand how artificial stimulation of fear affects intra-hippocampal neuron-astrocyte dynamics as well as their behavioral consequences, we express channelrhodopsin-2 in an activity-dependent manner within dentate gyrus neurons while recording both cell types with fiber photometry in hippocampal ventral CA1 across learning and memory. Both cell types exhibit shock responsiveness, with astrocytic calcium events uniquely modulated by fear conditioning. Optogenetic stimulation of a hippocampus-mediated engram recapitulates coordinated calcium signatures time locked to freezing, mirroring those observed during natural fear memory recall. Our findings reveal cell-type-specific dynamics in the hippocampus during freezing behavior, emphasizing neuronal-astrocytic coupling as a shared mechanism enabling both natural and artificially induced memory retrieval and the behavioral expression of fear.

FiPhA: an open-source platform for fiber photometry analysis.

Significance: Fiber photometry (FP) is a widely used technique in modern behavioral neuroscience, employing genetically encoded fluorescent sensors to monitor neural activity and neurotransmitter release in awake-behaving animals. However, analyzing photometry data can be both laborious and time-consuming. Aim: We propose the fiber photometry analysis (FiPhA) app, which is a general-purpose FP analysis application. The goal is to develop a pipeline suitable for a wide range of photometry approaches, including spectrally resolved, camera-based, and lock-in demodulation. Approach: FiPhA was developed using the R Shiny framework and offers interactive visualization, quality control, and batch processing functionalities in a user-friendly interface. Results: This application simplifies and streamlines the analysis process, thereby reducing labor and time requirements. It offers interactive visualizations, event-triggered average processing, powerful tools for filtering behavioral events, and quality control features. Conclusions: FiPhA is a valuable tool for behavioral neuroscientists working with discrete, event-based FP data. It addresses the challenges associated with analyzing and investigating such data, offering a robust and user-friendly solution without the complexity of having to hand-design custom analysis pipelines. This application thus helps standardize an approach to FP analysis.