Direct Imaging of Hippocampal Epileptiform Calcium Motifs Following Kainic Acid Administration in Freely Behaving Mice

Three dimensional (3D) and four dimensional (4D) live imaging to study mechanisms of progressive neurodegeneration

Neurodegenerative diseases are complex and progressive, posing challenges to their study and understanding. Recent advances in microscopy imaging technologies have enabled the exploration of neurons in three spatial dimensions (3D) over time (4D). When applied to 3D cultures, tissues or animals, these technologies can provide valuable insights into the dynamic and spatial nature of neurodegenerative diseases. This review focuses on the use of imaging techniques and neurodegenerative disease models to study neurodegeneration in 4D. Imaging techniques such as confocal microscopy, two-photon microscopy, miniscope imaging, light sheet microscopy, and robotic microscopy offer powerful tools to visualize and analyze neuronal changes over time in 3D tissue. Application of these technologies to in vitro models of neurodegeneration such as mouse organotypic culture systems and human organoid models provide versatile platforms to study neurodegeneration in a physiologically relevant context. Additionally, use of 4D imaging in vivo, including in mouse and zebrafish models of neurodegenerative diseases, allows for the investigation of early dysfunction and behavioral changes associated with neurodegeneration. We propose that these studies have the power to overcome the limitations of two-dimensional (2D) monolayer neuronal cultures, and pave the way for improved understanding of the dynamics of neurodegenerative diseases and the development of effective therapeutic strategies.

Early and widespread engagement of the cerebellum during hippocampal epileptiform activity Format: Brief Communication

Despite research illustrating the cerebellum may be a critical circuit element in the epilepsies, remarkably little is known about cerebellar engagement during seizures. We therefore implemented a novel method for repeated imaging of the cerebellum in awake, chronically epileptic animals. We found widespread changes in cerebellar calcium signals during behavioral seizures and during hippocampal seizures that remained electrographic only, arguing against cerebellar modulation simply reflecting motor components. Moreover, even brief interictal spikes produced widespread alterations in cerebellar activity. Changes were noted in the anterior and posterior cerebellum, along the midline, and both ipsilaterally and contralaterally to the seizure focus. Remarkably, changes in the cerebellum also occurred prior to any noticeable change in the hippocampal electrographic recordings, suggesting a special relationship between the cerebellum and hippocampal epileptiform activity. Together these results underscore the importance of the cerebellum in epilepsy, warranting a more consistent consideration of the cerebellum when evaluating epilepsy patients.

Cholinergic Interneurons in the Accumbal Shell Region Regulate Binge Alcohol Self-Administration in Mice: An In Vivo Calcium Imaging Study

Recently, we and others have shown that manipulating the activity of cholinergic interneurons (CIN) present in the NAc can modulate binge alcohol consumption. The present study is designed to examine the relationship between binge alcohol consumption and the activity of the CIN in real time by using an in vivo microendoscopic technique. We hypothesized that mice exposed to Drinking in the Dark (DID)-a recognized mouse model for binge drinking-would exhibit increased activity in the accumbal shell region (NAcSh). To test this hypothesis, male mice expressing Cre-recombinase in the cholinergic neurons were exposed to binge alcohol consumption (alcohol group), employing the DID method, and utilized in vivo calcium imaging to observe CIN activity in real time during alcohol consumption. The control (sucrose) group was exposed to 10% (w/v) sucrose. As compared to sucrose, mice in the alcohol group displayed a significant increase in the frequency and amplitude of discharge activity, which was measured using calcium transients in the CIN present in the NAcSh. In summary, our findings suggest that the activity of CIN in the NAcSh plays a crucial role in alcohol self-administration. These results emphasize the potential significance of targeting CIN activity as a therapeutic approach for addressing AUD.

Targeted micro-fiber arrays for measuring and manipulating localized multi-scale neural dynamics over large, deep brain volumes during behavior

Neural population dynamics relevant to behavior vary over multiple spatial and temporal scales across three-dimensional volumes. Current optical approaches lack the spatial coverage and resolution necessary to measure and manipulate naturally occurring patterns of large-scale, distributed dynamics within and across deep brain regions such as the striatum. We designed a new micro-fiber array approach capable of chronically measuring and optogenetically manipulating local dynamics across over 100 targeted locations simultaneously in head-fixed and freely moving mice, enabling the investigation of cell-type- and neurotransmitter-specific signals over arbitrary 3D volumes at a spatial resolution and coverage previously inaccessible. We applied this method to resolve rapid dopamine release dynamics across the striatum, revealing distinct, modality-specific spatiotemporal patterns in response to salient sensory stimuli extending over millimeters of tissue. Targeted optogenetics enabled flexible control of neural signaling on multiple spatial scales, better matching endogenous signaling patterns, and the spatial localization of behavioral function across large circuits.

A comprehensive assessment of palmatine as anticonvulsant agent - In vivo and in silico studies

Previously, we demonstrated that palmatine (PALM) - an isoquinoline alkaloid from Berberis sibrica radix, exerted antiseizure activity in the pentylenetetrazole (PTZ)-induced seizure assay in larval zebrafish. The aim of the present study was to more precisely characterize PALM as a potential anticonvulsant drug candidate. A range of zebrafish and mouse seizure/epilepsy models were applied in the investigation. Immunostaining analysis was conducted to assess the changes in mouse brains, while in silico molecular modelling was performed to determine potential targets for PALM. Accordingly, PALM had anticonvulsant effect in ethyl 2-ketopent-4-enoate (EKP)-induced seizure assay in zebrafish larvae as well as in the 6 Hz-induced psychomotor seizure threshold and timed infusion PTZ tests in mice. The protective effect in the EKP-induced seizure assay was confirmed in the local field potential recordings. PALM did not affect seizures in the gabra1a knockout line of zebrafish larvae. In the scn1Lab-/- zebrafish line, pretreatment with PALM potentiated seizure-like behaviour of larvae. Repetitive treatment with PALM, however, did not reduce development of PTZ-induced seizure activity nor prevent the loss of parvalbumin-interneurons in the hippocampus of the PTZ kindled mice. In silico molecular modelling revealed that the noted anticonvulsant effect of PALM in EKP-induced seizure assay might result from its interactions with glutamic acid decarboxylase and/or via AMPA receptor non-competitive antagonism. Our study has demonstrated the anticonvulsant activity of PALM in some experimental models of seizures, including a model of pharmacoresistant seizures induced by EKP. These results indicate that PALM might be a suitable new drug candidate but the precise mechanism of its anticonvulsant activity has to be determined.

MicroRNA-9 promotes axon regeneration of mauthner-cell in zebrafish via her6/ calcium activity pathway

MicroRNA (miRNA), functioning as a post-transcriptional regulatory element, plays a significant role in numerous regulatory mechanisms and serves as a crucial intrinsic factor influencing axon regeneration. Prior investigations have elucidated the involvement of miRNA-9 in various processes, however, its specific contribution to axon regeneration in the central nervous system (CNS) remains uncertain. Hence, the zebrafish Mauthner axon regeneration model was employed to manipulate the expression of miRNA-9 in single cells, revealing that upregulation of miRNA-9 facilitated axon regeneration. Additionally, her6, a downstream target gene of miRNA-9, was identified as a novel gene associated with axon regeneration. Suppression of her6 resulted in enhanced Mauthner axon regeneration, as evidenced by the significantly improved regenerative capacity observed in her6 knockout zebrafish. In addition, modulation of her6 expression affects intracellular calcium levels in neurons and promoting her6 expression leads to a decrease in calcium levels in vivo using the new NEMOf calcium indicator. Moreover, the administration of the neural activity activator, pentylenetetrazol (PTZ) partially compensated for the inhibitory effect of her6 overexpression on the calcium level and promoted axon regeneration. Taken together, our study revealed a role for miRNA-9 in the process of axon regeneration in the CNS, which improved intracellular calcium activity and promoted axon regeneration by inhibiting the expression of downstream target gene her6. In our study, miRNA-9 emerged as a novel and intriguing target in the intricate regulation of axon regeneration and offered compelling evidence for the intricate relationship between calcium activity and the facilitation of axon regeneration.

Regulation of specific abnormal calcium signals in the hippocampal CA1 and primary cortex M1 alleviates the progression of temporal lobe epilepsy

Temporal lobe epilepsy is a multifactorial neurological dysfunction syndrome that is refractory, resistant to antiepileptic drugs, and has a high recurrence rate. The pathogenesis of temporal lobe epilepsy is complex and is not fully understood. Intracellular calcium dynamics have been implicated in temporal lobe epilepsy. However, the effect of fluctuating calcium activity in CA1 pyramidal neurons on temporal lobe epilepsy is unknown, and no longitudinal studies have investigated calcium activity in pyramidal neurons in the hippocampal CA1 and primary motor cortex M1 of freely moving mice. In this study, we used a multi-channel fiber photometry system to continuously record calcium signals in CA1 and M1 during the temporal lobe epilepsy process. We found that calcium signals varied according to the grade of temporal lobe epilepsy episodes. In particular, cortical spreading depression, which has recently been frequently used to represent the continuously and substantially increased calcium signals, was found to correspond to complex and severe behavioral characteristics of temporal lobe epilepsy ranging from grade II to grade V. However, vigorous calcium oscillations and highly synchronized calcium signals in CA1 and M1 were strongly related to convulsive motor seizures. Chemogenetic inhibition of pyramidal neurons in CA1 significantly attenuated the amplitudes of the calcium signals corresponding to grade I episodes. In addition, the latency of cortical spreading depression was prolonged, and the above-mentioned abnormal calcium signals in CA1 and M1 were also significantly reduced. Intriguingly, it was possible to rescue the altered intracellular calcium dynamics. Via simultaneous analysis of calcium signals and epileptic behaviors, we found that the progression of temporal lobe epilepsy was alleviated when specific calcium signals were reduced, and that the end-point behaviors of temporal lobe epilepsy were improved. Our results indicate that the calcium dynamic between CA1 and M1 may reflect specific epileptic behaviors corresponding to different grades. Furthermore, the selective regulation of abnormal calcium signals in CA1 pyramidal neurons appears to effectively alleviate temporal lobe epilepsy, thereby providing a potential molecular mechanism for a new temporal lobe epilepsy diagnosis and treatment strategy.

Targeted micro-fiber arrays for measuring and manipulating localized multi-scale neural dynamics over large, deep brain volumes during behavior

Neural population dynamics relevant for behavior vary over multiple spatial and temporal scales across 3-dimensional volumes. Current optical approaches lack the spatial coverage and resolution necessary to measure and manipulate naturally occurring patterns of large-scale, distributed dynamics within and across deep brain regions such as the striatum. We designed a new micro-fiber array and imaging approach capable of chronically measuring and optogenetically manipulating local dynamics across over 100 targeted locations simultaneously in head-fixed and freely moving mice. We developed a semi-automated micro-CT based strategy to precisely localize positions of each optical fiber. This highly-customizable approach enables investigation of multi-scale spatial and temporal patterns of cell-type and neurotransmitter specific signals over arbitrary 3-D volumes at a spatial resolution and coverage previously inaccessible. We applied this method to resolve rapid dopamine release dynamics across the striatum volume which revealed distinct, modality specific spatiotemporal patterns in response to salient sensory stimuli extending over millimeters of tissue. Targeted optogenetics through our fiber arrays enabled flexible control of neural signaling on multiple spatial scales, better matching endogenous signaling patterns, and spatial localization of behavioral function across large circuits.

Cerebral cortex and hippocampus neural interaction during vagus nerve stimulation under in vivo large-scale imaging

Objective

The purpose of this study was to study mechanisms of VNS modulation from a single neuron perspective utilizing a practical observation platform with single neuron resolution and widefield, real-time imaging coupled with an animal model simultaneously exposing the cerebral cortex and the hippocampus.

Methods

We utilized the observation platform characterized of widefield of view, real-time imaging, and high spatiotemporal resolution to obtain the neuronal activities in the cerebral cortex and the hippocampus during VNS in awake states and under anesthesia.

Results

Some neurons in the hippocampus were tightly related to VNS modulation, and varied types of neurons showed distinct responses to VNS modulation.

Conclusion

We utilized such an observation platform coupled with a novel animal model to obtain more information on neuron activities in the cerebral cortex and the hippocampus, providing an effective method to further study the mechanisms of therapeutic effects modulated by VNS.

A luciferase prosubstrate and a red bioluminescent calcium indicator for imaging neuronal activity in mice

Although fluorescent indicators have been broadly utilized for monitoring bioactivities, fluorescence imaging, when applied to mammals, is limited to superficial targets or requires invasive surgical procedures. Thus, there is emerging interest in developing bioluminescent indicators for noninvasive mammalian imaging. Bioluminescence imaging (BLI) of neuronal activity is highly desired but hindered by insufficient photons needed to digitalize fast brain activities. In this work, we develop a luciferase prosubstrate deliverable at an increased dose and activated in vivo by nonspecific esterase. We further engineer a bright, bioluminescent indicator with robust responsiveness to calcium ions (Ca²⁺) and appreciable emission above 600 nm. Integration of these advantageous components enables the imaging of the activity of neuronal ensembles in awake mice minimally invasively with excellent signal-to-background and subsecond temporal resolution. This study thus establishes a paradigm for studying brain function in health and disease.

Comparison of clinical characteristics between cluster and isolated seizures associated with benign convulsions with mild gastroenteritis

BACKGROUND AND PURPOSE

Cluster seizures have not been specifically reported in benign convulsions with mild gastroenteritis (CWG), which are usually considered to have serious outcomes. We aimed to identify the differences between cluster and isolated seizures associated with CWG.

METHOD

We retrospectively analyzed the medical data of children hospitalized and diagnosed with CWG from May 2018 to December 2020. A case-control study approach was adopted and patients who met the inclusion criteria were divided into a cluster seizures group and an isolated seizures group. Then, the clinical characteristics of the patients in the two groups were compared.

RESULTS

30 patients（36.6%） were in the cluster seizures group while 52 patients (63.4%) were in the isolated seizures group. The highest incidence of CWG occurs between 12 and 24 months of age. While serum sodium and calcium were within the normal range for both groups, they were lower in the cluster seizures group compared to the isolated seizures group (136.74 ± 2.78 vs 134.65 ± 2.85, P = 0.002; 2.43 ± 0.13 vs 2.37 ± 0.14, P = 0.04). A total of 123 seizures was recorded during the research period and 25 were treated with anticonvulsant drugs. The outcome of anticonvulsant therapy and the prognosis showed no differences between the two groups.

CONCLUSION

Clinicians need to be highly alert to the possibility of cluster seizures in CWG patients who have reduced sodium and calcium. Besides, CWG patients with cluster seizures do not require excessive investigations, overuse of anticonvulsant therapy compared to those with isolated seizures.

Miniature microscopes for manipulating and recording in vivo brain activity

Here we describe the development and application of miniature integrated microscopes (miniscopes) paired with microendoscopes that allow for the visualization and manipulation of neural circuits in superficial and subcortical brain regions in freely behaving animals. Over the past decade the miniscope platform has expanded to include simultaneous optogenetic capabilities, electrically-tunable lenses that enable multi-plane imaging, color-corrected optics, and an integrated data acquisition platform that streamlines multimodal experiments. Miniscopes have given researchers an unprecedented ability to monitor hundreds to thousands of genetically-defined neurons from weeks to months in both healthy and diseased animal brains. Sophisticated algorithms that take advantage of constrained matrix factorization allow for background estimation and reliable cell identification, greatly improving the reliability and scalability of source extraction for large imaging datasets. Data generated from miniscopes have empowered researchers to investigate the neural circuit underpinnings of a wide array of behaviors that cannot be studied under head-fixed conditions, such as sleep, reward seeking, learning and memory, social behaviors, and feeding. Importantly, the miniscope has broadened our understanding of how neural circuits can go awry in animal models of progressive neurological disorders, such as Parkinson's disease. Continued miniscope development, including the ability to record from multiple populations of cells simultaneously, along with continued multimodal integration of techniques such as electrophysiology, will allow for deeper understanding into the neural circuits that underlie complex and naturalistic behavior.

Differential contribution of excitatory and inhibitory neurons in shaping neurovascular coupling in different epileptic neural states

Understanding the neurovascular coupling (NVC) underlying hemodynamic changes in epilepsy is crucial to properly interpreting functional brain imaging signals associated with epileptic events. However, how excitatory and inhibitory neurons affect vascular responses in different epileptic states remains unknown. We conducted real-time in vivo measurements of cerebral blood flow (CBF), vessel diameter, and excitatory and inhibitory neuronal calcium signals during recurrent focal seizures. During preictal states, decreases in CBF and arteriole diameter were closely related to decreased γ-band local field potential (LFP) power, which was linked to relatively elevated excitatory and reduced inhibitory neuronal activity levels. Notably, this preictal condition was followed by a strengthened ictal event. In particular, the preictal inhibitory activity level was positively correlated with coherent oscillating activity specific to inhibitory neurons. In contrast, ictal states were characterized by elevated synchrony in excitatory neurons. Given these findings, we suggest that excitatory and inhibitory neurons differentially contribute to shaping the ictal and preictal neural states, respectively. Moreover, the preictal vascular activity, alongside with the γ-band, may reflect the relative levels of excitatory and inhibitory neuronal activity, and upcoming ictal activity. Our findings provide useful insights into how perfusion signals of different epileptic states are related in terms of NVC.

Precision Calcium Imaging of Dense Neural Populations via a Cell-Body-Targeted Calcium Indicator

Methods for one-photon fluorescent imaging of calcium dynamics can capture the activity of hundreds of neurons across large fields of view at a low equipment complexity and cost. In contrast to two-photon methods, however, one-photon methods suffer from higher levels of crosstalk from neuropil, resulting in a decreased signal-to-noise ratio and artifactual correlations of neural activity. We address this problem by engineering cell-body-targeted variants of the fluorescent calcium indicators GCaMP6f and GCaMP7f. We screened fusions of GCaMP to natural, as well as artificial, peptides and identified fusions that localized GCaMP to within 50 μm of the cell body of neurons in mice and larval zebrafish. One-photon imaging of soma-targeted GCaMP in dense neural circuits reported fewer artifactual spikes from neuropil, an increased signal-to-noise ratio, and decreased artifactual correlation across neurons. Thus, soma-targeting of fluorescent calcium indicators facilitates usage of simple, powerful, one-photon methods for imaging neural calcium dynamics.

Simultaneous calcium recordings of hippocampal CA1 and primary motor cortex M1 and their relations to behavioral activities in freely moving epileptic mice

Epilepsy is a common neurological disorder characterized by recurrent epileptic seizures. The cause of most cases of epilepsy is unknown. Although changes of calcium events in a single brain region during seizures have been reported before, there have been few studies on relations between calcium events of two different brain regions and epileptic behaviors in freely moving mice. To analyze calcium events simultaneously recorded in hippocampal CA1 (CA1) and primary motor cortex M1 (M1), and to explore their relations to various epileptic behaviors in freely moving epileptic models. Epileptic models were induced by Kainic acid (KA), a direct agonist of glutamatergic receptor, on adult male C57/BL6J mice. Calcium events of neurons and glia in CA1 and M1 labeled by a calcium indicator dye were recorded simultaneously with a multi-channel fiber photometry system. Three typical types of calcium events associated with KA-induced seizures were observed, including calcium baseline-rising, cortical spreading depression (CSD) and calcium flashing with a steady rate. Our results showed that the calcium baseline-rising occurred in CA1 was synchronized with that in M1, but the CSD waves were not. However, synchronization of calcium flashing in the two areas was uncertain, because it was only detected in CA1. We also observed that different calcium events happened with different epileptic behaviors. Baseline-rising events were accompanied by clonus of forelimbs or trembling, CSD waves were closely related to head movements (15 out of 18, 6 mice). Calcium flashing occurred definitely with drastic convulsive motor seizures (CMS, 6 mice). The results prove that the synchronization of calcium event exists in CA1 and M1, and different calcium events are related with different seizure behaviors. Our results suggest that calcium events involve in the synchronization of neural network and behaviors in epilepsy.

Overview on Emotional Behavioral Testing in Rodent Models of Pediatric Epilepsy

Psychiatric and cognitive disturbances are the most common comorbidities of epileptic disorders in children. The successful treatment of these comorbidities faces many challenges including their etiologically heterogonous nature. Translational neurobehavioral research in age-tailored and clinically relevant rodent seizure models offers a controlled setting to investigate emotional and cognitive behavioral disturbances, their causative factors, and potentially novel treatment interventions. In this review, we propose a conceptual framework that provides a nonsubjective approach to rodent emotional behavioral testing with a focus on the clinically relevant outcome of behavioral response adaptability. We also describe the battery of neurobehavioral tests that we tailored to seizure models with prominent amygdalo-hippocampal involvement, including testing panels for anxiety-like, exploratory, and hyperactive behaviors (the open-field and light-dark box tests), depressive-like behaviors (the forced swim test), and visuospatial navigation (Morris water maze). The review also discusses the modifications we introduced to active avoidance testing in order to simultaneously test auditory and hippocampal-dependent emotionally relevant learning and memory. When interpreting the significance and clinical relevance of the behavioral responses obtained from a given testing panel, it is important to avoid a holistic disease-based approach as a specific panel may not necessarily mirror a disease entity. The analysis of measurable behavioral responses has to be performed in the context of outcomes obtained from multiple related and complementary neurobehavioral testing panels. Behavioral testing is also complemented by mechanistic electrophysiological and molecular investigations.

Interneuron Desynchronization Precedes Seizures in a Mouse Model of Dravet Syndrome

Recurrent seizures, which define epilepsy, are transient abnormalities in the electrical activity of the brain. The mechanistic basis of seizure initiation, and the contribution of defined neuronal subtypes to seizure pathophysiology, remains poorly understood. We performed in vivo two-photon calcium imaging in neocortex during temperature-induced seizures in male and female Dravet syndrome (Scn1a+/-) mice, a neurodevelopmental disorder with prominent temperature-sensitive epilepsy. Mean activity of both putative principal cells and parvalbumin-positive interneurons (PV-INs) was higher in Scn1a+/- relative to wild-type controls during quiet wakefulness at baseline and at elevated core body temperature. However, wild-type PV-INs showed a progressive synchronization in response to temperature elevation that was absent in PV-INs from Scn1a+/- mice. Hence, PV-IN activity remains intact interictally in Scn1a+/- mice, yet exhibits decreased synchrony immediately before seizure onset. We suggest that impaired PV-IN synchronization may contribute to the transition to the ictal state during temperature-induced seizures in Dravet syndrome.SIGNIFICANCE STATEMENT Epilepsy is a common neurological disorder defined by recurrent, unprovoked seizures. However, basic mechanisms of seizure initiation and propagation remain poorly understood. We performed in vivo two-photon calcium imaging in an experimental model of Dravet syndrome (Scn1a+/- mice)-a severe neurodevelopmental disorder defined by temperature-sensitive, treatment-resistant epilepsy-and record activity of putative excitatory neurons and parvalbumin-positive GABAergic neocortical interneurons (PV-INs) during naturalistic seizures induced by increased core body temperature. PV-IN activity was higher in Scn1a+/- relative to wild-type controls during quiet wakefulness. However, wild-type PV-INs showed progressive synchronization in response to temperature elevation that was absent in PV-INs from Scn1a+/- mice before seizure onset. Hence, impaired PV-IN synchronization may contribute to transition to seizure in Dravet syndrome.

Metabolism-based drug discovery in zebrafish: An emerging strategy to uncover new anti-seizure therapies

As one of the most common neurological disorders, epilepsy can occur throughout the lifespan and from a multiplicity of causes, including genetic mutations, inflammation, neurotrauma, or brain malformations. Although pharmacological agents are the mainstay of treatment for seizure control, an unyielding 30-40% of patients remain refractory to these medications and continue to experience spontaneous recurrent seizures with attendant life-long cognitive, behavioural, and mental health issues, as well as an increased risk for sudden unexpected death. Despite over eight decades of antiseizure drug (ASD) discovery and the approval of dozens of new medications, the percentage of this refractory population remains virtually unchanged, suggesting that drugs with new and unexpected mechanisms of action are needed. In this brief review, we discuss the need for new animal models of epilepsy, with a particular focus on the advantages and disadvantages of zebrafish. We also outline the evidence that epilepsy is characterized by derangements in mitochondrial function and introduce the rationale and promise of bioenergetics as a functional readout assay to uncover novel ASDs. We also consider limitations of a zebrafish metabolism-based drug screening approach. Our goal is to discuss the opportunities and challenges of further development of mitochondrial screening strategies for the development of novel ASDs. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Calcium Imaging in Drug Discovery for Psychiatric Disorders

The past 5 years have seen a sharp increase in the number of studies using calcium imaging in behaving rodents. These studies have helped identify important roles for individual cells, brain regions, and circuits in some of the core behavioral phenotypes of psychiatric disorders, such as schizophrenia and autism, and have characterized network dysfunction in well-established models of these disorders. Since rescuing clinically relevant behavioral deficits in disease model mice remains a foundation of preclinical CNS research, these studies have the potential to inform new therapeutic approaches targeting specific cell types or projections, or perhaps most importantly, the network-level context in which neurons function. In this mini-review, we will provide a brief overview of recent insights into psychiatric disease-associated mouse models and behavior paradigms, focusing on those achieved by cellular resolution imaging of calcium dynamics in neural populations. We will then discuss how these experiments can support efforts within the pharmaceutical industry, such as target identification, assay development, and candidate screening and validation. Calcium imaging is uniquely capable of bridging the gap between two of the key resources that currently enable CNS drug discovery: genomic and transcriptomic data from human patients, and translatable, population-resolution measures of brain activity (such as fMRI and EEG). Applying this knowledge could yield real value to patients in the near future.

MIN1PIPE: A Miniscope 1-Photon-Based Calcium Imaging Signal Extraction Pipeline

In vivo calcium imaging using a 1-photon-based miniscope and a microendoscopic lens enables studies of neural activities in freely behaving animals. However, the high and fluctuating background, the inevitable movements and distortions of imaging field, and the extensive spatial overlaps of fluorescent signals emitted from imaged neurons inherent in this 1-photon imaging method present major challenges for extracting neuronal signals reliably and automatically from the raw imaging data. Here, we develop a unifying algorithm called the miniscope 1-photon imaging pipeline (MIN1PIPE), which contains several stand-alone modules and can handle a wide range of imaging conditions and qualities with minimal parameter tuning and automatically and accurately isolate spatially localized neural signals. We have quantitatively compared MIN1PIPE with other existing partial methods using both synthetic and real datasets obtained from different animal models and show that MIN1PIPE has superior efficiency and precision in analyzing noisy miniscope calcium imaging data.

Stereotypical patterns of epileptiform calcium signal in hippocampal CA1, CA3, dentate gyrus and entorhinal cortex in freely moving mice

Epilepsy is a multi-etiological brain dysfunction syndrome. Hippocampal neuronal damage induced by seizures may be one of the causes leading to cognitive impairment, but the underlying mechanism remains to be further elucidated. The kainic acid (KA) model of temporal lobe epilepsy is widely used in understanding of the epileptogenesis. Fiber photometry is a signal detection technology suitable for recording calcium activity of neurons in the deep brain of freely moving animal. Here, we used the optical fiber-based method to monitor the real-time neuronal population activities of freely moving mice after subcutaneous injection of KA. We observed that KA administration led to one to three kinds of stereotypical patterns of epileptiform calcium activity in CA1, CA3, and dentate gyrus (DG) of the hippocampus, as well as the entorhinal cortex (EC). There were three kinds of waves in the hippocampal CA1, which we named wave 1, wave 2 and slow flash. Wave 1 and wave 2 appeared in both the CA3 and DG regions, but the EC only showed wave 1. In these epileptiform calcium signals, we observed a high amplitude and long duration calcium wave as a part of wave 2, which resembled cortical spreading depression (CSD) and always appeared at or after the end of seizure. Because the same characteristic of epileptiform calcium signal appeared in different brain regions, calcium signal may not exist with region specificity, but may exhibit a cell type specific manner. Thus, our work provides a support for the pathogenesis of epilepsy and epileptiform signal transmission research.

Transient Cognitive Impairment in Epilepsy

Impairments of the dialog between excitation and inhibition (E/I) is commonly associated to neuropsychiatric disorders like autism, bipolar disorders and epilepsy. Moderate levels of hyperexcitability can lead to mild alterations of the EEG and are often associated with cognitive deficits even in the absence of overt seizures. Indeed, various testing paradigms have shown degraded performances in presence of acute or chronic non-ictal epileptiform activity. Evidences from both animal models and the clinics suggest that anomalous activity can cause cognitive deficits by transiently disrupting cortical processing, independently from the underlying etiology of the disease. Here, we will review our understanding of the influence of an abnormal EEG activity on brain computation in the context of the available clinical data and in genetic or pharmacological animal models.

Left Habenular Activity Attenuates Fear Responses in Larval Zebrafish

Fear responses are defensive states that ensure survival of an organism in the presence of a threat. Perception of an aversive cue causes changes in behavior and physiology, such as freezing and elevated cortisol, followed by a return to the baseline state when the threat is evaded [1]. Neural systems that elicit fear behaviors include the amygdala, hippocampus, and medial prefrontal cortex. However, aside from a few examples, little is known about brain regions that promote recovery from an aversive event [2]. Previous studies had implicated the dorsal habenular nuclei in regulating fear responses and boldness in zebrafish [3-7]. We now show, through perturbation of its inherent left-right (L-R) asymmetry at larval stages, that the dorsal habenulo-interpeduncular (dHb-IPN) pathway expedites the return of locomotor activity following an unexpected negative stimulus, electric shock. Severing habenular efferents to the IPN, or only those from the left dHb, prolongs the freezing behavior that follows shock. Individuals with a symmetric, right-isomerized dHb also exhibit increased freezing. In contrast, larvae that have a symmetric, left-isomerized dHb, or in which just the left dHb-IPN projection is optogenetically activated, rapidly resume swimming post shock. In vivo calcium imaging reveals a neuronal subset, predominantly in the left dHb, whose activation is correlated with resumption of swimming. The results demonstrate functional specialization of the left dHb-IPN pathway in attenuating the response to fear.