Miniature microscopes for manipulating and recording in vivo brain activity

A modular, cost-effective, versatile, open-source operant box solution for long-term miniscope imaging, 3D tracking, and deep learning behavioral analysis

In this procedure we have included an open-source method for a customized operant chamber optimized for long-term miniature microscope (miniscope) recordings. •The miniscope box is designed to function with custom or typical med-associates style accessories (e.g., houselights, levers, etc.).•The majority of parts can be directly purchased which minimizes the need for skilled and time-consuming labor.•We include designs and estimated pricing for a single box but it is recommended to build these in larger batches to efficiently utilize bulk ordering of certain components.

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

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

Modulation of aggression by social novelty recognition memory in the hippocampal CA2 region

The dorsal CA2 subregion (dCA2) of the hippocampus exerts a critical role in social novelty recognition (SNR) memory and in the promotion of social aggression. Whether the social aggression and SNR memory functions of dCA2 are related or represent independent processes is unknown. Here we investigated the hypotheses that an animal is more likely to attack a novel compared to familiar animal and that dCA2 promotes social aggression through its ability to discriminate between novel and familiar conspecifics. To test these ideas, we conducted a multi-day resident intruder (R-I) test of aggression towards novel and familiar conspecifics. We found that mice were more likely to attack a novel compared to familiarized intruder and that silencing of dCA2 caused a more profound inhibition of aggression towards a novel than familiarized intruder. To explore whether and how dCA2 pyramidal neurons encode aggression, we recorded their activity using microendoscopic calcium imaging throughout the days of the R-I test. We found that a fraction of dCA2 neurons were selectively activated or inhibited during exploration, dominance, and attack behaviors and that these signals were enhanced during interaction with a novel compared to familiarized conspecific. Based on dCA2 population activity, a set of binary linear classifiers accurately decoded whether an animal was engaged in each of these forms of social behavior. Of particular interest, the accuracy of decoding aggression was greater with novel compared to familiarized intruders, with significant cross-day decoding using the same familiar animal on each day but not for a familiar-novel pair. Together, these findings demonstrate that dCA2 integrates information about social novelty with signals of behavioral state to promote aggression towards novel conspecifics.

Memory encoding and retrieval by retrosplenial parvalbumin interneurons are impaired in Alzheimer's disease model mice

Memory deficits in Alzheimer's disease (AD) show a strong link with GABAergic interneuron dysfunctions.1,2,3,4,5,6,7 The ensemble dynamics of GABAergic interneurons represent memory encoding and retrieval,8,9,10,11,12 but how GABAergic interneuron dysfunction affects inhibitory ensemble dynamics in AD is unknown. As the retrosplenial cortex (RSC) is critical for episodic memory13,14,15,16 and is affected by β-amyloid accumulation in early AD,17,18,19,20,21 we address this question by performing Ca2+ imaging in RSC parvalbumin (PV)-expressing interneurons during a contextual fear memory task in healthy control mice and the 5XFAD mouse model of AD. We found that populations of PV interneurons responsive to aversive electric foot shocks during contextual fear conditioning (shock-responsive) significantly decreased in the 5XFAD mice, indicating dysfunctions in the recruitment of memory-encoding PV interneurons. In the control mice, ensemble activities of shock-responsive PV interneurons were selectively upregulated during the freezing epoch of the contextual fear memory retrieval, manifested by synaptic potentiation of PV interneuron-mediated inhibition. However, such changes in ensemble dynamics during memory retrieval and synaptic plasticity were both absent in the 5XFAD mice. Optogenetic silencing of PV interneurons during contextual fear conditioning in the control mice mimicked the memory deficits in the 5XFAD mice, while optogenetic activation of PV interneurons in the 5XFAD mice restored memory retrieval. These results demonstrate the critical roles of contextual fear memory-encoding PV interneurons for memory retrieval. Furthermore, synaptic dysfunction of PV interneurons may disrupt the recruitment of PV interneurons and their ensemble dynamics underlying contextual fear memory retrieval, subsequently leading to memory deficits in AD.

Functional imaging of nine distinct neuronal populations under a miniscope in freely behaving animals

Head-mounted miniscopes have allowed for functional fluorescence imaging in freely moving animals. However, current capabilities of state-of-the-art technology can record only up to two, spectrally distinct fluorophores. This severely limits the number of cell types identifiable in a functional imaging experiment. Here we present a pipeline that enables the distinction of nine neuronal subtypes from regions defined by behaviorally relevant cells during in vivo GCaMP imaging. These subtypes are identified utilizing unique fluorophores that are co-expressed with GCaMP, unmixed by spectral imaging on a confocal microscope and co-registering these spectral fingerprints with functional data obtained on miniaturized microscopes. This method facilitates detailed analyses of circuit-level encoding of behavior.

Deep-brain optical recording of neural dynamics during behavior

In vivo fluorescence recording techniques have produced landmark discoveries in neuroscience, providing insight into how single cell and circuit-level computations mediate sensory processing and generate complex behaviors. While much attention has been given to recording from cortical brain regions, deep-brain fluorescence recording is more complex because it requires additional measures to gain optical access to harder to reach brain nuclei. Here we discuss detailed considerations and tradeoffs regarding deep-brain fluorescence recording techniques and provide a comprehensive guide for all major steps involved, from project planning to data analysis. The goal is to impart guidance for new and experienced investigators seeking to use in vivo deep fluorescence optical recordings in awake, behaving rodent models.

Dual-color miniscope imaging of microvessels and neuronal activity in the hippocampus CA1 region of freely moving mice following alcohol administration

Moderate-to-heavy episodic ("binge") drinking is the most common form of alcohol consumption in the United States. Alcohol at binge drinking concentrations reduces brain artery diameter in vivo and in vitro in many species including rats, mice, and humans. Despite the critical role played by brain vessels in maintaining neuronal function, there is a shortage of methodologies to simultaneously assess neuron and blood vessel function in deep brain regions. Here, we investigate cerebrovascular responses to ethanol by choosing a deep brain region that is implicated in alcohol disruption of brain function, the hippocampal CA1, and describe the process for obtaining simultaneous imaging of pyramidal neuron activity and diameter of nearby microvessels in freely moving mice via a dual-color miniscope. Recordings of neurovascular events were performed upon intraperitoneal injection of saline versus 3 g/kg ethanol in the same mouse. In male mice, ethanol mildly increased the amplitude of calcium signals while robustly decreasing their frequency. Simultaneously, ethanol decreased microvessel diameter. In females, ethanol did not change the amplitude or frequency of calcium signals from CA1 neurons but decreased microvessel diameter. A linear regression of ethanol-induced reduction in number of active neurons and microvessel constriction revealed a positive correlation (R = 0.981) in females. Together, these data demonstrate the feasibility of simultaneously evaluating neuronal and vascular components of alcohol actions in a deep brain area in freely moving mice, as well as the sexual dimorphism of hippocampal neurovascular responses to alcohol.

Astrocyte-specific Ca2+ activity: Mechanisms of action, experimental tools, and roles in ethanol-induced dysfunction

Astrocytes are a subtype of non-neuronal glial cells that reside in the central nervous system. Astrocytes have extensive peripheral astrocytic processes that ensheathe synapses to form the tripartite synapse. Through a multitude of pathways, astrocytes can influence synaptic development and structural maturation, respond to neuronal signals, and modulate synaptic transmission. Over the last decade, strong evidence has emerged demonstrating that astrocytes can influence behavioral outcomes in various animal models of cognition. However, the full extent of how astrocytes influence brain function is still being revealed. Astrocyte calcium (Ca2+) signaling has emerged as an important driver of astrocyte-neuronal communication allowing intricate crosstalk through mechanisms that are still not fully understood. Here, we will review the field's current understanding of astrocyte Ca2+ signaling and discuss the sophisticated state-of-the-art tools and approaches used to continue unraveling astrocytes' interesting role in brain function. Using the field of pre-clinical ethanol (EtOH) studies in the context of alcohol use disorder, we focus on how these novel approaches have helped to reveal an important role for astrocyte Ca2+ function in regulating EtOH consumption and how astrocyte Ca2+ dysfunction contributes to the cognitive deficits that emerge after EtOH exposure in a rodent model.

110 μm thin endo-microscope for deep-brain in vivo observations of neuronal connectivity, activity and blood flow dynamics

Light-based in-vivo brain imaging relies on light transport over large distances of highly scattering tissues. Scattering gradually reduces imaging contrast and resolution, making it difficult to reach structures at greater depths even with the use of multiphoton techniques. To reach deeper, minimally invasive endo-microscopy techniques have been established. These most commonly exploit graded-index rod lenses and enable a variety of modalities in head-fixed and freely moving animals. A recently proposed alternative is the use of holographic control of light transport through multimode optical fibres promising much less traumatic application and superior imaging performance. We present a 110 μm thin laser-scanning endo-microscope based on this prospect, enabling in-vivo volumetric imaging throughout the whole depth of the mouse brain. The instrument is equipped with multi-wavelength detection and three-dimensional random access options, and it performs at lateral resolution below 1 μm. We showcase various modes of its application through the observations of fluorescently labelled neurones, their processes and blood vessels. Finally, we demonstrate how to exploit the instrument to monitor calcium signalling of neurones and to measure blood flow velocity in individual vessels at high speeds.

Modern Microscopic Approaches to Astrocytes

Microscopy started as the histological analysis based on intrinsic optical properties of tissues such as the refractive index and light absorption, and is expanding to include the visualization of organelles by chemical staining, localization of molecules by immunostaining, physiological measurements such as Ca²⁺ imaging, functional manipulation by optogenetics, and comprehensive analysis of chemical composition by Raman spectra. The microscope is one of the most important tools in neuroscience, which aims to reveal the complex intercellular communications underlying brain function and pathology. Many aspects of astrocytes, including the structures of their fine processes and physiological activities in concert with neurons and blood vessels, were revealed in the course of innovations in modern microscopy. The evolution of modern microscopy is a consequence of breakthroughs in spatiotemporal resolutions and expansions in molecular and physiological targets due to the progress in optics and information technology, as well as the inventions of probes using organic chemistry and molecular biology. This review overviews the modern microscopic approach to astrocytes.

GRIN lens applications for studying neurobiology of substance use disorder

Substance use disorder (SUD) is associated with severe health and social consequences. Continued drug use results in alterations of circuits within the mesolimbic dopamine system. It is critical to observe longitudinal impacts of SUD on neural activity in vivo to identify SUD predispositions, develop pharmaceuticals to prevent overdose, and help people suffering from SUD. However, implicated SUD associated areas are buried in deep brain which makes in vivo observation of neural activity challenging. The gradient index (GRIN) lens can probe these regions in mice and rats. In this short communications review, we will discuss how the GRIN lens can be coupled with other technologies such as miniaturized microscopes, fiberscopes, fMRI, and optogenetics to fully explore in vivo SUD research. Particularly, GRIN lens allows in vivo observation of deep brain regions implicated in SUD, differentiation of genetically distinct neurons, examination of individual cells longitudinally, correlation of neuronal patters with SUD behavior, and manipulation of neural circuits.

Dissociable effects of oxycodone on behavior, calcium transient activity, and excitability of dorsolateral striatal neurons

Opioids are the most common medications for moderate to severe pain. Unfortunately, they also have addictive properties that have precipitated opioid misuse and the opioid epidemic. In the present study, we examined the effects of acute administration of oxycodone, a μ-opioid receptor (MOR) agonist, on Ca²⁺ transient activity of medium-sized spiny neurons (MSNs) in freely moving animals. Ca²⁺ imaging of MSNs in dopamine D1-Cre mice (expressing Cre predominantly in the direct pathway) or adenosine A2A-Cre mice (expressing Cre predominantly in the indirect pathway) was obtained with the aid of miniaturized microscopes (Miniscopes) and a genetically encoded Cre-dependent Ca²⁺ indicator (GCaMP6f). Systemic injections of oxycodone (3 mg/kg) increased locomotor activity yet, paradoxically, reduced concomitantly the number of active MSNs. The frequency of Ca²⁺ transients was significantly reduced in MSNs from A2A-Cre mice but not in those from D1-Cre mice. For comparative purposes, a separate group of mice was injected with a non-Cre dependent Ca²⁺ indicator in the cerebral cortex and the effects of the opioid also were tested. In contrast to MSNs, the frequency of Ca²⁺ transients in cortical pyramidal neurons was significantly increased by oxycodone administration. Additional electrophysiological studies in brain slices confirmed generalized inhibitory effects of oxycodone on MSNs, including membrane hyperpolarization, reduced excitability, and decreased frequency of spontaneous excitatory and inhibitory postsynaptic currents. These results demonstrate a dissociation between locomotion and striatal MSN activity after acute administration of oxycodone.

A miniature fluorescence microscope for multi-plane imaging

Miniature fluorescence microscopes are becoming an increasingly established tool to investigate neural circuits in freely moving animals. In this work we present a lightweight one-photon microscope capable of imaging at different focal depths. The focal plane can be changed dynamically by modulating the pulse width of the control signal to a variable focus liquid lens, which is synchronized to the image sensor to enable changing focal plane between frames. The system was tested by imaging GCaMP7f expressing neurons in the mouse medial prefrontal cortex (mPFC) in vivo during open field test. Results showed that with the proposed design it is possible to image neurons across an axial scan of ~ 60 μm, resulting in a ~ 40% increase of total neurons imaged compared to single plane imaging.

Early Changes in Striatal Activity and Motor Kinematics in a Huntington's Disease Mouse Model

BACKGROUND

Huntington's disease is a progressive neurodegenerative disorder with no disease-modifying treatments. Patients experience motor, cognitive, and psychiatric disturbances, and the dorsal striatum is the main target of neurodegeneration. Mouse models of Huntington's disease show altered striatal synaptic signaling in vitro, but how these changes relate to behavioral deficits in vivo is unclear.

OBJECTIVES

We aimed to investigate how striatal activity correlates with behavior in vivo during motor learning and spontaneous behavior in a Huntington's disease mouse model at two disease stages.

METHODS

We used fiber photometry to record jGCaMP7f fluorescence, a read-out of neuronal activity, in the dorsal striatum of YAC128 (yeast artificial chromosome-128CAG) mice during accelerating rotarod and open-field behavior.

RESULTS

Mice showed increased striatal activity on the rotarod, which diminished by late stages of learning, leading to an inverse correlation between latency to fall and striatal activity. The 2- to 3-month-old YAC128 mice did not show a deficit in latency to fall, but displayed significant differences in paw kinematics, including increased paw slip frequency and variability in paw height. These mice exhibited a weaker correlation between latency to fall and striatal activity and aberrant striatal activity during paw slips. At 6 to 7 months, the YAC128 mice showed significantly reduced latency to fall, impaired paw kinematics, and increased striatal activity while on the rotarod. In the open field, the YAC128 mice showed elevated neuronal activity at rest.

CONCLUSIONS

We uncovered impaired motor coordination at a stage thought to be premotor manifest in YAC128 mice and aberrant striatal activity during the accelerating rotarod and open-field exploration. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Kisspeptin neuron electrophysiology: Intrinsic properties, hormonal modulation, and regulation of homeostatic circuits

The obligatory role of kisspeptin (KISS1) and its receptor (KISS1R) in regulating the hypothalamic-pituitary-gonadal axis, puberty and fertility was uncovered in 2003. In the few years that followed, an impressive body of work undertaken in many species established that neurons producing kisspeptin orchestrate gonadotropin-releasing hormone (GnRH) neuron activity and subsequent GnRH and gonadotropin hormone secretory patterns, through kisspeptin-KISS1R signaling, and mediate many aspects of gonadal steroid hormone feedback regulation of GnRH neurons. Here, we review knowledge accrued over the past decade, mainly in genetically modified mouse models, of the electrophysiological properties of kisspeptin neurons and their regulation by hormonal feedback. We also discuss recent progress in our understanding of the role of these cells within neuronal circuits that control GnRH neuron activity and GnRH secretion, energy balance and, potentially, other homeostatic and reproductive functions.

Cranial and Spinal Window Preparation for in vivo Optical Neuroimaging in Rodents and Related Experimental Techniques

Optical neuroimaging provides an effective neuroscience tool for multi-scale investigation of the neural structures and functions, ranging from molecular, cellular activities to the inter-regional connectivity assessment. Amongst experimental preparations, the implementation of an artificial window to the central nervous system (CNS) is primarily required for optical visualization of the CNS and associated brain activities through the opaque skin and bone. Either thinning down or removing portions of the skull or spine is necessary for unobstructed long-term in vivo observations, for which types of the cranial and spinal window and applied materials vary depending on the study objectives. As diversely useful, a window can be designed to accommodate other experimental methods such as electrophysiology or optogenetics. Moreover, auxiliary apparatuses would allow the recording in synchrony with behavior of large-scale brain connectivity signals across the CNS, such as olfactory bulb, cerebral cortex, cerebellum, and spinal cord. Such advancements in the cranial and spinal window have resulted in a paradigm shift in neuroscience, enabling in vivo investigation of the brain function and dysfunction at the microscopic, cellular level. This Review addresses the types and classifications of windows used in optical neuroimaging while describing how to perform in vivo studies using rodent models in combination with other experimental modalities during behavioral tests. The cranial and spinal window has enabled longitudinal examination of evolving neural mechanisms via in situ visualization of the brain. We expect transformable and multi-functional cranial and spinal windows to become commonplace in neuroscience laboratories, further facilitating advances in optical neuroimaging systems.

Development of an Ergonomic User Interface Design of Calcium Imaging Processing System

An optical brain-machine interface (O-BMI) system using calcium imaging has various advantages such as high resolution, a comprehensive view of large neural populations, abilities such as long-term stable recording, and applicability to freely behaving animals in neuroscience research. The present study developed an ergonomic user interface (UI) design, based on a use scenario for an O-BMI system that can be used for the acquisition and processing of calcium imaging in freely behaving rodents. The UI design was developed in three steps: (1) identification of design and function requirements of users, (2) establishment of a use scenario, and (3) development of a UI prototype. The UI design requirements were identified by a literature review, a benchmark of existing systems, and a focus group interview with five neuroscience researchers. Then, the use scenario was developed for tasks of data acquisition, feature extraction, and neural decoding for offline and online processing by considering the sequences of operations and needs of users. Lastly, a digital prototype incorporating an information architecture, graphic user interfaces, and simulated functions was fabricated. A usability test was conducted with five neuroscientists (work experience = 3.4 ± 1.1 years) and five ergonomic experts (work experience = 3.6 ± 2.7 years) to compare the digital prototypes with four existing systems (Miniscope, nVista, Mosaic, and Suite2p). The usability testing results showed that the ergonomic UI design was significantly preferred to the UI designs of the existing systems by reducing the task completion time by 10.1% to 70.2% on average, the scan path length by 14.4% to 88.7%, and perceived workload by 12.2% to 37.9%, increasing satisfaction by 11.3% to 74.3% in data acquisition and signal-extraction tasks. The present study demonstrates the significance of the user-centered design approach in the development of a system for neuroscience research. Further research is needed to validate the usability test results of the UI prototype as a corresponding real system is implemented.

In vivo imaging of the GnRH pulse generator reveals a temporal order of neuronal activation and synchronization during each pulse

Hypothalamic oscillators that generate pulsatile patterns of hormone secretion represent a fundamental physiological feature regulating homeostatic systems. How individual cells within these neural ensembles generate and coordinate episodic activity and resultant pulse secretion is unknown. Recently, arcuate KNDy (kisspeptin/neurokinin B/dynorphin) cells were identified as a critical component of the gonadotrophin-releasing hormone (GnRH) pulse generator required for reproduction. Using in vivo calcium imaging of KNDy neurons in freely moving mice, we reveal that, prior to each GnRH pulse, individual KNDy cells demonstrate synchronized activity with striking temporal order, with subsets of cells behaving as “leaders” or “followers.” Future work to distinguish these novel subpopulations and define mechanisms underlying the temporal ordering of cellular synchronization may provide avenues to regulate pulse secretion.

A hypothalamic pulse generator located in the arcuate nucleus controls episodic release of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH) and is essential for reproduction. Recent evidence suggests this generator is composed of arcuate “KNDy” cells, the abbreviation based on coexpression of kisspeptin, neurokinin B, and dynorphin. However, direct visual evidence of KNDy neuron activity at a single-cell level during a pulse is lacking. Here, we use in vivo calcium imaging in freely moving female mice to show that individual KNDy neurons are synchronously activated in an episodic manner, and these synchronized episodes always precede LH pulses. Furthermore, synchronization among KNDy cells occurs in a temporal order, with some subsets of KNDy cells serving as “leaders” and others as “followers” during each synchronized episode. These results reveal an unsuspected temporal organization of activation and synchronization within the GnRH pulse generator, suggesting that different subsets of KNDy neurons are activated at pulse onset than afterward during maintenance and eventual termination of each pulse. Further studies to distinguish KNDy “leader” from “follower” cells is likely to have important clinical significance, since regulation of pulsatile GnRH secretion is essential for normal reproduction and disrupted in pathological conditions such as polycystic ovary syndrome and hypothalamic amenorrhea.

Interactions between glial cells and the blood-brain barrier and their role in Alzheimer's disease

Alzheimer's disease (AD), which is an irreversible neurodegenerative disorder characterized by senile plaques and neurofibrillary tangles, is the most common form of dementia worldwide. However, currently, there are no satisfying curative therapies for AD. The blood-brain barrier (BBB) acts as a selective physical barrier and plays protective roles in maintaining brain homeostasis. BBB dysfunction as an upstream or downstream event promotes the onset and progression of AD. Moreover, the pathogenesis of AD caused by BBB injury hasn't been well elucidated. Glial cells, BBB compartments and neurons form a minimal functional unit called the neurovascular unit (NVU). Emerging evidence suggests that glial cells are regulators in maintaining the BBB integrity and neuronal function. Illustrating the regulatory mechanism of glial cells in the BBB assists us in drawing a glial-vascular coupling diagram of AD, which may offer new insight into the pathogenesis of AD and early intervention strategies for AD. This review aims to summarize our current knowledge of glial-BBB interactions and their pathological implications in AD and to provide new therapeutic potentials for future investigations.