The Promise of Automated Home-Cage Monitoring in Improving Translational Utility of Psychiatric Research in Rodents

Environmental enrichment: a systematic review on the effect of a changing spatial complexity on hippocampal neurogenesis and plasticity in rodents, with considerations for translation to urban and built environments for humans

Introduction

Hippocampal neurogenesis is critical for improving learning, memory, and spatial navigation. Inhabiting and navigating spatial complexity is key to stimulating adult hippocampal neurogenesis (AHN) in rodents because they share similar hippocampal neuroplasticity characteristics with humans. AHN in humans has recently been found to persist until the tenth decade of life, but it declines with aging and is influenced by environmental enrichment. This systematic review investigated the impact of spatial complexity on neurogenesis and hippocampal plasticity in rodents, and discussed the translatability of these findings to human interventions.

Methods

Comprehensive searches were conducted on three databases in English: PubMed, Web of Science, and Scopus. All literature published until December 2023 was screened and assessed for eligibility. A total of 32 studies with original data were included, and the process is reported in accordance with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement and checklist.

Results

The studies evaluated various models of spatial complexity in rodents, including environmental enrichment, changes to in-cage elements, complex layouts, and navigational mazes featuring novelty and intermittent complexity. A regression equation was formulated to synthesize key factors influencing neurogenesis, such as duration, physical activity, frequency of changes, diversity of complexity, age, living space size, and temperature.

Conclusion

Findings underscore the cognitive benefits of spatial complexity interventions and inform future translational research from rodents to humans. Home-cage enrichment and models like the Hamlet complex maze and the Marlau cage offer insight into how architectural design and urban navigational complexity can impact neurogenesis in humans. In-space changing complexity, with and without physical activity, is effective for stimulating neurogenesis. While evidence on intermittent spatial complexity in humans is limited, data from the COVID-19 pandemic lockdowns provide preliminary evidence. Existing equations relating rodent and human ages may allow for the translation of enrichment protocol durations from rodents to humans.

Chronic consequences of ischemic stroke: Profiling brain injury and inflammation in a mouse model with reperfusion

Stroke is a pervasive and debilitating global health concern, necessitating innovative therapeutic strategies, especially during recovery. While existing literature often focuses on acute interventions, our study addresses the uniqueness of brain tissue during wound healing, emphasizing the chronic phase following the commonly used middle cerebral artery (MCA) occlusion model. Using clinically relevant endpoints in male and female mice such as magnetic resonance imaging (MRI) and plasma neurofilament light (NFL) measurement, along with immunohistochemistry, we describe injury evolution. Our findings document significant alterations in edema, tissue remodeling, and gadolinium leakage through MRI. Plasma NFL concentration remained elevated at 30 days poststroke. Microglia responses are confined to the region adjacent to the injury, rather than continued widespread activation, and boron-dipyrromethene (BODIPY) staining demonstrated the persistent presence of foam cells within the infarct. Additional immunohistochemistry highlighted sustained B and T lymphocyte presence in the poststroke brain. These observations underscore potentially pivotal roles played by chronic inflammation brought on by the lipid-rich brain environment, and chronic blood-brain barrier dysfunction, in the development of secondary neurodegeneration. This study sheds light on the enduring consequences of ischemic stroke in the most used rodent stroke model and provides valuable insights for future research, clinical strategies, and therapeutic development.

Investigation of Mild Traumatic Brain Injury Home Cage Behavior: The Home Cage Assay Advantages

This study utilized the Noldus PhenoTyper Home Cage Monitoring system (HCM) to assess the behavioral and cognitive changes of experimental closed-head mild traumatic brain injury (mTBI). Seventy-nine adult male Institute of Cancer Research (ICR) mice were subjected to either a sham procedure or closed-head mTBI using the weight-drop model. Seven days post-injury, separate cohorts of mice underwent either a non-cognitive or a cognitive home cage assessment, a treadmill fatigue test, or the Open Field Test. mTBI significantly influenced habituation behavior and circadian wheel-running activity. Notably, mTBI mice exhibited an increased frequency of visits to the running wheel, but each visit was shorter than those of controls. No significant differences between the groups in discrimination or reversal learning performance were observed. However, during the reversal learning stage, mTBI mice performed similarly to their initial discrimination learning levels, suggesting an abnormally faster rate of reversal learning. Home cage monitoring is a valuable tool for studying the subtle effects of mTBI, complementing traditional assays. The automated evaluation of habituation to novel stimuli (e.g., novel environment) could serve as a potentially sensitive tool for assessing mTBI-associated behavioral deficits.

Rodent tests of depression and anxiety: Construct validity and translational relevance

Behavioral testing constitutes the primary method to measure the emotional states of nonhuman animals in preclinical research. Emerging as the characteristic tool of the behaviorist school of psychology, behavioral testing of animals, particularly rodents, is employed to understand the complex cognitive and affective symptoms of neuropsychiatric disorders. Following the symptom-based diagnosis model of the DSM, rodent models and tests of depression and anxiety focus on behavioral patterns that resemble the superficial symptoms of these disorders. While these practices provided researchers with a platform to screen novel antidepressant and anxiolytic drug candidates, their construct validity-involving relevant underlying mechanisms-has been questioned. In this review, we present the laboratory procedures used to assess depressive- and anxiety-like behaviors in rats and mice. These include constructs that rely on stress-triggered responses, such as behavioral despair, and those that emerge with nonaversive training, such as cognitive bias. We describe the specific behavioral tests that are used to assess these constructs and discuss the criticisms on their theoretical background. We review specific concerns about the construct validity and translational relevance of individual behavioral tests, outline the limitations of the traditional, symptom-based interpretation, and introduce novel, ethologically relevant frameworks that emphasize simple behavioral patterns. Finally, we explore behavioral monitoring and morphological analysis methods that can be integrated into behavioral testing and discuss how they can enhance the construct validity of these tests.

IntelliCage: the development and perspectives of a mouse- and user-friendly automated behavioral test system

IntelliCage for mice is a rodent home-cage equipped with four corner structures harboring symmetrical double panels for operant conditioning at each of the two sides, either by reward (access to water) or by aversion (non-painful stimuli: air-puffs, LED lights). Corner visits, nose-pokes and actual licks at bottle-nipples are recorded individually using subcutaneously implanted transponders for RFID identification of up to 16 adult mice housed in the same home-cage. This allows for recording individual in-cage activity of mice and applying reward/punishment operant conditioning schemes in corners using workflows designed on a versatile graphic user interface. IntelliCage development had four roots: (i) dissatisfaction with standard approaches for analyzing mouse behavior, including standardization and reproducibility issues, (ii) response to handling and housing animal welfare issues, (iii) the increasing number of mouse models had produced a high work burden on classic manual behavioral phenotyping of single mice. and (iv), studies of transponder-chipped mice in outdoor settings revealed clear genetic behavioral differences in mouse models corresponding to those observed by classic testing in the laboratory. The latter observations were important for the development of home-cage testing in social groups, because they contradicted the traditional belief that animals must be tested under social isolation to prevent disturbance by other group members. The use of IntelliCages reduced indeed the amount of classic testing remarkably, while its flexibility was proved in a wide range of applications worldwide including transcontinental parallel testing. Essentially, two lines of testing emerged: sophisticated analysis of spontaneous behavior in the IntelliCage for screening of new genetic models, and hypothesis testing in many fields of behavioral neuroscience. Upcoming developments of the IntelliCage aim at improved stimulus presentation in the learning corners and videotracking of social interactions within the IntelliCage. Its main advantages are (i) that mice live in social context and are not stressfully handled for experiments, (ii) that studies are not restricted in time and can run in absence of humans, (iii) that it increases reproducibility of behavioral phenotyping worldwide, and (iv) that the industrial standardization of the cage permits retrospective data analysis with new statistical tools even after many years.

Mitochondrial dysfunction following repeated administration of alprazolam causes attenuation of hippocampus-dependent memory consolidation in mice

The frequently repeated administration of alprazolam (Alp), a highly effective benzodiazepine sedative-hypnotic agent, in anxiety, insomnia, and other diseases is closely related to many negative adverse reactions that are mainly manifested as memory impairment. However, the exact molecular mechanisms underlying these events are poorly understood. Therefore, we conducted a proteomic analysis on the hippocampus in mice that received repeated administration of Alp for 24 days. A total of 439 significantly differentially expressed proteins (DEPs) were identified in mice with repeated administration of Alp compared to the control group, and the GO and KEGG analysis revealed the enrichment of terms related to mitochondrial function, cycle, mitophagy and cognition. In vitro experiments have shown that Alp may affect the cell cycle, reduce the mitochondrial membrane potential (MMP) to induce apoptosis in HT22 cells, and affect the progress of mitochondrial energy metabolism and morphology in the hippocampal neurons. Furthermore, in vivo behavioral experiments including IntelliCage System (ICS) and nover object recognition (NOR), hippocampal neuronal pathological changes with HE staining, and the expression levels of brain-deprived neuron factor (BDNF) with immunohistochemistry showed a significant decrease in memory consolidation in mice with repeated administration of Alp, which could be rescued by the co-administration of the mitochondrial protector NSI-189. To the best of our knowledge, this is the first study to identify a link between repeated administration of Alp and mitochondrial dysfunction and that mitochondrial impairment directly causes the attenuation of memory consolidation in mice.

A fully automated home cage for long-term continuous phenotyping of mouse cognition and behavior

Automated home-cage monitoring systems present a valuable tool for comprehensive phenotyping of natural behaviors. However, current systems often involve complex training routines, water or food restriction, and probe a limited range of behaviors. Here, we present a fully automated home-cage monitoring system for cognitive and behavioral phenotyping in mice. The system incorporates T-maze alternation, novel object recognition, and object-in-place recognition tests combined with monitoring of locomotion, drinking, and quiescence patterns, all carried out over long periods. Mice learn the tasks rapidly without any need for water or food restrictions. Behavioral characterization employs a deep convolutional neural network image analysis. We show that combined statistical properties of multiple behaviors can be used to discriminate between mice with hippocampal, medial entorhinal, and sham lesions and predict the genotype of an Alzheimer's disease mouse model with high accuracy. This technology may enable large-scale behavioral screening for genes and neural circuits underlying spatial memory and other cognitive processes.

Socially Integrated Polysubstance (SIP) system: An open-source solution for continuous monitoring of polysubstance fluid intake in group housed mice

Despite impressive results from neuroscience research using rodent models, there is a paucity of successful translation from preclinical findings to effective pharmacological interventions for treatment of substance use disorder (SUD) in humans. One potential reason for lack of translation from animal models is difficulty in accurately replicating the lived experience of people who use drugs. Aspects of substance use in humans that are often not modeled in animal research include but are not limited to 1) voluntary timing and frequency of substance intake, 2) social environment during substance use, and 3) access to multiple substances and multiple concentrations of each substance. Critically, existing commercial equipment that allows for social housing and voluntary polysubstance use (e.g., home cage monitoring system) is prohibitively expensive and no open-source solutions exist. With these goals in mind, here we detail development of the Socially Integrated Polysubstance (SIP) system, an open-source and lower cost solution that allows for group housed rodents to self-administer multiple substances with continuous monitoring and measurement. In our current setup, each SIP cage contains four drinking stations, and each station is equipped with a RFID sensor and sipper tube connected to a unique fluid reservoir. Using this system, we can track which animal (implanted with unique RFID transponder) visits which drinking location and the amount they drink during each visit (in 20 ul increments). Using four flavors of Kool-Aid, here we demonstrate that the SIP system is reliable and accurate with high temporal resolution for long term monitoring of substance intake and behavior tracking in a social environment. The SIP cage system is a first step towards designing an accessible and flexible rodent model of substance use that more closely resembles the experience of people who use drugs.

LIQ HD (Lick Instance Quantifier Home Cage Device): An Open-Source Tool for Recording Undisturbed Two-Bottle Drinking Behavior in a Home Cage Environment

Investigation of rodent drinking behavior has provided insight into drivers of thirst, circadian rhythms, anhedonia, and drug and ethanol consumption. Traditional methods of recording fluid intake involve weighing bottles, which is cumbersome and lacks temporal resolution. Several open-source devices have been designed to improve drink monitoring, particularly for two-bottle choice tasks. However, beam-break sensors lack the ability to detect individual licks for bout microstructure analysis. Thus, we designed LIQ HD (Lick Instance Quantifier Home cage Device) with the goal of using capacitive sensors to increase accuracy and analyze lick microstructure, building a device compatible with ventilated home cages, increasing scale with prolonged undisturbed recordings, and creating a design that is easy to build and use with an intuitive touchscreen graphical user interface. The system tracks two-bottle choice licking behavior in up to 18 rodent cages, or 36 single bottles, on a minute-to-minute timescale controlled by a single Arduino microcontroller. The data are logged to a single SD card, allowing for efficient downstream analysis. LIQ HD accuracy was validated with sucrose, quinine, and ethanol two-bottle choice tasks. The system measures preference over time and changes in bout microstructure, with undisturbed recordings tested up to 7 d. All designs and software are open-source to allow other researchers to build on the system and adapt LIQ HD to their animal home cages.

Longitudinal home-cage automated assessment of climbing behavior shows sexual dimorphism and aging-related decrease in C57BL/6J healthy mice and allows early detection of motor impairment in the N171-82Q mouse model of Huntington's disease

Monitoring the activity of mice within their home cage is proving to be a powerful tool for revealing subtle and early-onset phenotypes in mouse models. Video-tracking, in particular, lends itself to automated machine-learning technologies that have the potential to improve the manual annotations carried out by humans. This type of recording and analysis is particularly powerful in objective phenotyping, monitoring behaviors with no experimenter intervention. Automated home-cage testing allows the recording of non-evoked voluntary behaviors, which do not require any contact with the animal or exposure to specialist equipment. By avoiding stress deriving from handling, this approach, on the one hand, increases the welfare of experimental animals and, on the other hand, increases the reliability of results excluding confounding effects of stress on behavior. In this study, we show that the monitoring of climbing on the wire cage lid of a standard individually ventilated cage (IVC) yields reproducible data reflecting complex phenotypes of individual mouse inbred strains and of a widely used model of neurodegeneration, the N171-82Q mouse model of Huntington's disease (HD). Measurements in the home-cage environment allowed for the collection of comprehensive motor activity data, which revealed sexual dimorphism, daily biphasic changes, and aging-related decrease in healthy C57BL/6J mice. Furthermore, home-cage recording of climbing allowed early detection of motor impairment in the N171-82Q HD mouse model. Integrating cage-floor activity with cage-lid activity (climbing) has the potential to greatly enhance the characterization of mouse strains, detecting early and subtle signs of disease and increasing reproducibility in preclinical studies.

The importance of a multidimensional approach to the preclinical study of major depressive disorder and apathy

Both the neuropsychiatric syndrome of apathy and major depressive disorder comprise a heterogenous cluster of symptoms which span multiple behavioural domains. Despite this heterogeneity, there is a tendency in the preclinical literature to conclude a MDD or apathy-like phenotype from a single dimensional behavioural task used in isolation, which may lead to inaccurate phenotypic interpretation. This is significant, as apathy and major depressive disorder are clinically distinct with different underlying mechanisms and treatment approaches. At the clinical level, apathy and major depressive disorder can be dissociated in the negative valence (loss) domain of the Research Domain Criteria. Symptoms of MDD in the negative valence (loss) domain can include an exaggerated response to emotionally salient stimuli and low mood, while in contrast apathy is characterised by an emotionally blunted state. In this article, we highlight how using a single dimensional approach can limit psychiatric model interpretation. We discuss how integrating behavioural findings from both the positive and negative (loss) valence domains of the Research Domain Criteria can benefit interpretation of findings. We focus particularly on behaviours relating to the negative valence (loss) domain, which may be used to distinguish between apathy and major depressive disorder at the preclinical level. Finally, we consider how future approaches using home cage monitoring may offer a new opportunity to detect distinct behavioural profiles and benefit the overall translatability of findings.

How can we obtain truly translational mouse models to improve clinical outcomes in schizophrenia?

Schizophrenia is a serious mental illness affecting 0.7% of the world's population. Despite over 50 years of schizophrenia drug identification and development, there have been no fundamental advances in the treatment of schizophrenia since the 1980s. Complex genetic aetiology and elusive pathomechanisms have made it difficult for researchers to develop models that sufficiently reflect pathophysiology to support effective drug discovery. However, recent large-scale, well-powered genomic studies have identified risk genes that represent tractable entry points to decipher disease mechanisms in heterogeneous patient populations and develop targeted treatments. Replicating schizophrenia-associated gene variants in mouse models is an important strategy to start understanding their pathogenicity and role in disease biology. Furthermore, longitudinal studies in a wide range of genetic mouse models from early postnatal life are required to assess the progression of this disease through developmental stages to improve early diagnostic strategies and enable preventative measures. By expanding and refining our approach to schizophrenia research, we can improve prevention strategies and treatment of this debilitating disease.

Challenges of a small world analysis for the continuous monitoring of behavior in mice

Documenting a mouse's "real world" behavior in the "small world" of a laboratory cage with continuous video recordings offers insights into phenotypical expression of mouse genotypes, development and aging, and neurological disease. Nevertheless, there are challenges in the design of a small world, the behavior selected for analysis, and the form of the analysis used. Here we offer insights into small world analyses by describing how acute behavioral procedures can guide continuous behavioral methodology. We show how algorithms can identify behavioral acts including walking and rearing, circadian patterns of action including sleep duration and waking activity, and the organization of patterns of movement into home base activity and excursions, and how they are altered with aging. We additionally describe how specific tests can be incorporated within a mouse's living arrangement. We emphasize how machine learning can condense and organize continuous activity that extends over extended periods of time.

Animal Study Translation: The Other Reproducibility Challenge

Animal research is currently an irreplaceable contributor to our efforts to protect and improve public health. Its relevance, importance, and contributions are represented in historical precedent, regulatory expectations, evidence of our rapidly developing understanding of human health and disease, as well as success in the development of novel therapeutics that are improving quality of life and extending human and animal life expectancy. The rapid and evolving success in responding to the current COVID pandemic significantly supported by animal studies is a clear example of the importance of animal research. But there is growing interest in reducing our dependence on animals and challenges to the effective translation of current animal studies to human applications. There are several potential contributors to gaps in the translatability of animal research to humans, including our approaches to choosing or rationalizing the relevance of a particular animal model, our understanding of their biological variability and how that applies to outcomes, the data we collect from animal studies, and even how we manage the animals. These important contributors to the success of animal research are explored in this issue of the ILAR Journal.

Roadbumps at the Crossroads of Integrating Behavioral and In Vitro Approaches for Neurotoxicity Assessment

With the appreciation that behavior represents the integration and complexity of the nervous system, neurobehavioral phenotyping and assessment has seen a renaissance over the last couple of decades, resulting in a robust database on rodent performance within various testing paradigms, possible associations with human disorders, and therapeutic interventions. The interchange of data across behavior and other test modalities and multiple model systems has advanced our understanding of fundamental biology and mechanisms associated with normal functions and alterations in the nervous system. While there is a demonstrated value and power of neurobehavioral assessments for examining alterations due to genetic manipulations, maternal factors, early development environment, the applied use of behavior to assess environmental neurotoxicity continues to come under question as to whether behavior represents a sensitive endpoint for assessment. Why is rodent behavior a sensitive tool to the neuroscientist and yet, not when used in pre-clinical or chemical neurotoxicity studies? Applying new paradigms and evidence on the biological basis of behavior to neurobehavioral testing requires expertise and refinement of how such experiments are conducted to minimize variability and maximize information. This review presents relevant issues of methods used to conduct such test, sources of variability, experimental design, data analysis, interpretation, and reporting. It presents beneficial and critical limitations as they translate to the in vivo environment and considers the need to integrate across disciplines for the best value. It proposes that a refinement of behavioral assessments and understanding of subtle pronounced differences will facilitate the integration of data obtained across multiple approaches and to address issues of translation.

Automated home-cage for the evaluation of innate non-reflexive pain behaviors in a mouse model of inflammatory pain

The failure to develop analgesic drugs is attributed not only to the complex and diverse pathophysiology of pain in humans but also to the poor experimental design and poor preclinical assessment of pain. Although considerable efforts have been devoted to overcoming the relevant problems, many features of the behavioral pain assessment remain to be characterized. For example, a decreased locomotor activity as a common presentation of pain-like behavior has yet to be described. Studies on mice experimentally induced with carrageenan have provided opportunities to explore pain-related behaviors in automated home-cage monitoring. Through this approach, the locomotor activities of mice with carrageenan-induced inflammatory pain can be precisely and objectively captured. Here, we found that the mobile behaviors of mice reduced, and their immobility increased, indicating that carrageenan induction in mice caused a significant decrease in locomotor activity. These non-reflexive pain behaviors were strongly correlated with the reflexive pain behaviors measured via von Frey and plantar tests. Furthermore, the pharmacological intervention using indomethacin improved the locomotor activity of mice with carrageenan-induced pain. Thus, the analysis of the locomotor activity in automated home-cage monitoring is useful for studying the behavioral analgesia and the pharmacological screening of analgesic drugs. The combined evaluation of reflexive and non-reflexive pain behaviors enhances the translational utility of preclinical pain research in rodents.

The IntelliCage System: A Review of Its Utility as a Novel Behavioral Platform for a Rodent Model of Substance Use Disorder

The use of animal models for substance use disorder (SUD) has made an important contribution in the investigation of the behavioral and molecular mechanisms underlying substance abuse and addiction. Here, we review a novel and comprehensive behavioral platform to characterize addiction-like traits in rodents using a fully automated learning system, the IntelliCage. This system simultaneously captures the basic behavioral navigation, reward preference, and aversion, as well as the multi-dimensional complex behaviors and cognitive functions of group-housed rodents. It can reliably capture and track locomotor and cognitive pattern alterations associated with the development of substance addiction. Thus, the IntelliCage learning system offers a potentially efficient, flexible, and sensitive tool for the high-throughput screening of the rodent SUD model.

Sleep Disorders in Children With Autism Spectrum Disorder: Insights From Animal Models, Especially Non-human Primate Model

Autism Spectrum Disorder (ASD) is a heterogeneous neurodevelopmental disorder with deficient social skills, communication deficits and repetitive behaviors. The prevalence of ASD has increased among children in recent years. Children with ASD experience more sleep problems, and sleep appears to be essential for the survival and integrity of most living organisms, especially for typical synaptic development and brain plasticity. Many methods have been used to assess sleep problems over past decades such as sleep diaries and parent-reported questionnaires, electroencephalography, actigraphy and videosomnography. A substantial number of rodent and non-human primate models of ASD have been generated. Many of these animal models exhibited sleep disorders at an early age. The aim of this review is to examine and discuss sleep disorders in children with ASD. Toward this aim, we evaluated the prevalence, clinical characteristics, phenotypic analyses, and pathophysiological brain mechanisms of ASD. We highlight the current state of animal models for ASD and explore their implications and prospects for investigating sleep disorders associated with ASD.