Validating inactivity in the home-cage as a depression-like state indicator in mice

Lead Research Organisation: University of Bristol
Department Name: Faculty of Medical & Veterinary Sciences

Abstract

Non-human animals (hereafter animals) can become strangely inactive in their home pens, being motionless (although awake) and not interacting with their environment. The affective states associated with this waking inactivity are, however, still not well understood. Compellingly, reduced activity and lack of engagement with the environment is one phenomenon supporting clinical depression diagnosis in humans. Moreover, the aetiology of human depression emphasizes aversive life events and chronic stress as common triggers of the disorder, and animals showing waking inactivity have often experienced an array of stressors, such as living in socially and/or spatially restricted environments. We therefore propose that,in animals, specific forms of waking inactivity characterised by being immobile with eyes open represent a marker of depression-like conditions.

This project builds upon our research that has already delineated in mice Mus musculus a specific form of waking inactivity [being awake but motionless within the home cage], triggered by relatively barren lab cages and associated with a key depression-like symptom of the human illness: the tendency to give up when faced with challenge. Our goal is to further test the hypothesis that waking inactivity is a spontaneous depression-like symptom in mice, which would be an easily measured home-cage indicator of animal welfare that could be translated across species.

To achieve this goal, we will adopt a translational 'from humans to animals' approach, using depressed people as a 'model' for inactive mice. As such, potential markers of animal depression-like conditions are expected to co-vary with a range of symptoms in animals similar to those described in human depression. Moreover, for an animal condition to be deemed homologous to a human illness, the processes by which both animal and humans fall into, and are released from, this state must share similarities. If waking inactivity reflects depression-like states in mice, its risk and curative factors should thus be similar to those of the human disease. Our investigations will thus broadly target shared aetiology [is waking inactivity triggered by a combination of risk factors triggering clinical depression in humans?], symptomatic similarities [does waking inactivity co-vary with a range of symptoms similar to those of clinical depression in humans?], and common curative factors [is waking inactivity alleviated by treatments clinically efficient in humans?]. Cognitive symptoms are a frequent part of depression in humans. A quick and easy cognitive measure of depression-like states is however needed in animals, and we will thus first validate such a measure of in mice, and then use this later to assess the symptomatic similarities between waking inactivity in mice and depression in humans.

If confirmed, our results will validate in-cage waking inactivity as a marker of a depression-like condition in mice. This has clear implications for animal welfare, as validated methods of identifying states of mental suffering are first required if we are to detect welfare problems in situ, assess the effectiveness of refinements, and maximise the welfare of lab animals. The ability to detect depression-like states also has crucial implications from a research perspective, since mice in negative affective states may for instance represent improved models of human depression, while potentially invalidating research where stress and depression are not of interest. A new, non-invasive tool to measure affective states will thus be of interest to animal welfare scientists, neuroscientists & psychopharmacologists interested in the assessment of animal affect; biomedical scientists whose research may be impacted by spontaneous occurrence of depression-like states in their subject animals; and laboratory managers & scientists seeking to improve welfare of their research animals.

Technical Summary

This project build upon our previous research & aims to comprehensively investigate the hypothesis that displaying waking inactivity in the home-cage is a depression-like symptom in mice. If confirmed, our results would provide a new, non-invasive tool to assess affective states in the mouse, which has clear implications for animal welfare & refinement purposes. To achieve this goal, we will adopt a translational 'from humans to animals' approach, broadly investigating shared aetiological 'risk' factors (Objective 2), symptomatic similarities (Objectives 1,3) and common curative factors (Objective 4) between in-cage waking inactivity in the mouse and human depression. We will work with C57BL/6J & DBA/2 females (as depression is more prevalent in women), two strains of mice commonly used in research that differ in their tendencies to display both waking inactivity and depression-like features (allowing us to target differences in genetic backgrounds when investigating risk factors, Objective 2). We will use methods from: ethology (e.g. conducting repeated scan-sampling sessions using well-validated methods and ethograms to assess in-cage behaviour and quantify the time spent displaying waking inactivity (Objectives 2-4); welfare science (using behavioural assays to measure affect-related cognitive biases, Objectives 1,3; and more or less enriched home-cages to create comparatively less or more stressful adult life conditions, Objective 2); psychology and psychiatry (applying to mice diagnostic criteria from the Diagnostic Manual of Mental Disorders used in human medicine to investigate symptom similarities, Objective 3); biomedical research (using a maternal separation paradigm to manipulate early life experiences, Objective 2); and pharmacology (using an antidepressant that has been pre-clinically shown to reverse depression-like features in mice and is clinically efficient in depressed people (e.g. venlafaxine) to investigate common curative factors, Objective 4).

Planned Impact

Our goal is to comprehensively test the hypothesis that waking inactivity is a spontaneous depression-like symptom in mice. If confirmed, this will have implications for animal welfare & Refinement purposes. Beneficiaries include:

* Animal welfare scientists, neuroscientists & psychopharmacologists interested in the assessment of animal affect.
Impact will happen via publishing in peer-reviewed journals, attending the leading international conferences in the field & presenting our results at BBSRC UK Animal Welfare Research Network (AWRN) meetings to identify further potential collaborators & future funding opportunities.

* biomedical scientists interest in modelling depression.
Impact will happen via engaging with Bristol psychopharmacologists, clinical epidemiologists & 'Bristol Neuroscience'. Though seminar, meetings & while attending Brain Awareness Week, we will see if our results might be of interest for these communities; if so, we will discuss the best ways to proceed, e.g. presenting the work at tissue & disease focused meetings & via collecting murine samples for pilot translational epidemiological investigations (screening for common biomarker between depressed people & mice displaying waking inactivity using e.g. the Bristol cohort study Avon Longitudinal Study of Parents & Children resource).

* laboratory managers & scientists seeking to further refine the use of their research animals.
Impact will happen via collaborating with Dr Campbell (Bristol, computer vision), to see if there are opportunities to develop a tool based on image analysis to automatically quantify the time mice display waking inactivity. We will collect pilot videos of mice in-cage behaviours, to be analysed by an Engineering student. If the computer vision approach appears feasible, we will collect more videos during year 3 to allow further development. We will apply for funding for subsequent software development and testing (e.g. BBSRC Follow-on, NC3Rs Crack-it funds). Potential industrial partners will be identified through liaison with Home Office inspectors, & publicity using the AWRN, NC3Rs & Understanding Animal Research resources, to identify animal technicians and unit managers, and industry representatives who will be invited to attend a round-table at which we will discuss the work implications and record expression of interest in an automated tool. The longer-term impact goal will be to translate these fundamental results from animal welfare science into practical application to automatically quantify waking inactivity in rodent husbandry facilities. We will also organise a workshop uniting international experts in inactivity displays in several species, to discuss the potential for inactivity to measure affective states; knowledge to be presented at lab animal international conferences, published in specialist journals & translated into a booklet for lab managers.

* We also know from previous engagement activities that there is a *considerable public interest* in animal welfare & in the idea that depression might also happen in non-human animals. Mendl, Fureix & Paul have a strong record of commitment to public engagement activities; we will continue working with the Bristol University Centre for Public Engagement to give talks at events (e.g. Pint of science, Science Café), festivals (e.g. Festival of Nature in coll. with the @-Bristol Science Centre; Brain Awareness Week in coll. with the cross-departmental Bristol Neuroscience group) & at schools (e.g. as part of the STEM ambassador scheme & via the Understanding Animal Research resources for schools). We will also join the Speakeeze platform to increase our visibility as speakers to be invited to be part of events. We will liaise with the Bristol University Public Relations Office to write press releases to accompany new project publications, & post non-technical summaries (public accessible) of our research aims and findings on the AWRN website.

Publications

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Description Collaboration with Belgian researchers to develop computer vision methods for data collection 
Organisation Free University of Brussels
Country Belgium 
Sector Academic/University 
PI Contribution We have supplied video recordings and stipulated our requirements for automated data collection for a behavioural test that we are developing.
Collaborator Contribution Our partners have started to develop a bespoke computer vision application to allow us to collect the data that we require from the videos and hence speed up, and standardise, behaviour recording.
Impact This is a multi-disciplinary collaboration. There are no outputs yet - the grant has just commenced.
Start Year 2017
 
Description University of Bristol 3Rs Symposium 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact We attended the 2nd University of Bristol 3Rs workshop and presented posters of our ongoing work in laboratory rodents and other species.
Year(s) Of Engagement Activity 2018