Cancer blues? A promising judgment bias task indicates pessimism in nude mice with tumors
Introduction
Of the 115+ million animals used annually in biomedical research [1], most are rodents. They are often used to model potentially distressing conditions like cancer, arthritis and psychiatric disorders (e.g. anxiety, depression). But even conventional practices like handling (e.g. [2]) and the use of small, non-enriched cages (e.g. [3], [4], [5]) can compromise their wellbeing. These welfare costs may modify experimental outcomes in undesired ways [6]. They also have ethical implications, especially given the poor replicability [7] and translatability of biomedical research [8], [9], [10]. Our focus here is a potential method for assessing affective states (emotions and long-term moods [11]) in mice: the most widely used vertebrate in both basic and translational research [12]. Such methods are important for assessing mouse welfare, as well as for understanding the neurobiological mechanisms underlying normal and pathological affective functioning.
In humans, affective states modulate the interpretation of ambiguous information, a phenomenon known as judgment bias (JB). JB refers to the way that individuals experiencing negative affect (e.g. anxiety, depression) can process ambiguous information (e.g. neutral facial expressions) ‘pessimistically’, as if negative, while individuals in positive states might demonstrate more ‘optimistic’ interpretations of the same ambiguous cues [see 13, 14-15]. In animal JB studies, optimism can be operationalized as increased expectations of reward when faced with ambiguous cues, and pessimism, by increased expectations of punishment [16]. Harding et al., [17] pioneered this method of animal JB assessment: rats trained that one cue predicts reward while another predicts punishment, were exposed to ambiguous (intermediate) cues. Rats exposed to unpredictable housing showed pessimistic JBs, treating the ambiguous cues as if predicting punishment. Since this seminal work, JB tasks have gained popularity as potentially powerful tools for assessing animal affect due to their sensitivity to changes in both valence and intensity of these states [18]. Thus JB tasks have been developed for a wide range of species (e.g. dogs, sheep, horses, honeybees), using a variety of cues (e.g. visual, olfactory, tactile), and across diverse fields of research (e.g. behavioral biology, neuroscience and animal welfare) [19,20].
For mice, however, validated JB tasks had remained elusive. Valid JB tasks must meet two technical criteria: that animals discriminate between positive and negative cues, and then interpret intermediate cues as ambiguous [20,21]. But like any putative indicator of affective state, they must also demonstrate construct validity: sensitivity to deliberate affect manipulations (c.f. [22,23]). For mice, previous efforts have either not attempted construct validation (5/16 experiments [24], [25], [26]), or attempted it and failed (11/16 experiments [27], [28], [29], [30], [31], [32], [33], [34]; Table S1). Here, we therefore aimed to validate a novel JB task, manipulating affective state through the use of highly preferred environmentally enriched cages [35], versus conventional cages known to induce stress [36], anxiety [37,38], and depression-like effects [36,39,40]. Environmental enrichment (modification of an animal's environment to improve well-being and meet species-specific needs [41]), has been used in neuroscience for decades for its positive effects in neuroplasticity and disease recovery [42]. Morphological and physiological changes in the brain due to enrichment have also been associated with improved welfare [43], and JB has been shown to be sensitive to the effects of enrichment in other species (e.g. rats [44,45]).
In a second experiment, we applied the newly validated task to mice with tumors, to assess its utility in biomedical research. It is well established that cancer can be debilitating when tumors cause pain and discomfort (e.g. [46]), and rodent welfare guidelines for oncology already focus on such harms (e.g. [47]). However, tumors are known to reduce human well-being at much earlier stages: tumors can induce depression-like feelings of sadness and hopelessness [48,49], even before cancer is diagnosed (e.g. [50,51]), thanks to elevated pro-inflammatory cytokines [52,53]. Mice with tumors likewise show signs of depression (e.g. increased anhedonia [54]). And again these reflect inflammatory responses [55], [56], [57], [58], and are manifest before clinical signs emerge [47,59]. However, these subtle changes have received negligible attention in mouse welfare guidelines. Nor have more nuanced measures of mood yet been developed for researchers interested in the translational benefits of mouse models of cancer. To bridge these research gaps, we thus aimed to assess mood in mice with tumors through changes in their judgment bias.
Section snippets
Ethical note
Both experiments were approved by institutional ethics committees. Experiment 1 (AUP #3700) complied with Canadian Council on Animal Care guidelines, and Experiment 2 (protocol number 42–1–14T) complied with Guidelines for the Welfare and Use of Animals in Cancer Research [47]. One C57BL/6NCrl was removed before testing for barbering a cagemate (Experiment 1), and one male nude mouse was removed due an eye abscess (Experiment 2). This report also meets ARRIVE (Animal Research: Reporting of In
Discussion
To our knowledge, Experiment 1 represents the first evidence of construct validation in a mouse judgment bias (JB) task. Although sometimes omitted (5 studies in Table S1), or downplayed [26,79,80], the construct validation of any new indicator of affective state is a crucial step. This is especially important for animal JB tasks, which differ greatly from the unconditioned human tasks that inspired them [21] and which, perhaps as a consequence, can sometimes produce counterintuitive results
Conclusion
In summary, this novel JB task appears to be a valid indicator of affective state in mice. For C57 and Balb females, CH animals showed predicted pessimistic responses to ambiguous cues when their latency to dig was assessed. For tumor-bearing nude mice, this task also indicated negative states through pessimistic responses to ambiguity, even before the occurrence of clinical signs of disease. Together, these results highlight the potential value of this novel murine JB task across diverse
Funding sources
An NSERC Natural Sciences and Engineering Research Council (Canada) Discovery grant to GJM (no. 05,828 / 145,607,139), and a grant from the National University of La Plata to MAA (Argentina) (no. 11/V253).
Acknowledgments
The authors would like to acknowledge that Experiment 1 was completed on the ancestral lands of the Attawandaron people and the treaty lands and territory of the Mississaugas of the Credit. The authors would also like to thank the mice, Dr. Jim Petrik for providing comments on the manuscript and our wonderful animal care technicians Michaela Randall and Michelle Cieplak.
References (94)
- et al.
Cognitive bias as an indicator of animal emotion and welfare: emerging evidence and underlying mechanisms
Appl. Anim. Behav. Sci.
(2009) - et al.
Environmental enrichment induces optimistic cognitive biases in pigs
Appl. Anim. Behav. Sci.
(2012) - et al.
Cognitive bias as an indicator of animal emotion and welfare: emerging evidence and underlying mechanisms
Appl. Anim. Behav. Sci.
(2009) The A to Z of statistics for testing cognitive judgement bias
Anim. Behav.
(2014)- et al.
Optimism, pessimism and judgement bias in animals: a systematic review and meta-analysis
Neurosci. Biobehav. Rev.
(2020) - et al.
Play and optimal welfare: does play indicate the presence of positive affective states?
Behav. Processes.
(2018) - et al.
Pavlovian influences on learning differ between rats and mice in a counter-balanced Go/NoGo judgement bias task
Behav. Brain Res.
(2017) - et al.
Technology or ecology? New tools to assess cognitive judgement bias in mice
Behav. Brain Res
(2019) - et al.
A test to identify judgement bias in mice
Behav. Brain Res.
(2012) - et al.
Effects of stereotypic behaviour and chronic mild stress on judgement bias in laboratory mice
Appl. Anim. Behav. Sci.
(2016)
Middle-aged mice with enrichment-resistant stereotypic behaviour show reduced motivation for enrichment
Anim. Behav.
Social and structural housing conditions influence the development of a depressive-like phenotype in the learned helplessness paradigm in male mice
Behav. Brain Res.
Where are you from? Female mice raised in enriched or conventional cages differ socially, and can be discriminated by other mice
Behav. Brain Res.
Stereotypic behaviour in standard non-enriched cages is an alternative to depression-like responses in C57BL/6 mice
Behav. Brain Res.
Why are enriched mice nice ? Investigating how environmental enrichment reduces agonism in female C57BL/6, DBA/2, and BALB/c mice
Appl. Anim. Behav. Sci.
Validation of hippocampal biomarkers of cumulative affective experience
Neurosci. Biobehav. Rev.
Environmental enrichment induces optimistic cognitive bias in rats
Anim. Behav.
Pre-treatment effects of peripheral tumors on brain and behavior: neuroinflammatory mechanisms in humans and rodents
Brain. Behav. Immun.
Cytokines and advanced cancer
J. Pain Symptom Manage.
Combined anxiety and depressive symptoms before diagnosis of breast cancer
J. Affect. Disord.
Depression in cancer: the many biobehavioral pathways driving tumor progression
Cancer Treat. Rev.
Depressive-like behaviours and decreased dendritic branching in the medial prefrontal cortex of mice with tumors: a novel validated model of cancer-induced depression
Behav. Brain Res.
Fluoxetine prevents the development of depressive-like behavior in a mouse model of cancer related fatigue
Physiol. Behav.
Cancer induces inflammation and depressive-like behavior in the mouse: modulation by social housing
Brain. Behav. Immun.
Hippocampal dysfunctions in tumor-bearing mice
Brain. Behav. Immun.
The antioxidant and immunomodulatory compound 3-[(4-chlorophenyl)selanyl]-1-methyl-1H-indole attenuates depression-like behavior and cognitive impairment developed in a mouse model of breast tumor
Brain. Behav. Immun.
Tumor growth increases neuroinflammation, fatigue and depressive-like behavior prior to alterations in muscle function
Brain. Behav. Immun.
The odour span task: a novel paradigm for assessing working memory in mice
Neuropharmacology
Reverse-translational biomarker validation of Abnormal Repetitive Behaviors in mice: an illustration of the 4P’s modeling approach
Behav. Brain Res.
Cholinergic modulation of olfactory pattern separation
Neurosci. Lett.
Are hungry sheep more pessimistic? The effects of food restriction on cognitive bias and the involvement of ghrelin in its regulation
Physiol. Behav
From house mouse to mouse house: the behavioural biology of free-living Mus musculus and its implications in the laboratory
Appl. Anim. Behav. Sci.
A shortened protocol for assessing cognitive bias in rats
J. Neurosci. Methods.
Mood and the speed of decisions about anticipated resources and hazards
Evol. Hum. Behav.
Measuring emotional processes in animals: the utility of a cognitive approach
Neurosci. Biobehav. Rev.
Environmental and genetic activation of a brain-adipocyte BDNF/Leptin axis causes cancer remission and inhibition
Cell
Wasted money in United States biomedical and agricultural animal research
Optimising reliability of mouse performance in behavioural testing: the major role of non-aversive handling
Sci. Rep.
Laboratory environments and rodents’ behavioural needs: a review
Lab. Anim.
The impact of the environment on laboratory animals
Improving housing conditions for laboratory mice: a review of “environmental enrichment
Lab. Anim.
Happy animals make good science
Lab. Anim.
The economics of reproducibility in preclinical research
PLoS Biol
Lost in translation: animal models and clinical trials in cancer treatment
Am. J. Transl. Res.
Estimation of clinical trial success rates and related parameters
Biostatistics
The significance of meaning: why do over 90% of behavioral neuroscience results fail to translate to humans, and what can we do to fix it?
ILAR J
Cited by (11)
Why does lifelong conventional housing reduce the sociability of female mice?
2022, Applied Animal Behaviour ScienceCitation Excerpt :Female laboratory mice are a useful model because conventional laboratory housing (‘CH’: the ubiquitous small barren cages used in laboratories) has profound impacts on their behaviour and welfare that could affect their social behaviours, in addition to the way that CH can increase agonism between cage-mates. First, conventionally housed mice exhibit some responses consistent with depressive-like states: learned helplessness (e.g. Fureix et al., 2016; Llorens-Martín et al., 2007; Nip et al., 2019), pessimistic judgement biases (Resasco et al., 2021) and depressive-like inactive but awake behaviour, in which they spend their active period standing still in the cage, doing nothing (‘IBA’ e.g. Fureix et al., 2016; Harper et al., 2015; Nip et al., 2019). Such mice could potentially find social interactions unrewarding, or even threatening, much like depressed humans (e.g. Amin et al., 1998; Goetz and Dweck, 1980; Reid et al., 2006).
Development of an IntelliCage-based cognitive bias test for mice
2023, Open Research EuropeEnriched environment-induced neuroplasticity in ischemic stroke and its underlying mechanisms
2023, Frontiers in Cellular NeuroscienceMouse breeding facilities in Argentina: Current state, challenges, and strengths in relation to animal welfare
2022, Frontiers in Veterinary Science
- #
These authors contributed equally to this work.