Do housing-induced changes in brain activity cause stereotypic behaviours in laboratory mice?

Abnormal repetitive stereotypic behaviours (SBs) (e.g. pacing, body-rocking) are common in animals with poor welfare (e.g. socially isolated/in barren housing). But how (or even whether) poor housing alters animals' brains to induce SBs remains uncertain. To date, there is little evidence for environmental effects on the brain that also correlate with individual SB performance. Using female mice from two strains (SB-prone DBA/2s; SB-resistant C57/BL/6s), displaying two forms of SB (route-tracing; bar-mouthing), we investigated how housing (conventional laboratory conditions vs. well-resourced 'enriched' cages) affects long-term neuronal activity as assessed via cytochrome oxidase histochemistry in 13 regions of interest (across cortex, striatum, basal ganglia and thalamus). Conventional housing reduced activity in the cortex and striatum. However, DBA mice had no cortical or striatal differences from C57 mice (just greater basal ganglia output activity, independent of housing). Neural correlates for individual levels of bar-mouthing (positive correlations in the substantia nigra and thalamus) were also independent of housing; while route-tracing levels had no clear neural correlates at all. Thus conventional laboratory housing can suppress cortico-striatal activity, but such changes are unrelated to SB (since not mirrored by congruent individual and strain differences). Furthermore, the neural correlates of SB at individual and strain levels seem to reflect underlying predispositions, not housing-mediated changes. To aid further work, hypothesis-generating model fit analyses highlighted this unexplained housing effect, and also suggested several regions of interest across cortex, striatum, thalamus and substantia nigra for future investigation (ideally with improved power to reduce risks of Type II error).

A call to implement preclinical study registration in animal ethics review.

Protocol registration is required in clinical trials. Registration of animal studies could improve research transparency and reduce redundancy, yet uptake has been minimal. Integrating study registration into institutional approval of animal use protocols is a promising approach to increase uptake.

Waking inactivity as a welfare indicator in laboratory mice: investigating postures, facial expressions and depression-like states.

Animal welfare assessment relies on valid and practical indicators of affect. In mice, the most widely used research vertebrates, lying still with eyes open, inactive-but-awake (IBA) in the home cage, has potential to be one such indicator. IBA is elevated in barren, conventional housing compared with well-resourced, enriched housing, and predicts immobility in Forced Swim Tests, a common measure of 'helplessness' in depression research. In Experiment 1, using females from three strains (C57BL/6, Balb/c and DBA/2), we first replicated past findings, confirming higher levels of IBA in conventional cages and a positive relationship between IBA and helplessness. We then extended this research to three other signs of depression: changes in weight and sleep, and reduced hippocampal volume. Here, IBA positively covaried with body mass index, with sleep in DBA/2s and conventionally housed BALB/cs, and negatively covaried with hippocampal volume in conventionally housed C57BL/6s. In Experiment 2, we sought to refine the phenotype of IBA to improve its accuracy as a welfare indicator. Here, scoring IBA performed in hunched postures appeared to improve its accuracy as an indicator in Balb/c mice. Additional research is now needed to further refine the phenotype of IBA and to confirm whether it reflects states consistent with depression, or instead other underlying poor welfare conditions.

Assessment of Mouse Judgment Bias through an Olfactory Digging Task.

Judgment biases (JB) are differences in the way that individuals in positive and negative affective/emotional states interpret ambiguous information. This phenomenon has long been observed in humans, with individuals in positive states responding to ambiguity 'optimistically' and those in negative states instead showing 'pessimism'. Researchers aiming to assess animal affect have taken advantage of these differential responses, developing tasks to assess judgment bias as an indicator of affective state. These tasks are becoming increasingly popular across diverse species and fields of research. However, for laboratory mice, the most widely used vertebrates in research and a species heavily relied upon to model affective disorders, only one JB task has been successfully validated as sensitive to changes in affective state. Here, we provide a detailed description of this novel murine JB task, and evidence of its sensitivity to mouse affect. Though refinements are still necessary, assessment of mouse JB opens the door for answering both practical questions regarding mouse welfare, and fundamental questions about the impact of affective state in translational research.

Where are you from? Female mice raised in enriched or conventional cages differ socially, and can be discriminated by other mice.

Laboratory rodents raised in environmentally-enriched (EE) cages differ behaviourally and cognitively from conventionally-housed (CH) animals. We hypothesised that mice can detect such differences, testing this using differentially-raised female C57BL/6 s as subjects, and differentially-raised female BALB/cs and DBA/2 s as stimuli, in Social Approach Tests. Because more prone to signs of depression, anxiety, stereotypic behaviour (SB) and aggression, we further hypothesised that CH mice would be less sociable and socially attractive than EE mice. A novel familiarisation paradigm pre-exposed subjects to non-cagemate EE and CH stimulus mice before testing in Social Approach Tests. CH subjects proved less sociable than EE subjects: an effect unrelated to general exploration, anxiety or depression-like traits, and driven specifically by reduced interest in CH stimulus mice. Providing further evidence that CH and EE stimulus mice could be distinguished, subjects proved most attracted to mice from housing unlike their own. CH subjects thus preferred EE over CH stimulus mice, while EE subjects tended to prefer CH over EE: patterns that were not mediated by any measured aspect of stimulus mouse behaviour. Differential bodyweight also seemed unimportant, as was scent: soiled CH and EE bedding/nesting did not elicit the same discrimination. Instead, subjects who avoided CH stimulus mice and were attracted to EE stimulus mice were those who received the most agonism in their home cages. Together this provides the first demonstration that mice can distinguish between individuals raised in enriched or conventional cages, and suggests that receiving agonism from cagemates may motivate mice to seek new, less aggressive companions.