Physiological and behavioural adjustment of a wild rodent to laboratory conditions.

Wild animals are brought to captivity for different reasons, for example to be kept in zoos and rehabilitation centres, but also for basic research. Such animals usually undergo a process of adjustment to captive conditions. While this adjustment occurs on the behavioural and the physiological level, those are usually studied separately. The aim of this study was to assess both the physiological and behavioural responses of wild wood mice, Apodemus sylvaticus, while adjusting to laboratory conditions. Over the course of four weeks, we measured in wild-caught mice brought to the laboratory faecal corticosterone metabolites and body mass as physiological parameters, stereotypic behaviour and nest-quality, as welfare-linked behavioural parameters, and four personality measures as additional behavioural parameters. The results of our study indicate that mice exhibited an adjustment in both behaviour and physiology over time in the laboratory. While the hormonal stress response decreased significantly, body mass and the proportion of stereotypic behaviours showed a tendency to increase over time. The slight increase of stereotypic behaviours, although not statistically significant, suggests the development of repetitive and non-functional behaviours as a response to laboratory conditions. However, we suggest that those behaviours might have been used by animals as a coping strategy to decrease the physiological stress response. Other behavioural parameters measured, such as boldness and nestbuilding behaviour were stable over time. The information obtained in the present study hints at a complex interplay between behavioural and physiological adjustments of wild animals to laboratory conditions, which should be considered when intending to use wild animals in experimental research.

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).