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

Do white-footed mice, the main reservoir of the Lyme disease pathogen in the United States, clinically respond to the borrelial tenancy?

As white-footed mice, Peromyscus leucopus, are considered the primary animal reservoir of Borreliella burgdorferi sensu stricto (Bb), the main agent of Lyme disease (LD) in the United States, these animals represent the most relevant model to study borrelial spirochetes in the context of their natural life cycle. Previous studies have consistently demonstrated that although white-footed mice respond immunologically to the invasion of the Lyme pathogen, P. leucopus adults do not develop a clinically detectable disease. This tolerance, which is common for mammalian reservoirs of different pathogens, contrasts with detrimental anti-borrelial responses of C3H mice, a widely used animal model of LD, which always result in a clinical manifestation (e.g., arthritis). The current investigation is a follow-up of our recent study that already showed a relative quiescence of the spleen transcriptome for Bb-infected white-footed mice compared to the infected C3H mice. In an effort to identify the mechanism behind this tolerance, in this study, we have evaluated an extensive list of hematological and biochemical parameters measured in white-footed mice after their 70-day-long borrelial infection. Despite missing reference intervals for Peromyscus mice, our sex- and age-matched uninfected controls allowed us to assess the blood and serum parameters. In addition, for our assessment, we also utilized behavioral, immunological, and histological analyses. Collectively, by using the metrics reported herein, the present results have demonstrated clinical unresponsiveness of P. leucopus mice to the borrelial infection, presenting no restriction to a long-term host-pathogen co-existence.

Uncovering hidden prosocial behaviors underlying aggression motivation in mice and young children

BACKGROUND

Animals exhibit a wide range of social behaviors, including positive actions that promote social cohesion and negative behaviors associated with asserting dominance. While these behaviors are often viewed as opposites, they can also exist independently or coexist in complex ways, necessitating further investigation into their interrelationships.

RESULTS

To study the interplay between these two types of behaviors, we examined mouse social behaviors using resident-intruder assays and revealed a negative correlation between social aggression and prosocial allogrooming. Suppressing aggressive motivation through various manipulations, including social subordination, olfaction ablation, and inhibition of aggressive neural circuits, led to an increased display of allogrooming behavior. The mouse findings prompted us to further explore the relationship between aggression and prosocial behaviors in preschool children. Similarly, we observed a negative association between aggression and prosocial behaviors, which were potentially influenced by their inhibitory control abilities.

CONCLUSIONS

Through this cross-species study, we uncovered the inhibitory impact of aggressive neural circuits on mouse allogrooming and established a link between aggression and prosocial behaviors in children. These insights offer valuable implications for understanding and potentially influencing social interactions in both animal and human contexts, with potential applications in preschool education practices.

Novel enrichment reduces boredom-associated behaviors in housed dairy cows

There is currently societal interest and concern for dairy cow welfare. It has been suggested that boredom poses a welfare issue for dairy cows, particularly when presented with extended disposable time in housed environments that lack stimuli. Farm animals experience a multitude of affective states, which has created a need for positive experiences to be included in welfare management. Environmental enrichment can reduce boredom and facilitate positive experiences; however, the research in cows is limited. To assess the behavioral impact of a simple enrichment on commercially housed dairy cows, we provided 24-h access to a novel object, for 3 wk, for 2 separate groups of cows. Two boredom-associated behaviors significantly decreased when the object was present compared with when it was not present: "idling" behavior and unsuccessful robotic milking attempts ("refusals"). In addition, there was a significant increase in the occurrence of self-grooming during treatment weeks, when the novel object was present. These results suggest that idling and refusals may be behavioral indicators of boredom in dairy cows.

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.

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).

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.