Environmental enrichment (EE) is widely accepted as a way to improve laboratory rodent wellbeing, but less is known with regards to its impact on zebrafish. Although several studies have shown positive effects of EE in zebrafish, some studies have yielded contradictory results due to variations in the EE protocols applied. In a new Article, Gallas-Lopes et al. performed a systematic review of the literature to summarize available evidence on the effects of EE on zebrafish.

See Marcon et al.

The Nile rat model, which develops diet-induced diabetes on conventional rodent chow, is highly valuable for mechanistic studies of type 2 diabetes. Applying metabolomic profiling on this model, Anderson et al. showed that non-fasted plasma sampling has some advantages when compared with fasted sampling, including lower replicate variance. On the cover, a photo of a pre-diabetic female Nile rat.

See Toh et al.

Bioluminescence imaging (BLI) using luciferase reporters is a useful method for the noninvasive visualization of molecular and cellular behaviors in living animals. Nakashiba et al. generated and characterized two new reporter mouse lines for BLI using the highly bright luciferases oFluc and Akaluc. These strains can be used in combination with a variety of Cre-driver mice to study various biological processes in vivo.

See Nakashiba et al.

Over 40% of SARS-CoV-2-infected individuals experience lasting neurological issues; suitable animal models are needed to better understand these issues. In a new Perspective, Usai et al. provide an overview of the animal models that are available to mimic human post-COVID-19 condition, with a focus on neurological symptoms.

See Usai et al.

Colony management of gene-modified animals is time-consuming, costly and affected by random events related to Mendelian genetics, fertility and litter size. In a new Article, Milchevskaya, Bugnon et al. developed an R package that enables the estimation of group size required for mouse breeding, taking into account Mendelian genetics, fertility and litter size.

See Milchevskaya, Bugnon et al.

Humanized mouse models with human fetal-derived hematopoietic system and lymphoid tissues are well-established, but ethical constraints and difficulties to access human fetal tissues limit their use. In a new Protocol, Del Rio, Huang et al. describe the development of the NeoThy mouse model, a humanized mouse model that incorporates neonatal thymus tissue and umbilical cord blood hematopoietic stem cells as non-fetal human tissue sources.

See Del Rio et al.

Housing laboratory rodents in individually ventilated cages (IVCs) improves the environment of both animals and lab personnel, but ammonia build up might go undetected in IVCs. In a new article, Eskandarani et al. sampled mouse IVCs in their facility for ammonia levels. They found that smaller Type II IVCs accumulated more ammonia than larger Type III IVCs, with several Type II cages showing ammonia levels > 50 ppm.

See Eskandarani et al.

Male mice have been the default in scientific experiments for decades, based on the assumption that hormonal fluctuations across the estrous cycle make females more variable than males. In a News & Views this month, Bronwyn Graham discusses recent findings showing that the estrous phase had little effect on the exploratory behavior of female mice, and that female mice were actually less variable than males.

See Graham

In vivo cardiac electrophysiology studies in mice are useful for studying the mechanisms of cardiac arrhythmias and identifying therapies. However, most procedures are invasive and require anesthesia, which can affect cardiac parameters. In a new article, Tomsits et al. compared the effects of two narcosis regimens on mouse cardiac electrophysiology to determine which regimen is more suitable for electrophysiology and arrhythmia studies.

See Tomsits et al.

Housing and husbandry conditions are known to affect animal welfare and research outcomes. In a new article, Neville et al. conducted a mapping review of refinements to laboratory rat housing and husbandry, and identified specific interventions that are likely to generate welfare improvements.

See Neville et al.

Social isolation is known to alter social behaviors in mice, but the underlying mechanisms are unclear. In a new article, Zhang et al. identify early growth response 2 (Egr2/Krox-20) in the medial prefrontal cortex as a major target of social isolation and resocialization, and uncover its critical role in the development mouse social and cooperative behaviors.

See Zhang et al.

Septic arthritis is a serious type of joint infection, often caused by Staphylococcus aureus. The infection can lead to rapid joint destruction and associated morbidity and mortality, particularly in cases of methicillin-resistant S. aureus (MRSA) infections. In a new protocol, Kwon et al. describe a mouse model of septic arthritis via direct inoculation of MRSA into the knee joint; the authors also detail methods for mouse serum, synovial fluid and knee joint tissue analysis that can be used to evaluate new therapies.

See Kwon et al.