Mice with a natural microbiome are a promising research model for basic and applied science because of their closer resemblance to the human superorganism compared to mice born and raised under stringent hygiene conditions. Consequently, biomedical therapies developed and tested in “Wildling mice” hold great potential for successful translation into clinical applications. Over the past four years, scientists, veterinarians and institutional officials at Charité – Universitätsmedizin Berlin, supported by the University Hospital Erlangen, have designed a facility for Wildling mice and developed a conceptual framework for safe and ethical preclinical research involving mice with a natural microbiome.

The blood-brain barrier (BBB) poses a substantial obstacle to the successful delivery of therapeutics to the central nervous system (CNS). The transnasal route has been extensively explored, but success rates have been modest due to challenges related to the precise anatomical placement of drugs, the small volumes that the olfactory cleft can accommodate and short drug residence times due to mucociliary clearance. Here, to address these issues, we have developed a surgical technique known as the minimally invasive nasal depot (MIND), which allows the accurate placement of depot drugs into the submucosal space of the olfactory epithelium of rats. This technique exploits the unique anatomy of the olfactory apparatus to enable transnasal delivery of drugs into the CNS, bypassing the BBB. In our rat model, a bony window is created in the animal snout to expose the submucosal space. Using the MIND technique, we have successfully delivered oligonucleotides to the CNS in Sprague-Dawley and Long-Evans rats, leading to an upregulation of brain-derived neurotrophic factor in the substantia nigra and hippocampus. In this Protocol, we describe the procedural steps for MIND. This procedure takes about 45 min and can be performed by researchers with basic surgical skills. We additionally describe modifications to perform MIND in mice, which are anatomically smaller. The MIND procedure represents a unique platform that can be used to overcome the limitations posed by the BBB. This technique can potentially expand the therapeutic toolkit in the treatment of neurological diseases.

Many scientific breakthroughs have depended on animal research, yet the ethical concerns surrounding the use of animals in experimentation have long prompted discussions about humane treatment and responsible scientific practice. First articulated by Russell and Burch, the 3Rs Principles of Replacement, Reduction, and Refinement have gained widespread recognition as basic guidelines for animal research. Over time, the 3Rs have transcended the research community, influencing policy decisions, animal welfare advocacy and public perception of animal experimentation. Despite their broad acceptance, interpretations of the 3Rs vary substantially, shaping statutory frameworks at various levels, with both technical and practical impacts.

The translational value of the marble burying task (MBT) is debatable. Here we performed video analysis of behaviors during the MBT to accurately capture the details of all behaviors displayed during this task. Our results show that a count of marbles buried at the end of the task may not be a good translational correlate of the 'intentional marble burying' that the task is assumed to measure. Rather, the number of marbles buried may be measuring accidental marble burying due to 'rapid digging'. Video analysis during MBT provides a novel approach to characterize the many behaviors displayed during this task and may explain inconsistencies reported in the literature. However, the number of marbles buried at the end of the MBT may still have value as a screening test for anxiogenic or anxiolytic interventions. Any interventions that show significant alterations in the number of marbles buried can be pursued further through more robust and comprehensive behavior scoring methods.

Preclinical mouse models are extensively used in biomedical research to gain insight into disease mechanisms and to test new drug treatments. Glucose and insulin tolerance tests are simple experimental tests frequently used worldwide to assess glucose metabolism in mice. Various guidelines and methodological considerations have been published to help researchers standardize procedures and optimize research outcomes. Yet, there is still important experimental heterogeneity in the way these simple procedures are performed, with no real consensus on what the best practices are to achieve high-quality research and reproducible results. Here we critically examine several published guidelines and recent technical reports on how to perform these metabolic tests in laboratory mice and discuss the influence of various confounding factors on test results. We hope this work will help scientists establish more consensual guidelines for maximizing the relevance and clinical translation of studies using mouse models in metabolic research.

The laboratory mouse has been the premier model organism for biomedical research owing to the availability of multiple well-characterized inbred strains, its mammalian physiology and its homozygous genome, and because experiments can be performed under conditions that control environmental variables. Moreover, its genome can be genetically modified to assess the impact of allelic variation on phenotype. Mouse models have been used to discover or test many therapies that are commonly used today. Mouse genetic discoveries are often made using genome-wide association study methods that compare allelic differences in panels of inbred mouse strains with their phenotypic responses. Here we examine changes in the methods used to analyze mouse genetic models of biomedical traits during the twenty-first century. To do this, we first examine where mouse genetics was before the first inflection point, which was just before the revolution in genome sequencing that occurred 20 years ago, and then describe the factors that have accelerated the pace of mouse genetic discovery. We focus on mouse genetic studies that have generated findings that either were translated to humans or could impact clinical medicine or drug development. We next explore how advances in computational capabilities and in DNA sequencing methodology during the past 20 years could enhance the ability of mouse genetics to produce solutions for twenty-first century public-health problems.