LAUSR

Abstract The development of modern housing regimes such as individually ventilated cage (IVC) systems has become very popular and attractive in order to reduce spreading of pathogenic organisms and to lower the risk to develop a laboratory animal allergy for staff members. Additionally, optimal housing of laboratory animals contributes to improve animal health status and ensures high and comparable experimental and animal welfare standards. However, it has not been clearly elucidated whether 1) a change to IVC systems have an impact on various physiological phenotypic parameters of mice when compared to conventional, standard cages and 2) if this is further affected by changing from social to single housing. Therefore, we investigated the influence of a change in housing conditions (standard cages with social housing changed to standard or IVC cages combined with social or single housing) on body weight, behavior and a neurochemical fingerprint of male C57BL/6J mice. Body weight progression was significantly reduced when changing mice to single or social IVC cages as well as in single standard cages when compared to social standard housing. Automated motor activity measurement in the open field showed that mice maintained in social husbandry with standard cages displayed the lowest exploratory behavior but the highest activity difference upon amphetamine treatment. Elevated plus maze test revealed that a change to IVC single and social housing as well as single standard housing produced anxiety‐related behavior when compared to maintenance in social standard housing. Additionally, postmortem neurochemical analysis of the striatum using high‐performance liquid chromatography coupled to electrochemical detection showed significant differences in striatal dopamine and serotonin turnover levels. In summary, our data indicate a crucial influence of a change in housing conditions on several mouse phenotype parameters. We propose that the maintenance of well‐defined housing conditions is mandatory to ensure reproducible and comparable results and contributes to the application of the 3R refinement principle in animal studies by contributing to welfare and hygienical standards.