Mouse strains differ markedly in all behaviors, independently of their genetic background. We undertook this study to disentangle the diurnal activity and feature key aspects of three non-genetically altered mouse strains widely used in research, C57BL/6NCrl (inbred), BALB/cAnNCrl (inbred) and CRL:CD1(ICR) (outbred). With this aim, we conducted a longitudinal analysis of the spontaneous locomotor activity of the mice during a 24-h period for 2 months, in two different periods of the year to reduce the seasonality effect. Mice (males and females) were group-housed in Digital Ventilated Cages (Tecniplast), mimicking standard housing conditions in research settings and avoiding the potential bias provided in terms of locomotor activity by single housing. The recorded locomotor activity was analyzed by relying on different and commonly used circadian metrics (i.e., day and night activity, diurnal activity, responses to lights-on and lights-off phases, acrophase and activity onset and regularity disruption index) to capture key behavioral responses for each strain. Our results clearly demonstrate significant differences in the circadian activity of the three selected strains, when comparing inbred versus outbred as well as inbred strains (C57BL/6NCrl versus BALB/cAnNCrl). Conversely, males and females of the same strain displayed similar motor phenotypes; significant differences were recorded only for C57BL/6NCrl and CRL:CD1(ICR) females, which displayed higher average locomotor activity from prepuberty to adulthood. All strain-specific differences were further confirmed by an unsupervised machine learning approach. Altogether, our data corroborate the concept that each strain behaves under characteristic patterns, which needs to be taken into consideration in the study design to ensure experimental reproducibility and comply with essential animal welfare principles.

小鼠品系在所有行为上都存在显着差异，与其遗传背景无关。我们进行了这项研究，以解开研究中广泛使用的三种非遗传改变的小鼠品系 C57BL/6NCrl（近交）、BALB/cAnNCrl（近交）和 CRL:CD1(ICR)（远交）的昼夜活动和特征关键方面。为此，我们在一年的两个不同时期对小鼠在 24 小时内的自发运动活动进行了纵向分析，为期 2 个月，以减少季节性影响。小鼠（雄性和雌性）被集体饲养在数字通风笼（Tecniplast）中，模仿研究环境中的标准住房条件，并避免单一住房在运动活动方面提供的潜在偏差。通过依赖不同且常用的昼夜节律指标（即，昼夜活动、昼夜活动、对开灯和关灯阶段的反应、高峰期和活动开始以及规律性中断指数）来分析记录的运动活动，以捕获关键的行为每个菌株的反应。我们的结果清楚地表明，在比较近交与远交以及近交菌株（C57BL/6NCrl 与 BALB/cAnNCrl）时，三种选定菌株的昼夜节律活性存在显着差异。相反，同一品系的雄性和雌性表现出相似的运动表型；仅在 C57BL/6NCrl 和 CRL:CD1(ICR) 雌性中记录到显着差异，从青春期前到成年期显示出更高的平均运动活性。通过无监督机器学习方法进一步证实了所有菌株特异性差异。总而言之，我们的数据证实了每个菌株在特征模式下行为的概念，需要在研究设计中考虑到这一点，以确保实验的可重复性并遵守基本的动物福利原则。