Abstract
Introduction: Single housing of laboratory mice is a common practice to meet experimental needs, or to avoid intermale aggression. However, single housing is considered to negatively affect animal welfare and may compromise the scientific validity of experiments. The aim of this study was to investigate whether the use of a cage with a cage divider, which avoids physical contact between mice while maintaining sensory contact, may be a potential refinement strategy for experiments in which group housing of mice is not possible.Methods: Eight-week-old male C57BL/6JRj mice were single housed, pair housed or pair housed with a cage divider for four (experiment 1) or ten (experiment 2) weeks, after which we performed an open field test, Y-maze spontaneous alternation test, elevated plus maze test, an auditory fear conditioning task, and assessed responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis.Results: Housing conditions did not affect body weight, exploratory activity, anxiety, working memory, fear memory processing or markers for HPA-axis functioning in either experiment 1 or experiment 2. There was an increased distance traveled in mice housed with a cage divider compared to pair housed mice after 4 weeks, and after 10 weeks mice housed with a cage divider made significantly more arm entries in the Y-maze spontaneous alternation test.Conclusion: Taken together, our study did not provide evidence for robust differences in exploratory activity, anxiety, working memory and fear memory processing in male C57BL/6JRj mice that were single housed, pair housed or pair housed with a cage divider.
Highlights
Single housing of laboratory mice is a common practice to meet experimental needs, or to avoid intermale aggression
In this study we aimed to investigate the effects of long-term single housing, pair housing and pair housing with a cage divider on exploratory activity, anxiety, working memory, fear memory processing and HPA-axis activity in C57BL/6JRj mice
The time spent in the center zone, a measure to evaluate anxiety-like behavior, was not significantly different between housing conditions in experiment 1 [F(2, 27) = 2.064, P = 0.1465; Figure 3B] and experiment 2 [F(2, 27) = 1.403, P = 0.2633; Figure 3G]
Summary
Single housing of laboratory mice is a common practice to meet experimental needs, or to avoid intermale aggression. Male wild mice live solitary to establish territory, and if successful, in polygamous groups comprising a dominant male, several females and their offspring (Latham and Mason, 2004) This natural social behavior of male mice is challenging to replicate in a laboratory setting. Male mice housed in single sex groups will form despotic hierarchies with dominant-subordinate relationships (Williamson et al, 2016; Kappel et al, 2017) This can lead to inter-individual aggression, and the inability to escape from the aggressor in a confined cage can lead to stress, injuries, pain and even death (Weber et al, 2017; Lidster et al, 2019). The potential benefits of single housing should be weighed against the social needs of mice (Van Loo et al, 2003)
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