The effect of housing conditions on working memory and anxiety in male C57BL/6 mice

Abstract

Event Abstract Back to Event The effect of housing conditions on working memory and anxiety in male C57BL/6 mice An Buckinx1*, Andries Van Schuerbeek1*, Yana Van Den Herrewegen1, Ilse Smolders1 and Dimitri De Bundel1* 1 Experimental Pharmacology (EFAR/FASC), Vrije Universiteit Brussel, Belgium Laboratory mice are often single housed during experiments due to protocol requirements or in case of aggression towards cage mates. Several conflicting studies exist regarding behavioral consequences of individual housing of mice. However, the overall suggestion is that individual housing of mice is associated with increased anxiety and memory impairments (1, 2), and may affect scientific endpoints of experiments. In an attempt to reduce negative effects associated with single housing, we wanted to explore the potential use of a new type of cage that could improve animal welfare. This cage includes a cage divider that separates mice, as such avoiding physical contact while maintaining olfactory contact. The aim of this study is therefore to investigate anxiety and memory processing in mice housed in this new cage set-up compared to mice that are paired housed and single housed. 8-week-old male C57BL/6 mice were paired housed, single housed, or housed in a cage with a cage divider for a duration of four weeks, after which we performed behavioral tests, fear conditioning and the dexamethasone suppression test to assess plasma corticosterone levels. First, we performed the Y maze spontaneous alternation test, a test that is used to assess working memory, locomotor activity and exploratory drive in mice (2). The total number of arm entries and the spontaneous alternation percentage did not differ between the three groups. The open field test revealed no difference between the three experimental groups regarding locomotor activity nor anxiety-like behavior. An elevated plus maze test was performed to evaluate anxiety-like behavior. The total time spent in the open arms and the total distance travelled did not differ between groups, confirming the results obtained in the previous test. We performed a discriminative fear conditioning protocol (3), in which no significant differences were observed between experimental groups. The dexamethasone suppression test was performed at the end of the experiment to evaluate the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis (4, 5). Dexamethasone-treated mice had significantly lower corticosterone plasma levels compared to vehicle-treated mice, while basal corticosterone levels did not differ between groups. We dissected the adrenal glands and pituitary gland for further analysis, as the weight of the adrenal glands is associated with anxiety and stress (6). The weight of the pituitary gland and adrenal gland normalized against body weight did not significantly differ between experimental groups. Our results suggest that four weeks of single housing did not affect anxiety nor working memory in single housed mice, a much-debated topic in view of animal welfare. Behavioral observations were consistent with serum corticosterone levels, as the dexamethasone suppression test suggested no HPA axis dysregulation in neither of the experimental conditions. These results are possibly due to the short duration of housing conditions as previous studies were able to demonstrate differences in anxiety-like behavior, memory impairments and an increase in locomotor activity after eight weeks of single housing (1, 2). Therefore, future perspectives are to evaluate anxiety-like behavior and working memory after a housing duration of ten weeks. This will enable us to more effectively study the potential use of the cage with a cage divider that could improve animal welfare. * These authors contributed equally to this work.