Housing mice in the individually ventilated or open cages-Does it matter for behavioral phenotype?

Abstract

Individually ventilated caging (IVC) systems for rodents are increasingly common in laboratory animal facilities. However, the impact of such substantial change in housing conditions on animal physiology and behavior is still debated. Most importantly, there arise the questions regarding reproducibility and comparison of previous or new phenotypes between the IVC and open cages. The present study was set up for detailed and systematic comparison of behavioral phenotypes in male and female mice of three widely used inbred strains (C57BL/6JRccHsd, DBA/2JRccHsd, 129S2/SvHSd) after being kept in two housing environments (IVC and open cages) for 6 weeks (since 4 weeks of age) before behavioral testing. The tests addressed exploratory, anxiety-like and stress-related behavior (light-dark box, open field, forced swim test, stress-induced hyperthermia), social approach and species-specific behavior (nest building, marble burying). In all tests, large and expected strain differences were found. Somewhat surprisingly, the most striking effect of environment was found for basal body temperature and weight loss after one night of single housing in respective cages. In addition, the performance in light-dark box and open field was affected by environment. Several parameters in different tests showed significant interaction between housing and genetic background. In summary, the IVC housing did not invalidate the well-known differences between the mouse strains which have been established by previous studies. However, within the strains the results can be influenced by sex and housing system depending on the behavioral tasks applied. The bottom-line is that the environmental conditions should be described explicitly in all publications.

Keywords: IVC; behavior; environment; housing; inbred; mice; phenotyping; reproducibility; sex; species-specific.

Figure 1

A, Timeline of the experiment. The mice arrived at the age of 4 weeks and randomly assigned to either IVC or open cages (OC). After 5 weeks of adaptation (age of mice 5‐9 weeks), the behavioral test battery was carried out during 2 weeks (age of mice 10‐11 weeks): FST, forced swim test; LD, light‐dark test; MBT, marble burying test; Nest, nest building; OF, open field; SIH, stress‐induced hyperthermia; SOC, social approach. B, Body weight of male mice during the observation period (age 4‐11 weeks). C, Body weight of female mice during the observation period (age 4‐11 weeks). Data are expressed as mean ± SEM; N = 10 B6 males in open field (OC); N = 12 for all other groups

Figure 2

Results of anxiety‐like and exploratory behavior in the light‐dark box. A, Latency to the first entry from dark to light compartment. B, Total distance in travelled during 10 minutes of testing. C, Percentage of the distance travelled in the light compartment. D, Percentage of time spent in the light compartment during 10 minutes test. Data are expressed as mean ± SEM; N = 10 B6 males in open field (OC); N = 12 for all other groups

Figure 3

Results of exploratory behavior in the open field arena. A, Total distance travelled during 20 minutes of testing. B, Number of rearings during test. C, Distance travelled in 5‐minute intervals (males). D, Distance travelled in 5‐minute intervals (females). E, Percentage of time spent in the center of open field arena during 20 minutes of testing. F, Percentage of distance in the center of open field arena during 20 minutes of testing. Data are expressed as mean ± SEM; N = 10 B6 males in open field (OC); N = 12 for all other groups; *P < 0.05 Bonferroni post‐hoc comparison

Figure 4

Social approach. A, distance travelled during 10 minutes of testing. B, Time in social interaction zone (surrounding perforated cylinder with stimulus mouse). Data are expressed as mean ± SEM; N = 10 B6 males in open field (OC); N = 12 for all other groups

Figure 5

Species‐specific and stress‐related measures. A, Marble burying test—number of marbles completely hidden after 30 minutes. B, Nest construction—quality of the nest assessed in 5‐point scale. C, Change in body weight after single housing for one night—ratio between the second and initial measurements. D, Basal rectal temperature. E, Stress‐induced hyperthermia (difference between two measurements of rectal temperature in 10‐minute interval). F, Forced swim test—immobility in 2‐minute intervals, male mice. G, Forced swim test—immobility in 2‐minute intervals, female mice. Data are expressed as mean ± SEM; N = 10 B6 males in open field (OC); N = 12 for all other groups; *P < 0.05 Bonferroni post‐hoc comparison