The effects of group and single housing and automated animal monitoring on urinary corticosterone levels in male C57BL/6 mice

Abstract

Mice are used extensively in physiological research. Automated home-cage systems have been developed to study single-housed animals. Increased stress by different housing conditions might affect greatly the results when investigating metabolic responses. Urinary corticosteroid concentration is considered as a stress marker. The aim of the study was to compare the effects of different housing conditions and an automated home-cage system with indirect calorimetry located in an environmental chamber on corticosterone levels in mice. Male mice were housed in different conditions and in automated home-cage system to evaluate the effects of housing and measuring conditions on urine corticosterone levels. Corticosterone levels in single-housed mice in the laboratory animal center were consistently lower compared with the group-housed mice. Single-housed mice in a separate, small animal unit showed a rise in their corticosterone levels a day after they were separated to their individual cages, which decreased during the following 2 days. The corticosterone levels of group-housed mice in the same unit were increased during the first 7 days and then decreased. On day 7, the corticosterone concentrations of group-housed mice were significantly higher compared with that of single-housed mice, including the metabolic measurement protocol. In conclusion, single housing caused less stress when compared with group-housed mice. In addition, the urine corticosterone levels were decreased in single-housed mice before the metabolic measurement started. Thus, stress does not affect the results when utilizing the automated system for measuring metabolic parameters like food and water intake and calorimetry.

Keywords: metabolic measurements; mice; stress; urinary corticosterone.

Figure 1

The experimental protocol.

Figure 2

Effect of circadian rhythm on urine corticosterone levels. Corticosterone level (mg/mmol creatinine) of mice urine at different time points in a day. Each value represents the mean ± SEM for three mice. Value with * is significantly different at P < 0.05 by one‐way ANOVA followed with Tukey's multiple comparisons test.

Figure 3

The effect of different housing condition on urine corticosterone levels. Urine corticosterone level (mg/mmol creatinine) of different housing condition of mice. Each value represents the mean ± SEM for nine (group) and eight (single) mice. Value with *** is significantly different at P < 0.01 by Student's t test.

Figure 4

Effect of different housing condition and measuring metabolic performance in an environmental chamber on mice stress. Urine corticosterone level (mg/mmol creatinine) of different housing condition of mice. Each value represents the mean ± SEM for eight mice. At day 0, **P < 0.01 for group housed versus monitoring system; at day 7, **P < 0.01 for group housed versus monitoring system and **P < 0.0001 for group housed versus single housed.

Figure 5

Physiological and behavioral measurements demonstrated normal pattern for food and water consumption and total activity (n = 8, mean ± SEM). In all figures, the light (L) and dark (D) periods are separated with dashed lines.

Figure 6

Body weights of mice with different housing conditions. (A) Body weights of group‐housed and single‐housed mice in laboratory animal center. (B) Body weights of group‐housed, monitoring system, and single‐housed mice.