Korean J Physiol Pharmacol.  2009 Oct;13(5):357-360. 10.4196/kjpp.2009.13.5.357.

Social Isolation Selectively Increases Anxiety in Mice without Affecting Depression-like Behavior

• Kwak C
• Lee SH
• Kaang BK

• KMID: 1982568
• DOI: http://doi.org/10.4196/kjpp.2009.13.5.357

Abstract

It is hypothesized that a number of environmental factors affect animals' behavior. Without controlling these variables, it is very hard for researchers to get not only reliable, but replicable data from various behavioral experiments testing animals' cognitive as well as emotional functions. For example, laboratory mice which had restricted environment showed different synaptic potentiation properties with wild mice (Zhao MG et al., 2009). While performing behavioral experiments, however, it is sometimes inevitable that the researcher changes the animals' environments, as by switching the cages in which experimental animals are housed and separating animals raised together into small experimental groups. In this study, we investigated the effect of environmental changes on mice's emotional behaviors by socially isolating them or reducing the size of their cage. We found that social isolation selectively increases the animals' levels of anxiety, while leaving depression-like behaviors unchanged. On the other hand, alteration of the housing dimensions affected neither their anxiety levels nor their depression-like behaviors. These results suggest that environmental variables may have a prominent impact on experimental animals' emotional behaviors and possibly their psychological states, leading to bias in the behavioral data produced from experiments.

Keyword

Anxiety level; Social isolation; Housing environment; Experimental animals; Open field test; Tail suspension test; Forced swim test

MeSH Terms

Animals
Anxiety
Bias (Epidemiology)
Hand
Housing
Mice
Social Isolation

Figure

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  Fig. 1. Experimental design. (A) Procedure of behavior experiment. (B) Experimental groups. LtL, large to large cage; LtS, large to small cage; StS, small to small cage; LtiS, large to small cage, isolated; StiS, small to small cage, isolated.

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  Fig. 2. (A) The result of the open field (OF) test indicates that social isolation induced increasing anxiety levels (LtS vs. LtiS; LtS, 94.73±10.37 s, n=6; LtiS, 63.37±14.15 s, n=6; unpaired t-test, #p= 0.1041; StS vs. StiS; StS, 90.70±10.55 s, n=9; StiS, 52.53±11.03 s, n=6; unpaired t-test, ∗p=0.0317). (B) Not all mice showed different locomotion activity levels (one-way ANOVA, p=0.5529).

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  Fig. 3. In the tail suspension test (TST) and forced swim test (FST), groups didn't show notably different levels of depression-like behavior among groups (TST: LtL, 160.33± 7.38 s, n=6; LtS, 160.20±17.32 s, n=5; LtiS, 134.00±18.59 s, n=6; StS, 185.00± 9.10 s; StiS, 146.11±15.21 s, n=9; oneway ANOVA, p=0.3152. FST: LtL, 197.50±23.42 s, n=6; LtS, 184.16± 21.94 s; LtiS, 189.67±28.00 s, n=6; StS, 176.17±22.65 s, n=6; StiS, 171.33± 11.85 s, n=9; one-way ANOVA, p=0.8973).

Reference

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