Measuring Behavior 2005: Van den Harst et al.

Monitoring the effects of social defeat in mice by automated observation in the home-cage and observer-based scoring during a social-interest test

J.E. van der Harst, M. Lubbers, M. Eijkhoudt and B.M. Spruijt

Department of Animals, Science & Society, Utrecht University, Utrecht, The Netherlands

Social defeat in mice has been applied in several different paradigms and for several different reasons. However, as a model for depression it has only been studied on a few occasions. Mostly a long period of daily defeats is applied of which the effects are investigated immediately afterwards. Therefore, little is known about the time of onset and development of the effects of this chronic social stress. This study aimed to investigate the effects of a particular defeat-paradigm in mice during the long-term social-stress period of 20 days. For this, home cage behavior was automatically and continuously recorded during both the light and the dark phase in specially designed cages (PhenoTyper^®, Noldus Information Technology bv, The Netherlands). Several parameters that may reveal depressive-like symptoms such as altered locomotor activity and sleep/wake cycle were analyzed.

It became apparent that social defeat resulted in several acute effects (thus, at day 1) on activity, velocity and use of the shelter that were not all persistent over time. Other measures, such as a decreased frequency of movement and increased time spent in the shelter during the first part of the dark-phase seemed to become more persistent over time indicating chronic stress effects, possibly related to the development of depressive-like symptoms.

To further validate the applied defeat-paradigm as a model for depression, a so-called Partition-test was conducted at the end of the long-term defeat-period. During this test the defeated mouse was confronted with another unfamiliar mouse at the other side of a perforated partition-wall. This test is used in several depression-studies to investigate anxiety-related behavior and social interest. Using observer-based scoring (The Observer^®, Noldus Information Technology bv, The Netherlands), 2 classes were investigated in this test: zone and behavior.

It appeared that defeated animals displayed a significant decrease in social interest, activity and exploration and an increased alertness.

The results will be discussed in the light of the success of the applied social-stress paradigmas a model for depression in mice and the development and onset of the symptoms.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.