Inhibitory avoidance learning in CD1 mice: Effects of chronic social defeat stress

• A moderate degree of CSDS (chronic social defeat stress) enhances inhibitory avoidance in post-pubertal mice.
• A moderate degree of CSDS has no significant effects on inhibitory avoidance in adult mice.
• A high degree of CSDS prevents the memory formation of inhibitory avoidance in post-pubertal mice.
• The effects of CSDS on memory are not secondary to motor or emotional effects of stress.
• CD1, instead of C57BL/6J, has been shown to be a valid strain for the stressed mice in the CSDS protocol.

Chronic social defeat stress (CSDS) is an animal model widely used to determine the neurobiological mechanisms of stress and its associated pathologies. In this study, the effects of CSDS on inhibitory avoidance (IA) were evaluated in post-pubertal and adult male CD1 mice, instead of the C57BL/6J strain used in the CSDS standard protocol. CSDS consisted of daily 5-min (experiments 1 and 2) or 10-min (experiment 3) agonistic encounters on 21 consecutive days. Twenty four hours after the last session of CSDS, all the mice were tested for IA. They were also evaluated in an elevated plus-maze, obtaining complementary measures of locomotor activity and emotionality. In experiments 1 and 2, IA learning was confirmed in both non-stressed and stressed groups, showing stressed post-pubertal mice higher test latencies than controls. In experiment 3, IA was confirmed in the non-stressed but not in the stressed group. In conclusion, a moderate degree of CSDS (5-min encounters) enhances memory in post-pubertal but not in adult mice, while a high degree (10-min encounters) prevents the memory formation of IA in mice. These effects of CSDS on memory are not secondary to motor or emotional effects of stress. Furthermore, CD1 has been shown to be a valid strain for the stressed mice in the CSDS model.