Social defeat stress induced analgesia: short- and long-term effects on the nociceptive threshold in C57BL/6J male mice

Stress is a main risk factor for psychopathology. Understanding the etiopathogenesis of psychiatric disorders would benefit from developing animal models by means of stressors with an eco-ethological relevance, as well as from the identification of reliable stress-related markers. To this end, 3-month-old C57BL/6J male mice were exposed to chronic social defeat - SD - stress for 10 consecutive days; control subjects were group-housed. Corticosterone levels and nociceptive threshold were assessed in addition to short- (24 hrs) and long-term (4 weeks) memory by means of a previously described cognitive test (Berton et al., 2006). SD subjects are characterized by increased corticosterone levels, short-term memory for the SD and by increased emotionality on the long-term. Memory recall for the SD is associated to short-term increase in the nociceptive threshold (stress-induced analgesia) that remains unchanged 4 weeks following the end of stress. These data show that the SD paradigm is able to induce some cognitive and emotional aspects associated to the recall of a stressful event. In addition they suggest that variations in the nociceptive threshold might represent a main marker of short- and long-term effects of stress.