Long-Term Changes in Pain Sensitivity in an Animal Model

Animal models with an eco-ethological relevance can help in identifying novel and reliable stress-related markers. To this end, 3-month-old C57BL/6J male mice were exposed to social defeat (SD) stress for 10 days as this stressor shows good face and predictive validity for several models of human affective disorders including depression, social phobia and post-traumatic stress disorder. Social avoidance and pain threshold were assessed 24 h and 4 weeks after the end of SD stress, while corticosterone was assayed at the beginning and at the end of the stressful procedure (days 1 and 10). SD subjects were characterized by increased corticosterone levels (30 min following stress exposure), increased latency to approach the social target in the short-term as well as increased emotionality in the long-term. Moreover, an increase in nociceptive threshold (stress-induced analgesia) was found both in the short-term and 4 weeks after the end of stress. These data indicate that the SD paradigm is able to induce emotional changes associated with a stressful/traumatic event. In addition, they indicate that variations in the nociceptive threshold might represent a physiological marker of both shortand long-term effects of stress. OPEN ACCESS Vet. Sci. 2014, 1 78