Low emotional contagious behavior induces PTSD susceptibility in observers and is related to the regulation of oxytocin receptor in mice

Background: Post-traumatic stress disorder (PTSD) is a serious psychiatric disorder that occurs after an individual has witnessed or experienced a major traumatic event. Emotional contagion seems to play an important role in witnessing trauma, highlighting the importance of understanding the neurobiological consequences of psychological or emotional stress and its impact on the individual's mental health. Therefore, understanding the relationship between emotional contagion and PTSD susceptibility and the abnormal neurobiological and behavioral changes behind it could help find effective molecular treatment targets.

Methods: The formalin pain test was used to distinguish the level of emotional contagion in observer mice, dividing them into quartiles according to their pain response. The upper and lower quartiles were the emotional contagion-prone (ECP) and -resistant (ECR) groups, respectively. The vicarious social defeat stress (VSDS) procedure was used to establish PTSD models in mice with various emotional contagion levels when witnessing stress. Open field, elevated plus maze, social interaction test, and forced swimming test were used to examine PTSD-like symptoms. Changes in the medial prefrontal cortex (mPFC) mRNA expression of brain-derived neurotrophic factor (BDNF) and oxytocin receptor (OTR) were detected by qPCR, and their protein levels were analyzed by Western blot and immunofluorescence staining.

Results: The formalin pain test induced emotional contagion behaviors in mice between the ECP and ECR levels. The VSDS procedure resulted in PTSD symptoms in mice; mice in the lowest quartile were characterized by high levels of anxiety, depression, and social avoidance behaviors, such as decreased autonomous activity and residence time in the open field test or open arms position and increased immobility time and social avoidance behavior. These were accompanied by reduced OTR and BDNF protein expression levels and fluorescence intensity, as well as reduced OTR and BDNF mRNA levels in the mPFC.

Conclusions: Emotional contagion can induce PTSD-like behavior in mice that witnessed stress. Low emotional contagion behavior increased PTSD susceptibility in the observer mice and might be related to the regulation of their oxytocin receptors.