A new mouse model to study the empathic fear and pain behavior / 中国药理学与毒理学杂志

ABSTRACT

OBJECTIVE Human beings possess the ability to indirectly acquire the emotions of others.This also known as emotional contagion or empathy,enables us to rapidly perceive the emotions of others.However,an excessive empathy may result in heightened fear and sensitivity to pain.Therefore,the establishment of appropri-ate animal models for analyzing neural mechanisms underlying empathy would contribute to pharmacological research on pain sensitivity caused by psychological sus-ceptibility.METHODS We used the observed fear para-digm for assessing contagion of negative emotions in mice.To minimize the impact of emotional contagion dif-ferences caused by the subject change,we established a bilateral observation area and the two mice were trained to observe fear simultaneously.First,two observer(OB)mice were placed on either side of the observational area.Next,a demonstrator(DM)mouse was introduced into the cylindrical shock cage located at the center of the apparatus.The shock cage is made of transparent organic plastic with air holes and has provided ample space for free movement by the DM mouse.During the shock stage,DM mice were subjected to electric stimulation while the behaviors of OB mice on both sides was observed,including freezing,the side and corner time,social interaction behavior.Additionally,c-Fos staining was utilized to confirm distinct local brain activities.RESULTS In the habituation stage,OB mice on both sides showed more social preference for DM mouse,as evidenced by an increase in duration time in the designat-ed interaction zone.During the shock phase,OB mice observed the DM mouse receiving electric shocks and displayed significantly higher levels of fear contagion;however,their fear behavior was not entirely consistent.Some mice exhibited a significant increase in freezing time,while others demonstrated a significant increase in corner and side exploration time.We utilized Z-normal-ization to evaluate changes in emotionality across vari-ous behaviors and identified mice with distinct susceptibil-ities.Fos-positive neurons exhibited higher expression levels in susceptible OB mice,primarily concentrated within brain regions associated with the ascending path-ways of pain perception,such as thalamus,the anterior insular cortex,and anterior cingulate cortex.CONCLU-SION In this study,we have developed an innovative experimental facility that integrates various behavioral tests to evaluate empathic behavior in mice.Our findings highlight the robustness of emotionality measures obtained from individual mice by combining this experi-mental model with the Z-scoring method,facilitating screening for empathic fear or pain-susceptible mice and will helpful for pharmacological evaluation.