Pain-related aversion and Fos expression in the central nervous system in rats

Patients with chronic pain suffer from much more affective emotional disturbance than pain sensation. The present study examined Fos expression associated with pain-related aversion in rats, using formalin-induced conditioned place avoidance (F-CPA) test, which could distinguish pain emotion from pain sensation. When pain experience was retrieved, the rats with F-CPA produced rigorous emotion-like behaviors. As a result, more Fos-Ll neurons were observed in anterior cingulate cortex, retrosplenial cortex, insular cortex, parietal cortex area 2, frontal cortex area 1-3, claustrum, lateral septal area, amygdala, dorsomedial hypothalamic nucleus, central medial nucleus, paraventricular nucleus, superior colliculus, inferior colliculus and periaqueductal gray. The results for the first time mapped the brain regions associated with processing of pain affect and emotion in rats.