The pain history was an important predictive factor of future pain-related distress. Previous animal studies have illustrated the modulatory effect of neonatal pain experience on subsequent pain-related behaviors. However, the relationship between chronic pain status in adulthood and future pain perception remains unclear. In the current study, we investigated the effects of previous chronic inflammatory pain on the subsequent formalin-evoked pain behaviors and cue-elicited anticipatory responses in adult rats. In addition, a multi-channel single-unit recording technique was used to investigate the possible mechanism underlying the effect of pain experience on pain-related expectation in healthy rats. Four important findings emerged from this study: 1. We demonstrated an increase of the second but not the first phase of the formalin-induced pain behaviors in animals with a history of recovered chronic inflammatory pain. 2. Rats with a chronic pain experience also displayed a facilitated acquisition, an elevated anticipatory response, and a persistent retention of pain-related conditioning behaviors. The hyperalgesia in the late phase of the previous inflammatory pain that correlated with the level of sustained high vigilance. 3. The long-term detrimental influences of prior pain experience could be successfully prevented by successive morphine administration at the early stage of chronic pain. 4. Prior chronic mild stress inhibited subsequent the acquisition and retention of pain-related conditioned response, which was significant correlated with the degree of stress. 5. Under anticipation condition, the neuronal activities to actual noxious stimuli were enhanced in all the recorded areas, including mPFC, BLA, SI and VPL. 6. The repetition of noxious laser stimulation significantly not only resulted in the reinstatement of conditioned response but also the increase in the neuronal activities to auditory cue in BLA and SI areas. The cross-correlation analysis also demonstrated the increase in correlated neuronal activities between BLA, mPFC, and SI after repetition of noxious laser stimulation. In conclusion, it is the first report that chronic pain history exacerbated the subsequent spontaneous pain in adult rats, and exerted long-term effects on the anticipatory and affective response related to pain. All the long-term detrimental effects of chronic pain could be effectively prevented by early-stage pain relief. We first confirmed that the extent of hyperalgesia in the late stage of previous chronic pain was a good tool for prognosis of future susceptibility to pain disorders. In addition to basolateral amygdala, for the first time, we found that the CS-induced neuronal activities in primary somatosensory cortex could be reshaped by pain experience.
修改评论