Much variation of individual pains has been demonstrated to result from the integration of their past experiences and future predictions about noxious stimulation. Previous animal studies indicated that neonatal pain experiences produce long-lasting and potentially detrimental alterations in the nociceptive system, leading to aberrant pain sensitivity in adult age. (This effect can be attributed to the high plasticity in the neonatal central nervous system.) However, whether the chronic pain experience in adulthood persons can shapes their future pain perception and pain-related cognition remains unclear.
Evolving around this concern, Professor Luo Fei’s team from the Key Laboratory of Mental Health in the Institute of Psychology has conducted a series of studies to answer the above question. They examined the effects of CFA-induced inflammatory pain on subsequent acute spontaneous pain behaviors (formalin injection-evoked pain) and pain-related conditioning induced by noxious laser stimulation in adult rats. They found an increase in the second but not the first phase activity following formalin injection in rats with a history of CFA inflammatory pain. The second phase of formalin pain is presumed to have a motivational-affective component as compared to the first phase. Therefore, the results indicate that prior chronic pain experience facilitates the subsequent affective pain processing rather than the nociceptive afferents.
Moreover, in the tone-laser conditioning experiment, the rats with pain history displayed facilitated acquisition and prolonged retention of the pain-related conditioning, which persisted more than 8 weeks. Intriguingly, a stage-specific effect of pain history was found on the long-term pain-related anticipation. Significant negative correlations were found between the late stage of CFA-induced inflammation (days 7–28) and the conditioned response, rather than the early stage (days 1-3), indicating that the pain sensitivity in the recovery period of previous chronic pain could predict the future response to environmental alarming stimulations.
The above results suggest that chronic pain diseases in adulthood, if not properly and promptly treated, may have a long-lasting impact on the processing and perception of environmental threats. This may increase the susceptibility of patients to subsequent pain-related disorders. These data also provide new evidence in the adult neural plasticity related to pain processing, and highlight the importance of treatment of chronic pain at an early stage.
This work has been published on the journal PLoS ONE and supported the NNSF grants (30970959, 61033011, and 31171067), the Knowledge Innovation Project from the Chinese Academy of Sciences (KSCX2-EW-Q-18, YZ200944, KSCX2-YW-R-254, and KSCX2-EW-J-8) :
Li S-G, Wang J-Y*, Luo F* (2012) Adult-Age Inflammatory Pain Experience Enhances Long-Term Pain Vigilance in Rats. PLoS ONE 7(5): e36767.
doi:10.1371/journal.pone.0036767.
