The persistence of a long-term negative affective state following the induction of either acute or chronic pain

Clinically, pain is a complex phenomenon consisting of both sensory and affective aberrations that call persist indefinitely. Preclinically, several animal paradigms have been established that reliably mimic both the acute and chronic aspects of pain pertinent to the human condition; however, the commonly Used behavioral models only assess the sensory component of pain elicited by an evoked nociceptive stimulus. Since the affective-motivational component of pain is an important determinant of the overall pain experience in man, we investigated how this aspect may be modeled long-term ill rats using novel objects and a modified conditioned place aversion (CPA) paradigm. Findings demonstrate that animals subjected to either neuropathic injury Or inflammatory insult display a significant conditioned place aversion to a pain-paired environment that is paralleled by all increased number of hind paw withdrawals and fewer number of novel object interactions during painful conditioning sessions. Moreover. this aversion is maintained for 1 month in the absence Of further conditioning. We also determined that a non-analgesic. non-rewarding dose of morphine administered prior to pain-paired conditioning sessions attenuates the pain-induced aversion and its relative persistence in both pain models. Together. these findings underscore the importance of negative affect accompanying, painful conditions and its long-term persistence even when the injury Or insult has resolved. Lastly. these results suggest how both sensory and affective aberrations associated with neuropathic- bind inflammatory-like conditions and the memory of Such known to impact quality Of life in man may be addressed pre-clinically in rodents. (C) 2008 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.