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Role of Opioid‐Sensitive Descending Pain Modulatory Pathways in Affective and Sensory Components of Chronic Pain in Rats
Author(s) -
Robles Dagoberto,
Gomtsian Lusine,
Navratilova Edita,
Porreca Frank
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.985.16
Subject(s) - chronic pain , neuropathic pain , morphine , opioid , medicine , sensory system , context (archaeology) , neuroscience , rostral ventromedial medulla , nociception , analgesic , anesthesia , hyperalgesia , anterior cingulate cortex , psychology , cognition , receptor , paleontology , biology
Pain is a complex, multidimensional experience that is composed of sensory, affective and cognitive features. For unknown reasons, in some individuals, pain may become chronic. Unfortunately, there are no cures for chronic pain. Opioids remain one of the most important classes of drugs to treat pain but whether they are useful in chronic pain remains uncertain. Additionally, these drugs have significant side effects including tolerance, dependence and addiction. As a result, there is an urgent medical need to elucidate the underlining mechanisms by which relief of pain occurs. Opioids produce their effects primarily by alleviating the aversive qualities of pain. How this occurs is not known but pain aversiveness is thought to be integrated, in part, in the anterior cingulate cortex (ACC). Cortical regions in the brain likely contribute to context dependent modulation of the pain experience through projections that ultimately converge on the rostral ventromedial medulla (RVM). Here, we determined the effects of microinjection of morphine in several regions of the rat ACC in rats with chronic experimental neuropathic pain induced by ligation of the spinal nerve (SNL model). The possible effect of ACC or RVM morphine on mechanical hypersensitivity was evaluated using von Frey filaments. Microinjection of morphine into different sites of the ACC failed to reverse mechanical hypersensitivity in nerve‐injured animals. In contrast, morphine injection in the RVM reversed evoked thresholds in SNL animals. These findings suggest that morphine may differentially modulate affective dimensions of pain within the ACC without altering sensory components. The primary goal of this research is to understand the nature of the neuroanatomical contributions of the ACC and its role in descending pain modulatory pathways. Further studies exploring other sites within the ACC with measures of affective qualities of pain may ultimately lead to a better understanding of opioid‐sensitive circuitry. Support or Funding Information Supported by DA034975 from the NIH.