Journal
EUROPEAN JOURNAL OF PAIN
Volume 14, Issue 5, Pages 487-495Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ejpain.2009.08.009
Keywords
Pain; Cannabinoid; Conditioned fear; cFos; Rimonabant (SR141716A)
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Funding
- Irish Health Research Board
- Science Foundation Ireland
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The basolateral amygdala (BLA) contains a high density of cannabinoid CB(1) receptors and is critically involved in pain and fear-related behaviour. We investigated the effects of bilateral intra-BLA administration of the CB(1) receptor antagonist/inverse agonist, rimonabant, on formalin-evoked nociceptive behaviour, fear-conditioned behaviour including analgesia, and associated brain regional alterations in Fos expression in rats. Intra-BLA administration of rimonabant significantly reduced formalin-evoked nociceptive behaviour in the absence, but not presence, of conditioned fear. Rimonabant attenuated a formalin-evoked reduction in freezing while emitting 22 kHz ultrasonic vocalisation in the early part of the fear expression trial. Formalin-evoked nociceptive behaviour was associated with increased Fos immunoreactivity (FI) in the CA2/3 region of the hippocampus and rostral ventromedial medulla, effects attenuated by intra-BLA rimonabant. Formalin also decreased FI in the cingulate cortex, an effect which was not observed in fear-conditioned rats. Contextually-induced fear was associated with increased FI in the dorsal caudal periaqueductal grey in the absence, but not presence, of formalin-evoked nociceptive tone. In conclusion, bilateral intra-BLA administration of rimonabant reduces nociceptive behaviour in a model of tonic, persistent inflammatory pain, an effect associated with reduced activation of neurons in the CA2/3 hippocampus and rostral ventromedial medulla. The data also provide evidence for differential pain-and fear-related brain regional activity in the presence or absence of contextually-induced aversion and nociceptive tone. (C) 2009 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.
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