title: Nocifensive behavior-related laser heat-evoked component in the rostral agranular insular cortex revealed using morphine analgesia.
abstract: The rostral agranular insular cortex (RAIC), an opioid-responsive site, is essential for modulating nociception in rats. Our previous studies have shown that morphine suppressed long latency laser heat-evoked nociceptive responses in the primary somatosensory cortex (SmI). By contrast, morphine significantly attenuated both short and long latency responses in the anterior cingulate cortex (ACC). The present study assessed the effect of morphine on laser heat-evoked responses in the RAIC. Laser heat irradiation applied to the rat forepaws at graded levels was used as a specific noxious stimulus. In the RAIC, the first part of the long latency component (140-250ms) of the laser heat-evoked response was enhanced by intraperitoneal morphine (5mg/kg). When the laser heat-evoked cortical responses were examined for trials showing strong nocifensive movement (paw licking), moderate nocifensive movement (paw lifting), and no nocifensive movement, a 140-250ms period enhancement was observed in the RAIC only for the paw lifting movement. This enhancement was absent in the SmI. Thus, our data suggest that the RAIC has a pain-related behavior-dependent neuronal component. Furthermore, the RAIC, ACC, and SmI are differentially modulated by morphine analgesia.
authors.affiliation: Department of Life Science, Taipei, Taiwan.
authors.forename: Wen-Yi
authors.initials: WY
authors.lastname: Wu
authors.affiliation: Department of Life Science, Taipei, Taiwan.
authors.forename: Chan-Ying
authors.initials: CY
authors.lastname: Liu
authors.affiliation: Department of Biomechatronic Engineering, National Ilan University, Ilan, Taiwan.
authors.forename: Meng-Li
authors.initials: ML
authors.lastname: Tsai
authors.affiliation: Department of Life Science, Taipei, Taiwan; Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan. Electronic address: ctyen@ntu.edu.tw.
authors.forename: Chen-Tung
authors.initials: CT
authors.lastname: Yen
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D002540:Cerebral Cortex / Q000187:drug effects*; D004307:Dose-Response Relationship, Radiation; D004569:Electroencephalography; D004576:Electromyography; D005260:Female; D006358:Hot Temperature; D007834:Lasers / Q000009:adverse effects*; D009020:Morphine / Q000494:pharmacology*; D059226:Nociceptive Pain / Q000188:drug therapy* / Q000209:etiology; D010147:Pain Measurement; D025341:Principal Component Analysis; D051381:Rats; D020318:Rats, Long-Evans; D011930:Reaction Time / Q000187:drug effects*
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine
keywords: Behavioral electrophysiology; Ensemble neuronal activity; Pain; Primary somatosensory cortex