Continuous intravenous infusion of naloxone does not change behavioral,cardiovascular, or inflammatory responses to subcutaneous formalin in the rat |
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| Affiliation: | 1. W. M. Keck Foundation Center for Integrative Neuroscience, University of California San Francisco, San Francisco, CA 94143-0452, USA;2. Department of Anatomy, University of California San Francisco, San Francisco, CA 94143-0452, USA;3. Department of Physiology, University of California San Francisco, San Francisco, CA 94143-0452, USA;1. Anesthesiology & Pain Medicine University of Washington, Seattle, WA, United States;2. Neuroscience Graduate Program, University of Michigan, Ann Arbor, MI, United States;3. Program in Neurobiology and Behavior University of Washington, Seattle, WA, United States;1. Bio-Organic and Photochemistry Laboratory, Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar, 143 005, Punjab, India;2. Vice Chancellor, Maharaja Ranjit Singh Punjab Technical University, Badal Road, Bathinda, India;3. Cancer Pharmacology Division, Indian Institute of Integrative Medicine (CSIR), Jammu, 180001, India;1. Department of Anesthesia, University Health Network, Toronto Western Hospital, Toronto, Ontario, Canada;2. Division of Neurosurgery, Department of Surgery, University Health Network, Toronto Western Hospital, 399 Bathurst Street, West Wing 4-439, M5T 2S8 Toronto, Ontario, Canada;3. Department of Anesthesia, Christian Medical College Hospital, Vellore, India;1. Department of Anatomy, Faculty of Medicine, Kahramanmaras Sütcü Imam University, Kahramanmaras, Turkey;2. Department of Oral and Maxillofacial Surgery, Faculty of Dentistry, Gaziosmanpasa University, Tokat, Turkey;3. Department of Medical Biology, Faculty of Medicine, Gaziosmanpasa University, Tokat, Turkey;4. Faculty of Health Sciences and Central Research Laboratory, Mardin Artuklu University, Mardin, Turkey |
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| Abstract: | The opioid antagonist, naloxone, produces equivocal effects on the magnitude of nociceptive responses in several animal models of persistent pain, including the formalin test. Hindpaw injection of dilute formalin produces not only inflammation but also phasic (Phase 1) and persistent (Phase 2) behavioral and cardiovascular nociceptive responses in the rat. To test the hypothesis that endogenous opioid systems contribute to the magnitude of responses to intraplantar formalin injection, we evaluated the effects of continuous naloxone administration (0.01–100 mg/kg per h, i.v.) on formalin-evoked hindpaw inflammation, on behavioral indices of pain, flinching and licking pain behavior, and on changes in mean arterial pressure and heart rate. We report that naloxone, at doses less than 100 mg/kg per h, did not change any formalin-evoked response. Although the 100 mg/kg per h dose significantly decreased these responses, it also produced muscle rigidity and profound bradycardia. We conclude that endogenous opioids do not significantly modulate the nociceptive processing induced by subcutaneous formalin. |
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