Basic and Clinical 305 July, Augus 2019, Volume 10, Number 4 Research Paper: Involvement of Endogenous Opioid Sysem in Swim Stre ss-Induced Pain Modulation During the Interphase of the Formalin Te s Ali Reza Moslem 1 , Bahareh Amin 2 , Nima Heidari-Oranjaghi 3 , Hassan Azhdari-Zarmehri 4,5* 1. Department of Aneshesiology, School of Medicine, Sabzevar University of Medical Sciences, Sabzevar, Iran. 2. Cellular and Molecular Research Center, Department of Physiology and Pharmacology, School of Medicine, Sabzevar University of Medical Sciences, Sabzevar, Iran. 3. Department of Physiology and Pharmacology, School of Medicine, Zanjan University of Medical Sciences, Zanjan, Iran. 4. Neurosciences Research Center, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran. 5. Department of Physiology, School of Paramedical Sciences, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran. * Corresponding Author: Hassan Azhdari-Zarmehri, PhD. Address: Department of Physiology, School of Paramedical Sciences, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, Iran. Tel: +98 (912) 4801826 E-mail: hasan.azhdari@gmail.com; azhdarih1@thums.ac.ir Introduction: Some evidence demonsrates endogenous inhibitory pathways of pain involved in the interphase (phase between early and later phase) of the formalin tes. We previously showed that swimming sress modulates the pain-related behaviors during the interphase of the formalin tes. In this sudy, we evaluated the role of the endogenous opioid sysem in modulating nociceptive responses of the formalin tes. Methods: Swim sress was performed in diferent heights of water (5, 25, 50 cm) in a swimming tank. The mean nociceptive scores were measured during phase 1 (1-7 min), interphase (8-14 min), and phase 2 (15-90 min) of the formalin tes. Opioid receptor antagonis, naloxone (3 mg/kg; IP) was injected immediately before swim sress. Results: Swim sress attenuated nociceptive behaviors in the frs phase and increased the duration of interphase in the formalin tes in a water-height-dependent manner, compared to the control group. Naloxone signifcantly increased nociceptive behaviors in the frs phase, interphase, and the second phase of the formalin tes, compared to the control group. Conclusion: Stress could afect the nociceptive response. Swim sress in diferent heights of water could have diferent efects on the nociception in diferent phases of the formalin tes. In addition, the involvement of the endogenous opioid sysem is further demonsrated in the swim sress-induced modulation of pain behaviors in phase 1, phase 2, as well as interphase of formalin tes in rats. Article info: Received: 17 May 2017 Firs Revision: 03 Jun 2017 Accepted: 03 Mar 2018 Available Online: 01 Jul 2019 Keywords: Swim sress, Rat, Formalin tes, Naloxone Citation: Moslem, A., R, Amin, B., Heidari-Oranjaghi, N., & Azhdari-Zarmehri, H. (2019). Involvement of Endogenous Opioid Sysem in Swim Stress-Induced Pain Modulation During the Interphase of the Formalin Tes. Basic and Clinical Neuroscience, 10(4), 305-312. http://dx.doi.org/10.32598/bcn.9.10.220 http://dx.doi.org/10.32598/bcn.9.10.220 Use your device to scan and read the artcle online A B S T R A C T