Administration of orexin receptor ۱ antagonist into the rostral ventromedial medulla increased swim stress-induced antinociception in rat

Objective(s): Intracerebroventricular injection of orexin-A (hypocretin-۱) antagonist has been shown to inhibit stress-induced analgesia. However the locations of central sites that may mediate these effects have not been totally demonstrated. This study was performed to investigate the role of rostral ventromedial medulla (RVM) orexin receptor ۱ in stress-induced analgesia (SIA). Materials and Methods: Forced swim stress in water was employed to adult male rats (۲۰۰-۲۵۰ g). Nociceptive responses were measured by formalin test (۵۰ µl injection of formalin ۲% subcutaneously into hind paw) and, pain related behaviors were monitored for ۹۰ min following intra-microinjection of SB-۳۳۴۸۶۷ (orexin receptor ۱ antagonist) into RVM. Results: Exposure to swimming stress test after administration of SB-۳۳۴۸۶۷ into RVM significantly reduces the formalin-induced nociceptive behaviors in phase۱, interphase, and phase ۲ in rats. Conclusion: The result demonstrated the involvement of OXR۱ in antinociceptive behaviors induced by swim stress in RVM.

کلیدواژه ها:

Formalin test ، Orexin receptors ، Rostral ventromedial medulla ، Stress induced analgesia