en 38605740 <p style="text-align:justify"><span style="font-size:16pt"><strong><span style="font-size:10.0pt">Background:</span></strong><span style="font-size:10.0pt"> Orexin (hypocretin) is one of the hypothalamic neuropeptides that plays a critical role in some behaviors including feeding, sleep, arousal, reward processing, and drug addiction. Neurons that produce orexin are scattered mediolaterally within the Dorsomedial Hypothalamus (DMH) and the lateral hypothalamus. In the current research, we assessed the impact of prolonged application of the antagonist of Orexin Receptor 1 (</span><span style="font-size:10.0pt">OXR1) on nociceptive behaviors in adult male rats. </span></span></p> <p style="text-align:justify"><span style="font-size:16pt"><strong><span style="font-size:10.0pt">Methods:</span></strong><span style="font-size:10.0pt"> Sixteen Wistar rats received subcutaneous (s.c.) injections of the OXR1 antagonist, SB-334867 (20 <em>mg/kg</em>, <em>i.p</em>.), or its vehicle repetitively from Postnatal Day 1 (PND1)-PND30. On the 30^th day following the final application of the </span><span style="font-size:10.0pt">OXR1</span><span style="font-size:10.0pt"> antagonist formalin-provoked pain was evaluated by injecting formalin. </span></span></p> <p style="text-align:justify"><span style="font-size:16pt"><strong><span style="font-size:10.0pt">Results:</span></strong> <span style="font-size:10.0pt">Administration of the OXR1 antagonist in the long-term augmented the formalin-provoked nociceptive behaviors in interphase and phase II of the formalin-induced pain. </span></span></p> <p style="text-align:justify"><span style="font-size:16pt"><strong><span style="font-size:10.0pt">Conclusion:</span></strong> <span style="font-size:10.0pt">Current results showed that the continued inhibiting OXR1 might be implicated in formalin-induced nociceptive behaviors. Therefore, the present study highlighted the effect of orexin on analgesia.</span></span></p> Formalin, Nociception, Orexin receptor 1, Orexin, SB-334867 29 33 https://www.ajmb.org/En/Article.aspx?id=60563 https://www.ajmb.org/PDF/En/FullText/60563.pdf MasoumehKourosh-Arami92125AlirezaKomakiDepartment of Neuroscience, School of Science and Advanced Technologies in Medicine, Hamadan University of Medical Sciences, Hamadan, Iran92126MasoumehGholamiDepartment of Physiology, Medical College, Arak University of Medical Sciences, Arak, Iran92127