Repeated Administration of Orexin into the Thalamic Paraventricular Nucleus Inhibits the Development of Morphine-Induced Analgesia

Title:Repeated Administration of Orexin into the Thalamic Paraventricular Nucleus Inhibits the Development of Morphine-Induced Analgesia

Volume: 29 Issue: 1

Author(s): Fatemeh Samani and Masoumeh Kourosh Arami*

Affiliation:

• Department of Neuroscience, School of Advanced Technologies in Medicine, Iran University of Medical Sciences, Tehran, Iran
• Neuroscience Research Center, Iran University of Medical Sciences, Tehran, Iran

Keywords: Paraventricular nucleus, Orexin, Morphine, Nociceptive behaviors, Formalin test, Analgesic effect.

Abstract: Background: Hypothalamic neuropeptides, orexins, play pivotal roles in nociception and pain modulation.

Objective: In this study, we investigated the effect of the administration of orexin into the paraventricular nucleus (PVT) on the development of morphine-induced analgesia in rats.

Method: Male Wistar rats weighing 250-300g received subcutaneous (s.c.) chronic morphine (6, 16, 26, 36, 46, 56 and 66 mg/kg, 2 ml/kg) at an interval of 24 hours for 7 days. Animals were divided into two experimental groups in which the orexin (100 μM, 200 nl) and its vehicle were microinjected into the PVT nucleus for 7 days before each morphine injection. Then, the formalin test was performed for the assessment of pain-related behaviors.

Results: The results demonstrated that the rats pretreated by intra-PVT orexin exhibited higher pain-related behaviors than the morphine-treated group. The analgesic effects of morphine were significantly lower in orexin plus morphine-treated rats than the vehicle plus morphine-treated ones.

Conclusion: Our findings suggested that the animals receiving the prolonged intra-PVT application of orexin before morphine injection demonstrated a significant increase in the development of nociceptive behaviors in all phases. There fore, the present study highlighted a new area of the brain involved in the effect of orexin on analgesia induced by morphine.

Cite this article as:

Samani Fatemeh and Arami Kourosh Masoumeh*, Repeated Administration of Orexin into the Thalamic Paraventricular Nucleus Inhibits the Development of Morphine-Induced Analgesia, Protein & Peptide Letters 2022; 29 (1) . https://dx.doi.org/10.2174/0929866528666211214170247