Effect of Orexin receptor-1 antagonist in acute food deprivation on formalin test

  Background: Orexin-A and orexin-B are novel hypothalamic peptides which have a role in the regulation of feeding behaviour and pain modulation .   Objective: The purpose of this study was to investigate the role of Orexin-A receptor antagonist (SB334867) on the analgesia produced by 12-14 h of food deprivation in rats.   Methods: This experimental study was performed on 32 Male rats weighing 2 20 -300gr in Qazvin University of Medical Science in 2010 . Animals underwent stereotaxic surgery and a guide cannula was inserted into the lateral ventricle of their brai n. One week after surgery , food was withdrawn 12-14 h prior to performing the formalin test, but water continued to be available ad labium . Formalin was injected subcutaneously into the dorsal surface of the right hindpaw and their pain behaviors observed and recorded for 90 minutes. SB334867 or vehicle (5 μ l, icv) were injected 5 min before formalin injection. Data were analyzed by T-test and one way ANOVA.   Findings: Formalin injection into the right foot caused pain responses in two phases first phase and second phase were separated with an interphase in which pain behavior was decreased to single and transient responses. 12-14 h starvation reduced pain behavior (analgesia) but Orexin antagonist injection prevent from the reduction of pain behaviors caused by acute food deprivation.   Conclusion: The results of this study suggest that the orexinergic system has a role in the modulation of the pain following food deprivation.