Effect of Adenylyl Cyclase Inhibitor (SQ-22536) Injection in Rostral Ventromedial Medulla on Formalin Induced Nociceptive Behavior in Rats

Introduction: Activation of the cyclic adenosine monophosphate (cAMP) pathway produces mechanical hyperalgesia, sensitizes nociceptive spinal neurons, and phosphorylates the transcription factor cAMP-responsive element binding protein (CREB), which initiates gene transcription. This study examined the role of the cAMP pathway in a model of chronic pain, by assessing associated behavioral changes after inhibition of Adenylyl syclase in rostral ventromedial medulla (RVM). Methods: In this study, thirty-six Sprague- Dawley rats (weighing 250-300 g) were divided into six groups including control, vehicle, sham and SQ-22536 (50, 100 and 200 nmol) groups. Formalin was injected into the right paws of all groups. Results: Intra-RVM injection of SQ-22536 (100 nmol) decreased formalin induced nociceptive pain in the 5th, 10th, 15th, 25th, 35th, 50th and 55th minutes. Also, SQ-22536 (200 nmol) decreased formalin induced nociceptive pain in the 15th minute. Conclusion: Therefore, inhibition of the adenylyl cyclase inhibitoion in the rostral ventromedial medulla decreases formalin induced nociceptive behaviors in rats.