Introduction: To better understand the pathophysiology of chronic muscle pain, there are multiple animal models that mimic different acute/chronic pain conditions, such as carrageenan injection. Our previous studies demonstrated differences between muscles of different innervation in acute pain. In this study we characterized the effect of carrageenan in 2 muscles: masseter (trigeminal innervation) and gastrocnemius (spinal innervation).
Methods: Carrageenan (3%, 6%, and 9%) was injected into the masseter and gastrocnemius of rats. Mechanical, heat, and chemical nociceptive thresholds were measured for 14 days.
Results: Carrageenan did not induce mechanical allodynia or thermal hypersensitivity in either muscle. Instead, it induced a short-lasting mechanical hyperalgesia, greater in the masseter than in the gastrocnemius.
Conclusion: Carrageenan injected into the masseter and gastrocnemius induces a short-lasting hyperalgesia. These results could indicate a higher susceptibility of orofacial muscles to this type of insult and, consequently, a difference between trigeminal and spinal innervation. Muscle Nerve 56: 804-813, 2017.
Keywords: carrageenan; gastrocnemius; masseter; muscle pain; rat.
© 2016 Wiley Periodicals, Inc.