The effect of peripheral analgesia on “pain memory” changes in modified formalin test

Abstract

Peripheral tissue damage or nerve injury often leads to development of pathological pain processes, such as spontaneous pain, hyperalgesia and allodynia that persist for years or decades after all possible tissue healing has occurred. The modification of classic formalin test with two subsequent injections of formalin can be useful to investigate central mechanisms of “pain memory”. To evaluate the effect of analgesia of periphery on central pathways of nociception we used four groups of analgesics: a local anaesthetic-lidocaine, NSAID-diclofenac, a mu-opioid receptor agonist-DAMGO, anticonvulsant with chronic pain-relieving action-gabapentin. We studied the impact of analgesic drugs on acute and chronic pain conditions taking as a basis c-Fos as a pain intensity marker.