RESUMO
There is preclinical evidence that nerve growth factor (NGF) contributes toward inflammatory hyperalgesia in the orofacial region, but the mechanisms underlying its hyperalgesic effect as well as its role in trigeminal neuropathic pain require further investigation. This study investigated the ability of NGF to induce facial heat hyperalgesia and the involvement of tyrosine kinase receptor A, transient receptor potential vanilloid 1, and mast cells in NGF pronociceptive effects. In addition, the role of NGF in heat hyperalgesia in a model of trigeminal neuropathic pain was evaluated. NGF injection into the upper lip of naive rats induced long-lasting heat hyperalgesia. Pretreatment with an antibody anti-NGF, antagonists of tyrosine kinase receptor A, and transient receptor potential vanilloid 1 receptors or compound 48/80, to induce mast-cell degranulation, all attenuated NGF-induced hyperalgesia. In a rat model of trigeminal neuropathic pain, local treatment with anti-NGF significantly reduced heat hyperalgesia. In addition, increased NGF levels were detected in the ipsilateral infraorbital nerve branch at the time point that represents the peak of heat hyperalgesia. The results suggest that NGF is a prominent hyperalgesic mediator in the trigeminal system and it may represent a potential therapeutic target for the management of painful orofacial conditions, including trigeminal neuropathic pain.
