Descending facilitatory pain pathways mediate ongoing pain and tactile hypersensitivity in a rat model of trigeminal neuropathic pain. (22nd March 2017)

• Record Type: Journal Article
• Authors: Nones, C.F.M.; Claudino, R.F.; Ferreira, L.E.N.; Dos Reis, R.C.; King, T.; Chichorro, J.G.
• Is Part Of: Neuroscience letters. Volume 644(2017)
• Page Start: 18
• Page End: 23
• Publication Date: 2017-03-22
• Subjects: Trigeminal neuropathic pain -- RVM -- Spontaneous pain -- Hypersensitivity; Neurology -- Periodicals; Neurology -- Periodicals; Research -- Periodicals; Neurologie -- Périodiques; Neuroanatomie -- Périodiques; Neuropharmacologie -- Périodiques; Neurophysiologie -- Périodiques; Neurology; Periodicals; Electronic journals; 617.48
• DOI: 10.1016/j.neulet.2017.02.047
• Languages: English
• ISSNs: 0304-3940

Abstract

Highlights: Constriction of the trigeminal nerve induces early heat and late tactile facial hypersensitivity. CCI-ION induced spontaneous pain emerges between 5 and 15 days post injury. Descending pain facilitatory pain pathways mediate evoked and spontaneous pain 15 but not 5 days post-CCI-ION. Targeting RVM facilitatory pathways may improve treatment of chronic trigeminal neuropathic pain. Abstract: The Chronic Constriction Injury of the Infraorbital Nerve (CCI-ION) is a well-established model to study facial sensory changes related to trigeminal neuropathic pain. CCI-ION induces heat hypersensitivity that resolves within 2–3 weeks and a delayed mechanical hypersensitivity that emerges during the second week post-injury. The role of descending facilitatory pain pathways from the rostro ventromedial medulla (RVM) in mediating the heat and tactile hypersensitivity was examined. CCI-ION induced heat hypersensitivity observed 5 days post-surgery was reversed by systemic, but not RVM lidocaine. CCI-ION-induced tactile hypersensitivity observed 15 days post-surgery was reversed by systemic lidocaine and attenuated by RVM lidocaine. CCI-ION-induced spontaneous pain was determined using conditioned place preference (CPP) to pain relief at each time-point. At day 5 post-CCI-ION, neither systemic nor RVM lidocaine induced CPP. However, at 15 days post-CCI-ION, CPP was observed to the chamber paired with RVM lidocaine, but not systemic lidocaine. These data indicate that CCI-ION induced heat hypersensitivity is not dependent on descending facilitatory pain pathways 5-days post-injury whereas descending facilitatory pain pathways mediate tactile allodynia and spontaneous pain 15 days post-CCI-ION. This suggests that CCI-ION induces early peripheral sensitization followed by development of central sensitization that mediates spontaneous pain and contributes to mechanical hypersensitivity.