Neuropeptide Y in trigeminal ganglion following chronic constriction injury of the rat infraorbital nerve: is there correlation to somatosensory parameters?

The aim of this study was to investigate neuropeptide Y (NPY) levels in tri geminal ganglia following infraorbital nerve injury. Two experimental proce dures were performed in three groups of rats: a unilateral chronic constric tion injury (CCI) to the infraorbital nerve (n = 13), nerve manipulation wi thout CCI (n = 13) and unoperated controls (n = 8), All rats underwent base line and regular assessment of mechanical withdrawal threshold (Von Frey) a nd reaction to pin prick as well as free behavior evaluations. CCI to the i nfraorbital nerve induced significant hyperalgesia and allodynia within 9-1 2 days. At 6 days seven rats were euthanized and trigeminal ganglia harvest ed for immunocytochemical (ICC) studies. The study was ended at 14 days whe n all rats were euthanized and their ganglia harvested for ICC and radioimm unoassay (RIA) studies. An increase in NPY levels was seen in the ipsilater al ganglia of manipulated and CCI rats at 6 days, when rats displayed no pa in-related behavior. At 14 days, ICC and RIA both detected significant incr eases in NPY levels in the ipsilateral ganglia of CCI and manipulated rats but not in unoperated controls. The possible roles of NPY in pain modulatio n and nerve injury are discussed in light of these findings, (C) 2001 Inter national Association for the Study of Pain. Published by Elsevier Science B .V. All rights reserved.