title: Selective mediation of nerve injury-induced tactile hypersensitivity by neuropeptide Y.
abstract: Prevention of nerve injury-induced tactile, but not thermal, hypersensitivity is achieved by ipsilateral lesions of the dorsal columns or lidocaine microinjection into the nucleus gracilis (n. gracilis). These and other data support the possibility that tactile hyperresponsiveness after nerve injury may be selectively mediated by a low-threshold myelinated fiber pathway to the n. gracilis. Here we identify a transmitter that might selectively mediate such injury-induced tactile hypersensitivity. Neuropeptide Y (NPY), normally not detected in the dorsal root ganglion (DRG) or in the n. gracilis of rats, became markedly upregulated at both sites and in the spinal cord after spinal nerve injury. Injury-induced NPY-IR occurred predominately in large-diameter DRG cells, and the NPY-IR in the n. gracilis was blocked by dorsal rhizotomy or dorsal column lesion. NPY microinjection into the n. gracilis of uninjured rats elicited reversible tactile, but not thermal, hypersensitivity only in the ipsilateral hindpaw. Administration of anti-NPY antiserum, but not control serum or preabsorbed serum, into the n. gracilis ipsilateral to nerve injury reversed tactile, but not thermal, hypersensitivity. Similarly, microinjection of the NPY antagonists NPY(18-36) and (R)-N-[[4-(aminocarbonylaminomethyl)-phenyl]methyl]-N2-(diphenylacetyl)-argininamide trifluoroacetate, into the n. gracilis ipsilateral to the injury reversed tactile, but not thermal, hypersensitivity. Antagonist administration into the contralateral n. gracilis had no effect on injury-induced hypersensitivity. These data suggest the selective mediation of nerve injury-induced tactile hypersensitivity by upregulated NPY via large fiber input to n. gracilis. Selective reversal of injury-induced tactile allodynia by NPY receptor antagonists would have significant implications for human neuropathic conditions.
authors.affiliation: Department of Pharmacology, College of Medicine, University of Arizona, Tucson, Arizona 85724, USA.
authors.forename: Michael H
authors.initials: MH
authors.lastname: Ossipov
authors.forename: En-Tan
authors.initials: ET
authors.lastname: Zhang
authors.forename: Cristina
authors.initials: C
authors.lastname: Carvajal
authors.forename: Luis
authors.initials: L
authors.lastname: Gardell
authors.forename: Remi
authors.initials: R
authors.lastname: Quirion
authors.forename: Yvan
authors.initials: Y
authors.lastname: Dumont
authors.forename: Josephine
authors.initials: J
authors.lastname: Lai
authors.forename: Frank
authors.initials: F
authors.lastname: Porreca
mesh_terms: D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001552:Benzazepines / Q000494:pharmacology; D004195:Disease Models, Animal; D018450:Disease Progression; D005727:Ganglia, Spinal / Q000378:metabolism / Q000473:pathology; D006930:Hyperalgesia / Q000473:pathology / Q000503:physiopathology* / Q000517:prevention & control; D007106:Immune Sera / Q000494:pharmacology; D008026:Ligation; D008161:Lumbosacral Region; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D008845:Microinjections; D009409:Nerve Crush; D009478:Neuropeptide Y / Q000008:administration & dosage / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010147:Pain Measurement / Q000187:drug effects; D017288:Pain Threshold; D051381:Rats; D017207:Rats, Sprague-Dawley; D017476:Receptors, Neuropeptide Y / Q000819:agonists / Q000037:antagonists & inhibitors; D019051:Rhizotomy; D013116:Spinal Cord / Q000378:metabolism / Q000473:pathology; D013127:Spinal Nerves / Q000293:injuries* / Q000473:pathology / Q000503:physiopathology*
chemical_list: D001552:Benzazepines; D007106:Immune Sera; D009478:Neuropeptide Y; D017476:Receptors, Neuropeptide Y; D001120:Arginine; C403256:BIIE 0246; C117416:BIBO 3304