title: Retrograde viral vector-mediated inhibition of pontospinal noradrenergic neurons causes hyperalgesia in rats.
abstract: Pontospinal noradrenergic neurons form a component of an endogenous analgesic system and represent a potential therapeutic target. We tested the principle that genetic manipulation of their excitability can alter nociception using an adenoviral vector (AVV-PRS-hKir(2.1)) containing a catecholaminergic-selective promoter (PRS) to retrogradely transduce and inhibit the noradrenergic neurons projecting to the lumbar dorsal horn through the expression of a potassium channel (hKir(2.1)). Expression of hKir(2.1) in catecholaminergic PC12 cells hyperpolarized the membrane potential and produced a barium-sensitive inward rectification. LC neurons transduced by AVV-PRS-hKir(2.1) in slice cultures also showed barium-sensitive inward rectification and reduced spontaneous firing rate (median 0.2 Hz; n = 19 vs control 1.0 Hz; n = 18, p < 0.05). Pontospinal noradrenergic neurons were retrogradely transduced in vivo by injection of AVV into the lumbar dorsal horn (L4-5). Rats transduced with AVV-PRS-hKir(2.1) showed thermal but not mechanical hyperalgesia. Similar selective augmentation of thermal hyperalgesia was seen in the CFA-inflammatory pain model after AVV-PRS-hKir(2.1). In the formalin test, rats transduced with hKir(2.1) showed enhanced nocifensive behaviors (both Phase I and II, p < 0.05, n = 11/group) and increased c-Fos-positive cells in the lumbar dorsal horn. Transduction with AVV-PRS-hKir(2.1) before spared nerve injury produced no change in tactile or cold allodynia. Thus, the selective genetic inhibition of approximately 150 pontospinal noradrenergic neurons produces a modality-specific thermal hyperalgesia, increased nocifensive behaviors, and spinal c-Fos expression in the formalin test, but not in the spared nerve injury model of neuropathic pain, indicating that these neurons exert a selective tonic restraining influence on in vivo nociception.
authors.affiliation: Department of Physiology & Pharmacology, University of Bristol, Bristol BS8 1TD, United Kingdom.
authors.forename: Patrick W
authors.initials: PW
authors.lastname: Howorth
authors.forename: Simon R
authors.initials: SR
authors.lastname: Thornton
authors.forename: Victoria
authors.initials: V
authors.lastname: O'Brien
authors.forename: Wynne D
authors.initials: WD
authors.lastname: Smith
authors.forename: Natalia
authors.initials: N
authors.lastname: Nikiforova
authors.forename: Anja G
authors.initials: AG
authors.lastname: Teschemacher
authors.forename: Anthony E
authors.initials: AE
authors.lastname: Pickering
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D002395:Catecholamines / Q000235:genetics; D002452:Cell Count / Q000379:methods; D004195:Disease Models, Animal; D004299:Dopamine beta-Hydroxylase / Q000378:metabolism; D005822:Genetic Vectors / Q000235:genetics*; D049452:Green Fluorescent Proteins / Q000235:genetics; D006930:Hyperalgesia / Q000209:etiology* / Q000473:pathology*; D066298:In Vitro Techniques; D007796:Laminectomy / Q000379:methods; D008297:Male; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D009043:Motor Activity / Q000235:genetics; D009474:Neurons / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D016716:PC12 Cells; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology; D011149:Pons / Q000473:pathology*; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014162:Transfection / Q000379:methods
chemical_list: D002395:Catecholamines; C489461:Kir2.1 channel; D024661:Potassium Channels, Inwardly Rectifying; D016760:Proto-Oncogene Proteins c-fos; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins; D004299:Dopamine beta-Hydroxylase; D009638:Norepinephrine