title: Neuronal hyperexcitability in the dorsal horn after painful facet joint injury.
abstract: Excessive cervical facet capsular ligament stretch has been implicated as a cause of whiplash-associated disorders following rear-end impacts, but the pathophysiological mechanisms that produce chronic pain in these cases remain unclear. Using a rat model of C6-C7 cervical facet joint capsule stretch that produces sustained mechanical hyperalgesia, the presence of neuronal hyperexcitability was characterized 7 days after joint loading. Extracellular recordings of spinal dorsal horn neuronal activity between C6 and C8 (117 neurons) were obtained from anesthetized rats, with both painful and non-painful behavioral outcomes established by the magnitude of capsule stretch. The frequency of neuronal firing during noxious pinch (p<0.0182) and von Frey filaments applications (4-26g) to the forepaw was increased (p<0.0156) in the painful group compared to the non-painful and sham groups. In addition, the incidence and frequency of spontaneous and after discharge firing were greater in the painful group (p<0.0307) relative to sham. The proportion of cells in the deep laminae that responded as wide dynamic range neurons also was increased in the painful group relative to non-painful or sham groups (p<0.0348). These findings suggest that excessive facet capsule stretch, while not producing visible tearing, can produce functional plasticity of dorsal horn neuronal activity. The increase in neuronal firing across a range of stimulus magnitudes observed at day 7 post-injury provides the first direct evidence of neuronal modulation in the spinal cord following facet joint loading, and suggests that facet-mediated chronic pain following whiplash injury is driven, at least in part, by central sensitization.
authors.affiliation: Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA Department of Clinical Studies - Philadelphia, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA Department of Neurosurgery, University of Pennsylvania, Philadelphia, PA, USA.
authors.forename: Kyle P
authors.initials: KP
authors.lastname: Quinn
authors.forename: Ling
authors.initials: L
authors.lastname: Dong
authors.forename: Francis J
authors.initials: FJ
authors.lastname: Golder
authors.forename: Beth A
authors.initials: BA
authors.lastname: Winkelstein
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002574:Cervical Vertebrae; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000209:etiology / Q000473:pathology*; D008297:Male; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000502:physiology; D010812:Physical Stimulation / Q000009:adverse effects; D020671:Posterior Horn Cells / Q000502:physiology*; D011601:Psychophysics / Q000379:methods; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000473:pathology*; D021801:Zygapophyseal Joint / Q000293:injuries / Q000503:physiopathology*