title: Abnormal spontaneous activities on needle electromyography and their relation with pain behavior and nerve fiber pathology in a rat model of lumbar disc herniation.
abstract: METHODS
  This longitudinal experimental study was conducted to investigate electrophysiologic characteristics, pain behavior, and histological changes in a rat model of lumbar disc herniation.
  
  
  OBJECTIVE
  To observe abnormal spontaneous activity (ASA) on needle electromyography (EMG) and to determine its relation with neuropathic pain behavior and histological changes longitudinally in a rat model of lumbar disc herniation.
  
  
  BACKGROUND
  Needle EMG is generally performed to determine the existence and the degree of radiculopathy caused by disc herniation. The local application of autologous nucleus pulposus to the spinal nerve has been shown to induce neuropathic pain. However, little is known about the relations between neuropathic pain and abnormal EMG findings and the manner in which they change with time in rat models of lumbar disc herniation.
  
  
  METHODS
  Twenty-five Sprague-Dawley rats were randomly assigned to either sham or experimental groups. In the experimental group, autologous nucleus pulposus was grafted on the left L5 dorsal root ganglion. All rats were evaluated for mechanical allodynia and thermal hyperalgesia and underwent needle EMG examinations before and on days 1, 5, 10, 20, 30, 40, and 50 after surgery. Morphologic changes of L5 spinal nerves and of sciatic nerves were assessed by toluidine blue staining on days 1, 5, and 50 after surgery.
  
  
  RESULTS
  A dramatic decrease in mechanical withdrawal threshold and in thermal withdrawal latency was observed on day 1 after surgery, and these changes persisted until day 50 after surgery. ASAs on needle EMG were observed on day 1 (33%), peaked on day 5 (93%), and gradually decreased from day 10 (69%) to day 40 (18%) after surgery. Pathologic findings of nerve fibers, such as swelling of myelin sheaths, demyelination, and degeneration of axoplasms were observed from day 1. These findings were exaggerated on day 5 and then diminished but were still evident on day 50.
  
  
  CONCLUSIONS
  Neuropathic pain and pathologic changes in spinal nerve fibers probably remain even after ASAs in EMG have disappeared in our rat model of lumbar disc herniation. These results provide baseline data concerning the natural courses of electrophysiologic findings and of radicular pain in patients with intervertebral disc herniation.
authors.affiliation: Institute of Medical Science, Yeungnam University, Daegu, Korea.
authors.forename: Su-Jeong
authors.initials: SJ
authors.lastname: Kim
authors.forename: Wook-Ro
authors.initials: WR
authors.lastname: Kim
authors.forename: Han-Seon
authors.initials: HS
authors.lastname: Kim
authors.forename: Hea-Woon
authors.initials: HW
authors.lastname: Park
authors.forename: Yun-Woo
authors.initials: YW
authors.lastname: Cho
authors.forename: Sung-Ho
authors.initials: SH
authors.lastname: Jang
authors.forename: Se-Jin
authors.initials: SJ
authors.lastname: Hwang
authors.forename: Sang-Ho
authors.initials: SH
authors.lastname: Ahn
mesh_terms: D000818:Animals; D004576:Electromyography / Q000295:instrumentation / Q000379:methods*; D005260:Female; D005727:Ganglia, Spinal / Q000503:physiopathology / Q000601:surgery; D006614:Hindlimb / Q000503:physiopathology; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology; D007403:Intervertebral Disc / Q000637:transplantation; D007405:Intervertebral Disc Displacement / Q000150:complications*; D008159:Lumbar Vertebrae / Q000473:pathology; D009412:Nerve Fibers / Q000473:pathology*; D009437:Neuralgia / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold; D011843:Radiculopathy / Q000209:etiology / Q000503:physiopathology; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012584:Sciatic Nerve / Q000473:pathology; D013127:Spinal Nerves / Q000473:pathology; D013997:Time Factors; D014182:Transplantation, Autologous