Epidural application of nucleus pulposus enhances nociresponses of rat dorsal horn neurons.
METHODS
An electrophysiologic study to examine responses of dorsal horn neurons in the rat L5 spinal cord to noxious stimuli after disc herniation or application of the nucleus pulposus to the L5 nerve root.


OBJECTIVE
To investigate the pathogenic role of nucleus pulposus in the neural mechanism underlying sciatica and low back pain.


BACKGROUND
Application of the nucleus pulposus to the lumbar nerve root induced morphologic, vascular, and functional changes in the nerve root, suggesting that some factors in the nucleus pulposus may be implicated in the pathogenesis of chronic changes. However, it has not been studied whether the epidural application of nucleus pulposus enhances nociresponses of pain-processing neurons in the superficial dorsal horn of the spinal cord.


METHODS
Extracellular recordings were made from the L5 dorsal horn neurons in 20 Wistar rats. The wide-dynamic-range (WDR) neurons activated by electric stimulation of the ipsilateral footpad of hindpaw were selected, and their responses to noxious and innocuous stimulation were examined after L5-L6 disc herniation onto the L5 nerve root (Group A) and application of the autologous nucleus pulposus (Group B) or fat tissues (Groups C and D).


RESULTS
The herniation of the nucleus pulposus (Group A) and application of the autologous nucleus pulposus (Group B) to the nerve root remarkably enhanced responses of WDR neurons to noxious stimuli for hours, whereas application of fat tissue scarcely enhanced nociresponses (Groups C and D).


CONCLUSIONS
Results suggest that somewhat pathogenic factors in the nucleus pulposus may have a crucial role in the induction of hyperalgesia. This may help to elucidate the reason why a severe pain is sometimes induced without a visually identified protrusion.
Anzai
Hiroyuki
H
Department of Orthopaedic Surgery, Fukushima Medical University, School of Medicine, Fukushima, Japan.
Hamba
Michiko
M
Onda
Akira
A
Konno
Shinichi
S
Kikuchi
Shinichi
S
D000200:Action Potentials; D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006930:Hyperalgesia / Q000209:etiology* / Q000503:physiopathology; D007268:Injections, Epidural; D007403:Intervertebral Disc / Q000637:transplantation*; D007405:Intervertebral Disc Displacement / Q000503:physiopathology; D008161:Lumbosacral Region; D010147:Pain Measurement; D010812:Physical Stimulation; D020671:Posterior Horn Cells / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012585:Sciatica / Q000209:etiology / Q000503:physiopathology; D013126:Spinal Nerve Roots / Q000503:physiopathology; D013997:Time Factors; D016378:Tissue Transplantation / Q000009:adverse effects; D014182:Transplantation, Autologous / Q000009:adverse effects*