THE EFFECTS OF MECHANICAL COMPRESSION AND HYPOXIA ON NERVE ROOT AND DORSAL-ROOT GANGLIA - AN ANALYSIS OF ECTOPIC FIRING USING AN IN-VITRO MODEL

Study Design. This study analyzed in vitro experiments of ectopic firi ng evoked by mechanical compression or hypoxia of canine lumbar dorsal roots with dorsal root ganglia using an in vitro model. Objectives. T he results were correlated to understand the pathophysiology of radicu lopathy, which manifests abnormal sensation and pain. Summary of Backg round Data. It has been speculated that blood flow in the nerve root a nd mechanical compression play major roles in the production of radicu lopathy symptoms. However, no precise experimental studies have been c onducted on the relationship between these factors and the development of ectopic firing. Methods. Canine lumber dorsal roots with dorsal ro ot ganglia were immersed in an oxygenated artificial cerebrospinal flu id, and activity of the nerve root was recorded using bipolar platinum electrodes. Using this model, the effects of quantitative mechanical compression and hypoxia on the ectopic firing were analyzed. Results. When compression was applied, mechanical thresholds for eliciting firi ng were much lower in dorsal root ganglia than in dorsal roots, and th e firing lasted for a longer period in dorsal root ganglia. Under hypo xia, dorsal root ganglia showed firing, and their thresholds from mech anical stimuli decreased significantly, whereas firing was seen under the hypoxic condition. Conclusion. Dorsal root ganglia are highly sens itive to mechanical compression and hypoxia and closely related to abn ormal sensations and pain in radiculopathy.