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 firing evoked by mechanical compression or hypoxia of canine lumbar dorsal roots with dorsal root ganglia using an in vitro model.
OBJECTIVES: The results were correlated to understand the pathophysiology of radiculopathy, which manifests abnormal sensation and pain. SUMMARY OF BACKGROUND DATA: It has been speculated that blood flow in the nerve root and mechanical compression play major roles in the production of radiculopathy symptoms. However, no precise experimental studies have been conducted on the relationship between these factors and the development of ectopic firing.
METHODS: Canine lumbar dorsal roots with dorsal root ganglia were immersed in an oxygenated artificial cerebrospinal fluid, 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 firing were much lower in dorsal root ganglia than in dorsal roots, and the firing lasted for a longer period in dorsal root ganglia. Under hypoxia, dorsal root ganglia showed firing, and their thresholds from mechanical stimuli decreased significantly. In dorsal roots, impulse propagation was not affected, whereas firing was seen under the hypoxic condition.
CONCLUSION: Dorsal root ganglia are highly sensitive to mechanical compression and hypoxia and closely related to abnormal sensations and pain in radiculopathy.