Electrophysiologic changes in dorsal root ganglion neurons and behavioral changes in a lumbar radiculopathy model

Study Design. The DRG neuron was electro-physiologically investigated using a rat model with constriction of the proximal site of the DRG. Objectives. To investigate the pathomechanisms of lumbar radiculopathy, we established a rat model with constriction of the proximal site of the DRG. And to characterize the DRG neurons in the rat model of lumbar radiculopathy, the physiologic properties regarding action potential, Na+, and K+ current of the DRG neurons were analyzed through the use of patch clamp recordings. Summary of Background Data. In lumbar root constriction models, properties of secondary afferent neurons in the dorsal horn have been investigated. However, the electrical properties of DRG neuron have not been well investigated. Methods. To compare the excitability of DRG neurons between root constriction models and sham, we examined the threshold current, action potential (AP) threshold, resting membrane potential (RMP), afterhyperpolarization (AHP), action potential duration 50 (APD50), action potential amplitude, maximum rise time of AP, and pattern of discharges evoked by depolarizing current. We also examined the peak Na+ current and steady-state Na+ and K+ currents with the voltage clamp technique. Results. The rats in the root constriction group demonstrated mechanical allodynia and thermal hyperalgesia. In measurement of the action potential, lower threshold current, more depolarized RMP, larger AHP, and prolonged APD50 were measured in the root constriction neurons compared with the sham group. The incidence of sustained burst was significantly higher in root constriction neurons. The Na+ current in root constriction neurons was markedly larger. There were no significant differences in K+ current density and voltage dependency. Conclusions. The constriction of lumbar root increased excitability and Na+ current amplitude of DRG neurons. These findings indicate that lumbar radicular pain may be associated with increased excitability of involved DRG neurons.