The effect of serotonin-noradrenaline reuptake inhibitor duloxetine on the intervertebral disk-related radiculopathy in rats.

Abstract

Neuropathic pain, commonly related to intervertebral disk (IVD) degeneration, responds poorly to standard pain treatments. Serotonin-noradrenaline reuptake inhibitors (SNRIs) have been reported to reduce neuropathic pain; however their effect on radiculopathy induced by lumbar disk herniation remains unclear. The aim of this study was to investigate the effect of SNRI duloxetine in rat model of IVD-related neuropathic pain. Effects of SNRI duloxetine were tested in Sprague-Dawley rats (n = 135). Neuropathic pain was induced by applying autologous nucleus pulposus (NP) on the left L5 dorsal root ganglion (DRG). Duloxetine in concentrations 0.4 mg/kg (low dose) and 1.2 mg/kg (high dose) or saline were administered orally for 10 days. Von Frey test was carried out on post-operative days 2, 7, 14, 21, and 28 to test pain sensitivity. Immunohistochemistry of L5 DRG and L5 segment of spinal cord (SC) was performed on days 7 and 21 to examine expressions of tumor necrosis factor alpha (TNF), nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and ionized calcium-binding adapter molecule 1 (Iba1). On days 14, 21, and 28, expressions of TNF in DRG as well as NGF and BDNF in SC were tested by immunoblotting. Sham-operated rats and naive rats were used as controls. Duloxetine in both concentrations significantly improved pain threshold from postoperative day 21 onward, compared to the NP + saline group (p < 0.05). High-dose duloxetine significantly inhibited the expression of TNF in DRG (day 28, p < 0.05). Both duloxetine concentrations reduced the expression of NGF in SC (day 21, p < 0.05), but the expression of BDNF remained unchanged. SNRI duloxetine inhibited neuropathic pain in rats possibly via down-regulating TNF, NGF, and microglia activation. We conclude that duloxetine, and most likely other SNRIs, may be used for the management of lumbar neuropathic pain.