Changes in TRPV1 Receptor, CGRP, and BDNF Expression in Rat Dorsal Root Ganglion with Resiniferatoxin-Induced Neuropathic Pain: Modulation by Pulsed Radiofrequency Applied to the Sciatic Nerve

Pulsed radiofrequency (PRF) is a safe method of treating neuropathic pain by generating intermittent electric fields at the needle tip. Resiniferatoxin (RTX) is an ultrapotent agonist of transient receptor potential vanilloid subtype-1 (TRPV1) receptors. We investigated the mechanism of PRF using a rat model of RTX-induced neuropathic pain. After administering RTX intraperitoneally, PRF was applied to the right sciatic nerve. We observed the changes in TRPV1, calcitonin gene-related peptide (CGRP), and brain-derived neurotrophic factor (BDNF) in the dorsal root ganglia by western blotting. Expressions of TRPV1 and CGRP were significantly lower in the contralateral (RTX-treated, PRF-untreated) tissue than in control rats (p<0.0001 and p<0.0001, respectively) and the ipsilateral tissues (p<0.0001 and p<0.0001, respectively). BDNF levels were significantly higher in the contralateral tissues than in the control rats (p<0.0001) and the ipsilateral tissues (p<0.0001). These results suggest that, while TRPV1 and CGRP are decreased by RTX-induced neuronal damage, increased BDNF levels result in pain development. PRF may promote recovery from neuronal damage with concomitant restoration of TRPV1 and CGRP, and exert its analgesic effect by reversing BDNF increase. Further research is required to understand the role of TRPV1 and CGRP restoration in improving mechanical allodynia

Upregulation of ERK phosphorylation in rat dorsal root ganglion neurons contributes to oxaliplatin-induced chronic neuropathic pain.

Oxaliplatin is the first-line chemotherapy for metastatic colorectal cancer. Unlike other platinum anticancer agents, oxaliplatin does not result in significant renal impairment and ototoxicity. Oxaliplatin, however, has been associated with acute and chronic peripheral neuropathies. Despite the awareness of these side-effects, the underlying mechanisms are yet to be clearly established. Therefore, in this study, we aimed to understand the factors involved in the generation of chronic neuropathy elicited by oxaliplatin treatment. We established a rat model of oxaliplatin-induced neuropathic pain (4 mg kg-1 intraperitoneally). The paw withdrawal thresholds were assessed at different time-points after the treatment, and a significant decrease was observed 3 and 4 weeks after oxaliplatin treatment as compared to the vehicle treatment (4.4 ± 1.0 vs. 16.0 ± 4.1 g; P < 0.05 and 4.4 ± 0.7 vs. 14.8 ± 3.1 g; P < 0.05, respectively). We further evaluated the role of different mitogen-activated protein kinases (MAPKs) pathways in the pathophysiology of neuropathic pain. Although the levels of total extracellular signal-regulated kinase (ERK) 1/2 in the dorsal root ganglia (DRG) were not different between oxaliplatin and vehicle treatment groups, phosphorylated ERK (p-ERK) 1/2 was up-regulated up to 4.5-fold in the oxaliplatin group. Administration of ERK inhibitor PD98059 (6 μg day-1 intrathecally) inhibited oxaliplatin-induced ERK phosphorylation and neuropathic pain. Therefore, upregulation of p-ERK by oxaliplatin in rat DRG and inhibition of mechanical allodynia by an ERK inhibitor in the present study may provide a better understanding of intracellular molecular alterations associated with oxaliplatin-induced neuropathic pain and help in the development of potential therapeutics