Pulsed radiofrequency inhibited activation of spinal mitogen-activated protein kinases and ameliorated early neuropathic pain in rats

Background Pulsed radiofrequency (PRF) has been widely used to treat chronic pain, but the effectiveness and mechanisms in preventing early neuropathic pain have not been well explored. Even fewer knowledge is available in its impact on glia-mediated nociceptive sensitization. This study aims to elucidate the modulation of PRF on nerve injury-induced pain development and activation of spinal mitogen-activated protein kinases (MAPKs). Methods In a rat spinal nerve ligation (SNL) model, a low-volt PRF treatment was applied to the L5 dorsal root ganglion after nerve injury. Nociceptive behaviours were measured by von Frey and heat withdrawal tests at multiple time points. MAPK activations, including p-ERK and p-p38, as well as TNF-alpha level in the spinal dorsal horn were assessed and the cell types that expressed MAPK activation were identified by double immunofluorescence staining. Results We found that SNL promptly induced neuropathic pain in the affected hind limb for over 1 week as well as increased p-ERK and p-p38 in the spinal dorsal horn. PRF significantly attenuated SNL-induced mechanical allodynia and thermal hyperalgesia for 5-7 days. PRF also inhibited ERK and p38 activations, which were found majorly located within neurons and microglia, respectively. Besides, PRF significantly suppressed expression of TNF-alpha in the spinal dorsal horn throughout the course. Conclusions Low-volt PRF significantly ameliorated SNL-induced acute pain. Inferentially, PRF may inhibit spinal sensitization by down-regulating spinal MAPK activations and activation-mediated cytokine release. We demonstrated that early PRF treatment in acute nerve injury helps to ameliorate neuropathic pain development.