The Effect of Therapeutic Ultrasound on Neuropathic Pain and the Related Molecular Biology in Rats with Peripheral Nerve Injury
Po-Ching Huang1*, Yu-Wen Chen2, Ching-Hsia Hung1,3
1Institute of Allied Health Science, National Cheng Kung University, Tainan, Taiwan
2Department of Physical Therapy, China Medical University, Taichung, Taiwan
3Department of Physical Therapy, National Cheng Kung University, Tainan, Taiwan
Introduction: Sciatica is a condition derived from a compression of the sciatic nerve which results in neurological symptoms such as neuropathic pain and severely affects quality of life. Clinical interventions including medication and rehabilitation modalities to ease the symptoms. Ultrasound had been used to treat several neurological conditions such as carpel tunnel syndrome, but the effect remains unclear. The aim of the study was to investigate the effect of ultrasound for treating neuropathic pain and related cytokine regulation. Methods: We chose chronic constriction injury (CCI) animal model to mimic sciatica. Male Sprague-Dawley rats underwent the CCI surgery and received 5 minutes therapeutic ultrasound with 1 W/cm2 intensity and 100% duty cycle 5 days/week for 4 weeks. Behavior testing for thermal hyperalgesia and mechanical hypersensitivity was measured 1 hour after ultrasound treatment daily. After 4 weeks ultrasound treatment, peripheral and central nerves were harvested for ELISA analyses. Results: Both thermal withdrawal latencies and mechanical withdrawal thresholds had a significant decrease after 4 weeks ultrasound intervention. Proinflammatory cytokines of tumor necrosis factor-alpha (TNF-) and interleukin-6 (IL-6) had the tendency of decreasing in both peripheral nerve (i.e., sciatic nerve and peripheral nerve) and central nerve (i.e., spinal cord and dorsal root ganglion). Discussion: Our resulting data suggested that ultrasound could effectively reduce neuropathic pain. The tendency of TNF- and IL-6 implied the possibility of a reduction in inflammation. We had also analyzed the expression of interleukin-10, substance P and neurokinin 1 receptor, but inconsistent patterns were found. Conclusion: A 4-week ultrasound treatment could alleviate neuropathic pain in CCI rats although the decreasing expression of TNF- and IL-6 was no significant. Further studies on central regulation of peripheral neuropathic pain should be considered.