Comparison of the effects of pulsed and continuous wave light on axonal regeneration in a rat model of spinal cord injury

Abstract

Light therapy (LT) has been investigated as a viable treatment for injuries and diseases of the central nervous system in both animal models and clinical trials. Based on in vivo studies, LT has beneficial effects on the treatment of spinal cord injury (SCI) [1–3], traumatic brain injury [4], stroke [5–9] and neurodegenerative diseases [10, 11]. Recent clinical trials on stroke have demonstrated that light is safe for the treatment of ischemic stroke in humans [12, 13]. The biomodulatory effects of LT have been investigated to a much greater extent with continuous wave (CW) mode than in pulsed mode. However, there is no clear consensus that one mode is superior to the other. A recent review of the published literature that compared the effects of light in CWor pulsed mode reported that some studies have shown pulsed light to be more effective than CW light, while other studies have shown no effect or a worsening effect with pulsed light compared to no treatment [14]. The studies in which pulsed light was more effective than CW light include LTon wound healing, pain attenuation, bone stimulation and ischemic stroke in animal models and human studies [14]. Lapchak et al. compared CW light with two different frequencies of pulsed light and found that transcranial treatment with both pulsing regimes significantly improved behavioral deficits compared to the CW light [6]. Why pulsed light in some cases improves the outcome of LT is currently unclear, and further investigation is needed. Our previous studies have shown that LT promotes axonal regeneration and functional recovery in both hemisection and contusion models of SCI in rats with CW laser light [2, 3]. The purpose of this study was to compare the effects of CW and pulsed laser light on nerve regeneration in a hemisection model of SCI.