title: Inhibitory effects of laser irradiation on peripheral mammalian nerves and relevance to analgesic effects: a systematic review.
abstract: OBJECTIVE
  The objective of this review was to systematically identify experimental studies of non-ablative laser irradiation (LI) on peripheral nerve morphology, physiology, and function. The findings were then evaluated with special reference to the neurophysiology of pain and implications for the analgesic effects of low-level laser therapy (LLLT).
  
  
  BACKGROUND
  LLLT is used in the treatment of pain, and laser-induced neural inhibition has been proposed as a mechanism. To date, no study has systematically evaluated the effects of LI on peripheral nerve, other than those related to nerve repair, despite the fact that experimental studies of LI on nerves have been conducted over the past 25 years.
  
  
  METHODS
  We searched computerized databases and reference lists for studies of LI effects on animal and human nerves using a priori inclusion and exclusion criteria.
  
  
  RESULTS
  We identified 44 studies suitable for inclusion. In 13 of 18 human studies, pulsed or continuous wave visible and continuous wave infrared (IR) LI slowed conduction velocity (CV) and/or reduced the amplitude of compound action potentials (CAPs). In 26 animal experiments, IR LI suppressed electrically and noxiously evoked action potentials including pro-inflammatory mediators. Disruption of microtubule arrays and fast axonal flow may underpin neural inhibition.
  
  
  CONCLUSIONS
  This review has identified a range of laser-induced inhibitory effects in diverse peripheral nerve models, which may reduce acute pain by direct inhibition of peripheral nociceptors. In chronic pain, spinal cord changes induced by LI may result in long-term depression of pain. Incomplete reporting of parameters limited aggregation of data.
authors: Nerve Research Foundation, Brain and Mind Research Institute, The University of Sydney, Camperdown, New South Wales, Australia. robertachow@iinet.net.au
authors: Roberta
authors: R
authors: Chow
authors: Patricia
authors: P
authors: Armati
authors: E-Liisa
authors: EL
authors: Laakso
authors: Jan M
authors: JM
authors: Bjordal
authors: G David
authors: GD
authors: Baxter
mesh_terms: D000200:Action Potentials; D000698:Analgesia; D000818:Animals; D005071:Evoked Potentials; D006801:Humans; D028022:Low-Level Light Therapy; D009431:Neural Conduction; D010146:Pain / Q000532:radiotherapy*; D010525:Peripheral Nerves / Q000503:physiopathology / Q000528:radiation effects*