Neurotransmitter release changes induced by low power 830 nm diode laser irradlation on the neuromuscular junctions of the mouse

Background and Objective: Treating patients with a Gallium-Aluminum-Arsenide (GaAlAS) infrared (IR) diode laser reduces muscle spasm and increases mobility in the muscles. The effect of low intensity laser irradiation on nerve function, growth, and repair mechanisms is a contentious area of research. We have addressed one aspect of this controversy by systematically examining the influence of 830 nm laser radiation on neurotransmitter release in neuromuscular junctions (NMJ) of the mouse diaphragm. Study Design/Materials and Methods: Thirty adult mice were studied. Diode laser GaAlAs 830 nm (4 and 12 J/cm(2)) was used. Neurotransmitter release was studied by conventional intracellular recording techniques on curarized muscles or high magnesium media. The quantal content, amplitude, and latency of the end-plate potentials (EPPs) were analyzed. Frequency and amplitude were evaluated for the miniature end-plate potentials (MEPPs). Facilitation of the neurotransmitter release was also evaluated by paired pulse stimulation. Results and Conclusions: The irradiated (12 J/cm(2)) muscles showed a significant reduction in quantal content (P = 0.01) and EPP amplitude (P = 0.04), but the latency, spontaneous transmitter release (MEPPs) and paired pulse facilitation did not change. No alterations were observed in NMJ irradiated with 4 J/cm(2). We conclude that 830 nm diode laser irradiation (at a dose of 12 J/cm(2)) can affect the evoked neurotransmitter release in the mouse motor endplates. Lasers Surg. Med. 35:236-241, 2004.