Thermographic Analysis on the Effects of Low-power Ar⁺ Laser Irradiation on Polar Excitations in Frog Sciatic Nerve

Abstract

It has been reported that low-power laser irradiation (LLI) can block the conduction of nerve impulses and improve recovery from nerve injuries. Since the underlying mechanism remains unclear, we examined thermographic analysis on the effect of LLI on compound action potentials (CAPs) using the law of polar excitation in frog sciatic nerve. Eighteen frogs (Xenopus laevis) were used and their bilateral sciatic nerves were prepared. Amplitudes of cathode-make-exciation (CE) and anode-break-excitation (AE) induced by a supramaximal stimulus with 10 ms pulse duration, and temperature on the nerve surface were simultaneously recorded during LLI (Ar+ laser; 488 nm or 514 nm; 50 mW; 30 min). In the case of 514 nm LLI, standardized CE and AE amplitudes gradually attenuated to 81±5% and 74±7% at 30 min after the onset of LLI, while temperature increased to 38.9±2.4 °C. In the case of 488 nm LLI, CE and AE amplitude attenuated to 74±10% and 42±14% (p<0.01) at 30 min after, while temperature increased to 40.9±2.5°C. Negative correlations between each type of CAP amplitude and temperature deviation were obtained, resulting in good fitting curves of a quadratic function. We conclude that the suppressive effects of LLI on the polar excitations are mainly based on the thermal influence.