Effect of semiconductor GaAs laser irradiation on pain perception in mice

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Abstract
The influence of subacute exposure (11 exposures within 16 days) of mice to the low power (GaAs) semiconductive laser‐stimulated irradiation on pain perception was investigated. The pain perception was determined by the latency of foot‐licking or jumping from the surface of a 53°C hot plate.Repeated hot‐plate testing resulted in shortening of latencies in both sham‐ and laser‐irradiated mice. Laser treatment (wavelength, 905 nm; frequency, 256 Hz; irradiation time, 50 sec; pulse duration, 100 nsec; distance, 3 cm; peak irradiance, 50 W/cm2 in irradiated area; and total exposure, 0.41 mJ/cm2) induced further shortening of latencies, suggesting its stimulatory influence on pain perception.Administration of morphine (20 mg/kg) prolonged the latency of response to the hot plate in both sham‐ and laser‐irradiated mice. This prolongation tended to be lesser in laser‐irradiated animals.Further investigations are required to elucidate the mechanism of the observed effect of laser.