Effect of transcranial laser exposure on conditioned-reflex activity of rats

Growing interest in the use of near-infrared laser radiation for the treatment of numerous neurological disorders exists. However the safety of transcranial laser therapy is studied insufficiently. The optimal parameters of low level laser therapy are still discussed. The aim of the present study is to investigate the possible short- and long-term effects of a single or fivefold transcranial laser irradiation of the rat brain (wavelength 890 nm, the pulse duration was 100 ns) on the conditioned-reflex activity of Wistar rat males. Two radiation schedules were used: schedule 1 - impulse frequency 2500 Hz, the output power - 0.7 mW or 1.5 mW; schedule 2 - impulse frequency 10000 Hz, output power - 1.7 mW or 5.0 mW. One hundred and sixty-seven rats were used in the study. Cognitive functions of the rats were tested with the use of the shuttle-box avoidance method. Small transient effect stimulating cognitive function of rats has been registered after daily 15-minutes exposure to 10000 Hz (output power of 5 mW) during 5 days, however this effect had transient character. No essential differences in behavior of experimental and false irradiated control animals are registered after the use of other exposure schedules. According to obtained data one can say that intracranial exposure of rats to near-infrared laser radiation of used frequencies and output power does not produce stimulating effect on their higher nervous activity.