Combined effects of chronic ionizing radiation and repeated laser exposure on cognitive functions of rats

Low-level laser therapy (LLLT) may have utility in the management of side effects of radiation therapy in head and neck cancer (HNC) patients. Although evidence suggests that LLLT is safe treatment for HNC patients, more research is imperative and vigilance remains warranted to detect any potential adverse effects of LLLT on treatment outcomes and survival of HNC patients. The purpose of this study was to evaluate the effect of transcranial low-level laser irradiation (LLLI) in combined with whole-body ionizing radiation (IR) on conditioned-reflex activity of rats. Seventy healthy Wistar female rats were distributed into the following groups: Group 1, sham control; Group 2, LLLI; Group 3, IR; Group 4, IR and LLLI. Group 3 and Group 4 chronically exposed to IR (30 days; 5,3±0,5 mGy/h; 3,7 Gy). Group 2 and Group 4 received five applications of LLLI, once a day for 15 min (wavelength 890 nm, the pulse duration was 100 ns, impulse frequency 10000 Hz, output power - 1,7 mW). Cognitive functions of the rats were tested using shuttle-box avoidance method. The rats were tested 30 minutes later, 24 hours later, and 14 days after the end of LLLI. LLLI and IR in isolated action (groups 2 and 3) did not significantly affect the conditioned reflex activity of rats. The negative effect of combined exposure to these factors (group 4) on the development and reproduction of an active avoidance reflex within 24 hours after exposure was revealed. Gradually this negative effect weakened and within two weeks was leveled. Thus, the combined action of IR and LLLI may pose a potential danger to the cognitive function of the brain.