ANALGESIC EFFECTS OF CRANIAL LASER TREATMENT IN 2 RAT NOCICEPTION MODELS

The present experiments sought to establish dose dependency and time c ourse for effects of cranial laser irradiation in two rodent models of pain. These were the hot plate and tail flick tests, which are both w idely used to quantify analgesic drug effects. The laser used was an O mega Biotherapy 3ML (wavelength 820 nM, average power output 100 mW, p ulse frequency 5 kHz) and irradiation was applied to rats' shaved head s above the midbrain. In the first experiment, four groups of 10 rats received doses of 0, 6, 12, 18, and 24 J/cm(2) in random orders prior to hot plate testing either immediately, 30 min, 1 h or 24 h postlaser . The second study employed three groups of 10 rats receiving 0, 12, a nd 18 J/cm(2) in random orders prior to tail flick testing at the thre e shorter times above. Latency to lick hind paws on the hot plate was highly significantly prolonged by laser treatment across all doses and time periods, F(4, 126) = 4.51, p < 0.01. There was good dose depende ncy for immediate observations, but at 24 h 18 J/cm(2) was the most ef fective dose. Laser treatment also delayed tail flick responses at bot h doses and all time periods, F(2, 54) = 10.60, p < 0.001, but 12 and 18 J/cm(2) doses were similar in efficacy.