Hypoalgesic effect of laser photobiostimulation shown by rat tail flick test.

We demonstrated a 50% increase in pain threshold following laser photobiostimulation (LPBS), employing rat tail-flick test. Helium-neon laser (1 mW) of three different pulsing frequencies (4, 60, and 200 Hz) was applied on tail low resistance point for 15 seconds and tail-flick latencies were measured 30 minutes, 1 hour, 24 hours, 48 hours and 7 days later. LPBS of 4 Hz produced hypoalgesia of rapid onset and short duration while the response to 60 Hz was delayed and lasted longer. LPBS of 200 Hz did not produce any hypoalgesia.