CRANIAL IRRADIATION WITH GAALAS LASER LEADS TO NALOXONE REVERSIBLE ANALGESIA IN RATS

Laser irradiation of the rat cranium can produce analgesia. The presen t experiment investigated the mechanism of such action. 27 rats receiv ed all possible combinations of laser (0, 6.4, and 12J/cm(2)) and nalo xone (0, 5, and 10 mg/kg) prior to a hot plate test. Laser (820 nm, KH z pulsing, Omega Laser Systems, London) was applied to the rats' skull s and hind paw lick latencies (in seconds) were recorded immediately, 30 min., and 24 hr. after the administration of treatment. When animal s were tested immediately following laser irradiation at 12J/cm(2) sig nificant analgesia resulted. Treatment with naloxone at either dose an tagonised this effect, but naloxone produced no significant hyperalges ia when given alone. This suggests that opioid peptide mechanisms medi ate the analgesic action of low-intensify laser irradiation of the cra nium.