LASER IRRADIATION ABATES NEURONAL RESPONSES TO NOCICEPTIVE STIMULATION OF RAT-PAW SKIN

The effects of diode laser irradiation on peripheral nerves was examin ed by monitoring neuronal discharges elicited by application of variou s stimuli to the hind-paw skin of rats. Neuronal discharges elicited b y brush, pinch, cold, and/or heat stimulation, as well as chemical sti mulation by injection of turpentine (0.1 ml, SC) were recorded from L5 dorsal roots in urethane-anesthetized rats. Diode laser irradiation ( 830 nm, 40 mW, 3 min, continuous wave) of the saphenous nerve exposed from the muscle of the lower leg significantly inhibited neuronal disc harges elicited by pinch (68.4 +/- 6.5%), cold (45.4 +/- 9.2%), and he at stimulation (49.2 +/- 11.3%). Neuronal discharges induced by brush stimulation (104.3 +/- 4.7%) were not affected by laser irradiation. I njection of turpentine, a chemical irritant, into the hind-paw skin (0 .1 ml, SC) elicited neuronal discharges in the ipsilateral dorsal root , and these discharges were significantly inhibited or abolished by la ser irradiation. In 6- to 7-week-old rats treated neonatally with caps aicin (10 mg/kg, SC), injection of turpentine into the hind-paw skin d id not elicit neuronal discharges and laser irradiation did not affect the background discharges. These data suggest that laser irradiation may selectively inhibit nociceptive neuronal activities.