PAIN-RELATED LASER-EVOKED POTENTIALS IN AWAKE MONKEYS - IDENTIFICATION OF COMPONENTS, BEHAVIORAL-CORRELATES AND DRUG EFFECTS

Cutaneous stimulation with CO2 laser pulses activates small diameter s ensory afferents and evokes a pain-related potential best recorded fro m the vertex (Cz) of humans. We report here the first successful recor ding of pain-related laser evoked potentials (LEPs) from awake monkeys . Laser pulses with stimulus intensities adjusted to the lowest level giving reproducible cerebral responses were delivered to the shaved ra il of three awake African green monkeys. The proximal and distal tail were stimulated to calculate the conduction velocity of the activated fibers. The effects of subcutaneous injections of morphine and cocaine on the LEPs were evaluated. The results indicate that reproducible LE Ps, with a morphology similar to those obtained from humans, can be re corded from the awake monkey. The calculated conduction velocity of th e activated fibers averaged 8.7 m/s, which is in the range of A delta fibers. Following subcutaneous morphine injections; the LEPs disappear ed and were quickly restored to their baseline amplitude following adm inistration of naloxone. Cocaine administered subcutaneously led to a significant attenuation of LEP amplitudes without producing behavioral sedation. These findings suggest that the LEPs recorded from monkeys represent analgesic-sensitive, nociceptive-related potentials similar to those recorded from humans. (C) 1997 International Association for the Study of Pain. Published by Elsevier Science B.V.