Laser-induced withdrawal test for electrophysiological recordings of nociception.

CO(2) lasers are often used in pain research. However, the stimulation parameters of the CO(2) lasers, such as beam diameter, laser power, etc., used for these animal nociceptive studies vary across laboratories. The differences of the parameters usually make novices who want to reproduce the laser-evoked responses confused to follow. In this study, we quantitatively measured the laser-withdrawal reflex of the rat to ascertain the individual laser-withdrawal threshold and then found the thresholds were diverse among the rats we adopted. Furthermore, the optimal stimulation distance, the most conveniently modified stimulation parameter of CO(2) laser stimuli, was also determined. We suggest that laser-withdrawal tests should be applied before the electrophysiological recordings in order to verify the efficiency of the induced nociception and substantiate the operational parameters of the CO(2) laser device.