Selective Decrease of Small Sensory Neurons in Lumbar Dorsal Root Ganglia Labeledwith Horseradish Peroxidase after Nd:YAG Laser Irradiation of the Tibial Nerve in the Rat

摘要

Recent electrophysiological evidence indicates that Q-switched Nd:YAG laserirradiation might have selective effects on neural impulse transmission in small slow conducting sensory nerve fibers as compared to large diameter afferents. In an attempt to clarify the ultimate fate of sensory neurons after laser application to their peripheral axons, we have used horseradish peroxidase (HRP) as a cell marker to retrogradely label sensory neurons innervating the distal hindlimb in the rat. Pulsed Nd:YAG laser light was applied to the tibial nerve at pulse energies of 70 or 80 mJ/pulse for 5 min in experimental rats. Seven days later HRP was applied to the left (laser-treated) and to the contralateral (untreated) tibial nerve proximal to the site of laser irradiation. In control animals the numbers of HRP-labeled dorsal root ganglion cells were not significantly different between the right and the left side. In contrast, after previous laser irradiation labeling was always less on the laser treated side. Analysis of the dimensions of labeled cells suggested that the reduction of labeled cells on the laser-treated side was mainly due to a deficit in small sensory neurons.