Systemic capsaicin treatment has been used in animal research to eliminate sensory nerve function, but little is known about physiological and morphological effects. We investigated the time-dependent changes in nociception and the ultrastructure of sensory nerve fibers after administration of capsaicin in rats. Capsaicin treatment caused transient loss of sensitivity, but transmission electron microscopy showed no structural changes of trigeminal nerve fibers in capsaicin- treated rats as well as controls. These results suggest that the structural damage to sensory nerve fibers may not be a cause of the reduction of sensitivity.
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