Stimulation in the rat of a nerve fiber bundle by a short UV pulse from an excimer laser

A bundle of central nervous fibers was excited in the rat with a short pulse (40 ns) of UV light produced by an excimer laser. Evoked responses were recorded in the thalamic ventralis posterior nucleus after stimulation of the medial lemniscus or the cuneate bundle in the spinal cord. The effects of electrical and optical fiber applied UV stimulation were compared in both cases. At threshold, the latency for the UV light stimulation was slightly longer than for electrical stimulation. The excitation threshold was 0.9 J/cm2, very close to the UV photoablation threshold (order of 1 J/cm2). The intermediary events mediating the light excitation are discussed.