Effects of small myelinated afferent fiber stimulation on the threshold of tail flick reflex in the rat

Effects of A-delta afferent fiber stimulation on the response threshold in the tail flick reflex were examined in rats anesthetized with thiamylal sodium. In a statistical analysis, the suppressive effect on the skin temperature at the time of the tail flick (tail flick temperature) was represented as a percent of maximal possible effect (%MPE) expressing more clearly the degree of change of the tail flick temperature. A-delta afferent fiber stimulation produced a reduction of EMG activity of the tail muscle, but no changes of both the tail flick latency and the tail flick temperature were observed. The results of the present study and the previously reported modulation system in the spinal cord dorsal horn are discussed.