Fig. 1. Induction of long-term potentiation of synaptic strength between primary afferent C fibers and neurons in superficial spinal dorsal horn by high-frequency stimulation (HFS) of sciatic nerve fibers at C-fiber strength. In each experiment, C fiber–evoked potentials were provoked by electrical stimulation of the sciatic nerve. Responses were normalized to the area of C fiber–evoked potentials recorded 60 min before HFS was applied. Mean areas ± SEMs were expressed as percent of controls and were plotted versus time. HFS resulted in long-term potentiation during urethane anesthesia, isoflurane, and sevoflurane. Original recordings from field potentials immediately before and 30 min after HFS during isoflurane anesthesia are shown above the graphs. 1,2