Peripheral administration of low pH solutions causes activation and sensitisation of convergent dorsal horn neurones in the anaesthetised rat.

This is the first study to examine the effects of peripheral administration of acid on the activity of dorsal horn neurones in vivo. Extracellular recordings from convergent neurones revealed increases in neuronal activity evoked by administration of low pH solutions into the peripheral receptive field. Threshold for activity ranged from pH 5.85 to 2.5. The magnitude of responses increased with decreasing pH; maximum effects were achieved with pH 2.5 (648+/-181 action potentials/60 s, as compared to control-evoked activity of 86.3+/-29 action potentials/60 s). Activity lasted for up to 60 s, likely to represent the time for which the solutions were able to surmount the buffering capacity of the intact hindpaw. Significant sensitisation of the neurones to both innocuous (von Frey filament 9 g) and noxious (30 g) mechanical punctate stimuli was also observed.