The effects of Na+ channel blockers on somatosensory processing by rat dorsal horn neurones

Two voltage-activated Na+ channel blockers, lamotrigine and flunarizine were applied ionophoretically to extracellularly recorded dorsal horn neurones to assess effects on activation by noxious (mustard oil) and innocuous (brush) stimuli. Lamotrigine and flunarizine caused significantly greater reductions in mustard oil-evoked activity (> 50% in both cases) than in brush-evoked activity (13 +/- 7% and 29 +/- 6%; p < 6%; +/- 0.005 and p < 0.05 respectively) at equivalent ionophoretic currents. Similar results were observed when lamotrigine was administered i.v. Thus, the activation of dorsal horn neurones by nociceptive and non-nociceptive afferent inputs can be differentiated by the blockade of a lamotrigine/flunarizine-sensitive Na+ channel, at a spinal site.