The effect of veratrine and aconitine on the excitability of sensory units in the tooth of the cat.

Intradental sensory nerve impulse activity was recorded by means of electrodes inserted into dentinal cavities in the tooth of the cat. Impulses of different amplitudes was recorded. Local application of aconitine (10(-3) g/ml) and veratrine (10(-3) g/ml) induced nerve impulse activity. A rapid increase in the temperature of the tooth surface to 45-47 degrees C, which is known to induce fluid movements in the dentinal tubuli, did not induce any nerve impulse activity. However, after pretreatment of a tooth cavity with veratrine a rapid increase in the temperature of the tooth surface gave rise to nerve impulse activity. Steady state impulse activity induced by brief local application of aconitine was influenced by a rapid increase in the temperature of the tooth; during the increase in temperature impulses of low amplitude increased in frequency while impulses of high amplitude were blocked. Furthermore, reduced pressure applied to the exposed dentin, which also induces fluid movements in the dentin, gave rise to nerve impulse activity. Thus the sensory units in the tooth are stimulated by dentinal fluid movements and alkaloids known to excite mechanoreceptors increase their excitability. It is therefore suggested that the intradental sensory nerve endings are mechanosensitive structures.