Effect of serotonin (5-HT) and calcitonin gene-related peptide (CGRP) on the function of intradental nerves in the dog.

Several inflammatory mediators including serotonin (5-HT) have been indicated to play a role in the sensitization of intradental nerves. In the present investigation, using the single fibre recording technique, the effect of locally applied 5-HT (1 mg/ml) and calcitonin gene-related peptide (rat CGRP 2 micrograms/microliters) on the function of intradental nerves in the dog was studied. The effect of these substances on the pulpal blood flow was also investigated to check their effective diffusion into the dental pulp. 5-HT induced a low-frequency background firing in 11 out of 30 nerve fibres. The number of fibres responding to probing, air blast and osmotic stimulation was increased significantly after 5-HT application. Three fibres responded to cold stimulation after 5-HT application; no responses were induced before. After CGRP application, a continuous low-frequency firing was induced only in 1 fibre out of 11 and 1 fibre which before did not respond to osmotic stimulation gave responses to saturated glucose. The responses to probing and air blasts were qualitatively unchanged. Local application of either of the substances induced a change in pulpal blood flow. It is suggested that while 5-HT is able to sensitize intradental nerves to various hydrodynamic stimuli, CGRP seems to be less effective. Pulpal inflammation with the release of inflammatory mediators may significantly affect the degree of dentine sensitivity.