Tissue pH and temperature regulate pulpal nociceptors

The TRPV1 receptor acts as a sensor for environmental changes in pH and temperature. Since many nociceptors express TRPV1, it is possible that local tissue-cooling may inhibit nociceptor activity via reduction of TRPV1 activation. The present study used isolated superfused rat dental pulp to test the hypothesis that capsaicin receptors are activated in inflamed tissue, as measured by alterations in neuropeptide release. We tested the hypothesis that alterations in the tissue temperature and pH of isolated superfused rat dental pulp regulate capsaicin-induced release of calcitonin gene-related peptide (CGRP). Application of capsaicin with increased proton concentration (i.e., lowered pH) produced a nearly two-fold increase in peak immunoreactive CGRP release, as compared with capsaicin applied at a pH of 7.4. Reduction in tissue temperature from 37 degrees C to 26 degrees C completely blocked the capsaicin effect. The study indicates that environmental stimuli regulate the activity of capsaicin-sensitive neurons innervating dental pulp, and these factors may be significant clinically in the development and amelioration of dental pain.