Highlights
- •Neonatal capsaicin treatment led to selective ablation of TRPV1 containing neurons.
- •Neonatal capsaicin treatment reduced peptidergic innervation content in the dental pulp.
- •Loss of peptidergic innervation resulted in early development of apical periodontitis.
Abstract
Introduction
Nociceptive neurons play a critical role in the detection of stimuli evoking actual
or potential tissue injury. In addition, they are involved in neurogenic inflammation
by the peripheral release of neuropeptides such as calcitonin gene-related peptide
(CGRP). The dental pulp and periradicular tissues are innervated by capsaicin-sensitive
neurons known to release CGRP. However, the role of these capsaicin-sensitive neurons
in the development of apical periodontitis is largely unknown. The aim of this study
was to evaluate the contribution of peptidergic neurons to the development of apical
periodontitis.
Methods
Neonatal Sprague-Dawley rats were injected with vehicle (control group) or a single
subcutaneous capsaicin dose to cause the selective ablation of peptidergic neurons
(neonatal capsaicin group). Ablation of capsaicin-sensitive neurons was verified with
confocal microscopy, capsaicin-induced eye-wipe nocifensive behavior test, and by
measurement of immunoreactive CGRP levels in the dental pulp. Five weeks after ablation,
standardized pulp exposures were made in the mandibular left first molars. Mandibles
were harvested at 7, 14, 21, and 28 days after pulp exposure and imaged with micro–computed
tomography (μCT) to quantify apical lesion volume. Data were analyzed by using 2-way
ANOVA analysis with Bonferroni post hoc test.
Results
Rats in the control group displayed a robust capsaicin-induced nocifensive behavior,
which was nearly abolished in the neonatal capsaicin group. In addition, the neonatal
capsaicin group showed a significant depletion of susceptible neurons and CGRP in
the dental pulp compared with control. Importantly, micro–computed tomography analysis
showed larger periradicular lesions at 7 and 14 days after pulp exposure in the neonatal
capsaicin group when compared with control.
Conclusions
Results identify a protective role for capsaicin-sensitive neurons in the initial
phase of apical periodontitis. Thus, interventions or disorders that alter activity
of capsaicin-sensitive fibers are likely to alter the development of apical periodontitis.
Key Words
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Article info
Publication history
Published online: August 11, 2016
Identification
Copyright
Copyright © 2016 American Association of Endodontists.
