Proceedings of The Physiological Society

University of Cambridge (2008) Proc Physiol Soc 11, C75

Oral Communications

Primary afferent neuropeptide mRNA regulation in experimental periodontitis in the rat

S. Abd El-Aleem1, B. Morales Aza2, L. F. Donaldson2

1. Histology, Minia University, Minia, Egypt. 2. Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom.

Previously we have shown that chronic periodontal bone loss in rats is associated with an alteration in the expression of neuropeptide mRNAs in both ipsi- and contralateral trigeminal ganglia (TG) (1), indicating a possible neurogenic component to periodontitis. The aim of this study was to determine whether denervation of the periodontium prior to induction of periodontitis would affect the expression of neuropeptide mRNA in TG. Periodontitis was induced in adult male rats (250-300g) by unilateral buccal intragingival injection of lipopolysaccharide (LPS, 10mg/ml; 1µl) between the first and second mandibular molars (1) under recoverable anaesthesia (Hypnorm 0.3 mg/kg (fentanyl citrate 0.1 mg/kg and fluanisone 3 mg/kg) i.m. injection + Diazepam 2.5 mg/kg i.p.). The effect of denervation ± periodontal inflammation was studied using inferior alveolar nerve (IAN) section either ipsilateral or contralateral to periodontitis. Animals with IAN section alone, and surgical exposure with no section served as control groups. Animals were killed by decapitation under halothane anaesthesia 7 days after periodontitis induction, and TG removed, rapidly frozen, sectioned and processed for in situ hybridisation for preprotachykinin (PPT) and calcitonin gene-related peptide (CGRP) mRNA expression. Levels of mRNA expression were determined by silver grain counting in small (<30µm diameter) neurons in both TG. Data were compared using one way ANOVA followed by Tukey-Kramer multiple comparisons test comparing the expression levels in the experimental groups to those of the controls. LPS injection, and subsequent unilateral periodontitis resulted in significant up-regulation in small neurons in the ipsilateral (p<0.05) contralateral TG (p<0.05) as found previously (1). IAN section alone resulted in significant (p<0.03) down-regulation of both PPT and CGRP mRNA in the ipsilateral TG, with no changes on the contralateral side. Surprisingly, unilateral periodontitis with contralateral IAN section was associated with a significant (p<0.03) down-regulation ipsilateral, and up-regulation (p<0.04) of PPT and CGRP contralateral to the periodontitis. Periodontitis + ipsilateral IAN section resulted in significant ipsilateral down-regulation (p<0.05) of PPT and CGRP, with no contralateral changes. Sham IAN section did not result in any significant changes in mRNA expression. While unilateral experimental periodontitis was associated with increased expression of PPT and CGRP in TG neurons ipsilateral and contralateral to the inflammation, denervation prior to induction of periodontitis resulted in an alteration in these changes. This suggests that mRNA changes are regulated in TG by the presence of inflammation. We speculate that neurogenic inflammation could be a contributing factor to periodontal disease.

Where applicable, experiments conform with Society ethical requirements