Neuropeptide expression in the ferret trigeminal ganglion following ligation of the inferior alveolar nerve

Abstract 

Previous studies have found changes in neuropeptide expression in trigeminal ganglion cells after inferior alveolar nerve (IAN) section. These changes may play a part in the persistent sensory abnormalities that can be experienced after trigeminal nerve injuries. Here, neuropeptide expression after IAN ligation was studied, as this type of injury is thought to be more likely to result in sensory disturbances. The neuropeptides investigated were substance P, calcitonin gene-related peptide, enkephalin (ENK), galanin (GAL), neuropeptide Y (NPY) and vasoactive intestinal polypeptide. In anaesthetised adult female ferrets the left IAN was sectioned and the central stump tightly ligated. Recovery was allowed for 3 days, 3 or 12 weeks before perfusion-fixation. In a second procedure, 1 week before perfusion, the IAN was exposed and an injection made central to the injury site, using a mixture of 4% Fluorogold and 4% Isolectin B4 conjugated to horseradish peroxidase, to identify cell bodies with axons in the inferior alveolar nerve and cells with unmyelinated axons within this population, respectively. Control experiments involved tracer injection alone. After harvesting the tissue, sagittal sections were taken from both the right and left ganglia and immunohistochemical staining used to reveal the presence of peptides and Isolectin B4 tracer. The results showed a significant decrease in GAL expression after injury and an increase in ENK and NPY expression. No significant differences were seen in the expression of the other peptides or in the proportion of lectin-positive cells at any time after injury. When compared with previous data, significant differences were found between peptide expression following nerve ligation and nerve section. These results reveal that the changes in neuropeptide expression in the trigeminal ganglion that follow IAN injury are dependent upon the type of injury. The extent to which changes in the central neuropeptide levels contribute to the development of sensory disorders remains to be established.

Keywords:  Trigeminal ganglion, Inferior alveolar nerve, Fluorogold, Neuropeptides

Abbreviations:  B4-HRP, Isolectin B4 conjugated to horseradish peroxidase, CGRP, calcitonin gene-related peptide, FITC, fluorescein isothiocyanate, PBS, phosphate-buffered saline