Changes in neuropeptide expression in the trigeminal ganglion following inferior alveolar nerve section in the ferret

Abstract

Changes in neuropeptide expression in afferent nerve fibres may play a role in the persistent sensory abnormalities that can be experienced following trigeminal nerve injuries. We have therefore studied changes in the expression of the neuropeptides substance P, calcitonin gene-related peptide, enkephalin, galanin, neuropeptide Y and vasoactive intestinal polypeptide in the trigeminal ganglion following peripheral nerve injury. In anaesthetised adult female ferrets, the left inferior alveolar nerve was sectioned and recovery allowed for three days, three weeks or 12 weeks prior to perfusion–fixation. During a second procedure, one week prior to perfusion, the inferior alveolar nerve 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 animals received tracer injection alone. After harvesting the tissue, sagittal sections were taken from both the right and left ganglia and immunohistochemical staining was used to reveal the presence of peptides and isolectin B4–horseradish peroxidase tracer. Within the Fluorogold-labelled population, cell counts revealed a significant reduction in the proportion of substance P-containing cells at three days ( P=0.0025), three weeks ( P=0.0094) and three months ( P=0.0149) after nerve section, and a significant reduction in the proportion of calcitonin gene-related peptide-containing cells at three days ( P=0.0003) and three weeks ( P=0.007). No significant changes were seen in the expression of the other peptides, or at other time periods. A significant reduction in the number of isolectin B4–horseradish peroxidase-positive cells (with unmyelinated axons) was seen at three days ( P=0.0025), three weeks ( P=0.0074) and three months after the injury ( P=0.0133). These results demonstrate a significant reduction in the expression of some neuropeptides in the early stages after inferior alveolar nerve section. Some of the results differ markedly from those reported previously in other systems, and may be related to the specific nerve studied, species variations or differences between spinal and trigeminal nerves.