Immunohistochemical Analysis of Inflammatory Mediators in NPY Knockout Mice

Objectives: Inflammation of the TMJ is responsible for nociception in 7-15% of the adult population and may cause nociceptive responses including neural, physiological or behavioral reactions that are typically reported as painful. Few reports describe the contributions of Neuropeptide Y (NPY) to TMJ nociception. The aim of this study was to utilize NPY knockout mice to examine changes in substance P (SP) and calcitonin gene-related peptide (CGRP) in the TMJ tissues and trigeminal ganglia (TG) in response to inflammation. Methods: Twenty adult male NPY knockout mice were divided into two groups, of which one group of ten was injected with complete Freund's adjuvant (CFA, 30 μg in 6 μl of paraffin oil) into the TMJ to induce acute inflammation (KO+CFA) while the other group of ten mice did not receive CFA (KO only). In addition, twenty age matched wild type male mice were grouped similarly and received the same treatments (WT+CFA or WT only). All mice were sacrificed one week later and TMJ tissues (disc, retrodiscal, and capsule) and TG were removed and processed for immunohistochemical analysis of CGRP and SP. Results: A significant increase in SP and CGRP expression relative to the uninjected controls for both KO+CFA versus KO only and WT+CFA versus WT only in both the TG (p£0.05) and the TMJ tissues (p£0.01) was observed. However, levels for both SP and CGRP were significantly decreased in the TMJ tissues of the KO+CFA mice in comparison to the WT+CFA mice (p£0.01) and TG (p£0.05). Conclusions: The significant decrease in SP and CGRP levels in NPY knockout mice indicates that NPY may be involved in the inflammatory process during adjuvant-induced inflammation of the TMJ, providing further evidence of its role and importance in this process. Supported by the Baylor Oral Health Foundation.