Neuropeptide Y Knockout Alters Periapical Lesion Development

Objectives: Contributions from sympathetic efferents, such as neuropeptide Y (NPY), may play a role in pathological states associated with nociception and hyperalgesia. Contamination of the tooth pulp often leads to pulpal necrosis and formation of periapical granulomas and cysts. The purpose of this study was to determine the effects of NPY on development of periapical lesions. Methods: Forty mice, either wild type or NPY knockout, had periapical lesions made to the left mandibular and maxillary first molars. The right first molars were left as untreated controls. The mice were sacrificed 1, 2, 4, and 8 weeks after pulpal exposure. All first molars were removed as part of four groups: wild type plus lesion (WT+L), wild type without lesion (WT only), NPY knockout plus lesion (KO+L) and NPY knockout without lesion (KO only). Pulp tissues and trigeminal ganglia (TG) were removed and homogenized. RNA was extracted and real time RT-PCR was run to examine changes in expression of IL-1β, SP and CGRP. Results: A significant increase in the expression of SP and CGRP was observed in the WT+L versus WT only and KO only in both the TG (p£0.01) and pulp tissues (p£0.05), the levels of which increased over time. However, levels for both SP and CGRP were significantly decreased in both tissues of the KO+L mice in comparison to the WT+L mice (p£0.01). This same trend held true for IL-1β expression in the pulp tissue (p£0.05). Conclusions: The significant decrease in IL-1β, SP and CGRP levels in NPY knockout mice with periapical lesions indicate that NPY may be play a role in the development of periapical lesions, providing further evidence of its role and importance in this process. Supported by the American Association of Endodontists Foundation and the Baylor Oral Health Foundation.