NPY-Y1 receptors in normal and inflamed dental pulp

Accumulating research has shown interplay between sympathetic nerves and the immune system during inflammation. Neuropeptide Y (NPY) is a neuropeptide found mainly in the sympathetic nervous system. Recent findings show that NPY immunoreactive nerve fibers undergo sprouting during pulpitis, and that NPY is involved in the regulation of immune responses via its Y1 receptor (NPY-Y1R). Objectives: To map out the distribution and location of NPY-Y1R in normal and inflamed rat dental pulp. Methods: A total of 14 adult male Sprague-Dawley rats were used; sham (n=6), experimental (n=6). Sham animals received no treatment, while experimental animals were deeply anesthetized and had large pulp exposures on maxillary first molars. After 7 days the rats were perfused with 4% paraformaldehyde and 0.2% picric acid. Following decalcification in 10% EDTA, serial sections of 30 µm were processed for double labeling immunohistochemistry with primary antibodies for NPY-Y1R and laminin. Two rats were sacrificed with CO2 inhalation and had molar pulp, incisor pulp, gingiva and trigeminal ganglion removed, snap frozen and processed for RT-PCR. Results: In control rats the NPY-Y1R was mainly located in capillaries and small vessels (mean diamater 10µm) beneath and within the odontoblast layer in the coronal dental pulp. Double labeling with laminin confirmed the colocalization of NPY-Y1R within the wall of blood vessels. Immune cells were not NPY-Y1R in the normal dental pulp. During inflammation, larger blood vessels (mean diameter 25 µm) appeared to be NPY-Y1R immunoreactive as well as immune cells localized around the inflammatory site. RT-PCR revealed the presence of NPY-Y1R in the dental pulp, trigeminal ganglion and gingiva. Conclusion: The NPY-Y1R is mainly located to small blood vessels in the dental pulp. During inflammation it is expressed in larger blood vessels and in immune cells.