Neuropeptide Y Y1 receptor effects on pulpal nociceptors

Abstract

Neuropeptide Y (NPY) is an important modulatory neuropeptide that regulates several physiological systems, including the activity of sensory neurons. We evaluated whether activation of the NPY Y1 receptor could modulate the activity of capsaicin-sensitive nociceptors in trigeminal ganglia and dental pulp. We tested this hypothesis by measuring capsaicin-stimulated calcitonin gene-related peptide release (CGRP) as a measure of nociceptor activity. Capsaicin-evoked CGRP release was inhibited by 50% (p < 0.05) in trigeminal ganglia and by 26% (p < 0.05) in dental pulp when tissues were pre-treated with [Leu(31),Pro(34)]NPY. The Y1 receptor was found to co-localize with the capsaicin receptor TRPV1 in trigeminal ganglia. These results demonstrate that activation of the Y1 receptor results in the inhibition of the activity of capsaicin-sensitive nociceptors in the trigeminal ganglia and dental pulp. These findings are relevant to the physiological modulation of dental nociceptors by endogenous NPY and demonstrate an important novel analgesic target for the treatment of dental pain.

Figure 1

Effect of [Leu³¹,Pro³⁴]NPY on capsaicin-stimulated CGRP release from trigeminal ganglia. Freshly isolated ganglia were chopped and placed in perfusion chambers. Tissues were pre-treated with the Y1 agonist [Leu³¹,Pro³⁴]NPY (30 nM) for 1 fraction (7 min). Tissues were then co-treated with [Leu³¹,Pro³⁴]NPY (30 nM) and capsaicin (30 μM) for 1 fraction (7 min). Data are presented as fold-increase over baseline (BL), where the baseline represents the average CGRP release from the first 3 fractions (mean BL = 53.1 ± 4.0 fmol/mL). Statistical analysis by two-way ANOVA demonstrated a significant effect of drug treatment (F = 5.35, p < 0.05) and time (F = 8.21, p < 0.0001) on the measured outcome of CGRP release. A Bonferroni post hoc test demonstrates that the agonist-treated tissues released significantly less CGRP when stimulated by capsaicin in fraction 6 compared with vehicle-treated (veh) tissues (p < 0.001). Error bars = SEM. N = 15.

Figure 2

Effect of [Leu³¹,Pro³⁴]NPY on peak capsaicin-stimulated CGRP release from trigeminal ganglia and dental pulp. Data are presented as fold-increase over baseline (BL), where baseline represents the average CGRP release prior to drug treatment (3 fractions in trigeminal ganglia and 5 fractions in dental pulp; BL = 53.1 ± 4.0 fmol/mL for trigeminal ganglia and 4.6 ± 0.3 fmol/mL for dental pulp). Statistical analysis by an unpaired two-tailed t test demonstrated that tissues pre-treated with [Leu³¹,Pro³⁴]NPY (30 nM) released significantly less CGRP when stimulated with capsaicin (30 μM in trigeminal ganglia and dental pulp) (p < 0.05 for trigeminal ganglia and dental pulp). Error bars = SEM. N = 13 for trigeminal ganglia; n = 18 for dental pulp.

Figure 3

Co-localization of TRPV1 receptor immunoreactivity (green) with Y1 receptor immunoreactivity (red) in rat trigeminal ganglia (magnification = 20X). White arrows indicate examples of cells demonstrating co-localization. The co-localization of the Y1 receptor with the TRPV1 receptor indicates that Y1 receptors are localized on capsaicin-sensitive nociceptors.