Expression patterns of nociceptin in rats following experimental tooth movement

Behavioral Responses and Expression of Nociceptin/Orphanin FQ and Its Receptor (N/OFQ-NOP System) during Experimental Tooth Movement in Rats

Objective

To determine behavioral testing after experimental tooth movement in rats and to explore the role of nociceptin/orphanin FQ and its receptor (the N/OFQ-NOP system) in pain induced by experimental tooth movement.

Design

The mouth-wiping behavior of rats was assessed by studying behavioral responses after experimental tooth movement. The distribution of N/OFQ in the periodontal ligament, the trigeminal ganglion (TG), and the caudal one-third of the trigeminal subnucleus caudalis (Vc) was assessed by immunohistochemistry. The variations in N/OFQ expression in the TG and Vc were measured by Western blotting. The ongoing changes in the gene expression of the prepronociceptin gene and opioid receptor-like 1 receptor were assessed in the TG and Vc by real-time polymerase chain reaction (RT-PCR).

Results

Overall, the mouth-wiping behavior increased significantly. The behavior first increased and then gradually decreased to a low level, showing cyclical variation. N/OFQ immunoreactivity increased in the periodontal ligament after tooth movement. ppN/OFQ mRNA and protein levels showed a time-dependent increase in the TG and were positively correlated with pain stimulus. NOP gene levels showed large fluctuations. In the Vc, the expression and changes in the N/OFQ-NOP system showed the opposite trend as those noted in TG and the periodontal membrane.

Conclusion

The N/OFQ system may have a complex regulatory function in the pain induced by tooth movement and may be related to inflammation caused by orthodontic tooth movement and periodontal damage. The specific mechanism remains to be further studied.

N/OFQ modulates orofacial pain induced by tooth movement through CGRP-dependent pathways

BACKGROUND

Nociceptin/orphanin FQ (N/OFQ) has been revealed to play bidirectional roles in orofacial pain modulation. Calcitonin gene-related peptide (CGRP) is a well-known pro-nociceptive molecule that participates in the modulation of orofacial pain. We aimed to determine the effects of N/OFQ on the modulation of orofacial pain and on the release of CGRP.

METHODS

Orofacial pain model was established by ligating springs between incisors and molars in rats for the simulation of tooth movement. The expression level of N/OFQ was determined and pain level was scored in response to orofacial pain. Both agonist and antagonist of N/OFQ receptor were administered to examine their effects on pain and the expression of CGRP in trigeminal ganglia (TG). Moreover, gene therapy based on the overexpression of N/OFQ was delivered to validate the modulatory role of N/OFQ on pain and CGRP expression.

RESULTS

Tooth movement elicited orofacial pain and an elevation in N/OFQ expression. N/OFQ exacerbated orofacial pain and upregulated CGRP expression in TG, while UFP-101 alleviated pain and downregulated CGRP expression. N/OFQ-based gene therapy was successful in overexpressing N/OFQ in TG, which resulted in pain exacerbation and elevation of CGRP expression in TG.

CONCLUSIONS

N/OFQ exacerbated orofacial pain possibly through upregulating CGRP.

Botulinum toxin A alleviates orofacial nociception induced by orthodontic tooth movement through nociceptin/orphanin-FQ pathway in rats

OBJECTIVES

To investigate the effect and mechanism of botulinum neurotoxin type A (BoNT/A) in the modulation of orofacial nociception induced by orthodontic tooth movement in rats.

METHODS

An orofacial nociception model was established in male Sprague-Dawley rats by ligating closed-coil springs between incisors and ipsilateral molars. There were two group sets of animals. For the first group set, 120 rats were randomly divided into four groups: no-force group (n = 30), force + saline group (n = 30), force + low dose BoNT/A group (1U/6 μL, n = 30), and force + high dose BoNT/A group (1U/6 μL, n = 30). BoNT/A and saline were injected into periodontal ligament to explore the nociceptive effect of BoNT/A. Ipsilateral trigeminal ganglia (TG) were harvested for detecting the expression levels of nociceptin/orphanin-FQ (N/OFQ). For the second group set, 36 rats were randomly divided into three force groups: BoNT/A + saline group (n = 12), BoNT/A + UFP-101 group (n = 12), and saline + UFP-101 group (n = 12). A potent N/OFQ receptor (NOP) antagonist (UFP-101) was used to examine the role of N/OFQ in BoNT/A-induced antinociception. Tooth-movement nociception level of all groups was evaluated by bite force and rat grimace scale (RGS) at baseline, day 1, day 3, day 5, day 7, day 14.

RESULTS

The behavioral assessments showed the orofacial nociception level in the force + low dose BoNT/A group and force + high dose BoNT/A group were lower than that in the force + saline group. No significant difference was observed in orofacial nociception among no-force group, force + low dose and force + high dose group. The expression levels of N/OFQ in TG were elevated from day 1 and maintained a high level, presenting in descending order among the force + high dose, force + low dose, force + saline and no-force group, respectively. The nociception level of the BoNT/A + UFP-101 group was higher than that of the BoNT/A + saline group. No significant difference was observed between the BoNT/A + UFP-101 group and the saline + UFP-101 group.

CONCLUSIONS

BoNT/A can exert an antinociceptive effect on orofacial nociception induced by tooth movement by stimulating the expression of N/OFQ in TG.

Effect of endomorphin-2 on orofacial pain induced by orthodontic tooth movement in rats

Endomorphin-2 demonstrates potent antinociceptive effects in various pain models. The objectives of the present study were to explore the role of endomorphin-2 in the modulation of orofacial pain induced by orthodontic tooth movement in rats. An orthodontic pain model was established in male Sprague-Dawley rats by ligating coiled springs to mimic orthodontic force (40 g). On days 0, 1, 3, 5, 7, and 14 following orthodontic tooth movement, bite force was recorded as a surrogate measure of orthodontic pain. Ipsilateral trigeminal ganglia, trigeminal nucleus caudalis, and periodontal tissues were harvested for immunostaining. Endomorphin-2, endomorphin-2 + naloxone (a non-selective opioid receptor antagonist), naloxone, and saline were injected into trigeminal ganglia and periodontal tissues to explore the role of endomorphin-2 on orthodontic pain. The results showed that following orthodontic tooth movement, endomorphin-2 expression levels in trigeminal ganglia were elevated on days 1, 3, 5, and 7. Orthodontic pain levels were increased on days 1, 3, and 5. The administration of endomorphin-2 into both trigeminal ganglia and periodontal tissues alleviated orthodontic pain. Moreover, the effects of endomorphin-2 could be blocked by naloxone completely in trigeminal ganglia but only partially in periodontal tissues. Therefore, endomorphin-2 plays an important role in the modulation of orthodontic pain both centrally and peripherally, probably through different pathways.

The effect of capsaicin on expression patterns of CGRP in trigeminal ganglion and trigeminal nucleus caudalis following experimental tooth movement in rats

Objectives

The aim of this study was to explore the effect of capsaicin on expression patterns of calcitonin gene-related peptide (CGRP) in the trigeminal ganglion (TG) and trigeminal subnucleus caudalis (Vc) following experimental tooth movement.

Material and Methods

Male Sprague-Dawley rats were used in this study and divided into small-dose capsaicin+force group, large-dose capsaicin+force group, saline+force group, and no force group. Closed coil springs were used to mimic orthodontic forces in all groups except for the no force group, in which springs were inactivated. Capsaicin and saline were injected into periodontal tissues. Rats were euthanized at 0 h, 12 h, 1 d, 3 d, 5 d, and 7 d following experimental tooth movement. Then, TG and Vc were obtained for immunohistochemical staining and western blotting against CGRP.

Results

Immunohistochemical results indicated that CGRP positive neurons were located in the TG, and CGRP immunoreactive fibers were distributed in the Vc. Immunohistochemical semiquantitative analysis and western blotting analysis demonstrated that CGRP expression levels both in TG and Vc were elevated at 12 h, 1 d, 3 d, 5 d, and 7 d in the saline + force group. However, both small-dose and large-dose capsaicin could decrease CGRP expression in TG and Vc at 1 d and 3 d following experimental tooth movement, as compared with the saline + force group.

Conclusions

These results suggest that capsaicin could regulate CGRP expression in TG and Vc following experimental tooth movement in rats.

Current advances in orthodontic pain

Orthodontic pain is an inflammatory pain that is initiated by orthodontic force-induced vascular occlusion followed by a cascade of inflammatory responses, including vascular changes, the recruitment of inflammatory and immune cells, and the release of neurogenic and pro-inflammatory mediators. Ultimately, endogenous analgesic mechanisms check the inflammatory response and the sensation of pain subsides. The orthodontic pain signal, once received by periodontal sensory endings, reaches the sensory cortex for pain perception through three-order neurons: the trigeminal neuron at the trigeminal ganglia, the trigeminal nucleus caudalis at the medulla oblongata and the ventroposterior nucleus at the thalamus. Many brain areas participate in the emotion, cognition and memory of orthodontic pain, including the insular cortex, amygdala, hippocampus, locus coeruleus and hypothalamus. A built-in analgesic neural pathway—periaqueductal grey and dorsal raphe—has an important role in alleviating orthodontic pain. Currently, several treatment modalities have been applied for the relief of orthodontic pain, including pharmacological, mechanical and behavioural approaches and low-level laser therapy. The effectiveness of nonsteroidal anti-inflammatory drugs for pain relief has been validated, but its effects on tooth movement are controversial. However, more studies are needed to verify the effectiveness of other modalities. Furthermore, gene therapy is a novel, viable and promising modality for alleviating orthodontic pain in the future.

The effects of blocking N/OFQ receptors on orofacial pain following experimental tooth movement in rats

Objective

The aim of this study was to determine the effects of nociceptin/orphanin FQ peptide receptor (N/OFQ receptor) antagonist on orofacial pain induced by experimental tooth movement in rats.

Methods

A total of 36 male Sprague-Dawley rats weighing 200–300 g were divided into six groups: a control group, force group, force+saline intraperitoneal group, force+saline periodontal group, force+UFP-101 ([Nphe1,Arg14,Lys15]N/OFQ-NH2; antagonist for N/OFQ receptor) intraperitoneal group, and force+UFP-101 periodontal group. Closed coil springs were ligated between the upper incisors and first molar to exert an orthodontic force (40 g) between the teeth. Injectable administration dosages were 30 μl saline or 30 μl saline containing 0.03 mg/kg UFP-101. Following the injections, orofacial pain levels were assessed through directed face grooming (mouth wiping). Statistical analyses were performed in SPSS 17.0 (Statistical Package for the Social Sciences) and p values less than 0.05 were considered as statistically significant.

Results

Orofacial pain levels were significantly higher in the force group than in the control group. Orofacial pain levels differed significantly between the force group, force+saline periodontal group and force+UFP-101 periodontal group, but were similar between the control group, force+UFP-101 intraperitoneal group and force+saline intraperitoneal group. Moreover, orofacial pain levels did not differ between the force group, force+saline intraperitoneal group and force+UFP-101 intraperitoneal group.

Conclusions

Periodontal, but not intraperitoneal, administration of UFP-101 could alleviate orofacial pain induced by experimental tooth movement in rats, suggesting that periodontal N/OFQ receptors participate in orofacial pain induced by experimental tooth movement.

Periodontal CGRP contributes to orofacial pain following experimental tooth movement in rats

Calcitonin-related gene peptide (CGRP) plays an important role in orofacial inflammatory pain. The aim of this study was to determine whether periodontal CGRP contributes to orofacial pain induced by experimental tooth movement in rats. Male Sprague-Dawley rats were used in this study. Closed coil springs were used to deliver forces. Rats were euthanized on 0d, 1d, 3d, 5d, 7d, and 14d following experimental tooth movement. Then, alveolar bones were obtained for immunostaining of periodontal tissues against CGRP. Two hours prior to euthanasia on each day, orofacial pain levels were assessed through rat grimace scale. CGRP and olcegepant (CGRP receptor antagonist) were injected into periodontal tissues to verify the roles of periodontal CGRP in orofacial pain induced by experimental tooth movement. Periodontal CGRP expression levels and orofacial pain levels were elevated on 1d, 3d, 5d, and 7d following experimental tooth movement. The two indices were significantly correlated with each other and fitted into a dose-response model. Periodontal administration of CGRP could elevate periodontal CGRP expressions and exacerbate orofacial pain. Moreover, olcegepant administration could decrease periodontal CGRP expressions and alleviate orofacial pain. Therefore, periodontal CGRP plays an important role in pain transmission and modulation following experimental tooth movement. We suggest that it may participate in a positive feedback aiming to amplify orofacial pain signals.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.