Parvalbumin-, substance P- and calcitonin gene-related peptide-immunopositive axons in the human dental pulp differ in their distribution of varicosities

Neuronal-immune axis alters pain and sensory afferent damage during dental pulp injury

ABSTRACT

Dental pulp tissue is densely innervated by afferent fibers of the trigeminal ganglion. When bacteria cause dental decay near the pulpal tissue, a strong neuronal and immune response occurs, creating pulpitis, which is associated with severe pain and pulp tissue damage. Neuroimmune interactions have the potential to modulate both the pain and pathological outcome of pulpitis. We first investigated the role of the neuropeptide calcitonin gene-related peptide (CGRP), released from peptidergic sensory afferents, in dental pain and immune responses by using Calca knockout (Calca -/- ) and wild-type (Calca +/+ ) mice, in a model of pulpitis by creating a mechanical exposure of the dental pulp horn. We found that the neuropeptide CGRP, facilitated the recruitment of myeloid cells into the pulp while also increasing spontaneous pain-like behavior 20% to 25% at an early time point. Moreover, when we depleted neutrophils and monocytes, we found that there was 20% to 30% more sensory afferent loss and increased presence of bacteria in deeper parts of the tissue, whereas there was a significant reduction in mechanical pain response scores compared with the control group at a later time point. Overall, we showed that there is a crosstalk between peptidergic neurons and neutrophils in the pulp, modulating the pain and inflammatory outcomes of the disease.

Pinocembrin relieves hip fracture-induced pain by repressing spinal substance P signaling in aged rats

Whether pinocembrin (PCN) could be utilized to alleviate hip fracture-induced pain is investigated in this research. Aged rats with hip fractures were treated with vehicle or 80 mg/kg/day PCN from week 3 to week 4. Then hind paw mechanical allodynia, unweighting, warmth, and thickness were measured. The microglia and astrocytes activation and proliferation markers in the spinal dorsal horn were detected with real-time PCR and immunofluorescence staining. The relative expression of substance P and its receptor, tachykinin receptor 1 (Tacr1), were detected with enzyme-linked immunosorbent assay (ELISA) and Western blots. The antinociceptive effect of Tacr1 inhibitor LY303870 was also testified. PCN alleviated hip fracture-induced hind paw nociceptive (allodynia and unweighting) and vascular changes (warmth and thickness) in aged rats with diminished microglia and astrocytes activation and proliferation in the spinal dorsal horn. Up-regulated substance P and Tacr1 were induced after hip fracture, which could be reversed by PCN treatment. Furthermore, LY303870 treatment partially reversed both spinal nociceptive sensitization and vascular changes after hip fracture. Substance P signaling contributes to the nociceptive and vascular changes observed in the hip fracture, which could be alleviated by PCN.

Associations between Pain Severity, Clinical Findings, and Endodontic Disease: A Cross-Sectional Study

INTRODUCTION

Thorough pain assessment and thermal and mechanical testing are the primary diagnostic tools used to assess the status of pulp and periapical tissues in teeth with potential endodontic pathology. This study evaluated predictors of acute odontogenic pain to better understand the relationship between endodontic pain, clinical testing, endodontic disease, and diagnoses.

METHODS

Participants (N = 228) presenting with acute odontogenic pain underwent standardized clinical testing and reported their pain intensity. Univariate and multiple regression analyses were performed to evaluate the predictors of acute endodontic pain. Chi-square tests with Bonferroni adjustments were conducted to measure the frequency of endodontic diagnostic test findings and clinical observations in patients with different pulpal diagnoses.

RESULTS

A negative response to cold stimulation on the causative tooth and percussion hypersensitivity on the healthy adjacent tooth were the strongest predictors of higher levels of acute endodontic pain. Percussion hypersensitivity on the healthy adjacent tooth was present in a quarter of the cohort and was reported with equal frequency in teeth diagnosed with irreversible pulpitis, necrotic pulp, and previously initiated/treated teeth. Although painful percussion on the causative tooth was more frequently reported in teeth diagnosed with necrotic pulp, painful palpation was more frequently reported on teeth diagnosed with previously initiated/treated teeth.

CONCLUSIONS

Percussion hypersensitivity on the healthy adjacent tooth may reveal a lowered pain threshold and heightened pain sensitization. It is also possible that the 2 commonly performed mechanical sensory tests, percussion and palpation hypersensitivity, may detect different aspects of endodontic pathophysiology and pain processing.