Occurrence and distribution of different neurochemical markers in the human dental pulp

Functional Expression of IP, 5-HT4, D1, A2A, and VIP Receptors in Human Odontoblast Cell Line

Odontoblasts are involved in sensory generation as sensory receptor cells and in dentin formation. We previously reported that an increase in intracellular cAMP levels by cannabinoid 1 receptor activation induces Ca²⁺ influx via transient receptor potential vanilloid subfamily member 1 channels in odontoblasts, indicating that intracellular cAMP/Ca²⁺ signal coupling is involved in dentinal pain generation and reactionary dentin formation. Here, intracellular cAMP dynamics in cultured human odontoblasts were investigated to understand the detailed expression patterns of the intracellular cAMP signaling pathway activated by the G_s protein-coupled receptor and to clarify its role in cellular functions. The presence of plasma membrane Gα_s as well as prostaglandin I₂ (IP), 5-hydroxytryptamine 5-HT₄ (5-HT₄), dopamine D₁ (D₁), adenosine A_2A (A_2A), and vasoactive intestinal polypeptide (VIP) receptor immunoreactivity was observed in human odontoblasts. In the presence of extracellular Ca²⁺, the application of agonists for the IP (beraprost), 5-HT₄ (BIMU8), D₁ (SKF83959), A_2A (PSB0777), and VIP (VIP) receptors increased intracellular cAMP levels. This increase in cAMP levels was inhibited by the application of the adenylyl cyclase (AC) inhibitor SQ22536 and each receptor antagonist, dose-dependently. These results suggested that odontoblasts express G_s protein-coupled IP, 5-HT₄, D₁, A_2A, and VIP receptors. In addition, activation of these receptors increased intracellular cAMP levels by activating AC in odontoblasts.

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

Nitric oxide (NO), which is synthesized by the enzyme NO synthase (NOS), is a versatile endogenous molecule with multiple biological effects on many tissues and organs. In dental pulp tissue, NO has been found to play multifaceted roles in regulating physiological activities, inflammation processes, and tissue repair events, such as cell proliferation, neuronal degeneration, angiogenesis, and odontoblastic differentiation. However, there is a deficiency of detailed discussion on the NO-mediated interactions between inflammation and reparative/regenerative responses in wounded dental pulp tissue, which is a central determinant of ultimate clinical outcomes. Thus, the purpose of this review is to outline the current molecular understanding on the roles of Janus-faced molecule NO in dental pulp physiology, inflammation, and reparative activities. Based on this knowledge, advanced physicochemical techniques designed to manipulate the therapeutic potential of NOS and NO production in endodontic regeneration procedures are further discussed. Impact statement The interaction between inflammation and reparative/regenerative responses is very important for regenerative endodontic procedures, which are biologically based approaches intended to replace damaged tissues. Inside dental pulp tissue, endogenous nitric oxide (NO) is generated mainly by immunocompetent cells and dental pulp cells and mediates not only inflammatory/immune activities but also signaling cascades that regulate tissue repair and reconstruction, indicating its involvement in both tissue destruction and regeneration. Thus, it is feasible that NO acts as one of the indicators and modulators in dental pulp repair or regeneration under physiological and pathological conditions.

Modulation of Dental Inflammation by the Sympathetic Nervous System

Recent findings have indicated that immune responses are subjected to modulation by the sympathetic nervous system (SNS). Moreover, the findings show that the SNS inhibits the production of pro-inflammatory cytokines, while stimulating the production of anti-inflammatory cytokines. The present review is an attempt to summarize the current results on how the SNS affects inflammation in dental tissues. In dental tissues, it has been found that the SNS is significant for recruitment of inflammatory cells such as CD 43+ granulocytes. Sympathetic nerves appear to have an inhibitory effect on osteoclasts, odontoclasts, and on IL-1α production. The SNS stimulates reparative dentin production, since reparative dentin formation was reduced after sympathectomy. Sprouting of sympathetic nerve fibers occurs in chronically inflamed dental pulp, and neural imbalance caused by unilateral sympathectomy recruits immunoglobulin-producing cells to the dental pulp. In conclusion, this article presents evidence in support of interactions between the sympathetic nervous system and dental inflammation.

Sympathetic Regulation of Tertiary Dentinogenesis via Beta-2 Adrenergic Receptor on Rat Odontoblasts

INTRODUCTION

Beta-2 adrenergic receptor has been found within the osteoblast membrane meditating bone remodeling. Propranolol is a sympatholytic beta antagonist commonly used as long-term medication for the management of many common diseases such as hypertension. This study was performed to verify the presence of this receptor on odontoblasts in rats and, if present, to investigate its possible association with tertiary dentinogenesis.

METHODS

Twenty male Sprague-Dawley rats (9 weeks old) were randomly assigned to 4 groups: CP0.8 group, cavity preparation + propranolol treatment (0.8 mg/day, n = 5); CP4 group, cavity preparation + propranolol treatment (4.0 mg/day, n = 7); CON group, cavity preparation + saline treatment (0.2 mL/day, n = 5); and NT group, no treatment (n = 3). Cavity preparation was performed on the mesial aspect of the maxillary first molars bilaterally. After 2 weeks, the tertiary dentinogenesis (CP0.8, CP4, and CON) was examined by hematoxylin-eosin staining, and the localization of beta-2 adrenergic receptor (NT) was examined by immunohistochemistry.

RESULTS

The beta-2 adrenergic receptor immunoreactivity was observed in the odontoblastic layer in normal rat molar dental pulp. The tertiary dentinogenesis beneath the prepared cavity was significantly higher in the rats receiving 2-week systemic administration of propranolol than in those without the propranolol treatment. The higher-dose treatment of propranolol (P < .001) presented more effective up-regulation of tertiary dentinogenesis than the lower-dose treatment (P < .01).

CONCLUSIONS

These results indicate that the sympathetic nervous system decreases tertiary dentin formation via beta-2 adrenergic receptors located on rat odontoblasts. It suggests that adrenergic beta antagonist is expected to use in the treatment of inducing tertiary dentin formation to protect dental pulp.

Differential cholinoceptor modulation of nitric oxide isoforms in experimentally-induced inflammation of dental pulp tissue

AIM

The aim of the study was to investigate the role of muscarinic acetylcholine receptor (mAChR) activity in the regulation of endothelial (e), neuronal (n) and inducible (i) nitric oxide synthase (NOS) activity and expression in experimentally induced inflammation of rat dental pulp tissue.

METHODOLOGY

Inflammation was induced by application of bacterial lipopolysaccharide (LPS) to the pulp. Extirpated pulp-tissue samples were incubated in saline solution until the various experiments were performed. Saline-treated pulp and healthy pulp tissues were used as controls. NOS activity was measured by the production of [U-(14)C]-citrulline from [U-(14)C]-arginine. Nitrite/nitrate assay was evaluated by the conversion of nitrate to nitrite in the presence of nicotinamide adenine dinucleotide phosphate. i-nos, e-nos and n-nos mRNA levels were measured using reverse-transcriptase polymerase chain reaction by co-amplification of target cDNA with a single set of primers.

RESULTS

Application of LPS to the pulp increased NOS activity and nitrate production (P < 0.001), generated by iNOS over-activity and expression. Pilocarpine acting on mAChRs triggered a biphasic action on NOS activity and NO accumulation. At low concentrations, pilocarpine induced a negative effect associated with a decrease in i-nos mRNA level, whilst at high concentration, it produced a positive effect associated with increased e-nos and n-nos mRNA levels. In control pulp tissue, only the positive effect of pilocarpine was observed.

CONCLUSIONS

Irreversible pulpitis changes mAChR conformation increasing its efficiency of coupling to transducing molecules that in turn induce activate iNOS. The capacity of pilocarpine to prevent NO accumulation and iNOS activity, by acting on mAChR mutation induced by pulpitis, might be useful therapeutically as a local treatment.

Vasoactive intestinal polypeptide (VIP) and VPAC1 receptor in adult human dental pulp in relation to caries

OBJECTIVE

To quantitatively measure VIP levels and to qualitatively study the distribution of VIP fibres and demonstrate the presence of the VPAC1 receptor in human dental pulp from carious and non-carious adult human teeth.

DESIGN

Dental pulp samples were collected from non-carious, moderately carious and grossly carious adult human teeth. VIP levels were determined using radioimmunoassay. The distribution of VIP fibres was studied using immunohistochemistry. The VPAC1 receptor protein expression was determined by Western blotting.

RESULTS

VIP levels were found to be significantly elevated in the dental pulp of moderately carious compared with non-carious (p=0.0032) or grossly carious teeth (p=0.0029). The distribution of VIP fibres was similar in non-carious and carious teeth, except that nerve bundles appeared thicker in the pulp samples from carious compared with non-carious teeth. Western blotting indicated that the VPAC1 receptor proteins were detected in similar levels in pooled dental pulp samples from both carious and non-carious teeth.

CONCLUSION

It is concluded that quantitative changes in the levels of VIP in human dental pulp during the caries process and the expression of VPAC1 receptor proteins in membrane extracts from carious and non-carious teeth suggests a role for VIP in modulating pulpal health and disease.

Comparative evaluation of neural tissue antigens--neurofilament protein (NF), peripherin (PRP), S100B protein (S100B), neuron-specific enolase (NSE) and chromogranin-A (CgA)--in both normal and inflamed human mature dental pulp

The immunohistochemical detection of neurofilament protein (NF), peripherin (PRP), S100B protein (S100B), neuron-specific enolase (NSE) and chromogranin-A (CgA) has been studied in nerve fibres and bundles of human dental pulp. This was done in order to identify possible differences in the distribution pattern of the above markers between normal and inflamed pulp and, further, to evaluate their potential use as peripheral markers of dental innervation as well as objective markers for the determination of the extent of inflammation. Both normal and inflamed human dental pulp showed positive immunolabelling for NF, S100B and NSE and lack of labelling for PRP and CgA protein. An increased density of NF, S100B and NSE immunoreactive nerve fibres was observed in inflamed pulp samples compared to non-inflamed. The findings of this study suggest the possible application of NF, S100B and NSE as markers of dental innervation. Furthermore, they may be useful for the determination of the extent of pulpal inflammation, and might be utilized in alternative modalities of biological pulp therapy to reduce the inflammation process. The absence of CgA immunolabelling implies the presumptive absence of neuroendocrine antigens, while further research is required in order to clarify the involvement of PRP in dental pulp.

Caries-induced changes in the expression of pulpal neuropeptide Y

Recent evidence suggests that the sympathetic nervous system may have a role in modulating neurogenic inflammation and bone remodelling. Neuropeptide Y (NPY) is a well-characterized neuropeptide transmitter in the peripheral sympathetic nervous system. NPY is known to be present in human dental pulp; however, quantitative data on NPY levels in pulpal health and disease in an adult population remain to be determined. The aims of the current study were to assess, quantitatively, NPY levels by radioimmunoassay and confirm the distribution of NPY fibres by immunocytochemistry in carious and non-carious adult human pulp tissue. Our results suggest changes in the levels and distribution of NPY in human dental pulp during the caries process, with significantly higher levels of NPY in carious compared with non-carious adult human teeth. Within the carious samples studied, our finding, that NPY levels were significantly elevated in mild/moderate caries, concurs with the hypothesis that NPY could have a modulatory role in pulpal inflammation and in reparative dentine formation.

Microhardness changes in dentine after neonatal capsaicin application

AIM

To determine if desensitization of the nociceptive innervation in the dental pulp has an effect on odontoblast function in the rat.

METHODOLOGY

Neonatal systemic application of capsaicin was used to selectively eliminate nociceptive innervation. 12 capsaicin-treated rats were intravitally perfused at 150 days of life with 4% formaldehyde and jaws were prepared for Vicker's microhardness (VMH) measurement. As a control, 12 rats were injected with vehicle on the 3rd day of life and intravital perfusion was carried out exactly as those used for the experimental group. Immunohistological labeling of CGRP was carried out in both groups to assure the efficiency of desensitization in the experimental group. The VMH was measured in the incisors of each animal for a quantitative analysis of dentine quality.

RESULTS

Vicker's microhardness was significantly higher in the control rats compared with the capsaicin-treated rats (P < 0.001).

CONCLUSIONS

Neonatal systemic application of capsaicin produces changes in the quality of dentine in the rat over time and therefore it is suggestive that selective elimination of the nociceptive innervation in pulpal tissue may effect odontoblast function.

Substance P activates p38 mitogen-activated protein kinase to promote IL-6 induction in human dental pulp fibroblasts

Substance P (SP) induces the expression of proinflammatory cytokines, such as interleukin (IL)-6, which are implicated in pulp inflammation. To determine the signal pathway of SP-induced IL-6, we examined the activities of the mitogen-activated protein kinases (MAPKs) in human dental pulp cell (PF-10) cultures. SP induced the phosphorylation of p38 MAPK within 5 min; this activation persisted for up to 40 min and was independent of the activation of extracellular signal-related kinases (ERK-1 and ERK-2) that were induced after SP stimulation of PF-10 cells. As shown by electrophoretic mobility shift assay p38 MAPK was not involved in SP-induced activation of nuclear factor-kappa B (NF-kappaB). However, p38 MAPK mediated SP-induced IL-6 production, as shown by the use of specific inhibitors of this kinase. Our results suggest that the activation of p38 MAPK is important for NF-kappaB-independent regulator of neurogenic inflammation in dental pulp tissues.

Development of innervation in primary incisors in the foetal period

Sections from the frontal part of the mandible of 43 human foetuses from 9 to 39 weeks of prenatal age, which contained two, three and sometimes four lower incisors were immunohistochemically examined using protein gene product and neuron specific enolase (NSE) antibodies in order to establish the time of appearance of nerve fibres in the developing tooth germ and to define their topography. Nerve fibres were first detected in the dental follicle in the 11th week of intrauterine life. Their presence in the dental papilla was confirmed in the 18th week when the first layers of dentine and enamel were deposited. In the 24th week of intrauterine life, the nerve fibres first reached the subodontoblastic region. In the subsequent weeks, an increase in the number of nerve fibres accompanying blood vessels in the central portion of the dental papilla resulted in the formation of neuro-vascular bundles. Moreover, the progressive deposition of enamel and dentine was accompanied by branching of papillary nerves, which thereby formed a fan-pattern. In the foetal period, no evidence was found for the formation of a subodontoblastic plexus. However, we did observe single nerve fibres in close proximity to the odontoblast layer at the end of intrauterine life. Nerve fibres were not detected in either predentine or dentine throughout foetal life.

Pituitary adenylate cyclase-activating polypeptide-immunoreactive nerve fibers in rat and human tooth pulps

The distribution of pituitary adenylate cyclase-activating polypeptide (PACAP) was examined in the tooth pulp. In rat and human tooth pulps, PACAP-immunoreactive (IR) nerve fibers were observed around blood vessels and in the subodontoblastic and odontoblastic layers. The predentine and dentine were devoid of such nerve fibers. The double immunofluorescence method indicated the co-expression of PACAP with calcitonin gene-related peptide (CGRP) or vasoactive intestinal polypeptide (VIP). Virtually all PACAP-IR nerve fibers co-expressed CGRP-immunoreactivity (IR) in the rat tooth pulp suggesting their sensory function. In addition, a retrograde tracing method indicated that PACAP-IR nerve fibers in the rat tooth pulp originated from the trigeminal ganglion. On the other hand, almost all PACAP-IR nerve fibers in the human tooth pulp co-expressed VIP-IR and, thus, thought to be autonomic in nature.

Extraction and radioimmunoassay quantitation of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) from human dental pulp tissue

The measurement of neuropeptides in complex biological tissue samples requires efficient and appropriate extraction methods so that immunoreactivity is retained for subsequent radioimmunoassay detection. Since neuropeptides differ in their molecular mass, charge and hydrophobicity, no single method will suffice for the optimal extraction of various neuropeptides. In this study, dental pulp tissue was obtained from 30 human non-carious teeth. Of the three different neuropeptide extraction methods employed, boiling in acetic acid in the presence of protease inhibitors yielded the highest levels of neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP). High pressure liquid chromatography (HPLC) analysis of dental pulp tissue verified the authenticity of the neuropeptides extracted.

NK1, NK2, NK3 and CGRP1 receptors identified in rat oral soft tissues, and in bone and dental hard tissue cells

The distribution of the tachykinin receptors neurokinin-1 (NK1), neurokinin-2 (NK2) and neurokinin-3 (NK3), and the calcitonin gene-related peptide-1 (CGRP1) receptor were examined in rat teeth and tooth-supporting tissues by immunohistochemical methods and light and confocal microscopy. Western blot analysis was performed to identify the NK1- and the CGRP1-receptor proteins in the dental pulp. The results showed that odontoblasts and ameloblasts, cementoblasts and cementocytes, osteoblasts and osteocytes are all supported with the tachykinin receptors NK1 and NK2, but a distinct, graded cellular labeling pattern was demonstrated. The ameloblasts were also positive for CGRP1 receptor. Blood vessels in oral tissues expressed the tachykinin receptors NK1, NK2 and NK3, and the CGRP1 receptor. Both gingival and Malassez epithelium were abundantly supplied by NK2 receptor. Pulpal and periodontal fibroblasts demonstrated NK1 and NK2 receptors. Western blot analysis identified both the NK1- and the CGRP1-receptor proteins in the dental pulp. These results clearly indicate that the neuropeptides substance P, neurokinin A, neurokinin B and CGRP, released from sensory axons upon stimulation, directly modulate the function of the different types of bone and dental hard tissue cells, and regulate functions of blood vessels, fibroblasts and epithelial cells in oral tissues.

Comparative immunohistochemical analysis of the peptidergic innervation of human primary and permanent tooth pulp

This immunohistochemical study sought to determine whether there are any differences in the peptidergic innervation of these pulps and whether dental caries is associated with changes in neuropeptide expression. Mandibular first permanent molars and second primary molars (n=120) were obtained from children requiring dental extractions under general anaesthesia. Extracted teeth were split longitudinally, placed in fixative, and categorized as intact, moderately carious or grossly carious. The coronal pulps were removed and 10-microm frozen sections were processed for indirect immunofluorescence. Double labelling employed combinations of the following antisera: (1) protein gene product 9.5, a general neuronal marker; (2) one of the neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP), vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), galanin (GAL), enkephalin (ENK) and somatostatin (SOM). Image analysis was then used to determine the percentage area of immunostaining for each label within different anatomical regions of the coronal pulp. Sparse or absent immunoreactivity for GAL, ENK and SOM made analysis impossible. Analysis of CGRP, SP and VIP revealed significant interdentition differences, with their expression being significantly greater in permanent teeth, but this was not the case for NPY, with primary and permanent teeth demonstrating a similar amount of label for this peptide. Both dentitions showed significant increases in CGRP, SP, VIP and NPY expression with caries progression. These findings could have biological and clinical importance in connection with nociception, inflammation and healing.

Three-dimensional wall structure and the innervation of dental pulp blood vessels

The involvement of neural components in plasma extravasation and blood flow in the dental pulp has been established by pharmacological and physiological studies. We review here the segmental constitution of pulp vessels and the possible involvement of neural components in both the contractility and permeability of the pulp vessels from a morphological viewpoint. Six vascular segments can be identified based on the morphology of peri-endothelial cells, such as smooth muscle cells and pericytes. These are: muscular arterioles, terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and collecting or muscular venules. The perivascular nerve forms a mesh with numerous terminal varicosities, some of which attach directly to arteriolar smooth muscle cells. This mesh can be seen by scanning electron microscopy, and indicates the important role of neural components in regulating the pulpal circulation. After administering norepinephrine (0.2 mg/kg/dog), the surface texture of the smooth muscle cells of pulp arterioles reveals marked irregularities, which are correlated with arteriolar contraction. The pericytes in larger postcapillary venules (diameter 20 microm or larger) also show irregularities, whereas no changes are seen in the pericytes of either smaller postcapillary venules or capillaries. The intercellular spaces of pericytes in the postcapillary venules are wide enough for leukocytes to pass through, and the occasional extravasation of leukocytes through venule walls can be seen under electron microscopy. The microvessels of healthy human dental pulp react weakly to selectins, indicating that apparently healthy dental pulp may be weakly inflamed. In rat dental pulp, CGRP-immunoreactive nerves and nerve terminals containing many granular vesicles supply the postcapillary venules more densely than the arterioles, which suggests the involvement of postcapillary venules in neurogenic inflammation in the dental pulp.

Effects of deprivation of neonatal nerve growth factor on the expression of neurotrophin receptors and brain-derived neurotrophic factor by dental pulp afferents of the adult rat

The dental pulp is richly innervated by peptidergic nociceptive neurones that are of special interest because of their central role in dental pain and because they have some features that are not typical of other somatic nociceptors. Here, (35)S-riboprobes were used to determine whether pulpal afferents of adult (2-month-old) rats express the nerve growth-factor (NGF) receptors, p75(NTR) and trkA, which are characteristic of peptidergic nociceptors, and additionally, whether these cells express receptors (trkB and trkC) for other members of the neurotrophin family. In order to begin characterizing the postnatal role of NGF in regulating these neurones, the susceptibility of pulpal afferents to antiserum-mediated early postnatal NGF depletion spanning the period of pulpal innervation development was also examined. In control animals, about 200 trigeminal ganglion cells were labelled after application of the retrograde tracer Fluoro-gold to the first maxillary molar. Among the labelled cells, 79% had positive hybridization signals for p75(NTR), 72% for trkA, 34% for trkB, 1% for trkC, and 77% for BDNF. Neonatal NGF depletion reduced the number of retrogradely labelled pulpal afferents by 33%, with numbers of smaller neurones being most strikingly subnormal. This reduction could be attributed to a partial depletion of the neurone population that expressed p75(NTR) and trkA. Consistent with reports that NGF-responsive neurones also express BDNF, NGF deprivation resulted in a reduction in the number of pulpal afferents that expressed BDNF to an extent similar to that seen for trkA. In contrast, anti-NGF exposure had little effect on the number of pulpal afferents that expressed trkB. These findings indicate that most pulpal afferents in the adult express the NGF receptors p75(NTR) and trkA, and thus have a continuing potential susceptibility to NGF-mediated regulation of functions such as neuropeptide and BDNF synthesis. However, only a subpopulation of this group of neurones requires NGF in order to develop connections to the pulp during the neonatal period. Few, if any, pulpal afferents express the high-affinity neurotrophin-3 (NT3) receptor trkC, although many have large cell bodies typical of NT3-responsive sensory neurones. A small subpopulation of pulpal afferents seems to express no neurotrophin receptors, yet it is unlikely that these cells belong to the class of small sensory cells known to bind isolectin IB4.

Dental injury models: experimental tools for understanding neuroinflammatory interactions and polymodal nociceptor functions

Recent research has shown that peripheral mechanisms of pain are much more complex than previously thought, and they differ for acutely injured normal tissues compared with chronic inflammation or neuropathic (nerve injury) pain. The purpose of the present review is to describe uses of dental injury models as experimental tools for understanding the normal functions of polymodal nociceptive nerves in healthy tissues, their neuroinflammatory interactions, and their roles in healing. A brief review of normal dental innervation and its interactions with healthy pulp tissue will be presented first, as a framework for understanding the changes that occur after injury. Then, the different types of dental injury that allow gradation of the extent of tissue damage will be described, along with the degree and duration of inflammation, the types of reactions in the trigeminal ganglion and brainstem, and the type of healing. The dental injury models have some unique features compared with neuroinflammation paradigms that affect other peripheral tissues such as skin, viscera, and joints. Peripheral inflammation models can all be contrasted to nerve injury studies that produce a different kind of neuroplasticity and neuropathic pain. Each of these models provides different insights about the normal and pathologic functions of peripheral nerve fibers and their effects on tissue homeostasis, inflammation, and wound healing. The physical confinement of dental pulp and its innervation within the tooth, the high incidence of polymodal A-delta and C-fibers in pulp and dentin, and the somatotopic organization of the trigeminal ganglion provide some special advantages for experimental design when dental injury models are used for the study of neuroinflammatory interactions.

NPY/sympathetic and NPY/VIP innervation of the blood vessels supplying rat tooth-related structures: effects of sympathectomy

In order to better understand the regulation of blood flow to tooth-related structures, the patterns of VIP- and NPY-ergic innervations in the rat were examined. Nerve fibers showing NPY-like immunoreactivity (NPY-LI) frequently occurred in the walls of the large main arteries, as well as in association with the arterioles, to a high degree co-existing with tyrosine hydroxylase (TH), whereas VIP-LI was mainly restricted to the walls of the large arteries. After sympathectomy, no NPY/TH-LI nerve fibers were seen in blood vessel walls. However, a NPY-immunoreactive nerve population remained in the walls of the large arteries, NPY- and VIP-LI co-existing in this nerve population. Both immunoreactions were intense. The present study suggests that a NPY/sympathetic innervation as well as a VIP innervation (large arteries) are likely to have substantial roles in the balance and maintenance of vasoregulation in tooth-related structures and that a NPY/VIP innervation becomes of particular importance when the NPY/sympathetic innervation is destroyed.

Immunohistochemical demonstration of exocytosis-regulating proteins within rat molar dentinal tubules

No morphologically defined synaptic structures have so far been detected between nerve terminals and the dentine-producing odontoblasts. Recent studies of the molecular mechanisms in neuronal exocytosis have identified several proteins that participate in synaptic-vesicle exocytosis. By localizing these proteins with immunohistochemical methods, information about the capacity for synaptic exocytosis should be obtained. Here, antibodies directed against some of the exocytosis-related proteins were used to investigate whether they are present in nerve fibers within the dentinal tubules in rat molars. Antibodies against synaptosome-associated protein of 25 kDa, Rab 3, synaptotagmin and synapsin all produced a punctuate staining pattern, suggesting that the proteins are accumulated in bouton-like elements. The results demonstrate that a set of exocytosis-related proteins is accumulated in the dentinal tubules, most probably within the intradentinal nerves. This finding is consistent with the hypothesis that intradentinal nerves can mediate efferent signals.

Neurokinin-1 receptor expression in the mature dental pulp of rats

Substance P induces inflammatory reactions in peripheral tissues including the dental pulp, but its regulatory effects in target tissues are dependent on receptor signalling. Here the expression of the substance-P receptor neurokinin-1 (NK1) in the mature molar pulp of the rat was examined in order to localize the main target areas for substance P. A polyclonal antibody directed against the C-terminal of the receptor was used, and immunohistochemistry was performed by the avidin-biotin peroxidase complex method. The results showed that the NK1 receptor was intensely expressed along vessel-like structures in the odontoblast and subodontoblast layer. A granulated and diffusely distributed NK1-receptor labelling was found along larger blood vessels in the root pulp and pulp proper. NK1 receptor-positive cells were frequently observed in the cell-rich zone beneath the odontoblast layer. The results indicate that, in the mature rat molar pulp, the main targets for substance P acting through the NK1 receptors are tissues related to blood vessels in the odontoblast and subodontoblast area. Furthermore, the expression of NK1 receptors on cells located in the subodontoblast area could indicate that substance P also affects cell functions in this area.

Expression of calcitonin gene-related peptide-1 receptor mRNA in human tooth pulp and trigeminal ganglion

Numerous nerve fibres containing calcitonin gene-related peptide (CGRP) were found by immunocytochemistry in human molar pulp. These nerves were often seen around small blood vessels and as free endings without vascular contact. In the trigeminal ganglion a large number of CGRP-immunoreactive nerve-cell bodies, mostly of small to medium size, was encountered. Reverse transcriptase-polymerase chain reaction, using specific sense and antisense primers, detected mRNA expression of the human CGRP1 receptor in the pulp tissue and the trigeminal ganglion. Thus, both CGRP-containing nerve fibres and CGRP1 receptor mRNA are present in human tooth pulp, where they may be involved in the regulation of vascular tone and other local reactions to injury.

Modulation by presynaptic beta-adrenoceptors of noradrenaline release from sympathetic nerves in human dental pulp

This study was undertaken to test for the presence of presynaptic beta-adrenoceptors on sympathetic nerves in human dental pulp and, if present, to investigate the subtype. Pulp was excised from freshly extracted teeth, incubated with [3H]-noradrenaline (0.6 micromol/l) and subsequently superfused with Krebs solution. Sympathetic nerves were stimulated at 5 Hz for 100 sec. The non-specific beta-adrenoceptor agonist isoprenaline (1.0 micromol/l), and the selective beta2-agonist salbutamol (10 micromol/l) facilitated the release of [3H]-noradrenaline; isoprenaline, but not salbutamol, also facilitated this release in the presence of desipramine (DMI, 0.3 micromol/l), corticosterone (10 micromol/l) and rauwolscine (0.1 micromol/l). BRL 37344 (1.0 micromol/l), a beta3-agonist, had no effect on [3H]-noradrenaline release. The facilitatory effects of isoprenaline and salbutamol were inhibited by the non-specific beta-antagonist propranolol (1.0 micromol/l), while that of salbutamol was inhibited in the presence of ICI-188,551 (1.0 micromol/l), a selective beta2-antagonist, as well. The beta1-antagonist atenolol (1.0 micromol/l) potentiated the facilitatory effects of isoprenaline in the presence of DMI and corticosterone. Neither propranolol nor ICI-188,551 alone affected the release of [3H]-noradrenaline. These results establish the presence of presynaptic beta-adrenoceptors on sympathetic nerves in human dental pulp. It is suggested that they are of the beta2-subtype, although a greater range of agonists and antagonists needs to be used to clarify the nature of the the beta-adrenoceptors.

Scanning electron microscopy and immunohistochemical observations of the vascular nerve plexuses in the dental pulp of rat incisor

BACKGROUND

The innervation of rat incisors, which are continuously erupting teeth, is quite unique. Although many reports have documented the neural control of the pulpal blood flow, only a few studies have examined the structure and distribution of vascular nerves in the rat incisors. This study examined the nerve plexuses and the spatial relationship of nerve terminals to smooth muscle cells of the pulp vessels of rat incisors.

METHODS

The innervation of the pulp vessels of rat incisors was studied using immunohistochemical evaluations of calcitonin gene-related peptide (CGRP) and neuropeptide-Y (NPY). The three-dimensional ultrastructure of nerve meshworks and terminals on smooth muscle cells of pulp arterioles were examined by scanning electron microscopy (SEM) with a KOH digestion method.

RESULTS

The blood vessels were associated with many nerve fibers immunoreactive for CGRP and NPY. Some NPY and frequent CGRP-immunoreactive nerve fibers were observed in the labial odontoblast layer. Three different morphologies of nerve fibers could be distinguished: fine nerve fibers with numerous terminal varicosities, medium-sized fibers associated with occasional or much scarcer varicosities, and thick fibers that had no varicosity and sometimes ran apart from blood vessels. The SEM observations identified five vascular segment types: terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and muscular venules. Nerve meshworks were observed around the large terminal arterioles; these meshworks were very comparable to those revealed by immunohistochemistry. The vascular smooth muscle cells were closely attached by one or more terminal varicosities.

CONCLUSIONS

It has become evident that the large terminal arterioles in the rat incisors receive a dense nerve supply and provide well-developed wall architecture, suggesting an important role of neuronal regulation on the vessels.

Localization of neuropeptide Y Y1 receptor mRNA in human tooth pulp

With immunocytochemistry numerous nerve fibres containing neuropeptide Y (NPY) were found in human molar pulp tissue, often around small blood vessels. Reverse transcriptase-polymerase chain reaction, using specific primers, detected mRNA of the human NPY Y1 receptor in the human pulp tissue. Thus, both NPY-containing nerve fibres and NPY Y1 receptor mRNA are present in human tooth pulp, possibly regulating vascular tone and pain perception.

Secretoneurin, a novel neuropeptide, in the human dental pulp

Secretoneurin is a neuropeptide that is stored in and released from primary afferent neurones. By radioimmunoassay and immunohistochemistry, secretoneurin was here demonstrated in the human dental pulp and localized in varicose nerve fibres that were frequently associated with blood vessels. No significant correlation was found between the levels of immunoreactive secretoneurin and immunoreactive calcitonin-gene related peptide. The results suggest that primary afferent neurones of the human dental pulp contain secretoneurin, which may influence local inflammatory responses if it is released together with other neuropeptides.

Coexpression of vasoactive intestinal polypeptide and substance P in reinnervating pulpal nerves and in trigeminal ganglion neurones after axotomy of the inferior alveolar nerve in the rat

The effect of this axotomy on the expression of vasoactive intestinal polypeptide (VIP) in trigeminal ganglion neurones and nerve fibres in the first molar was examined immunohistochemically 3 weeks postsurgically in rats. A distinct upregulation of VIP-like immunoreactivity was found in 3 to 4% of the neurones (mean dia., 20.9 +/- 0.45 microns; mean cross-sectional area, 367 +/- 13.2 microns 2) in the mandibular region after axotomy. An almost complete coexpression was registered in neurones upregulated for VIP and growth-associated protein 43. Coexpression of VIP and substance P (SP) was found in a small number of the immunoreactive (IR) small-sized neurones, mainly in those in which VIP and SP were both weakly immunoreactive. In the uninjured ganglion, weakly labelled VIP-positive granules were frequently traced at high magnification in the cytoplasm of small neurones. No VIP-IR fibres were found in the control molar pulp, except for a few in the root pulp near the apex. However, 3 weeks after axotomy, a number of VIP-containing nerve fibres were found in the molar pulp and apical periodontium. Coarse VIP-IR fibres directed towards the odontoblast layer were a common finding. In some of these fibres VIP was shown to colocalize with SP. These results indicate that VIP is clearly expressed and transported in regenerating primary afferent neurones after axotomy of the inferior alveolar nerve.

Evidence for presynaptic cholinergic receptors in sympathetic nerves in human dental pulp

The purpose of this study was to determine whether presynaptic cholinergic receptors are present in sympathetic nerves in human dental pulp. Pulp was incubated with [3H]noradrenaline (0.6 mumol/l) for 30 min and then superfused with Krebs' solution at 1.0 ml/min. Electrical stimulation (100 sec, 5 Hz) increased the overflow of [3H]noradrenaline into the superfusate. Carbachol (10 and 100 mumol/l), an agonist of muscarinic receptors, decreased the stimulation-induced (SI) overflow of 3H, an effect blocked by atropine but not hexamethonium. Carbachol, atropine and hexamethonium had no effect on the resting overflow. Nicotine (10 mumol/l) increased the resting overflow and inhibited the SI overflow, although the inhibition was variable. Cytisine, another agonist of nicotinic receptors, also increased the resting overflow, but did not affect the SI overflow. To ascertain whether the actions of nicotine and electrical stimulation were influenced by the release of nitric oxide (NO), the effects of an NO donor and two NO-synthase inhibitors were examined. With the exception of one of the NO-synthase inhibitors (L-NAME), the agents were without effect on the overflow of 3H in the absence or presence of nicotine. It was concluded that sympathetic nerves in human dental pulp possess (a) presynaptic muscarinic receptors that inhibit the SI release of noradrenaline, and (b) nicotinic receptors that evoke the release of noradrenaline and that inhibit the SI release of the transmitter. The results do not point to a significant role for NO in the effects of stimulation or nicotine on the overflow of 3H.

Structural and functional association between substance P- and calcitonin gene-related peptide-immunoreactive nerves and accessory cells in the rat dental pulp

Defense mechanisms of the dentin/pulp complex involve a variety of biological systems in which immunocompetent cells, the nervous system, and the vascular supply play important roles. In the present study, pulpal accessory cells were examined regarding (i) their structural relationship to nerves and (ii) how the functional capacities of these cells were affected by neuropeptides. Micro-anatomic association was investigated in the normal rat molar pulp with the use of double-immunofluorescence staining and dual-channel confocal laser scanning microscopy. Examinations of confocal laser scanning microscopic images from single focal planes revealed the presence of apparent contacts between thin, varicose nerve fibers and immunocompetent cells, indicating proximity between these two structures. The close associations were most frequently observed in the para-odontoblastic region of the coronal pulp, where more than 70% of class II antigen-expressing (OX6+) cells showed proximity to nerve fibers immunoreactive to calcitonin gene-related peptide. The corresponding figure for substance P was about 50%. ED2+ macrophages closely associated with nerves were less frequently observed. Functional studies conducted in vitro demonstrated that 10(-9) to 10(-7) mol/L of substance P significantly increased (p < 0.05), while 10(-7) to 10(-6) mol/L of calcitonin gene-related peptide suppressed (p < 0.01) proliferation of purified T-lymphocytes stimulated with sub-optimal concentrations of concanavalin A in the presence of rat incisor pulpal cells as accessory cells. These data suggest that pulpal sensory nerve fibers and their products may have an influence upon the immune defense of the dental pulp.

Dental innervation: functions and plasticity after peripheral injury

Oral tissues including the periodontal ligament, gingiva, and tooth pulp have a relatively dense sensory innervation and a rich vascular supply. Teeth and supporting tissues are susceptible to tissue injury and inflammation, partly due to lack of collateral blood and nerve supply and to their low compliance. This review focuses on dental nerve functions and adaptive changes in the trigeminal ganglion and tooth pulp after peripheral injuries. An overview of the peptidergic innervation of oral tissues is presented, followed by a discussion of plasticity in neuropeptide expression in trigeminal peripheral neurons after local insults to teeth and peripheral nerve injuries. The functional implications of these adaptive changes are considered, with special reference to nerve regeneration, inflammation, and hemodynamic regulation.

Effects of local anesthesia on substance P and CGRP content of the human dental pulp

The aim of the study was to determine immunoreactive Substance P (iSP) and immunoreactive calcitonin gene-related peptide (iCGRP) content in the human dental pulp and whether local anesthesia has an effect on the neuropeptide content. Dental pulps were obtained from patients, who underwent surgical extraction of all 4 impacted wisdom teeth under general isoflurane gas anesthesia. There was a very high interindividual variation in tissue content, with small variation in levels found in teeth from the same patient. Pulps obtained from lower teeth without local anesthesia contained an average of 131 +/- 62 fmol/mg protein of iCGRP and 15 +/- 9 fmol/mg iSP (n = 10). With additional mandibular block anesthesia the values were 194 +/- 71 fmol/mg iCGRP (statistically significant, p = 0.0356, Mann-Whitney-rank-sum-test) and 12 +/- 3.6 fmol/mg iSP. The results suggest that local anesthesia attenuates neuropeptide release in the human dental pulp during surgical extraction.

Protein gene product 9.5-immunoreactive nerves and cells in human oral mucosa

BACKGROUND

Current conflicting information on the innervation of the human oral cavity indicates technical problems such as different detectability of the neural structures according to the various staining methods used and difficulties in reproducibility. The possibility of intraoral regional differences has not been properly considered.

METHODS

Human biopsies of mucosa from different intraoral regions were prepared for immunohistochemistry using protein gene product 9.5 (PGP 9.5; a marker for neuronal structures).

RESULTS

Nerves were found consistently in all the biopsies. The neural pattern showed clear regional differences. Intraepithelial nerve fibers were found in the gingiva, labia, palate, within certain fungiform papillae, and in some salivary excretory ducts. Organized nerve endings were found in varying frequencies in all but one (sublingual) region, appearing as lamellar (Meissner-like), coiled or glomerular neural structures. Merkel cell-neurite complexes were observed in the buccal, gingival, and palatal epithelia. Immunoreactive cells with many similarities to Merkel cells but without a neural connection were also encountered.

CONCLUSIONS

Conflicting results from earlier innervation studies of the oral cavity could be attributed to regional innervation differences. The distribution of the nerves also casts doubt on some of the present theories concerning the function(s) of intraoral nerves, such as the free nerve endings and the Merkel cell-neurite complexes.

The disodium salt of EDTA inhibits the binding of vasoactive intestinal peptide to macrophage membranes: endodontic implications

The purpose of this study was to investigate the effect of the disodium salt of ethylenediamine tetraacetate (EDTA), a calcium ion chelator used in the root canal therapy, on vasoactive intestinal peptide (VIP) binding to macrophage membranes (MM's). Binding assays were conducted at 15 degrees C in 0.5 ml of 50 mM Tris-HCl buffer (pH 7.5) containing 1.6% (w/v) bovine serum albumin, 1.2 mg/ml of bacitracin, and different EDTA concentrations, using 45 pM of [125I]VIP as tracer. Results showed that EDTA inhibits VIP binding to MM's in a dose-dependent manner, with an IC50 value of 5.4 mM (p < 0.01). EDTA concentrations equal or higher than 100 mM of abolished VIP-MM interaction. Taking into account that the macrophage plays an essential role in inflammatory reactions and the immune response, we conclude that the apical extrusion of EDTA during root canal therapy could modify VIP-macrophage interaction modulating the inflammatory mechanisms involved in periapical lesions.

5-Hydroxytryptamine immunoreactivity is detectable in sympathetic nerve fibres in rat oral tissues

The aim of this investigation was to examine if 5-hydroxytryptamine (5-HT) is detectable not only in mast cells but also in sympathetic nerve fibres in oral sites of the rat, including the periodontal ligament, pulp, palatal mucosa, and vestibular sulcus. Antibodies against 5-HT and tyrosine hydroxylase were used. Maxillae from rats were dissected free, fixed, decalcified, cut transversally, and processed for immunohistochemistry. Nerve fibres showing 5-HT-like immunoreactivity were regularly observed in the walls of the arteries and arterioles in the vestibular sulcus and the periodontal ligament. However, 5-HT-like immunoreactivity was not seen in the walls of the vessels of the palatal mucosa. Interestingly, 5-HT-like immunoreactivity coexisted with tyrosine hydroxylase-like immunoreactivity in the innervation of the periodontal ligament and the vestibular sulcus. Thus, the present study gives morphological correlate for the occurrence of effects of 5-HT derived not only from mast cells but also from sympathetic nerve fibres in oral tissues. The source of 5-HT in the nerve fibres as well as the functional implications of the observations remain to be determined.

Distribution and possible origin of galanin-like immunoreactive nerve fibers in the mammalian dental pulp

Human, dog, cat and rat dental pulps were investigated for the presence and distribution of galanin-like immunoreactive (-IR) nerve fibers, and the possible origin of pulpal galanin-IR nerve fibers in the rat was examined. Galanin-IR nerve fibers were present in the dental pulps of all species examined. Two types of galanin-IR nerve fibers were distinguished with regard to morphology; thin varicose nerve fibers and thick smooth-surfaced nerve fibers. Thin varicose galanin-IR nerve fibers were seen to run along the blood vessel in the human, dog and cat root pulp. In the coronal pulp, galanin-IR nerve fibers ran toward the odontoblastic layer but they did not form the subodontoblastic nerve plexus. In rat molar pulp, few galanin-IR nerve fibers were observed; the distribution of these nerve fibers was similar to those in human, dog and cat pulp. In contrast, many thick smooth-surfaced galanin-IR nerve fibers were observed near the blood vessels in incisor pulp of the rat; occasionally a few varicose galanin-IR nerve fibers were also observed. Transection of the inferior alveolar nerve or mandibular nerve caused complete disappearance of galanin-IR nerve fibers in rat dental pulp, while surgical sympathectomy of the superior cervical ganglion did not affect their distribution. The present results indicate that galanin-IR nerve fibers are present in the mammalian dental pulp, and that the intrapulpal galanin-IR nerve fibers in the rat originate from the trigeminal ganglion and are primary afferents.

Neural control of pulpal blood flow

Blood flow of mammalian dental pulp is under both remote and local control. There is evidence for the existence of parasympathetic nerves in the pulp, but functionally the cholinergic influence is weak, and the physiological significance of this autonomic system seems to be low. The evidence for sympathetic vasoconstrictor nerves in the pulp is robust, and there is convincing support for the contention that these nerves play a physiological role, operating via release of noradrenaline and neuropeptide Y. However, there is no significant functional evidence in support of sympathetic beta-adrenoceptor-mediated vasodilation in the pulp. The local control of blood flow involves a subset of intradental sensory nerves. By virtue of their neuropeptide content, these afferent fibers cause vasodilation and inhibit sympathetic vasoconstriction in response to painful stimulation of the tooth. Such locally governed control may serve to meet immediate demands of the pulp tissue. A locally triggered reflex activation of sympathetic nerves in the pulp may modulate this control and limit its magnitude. Thus, there are competitive interactions between local and remote vascular controls which may be put out of balance in the injured and inflamed dental pulp.

Dynamics of the pulpo-dentin complex

Dentin has a relatively high water content due to its tubular structure. Once dentin is exposed, this intratubular water is free to move in response to thermal, osmotic, evaporative, or tactile stimuli. Fluid shifts across dentin are thought to cause sufficient shear forces on odontoblasts, nerve endings, nearby fibroblasts, and blood vessels to cause significant mechanical irritation, disruption, or damage, depending on the magnitude of the fluid shift. Even in the absence of fluid shifts, the water-filled tubules provide diffusion channels for noxious (i.e., bacterial products) substances which diffuse inward toward the pulp, where they can activate the immune system, provide chemotactic stimuli, cytokine production, and produce pain and pulpal inflammation. Viewed from this perspective, dentin is a poor barrier to external irritants. However, pulpal tissues react to these challenges by increasing the activity of nerves, blood vessels, the immune system, and interstitial fluid turnover, to make the exposed dentin less permeable either physiologically, via increased outward fluid flow, or microscopically, by lining tubules with proteins, mineral deposits, or tertiary dentin, thereby enhancing the barrier properties of dentin, and providing additional protection to pulpal tissues. These reactions involve dentin and pulp, both in the initiation of the processes and in their resolution. These responses of the dental pulp to irritation of dentin demonstrate the dynamic nature of the pulpo-dentin complex.

Effects of neuropeptides on growth of cultivated rat molar pulp fibroblasts

The effect of the neuropeptides substance P (SP), neurokinin A (NKA), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and vasoactive intestinal polypeptide (VIP) on DNA synthesis of dental pulp cells was investigated in cells grown from molar tooth bud explants from 4-6 days old rat pups. A concentration response-assay of the proliferative response of pulpal cells was performed with SP, NPY, NKA, CGRP and VIP (0.01 to 1 nM) in the presence of EGF (10 ng/ml), hydrocortisone (0.4 microgram/ml) and 3% FCS, using [3H]thymidine incorporation. The results showed that SP, NKA and CGRP, but not NPY and VIP, increased the cell number in a concentration-dependent manner, with maxima at 10(-10)-10(-9) M (SP, NKA) and 10(-7) M (CGRP). No potentiating effect was noted when cells were simultaneously stimulated with SP and CGRP. The finding that SP, NKA and CGRP have growth regulatory properties on pulpal cells in vitro suggests that sensory neuropeptides may be involved during pulpal development or in wound healing after pulpal injury.

Neurochemical markers of human fungiform papillae and taste buds

The presence of distribution of several neurochemical markers in human fungiform papillae and taste buds were investigated by the immunohistochemical technique. The gustatory cells of the taste buds are in synaptic contact with sensory nerve endings, and considering the taste buds strictly as specialized sensory organs, the amounts and distribution of some of the neurochemical markers were different to what we expected. For example, few structures showed immunoreactivity to the tachykinins substance P (SP), calcitonin gene-related peptide (CGRP), and neurokinin A (NKA) also for the peptides vasoactive intestinal polypeptide (VIP), neuropeptide tyrosine (NPY) and galanin, low amounts of immunoreactivity occurred. On the other hand, using antibodies to protein gene product 9.5 (PGP 9.5), protein S-100, and glutamate, numerous nerve fibres and/or immunoreactive cells were found in the fungiform papillae, in the epithelium, in the connective tissue and around blood vessels, as well as in or near taste buds. Incubation with the antibodies against somatostatin, enkephalin, bombesin, peptide histidine isoleucine amide (PHI), cholecystokinin (CCK)/gastrin and dopamine-beta-hydroxylase (DBH) was negative for the fungiform papillae. In conclusion, the present study has shown several immunoreactive structures using antibodies against certain neurochemical markers. Further investigations will hopefully correlate these morphological findings with functional taste perception data. Future studies of patients with taste disorders or other pathological changes correlated with taste and tongue will also be of utmost importance.

Haemodynamic and immunohistochemical studies of rat incisor pulp after denervation and subsequent re-innervation

The effects of injury to the inferior alveolar nerve on the distribution of neuropeptides and neurogenic blood-flow reactions were studied in rat mandibular dental pulp. In normal incisor pulps, calcitonin gene-related peptide (CGRP)-like immunoreactivity was common, while substance P- and neurokinin (NKA)-positive nerve fibres were much less abundant. There were no signs of vasoactive intestinal peptide-like, neuropeptide Y-like or 5-hydroxytryptamine-like immunoreactivity. In normal pulps, electrical stimulation (100 microA, 5 ms, 15 Hz for 30 s) of the tooth crown resulted in transient vasoconstriction followed by vasodilation, which was enhanced after alpha-adrenoceptor blockade. At 3 days-4 weeks after unilateral nerve section there were no signs of CGRP-, substance P- and NKA-immunoreactivity, and there was no vasodilation in response to tooth stimulation. The vasoconstrictor response was also absent during this period but at 4 weeks postoperatively a weak response was obtained and after 7 weeks the vasoconstrictor response had regained normal amplitude. At 7 weeks postoperatively, a large number of CGRP-positive fibres had reappeared and at 11 weeks the pattern of CGRP-immunoreactivity was normal. However, substance P- and NKA-immunoreactivity were not found at 7 or 11 weeks after surgery. Vasodilator responses appeared at 7 weeks, and showed normal amplitude at 11 weeks after the creation of the nerve lesion. The results show that during nerve regeneration, sympathetic vasoconstriction was regained earlier than neurogenic vasodilation in rat incisor teeth. The reappearance of neurogenic vasodilation after nerve injury was temporarily associated with the presence of CGRP-immunoreactivity in regenerating trigeminal afferent nerves.

Teeth and tooth nerves

(1) Although our knowledge on teeth and tooth nerves has increased substantially during the past 25 years, several important issues remain to be fully elucidated. As a result of the work now going on at many laboratories over the world, we can expect exciting new findings and major break-throughs in these and other areas in a near future. (2) Dentin-like and enamel-like hard tissues evolved as components of the exoskeletal bony armor of early vertebrates, 500 million years ago, long before the first appearance of teeth. It is possible that teeth developed from tubercles (odontodes) in the bony armor. The presence of a canal system in the bony plates, of tubular dentin, of external pores in the enamel layer and of a link to the lateral line system promoted hypotheses that the bony plates and tooth precursors may have had a sensory function. The evolution of an efficient brain, of a head with paired sense organs and of toothed jaws concurred with a shift from a sessile filter-feeding life to active prey hunting. (3) The wide spectrum of feeding behaviors exhibited by modern vertebrates is reflected by a variety of dentition types. While the teeth are continuously renewed in toothed non-mammalian vertebrates, tooth turnover is highly restricted in mammals. As a rule, one set of primary teeth is replaced by one set of permanent teeth. Since teeth are richly innervated, the turnover necessitates a local neural plasticity. Another factor calling for a local plasticity is the relatively frequent occurrence of age-related and pathological dental changes. (4) Tooth development is initiated through interactions between the oral epithelium and underlying neural crest-derived mesenchymal cells. The interactions are mediated by cell surface molecules, extracellular matrix molecules and soluble molecules. The possibility that the initiating events might involve a neural component has been much discussed. With respect to mammals, the experimental evidence available does not support this hypothesis. In the teleost Tilapia mariae, on the other hand, tooth germ formation is interrupted, and tooth turnover ceases after local denervation. (5) Prospective dental nerves enter the jaws well before onset of tooth development. When a dental lamina has formed, a plexus of nerve branches is seen in the subepithelial mesenchyme. Shortly thereafter, specific branches to individual tooth primordia can be distinguished. In bud stage tooth germs, axon terminals surround the condensed mesenchyme and in cap stage primordia axons grow into the dental follicle.(ABSTRACT TRUNCATED AT 400 WORDS)

An immunohistochemical and ultrastructural study of vasomotor nerves in the microvasculature of human dental pulp

Immunohistochemical methods for S-100 protein and neurone-specific enolase showed two types of nerve endings around the pulp microvasculature: the free endings, which comprise the major neural component and are distributed in all types of microvessel such as arterioles, venules and capillaries; and the varicose endings. The varicose ending was a less frequent, minor component observed only in the arterioles. Both immunohistochemical and ultrastructural observations confirmed that the varicose endings were the terminal axons of efferent vasomotor nerves. Further extensive ultrastructural examinations on the vasomotor nerves added the following new findings to our previous reports. Vasomotor nerves sometimes ramified into more than two terminal axons around arterioles, and most of these ramified axons ended in the adventitia-media junction of the arteriolar wall; however, nerve endings occasionally penetrated into the media. These findings suggest an intimate structural association between vasomotor nerves and arterioles in regulating the arteriolar microcirculation in human dental pulp by stimulating smooth-muscle cells not only of the outermost but also of the inner layers. Furthermore, the deep penetration of terminal axons into the arteriolar wall seems to provide effective regulation of pulpal blood flow under physiological and pathological conditions.

Nerve fibres and cells immunoreactive to neurochemical markers in developing rat molars and supporting tissues

The distribution of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY) was compared to the general neurochemical markers for nerves and neuroendocrine cells protein gene product 9.5 (PGP 9.5) and neurone-specific enolase (NSE), by use of the avidin-biotin peroxidase complex method in developing dental structures in rats aged 13 to 27 days. A substantially greater part of the nerve fibres was immunoreactive to CGRP and SP than to NPY. In the bell stage, nerve fibres immunoreactive to PGP 9.5, CGRP and SP were found in the dental follicle but not in the dental papilla and stellate reticulum. In the advanced bell stage, after initiation of dentine and enamel formation, PGP 9.5, CGRP- and SP-immunoreactive fibres were found in the dental papilla, while the first NPY-immunoreactive fibres were observed in the papilla when root formation started. Concomitant with the beginning of root development, a subodontoblastic nerve plexus was gradually formed and PGP 9.5-, CGRP- and SP-immunoreactive fibres were found within the dentinal tubules. From the start of root formation, CGRP-, SP- and NPY-immunoreactive nerves were shown in the developing periodontal ligament, although a mature distribution pattern was not observed until root formation was nearly completed. Ameloblasts, odontoblasts and cell-like structures in the outer enamel epithelium and within the dental lamina were PGP 9.5-immunoreactive at the bell stage. As the tooth matured, the immunolabelling gradually decreased, but was still present in some odontoblasts after tooth eruption. NSE-immunoreactive, cell-like structures were found in the periphery of the dental follicle, and persisted close to alveolar bone in the periodontal ligament when the tooth reached occlusion. Hence, it may be concluded that sensory nerves containing SP and CGRP are present in the pulp in advance of sympathetic nerves immunoreactive to NPY.

Effects of postnatal anti-nerve growth factor serum exposure on development of apical nerves of the rat molar

The present study was undertaken to test the hypothesis that development of the pulpal innervation is dependent on nerve growth factor (NGF). Newborn rats were given subcutaneous injections of a rabbit anti-mouse NGF serum on alternate days for the first 24 days postnatally. Control animals were untreated and normal rabbit serum-treated litter mates. The animals were deeply anesthetized on postnatal day 26, perfused with fixative and the first mandibular molars were processed for transmission electron microscopy to obtain a complete census of axons entering the four roots. The composition of the mental nerve was also examined. Compared to control animals, the apical innervation of molars from anti-NGF-treated rats had only 62% as many myelinated fibers and 41% as many unmyelinated axons. Those myelinated fibers present in antiserum-treated animals were slightly, but significantly, smaller in average diameter than controls. In teeth of control animals, about 20% of all unmyelinated axons were located in fibers coursing outside of nerve fascicles; these isolated fibers were disproportionately rare after antiserum exposure. The average number of unmyelinated axons per Schwann cell unit was also significantly lower. Postnatal exposure to anti-NGF had milder effects on mental nerve composition compared to the tooth innervation. Numbers of myelinated fibers were 83% of controls, unmyelinated axons were 74% of controls and there was no change in the average number of unmyelinated axons per Schwann cell unit. We conclude that development of dental innervation is highly susceptible to postnatal NGF deprivation. This may be a consequence of the mostly nociceptive composition of dental nerves and their late development.