An in vitro method to evaluate regulation of neuropeptide release from dental pulp

Tissue pH and Temperature Regulate Pulpal Nociceptors

The TRPV1 receptor acts as a sensor for environmental changes in pH and temperature. Since many nociceptors express TRPV1, it is possible that local tissue-cooling may inhibit nociceptor activity via reduction of TRPV1 activation. The present study used isolated superfused rat dental pulp to test the hypothesis that capsaicin receptors are activated in inflamed tissue, as measured by alterations in neuropeptide release. We tested the hypothesis that alterations in the tissue temperature and pH of isolated superfused rat dental pulp regulate capsaicin-induced release of calcitonin gene-related peptide (CGRP). Application of capsaicin with increased proton concentration ( i.e., lowered pH) produced a nearly two-fold increase in peak immunoreactive CGRP release, as compared with capsaicin applied at a pH of 7.4. Reduction in tissue temperature from 37°C to 26°C completely blocked the capsaicin effect. The study indicates that environmental stimuli regulate the activity of capsaicin-sensitive neurons innervating dental pulp, and these factors may be significant clinically in the development and amelioration of dental pain.

Lipopolysaccharide from Porphyromonas gingivalis sensitizes capsaicin-sensitive nociceptors

Although odontogenic infections are often accompanied by pain, little is known about the potential mechanisms mediating this effect. In this study we tested the hypothesis that trigeminal nociceptive neurons are directly sensitized by lipopolysaccharide (LPS) isolated from an endodontic pathogen, Porphyromonas gingivalis. In vitro studies conducted with cultures of rat trigeminal neurons demonstrated that pretreatment with LPS produced a significant increase in the capsaicin-evoked release of calcitonin gene-related peptide (CGRP) when compared with vehicle pretreatment, thus showing sensitization of the capsaicin receptor, TRPV1, by LPS. Furthermore, confocal microscopic examination of human tooth pulp samples showed the colocalization of the LPS receptor (toll-like receptor 4, TLR4) with CGRP-containing nerve fibers. Collectively, these results suggest the direct sensitization of nociceptors by LPS at concentrations found in infected canal systems as one mechanism responsible for the pain associated with bacterial infections.

Sex differences in neuropeptide content and release from rat dental pulp

INTRODUCTION

Studies to examine sex differences in response to pain have suggested that females exhibit lower threshold responses to painful stimuli and that threshold response varies greatly at different stages of the menstrual cycle. Additional studies suggest that sex differences may be caused by societal sex roles or differences in anxiety responses by men and women.

OBJECTIVE

The purpose of this study was to evaluate biologically evident sex differences in male and female rats chronically treated with a systemic algogen, the nerve growth factor (NGF), by measuring neuropeptides (calcitonin gene-related peptide) content and release from isolated dental pulp.

METHODS

Rats were injected subcutaneously every other day with either murine NGF (1 mg/kg) or vehicle for 7 or 13 days. Isolated incisor pulp tissue was evaluated from these male and female rats (n = 96). Capsaicin-evoked neurosecretion of CGRP and tissue content were measured using a previously validated radioimmunoassay.

RESULTS

Dental pulp from female rats at 7 days showed significantly increased capsaicin-evoked immunoreactive CGRP release (>50% increase) compared with tissue from male rats. After 13 days, this release was significantly increased only in NGF-treated female rats (3-fold increase) when compared with control females or both male groups. The CGRP content in tissue from both female groups was also significantly increased after 7 days of treatment (>3 fold), but after 13 days this content was only significantly increased in tissue from NGF-treated female rats (P = .0001).

CONCLUSIONS

These data suggest that sex differences affect the role of NGF in the modulation of inflammation through the regulation of peripheral neuropeptide release and content.

Neuropeptide Y Y1 receptor effects on pulpal nociceptors

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.

Cannabinoid WIN 55,212-2 regulates TRPV1 phosphorylation in sensory neurons

Cannabinoids are known to have multiple sites of action in the nociceptive system, leading to reduced pain sensation. However, the peripheral mechanism(s) by which this phenomenon occurs remains an issue that has yet to be resolved. Because phosphorylation of TRPV1 (transient receptor potential subtype V1) plays a key role in the induction of thermal hyperalgesia in inflammatory pain models, we evaluated whether the cannabinoid agonist WIN 55,212-2 (WIN) regulates the phosphorylation state of TRPV1. Here, we show that treatment of primary rat trigeminal ganglion cultures with WIN led to dephosphorylation of TRPV1, specifically at threonine residues. Utilizing Chinese hamster ovary cell lines, we demonstrate that Thr(144) and Thr(370) were dephosphorylated, leading to desensitization of the TRPV1 receptor. This post-translational modification occurred through activation of the phosphatase calcineurin (protein phosphatase 2B) following WIN treatment. Furthermore, knockdown of TRPA1 (transient receptor potential subtype A1) expression in sensory neurons by specific small interfering RNA abolished the WIN effect on TRPV1 dephosphorylation, suggesting that WIN acts through TRPA1. We also confirm the importance of TRPA1 in WIN-induced dephosphorylation of TRPV1 in Chinese hamster ovary cells through targeted expression of one or both receptor channels. These results imply that the cannabinoid WIN modulates the sensitivity of sensory neurons to TRPV1 activation by altering receptor phosphorylation. In addition, our data could serve as a useful strategy in determining the potential use of certain cannabinoids as peripheral analgesics.

Vascular and cellular responses to pro-inflammatory stimuli in rat dental pulp

Dental pulp reactivity to various pro-inflammatory stimuli was independently evaluated in rats in terms of a vascular permeability increase and leukocyte recruitment. Substance P, calcitonin-gene related peptide (CGRP) and prostaglandin E(2) (in the picomol range) were applied to the exposed pulp from anesthetised animals and the plasma extravasation measured by the Evans blue content in the tissue following 10 min of administration. Leukocyte recruitment was evaluated morphometrically by counting the cell number present in serial sections of 1:3 4 microm pulp tissue 6 h after bacterial endotoxin (LPS; 0.06-1.2 microg/site) administration. Increase in pulp vascular permeability and cellular recruitment due to the injection of mentioned mediators in the skin or LPS in the peritoneal cavity were used as positive controls. Increase in vascular permeability in the pulp occurred in the same dose-range as observed in the skin, being CGRP the most active substance in both cases. However, it was necessary a higher dose of LPS (1.2 microg) to induce a similar cell recruitment in the pulp as that observed in the rat peritoneal cavity (0.3 microg). These data indicate that dental pulp reactivity presents the same pattern of increase in vascular permeability to other tissues in the rat, being CGRP the most potent mediator in this respect. In addition, they suggest the presence of CGRP receptors in the dental pulp. However, an adequate leukocyte recruitment response to bacterial endotoxin was not mounted, suggesting a deficiency in adhesion molecules in blood vessels in the rat dental pulp.

Potentiation of evoked calcitonin gene-related peptide release from oral mucosa: a potential basis for the pro-inflammatory effects of nicotine

Inflammation of the buccal mucosa, gingiva and periodontal tissues is a significant problem in users of nicotine-containing tobacco products; however, the potential role of nicotine in the development of this inflammation is unclear. In many tissues, nicotine, acting through nicotinic acetylcholine receptors (nAChRs), has been shown to increase the release of the pro-inflammatory mediator calcitonin gene-related peptide (CGRP) thereby potentially contributing to neurogenic inflammation. The purpose of the present studies was to determine the effects of nicotine and other nAChR agonists on capsaicin-evoked immunoreactive CGRP (iCGRP) release from rat buccal mucosa and to identify a potential cellular basis for these effects. Using a previously validated model of in vitro superfusion, we show that the nAChR agonists nicotine (EC50 557 micro m), epibatidine (EC50 317 pm) and cytisine (EC50 4.83 nm) potentiated capsaicin-evoked iCGRP release in a concentration-dependent manner by 123, 70 and 76%, respectively. The expression and distribution patterns of the mRNA transcripts encoding the alpha3, alpha4 and alpha6 nAChR subunits and their colocalization with CGRP and the capsaicin receptor VR1 were examined in rat trigeminal ganglion using combined in situ hybridization and immunohistofluorescence. Of all trigeminal neurons counted, mRNA encoding the alpha3, alpha4 and alpha6 subunits was found, respectively, in 14.45, 9.2 and 19.21% of neurons. The cell body diameter of most neurons containing any nAChR subunit was in the 30-40 micro m range with slightly fewer in the 20-30 micro m range. Co-localization of these alpha subunit transcripts with either CGRP or VR1 immunoreactivity ranged from approximately 5 to 7% for alpha4 and over 8% for alpha3 to 18% for alpha6. These data support the hypothesis that nicotinic agents, acting at nAChRs contained on primary sensory neurons, are capable of directly modulating the stimulated release of iCGRP. In the case of users of nicotine-containing tobacco products, this modulation could contribute to inflammatory processes within the oral cavity.

Capsaicin-sensitive nerve fibers: a potential extra-ACTH mechanism participating in adrenal regeneration in rats

Pituitary-derived factors, including ACTH, have been widely implicated in initiating adrenal regeneration. However, recent work has demonstrated that adrenal regeneration is also modulated by adrenal nerves that extensively reinnervate the regenerating adrenal. Moreover, transection of the splanchnic nerve removes sensory calcitonin gene-related peptide (CGRP) and preganglionic sympathetic vesicular acetylcholine transporter (VAChT)-positive fibers from the regenerating gland and delays regeneration. However, it is not known whether the splanchnic nerve effects on adrenal regeneration are mediated by the CGRP-positive or VAChT-positive innervation. The present studies use the drug capsaicin, a neurotoxin selective for a subset of primary afferent neurons, to specifically remove CGRP-positive fibers from the adrenal gland and assess subsequent effects on the recovery of adrenal mass and function after surgical enucleation. Male, Sprague-Dawley rats were anesthetized and treated with capsaicin (vs. vehicle) periaxonally to the thoracic splanchnic nerve (33 mM, 15 minutes) or systemically (30-100 mg/kg for 4 days, s.c.). After 7-12 days of recovery, rats received right adrenalectomy and left adrenal enucleation. At 14 and 21 days postenucleation, prestress and poststress plasma and adrenals glands were collected; adrenals were weighed and fixed for immunolabeling of CGRP-positive nerve fibers. Periaxonal capsaicin treatment decreased adrenal CGRP content prior to surgical enucleation; however, reinnervation by CGRP-positive fibers was not prevented and regeneration was not affected. Systemic capsaicin treatment attenuated the reinnervation by CGRP-positive fibers and increased the rate, but not extent, of adrenal regeneration. These results support the hypothesis that adrenal innervation represents an extra-ACTH mechanism to modulate the rate of adrenal regeneration.

Adrenergic regulation of capsaicin-sensitive neurons in dental pulp

Alpha adrenergic agonists (e.g. vasoconstrictors) represent one of the most commonly used drug classes in dentistry. Although adrenergic agonists have potent vascular effects, recent studies suggest that capsaicin-sensitive nociceptors may express adrenoceptors, suggesting that these drugs may directly modulate the function of an important class of pain-signaling neurons in peripheral tissues. In this study, we tested the hypothesis that adrenergic agonists inhibit activation of peripheral terminals of capsaicin-sensitive fibers innervating dental pulp. Pretreatment with epinephrine or clonidine significantly inhibited capsaicin-evoked release of immunoreactive calcitonin gene-related peptide from superfused bovine dental pulp. These studies suggest that adrenergic agonists may reduce postoperative pain in part via a direct inhibition of capsaicin-sensitive nociceptors. This finding may lead to the development of selective, peripherally acting, adrenergic analgesics. Moreover, because neuropeptide release alters blood flow, it is possible that the vascular effects of these drugs are caused by both vasoconstriction and inhibition of peripheral neuropeptide release.

Intrinsic regulation of CGRP release by dental pulp sympathetic fibers

Neurotransmission from sympathetic and peptidergic afferent fibers participates in the regulation of pulpal blood flow (PBF) via opposing effects. In this study, we directly tested the hypothesis that activation of pulpal sympathetic terminals inhibits exocytosis of immunoreactive calcitonin gene-related peptide (iCGRP) from peptidergic afferents innervating bovine dental pulp. The results demonstrate that norepinephrine inhibits capsaicin-evoked iCGRP release. The application of alpha-adrenergic antagonists (phentolamine or phenoxybenzamine) increased spontaneous release of iCGRP. Moreover, administration of agents that evoke the release of sympathetic neurotransmitters (guanethidine or reserpine) inhibited capsaicin-evoked iCGRP release. Collectively, these results indicate that sympathetic neurotransmission inhibits exocytosis from pulpal peptidergic afferent fibers. Analysis of these data supports the hypothesis that peripheral sympathetic vasomotor control may operate by a direct mechanism (vasoconstriction) as well as by an indirect mechanism (e.g., inhibition of exocytosis from afferent fibers). Since capsaicin-sensitive neurons are nociceptors, it is possible that certain sympathetic neurotransmission may modulate pain.

beta 2-Adrenoceptor regulation of CGRP release from capsaicin-sensitive neurons

Previous studies have suggested that neurotransmitter substances from the sympatho-adrenomedullary system regulate pulpal blood flow (PBF), in part, by the inhibition of vasoactive neuropeptide release from pulpal sensory neurons. However, no study has evaluated the role of beta-adrenoceptors. We evaluated the hypothesis that activation of beta-adrenoceptors inhibits immunoreactive calcitonin gene-related peptide (iCGRP) release from capsaicin-sensitive nociceptive neurons via in vitro superfusion of bovine dental pulp. Either norepinephrine or epinephrine inhibited capsaicin-evoked iCGRP. The norepinephrine effect was blocked by the selective beta(2)-adrenoceptor antagonist, ICI 118,551, but not by pre-treatment with the selective beta(1)-adrenoceptor antagonist, atenolol. In addition, application of albuterol, a selective beta(2)-adrenoceptor agonist, significantly blocked capsaicin-evoked release of iCGRP. Collectively, these studies demonstrate that activation of beta(2)-adrenoceptors in dental pulp significantly reduces exocytosis of neuropeptides from capsaicin-sensitive nociceptors. This effect may have physiologic significance in regulating PBF. Moreover, since capsaicin selectively activates nociceptors, beta(2)-adrenoceptor agonists may have clinical utility as peripherally acting therapeutics for dental pain and inflammation.

Capsaicin-evoked CGRP release from rat buccal mucosa: development of a model system for studying trigeminal mechanisms of neurogenic inflammation

Many of the physiological hallmarks associated with neurogenic inflammatory processes in cutaneous tissues are similarly present within orofacial structures. Such attributes include the dependence upon capsaicin-sensitive sensory neurons and the involvement of certain inflammatory mediators derived therein, including calcitonin gene-related peptide (CGRP). However, there are also important differences between the trigeminal and spinal nervous systems, and the potential contributions of neurogenic processes to inflammatory disease within the trigeminal system have yet to be fully elucidated. We present here a model system that affords the ability to study mechanisms regulating the efferent functions of peptidergic terminals that may subserve neurogenic inflammation within the oral cavity. Freshly dissected buccal mucosa tissue from adult, male, Sprague-Dawley rats was placed into chambers and superfused with oxygenated, Krebs buffer. Serial aliquots of the egressing superfusate were acquired and analysed by radioimmunoassay for immunoreactive CGRP (iCGRP). Addition of the selective excitotoxin, capsaicin (10-300 microm), to the superfusion buffer resulted in a significant, concentration-dependent increase in superfusate levels of iCGRP. Similarly, release of iCGRP from the buccal mucosa could also be evoked by a depolarizing concentration of potassium chloride (50 mm) or by the calcium ionophore A23187 (1 microm). The specific, capsaicin receptor antagonist, capsazepine (300 microm), completely abolished the capsaicin-evoked release of iCGRP while having no effect whatsoever on the potassium-evoked release. Moreover, capsaicin-evoked release was dependent upon the presence of extracellular calcium ions and was significantly, though incompletely, attenuated by neonatal capsaicin denervation. Collectively, these data indicate that the evoked neurosecretion of iCGRP in response to capsaicin occurs via a vanilloid receptor-mediated, exocytotic mechanism. The model system described here should greatly facilitate future investigations designed to identify and characterize the stimuli that regulate the release of CGRP or other neurosecretory substances in isolated tissues. This system may also be used to elucidate the role of these mediators in the aetiology of inflammatory processes within the trigeminal field of innervation.

Prostaglandin E2 enhances bradykinin-evoked iCGRP release in bovine dental pulp

Mediators produced during inflammation are responsible for hyperalgesia and expression of neurotransmitters and receptors in the nervous system. The production of bradykinin (BK) and the prostaglandins (PGs) may regulate initiation of pain. This study tested the hypothesis that BK and prostaglandin E2 (PGE2) have a positive interaction in evoking neurosecretion of immunoreactive calcitonin gene-related peptide (iCGRP). Bovine dental pulp was prepared and stimulated by the superfusion method with BK alone and in combination with PGE2. Kinin receptor antagonists to bradykinin-evoked release of iCGRP were also tested. Also tested was the hypothesis that dental pulp contains either the B1 or B2 or both BK receptors. Results showed that PGE2 enhanced BK-evoked iCGRP release by more than 50%. Western immunoblots revealed detectable B2 receptor protein with no detectable B1 receptor protein. We conclude that BK evokes iCGRP release from bovine dental pulp which is enhanced by a positive interaction with PGE2. Neurosecretion is evoked from isolated terminals of dental pulp fibers via the bradykinin B2 receptor-dependent mechanism.

Pulpal exposure alters neuropeptide levels in inflamed dental pulp and trigeminal ganglia: evaluation of axonal transport

Dental pulp is richly innervated with neurons containing calcitonin gene-related peptide (CGRP) or substance P (SP). Prior studies have demonstrated that inflammation alters these pulpal neuropeptides. In this study, we used a radioimmunoassay to evaluate the specificity of this response and the contribution of axonal transport. Rat mandibular molars were exposed and immunoreactive CGRP (iCGRP) and immunoreactive SP were measured. At 7 to 14 days after exposure, both pulpal iCGRP (73%) and immunoreactive SP (135%) displayed peak increases above control levels. This response was somatotopically restricted, with no changes observed in contralateral (intact) molars, or in ipsilateral mandibular molars after exposure of maxillary molars. Transection of the inferior alveolar nerve on day 13 significantly reduced pulpal levels of iCGRP on day 14. Collectively, these studies indicate that pulpal inflammation evokes a selective alteration in neuropeptide levels, due at least in part to alterations in transport or synthesis of neuropeptides in the trigeminal ganglion.

The role of sensory neuropeptides and nitric oxide on pulpal blood flow and tissue pressure in the ferret

A study was designed to investigate the effects of close intra-arterial infusion of antagonists to the sensory neuropeptides calcitonin gene-related peptide and substance P, as well as the effect of the nitric oxide synthesis inhibitor L-NAME on pulpal blood flow and interstitial fluid pressure during resting conditions and after electrical tooth stimulation. The micropuncture technique was used to measure tissue pressure and laser-Doppler flowmetry for blood flow recordings in ferret canine teeth. Close intra-arterial infusion of antagonists to calcitonin gene-related peptide and substance P significantly reduced resting blood flow (p < 0.05) and interstitial fluid pressure (p < 0.005) by unchanged systemic arterial pressure, while L-NAME administration caused a significant rise in interstitial fluid pressure (p < 0.05) and systemic arterial pressure (p < 0.005), with a concomitant fall in resting blood flow (p < 0.005). Tooth stimulation after calcitonin gene-related peptide antagonist infusion gave no significant change in blood flow or interstitial fluid pressure, whereas substance P antagonist infusion only partly eliminated the vasodilator response. L-NAME had no effect on the vasodilation induced by tooth stimulation. It is concluded that a resting vasodilator tone due to release of calcitonin gene-related peptide, substance P, and nitric oxide exists in the ferret dental pulp. The sensory neuropeptides exert their effect predominantly on pre-capillary vessels, and nitric oxide predominantly on post-capillary vessels. The sensory neuropeptide calcitonin gene-related peptide seems to be mainly responsible for the increase in blood flow and interstitial fluid pressure during tooth stimulation, whereas there was no evidence that nitric oxide participates in the vasodilation induced by tooth stimulation.

Activation of excitatory amino acid receptors in bovine dental pulp evokes the release of iCGRP

The activation of excitatory amino acid (EAA) receptors within the central nervous system is associated with numerous centrally mediated phenomena, including hyperalgesia. However, relatively little is known about the peripheral mechanisms which these receptors may regulate when activated. This research evaluated the hypothesis that EAA receptors in bovine dental pulp activate a population of peptidergic sensory neurons as measured by the release of immunoreactive calcitonin gene-related peptide (iCGRP), a neuropeptide associated with neurogenic inflammation. In vitro superfusion of bovine dental pulp was used to evaluate the regulation of iCGRP secretion by the EAA receptor agonists AMPA, kainate, NMDA, and L-glutamate. Both AMPA and kainate stimulated the release of iCGRP in a concentration-dependent manner (AMPA EC50 = 0.27 +/- 3.3 nM; kainate EC50 = 3.2 +/- 1.1 microM). Pre-treatment and co-administration of the AMPA/kainate receptor antagonist CNQX significantly reduced the iCGRP release evoked by either of these agonists. In contrast, neither NMDA nor L-glutamate induced any consistent changes in iCGRP release. These results suggest that the activation of AMPA and kainate receptors in dental pulp may contribute to peripheral release of vasoactive neuropeptides which mediate a neurogenic component of inflammation.

Periapical inflammatory responses and their modulation

Periapical inflammatory responses occur as a consequence of bacterial infection of the dental pulp, as a result of caries, trauma, or iatrogenic insult. Periapical inflammation stimulates the formation of granulomas and cysts, with the destruction of bone. These inflammatory responses are complex and consist of diverse elements. Immediate-type responses--including vasodilatation, increased vascular permeability, and leukocyte extravasation--are mediated by endogenous mediators, including prostanoids, kinins, and neuropeptides. Non-specific immune responses--including polymorphonuclear leukocyte and monocyte migration and activation, and cytokine production--are elicited in response to bacteria and their products. Interleukin-1 and prostaglandins in particular have been implicated as central mediators of periapical bone resorption. Chronic periapical inflammation further involves specific T- and B-cell-mediated anti-bacterial responses, and activates a network of regulatory cytokines which are produced by Th1- and Th2-type T-lymphocytes. Various naturally occurring and genetically engineered models of immunodeficiency are beginning to help elucidate those components of the immune system which protect the pulpal/periapical complex. Both specific and non-specific responses interface with and are regulated by the neural system. The modulation of these responses by immune response modifies, cytokine antagonists, and other novel therapeutic agents is discussed. As an experimental model, periapical inflammation has many advantages which permit it to be used in studies of microbial ecology and pathogenesis, host response, neuroimmunology, and bone resorption and regeneration.

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.

Pulp interstitial fluid pressure and blood flow after denervation and electrical tooth stimulation in the ferret

The effects of sensory and sympathetic denervation on simultaneously measured interstitial fluid pressure and blood flow in the canine pulp before, during and after electrical tooth stimulation were investigated in 25 ferrets. The micropuncture technique was used to measure interstitial fluid pressure and laser-Doppler flowmetry was used to record pulpal blood flow. Animals with an intact innervation (group 1) served as controls. Sensory denervation was by axotomy of the left inferior alveolar nerve 10 days before the experiment (group 2) and sympathectomy by removal of the left cervical ganglion 5 days before the experiments (group 3). The study was designed to verify whether denervation affected basal pulp blood flow and interstitial fluid pressures during control conditions and/or after tooth stimulation. During control conditions the interstitial fluid pressure averaged 1.32 +/- 0.07 kPa in group 1, whereas the mean was only 0.51 +/- 0.13 kPa in the axotomized animals (group 2). The difference was highly significant, indicating decreased blood or interstitial fluid volume in the pulp after inferior alveolar nerve axotomy. In the sympathectomized group neither the interstitial fluid pressure nor the pulp blood flow was significantly different from those of group 1. Electrical tooth stimulation caused an almost simultaneous increase in interstitial fluid pressure and pulp blood flow in groups 1 and 3, whereas stimulation did not significantly change either variable in the axotomized animals (group 2). It is concluded that a resting nervous vasodilator tone of sensory origin exists in the ferret dental pulp, and that the sensory nerves are responsible for the increased interstitial fluid pressure and pulp blood flow during tooth stimulation.

Chromic gut suture reduces calcitonin-gene-related peptide and substance P levels in the spinal cord following chronic constriction injury in the rat

The chronic constriction injury (CCI) is an animal model of an experimental peripheral neuropathy. In this model, a mononeuropathy is produced by loosely ligating the left sciatic nerve of the rat with chromic gut suture (Bennett and Xie 1988). Maves et al. (1993) have proposed that chemical constituents of chromic gut suture influence the behavioral changes of rats with the CCI. Considering their results, we became interested in evaluating whether the type of suture material used to produce the CCI also affected spinal levels of calcitonin-gene-related peptide immunoreactivity (CGRP-ir) and substance P immunoreactivity (SP-ir), peptides that are associated with small primary afferent neurons. Using methods of radioimmunoassay (RIA), we measured levels of CGRP-ir and SP-ir in the dorsal quadrants of approximately the lumbar 4-5 (L4-L5) spinal segments of rats with a CCI induced using polyglactin (Vicryl), plain gut, or chromic gut suture. We observed bilateral decreases in CGRP-ir and SP-ir 60 days after a CCI induced with chromic gut suture, but no changes in peptide levels after a CCI induced with either polyglactin or plain gut suture. These results suggest two possibilities: (1) chromic gut suture, when used to produce the CCI, has more than just a constrictive effect on the sciatic nerve, and/or (2) different suture materials produce changes in CGRP-ir and SP-ir with a differential time-course. Our experiments are unable to distinguish between these two possibilities.

Pharmacology of peripheral neuropeptide and inflammatory mediator release

Research conducted in the last 10 years has increased our knowledge on pain mechanisms substantially. Although many local tissue mediators, including neuropeptides, are known to exert pro-inflammatory effects, comparatively little is known about the actual tissue levels of these inflammatory mediators and their pharmacologic regulation. This article describes two new methods, clinical microdialysis and superfusion of dental pulp, which provide data on the pharmacology of peripheral neuropeptide and inflammatory mediator release. Collectively, these methods provide a biochemically based approach toward determining the mechanisms and management of orofacial pain.

CGRP (8-37) reduces the duration but not the maximal increase of antidromic vasodilation in dental pulp and lip of the rat

In this study the newly developed blockers of substance P (CP-96,345) and calcitonin gene-related peptide (CGRP8-37) were used to examine whether substance P and CGRP are involved in the afferent nerve induced vasodilation in the rat lower incisor pulp and lip. Electrical stimulation of the inferior alveolar nerve (10 V, 2 ms, 10 Hz, 30 s) in the presence of phenoxybenzamine (3 mg kg-1) induced an immediate vasodilation in the pulp and lip (52 and 186% increase in blood flow respectively, n = 12) with a long duration. Infusion of 2 mg kg-1 CP-96,345, a dose that inhibited the vasodilator effects of substance P (5-25 ng kg-1) in oral tissues, did not have any effect on antidromic vasodilation in either tissue. After infusion of CGRP8-37 (0.3 mg kg-1) the duration of the antidromic vasodilation in the pulp and lip was significantly reduced by 72 and 67% respectively (P < 0.05, n = 4), whereas the maximal increase of the response was unaffected. The blocking effect of the drug was short-lasting. When combined infusions of CP-96,345 and CGRP8-37 were given, a similar reduction in the duration of antidromic vasodilation in the pulp and lip occurred but in this case the amplitude of vasodilation in the pulp was reduced (from 35 +/- 9 to 12 +/- 3%, P < 0.05, n = 4). However, in the lip, the amplitude of vasodilation was not significantly reduced. The present findings indicate an involvement of CGRP in the mediation of the late phase of antidromic vasodilation in rat oral tissues and a role of substance P in the initiation of antidromic vasodilation in the incisor pulp.