Quantitative assessment of microcirculation in the rat dental pulp in response to alpha- and beta-adrenergic agonists

Adrenergic regulation of the vasculature impairs leukocyte interstitial migration and suppresses immune responses

The sympathetic nervous system (SNS) controls various physiological functions via the neurotransmitter noradrenaline. Activation of the SNS in response to psychological or physical stress is frequently associated with weakened immunity. Here, we investigated how adrenoceptor signaling influences leukocyte behavior. Intravital two-photon imaging after injection of noradrenaline revealed transient inhibition of CD8⁺ and CD4⁺ T cell locomotion in tissues. Expression of β-adrenergic receptor in hematopoietic cells was not required for NA-mediated inhibition of motility. Rather, chemogenetic activation of the SNS or treatment with adrenergic receptor agonists induced vasoconstriction and decreased local blood flow, resulting in abrupt hypoxia that triggered rapid calcium signaling in leukocytes and halted cell motility. Oxygen supplementation reversed these effects. Treatment with adrenergic receptor agonists impaired T cell responses induced in response to viral and parasitic infections, as well as anti-tumor responses. Thus, stimulation of the SNS impairs leukocyte mobility, providing a mechanistic understanding of the link between adrenergic receptors and compromised immunity.

An insight into neurophysiology of pulpal pain: facts and hypotheses

Pain and pain control are important to the dental profession because the general perception of the public is that dental treatment and pain go hand in hand. Successful dental treatment requires that the source of pain be detected. If the origin of pain is not found, inappropriate dental care and, ultimately, extraction may result. Pain experienced before, during, or after endodontic therapy is a serious concern to both patients and endodontists, and the variability of discomfort presents a challenge in terms of diagnostic methods, endodontic therapy, and endodontic knowledge. This review will help clinicians understand the basic neurophysiology of pulpal pain and other painful conditions of the dental pulp that are not well understood.

An overview of the dental pulp: its functions and responses to injury

The dental pulp is a unique tissue and its importance in the long-term prognosis of the tooth is often ignored by clinicians. It is unique in that it resides in a rigid chamber which provides strong mechanical support and protection from the microbial rich oral environment. If this rigid shell loses its structural integrity, the pulp is under the threat of the adverse stimuli from the mouth, such as caries, cracks, fractures and open restoration margins, all of which provide pathways for micro-organisms and their toxins to enter the pulp. The pulp initially responds to irritation by becoming inflamed and, if left untreated, this will progress to pulp necrosis and infection. The inflammation will also spread to the surrounding alveolar bone and cause periapical pathosis. The magnitude of pulp-related problems should not be underestimated since their most serious consequence is oral sepsis, which can be life threatening, and hence correct diagnosis and management are essential. Clinicians must have a thorough understanding of the physiological and pathological features of the dental pulp as well as the biological consequences of treatment interventions.

Agonist-induced vasoactive responses in isolated perfused porcine dental pulpal arterioles

A novel isolated perfused pulpal arteriole preparation and microperfusion system was used to evaluate the direct vasoactive responses of pulpal arterioles to selected agonists. Short lengths of porcine pulpal arterioles (101.7+/-2.2 microm o.d., n=105) were dissected out and placed in an environment-controlled bath on the stage of an inverted microscope. Both ends of the vessel were cannulated and perfused at a controlled rate through the lumen. The diameter of the vessel was measured online. Following equilibration, the vessel was challenged with various agonists: adrenaline (epinephrine), noradrenaline (norepinephrine), phenylephrine, dopamine, isoproterenol, 5-hydroxytryptamine, histamine and adenosine. The endothelium-dependent vasodilator acetylcholine was used to evaluate endothelial cell function. Adrenaline, noradrenaline, phenylephrine, 5-hydroxytryptamine and dopamine caused dose-dependent contractions (adrenaline=noradrenaline>phenylephrine>dopamine>5-hydroxytryptamine). Isoproterenol and histamine provoked a dose-dependent dilation. Adenosine produced pronounced vasodilatation in vessels precontracted with 10(-8)M endothelin-1. Functional adrenergic, histamine, 5-hydroxytryptamine and adenosine receptors are, therefore, present in porcine pulpal arterioles. The isolated perfused pulpal arteriole preparation may prove valuable in understanding local control mechanisms of pulpal microcirculation.

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.

Dose-response effects of adrenergic drugs on axial movements of the rat mandibular incisor and on arterial blood pressure

Axial tooth movements and arterial blood pressure were measured following the intravenous injection of 0, 0.01, 0.1, 1, or 10 micrograms/kg of adrenaline, noradrenaline or isoprenaline. Adrenaline caused a dose-dependent, rapid, extrusive tooth movement with a nearly simultaneous increase in blood pressure, followed by a marked intrusive tooth movement and a decrease in blood pressure. Noradrenaline caused a dose-dependent, rapid, extrusive tooth movement and an increase in blood pressure, but a subsequent intrusive tooth movement and decrease in blood pressure were not so marked. Isoprenaline caused a marked intrusive tooth movement and a decrease in blood pressure, without an extrusive tooth movement and increase in blood pressure. The time required to reach the maximum intrusive tooth movement was delayed after that to reach the maximum decrease in blood pressure. The recovery time of the intrusive tooth movement was much more delayed than that of blood pressure. These results suggest that the extrusive movement of the rat incisor was primarily related to the rise of arterial blood pressure due to stimulation of vascular alpha-receptors. It is also suggested that stimulation of beta-receptors would probably cause vasodilatation of arteries that would make the pressure in the small vessels in the microcirculation of the socket fall, so reducing the volume of blood and interstitial fluid in the socket followed by a marked and continuing intrusive tooth movement.

Measurement of the force needed to restrain eruptive movement of the rat mandibular incisor

This study describes the precise determination of the extrusive force in the rat mandibular incisor measured for a relatively longer period of time under artificial respiration with halothane anaesthesia. Following restraint of the eruptive movement of the incisor for a period of 20 h, the pushing force increased gradually and was maintained as an extremely gentle slope toward the end of the experimental period. The maximum pushing forces were estimated to be 9.1 +/- 2.5 (SD) mN in impeded incisors and 9.8 +/- 2.3 mN in unimpeded incisors. When force was converted to pressure, values were 30 +/- 8 (SD)mmHg and 32 +/- 8 mmHg, respectively; the difference was not significant. The maximum pushing force decreased rapidly--almost in parallel--with the fall of systemic arterial blood pressure after death of the animals; the amounts of reduction were 7.2 +/- 1.8 mN (24 +/- 6 mmHg) in impeded incisors and 7.0 +/- 2.0 mN (23 +/- 7 mmHg) in unimpeded incisors. Residual pushing forces were 1.7 +/- 1.0 mN (5.6 +/- 3.3 mmHg) in impeded incisors and 2.5 +/- 0.6 mN (8.2 +/- 2.0 mmHg) in unimpeded incisors; the difference was significant (P < 0.05). These results suggest that, under these experimental conditions, the pushing force of the rat incisor originates primarily from localized blood pressure within the incisor socket and, in part, from tissue growth.

Metabolism of [3H]-noradrenaline in human dental pulp in vitro

Slices of pulp from human maxillary and mandibular molar and promolar teeth were incubated with [3H]-noradrenaline (0.2 mumol/l) for 30 min after which the [3H]-noradrenaline and [3H]-metabolites in the tissue and medium were assayed by column chromatography. The deaminated metabolites 3,4-dihydroxy phenyl glycol (DOPEG) and 3,4-dihydroxy mandelic acid (DOMA) constituted 81% of the metabolites formed. Cocaine, an inhibitor of uptake1, decreased the formation of DOPEG and DOMA as well as the accumulation of [3H]-noradrenaline. In contrast to findings in rabbit pulp, when the disposition of exogenous noradrenaline in human pulp was examined by monoamine fluorescence histochemistry there was no evidence of extraneuronal accumulation of noradrenaline by connective tissue cells. In further experiments, pulp that had been incubated in [3H]-noradrenaline (0.6 mumol/l) for 30 min and superfused for 200 min contained [3H]-noradrenaline (183 pmol/g) and [3H]-DOMA (89 pmol/g). The 3H that overflowed into the perfusate between 85 and 90 min consisted mainly of metabolites. Stimulation of the sympathetic nerves through field electrodes increased the overflow of [3H]-noradrenaline into the perfusate threefold without affecting the overflow of metabolites. The increase was much greater (eightfold) in the presence of an alpha-adrenoceptor antagonist (rauwolscine; 0.1 mumol/l), plus inhibitors of uptake1 (desipramine; 0.3 mumol/l) and uptake 2 (corticosterone; 10 mumol/l). The results are interpreted as evidence that in human dental pulp the disposition of exogenous noradrenaline is determined largely by uptake by sympathetic nerves. After uptake, noradrenaline is deaminated by intraneuronal monoamine oxidase to DOPEG and DOMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Presynaptic control of noradrenaline release from sympathetic nerves in human dental pulp

This study was undertaken to determine whether release of noradrenaline from sympathetic nerves in human dental pulp in vitro was modulated by presynaptic adrenoceptors and by dopamine receptors. Pulp was incubated for 30 min with 3H-noradrenaline (0.6 mumol/l) and then perfused continuously with Krebs solution. Field stimulation of the sympathetic nerves at 5 Hz increased the overflow of 3H into the perfusate three-to fourfold. The stimulation-induced overflow of 3H was abolished by tetrodotoxin (0.1 mumol/l) and under Ca(2+)-free conditions, indicating that the increased 3H was derived from nerves. The stimulation-induced overflow was inhibited by noradrenaline (0.1 and 1.0 mumol/l), the alpha 2-adrenoceptor agonist UK14,304 (0.1 mumol/l), dopamine (1.0 mumol/l) and the dopamine receptor agonist, apomorphine (1.0 mumol/l). When the receptor agonists were noradrenaline or dopamine, desipramine (0.3 or 3.0 mumol/l) was present to prevent their uptake by the sympathetic nerves. Clonidine (1.0 mumol/l; tested at 2 Hz as well as 5 Hz) and the alpha 1-receptor agonist methoxamine (1.0 mumol/l) were without effect. The alpha 2-receptor antagonist/rauwolscine (0.1 mumol/l) prevented the inhibitory effects of noradrenaline and UK14,304, but had little effect on the inhibition produced by dopamine. Inhibition of the stimulation-induced overflow by apomorphine was prevented by the dopamine receptor antagonist haloperidol (0.1 mumol/l). The resting overflow of 3H was unaffected by any of the above agents except dopamine, which caused a small increase. It is concluded that the sympathetic nerves in human dental pulp possess inhibitory presynaptic alpha 2-adrenoceptors and dopamine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of systemic and topical nicotine on pulpal blood flow in dogs

It has been suggested that nicotine exerts cardiovascular effects which are similar to stimulation of the sympathoadrenal system. If this observation is true, nicotine administration would decrease pulpal blood flow and possible alter the pulpal response to injury. The purpose of this study was to measure pulpal blood flow in dogs using the radiolabelled microsphere method following topical or systemic administration of nicotine for 28 days. Thirteen dogs were divided into three groups. Group one received topical nicotine (8 mg nicotine/kg/day) combined with orabase which was applied in two equal doses to the mandibular anterior gingiva. Group two received systemic nicotine (2.5 mg/kg/day) delivered by osmotic pumps implanted subcutaneously in the back of each animals' neck. Group three were controls, and these animals received either topical orabase twice daily applied to the mandibular anterior gingiva or saline via osmotic pumps. Results indicated pulpal blood flow increased from Day 0 to Day 28 in both nicotine treated groups. Group one (topical nicotine) exhibited a mean increase in blood flow of 21.8 ml/min/100 g, while group two exhibited a mean increase of 50.1 ml/min/100 g. Group three, the control animals, exhibited a mean decrease in pulpal blood flow of 22.1 ml/min/100 g over the 28-day interval. These changes were not statistically significant (p > 0.05).

A scanning electron microscopic study of the contraction of vascular wall cells in dog dental pulp

Ultrastructural changes in vascular wall cells in dog dental pulp after removal of connective tissue components were studied by scanning electron microscopy following administration of norepinephrine (0.2 mg/kg). Contracted smooth-muscle cells were frequently seen in arterioles of all sizes. The surfaces of these cells were highly irregular with numerous evaginations and invaginations, varying considerably in configuration and size. Many evaginations ran longitudinally or obliquely to the long axis of the vessel. Some meandering evaginations were also observed as, rarely, were small spherical or bulbous projections. Spidery smooth-muscle cells frequently seen in the tunica media of terminal arterioles and thought to be primitive smooth-muscle cells exhibited fewer irregularities than the typical spindle-shaped smooth-muscle cells beneath them. Pericytes in the larger post-capillary venules (20 microns or larger in diameter) often showed evaginations and invaginations, mainly running parallel to the vessel axis. On the other hand, no surface irregularities could be seen in pericytes of either the smaller post-capillary venules (less than 20 microns in diameter) or the capillaries, although occasional evaginations running parallel to the vessel axis were noted on the outer surface of the endothelium.