Discriminating movements of liquid and gas in the rabbit colon with impedance manometry

BACKGROUND

High-resolution impedance manometry is a technique that is well established in esophageal motility studies for relating motor patterns to bolus flow. The use of this technique in the colon has not been established.

METHODS

In isolated segments of rabbit proximal colon, we recorded motor patterns and the movement of liquid or gas boluses with a high-resolution impedance manometry catheter. These detected movements were compared to video recorded changes in gut diameter. Using the characteristic shapes of the admittance (inverse of impedance) and pressure signals associated with gas or liquid flow we developed a computational algorithm for the automated detection of these events.

KEY RESULTS

Propagating contractions detected by video were also recorded by manometry and impedance. Neither pressure nor admittance signals alone could distinguish between liquid and gas transit, however the precise relationship between admittance and pressure signals during bolus flow could. Training our computational algorithm upon these characteristic shapes yielded a detection accuracy of 87.7% when compared to gas or liquid bolus events detected by manual analysis.

CONCLUSIONS & INFERENCES

Characterizing the relationship between both admittance and pressure recorded with high-resolution impedance manometry can not only help in detecting luminal transit in real time, but also distinguishes between liquid and gaseous content. This technique holds promise for determining the propulsive nature of human colonic motor patterns.

Novel methodology for determining the effect of adsorbates on human enamel acid dissolution

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Method for investigating effect of adsorbates on acid dissolution of enamel.

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Effect of repeated acid exposures on adsorbates can be measured over time.

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Specific salivary proteins significantly reduced acid demineralisation of enamel.

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Desorption of specific proteins corresponds to reduction in protection against acid.

Objective

The effect of various interventions on enamel demineralisation can be determined by chemically measuring mineral ions dissolved by the attacking acid. Results are usually expressed as mineral loss per surface area of enamel exposed. Acid resistant varnish or adhesive tape are typically used to delineate an area of enamel. However, enamel surface curvature, rugosity and porosity reduce the reliability of simple area measurements made at the macro scale. Our aim was to develop a simple method for investigating the effect of adsorbates on enamel demineralisation that does not rely on knowing the area of enamel exposed. As an exemplar we have used salivary proteins as a model adsorbate.

Design

Natural human tooth enamel surfaces were subjected to five sequential acid challenges and then incubated in adsorbate (whole clarified saliva) followed by a further 15 acid challenges. Demineralisation was determined by measuring the phosphate released into the acid during each exposure by a spectrophotometric assay. The initial five challenges established a mean baseline mineral loss for each tooth against which the effect of subsequently adsorbed proteins could be compared.

Results

Salivary proteins significantly reduced the acid demineralisation of human enamel by 43% (p < 0.01). Loss of proteins during each challenge corresponded to a gradual reduction in the degree of protection afforded.

Conclusions

The methodology provides a simple and flexible means to investigate the effect of any adsorbate on enamel acid dissolution. Knowledge of the area of exposed enamel is irrelevant as each tooth acts as its own negative control.

The Effect of Copper on Demineralization of Dental Enamel

Previous studies have concluded that copper might inhibit enamel demineralization in vitro. Our aim was to assess the effect of copper (Cu2+), with and without amine fluoride, on human dental enamel under cariogenic challenge in situ. In a double-blind randomized four-leg crossover trial, 14 individuals wore a removable appliance containing 2 enamel slabs, 1 containing an artificial caries lesion. During each leg, the appliance was exposed twice daily to one of the test solutions: 1.25 mM CuSO4, amine fluoride (250 ppm F), copper and amine fluoride combined, or a placebo (water). A cariogenic challenge was provided in all cases by 5 daily exposures to 10% sucrose. Slabs were assessed before and after 21 days’ exposure by Knoop microhardness and transverse microradiography. Significantly less demineralization was observed with Cu2+ and fluoride in combination than with fluoride treatment alone (p < 0.05), whereas copper alone had no significant protective effect.

The Importance of Serine Phosphorylation of Ameloblastin on Enamel Formation

FAM20C is a newly identified kinase on the secretory pathway responsible for the phosphorylation of serine residues in the Ser-x-Glu/pSer motifs in several enamel matrix proteins. Fam20C-knockout mice showed severe enamel defects very similar to those in the ameloblastin ( Ambn)-knockout mice, implying that phosphoserines may have a critical role in AMBN function. To test this hypothesis, we generated amelogenin ( Amel) promoter-driven Ambn-transgenic mice, in which Ser⁴⁸, Ser²²⁶, and Ser²²⁷ were replaced by aspartic acid (designated as D-Tg) or alanines (designated as A-Tg). The negative charge of aspartic acid is believed to be able to mimic the phosphorylation state of serine, while alanine is a commonly used residue to substitute serine due to their similar structure. Using Western immunoblotting and quantitative polymerase chain reaction, the authors identified transgenic lines expressing transgenes somewhat higher (Tg+) or much higher (Tg++) than endogenous Ambn. The lower incisors collected from 7-d-old and 7-wk-old mice were analyzed by histology, scanning electron microscopy, immunohistochemistry, and Western immunoblotting to examine the morphology and microstructure changes in enamel, as well as the expression pattern of enamel matrix proteins. The A-Tg+ and A-Tg++ mice displayed severe enamel defects in spite of the expression level of transgenes, while the D-Tg+ and D-Tg++ mice showed minor to mild enamel defects, indicating that the D-Tg transgenes disturbed enamel formation less than the A-Tg transgenes did. Our results suggest that the phosphorylation state of serines is likely an essential component for the integrity of AMBN function.

Neuromechanical factors involved in the formation and propulsion of fecal pellets in the guinea-pig colon

BACKGROUND

The neuromechanical processes involved in the formation and propulsion of fecal pellets remain incompletely understood.

METHODS

We analyzed motor patterns in isolated segments of the guinea-pig proximal and distal colon, using video imaging, during oral infusion of liquid, viscous material, or solid pellets.

KEY RESULTS

Colonic migrating motor complexes (CMMCs) in the proximal colon divided liquid or natural semisolid contents into elongated shallow boluses. At the colonic flexure these boluses were formed into shorter, pellet-shaped boluses. In the non-distended distal colon, spontaneous CMMCs produced small dilations. Both high- and low-viscosity infusions evoked a distinct motor pattern that produced pellet-shaped boluses. These were propelled at speeds proportional to their surface area. Solid pellets were propelled at a speed that increased with diameter, to a maximum that matched the diameter of natural pellets. Pellet speed was reduced by increasing resistive load. Tetrodotoxin blocked all propulsion. Hexamethonium blocked normal motor patterns, leaving irregular propagating contractions, indicating the existence of neural pathways that did not require nicotinic transmission.

CONCLUSIONS & INFERENCES

Colonic migrating motor complexes are responsible for the slow propulsion of the soft fecal content in the proximal colon, while the formation of pellets at the colonic flexure involves a content-dependent mechanism in combination with content-independent spontaneous CMMCs. Bolus size and consistency affects propulsion speed suggesting that propulsion is not a simple reflex but rather a more complex process involving an adaptable neuromechanical loop.

Treatment of early caries lesions using biomimetic self-assembling peptides--a clinical safety trial

OBJECTIVE

We previously reported that a rationally designed biomimetic self-assembling peptide, P₁₁-4, nucleated hydroxyapatite de novo and was apparently capable of in situ enamel regeneration following infiltration into caries-like lesions. Our present aim was to determine the safety and potential clinical efficacy of a single application of P₁₁-4 on early enamel lesions.

MATERIALS AND METHODS

Fifteen healthy adults with Class V 'white spot' lesions received a single application of P₁₁-4. Adverse events and lesion appearances were recorded over 180 days.

RESULTS

Patients treated with P₁₁-4 experienced a total of 11 adverse events during the study, of which two were possibly related to the protocol. Efficacy evaluation suggested that treatment with P₁₁-4 significantly decreased lesion size (p = 0.02) after 30 days and shifted the apparent progression of the lesions from 'arrested/progressing' to 'remineralising' (p <0.001). A highly significant improvement in the global impression of change was recorded at day 30 compared with baseline (p <0.001).

CONCLUSIONS

The results suggest that treatment of early caries lesions with P₁₁-4 is safe, and that a single application is associated with significant enamel regeneration, presumably by promoting mineral deposition within the subsurface tissue.

The neurochemical changes in the innervation of human colonic mesenteric and submucosal blood vessels in ulcerative colitis and Crohn's disease

BACKGROUND

Neurogenic inflammation involves vasodilation, oedema and sensory nerve hypersensitivity. Extrinsic sensory nerves to the intestinal wall mediate these effects and functional subsets of these extrinsic nerves can be characterized by immunohistochemical profiles. In this study such profiles were examined in samples from patients with inflammatory bowel disease (IBD), in particular ulcerative colitis (UC) and Crohn's disease (CD).

METHODS

Healthy margins from cancer patients were compared to specimens from IBD patients. All nerve fibres were labelled by PGP 9.5. Double and triple labelling with TH, NPY, SP, SOM, NOS, VIP, VAChT, CGRP, TRPv1 were performed. Perivascular nerve fibres in the mesentery, and submucosa, were examined. The percentage of all labelled nerve fibres was calculated with a transect method.

KEY RESULTS

Total number of varicosities on mesenteric vessels increased in IBD but decreased around submucosal vessels. The percentage of nerve fibres around submucosal arteries labelled by SP increased from 11% in controls to 20% (UC) and 24% (CD) and mesenteric artery nerve fibres were unchanged. Nerve fibres labelled by SOM were markedly reduced surrounding submucosal arteries, from 22% to 1% (UC) and 2% (CD), but not perivascular mesenteric nerve fibres. 87 to 93% of SP immunoreactive nerve fibres were also reactive for TRvP1. TRPv1 labelling without SP was 12%in controls and increased to 40% in CD submucosal specimens.

CONCLUSIONS & INFERENCES

There is an increase in SP and TRPv1, and a reduction in SOM immunoreactive nerve fibres in IBD. Changes in the perivascular functional nerve subclasses may underlie the hyperaemia, and ulceration, characteristic of IBD. Furthermore, pain may relate to underlying neural changes.

Peristalsis and propulsion of colonic content can occur after blockade of major neuroneuronal and neuromuscular transmitters in isolated guinea pig colon

We recently identified hexamethonium-resistant peristalsis in the guinea pig colon. We showed that, following acute blockade of nicotinic receptors, peristalsis recovers, leading to normal propagation velocities of fecal pellets along the colon. This raises the fundamental question: what mechanisms underlie hexamethonium-resistant peristalsis? We investigated whether blockade of the major receptors that underlie excitatory neuromuscular transmission is required for hexamethonium-resistant peristalsis. Video imaging of colonic wall movements was used to make spatiotemporal maps and determine the velocity of peristalsis. Propagation of artificial fecal pellets in the guinea pig distal colon was studied in hexamethonium, atropine, ω-conotoxin (GVIA), ibodutant (MEN-15596), and TTX. Hexamethonium and ibodutant alone did not retard peristalsis. In contrast, ω-conotoxin abolished peristalsis in some preparations and reduced the velocity of propagation in all remaining specimens. Peristalsis could still occur in some animals in the presence of hexamethonium + atropine + ibodutant + ω-conotoxin. Peristalsis never occurred in the presence of TTX. The major finding of the current study is the unexpected observation that peristalsis can occur after blockade of the major excitatory neuroneuronal and neuromuscular transmitters. Also, the colon retained an intrinsic polarity in the presence of these antagonists and was only able to expel pellets in an aboral direction. The nature of the mechanism(s)/neurotransmitter(s) that generate(s) peristalsis and facilitate(s) natural fecal pellet propulsion, after blockade of major excitatory neurotransmitters, at the neuroneuronal and neuromuscular junction remains to be identified.

Is serotonin in enteric nerves required for distension-evoked peristalsis and propulsion of content in guinea-pig distal colon?

Recent studies have shown genetic deletion of the gene that synthesizes 5-HT in enteric neurons (tryptophan hydroxylase-2, Tph-2) leads to a reduction in intestinal transit. However, deletion of the Tph-2 gene also leads to major developmental changes in enteric ganglia, which could also explain changes in intestinal transit. We sought to investigate this further by acutely depleting serotonin from enteric neurons over a 24-h period, without the confounding influences induced by genetic manipulation. Guinea-pigs were injected with reserpine 24h prior to euthanasia. Video-imaging and spatio-temporal mapping was used to record peristalsis evoked by natural fecal pellets, or slow infusion of intraluminal fluid. Immunohistochemical staining for 5-HT was used to detect the presence of serotonin in the myenteric plexus. It was found that endogenous 5-HT was always detected in myenteric ganglia of control animals, but never in guinea-pigs treated with reserpine. Interestingly, peristalsis was still reliably evoked by either intraluminal fluid, or fecal pellets in reserpine-treated animals that also had their entire mucosa and submucosal plexus removed. In these 5-HT depleted animals, there was no change in the frequency of peristalsis or force generated during peristalsis. In control animals, or reserpine treated animals, high concentrations (up to 10 μM) of ondansetron and SDZ-205-557, or granisetron and SDZ-205-557 had no effect on peristalsis. In summary, acute depletion of serotonin from enteric nerves does not prevent distension-evoked peristalsis, nor propulsion of luminal content. Also, we found no evidence that 5-HT3 and 5-HT4 receptor activation is required for peristalsis, or propulsion of contents to occur. Taken together, we suggest that the intrinsic mechanisms that generate peristalsis and entrain propagation along the isolated guinea-pig distal colon are independent of 5-HT in enteric neurons or the mucosa, and do not require the activation of 5-HT3 or 5-HT4 receptors.

Neurogenic and myogenic motor patterns of rabbit proximal, mid, and distal colon

The rabbit colon consists of four distinct regions. The motility of each region is controlled by myogenic and neurogenic mechanisms. Associating these mechanisms with specific motor patterns throughout all regions of the colon has not previously been achieved. Three sections of the colon (the proximal, mid, and distal colon) were removed from euthanized rabbits. The proximal colon consists of a triply teniated region and a single tenia region. Spatio-temporal maps were constructed from video recordings of colonic wall diameter, with associated intraluminal pressure recorded from the aboral end. Hexamethonium (100 μM) and tetrodotoxin (TTX; 0.6 μM) were used to inhibit neural activity. Four distinct patterns of motility were detected: 1 myogenic and 3 neurogenic. The myogenic activity consisted of circular muscle (CM) contractions (ripples) that occurred throughout the colon and propagated in both antegrade (anal) and retrograde (oral) directions. The neural activity of the proximal colon consisted of slowly (0.1 mm/s) propagating colonic migrating motor complexes, which were abolished by hexamethonium. These complexes were observed in the region of the proximal colon with a single band of tenia. In the distal colon, tetrodotoxin-sensitive, thus neurally mediated, but hexamethonium-resistant, peristaltic (anal) and antiperistaltic (oral) contractions were identified. The distinct patterns of neurogenic and myogenic motor activity recorded from isolated rabbit colon are specific to each anatomically distinct region. The regional specificity motor pattern is likely to facilitate orderly transit of colonic content from semi-liquid to solid composition of feces.

Changes in the structure and density of oral plaque biofilms with increasing plaque age

In common with many biofilms in nature, oral plaque has been shown to have a heterogeneous structure as shown by confocal microscopy. In the present study we have used confocal laser scanning microscopy (CLSM) to determine changes in the structure of plaque biofilms with increasing plaque age. Natural human plaque biofilms were formed using the Leeds in situ device. Plaque biofilms were allowed to form for periods of 2 days, 1 week, 2 weeks and 4 weeks before removal of the devices and immediate imaging using the CLSM. Confocal imaging showed that the biofilms retained their heterogeneous appearance at each of the time points studied but appeared to have a tendency to become somewhat more dense with increasing time. Image analysis demonstrated that the percentage of biomass within each biofilm increased over time, particularly between 2 days and 1 week, and with increasing depth into the biofilms. In addition, using the CLSM we were able to demonstrate changes in the bacterial flora of the biofilms with time, with many more filamentous forms being present at the 2- and 4-week time points.

Neuroanatomy and physiology of colorectal function and defaecation: from basic science to human clinical studies

Colorectal physiology is complex and involves programmed, coordinated interaction between muscular and neuronal elements. Whilst a detailed understanding remains elusive, novel information has emerged from recent basic science and human clinical studies concerning normal sensorimotor mechanisms and the organization and function of the key elements involved in the control of motility. This chapter summarizes these observations to provide a contemporary review of the neuroanatomy and physiology of colorectal function and defaecation.

Enamel matrix proteins; old molecules for new applications

Emdogain (enamel matrix derivative, EMD) is well recognized in periodontology, where it is used as a local adjunct to periodontal surgery to stimulate regeneration of periodontal tissues lost to periodontal disease. The biological effect of EMD is through stimulation of local growth factor secretion and cytokine expression in the treated tissues, inducing a regenerative process that mimics odontogenesis. The major (>95%) component of EMD is Amelogenins (Amel). No other active components have so far been isolated from EMD, and several studies have shown that purified amelogenins can induce the same effect as the complete EMD. Amelogenins comprise a family of highly conserved extracellular matrix proteins derived from one gene. Amelogenin structure and function is evolutionary well conserved, suggesting a profound role in biomineralization and hard tissue formation. A special feature of amelogenins is that under physiological conditions the proteins self-assembles into nanospheres that constitute an extracellular matrix. In the body, this matrix is slowly digested by specific extracellular proteolytic enzymes (matrix metalloproteinase) in a controlled process, releasing bioactive peptides to the surrounding tissues for weeks after application. Based on clinical and experimental observations in periodontology indicating that amelogenins can have a significant positive influence on wound healing, bone formation and root resorption, several new applications for amelogenins have been suggested. New experiments now confirm that amelogenins have potential for being used also in the fields of endodontics, bone regeneration, implantology, traumatology, and wound care.

Self-assembling peptide scaffolds promote enamel remineralization

Rationally designed beta-sheet-forming peptides that spontaneously form three-dimensional fibrillar scaffolds in response to specific environmental triggers may potentially be used in skeletal tissue engineering, including the treatment/prevention of dental caries, via bioactive surface groups. We hypothesized that infiltration of caries lesions with monomeric low-viscosity peptide solutions would be followed by in situ polymerization triggered by conditions of pH and ionic strength, providing a biomimetic scaffold capable of hydroxyapatite nucleation, promoting repair. Our aim was to determine the effect of an anionic peptide applied to caries-like lesions in human dental enamel under simulated intra-oral conditions of pH cycling. Peptide treatment significantly increased net mineral gain by the lesions, due to both increased remineralization and inhibition of demineralization over a five-day period. The assembled peptide was also capable of inducing hydroxyapatite nucleation de novo. The results suggest that self-assembling peptides may be useful in the modulation of mineral behavior during in situ dental tissue engineering.

Surface chemistry of enamel apatite during maturation in relation to pH: implications for protein removal and crystal growth

Apatite crystal growth rate and morphology in mineralized tissues are considered to be controlled by surface interaction with extracellular matrix proteins. During enamel maturation where protein is finally removed from crystal surfaces to permit massive crystal growth, pH oscillates between approximately 5.8 and approximately 7.2. With this in mind, a study of enamel apatite surface chemistry in terms of local environmental pH was undertaken. Using atomic force microscopy adhesion force measurements were made between hydroxylated or carboxylated cantilever tips and maturation stage crystals between pH 2 and 10. Adhesion force increased from pH 10 to a maximum at pH 6.6 presumably due to increased hydrogen bonding due to replacement of surface cations (Na, Ca, Mg) with protons and/or protonation of phosphate per se. Below pH 6.6 adhesion force decreased and became very variable indicating that the surface had become unstable probably due to removal of fully protonated phosphate from the surface by adherence to the cantilever tip. Frictional force measurements also revealed 2-3, approximately 30 nm diameter high friction domains in bands across the crystal long axis. Their location mirrored the binding pattern of similarly sized amelogenin aggregates seen in vitro. The data suggests that specific protein binding sites may exist on crystal surfaces and may be released at lower pH by protonation which would lower cationic charge on both crystal surface and ionic charge on the protein. Instability of the crystal surface could also play a role.

The effect of fluoride on the developing tooth

This review aims to outline the effects of fluoride on the biological processes involved in the formation of tooth tissues, particularly dental enamel. Attention has been focused on mechanisms which, if compromised, could give rise to dental fluorosis. The literature is extensive and often confusing but a much clearer picture is emerging based on recent more detailed knowledge of odontogenesis. Opacity, characteristic of fluorotic enamel, results from incomplete apatite crystal growth. How this occurs is suggested by other changes brought about by fluoride. Matrix proteins, associated with the mineral phase, normally degraded and removed to permit final crystal growth, are to some extent retained in fluorotic tissue. Fluoride and magnesium concentrations increase while carbonate is reduced. Crystal surface morphology at the nano-scale is altered and functional ameloblast morphology at the maturation stage also changes. Fluoride incorporation into enamel apatite produces more stable crystals. Local supersaturation levels with regard to the fluoridated mineral will also be elevated facilitating crystal growth. Such changes in crystal chemistry and morphology, involving stronger ionic and hydrogen bonds, also lead to greater binding of modulating matrix proteins and proteolytic enzymes. This results in reduced degradation and enhanced retention of protein components in mature tissue. This is most likely responsible for porous fluorotic tissue, since matrix protein removal is necessary for unimpaired crystal growth. To resolve the outstanding problems of the role of cell changes and the precise reasons for protein retention more detailed studies will be required of alterations to cell function, effect on specific protein species and the nano-chemistry of the apatite crystal surfaces.

Subunit structures in hydroxyapatite crystal development in enamel: implications for amelogenesis imperfecta

Previous freeze-etching studies of developing enamel revealed collinear arrays of spherical structures (approximately 50 nM dia) of similar width to the crystals of mature tissue. Concomitant with matrix degradation/processing, spherical structures became less distinct until, coincident with massive matrix loss, only crystal outlines were seen. More recently, using Atomic force microscopy technology, early crystals exhibited topology reminiscent of these collinear spherical structures. After matrix loss these were replaced by similarly sized bands of positive charge density on the crystal surfaces. The data suggest enamel crystals may form from mineral-matrix spherical subunits. Matrix processing may generate mineral nuclei and lead to their fusion and transformation into long apatite crystals. Support for this view derives from the appearance of short crystal segments in amelogenesis imperfecta (hypoplastic AI) or abnormally large crystals alongside 50 nM diameter spherical mineral subunits (hypomaturation AI). Mutation of matrix or processing enzymes leading to defective processing may have impaired mineral initiation, fusion, and subsequent growth.

Enamelin compartmentalization in developing porcine enamel

The tissue compartmentalization of enamelin-processing products has been investigated in developing pig enamel using a sequential extraction procedure. Only trace amounts of enamelin-processing products were detected in simulated enamel fluid extracts, suggesting that enamelins are not solubilized in the matrix to any great extent. Subsequent phosphate buffer extraction desorbed and extracted several enamelin-processing products that were presumably bound to the mineral phase. A 35-kD processing product dominated the phosphate extract, suggesting that enamelin processing leads to an accumulation of this mineral-bound molecule. Dissociative extraction with urea subsequently extracted the remainder of the enamelin-processing products present. This material was presumably present in the tissue in an aggregated insoluble state. Several enamelin-processing products were only extracted by specific extraction procedures, suggesting that different enamelin-processing products are differentially compartmentalized. This may indicate that specific enamelin-processing products have different functions. In contrast to amelogenins, which are processed in the deeper tissue to generate products having a low affinity for the mineral, enamelin processing appears to produce products (those enamelins desorbed by phosphate buffer) that have a high affinity for the mineral. These products, appearing in the deeper enamel layers, may serve to influence crystal growth kinetics in the absence of any mineral-binding amelogenins.

Inheritance pattern and elemental composition of enamel affected by hypomaturation amelogenesis imperfecta

Hypomaturation amelogenesis imperfecta (AI) is characterized clinically by enamel of normal thickness that is hypomineralized, mottled, and detaches easily from the underlying dentin. Autosomal dominant, autosomal recessive, X-linked, and sporadic modes of inheritance have been documented. The present study investigated the elemental composition of the enamel of teeth from individuals demonstrating clinical hypomaturation AI from families representing three of these patterns of inheritance. The aim of the study was to determine if there was any commonality in microscopic phenotype of this defect between families demonstrating the various inheritance patterns. One section from each tooth was microradiographed and then viewed in a scanning electron microscope (SEM) equipped with an ultrathin window energy-dispersive x-ray spectroscopy (EDX) detector. In the SEM, prisms and constituent crystals in discrete areas appeared to be largely obscured by an amorphous material. EDX analysis showed enamel outside these areas to have a composition indistinguishable from control teeth. However, within these affected areas there was a large increase in carbon content (up to a fivefold increase). In some teeth there was also a detectable but smaller increase in the relative amounts of nitrogen or oxygen. The results suggest the defect in these teeth with a common clinical phenotype, irrespective of the pattern of inheritance, demonstrates a commonality in microscopic phenotype. The large increase in carbon content, not matched by an equivalent increase in nitrogen or oxygen, suggests a possible increased lipid content. In those teeth with elevated nitrogen levels there may also be retained protein.

Characterization of a porcine amelogenin preparation, EMDOGAIN, a biological treatment for periodontal disease

EMDOGAIN is derived from porcine developing enamel matrix and has been shown to facilitate regeneration of the periodontium, although its mechanism of action is unknown. The aim of the present study was to identify enamel matrix proteins and proteolytic enzymes present in EMDOGAIN and compare them with those extracted from developing porcine enamel itself. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Western blotting, and zymography were used to identify the proteins present and to determine their enzyme activity. The results showed that developing enamel contained amelogenins, albumin, amelin, and enamelin. EMDOGAIN, however, contained only amelogenins. Both metalloendoproteases and serine protease activity were revealed in both EMDOGAIN and developing enamel. The roles of the amelogenin and enzyme components, if any, in periodontal regeneration are unknown.

Are alpha-gliadins glycosylated?

Alpha-gliadins isolated by carboxymethylcellulose chromatography contain noncovalently bound glucose probably due to contaminating proteoglycans and to material shed from the column. Traces of carbohydrate remain strongly bound to alpha-gliadins even after harsh denaturation, but our results indicate alpha-gliadins are not glycoproteins. Suggestions that gliadins are glycoproteins are probably due to contamination with this glucose and the presence of these proteoglycans.

Propagating contractions of the circular muscle evoked by slow stretch in flat sheets of guinea-pig ileum

Flat sheet preparations of guinea-pig ileum were stretched circumferentially and the propagation of circular muscle contractions along the preparation was investigated. Slow stretch, at 100 microm s-1, of a 50-mm long flat sheet of intestine, evoked circular muscle contraction orally, which propagated, without decrement, for up to 30 mm. This occurred despite circular muscle shortening being prevented, and in the absence of propulsion of contents. Thus, propagation in this flat sheet preparation could not explained on the basis of neuro-mechanical interactions, as previously proposed. Irrespective of the length of preparations, contraction amplitude decreased significantly in the most aboral 10-15 mm of intestine. This was not due to descending inhibitory pathways, but was associated with interruption of ascending excitatory pathways near the aboral end. Slow waves were not detected in circular muscle cells in any preparation (n=8). Smooth muscle action potentials evoked in circular muscle cells, in the presence of tetrodotoxin (TTX, 0.6 micromol L-1), did not propagate for more than 1 mm in the longitudinal axis. Propagation of circular muscle activity, evoked by slow stretch of flat sheet preparations, reveals the presence of a mechanism other than myogenic spread or the neuro-mechanical interactions previously proposed to account for propagation; the nature of this mechanism remains to be determined.

Analysis of motor patterns in the isolated guinea-pig large intestine by spatio-temporal maps

We investigated and quantified the spontaneous patterns of motility in the isolated guinea-pig proximal and distal colon taken from adult animals. During spontaneous emptying, profiles of proximal and distal colon were recorded with a video camera, and image analysis was used to construct spatio-temporal maps of the motions of the intestinal wall. Four patterns of motility were recorded. In the proximal colon there were neurally mediated contractions that propagated in the aboral direction at 4.1 mm s(-1), gently pushing the soft contents aborally; these are likely to represent spontaneous peristaltic behaviour. A second pattern, insensitive to tetrodotoxin (TTX; 0.6 microM), consisted, in both oral and aboral propagation, of shallow contractions of the circular muscle (ripples). These contractions propagated aborally at 2.8 +/- 0.45 mm s(-1) and orally at 2.03 +/- 0.31 mm s(-1) (n=10). Of these TTX-resistant contractions, 22.5% propagated both orally and aborally from a common origin. The orally propagated component of these myogenic contractions is likely to correspond to the antiperistalsis widely described in the proximal colon. In the distal colon, two patterns of motor activity were observed. One, induced by natural or artificial pellets, consisted of peristaltic contractions that pushed the pellets aborally at 0.8 mm s(-1) and expelled a pellet every 108 s. In the interval between pellet propulsion and after the distal colon had emptied all of its pellets a second, nerve-mediated pattern of motor activity, consisting of clusters of annular circular muscle contractions separated by short dilated regions, slowly propagated aborally at 0.3 mm s(-1). Both of these motor patterns were abolished by TTX (0.6 microM). A latex balloon, inserted at the oral end of the empty isolated distal colon and inflated to a size similar to faecal pellets, was propelled at 1.4 mm s(-1). Epoxy resin-covered natural pellets were propelled at a similar speed of 1.6 mm s(-1). Our data revealed that myogenic and neurogenic patterns of propagated contractions in the colon occur in isolated preparations and are involved in emptying the colon.

Intraganglionic laminar endings are mechano-transduction sites of vagal tension receptors in the guinea-pig stomach

1. Distension-sensitive vagal afferent fibres from the cardiac region of the guinea-pig stomach were recorded extracellularly, then filled with biotinamide, using an anterograde tracing technique. 2. Most of the stretch-sensitive units of the guinea-pig stomach (41 out of 47; number of animals N = 26) had low thresholds (less than 1 mm) to circumferential stretch and showed slow adaptation. Twenty of these units fired spontaneously under resting conditions (mean: 1.9 +/- 0.3 Hz, n = 20, N = 14). 3. Adaptation of firing during slow or maintained stretch correlated closely with accommodation of intramural tension, but tension-independent adaptation was also present. 4. Nicardipine (3 microM) with hyoscine (3 microM) reduced stretch-evoked firing of gastric vagal afferents, by inhibiting smooth muscle contraction. Gadolinium (1 mM) blocked distension-evoked firing. 5. Focal stimulation of the stomach muscle wall with a von Frey hair (0.4 mN) identified one to six punctate receptive fields in each low threshold vagal distension-sensitive afferent. These were marked on the serosal surface of the stomach wall. 6. Anterograde filling of recorded nerve trunks revealed intraganglionic laminar endings (IGLEs) within 142 +/- 34 microm (n = 38; N = 10) of marked receptive fields. The mean distance from randomly generated sites to the nearest IGLE was significantly greater (1500 +/- 48 microm, n = 380, N = 10, P < 0.0001). Viscerofugal nerve cell bodies, intramuscular arrays and varicose axons were not associated with receptive fields. The results indicate that IGLEs are the mechanotransduction sites of low threshold, slowly adapting vagal tension receptors in the guinea-pig upper stomach.

Neuronal control of the pyloric sphincter of the guinea-pig

The pyloric sphincter (PS) controls gastric emptying and prevents the reflux of duodenal content into the stomach. Neuronal pathways and reflexes controlling the guinea-pig PS were physiologically investigated in isolated preparations. Simultaneous intracellular or extracellular and tension recordings from PS circular muscle with electrical and stretch stimulation were used. Electrical stimulation evoked an initial small contraction followed by a relaxation with a corresponding inhibitory junction potential (IJP) then a second large contraction with a corresponding excitatory junction potential (EJP). Hyoscine (1 micromol L-1) blocked the first contraction, and reduced the second contraction and EJP by 52.5% and 61%, respectively. These responses were further reduced by the NK2 antagonist, MEN10627 (1 micromol L-1), and the NK1 antagonist, SR140333 (1 micromol L-1). N-nitro-L-arginine (100 micro;mol L-1) and apamin (0.5 micromol L-1) blocked the relaxation and the IJP. Duodenal electrical stimulation evoked an EJP, whereas antral stimulation evoked an IJP followed by a small EJP. All were blocked by hexamethonium (100 micromol L-1). Duodenal stretch evoked tetrodotoxin-sensitive reflex contractions and membrane depolarization with action potentials in the PS. Thus, PS enteric motor neurones receive inputs from the duodenum and the stomach. There are stretch-sensitive ascending excitatory reflex pathways from the duodenum to the PS.

Distribution of nitric oxide synthase and vasoactive intestinal polypeptide immunoreactivity in the sphincter of Oddi and duodenum of the possum

The nitrergic innervation of the sphincter of Oddi (SO) and duodenum in the Australian brush-tailed possum and the possible association of this innervation with the neuropeptide vasoactive intestinal polypeptide (VIP) were investigated by using immunohistochemical localisation of nitric oxide synthase (NOS) and VIP, together with the general neuronal marker, protein gene product 9.5 (PGP9.5). Whole-mount preparations of the duodenum and attached SO without the mucosa, submucosa and circular muscle (n=12) were double- and triple-labelled. The density of myenteric nerve cell bodies of the SO in the more distal region (duodenal end) was significantly higher than that in the more proximal region. In the SO, approximately 50% of all cells were NOS-immunoreactive (IR), with 27% of the NOS-IR cells being VIP-IR. Within the duodenal myenteric plexus, NOS immunoreactivity was present in about 25% of all neurons, with 27% of these NOS-IR neurons also being VIP-IR, a similar proportion to that in the SO. Varicose nerve fibres with NOS and VIP immunoreactivity were present within the myenteric and submucous plexuses of the SO and duodenum, and in the circular and longitudinal muscle layers. The NOS-positive cells within both the SO and duodenum were unipolar, displaying a typical Dogiel type I morphology. The myenteric plexuses of the SO and duodenum were in direct continuity, with many interconnecting nerve trunks, some of which showed NOS and VIP immunoreactivity. Thus, the possum possesses an extensive NOS innervation of the SO and duodenum, with a significantly higher proportion of NOS-IR neurons within the SO, a subset of which contains VIP.

The chemistry of enamel caries

The chemical changes which occur during the process of carious destruction of enamel are complex due to a number of factors. First, substituted hydroxyapatite, the main component of dental enamel, can behave in a very complex manner during dissolution. This is due not only to its ability to accept substituent ions but also to the wide range of calcium phosphate species which can form following dissolution. In addition, the composition, i.e., the extent of substitution, changes throughout enamel in the direction of carious attack, i.e., from surface to interior. Both surface and positively birefringent zones of the lesion clearly illustrate that carious destruction is not simple dissolution. Selective dissolution of soluble minerals occurs, and there is the probability of reprecipitation. The role of fluoride here is crucial in that not only does it protect enamel per se but also its presence in solution means that rather insoluble fluoridated species can form very easily, encouraging redeposition. The role of organic material clearly needs further investigation, but there is the real possibility of both inhibition of repair and facilitation of redeposition. For the future, delivering fluoride deep into the lesion would appear to offer the prospect of improved repair. This would entail a delivery vehicle which solved the problem of fluoride uptake by apatite at the tooth surface. Elucidation of the role of organic material may also reveal putative mechanisms for encouraging repair and/or protecting the enamel mineral.

Amelin extracellular processing and aggregation during rat incisor amelogenesis

Amelin (also known as ameloblastin and sheathlin) is a recently described protein that is secreted by ameloblasts during enamel formation. Here, the extracellular distribution and processing of amelin during rat incisor amelogenesis were investigated by Western blot probing using anti-recombinant rat amelin antibodies. In addition, the solubility behaviour and aggregative properties of rat amelin were investigated using a sequential extraction procedure involving (1) extraction with simulated enamel fluid to extract proteins most likely to be soluble in vivo; (2) extraction with phosphate buffer to desorb proteins bound to enamel crystal surfaces; (3) extraction with sodium dodecyl sulphate (SDS) to extract proteins present as insoluble aggregates; followed by (4) a final acid demineralization step to release any remaining proteins. Proteins immunoreactive to the anti-amelin antibodies were detectable in secretory- and transition-stage enamel. Maturation-stage enamel appeared devoid of amelin. The largest immunoreactive protein detected migrated at 68 kDa on SDS gels, corresponding to the M(r) of nascent amelin. Other immunoreactive bands at 52, 40, 37, 19, 17, 16, 15, 14 and 13 kDa were presumably amelin processing products. The sequential extraction procedure revealed that the 68-, 52-, 40-, 37- and 13-kDa amelins were completely extracted under solution conditions similar to those reported to exist in vivo. In contrast, the 19-, 17- and 16-kDa amelins were only partially extracted, whilst the 15- and 14-kDa amelins could not be extracted with simulated enamel fluid. A proportion of the remaining 17- and 16-kDa amelins was desorbed from the enamel crystals with phosphate buffer and appeared to have been mineral-bound. The 15- and 14-kDa amelins and the remainder of the 17- and 16-kDa amelins were extracted with SDS only, suggesting that these species were present in vivo as an insoluble aggregate. The results provide additional information on amelin processing and degradation, and on how such processing influences the solubility and aggregative properties of amelin-derived proteins.

In vitro studies of the penetration of adhesive resins into artificial caries-like lesions

Instead of removing the porous carious tissue at a relatively late stage in the disease process, attempts have been made to 'fill' the microporosities of lesions at a much earlier stage of lesion development. This would not only reduce the porosity and therefore access of acid and egress of dissolved material, but also afford some mechanical support to the tissue and perhaps inhibit further attack. Successful infiltration of materials into lesions has been demonstrated previously using resorcinol-formaldehyde which, however, was clinically unacceptable. The advent of dental adhesives with potentially suitable properties has prompted a re-examination of this concept. Artificial lesions of enamel were generated in extracted human teeth using acidified gels. A range of currently available adhesive materials was then used to infiltrate the porosities. The extent of occlusion of the lesion porosities was determined both qualitatively using light microscopy and quantitatively using a chloronaphthalene imbibition technique. The effect of such treatment upon subsequent exposure to acid gels was also investigated. Results showed that up to 60% of the lesion pore volume had been occluded following infiltration with some of the materials and that this treatment was capable of reducing further acid demineralization. The development of such treatment strategies could offer potential noninvasive means of treating early enamel lesions.

Enzyme compartmentalization during biphasic enamel matrix processing

Processing of enamel matrix proteins is essentially biphasic. Secretory stage metalloprotease activity generates a discrete, presumably functional, spectrum of molecules which may also undergo dephosphorylation. Maturation stage serine proteases almost completely destroy the matrix. The present aim was to examine the tissue compartmentalization of these enzyme activities in relation to their possible function. A sequential extraction using synthetic enamel fluid, phosphate buffer and SDS was used to identify enzymes free in the enamel fluid, crystal bound or aggregated with the bulk matrix respectively. Results indicated that the metallo-proteases and alkaline phosphatase were free in the secretory stage enamel fluid while the serine proteases appeared to be largely bound to the maturation stage crystals. The mobility of the metallo-proteases and alkaline phosphatase would ensure efficient initial processing of secretory matrix, while the largely mineral bound serine proteases would ensure retention of protease activity despite massive destruction and protein removal.

Identification of rat enamel organ RNA transcripts using differential-display

Enamel formation is a complex process which involves the expression of a number of genes, the most obvious being those related to the mineralized extracellular matrix. In this study the differential-display technique, first described by Liang and Pardee, has been used to identify genes specifically expressed in enamel organ cells. By comparing results obtained from RNA derived from rat enamel organ with RNA derived from other cellular sources, a number of differentially expressed transcripts have been identified. The nucleotide sequences of two of these have been analyzed and shown to have no homology with any previously published sequences. Further analysis will provide information on the type of protein that they may encode, their tissue distribution and their potential role in enamel formation.

Atomic force microscopy studies of crystal surface topology during enamel development

During the secretory stage of enamel development, the hydroxyapatite crystals appear as thin ribbons which grow substantially in width and thickness during the later maturation stage. In this study, the atomic force microscope (AFM) was used to investigate developmentally-related changes in deproteinized enamel crystal surface topography in normal animals and in those receiving daily doses of fluoride. The AFM revealed previously undescribed surfaces features, some of which may represent growth sites or different crystalline phases. Secretory stage crystals had greater surface rugosity and were more irregular, with spherical sub-structures of 20-30 nm diameter arranged along the "c"-axis. Maturation stage crystals were smoother and larger but revealed both subnanometer steps and lateral grooves running parallel to the "c"-axis. Crystals from fluorotic tissue showed similar features but were more irregular with a higher degree of surface roughness, suggesting abnormal growth. The AFM may prove an important adjunct in determination of the mechanisms controlling crystal size and morphology in skeletal tissues.

Classes of enteric nerve cells in the guinea-pig small intestine

The guinea-pig small intestine has been very widely used to study the physiology, pharmacology and morphology of the enteric nervous system. It also provides an ideal, simple mammalian preparation for studying how nerve cells are organised into functional circuits underlying simple behaviours. Many different types of nerve cells are present in the enteric nervous system and they show characteristic combinations of morphological features, projections, biophysical properties, neurochemicals, and receptors. To identify the different functional classes is an important prerequisite for systematic analysis of how the enteric nervous system controls normal gut behaviour. Based on combinations of multiple-labelling immunohistochemistry and retrograde tracing, it has been possible to account quantitatively for all of the neurones in the guinea-pig small intestine. This article summarises that account and updates it in the light of recent data. A total of 18 classes of neurones are currently distinguishable, including primary afferent neurones, motor neurones, interneurones, secretomotor and vasomotor neurones. It is now possible to take an individual nerve cell and use a few carefully chosen criteria to assign it to a functional class. This provides a firm anatomical foundation for the systematic analysis of how the enteric nervous system normally functions and how it goes wrong in various clinically important disorders.

Classes of enteric nerve cells in the guinea-pig small intestine

The guinea-pig small intestine has been very widely used to study the physiology, pharmacology and morphology of the enteric nervous system. It also provides an ideal, simple mammalian preparation for studying how nerve cells are organised into functional circuits underlying simple behaviours. Many different types of nerve cells are present in the enteric nervous system and they show characteristic combinations of morphological features, projections, biophysical properties, neurochemicals, and receptors. To identify the different functional classes is an important prerequisite for systematic analysis of how the enteric nervous system controls normal gut behaviour. Based on combinations of multiple-labelling immunohistochemistry and retrograde tracing, it has been possible to account quantitatively for all of the neurones in the guinea-pig small intestine. This article summarises that account and updates it in the light of recent data. A total of 18 classes of neurones are currently distinguishable, including primary afferent neurones, motor neurones, interneurones, secretomotor and vasomotor neurones. It is now possible to take an individual nerve cell and use a few carefully chosen criteria to assign it to a functional class. This provides a firm anatomical foundation for the systematic analysis of how the enteric nervous system normally functions and how it goes wrong in various clinically important disorders.

Classes of enteric nerve cells in the guinea-pig small intestine

The guinea-pig small intestine has been very widely used to study the physiology, pharmacology and morphology of the enteric nervous system. It also provides an ideal, simple mammalian preparation for studying how nerve cells are organised into functional circuits underlying simple behaviours. Many different types of nerve cells are present in the enteric nervous system and they show characteristic combinations of morphological features, projections, biophysical properties, neurochemicals, and receptors. To identify the different functional classes is an important prerequisite for systematic analysis of how the enteric nervous system controls normal gut behaviour. Based on combinations of multiple-labelling immunohistochemistry and retrograde tracing, it has been possible to account quantitatively for all of the neurones in the guinea-pig small intestine. This article summarises that account and updates it in the light of recent data. A total of 18 classes of neurones are currently distinguishable, including primary afferent neurones, motor neurones, interneurones, secretomotor and vasomotor neurones. It is now possible to take an individual nerve cell and use a few carefully chosen criteria to assign it to a functional class. This provides a firm anatomical foundation for the systematic analysis of how the enteric nervous system normally functions and how it goes wrong in various clinically important disorders.

Classes of enteric nerve cells in the guinea-pig small intestine

The guinea-pig small intestine has been very widely used to study the physiology, pharmacology and morphology of the enteric nervous system. It also provides an ideal, simple mammalian preparation for studying how nerve cells are organised into functional circuits underlying simple behaviours. Many different types of nerve cells are present in the enteric nervous system and they show characteristic combinations of morphological features, projections, biophysical properties, neurochemicals, and receptors. To identify the different functional classes is an important prerequisite for systematic analysis of how the enteric nervous system controls normal gut behaviour. Based on combinations of multiple-labelling immunohistochemistry and retrograde tracing, it has been possible to account quantitatively for all of the neurones in the guinea-pig small intestine. This article summarises that account and updates it in the light of recent data. A total of 18 classes of neurones are currently distinguishable, including primary afferent neurones, motor neurones, interneurones, secretomotor and vasomotor neurones. It is now possible to take an individual nerve cell and use a few carefully chosen criteria to assign it to a functional class. This provides a firm anatomical foundation for the systematic analysis of how the enteric nervous system normally functions and how it goes wrong in various clinically important disorders.

Effect of experimental fluorosis on the surface topography of developing enamel crystals

Dental fluorosis is an increasing problem, yet the precise mechanism by which fluoride exerts its effects remains obscure. In the present study, we have used atomic force microscopy to image and quantitate surface features of enamel crystals isolated from specific developmental stages of fluorotic and control rat incisors. The results showed a significant decrease in crystal surface roughness with development in control tissue. Crystals from fluorotic tissue were significantly rougher than controls at all stages of development, did not decrease in roughness during the later stages of their development and had many morphological abnormalities. These data clearly demonstrate an effect for fluoride on enamel crystal surfaces which could reflect changes in the nature and distribution of growth sites and/or in mineral-matrix interactions. These would be expected to affect crystal growth during maturation, resulting in the characteristic porous appearance of fluorotic lesions in mature teeth.

Evidence for charge domains on developing enamel crystal surfaces

The control of hydroxyapatite crystal initiation and growth during enamel development is thought to be mediated via the proteins of the extracellular matrix. However, the precise nature of these matrix-mineral interactions remains obscure. The aim of the present study was to use a combination of atomic and chemical force microscopy to characterize developing enamel crystal surfaces and to determine their relationship with endogenous enamel matrix protein (amelogenin). The results show regular and discrete domains of various charges or charge densities on the surfaces of hydroxyapatite crystals derived from the maturation stage of enamel development. Binding of amelogenin to individual crystals at physiological pH was seen to be coincident with positively charged surface domains. These domains may therefore provide an instructional template for matrix-mineral interactions. Alternatively, the alternating array of charge on the crystal surfaces may reflect the original relationship with, and influence of, matrix interaction with the crystal surfaces during crystal growth.

Spatially related amelogenin interactions in developing rat enamel as revealed by molecular cross-linking studies

A cleavable cross-linker (dithiobis[succinimidyl propionate], DTSP) was used to investigate the subunit structure of the developing enamel matrix. Intact matrix was cross-linked under conditions chosen to simulate those found in vivo. The cross-linked complexes were isolated by preparative sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and their subunit composition determined by analytical SDS-PAGE following reductive cleavage of the cross-links. Western blotting using antiamelogenin antibodies was used to confirm the identity of the proteins involved. The results showed that nascent amelogenins tended to be cross-linked to other nascent amelogenins while amelogenin-processing products tended to be cross-linked to other processed molecules at the same stage of processing. The results suggest that nascent amelogenins are in close association after secretion and during extracellular processing, and that processed products are not free to associate with nascent molecules, presumably due to diffusion constraints in the tissue. This conclusion implies that individual amelogenin molecules within supramolecular aggregates (nanospheres) are processed in situ and remain in the same nanosphere while all the individual component amelogenins undergo processing. The biological function of amelogenin processing remains unclear but the fact that amelogenin-amelogenin associations are maintained during processing indicates that matrix stability is an important factor while the enamel layer is being deposited.

Identification of human serum albumin in human caries lesions of enamel: the role of putative inhibitors of remineralisation

Carious attack on enamel is not a unidirectional process but involves both demineralisation and remineralisation. The chemistry of carious attack on enamel has, to a large extent, now been clarified as far as mineral components are concerned but little attention, however, has been paid to the identity of organic material in carious lesions and its possible role in the caries process. The only clear information available is that organic material accumulates with time within enamel lesions. The present study was aimed at identifying a specific protein component known to bind to hydroxyapatite (albumin) in carious lesions with a view to investigating its role in the disease process. The distribution of albumin within both white spot and fissure lesions and adjacent sound enamel of extracted human teeth was investigated using SEM immunohistochemistry on undermineralised sections of human enamel and employing a polyclonal antibody to human serum albumin. The nature of the protein, i.e. whether it was in the form of intact molecules or degraded fragments, was investigated by Western blotting, employing the same antibody. The immunohistochemistry revealed the presence of albumin within both interproximal white spot and fissure lesions with little if any present in sound enamel. The Western blotting indicated that the albumin was in the intact form with no evidence of degradation products. The ability of albumin to bind and to inhibit growth of calcium phosphate crystals raises the question as to the possible role of such a molecule in the development of carious lesions.

Transduction sites of vagal mechanoreceptors in the guinea pig esophagus

Extrinsic afferent neurons play an essential role in both sensation and reflex control of visceral organs, but their specialized morphological peripheral endings have never been functionally identified. Extracellular recordings were made from fine nerve trunks running between the vagus nerve and esophagus of the guinea pig. Mechanoreceptors, which responded to esophageal distension, fired spontaneously, had low thresholds to circumferential stretch, and were slowly adapting. Calibrated von Frey hairs (0.12 mN) were used to probe the serosal surface at 100-200 sites, which were mapped on a video image of the live preparation. Each stretch-sensitive unit had one to three highly localized receptive fields ("hot spots"), which were marked with Indian ink applied on the tip of the von Frey hair. Recorded nerve trunks were then filled anterogradely, using biotinamide in an artificial intracellular solution. Receptive fields were consistently associated with intraganglionic laminar endings (IGLEs) in myenteric ganglia, but not with other filled neuronal structures. The average distance of receptive fields to IGLEs was 73 +/- 14 microm (24 receptive fields, from 12 units; n = 5), compared to 374 +/- 17 microm for 240 randomly generated sites (n = 5; p < 0.001). After maintained probing on a single receptive field, spontaneous discharge of units was inhibited, as were responses to distension. During adapted discharge to maintained distension, interspike intervals were distributed in a narrow range. This indicates that multiple receptive fields interact to encode mechanical distortion in a graded manner. IGLEs are specialized transduction sites of mechanosensitive vagal afferent neurons in the guinea pig esophagus.

The chemical composition of tooth enamel in junctional epidermolysis bullosa

The junctionalis form of epidermolysis bullosa (EBJ) is associated with a number of clinical problems involving tooth enamel, including increased susceptibility to caries. The aim here was to carry out a chemical characterization of the enamel of teeth from EBJ patients compared with that of unaffected controls. The results showed that while protein concentration, amino acid composition and carbonate content were similar in both groups, EBJ enamel contained a significantly reduced mineral per volume content, resulting in enamel hypoplasia. In addition, Western blotting revealed the presence of serum albumin (a known inhibitor of enamel crystal growth) in EBJ enamel. This was not detected in control enamel or in enamel of teeth from patients with the dystrophic form of the disease. It is concluded that EBJ enamel is developmentally compromised and that the enamel defects are commensurate with the reported genetic lesions.

Distribution of exogenous proteins in caries lesions in relation to the pattern of demineralisation

While it is believed that proteins may protect enamel from demineralisation, recent work has indicated that such material may also hinder remineralisation. For example, albumin will inhibit apatite crystal growth in vitro and is present in carious enamel in vivo. However, it is not clear whether (1) the distribution of proteins within lesions is restricted to specific lesion zones or (2) the origin of such proteins is endogenous (i.e. as a remnant of the developmental process) or exogenous, originating in the saliva or gingival crevicular fluid. The present study used a combination of immunohistochemistry and microradiography to determine the distribution of two proteins, serum albumin and salivary amylase, within natural white-spot carious lesions in relation to specific levels of demineralisation. The results indicated that albumin is found primarily in a region of between 10 and 20% demineralisation (an area of transition between the 'dark' zone and lesion 'body'), with smaller quantities occurring in the region between 0 and 10% demineralisation and trace amounts in the zone indistinguishable from sound enamel by microradiography. A similar distribution was found for amylase in that the heaviest labelling was within the 10-20% demineralisation zone, although little if any was present in the 0-10% zone. The presence of these molecules in a region of the lesion where some potential for reprecipitation may exist will have important implications with respect to lesion progression.

Projections of nitric oxide synthase and vasoactive intestinal polypeptide-reactive submucosal neurons in the human colon

BACKGROUND

The submucosal plexus is important in the control of secretomotor and motor function of the intestine. Our aim was to describe the projections of submucosal neurons to the mucosa within the submucosal plexus and to the circular muscle of human colon and to determine whether submucosal neurons that projected to different layers were located at different levels of the submucosa.

METHODS

A retrogradely transported fluorescent dye was applied to the mucosa, submucosa or circular muscle layer of human colon which was then maintained in organotypic culture for 5 days. The submucosa was then dissected into two preparations, one containing the inner layer of the submucosal plexus and the other containing both the intermediate and outer layers. The dissected preparations were labelled with antibodies to nitric oxide synthase (NOS) or vasoactive intestinal peptide (VIP).

RESULTS

Submucosal neurons projected to the mucosa, submucosa and circular muscle layers for mean distances of 3.7, 3.0 and 4.3 mm, respectively. Ninety-seven per cent of submucosal neurons labelled from the circular muscle were located in the outer or the intermediate layers, while 51% of those projecting to the mucosa were in inner layer and 49% in the intermediate/outer layers of the submucosal plexus. Eleven per cent of submucosal neurons projecting to the circular muscle were immunoreactive for NOS and 12% were immunoreactive for VIP. Forty-five per cent of those projecting within the submucosa were immunoreactive for VIP and 38% of those projecting to the mucosa were immunoreactive for VIP.

CONCLUSIONS

Submucosal neurons in the human colon innervate the mucosa, circular muscle and submucosa and different functional classes of neurons are located in different layers of the submucosal plexus.

Neuronal control of the gastric sling muscle of the guinea pig

The gastric sling (oblique) muscle (GSM), located close to the lower esophageal sphincter (LES), is involved in gastric motor function and may cooperate with the LES in controlling propulsion between the esophagus and stomach. Neuronal pathways and transmission to the GSM were investigated in isolated esophagus-stomach preparations by using intracellular recording with the focal electrical stimulation and neuroanatomical tracing method. Focal stimulation on the GSM evoked inhibitory junction potentials (IJPs) that were reduced to 45% by 100 microM N-nitro-L-arginine and subsequently blocked by 0.5 microM apamin, thereby unmasking excitatory junction potentials (EJPs), which were abolished by 1 microM hyoscine. Vagal and esophageal stimulation evoked IJPs that were blocked by 100 microM hexamethonium. Vagal stimulation also evoked EJPs after blockade of IJPs. Application of 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate to the GSM labeled muscle motor neurons located in the stomach mainly close to the GSM, with a few neurons (2%) in the esophagus. The majority (79%) of labeled neurons were immunoreactive for choline acetyltransferase and, hence, excitatory motor neurons. Inhibitory motor neurons (nitric oxide synthase immunoreactive; 15%) were clustered in the midline near the gastroesophageal region. These results demonstrate that the GSM is innervated primarily by gastric excitatory and inhibitory motor neurons and some esophageal neurons. Both excitatory (acetylcholine) and inhibitory (nitric oxide and apamin-sensitive component) transmission can be activated via vagal-enteric pathways.

Quantitative analysis of peristalsis in the guinea-pig small intestine using spatio-temporal maps

1. Peristalsis was evoked in guinea-pig small intestine by slow fluid infusion and recorded onto video and digitized. Spatio-temporal maps of diameter and longitudinal movement were constructed and parameters of motion were calculated. 2. During the filling of the isolated segments of intestine, rhythmic local longitudinal movements were observed at several points along the preparation. These phasic longitudinal muscle contractions were associated with small but significant local increases in diameter and probably reflect a passive mechanical coupling by connective tissue in the gut wall. In addition, occasional synchronized longitudinal muscle contractions caused net shortening of the preparation and always preceded the onset of peristaltic emptying. 3. Peristaltic emptying was characterized by a contraction of the circular muscle which usually started at the oral end of the preparation, that propagated aborally, propelling the contents. However, in 19 % of trials, the first circular muscle contraction occurred in the aboral half of the preparation. 4. The propagation of peristalsis consisted of separate sequential circular muscle contractions several centimetres long, particularly in the oral half of the preparation, giving a 'step-like' appearance to the spatio-temporal map. The gut was transiently distended aboral to the propagating circular muscle contraction due to the propulsion of contents. 5. At each point in the preparation, the longitudinal muscle remained contracted during the propulsive part of the circular muscle contraction. Only when the circular muscle contraction became lumen occlusive did lengthening of the longitudinal muscle take place. 6. Spatio-temporal maps are a powerful tool to visualize and analyse the complexity of gastrointestinal motility patterns.

Initiation of peristalsis by circumferential stretch of flat sheets of guinea-pig ileum

1. Segments of isolated guinea-pig intestine, 12 mm long, were distended slowly by intraluminal fluid infusion or by mechanical stretch as either a tube or flat sheet. In all cases, at a constant threshold length, a sudden, large amplitude contraction of the circular muscle occurred orally, corresponding to the initiation of peristalsis. 2. Circumferential stretch of flat sheet preparations evoked graded contractions of the longitudinal muscle (the 'preparatory phase'), which were maintained during circular muscle contraction. This suggests that the lengthening reported during the emptying phase of peristalsis is due to mechanical interactions. 3. The threshold for peristalsis was lower with more rapid stretches and was also lower in long preparations (25 mm) compared with short preparations (5-10 mm), indicating that ascending excitatory pathways play a significant role in triggering peristalsis. 4. Stretching a preparation beyond the threshold for peristalsis evoked contractions of increasing amplitude; thus peristalsis is graded above its threshold. However, during suprathreshold stretch maintained at a constant length, contractions of the circular muscle quickly declined in amplitude and frequency. 5. Circular muscle cells had a resting membrane potential approximately 6 mV more negative than the threshold for action potentials. During slow circumferential stretch, subthreshold graded excitatory motor input to the circular muscle occurred, prior to the initiation of peristalsis. However, peristalsis was initiated by a discrete large excitatory junction potential (12 +/- 2 mV) which evoked bursts of smooth muscle action potentials and which probably arose from synchronized firing of ascending excitatory neuronal pathways.

Rapid anterograde and retrograde tracing from mesenteric nerve trunks to the guinea-pig small intestine in vitro

A novel technique for rapid anterograde labelling of cut axons in vitro was used to visualise the peripheral branches of mesenteric nerve trunks supplying the guinea-pig small intestine. Biotinamide, dissolved in an artificial intracellular solution, was applied to the cut ends of the mesenteric nerves and the tissue was maintained in organ culture overnight. Labelled nerve fibres were visualised by fluorescein isothiocyanate (FITC)-conjugated streptavidin. Intense staining of nerve fibres and terminal varicosities in the ganglia and internodal strands of the myenteric plexus was achieved up to 15 mm from the application site. Filled fibres formed baskets around some myenteric nerve cell bodies, suggesting target-specific neurotransmission. When combined with multiple-labelling immunohistochemistry for tyrosine hydroxylase (TH), calcitonin gene-related protein (CGRP) or choline acetyltransferase (ChAT), most anterogradely labelled nerve fibres, and many pericellular baskets, were found to be TH immunoreactive, indicating their postganglionic sympathetic origin. Double-labelling immunohistochemistry revealed that the postganglionic sympathetic pericellular baskets preferentially surrounded 5-hydroxytryptamine (5-HT)-handling myenteric neurons. Some biotinamide-filled fibres were CGRP immunoreactive, and are likely to originate from spinal sensory neurons. We describe for the first time many pericellular baskets labelled from the mesenteric nerves which were ChAT immunoreactive. Retrogradely filled intestinofugal nerve cell bodies were also observed, all of which had a single axon arising from a small nerve cell body with short filamentous or lamellar dendrites. Many of these cells were ChAT immunoreactive. This in vitro technique is effective in identifying the fine arrangement of nerve terminals arising from nerve trunks in the periphery.