Projections of submucous neurons to the myenteric plexus in the guinea pig small intestine

The distribution of submucous neurons that project to the myenteric plexus of the guinea pig small intestine was established by retrograde transport of the carbocyanine dye 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI) from myenteric ganglia in organ culture in combination with immunohistochemistry. Following the application of DiI to the serosal surface of a single myenteric ganglion, from 2 to 15 DiI-labelled nerve cell bodies were labelled in the submucous plexus up to 7.9 mm circumferentially, 4.5 mm orally, and 3.4 mm aborally to the DiI application site. No cells were labelled in preparations in which connections between myenteric and submucous plexuses had been severed prior to DiI application. Cells that were immunoreactive for vasoactive intestinal polypeptide (VIP) or for substance P (SP) accounted for about 75% and 11% of DiI-labelled cells, respectively. Neither neuropeptide Y- nor calretinin-immunoreactive submucous neurons were labelled by DiI, indicating that these classes of neurons do not project to the myenteric plexus. Retrograde tracing from the myenteric plexus with Neurobiotin revealed that labelled VIP-immunoreactive neurons had several short, filamentous processes and a single long axon that could be followed through the circular muscle to myenteric ganglia without branches to the mucosa. The previously described projection of submucous, SP-immunoreactive putative sensory neurons to the myenteric plexus was confirmed. However, this study has identified a considerably larger population of presumed interneurons that are immunoreactive for VIP that likely transmit information from the submucous plexus to the myenteric plexus and presumably coordinate activity between the two ganglionated plexuses.

Neuronal pathways and transmission to the lower esophageal sphincter of the guinea Pig

BACKGROUND & AIMS

The lower esophageal sphincter (LES) normally controls the opening and closing of the gastroesophageal junction to resist gastric reflux but allow swallowing. Neuronal pathways controlling the guinea pig LES were investigated anatomically and physiologically in isolated preparations.

METHODS

Intracellular recording from the LES with focal electrical stimulation and retrograde and anterograde neuronal tracing were used.

RESULTS

Electrical stimulation on the LES evoked inhibitory junction potentials (IJPs), which were reduced by 60% by 100 micromol/L N-nitro-L-arginine and subsequently blocked by 0.5 micromol/L apamin, unmasking excitatory junction potentials, which were abolished by 1 micromol/L hyoscine. Esophageal or vagal stimulation evoked IJPs, which were blocked by 100 micromol/L hexamethonium. Focal stimulation of the upper stomach evoked IJPs at 5-8 of 20 stimulation sites, which were abolished by cutting between the stimulation site and sphincter. Application of 1,1'-didodecyl-3,3,3', 3'-tetramethyl indocarbocyanine perchlorate (DiI) to the gastric sling muscle anterogradely labeled many motor axons in the sling muscle but few in the LES, confirming that the two muscles are separately innervated. DiI on the esophagus labeled nerve fibers, but not cell bodies, in the upper stomach.

CONCLUSIONS

The inhibitory motor neurons of the LES receive inputs from the vagus nerve, esophagus, and upper stomach.

Identification of motor neurons to the circular muscle of the guinea pig gastric corpus

The projections of enteric neurons to the circular muscle of the guinea pig gastric corpus were investigated systematically by using the retrogradely transported fluorescent carbocyanine dye 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI), applied to the muscle layer or myenteric plexus in vitro. DiI-labeled motor neuron cell bodies were located up to 6.3 mm aboral, 17 mm oral, and up to 20 mm circumferential to the DiI application site. Labeled nerve fibers ran for long distances from the DiI application site toward the greater and lesser curvatures, where they coursed parallel to the bundles of the "gastric sling" muscle. The majority of labeled cells were located toward the lesser curvature of the stomach. Nerve cell bodies that were aboral to the DiI application site were usually small, immunoreactive for choline acetyltransferase, and, thus, were likely to be excitatory motor neurons. Neurons that were located orally were larger, fewer in number, and immunoreactive for nitric oxide synthase and, thus, were likely to be inhibitory motor neurons. Application of DiI directly to the myenteric plexus filled neurons up to 15 mm aborally and up to 21 mm orally but labeled few neurons circumferentially. All nerve cells that were filled from either the circular muscle or the myenteric plexus had Dogiel type I morphological features. These results demonstrate a clear polarity of projection of inhibitory and excitatory motor neurons and a functionally continuous innervation of the circular and gastric sling muscle layers. Nonmotor neurons in the myenteric plexus were demonstrated, but neurons with Dogiel type II morphological features are apparently absent.

The projections of 5-hydroxytryptamine-accumulating neurones in the myenteric plexus of the small intestine of the guinea-pig

Retrograde tracing, combined with immunohistochemistry, was used to study the projections of 5-hydroxytryptamine (5-HT)-accumulating neurones within the ileum of the guinea-pig, with confocal microscopy being used to characterise further their morphology. Two classes of neurones in the myenteric plexus, capable of taking up 5-HT or analogues, were distinguished. One class had Dogiel type I morphology with lamellar dendrites, was located on the edge or in the middle of ganglia and lacked immunoreactivity for somatostatin (SOM). The other class had smooth ovoid cell bodies with multiple filamentous dendrites and a single axon and represented a subset of the SOM-immunoreactive interneurones in the myenteric plexus. Varicosities immunoreactive for 5-HT alone, 5-HT/SOM or SOM alone were present in the myenteric ganglia. Both classes of 5-HT-accumulating neurones had long aboral projections within the myenteric plexus (up to 100 mm long) and to the submucous plexus and probably function as descending interneurones.

The developing enamel matrix: nature and function

The hydroxyapatite crystals of mature enamel are unusually large, uniform and regularly disposed within the tissue, implying that their development is a highly controlled process. The organic matrix of developing enamel is presumed to play an important role in the modulation of mineral deposition and growth during tooth morphogenesis but the precise functions of individual matrix proteins remain unclear. The aim of this review was to survey the current knowledge of enamel matrix proteins with a view to suggesting possible functions. The organic matrix is highly heterogeneous, comprising proteins derived from a number of different genes, including amelogenin, enamelin, ameloblastin (amelin/sheathlin), tuftelin, dentine sialophosphoprotein, enzymes and serum proteins such as albumin. Each of these classes appears to undergo post-secretory sequential degradation which contributes further towards matrix heterogeneity. Possible functions of these proteins include de novo mineral nucleation/initiation (dentine sialophosphoprotein, tuftelin), mineral ion binding as crystal precursors (amelogenin, enamelin), control of crystal growth (amelogenin, enamelin, ameloblastin), support of growing crystals (amelogenin, enamelin), determination of prismatic structure (ameloblastin), cell signalling (tuftelin, ameloblastin), control of secretion (breakdown products) and protection of the mineral phase (amelogenin, enamelin). Failure of these mechanisms could lead to incomplete maturation of the enamel and the eruption of dysplastic tissue.

The neurochemical coding and projections of circular muscle motor neurons in the human colon

BACKGROUND & AIMS

Enteric neurons can be characterized by their chemical coding, projections, and morphology. The aim of this study was to describe the different classes of human colonic circular muscle motor neurons.

METHODS

Human colonic circular muscle motor neurons were identified by retrograde tracing with 1,1'-didodecyl 3,3,3',3'-indocarbocyanine perchlorate (Dil) applied to the circular muscle layer. Whole-mount preparations of the myenteric plexus were then double-labeled with antisera to choline acetyltransferase (ChAT) and/or nitric oxide synthase (NOS), or NOS and vasoactive intestinal peptide (VIP), and the position and immunoreactivity of Dil-filled neurons were recorded.

RESULTS

Fifty-two percent of all Dil-filled neurons were ChAT immunoreactive, and 86% of these projected up to 11 mm orally, with 14% projecting short distances anally. Forty-eight percent of the Dil-filled neurons were NOS immunoreactive, and 77% of these projected up to 19 mm anally, with 23% projecting no more than 6 mm orally. A subpopulation of these NOS-immunoreactive motor neurons were also VIP-immunoreactive. A small population of myenteric neurons was immunoreactive for both ChAT and NOS, but none projected to the circular muscle. NOS-immunoreactive motor neurons projected for longer distances than those with ChAT immunoreactivity and were larger.

CONCLUSIONS

There are two classes of human colonic motor neurons: one is excitatory (ChAT-immunoreactive) and mainly projects orally and the other is inhibitory (NOS +/- VIP immunoreactive) and projects preferentially anally.

Orally projecting interneurones in the guinea-pig small intestine

1. Orally projecting, cholinergic interneurones are important in mediating ascending excitatory reflexes in the small intestine. We have shown that there is just one major class of orally projecting interneurone, which we have characterized using retrograde labelling in organ culture, combined with immunohistochemistry, intracellular recording and dye filling. 2. Orally projecting interneurones, previously shown to be immunoreactive for choline acetyltransferase, tachykinins, enkephalin, calretinin and neurofilament protein triplet, have axons up to 14 mm long and are the only class of cells with orally directed axons more than 8.5 mm long. 3. They are all small Dogiel type I neurones with short dendrites, usually lamellar in form, and a single axon which sometimes bifurcates. Their axons give rise to short varicose collaterals in myenteric ganglia more than 3 mm oral to their cell bodies. 4. Orally projecting interneurones receive prominent fast excitatory post synaptic potentials (fast EPSPs). A major source of fast EPSPs is other ascending interneurones located further aborally. They also receive fast EPSPs from circumferential pathways. 5. In the stretched preparations used in this study, orally projecting interneurones were highly excitable, firing repeatedly to depolarizing current pulses and had negligible long after-hyperpolarizations following their action potentials. They did not receive measurable non-cholinergic slow excitatory synaptic inputs. 6. Ascending interneurones had a characteristic inflection in their membrane responses to depolarizing current pulses and their first action potential was typically delayed by approximately 30 ms. Under single electrode voltage clamp, ascending interneurones had a transient outward current when depolarized above -70 mV from more hyperpolarized holding potentials. Ascending interneurones also consistently showed marked inward rectification under both current clamp and voltage clamp conditions. 7. This class of cells has consistent morphological, neurochemical and electrophysiological characteristics and are important in mediating orally directed enteric reflexes.

Characterization of myenteric interneurons with somatostatin immunoreactivity in the guinea-pig small intestine

The projections, connections, morphology and electrophysiological features of the myenteric interneurons with somatostatin immunoreactivity in the guinea-pig small intestine have been established using retrograde tracing, immunohistochemistry, confocal microscopy and intracellular recording. After application of the fluorescent dye, 1,1'-didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (DiI), to the myenteric plexus, up to 900 nerve cell bodies were labelled in each preparation. Somatostatin-immunoreactive neurons accounted for 13% of all retrogradely labelled cells and were located up to 70 mm orally. When DiI was applied to the submucous ganglia, many myenteric neurons were labelled and 8% of all retrogradely labelled cells were somatostatin immunoreactive and were located up to 60 mm oral to the DiI application sites. These neurons had ovoid cell bodies, a single axon, several long filamentous dendrites and received close contacts from 40-200 somatostatin-immunoreactive varicosities. Intracellular recordings revealed that these cells had features of both S (i.e. with Synaptic inputs) and AH (i.e. neurons with After Hyperpolarization) cells, receiving fast excitatory synaptic inputs, having characteristic "sag" in their response to hyperpolarizing current pulses and sometimes a long afterhyperpolarization following soma action potentials. It is concluded that somatostatin-immunoreactive neurons have distinct electrophysiological features and form very long anally directed interneuronal chains that connect with both myenteric and submucous neurons.

The polarity of neurochemically defined myenteric neurons in the human colon

BACKGROUND & AIMS

Functional classes of enteric neurons in small mammals can be determined by neurochemical coding and axonal projections. The aim of this study was to describe the projections of vasoactive intestinal peptide (VIP)-, tachykinin (TK)-, and calretinin-immunoreactive (IR) interneurons and circular muscle motor neurons in human colon.

METHODS

Human colonic myenteric neurons were retrogradely filled with 1,1'-didodecyl 3,3,3',3'-indocarbocyanine perchlorate (DII) from either the myenteric plexus or the circular muscle layers in organotypic culture preparations. The preparations were then labeled with antisera, and the position and immunoreactivity of DII-filled neurons was recorded.

RESULTS

Nine percent of circular muscle motor neurons were labeled with TK immunoreactivity and these projected orally; 22% were VIP-IR and projected anally. Fifty-one percent of myenteric neurons that projected anally to the myenteric ganglia were VIP-IR and none were TK-IR. In contrast, 23% of neurons projecting orally were TK-IR but only 2% were VIP-IR. Calretinin immunoreactivity was present in 23% of neurons projecting anally and 3% projecting orally within the myenteric plexus. Six percent of circular muscle motor neurons had Dogiel type II morphology, and 50% of these were TK-IR.

CONCLUSIONS

Circular muscle motor neurons and myenteric interneurons with TK, VIP, and calretinin immunoreactivity in the human colon have distinct projections and polarity.

Excitatory and inhibitory motor reflexes in the isolated guinea-pig stomach

1. We have described and analysed the movements of the isolated stomach during distension by correlating intragastric pressure with video recordings, and investigated the presence of intrinsic inhibitory and excitatory reflexes. 2. Isolated guinea-pig stomachs, placed in an organ bath, were slowly distended with Krebs solution using a syringe pump via a cannula through the pylorus. The changes in intragastric pressure during cycles of distension were monitored by pressure transducers connected to both oesophageal and pyloric cannulae. The resistivity of the gastric wall (change in pressure with volume, delta P/delta V) and the amplitude and frequency of phasic pressure events were calculated from pressure recordings. 3. The movements of the stomach were also recorded onto videotape. The motion of the gastric wall during distension cycles was analysed to establish the patterns of contractions, their propagation and the distribution of fluid in the stomach. During filling, fluid was preferentially accommodated in the fundus. Propagating (peristaltic) contractions, often starting in the fundus, moved aborally towards the pylorus. The peak of the phasic pressure event was observed when a contraction reached the orad antrum. As it reached the pylorus, intragastric pressure was at its minimum. 4. During the initial phase of distension, intragastric pressure increased steeply. Tetrodotoxin and hyoscine reduced both the resistivity and amplitude of phasic pressure events. Hexamethonium had a similar effect. Thus distension appears to activate an excitatory reflex pathway, involving nicotinic ganglionic transmission. This reflex increases wall tension and enhances myogenic peristaltic contractions. 5. In control preparations, with larger distension volumes, the intragastric pressure decreased, despite the continued infusion of Krebs solution. L-NAME and apamin abolished this drop in pressure, indicating that gastric enteric inhibitory mechanisms prevail at larger distension volumes. After blockade of the excitatory reflex, hexamethonium antagonized the inhibitory response, indicating that activation of inhibitory mechanisms involves nicotinic transmission, probably on enteric inhibitory motoneurons. 6. Both the excitatory and inhibitory reflexes in the isolated stomach operate within a physiological range of gastric volumes. The excitatory reflex predominates at small distension volumes, leading to large phasic propagated contractions that mix the contents and may lead to emptying of the stomach. The inhibitory reflex, described previously as adaptive relaxation, can maximally relax the stomach and is activated preferentially at higher distension volumes to accommodate the contents. The interplay of these reflex pathways in the isolated stomach produces a rich repertoire of gastric movements. 7. The isolated stomach preparation, used with a combination of kinematic, kinetic and pharmacological methods, provides a highly suitable means of investigating the mechanisms of gastric motility.

Immunohistochemical and electrophysiological characterization of submucous neurons from the guinea-pig small intestine in organ culture

Immunohistochemical and electrophysiological properties of submucous neurons were investigated in organ cultures of the guinea-pig small intestine. Preparations of submucosa, with or without the myenteric plexus attached, were maintained in vitro for 3 to 5 days. Immunohistochemical labelling for peptides revealed that the cultured submucous plexus remained substantially intact and the immunoreactivity of cell bodies was well preserved. Substantial sprouting of nerve fibers immunoreactive for vasoactive intestinal peptide (VIP) or neuropeptide Y (NPY) was evident in submucous ganglia after 5 days in organ culture. Nerve fibers immunoreactive for substance P. somatostatin, 5-hydroxytryptamine or tyrosine hydroxylase were substantially depleted in submucous ganglia or perivascular nerves at 3 days and had virtually disappeared after 5 days in cultures of isolated submucosa. During intracellular recording from submucous neurons, action potentials were initiated by depolarizing current pulses in all neurons cultured with or without the myenteric plexus and muscle layers. Electrical stimulation of internodal strands evoked fast excitatory synaptic potentials (fast EPSPs) in nearly all neurons whether or not the myenteric plexus was present during the culture period up to 5 days. The removal of myenteric plexus and extrinsic nerves did not abolish fast EPSPs from submucous neurons, suggesting that some fast EPSPs may originate from neurons in the submucous plexus, although the possibility that new synapses formed by sprouting, or surviving axons severed from myenteric or sympathetic ganglia may have been functional, cannot be entirely excluded. This work demonstrates that the immunohistochemical and electrophysiological characteristics of submucous neurons are largely maintained in organ cultures of the submucosa.

Distension-evoked ascending and descending reflexes in the isolated guinea-pig stomach

Distension-evoked gastric reflexes were studied by intracellular recording from circular muscle cells in the gastric fundus, corpus and antrum in the isolated guinea-pig stomach. Localised electrical stimulation, 2 mm circumferential to the recording electrode, evoked inhibitory junctions potentials in all three gastric regions, sometimes followed by depolarisations in the antrum. In the mid corpus, the inhibitory responses were substantially reduced by Nw-nitro-L-arginine (100 microM), unmasking excitatory junction potentials. Residual hyperpolarisations were blocked by apamin (0.5 microM) which also enhanced the amplitude of excitatory junction potentials. These excitatory junction potentials were abolished by hyoscine (1 microM). Thus transmission from inhibitory motor neurons is mediated by both nitric oxide and an apamin-sensitive mechanism. Transmission from excitatory motor neurons to the circular muscle is mediated by acetylcholine via muscarinic receptors. Balloon distension of 10 s duration of the fundus or antrum elicited inhibitory junction potentials in circular muscle cells of the mid corpus. These inhibitory junction potentials were blocked by tetrodotoxin (0.6 microM) and were greatly reduced by Nw-nitro-L-arginine (100 microM). The residual hyperpolarisations were blocked by apamin (0.5 microM). This indicates the presence of ascending and descending inhibitory reflex pathways in the stomach. In 3 out of 7 experiments, following blockade of inhibitory transmission, small nerve-mediated excitatory junction potentials were evoked by antral distension indicating the presence of an additional ascending excitatory reflex pathway. Distension of the corpus elicited prominent inhibitory junction potentials, sometimes followed by large depolarisations, in circular muscle cells in the fundus, but not in the antrum. This suggests that there is also an ascending inhibitory reflex pathway from the corpus to the fundus but no distension-sensitive descending reflex pathway from the corpus to the antrum. These results demonstrate that within the stomach there are reflex pathways which can be activated by localised distension and project at some distance orally and aborally within the gastric wall. It is likely that the inhibitory reflex pathways are involved in gastric adaptive relaxation which occurs when the intact, isolated stomach is distended. The excitatory reflex pathways from the antrum to the corpus are likely to be involved in the intrinsic excitatory reflex responses observed in the isolated intact stomach to distension and thus be involved in the mixing and emptying of gastric contents.

A method for the quantitative site-specific study of the biochemistry within dental plaque biofilms formed in vivo

The study of plaque biofilms in the oral cavity is difficult as plaque removal inevitably disrupts biofilm integrity precluding kinetic studies involving the penetration of components and metabolism of substrates in situ. A method is described here in which plaque is formed in vivo under normal (or experimental) conditions using a collection device which can be removed from the mouth after a specified time without physical disturbance to the plaque biofilm, permitting site-specific analysis or exposure of the undisturbed plaque to experimental conditions in vitro. Microbiological analysis revealed plaque flora which was similar to that reported from many natural sources. Analytical data can be related to plaque volume rather than weight. Using this device, plaque fluoride concentrations have been shown to vary with plaque depth and in vitro short-term exposure to radiolabelled components may be carried out, permitting important conclusions to be drawn regarding the site-specific composition and dynamics of dental plaque.

Enamel maturation

Enamel maturation is characterized by massive crystal growth in both width and thickness, resulting in the most highly mineralized of all mammalian skeletal tissues. The control of this process is mediated via a carefully orchestrated series of events that are temporally and spatially regulated, and it requires the co-ordinated degradation and removal of the endogenous enamel matrix. This is affected by both neutral metalloproteases and serine proteases, which are developmentally restricted and may be further modulated by changes in the chemistry of the enamel crystals themselves. Failure of these mechanisms, or the adventitious entry of mineral-binding proteins during the later stages of maturation, may result in the incomplete maturation of the enamel crystals and the eruption of dysplastic tissue.

Neurochemical classification of myenteric neurons in the guinea-pig ileum

A strategy has been developed to identify and quantify the different neurochemical populations of myenteric neurons in the guinea-pig ileum using double-labelling fluorescence immunohistochemistry of whole-mount preparations. First, six histochemical markers were used to identify exclusive, non-overlapping populations of nerve cell bodies. They included immunoreactivity for the calcium binding proteins calbindin and calretinin, the neuropeptides vasoactive intestinal polypeptide, substance P and somatostatin, and the amine, 5-hydroxytryptamine. The sizes of these populations of neurons were established directly or indirectly in double-labelling experiments using a marker for all nerve cell bodies. Each of these exclusive populations was further subdivided into classes by other markers, including immunoreactivity for enkephalins and neurofilament protein triplet. The size of each class was then established directly or by calculation. These distinct, neurochemically-identified classes were related to other published work on the histochemistry, electrophysiology and retrograde labelling of enteric neurons and to the simple Dogiel morphological classification. A classification scheme, consistent with previous studies, is proposed. It includes 14 distinct classes of myenteric neurons and accounts for nearly all neurons in the myenteric plexus of the guinea-pig ileum.

The rat amelogenin gene--some aspects of evolution and expression

This study presents data to support the hypothesis that a major portion of the coding sequence of the amelogenin gene may have arisen by tandem duplication of internal sequences which as a consequence has introduced several additional potential RNA splice acceptor sites into the sequence. This duplication of splice sites has led to an increase in the heterogeneity of amelogenin forms found in developing enamel. By screening a rat enamel organ cDNA library for alternatively spliced products, it appears that as much as 20% of the amelogenin mRNA molecules may be alternatively spliced forms.

Crystal growth in dental enamel: the role of amelogenins and albumin

Amelogenin-mineral interactions were investigated using an in vitro binding approach. Rat incisor enamel matrix proteins (mainly amelogenins) were dissolved in synthetic enamel fluid and allowed to equilibrate with deproteinised developing enamel crystals. The results showed that amlogenin proteins of 21, 23, 24, 26 and 27-kDa (corresponding to nascent and partially degraded amelogenins) were associated with the crystals whilst the lower Mr amelogenins (< 21 KDa) remained free in the synthetic enamel fluid. These data suggest the nascent and partially degraded amelogenins may interact with developing enamel crystals and could influence their growth. Albumin-mineral interactions were investigated by extracting developing rat incisor enamel with synthetic enamel fluid. Insoluble material (including the enamel crystals) was then further extracted with 0.1 M phosphate buffer (pH 7.4) to desorb any mineral bound proteins. Western blotting using anti-albumin antibodies showed that almost all of the albumin from the secretory stage enamel and a significant proportion of the albumin present in early transition stage was extractable in the synthetic enamel fluid. However, synthetic enamel fluid did not extract albumin from late transition or maturation stage tissue, which could only be removed following further extraction with phosphate buffer. Albumin degradation was apparent during the transition and maturation stages, where it is degraded and ultimately removed. This binding pattern may be related to amelogenin degradation and removal during the transition stage, permitting albumin access to the previously obscured crystal surfaces. That the secretory stage matrix appears to "protect" secretory stage crystals from albumin may be an important consideration in the aetiology of enamel hypoplasias (i.e. incomplete crystal growth) and when using dissociative extraction procedures for the identification of mineral bound proteins.

The enteric neural network and three dimensional computer modelling of intestinal peristalsis

A computer model of the enteric nervous system has been developed using MATLAB in order to determine the extent to which the nature of intestinal activity can be explained by our current understanding of the projections and connectivity of enteric neurons. The model is based on repeated, identical overlapping modules, each of which contains the same number of neurones and circular muscle. The connections between modules were derived from microanatomical data. This simple model explains some characteristic features of the generation of an intestinal motor pattern.

The chemical composition of tooth enamel in recessive dystrophic epidermolysis bullosa: significance with respect to dental caries

Previous reports have linked the prevalence of tooth abnormalities with high caries experience in the different types of epidermolysis bullosa (EB). However, it is not known to what extent the apparent susceptibility to enamel caries is due to disease-related altered enamel chemistry in these cases. The aim of this study was to characterize the enamel of teeth from patients suffering from recessive epidermolysis bullosa dystrophica (rEBD) in terms of its mineral content, carbonate content, protein content, and amino acid composition. The results showed that dental enamel from these patients was essentially normal in terms of its chemistry. It is therefore concluded that the high caries experience in recessive dystrophic epidermolysis bullosa patients is probably related to other factors, such as compromised oral hygiene and prolonged oral clearance due to extensive oral soft tissue damage and a cariogenic diet.

Choline acetyltransferase immunoreactivity in the human small and large intestine

BACKGROUND & AIMS

Choline acetyltransferase, an enzyme involved in the synthesis of acetylcholine, is a marker of cholinergic neurons. In this study, the distribution of choline acetyltransferase immunoreactivity in human intestine is described.

METHODS

Frozen-section and whole-mount preparations of human small and large bowels were made and labeled with antiserum to choline acetyltransferase. Double labeling with antiserum to neuron-specific enolase enabled the proportion of all neurons that were immunoreactive for choline acetyltransferase to be determined.

RESULTS

Nerve fibers, immunoreactive for choline acetyltransferase, were frequent in the circular and longitudinal muscle layers and were widespread in the myenteric and submucous plexuses, but none was observed in the mucosa. Myenteric neurons, immunoreactive for choline acetyltransferase, showed various morphologies, the most common being unipolar and having an irregular outline with several short, lamellar processes. Sixty-four percent of all myenteric neurons were immunoreactive for choline acetyltransferase. Cholinergic submucous neurons were homogeneous in appearance with oval, smooth cell bodies and filamentous dendrites and accounted for 53% of all submucous neurons. A number of cells resembling enteroendocrine cells in the epithelium of the small and large bowels had intense choline acetyltransferase immunoreactivity.

CONCLUSIONS

The majority of neurons in human small and large intestines are cholinergic.

Dissociation of the ascending excitatory reflex from peristalsis in the guinea-pig small intestine

Localized distension of the intestine evokes an ascending excitatory reflex and a descending inhibitory reflex in the circular muscle layer. The sequential activation of these two reflexes is believed to underlie the motor pattern of peristalsis, which is responsible for the co-ordinated propulsion of intestinal contents. In this study we have shown that the initiation of peristalsis involves mechanisms additional to those mediating the ascending excitatory reflex. A short length of guinea-pig small intestine was mounted in a partitioned organ bath so that the lumen was occluded by the partition, but neuronal continuity was maintained. The anal segment was distended by intraluminal fluid infusion to evoke a peristalsis; in the oral segment, an isotonic transducer was used to record circular muscle contractions due to ascending excitatory reflexes. Stepwise distension of the anal segment with 5 microliters increments at 10 s intervals, or with a large, single-step infusion, elicited both the ascending excitatory reflex and peristalsis, when carried out at 3 min intervals. The threshold volume for the ascending excitatory reflex was smaller than the threshold for peristalsis with either incremental or single-step distensions. The ascending excitatory reflex appeared with a shorter delay than peristalsis. Tetrodotoxin (0.6 microM) or hexamethonium (100 microM) added to the oral compartment abolished the ascending excitatory reflex but not peristalsis. These drugs abolished both the ascending excitatory reflex and peristalsis when added to the anal compartment. When stimuli were delivered at 1 min intervals, peristalsis failed completely after the first trial, but the ascending excitatory reflex persisted, at a slightly reduced amplitude. When the anal segment was distended to just-subthreshold volume, electrical field stimulation (0.25-0.5 ms, 1-5 Hz for 1 s), delivered at 3 min intervals, evoked ascending excitatory responses but not peristalsis. Higher frequency stimulation (10 Hz) consistently evoked both peristalsis and the ascending excitatory responses. When trains of electrical stimulation were repeated at 1 min intervals, peristalsis quickly failed, but the ascending excitatory response persisted, although reduced in amplitude. The initiation of peristalsis can be dissociated from the ascending excitatory reflex by its threshold volume, by the duration of distension or the intensity of electrical stimulation required, and by its susceptibility to fatigue with repeated mechanical or electrical stimuli. This suggests that the ascending excitatory reflex may be part of the mechanism underlying the initiation of peristalsis, but that additional mechanisms must also be involved. Peristalsis should not be regarded as a reflex response but rather as an all-or-nothing motor pattern, triggered by mechanical stimulation, similar to other co-ordinated motor patterns in vertebrates and invertebrates.

Projections of specific morphological types of neurons within the myenteric plexus of the small intestine of the guinea-pig

The projections of myenteric neurons within the myenteric plexus of the guinea-pig small intestine were established using retrograde tracing in organotypic culture. Three days after applying the fluorescent dye DiI to a single internodal strand in the myenteric plexus, 500-1000 nerve cell bodies were labelled. Of these, 77% were located oral to the application site, 15% were located anally and 7% were located within 1 mm of this site. Three major morphological types of neurons could be distinguished. Dogiel type I neurons had lamellar dendrites and single axons, Dogiel type II neurons had large smooth cell bodies and several long processes, and filamentous neurons had smooth ovoid cell bodies, single axons and several filamentous dendrites. Dogiel type I, II and filamentous neurons accounted for 54.6%, 38% and 7.4% of all filled cells, respectively. Labelled nerve cell bodies were present up to 13 mm aboral to the DiI application site; all neurons more than 2 mm aboral had Dogiel type I features. On the oral side, Dogiel type I neurons were found up to 110 mm, Dogiel type II neurons up to 100 mm and filamentous neurons up to 80 mm. Neurons with 2 mm oral or aboral to the DiI application site were located up to 7 mm circumferentially and were mainly Dogiel type II cells. This work revealed remarkable polarity within the myenteric plexus, with a significant prevalence of myenteric neurons projecting anally for longer distances than those projecting orally. These long pathways are probably involved in the coordination of intestinal motility.

Characterization of excitatory and inhibitory motor neurons to the guinea pig lower esophageal sphincter

BACKGROUND & AIMS

The lower esophageal sphincter is innervated primarily by enteric motor neurons. The somata of excitatory and inhibitory motor neurons were identified and mapped.

METHODS

Retrograde labeling in organotypic culture and immunohistochemistry were used to identify motor neuron somata.

RESULTS

1,1'-Didodecyl-3,3,3',3'-tetramethyl indocarbocyanine perchlorate (Dil) on the left side of the sphincter labeled descending motor neurons located up to 26 mm along the esophagus and locally (within 2 mm) and gastric motor neurons. Dil applied to the right side of the sphincter labeled descending and local motor neurons but very few gastric motor neurons. Inhibitory motor neuron cell bodies, identified by nitric oxide synthase immunoreactivity, accounted for 86% +/- 4% (n = 6) of descending motor neurons and 53% +/- 4% of local motor neurons labeled from the right side. Excitatory motor neurons, immunoreactive for choline acetyltransferase, accounted for 20% +/- 3% (n = 6) of descending motor neurons and for 47% +/- 4% of local motor neurons. All motor neurons were unipolar, but inhibitory motor neurons were significantly larger than excitatory neurons.

CONCLUSIONS

The lower esophageal sphincter is innervated by local excitatory and inhibitory motor neurons and by descending esophageal inhibitory neurons. The oblique muscle, supplied by gastric motor neurons, is closely associated with the gastroesophageal junction.

Regeneration of nerve fibres across a colonic anastomosis in the guinea-pig

Resection and re-anastomosis of the bowel interrupts enteric neuronal pathways. The reestablishment of neuronal connections across a colonic anastomosis was studied using immunohistochemical, retrograde tracing and physiological techniques. In control guinea-pig proximal colon, retrograde labelling with 1,1'-didodecyl-3,3,3,3'-tetramethylindocarbocyanine perchlorate (DiI) revealed that enteric neurons with anally-directed projections are more numerous and have longer axons than orally-projecting neurons. In resected bowel, up to 26 weeks after re-anastomosis, descending neuronal pathways were substantially interrupted. Immunohistochemical labelling of nerve fibres revealed that some enteric nerve fibres did regenerate across narrow regions of the anastomosis, growing preferentially in the oral to anal direction. However, nerve fibres immunoreactive for neurofilament protein triplet were substantially depleted in myenteric ganglia anal to the anastomosis, even after the longest recovery periods, demonstrating that axonal regrowth was limited. This was confirmed in retrograde tracing studies, as no nerve cell bodies oral to an anastomosis were labelled when DiI was placed on myenteric ganglia just anal to the anastomosis. Physiological studies confirmed that regrowth of nerve fibres across the anastomosis occurred and that it was asymmetric, as electrical stimulation led to aboral conduction across the anastomosis more reliably than oral conduction, as measured by circular muscle contraction. After resection and re-anastomosis of the colon, the disruption of neuronal pathways in the enteric nervous system was observed, with limited and preferential re-establishment of aborally-directed long connections.