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.