[Actinic keratoses : Current guideline and practical recommendations]. / Aktinische Keratosen : Aktuelle Leitlinie und praxisbezogene Empfehlungen.

The S3 guideline "Actinic keratosis and squamous cell carcinoma of the skin" was published on 30 June 2019. Subsequently, publications, reviews and meta-analyses appeared with new questions regarding the comparability of study data and heterogeneity of the evaluations, which are caused, among other things, by divergent measurement parameters as well as insufficient consideration of pretreatments and combined treatments. This concise overview was written in the context of criticism and in view of necessary developments and research. Topics include epidemiology, pathogenesis, prevention, clinical presentation, therapy and BK5103. Therapy is divided into local destructive procedures and topical applications. Recommendations with quotation marks are based on the actual guideline. Corresponding evidence levels are given. For the implementation in daily routine basic data, side effects and features of therapeutic options are mentioned. The current developments and questions concerning actinic keratoses become clear.

Relation between mast cells concentration and serotonin expression in chagasic megacolon development.

Chagas' disease is still reaching about 10 million people in the world. In South America, one of the most severe forms of this disease is the megacolon, characterized by severe constipation, dilated sigmoid colon and rectum and severe malnutrition. Previous data suggested that mast cells and serotonin (5-hydroxytryptamine [5-HT]) expression could be involved in intestinal homeostasis control, avoiding the chagasic megacolon development. The aim at this study was to characterize the presence of mast cells and expression of serotonin in chagasic patients with and without megacolon and evaluate the relation between mast cells, serotonin and megacolon development. Our results demonstrated that patients without megacolon feature a large amount of serotonin and few mast cells, while patients with megacolon feature low serotonin expression and a lot of mast cells. We believe that serotonin may be involved in the inflammatory process control, triggered by mast cells, and the presence of this substance in large quantities of the intestine could represent a mechanism of megacolon prevention.

Interstitial cells of Cajal: crucial for the development of megacolon in human Chagas' disease?

AIM: Megacolon, chronic dilation of a colonic segment,is accompanied by extensive myenteric neuron loss. However, this fails to explain unequivocally the formation of megacolon. We aimed to study further enteric structures that are directly or indirectly involved in colonic motility. METHOD: From surgically removed megacolon segments of seven Chagasic patients, three sets of cryosections from oral, megacolonic and anal zones were immunohistochemically quadruple-stained for smooth-muscle actin (SMA), synaptophysin (SYN, for nerve fibres), S100 (glia) and c-Kit (interstitial cells of Cajal, ICCs). Values of area measurements were related to the appropriate muscle layer areas and these proportions were compared with those of seven non-Chagasic control patients. RESULTS: Whereas nerve and glia profile proportions did not mirror unequivocally the changes of Chagasic colon calibre (nondilation/dilation/nondilation), the proportions of SMA (i.e. muscle tissue density) and c-Kit (i.e. ICC density) did so: they decreased from the oral to the megacolonic segment but increased to the anal zones (muscle tissue density: control 68.3%, oral 54.3%, mega 42.1%, anal 47.6%; ICC-density: control 1.8%, oral 1.1%, mega 0.4, anal 0.8%). CONCLUSION: Of the parameters evaluated, muscle tissue and ICC densities may be involved in the formation of Chagasic megacolon, although the mechanism of destruction cannot be deduced.

Structure of enteric neurons.

The ENS contains numerous different neuron populations which belong to three main groups, primary afferent neurons, interneurons and effector neurons. The most extensive knowledge on the different enteric neuron types is derived from studies in the guinea pig. A significant obstacle for the transfer of this knowledge to putative equivalent enteric neurons of other species, including human, is species differences as to their morphological, chemical, physiological etc. phenotypes. Modern morphological classifications are based on the work of the Russian histologist Dogiel. Since the late 1970s, refined morphological classifications of enteric neurons beyond Dogiel have been attempted mainly in two species, the pig and the guinea pig. These reflect the immunohistochemical diversity of enteric neurons more precisely but are far from being complete. In this paper, we follow two aims. First, we have presented an overview on the chemical coding of the morphological neuron types described by Stach in the pig intestine. In doing so, we have pointed out the difference between the definitions of type I neurons given by Dogiel and Stach. Second, we have attempted to provide a basis for the morpho-chemical classification of human enteric neurons as revealed by their immunoreactivity for NFs and several neuroactive substances or related markers. According to results from guinea pig, where there is functional evidence, human morphological type II neurons (non-dendritic, multiaxonal; co-reactive for NF, CAR, SOM, SP) seem to be the intrinsic primary afferent neurons. This conclusion is based primarily on structural equivalence. Human ENK-positive, stubby (type I) neurons maybe ascending interor motorneurons. In contrast, nitrergic, VIP-reactive spiny (type I) neurons maybe descending inter- or motor neurons. Further, morphologically defined human neuron types, i.e. type III, type V and dendritic type II neurons, are non-nitrergic but could not be chemically defined as yet. Future investigations of morpho-chemical characteristics of human enteric neurons including also other cytoskeletal markers will provide a broader basis for neurohistopathological diagnostics of gut diseases.

Morphology of VIP/nNOS-immunoreactive myenteric neurons in the human gut.

In this study, we characterized human myenteric neurons co-immunoreactive for neuronal nitric oxide synthase (nNOS) and vasoactive intestinal peptide (VIP) by their morphology and their proportion as related to the putative entire myenteric neuronal population. Nine wholemounts (small and large intestinal samples) from nine patients were triple-stained for VIP, neurofilaments (NF) and nNOS. Most neurons immunoreactive for all three markers displayed radially emanating, partly branching dendrites with spiny endings. These neurons were called spiny neurons. The spiny character of their dendrites was more pronounced in the small intestinal specimens and differed markedly from enkephalinergic stubby neurons described earlier. Exclusively in the duodenum, some neurons displayed prominent main dendrites with spiny side branches. Of the axons which could be followed from the ganglion of origin within primary strands of the myenteric plexus beyond the next ganglion (70 out of 140 traced neurons), 94.3% run anally and 5.7% orally. Very few neurons reactive for both VIP and nNOS could not be morphologically classified due to weak or absent NF-immunoreactivity. Another six wholemounts were triple-stained for VIP, nNOS and Hu proteins (HU). The proportion of VIP/nNOS-coreactive neurons in relation to the number of HU-reactive neurons was between 5.8 and 11.5% in the small and between 10.6 and 17.5% in the large intestinal specimens. We conclude that human myenteric spiny neurons co-immunoreactive for VIP and nNOS represent either inhibitory motor or descending interneurons.

Investigation of general and cytoskeletal markers to estimate numbers and proportions of neurons in the human intestine.

An important requirement in pathological diagnostics in the human enteric nervous system (ENS) is the estimation of the total numbers of neurons and of proportions of distinct subpopulations. In this study, we compared the suitability of two suggested panneuronal markers, cuprolinic blue (CB) and anti-Hu-protein (HU), for staining and counting human myenteric neurons in wholemounts, derived from small and large intestinal samples. Furthermore, the proportional expression of three cytoskeletal intermediate filaments, alpha-internexin (IN), neurofilament 200 (NF) and peripherin (PE), was correlated with both CB and HU. In 8 CB- and HU-stained wholemounts, 93.3% of all neurons were double labeled, 3.3% of neurons were stained only with CB whereas 3.3% were immuno-stained only for HU. Thus, both markers were comparably reliable in representing the putative total human myenteric neuron population in our material. The wholemounts double stained for IN/CB or IN/HU revealed between 56.2 and 71.5% of neurons to be IN-reactive. Between 42.8 and 50.9% of neurons were immunoreactive for NF whereas 53.9 to 62.4% of neurons were reactive for PE. Although our sample number was too small to allow final conclusions, we suggest that the variations in proportions of intermediate filament expression we observed may be due to individual circumstances rather than to correlation with age or region. The proportions of neurons positive for IN, NF or PE but unstained by CB histochemical or HU immunohistochemical techniques was between 0 and 2.2%. We conclude that both CB and HU techniques are suitable methods for representation of almost all myenteric neurons in the human gut and that the differential expression of the cytoskeletal proteins investigated has to be included in the classification of enteric neurons in pathological diagnostics of human gastrointestinal diseases.

Morphology of enkephalin-immunoreactive myenteric neurons in the human gut.

The aim of this study was the morphological and further chemical characterisation of neurons immunoreactive for leu-enkephalin (leuENK). Ten wholemounts of small and large intestinal segments from nine patients were immunohistochemically triple-stained for leuENK/neurofilament 200 (NF)/substance P (SP). Based on their simultaneous NF-reactivity and 3D reconstruction of single NF-reactive cells, 97.5% of leuENK-positive neurons displayed the appearance of stubby neurons: small somata; short, stubby dendrites and one axon. Of these leuENK-reactive stubby neurons, 91.3% did not display co-reactivity for SP whereas 8.7% were SP-co-reactive. As to their axonal projection pattern, 50.4% of the recorded leuENK stubby neurons had axons running orally whereas in 29.4% they ran anally; the directions of the remaining 20.2% could not be determined. No axons were seen to enter into secondary strands of the myenteric plexus. Somal area measurements revealed clearly smaller somata of leuENK-reactive stubby neurons (between 259+/-47 microm(2) and 487+/-113 microm(2)) than those of putative sensory type II neurons (between 700+/-217 microm(2) and 1,164+/-396 microm(2)). The ratio dendritic field area per somal area of leuENK-reactive stubby neurons was between 2.0 and 2.8 reflecting their short dendrites. Additionally, we estimated the proportion of leuENK-positive neurons in comparison to the putative whole myenteric neuron population in four leuENK/anti-Hu doublestained wholemounts. This proportion ranged between 5.9% and 8.3%. We suggest leuENK-reactive stubby neurons to be muscle motor neurons and/or ascending interneurons. Furthermore, we explain why we do not use the term "Dogiel type I neurons" for this population.

Dendritic hypertrophy of Stach type VI neurons within experimentally altered ileum of pigs.

Myenteric neurons were investigated morphometrically to answer the question if type-specific somal hypertrophy of type VI neurons in mechanically stressed ileum of pigs, which was known from an earlier study, is correlated with an increased dendritic arborization, that is, with dendritic hypertrophy. Muscular hypertrophy was induced in the ileum of two juvenile pigs by narrowing the gut circumference (mechanical stenosis) and by reversing a loop of ileum which results in an antiperistaltic segment (functional stenosis), respectively. After a survival time of 6 weeks, wholemounts from the pre- and poststenotic ileal regions, from the antiperistaltic segment as well as from an age matched control animal, were silver impregnated. Dendritic parameters of Stach types IV and VI neurons were recorded using a computer-aided morphometric program and analysed statistically. Type IV neurons showed no change of dendritic parameters, neither within control nor within stenosed ileal segments. In contrast, the type VI neurons displayed increased dendritic parameters within zones of muscular hypertrophy such as total dendritic length, numbers of dendrites, of dendritic branching points and of dendritic endings. We suggest that type VI neurons may participate as descending nitrergic interneurons or motorneurons in the control of muscular function, thus, undergoing plastic changes in case of experimental muscular hypertrophy. Type IV neurons which are involved in the regulation of mucosal processes were not affected by muscular hypertrophy.

Intrinsic choroidal neurons in the duck eye receive sympathetic input: anatomical evidence for adrenergic modulation of nitrergic functions in the choroid.

Intrinsic choroidal neurons (ICN) in the duck eye form an intramural ganglionic plexus that may subserve complex integrative functions. A key feature of such ganglia is an innervation by sympathetic postganglionic neurons. The present study was thus aimed at determining the sympathetic postganglionic innervation of ICN. Choroids were processed for double immunofluorescence labelling with the following markers: tyrosine-hydroxylase (TH)/nitric oxide synthase (nNOS), TH/galanin (GAL), dopamine-beta-hydroxylase (DBH)/vasoactive intestinal polypeptide (VIP), TH/DBH and DBH/alpha-smooth-muscle actin (alphaSMA), and for triple immunofluorescence labelling with VIP/DBH/TH. Epifluorescence and confocal laser scanning microscopy were used for evaluation. Immunoperoxidase staining for TH or DBH in combination with NADPH-diaphorase histochemistry was applied for electron microscopy. ICN spread over the entire choroid but were concentrated in an equatorial zone passing obliquely from naso-cranial to temporocaudal. More than 80% of nNOS-positive ICN showed close appositions of TH/DBH-immunoreactive varicose nerve fibres at the light-microscopic level, as could be confirmed by confocal laser scanning microscopy. Ultrastructurally, these appositions could be defined as both synapses or close contacts without synaptic specialisation. Vascular and non-vascular smooth muscle fibres also received TH/DBH-immunopositive innervation. Our findings suggest that most ICN receive a sympathetic input that might modulate their nitrergic effects upon vascular and non-vascular smooth muscle fibres in the choroid and that they may have more complex functions than merely being a simple parasympathetic relay.

Intrinsic neurons in the duck choroid are contacted by CGRP-immunoreactive nerve fibres: evidence for a local pre-central reflex arc in the eye.

Intrinsic choroidal neurons represent peripherally displaced autonomic nerve cells supposed to work as a local integrative network similar to the enteric nervous system, to control choroidal vasculature and stromal smooth muscle. A typical feature of such intramural neuronal networks is the innervation by primary afferent collaterals expressing peptides, e.g. CGRP. The present study was aimed at determining primary afferent contacts on nitrergic intrinsic choroidal neurons (ICN) in the duck eye. In addition, a sympathetic innervation of ICN was assessed. Choroids were immunohistochemically processed for the following markers: neuronal nitric oxide synthase (nNOS), galanin (GAL), calcitonin gene-related peptide (CGRP), and tyrosine hydroxylase (TH). For evaluation, fluorescence as well as confocal laser scanning microscopy were used. For electron microscopy, immunoperoxidase staining for CGRP in combination with NADPH-diaphorase histochemistry was applied. ICN immunoreactive for nNOS or GAL spread over the entire choroid, although they were concentrated in an equatorial zone passing obliquely from naso-cranial to temporo-caudal. About 40% of ICN showed close relationships with CGRP-immunoreactive nerve fibres, originating most likely in the trigeminal ganglion, as seen in the fluorescence and confocal laserscanning microscope. These appositions could be ultrastructurally defined as both synapses and close contacts without synaptic specialization. Some ICN endowed with CGRP-positive fibres also received TH-immunoreactive boutons. CGRP-immunoreactive profiles were also detected in close relationship to choroidal non-vascular smooth muscle cells and collagen fibres connected to them. In many instances, they were intercalated between smooth muscle cells and processes of ICN forming triads. These results suggest that ICN, similar to other intramural autonomic systems integrate signals from trigeminal primary afferent collaterals. The 'sensory' terminals of these primary afferents may be located in the anterior eye segment but also within the smooth muscle stroma of the choroid itself. Thus, ocular homeostasis may be regulated via intraocular pre-central reflexes which are probably subject to sympathetic modulation.

Intrinsic choroidal neurons in the duck eye express galanin.

Recently, it has been shown that the choroid of the duck eye harbours approximately 1,000 intrinsic choroidal neurons positive for vasoactive intestinal polypeptide and neuronal nitric oxide synthase. Their connections and functional significance are largely unknown. This study was performed to establish a typical chemical code for these neurons and to define their targets by using immunocytochemistry and confocal laser scanning microscopy. Almost all intrinsic choroidal neurons coexpressed galanin (GAL), vasoactive intestinal polypeptide (VIP), and neuronal nitric oxide synthase (nNOS)/NADPH-diaphorase. A few stained for GAL and/or nNOS only. Among extrinsic ganglia, GAL/VIP/nNOS coexpressing neurons were only found in the pterygopalatine ganglion where they accounted for approximately 30% of the neuronal population. Thus, GAL/VIP/nNOS-positive nerve fibres around branches of the ciliary artery and within the nonvascular smooth muscle stroma of the choroid may originate mainly from intrinsic neurons and to some extent in a subpopulation of pterygopalatine ganglionic neurons exhibiting the same chemical coding. Close contacts of GAL-positive fibres upon intrinsic choroidal neurons may indicate reciprocal connections between them. Thus, intrinsic choroidal neurons may represent peripherally displaced pterygopalatine ganglion neurons forming a local network for regulation of vascular and nonvascular smooth muscle tone in the duck choroid. They may be integrated in the neuronal circuitry controlling intraocular pressure, choroidal thickness, accommodation, and axial bulbus length.

Experimental hypertrophy of myenteric neurones in the pig: a morphometric study.

Muscular hypertrophy in the ileum of two pigs aged 6 weeks was induced using two different surgical techniques, narrowing of the gut circumference (mechanical stenosis) and segmental reversal of an ileal loop which results in a persistent antiperistalsis of that segment (functional stenosis). These pigs were sacrificed 5-6 weeks postoperatively. Cross sections through the gut wall at various distances from the operation sites revealed marked muscular hypertrophy in the pre-stenotic regions and in the reversed segment. Whole mounts from pre- and post-stenotic, as well as reversed ileal regions, were silver- impregnated. The corresponding ileal region of a third, nonoperated pig served as control. Using a computer-aided morphometric device, somal areas of five morphological neurone types were measured at various distances orally and anally from the operation sites and along the control ileum. Values between hypertrophic and nonhypertrophic zones as well as between two corresponding zones of nonoperated ileum were compared statistically. Along the control ileum, values revealed no differences in soma sizes. Within the experimentally altered material, somal areas of type VI neurones showed marked hypertrophy related to the sites of muscular hypertrophy whereas the other types remained constant throughout (II, IV in segmental reversal) or showed slightly larger somal areas within the post-stenotic, nonhypertrophied zones (I, V, IV in stenosis). Additionally, within the reversed segment, neuronal perikarya of type I, II, IV and V neurones were larger as compared to the neighbouring regions. However, this enlargement of perikarya within the reversed segment may not be correlated with muscular hypertrophy but rather with the transections of intramural axons before reversing this segment. The results suggest that morphologically distinct neurone types may play different roles within the mechanically stressed small intestine and possibly also in the coordination of normal muscular function.

Mucosal projections of enteric neurons in the porcine small intestine.

In the present study, a combination of immunohistochemistry and retrograde 1,1;-didodecyl-3,3,3;,3;-tetramethylindocarbocyanine perchlorate (DiI) tracing was used to unravel the morphology, distribution, and neurochemical coding of submucous and myenteric neurons with axonal projections to the mucosa of the porcine small intestine. The majority of traced neurons was located in the inner submucous plexus (ISP; 78%), whereas the remaining part was distributed between the outer submucous plexus (OSP; 10%) and myenteric plexus (MP; 12%). Among these traced neurons, some distinct neuronal populations could be distinguished according to their morphologic and neurochemical properties. In the ISP, several types of traced neurons were detected: 1) morphologic type II neurons expressing choline acetyltransferase (ChAT) immunoreactivity, calcitonin gene-related peptide (CGRP) immunoreactivity, and substance P (SP) immunoreactivity; 2) ChAT/SP-immunoreactive (-IR) small neurons; 3) vasoactive intestinal polypeptide (VIP) -IR small neurons; and 4) multidendritic ChAT/somatostatin (SOM) -IR neurons. The traced neuronal populations of the OSP and MP were similar to each other. In both plexuses, the following DiI-labelled neurons were found: 1) ChAT/CGRP/(SP)-IR type II neurons; 2) multidendritic ChAT/SP-IR neurons; and 3) multidendritic ChAT/SOM-IR neurons. Comparison of the present findings with previously obtained data concerning the mucosal innervation pattern of the intestine of small mammals, revealed significant species differences with respect to the morphologic and neurochemical features of the involved enteric neuronal classes. Although not identical, a closer resemblance between pig and human enteric nervous system seems to be at hand, as far as the anatomic organization and the presence of neurochemically identified neuronal subtypes within the enteric nervous system are concerned.

Morphological classifications of enteric neurons--100 years after Dogiel.

The first differentiation of enteric neurons into three morphological types was done by the russian histologist A. S. Dogiel on the basis of the different shapes and lengths of their dendrites. Although a number of authors considered his results during the following decades, only a division into two types withstood time: type I neurons had one long and several short processes, whereas type II neurons were characterized by several long processes. Some further structural features were discussed but substantial progress was not made until the late 1970s. This stagnation was due to some inaccuracies in Dogiel's descriptions, to the fact that most histologists in this field followed the reticular concept of the nervous system, to the idea that enteric neurons represent no more than a vegetative, postganglionic relay station between the central nervous system and the periphery, and to methodological difficulties. With the application of modern neuroanatomical techniques it was realized that the enteric nervous system contains a considerable number of neuronal subpopulations. The search for morphological correlates of the chemical diversity of enteric neurons was done mainly in the pig and the guinea-pig. In the pig, additional structural features such as axonal projection, distribution of neurons within ganglia, within different plexuses and along the length of the gut, blood supply etc. were included as criteria for further refining neuronal classification. Most of our knowledge about functional features of enteric neurons, e.g. chemical coding, neuronal connectivity, electrophysiological behaviour, was derived from studies in the guinea-pig small intestine. In light of interspecies differences, comparison of findings from different species is mandatory. The search for morphological and functional peculiarities of human enteric neuronal circuitry has to consider all methodological and conceptual advances made within the past 100 years since the pioneering work of Dogiel.

Comparison of enteric neuronal morphology as demonstrated by Dil-tracing under different tissue-handling conditions.

The aim of this study was to determine locations and morphologies of enteric neurons innervating the small intestinal mucosa of the pig after application of the carbocyanine tracer Dil onto a single villus. The tissue was processed in two ways: incubation (1) of fixed material (postmortem tracing) for several months and (2) of living specimens within organotypic culture in vitro for several days (supravital tracing). In both procedures Dil-labelled neurons were found in the three ganglionated plexuses, the internal and external submucous plexus as well as the myenteric plexus. Postmortem tracing revealed different neuronal morphologies. Adendritic type II neurons were present in all three plexuses, type IV neurons with short, scarcely branched, polarly emerging dendrites were mainly found in the myenteric plexus and small dendritic neurons were mainly present in the internal submucous plexus. The latter may correspond to minineurons hitherto described only immunohistochemically. Tracing within tissue culture showed somata of neurons and, partly, proximal segments of processes to be labelled. Subsequent immunohistochemistry using general neuronal markers revealed some neurons to be adendritic type II neurons. Visualization of dendrites was less clear, hampering an accurate morphological classification of dendritic neurons. Our results suggest that neurons of all ganglionated enteric nerve plexuses of the pig participate in the innervation of the mucosa, and that postmortem tracing revealed enteric neuronal morphology more clearly than supravital tracing. Since the former method cannot be applied for deciphering the chemical coding of enteric neurons, combination of both methods will extend our knowledge of the morphological substrate for the intrinsic neuronal microcircuits in the gastrointestinal tract.

Regional structural differences in the neuronal composition of myenteric ganglia along the pig small intestine.

BACKGROUND: Data on structural variations in the neuronal composition of myenteric ganglia along the small intestine of various species are scarcely available. The aim of this study was to compare morphologically the ganglia and neurons of different parts of this organ in the pig. METHODS: Wholemounts from jejunum and ileum of two 14-week-old pigs were silver impregnated. The number of morphologically defined neuron types I-VI were counted per cm2. To relate these numbers to the putative whole neuron population, all impregnated neuronal nucleoli were counted in the same areas. RESULTS: Morphologically classifiable, impregnated neurons ranged between 17.9 and 23.1% of the putative whole population as determined by neuronal nucleoli counting. The proportions of type I neurons (jejunum, 22-25%; ileum, 19%) and type II neurons (jejunum, 30%; ileum, 37%) were considerable in both segments. The proportion of type III neurons was about 30% in jejunum and 2% in ileum whereas the percentages of type IV (jejunum, 10%; ileum, 18%), type V (jejunum, 2%; ileum, 12%) and type VI neurons (jejunum, 3%; ileum, 11%) were higher in the ileum. All differences between jejunal and ileal percentages were significant as determined by chi square test. CONCLUSIONS: Ganglia from the upper jejunum and the lower ileum reveal distinct differences in terms of neuron type composition. We suggest that these morphological differences reflect well known functional differences, e.g. in terms of motility, between different parts of the small intestine.

Distribution, morphology and projections of nitrergic and non-nitrergic submucosal neurons in the pig small intestine.

Sequential nitric oxide synthase immunohistochemistry and nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry in pig small intestinal wholemounts revealed a complete colocalisation of the two nitrergic markers in submucous neurons. The external submucous plexus (ESP) contained nitrergic neurons throughout. In the internal submucous plexus (ISP) we found a moderate number of nitrergic neurons in the duodenum, while they were rare in the jejunum and nearly absent in the ileum. Combined NADPHd histochemistry and silver impregnation showed morphological ESP type III and VI neurons to be NADPHd positive whereas ESP type II, IV and V neurons were NADPHd negative. Axons of ESP type III, IV and VI neurons were often observed to enter interconnecting strands directed abluminally. ESP type II neurons projected mainly to the ISP. In special silver-impregnated wholemounts containing both external muscle layers and the abluminal part of the submucous layer, i.e. the myenteric plexus and the ESP, the great majority of impregnated axons within the interconnecting strands were observed to run between both plexuses and did not enter the circular muscle layer. We conclude that ESP type III and VI neurons are nitrergic while ESP type II, IV and V neurons are non-nitrergic. Furthermore, we assume that ESP type III, IV and VI neurons may represent a submucosal input to the myenteric plexus.

Morphological classification of NADPHd-positive and -negative myenteric neurons in the porcine small intestine.

In this study, the neuronal nitric oxide synthase (nNOS)-related NADPHd reaction was combined with a silver impregnation method to visualize the morphology of nitrergic and non-nitrergic enteric neurons in the pig. Based on colour combination, NADPHd-positive and impregnated, NADPHd-negative but impregnated and NADPHd-positive but non-impregnated groups of nerve cells could be distinguished in whole-mounts of the small intestine. Neurons of the first two groups could be classified morphologically. NADPHd-positive and impregnated cells showed type III and type VI morphology, the first being located preferably in the upper, the latter in the lower small intestine. Both project largely in an aboral direction. NADPHd-negative but silver impregnated are the orally projecting type I, the adendritic, mostly circumferentially projecting type II, the vertically - to the submucous plexuses - projecting type IV and the aborally projecting type V neurons. Given that NADPHd and nNOS are identical, we conclude that type III and type VI neurons are nitrergic and type I, II, IV and V neurons are non-nitrergic. A considerable number of mostly smaller NADPHd-positive but non-impregnated neurons could not be classified.

Myenteric neurons with different projections have different dendritic tree patterns: a morphometric study in the pig ileum.

Morphometric analysis was performed of two types of myenteric neurons with at first glance, very similar morphology, but different projections in the pig ileum. 50 type IV cells projecting vertically to the outer submucosal plexus, and 50 solitary type V neurons projecting aborally, within the myenteric plexus, were evaluated. Using a computer-aided morphometric device, the following parameters were recorded: somal area, longest somal diameter, number of primary dendrites, dendritic length, number of dendritic branching points and number of terminal segments. In addition to other significant differences, the most prominent discriminating parameter between the two populations of nerve cells estimated in this study was the length of the longest dendrite of each cell type. The longest dendrite of an individual type V neuron is a manifold longer than the corresponding somal diameter, in contrast to type IV neurons where it is at most twice the somal diameter. In addition, all type IV and type V single dendritic lengths were arranged in histogramms, where the type V dendrites showed two frequency peaks. Thus, we assume that solitary type V neurons can develop two populations of dendrites: a short and a long one. These results demonstrate that myenteric neurons with different projections (and hence different functions) display strikingly different dendritic morphology.