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M Schemann

Publications and source records attributed to M Schemann.

At least 73 records · Page 4Linked to original sources
PubMed1997

Leukotriene-evoked cyclic chloride secretion is mediated by enteric neuronal modulation in guinea-pig colon.

Short term exposure to leukotrienes evoked a well known nerve mediated increase in short circuit current. It is unknown whether leukotrienes evoke in addition oscillations in chloride secretion, as has been reported for some of the other mediators released during inflammation. Therefore, the aim of this study was to characterize the effects of a long time exposure of leukotrienes on mucosal functions. Conventional Ussing chamber, and intracellular recording techniques were used to investigate the actions of leukotriene D4 and C4 on short-circuit current and excitability of submucosal neurons in guinea-pig distal colon. In Ussing chambers, long term exposure to leukotriene D4 or C4 evoked rhythmic oscillations in short-circuit current in 35% and 50% of tissues, respectively. These current bursts were blocked by tetrodotoxin, atropine, hexamethonium and piroxicam. Secretory response to short term exposure of leukotrienes was significantly higher in tissues exhibiting current bursts. Likewise, the potentiating effects of leukotrienes on the response to field stimulation was only observed in tissues exhibiting current bursts. In intracellular recording experiments, leukotriene C4 evoked activation of submucosal neurons that was partly sensitive to indomethacin; no oscillations in neuronal excitability could be demonstrated. Results suggested that long term exposure to leukotrienes evoked current bursts that were mediated by neural, cholinergic mechanisms as well as endogeneous prostaglandins.

Animals↗
PubMed1997

Projections and neurochemical coding of myenteric neurons innervating the mucosa of the guinea pig proximal colon.

Myenteric neurons projecting to the mucosa of the guinea pig proximal colon were identified using the combination of a neuronal tracing method and immunohistochemical techniques. The tracer DiI (1, 1'didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate) was applied onto the mucosa of a specimen of proximal colon which was then placed in organotypic culture to allow retrograde transport of the dye. After culture, the myenteric plexus was stained with antisera raised against choline acetyltransferase (ChAT) and calbindin (Calb). Of the myenteric neurons labeled with DiI, 99% had smooth cell bodies with Dogiel Type II morphology. Of these neurons, 70% projected in the longitudinal direction and the majority of them (65%) were located anally from the DiI application site, i.e., had ascending projections. Ascending neurons projected over significantly shorter distances than descending ones (3.1+/-0.5 mm vs. 4.6+/-1.2 mm, respectively; P<0.01). Of the labeled myenteric neurons, 98% were ChAT immunoreactive. Of these neurons, 78% were also immunoreactive for Calb and were preferentially ascending neurons. ChAT-immunoreactive but Calb-negative neurons did not have preferential projection. This study revealed the presence of two populations of myenteric neurons projecting to the mucosa of the guinea pig proximal colon. Morphological characteristics and neurochemical coding were suggestive for a putative sensory function for these neurons.

Animals↗
PubMed1997

Differential effects of inflammatory mediators on ion secretion in the guinea-pig colon.

Bi-directional interactions between the enteric nervous system and the immune system play an important role in gut inflammation. We therefore investigated the effects of the inflammatory mediators, prostaglandin (PGD2, PGE2, PGI2, and PGF2 alpha) and leukotriene (LTC4), on guinea-pig colonic secretion and on electrophysiological behaviour of submucosal neurones. In Ussing chambers, all inflammatory mediators evoked a dose-dependent increase in short circuit current (Isc) that represented electrogenic chloride secretion. The secretory response was significantly reduced by tetrodotoxin (TTX) and atropine suggesting involvement of cholinergic submucosal neurones. Long-term application of prostaglandins and LTC4 induced TTX- and atropine-sensitive cyclical chloride secretions. Intracellular recordings revealed activation of submucosal neurones by all inflammatory mediators. This activation consisted of depolarisation of the membrane associated with increased spike discharge. Frequently, prostaglandins and LTC4 induced spontaneous occurrence of cholinergic fast excitatory postsynaptic potentials. Results suggest that the role of the enteric nervous system in neuroimmune interactions consists of a potentiation of the direct epithelial effect of inflammatory mediators by the activation of submucosal neurones. Ongoing nerve-mediated cyclical changes in chloride secretion may be interpreted as the induction of intrinsic alarm programs. The effects of inflammatory mediators may serve as a defense mechanism to dilute noxious substances in the lumen.

Animals↗
PubMed1997

Nitric oxide synthase, choline acetyltransferase, catecholamine enzymes and neuropeptides and their colocalization in the anterior pelvic ganglion, the inferior mesenteric ganglion and the hypogastric nerve of the male guinea pig.

By the indirect immunofluorescence method, the distribution of nitric oxide synthase (NOS)-like immunoreactivity (LI) and its possible colocalization with neuropeptide immunoreactivities, with two enzymes for the catecholamine synthesis pathway, tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH), as well as the enzyme for the acetylcholine synthesis pathway, choline acetyltransferase (ChAT) were studied in the anterior pelvic ganglion (APG), the inferior mesenteric ganglion (IMG) and the hypogastric nerve in the male guinea pig. The analyses were performed on tissues from intact animals, as well as after compression/ligation or cut of the hypogastric nerve. In some cases the colonic nerves were also cut. Analysis of the APG showed two main neuronal cell populations, one group containing NOS localized in the caudal part of the APG and one TH-positive group lacking NOS in its cranial part. The majority of the NOS-positive neurons contained ChAT-LI. Some NOS-positive cells did not contain detectable ChAT, but all ChAT-positive cells contained NOS. NOS neurons often contained peptides, including vasoactive intestinal peptide (VIP), neuropeptide tyrosine (NPY), somatostatin (SOM) and/or calcitonin gene-related peptide (CGRP). Some NOS cells expressed DBH, but never TH. The second cell group, characterized by absence of NOS, contained TH, mostly DBH and NPY and occasionally SOM and CGRP. Some TH-positive neurons lacked DBH. In the IMG, the NOS-LI was principally in nerve fibers, which were of two types, one consisting of strongly immunoreactive, coarse, varicose fibers with a patchy distribution, the other one forming fine, varicose, weakly immunoreactive fibers with a more general distribution. In the coarse networks, NOS-LI coexisted with VIP- and DYN-LI and the fibers surrounded mainly the SOM-containing noradrenergic principal ganglion cells. A network of ChAT-positive, often NOS-containing nerve fibers, surrounded the principal neurons. Occasional neuronal cell bodies in the IMG contained both NOS- and ChAT-LI. Accumulation of NOS was observed, both caudal and cranial, to a crush of the hypogastric nerve. VIP accumulated mainly on the caudal side and often coexisted with NOS. NPY accumulated on both sides of the crush, but mainly on the cranial side, and ENK was exclusively on the cranial side. Neither peptide coexisted with NOS. Both substance P (SP) and CGRP showed the strongest accumulation on the cranial side, possibly partly colocalized with NOS. It is concluded that the APG in the male guinea-pig consists of two major complementary neuron populations, the cholinergic neurons always containing NOS and the noradrenergic neurons containing TH and DBH. Some NOS neurons lacked ChAT and could represent truly non-adrenergic, non-cholinergic neurons. In addition, there may be a small dopaminergic neuron population, that is containing TH but lacking DBH. The cholinergic NOS neurons contain varying combinations of peptides. The noradrenergic population often contained NPY and occasionally SOM and CGRP. It is suggested that NO may interact with a number of other messenger molecules to play a role both within the APG and IMG and also in the projection areas of the APG.

Animals↗
PubMed1997

Innervation pattern of guinea pig pulmonary vasculature depends on vascular diameter.

The pulmonary vasculature is supplied by various neurochemically distinct types of nerve fibers, including sensory substance P-containing and autonomic noradrenergic, nitrergic, and cholinergic axons. Pharmacological experiments have suggested that various segments of the pulmonary vascular tree respond differently to the respective neuromediators. We, therefore aimed to determine histochemically and immunohistochemically for each of these neurochemically distinct perivascular axons their quantitative distribution along the vascular tree from the extrapulmonary trunks to the smallest intraparenchymal ramifications in control guinea pigs (n = 5). Generally, arterial innervation was more developed than that of veins. Along the arterial tree, noradrenergic and substance P-containing axons were ubiquitous from the pulmonary trunk to smallest intraparenchymal vessels, whereas nitrergic axons were practically restricted to large (> 700-microns) extrapulmonary arteries. Cholinergic axons were regularly present at arteries down to 100 microns in diameter and innervated two-thirds of small arteries (50-100 microns). The results demonstrate that the noradrenergic vasoconstrictor innervation extends throughout the pulmonary vascular system whereas the innervation pattern with various types of vasodilator fibres changes with vascular diameter, parallel to known pharmacological differences in cholinergic and nitrergic vasodilator effects.

Animals↗
PubMed1996

Neurogenic inflammation in the gastrointestinal tract of the rat.

In contrast to the skin and some visceral organs the capability of capsaicin-sensitive sensory nerves of evoking an inflammatory response in the gastrointestinal tract is equivocal. We have therefore investigated the neurogenic plasma extravasation induced by local application of capsaicin to the stomach, duodenum, jejunum, ileum and colon of the rat. Permeable vessels were visualised histologically with the vascular labelling technique using colloidal silver. In the smooth muscle layer of the small intestine, capsaicin elicited a 3-fold increase in the density of labelled blood vessels (diameter, 7-35 microns). Significant capsaicin-evoked plasma extravasation was also observed in the submucosa of the jejunum and ileum, and in the basal layer of the jejunal mucosa. Capsaicin-induced extravasation was not noted in the stomach and the colon. The data suggest the involvement of capsaicin-sensitive afferents in inflammatory processes in the rat small intestine.

Animals↗
PubMed1996

Structure and chemical coding of human, canine and opossum gallbladder ganglia.

Immunohistochemistry and cholinesterase histochemistry were used to evaluate the structure and neurotransmitter content of the ganglionated plexuses of the human, canine, and opossum (Monodelphis domestica) gallbladders. In each species, the ganglionated plexus consisted of small (mean approximately 4 neurons/ganglion), irregularly dispersed ganglia that were interconnected by bundles of nerve fibers. The density of ganglia was about ten-fold higher in the opossum than in the human or the dog. Immunostaining for choline acetyltransferase (ChAT) was accomplished in the human, dog, opossum, and the guinea pig where all neurons were found to express ChAT-immunoreactivity. In the human, immunoreactivities for vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) were the most abundant followed by substance P (SP). In the dog, immunoreactivity for galanin (GAL) was the strongest, followed closely by VIP and then by SP. NPY-immunoreactive neurons were not observed in the dog, but immunoreactive nerve fibers were seen in the perivascular plexus. In the opossum, immunoreactivity for GAL was the most intense and abundant followed by SP, which was followed by VIP. NPY-immunoreactivity in the opossum was limited to scarce perivascular nerve fibers. Immunoreactivity for calcitonin-gene-related peptide (CGRP) was not observed in neuronal somata, but CGRP/SP-immunoreactive nerve fibers were a feature of each species studied. These findings, along with previously published work on the guinea pig, indicate that it is likely that all gallbladder neurons are cholinergic, and that VIP, SP, and NPY and/or GAL are commonly expressed in gallbladder neurons.

Acetylcholinesterase↗
PubMed1996

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.

Aged↗
PubMed1995

Choline acetyltransferase-like immunoreactivity in small diameter neurones of the rat dorsal root ganglion.

In the rat choline acetyltransferase (ChAT)-like immunoreactivity (ChAT-LI) was demonstrated in the dorsal root ganglion (DRG), in the superficial spinal cord and in the subepithelial layer of the ureter using immunohistochemical techniques. In the L1 DRG, 66% of the neurones were ChAT-LI. They did not express neurofilament immunoreactivity (RT97 negative) but could also contain calcitonin gene-related peptide-like immunoreactivity (CGRP-LI). In the superficial spinal cord and in the subepithelial plexus of the ureter--both areas where high numbers of fine afferent fibres have been demonstrated--CGRP-LI and ChAT-LI were co-distributed, indicating that ChAT can be found in the peripheral and central endings of small afferents. The data provide morphological evidence that a substantial proportion of afferent fibres are cholinergic.

Animals↗
PubMed1995

Choline acetyltransferase-immunoreactive neurones in a prevertebral sympathetic ganglion, the inferior mesenteric ganglion.

Using immunohistochemical techniques a small population of choline acetyltransferase (ChAT) immunoreactive (IR) neurones has been identified in the inferior mesenteric ganglion (IMG) of guinea pig (4.6% of all neurones), ferret (6.4%) and rat (0.4%). A detailed study in the guinea-pig IMG revealed that the vast majority of cholinergic neurones did not express tyrosine hydroxylase (TH)-IR, indicating that they were non-catecholaminergic. The cholinergic neurones were significantly larger than the TH-positive neurones. The majority of the ChAT-IR cells (64%) was observed in small clusters which were consistently located in the caudal lobe of the IMG close to the entry of the hypogastric nerves. 83% of the ChAT-IR cells also contained neuropeptide Y (NPY). Since the vast majority of TH-negative cells were ChAT-positive (94%), the TH negativity was taken as an indirect indication for ChAT-IR. NPY-IR, somatostatin (SOM)-IR and vasoactive intestinal peptide (VIP)-IR were found in both the TH-IR cells (22, 84 and 1%, respectively) and the putative cholinergic population (95, 84 and 70, respectively). Thus the majority of cholinergic neurones in the IMG were likely to contain NPY, SOM and VIP. TH-IR cells exhibited an extensive innervation of fibers immunoreactive for ChAT, VIP, ENK and NOS. In contrast, only a sparse plexus of ChAT-, ENK-, NOS-, NPY- and SOM-positive fibres was found around the TH-negative cells. VIP-IR fibres did not appear to innervate ChAT neurones.

Animals↗
PubMed1995

All pelvic neurons in male rats contain immunoreactivity for the synthetic enzymes of either noradrenaline or acetylcholine.

The pelvic ganglia contain sympathetic and parasympathetic neurons that supply the lower urinary and digestive tracts and internal reproductive organs. Although synthetic enzymes for noradrenaline have been previously identified in about one-third of these neurons, until very recently the methodology has not been available to directly determine whether all of the remaining neurons are cholinergic. The present immunohistochemical study has used a new antibody directed against a peptide fragment of choline acetyltransferase (ChAT) to identify pelvic cholinergic neurons. The results show that all pelvic neurons are either noradrenergic or cholinergic (as seen by the presence of tyrosine hydroxylase (TH) or ChAT, respectively). Neurons containing neither or both enzymes are extremely rare. It is concluded that the neuropeptides found in most pelvic neurons coexist with either noradrenaline or acetylcholine and may be involved in cotransmission in the pelvic viscera.

Acetylcholine↗
PubMed1995

Preganglionic sympathetic neurones, innervating the guinea pig adrenal medulla, immunohistochemically contain choline acetyltransferase and also leu-enkephalin.

Applying retrograde neuronal tracing combined with double labelling immunofluorescence, preganglionic nerve cell bodies in the intermediate grey matter of the guinea pig thoracic spinal cord, projecting to the adrenal gland, co-exhibited immunolabelling for choline-acetyltransferase (ChAT) and sometimes, also for leu-enkephalin. Likewise, ChAT-immunoreactive nerve fibres, forming a dense meshwork in the adrenal medulla, partly contained immunostaining also for leu-enkephalin. Some of the intramedullary nerve cell bodies were ChAT-positive but were non-reactive for leu-enkephalin. The findings provide evidence for an extrinsic (preganglionic) and an intrinsic (postganglionic) cholinergic nerve system in the guinea pig adrenal medulla, the preganglionic system utilising leu-enkephalin as co-mediator.

Adrenal Medulla↗
PubMed1995

Neurochemical coding of enteric neurons in the guinea pig stomach.

The aim of this study was to investigate the neurochemical coding of myenteric neurons in the guinea pig gastric corpus by using immunohistochemical methods. Antibodies and antisera against calbindin (CALB), calretinin (CALRET), choline acetyltransferase (ChAT), calcitonin gene-related peptide (CGRP), dopamine beta-hydroxylase (DBH), beta-endorphin (ENK), neuropeptide Y (NPY), neuron-specific enolase (NSE), nitric oxide synthase (NOS), protein gene product 9.5 (PGP), parvalbumin (PARV), serotonin (5-HT), somatostatin (SOM), substance P (SP), tyrosine hydroxylase (TH), and vasoactive intestinal peptide (VIP) were used. Double- and triple-labeling studies revealed colocalization of certain transmitters and enabled the identification of distinct subpopulations of gastric enteric neurons. NPY/VIP/NOS/ENK were present in 28% of all neurons, whereas 11% had NPY/VIP/DBH/ChAT; NOS-only neurons made up 2% of the population. The combination SP/ChAT/ENK occurred in 21% of the population, whereas SP/ChAT/ENK/CALRET and SP/CHAT/SOM/ +/- CALRET was identified in 5% and 6% of all cells, respectively. 5-HT-containing neurons comprised 2% of all cells and could be further classified by the presence of additional antigens as 5-HT/SP/(ChAT) or 5-HT/VIP/(ChAT). Approximately 21% of all neurons contained only ChAT with no additional antigen present and are referred to as ChAT/-. Gastric myenteric ganglion cells were not immunoreactive for CALB, PARV, CGRP, or TH. The results of this study indicate that gastric myenteric neurons can be characterized on the basis of different chemical coding. Neurochemical coding of corpus myenteric neurons revealed some similarities and significant differences in comparison with other regions of the gut. These differences might reflect adaptation of enteric nerves according to regional specialization and the distinct functions of the proximal stomach as a gastric reservoir.

Animals↗
PubMed1995

Effects of prostaglandin F2 alpha (PGF2 alpha) and prostaglandin I2 (PGI2) on nerve-mediated secretion in guinea-pig colon.

We have applied conventional flux-chamber and intracellular recording methods to investigate the effects of the prostaglandins PGF2 alpha and PGI2 upon epithelial ion transport and on the electrical behaviour of submucosal neurones in guinea-pig colon. In flux-chamber experiments on segments of colon, both prostaglandins evoked a dose-dependent increase in short-circuit current that was reduced in chloride-depleted Krebs solution and by serosal addition of tetrodotoxin or atropine, but was unaffected by hexamethonium. These results indicate activation of chloride secretion via submucosal neurones. The response to PGF2 alpha was decreased by piroxicam. Application of PGF2 alpha or PGI2 to submucosal neurones evoked depolarization of the membrane potential associated with an enhanced spike discharge. The depolarizing response was tetrodotoxin insensitive, indicating a direct effect of the prostaglandins on the impaled neurones. Membrane depolarization was frequently associated with the occurrence of fast excitatory postsynaptic potentials, suggesting in addition that part of the excitatory effect is mediated by the activation of neural circuits that drive the impaled neurone synaptically. The results of this study indicate that the secretory effects of prostaglandins are mediated in part by submucosal neurones and further suggest that the colonic submucosal plexus may function as an amplifier to enhance the epithelial response to inflammatory mediators.

Animals↗
PubMed1995

Differential projection of cholinergic and nitroxidergic neurons in the myenteric plexus of guinea pig stomach.

The aim of this study was to investigate the organization of myenteric circuits in the guinea pig stomach. Intracellular neurobiotin injections followed by choline acetyltransferase (ChAT) immunohistochemistry and NADPH-diaphorase reaction were used to identify projections of cholinergic and nitroxidergic neurons. Neurons were classified as motor neurons based on varicose endings in the muscle or the occurrence of retraction bulbs, as nonmotor neurons if varicose endings terminated onto other ganglion cells, or as multitargeted neurons. ChAT-positive cells are composed of 64% motor, 27% nonmotor, and 9% multitargeted neurons. The percentages for NADPH-reactive motor, nonmotor, and multitargeted neurons were 57, 39, and 4%, respectively. The majority of ChAT-positive motor (81%) and nonmotor neurons (85%) had ascending projections. In contrast, the majority of NADPH-reactive motor (86%) and nonmotor neurons (86%) had descending projections. Cell bodies of ascending neurons were smaller in size than the descending neurons. The results indicate that ChAT- and NADPH-neurons in the stomach have preferred projections, the former being primarily ascending, the latter mainly descending neurons. This suggests the existence of a basic circuit for polarized reflexes in the myenteric plexus of the stomach, which might mediate descending relaxation and ascending excitation.

Amino Acid Oxidoreductases↗
PubMed1994

Effects of the inflammatory mediator prostaglandin D2 on submucosal neurons and secretion in guinea pig colon.

Conventional flux chamber and intracellular recording methods were used to investigate the mode of action of prostaglandin D2 (PGD2) on ion transport in muscle-stripped segments of guinea pig colon and on colonic submucosal ganglion cells. Application of PGD2 resulted in a dose-dependent increase in short-circuit current that was reduced by serosal addition of bumetanide, tetrodotoxin, atropine, or piroxicam, but not hexamethonium. Application of PGD2 to submucosal neurons evoked a depolarization of the membrane potential that was associated with an enhanced spike discharge. In AH/type 2 neurons, postspike afterhyperpolarizations were reduced in amplitude and duration. The depolarizing responses to PGD2 were not affected by tetrodotoxin, indicative of a direct effect of PGD2 on the impaled neurons. Whereas fast excitatory postsynaptic potentials (EPSPs) were not affected by PGD2, slow EPSPs were reduced by a presynaptic effect, indicating presynaptic suppression of noncholinergic neurotransmitter release. The study demonstrates that PGD2 acts as a neuromodulator to evoke nerve-mediated chloride secretion, predominantly through activation of cholinergic submucosal neurons. The results further indicate that PGD2 released from lamina propria immune cells during antigenic stimulation may influence mucosal function by altering electrical behavior of submucosal neurons.

Animals↗
PubMed1993

Identification of cholinergic neurons in enteric nervous system by antibodies against choline acetyltransferase.

Several different monoclonal and polyclonal antibodies to choline acetyltransferase (ChAT) were screened to identify effective antibodies for immunocytochemical marking of cholinergic neurons in the enteric nervous system. Excellent immunohistochemical results were obtained with two of the antibodies in the myenteric plexus of the guinea pig stomach and small intestine. One was a mouse monoclonal antibody designated B3.9B3, and the second was a rabbit polyclonal antibody referred to as Peptide 3. Both antibodies clearly stained neuronal cell bodies as well as nerve fibers to the muscle layers and fibers encircling stained and unstained cell bodies. Cell counts indicated that approximately 64% (21.0 +/- 8.6 cells/ganglion) of gastric myenteric neurons are ChAT positive. Pelvic ganglia and the inferior mesenteric ganglia were examined as controls. Strong labeling of the majority of neurons was found in the pelvic ganglia, whereas few immunoreactive cells were apparent in the predominantly noradrenergic inferior mesenteric ganglion. Lack of effective antibodies to enteric neuronal ChAT has hampered progress in the study of the neurophysiology of cholinergic neurons in the digestive tract. Application of the B3.9B3 and Peptide 3 antibodies now promises to facilitate investigation of this important subset of enteric neurons.

Animals↗