Control Of Gastrointestinal Function Research Articles

A8 LUMINAL SHORT CHAIN FATTY ACIDS INCREASE ACTIVITY IN COLONIC MYENTERIC PLEXUS NEURONS IN MICE

Abstract Background The enteric nervous system (ENS) plays a critical role in the control of gastrointestinal functions. Short chain fatty acids (SCFAs) are the products of non-digestible dietary fiber fermentation by gut microbial metabolism and are a primary energy source for enterocytes. However, the impact of SCFAs on the ENS is not well understood. Aims We aimed to test whether SCFAs affect enteric neuronal function using a novel intact preparation of the colon. Methods Intact segments of the colon from mice expressing a genetically encoded fluorescent calcium (Ca2+) reporter specifically in all enteric neurons (Wnt-1-GCaMP6 mice) or in intrinsic primary afferent neurons (IPANs, Calb1-GCaMP6 mice) were bathed and luminally perfused with Krebs solution. Contractility was inhibited by nicardipine (3 µM) and scopolamine (1 µM). The duration and intensity of neuronal intracellular Ca2+ fluorescence responses to SCFA were visualized by live-cell confocal microscopy and were analyzed using Imaris™ software. The SCFAs were luminally perfused at a constant rate of 10 mL/h for 3 min. NaCl was modified in Krebs solution to correct for the osmolarity of SCFAs. Results In the myenteric plexus of Wnt-1-GCaMP6 mice, SCFAs (acetate, 60 mM; propionate, 20 mM or butyrate, 20 mM) caused a rapid and sustained increase in Ca2+ fluorescence (26.8±5.9, 25.8±1.7, and 27.4±5.9 min, respectively). The peak Ca2+ responses were 92.5%± 28.3%, 122.6%±21.5% and 111.7%± 23.0%, respectively. The combination of these three SCFAs increased Ca2+ fluorescence for 20.5±6.3 min and potentiated levels of Ca2+ fluorescence to 125.1%±21.6% above baseline. The percentages of neurons responding to SCFAs were 85.7%, 94.4%, 97.7% and 93.3 % for acetate, propionate, butyrate and a combination of SCFAs, respectively. In Calb1-GCaMP6 mice, IPANs showed a similar pattern of Ca2+ responses and a proportion of neurons that responded to the SCFAs. Following acetate, propionate, butyrate and combination of SCFAs administration, fluorescence was increased for 13.5±1.2, 20.6±2.7, 24.9±2.2 and 46.1±4.6 min, by a magnitude of 404.3%±153.7%, 129.0%±0.4%, 73.9%±18.8% and 717%±267.0% above baseline and the percentages of neuronal response were 100.0%, 100.0%, 100.0% and 87.5 %, respectively. Conclusions We show that SCFAs activate neurons of the myenteric plexus including IPANs. These studies suggest that some of the actions of SCFAs are mediated by the ENS, but further studies are needed to identify the underlying mechanisms of action of SCFAs in the myenteric plexus. Funding Agencies CAG, CIHRTRIANGLE Canada

The nature of catecholamine-containing neurons in the enteric nervous system in relationship with organogenesis, normal human anatomy and neurodegeneration.

The gastrointestinal tract is provided with extrinsic and intrinsic innervation. The extrinsic innervation includes the classic vagal parasympathetic and sympathetic components, with afferent sensitive and efferent secretomotor fibers. The intrinsic innervations is represented by the enteric nervous system (ENS), which is recognized as a complex neural network controlling a variety of cell populations, including smooth muscle cells, mucosal secretory cells, endocrine cells, microvasculature, immune and inflammatory cells. This is finalized to regulate gastrointestinal secretion, absorption and motility. In particular, this network is organized in several plexuses each one providing quite autonomous control of gastrointestinal functions (hence the definition of "second brain"). The similarity between ENS and CNS is further substantiated by the presence of local sensitive pseudo- unipolar ganglionic neurons with both peripheral and central branching which terminate in the enteric wall. A large variety of neurons and neurotransmitters takes part in the ENS. However, the nature of these neurons and their role in the regulation of gastrointestinal functions is debatable. In particular, the available literature reporting the specific nature of catecholamine- containing neurons provides conflicting evidence. This is critical both for understanding the specific role of each catecholamine in the gut and, mostly, to characterize specifically the enteric neuropathology occurring in a variety of diseases. An emphasis is posed on neurodegenerative disorders, such as Parkinson's disease, which is associated with the loss of catecholamine neurons. In this respect, the recognition of the nature of such neurons within the ENS would contribute to elucidate the pathological mechanisms which produce both CNS and ENS degeneration and to achieve more effective therapeutic approaches. Despite a great emphasis is posed on the role of noradrenaline to regulate enteric activities only a few reports are available on the anatomy and physiology of enteric dopamine neurons. Remarkably, this review limits the presence of enteric noradrenaline (and adrenaline) only within extrinsic sympathetic nerve terminals. This is based on careful morphological studies showing that the only catecholamine-containing neurons within ENS would be dopaminergic. This means that enteric pathology of catecholamine neurons should be conceived as axon pathology for noradrenaline neurons and whole cell pathology for dopamine neurons which would be the sole catecholamine cell within intrinsic circuitries affecting gut motility and secretions.The gastrointestinal tract is provided with extrinsic and intrinsic innervation. The extrinsic innervation includes the classic vagal parasympathetic and sympathetic components, with afferent sensitive and efferent secretomotor fibers. The intrinsic innervations is represented by the enteric nervous system (ENS), which is recognized as a complex neural network controlling a variety of cell populations, including smooth muscle cells, mucosal secretory cells, endocrine cells, microvasculature, immune and inflammatory cells. This is finalized to regulate gastrointestinal secretion, absorption and motility. In particular, this network is organized in several plexuses each one providing quite autonomous control of gastrointestinal functions (hence the definition of "second brain"). The similarity between ENS and CNS is further substantiated by the presence of local sensitive pseudounipolar ganglionic neurons with both peripheral and central branching which terminate in the enteric wall. A large variety of neurons and neurotransmitters takes part in the ENS. However, the nature of these neurons and their role in the regulation of gastrointestinal functions is debatable. In particular, the available literature reporting the specific nature of catecholamine-containing neurons provides conflicting evidence. This is critical both for understanding the specific role of each catecholamine in the gut and, mostly, to characterize specifically the enteric neuropathology occurring in a variety of diseases. An emphasis is posed on neurodegenerative disorders, such as including Parkinson's disease, which is associated with the loss of catecholamine neurons. In this respect, the recognition of the nature of such neurons within the ENS would contribute to elucidate the pathological mechanisms which produce both CNS and ENS degeneration and to achieve more effective therapeutic approaches. Despite a great emphasis is posed on the role of noradrenaline to regulate enteric activities only a few reports are available on the anatomy and physiology of enteric dopamine neurons. Remarkably, this review limits the presence of enteric noradrenaline (and adrenaline) only within extrinsic sympathetic nerve terminals. This is based on careful morphological studies showing that the only catecholamine-containing neurons within ENS would be dopaminergic. This means that enteric pathology of catecholamine neurons should be conceived as axon pathology for noradrenaline neurons and whole cell pathology for dopamine neurons which would be the sole catecholamine cell within intrinsic circuitries affecting gut motility and secretions.

Regulation of nutrition-associated receptors in blood monocytes of normal weight and obese humans

Obesity, type 2 diabetes and associated metabolic diseases are characterized by low-grade systemic inflammation which involves interplay of nutrition and monocyte/macrophage functions. We suggested that some factors such as nutrient components, neuropeptides involved in the control of gastrointestinal functions, and gastrointestinal hormones might influence immune cell functions and in this way contribute to the disease pathogenesis. The aim of this study was to investigate the mRNA expression of twelve nutrition-associated receptors in peripheral blood mononuclear cells (PBMC), isolated monocytes and monocyte-derived macrophages and their regulation under the switching from the high-carbohydrate low-fat diet to the low-carbohydrate high-fat (LC/HFD) isocaloric diet in healthy humans. The mRNA expression of receptors for short chain fatty acids (GPR41, GPR43), bile acids (TGR5), incretins (GIPR, GLP1R), cholecystokinin (CCKAR), neuropeptides VIP and PACAP (VIPR1, VIPR2), and neurotensin (NTSR1) was detected in PBMC and monocytes, while GPR41, GPR43, GIPR, TGR5, and VIPR1 were found in macrophages. Correlations of the receptor expression in monocytes with a range of metabolic and inflammatory markers were found. In non-obese subjects, the dietary switch to LC/HFD induced the increase of GPR43 and VIPR1 expression in monocytes. No significant differences of receptor expression between normal weight and moderately obese subjects were found. Our study characterized for the first time the expression pattern of nutrition-associated receptors in human blood monocytes and its dietary-induced changes linking metabolic responses to nutrition with immune functions in health and metabolic diseases.

The astrocyte marker Aldh1L1 does not reliably label enteric glial cells

Enteric glial cells are increasingly acknowledged as important partners of enteric neurons in the control of gastrointestinal function. They share morphological features and expression of antigenic markers with astrocytes of the central nervous system. Recently, aldehyde dehydrogenase 1 family member L1 (Aldh1L1) has been proposed as a novel and specific marker for astrocytes. Taking the known similarities between astrocytes and enteric glia into account, we sought to investigate whether enteric glial cells also express Aldh1L1. To this end, we performed immunostaining on preparations of myenteric plexus obtained from adult Aldh1L1-eGFP bacterial artificial chromosome (BAC) transgenic mice and found that the Aldh1L1 promoter is indeed active in enteric glia, albeit mainly in cells residing outside the myenteric ganglia. Apart from enteric glia, we also observed eGFP expression in interstitial cells of Cajal. Furthermore, myenteric ganglia of the large intestine contained eGFP positive neurons. Taken together, our data indicate that Aldh1L1 is not a suitable marker for enteric glial cells.

The heat is on: does direct application of capsaicin to autonomic nerves produce a specific deafferentation?

The discovery that capsaicin could excite and block transmission in small-diameter afferent nerve fibres provided an important tool for many researchers to investigate the role of this class of neuron in the regulation of physiological and pathophysiological processes. Systemic administration of capsaicin to neonatal animals produces a life-long deafferentation of all capsaicin-sensitive neurons and, in adults, produces a temporary ‘defunctionalization’ (Holzer, 1991). However, for those interested in reflex regulation of gastrointestinal (GI) function, these useful techniques were limited because the gut receives a dual afferent innervation from both the craniosacral and the thoracolumbar outflow from the central nervous system. The use of perineural application of capsaicin to nerve bundles provided an extremely important tool to determine the specific role of an afferent pathway in homeostatic reflexes. For example, total cervical or subdiaphragmatic vagal transection had been used experimentally to demonstrate a vago-vagal reflex pathway in the regulation of gastric motility and secretion, but delineation of the vagal afferent pathway was confounded by concomitant removal of the vagal efferent pathway. Application of capsaicin to the cervical vagal trunks clearly showed a role for the vagal afferent pathway in mediating inhibition of gastric emptying in response to gut peptides and intestinal nutrients (Raybould & Tache, 1988; Raybould & Holzer, 1992). Taken together with morphological studies (in particular those of Powley and his group; see Powley & Philips, 2002) and electrophysiological recordings (for example, Blackshaw & Grundy, 1990), the importance of vagal afferent neurons in the regulation of postprandial gastrointestinal function became evident. Observations using perineural application of capsaicin were also key in uncovering the ability of the gut peptide cholecystokinin to act via the vagal afferent pathway to inhibit food intake (South & Ritter, 1988). Fast forwarding to today, these initial observations led to profound changes in the way we think about the role of the gut and the gut–brain axis in control of body weight and glucose homeostasis. Decades later, however, it is not necessarily surprising to find that direct application of capsaicin to nerve bundles does not produce a specific ‘defunctionalization’ of afferent neurons, as previously supposed (or hoped). In this issue of The Journal of Physiology, Browning et al. (2013) convincingly show that perivagal application of capsaicin induces a degeneration of vagal efferent neurons and a decrease in vagal efferent responses. Researchers using perineural application of capsaicin attempted to control for the specificity of the treatment, but Browning et al. (2013) perform a number of well-designed morphological and electrophysiological experiments that clearly show the lesion produced by perivagal application of capsaicin is not restricted to vagal afferent fibres. One can quibble with the technique of capsaicin application – the use of DMSO and ethanol as the vehicle rather than oil as used by most previous investigators – oil allows for a much more controlled, local application with reduced risk of systemic absorption. The important message from the data in this study is to call into question some previous conclusions that the vagal afferent pathway is the sole mediator of changes in GI function in response to peripheral stimuli. The receptor for capsaicin has been identified and mapped, and capsaicin (particularly at high concentrations) has been shown to have non-TRPV1 receptor-mediated effects. Earlier publications showing altered functional response to vagal ‘efferent’ stimulation by perineural application of capsaicin ascribed these unexpected effects to retrograde activation of vagal afferent neurons or the lack of input to second-order neurons in the nucleus tractus solitarii as being important in the function of the overall reflex pathway (Raybould et al. 1990; Thiefin et al. 1990). The data of Browning et al. (2013) suggest a different interpretation to explain these findings, and the authors urge caution in the use of this technique. Happily, since the heyday of the use of this technique in the 1980s and 1990s, the advent of different technologies, including transgenic mice with specific receptor deletions, have, to a large extent, reinforced initial observations from the early work using perineural application of capsaicin. While past studies may have been overinterpreted, the central tenet that the vagal afferent pathway plays a crucial role in the control of GI function and food intake remains vindicated.

Enteric glial cells protect neurons from oxidative stress in partviareduced glutathione

Enteric glial cells (EGCs) are essential in the control of gastrointestinal functions. Although lesions of EGCs are associated with neuronal degeneration in animal models, their direct neuroprotective role remains unknown. Therefore, the aims of this study were to demonstrate the direct neuroprotective effects of EGCs and to identify putative glial mediators involved. First, viral targeted ablation of EGCs in primary cultures of enteric nervous system increased neuronal death both under basal conditions and in the presence of oxidative stress (dopamine, hydrogen peroxide). Second, direct or indirect coculture experiments of EGC lines with primary cultures of enteric nervous system or neuroblastoma cell lines (SH-SY5Y) prevented neurotoxic effects induced by oxidative stress (increased membrane permeability, release of neuronal specific enolase, caspase-3 immunoreactivity, changes in [Ca(2+)](i) response). Finally, combining pharmacological inhibition and mRNA silencing methods, we demonstrated that neuroprotective effects of EGCs were mediated in part by reduced glutathione but not by oxidized glutathione or by S-nitrosoglutathione. Our study identified the neuroprotective effects of EGCs via their release of reduced glutathione, extending their critical role in physiological contexts and in enteric neuropathies.-Abdo, H., Derkinderen, P., Gomes, P., Chevalier, J., Aubert, P., Masson, D., Galmiche, J.-P., Vanden Berghe, P., Neunlist, M., Lardeux, B. Enteric glial cells protect neurons from oxidative stress in part via reduced glutathione.

S8. Neural control of gut functions: S8.1 Plasticity of vagal brainstem circuits in the control of gastrointestinal function

Sensory information from the gastrointestinal (GI) tract is transmitted centrally through vagal afferents that terminate within the nucleus of the tractus solitarius (NTS) and utilize glutamate as their principal neurotransmitter. Neurons of the NTS integrate this sensory information with inputs received from other brainstem and “higher” CNS center and relay the integrated signal to the adjacent dorsal motor nucleus of the vagus (DMV) using principally glutamate, GABA and norepinephrine as neurotransmitters.

Total Enzymatic Synthesis of the Cholecystokinin Octapeptide (CCK‐8)

AbstractThe enzymatic synthesis of the cholecystokinin octapeptide (CCK‐8) is reported. The target octapeptide CCK‐8 is the minimum active sequence with the same biological activity as naturally occurring cholecystokinin and is a potential therapeutic agent in the control of gastrointestinal function as well as a drug candidate for the treatment of epilepsy and obesity. The protected CCK‐8 was obtained by incubation of Bz‐Arg‐Asp(OEt)‐Tyr‐Met‐OAl and Gly‐Trp‐Met‐Asp(OMe)‐Phe‐NH2 with immobilized α‐chymotrypsin. The Bz‐Arg group was used as an N‐terminal protecting group in the synthesis of the tripeptide fragment. The protected CCK‐8 was treated with trypsin to remove the Bz‐Arg group successfully. Free or immobilized enzymes were used as catalysts. The effect of the acyl donor ester structure, the C(α) protecting group of the nucleophile, reaction media, enzyme, and the carrier of the enzymes on the outcome of the coupling reaction was studied.

Protease-catalyzed synthesis of the tripeptide CCK26–28, a fragment of CCK-8

Two enzymatically synthetic strategies of the tripeptide derivative PhAc-Asp(OMe)-Tyr-Met-OAl are reported. The second strategy gains the advantage of more economical starting materials, less reaction steps and a higher overall isolated yield of this tripeptide fragment over the first strategy. The effect of the acyl-donor ester concentration and structure, the C-alpha protecting group of the nucleophile, reaction media, enzyme and the carrier on the tripeptide derivative synthesis were studied. This tripeptide selected is a fragment of the cholecystokinin C-terminal octapeptide (CCK-8), a potential therapeutic agent in the control of gastrointestinal function and also a drug candidate for the treatment of epilepsy.

Targeted disruption of the murine CCK1 receptor gene reduces intestinal lipid-induced feedback inhibition of gastric function

Cholecystokinin (CCK), acting at CCK1 receptors (CCK1Rs) on intestinal vagal afferent terminals, has been implicated in the control of gastrointestinal function and food intake. Using CCK1R(-/-) mice, we tested the hypothesis that lipid-induced activation of the vagal afferent pathway and intestinal feedback of gastric function is CCK1R dependent. In anesthetized CCK1R(+/+) ("wild type") mice, meal-stimulated gastric acid secretion was inhibited by intestinal lipid infusion; this was abolished in CCK1R(-/-) mice. Gastric emptying of whole egg, measured by nuclear scintigraphy in awake mice, was significantly faster in CCK1R(-/-) than CCK1R(+/+) mice. Gastric emptying of chow was significantly slowed in response to administration of CCK-8 (22 pmol) in CCK1R(+/+) but not CCK1R(-/-) mice. Activation of the vagal afferent pathway was measured by immunohistochemical localization of Fos protein in the nucleus of the solitary tract (NTS; a region where vagal afferents terminate). CCK-8 (22 pmol ip) increased neuronal Fos expression in the NTS of fasted CCK1R(+/+) mice; CCK-induced Fos expression was reduced by 97% in CCK1R(-/-) compared with CCK1R(+/+) mice. Intralipid (0.2 ml of 20% Intralipid and 0.04 g lipid), but not saline, gavage increased Fos expression in the NTS of fasted CCK1R(+/+) mice; lipid-induced Fos expression was decreased by 47% in CCK1R(-/-) compared with CCK1R(+/+)mice. We conclude that intestinal lipid activates the vagal afferent pathway, decreases gastric acid secretion, and delays gastric emptying via a CCK1R-dependent mechanism. Thus, despite a relatively normal phenotype, intestinal feedback in response to lipid is severely impaired in these mice.

Glial cells in the gut

The enteric nervous system is composed of both neurons and glia. Recent evidence indicates that enteric glia-which vastly outnumber enteric neurons-are actively involved in the control of gastrointestinal functions: they contain neurotransmitter precursors, have the machinery for uptake and degradation of neuroligands, and express neurotransmitter-receptors which makes them well suited as intermediaries in enteric neurotransmission and information processing in the ENS. Novel data further suggest that enteric glia have an important role in maintaining the integrity of the mucosal barrier of the gut. Finally, enteric glia may also serve as a link between the nervous and immune systems of the gut as indicated by their potential to synthesize cytokines, present antigen and respond to inflammatory insults. The role of enteric glia in human disease has not yet been systematically studied, but based on the available evidence it is predictable that enteric glia are involved in the etiopathogenesis of various pathological processes in the gut, particularly such with neuroinflammatory or neurodegenerative components.

The pattern of c-Fos immunoreactivity in the hindbrain of the rat following stomach distension.

It has been previously shown that the walls of the stomach contain vagal and splanchnic afferents, connected to low and high threshold (LT and HT) gastric receptors, that convey physiological and noxious information to areas of the hindbrain involved mainly in the control of gastrointestinal function. Because distension of the stomach also reflexly increases the sympathetic drive to the cardiovascular system, the present study was planned to examine the pattern of activation of all nuclei encountered throughout the hindbrain in response to gastric distension. In anaesthetized rats, the stimulus was controlled by employing different transmural pressures and frequencies of distension, and c-Fos immunohistochemistry was used to characterize neuronal activation. Low intensity stimulation induced c-Fos expression in the cranial part of nucleus of solitary tract (NTS), the nucleus ambiguus (NA), the lateral reticular area (LRt) and the ventrolateral medulla (RVL/CVL). At low frequency of stimulation c-Fos positive nuclei (p.n.) were found in NTS only. At high frequency of stimulation an increase in c-Fos immunoreactivity was found. High intensity stimulation induced c-Fos expression in area postrema (AP), the lateral vestibular nucleus (LVe) and the caudal part of the NTS. At low frequency, only the number of c-Fos p.n. was increased. Increasing the frequency of stimulation induced c-Fos expression in further nuclei such as the parabrachial nucleus (PBN), the inferior olive subnuclei (IOn), the oral part of spinal trigeminal nucleus (Sp5O) and locus coeruleus (LC). At higher frequencies c-Fos immunoreactivity decreased in NTS and LRt, disappeared in VLM and increased in NA. Thus stomach distension activated several neuronal excitatory and inhibitory circuits that are involved in the control of gastrointestinal function as well as in cardiovascular, respiratory and pain regulation. The differences in c-Fos immunoreactivity induced by changing the distension patterns suggested interactions between groups of vagal and splanchnic afferents.

Molecular mechanisms in the control of gastrointestinal function

Molecular mechanisms in the control of gastrointestinal function

Molecular mechanisms in the control of gastrointestinal function

Molecular mechanisms in the control of gastrointestinal function

Leptin acts in the rat hypothalamic paraventricular nucleus to induce gastric mucosal damage.

Leptin is produced and secreted by adipocytes to regulate body weight homeostasis. Leptin acts centrally to reduce weight by decreasing food intake and increasing energy expenditure. The paraventricular nucleus (PVN) is a central nervous system structure suggested as a site at which leptin acts to exert its central effects. Leptin microinjection (10(-6) M, 0.5 microl) into the PVN of urethan-anesthetized male Sprague-Dawley rats (150-300 g) resulted in significant gastric damage (mean score = 1.75, n = 16). Damage scores were significantly different than those observed after saline microinjection into the PVN (mean score = 0.00, n = 5, P < 0. 05), or leptin microinjection into non-PVN sites (mean score = 0.33, n = 6, P < 0.05). There were no changes in blood pressure (mean area under curve = 401.9 +/- 224.2 mmHg * s, n = 11, P > 0.05) or heart rate (mean area under curve = 40.9 +/- 25.9 beats, n = 10, P > 0.05) in response to leptin microinjection into PVN. These results suggest that leptin acts on a functionally specific population of PVN neurons involved in the control of gastrointestinal function.

Epidermal growth factor (EGF)

Despite the wealth of information concerning EGF and its related peptides, its precise role in the control of gastrointestinal functions is still not fully resolved. However, there is no doubt that it can have some very potent effects on the gastrointestinal tract. These may be related to the control of growth and development and to the regular control of cell renewal. Nevertheless, in the adult, EGF may only be active in response to luminal damage and repair, and furthermore this may also only occur if the luminal EGF is protected from proteolytic degradation. Notwithstanding this, ‘EGF’-like responses may be evoked in the gut by intestinal TGF-α. The possible therapeutic use of EGF and members of its family in ulcer therapy will be discussed in later Chapters of this volume, other potential uses are in the control of necrotising enteritis and in the alleviation of the mucositis associated with cancer treatment.

Interstitial cells of Cajal: are they major players in control of gastrointestinal motility?

AbstractThis review examines recent evidence from structural and functional studies that interstitial cells of Cajal (ICC) play a major role in control of gastrointestinal function. These cells, identified to date only by their structural and somewhat selective staining characteristics, form networks in the region of the myentehc plexus and in or adjacent to circular muscle. Those in circular muscle are often coupled to one another and to smooth muscle cells by gap junctions and are closely innervated by a high proportion of enteric nerves, especially those containing vasoactive intestinal polypeptide (VIP). ICC in the myenteric plexus often have no visible connections by gap junctions to smooth muscle. There is a growing body of evidence from study of small intestine and colon that these cells are either the pacemakers or provide clocks for the pacemaking function of the gut (vahously known as slow waves, pacesetter potentials or control potentials). Additional evidence suggests that they may play a role in neurotransmission of non‐adrenergic, non‐cholinergic inhibitory activity. This review summarizes our current understanding and attempts to point the way for future research.

Dorsal medullary injection of atrial natriuretic factor (ANF) excites vagal efferents and inhibits gastric motility

Atrial natriuretic factor (ANF)-immunoreactive fibers are found in the dorsal motor nucleus of the vagus (DMN) along with receptors for that peptide. Previous investigations showed that ANF injections into the DMN did not influence cardiovascular functions. Since the DMN is largely (but not exclusively) involved with the control of gastrointestinal functions, we hypothesized that ANF may act on gastric, rather than cardiovascular vagal efferents. Injections of ANF (20 pmol rat atriopeptin III in 20 nl) into the DMN evoked a vagally dependent reduction in gastric motility. In a separate electrophysiological study, 10 of 15 (66%) antidromically identified DMN neurons were excited by micropressure-applied ANF (25–500 fmol in 50–1000 pl). We propose that ANF-containing neurons in the DMN reduce gastric motility by activating vagal efferents that synapse with inhibitory neurons in the gastric enteric nervous system.

Endothelin in the gastrointestinal tract: Presence of endothelinlike immunoreactivity, endothelin-1 messenger RNA, endothelin receptors, and pharmacological effect

The possible production and role of endothelin in the gastrointestinal tract was investigated in rats by radioimmunoassay, Northern-blot hybridization, receptor assay using membrane preparations, and pharmacological study using gut strips. Endothelinlike immunoreactivity was detected in all regions (from stomach to colon) of the rat gastrointestinal tract (13–48 fmol/g wet tissue) including the mucosal layer of the ileum and colon (8.4 ± 2.0 fmol/g wet tissue and 18.4 ± 2.1 fmol/g wet tissue, respectively, mean ± SEM; n = 5). Fast protein liquid chromatographic analysis of the endothelinlike immunoreactivity in jejunum, ileum, colon, and colon mucosa extracts showed peaks in the positions of endothelin-1 and endothelin-3. The presence of endothelin-1 messenger RNA was demonstrated by Northern-blot hybridization in the whole colon and pooled ileal and colonic mucosa, but not in the whole jejunum. Specific binding in the rat gastrointestinal tract was particularly high in the fundus of stomach, jejunum, ileum, and colon. In the ileum, many binding sites were found in the circular and longitudinal muscle layers, but few in the mucosal layer. Endothelin-1 and endothelin-3 caused contraction of rat stomach strips, rat colon, and guinea pig ileum. These findings indicate that endothelin is present in the rat gastrointestinal tract, perhaps produced by both vascular endothelial cells and mucosal epithelial cells, and can cause contraction of gastrointestinal smooth muscle. Thus, endothelin may have a physiological role in the control of gastrointestinal function.

Identification of peptidergic nervous control of gastrointestinal functions.

The last 10–12 years of research have revealed that the entire gastrointestinal tract has a dense innvervation of peptidergic nerves, i.e. nerves that contain neuropeptides [2]. However, the precise physiological role of the neuropeptides has proven very difficult to define. An additional problem was presented by the recent identification of co-existing transmitters in the gastrointestinal nerve fibres. Thus acetylcholine has been demonstrated to co-exist with peptides; amines (noradrenaline, dopamine) with peptides, and neuropeptides with other neuropeptides [15].