CRF microinjected into the dorsal vagal complex inhibits TRH analog- and kainic acid-stimulated gastric contractility in rats

Inflammation and Impaired Gut Physiology in Post-operative Ileus: Mechanisms and the Treatment Options

Post-operative ileus (POI) is the transient cessation of coordinated gastrointestinal motility after abdominal surgical intervention. It decreases quality of life, prolongs length of hospital stay, and increases socioeconomic costs. The mechanism of POI is complex and multifactorial, and has been broadly categorized into neurogenic and inflammatory phase. Neurogenic phase mediated release of corticotropin-releasing factor (CRF) plays a central role in neuroinflammation, and affects both central autonomic response as well hypothalamic-pituitary-adrenal (HPA) axis. HPA-stress axis associated cortisol release adversely affects gut microbiota and permeability. Peripheral CRF (pCRF) is a key player in stress induced gastric emptying and colonic transit. It functions as a local effector and interacts with the CRF receptors on the mast cell to release chemical mediators of inflammation. Mast cells proteases disrupt epithelial barrier via protease activated receptor-2 (PAR-2). PAR-2 facilitates cytoskeleton contraction to reorient tight junction proteins such as occludin, claudins, junctional adhesion molecule, and zonula occludens-1 to open epithelial barrier junctions. Barrier opening affects the selectivity, and hence permeation of luminal antigens and solutes in the gastrointestinal tract. Translocation of luminal antigens perturbs mucosal immune system to further exacerbate inflammation. Stress induced dysbiosis and decrease in production of short chain fatty acids add to the inflammatory response and barrier disintegration. This review discusses potential mechanisms and factors involved in the pathophysiology of POI with special reference to inflammation and interlinked events such as epithelial barrier dysfunction and dysbiosis. Based on this review, we recommend CRF, mast cells, macrophages, and microbiota could be targeted concurrently for efficient POI management.

Central Neurocircuits Regulating Food Intake in Response to Gut Inputs-Preclinical Evidence

The regulation of energy balance requires the complex integration of homeostatic and hedonic pathways, but sensory inputs from the gastrointestinal (GI) tract are increasingly recognized as playing critical roles. The stomach and small intestine relay sensory information to the central nervous system (CNS) via the sensory afferent vagus nerve. This vast volume of complex sensory information is received by neurons of the nucleus of the tractus solitarius (NTS) and is integrated with responses to circulating factors as well as descending inputs from the brainstem, midbrain, and forebrain nuclei involved in autonomic regulation. The integrated signal is relayed to the adjacent dorsal motor nucleus of the vagus (DMV), which supplies the motor output response via the efferent vagus nerve to regulate and modulate gastric motility, tone, secretion, and emptying, as well as intestinal motility and transit; the precise coordination of these responses is essential for the control of meal size, meal termination, and nutrient absorption. The interconnectivity of the NTS implies that many other CNS areas are capable of modulating vagal efferent output, emphasized by the many CNS disorders associated with dysregulated GI functions including feeding. This review will summarize the role of major CNS centers to gut-related inputs in the regulation of gastric function with specific reference to the regulation of food intake.

Brain and Gut CRF Signaling: Biological Actions and Role in the Gastrointestinal Tract

BACKGROUND

Corticotropin-releasing factor (CRF) pathways coordinate behavioral, endocrine, autonomic and visceral responses to stress. Convergent anatomical, molecular, pharmacological and functional experimental evidence supports a key role of brain CRF receptor (CRF-R) signaling in stress-related alterations of gastrointestinal functions. These include the inhibition of gastric acid secretion and gastric-small intestinal transit, stimulation of colonic enteric nervous system and secretorymotor function, increase intestinal permeability, and visceral hypersensitivity. Brain sites of CRF actions to alter gut motility encompass the paraventricular nucleus of the hypothalamus, locus coeruleus complex and the dorsal motor nucleus while those modulating visceral pain are localized in the hippocampus and central amygdala. Brain CRF actions are mediated through the autonomic nervous system (decreased gastric vagal and increased sacral parasympathetic and sympathetic activities). The activation of brain CRF-R2 subtype inhibits gastric motor function while CRF-R1 stimulates colonic secretomotor function and induces visceral hypersensitivity. CRF signaling is also located within the gut where CRF-R1 activates colonic myenteric neurons, mucosal cells secreting serotonin, mucus, prostaglandin E2, induces mast cell degranulation, enhances mucosal permeability and propulsive motor functions and induces visceral hyperalgesia in animals and humans. CRF-R1 antagonists prevent CRF- and stressrelated gut alterations in rodents while not influencing basal state.

DISCUSSION

These preclinical studies contrast with the limited clinical positive outcome of CRF-R1 antagonists to alleviate stress-sensitive functional bowel diseases such as irritable bowel syndrome.

CONCLUSION

The translational potential of CRF-R1 antagonists in gut diseases will require additional studies directed to novel anti-CRF therapies and the neurobiology of brain-gut interactions under chronic stress.

Corticotrophin-releasing factor-mediated effects of DA-9701 in Postoperative Ileus Guinea Pig Model

BACKGROUND

Postoperative ileus (POI) is abdominal surgery-induced impaired gastrointestinal (GI) motility. We aimed to investigate the effects of DA-9701, a prokinetic agent formulated from Pharbitis Semen and Corydalis tuber, likely mediated via corticotrophin-releasing factor (CRF) pathways, in a POI model.

METHODS

A laparotomy with cecal manipulation was performed to induce POI in guinea pigs. GI transit was measured based on charcoal migration after intragastric administration of DA-9701 1, 3, and 10 mg kg^-1 . CRF1 receptor antagonist, CP-154 526 (subcutaneous) or agonist, human/rat (h/r) CRF (intraperitoneal) was injected. Then, plasma adrenocorticotropic hormone (ACTH) levels were measured, and the average intensity of the CRF expression was analyzed in the proximal colon and hypothalamus, and c-Fos in the hypothalamus.

KEY RESULTS

DA-9701 significantly increased delayed GI transit in POI in a dose-dependent manner and decreased plasma ACTH levels at 10 mg kg^-1 . CP-154 526 significantly decreased plasma ACTH levels but was not as effective on GI transit as DA-9701 was. h/r CRF did not significantly affect GI transit and plasma ACTH levels. No significant difference was observed in GI transit and plasma ACTH levels in both groups administered DA-9701 with h/r CRF and h/r CRF alone. CRF expression in the proximal colon decreased after DA-9701 administration, but not significantly, compared with levels in POI alone. However, CRF expression in the hypothalamus was significantly lower in the DA-9701-pretreated POI than in the untreated POI.

CONCLUSIONS AND INFERENCES

The DA-9701-induced improvement in GI transit and inhibition of plasma ACTH levels was mediated by the central CRF pathway.

Fourth ventricular CART peptide induces c-fos in the area postrema and nucleus of the solitary tract via a CRF-receptor dependent mechanism

Cocaine-and amphetamine-regulated transcript peptides (CARTp) suppress gastric emptying and nutritional intake following 4th icv administration. Whereas, the CARTp inhibition of gastric emptying was blocked by pre-treatment with a non-selective corticotropin releasing factor (CRF) antagonist, sucrose drinking was not, suggesting that CARTp- and CRF controls for food intake and gastric emptying are operated through separable dorsal hindbrain mechanisms. The aim of the study was to explore CARTp-CRF brainstem interactions on patterns of neuronal activation in areas of the brainstem and midbrain relevant to gastrointestinal control and feeding regulation. Rats received 4th icv injections of combinations of vehicle, CARTp (1μg), or the nonselective CRF antagonist, α-helical CRF9-41 (αCRF), in a randomized order. Brain sections were processed for c-fos by immunohistochemistry followed by image analysis at defined levels of the brain. CARTp (1μg, 4th icv) induced a robust c-fos response in the nucleus of the solitary tract (NTS) and area postrema (AP), whereas, no c-fos could be detected in the parabrachial nucleus (PBN), the paraventricular nucleus of the hypothalamus (PVN) or the arcuate nucleus of the hypothalamus (ARC). The c-fos expression in the structures of the dorsal vagal complex (DVC) was completely blocked by pre-treatment with the CRF antagonist, which did not by itself induce c-fos at any examined level. After CARTp and αCRF in combination, there was a tendency towards an increased c-fos response in the ARC. We conclude that CARTp activates cells of the area postrema and NTS via a downstream, CRF-dependent mechanism.

Central nervous system control of gastrointestinal motility and secretion and modulation of gastrointestinal functions

Although the gastrointestinal (GI) tract possesses intrinsic neural plexuses that allow a significant degree of autonomy over GI functions, the central nervous system (CNS) provides extrinsic neural inputs that regulate, modulate, and control these functions. While the intestines are capable of functioning in the absence of extrinsic inputs, the stomach and esophagus are much more dependent upon extrinsic neural inputs, particularly from parasympathetic and sympathetic pathways. The sympathetic nervous system exerts a predominantly inhibitory effect upon GI muscle and provides a tonic inhibitory influence over mucosal secretion while, at the same time, regulates GI blood flow via neurally mediated vasoconstriction. The parasympathetic nervous system, in contrast, exerts both excitatory and inhibitory control over gastric and intestinal tone and motility. Although GI functions are controlled by the autonomic nervous system and occur, by and large, independently of conscious perception, it is clear that the higher CNS centers influence homeostatic control as well as cognitive and behavioral functions. This review will describe the basic neural circuitry of extrinsic inputs to the GI tract as well as the major CNS nuclei that innervate and modulate the activity of these pathways. The role of CNS-centered reflexes in the regulation of GI functions will be discussed as will modulation of these reflexes under both physiological and pathophysiological conditions. Finally, future directions within the field will be discussed in terms of important questions that remain to be resolved and advances in technology that may help provide these answers.

Plasticity in the brainstem vagal circuits controlling gastric motor function triggered by corticotropin releasing factor

Stress impairs gastric emptying, reduces stomach compliance and induces early satiety via vagal actions. We have shown recently that the ability of the anti-stress neuropeptide oxytocin (OXT) to modulate vagal brainstem circuits undergoes short-term plasticity via alterations in cAMP levels subsequent to vagal afferent fibre-dependent activation of metabotropic glutamate receptors. The aim of the present study was to test the hypothesis that the OXT-induced gastric response undergoes plastic changes in the presence of the prototypical stress hormone, corticotropin releasing factor (CRF). Whole cell patch clamp recordings showed that CRF increased inhibitory GABAergic synaptic transmission to identified corpus-projecting dorsal motor nucleus of the vagus (DMV) neurones. In naive brainstem slices, OXT perfusion had no effect on inhibitory synaptic transmission; following exposure to CRF (and recovery from its actions), however, re-application of OXT inhibited GABAergic transmission in the majority of neurones tested. This uncovering of the OXT response was antagonized by pretreatment with protein kinase A or adenylate cyclase inhibitors, H89 and di-deoxyadenosine, respectively, indicating a cAMP-mediated mechanism. In naive animals, OXT microinjection in the dorsal vagal complex induced a NO-mediated corpus relaxation. Following CRF pretreatment, however, microinjection of OXT attenuated or, at times reversed, the gastric relaxation which was insensitive to l-NAME but was antagonized by pretreatment with a VIP antagonist. Immunohistochemical analyses of vagal motoneurones showed an increased number of oxytocin receptors present on GABAergic terminals of CRF-treated or stressed vs. naive rats. These results indicate that CRF alters vagal inhibitory circuits that uncover the ability of OXT to modulate GABAergic currents and modifies the gastric corpus motility response to OXT.

Modulation of gastric motility by brain-gut peptides using a novel non-invasive miniaturized pressure transducer method in anesthetized rodents

Acute in vivo measurements are often the initial, most practicable approach used to investigate the effects of novel compounds or genetic manipulations on the regulation of gastric motility. Such acute methods typically involve either surgical implantation of devices or require intragastric perfusion of solutions, which can substantially alter gastric activity and may require extended periods of time to allow stabilization or recovery of the preparation. We validated a simple, non-invasive novel method to measure acutely gastric contractility, using a solid-state catheter pressure transducer inserted orally into the gastric corpus, in fasted, anesthetized rats or mice. The area under the curve of the phasic component (pAUC) of intragastric pressure (IGP) was obtained from continuous manometric recordings of basal activity and in responses to central or peripheral activation of cholinergic pathways, or to abdominal surgery. In rats, intravenous ghrelin or intracisternal injection of the thyrotropin-releasing hormone agonist, RX-77368, significantly increased pAUC while coeliotomy and cacal palpation induced a rapid onset inhibition of phasic activity lasting for the 1-h recording period. In mice, RX-77368 injected into the lateral brain ventricle induced high-amplitude contractions, and carbachol injected intraperitoneally increased pAUC significantly, while coeliotomy and cecal palpation inhibited baseline contractile activity. In wild-type mice, cold exposure (15 min) increased gastric phasic activity and tone, while there was no gastric response in corticotropin releasing factor (CRF)-overexpressing mice, a model of chronic stress. Thus, the novel solid-state manometric approach provides a simple, reliable means for acute pharmacological studies of gastric motility effects in rodents. Using this method we established in mice that the gastric motility response to central vagal activation is impaired under chronic expression of CRF.

Cold ambient temperature reverses abdominal surgery-induced delayed gastric emptying and decreased plasma ghrelin levels in rats

We investigated whether acute cold-induced vagal activation through brainstem thyrotropin-releasing hormone (TRH) signaling influences abdominal surgery-induced delayed gastric emptying (GE) in fasted rats. Laparotomy and cecal palpation or sham (short anesthesia alone) was performed 10 min before or 30 min after cold exposure (4-6°C) lasting 90 min. Non-nutrient GE was assessed during 70-90 min of cold exposure. Control groups remained at room temperature (RT). The stable TRH analog, RX-77368 (50 ng/rat) was injected intracisternally immediately before surgery and GE monitored 30-50 min postsurgery in rats maintained at RT. Plasma acyl (AG) and total ghrelin levels were assessed using the new RAPID blood processing method and radioimmunoassays. Desacyl ghrelin (DAG) was derived from total minus AG. In rats maintained at RT, abdominal surgery decreased GE by 60% compared to sham. Cold before or after surgery or RX-77368 normalized the delayed GE. In non-fasted rats, cold exposure increased plasma AG and DAG levels at 2 h (2.4- and 2.7-times, respectively) and 4 h (2.2- and 2.0-times, respectively) compared to values in rats maintained at RT. In fasted rats, abdominal surgery decreased AG and DAG levels by 2.4- and 2.1-times, respectively, at 90 min. Cold for 90 min after surgery normalized AG and DAG levels to those observed in sham-treated animals kept at RT. These data indicate that endogenous (cold exposure) and exogenous (TRH analog) activation of medullary TRH vagal signaling prevent abdominal surgery-induced delayed GE. The restoration of circulating AG levels inhibited by abdominal surgery may contribute to alleviate postoperative gastric ileus.

Corticotropin-releasing factor signaling and visceral response to stress

Stress may cause behavioral and/or psychiatric manifestations such as anxiety and depression and also impact on the function of different visceral organs, namely the gastrointestinal and cardiovascular systems. During the past years substantial progress has been made in the understanding of the underlying mechanisms recruited by stressors. Activation of the corticotropin-releasing factor (CRF) signaling system is recognized to be involved in a large number of stress-related behavioral and somatic disorders. This review will outline the present knowledge on the distribution of the CRF system (ligands and receptors) expressed in the brain and peripheral viscera and its relevance in stress-induced alterations of gastrointestinal and cardiovascular functions and the therapeutic potential of CRF(1) receptor antagonists.

Neuroendocrine control of the gut during stress: corticotropin-releasing factor signaling pathways in the spotlight

Stress affects the gastrointestinal tract as part of the visceral response. Various stressors induce similar profiles of gut motor function alterations, including inhibition of gastric emptying, stimulation of colonic propulsive motility, and hypersensitivity to colorectal distension. In recent years, substantial progress has been made in our understanding of the underlying mechanisms of stress's impact on gut function. Activation of corticotropin-releasing factor (CRF) signaling pathways mediates both the inhibition of upper gastrointestinal (GI) and the stimulation of lower GI motor function through interaction with different CRF receptor subtypes. Here, we review how various stressors affect the gut, with special emphasis on the central and peripheral CRF signaling systems.

Corticotropin-releasing factor (CRF) receptor type 2 in the human stomach: protective biological role by inhibition of apoptosis

Corticotropin-releasing factor agonists exert inhibitory effects in stomach functions possibly through peripheral routes. We have previously reported the expression of Urocortin (Ucn) I, an endogenous ligand of both CRF receptor types CRF(1) and CRF(2), in the human stomach. We examined CRF(1) and CRF(2) expression in the same tissue. Using RT-PCR, CRF(2) but not CRF(1) transcripts were detected in RNA extracts from normal human stomach. In addition, immunohistochemical analysis revealed receptor protein in epithelial gastric cells. In order to investigate the biological role of CRF(2) in these cells, an in vitro model was established, using the gastric cancer cell line AGS transiently transfected to express functional CRF(2). The effect of the CRF(2) endogenous ligands CRF, Ucns I and II on the growth parameters of the AGS/CRF(2) was examined. After 1 day of exposure, all three ligands reduced the degree of apoptosis (16%-19%, n = 9, P < 0.05) compared to non-treated controls and this effect was observed for 3 days of treatment. No such effect was detected in non-transfected cells, suggesting mediation through CRF(2) receptors. Administration of CRF, Ucns I and II had no effect on the proliferation rate of AGS/CRF(2) cells or on the release of PGE(2) by them. Our results demonstrate CRF(2) expression in the human gastric mucosa and indicate a physiological role of this receptor type in regulating apoptosis, an important parameter of gastric cell regeneration. Paracrine effects exerted by locally expressed endogenous ligands, such as Ucn I, support a significant role of the peripheral CRF system in gastric physiology. J. Cell. Physiol. 209: 905-911, 2006. (c) 2006 Wiley-Liss, Inc.

The corticotropin-releasing factor receptor: a novel target for the treatment of depression and anxiety-related disorders

The treatment of mood disorders has been the subject of intense study for more than half a century and has resulted in the discovery and availability of a number of compounds that have seen tremendous success in the management of major depression and anxiety-related disorders. In spite of this success, these drugs have not provided a complete therapeutic solution for all patients and this has revitalised the need for a greater understanding of the underlying molecular mechanisms and targets involved in these disorders. Elucidation of these novel targets will enable the development of a better class of compounds which could benefit a greater majority of the patient population and be devoid of the current side effect liabilities. Towards that end, this review examines, in detail, the prospect of one such target, the corticotropin-releasing factor system, as having an enhanced therapeutic profile with the potential of a broader range of efficacy with reduced side effect liabilities.

A reevaluation of the effects of stimulation of the dorsal motor nucleus of the vagus on gastric motility in the rat

Our primary purpose was to characterize vagal pathways controlling gastric motility by microinjecting l-glutamate into the dorsal motor nucleus of the vagus (DMV) in the rat. An intragastric balloon was used to monitor motility. In 39 out of 43 experiments, microinjection of l-glutamate into different areas of the DMV rostral to calamus scriptorius (CS) resulted in vagally mediated excitatory effects on motility. We observed little evidence for inhibitory effects, even with intravenous atropine or with activation of gastric muscle muscarinic receptors by intravenous bethanechol. Inhibition of nitric oxide synthase with N(omega)-nitro-l-arginine methyl ester (l-NAME) HCl did not augment DMV-evoked excitatory effects on gastric motility. Microinjection of l-glutamate into the DMV caudal to CS produced vagally mediated gastric inhibition that was resistant to l-NAME. l-Glutamate microinjected into the medial subnucleus of the tractus solitarius (mNTS) also produced vagally mediated inhibition of gastric motility. Motility responses evoked from the DMV were always blocked by ipsilateral vagotomy, while responses evoked from the mNTS required bilateral vagotomy to be blocked. Microinjection of oxytocin into the DMV inhibited gastric motility, but the effect was never blocked by ipsilateral vagotomy, suggesting that the effect may have been due to diffusion of oxytocin to the mNTS. Microinjection of substance P and N-methyl-d-aspartate into the DMV also produced inhibitory effects attributable to excitation of nearby mNTS neurons. Our results do not support previous studies indicating parallel vagal excitatory and inhibitory pathways originating in the DMV rostral to CS. Our results do support previous findings of vagal inhibitory pathways originating in the DMV caudal to CS.

Corticotropin-releasing hormone, arginine vasopressin, gastrin-releasing peptide, and neuromedin B alterations in stress-relevant brain regions of suicides and control subjects

BACKGROUND

Postmortem levels of several stress- and depression-relevant neuropeptides were assessed in brain regions of depressed suicides relative to control subjects that had died of other causes.

METHODS

Brains of suicides and those that died from other causes were collected soon after death (typically <6 hours). Immunoreactivity levels (ir) of corticotropin-releasing hormone (CRH-ir) and arginine vasopressin (AVP-ir), and the bombesin analogs, gastrin-releasing peptide (GRP-ir), and neuromedin B (NMB-ir), were assessed.

RESULTS

Levels of CRH-ir among suicides were elevated in the locus coeruleus (LC), frontopolar, dorsolateral prefrontal (DMPFC) and ventromedial prefrontal cortices, but were reduced at the dorsovagal complex (DVC). The concentration of AVP-ir was elevated at the paraventricluar hypothalamic nucleus, LC, and DMPFC, and reduced at the DVC. Finally, GRP and NMB variations, which might influence anxiety states, were limited, although GRP-ir within the LC of suicides was higher than in control subjects, while NMB-ir was reduced at the DVC of suicides.

CONCLUSIONS

The data show several neuropeptide changes in relation to suicide, although it is premature to ascribe these outcomes specifically to the suicide act versus depression. Likewise, it is uncertain whether the neuropeptide alterations were etiologically related to suicide/depression or secondary to the depressive state.

Role of brainstem TRH/TRH-R1 receptors in the vagal gastric cholinergic response to various stimuli including sham-feeding

Pavlov's pioneering work established that sham-feeding induced by sight or smell of food or feeding in dogs with permanent esophagostomy stimulates gastric acid secretion through vagal pathways. Brain circuitries and transmitters involved in the central vagal regulation of gastric function have recently been unraveled. Neurons in the dorsal vagal complex including the dorsal motor nucleus of the vagus (DMN) express thyrotropin-releasing hormone (TRH) receptor and are innervated by TRH fibers originating from TRH synthesizing neurons in the raphe pallidus, raphe obscurus and the parapyramidal regions. TRH injected into the DMN or cisterna magna increases the firing of DMN neurons and gastric vagal efferent discharge, activates cholinergic neurons in gastric submucosal and myenteric plexuses, and induces a vagal-dependent, atropine-sensitive stimulation of gastric secretory (acid, pepsin) and motor functions. TRH antibody or TRH-R1 receptor oligodeoxynucleotide antisense pretreatment in the cisterna magna or DMN abolished vagal-dependent gastric secretory and motor responses to sham-feeding, 2-deoxy-D-glucose, cold exposure and chemical activation of cell bodies in medullary raphe nuclei. TRH excitatory action in the DMN is potentiated by co-released prepro-TRH-(160-169) flanking peptide, Ps4 and 5-HT, and inhibited by a number of peptides involved in the stress/immune response and inhibition of food-intake. These neuroanatomical, electrophysiological and neuropharmacological data are consistent with a physiological role of brainstem TRH in the central vagal stimulation of gastric myenteric cholinergic neurons in response to several vagal dependent stimuli including sham-feeding.

Urocortin 2 acts centrally to delay gastric emptying through sympathetic pathways while CRF and urocortin 1 inhibitory actions are vagal dependent in rats

We characterized the influence of the selective corticotropin-releasing factor 2 (CRF(2)) receptor agonist human urocortin 2 (Ucn 2), injected intracisternally, on gastric emptying and its mechanism of action compared with intracisternal CRF or urocortin (Ucn 1) in conscious rats. The methylcellulose phenol red solution was gavaged 20 min after peptide injection, and gastric emptying was measured 20 min later. The intracisternal injection of Ucn 2 (0.1 and 1 microg) and Ucn 1 (1 microg) decreased gastric emptying to 37.8 +/- 6.9%, 23.1 +/- 8.6%, and 21.6 +/- 5.9%, respectively, compared with 58.4 +/- 3.8% after intracisternal vehicle. At lower doses, Ucn 2 (0.03 microg) and Ucn 1 (0.1 microg) had no effect. The CRF(2) antagonist astressin(2)-B (3 microg ic) antagonized intracisternal Ucn 2 (0.1 microg) and CRF (0.3 microg)-induced inhibition of gastric emptying. Vagotomy enhanced intracisternal Ucn 2 (0.1 or 1 microg)-induced inhibition of gastric emptying compared with sham-operated group, whereas it blocked intracisternal CRF (1 microg) inhibitory action (45.5 +/- 8.4% vs. 9.7 +/- 9.7%). Sympathetic blockade by bretylium prevented intracisternal and intracerebroventricular Ucn 2-induced delayed gastric emptying, whereas it did not influence intravenous Ucn 2-, intracisternal CRF-, and intracisternal Ucn 1-induced inhibition of gastric emptying. Prazosin abolished the intracisternal Ucn 2 inhibitory effect, whereas yohimbine and propranolol did not. None of the pretreatments modified basal gastric emptying. These data indicate that intracisternal Ucn 2 induced a central CRF(2)-mediated inhibition of gastric emptying involving sympathetic alpha(1)-adrenergic mechanisms independent from the vagus contrasting with the vagal-dependent inhibitory actions of CRF and Ucn 1.

The dorsal vagal complex as a site for cocaine- and amphetamine-regulated transcript peptide to suppress gastric emptying

Cocaine- and amphetamine-regulated transcript-derived peptides (CARTp) and corticotropin-releasing factor (CRF) alter feeding and gastrointestinal function after central administration, and the gastric inhibitory effects are mediated through CRF. We hypothesized that dorsal hindbrain effects of CARTp on gastric emptying are mediated by the vagus nerve and that the dorsal vagal complex (DVC) is a site of action for the gastric inhibitory effects of both CARTp and CRF. Rats were equipped with chronic intragastric fistulas and guide cannulas aimed at the fourth ventricle or the DVC. Fourth intracerebroventricular CARTp-induced suppression of 12 ml glucose (12.5%) gastric emptying during fill was blocked by subdiaphragmatic vagotomy. To establish whether the DVC may be a site of action for CARTp and/or CRF, intraparenchymal microinjections (0.25 microl) of CARTp (0.1 and 0.5 microg) and CRF (5 and 10 pmol) were administered in the DVC. Each dose, previously shown to be ineffective after fourth intracerebroventricular administration, suppressed gastric emptying during gastric fill vs. vehicle, but neither peptide changed gastric secretion volume or gastric acidity. The results indicate that the DVC is a target site for CRF and CARTp to inhibit gastric emptying and that the vagus mediates dorsal hindbrain effects of CARTp on gastric motor function.

Basal and stimulated hypothalamic-pituitary-adrenal axis activity in patients with functional gastrointestinal disorders and healthy controls

OBJECTIVE

The aim of this study was to investigate alterations of pituitary-adrenal activity under both stimulated and unstimulated conditions in patients with functional gastrointestinal disorders.

METHODS

Thirty subjects who fulfilled the Rome Diagnostic Criteria for either irritable bowel syndrome or nonulcer dyspepsia and 24 healthy controls took part in the study. Free salivary morning cortisol and diurnal cortisol profiles were obtained for all subjects. On a second day, a low-dose dexamethasone suppression test was applied. Additionally, in all subjects a corticotropin-releasing hormone (CRH) challenge test was performed.

RESULTS

The results show attenuated unstimulated cortisol levels in patients compared with controls. After CRH challenge, blunted adrenocorticotropic hormone and cortisol responses were observed. These findings suggest lower pituitary and adrenocortical activity in patients with functional gastrointestinal disorders.

CONCLUSION

The observed pituitary-adrenal reactivity in these patients is discussed as a possible consequence of lower adrenocortical activity, possibly resulting in a disinhibition of CRH in the brain.

Corticotropin releasing factor 2 receptor agonists reduce the denervation-induced loss of rat skeletal muscle mass and force and increase non-atrophying skeletal muscle mass and force

Of the two corticotropin releasing factor receptors known, corticotrophin releasing factor 2 receptor (CRF2R) is expressed in skeletal muscle. The function of this receptor in skeletal muscle is at present unknown. In order to better understand the role of the CRF2R in skeletal muscle, we treated rats with CRF2R agonists and evaluated the effect of these agents on normal and denervated muscle mass. Rats treated with the non-selective CRFR agonist, sauvagine, did not demonstrate any significant and consistent change in non-denervated and denervated fast twitch [tibialis anterior (TA) or extensor digitorum longus (EDL)] or slow/mixed twitch [medial gastrocnemius (MG) or soleus] fiber muscle mass. In adrenalectomized rats, sauvagine treatment resulted in no significant and consistent change in non-denervated fast or slow/mixed twitch fiber muscles but did cause a significant and consistent increase in denervated fast twitch (TA and EDL) but not slow/mixed twitch muscle mass. Interestingly adrenalectomy had no effect on the degree of muscle atrophy. Rats treated with the CRF2R selective agonist urocortin 2 demonstrated an increase in non-denervated and denervated fast and slow/mix twitch fiber muscle mass. The urocortin 2 induced increase in muscle mass was accompanied by an increase in muscle fiber cross-sectional area and muscle absolute force. These studies demonstrated that activation of the CRF2R decreased the level of skeletal muscle mass, force, and myocyte cross-sectional area loss resulting from sciatic nerve damage and increased the mass, force and myocyte cross-sectional area of normal (non-atrophying) skeletal muscle. In addition, we also observed that removal of the adrenals increased the effectiveness of the non-selective CRFR agonists sauvagine, presumably via the removal of the pro-atrophy influence of adrenal produced corticosteroids. These results demonstrate that pharmacological modulation of the CRF2R may be a viable method to treat skeletal muscle atrophy.

Urocortins and the regulation of gastrointestinal motor function and visceral pain

Urocortin (Ucn) 1, 2 and 3 are corticotropin-releasing factor (CRF)-related peptides recently characterized in mammals. Urocortin 1 binds with high affinity to CRF type 1 (CRF1) and type 2 (CRF2) receptors while Ucn 2 and Ucn 3 are selective CRF2 ligands. They also have a distinct pattern of distribution, both in the brain and the gastrointestinal tract, compatible with a role mediating, with CRF, the response to stress. In rats and mice, Ucn 1 injected centrally or peripherally inhibited gastric emptying and stimulated colonic propulsive motor function, mimicking the effects of stress or exogenous CRF. Centrally administered Ucn 2 inhibited gastric emptying with similar potency as CRF, while Ucn 1 and Ucn 3 were less potent. However, after peripheral administration, Ucn 1 and Ucn 2 were more potent than CRF. In mice, centrally administered Ucn 1 and 2 stimulated colonic motility with lower potency than CRF, and Ucn 3 was inactive. Studies with selective CRF1 and CRF2 antagonists demonstrated that the gastric-inhibitory and colonic-stimulatory effects of exogenously administered Ucns are mediated through CRF2 and CRF1 receptors, respectively. In addition, Ucn 2 showed visceral anti-nociceptive activity associated with the selective activation of CRF2 receptors. These observations suggest that, acting centrally and peripherally, Ucns might play a significant role in the modulation of gastrointestinal motor and pain responses during stress and stress-related pathophysiological conditions.

Corticotropin-releasing factor 2 receptor localization in skeletal muscle

Our objective in this study was to localize the corticotropin-releasing factor 2 receptor (CRF2R) in rodent and human skeletal muscle. We found CRF2R protein to be abundant in neural tissues in skeletal muscle, including large nerve fibers and bundles, neural tissue associated with mechanoreceptors, muscle spindles, and the Golgi tendon organ. CRF2R protein was also abundant in blood vessels in skeletal muscle. CRF2R protein was also observed, although with less abundance, in the endo/perimysial regions in skeletal muscle. The localization of the CRF2R to blood vessels is consistent with the CRF2R-mediated vascular phenomena observed previously, but the observation of CRF2R in neural tissue in skeletal muscle is a novel finding with an unknown function.

Differential profile of CRF receptor distribution in the rat stomach and duodenum assessed by newly developed CRF receptor antibodies

Peripheral corticotropin-releasing factor (CRF) receptor ligands inhibit gastric acid secretion and emptying while stimulating gastric mucosal blood flow in rats. Endogenous CRF ligands are expressed in the upper gastrointestinal (GI) tissues pointing to local expression of CRF receptors. We mapped the distribution of CRF receptor type 1 (CRF1) and 2 (CRF2) in the rat upper GI. Polyclonal antisera directed against the C-terminus of the CRF receptor protein were generated in rabbits and characterized by western blotting and immunofluorescence using CRF1- and CRF2-transfected cell lines and in primary cultured neurons from rat brain cortex. A selective anti-CRF1 antiserum (4467a-CRF1) was identified and used in parallel with another antiserum recognizing both CRF1 and CRF2 (4392a-CRF1&2) to immunostain gastric tissue sections. Antiserum 4467a-CRF1 demonstrated specific immunostaining in a narrow zone in the upper oxyntic gland within the stomach corpus. Conversely, 4392a-CRF1&2 labeled cells throughout the oxyntic gland and submucosal blood vessels. Pre-absorption with the specific antigen peptide blocked immunostaining in all experiments. Doublestaining showed co-localization of 4392a-CRF1&2 but not 4467a-CRF1 immunoreactivity with H/K-ATPase and somatostatin immunostaining in parietal and endocrine cells of the oxyntic gland. No specific staining was observed in the antrum with either antisera, whereas only antiserum 4392a-CRF1&2 showed modest immunoreactivity in the duodenal mucosa. Finally, co-localization of CRF2 and urocortin immunoreactivity was found in the gastric glands. These results indicate that both CRF receptor subtypes are expressed in the rat upper GI tissues with a distinct pattern and regional differences suggesting differential function.

Stress-induced attenuation of brain stem activation following intestinal anaphylaxis in the rat

Intestinal anaphylaxis triggers neuronal activation in the nucleus tractus solitarius (nTS) of the rat brain stem. Stress may modulate reflex circuitry in the brain stem and facilitate intestinal inflammatory responses. We hypothesized that stress would modulate central neuronal activation during intestinal anaphylaxis. NTS neurons were activated following intestinal antigen challenge in sensitized Hooded Lister rats but not in negative controls (P < 0.05). The number of Fos-positive neurons following intestinal anaphylaxis decreased in animals exposed to water-avoidance stress (P < 0.05), although serum levels of rat mast cell protease II were not different in stressed and unstressed animals, indicating a similar degree of mast cell degranulation. Stress seems to inhibit neuronal activation in the rat brain stem during intestinal inflammation without modulation of the inflammatory response itself. This may have implications for a potential efferent neuronal modulation of inflammatory responses in the gut.

In vitro and in vivo analysis of the effects of corticotropin releasing factor on rat dorsal vagal complex

In vivo and in vitro electrophysiological experiments were performed on the rat dorsal vagal complex (DVC, i.e. nucleus of the tractus solitarius, NTS, and dorsal motor nucleus of the vagus, DMV) to examine the effects of corticotropin releasing hormone (CRF) on the central components of the vago-vagal reflex control of gastric function. When applied to gastrointestinal projecting DMV neurones, CRF (10-300 nM) induced a concentration-dependent membrane depolarization, an increase in action potential firing rate and decrease in amplitude of the action potential afterhyperpolarization (P < 0.05). Pretreatment with the non-selective CRF antagonist, astressin (0.5-1 microM) or the selective CRF(2) receptor antagonist, astressin 2B (500 nM) attenuated the CRF-induced increase in firing rate but did not alter basal discharge rate. CRF (30-300 nM) increased the amplitude of excitatory postsynaptic currents (EPSCs) evoked by stimulation of the NTS (P < 0.05). An alteration in the paired pulse ratio indicated the EPSC's increase occurred due to actions at presynaptic sites. In the in vivo anaesthetized rat preparation, bilateral microinjections (20 fmol in 20 nl for each site) of CRF in the DVC decreased gastric motility in rats pretreated with the muscarinic agonist, bethanecol (P < 0.05). The effects of CRF were abolished by systemic administration of the NOS inhibitor, L-NAME, or by bilateral vagotomy. We concluded that CRF had both a direct and an indirect excitatory effect on DMV neurones via activation of CRF(2) receptors and the decrease in gastric motility observed following microinjection of CRF in the DVC is due to the activation of an inhibitory non-adrenergic non-cholinergic input to the gastrointestinal tract.

Intracisternal urocortin inhibits vagally stimulated gastric motility in rats: role of CRF(2)

1. Corticotropin-releasing factor (CRF) acts in the brain to inhibit thyrotropin-releasing hormone (TRH) analogue, RX-77368-induced vagal stimulation of gastric motility. We investigated CRF receptor-mediated actions of rat urocortin (rUcn) injected intracisternally (ic) on gastric motor function. 2. Urethane-anaesthetized rats with strain gauges on the gastric corpus were injected i.c. with rUcn and 20 min later, with i.c. RX-77368. CRF antagonists were injected i.c. 10 min before rUcn. 3. RX-77368 (1.5, 3, 10, 30 and 100 ng, i.c.) dose-dependently increased corpus contractions, expressed as total area under the curve (AUC, mV min(-1)) to 2.6+/-2.5, 6.1+/-5.9, 9.8+/-2.6, 69.7+/-21.7 and 74.9+/-28.7 respectively vs 0.2+/-0.1 after i.c. saline. Ucn (1, 3 or 10 microg) inhibited RX-77368 (30 ng)-induced increase in total AUC by 28, 62 and 93% respectively vs i.c. saline+RX-77368. 4. The CRF(1)/CRF(2) antagonist, astressin-B (60 microg, i.c.) completely blocked i.c. rUcn (3 microg, i.c.)-induced inhibition of gastric motility stimulated by RX-77368 (30 ng). 5. The selective CRF(2) antagonist, astressin(2)-B (30, 60 or 100 microg, i.c. ) dose-dependently prevented i.c. rUCn action while the CRF(1) antagonist, NBI-27914 did not. 6. In conscious rats, rUcn (0.6 or 1 microg, i.c.) inhibited gastric emptying of an ingested chow meal by 61 and 92% respectively. rUcn action was antagonized by astressin(2)-B. 7. These data show that i.c. rUcn acts through CRF(2) receptors to inhibit central vagal gastric contractile response and postoprandial emptying.

Effects of central and peripheral urocortin on fed and fasted gastroduodenal motor activity in conscious rats

Since few previous studies have examined the effects of urocortin on physiological fed and fasted gastrointestinal motility, we administered urocortin intracerebroventricularly (icv) or intravenously (iv) in freely moving conscious rats and examined the changes in antral and duodenal motility. Icv and iv injection of urocortin disrupted fasted motor patterns of gastroduodenal motility, which were replaced by fed-like motor patterns. When urocortin was given icv and iv in the fed state, the motor activity remained like the fed patterns but % motor index (%MI) was decreased in the antrum and increased in the duodenum. Increase in the %MI in the duodenum induced by urocortin was shown as a nonpropagated event, since the transit of nonnutrient contents in the duodenum was decreased by icv and iv injection of urocortin. Changes in the gastroduodenal motility induced by icv injection of urocortin were abolished in animals with truncal vagotomy but not altered in animals with mechanical sympathectomy, suggesting that the vagal pathway may mediate the central action of urocortin. Neither urocortin antiserum nor alpha-helical CRF-(9-41) affected fed and fasted gastroduodenal motility, suggesting that endogenous urocortin is not involved in regulation of basal gastroduodenal motility.

Peptidergic regulation of gastrointestinal motility in rodents

Peptides involved in the endocrine and enteric nervous systems as well as in the central nervous system exert concerted action on gastrointestinal motility. Mechanical and chemical stimuli which induce peptide release from the epithelial endocrine cells are the earliest step in the initiation of peristaltic activities. Gut peptides exert hormonal effects, but peptide-containing stimulatory (Ach/substance P/tachykinin) and inhibitory (VIP/PACAP/NO) neurons are also involved in the induction of ascending contraction and descending relaxation, respectively. The dorsal vagal complex (DVC), located in the medulla of the brainstem, constitutes the basic neural circuitry of vago-vagal reflex control of gastrointestinal motility. Several gut peptides act on the DVC to modify vagal cholinergic reflexes directly (PYY and PP) or indirectly via afferent fibers in the periphery (CCK and GLP-1). The DVC is also a primary site of action of many neuropeptides (such as TRH and NPY) in mediating gastrointestinal motor activities. The identification over the last few years of a number of neuropeptide systems has greatly changed the field of feeding and body weight regulation. By exploring the brain and gut systems that employ recently identified peptidergic molecules, it will be possible to elaborate on the central and peripheral pathways involved in the regulation of gastrointestinal motility.

Opposite effects of gentle handling on body temperature and body weight in rats

Opposite effects of gentle handling on body temperature and body weight in rats. PHhe aim of this study was to measure the body weight set point when rats are being handled gently and thus experience emotional rise in body temperature. Wistar male rats were used in this experiment, and each rat was its own control. Body weight set point was estimated from the rat's food hoarding behavior. The set point is the intersection of the regression line for hoarding with the X axis. During hoarding sessions the experimenter handled the rat and took its colonic temperature six to eight times, an action sufficient to arouse emotional fever. On alternate days the rats were not handled. Thus, body weight set point was obtained for each rat without handling and with handling. In sessions with handling, rats raised their body temperature, ate less, and defecated more than in control sessions. When handled, the body weight set point declined from 388 +/- 44 g to 366 +/- 47 g (p = 0.048, t = 2,39). The decline in the set point induced by gentle handling is believed to result from an elevation of the hypothalamic CRH.

Acute intracranial hypertension-induced inhibition of gastric emptying: evaluation in conscious rats

To study the effect of raised intracranial pressure (ICP)-induced alterations in gastric emptying, and their modulation by pharmacological interventions, an experimental model was standardized in rats. A test meal of methylcellulose and phenol red was administered intragastrically. ICP was raised to 40, 60 and 80 mmHg by connecting a buffered saline pressure head to an intracerebroventricular (i.c.v.) cannula. Gastric emptying was estimated after killing the animals, from the residual stomach phenol red content. Inhibition of gastric emptying was observed when ICP was raised, the maximum being at 80 mmHg ICP (percent gastric emptying 26.5%+/-2.8 vs. 83.4+/-4.7 in sham-ICP). Pretreatment with clonidine, prazosin or ondansetron did not modify the raised ICP-induced inhibition of gastric emptying. Cisapride was ineffective at 1 mg/kg but caused a partial reversal at the 5- and 10-mg/kg doses (46.9+/-3.1% and 42.6+/-4.0%, respectively). Carbachol at a lower dose of 0.1 mg/kg i.p., produced a greater reversal (78.3+/-6.0%) than did the high dose (52.8+/-4.1). Bretylium partially reversed the inhibition of gastric emptying (45.7+/-4.3%). The protective effect of carbachol and cisapride suggests that suppression of vagal activity due to increased ICP may play an important role in the inhibition of gastric emptying due to intracranial hyper-tension.

Intracisternal sauvagine is more potent than corticotropin-releasing factor to decrease gastric vagal efferent activity in rats

Consecutive intracisternal (ic) injections of corticotropin-releasing factor (CRF) (21, 63, and 126 pmol, ic) or sauvagine (2.1, 6.3, and 21 pmol, ic) decreased gastric vagal efferent multiunit discharge (GVED) to 82%, 75% and 69% and 71%, 40% and 21%, respectively, from preinjection basal levels (taken as 100%). The inhibitory action was dose related (magnitude and duration of the response, 7-45 min). The CRF antagonist, [D-Phe12,Nle21,38,Calpha-MeLeu37]-rCRF12-4 1 (6.25 nmol, ic) increased GVED by 43.5+/-4.3% and blocked the decrease in GVED induced by CRF (21 pmol, ic) for >90 min with a complete recovery after 3 h. Vehicles (injected intracisternally) had no effect. These data indicate that: 1) CRF injected intracisternally decreases GVED through the activation of CRF receptors and sauvagine is more potent than CRF to inhibit GVED; and 2) endogenous CRF exerts an inhibitory tone on basal GVED in urethane-anesthetized rats undergoing surgery.

Central CRF inhibits gastric emptying of a nutrient solid meal in rats: the role of CRF2 receptors

Corticotropin-releasing factor (CRF)-related peptides exhibit different affinity for the receptor subtypes 1 and 2 cloned in the rat brain. We investigated, in conscious rats, the effects of intracisternal (i.c.) injection of CRF (rat/human) on the 5-h rate of gastric emptying of a solid nutrient meal (Purina chow and water ad libitum for 3 h) and the CRF receptor subtype involved. CRF, urotensin I (suckerfish), and sauvagine (frog) injected i.c. inhibited gastric emptying in a dose-dependent manner, with ED50 values of 0.31, 0.13, and 0.08 microgram/rat, respectively. Rat CRF-(6-33) (0.1-10 micrograms i.c.) had no effect. The nonselective CRF1 and CRF2 receptor antagonist, astressin, injected i.c. completely blocked the inhibitory effect of i.c. CRF, urotensin I, and sauvagine with antagonist-to-agonist ratios of 3:1, 10:1, and 16:1, respectively. The CRF1-selective receptor antagonist NBI-27914 injected i.c. at a ratio of 170:1 had no effect. These data show that central CRF and CRF-related peptides are potent inhibitors of gastric emptying of a solid meal with a rank order of potency characteristic of the CRF2 receptor subtype affinity (sauvagine > urotensin I > CRF). In addition, the reversal by astressin but not by the CRF1-selective receptor antagonist further supports the view that the CRF2 receptor subtype is primarily involved in central CRF-induced delayed gastric emptying.

Pathways mediating CRF-induced inhibition of gastric emptying in rats

The corticotrophin-releasing factor (CRF) is shown to be released during stress suggesting that CRF has a physiological role in the mediation of central nervous system (CNS) response to stress, including an inhibitory effect on gastric emptying. In the present study, we have examined the pathways by which intracerebroventricularly (i.c.v.) administered CRF and central CRF activation during stress alter the gastric emptying rate of saline (0.14 M), acid (50 mM), peptone (4.5%) and peptone after preload. The emptying rates of all these test meals were significantly (p < 0.05-0.001) delayed with increasing doses of i.c.v. CRF (0.001, 0.003, 0.01, 0.1, 0.3 and 1 nmol/10 microl), when compared with their i.c.v. saline-treated controls. The 1-nmol dose of CRF inhibited the emptying of acid, peptone and peptone after a preload by 43.8%, 64.1% and 81.1%, respectively. Twenty-minute swim stress delayed gastric emptying rate of saline, acid and peptone solutions significantly (p < 0.001) and the CRF receptor antagonist, alpha-helical CRF (8 nmol/10 microl, i.c.v.), applied before the swim stress, abolished the inhibitory effect of stress on the emptying rate of these solutions. Acute intragastric administration of capsaicin (2 mg/rat) and systemic capsaicin (125 mg kg(-1)) treatment facilitated the gastric emptying rate of acid, peptone and peptone after preload significantly, almost abolishing the inhibitory effect of central CRF (p < 0.001). However, either capsaicin treatment had no effect on stress-induced inhibition of the gastric emptying of none of the solutions, except peptone after a preload. Our findings demonstrate that the gastric inhibitory response induced by swimming as a stress-producing stimulus is mediated by the endogenous release of CRF. They also suggest that CRF exerts its CNS actions on the gastrointestinal tract via vago-vagal, capsaicin-sensitive pathways, probably involving the central cholecystokinin (CCK) mechanisms.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

Intracerebroventricular CRF inhibits cold restraint-induced c-fos expression in the dorsal motor nucleus of the vagus and gastric erosions in rats

Acute exposure to cold-restraint induces vagal-dependent gastric erosions associated with activation of neurons in the dorsal motor nucleus of the vagus (DMN) in rats. The influence of intracerebroventricular (i.c.v.) injection of corticotropin-releasing factor (CRF) (10 micrograms) on c-fos expression in the brain and gastric erosions induced by 3 h cold-restraint was investigated in conscious rats. In cold-restraint exposed rats, CRF injected i.c.v. inhibited gastric erosions and the number of Fos positive neurons in the DMN by 93 and 72%, respectively, while Fos labelling in the nucleus tractus solitarius (NTS) was increased by 5-fold compared with vehicle group. c-fos expression was also induced in the central amygdala by i.c.v. CRF, unlike the vehicle-injected group exposed to cold-restraint. c-fos expression induced by cold-restraint in the raphe pallidus (Rpa) and paraventricular nucleus of the hypothalamus was not altered by i.c.v. CRF. These data indicate that central CRF-induced gastric protection results from the inhibition of DMN neuronal activity enhanced by cold-restraint. CRF action on DMN neurons may be related to the increase in the NTS and central amygdala inputs leading to inhibition of DMN neurons rather than to the decrease in the excitatory input from the caudal raphe projections to the DMN.

Microinfusion of corticotropin-releasing factor into the locus coeruleus/subcoeruleus nuclei inhibits gastric acid secretion via spinal pathways in the rat

Brain corticotropin-releasing factor (CRF) is involved in stress-related alterations of gastric acid secretion. CRF in the locus coeruleus has been shown to induce anxiogenic behavioral responses and to mimic stress-induced alterations of colonic motor function. Whether the locus coeruleus/subcoeruleus nucleus (LC/SC) is a site of action for CRF to alter gastric acid secretion was investigated in urethane-anesthetized gastric fistula rats. In sham-operated animals, CRF (126-420 pmol) microinfused bilaterally into the LC/SC induced a dose-dependent inhibition of pentagastrin (PG)-stimulated gastric acid secretion of 60-81% within the first hour after microinjection. At the 420 pmol dose, this inhibitory effect of CRF into the LC/SC lasted throughout the whole observation period of 120 min. After bilateral vagotomy, basal and PG-stimulated gastric acid secretion at microinjection of vehicle was reduced. Nevertheless, microinfusion of 420 pmol CRF into the LC/SC still inhibited significantly gastric acid secretion by 62.1%. In contrast, in spinal cord transected animals bilateral microinfusion of 420 pmol CRF into the LC/SC did not reduce PG-stimulated gastric acid secretion. These data indicate that CRF acts in the LC/SC to induce a long lasting inhibition of peripherally stimulated gastric acid secretion via spinal pathways. These findings suggest a possible role of the LC/SC in the regulation of gastric secretion and of endogenous CRF at these sites in the stress-related inhibition of gastric acid secretion by affecting autonomic nervous system activity.

Reversal by NPY, PYY and 3-36 molecular forms of NPY and PYY of intracisternal CRF-induced inhibition of gastric acid secretion in rats

1. The Y receptor subtype involved in the antagonism by neuropeptide Y (NPY) of intracisternal corticotropin-releasing factor (CRF)-induced inhibition of gastric acid secretion was studied in urethane-anaesthetized rats by use of peptides with various selectivity for Y1, Y2 and Y3 subtypes: NPY, a Y1, Y2 and Y3 agonist, peptide YY (PYY), a Y1 and Y2 agonist, [Leu31, Pro34]-NPY, a Y1 and Y3 agonist, NPY(3-36) and PYY(3-36), highly selective Y2 agonists and NPY(13-36) a weak Y2 and Y3 agonist. Peptides were injected intracisternally 10 min before intracisternal injection of CRF (10 micrograms) and gastric acid secretion was measured by the flushed technique for 1 h before and 2 h after pentagastrin-(10 micrograms kg-1 h-1, i.v.) infusion which started 10 min after CRF injection. 2. Intracisternal injection of CRF (10 micrograms) inhibited by 56% gastric acid secretion stimulated by pentagastrin. Intracisternal injection of NPY and PYY (0.1-0.5 microgram) did not influence the acid response to pentagastrin but blocked CRF-induced inhibition of pentagastrin-stimulated acid secretion. NPY(3-36) (0.5 microgram) and PYY(3-36) (0.25 and 0.5 microgram) also completely blocked the inhibitory action of CRF on pentagastrin-stimulated acid secretion. 3. [Leu31, Pro34]-NPY (0.5-5 micrograms) and NPY(13-36) (0.5-5 micrograms) injected intracisternally did not modify gastric acid secretion induced by pentagastrin or CRF inhibitory action. 4. The sigma antagonist, BMY 14802 (1 mg kg-1, s.c.) did not influence the acid response to pentagastrin but prevented the antagonism by PYY(3-36) (0.5 microgram) of the CRF antisecretory effect. 5. These results show that both PYY and NPY and the 3-36 forms of PYY and NPY are equipotent in blocking central CRF-induced inhibition of pentagastrin-stimulated gastric acid secretion. The structure-activity profile suggests a mediation through Y2 receptor subtype and the involvement of sigma binding sites.

TRH in the dorsal motor nucleus of vagus is involved in gastric erosion induced by excitation of raphe pallidus in rats

The influence of excitation of the raphe pallidus neurons on gastric mucosal lesions was examined in urethane-anesthetized rats pretreated with indomethacin (5 mg/kg, i.p., -60 min). Kainic acid (12 ng/30 nl), delivered into the raphe pallidus, increased gastric acid secretion (94.8 +/- 15.9 mumol/60 min) and produced gastric lesions in 2.7 +/- 0.3% of the corpus mucosa. No gastric erosions were observed when kainic acid was injected nearby, but outside, of the raphe pallidus. The gastric lesions induced by microinjection of kainic acid into the raphe pallidus neurons were completely prevented by atropine (0.3 mg/kg, -30 min, s.c.) and bilateral microinjection of TRH antibody # 8964 (1.3 microgram/site) into the dorsal motor nucleus of the vagus (DMN). Microinjection of the TRH antibody into the hypoglossal nucleus or control antibody into the DMN did not modify the mucosal lesions induced by kainic acid into the raphe pallidus. These data suggest that activation of raphe pallidus induced vagal cholinergic mediated gastric erosion through TRH release in the DMN.

Stimulation of the nucleus raphe obscurus produces marked serotonin release into the dorsal medulla of fed but not fasted rats--glutamatergic dependence

Serotonin interacts with TRH at the dorsal vagal complex (DVC) to augment gastric functional parameters. To ascertain physiologic relevance, patterns of stimulated release at the terminal field were characterized. Stimulation of the nucleus raphe obscurus (nRO) by kainic acid (423 pmol/10 nol) produced marked release of serotonin into dorsal medullary dialysates containing the DVC in freely fed, but no 24-h fasted rats. Probe infusion of kynurenic acid (1 mM), but not acute bilateral cervical vagotomy attenuated nRO-stimulated serotonin release in fed animals. The results suggest that the fed state facilitates serotonin release into the dorsal medulla by a mechanism mediated by activation of excitatory amino acid receptors in the dorsal medulla. Enhanced serotonergic neurotransmission at the DVC may comprise a heretofore unrecognized component of the integrated vago-vagal response to a meal.

Caudal raphe-dorsal vagal complex peptidergic projections: role in gastric vagal control

Subpopulations of raphe pallidus (Rpa) and raphe obscurus (Rob) neurons containing TRH, serotonin (5-HT), and substance P contribute projections to the dorsal vagal complex (DVC). Activation of Rpa and Rob neurons induces a vagal cholinergic-dependent stimulation of gastric secretory and motor function and modulates resistance of the gastric mucosa to gastric injury in rats and cats. The caudal raphe nuclei-DVC pathways containing TRH/5-HT are involved in mediating cold-induced vagal stimulation of gastric function and erosion formation. These results suggest that Rpa/Rob-DVC projections containing TRH/5-HT may be an important pathways in the medullary regulation of vagal activity to the viscera.

Microinfusion of corticotropin releasing factor into the locus coeruleus/subcoeruleus nuclei stimulates colonic motor function in rats

Convergent evidence indicates that brain corticotropin-releasing factor (CRF) participates in stress-related alterations of gastric and colonic motor function. CRF in the locus coeruleus has been shown to induce anxiogenic response. Whether the locus coeruleus/subcoeruleus nucleus (LC/SC) is a site of action for CRF to alter gastric and colonic transit was investigated in conscious, chronically cannulated rats. CRF (0.2 nmol) microinjected into the LC/SC did not influence gastric emptying of a non-caloric semi-liquid meal while stimulating colonic transit by 57% as assessed by the geometric center in fasted rats. Under the same conditions, i.c.v. injection of CRF (0.2 nmol) delayed gastric emptying by 31% and increased colonic transit by 103%. When colonic transit was evaluated as the time of appearance in the feces of a marker placed in the proximal colon, CRF (0.2 nmol) injected into the LC/SC or i.c.v. stimulated colonic transit by 77% and 48% respectively and fecal output/6h by 3.8 and 2.8 fold respectively. Microinjection of CRF into the medial and lateral parabrachial nucleus, postero-dorsal tegmental nucleus, dorsomedial tegmental area and the ventral part of the nucleus subcoeruleus did not influence colonic transit. These data indicate that CRF acts in the LC/SC to induce a long lasting stimulation of colonic transit and bowel discharge without influencing gastric emptying. These findings suggest a possible role of the LC/SC in the regulation of colonic motor function and of endogenous CRF at these sites in the stress-related activation of colonic motor function.

Raphe pallidus stimulation increases gastric contractility via TRH projections to the dorsal vagal complex in rats

The role of thyrotropin releasing hormone (TRH) in the dorsal vagal complex (DVC) in mediating the enhanced gastric contractility induced by glutamate (100 pmol) microinjected into the raphe pallidus (Rpa) was investigated in urethane-anesthetized rats acutely implanted with miniature strain gauge force transducers on the corpus of the stomach. Glutamate-induced stimulation of gastric contractility was dose-dependently inhibited by bilateral microinjection into the DVC of TRH antibody (0.17, 0.85 or 1.7 micrograms/100 nl/site) but not by vehicle. TRH antibody microinjected into the dorsal medullary reticular field had no effect. These data indicate that activation of Rpa neurons by glutamate increases gastric motor function through TRH release in the DVC.

Role of CRF in stress-related alterations of gastric and colonic motor function

Major advances have been made in the understanding of the pathophysiology of stress-related alteration of gut function. A wealth of information indicates that CRF is involved in the central mechanisms by which stress inhibits gastric emptying while stimulating colonic motor function. CRF acts in the PVN to trigger both the inhibition of gastric emptying and the stimulation of colonic motor function in response to stress, in addition to previously established endocrine and behavioral responses. Preliminary evidence exists that CRF acts in the locus coeruleus to induce a selective stimulation of colonic transit without influencing gastric emptying. The central actions of CRF to alter gastric and colonic motor function are conveyed by autonomic pathways and are unrelated to the associated stimulation of pituitary hormone secretion. The demonstration that central CRF plays a role in mediating gastric stasis resulting from surgery, peritonitis or high levels of central interleukin-1 provides new insight into the mechanisms involved in gastric ileus induced postoperatively or by infectious disease. Likewise, the demonstration that CRF in the PVN and locus coeruleus induce the anxiogenic and colonic motor responses to stress and that colonic distention activates neurons in the locus coeruleus opens new avenues for the understanding of the pathogenesis of a subset of IBS patients with colonic hypersensitivity associated with psychopathological disturbance and diarrhea-predominant symptoms.

CRF in the paraventricular nucleus of the hypothalamus stimulates colonic motor activity in fasted rats

The influence of corticotropin releasing factor (CRF) microinjected into the paraventricular nucleus of the hypothalamus (PVN) on colonic motility was investigated in conscious, fasted rats. Rats were chronically implanted with a bilateral guide cannula into the PVN and a catheter into the proximal colon to record motor activity manometrically. Microinjection of CRF (0.6 nmol/rat) into the PVN increased both phasic and tonic motor activity in the proximal colon. Atropine sulfate (1 mg/kg, IP) completely abolished the colonic motor response to CRF. Microinjection of CRF (0.6 nmol/rat) into sites outside of the PVN did not modify colonic motor activity. These data show that CRF acts in the PVN to stimulate tonic and phasic motor activity in the proximal colon. Corticotropin releasing factor action is site specific and mediated through cholinergic pathways.

CNS effects on gastric functions: from clinical observations to peptidergic brain-gut interactions

Clinical observations as early as the last century pointed to the stomach's link to the brain. Animal studies in this century have given us detailed information about the neuroanatomical and neurophysiological basis of brain-gut interactions. Psychological stress models and stereotaxic brain procedures have been important tools in gaining this information. During the last 10 years, there has been much focus on the effects of neuropeptides on gastric functions. Several CNS-peptides have indeed been shown to influence multiple gastric functions such as: acid secretion, bicarbonate secretion, mucus secretion, motility, blood flow and prostaglandin synthesis. Accordingly, direct CNS-application of these peptides also influences the development of gastric erosions during experimental stress procedures.