Peripherally administered CRF stimulates colonic motility via central CRF receptors and vagal pathways in conscious rats

Tea-derived exosome-like nanoparticles prevent irritable bowel syndrome induced by water avoidance stress in rat model

BACKGROUND AND AIM

Exosome-like nanoparticles (ELNs) have emerged as crucial mediators of intercellular communication, evaluated as potential bioactive nutraceutical biomolecules. We hypothesized that oral ELNs have some therapeutic effect on irritable bowel syndrome (IBS).

METHODS

In our study, ELNs from tea (Camellia sinensis) leaves were extracted by differential centrifugation. We investigated the role of ELNs by assessing visceral hypersensitivity, body weight, bowel habits, tight junctions, and corticotropin-releasing hormone (CRH) in rats subjected to water avoidance stress (WAS) to mimic IBS with and without ELNs (1 mg/kg per day) for 10 days.

RESULTS

The average diameter of ELNs from LCC, FD and MZ tea tree were 165 ± 107, 168 ± 94, and 168 ± 108 nm, the concentration of ELNs were 1.2 × 1013, 1 × 1013, and 1.5 × 1013 particles/mL, respectively. ELNs can be taken up by intestinal epithelial cells. In WAS rats, ELNs significantly restored weight, recovered tight junctions, decreased CRH, and CRH receptor 1 expression levels and inhibited abdominal hypersensitivity in comparison to positive control.

CONCLUSIONS

Oral tea-derived ELN improves symptoms of IBS by potentially modulating the CRH pathway.

Psychological stress induces an increase in cholinergic enteric neuromuscular pathways mediated by glucocorticoid receptors

Introduction

Repeated acute stress (RASt) is known to be associated with gastrointestinal dysfunctions. However, the mechanisms underlying these effects have not yet been fully understood. While glucocorticoids are clearly identified as stress hormones, their involvement in RASt-induced gut dysfunctions remains unclear, as does the function of glucocorticoid receptors (GR). The aim of our study was to evaluate the involvement of GR on RASt-induced changes in gut motility, particularly through the enteric nervous system (ENS).

Methods

Using a murine water avoidance stress (WAS) model, we characterized the impact of RASt upon the ENS phenotype and colonic motility. We then evaluated the expression of glucocorticoid receptors in the ENS and their functional impact upon RASt-induced changes in ENS phenotype and motor response.

Results

We showed that GR were expressed in myenteric neurons in the distal colon under basal conditions, and that RASt enhanced their nuclear translocation. RASt increased the proportion of ChAT-immunoreactive neurons, the tissue concentration of acetylcholine and enhanced cholinergic neuromuscular transmission as compared to controls. Finally, we showed that a GR-specific antagonist (CORT108297) prevented the increase of acetylcholine colonic tissue level and in vivo colonic motility.

Discussion

Our study suggests that RASt-induced functional changes in motility are, at least partly, due to a GR-dependent enhanced cholinergic component in the ENS.

Beyond depression and anxiety; a systematic review about the role of corticotropin-releasing hormone antagonists in diseases of the pelvic and abdominal organs

Evidence for beneficial effects of corticotropin releasing hormone (CRH) antagonists in abdominal and pelvic organs is emerging in preclinical studies. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement a compilation of preclinical studies using CRH receptor antagonists as a treatment for abdominal and pelvic disease was carried out. The Animal Research: Reporting of In Vivo Experiments (ARRIVE) essential 10 guidelines were used to determine quality of the included studies. A total of 40 studies from the last 15 years studying irritable bowel syndrome, inflammatory bowel disease, endometriosis, enteritis, stress impact on gastrointestinal processes and exogenous CRH administration effects were included. Blockage of the CRH receptor 1 was mainly associated with beneficial effects while that of CRH receptor 2 worsened studied effects. However, time of administration, route of administration and the animal model used, all had an impact on the beneficial outcomes. Frequency of drugs administered indicated that astressin-2B, astressin and antalarmin were among the most utilized antagonists. Of concern, studies included were predominantly carried out in male models only, representing a gender discrepancy in preclinical studies compared to the clinical scenario. The ARRIVE score average was 13 with ~60% of the studies failing to randomize or blind the experimental units. Despite the failure to date of the CRH antagonists in moving across the clinical trials pipeline, there is evidence for their beneficial effects beyond mood disorders. Future pre-clinical studies should be tailored towards effectively predicting the clinical scenario, including reduction of bias and randomization.

Urocortin 1: A putative excitatory neurotransmitter in the enteric nervous system

BACKGROUND

Urocortin 1 (Ucn1), a stress-related peptide, is a member of the corticotropin-releasing factor (CRF) family and acts as a CRF1 receptor agonist. Ucn1 and CRF1 receptor immunoreactivity are present in the enteric nervous system (ENS), and Ucn1 elicits contraction of colonic muscle strips. Considering these findings, we have hypothesized that Ucn1 acts as an excitatory neurotransmitter in the ENS. The present study was conducted to determine whether exogenously applied Ucn1 causes contractions, whether it participates in neurally mediated contraction, and whether it is released from the ENS of the rat colon.

METHODS

Isometric tension of the rat colonic muscle strips (middle to distal colon) in a longitudinal direction was measured. The effects of Ucn1 on phasic contractions were examined in the absence and presence of antalarmin (CRF1 receptor antagonist), tetrodotoxin (TTX), and atropine. The effects of antalarmin on electrical field stimulation (EFS)-induced contractions were examined in the absence and presence of atropine. Ucn1 peptide in the bath solution was measured after EFS using an EIA kit.

KEY RESULTS

Ucn1 caused a significant and dose-dependent increase in phasic contractions. These effects were completely inhibited by antalarmin, TTX, and atropine. EFS-induced contractions were inhibited by antalarmin. Atropine markedly reduced EFS-induced contractions, and antalarmin did not decrease these contractions further. EFS elicited a significant increase in the concentration of Ucn1 in the bath solution, and this increase was completely inhibited by TTX.

CONCLUSIONS AND INFERENCES

These results suggest that Ucn1 acts as an excitatory neurotransmitter in the ENS enhancing the cholinergic neurotransmission.

Assessments of plasma acyl-ghrelin levels in Parkinson's disease patients treated with deep brain stimulation

Gastrointestinal dysfunction is the most common non-motor symptom in Parkinson's disease (PD) with rates rising as the disease progresses. Deep brain stimulation of subthalamic nucleus (STN DBS) improves motor functions in advanced PD. However, the effect of STN DBS on ghrelin concentration and consequently on motility disturbances as well as body weight is unclear. The objective of this study was to assess acyl-ghrelin levels in comparison to weight in advanced PD patients treated with STN DBS. Plasma concentrations of acyl-ghrelin was measured in 29 PD patients in the fasting state and at 30, 60, 120, and 180 min after a standard meal preoperatively and 3 months after surgery. The level of acyl-ghrelin in PD patients were compared with 30 age and sex-matched healthy controls. We reported that mean plasma acyl-ghrelin levels were decreased in PD patients before STN DBS in fasting (p = 0.0003) and in 30 min postprandial phase (p = 0.04) compared with healthy controls. The plasma acyl-ghrelin levels after STN DBS increased in pre-prandial and postprandial phase in PD patients at the investigated time points. Body weight gained on average 2.33 kg during the first 3 months after surgery. There was no correlation between the acyl-ghrelin plasma levels and BMI. After STN DBS in fasting and postprandial phase plasma acyl-ghrelin levels were increased. The results showed that STN DBS therapy elicited a modification of ghrelin levels, increasing its concentration in pre- and postprandial state. In addition, body weight was increased during 3 months after surgery.

Central control of gastrointestinal motility

PURPOSE OF REVIEW

This review summarizes the organization and structure of vagal neurocircuits controlling the upper gastrointestinal tract, and more recent studies investigating their role in the regulation of gastric motility under physiological, as well as pathophysiological, conditions.

RECENT FINDINGS

Vagal neurocircuits regulating gastric functions are highly plastic, and open to modulation by a variety of inputs, both peripheral and central. Recent research in the fields of obesity, development, stress, and neurological disorders highlight the importance of central inputs onto these brainstem neurocircuits in the regulation of gastric motility.

SUMMARY

Recognition of the pivotal role that the central nervous system exerts in the regulation, integration, and modulation of gastric motility should serve to encourage research into central mechanisms regulating peripheral motility disorders.

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.

Altered brain and gut responses to corticotropin-releasing hormone (CRH) in patients with irritable bowel syndrome

Stress is a known trigger of irritable bowel syndrome (IBS) and exacerbates its gastrointestinal symptoms. However, underlying the physiological mechanism remains unknown. Here, we investigated hypothalamic–pituitary–adrenal (HPA) axis, colonic motility, and autonomic responses to corticotropin-releasing hormone (CRH) administration as well as brain activity alterations in IBS. The study included 28 IBS patients and 34 age and sex-matched healthy control subjects. IBS patients demonstrated greater adrenocorticotropic hormone (ACTH) responses to CRH than control subjects. Male IBS patients had greater increases in colonic motility than male HCs after CRH. Female IBS patients showed altered sympathovagal balance and lower basal parasympathetic tone relative to female control subjects. Brain responses to rectal distention were measured in the same subjects using functional magnetic resonance imaging, and their associations with individual ACTH responses to CRH were tested. A negative association between ACTH response to CRH and activity in the pregenual anterior cingulate cortex (pACC) during rectal distention was identified in controls but not in IBS patients. Impaired top-down inhibitory input from the pregenual ACC to the HPA axis may lead to altered neuroendocrine and gastrointestinal responses to CRH. Centrally acting treatments may dampen the stress induced physical symptoms in IBS.

Electroacupuncture ameliorates abnormal defaecation and regulates corticotrophin-releasing factor in a rat model of stress

Objective

To examine the effect of electroacupuncture (EA) treatment on abnormal defaecation in a rat model of chronic heterotypic stress (CHS) and investigate the underlying mechanisms.

Methods

20 male Sprague-Dawley rats were randomly divided into three groups: normal (n=6), CHS (n=7), and CHS+EA (n=7). Rats in the CHS group and CHS+EA groups received four different types of stressors for 7 days. For rats in the CHS+EA group, EA was applied at ST36 in the bilateral hind legs for 30 min before each stress-loading session. Rats in the normal group did not receive stressors or EA treatment. The faecal pellets of each rat were collected and weighed at a fixed time every day. Protein expression of corticotrophin-releasing factor (CRF) in the hypothalamus and colorectal tissues was measured by Western blotting at the end of the experiment on the 7th day.

Results

After 7 consecutive days of CHS, the number of faecal pellets, faecal wet weight, and faecal water content were significantly increased in the CHS group compared with the normal group (p=0.035, p=0.008 and p=0.008, respectively). All three parameters were significantly decreased in CHS+EA versus CHS groups (p=0.030, p=0.011 and p=0.006, respectively). Stress significantly increased CRF expression in both the hypothalamus and colorectal tissues. The excessive CRF responses seen following CHS were significantly suppressed by EA treatment.

Conclusions

EA treatment can ameliorate stress loading induced abnormal defaecation in rats and decrease protein expression of CRF centrally (hypothalamus) and peripherally (colorectal tissues), suggesting a potentially therapeutic role for EA in stress-related responses.

Stress increases descending inhibition in mouse and human colon

BACKGROUND

A relationship between stress and the symptoms of irritable bowel syndrome (IBS) has been well established but the cellular mechanisms are poorly understood. Therefore, we investigated effects of stress and stress hormones on colonic descending inhibition and transit in mouse models and human tissues.

METHODS

Stress was applied using water avoidance stress (WAS) in the animal model or mimicked using stress hormones, adrenaline (5 nM), and corticosterone (1 μM). Intracellular recordings were obtained from colonic circular smooth muscle cells in isolated smooth muscle/myenteric plexus preparations and the inhibitory junction potential (IJP) was elicited by nerve stimulation or balloon distension oral to the site of recording.

KEY RESULTS

Water avoidance stress increased the number of fecal pellets compared to control (p < 0.05). WAS also caused a significant increase in IJP amplitude following balloon distension. Stress hormones also increased the IJP amplitude following nerve stimulation and balloon distension (p < 0.05) in control mice but had no effect in colons from stressed mice. No differences were observed with application of ATP between stress and control tissues, suggesting the actions of stress hormones were presynaptic. Stress hormones had a large effect in the nerve stimulated IJP in human colon (increased >50%). Immunohistochemical studies identified alpha and beta adrenergic receptor immunoreactivity on myenteric neurons in human colon.

CONCLUSIONS & INFERENCES

These studies suggest that WAS and stress hormones can signal via myenteric neurons to increase inhibitory neuromuscular transmission. This could lead to greater descending relaxation, decreased transit time, and subsequent diarrhea.

Corticotropin-releasing factor receptor type 1 and type 2 interaction in irritable bowel syndrome

Irritable bowel syndrome (IBS) displays chronic abdominal pain or discomfort with altered defecation, and stress-induced altered gut motility and visceral sensation play an important role in the pathophysiology. Corticotropin-releasing factor (CRF) is a main mediator of stress responses and mediates these gastrointestinal functional changes. CRF in brain and periphery acts through two subtype receptors such as CRF receptor type 1 (CRF1) and type 2 (CRF2), and activating CRF1 exclusively stimulates colonic motor function and induces visceral hypersensitivity. Meanwhile, several recent studies have demonstrated that CRF2 has a counter regulatory action against CRF1, which may imply that CRF2 inhibits stress response induced by CRF1 in order to prevent it from going into an overdrive state. Colonic contractility and sensation may be explained by the state of the intensity of CRF1 signaling. CRF2 signaling may play a role in CRF1-triggered enhanced colonic functions through modulation of CRF1 activity. Blocking CRF2 further enhances CRF-induced stimulation of colonic contractility and activating CRF2 inhibits stress-induced visceral sensitization. Therefore, we proposed the hypothesis, i.e., balance theory of CRF1 and CRF2 signaling as follows. Both CRF receptors may be activated simultaneously and the signaling balance of CRF1 and CRF2 may determine the functional changes of gastrointestinal tract induced by stress. CRF signaling balance might be abnormally shifted toward CRF1, leading to enhanced colonic motility and visceral sensitization in IBS. This theory may lead to understanding the pathophysiology and provide the novel therapeutic options targeting altered signaling balance of CRF1 and CRF2 in IBS.

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.

Role of Corticotropin-releasing Factor Signaling in Stress-related Alterations of Colonic Motility and Hyperalgesia

The corticotropin-releasing factor (CRF) signaling systems encompass CRF and the structurally related peptide urocortin (Ucn) 1, 2, and 3 along with 2 G-protein coupled receptors, CRF₁ and CRF₂. CRF binds with high and moderate affinity to CRF₁ and CRF₂ receptors, respectively while Ucn1 is a high-affinity agonist at both receptors, and Ucn2 and Ucn3 are selective CRF₂ agonists. The CRF systems are expressed in both the brain and the colon at the gene and protein levels. Experimental studies established that the activation of CRF₁ pathway in the brain or the colon recaptures cardinal features of diarrhea predominant irritable bowel syndrome (IBS) (stimulation of colonic motility, activation of mast cells and serotonin, defecation/watery diarrhea, and visceral hyperalgesia). Conversely, selective CRF₁ antagonists or CRF₁/CRF₂ antagonists, abolished or reduced exogenous CRF and stress-induced stimulation of colonic motility, defecation, diarrhea and colonic mast cell activation and visceral hyperalgesia to colorectal distention. By contrast, the CRF₂ signaling in the colon dampened the CRF₁ mediated stimulation of colonic motor function and visceral hyperalgesia. These data provide a conceptual framework that sustained activation of the CRF₁ system at central and/or peripheral sites may be one of the underlying basis of IBS-diarrhea symptoms. While targeting these mechanisms by CRF₁ antagonists provided a relevant novel therapeutic venue, so far these promising preclinical data have not translated into therapeutic use of CRF₁ antagonists. Whether the existing or newly developed CRF₁ antagonists will progress to therapeutic benefits for stress-sensitive diseases including IBS for a subset of patients is still a work in progress.

The structures of the colonic mucosa-associated and luminal microbial communities are distinct and differentially affected by a prolonged murine stressor

The commensal microbiota of the human gastrointestinal tract live in a largely stable community structure, assisting in host physiological and immunological functions. Changes to this structure can be injurious to the health of the host, a concept termed dysbiosis. Psychological stress is a factor that has been implicated in causing dysbiosis, and studies performed by our lab have shown that restraint stress can indeed shift the cecal microbiota structure as well as increase the severity of a colonic infection caused by Citrobacter rodentium. However, this study, like many others, have focused on fecal contents when examining the effect of dysbiosis-causing stimuli (e.g. psychological stress) upon the microbiota. Since the mucosa-associated microbiota have unique properties and functions that can act upon the host, it is important to understand how stressor exposure might affect this niche of bacteria. To begin to understand whether chronic restraint stress changes the mucosa-associated and/or luminal microbiota mice underwent 7 16-hour cycles of restraint stress, and the microbiota of both colonic tissue and fecal contents were analyzed by sequencing using next-gen bacterial tag-encoded FLX amplicon technology (bTEFAP) pyrosequencing. Both control and stress groups had significantly different mucosa-associated and luminal microbiota communities, highlighting the importance of focusing gastrointestinal community structure analysis by microbial niche. Furthermore, restraint stress was able to disrupt both the mucosa-associated and luminally-associated colonic microbiota by shifting the relative abundances of multiple groups of bacteria. Among these changes, there was a significant reduction in the immunomodulatory commensal genus Lactobacillus associated with colonic mucosa. The relative abundance of Lactobacillus spp. was not affected in the lumen. These results indicate that stressor-exposure can have distinct effects upon the colonic microbiota situated at the mucosal epithelium in comparison to the luminal-associated microbiota.

A balance theory of peripheral corticotropin-releasing factor receptor type 1 and type 2 signaling to induce colonic contractions and visceral hyperalgesia in rats

Several recent studies suggest that peripheral corticotropin-releasing factor (CRF) receptor type 1 (CRF1) and CRF2 have a counter regulatory action on gastrointestinal functions. We hypothesized that the activity balance of each CRF subtype signaling may determine the changes in colonic motility and visceral sensation. Colonic contractions were assessed by the perfused manometry, and contractions of colonic muscle strips were measured in vitro in rats. Visceromotor response was determined by measuring contractions of abdominal muscle in response to colorectal distensions (CRDs) (60 mm Hg for 10 min twice with a 30-min rest). All drugs were administered through ip route in in vivo studies. CRF increased colonic contractions. Pretreatment with astressin, a nonselective CRF antagonist, blocked the CRF-induced response, but astressin2-B, a selective CRF2 antagonist, enhanced the response by CRF. Cortagine, a selective CRF1 agonist, increased colonic contractions. In in vitro study, CRF increased contractions of muscle strips. Urocortin 2, a selective CRF2 agonist, itself did not alter the contractions but blocked this increased response by CRF. Visceromotor response to the second CRD was significantly higher than that of the first. Astressin blocked this CRD-induced sensitization, but astressin2-B or CRF did not affect it. Meanwhile, astressin2-B together with CRF significantly enhanced the sensitization. Urocortin 2 blocked, but cortagine significantly enhanced, the sensitization. These results indicated that peripheral CRF1 signaling enhanced colonic contractility and induced visceral sensitization, and these responses were modulated by peripheral CRF2 signaling. The activity balance of each subtype signaling may determine the colonic functions in response to stress.

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.

Dopamine receptor D1 mediates the inhibition of dopamine on the distal colonic motility

The motility of distal colon could be inhibited by dopamine (DA), yet, the involved receptor is controversial according to the published reports. The goal of present study was to investigate DA receptor(s) mediated inhibition of DA on the colonic motility in rat. The contraction of isolated colon strips was assessed through isometric force transducer. The expressions of DA receptors in distal colon were detected through immunofluorescence and Western blot. DA concentration in colonic smooth muscle was measured by liquid chromatography/mass spectrometry. The results showed that DA inhibited the spontaneous motility of distal colon in a dose-dependent manner with EC50 8.3 μM. Tetrodotoxin increased colonic contractive frequency, but failed to affect the inhibition of DA on the colonic motility. Pretreatment with SCH-23390, an antagonist of dopaminergic receptor D1, shifted the dose-response curve to the right with EC50 of DA 37 μM. However, blocking dopaminergic receptor D2 with sulpiride, had no effect. The immunoreactivity of D1 and D2 were detected in the distal colon including myenteric plexus and smooth muscle. Acute cold-restraint stress (CRS) enhanced spontaneous contraction of rat distal colon, which was more sensitive to DA compared with control. Moreover, DA content and D1 expression in smooth muscle layer were increased under CRS condition. In conclusion, D1 in the smooth muscle is mediated DA inhibition on the spontaneous contraction of rat distal colon. The increased DA content and D1 receptor expression in the smooth muscle layer could be a compensatory effect under CRS condition to balance the enhanced colonic motility.

Exposure of the amygdala to elevated levels of corticosterone alters colonic motility in response to acute psychological stress

The amygdala is important for integrating the emotional, endocrine and autonomic responses to stress. Exposure of the amygdala to elevated levels of corticosterone (CORT) induces anxiety-like behavior and a hypersensitive colon in rodents; however, effects on colonic transit are unknown. Micropellets releasing CORT alone or combined with a selective glucocorticoid (GR) or mineralocorticoid (MR) receptor antagonist were implanted bilaterally at the dorsal boundary of the central amygdala in male rats. Inactive cholesterol implants served as controls. Seven days later, rats received water avoidance stress (WAS) for 1 h and the fecal pellet output was measured. Colorectal transit was also evaluated following the stressor by recording the time for expulsion of a glass bead placed into the colorectum. Plasma CORT levels were evaluated before WAS, after 60 min of WAS and 90 min post-WAS. Exposure of the amygdala to elevated CORT did not alter daily fecal pellet production or the number of fecal pellets released in response to WAS. However, following WAS, rats with CORT implants on the amygdala showed a delay in colorectal transit compared to cholesterol-implanted controls. Plasma CORT measurements showed that basal and WAS-induced increases in plasma CORT were similar in all groups but a prolonged increase in plasma CORT was observed 90 after cessation of WAS in rats with CORT implants. The post-WAS changes in colonic motility and plasma CORT were prevented by antagonism of GR or MR in the amygdala, suggesting their importance in driving stress-associated changes in colonic motility.

Differential actions of urocortins on neurons of the myenteric division of the enteric nervous system in guinea pig distal colon

BACKGROUND AND PURPOSE

Urocortins (Ucns) 1, 2 and 3 are corticotropin-releasing factor (CRF)-related neuropeptides and may be involved in neural regulation of colonic motor functions. Nevertheless, details of the neural mechanism of action for Ucns have been unclear. We have, here, tested the hypothesis that Ucns act in the enteric nervous system (ENS) to influence colonic motor behaviour.

EXPERIMENTAL APPROACH

We used intracellular recording with 'sharp' microelectrodes, followed by intraneuronal injection of biocytin, and immunohistochemical localization of CRF(1) and CRF(2) receptors in guinea pig colonic tissue.

KEY RESULTS

Application of Ucn1 depolarized membrane potentials and elevated excitability in 58% of AH-type and 60% of S-type colonic myenteric neurons. In most of the neurons tested, depolarizing responses evoked by Ucn-1 were suppressed by the CRF(1) receptor antagonist NBI 27914, but were unaffected by the CRF(2) receptor antagonist antisauvagine-30. The selective CRF(2) receptor agonists, Ucn2 and Ucn3, evoked depolarizing responses in 12 and 8% of the AH-type myenteric neurons, respectively, and had no effect on S-type neurons. Antisauvagine-30, but not NBI 27914, suppressed these Ucn2- and Ucn3-evoked responses. Immunohistochemical staining identified CRF(1) as the predominant CRF receptor subtype expressed by ganglion cell somas, while CRF(2)-immunoreactive neuronal somas were sparse. Ucns did not affect excitatory synaptic transmission in the ENS.

CONCLUSIONS AND IMPLICATIONS

The results suggest that Ucns act as neuromodulators to influence myenteric neuronal excitability. The excitatory action of Ucn1 in myenteric neurons was primarily at CRF(1) receptors, and the excitatory action of Ucn2 and Ucn3 was at CRF(2) receptors.

Alpha-melanocyte-stimulating hormone attenuates behavioral effects of corticotropin-releasing factor in isolated guinea pig pups

During a 3-hr period of social isolation in a novel environment, guinea pig pups exhibit an initial active phase of behavioral responsiveness, characterized primarily by vocalizing, which is then followed by a stage of passive responsiveness in which pups display a distinctive crouch, eye-closing, and extensive piloerection. Prior treatment of pups with alpha-melanocyte-stimulating hormone (alpha-MSH) reduces each of the passive behaviors. The onset of passive responding during separation can be accelerated with peripheral injection of corticotropin-releasing factor (CRF). To examine whether CRF produces its effects through a mechanism similar to that of prolonged separation, we examined the effect of administering alpha-MSH to pups injected with CRF. As expected, CRF markedly enhanced passive responding during a 60-min period of separation. alpha-MSH delivered by either intracerebroventricular infusion or intraperitoneal injection significantly reduced each of the passive behavioral responses without significantly affecting active behavior. These findings, together with previous results indicating that it is the anti-inflammatory property of alpha-MSH that is responsible for its behavioral effects during prolonged separation, suggest that peripheral CRF speeds the induction of passive responding through a mechanism involving enhanced proinflammatory activity.

Norepinephrine mediates the transcriptional effects of heterotypic chronic stress on colonic motor function

Chronic stress precipitates or exacerbates the symptoms of functional bowel disorders, including motility dysfunction. The cellular mechanisms of these effects are not understood. We tested the hypothesis that heterotypic chronic stress (HeCS) elevates the release of norepinephrine from the adrenal medulla, which enhances transcription of the gene-regulating expression of Ca(v)1.2 (L-type) channels in colonic circular smooth muscle cells, resulting in enhanced colonic motor function. The experiments were performed in rats using a 9-day heterotypic chronic stress (HeCS) protocol. We found that HeCS, but not acute stress, time dependently enhances the contractile response to ACh in colonic circular smooth muscle strips and in single dissociated smooth muscle cells, the plasma levels of norepinephrine and the mRNA and protein expressions of the alpha(1C) subunit of Ca(v)1.2 channels. These effects result in faster colonic transit and increase in defecation rate. The effects of HeCS are blocked by adrenalectomy but not by depletion of norepinephrine in sympathetic neurons. The inhibition of receptors for glucocortocoids, corticotropin-releasing hormone or nicotine also does not block the effects of heterotypic chronic stress. Norepinephrine acts on alpha- and beta(3)-adrenergic receptors to induce the transcription of alpha(1C) subunit. We conclude that HeCS alters colonic motor function by elevating the plasma levels of norepinephrine. Colonic motor dysfunction is associated with enhanced gene transcription of Ca(v)1.2 channels in circular smooth muscle cells. These findings suggest the potential cellular mechanisms by which heterotypic chronic stress may exacerbate motility dysfunction in patients with irritable bowel syndrome.

Peripheral and central administration of exogenous urocortin 1 disrupts the fasted motility pattern of the small intestine in rats via the corticotrophin releasing factor receptor 2 and a cholinergic mechanism

BACKGROUND AND AIM

The action of the corticotrophin releasing factor (CRF) receptor on the small intestinal motility has been rarely investigated. The present study aimed to determine the effects of urocortin 1 on small intestinal motility in rats and the CRF receptor subtypes and autonomic pathways mediating the effects.

METHODS

Fasted or fed rats were used to investigate the effect of intravenous or intracerebroventricular urocortin 1 on duodenum and jejunum motility. NBI-27914 and astressin(2)-B (CRF receptor 1 and 2 antagonists, respectively), atropine (an M-receptor antagonist), phentolamine (an alpha-receptor antagonist), propranolol (a beta-receptor antagonist) and N(omega)-Nitro-L-arginine (a nitric oxide synthase [NOS] inhibitor) were applied to determine the involved CRF receptor subtypes and autonomic pathways.

RESULTS

In fasted rats, intravenous or intracerebroventricular injection of urocortin 1 disrupted duodenal and jejunal migrating myoelectric complex pattern, leading to an irregular spiking activity similar to the fed motility pattern. When urocortin 1 was given in the fed state, the fed motility pattern remained unchanged. In addition, urocortin 1 also inhibited small intestinal transit function. Astressin(2)-B injected intraperitoneally or intracerebroventricularly blocked urocortin 1-induced change, while NBI-27914 had no effect. The disruption of migrating myoelectric complex induced by urocortin 1 was abolished by atropine, but not affected by phentolamine, propranolol and N(omega)-Nitro-L-arginine.

CONCLUSION

Intravenous or intracerebroventricular injection of urocortin 1 acts, respectively, on peripheral and central CRF receptor 2 to disrupt the intestinal migrating myoelectric complex through an M-receptor-dependent mechanism, and such change has an inhibitory effect as proved by measuring the small intestinal transit function.

Urocortin I is present in the enteric nervous system and exerts an excitatory effect via cholinergic and serotonergic pathways in the rat colon

Corticotropin-releasing factor (CRF) and urocortin I (UcnI) have been shown to accelerate colonic transit after central nervous system (CNS) or peripheral administration, but the mechanism of their peripheral effect on colonic motor function has not been fully investigated. Furthermore, the localization of UcnI in the enteric nervous system (ENS) of the colon is unknown. We investigated the effect of CRF and UcnI on colonic motor function and examined the localization of CRF, UcnI, CRF receptors, choline acetyltransferase (ChAT), and 5-HT. Isometric tension of rat colonic muscle strips was measured. The effect of CRF, UcnI on phasic contractions, and electrical field stimulation (EFS)-induced off-contractions were examined. The effects of UcnI on both types of contraction were also studied in the presence of antalarmin, astressin2-B, tetrodotoxin (TTX), atropine, and 5-HT antagonists. The localizations of CRF, UcnI, CRF receptors, ChAT, and 5-HT in the colon were investigated by immunohistochemistry. CRF and UcnI increased both contractions dose dependently. UcnI exerted a more potent effect than CRF. Antalarmin, TTX, atropine, and 5-HT antagonists abolished the contractile effects of UcnI. CRF and UcnI were observed in the neuronal cells of the myenteric plexus. UcnI and ChAT, as well as UcnI and 5-HT, were colocalized in some of the neuronal cells of the myenteric plexus. This study demonstrated that CRF and UcnI act on the ENS and increase colonic contractility by enhancing cholinergic and serotonergic neurotransmission. These peptides are present in myenteric neurons. CRF and, perhaps, to a greater extent, UcnI appear to act as neuromodulators in the ENS of the rat colon.

Gastric Vagal Efferent Inhibition Evoked by Intravenous CRF Is Unrelated to Simultaneously Recorded Vagal Afferent Activity in Urethane-Anesthetized Rats

Corticotropin-releasing factor (CRF) injected peripherally or released in response to stressful challenges to the organism reduces gastric tone and contractility, in part by vagal pathways. However, information on the changes in gastric vagal impulse activity evoked by peripheral CRF administration is entirely lacking. Using a novel “dual recording” method in urethane-anesthetized rats, vagal efferent (VE) and afferent (VA) impulse activities were recorded simultaneously from separate, fine bundles dissected from the ventral gastric vagus nerve branch innervating the glandular stomach. Activity records for 38 VA single units (SUs) and 33 VE SUs were sorted from multiunit records obtained from 13 preparations. Intravenous (iv) administration of saline had no effect on multiunit VE activity, whereas CRF (1 μg/kg, iv) immediately inhibited VE activity, reaching a nadir of 54 ± 8.0% of preinjection levels at 3.0 min postinjection. CRF (1 μg/kg, iv) inhibited 25/33 (75.8%) VE SUs and excited three of 33 (9.1%) VE SUs. In contrast to potent effects on VE activity, iv CRF did not alter multiunit VA activity. Single-unit analysis, however, revealed five of 38 (13.1%) VA SUs excited by iv CRF at widely varying latencies (suggesting an indirect mode of action) and one inhibited VA SU. VA SUs excited after iv CRF did not respond during gastric distention and vice versa. These experiments are the first to use simultaneous recording of gastric VA and VE units. The data demonstrate a predominantly inhibitory influence of iv CRF on VE outflow to the hindstomach, not driven by gastric vagovagal reflex activity.