Early life adversity as a risk factor for visceral pain in later life: importance of sex differences

A history of early life adversity (ELA) has health-related consequences that persist beyond the initial maltreatment and into adulthood. Childhood adversity is associated with abnormal glucocorticoid signaling within the hypothalamic-pituitary-adrenal (HPA) axis and the development of functional pain disorders such as the irritable bowel syndrome (IBS). IBS and many adult psychopathologies are more frequently diagnosed in women, and ovarian hormones have been shown to modulate pain sensitivity. Therefore, the sexually dimorphic effects of ELA and the role of ovarian hormones in visceral pain perception represent critical research concepts to enhance our understanding of the etiology of IBS. In this review, we discuss current animal models of ELA and the potential mechanisms through which ovarian hormones modulate the HPA axis to alter nociceptive signaling pathways and induce functionally relevant changes in pain behaviors following ELA.

Genetic diversity contributes to abnormalities in pain behaviors between young and old rats

Aging has profound yet unpredictable effects on pain perception and incidence of anxiety disorders. However, the mechanisms underlying age-related pathologies are confounded by contradictory observations in rodent models. Therefore, the goal of our study was to test the hypothesis that genetic variability contributes to age-related pain behaviors and susceptibility to anxiety. To address this hypothesis, we examined pain and anxiety-like behavior in young or old Brown Norway (BN), Fisher 344, and BN/F344 (F1), three rat strains used in studies to evaluate the effect of aging. Mechanosensitive thresholds were assessed using the Von Frey assay, and visceral pain sensitivity was measured via the visceromotor response to colorectal distension. Anxiety-like behavior and exploration was quantified in the elevated plus maze. In the BN strain, old rats exhibited increased mechanosensitive thresholds compared to young rats; however, age did not affect visceral sensitivity in this strain. In F344-BN rats, the number of abdominal contractions induced by the highest colonic distension pressure was significantly lower in old rats. However, following colonic sensitization, a difference was no longer apparent. In the F-344 strain, visceral hypersensitivity following afferent sensitization was evident in young rats at all distension pressures but was not observed in older animals at 20 mmHg. Aging significantly reduced maze exploration across all strains. Our data demonstrate that age- and strain-related alterations exist in pain behavior and highlight the effects of aging on exploratory behavior. These findings suggest that strain differences contribute to the controversial data on the effects of aging on pain perception.

Efficacy of ipamorelin, a ghrelin mimetic, on gastric dysmotility in a rodent model of postoperative ileus

Background

Delayed gastric emptying is a common disorder with few effective therapeutic options. The goal of this study was to investigate whether ipamorelin, a synthetic peptidomimetic that acts on the ghrelin receptor, accelerates gastric emptying in a rodent model of gastroparesis induced by abdominal surgery and intestinal manipulation.

Methods

Fasted adult male rats were subjected to laparotomy and intestinal manipulation. Following the surgery rats received ipamorelin (0.014–0.14 µmol/kg) or vehicle control via intravenous administration. Gastric emptying was measured by the percent of total recovered radioactivity remaining in the stomach 15 minutes after intragastric gavage of 1.5 mL of ^99mTc (technicium-99m) sulfur colloid in 0.5% methylcellulose. In a separate group of rats subjected to laparotomy and intestinal manipulation, the gastric fundus was isolated and tissue segments were suspended in an organ bath to assess the effect of ipamorelin (1 µM) on gastric smooth muscle contractility induced by acetylcholine and electrical field stimulation.

Results

Abdominal surgery caused a delay in gastric emptying with 78% ± 5% of the meal remaining in the stomach in vehicle controls. Ipamorelin (0.014 µmol/kg intravenous) resulted in a significant acceleration (P < 0.05 vs vehicle-treated rat) of gastric emptying with 52% ± 11% of the meal remaining in the stomach compared to nonsurgical control animals with 44% ± 6%. Following abdominal surgery and intestinal manipulation, isolated preparations of gastric smooth muscle exhibited a marked inhibition of acetylcholine and electrical field stimulation-induced contractile responses, which were reversed by ipamorelin and ghrelin.

Conclusion

These results suggest that ipamorelin accelerates gastric emptying in a rodent model of postoperative ileus through the stimulation of gastric contractility by activating a ghrelin receptor-mediated mechanism involving cholinergic excitatory neurons.

The role of the anteriolateral bed nucleus of the stria terminalis in stress-induced nociception

Activation of the central amygdala (CeA) by corticosterone (CORT) induces somatic and colonic hypersensitivity through corticotrophin-releasing factor (CRF)-dependent mechanisms. However, the importance of the bed nucleus of the stria terminalis (BNST), part of the extended amygdala, on nociception remains unexplored. In the present study, we test the hypothesis that stimulation of the CeA by CORT induces somatic and colonic hypersensitivity through activation of the anteriolateral BNST (BNST(AL)). Animals were implanted with micropellets of CORT or cholesterol (CHOL) onto the CeA or the BNST(AL). Mechanical sensitivity was quantified using electronic von Frey filaments, and colonic nociception was measured by quantifying a visceromotor response to graded colorectal distension. In situ hybridization was used to determine mRNA levels for CRF, CRF(1), and CRF(2) receptors in the BNST(AL). In a second group, animals were implanted bilaterally with 1) CORT or CHOL micropellets onto the CeA; and 2) cannulas localized to the BNST(AL) to administer a CRF(1) receptor antagonist (CP376395). Animals implanted with CORT onto the CeA, but not the BNST(AL), exhibited increased expression of CRF mRNA and increased CRF(1)-to-CRF(2) receptor ratio in the BNST, as well as somatic and colonic hypersensitivity compared with CHOL controls. Infusion of CP376395 into the BNST(AL) inhibited somatic and colonic hypersensitivity in response to elevated amygdala CORT. Somatic and colonic hypersensitivity induced by elevated amygdala CORT is mediated via a CRF(1) receptor-dependent mechanism in the BNST(AL). The CeA through a descending pathway involving the BNST(AL) plays a pivotal role in somatic and colonic nociception.

Importance of stress receptor-mediated mechanisms in the amygdala on visceral pain perception in an intrinsically anxious rat

BACKGROUND

Stress worsens abdominal pain experienced by patients with irritable bowel syndrome (IBS), a chronic disorder of unknown origin with comorbid anxiety. Previously, we have demonstrated colonic hypersensitivity in Wistar-Kyoto rats (WKYs), a high-anxiety strain, which models abdominal pain in IBS. In low-anxiety rats, we have demonstrated that the central nucleus of the amygdala (CeA) regulates colonic hypersensitivity and anxiety induced by selective activation of either glucocorticoid receptors (GR) or mineralocorticoid receptors (MR), which is also mediated by the corticotropin releasing factor (CRF) Type-1 receptor. The goal of the present study was to test the hypothesis that the CeA through GR, MR, and/or CRF-1R regulates colonic hypersensitivity in WKYs.

METHODS

One series of WKYs had micropellets of a GR antagonist, an MR antagonist or cholesterol (control) stereotaxically implanted onto the CeA. Another series were infused in the CeA with CRF-1R antagonist, or vehicle. Colonic sensitivity was measured as a visceromotor response (VMR) to graded colorectal distension (CRD).

KEY RESULTS

The exaggerated VMR to graded CRD in WKYs was unaffected by GR or MR antagonism in the CeA. In contrast, direct CeA infusion of CRF-1R antagonist significantly inhibited the VMR to CRD at noxious distension pressures.

CONCLUSIONS & INFERENCES

Stress hormones in the CeA regulate colonic hypersensitivity in the rat through strain-dependent parallel pathways. The colonic hypersensitivity in WKYs is mediated by a CRF-1R mechanism in the CeA, independent of GR and MR. These complementary pathways suggest multiple etiologies whereby stress hormones in the CeA may regulate abdominal pain in IBS patients.

Activation of colonic mucosal 5-HT(4) receptors accelerates propulsive motility and inhibits visceral hypersensitivity

BACKGROUND & AIMS

5-hydroxytryptamine receptor (5-HT(4)R) agonists promote gastrointestinal motility and attenuate visceral pain, but concerns about adverse reactions have restricted their availability. We tested the hypotheses that 5-HT(4) receptors are expressed in the colonic epithelium and that 5-HT(4)R agonists can act intraluminally to increase motility and reduce visceral hypersensitivity.

METHODS

Mucosal expression of the 5-HT(4)R was evaluated by reverse-transcriptase polymerase chain reaction and immunohistochemical analysis of tissues from 5-HT(4)R(BAC)-enhanced green fluorescent protein mice. Amperometry, histology, and short-circuit current measurements were used to study 5-HT, mucus, and Cl(-) secretion, respectively. Propulsive motility was measured in guinea pig distal colon, and visceromotor responses were recorded in a rat model of colonic hypersensitivity. 5-HT(4)R compounds included cisapride, tegaserod, naronapride, SB204070, and GR113808.

RESULTS

Mucosal 5-HT(4) receptors were present in the small and large intestines. In the distal colon, 5-HT(4) receptors were expressed by most epithelial cells, including enterochromaffin and goblet cells. Stimulation of 5-HT(4)Rs evoked mucosal 5-HT release, goblet cell degranulation, and Cl(-) secretion. Luminal administration of 5-HT(4)R agonists accelerated propulsive motility; a 5-HT(4)R antagonist blocked this effect. Bath application of 5-HT(4)R agonists did not affect motility. Oral or intracolonic administration of 5-HT(4)R agonists attenuated visceral hypersensitivity. Intracolonic administration was more potent than oral administration, and was inhibited by a 5-HT(4)R antagonist.

CONCLUSIONS

Mucosal 5-HT(4) receptor activation can mediate the prokinetic and antinociceptive actions of 5-HT(4)R agonists. Colon-targeted, intraluminal delivery of 5-HT(4)R agonists might be used to promote motility and alleviate visceral pain, while restricting systemic bioavailability and resulting adverse side effects.

Differential involvement of amygdala corticosteroid receptors in visceral hyperalgesia following acute or repeated stress

Symptoms of irritable bowel syndrome (IBS) are exacerbated by stress. Previously, we demonstrated that the stress hormone corticosterone applied directly to the amygdala induced visceral hypersensitivity through the actions of glucocorticoid receptor (GR) and mineralocorticoid receptor (MR). However, the involvement of amygdaloid GR and MR in the regulation of visceral sensitivity following psychological stress is unknown; therefore, the goal of the present study was to determine the relative importance of amygdaloid GR and MR in the regulation of visceral sensitivity in a rodent model of behavioral stress. Male F-344 rats were stereotaxically implanted with micropellets bilaterally on the dorsal margin of the amygdala containing the GR antagonist mifepristone, the MR antagonist spironolactone, or cholesterol as a control. Animals were then exposed to 1 h of water-avoidance stress (WAS) or sham stress for 1 day (acute) or 7 days (repeated). Visceral sensitivity was assessed either 1 h or 24 h after the final session of WAS and quantified as the number of contractions of the external abdominal oblique, a visceromotor response, in response to colorectal distension at pressures of 0-60 mmHg. Acute stress induced transient visceral hyperalgesia, which was absent 24 h after WAS and independent of GR and MR. Conversely, repeated WAS induced sustained visceral hyperalgesia that was abolished by specifically targeting the amygdala with GR and MR antagonists. These results demonstrate that the amygdala corticosteroid system plays an essential role in mediating the effects of repeated WAS on visceral sensitivity. Furthermore, our findings suggest that amygdaloid GR and MR may be involved in IBS symptomatology.

Ghrelin as a target for gastrointestinal motility disorders

The therapeutic potential of ghrelin and synthetic ghrelin receptor (GRLN-R) agonists for the treatment of gastrointestinal (GI) motility disorders is based on their ability to stimulate coordinated patterns of propulsive GI motility. This review focuses on the latest findings that support the therapeutic potential of GRLN-R agonists for the treatment of GI motility disorders. The review highlights the preclinical and clinical prokinetic effects of ghrelin and a series of novel ghrelin mimetics to exert prokinetic effects on the GI tract. We build upon a series of excellent reviews to critically discuss the evidence that supports the potential of GRLN-R agonists to normalize GI motility in patients with GI hypomotility disorders such as gastroparesis, post-operative ileus (POI), idiopathic chronic constipation and functional bowel disorders.

Amygdala activation by corticosterone alters visceral and somatic pain in cycling female rats

Irritable bowel syndrome (IBS) is often seen in women, and symptom severity is known to vary over the menstrual cycle. In addition, activation of the hypothalamic-pituitary-adrenal (HPA) axis enhances symptomology and patients with IBS have increased activation of the amygdala, a brain region known to facilitate HPA output. However, little is known about the effects of amygdala activation during different stages of the menstrual cycle. We therefore investigated the effects of amygdala activation on somatic and visceral pain perception over the rat estrous cycle. Female Wistar rats were implanted with either corticosterone (Cort) or cholesterol as a control onto the dorsal margin of the central amygdala. Visceral sensitivity was quantified by recording the visceromotor response (VMR) to colorectal distension (CRD) and somatic sensitivity was assessed via the Von Frey test. In cholesterol controls, both visceral and somatic sensitivity varied over the estrous cycle. Rats in proestrus/estrus responded to CRD with an increased VMR compared with rats in metestrus/diestrus. Somatic sensitivity followed a similar pattern with enhanced sensitivity during proestrus/estrus compared with metestrus/diestrus. Elevated amygdala Cort induced visceral hypersensitivity during metestrus/diestrus but had no effect during proestrus/estrus. In contrast, elevated amygdala Cort increased somatic sensitivity during both metestrus/diestrus and proestrus/estrous. These results suggests that amygdala activation by Cort eliminates spontaneously occurring differences in visceral and somatic pain perception, which could explain the lowered pain thresholds and higher incidence of somatic pain observed in women with IBS.

The aging colon: the role of enteric neurodegeneration in constipation

Constipation is a common problem in the elderly, and abnormalities in the neural innervation of the colon play a significant role in abnormalities in colonic motility leading to delayed colonic transit. The scope of this review encompasses the latest advances to enhance our understanding of the aging colon with emphasis on enteric neurodegeneration, considered a likely cause for the development of constipation in the aging gut in animal models. Neural innervation of the colon and the effects of aging on intrinsic and extrinsic nerves innervating the colonic smooth muscle is discussed. Evidence supporting the concept that neurologic disorders, such as Parkinson's disease, not only affect the brain but also cause neurodegeneration within the enteric nervous system leading to colonic dysmotility is presented. Further research is needed to investigate the influence of aging on the gastrointestinal tract and to develop novel approaches to therapy directed at protecting the enteric nervous system from neurodegeneration.

Sex steroids localized to the amygdala increase pain responses to visceral stimulation in rats

Females are disproportionately affected by irritable bowel syndrome (IBS) with menstrual cycle-dependent fluctuations in abdominal pain suggesting a role for ovarian hormones. IBS patients also exhibit greater activation of brain areas involved in pain affect such as the amygdala, yet the role of supraspinal processes in the effects of ovarian hormones on visceral pain is largely unexplored. The goal of the current study was to determine whether sex steroids act at the level of the amygdala to alter colonic pain sensitivity. Ovariectomized rats received implants on the amygdala of progesterone, estradiol, progesterone combined with estradiol, or cholesterol as a control to examine the involvement of the amygdala in ovarian hormone-mediated changes in visceral sensitivity. Visceral sensitivity was quantified as the number of abdominal contractions, a visceromotor response (VMR), in response to graded pressures of colorectal distension (CRD). Somatic sensitivity was also assessed by measuring the mechanical force required to elicit hindpaw withdrawal. Elevated levels of progesterone and/or estradiol on the amygdala heightened the responsiveness to CRD; in contrast, neither estradiol nor progesterone altered somatic sensation. Furthermore, administration of progesterone or estradiol to areas adjacent to the amygdala did not affect visceral sensitivity. Future studies will address the specific steroid receptors mediating the effects of progesterone and estradiol.

PERSPECTIVE

To our knowledge, this study represents the first description of a specific brain site mediating the effects of ovarian steroids on visceral sensitivity. These data also suggest that an amygdala-dependent mechanism may be responsible, at least in part, for the exacerbation of visceral symptomatology in females.

Elevated corticosterone in the amygdala leads to persistent increases in anxiety-like behavior and pain sensitivity

Corticosterone (CORT) localized to the amygdala induces anxiety-like behavior coupled with increased behavioral responses to visceral and somatic stimuli. In the current study, we investigated the long-term consequences of briefly exposing the amygdala to elevated levels of CORT with the hypothesis that modulation of the amygdala with CORT results in persistent increases in anxiety-like behavior and viscerosomatic sensitivity.

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.

Divergent effects of amygdala glucocorticoid and mineralocorticoid receptors in the regulation of visceral and somatic pain

Elevated amygdala activity and increased responsiveness of the hypothalamic-pituitary-adrenal axis have been observed in irritable bowel syndrome (IBS) patients. Recently, we demonstrated that corticosterone (Cort) placed on the amygdala induced anxiety-like behavior coupled with decreased thresholds for visceral and somatic pain in rats. Moreover, these studies suggested that the effects of Cort were dependent on both the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR); however, the specific contributions of these receptors to the interaction between corticosteroids and the amygdala are still unclear. In the present study, we sought to define the distinct roles of amygdaloid GR and MR in anxiety-like behavior, visceral sensitivity, and somatic sensitivity through selective pharmacological activation. Male Fischer 344 rats received bilateral implants on the dorsal margin of the central amygdala containing the GR agonist dexamethasone (Dex), the MR agonist aldosterone (Aldo), or cholesterol as a control. Our results showed that GR or MR activation significantly reduced open arm exploration on the elevated plus maze, a measure of anxiety-like behavior. Aldo increased the number of abdominal muscle contractions in response to all levels of colorectal distension (CRD). In contrast, Dex only increased visceral sensitivity at noxious levels of CRD. Furthermore, GR but not MR activation reduced somatic pain thresholds measured by the mechanical force required to elicit hindlimb withdrawal. In summary, GR and MR mediated-mechanisms induce anxiety and visceral hypersensitivity, whereas somatic sensitivity involves only GR, suggesting that corticosteroids may enhance visceral and somatic sensation via divergent processes originating in the amygdala and involving specific steroid receptor mechanisms.

Role of anxiety in the pathophysiology of irritable bowel syndrome: importance of the amygdala

A common characteristic of irritable bowel syndrome (IBS) is that symptoms, including abdominal pain and abnormal bowel habits, are often triggered or exacerbated during periods of stress and anxiety. However, the impact of anxiety and affective disorders on the gastrointestinal (GI) tract is poorly understood and may in part explain the lack of effective therapeutic approaches to treat IBS. The amygdala is an important structure for regulating anxiety with the central nucleus of the amygdala facilitating the activation of the hypothalamic-pituitary-adrenal axis and the autonomic nervous system in response to stress. Moreover, chronic stress enhances function of the amygdala and promotes neural plasticity throughout the amygdaloid complex. This review outlines the latest findings obtained from human studies and animal models related to the role of the emotional brain in the regulation of enteric function, specifically how increasing the gain of the amygdala to induce anxiety-like behavior using corticosterone or chronic stress increases responsiveness to both visceral and somatic stimuli in rodents. A focus of the review is the relative importance of mineralocorticoid receptor and glucocorticoid receptor-mediated mechanisms within the amygdala in the regulation of anxiety and nociceptive behaviors that are characteristic features of IBS. This review also discusses several outstanding questions important for future research on the role of the amygdala in the generation of abnormal GI function that may lead to potential targets for new therapies to treat functional bowel disorders such as IBS.

Effect of TZP-201, a novel motilin receptor antagonist, in the colon of the musk shrew (Suncus murinus)

OBJECTIVES

Motilin is the main gut peptide that stimulates propulsive motility in the upper gastrointestinal (GI) tract. Motilin receptors exist in the colon but little is known about their functional role, and species-dependent differences present a major obstacle to understanding the physiological significance and potential therapeutic implications of motilin receptors in the colon. Our study aimed to define whether a motilin receptor is functionally expressed in the colon of the Asian musk (or house) shrew (Suncus murinus) and to investigate the effect of a novel motilin receptor antagonist, TZP-201.

METHODS

GI tissue (gastric antrum, small intestine and colon) was isolated from male shrews and the effects of a motilin receptor agonist [Nle13]motilin and the antagonist TZP-201 on contractile activity and mucosal electrogenic transport of water and electrolytes were investigated in vitro.

KEY FINDINGS

[Nle13]motilin induced a moderate increase in spontaneous contractility in the stomach and no significant changes in the small intestine; a marked increase in contractility was found in the colon. Motilin-induced contractions in the colon were abolished by tetrodotoxin or atropine, and dose-dependently inhibited by 0.01-10 muM TZP-201. Neither [Nle13]motilin nor TZP-201 had any effect on basal mucosal transport.

CONCLUSIONS

Shrew colon expresses a functional motilin receptor that induces contractile activity by the activation of enteric cholinergic neurons. TZP-201 inhibited motilin-induced colonic contractions. Motilin antagonists may represent a new approach for the treatment of GI motility disorders characterised by hypercontractility.

Efficacy of ipamorelin, a novel ghrelin mimetic, in a rodent model of postoperative ileus

Ghrelin and ghrelin mimetics stimulate appetite and enhance gastric motility. The present study investigates whether ipamorelin, a selective growth hormone secretagogue and agonist of the ghrelin receptor, would accelerate gastrointestinal transit and ameliorate the symptoms in a rodent model of postoperative ileus (POI). Fasted male rats were subjected to laparotomy and intestinal manipulation. At the end of surgery, a dye marker was infused in the proximal colon to evaluate postsurgical colonic transit time, which was the time to the first bowel movement. In addition, fecal pellet output, food intake, and body weight were monitored regularly for 48 h. Ipamorelin (0.01-1 mg/kg), growth hormone-releasing peptide (GHRP)-6 (20 microg/kg), or vehicle (saline) were administered via intravenous bolus infusion after a single dosing or a 2-day repetitive dosing regimen (four doses a day at 3-h intervals). Compared with the vehicle, a single dose of ipamorelin (1 mg/kg) or GHRP-6 (20 microg/kg) decreased the time to the first bowel movement but had no effect on cumulative fecal output, food intake, or body weight gain measured 48 h after the surgery. In contrast, repetitive dosing of ipamorelin (0.1 or 1 mg/kg) significantly increased the cumulative fecal pellet output, food intake, and body weight gain. The results suggest that postsurgical intravenous infusions of ipamorelin may ameliorate the symptoms in patients with POI.

Methylnaltrexone in the treatment of opioid-induced constipation

Constipation is a significant problem related to opioid medications used to manage pain. This review attempts to outline the latest findings related to the therapeutic usefulness of a μ opioid receptor antagonist, methylnaltrexone in the treatment of opioid-induced constipation. The review highlights methylnaltrexone bromide (Relistor™; Progenics/Wyeth) a quaternary derivative of naltrexone, which was recently approved in the United States, Europe and Canada. The Food and Drug Administration in the United States approved a subcutaneous injection for the treatment of opioid bowel dysfunction in patients with advanced illness who are receiving palliative care and when laxative therapy has been insufficient. Methylnaltrexone is a peripherally restricted, μ opioid receptor antagonist that accelerates oral-cecal transit in patients with opioid-induced constipation without reversing the analgesic effects of morphine or inducing symptoms of opioid withdrawal. An analysis of the mechanism of action and the potential benefits of using methylnaltrexone is based on data from published basic research and recent clinical studies.

Effect of the ghrelin receptor agonist TZP-101 on colonic transit in a rat model of postoperative ileus

Ghrelin, the natural ligand of the growth hormone secretagogue receptor (ghrelin receptor), is an orexigenic gut hormone with prokinetic action in the upper gastrointestinal tract. Previously we have shown in a rodent model of postoperative ileus that the synthetic ghrelin receptor agonist TZP-101 prevents the delay in gastric emptying and improves small intestinal transit. The goal of the present study was to investigate whether TZP-101 affects colonic transit and food intake in rats with postoperative ileus. Fasted rats were treated with morphine and subjected to laparotomy under isoflurane anesthesia. Following surgery the animals were placed in clean home cages and fecal pellet output and food intake were monitored for 48 h. TZP-101 or vehicle were administered as 3 i.v. bolus infusions at 0 h, 2 h and 4 h post-surgery. TZP-101 (0.03-1 mg/kg) dose-dependently decreased the time to first bowel movement and increased fecal pellet output measured at 12 h and 24 h post-surgery compared to the vehicle. The administration of TZP-101 was not associated with a significant alteration in food intake. In conclusion, this study provides the first experimental evidence that a novel ghrelin receptor agonist improves large bowel function in rats with postoperative ileus, suggesting that TZP-101 may be useful in the clinic to accelerate upper gastrointestinal transit and to shorten the time to the first bowel movement following surgery.

Application of ghrelin to gastrointestinal diseases

This review outlines recent findings related to the therapeutic potential of ghrelin agonists or antagonists for the treatment of gastrointestinal (GI) motility disorders and the regulation of the hypothalamic control of feeding. The ability of ghrelin to promote GI motility in patients with postoperative ileus or gastroparesis, and to restore the normal feeding pattern and energy balance in the elderly and in cancer patients with impaired appetite are highlighted. A critical analysis of the possible mechanism of action and the potential benefits of using synthetic ghrelin agonists is based on data from preclinical research and recent clinical studies.

Changes in urinary bladder smooth muscle function in response to colonic inflammation

Visceral organ “cross talk” is suspected to contribute to multiorgan symptomatology found in conditions such as irritable bowel syndrome and interstitial cystitis. The goal of the present study was to investigate the short- and long-term effects of acute colitis on bladder detrusor muscle contractility. We hypothesized that inflammation of the colon leads to changes in bladder function via direct changes in detrusor smooth muscle contractility. In this study, colonic inflammation was induced in male rats via an enema of trinitrobenzenesulfonic acid (TNBS) (50 mg/kg, 0.5 ml, 25% ethanol). Colitis was confirmed using gross morphology, histology, and measurements of myeloperoxidase activity. Saline enema-treated rats served as controls. Three, 15, and 30 days postenema treatment, bladder detrusor muscle contractility was investigated in response to electrical field stimulation (EFS), cholinergic agonism with carbachol (CCh), and KCl. During active colonic inflammation ( day 3 post-TNBS enema), the bladder detrusor muscle appeared normal and showed no significant inflammation. However, abnormalities in bladder detrusor muscle contractility occurred in response to EFS and CCh but not KCl. During and after recovery from colonic inflammation ( days 15 and 30 post-TNBS enema), changes in bladder detrusor muscle contractility in response to EFS and CCh returned to control levels. We found that a transient colonic inflammatory insult significantly attenuates the amplitude of bladder detrusor muscle contractions in vitro, at least in part, through changes in cholinergic innervation, which are reversible after recovery from the colitis.

Prokinetic effects of a new ghrelin receptor agonist TZP-101 in a rat model of postoperative ileus

Postoperative ileus (POI) is a major cause of postoperative complications and prolonged hospitalization. Ghrelin, which is the endogenous ligand for the growth hormone secretagogue receptor, has been found to stimulate gastric motility and accelerate gastric emptying. The present study investigates whether TZP-101 (0.03-1 mg/kg i.v.), a synthetic ghrelin-receptor agonist, could improve gastrointestinal transit in rats with POI. Since the main factors for the development of POI are the surgical manipulation and the gastrointestinal effects of opioid-receptor agonists used for pain management, the effect of TZP-101 was investigated in rats subjected to surgery, to morphine treatment (3 mg/kg s.c.), or to a combination of both. The results showed that TZP-101 is equally effective against the delayed gastrointestinal transit induced by surgery, by morphine, or by the combination of both interventions. The prokinetic action of TZP-101 was more pronounced in the stomach compared to the small intestine.

Corticosteroid receptor-mediated mechanisms in the amygdala regulate anxiety and colonic sensitivity

Our previous studies have shown that stereotaxic implantation of corticosterone (Cort) onto the central amygdaloid nucleus increases both anxiety and colonic sensitivity. The goal of this study was to examine the relative importance of amygdaloid glucocorticoid (GR) and mineralocorticoid receptor (MR)-mediated mechanisms in the induction of anxiety and colonic hypersensitivity. In male Fischer 344 rats, Cort or cholesterol micropellets were stereotaxically implanted bilaterally at the dorsal boundary of the central amygdaloid nucleus either alone or in combination with a GR antagonist, mifepristone, or a MR antagonist, spironolactone. Anxiety was assessed on the elevated plus maze and quantified as the percentage of time spent in open arm exploration. Colonic sensitivity was measured by recording a visceromotor response, the number of abdominal muscle contractions in response to colorectal distension. In Cort-implanted rats there was a significant reduction in the percentage of time spent in the open arms of the elevated plus maze compared with cholesterol controls, indicating increased anxiety. Furthermore, colonic hypersensitivity was observed in response to colorectal distension compared with rats with cholesterol implants. In rats with Cort implants combined with either a GR or MR antagonist, there was a significant inhibition of anxiety and colonic hypersensitivity. Our data suggest that both GR and MR play a critical role in Cort-induced anxiety and colonic hypersensitivity.

Involvement of amygdaloid corticosterone in altered visceral and somatic sensation

Behavioral responses to thermal and mechanical stimuli were used to examine somatic sensitivity in rats with stereotaxic corticosterone (CORT) implants on the amygdala. These animals have previously been shown to display anxiety-like behavior coupled with colonic hypersensitivity; in this study, CORT induced not only visceral hypersensitivity but also somatic hypersensitivity. These findings suggest that modulation of the amygdala with CORT results in a generalized decrease in sensory thresholds via descending neuronal pathways.

Stress-induced breakdown of intestinal barrier function in the rat: reversal by wood creosote

Our previous studies demonstrated that wood creosote (Seirogan) inhibits intestinal secretion and normalizes the transport of electrolytes and water in rats subjected to restraint stress. The goal of the present study was to examine whether wood creosote has a protective effect against stress-induced breakdown of intestinal barrier function. F-344 rats were subjected to 90-min water avoidance stress (WAS) with wood creosote (30 mg/kg) or vehicle administered intragastrically 30 min prior to WAS. Sham stressed rats received wood creosote or vehicle treatment but did not experience the WAS. All rats were euthanized at the end of the WAS or sham-stress and the jejunum and colon were isolated. Epithelial transport was studied in modified Ussing chambers. Spontaneous secretion was assessed by electrophysiological measurement of the short circuit current (I(sc)) while electrical conductance (G) was calculated from the potential difference (PD) and I(sc) using Ohm's law. Intestinal permeability was defined by the mucosal-to-serosal flux of horseradish peroxidase (HRP). WAS significantly elevated basal I(sc) and G and increased epithelial permeability to HRP in the jejunum but not in the colon. Wood creosote resulted in a significant reduction of the stress-induced increase in I(sc), G and the mucosal-to-serosal flux of HRP compared to the vehicle-treated group. Wood creosote caused no significant effects in sham-stressed rats. The results suggest that oral administration of wood creosote may prevent stress-induced diarrhea by preventing aversive effects on small intestinal secretion and barrier function.

Long-term expression of corticotropin-releasing factor (CRF) in the paraventricular nucleus of the hypothalamus in response to an acute colonic inflammation

This study examined the long-term effects of an acute colitis on central corticotropin-releasing factor (CRF) expression. An increase in CRF mRNA in the paraventricular nucleus of the hypothalamus (PVN) and the central nucleus of the amygdala (CeA) was observed during active colitis, and the effect in the PVN was maintained following recovery. In summary, hypothalamic gene expression of CRF persists in the PVN despite resolution of an acute colitis.

Spinal cord stimulation attenuates visceromotor reflexes in a rat model of post-inflammatory colonic hypersensitivity

Spinal cord stimulation (SCS) has been found to relieve neuropathic and ischemic pain clinically and to attenuate a nociceptive reflex in an animal model of acute colonic hypersensitivity. The goal of the present study was to determine the effect of SCS in a rat model of post-inflammatory colonic hypersensitivity. Acute inflammation was induced in rats by a single enema of trinitrobenzenesulfonic acid (TNBS) (50 mg/kg, 0.5 ml, 25% EtOH). Control rats received a single saline enema. A visceromotor behavioral response (VMR), induced by innocuous colorectal distention (30 mm Hg, 10 min) was used to quantify the level of colonic sensitivity on day 3 and 30 post-enema. Prior to VMR testing, under general anesthesia, an electrode (cathode) was placed epidurally on the dorsal surface of the spinal cord at L1 with a paravertebral anode plate. Three to 7 days after implantation of the SCS electrode, the effect of SCS (50 Hz, 0.2 ms, amplitude 90% of motor threshold for 30 min) on colonic sensitivity was determined. On day 30, rats that had received a single TNBS enema were hypersensitive to innocuous colonic distention when compared to rats that received a saline enema (VMR/10 min: TNBS: 17.2+/-0.8 vs. Saline: 9.6+/-1.1, p<0.01). Spinal cord stimulation significantly reduced the VMR in the TNBS-enema group to a value that resembled the saline-enema group (VMR/10 min: TNBS: 11.2+/-1.2 vs. Saline: 10.0+/-1.0). This study provides the first evidence that SCS might be a potential therapeutic for the treatment of abdominal pain observed in patients with post-inflammatory irritable bowel syndrome.

Effects of TAK-637 on NK(1) receptor-mediated mechanisms regulating colonic secretion

This study investigates the effect of a selective NK(1) receptor antagonist TAK-637 on enteric mechanisms involved in regulation of epithelial secretion in the colon. Mucosal sheets isolated from guinea-pig colon were placed in modified Ussing chambers and the net active transport of electrolytes was measured as short-circuit current (Isc). GR-73632, a selective NK(1) receptor agonist, induced an increase in basal Isc, which was inhibited by TAK-637 (IC(50) of 21 nM). The increase in Isc induced by GR-73632 was significantly attenuated by tetrodotoxin (TTX, 1 microM), indicating that TAK-637 inhibits neuronal NK(1) receptors. Moreover, TAK-637 reduced the TTX-resistant component of the response to GR-73632 suggesting that NK(1) receptors expressed by epithelial cells are inhibited by TAK-637. In separate experiments, TAK-637 partially inhibited the submaximal Isc induced by electrical field stimulation (EFS, 0.5 ms, 15 Hz) of enteric nerves or by activation of primary afferent fibers using capsaicin (50 microM). TAK-637 had no significant effect on the basal Isc or on responses induced by neurokinin A (NKA), senktide, or forskolin. The results imply that inhibition of peripheral NK(1) receptors may reduce autonomic epithelial secretion in response to activation of autonomic secretomotor pathways, while having no significant effect on basal epithelial transport.

Oral Treatment with Recombinant Human Interleukin-11 Improves Mucosal Transport in the Colon of Human Leukocyte Antigen-B27 Transgenic Rats

Recombinant human interleukin (IL)-11 is a pleiotropic cytokine with anti-inflammatory activity. The objective of the study was to investigate whether oral treatment with rhIL-11 improves colonic epithelial dysfunction in the human leukocyte antigen (HLA)-B27 transgenic rat model of spontaneous chronic inflammation. Experiments were performed using adult male HLAB27 rats, whereas healthy nontransgenic F344 rats served as controls. Enteric-coated rhIL-11 multi-particles (equivalent to 500 microg/kg rhIL11) or placebo (formulation lacking rhIL-11) were administrated orally on alternate days for 2 weeks to HLA-B27 or F344 rats. Stool character was observed daily during the treatment period. Animals were euthanized at the end of treatment and colonic inflammation was evaluated be measuring tissue myeloperoxidase (MPO) activity. Epithelial transport in isolated colonic mucosal sheets was studied in modified Ussing chambers. Oral treatment of HLA-B27 rats with rhIL-11 reduced MPO activity in the colon and suppressed the clinical signs of diarrhea. The electrophysiological characteristics of mucosal transport were improved in the HLA-B27 rats treated with rhIL-11 compared with placebo. After rhIL-11 treatment the basal transepithelial resistance and the estimated paracellular resistance were significantly increased, neurally mediated secretory responses to electrical field stimulation were improved, and cholinoceptor sensitivity was normalized. Treatment with rhIL-11 had no significant effect on basal short circuit current and the maximal secretory response to carbachol or substance P. Our data demonstrate that oral rhIL-11 therapy is associated with suppression of mucosal inflammation and a concomitant improvement of epithelial resistance and neurally mediated secretion in a model of chronic HLA-B27 colitis.

Spinal neuronal responses to urinary bladder stimulation in rats with corticosterone or aldosterone onto the amygdala

Elevating glucocorticoids in the amygdala produces colorectal hypersensitivity through activation of lumbosacral spinal neurons. The aim of this study was to determine if descending modulation from the amygdala affects spinal processing of input from urinary bladder afferents. Fischer-344 rats received cholesterol (inactive control)-, corticosterone-, or aldosterone-containing micropellets placed stereotaxically on the dorsal margin of the left and right amygdala (n = 10 for each group). Seven days after amygdaloid implantation, extracellular potentials of single L6-S1 spinal neurons were examined for the responses to graded (0.5-2.0 ml, 20 s) urinary bladder distension (UBD). Spontaneous activity of neurons with excitatory responses to UBD in aldosterone-implanted rats [11.0 +/- 1.7 (SE) imp/s], but not in corticosterone-implanted rats, was higher than in the cholesterol-implanted group (6.6 +/- 1.1 imp/s, P < 0.05). Noxious UBD (1.5 ml) produced a greater excitatory response (21.6 +/- 2.6 imp/s) in aldosterone-implanted rats compared with cholesterol- or corticosterone-implanted rats (15.1 +/- 1.5 and 13.6 +/- 1.4 imp/s; P < 0.05). In contrast, the duration of excitatory responses to UBD in corticosterone-implanted rats (38.5 +/- 3.4 imp/s) was significantly longer than those in the aldosterone or control groups (26.8 +/- 1.8 and 24.7 +/- 1.5 imp/s). Neurons with low thresholds for excitatory responses to UBD were seen more frequently in aldosterone-implanted rats than in corticosterone or cholesterol treated rats (74 vs. 44% and 39%, P < 0.05). No difference in somatic field properties of spinal neurons responsive or nonresponsive to UBD was found among the three groups. These findings suggest that both mineralocorticoid- and glucocorticoid-mediated mechanisms in the amygdala are involved in descending modulation to lumbosacral spinal neurons receiving inputs from the urinary bladder; and this mechanism may play a role in the activation and maintenance of primary central sensitization to noxious visceral stimuli.

Seirogan (wood creosote) inhibits stress-induced ion secretion in rat intestinal epithelium

Acute stress in often associated with abnormalities in gastrointestinal function, including enhanced secretion of water and electrolytes that leads to diarrhea. The goal of our study was to investigate whether Seirogan inhibits stress-induced intestinal secretion in Wistar-Kyoto rats. Electrogenic ion secretion was measured in modified Ussing chambers as an increase in basal short-circuit current (Isc) across isolated rat jejunal or colonic mucosal sheets. Mucosal preparations from rats exposed to cold restraint stress showed a significant increase in basal Isc compared to controls. The cumulative addition of Seirogan to the Ussing chamber caused a concentration-dependent reduction of the stress-induced increase of basal Isc to levels resembling nonstressed controls. In a separate experiment, Seirogan (15 mg/kg) administered by oral gavage inhibited stress-induced secretion and normalized basal Isc in the jejunum and colon. The results suggest that Seirogan may be an effective therapy for patients with stress-associated diarrhea.

Visceromotor and spinal neuronal responses to colorectal distension in rats with aldosterone onto the amygdala

Stereotaxic delivery of corticosterone onto the amygdala produces colorectal hypersensitivity through activation of lumbosacral spinal neurons. Since corticosterone activates both the mineralocorticoid (MR) and glucocorticoid (GR) receptors, the aim of this study was to determine the importance of MRs in the regulation of colorectal hypersensitivity through the use of aldosterone that preferentially binds to MRs. Fischer-344 rats received either aldosterone (n = 18)- or cholesterol (control, n = 18)-containing micropellets bilaterally placed stereotaxically on the dorsal margin of the amygdala. After 1 wk, colorectal sensitivity to distension (30 mmHg) was measured in a subgroup of rats (n = 8/group). In other rats (n = 10/group), extracellular potentials of single L6-S1 spinal neurons in response to colorectal distension (CRD; 10-80 mmHg) were recorded. In aldosterone-implanted rats, CRD produced a greater visceromotor behavioral response compared with cholesterol controls (19 +/- 0.5 vs. 11.5 +/- 2.7; P < 0.01). A total of 68/182 (37%) and 56/167 (34%) of spinal neurons responded to noxious CRD in aldosterone-implanted and control groups, respectively. A total of 36/42 (86%) neurons excited by CRD had spontaneous activity in aldosterone-implanted groups compared with control (19/33, 58%, P < 0.01). Neurons with low thresholds for excitatory responses to CRD were seen more frequently in aldosterone-implanted rats than those in the control group (35/39 vs. 18/31, P < 0.05). Maximal excitatory responses of neurons to CRD in aldosterone-implanted rats were significantly greater (23.9 +/- 2.2 vs. 16.4 +/- 2.0 imp/s, P < 0.05), and the durations were longer (34.3 +/- 2.7 vs. 24.9 +/- 1.4 s, P < 0.05) than those in control group. Finally, a greater number of neurons had wide dynamic range responses to somatic stimulation in aldosterone-treated rats compared with cholesterol controls. Our findings suggest that, in the amygdala, MR receptor-mediated mechanisms are likely involved in descending pathways onto lumbosacral spinal neurons that induce colorectal hypersensitivity to luminal distension.

Corticosterone acts directly at the amygdala to alter spinal neuronal activity in response to colorectal distension

Administration of glucocorticoids to the amygdaloid nucleus facilitates visceromotor responses to colorectal distension in rats. The aim of this study was to determine if colorectal hypersensitivity develops through central modulation of spinal neuronal activity. Stereotaxic delivery of corticosterone (n = 10) or cholesterol (control, n = 10) onto the dorsal margin of the amygdala was performed on male Fischer-344 rats. Seven days later, extracellular potentials of single L(6)-S(1) spinal neurons were examined for responses to colorectal distension (CRD, 20-80 mmHg, 20 s) in sodium pentobarbital anesthetized and paralyzed animals. The proportions of neurons that responded to noxious CRD in corticosterone-implanted (62/186, 33%) and cholesterol-implanted (55/163, 34%) animals were virtually identical. However, the mean excitatory response of spinal neurons to CRD in corticosterone-treated rats was significantly greater (26.7 +/- 2.2 vs. 16.4 +/- 1.8 imp/s, P < 0.01) and the duration was longer (37.0 +/- 3.9 vs. 25.8 +/- 1.5 s, P < 0.05) than in the control group. No significant differences were found in neural responses to nonnoxious and noxious mechanical stimulation of somatic fields between corticosterone-implanted and control groups. In conclusion, our data support the hypothesis that central stimulation of the amygdala by corticosterone sensitizes the lumbosacral spinal neurons that mediate visceromotor reflexes to CRD.

NK1 receptor-mediated mechanisms regulate colonic hypersensitivity in the guinea pig

Neurokinin-1 (NK(1)) receptors activated by substance P (SP) are involved in the processing of nociceptive information and are a potential target for therapy of visceral pain. We have evaluated the role of NK(1) receptors using a selective antagonist of NK(1) receptors in two animal models of colorectal hypersensitivity. The behavioral response to colorectal distension was assessed in freely moving guinea pigs by recording visceromotor reflex contractions of the abdominal musculature. Colonic hypersensitivity was induced by intracolonic administration of a chemical irritant (0.6% of acetic acid), or by acute partial restraint stress. Sensitization was characterized by an exaggerated visceromotor response to a low level of colorectal distension (10 mm Hg). In both models of colonic hypersensitivity, oral administration of TAK-637 (0.1-10 mg/kg) normalized visceromotor responses. The intracerebroventricular (10 microg/kg) or intrathecal (10 microg/kg) administration of TAK-637 inhibited colonic hypersensitivity, suggesting an interaction with central NK(1) receptors. In contrast, TAK-637 had no effect on visceromotor responses to colorectal distension at 40 mm Hg in guinea pigs with normosensitive (nonsensitized) colons. In conclusion, central NK(1) receptors play a significant role in colonic hypersensitivity induced by visceral afferent nerve sensitization from gastrointestinal origin or acute psychosomatic stress, but not in the perception of colorectal distension in animals with normosensitive colons.

Attenuation by spinal cord stimulation of a nociceptive reflex generated by colorectal distention in a rat model

The mechanisms underlying the cause and treatment of visceral pain of gastrointestinal origin are poorly understood. Previous clinical studies have shown that spinal cord stimulation (SCS) attenuates neuropathic and ischemic pain, and animal experiments have provided knowledge about probable physiological mechanisms. The goal of the present study was to investigate whether SCS influences colonic sensitivity in a conscious rat. A visceromotor behavioral response (VMR), induced by colorectal distention, was used to quantify the level of colonic sensitivity. Under anesthesia, an electrode (cathode) was placed on the dorsal surface of the spinal cord at L1. One week after implantation of the SCS electrode, the effects of stimulation delivered with different intensities (50 Hz, 0.2 ms for 30 min) on colonic sensitivity were determined. Nociceptive levels of colorectal distention (60 mm Hg for 10 min) induced an enhanced VMR quantified as an increased number of abdominal muscle contractions compared to controls in which the balloon catheter was inserted into the colorectal region but not distended. Colonic sensitization with acetic acid increased the VMR to innocuous levels of colorectal distention (30 mm Hg for 10 min). We found that SCS induced a significant depression of the VMR produced by colorectal distention in both normal rats and those with sensitized colons. The suppressive effect of SCS on colonic sensitivity suggests that SCS may have therapeutic potential for the treatment of visceral pain of gastrointestinal origin associated with abdominal cramping and painful abdominal spasms.

Effects of seirogan (wood creosote) on propulsive colonic motility and stool characteristics in ambulatory mini-pigs

Our goal was to determine whether Seirogan, an herbal medicine used as an antidiarrheal agent, modifies colonic function, including motility. Experiments were performed on four female Yucatan mini-pigs with established permanent cecal fistulas providing direct access to the colon. Long-term recordings of proximal colonic motility were accomplished by a solid-state probe (six pressure ports 10 cm apart), and a motility index was calculated. Stool viscosity was also measured. The laxative bisacodyl (15 mg/kg) was used to induce colonic motility (increase in motility index) and stool softening, prior to investigating the effect of Seirogan (2-15 mg/kg per os twice a day) or a vehicle control. Seirogan (15 mg/kg), but not the placebo, reversed the bisacodyl-induced stool softening and restored the motility index to normal values by reducing the number of propagating contractions. Taken together the results suggest that inhibition of proximal colonic motility by Seirogan may contribute to its antidiarrheal action.