Anthony C. Johnson

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.

Corticotropin‐releasing factor 1 receptor‐mediated mechanisms inhibit colonic hypersensitivity in rats

Abstract  The potential relationship between stress and irritable bowel syndrome (IBS) symptomatology suggests a possible role for stress‐mediating hormones, such as corticotropin‐releasing factor (CRF), in the altered perception of stimuli in IBS patients. In previous studies, Wistar–Kyoto (WKY) rats with genetic indices of high anxiety demonstrated colonic hypersensitivity coupled with a high basal level of CRF within the central nervous system. In the current study we tested the hypothesis that a selective, non‐peptide CRF1 receptor antagonist, antalarmin, would inhibit hypersensitivity in the WKY rat colon. Colonic sensitivity was determined by monitoring a visceromotor behavioural response during innocuous levels of colorectal distention (30 mmHg). In high anxiety WKY rats we found that antalarmin (20 mg kg−1, i.p.) significantly decreased the visceromotor response induced by colorectal distention. In a second study central administration (i.c.v.) of CRF was used to induce colonic hypersensitivity in lower anxiety Fischer 344 (F‐344) rats, and in this model, antalarmin significantly inhibited the CRF‐induced colonic hypersensitivity. In summary, a selective CRF1 receptor antagonist, antalarmin, inhibits colonic hypersensitivity apparent in WKY rats or in F‐344 rats given a central administration of CRF. Our findings suggest that CRF1 receptor antagonism may represent a novel therapeutic approach for the treatment of IBS.

Effects of serotonin transporter inhibition on gastrointestinal motility and colonic sensitivity in the mouse

Abstract  Serotonin‐selective reuptake transporter (SERT) expression is decreased in animal models of intestinal inflammation and in individuals with inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS), and it is possible that resultant changes in intestinal serotonin signalling contribute to the manifestation of clinical features associated with these disorders. The objective of this investigation was to determine whether inhibition of SERT function leads to changes in gut motility and sensitivity. Mice underwent a 14‐day treatment with the SERT inhibitor, paroxetine (20 mg kg−1), or vehicle (saline/propylene glycol). Gastrointestinal (GI) transit following charcoal gavage, colonic motility, stool frequency and visceromotor responses to colorectal distension were evaluated. In mice treated with paroxetine, stool output was decreased, upper GI transit was delayed, and colonic sensitivity to a nociceptive stimulus was attenuated. These results demonstrate that reduced SERT function (via pharmacological blockade) significantly alters GI motility and sensitivity in mice, and support the concept that altered SERT expression and function could contribute to symptoms associated with IBS and IBD.

Stress and the Microbiota–Gut–Brain Axis in Visceral Pain: Relevance to Irritable Bowel Syndrome

Visceral pain is a global term used to describe pain originating from the internal organs of the body, which affects a significant proportion of the population and is a common feature of functional gastrointestinal disorders (FGIDs) such as irritable bowel syndrome (IBS). While IBS is multifactorial, with no single etiology to completely explain the disorder, many patients also experience comorbid behavioral disorders, such as anxiety or depression; thus, IBS is described as a disorder of the gut–brain axis. Stress is implicated in the development and exacerbation of visceral pain disorders. Chronic stress can modify central pain circuitry, as well as change motility and permeability throughout the gastrointestinal (GI) tract. More recently, the role of the gut microbiota in the bidirectional communication along the gut–brain axis, and subsequent changes in behavior, has emerged. Thus, stress and the gut microbiota can interact through complementary or opposing factors to influence visceral nociceptive behaviors. This review will highlight the evidence by which stress and the gut microbiota interact in the regulation of visceral nociception. We will focus on the influence of stress on the microbiota and the mechanisms by which microbiota can affect the stress response and behavioral outcomes with an emphasis on visceral pain.

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.

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.

Corticotropin‐releasing factor receptor 1‐deficient mice show decreased anxiety and colonic sensitivity

Abstract  Corticotropin releasing factor (CRF) is an important mediator in the stress response. Previous studies in rodent models demonstrated that stress‐induced colonic hypersensitivity was inhibited by CRF1 receptor antagonism. As CRF1R‐deficient mice have an impaired stress response our goal was to further explore the importance of CRF1R in the development of colonic hypersensitivity. Using conscious CRF1R (+/+), CRF1R (+/−) and CRF1R (−/−) mice colonic sensitivity was assessed via a visceromotor behavioural response (VMR) induced by colorectal distension (CRD, 0–60 mmHg). In the CRF1R (+/+) mice there was a pressure‐dependent increase in the VMR to CRD that was moderately attenuated in the CRF1R (+/−) mice. However in the CRF1R (−/−) mice a VMR to CRD was only observed at the highest distension pressure (60 mmHg). A CRF1R antagonist, NBI 30775 (30 mg kg−1 i.p.) significantly decreased the VMR to CRD in CRF1R +/+ mice. An identical inhibitory effect of NBI 30775 was observed in 43% of the CRF1R +/− mice. This study provides pharmacological and genetic evidence for the importance of CRF1R in colonic sensitivity and suggests a link between stress and visceral perception.

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.

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.

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.