5-HT (serotonin) physiology and related drugs

Similarities and differences between nigral and enteric dopaminergic neurons unravel distinctive involvement in Parkinson's disease

In addition to the well-known degeneration of midbrain dopaminergic neurons, enteric neurons can also be affected in neurodegenerative disorders such as Parkinson's disease (PD). Dopaminergic neurons have recently been identified in the enteric nervous system (ENS). While ENS dopaminergic neurons have been shown to degenerate in genetic mouse models of PD, analyses of their survival in enteric biopsies of PD patients have provided inconsistent results to date. In this context, this review seeks to highlight the distinctive and shared factors and properties that control the evolution of these two sets of dopaminergic neurons from neuronal precursors to aging neurons. Although their cellular sources and developmental times of origin differ, midbrain and ENS dopaminergic neurons express many transcription factors in common and their respective environments express similar neurotrophic molecules. For example, Foxa2 and Sox6 are expressed by both populations to promote the specification, differentiation, and long-term maintenance of the dopaminergic phenotype. Both populations exhibit sustained patterns of excitability that drive intrinsic vulnerability over time. In disorders such as PD, colon biopsies have revealed aggregation of alpha-synuclein in the submucosal plexus where dopaminergic neurons reside and lack blood barrier protection. Thus, these enteric neurons may be more susceptible to neurotoxic insults and aggregation of α-synuclein that spreads from gut to midbrain. Under sustained stress, inefficient autophagy leads to neurodegeneration, GI motility dysfunction, and PD symptoms. Recent findings suggest that novel neurotrophic factors such as CDNF have the potential to be used as neuroprotective agents to prevent and treat ENS symptoms of PD.

Crosstalk Between Intestinal Serotonergic System and Pattern Recognition Receptors on the Microbiota-Gut-Brain Axis

Disruption of the microbiota-gut-brain axis results in a wide range of pathologies that are affected, from the brain to the intestine. Gut hormones released by enteroendocrine cells to the gastrointestinal (GI) tract are important signaling molecules within this axis. In the search for the language that allows microbiota to communicate with the gut and the brain, serotonin seems to be the most important mediator. In recent years, serotonin has emerged as a key neurotransmitter in the gut-brain axis because it largely contributes to both GI and brain physiology. In addition, intestinal microbiota are crucial in serotonin signaling, which gives more relevance to the role of the serotonin as an important mediator in microbiota-host interactions. Despite the numerous investigations focused on the gut-brain axis and the pathologies associated, little is known regarding how serotonin can mediate in the microbiota-gut-brain axis. In this review, we will mainly discuss serotonergic system modulation by microbiota as a pathway of communication between intestinal microbes and the body on the microbiota-gut-brain axis, and we explore novel therapeutic approaches for GI diseases and mental disorders.

Post-inflammatory Abdominal Pain in Patients with Inflammatory Bowel Disease During Remission: A Comprehensive Review

Patients with inflammatory bowel disease often experience ongoing pain even after achieving mucosal healing (i.e., post-inflammatory pain). Factors related to the brain-gut axis, such as peripheral and central sensitization, altered sympatho-vagal balance, hypothalamic-pituitary-adrenal axis activation, and psychosocial factors, play a significant role in the development of post-inflammatory pain. A comprehensive study investigating the interaction between multiple predisposing factors, including clinical psycho-physiological phenotypes, molecular mechanisms, and multi-omics data, is still needed to fully understand the complex mechanism of post-inflammatory pain. Furthermore, current treatment options are limited and new treatments consistent with the underlying pathophysiology are needed to improve clinical outcomes.

Irritable Bowel Syndrome in Pregnancy

Irritable bowel syndrome (IBS) affects a significant percentage of the general population and is more common in women. A large proportion of women affected with IBS are of childbearing age; however, there is a paucity of studies and guidelines to specifically address the epidemiology, course, maternal/fetal prognosis, or management of IBS in pregnancy. This scarcity of literature on IBS and pregnancy poses significant challenges to healthcare providers in counseling and managing patients. In this comprehensive review, we summarize the current literature and knowledge gaps regarding the effects of pregnancy on IBS and vice versa, along with the efficacy and safety profiles of commonly used IBS diets and medications in pregnancy. The management of pregnant women with IBS should be multidisciplinary, with emphasis on education and judicious use of dietary modifications and pharmacologic options that are deemed relatively safe during pregnancy.

Neuronal innervation of the intestinal crypt

Mucosal damage is a key feature of inflammatory bowel diseases (IBD) and healing of the mucosa is an endpoint of IBD treatment that is often difficult to achieve. Autonomic neurons of the parasympathetic and sympathetic nervous system may influence intestinal epithelial cell growth and modulating epithelial innervation could for that reason serve as an interesting therapeutic option to improve mucosal healing. Understanding of the biological processes triggered by nonspecific and specific epithelial adrenergic and cholinergic receptor activation is of key importance. At present, with rising technological advances, bioelectronic neuromodulation as treatment modality has gained momentum. We discuss the current view on state-of-the-art innervation of the intestinal crypt and its impact on epithelial cell growth and differentiation. Furthermore, we outline bioelectronic technology and review its relevance to wound healing processes.

Dopamine receptors in emesis: Molecular mechanisms and potential therapeutic function

Dopamine is a member of the catecholamine family and is associated with multiple physiological functions. Together with its five receptor subtypes, dopamine is closely linked to neurological disorders such as schizophrenia, Parkinson's disease, depression, attention deficit-hyperactivity, and restless leg syndrome. Unfortunately, several dopamine receptor-based agonists used to treat some of these diseases cause nausea and vomiting as impending side-effects. The high degree of cross interactions of dopamine receptor ligands with many other targets including G-protein coupled receptors, transporters, enzymes, and ion-channels, add to the complexity of discovering new targets for the treatment of nausea and vomiting. Using activation status of signaling cascades as mechanism-based biomarkers to foresee drug sensitivity combined with the development of dopamine receptor-based biased agonists may hold great promise and seems as the next step in drug development for the treatment of such multifactorial diseases. In this review, we update the present knowledge on dopamine and dopamine receptors and their potential roles in nausea and vomiting. The pre- and clinical evidence provided in this review supports the implication of both dopamine and dopamine receptor agonists in the incidence of emesis. Besides the conventional dopaminergic antiemetic drugs, potential novel antiemetic targeting emetic protein signaling cascades may offer superior selectivity profile and potency.

What We Know and What We Need to Know about Aromatic and Cationic Biogenic Amines in the Gastrointestinal Tract

Biogenic amines derived from basic and aromatic amino acids (B/A-BAs), polyamines, histamine, serotonin, and catecholamines are a group of molecules playing essential roles in many relevant physiological processes, including cell proliferation, immune response, nutrition and reproduction. All these physiological effects involve a variety of tissue-specific cellular receptors and signalling pathways, which conforms to a very complex network that is not yet well-characterized. Strong evidence has proved the importance of this group of molecules in the gastrointestinal context, also playing roles in several pathologies. This work is based on the hypothesis that integration of biomedical information helps to reach new translational actions. Thus, the major aim of this work is to combine scientific knowledge on biomolecules, metabolism and physiology of the main B/A-BAs involved in the pathophysiology of the gastrointestinal tract, in order to point out important gaps in information and other facts deserving further research efforts in order to connect molecular information with pathophysiological observations.

Potential rat model of anxiety-like gastric hypersensitivity induced by sequential stress

AIM

To establish a rat model of anxiety-like gastric hypersensitivity (GHS) of functional dyspepsia (FD) induced by novel sequential stress.

METHODS

Animal pups were divided into two groups from postnatal day 2: controls and the sequential-stress-treated. The sequential-stress-treated group received maternal separation and acute gastric irritation early in life and restraint stress in adulthood; controls were reared undisturbed with their mothers. Rats in both groups were followed to adulthood (8 wk) at which point the anxiety-like behaviors and visceromotor responses to gastric distention (20-100 mmHg) and gastric emptying were tested. Meanwhile, alterations in several anxiety-related brain-stomach modulators including 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (GABA), brain-derived neurotrophic factor (BDNF) and nesfatin-1 in the rat hippocampus, plasma and gastric fundus and the 5-HT1A receptor (5-HT1AR) in the hippocampal CA1 subfield and the mucosa of the gastric fundus were examined.

RESULTS

Sequential-stress-treated rats simultaneously demonstrated anxiety-like behaviors and GHS in dose-dependent manner compared with the control group. Although rats in both groups consumed similar amount of solid food, the rate of gastric emptying was lower in the sequential-stress-treated rats than in the control group. Sequential stress significantly decreased the levels of 5-HT (51.91 ± 1.88 vs 104.21 ± 2.88, P < 0.01), GABA (2.38 ± 0.16 vs 5.01 ± 0.13, P < 0.01) and BDNF (304.40 ± 10.16 vs 698.17 ± 27.91, P < 0.01) in the hippocampus but increased the content of nesfatin-1 (1961.38 ± 56.89 vs 1007.50 ± 33.05, P < 0.01) in the same site; significantly decreased the levels of 5-HT (47.82 ± 2.29 vs 89.45 ± 2.61, P < 0.01) and BDNF (257.05 ± 12.89 vs 536.71 ± 20.73, P < 0.01) in the plasma but increased the content of nesfatin-1 in it (1391.75 ± 42.77 vs 737.88 ± 33.15, P < 0.01); significantly decreased the levels of 5-HT (41.15 ± 1.81 vs 89.17 ± 2.31, P < 0.01) and BDNF (226.49 ± 12.10 vs 551.36 ± 16.47, P < 0.01) in the gastric fundus but increased the content of nesfatin-1 in the same site (1534.75 ± 38.52 vs 819.63 ± 38.04, P < 0.01). The expressions of 5-HT1AR in the hippocampal CA1 subfield and the mucosa of the gastric fundus were down-regulated measured by IHC (Optical Density value: Hippocampus 15253.50 ± 760.35 vs 21149.75 ± 834.13; gastric fundus 15865.25 ± 521.24 vs 23865.75 ± 1868.60; P < 0.05, respectively) and WB (0.38 ± 0.01 vs 0.57 ± 0.03, P < 0.01) (n = 8 in each group).

CONCLUSION

Sequential stress could induce a potential rat model of anxiety-like GHS of FD, which could be used to research the mechanisms of this intractable disease.

An Initial Attack of Urinary Stone Disease Is Associated with an Increased Risk of Developing New-Onset Irritable Bowel Syndrome: Nationwide Population-Based Study

BACKGROUND

The neurotransmitter pathways in irritable bowel syndrome (IBS) and urinary stone attacks are both related to serotonin, and each disease may be influenced by viscero-visceral hyperalgesia. However, the relationship between urinary tract stone disease and IBS has never been addressed. We aimed to investigate the risk of suffering new-onset IBS after an initial urinary stone attack using a nationwide database.

METHODS

A study group enrolled a total of 13,254 patients who were diagnosed with an initial urinary stone attack; a comparison group recruited 39,762 matched non-urinary stone participants during 2003 and 2007. We followed each patient for 3 years to determine new-onset IBS. We also used Cox proportional hazards models to analyze the risk of IBS between the study and comparison groups after modified by demographics, residence, patient characteristics and personal histories.

RESULTS

The occurrence rates of IBS were 3.3% (n = 440) and 2.6% (n = 1,034) respectively in the study and comparison groups. A covariate-adjusted hazard ratio (HR) of IBS in the study group that was 1.28 times greater (HR = 1.29, 95% CI, 1.15-1.44) than that in the comparison group was showed in the stratified Cox proportional analysis. The adjusted HRs of IBS did not decrease after considering demographics and past histories. The majority of IBS (30.5%) occurred within the first 6 months after the stone attack.

CONCLUSION

Patients with an initial urinary stone attack are at increased risk of developing new-onset IBS. The HRs of IBS did not decrease even after adjusting for patient demographics and past histories. Most importantly, 30.5% of IBS occurred within the first 6 months after the urinary stone attack.

Role of serotonin signaling system in gastrointestinal tract: Implications for regulatory effect of acupuncture and moxibustion on irritable bowel syndrome

The 5-hydroxytryptamine (serotonin, or 5-HT) signaling system plays a key role in the gastrointestinal tract. There have been many studies on the 5-HT signaling system involved in the gastrointestinal tract. This article reviews the recent advances in the knowledge of 5-HT signaling pathways in the gastrointestinal tract, including 5-HT receptor types and subtypes, their distribution in the gastrointestinal tract, physiological and pathological roles of the 5-HT signal system in the gastrointestinal tract, and the change of the 5-HT signal pathway in the gastrointestinal tract. On the basis of the understanding of the above knowledge, we discuss how acupuncture and moxibustion regulate gastrointestinal diseases, especially IBS, through the 5-HT signal system.

Metabolic kinetics of 5-hydroxytryptamine and the research targets of functional gastrointestinal disorders

5-Hydroxytryptamine (5-HT) is an important neurotransmitter in both the central and enteric nervous systems. It has diverse functions in regulating gastrointestinal motility and visceral sensitivity, emotion, appetite, pain and sensory perception, cognition, sexual activity and sleep. These functions are mainly associated with the metabolic kinetics of 5-HT in different tissues. Tryptophan hydroxylase is the rate-limiting enzyme and modulates serotonin synthesis. Vesicular monoamine transporter 1 plays a role in 5-HT storage and release. Degradation of 5-HT is mediated by monoamine oxidase-A. All these factors influence the action of 5-HT in vivo. Functional gastrointestinal disorders (FGIDs) are characterized by a series of symptoms including abdominal pain, diarrhea, constipation, anxiety and depression, in the absence of identifiable structural or biochemical abnormalities. They are frequently accompanied by changed gut motility or visceral sensitivity. An increasing body of research has found FGIDs to be closely associated with 5-HT, and drugs such as citalopram, paroxetine, venlafaxine, alosetron, tegaserod, prucalopride and mosapride have all been developed or discovered from the perspective of the metabolic kinetics of 5-HT. This review discusses the relationship between the metabolic kinetics of 5-HT and research targets in the field of FGIDs and suggests areas of future study that may be useful for understanding these disorders and identification of potential therapeutic targets.

Visceral analgesic effect of 5-HT(4) receptor agonist in rats involves the rostroventral medulla (RVM)

The 5-HT(4) receptor agonist tegaserod (TEG) has been reported to modulate visceral pain. However, the underlying mechanism remains unknown. The objective of the present study was to examine the analgesic mechanism and site of action of TEG. In male rats, visceral pain was assessed by measuring visceromotor response (VMR) to colorectal distension (CRD). Inflammation was induced by intracolonic injection of tri-nitrobenzene sulfonic acid (TNBS). The effect of TEG on the VMR was tested by injecting intraperitoneal (i.p.), intrathecal (i.t.), intracerebroventricular (i.c.v) or in the rostroventral medulla (RVM). The effect of the drug was also tested on responses of CRD-sensitive pelvic nerve afferents (PNA) and lumbo-sacral (LS) spinal neurons. Systemic injection of TEG attenuated VMR in naive and TNBS-treated rats. Similarly, supraspinal, but not spinal, injection of TEG attenuated the VMR. While GR113808, (selective 5-HT(4) antagonist) blocked the effect, naloxone (NLX) an opioid receptor antagonist reversed the effect of TEG. Although i.t. NLX did not block the inhibitory effect of TEG in VMR study, i.t. injection of α2-adrenergic receptor antagonist yohimbine blocked the effect of TEG when given systemically. While TEG had no effect on the responses of CRD-sensitive PNA, it inhibited the responses of CRD-sensitive LS neurons in spinal intact condition. This inhibition was blocked by GR113808, NLX and β-funaltrexamine (β-FNA) when injected into the RVM. Results indicate that TEG produces analgesia via activation of supraspinal 5-HT(4) receptors which triggers the release of opioids at supraspinal site, which activates descending noradrenergic pathways to the spinal cord to produce analgesia.

Effects of 5-HT2B, 5-HT3 and 5-HT4 receptor antagonists on gastrointestinal motor activity in dogs

AIM: To study the effects of 5-hydroxytryptamine (5-HT) receptor antagonists on normal colonic motor activity in conscious dogs.

METHODS: Colonic motor activity was recorded using a strain gauge force transducer in 5 dogs before and after 5-HT2B, 5-HT3 and 5-HT4 receptor antagonist administration. The force transducers were implanted on the serosal surfaces of the gastric antrum, terminal ileum, ileocecal sphincter and colon. Test materials or vehicle alone was administered as an intravenous bolus injection during a quiescent period of the whole colon in the interdigestive state. The effects of these receptor antagonists on normal gastrointestinal motor activity were analyzed.

RESULTS: 5-HT2B, 5-HT3 and 5-HT4 receptor antagonists had no contractile effect on the fasting canine terminal ileum. The 5-HT3 and 5-HT4 receptor antagonists inhibited phase III of the interdigestive motor complex of the antrum and significantly inhibited colonic motor activity. In the proximal colon, the inhibitory effect was dose dependent. Dose dependency, however, was not observed in the distal colon. The 5-HT2B receptor antagonist had no contractile effect on normal colonic motor activity.

CONCLUSION: The 5-HT3 and 5-HT4 receptor antagonists inhibited normal colonic motor activity. The 5-HT2B receptor antagonist had no contractile effect on normal colonic motor activity.

Is serotonin in enteric nerves required for distension-evoked peristalsis and propulsion of content in guinea-pig distal colon?

Recent studies have shown genetic deletion of the gene that synthesizes 5-HT in enteric neurons (tryptophan hydroxylase-2, Tph-2) leads to a reduction in intestinal transit. However, deletion of the Tph-2 gene also leads to major developmental changes in enteric ganglia, which could also explain changes in intestinal transit. We sought to investigate this further by acutely depleting serotonin from enteric neurons over a 24-h period, without the confounding influences induced by genetic manipulation. Guinea-pigs were injected with reserpine 24h prior to euthanasia. Video-imaging and spatio-temporal mapping was used to record peristalsis evoked by natural fecal pellets, or slow infusion of intraluminal fluid. Immunohistochemical staining for 5-HT was used to detect the presence of serotonin in the myenteric plexus. It was found that endogenous 5-HT was always detected in myenteric ganglia of control animals, but never in guinea-pigs treated with reserpine. Interestingly, peristalsis was still reliably evoked by either intraluminal fluid, or fecal pellets in reserpine-treated animals that also had their entire mucosa and submucosal plexus removed. In these 5-HT depleted animals, there was no change in the frequency of peristalsis or force generated during peristalsis. In control animals, or reserpine treated animals, high concentrations (up to 10 μM) of ondansetron and SDZ-205-557, or granisetron and SDZ-205-557 had no effect on peristalsis. In summary, acute depletion of serotonin from enteric nerves does not prevent distension-evoked peristalsis, nor propulsion of luminal content. Also, we found no evidence that 5-HT3 and 5-HT4 receptor activation is required for peristalsis, or propulsion of contents to occur. Taken together, we suggest that the intrinsic mechanisms that generate peristalsis and entrain propagation along the isolated guinea-pig distal colon are independent of 5-HT in enteric neurons or the mucosa, and do not require the activation of 5-HT3 or 5-HT4 receptors.

Rethinking 5-HT1A receptors: emerging modes of inhibitory feedback of relevance to emotion-related behavior

The complexities of the involvement of the serotonin transmitter system in numerous biological processes and psychiatric disorders is, to a substantial degree, attributable to the large number of serotonin receptor families and subtypes that have been identified and characterized for over four decades. Of these, the 5-HT(1A) receptor subtype, which was the first to be cloned and characterized, has received considerable attention based on its purported role in the etiology and treatment of mood and anxiety disorders. 5-HT(1A) receptors function both at presynaptic (autoreceptor) and postsynaptic (heteroreceptor) sites. Recent research has implicated distinct roles for these two populations of receptors in mediating emotion-related behavior. New concepts as to how 5-HT(1A) receptors function to control serotonergic tone throughout life were highlights of the proceedings of the 2012 Serotonin Club Meeting in Montpellier, France. Here, we review recent findings and current perspectives on functional aspects of 5-HT(1A) auto- and heteroreceptors with particular regard to their involvement in altered anxiety and mood states.

Probing the diversity of serotonin neurons

The serotonin (5-HT) system is generally considered as a single modulatory system, with broad and diffuse projections. However, accumulating evidence points to the existence of distinct cell groups in the raphe. Here, we review prior evidence for raphe cell heterogeneity, considering different properties of 5-HT neurons, from metabolism to anatomy, and neurochemistry to physiology. We then summarize more recent data in mice and zebrafish that support a genetic diversity of 5-HT neurons, based on differential transcription factor requirements for the acquisition of the 5-HT identity. In both species, PET1 plays a major role in the acquisition and maintenance of 5-HT identity in the hindbrain, although some 5-HT neurons do not require PET1 for their differentiation, indicating the existence of several transcriptional routes to become serotoninergic. In mice, both PET1-dependent and -independent 5-HT neurons are located in the raphe, but have distinct anatomical features, such as the morphology of axon terminals and projection patterns. In zebrafish, all raphe neurons express pet1, but Pet1-independent 5-HT cell groups are present in the forebrain. Overall, these observations support the view that there are a number of distinct 5-HT subsystems, including within the raphe nuclei, with unique genetic programming and functions.

Serotonin: from top to bottom

Serotonin is a monoamine neurotransmitter, which is phylogenetically conserved in a wide range of species from nematodes to humans. In mammals, age-related changes in serotonin systems are known risk factors of age-related diseases, such as diabetes, faecal incontinence and cardiovascular diseases. A decline in serotonin function with aging would be consistent with observations of age-related changes in behaviours, such as sleep, sexual behaviour and mood all of which are linked to serotonergic function. Despite this little is known about serotonin in relation to aging. This review aims to give a comprehensive analysis of the distribution, function and interactions of serotonin in the brain; gastrointestinal tract; skeletal; vascular and immune systems. It also aims to demonstrate how the function of serotonin is linked to aging and disease pathology in these systems. The regulation of serotonin via microRNAs is also discussed, as are possible applications of serotonergic drugs in aging research and age-related diseases. Furthermore, this review demonstrates that serotonin is potentially involved in whole organism aging through its links with multiple organs, the immune system and microRNA regulation. Methods to investigate these links are discussed.

Disturbed development of the enteric nervous system after in utero exposure of selective serotonin re-uptake inhibitors and tricyclic antidepressants. Part 1: Literature review

The increase in selective serotonin re-uptake inhibitor (SSRI) use during pregnancy, questions concerning abnormal development of the enteric nervous system (ENS), increase in laxative use in children and the association of fluoxetine with infantile hypertrophic pyloric stenosis (IHPS) gave rise to this pharmacological literature review. The role of 5-HT and the NE uptake in ontogeny of the ENS and the effects SSRIs and TCAs might have on the development of the ENS were investigated. The literature study showed that SSRIs may influence the development of the ENS in two ways. Blockage of the serotonin re-uptake transporter (SERT) during foetal development could influence migration, differentiation and survival of cells. This could lead to abnormal development in the first trimester of pregnancy. The other way is that 5-HT seems to be a growth factor in the primitive ENS. This growth factor like action is mediated through the 5-HT(2B) receptor and stimulation of this receptor by SSRIs influences the fate of late-developing enteric neurons. This could lead to abnormal development in the second and third trimester. TCAs could influence the development of the ENS, besides through inhibition of the SERT, through inhibition of the norepinephrine transporter (NET). Expression of the NET seems to be essential for a full development of enteric neurons and especially for serotonergic neurons. In addition the NET was detected early in ontogeny and precedes neuronal differentiation, which suggests that TCAs might influence development of the ENS when exposed early in pregnancy. The insights of this study gave rise to hypotheses which will be tested in an epidemiological cohort study.

NUMERICAL SIMULATION OF THE ROLE OF CO-TRANSMISSION BY ACETYLCHOLINE AND SEROTONIN ON MOTILITY OF THE GUT

Electrophysiological mechanisms of co-transmission by serotonin (5-HT) and acetylcholine (ACh), co-expression of their receptor types, i.e., 5-HT type 3 and 4, nicotinic cholinerginc (nACh) and muscarinic cholinergic (μACh), and effects of selective and non-selective 5-HT3 and 5-HT4 receptor agonists/antagonists, on electromechanical activity of the gut were studied numerically. Two series of numerical experiments were performed. First, the dynamics of the generation and propagation of electrical signals interconnected with the primary sensory (AH) neurons, motor (S) neurons and smooth muscle cells were studied in a one-dimensional model. Simulations showed that stimulation of the 5-HT3 receptors reduced the threshold of activation of the mechanoreceptors by 17.6%. Conjoint excitation of the 5-HT3 and 5-HT4 receptors by endogenous serotonin converted the regular firing pattern of electrical discharges of the AH and S neurons to a beating mode. Activation confined to 5-HT3 receptors, located on the somas of the adjacent AH and S type neurons, could not sustain normal signal transduction between them. It required ACh as a co-transmitter and co-activation of the nACh receptors. Application of selective 5-HT3 receptor antagonists inhibited dose-dependently the production of action potentials at the level of mechanoreceptors and the soma of the primary sensory neuron and increased the threshold activation of the mechanoreceptors. Normal mechanical contractile activity depended on co-stimulation of the 5-HT4 and μACh receptors on the membrane of smooth muscle cells. In the second series of simulations, which involved a spatio-temporal model of the functional unit, effects of co-transmission by ACh and 5-HT on the electromechanical response in a segment of the gut were analyzed. Results indicated that propagation of the wave of excitation between the AH and S neurons within the myenteric nervous plexus in the presence of 5-HT3 receptor antagonists was supported by co-release of ACh. Co-stimulation of 5-HT3, nACh and μACh receptors impaired propulsive activity of the gut. The bolus showed uncoordinated movements. In an ACh-free environment Lotronex (GlaxoSmithKline), a 5-HT3 receptor antagonist, significantly increased the transit time of the pellet along the gut. In the presence of ACh, Lotronex produced intensive tonic-type contractions in the longitudinal and circular smooth muscle layers and eliminated propulsive activity. The 5HT4 receptor agonist, Zelnorm (Novartis), preserved the reciprocal electromechanical relationships between the longitudinal and circular smooth muscle layers. The drug changed the normal propulsive pattern of activity to an expulsive (non-mixing) type. Treatment of the gut with selective 5HT4 receptor antagonists increased the transit time by disrupting the migrating myoelectrical complex. Cisapride (Janssen), a mixed 5HT3 and 5HT4 receptor agonist, increased excitability of the AH and S neurons and the frequency of slow waves. Longitudinal and circular smooth muscle syncytia responded with the generation of long-lasting tonic contractions, resulting in a "squeezing" type of pellet movement. Comparison of the theoretical results obtained on one-dimensional and spatio-temporal models to in vivo and in vitro experimental data indicated satisfactory qualitative, and where available, quantitative agreement.

Mechanisms of Broad-Spectrum Antiemetic Efficacy of Cannabinoids against Chemotherapy-Induced Acute and Delayed Vomiting

Chemotherapy-induced nausea and vomiting (CINV) is a complex pathophysiological condition and consists of two phases. The conventional CINV neurotransmitter hypothesis suggests that the immediate phase is mainly due to release of serotonin (5-HT) from the enterochromaffin cells in the gastrointestinal tract (GIT), while the delayed phase is a consequence of release of substance P (SP) in the brainstem. However, more recent findings argue against this simplistic neurotransmitter and anatomical view of CINV. Revision of the hypothesis advocates a more complex, differential and overlapping involvement of several emetic neurotransmitters/modulators (e.g. dopamine, serotonin, substance P, prostaglandins and related arachidonic acid derived metabolites) in both phases of emesis occurring concomitantly in the brainstem and in the GIT enteric nervous system (ENS) [1]. No single antiemetic is currently available to completely prevent both phases of CINV. The standard antiemetic regimens include a 5-HT₃ antagonist plus dexamethasone for the prevention of acute emetic phase, combined with an NK₁ receptor antagonist (e.g. aprepitant) for the delayed phase. Although NK₁ antagonists behave in animals as broad-spectrum antiemetics against different emetogens including cisplatin-induced acute and delayed vomiting, by themselves they are not very effective against CINV in cancer patients. Cannabinoids such as D⁸-THC also behave as broad-spectrum antiemetics against diverse emetic stimuli as well as being effective against both phases of CINV in animals and patients. Potential side effects may limit the clinical utility of direct-acting cannabinoid agonists which could be avoided by the use of corresponding indirect-acting agonists. Cannabinoids (both phyto-derived and synthetic) behave as agonist antiemetics via the activation of cannabinoid CB₁ receptors in both the brainstem and the ENS emetic loci. An endocannabinoid antiemetic tone may exist since inverse CB₁ agonists (but not the corresponding silent antagonists) cause nausea and vomiting.

The role of 5-HT3 and 5-HT4 receptors in the adaptive mechanism of colonic transit following the parasympathetic denervation in rats

BACKGROUND

Clinical studies show that disturbed colonic motility induced by extrinsic nerves damage is restored over time. We studied whether 5-HT3 and 5HT4 receptors are involved in mediating the adaptive mechanisms following parasympathetic denervation.

METHODS

Parasympathetic denervation of the entire colon was achieved by bilateral pelvic nerve transection and truncal vagotomy in rats. Colonic transit was measured by calculating the geometric center (GC) of 51Cr distribution. Expression of 5-HT3 and 5HT4 receptor mRNA was determined by real time RT-PCR.

RESULTS

Parasympathetic denervation caused a significant delay in colonic transit (GC=4.36) at postoperative day (POD) 1, compared with sham operation (GC=6.31). Delayed transit was gradually restored by POD 7 (GC=5.99) after the denervation. Restored colonic transit was antagonized by the administration of 5-HT3 and 5HT4 receptors antagonists at POD 7. 5-HT3 and 5HT4 receptors mRNA expression were significantly increased in the mucosal/submucosal layer at POD 3 or POD 7, whereas no significant difference was observed in the longitudinal muscle layers adherent with the myenteric plexus (LMMP).

CONCLUSIONS

It is suggested that up-regulation of 5-HT3 and 5-HT4 receptors expression in the mucosal/submucosal layer is involved to restore the delayed transit after the parasympathetic denervation in rats.

The role of 5-HT3 and 5-HT4 receptors in the adaptive mechanism of colonic transit following the parasympathetic denervation in rats

BACKGROUND

Clinical studies show that disturbed colonic motility induced by extrinsic nerves damage is restored over time. We studied whether 5-HT3 and 5HT4 receptors are involved in mediating the adaptive mechanisms following parasympathetic denervation.

METHODS

Parasympathetic denervation of the entire colon was achieved by bilateral pelvic nerve transection and truncal vagotomy in rats. Colonic transit was measured by calculating the geometric center (GC) of 51Cr distribution. Expression of 5-HT3 and 5HT4 receptor mRNA was determined by real time RT-PCR.

RESULTS

Parasympathetic denervation caused a significant delay in colonic transit (GC=4.36) at postoperative day (POD) 1, compared with sham operation (GC=6.31). Delayed transit was gradually restored by POD 7 (GC=5.99) after the denervation. Restored colonic transit was antagonized by the administration of 5-HT3 and 5HT4 receptors antagonists at POD 7. 5-HT3 and 5HT4 receptors mRNA expression were significantly increased in the mucosal/submucosal layer at POD 3 or POD 7, whereas no significant difference was observed in the longitudinal muscle layers adherent with the myenteric plexus (LMMP).

CONCLUSIONS

It is suggested that up-regulation of 5-HT3 and 5-HT4 receptors expression in the mucosal/submucosal layer is involved to restore the delayed transit after the parasympathetic denervation in rats.

Expression and function of 5-HT7 receptors in smooth muscle preparations from equine duodenum, ileum, and pelvic flexure

In horses, gastrointestinal (GI) disorders occur frequently and cause a considerable demand for efficient medication. 5-Hydroxytryptamine receptors (5-HT) have been reported to be involved in GI tract motility and thus, are potential targets for treating functional bowel disorders. Our studies extend current knowledge on the 5-HT(7) receptor in equine duodenum, ileum and pelvic flexure by studying its expression throughout the intestine and its role in modulating contractility in vitro by immunofluorescence and organ bath experiments, respectively. 5-HT(7) immunoreactivity was demonstrated in both smooth muscle layers, particularly in the circular one, and within the myenteric plexus. Interstitial cells of Cajal (ICC), identified by c-Kit labeling, show a staining pattern similar to that of 5-HT(7) immunoreactivity. The selective 5-HT(7) receptor antagonist SB-269970 increased the amplitude of contractions in spontaneous contracting specimens of the ileum and in electrical field-stimulated specimens of the pelvic flexure concentration-dependently. Our in vitro experiments suggest an involvement of the 5-HT(7) receptor subtype in contractility of equine intestine. While the 5-HT(7) receptor has been established to be constitutively active and inhibits smooth muscle contractility, our experiments demonstrate an increase in contractility by the 5-HT(7) receptor ligand SB-269970, suggesting it exerting inverse agonist properties.

Norepinephrine transport-mediated gene expression in noradrenergic neurogenesis

Background

We have identified a differential gene expression profile in neural crest stem cells that is due to deletion of the norepinephrine transporter (NET) gene. NET is the target of psychotropic substances, such as tricyclic antidepressants and the drug of abuse, cocaine. NET mutations have been implicated in depression, anxiety, orthostatic intolerance and attention deficit hyperactivity disorder (ADHD). NET function in adult noradrenergic neurons of the peripheral and central nervous systems is to internalize norepinephrine from the synaptic cleft. By contrast, during embryogenesis norepinephrine (NE) transport promotes differentiation of neural crest stem cells and locus ceruleus progenitors into noradrenergic neurons, whereas NET inhibitors block noradrenergic differentiation. While the structure of NET und the regulation of NET function are well described, little is known about downstream target genes of norepinephrine (NE) transport.

Results

We have prepared gene expression profiles of in vitro differentiating wild type and norepinephrine transporter-deficient (NETKO) mouse neural crest cells using long serial analysis of gene expression (LongSAGE). Comparison analyses have identified a number of important differentially expressed genes, including genes relevant to neural crest formation, noradrenergic neuron differentiation and the phenotype of NETKO mice. Examples of differentially expressed genes that affect noradrenergic cell differentiation include genes in the bone morphogenetic protein (BMP) signaling pathway, the Phox2b binding partner Tlx2, the ubiquitin ligase Praja2, and the inhibitor of Notch signaling, Numbl. Differentially expressed genes that are likely to contribute to the NETKO phenotype include dopamine-β-hydroxylase (Dbh), tyrosine hydroxylase (Th), the peptide transmitter 'cocaine and amphetamine regulated transcript' (Cart), and the serotonin receptor subunit Htr3a. Real-time PCR confirmed differential expression of key genes not only in neural crest cells, but also in the adult superior cervical ganglion and locus ceruleus. In addition to known genes we have identified novel differentially expressed genes and thus provide a valuable database for future studies.

Conclusion

Loss of NET function during embryonic development in the mouse deregulates signaling pathways that are critically involved in neural crest formation and noradrenergic cell differentiation. The data further suggest deregulation of signaling pathways in the development and/or function of the NET-deficient peripheral, central and enteric nervous systems.

Effects of tegaserod and erythromycin in upper gut dysmotility: a comparative study

OBJECTIVES

Tegaserod may enhance upper gut transit, but, its prokinetic effects on antral/small bowel motility and how this compares with erythromycin is unknown. We prospectively assessed and compared the effects of tegaserod and erythromycin on upper gut motility.

METHODS

In an open label, non-crossover study, 22 patients (M/F=4/18; mean age=37 years) with symptoms of upper gut dysmotility underwent 24-hour ambulatory antroduodenojejunal manometry with a six-sensor solid state probe. The effects of 12 mg oral tegaserod were compared with 125 mg intravenous erythromycin by quantifying pressure wave activity and assessing motor patterns.

RESULTS

Motor activity increased (p<0.05) in antrum, duodenum and jejunum with both drugs when compared to baseline period. The motor response with tegaserod was higher (p<0.05) in jejunum and occurred during the second or third hours, whereas with erythromycin, it was higher (p<0.05) in antrum and occurred within 30 minutes. After tegaserod, a 'fed-response' like pattern was seen whereas after erythromycin, large amplitude (>100 mmHg) antral contractions at 3 cycles per minute were seen. Following tegaserod and erythromycin, phase III MMCs occurred in 12 (55%) and 8 (36%) patients respectively (p>0.05).

CONCLUSIONS

Both drugs increase upper gut motility and induce MMC's, but exert a differential response. Tegaserod produces a more sustained prokinetic effect in the duodenum/jejunum, whereas erythromycin predominantly increases antral motor activity.

Updates on treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by abdominal pain and discomfort in association with altered bowel habits. It is estimated to affect 10%-15% of the Western population, and has a large impact on quality of life and (in)direct healthcare costs. IBS is a multifactorial disorder involving dysregulation within the brain-gut axis, and it is frequently associated with gastrointestinal motor and sensory dysfunction, enteric and central nervous system irregularities, neuroimmune dysregulation, and post-infectious inflammation. As with other functional medical disorders, the treatment for IBS can be challenging. Conventional therapy for those with moderate to severe symptoms is largely unsatisfactory, and the development of new and effective drugs is made difficult by the complex pathogenesis, variety of symptoms, and lack of objective clinical findings that are the hallmark of this disorder. Fortunately, research advances over the past several decades have provided insight into potential mechanisms responsible for the pathogenesis of IBS, and have led to the development of several promising pharmaceutical agents. In recent years there has been much publicity over several of these new IBS medications (alosetron and tegaserod) because of their reported association with ischemic colitis and cardiovascular disease. While these agents remain available for use under restricted prescribing programs, this highlights the need for continued development of safe and effective medication for IBS. This article provides a physiologically-based overview of recently developed and frequently employed pharmaceutical agents used to treat IBS, and discusses some non-pharmaceutical options that may be beneficial in this disorder.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.

Meta-analysis: a functional polymorphism in the gene encoding for activity of the serotonin transporter protein is not associated with the irritable bowel syndrome

BACKGROUND

Serotonin is associated with symptoms of the irritable bowel syndrome, its action is terminated by the serotonin transporter protein.

AIM

To assess the association between a functional polymorphism in the gene encoding for activity of the serotonin transporter protein and the irritable bowel syndrome.

METHODS

Meta-analysis of studies identified through a Medline, PubMed and Web of Science search, describing the prevalence of a polymorphism in the serotonin transporter gene creating long and short alleles.

RESULTS

Eight eligible studies described a total of 1034 patients with the irritable bowel syndrome, and 1377 healthy controls. Presence of the short allele is not associated with an increased risk for the irritable bowel syndrome: OR 1.0; 95% CI: 0.7-1.4 for homozygous subjects, and OR 1.0; 95% CI: 0.8-1.2 for homozygous subjects and heterozygotes together. Although Caucasians and Asians had diverging genotypic frequencies, no association with the shot allele and irritable bowel syndrome was observed in subgroups: Asians OR 1.2; 95% CI: 0.9-1.6 and OR 1.1; 95% CI: 0.2-5.9; Caucasians OR 0.9; 95% CI: 0.5-1.7 and OR 0.9; 95% CI: 0.7-1.2, respectively, for homozygous subjects alone and for homozygous subjects and heterozygotes together.

CONCLUSION

A genetic polymorphism in the gene encoding for activity of the serotonin transporter protein is not associated with the irritable bowel.

The serotonin signaling system: from basic understanding to drug development for functional GI disorders

Serotonin is an important gastrointestinal signaling molecule. It is a paracrine messenger utilized by enterochromaffin (EC) cells, which function as sensory transducers. Serotonin activates intrinsic and extrinsic primary afferent neurons to, respectively, initiate peristaltic and secretory reflexes and to transmit information to the central nervous system. Serotonin is also a neurotransmitter utilized by a system of long descending myenteric interneurons. Serotonin is synthesized through the actions of 2 different tryptophan hydroxylases, TpH1 and TpH2, which are found, respectively, in EC cells and neurons. Serotonin is inactivated by the serotonin reuptake transporter (SERT)-mediated uptake into enterocytes or neurons. The presence of many serotonin receptor subtypes enables selective drugs to be designed to therapeutically modulate gastrointestinal motility, secretion, and sensation. Current examples include tegaserod, a 5-HT(4) partial agonist, which has been approved for treatment of irritable bowel syndrome (IBS) with constipation in women and for chronic constipation in men and women. The 5-HT(3) antagonists, granisetron and ondansetron, are useful in combating the nausea associated with cancer chemotherapy, and alosetron is employed in the treatment of IBS with diarrhea. Serotonergic signaling abnormalities have also been putatively implicated in the pathogenesis of functional bowel diseases. Other compounds, for which efficacy has not been rigorously established, but which may have value, include tricyclic antidepressants and serotonin selective reuptake inhibitors to combat IBS, and 5-HT(1) agonists, which enhance gastric accommodation, to treat functional dyspepsia. The initial success encountered with serotonergic agents holds promise for newer and more potent insights and therapies of brain-gut disorders.

Nerves, reflexes, and the enteric nervous system: pathogenesis of the irritable bowel syndrome

The bowel exhibits reflexes in the absence of CNS input. To do so, epithelial sensory transducers, such as enterochromaffin (EC) cells, activate the mucosal processes of intrinsic (IPANs) and extrinsic primary afferent (sensory) neurons. EC cells secrete serotonin (5-HT) in response to mucosal stimuli. Submucosal IPANs, which secrete acetylcholine and calcitonin gene-related peptide, initiate peristaltic and secretory reflexes and are activated via "5-HT1P" receptors. Release of neurotransmitters is enhanced by 5-HT4 receptors, which are presynaptic and strengthen neurotransmission in prokinetic pathways. 5-HT3 receptors mediate signaling to the CNS and thus ameliorate cancer chemotherapy-associated nausea and the visceral hypersensitivity of diarrhea-predominant irritable bowel syndrome (IBS-D); however, because 5-HT3 receptors also mediate fast ENS neurotransmission and activate myenteric IPANs, they may be constipating. 5-HT4 agonists are prokinetic and relieve discomfort and constipation in IBS-C and chronic constipation. 5-HT4 agonists do not initiate peristaltic and secretory reflexes but strengthen pathways that are naturally activated. Serotonergic signaling in the mucosa and the ENS is terminated by a transmembrane 5-HT transporter, SERT. Mucosal SERT and tryptophan hydroxylase-1 expression are decreased in experimental inflammation, IBS-C, IBS-D, and ulcerative colitis. Potentiation of 5-HT due to the SERT decrease could account for the discomfort and diarrhea of IBS-D, while receptor desensitization may cause constipation. Similar symptoms are seen in transgenic mice that lack SERT. The loss of mucosal SERT may thus contribute to IBS pathogenesis.

Review article: serotonin receptors and transporters -- roles in normal and abnormal gastrointestinal motility

The gut is the only organ that can display reflexes and integrative neuronal activity even when isolated from the central nervous system. This activity can be triggered by luminal stimuli that are detected by nerves via epithelial intermediation. Epithelial enterochromaffin cells act as sensory transducers that activate the mucosal processes of both intrinsic and extrinsic primary afferent neurones through their release of 5-hydroxytryptamine (5-HT). Intrinsic primary afferent neurones are present in both the submucosal and myenteric plexuses. Peristaltic and secretory reflexes are initiated by submucosal intrinsic primary afferent neurones, which are stimulated by 5-HT acting at 5-HT(1P) receptors. 5-HT acting at 5-HT4 receptors enhances the release of transmitters from their terminals and from other terminals in prokinetic reflex pathways. Signalling to the central nervous system is predominantly 5-HT3 mediated, although serotonergic transmission within the enteric nervous system and the activation of myenteric intrinsic primary afferent neurones are also 5-HT3 mediated. The differential distribution of 5-HT receptor subtypes makes it possible to use 5-HT3 antagonists and 5-HT4 agonists to treat intestinal discomfort and motility. 5-HT3 antagonists alleviate the nausea and vomiting associated with cancer chemotherapy and the discomfort from the bowel in irritable bowel syndrome; however, because 5-HT-mediated fast neurotransmission within the enteric nervous system and the stimulation of mucosal processes of myenteric intrinsic primary afferent neurones are 5-HT3 mediated, 5-HT3 antagonists tend to be constipating and should be used only when pre-existing constipation is not a significant component of the problem to be treated. In contrast, 5-HT4 agonists, such as tegaserod, are safe and effective in the treatment of irritable bowel syndrome with constipation and chronic constipation. They do not stimulate nociceptive extrinsic nerves nor initiate peristaltic and secretory reflexes. Instead, they rely on natural stimuli to activate reflexes, which they strengthen by enhancing the release of transmitters in prokinetic pathways. Finally, when all the signalling by 5-HT is over, its action is terminated by uptake into enterocytes or neurones, which is mediated by the serotonin reuptake transporter. In inflammation, serotonergic signalling is specifically diminished in the mucosa. Transcripts encoding tryptophan hydroxylase-1 and serotonin reuptake transporter are both markedly decreased. Successive potentiation of 5-HT and/or desensitization of its receptor could account for the symptoms seen in diarrhoea-predominant and constipation-predominant irritable bowel syndrome, respectively. Symptoms associated with the down-regulation of the serotonin reuptake transporter in the human mucosa in irritable bowel syndrome are similar to the symptoms associated with the knockout of the serotonin reuptake transporter in mice. The observation that molecular defects occur in the human gut in irritable bowel syndrome strengthens the hand of those seeking to legitimize the disease. At least it is not 'all in your head'. The bowel contributes.

Association of the -1438 G/A and 102 T/C polymorphism of the 5-Ht2A receptor gene with irritable bowel syndrome 5-Ht2A gene polymorphism in irritable bowel syndrome

GOALS

The aim of this study is to investigate whether there were any association between the 102 T/C and -1438 G/A polymorphisms of the 5-HT2A receptor gene and IBS, and abdominal pain, anxiety and depression.

BACKGROUND

Genes involved in serotonin (5-HT) metabolism are good candidates for the pathogenesis of irritable bowel syndrome (IBS). Recently, a silent polymorphism in the 5-HT2A receptor gene was identified that is defined by a T to C transition at position 102. Also, a novel G to A base change at position -1438 of the promoter region has been detected in 5-HT2A receptor gene.

STUDY

Fifty-four patients with IBS diagnosed according to the Rome 1 criteria and 107 healthy individuals were included in the study. PCR was used to amplify a 468-bp (G-->A) and 342-bp (T-->C) fragment of genomic DNA containing the polymorphism. Hospital anxiety and depression scale was used to assess the risk of depression and anxiety. Severity of chronic abdominal pain was determined by visual analogue scale (VAS).

RESULTS

It was shown that there was a high incidence of homozygote C allele of the 102T/C polymorphism (%22.2; OR: 7.89, P = 0.04) and homozygote A allele of the -1438 G/A promoter region (%%37; OR: 11.14, P = 0.01) in patients with IBS. The risk of having an anxiety disorder was 83.3% in patients with C/C genotype, which was higher than other allele carrying patients, and overall mean (%52.7). (chi = 8.56, P = 0.014). The patients with T/T genotype had a VAS score of 54.93 +/- 2.59 mm, which was significantly higher than that of the patients with other genotypes (p1 = 0.02, p2 = 0.001).

CONCLUSION

This study suggests that the patients with homozygote C allele of the 102 T/C polymorphisms or homozygote A allele of the -1438 G/A polymorphism of the 5-HT2A receptor gene, have a high risk of IBS. On the other hand, T/T genotype of 102 T/C polymorphism may be associated with more severe pain in patient with IBS.

Enteric dopaminergic neurons: definition, developmental lineage, and effects of extrinsic denervation

The existence of enteric dopaminergic neurons has been suspected; however, the innervation of the gut by sympathetic nerves, in which dopamine (DA) is the norepinephrine precursor, complicates analyses of enteric DA. We now report that transcripts encoding tyrosine hydroxylase (TH) and the DA transporter (DAT) are present in the murine bowel (small intestine > stomach or colon; proximal colon > distal colon). Because sympathetic neurons are extrinsic, transcripts encoding TH and DAT in the bowel are probably derived from intrinsic neurons. TH protein was demonstrated immunocytochemically in neuronal perikarya (submucosal >> myenteric plexus; small intestine > stomach or colon). TH, DA, and DAT immunoreactivities were coincident in subsets of neurons (submucosal > myenteric) in guinea pig and mouse intestines in situ and in cultured guinea pig enteric ganglia. Surgical ablation of sympathetic nerves by extrinsic denervation of loops of the bowel did not affect DAT immunoreactivity but actually increased numbers of TH-immunoreactive neurons, expression of mRNA encoding TH and DAT, and enteric DOPAC (the specific dopamine metabolite). The fetal gut contains transiently catecholaminergic (TC) cells. TC cells are the proliferating crest-derived precursors of mature neurons that are not catecholaminergic and, thus, disappear after embryonic day (E) 14 (mouse) or E15 (rat). TC cells appear early in ontogeny, and their development/survival is dependent on mash-1 gene expression. In contrast, the intrinsic TH-expressing neurons of the murine bowel appear late (perinatally) and are mash-1 independent. We conclude that the enteric nervous system contains intrinsic dopaminergic neurons that arise from a mash-1-independent lineage of noncatecholaminergic precursors.

Expression and function of 5-HT3 receptors in the enteric neurons of mice lacking the serotonin transporter

The actions of enteric 5-HT are terminated by 5-HT transporter (SERT)-mediated uptake, and gastrointestinal motility is abnormal in SERT -/- mice. We tested the hypothesis that adaptive changes in enteric 5-HT(3) receptors help SERT -/- mice survive despite inefficient 5-HT inactivation. Expression of mRNA encoding enteric 5-HT(3A) subunits was similar in SERT +/+ and -/- mice, but that of 5-HT(3B) subunits was fourfold less in SERT -/- mice. 5-HT(3B) mRNA was found, by in situ hybridization, in epithelial cells and enteric neurons. 5-HT evoked a fast inward current in myenteric neurons that was pharmacologically identified as 5-HT(3) mediated. The EC(50) of the 5-HT response was lower in SERT +/+ (18 microM) than in SERT -/- (36 microM) mice and desensitized rapidly in a greater proportion of SERT -/- neurons; however, peak amplitudes, steady-state current, and decay time constants were not different. Adaptive changes thus occur in the subunit composition of enteric 5-HT(3) receptors of SERT -/- mice that are reflected in 5-HT(3) receptor affinity and desensitization.

Alosetron controls bowel urgency and provides global symptom improvement in women with diarrhea-predominant irritable bowel syndrome

OBJECTIVES

Bowel urgency is one of the most bothersome symptoms for nonconstipated IBS patients. The efficacy of alosetron in control of bowel urgency and Global Improvement of IBS symptoms were evaluated in a multicenter double-blind, randomized, placebo-controlled study.

METHODS

Female IBS patients with lack of satisfactory control of bowel urgency were randomized 2:1 to alosetron 1 mg twice daily or placebo treatment groups. The primary endpoint was the proportion of days with satisfactory control of bowel urgency during the 12-wk treatment period and 2-wk follow-up period. Secondary endpoints included IBS Global Improvement (responder defined as patient-reported moderate or substantial improvement in IBS symptoms) and improvements in bowel function (stool frequency, consistency, and sensation of incomplete evacuation).

RESULTS

A total of 801 women were randomized to the alosetron (n = 532) or placebo groups (n = 269). Physicians classified 98% of patients with diarrhea-predominant IBS. Patients treated with alosetron had a significantly greater proportion of days with satisfactory control of urgency compared to placebo for the treatment period (73% vs 57%, p < 0.001). A significantly greater number of patients treated with alosetron were IBS Global Improvement responders compared to placebo at week 12 (76% vs 44%, p < 0.001). IBS Global Improvement responders had more days with satisfactory control of urgency at week 12 (88% vs 48%) as well as firmer stools, fewer stools/day, and fewer days with incomplete evacuation compared with nonresponders. Alosetron-treated patients showed improvements in bowel functions compared to placebo-treated patients. Constipation was the most commonly reported adverse event.