Sex differences of brain serotonin synthesis in patients with irritable bowel syndrome using alpha-[11C]methyl-L-tryptophan, positron emission tomography and statistical parametric mapping

Electrophysiology as a Tool to Decipher the Network Mechanism of Visceral Pain in Functional Gastrointestinal Disorders

Abdominal pain, including visceral pain, is prevalent in functional gastrointestinal (GI) disorders (FGIDs), affecting the overall quality of a patient's life. Neural circuits in the brain encode, store, and transfer pain information across brain regions. Ascending pain signals actively shape brain dynamics; in turn, the descending system responds to the pain through neuronal inhibition. Pain processing mechanisms in patients are currently mainly studied with neuroimaging techniques; however, these techniques have a relatively poor temporal resolution. A high temporal resolution method is warranted to decode the dynamics of the pain processing mechanisms. Here, we reviewed crucial brain regions that exhibited pain-modulatory effects in an ascending and descending manner. Moreover, we discussed a uniquely well-suited method, namely extracellular electrophysiology, that captures natural language from the brain with high spatiotemporal resolution. This approach allows parallel recording of large populations of neurons in interconnected brain areas and permits the monitoring of neuronal firing patterns and comparative characterization of the brain oscillations. In addition, we discussed the contribution of these oscillations to pain states. In summary, using innovative, state-of-the-art methods, the large-scale recordings of multiple neurons will guide us to better understanding of pain mechanisms in FGIDs.

Colonic mucosal eosinophilia and immunohistochemical expression of COX-2 and NF-kB in patients with irritable bowel syndrome

BACKGROUND

There is growing evidence that eosinophilic infiltration can release mediators which are harmful to the intestinal epithelium in patients with irritable bowel syndrome (IBS). Although cyclooxygenase 2 (COX-2) and nuclear factor-kappa beta (NF-kB) expression had been previously reported to increase in many inflammatory conditions, there is a paucity in data investigating their expressions in IBS. Our aim was to evaluate colonic mucosal eosinophilia and immunohistochemical expression of COX-2 and NF-kB in patients with irritable bowel syndrome.

METHODS

A total of 80 patients who met the inclusion criteria of IBS based on Rome IV symptoms questionnaire were subjected to abdominal ultrasound, laboratory investigations, serum immunoglobulin E (IgE) level assessment and colonoscopic examination. Immunohistochemistry was performed to detect COX-2 and NF-kB expression in colonic biopsies obtained from IBS patients.

RESULTS

Histopathological examination showed that 60 colonic biopsy specimens (75%) showed few mixed inflammatory cells ≤3 cells/ HPF, 12 biopsy specimens (15%) showed eosinophilic infiltration ≥25 eosinophils/HPF and 8 biopsy specimens (10%) showed severe lymphocytic infiltration and aggregation. Colonic eosinophilic infiltrate was significantly higher among patients presented with IBS-D subtype. Serum IgE was significantly higher among patients with colonic eosinophilic infiltrate than the others. In IBS-D patients, colonic mucosa showed positive expression of COX-2 and NF-kB in 52.1% and 81.25% of cases, respectively.

CONCLUSION

Patients with IBS -particularly IBS-D subtype- should undergo colonoscopy and biopsy to exclude underlying inflammatory pathology. Moreover, patients with positive COX-2 and NF-kB need further evaluation and follow-up.

Functional neuroimaging in Irritable Bowel Syndrome: a systematic review highlights common brain alterations with Functional Movement Disorders

Irritable bowel syndrome (IBS) is a chronic functional gastrointestinal disorder characterized by recurring abdominal pain and altered bowel habits without detectable organic causes. This study aims to provide a comprehensive overview of the literature on functional neuroimaging in IBS and to highlight brain alterations similarities with other functional disorders - functional movement disorders in particular. We conducted the bibliographic search via PubMed in August 2020 and included 50 studies following Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines for systematic reviews. Overall, our findings showed an aberrant activation and functional connectivity of the insular, cingulate, sensorimotor and frontal cortices, the amygdala and the hippocampus, suggesting an altered activity of the homeostatic and salience network and of the autonomous nervous system. Moreover, glutamatergic dysfunction in the anterior insula and hypothalamic pituitary axis dysregulation were often reported. These alterations seem to be very similar to those observed in patients with functional movement disorders. Hence, we speculate that different functional disturbances might share a common pathophysiology and we discussed our findings in the light of a Bayesian model framework.

Gut feelings: the microbiota-gut-brain axis on steroids

The intricate connection between central and enteric nervous systems is well established with emerging evidence linking gut microbiota function as a significant new contributor to gut-brain axis signaling. Several microbial signals contribute to altered gut-brain communications, with steroids representing an important biological class that impacts central and enteric nervous system function. Neuroactive steroids contribute pathologically to neurological disorders, including dementia and depression, by modulating the activity of neuroreceptors. However, limited information is available on the influence of neuroactive steroids on the enteric nervous system and gastrointestinal function. In this review, we outline how steroids can modulate enteric nervous system function by focusing on their influence on different receptors that are present in the intestine in health and disease. We also highlight the potential role of the gut microbiota in modulating neuroactive steroid signaling along the gut-brain axis.

Sex-Bias in Irritable Bowel Syndrome: Linking Steroids to the Gut-Brain Axis

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is more common in females. Despite its high global incidence, the disease mechanism is still unclear and therapeutic options remain limited. The sexual dimorphism in IBS incidence suggests that sex steroids play a role in disease onset and symptoms severity. This review considers sex steroids and their involvement in IBS symptoms and the underlying disease mechanisms. Estrogens and androgens play important regulatory roles in IBS symptomology, including visceral sensitivity, gut motility and psychological conditions, possibly through modulating the gut-brain axis. Steroids are regulators of hypothalamic-pituitary-adrenal activity and autonomic nervous system function. They also modulate gut microbiota and enteric nervous systems, impacting serotonin and mast cell signaling. Sex steroids also facilitate bidirectional cross-talk between the microbiota and host following bacterial transformation and recycling of steroids by the intestine. The sex-specific interplay between sex steroids and the host provides neuroendocrinology insight into the pathophysiology, epigenetics and treatment of IBS patients.

Effect of Caffeine on Endurance Performance in Athletes May Depend on HTR2A and CYP1A2 Genotypes

Guest, NS, Corey, P, Tyrrell, PN, and El-Sohemy, A. Effect of caffeine on endurance performance in athletes may depend on HTR2A and CYP1A2 genotypes. J Strength Cond Res XX(X): 000-000, 2020-This investigation determined whether variation in the HTR2A (serotonin receptor) gene modifies the ergogenic effects of caffeine on endurance and further modifies performance by the CYP1A2 genotype. Male athletes (n = 100; 25 ± 4 years) completed 10-km cycling time trials under 3 conditions as follows: 0, 2, or 4 mg of caffeine per kg body mass. Using a randomized, double-blinded, placebo-controlled design, data were analyzed using analysis of covariance to compare changes in cycling time between placebo (0 mg·kg) and each caffeine dose and adjusted for the placebo trial and order of treatment. A significance of ρ ≤ 0.05 was used. Subjects were genotyped for HTR2A (rs6313) and CYP1A2 (rs762551). A significant caffeine-HTR2A interaction (p = 0.003) was observed; however, after adjustment for placebo trials, the interaction was no longer significant (p = 0.37). Because of the strong caffeine-CYP1A2 interaction (p < 0.0001) previously reported in these subjects, where the 4-mg dose resulted in divergent effects (slower and faster) on the 10-km cycling time, we conducted a simplified model to examine these same factors by the HTR2A genotype. The post hoc analysis excluded HTR2A CT heterozygotes and 2-mg·kg caffeine trials. Among CYP1A2 fast metabolizers alone, a significant difference (1.7 minutes; p = 0.006) was observed when comparing (4- vs. 0-mg·kg caffeine trials) between the HTR2A CC (n = 16; 2.4 minutes) and TT (n = 7; 0.7 minutes) genotypes. Our results show that 4-mg·kg caffeine improves performance in individuals with the HTR2A CC genotype but only in those who are also CYP1A2 AA fast metabolizers. This study was registered with clinicaltrials.gov (NCT02109783).

Serotonin-estrogen interactions: What can we learn from pregnancy?

We have reviewed the scientific literature related to four diseases in which to serotonin (5-HT) is involved in the etiology, herein named 5-HT-linked diseases, and whose prevalence is influenced by estrogenic status: depression, migraine, irritable bowel syndrome and eating disorders. These diseases all have in common a sex-dimorphic prevalence, with women more frequently affected than men. The co-occurrence between these 5-HT-linked diseases suggests that they have common physiopathological mechanisms. In most 5-HT-linked diseases (except for anorexia nervosa and irritable bowel syndrome), a decrease in the serotonergic tone is observed and estrogens are thought to contribute to the improvement of symptoms by stimulating the serotonergic system. Human pregnancy is characterized by a unique 5-HT and estrogen synthesis by the placenta. Pregnancy-specific disorders, such as hyperemesis gravidarum, gestational diabetes mellitus and pre-eclampsia, are associated with a hyperserotonergic state and decreased estrogen levels. Fetal programming of 5-HT-linked diseases is a complex phenomenon that involves notably fetal-sex differences, which suggest the implication of sex steroids. From a mechanistic point of view, we hypothesize that estrogens regulate the serotonergic system, resulting in a protective effect against 5-HT-linked diseases, but that, in turn, 5-HT affects estrogen synthesis in an attempt to retrieve homeostasis. These two processes (5-HT and estrogen biosynthesis) are crucial for successful pregnancy outcomes, and thus, a disruption of this 5-HT-estrogen relationship may explain pregnancy-specific pathologies or pregnancy complications associated with 5-HT-linked diseases.

Understanding Neurogastroenterology From Neuroimaging Perspective: A Comprehensive Review of Functional and Structural Brain Imaging in Functional Gastrointestinal Disorders

This review provides a comprehensive overview of brain imaging studies of the brain-gut interaction in functional gastrointestinal disorders (FGIDs). Functional neuroimaging studies during gut stimulation have shown enhanced brain responses in regions related to sensory processing of the homeostatic condition of the gut (homeostatic afferent) and responses to salience stimuli (salience network), as well as increased and decreased brain activity in the emotional response areas and reduced activation in areas associated with the top-down modulation of visceral afferent signals. Altered central regulation of the endocrine and autonomic nervous responses, the key mediators of the brain-gut axis, has been demonstrated. Studies using resting-state functional magnetic resonance imaging reported abnormal local and global connectivity in the areas related to pain processing and the default mode network (a physiological baseline of brain activity at rest associated with self-awareness and memory) in FGIDs. Structural imaging with brain morphometry and diffusion imaging demonstrated altered gray- and white-matter structures in areas that also showed changes in functional imaging studies, although this requires replication. Molecular imaging by magnetic resonance spectroscopy and positron emission tomography in FGIDs remains relatively sparse. Progress using analytical methods such as machine learning algorithms may shift neuroimaging studies from brain mapping to predicting clinical outcomes. Because several factors contribute to the pathophysiology of FGIDs and because its population is quite heterogeneous, a new model is needed in future studies to assess the importance of the factors and brain functions that are responsible for an optimal homeostatic state.

Dopaminergic and serotonergic mechanisms in the modulation of pain: In vivo studies in human brain

Here we review the literature assessing the roles of the brain dopaminergic and serotonergic systems in the modulation of pain as revealed by in vivo human studies using positron emission tomography. In healthy subjects, dopamine D₂/D₃ receptor availability particularly in the striatum and serotonin 5-HT_1A and 5-HT_2A receptor availabilities in the cortex predict the subject's response to tonic experimental pain. High availability of dopamine D₂/D₃ or serotonin 5-HT_2A receptors is associated with high pain intensity, whereas high availability of 5-HT_1A receptors associates with low pain intensity. Chronic neuropathic pain is associated with high striatal dopamine D₂/D₃ receptor availability, for which low endogenous dopamine tone is a plausible explanation, although a compensatory increase in striatal dopamine D₂/D₃ receptor density may also contribute. In contrast, chronic musculoskeletal pain is associated with low baseline availability of striatal dopamine D₂/D₃ receptors. In healthy subjects, brain serotonin 5-HT_1A as well as dopamine D₂/D₃ receptor availabilities associate with the subject's response criterion rather than the capacity to discriminate painful thermal stimuli suggesting that these neurotransmitter systems act mainly on non-sensory rather than sensory factors of thermally induced pain experience. Additionally, 5-HT_1A receptor availability predicts the subject's discriminative ability but not response criterion for non-painful tactile test stimuli, while no such correlation is observed with dopamine D₂/D₃ receptors. These findings suggest that dopamine acting on striatal dopamine D₂/D₃ receptors and serotonin acting on cortical 5-HT_1A and 5-HT_2A receptors contribute to top-down pain regulation in humans.

Impact of the Gut Microbiota on Intestinal Immunity Mediated by Tryptophan Metabolism

The gut microbiota influences the health of the host, especially with regard to gut immune homeostasis and the intestinal immune response. In addition to serving as a nutrient enhancer, L-tryptophan (Trp) plays crucial roles in the balance between intestinal immune tolerance and gut microbiota maintenance. Recent discoveries have underscored that changes in the microbiota modulate the host immune system by modulating Trp metabolism. Moreover, Trp, endogenous Trp metabolites (kynurenines, serotonin, and melatonin), and bacterial Trp metabolites (indole, indolic acid, skatole, and tryptamine) have profound effects on gut microbial composition, microbial metabolism, the host's immune system, the host-microbiome interface, and host immune system-intestinal microbiota interactions. The aryl hydrocarbon receptor (AhR) mediates the regulation of intestinal immunity by Trp metabolites (as ligands of AhR), which is beneficial for immune homeostasis. Among Trp metabolites, AhR ligands consist of endogenous metabolites, including kynurenine, kynurenic acid, xanthurenic acid, and cinnabarinic acid, and bacterial metabolites, including indole, indole propionic acid, indole acetic acid, skatole, and tryptamine. Additional factors, such as aging, stress, probiotics, and diseases (spondyloarthritis, irritable bowel syndrome, inflammatory bowel disease, colorectal cancer), which are associated with variability in Trp metabolism, can influence Trp-microbiome-immune system interactions in the gut and also play roles in regulating gut immunity. This review clarifies how the gut microbiota regulates Trp metabolism and identifies the underlying molecular mechanisms of these interactions. Increased mechanistic insight into how the microbiota modulates the intestinal immune system through Trp metabolism may allow for the identification of innovative microbiota-based diagnostics, as well as appropriate nutritional supplementation of Trp to prevent or alleviate intestinal inflammation. Moreover, this review provides new insight regarding the influence of the gut microbiota on Trp metabolism. Additional comprehensive analyses of targeted Trp metabolites (including endogenous and bacterial metabolites) are essential for experimental preciseness, as the influence of the gut microbiota cannot be neglected, and may explain contradictory results in the literature.

Influence of Tryptophan and Serotonin on Mood and Cognition with a Possible Role of the Gut-Brain Axis

The serotonergic system forms a diffuse network within the central nervous system and plays a significant role in the regulation of mood and cognition. Manipulation of tryptophan levels, acutely or chronically, by depletion or supplementation, is an experimental procedure for modifying peripheral and central serotonin levels. These studies have allowed us to establish the role of serotonin in higher order brain function in both preclinical and clinical situations and have precipitated the finding that low brain serotonin levels are associated with poor memory and depressed mood. The gut-brain axis is a bi-directional system between the brain and gastrointestinal tract, linking emotional and cognitive centres of the brain with peripheral functioning of the digestive tract. An influence of gut microbiota on behaviour is becoming increasingly evident, as is the extension to tryptophan and serotonin, producing a possibility that alterations in the gut may be important in the pathophysiology of human central nervous system disorders. In this review we will discuss the effect of manipulating tryptophan on mood and cognition, and discuss a possible influence of the gut-brain axis.

Irritable bowel syndrome: Is it "irritable brain" or "irritable bowel"?

Irritable bowel syndrome (IBS) has been recognized as one of the most common and best studied disorders among the group of functional gastrointestinal disorders. It is a functional bowel disorder in which abdominal pain or discomfort is associated with defecation or a change in bowel habit. In the Western world, IBS appears to affect up to 20% of the population at any given time but in Asian countries, the median value of IBS prevalence defined by various criteria ranges between 6.5% and 10.1%, and community prevalence of 4% is found in North India. Those attending gastroenterology clinics represent only the tip of the iceberg. The disorder substantially impairs the quality of life, and the overall health-care costs are high. IBS has therefore gained increased attention from clinicians, researchers, and pharmaceutical industries. It is often frustrating to both patients and physicians as the disease is usually chronic in nature and difficult to treat. However, the understanding of IBS has been changing from time to time and still most of its concepts are unknown. In this review we have discussed, debated, and synthesized the evidence base, focusing on underlying mechanisms in the brain and bowel. We conclude that it is both brain and bowel mechanisms that are responsible. The clinical implication of such mechanisms is discussed.

Brain and gut interactions in irritable bowel syndrome: new paradigms and new understandings

Irritable bowel syndrome (IBS) is characterized by abdominal pain and altered bowel habits. Visceral hypersensitivity is believed to be a key underlying mechanism that causes pain. There is evidence that interactions within the brain and gut axis (BGA), that involves both the afferent-ascending and the efferent-descending pathways, as well as the somatosensory cortex, insula, amygdala, anterior cingulate cortex, and hippocampus, are deranged in IBS showing both the activation and inactivation. Clinical manifestations of IBS such as pain, altered gut motility, and psychological dysfunction may each be explained, in part, through the changes in the BGA, but there is conflicting information, and its precise role is not fully understood. A better understanding of the BGA may shed more knowledge regarding the pathophysiology of IBS that in turn may lead to the discovery of novel therapies for this common disorder.

Serotonin receptors and their role in the pathophysiology and therapy of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract characterized by abdominal discomfort, pain and changes in bowel habits, often associated with psychological/psychiatric disorders. It has been suggested that the development of IBS may be related to the body's response to stress, which is one of the main factors that can modulate motility and visceral perception through the interaction between brain and gut (brain-gut axis). The present review will examine and discuss the role of serotonin (5-hydroxytryptamine, 5-HT) receptor subtypes in the pathophysiology and therapy of IBS.

METHODS

Search of the literature published in English using the PubMed database.

RESULTS

Several lines of evidence indicate that 5-HT and its receptor subtypes are likely to have a central role in the pathophysiology of IBS. 5-HT released from enterochromaffin cells regulates sensory, motor and secretory functions of the digestive system through the interaction with different receptor subtypes. It has been suggested that pain signals originate in intrinsic primary afferent neurons and are transmitted by extrinsic primary afferent neurons. Moreover, IBS is associated with abnormal activation of central stress circuits, which results in altered perception during visceral stimulation.

CONCLUSIONS

Altered 5-HT signaling in the central nervous system and in the gut contributes to hypersensitivity in IBS. The therapeutic effects of 5-HT agonists/antagonists in IBS are likely to be due also to the ability to modulate visceral nociception in the central stress circuits. Further studies are needed in order to develop an optimal treatment.

Sex and gender differences in pain and analgesia

It is a clinical reality that women make up the large majority of chronic pain patients, and there is now consensus from laboratory experiments that when differences are seen, women are more sensitive to pain than men. Research in this field has now begun to concentrate on finding explanations for this sex difference. Although sex differences in sociocultural, psychological, and experiential factors likely play important roles, evidence largely from animal studies has revealed surprisingly robust and often qualitative sex differences at low levels of the neuraxis. Although not yet able to affect clinical practice, the continued study of sex differences in pain may have important implications for the development of new analgesic strategies.

Sex, gender, and pain: a review of recent clinical and experimental findings

Sex-related influences on pain and analgesia have become a topic of tremendous scientific and clinical interest, especially in the last 10 to 15 years. Members of our research group published reviews of this literature more than a decade ago, and the intervening time period has witnessed robust growth in research regarding sex, gender, and pain. Therefore, it seems timely to revisit this literature. Abundant evidence from recent epidemiologic studies clearly demonstrates that women are at substantially greater risk for many clinical pain conditions, and there is some suggestion that postoperative and procedural pain may be more severe among women than men. Consistent with our previous reviews, current human findings regarding sex differences in experimental pain indicate greater pain sensitivity among females compared with males for most pain modalities, including more recently implemented clinically relevant pain models such as temporal summation of pain and intramuscular injection of algesic substances. The evidence regarding sex differences in laboratory measures of endogenous pain modulation is mixed, as are findings from studies using functional brain imaging to ascertain sex differences in pain-related cerebral activation. Also inconsistent are findings regarding sex differences in responses to pharmacologic and non-pharmacologic pain treatments. The article concludes with a discussion of potential biopsychosocial mechanisms that may underlie sex differences in pain, and considerations for future research are discussed.

PERSPECTIVE

This article reviews the recent literature regarding sex, gender, and pain. The growing body of evidence that has accumulated in the past 10 to 15 years continues to indicate substantial sex differences in clinical and experimental pain responses, and some evidence suggests that pain treatment responses may differ for women versus men.

Correlation of human cold pressor pain responses with 5-HT(1A) receptor binding in the brain

We determined whether serotonin 5-HT(1A) receptor availability in the brain is associated with cold pressor pain (CPP) or sympathetic reflex responses. Psychophysical testing was performed in eleven healthy males who had participated in a positron emission tomography study with [carbonyl-(11)C]WAY-100635 ligand for the assessment of 5-HT(1A) receptor binding potential (BP). Psychophysical testing consisted of determining CPP threshold, tolerance, intensity, unpleasantness and CPP threshold modulation by conditioning CPP. Autonomic control was assessed by determining the cutaneous vasoconstriction responses in the finger induced by CPP and Valsalva maneuver. CPP intensity was inversely correlated with 5-HT(1A) BP in multiple cortical and subcortical areas, including the prefrontal and cingulate cortices, insula, amygdala and the dorsal raphe. CPP unpleasantness was not significantly correlated with 5-HT(1A) BP in any of the regions of interest. Increase of CPP threshold by conditioning CPP was directly correlated with 5-HT(1A) BP in the amygdala and medial prefrontal cortex. Vasoconstriction induced by Valsalva but not CPP was directly correlated with 5-HT(1A) BP in the ventral part of the anterior cingulate cortex and the anterior insula. The results suggest that 5-HT(1A) receptors in the brain influence pain and Valsalva-induced sympathetic vasoconstriction reflex. In general, subjects with high availability of 5-HT(1A) receptors have low CPP intensity accompanied by a high capacity for central suppression of pain or a sympathetic vasoconstriction response by a Valsalva maneuver.

The effect of culture on symptom reporting: Hispanics and irritable bowel syndrome

PURPOSE

To explore whether the symptoms reported by Mexican-American patients with irritable bowel syndrome (IBS) meet the current diagnostic criteria.

DATA SOURCES

A retrospective review of charts of Mexican-American patients diagnosed with IBS at three large medical centers in central California was performed. Demographic information was extracted, and descriptive statistics were used to determine how symptoms were reported and whether the described symptoms met the Rome II criteria.

CONCLUSIONS

Only 63% of the Mexican-American patients in this study reported symptoms that met any of the nine Rome II criteria. There was no significant difference between patients who were English dominant and those who were monolingual Spanish in the concordance of their presenting complaint and the current diagnostic criteria. In addition, there was no significant gender difference in the rate at which symptoms met the Rome II criteria.

IMPLICATIONS FOR PRACTICE

Assessment of illness and its symptoms requires that the practitioner have a clear understanding of what the illness means to the patient in order to develop an accurate diagnosis and an appropriate and timely plan of treatment. This study highlights the necessity of revising the symptom-based criteria for diagnosing IBS to include a wider array of reported complaints, taking into account the impact of culture on the perception and description of symptoms.

Cortical trapping of alpha-[(11)C]methyl-l-tryptophan, an index of serotonin synthesis, is lower in females than males

One neural system that may exhibit gender differences is serotonin (5-HT), a neurotransmitter implicated in the regulation of mood, cognitive processes, and impulse-control. However, most of the available evidence of gender-related differences in this system has been indirect and at times contradictory. The objective of the present study was to follow up on preliminary evidence that there are gender differences in brain regional 5-HT synthesis, as measured by trapping of alpha-[(11)C]methyl-l-tryptophan (alpha-[(11)C]MTrp). Sixty-minute dynamic scans were performed in healthy volunteers, 28 women and 31 men. Functional images of the brain trapping constant, used as a proxy for 5-HT synthesis, which correlate in the rat brain with tryptophan's conversion into 5-HT, were transferred to the standardized 3D space. The voxel based comparison was performed by Statistical Parametric Mapping with proportional normalization. There was lower normalized alpha-[(11)C]MTrp trapping in females than males throughout much of the cerebral cortex, including the left middle frontal gyrus, the bilateral inferior frontal gyrus, the bilateral precentral gyrus, the left supramarginal gyrus, the bilateral inferior parietal lobule, the left superior temporal gyrus, the bilateral posterior cingulate gyrus, and the bilateral precuneus. There were no regions in which the normalized trapping was significantly higher in females than in males. Gender differences in sub-cortical sites were not found. Women, compared to men, may have lower rates of this tracer trapping, used as a proxy for 5-HT synthesis, throughout much of the cerebral cortex which is likely related to differences in 5-HT synthesis because relative differences in the normalized trapping should be the same as those in 5-HT synthesis. These differences may be related, at least in part, to previously suggested gender differences in affect, cognitive processes, and susceptibility to 5-HT-related neuropsychiatric and neurological disorders.

New directions in brain imaging research in functional gastrointestinal disorders

Functional brain imaging has greatly enhanced the ability to investigate brain-gut interactions and to assess the central nervous system role on visceral pain perception. The results of studies using brain imaging in irritable bowel syndrome (IBS) have demonstrated differences in brain activation between patients with IBS and healthy controls. In addition, the more recent studies are starting to shed light on pathophysiological mechanisms that underlie the generation of functional gastrointestinal (GI) symptoms as well as the response to treatment. These studies highlight the potential of functional brain imaging to become an important and exciting investigative tool in research of functional GI disorders. However, the multifactorial, multideterminant nature of these disorders, the current limitations in the understanding of the pathophysiology of the disorders, and the heterogeneous patient population make brain imaging research in this field difficult and require caution in the interpretation of the data. The continued development of brain imaging techniques provides not only exciting opportunities but also significant challenges to the field. This article focuses on brain imaging research in functional GI disorders. It describes some of the recent developments in the use of brain imaging in research of the brain-gut axis and provides an overview of the current data.

The effects of the 5-HT3 antagonist, alosetron, on brain serotonin synthesis in patients with irritable bowel syndrome

Serotonin (5-HT) plays an important role in the pathophysiology of irritable bowel syndrome (IBS). Using alpha-[(11)C]methyl-L-tryptophan-positron emission tomography (PET), it was demonstrated that brain 5-HT synthesis is increased in patients with IBS, in a gender-specific manner. The aims of the study were to evaluate the effects of alosetron on brain 5-HT synthesis in patients with IBS. Six male and five female non-constipation-predominant IBS patients were enrolled. The subjects received alosetron or a placebo for 14 days, separated by a 2-week washout period. On day 14, rectal distensions commenced just prior to the PET scan (which was performed for 80 min), and continued for 20-min periods. The functional images were analysed with SPM99. Alosetron vs placebo treatments, in a randomized, double-blinded, crossover manner, were studied. 5-HT synthesis was greater in several regions in the males than in the females during the alosetron treatment, whereas there was no region in which the females had greater synthesis. There were significant gender-treatment interactions of synthesis in the cingulate gyrus, caudate nucleus, globus pallidus, and cerebellum. The gender differences in the effect of alosetron on brain 5-HT synthesis may be related to the gender differences in the efficacy of alosetron.

Human brain mechanisms of pain perception and regulation in health and disease

CONTEXT

The perception of pain due to an acute injury or in clinical pain states undergoes substantial processing at supraspinal levels. Supraspinal, brain mechanisms are increasingly recognized as playing a major role in the representation and modulation of pain experience. These neural mechanisms may then contribute to interindividual variations and disabilities associated with chronic pain conditions.

OBJECTIVE

To systematically review the literature regarding how activity in diverse brain regions creates and modulates the experience of acute and chronic pain states, emphasizing the contribution of various imaging techniques to emerging concepts.

DATA SOURCES

MEDLINE and PRE-MEDLINE searches were performed to identify all English-language articles that examine human brain activity during pain, using hemodynamic (PET, fMRI), neuroelectrical (EEG, MEG) and neurochemical methods (MRS, receptor binding and neurotransmitter modulation), from January 1, 1988 to March 1, 2003. Additional studies were identified through bibliographies.

STUDY SELECTION

Studies were selected based on consensus across all four authors. The criteria included well-designed experimental procedures, as well as landmark studies that have significantly advanced the field.

DATA SYNTHESIS

Sixty-eight hemodynamic studies of experimental pain in normal subjects, 30 in clinical pain conditions, and 30 using neuroelectrical methods met selection criteria and were used in a meta-analysis. Another 24 articles were identified where brain neurochemistry of pain was examined. Technical issues that may explain differences between studies across laboratories are expounded. The evidence for and the respective incidences of brain areas constituting the brain network for acute pain are presented. The main components of this network are: primary and secondary somatosensory, insular, anterior cingulate, and prefrontal cortices (S1, S2, IC, ACC, PFC) and thalamus (Th). Evidence for somatotopic organization, based on 10 studies, and psychological modulation, based on 20 studies, is discussed, as well as the temporal sequence of the afferent volley to the cortex, based on neuroelectrical studies. A meta-analysis highlights important methodological differences in identifying the brain network underlying acute pain perception. It also shows that the brain network for acute pain perception in normal subjects is at least partially distinct from that seen in chronic clinical pain conditions and that chronic pain engages brain regions critical for cognitive/emotional assessments, implying that this component of pain may be a distinctive feature between chronic and acute pain. The neurochemical studies highlight the role of opiate and catecholamine transmitters and receptors in pain states, and in the modulation of pain with environmental and genetic influences.

CONCLUSIONS

The nociceptive system is now recognized as a sensory system in its own right, from primary afferents to multiple brain areas. Pain experience is strongly modulated by interactions of ascending and descending pathways. Understanding these modulatory mechanisms in health and in disease is critical for developing fully effective therapies for the treatment of clinical pain conditions.

A dose-ranging, phase II study of the efficacy and safety of alosetron in men with diarrhea-predominant IBS

BACKGROUND

A randomized, double blind, placebo-controlled dose-ranging study was conducted to assess the efficacy of alosetron in men with diarrhea-predominant irritable bowel syndrome (IBS).

METHODS

Six hundred and sixty-two men were randomized to treatment with alosetron 0.5, 1.0, 2.0, 4.0 mg, or placebo twice daily for 12 wk, followed by a 4-wk posttreatment period. Adequate relief of IBS pain and discomfort during week 5-12 of the treatment phase was the primary endpoint; secondary endpoints included bowel urgency, stool frequency, and consistency, incomplete evacuation, bloating, and abdominal pain or discomfort.

RESULTS

Subjects ranked urgency and abdominal pain as their most bothersome IBS symptoms. The average rate of adequate relief during week 5-12 was significantly higher in the alosetron 1.0 mg twice-daily group compared to placebo (53%vs 40%, p= 0.04), and all doses of alosetron significantly reduced stool consistency scores (p < 0.001) indicating firmer stools. No significant effects of alosetron were seen with regard to urgency, number of bowel movements, bloating, and incomplete evacuation. Constipation was the most common adverse event and occurred in a dose-related manner among subjects receiving alosetron, 9% (0.5 mg twice daily), 15% (1.0 mg twice daily), 11% (2.0 mg twice daily), and 21% (4.0 mg twice daily). No serious adverse events of constipation were reported. One subject in the 0.5 mg twice-daily group had an episode of rectal bleeding suggestive of a possible diagnosis of ischemic colitis.

CONCLUSIONS

Alosetron 1 mg twice daily provided adequate relief of IBS pain and discomfort, and improved stool consistency in men with diarrhea-predominant IBS.

Experimental design for the formulation and optimization of novel cross-linked oilispheres developed for in vitro site-specific release of Mentha piperita oil

A Plackett-Burman design was employed to develop and optimize a novel crosslinked calcium-aluminum-alginate-pectinate oilisphere complex as a potential system for the in vitro site-specific release of Mentha piperita, an essential oil used for the treatment of irritable bowel syndrome. The physicochemical and textural properties (dependent variables) of this complex were found to be highly sensitive to changes in the concentration of the polymers (0%-1.5% wt/vol), crosslinkers (0%-4% wt/vol), and crosslinking reaction times (0.5-6 hours) (independent variables). Particle size analysis indicated both unimodal and bimodal populations with the highest frequency of 2 mm oilispheres. Oil encapsulation ranged from 6 to 35 mg/100 mg oilispheres. Gravimetric changes of the crosslinked matrix indicated significant ion sequestration and loss in an exponential manner, while matrix erosion followed Higuchi's cube root law. Among the various measured responses, the total fracture energy was the most suitable optimization objective (R2 = 0.88, Durbin-Watson Index = 1.21%, Coefficient of Variation (CV) = 33.21%). The Lagrangian technique produced no significant differences (P > .05) between the experimental and predicted total fracture energy values (0.0150 vs 0.0107 J). Artificial Neural Networks, as an alternative predictive tool of the total fracture energy, was highly accurate (final mean square error of optimal network epoch approximately 0.02). Fused-coated optimized oilispheres produced a 4-hour lag phase followed by zero-order kinetics (n > 0.99), whereby analysis of release data indicated that diffusion (Fickian constant k1 = 0.74 vs relaxation constant k2 = 0.02) was the predominant release mechanism.