Sex-related differences in IBS patients: central processing of visceral stimuli

Sex Differences in Visceral Pain and Comorbidities: Clinical Outcomes, Preclinical Models, and Cellular and Molecular Mechanisms

Sexual dimorphism of visceral pain has been documented in clinics and experimental animal models. Aside from hormones, emerging evidence suggests the sex-differential intrinsic neural regulation of pain generation and maintenance. According to the International Association for the Study of Pain (IASP) and the American College of Gastroenterology (ACG), up to 25% of the population have visceral pain at any one time, and in the United States 10-15 percent of adults suffer from irritable bowel syndrome (IBS). Here we examine the preclinical and clinical evidence of sex differences in visceral pain focusing on IBS, other forms of bowel dysfunction and IBS-associated comorbidities. We summarize preclinical animal models that provide a means to investigate the underlying molecular mechanisms in the sexual dimorphism of visceral pain. Neurons and nonneuronal cells (glia and immune cells) in the peripheral and central nervous systems, and the communication of gut microbiota and neural systems all contribute to sex-dependent nociception and nociplasticity in visceral painful signal processing. Emotion is another factor in pain perception and appears to have sexual dimorphism.

Gender differences in gastrointestinal, biopsychosocial and healthcare-seeking behaviors in Chinese patients with irritable bowel syndrome predominant with diarrhea

BACKGROUND

Evidences of comparison of sex difference in Chinese irritable bowel syndrome (IBS) patients were few. We aim to compare gender difference in the biopsychosocial characteristics of Chinese patients of IBS predominant with diarrhea (IBS-D).

METHODS

IBS-D patients meeting Rome III criteria were enrolled. We administered IBS symptom questionnaires, evaluation of psychological status (HAMD and HAMA scales) and IBS quality of life (IBS-QOL), dietary habits, healthcare seeking behaviors, and compared biopsychosocial characteristics between male and female patients.

RESULTS

Four hundred and ninety patients were enrolled including 299 males and 191 females. More female patients reported abdominal pain associated with defecation (84.3% vs. 74.9%, P = 0.014) while males reported more abdominal discomfort (39.8% vs. 26.7%, P = 0.003). Females had higher IBS symptom score (9.7 ± 1.7 vs. 9.4 ± 1.4, P = 0.025) and more of females had severe abdominal pain/discomfort (17.8% vs. 12.4%, P = 0.013) while there were no significant differences of other bowel symptoms. Females reported higher incidence of comorbid anxiety state (64.9% vs. 52.8%, P = 0.008) and depression state (35.6% vs. 19.7%, P < 0.001) than males. Female patients also had lower IBS-QOL score (70.2 ± 20.4 vs. 75.1 ± 16.8, P = 0.028) and more frequent consultations, as well as less response for dietary modification than males.

CONCLUSIONS

Chinese female patients with IBS-D had more prominent psychosocial disorders compared to male patients and their abdominal symptoms had minor differences.

Chemogenetic Modulation of Posterior Insula CaMKIIa Neurons Alters Pain and Thermoregulation

The posterior insular cortex (PIC) is well positioned to perform somatosensory-limbic integration; yet, the function of neuronal subsets within the PIC in processing the sensory and affective dimensions of pain remains unclear. Here, we employ bidirectional chemogenetic modulation to characterize the function of PIC CaMKIIa-expressing excitatory neurons in a comprehensive array of sensory, affective, and thermoregulatory behaviors. Excitatory pyramidal neurons in the PIC were found to be sensitized under inflammatory pain conditions. Chemogenetic activation of excitatory CaMKIIa-expressing PIC neurons in non-injured conditions produced an increase in reflexive and affective pain- and anxiety-like behaviors. Moreover, activation of PIC CaMKIIa-expressing neurons during inflammatory pain conditions exacerbated hyperalgesia and decreased pain tolerance. However, Chemogenetic activation did not alter heat nociception via hot plate latency or body temperature. Conversely, inhibiting CaMKIIa-expressing neurons did not alter either sensory or affective pain-like behaviors in non-injured or under inflammatory pain conditions, but it did decrease body temperature and decreased hot plate latency. Our findings reveal that PIC CaMKIIa-expressing neurons are a critical hub for producing both sensory and affective pain-like behaviors and important for thermoregulatory processing. PERSPECTIVE: The present study reveals that activation of the posterior insula produces hyperalgesia and negative affect, and has a role in thermal tolerance and thermoregulation. These findings highlight the insula as a key player in contributing to the multidimensionality of pain.

The Effects of Sex Hormones on Postoperative Pain in Patients with Laparoscopic Cholecystectomy

OBJECTIVE

There are many factors that affect postoperative pain. This study determines the effect of preoperative sex hormone levels on postoperative pain levels in patients undergoing laparoscopic cholecystectomy.

PATIENTS AND METHODS

This study included a total of 89 patients who met the study inclusion criteria. The patients were divided into 3 groups based on their sex and pre and postmenopausal periods: male patients (n = 28), postmenopausal female patients (n = 31), and female patients with normal cycles (n = 30). Normal-cycle women were also regrouped based on their follicular and luteal phases. Data were collected using a descriptive characteristics form, a patient follow-up form, and the Visual Analog Scale.

RESULTS

Venous blood samples taken from the patients before surgery were used to measure their levels of estradiol (EST), testosterone (TES), and progesterone levels. Male patients had lower pain levels than female patients. The male patients' Visual Analog Scale scores were inversely related and correlated strongly with their TES levels ( P < 0.05). However, subgroup analyses suggested that their EST level played a primary role in males and that the EST/TES ratio was determinant in the late postoperative period. In female patients, the EST/progesterone ratio was the most determining factor for the level of pain felt in the postmenopausal period, whereas there was no change in the premenopausal period at different stages of the menstrual cycle.

CONCLUSIONS

Sex hormones were found to be effective in predicting postoperative pain severity.

Contribution of sex and gender roles to the incidence of post-infectious irritable bowel syndrome in a prospective study

Post-infectious irritable bowel syndrome (PI-IBS) occurs in about 10% of cases following gastroenteritis. The incidence of IBS is higher in females. However, it is not clear whether this is due to biological or psychosocial factors. We aimed to investigate the influence of gender roles on the incidence of PI-IBS, alongside traditional risk factors. Our study included 231 patients diagnosed with gastroenteritis who were hospitalized and treated with antibiotics between 2018 and 2021. The Korean Sex Role Inventory-Short Form (KSRI-SF), based on the Bem Sex Role Inventory (BSRI) was used to categorize patients (androgynous, masculine, feminine, and undifferentiated types). Six months after treatment, we conducted a telephone survey to confirm the presence of PI-IBS using the ROME IV criteria. Among the patients, 43.3% were female, and the mean age was 43.67 ± 16.09 years. After 6 months, 34 patients developed PI-IBS. Univariate analysis revealed that younger age, female sex, KSRI-SF undifferentiated type, and longer duration of antibiotic use independently influenced the occurrence of PI-IBS. Multivariate analysis showed that PI-IBS was associated with the KSRI-SF undifferentiated type and higher C-reactive protein (CRP) levels. Our study showed that the KSRI-SF undifferentiated type and high CRP levels at initial infection were associated with PI-IBS.

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.

The neurobiology of irritable bowel syndrome

Irritable bowel syndrome (IBS) is the most prevalent disorder of brain-gut interactions that affects between 5 and 10% of the general population worldwide. The current symptom criteria restrict the diagnosis to recurrent abdominal pain associated with altered bowel habits, but the majority of patients also report non-painful abdominal discomfort, associated psychiatric conditions (anxiety and depression), as well as other visceral and somatic pain-related symptoms. For decades, IBS was considered an intestinal motility disorder, and more recently a gut disorder. However, based on an extensive body of reported information about central, peripheral mechanisms and genetic factors involved in the pathophysiology of IBS symptoms, a comprehensive disease model of brain-gut-microbiome interactions has emerged, which can explain altered bowel habits, chronic abdominal pain, and psychiatric comorbidities. In this review, we will first describe novel insights into several key components of brain-gut microbiome interactions, starting with reported alterations in the gut connectome and enteric nervous system, and a list of distinct functional and structural brain signatures, and comparing them to the proposed brain alterations in anxiety disorders. We will then point out the emerging correlations between the brain networks with the genomic, gastrointestinal, immune, and gut microbiome-related parameters. We will incorporate this new information into a systems-based disease model of IBS. Finally, we will discuss the implications of such a model for the improved understanding of the disorder and the development of more effective treatment approaches in the future.

Targeting the endocannabinoid system for the treatment of abdominal pain in irritable bowel syndrome

The management of visceral pain in patients with disorders of gut-brain interaction, notably irritable bowel syndrome, presents a considerable clinical challenge, with few available treatment options. Patients are increasingly using cannabis and cannabinoids to control abdominal pain. Cannabis acts on receptors of the endocannabinoid system, an endogenous system of lipid mediators that regulates gastrointestinal function and pain processing pathways in health and disease. The endocannabinoid system represents a logical molecular therapeutic target for the treatment of pain in irritable bowel syndrome. Here, we review the physiological and pathophysiological functions of the endocannabinoid system with a focus on the peripheral and central regulation of gastrointestinal function and visceral nociception. We address the use of cannabinoids in pain management, comparing them to other treatment modalities, including opioids and neuromodulators. Finally, we discuss emerging therapeutic candidates targeting the endocannabinoid system for the treatment of pain in irritable bowel syndrome.

Analysis of autonomic function during natural defecation in patients with irritable bowel syndrome using real-time recording with a wearable device

BACKGROUND

Autonomic dysfunction is a factor in irritable bowel syndrome (IBS). However, there are no reports of autonomic nervous system (ANS) activity during natural defecation in patients with IBS. We aimed to clarify the relationship between ANS activity and life events, such as defecation and abdominal symptoms, using real-time recording.

METHODS

Six patients with IBS and 14 healthy controls were enrolled in this prospective multicenter study. ANS activity was recorded for 24 h using a T-shirt wearable device, and life events were recorded simultaneously in real time using a smartphone application software. Low frequency/high frequency (LF/HF) and HF calculated by power spectrum analysis were defined as activity indicators of the sympathetic and parasympathetic nerves, respectively.

RESULTS

The means of LF/HF and HF in the period with positive symptoms were comparable between the groups; however, the sum of LF/HF, sum of ΔLF/HF, and the maximum variation in ΔLF/HF were significantly higher in the IBS group. In the IBS group, the sum of ΔLF/HF and LF/HF increased significantly from 2 min before defecation, and the sum of LF/HF remained significantly higher until 9 min after defecation. The sum of ΔLF/HF at 2 min before defecation was significantly positively correlated with the intensity of abdominal pain and diarrhea and constipation scores. In contrast, it was significantly negatively correlated with defecation satisfaction and health-related quality of life.

CONCLUSIONS

In patients with IBS, sympathetic nerve activity was activated 2 min before defecation, which was correlated with abdominal symptoms and lower QOL.

Anatomical Evidence for the Neural Connection from the Emotional Brain to Autonomic Innervation in the Anterior Chamber Structures of the Eye

OBJECTIVE

Previous studies have shown that the autonomic nervous system (ANS), which can be affected by emotions, is important in the occurrence or progression of glaucoma. The autonomic innervation distributed in the anterior chamber (AC) structures might play an efferent role in the neural regulation of intraocular pressure (IOP). This study aimed to investigate the anatomic neural connection from the emotional brain to autonomic innervation in the AC.

METHODS

A retrograde trans-multisynaptic pseudorabies virus encoded with an enhanced green fluorescent protein (PRV531) and non-trans-synaptic tracer FAST Dil were injected into the right eye of mice, respectively. Fluorescent localization in the emotional brain and preganglionic nuclei was studied. Five and a half days after PRV531 injection into the right AC, fluorescent signals were observed in several emotional brain regions, including the amygdala, agranular insular cortex, lateral septal nuclei, periaqueductal gray, and hypothalamus. Autonomic preganglionic nuclei, including Edinger-Westphal nucleus, superior salivatory nucleus, and intermediolateral nucleus, were labeled using PRV531.

RESULTS

The sensory trigeminal nuclei were not labeled using PRV531. The fluorescence signals in the nuclei mentioned above showed bilateral distribution, primarily on the ipsilateral side. Seven days after injecting FAST Dil into the AC, we observed no FAST Dil-labeled neurons in the central nervous system.

CONCLUSION

Our results indicate a neural connection from the emotional brain to autonomic innervation in the AC, which provides anatomical support for the emotional influence of IOP via the ANS.

Relationship Between Psychosocial Work Environment Factors and Presenteeism Among Workers With Diarrhea/Constipation Symptoms: A Cross-Sectional Study

OBJECTIVES

This study aimed to investigate the relationship of diarrhea/constipation symptoms with presenteeism and psychosocial work environment factors.

METHODS

This study analyzed 16,975 workers of 10 Japanese companies. Presenteeism was measured using a work functioning impairment scale. Odds ratios (ORs) and 95% confidence intervals (cis) for the relationship between diarrhea/constipation and presenteeism were estimated using a logistic model, adjusting for the psychosocial work environment.

RESULTS

Diarrhea/constipation symptoms were related to presenteeism. This relationship was weakened, but remained significant after adjusting for psychosocial work environment factors.

CONCLUSIONS

Diarrhea and constipation, which are highly prevalent in the workplace, are important pathological factors for presenteeism. Presenteeism can be partially suppressed by improving the psychosocial work environment.

Global prevalence and burden of meal-related abdominal pain

BACKGROUND

Patients with disorders of gut-brain interaction (DGBI) report meal intake to be associated with symptoms. DGBI patients with meal-related symptoms may have more severe symptoms overall and worse health outcomes, but this subgroup has not been well characterized. We aimed to describe the global prevalence of meal-related abdominal pain and characterize this subgroup.

METHODS

The data analyzed originated from the Internet survey component of the population-based Rome Foundation Global Epidemiology Study, completed in 26 countries (n = 54,127). Adult subjects were asked whether they had abdominal pain and how often this was meal-related. Respondents were categorized into "no," "occasional," and "frequent" meal-related abdominal pain groups based on 0%, 10-40%, and ≥50% of the pain episodes being meal-related, respectively. DGBI diagnoses, frequency of other GI symptoms, psychological distress, non-GI somatic symptoms, quality of life, and healthcare utilization were compared between groups. Mixed linear and ordinal regression was used to assess independent associations between psychological distress, non-GI somatic symptoms, quality of life, other GI symptoms, and meal-related abdominal pain.

RESULTS

Overall, 51.9% of the respondents reported abdominal pain in the last 3 months, and 11.0% belonged to the group with frequent meal-related abdominal pain, which included more females and younger subjects. DGBI diagnoses were more common in subjects with frequent meal-related abdominal pain, and the frequency of several GI symptoms was associated with having more frequent meal-related abdominal pain. Having meal-related abdominal pain more frequently was also associated with more severe psychological distress, non-GI somatic symptoms, and a poorer quality of life. The group with frequent meal-related abdominal pain also more often consulted a doctor for bowel problems compared to the other groups of meal-related abdominal pain.

CONCLUSION

Reporting frequent meal-related abdominal pain is common across the globe and associated with other GI and non-GI somatic symptoms, psychological distress, healthcare utilization, and a poorer quality of life. Individuals who frequently experience meal-related abdominal pain also more frequently fulfill the diagnostic criteria for DGBI. Assessing meal-related symptoms in all DGBI patients could be of major importance to improve and individualize symptom management.

Impact of intestinal disorders on central and peripheral nervous system diseases

Brain injuries and neurological diseases have a significant impact on the gut microbiome and the gut barrier. Reciprocally, gut disorders, such as Inflammatory Bowel Syndromes (IBS), can affect the development and pathology of neurodegenerative and neuropsychiatric diseases, although this aspect is less well studied and is the focus of this review. Inflammatory Bowel Syndrome (IBS) is a chronic and debilitating functional gastrointestinal disorder afflicting an estimated 9-23% of the world's population. A hallmark of this disease is leaky gut, a pathology in which the integrity of the gut blood barrier is compromised, causing gut contents such as immune cells and microbiota to enter the bloodstream leading to low-grade systemic inflammation. The increased levels of inflammation associated cytokines in circulation has the potential to affect all organs, including the brain. Although the brain is protected by the blood brain barrier, inflammation associated cytokines can damage the junctions in this barrier and allow brain infiltration of peripheral immune cells. Central inflammation in the brain is associated with various neurodegenerative disease such as Alzheimer's disease, Parkinson's disease, multiple sclerosis, and neuropsychiatric disorders, namely, depression, and anxiety. Neurodegenerative diseases are of particular concern due to the anticipated rise in the population of the elderly and consequently, the prevalence of these diseases. Additionally, depression and anxiety are the most common mental illnesses affecting roughly 18% of the American population. In this review, we will explore the mechanisms by which IBS can influence the risk and severity of neurological disease.

Sex- and Gender-Related Differences in Common Functional Gastroenterologic Disorders

Functional gastrointestinal (GI) disorders (FGIDs) result from central and peripheral mechanisms, cause chronic remitting-relapsing symptoms, and are associated with comorbid conditions and impaired quality of life. This article reviews sex- and gender-based differences in the prevalence, pathophysiologic factors, clinical characteristics, and management of functional dyspepsia (FD) and irritable bowel syndrome (IBS) that together affect approximately 1 in 4 people in the United States. These conditions are more common in women. Among patients with IBS, women are more likely to have severe symptoms and coexistent anxiety or depression; constipation or bloating and diarrhea are more common in women and men, respectively, perhaps partly because defecatory disorders, which cause constipation, are more common in women. Current concepts suggest that biological disturbances (eg, persistent mucosal inflammation after acute gastroenteritis) interact with other environmental factors (eg, abuse) and psychological stressors, which influence the brain and gut to alter GI tract motility or sensation, thereby causing symptoms. By comparison to a considerable understanding of sex-based differences in the pathogenesis of visceral hypersensitivity in animal models, we know less about the contribution of these differences to FGID in humans. Slow gastric emptying and colon transit are more common in healthy women than in men, but effects of gonadal hormones on colon transit are less important than in rodents. Although increased visceral sensation partly explains symptoms, the effects of sex on visceral sensation, colonic permeability, and the gut microbiome are less prominent in humans than rodents. Whether sex or gender affects response to medications or behavioral therapy in FD or IBS is unclear because most patients in these studies are women.

A systematic review and activation likelihood estimation meta-analysis of the central innervation of the lower urinary tract: Pelvic floor motor control and micturition

Purpose

Functional neuroimaging is a powerful and versatile tool to investigate central lower urinary tract (LUT) control. Despite the increasing body of literature there is a lack of comprehensive overviews on LUT control. Thus, we aimed to execute a coordinate based meta-analysis of all PET and fMRI evidence on descending central LUT control, i.e. pelvic floor muscle contraction (PFMC) and micturition.

Materials and methods

A systematic literature search of all relevant libraries was performed in August 2020. Coordinates of activity were extracted from eligible studies to perform an activation likelihood estimation (ALE) using a threshold of uncorrected p <0.001.

Results

20 of 6858 identified studies, published between 1997 and 2020, were included. Twelve studies investigated PFMC (1xPET, 11xfMRI) and eight micturition (3xPET, 5xfMRI). The PFMC ALE analysis (n = 181, 133 foci) showed clusters in the primary motor cortex, supplementary motor cortex, cingulate gyrus, frontal gyrus, thalamus, supramarginal gyrus, and cerebellum. The micturition ALE analysis (n = 107, 98 foci) showed active clusters in the dorsal pons, including the pontine micturition center, the periaqueductal gray, cingulate gyrus, frontal gyrus, insula and ventral pons. Overlap of PFMC and micturition was found in the cingulate gyrus and thalamus.

Conclusions

For the first time the involved core brain areas of LUT motor control were determined using ALE. Furthermore, the involved brain areas for PFMC and micturition are partially distinct. Further neuroimaging studies are required to extend this ALE analysis and determine the differences between a healthy and a dysfunctional LUT. This requires standardization of protocols and task-execution.

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.

Sex as a biological variable in irritable bowel syndrome

BACKGROUND

The pathophysiology and mechanisms of irritable bowel syndrome (IBS) involve both central and peripheral mechanisms that result in altered perception, as well as changes in bowel functions. These dysfunctions are associated with motor, sensory, immune, barrier, and intraluminal perturbations, including the microbiota, and their products and endogenous molecules with bioactive properties. There is evidence that these mechanisms are altered in both females and males. However, there is also increasing evidence that sex is a biological variable that impacts a number of aspects of the mechanisms, epidemiology, and manifestations of IBS.

PURPOSE

The objective of this article is to review the evidence of the differences among genders of the following factors in IBS: the brain-gut axis and sex hormones, epidemiology, diagnostic criteria and prognosis, pain perception, colonic transit, abdominal distension, overlap with urogynecological conditions, psychologic issues, anorexia, fibromyalgia, serotonin, and responsiveness to treatment of IBS. It is important to consider the variations attributable to sex in order to enhance the management of patients with IBS and the research of mechanisms involved in IBS.

The effects of gastrointestinal symptoms on structural grey matter volume in youth

Previous neuroimaging studies have examined the association between changes in brain structure and gastrointestinal symptoms (GIS), seen in disorders such as Irritable Bowel Syndrome and Irritable Bowel Disease. Studies in adults have found changes in white and grey matter volume (GMV) in patients with various gastrointestinal disorders. However, it is unclear whether GIS-related structural changes in the brain are limited to adults or could be present throughout the lifespan. Given that gastrointestinal disorders are typically diagnosed between 4 and 18 years old, we investigated GIS-induced morphological changes in pre-adolescents (8-10), adolescents (12-16 years) and young adults (17-21 years). Using a voxel-based morphometry (VBM) analysis, we compared regional grey matter volume (GMV) between participants with GIS and controls, using structural brain images from the Philadelphia Neurodevelopmental Cohort (PNC) database. A total of 211 participants (107 participants with GISs and 104 control participants) who had undergone structural magnetic resonance imaging were analysed. VBM analysis was used to objectively analyse GMV across the whole brain and compare between participants with GIS and controls. Participants experiencing GIS showed smaller GMV in regions within the limbic system/basal ganglia (bilateral caudate, bilateral ventral hippocampus, bilateral amygdala and bilateral superior orbital frontal cortex), and larger GMV in regions within the pain-matrix (thalamus, bilateral putamen, right mid-frontal gyrus) compared to controls. These differences were most prominent in the adolescent and young adult groups compared to pre-adolescents. In conclusion, the structural differences found in participants with GIS support the need for further research into the neurophysiological impact of these symptoms.

Gender differences in use of prolonged non-operative therapies prior to index ACDF surgery

Prior to anterior cervical discectomy and fusion (ACDF) surgery, patients suffering from cervical stenosis traditionally trial non-operative treatments for pain management. There is a paucity of data evaluating gender disparities in the prolonged utilization of conservative therapy prior to ACDF surgery. Therefore, the purpose of this study was to assess for gender-based differences in the utilization and cost of maximal non-operative therapy (MNT) for cervical stenosis prior to ACDF surgery. Medical records from patients with symptomatic cervical stenosis undergoing 1, 2, or 3-level index ACDF procedures between 2007 and 2016 were gathered from an insurance database consisting of 20.9 million covered lives. The utilization of MNTs within 5 years prior to index ACDF surgery was assessed. A total of 2254 patients (females: 53.1%) underwent an index ACDF surgery. There were a significantly greater percentage of female patients that utilized NSAIDs (p < 0.0001), opioids (p = 0.0019), muscle relaxants (p < 0.0001), cervical epidural steroid injections (p = 0.0428), and physical therapy/occupational therapy treatments (p < 0.0001). The total direct cost associated with all MNT prior to index ACDF was $4,833,384. On average, $2028.01 was spent per male patient while $2247.29 was spent per female patient. When normalized by number of pills billed per patient utilizing therapy, female patients utilized more NSAIDs (males: 591.8 pills, females: 669.3 pills), opioids (male: 1342.0 pills, female: 1650.1 pills), and muscle relaxants (males: 823.7 pills, females: 1211.1 pills). The results suggest that there may be gender differences in the utilization of non-operative therapies for symptomatic cervical stenosis prior to ACDF surgery.

Environmental enrichment prevents chronic stress-induced brain-gut axis dysfunction through a GR-mediated mechanism in the central nucleus of the amygdala

BACKGROUND

Cognitive behavioral therapy (CBT) improves quality of life of patients with irritable bowel syndrome (IBS), a disorder characterized by chronic visceral pain and abnormal bowel habits. Whether CBT can actually improve visceral pain in IBS patients is still unknown. The aim of this study is to evaluate whether environment enrichment (EE), the animal analog of CBT, can prevent stress-induced viscero-somatic hypersensitivity through changes in glucocorticoid receptor (GR) signaling within the central nucleus of the amygdala (CeA).

METHODS

Rats were housed in either standard housing (SH) or EE for 7 days before and during daily water avoidance stress (WAS) exposure (1-h/d for 7 days). In the first cohort, visceral and somatic sensitivity were assessed via visceromotor response to colorectal distention and von Frey Anesthesiometer 24 hous and 21 days after WAS. In another cohort, the CeA was isolated for GR mRNA quantification.

KEY RESULTS

Environment enrichment for 7 days before and during the 7 days of WAS persistently attenuated visceral and somatic hypersensitivity when compared to rats placed in SH. Environment enrichment exposure also prevented the WAS-induced decrease in GR expression in the CeA.

CONCLUSION & INFERENCES

Pre-exposure to short-term EE prevents the stress-induced downregulation of GR, and inhibits visceral and somatic hypersensitivity induced by chronic stress. These results suggest that a positive environment can ameliorate stress-induced pathology and provide a non-pharmacological therapeutic option for disorders such as IBS.

Status of Brain Imaging in Gastroparesis

The pathophysiology of nausea and vomiting in gastroparesis is complicated and multifaceted involving the collaboration of both the peripheral and central nervous systems. Most treatment strategies and studies performed in gastroparesis have focused largely on the peripheral effects of this disease, while our understanding of the central nervous system mechanisms of nausea in this entity is still evolving. The ability to view the brain with different neuroimaging techniques has enabled significant advances in our understanding of the central emetic reflex response. However, not enough studies have been performed to further explore the brain–gut mechanisms involved in nausea and vomiting in patients with gastroparesis. The purpose of this review article is to assess the current status of brain imaging and summarize the theories about our present understanding on the central mechanisms involved in nausea and vomiting (N/V) in patients with gastroparesis. Gaining a better understanding of the complex brain circuits involved in the pathogenesis of gastroparesis will allow for the development of better antiemetic prophylactic and treatment strategies.

Amygdala physiology in pain

The amygdala has emerged as an important brain area for the emotional-affective dimension of pain and pain modulation. The amygdala receives nociceptive information through direct and indirect routes. These excitatory inputs converge on the amygdala output region (central nucleus) and can be modulated by inhibitory elements that are the target of (prefrontal) cortical modulation. For example, inhibitory neurons in the intercalated cell mass in the amygdala project to the central nucleus to serve gating functions, and so do inhibitory (PKCdelta) interneurons within the central nucleus. In pain conditions, synaptic plasticity develops in output neurons because of an excitation-inhibition imbalance and drives pain-like behaviors and pain persistence. Mechanisms of pain related neuroplasticity in the amygdala include classical transmitters, neuropeptides, biogenic amines, and various signaling pathways. An emerging concept is that differences in amygdala activity are associated with phenotypic differences in pain vulnerability and resilience and may be predetermining factors of the complexity and persistence of pain.

The central nucleus of the amygdala lesion attenuates orthodontic pain during experimental tooth movement in rats

INTRODUCTION

Orthodontic pain is the most common adverse side effect reported in the context of tooth movement. Given its central role in processing pain and negative emotion, the central nucleus of the amygdala (CeA) is thought to be a key site involved in orthodontic pain sensation.

METHODS

In the present study, we therefore explored whether the CeA is involved in contributing to orthodontic pain in a rat model of tooth movement. For this study, we utilized adult male rats with bilateral sham or electrolytic CeA lesions (400 μA; 25 s), and then we analyzed face grooming behavior as a measure of pain sensation.

RESULTS

Through this approach, we found that there were time- and force-dependent factors influencing pain levels in these rats. We further found that bilateral CeA lesions markedly reduced tooth movement-induced orofacial pain and that unilateral CeA lesions did so to a lesser extent.

CONCLUSIONS

As such, these results suggest the CeA is a key area of orthodontic pain, with the results of this study highlighting potential avenues for achieving pain relief in those suffering from orthodontic pain.

5-HT3 Receptor Antagonists in Neurologic and Neuropsychiatric Disorders: The Iceberg Still Lies beneath the Surface

5-HT₃ receptor antagonists, first introduced to the market in the mid-1980s, are proven efficient agents to counteract chemotherapy-induced emesis. Nonetheless, recent investigations have shed light on unappreciated dimensions of this class of compounds in conditions with an immunoinflammatory component as well as in neurologic and psychiatric disorders. The promising findings from multiple studies have unveiled several beneficial effects of these compounds in multiple sclerosis, stroke, Alzheimer disease, and Parkinson disease. Reports continue to uncover important roles for 5-HT₃ receptors in the physiopathology of neuropsychiatric disorders, including depression, anxiety, drug abuse, and schizophrenia. This review addresses the potential of 5-HT₃ receptor antagonists in neurology- and neuropsychiatry-related disorders. The broad therapeutic window and high compliance observed with these agents position them as suitable prototypes for the development of novel pharmacotherapeutics with higher efficacy and fewer adverse effects.

An Association of Serotonin with Pain Disorders and Its Modulation by Estrogens

Ovarian hormones play an important role in pain perception, and are responsible, at least in part, for the pain threshold differences between the sexes. Modulation of pain and its perception are mediated by neurochemical changes in several pathways, affecting both the central and peripheral nervous systems. One of the most studied neurotransmitters related to pain disorders is serotonin. Estrogen can modify serotonin synthesis and metabolism, promoting a general increase in its tonic effects. Studies evaluating the relationship between serotonin and disorders such as irritable bowel syndrome, fibromyalgia, migraine, and other types of headache suggest a clear impact of this neurotransmitter, thereby increasing the interest in serotonin as a possible future therapeutic target. This literature review describes the importance of substances such as serotonin and ovarian hormones in pain perception and illustrates the relationship between those two, and their direct influence on the presentation of the aforementioned pain-related conditions. Additionally, we review the pathways and receptors implicated in each disorder. Finally, the objective was to stimulate future pharmacological research to experimentally evaluate the potential of serotonin modulators and ovarian hormones as therapeutic agents to regulate pain in specific subpopulations.

Sex differences in pain and opioid mediated antinociception: Modulatory role of gonadal hormones

Sex-related differences in pain and opioids has been the focus of many researches. It is demonstrated that women experience greater clinical pain, lower pain threshold and tolerance, more sensitivity and distress to experimentally induced pain compared to men. Sex differences in response to opioid treatment revealed inconsistent results. However, the etiology of these disparities is not fully elucidated. It is, therefore, conceivable now that this literature merits to be revisited comprehensively. Possible multifaceted factors seem to be associated. These include neuroanatomical, hormonal, neuroimmunological, psychological, social and cultural aspects and comorbidities. This review aims at providing an overview of the substantial literature documenting the sex differences in pain and analgesic response to opioids from animal and human studies within the context of the modulatory effects of the aforementioned factors. A detailed and critical discussion of the cellular and molecular signaling pathways underlying the modulatory actions of gonadal hormones in the sexual dimorphism in pain processing and opioid analgesia is extensively presented. It is indicated that sexual dimorphic activation of certain brain regions contributes to differential pain sensitivity between females and males. Plausible crosstalk between sex hormones and neuroimmunological signaling pertinent to toll-like and purinergic receptors is uncovered as causal cues underlying sexually dimorphic pain and opioid analgesia. Conceivably, a thorough understanding of these factors may aid in sex-related advancement in pain therapeutic management.

Role of brain imaging in disorders of brain-gut interaction: a Rome Working Team Report

Imaging of the living human brain is a powerful tool to probe the interactions between brain, gut and microbiome in health and in disorders of brain-gut interactions, in particular IBS. While altered signals from the viscera contribute to clinical symptoms, the brain integrates these interoceptive signals with emotional, cognitive and memory related inputs in a non-linear fashion to produce symptoms. Tremendous progress has occurred in the development of new imaging techniques that look at structural, functional and metabolic properties of brain regions and networks. Standardisation in image acquisition and advances in computational approaches has made it possible to study large data sets of imaging studies, identify network properties and integrate them with non-imaging data. These approaches are beginning to generate brain signatures in IBS that share some features with those obtained in other often overlapping chronic pain disorders such as urological pelvic pain syndromes and vulvodynia, suggesting shared mechanisms. Despite this progress, the identification of preclinical vulnerability factors and outcome predictors has been slow. To overcome current obstacles, the creation of consortia and the generation of standardised multisite repositories for brain imaging and metadata from multisite studies are required.

Altered Functional Connectivity of the Amygdala and Sex Differences in Functional Dyspepsia

INTRODUCTION

The influence of sex on the prevalence and clinical manifestations of functional dyspepsia (FD) has recently been a topic of increasing interest. However, brain MRI pathology based on sexual dimorphism in FD has not yet been investigated. The amygdala, which plays a vital role in processing gastrointestinal signals, may be associated with the sex-related pathophysiology of FD.

METHODS

We investigated the resting-state functional connectivity (rsFC) of amygdala subregions in patients with FD and healthy subjects as well as the sex differences between male and female FD patients.

RESULTS

The results showed that FD patients manifested altered rsFC in the basolateral amygdala (BLA) and centromedial amygdala subregions compared with HS and that female FD patients showed increased BLA rsFC with the insula (INS) and decreased BLA rsFC with the medial prefrontal cortex and dorsal lateral prefrontal cortex compared with male FD patients and female HS.

DISCUSSION

Our findings suggest that FD females tend to have more severe dysfunction of cognitive-affective processing among the brain regions associated with the salience network, central executive network, and default mode network.

Pathophysiology of the irritable bowel syndrome - Reflections of today

Irritable bowel syndrome (IBS) is a chronic gastrointestinal symptom complex defined by abdominal pain and disturbed bowel habits over 3 months within a period of 6 months, in absence of any identifiable organic pathology. Over the years, speculations of the pathophysiology of IBS has moved from elusive central nervous symptoms impinging on psychosomatic disease, to objective signs of intestinal fermentation with abdominal bloating and intestinal dysmotility. The specific subgroup of post-infectious IBS is of special interest since it opens the possibility of dysbiosis as the pivotal point for development of IBS in association with traveler's diarrhea or antibiotic treatment with ensuing dysbiosis and abdominal symptoms that may resolve over decades. The undefined disease mechanisms that take place within the gut seem responsible for the gut-brain signaling leading to activation of brain centers that drive the clinical picture of IBS, further modulated by the patient's social background and previous lifetime events.

Sex differences in insular functional connectivity in response to noxious visceral stimulation in rats

Insular cortex (INS) plays a critical role in pain processing and shows sex differences in functional activation during noxious visceral stimulation. Less is known regarding functional interactions within the INS and between this structure and other parts of the brain. Cerebral blood flow mapping was performed using [¹⁴C]-iodoantipyrine perfusion autoradiography in male and female rats during colorectal distension (CRD) or no distension (controls). Forty regions of interest (ROIs) were defined anatomically to represent the granular, dysgranular, and agranular INS along the anterior-posterior (A-P) axis. Inter-ROI correlation matrices were calculated for each group to characterize intra-insular functional connectivity (FC). Results showed a clear FC segregation within the INS into an anterior (rostral to bregma +2.4 mm), a posterior (caudal to bregma -1.2 mm), and a mid INS subregion in between. Female controls showed higher FC density compared to males. During CRD, intra-insular FC density decreased greatly in females, but only modestly in males, with a loss of long-range connections between the anterior and mid INS noted in both sexes. New functional organization was characterized in both sexes by a cluster in the mid INS and primarily short-range FC along the A-P axis. Seed correlation analysis during CRD showed sex differences in FC of the anterior and mid agranular INS with the medial prefrontal cortex, thalamus, and brainstem areas (periaqueductal gray, parabrachial nucleus), suggesting sex differences in the modulatory aspect of visceral pain processing. Our findings suggest presence of substantial sex differences in visceral pain processing at the level of the insula.

5-HT3 receptor signaling in serotonin transporter-knockout rats: a female sex-specific animal model of visceral hypersensitivity

The irritable bowel syndrome (IBS) is a functional gastrointestinal motor and visceral sensation disorder that is more common in women than men. Female serotonin transporter (SERT)-gene knockout (KO) rats exhibit hypersensitivity to colorectal balloon distention (CRD) that mimics colonic hypersensitivity occurring in female IBS patients. Alosetron (5-HT₃ receptor antagonist) is used to treat diarrhea-predominant IBS in female patients. Other 5-HT₃ receptor antagonists are ineffective at treating IBS symptoms. The visceromotor response (VMR) to CRD in SERT-KO and wild-type (WT) rats was measured following subcutaneous (sc), intracerobroventricular (icv), or intrathecal (it) treatment with 5-HT₃ receptor antagonists and an agonist. Alosetron (sc) and granisetron (antagonists) caused a paradoxical increase in the VMR to CRD in SERT-KO female rats. Alosetron (sc) increased the VMR to CRD in WT male rats. Alosetron (it) increased the VMR to CRD in SERT-KO female rats only, and the 5-HT₃ receptor agonist SR-52772 increased the VMR to CRD in SERT-KO male rats. Depletion of spinal 5-HT using 5,7-dihydroxytryptamine prevented the increase in VMR to CRD in SERT-KO female and male rats treated it with alosetron and SR-52772, respectively. Alosetron (icv) did not affect the VMR to CRD in WT or KO female rats, but it increased the VMR in male SERT-KO but not WT male rats. These data suggest that 5-HT₃ receptor signaling at the dorsal spinal cord mediates visceral hypersensitivity in female SERT-KO rats. Such differences could facilitate development of sex-specific drug treatments for visceral pain. NEW & NOTEWORTHY We studied a model of female sex-specific visceral hypersensitivity using rats that had a loss of function of the serotonin transporter (SERT) caused by gene truncation. Female SERT-KO rats exhibited visceral hypersensitivity in response to colorectal balloon distention. We found that increased 5-HT signaling at dorsal spine 5-HT₃ receptors was responsible for visceral hypersensitivity in female but not male SERT-KO rats.

Sex-Gender Differences in Irritable Bowel Syndrome

Because of the sex-gender differences that are shown in a diversity of physiological and psychological factors, it can be speculated that the clinical presentation of symptoms as well as treatment strategies in women and men with irritable bowel syndrome (IBS) may differ. Studies have revealed that IBS is more common in women than men. As for the IBS subtype, IBS with constipation is significantly more prevalent among women than men. Sex hormones and gender differences may play important roles in the pathophysiology of IBS. However, its pathophysiologic mechanisms still remain largely unknown, and therapeutic implications are limited. Moreover, women IBS patients have been reported to feel more fatigue, depression, anxiety, and lower quality of life than men IBS patients. Furthermore, there has been evidence of differences in the appropriate treatment efficacy to IBS in men and women, although relatively few men are enrolled in most relevant clinical trials. A more sex-gender-oriented approach in the medical care setting could improve understanding of heterogeneous patients suffering from IBS. An individualized and multicomponent approach including sex and gender issues might help improve the treatment of IBS.

Exploring Age-Related Changes in Resting State Functional Connectivity of the Amygdala: From Young to Middle Adulthood

Functional connectivities of the amygdala support emotional and cognitive processing. Life-span development of resting-state functional connectivities (rsFC) of the amygdala may underlie age-related differences in emotion regulatory mechanisms. To date, age-related changes in amygdala rsFC have been reported through adolescence but not as thoroughly for adulthood. This study investigated age-related differences in amygdala rsFC in 132 young and middle-aged adults (19–55 years). Data processing followed published routines. Overall, amygdala showed positive rsFC with the temporal, sensorimotor and ventromedial prefrontal cortex (vmPFC), insula and lentiform nucleus, and negative rsFC with visual, frontoparietal, and posterior cingulate cortex and caudate head. Amygdala rsFC with the cerebellum was positively correlated with age, and rsFCs with the dorsal medial prefrontal cortex (dmPFC) and somatomotor cortex were negatively correlated with age, at voxel p < 0.001 in combination with cluster p < 0.05 FWE. These age-dependent changes in connectivity appeared to manifest to a greater extent in men than in women, although the sex difference was only evident for the cerebellum in a slope test of age regressions (p = 0.0053). Previous studies showed amygdala interaction with the anterior cingulate cortex (ACC) and vmPFC during emotion regulation. In region of interest analysis, amygdala rsFC with the ACC and vmPFC did not show age-related changes. These findings suggest that intrinsic connectivity of the amygdala evolved from young to middle adulthood in selective brain regions, and may inform future studies of age-related emotion regulation and maladaptive development of the amygdala circuits as an etiological marker of emotional disorders.

Mechanisms of Stress-induced Visceral Pain

Evidence suggests that long-term stress facilitates visceral pain through sensitization of pain pathways and promotes chronic visceral pain disorders such as the irritable bowel syndrome (IBS). This review will describe the importance of stress in exacerbating IBS-induced abdominal pain. Additionally, we will briefly review our understanding of the activation of the hypothalamic-pituitary-adrenal axis by both chronic adult stress and following early life stress in the pathogenesis of IBS. The review will focus on the glucocorticoid receptor and corticotropin-releasing hormone-mediated mechanisms in the amygdala involved in stress-induced visceral hypersensitivity. One potential mechanism underlying persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in stress-induced visceral nociception, alterations in DNA methylation and histone acetylation patterns within the brain, have been linked to alterations in nociceptive signaling via increased expression of pro-nociceptive neurotransmitters. This review will discuss the latest studies investigating the long-term effects of stress on visceral sensitivity. Additionally, we will critically review the importance of experimental models of adult stress and early life stress in enhancing our understanding of the basic molecular mechanisms of nociceptive processing.

Stress-Induced Chronic Visceral Pain of Gastrointestinal Origin

Visceral pain is generally poorly localized and characterized by hypersensitivity to a stimulus such as organ distension. In concert with chronic visceral pain, there is a high comorbidity with stress-related psychiatric disorders including anxiety and depression. The mechanisms linking visceral pain with these overlapping comorbidities remain to be elucidated. Evidence suggests that long term stress facilitates pain perception and sensitizes pain pathways, leading to a feed-forward cycle promoting chronic visceral pain disorders such as irritable bowel syndrome (IBS). Early life stress (ELS) is a risk-factor for the development of IBS, however the mechanisms responsible for the persistent effects of ELS on visceral perception in adulthood remain incompletely understood. In rodent models, stress in adult animals induced by restraint and water avoidance has been employed to investigate the mechanisms of stress-induce pain. ELS models such as maternal separation, limited nesting, or odor-shock conditioning, which attempt to model early childhood experiences such as neglect, poverty, or an abusive caregiver, can produce chronic, sexually dimorphic increases in visceral sensitivity in adulthood. Chronic visceral pain is a classic example of gene × environment interaction which results from maladaptive changes in neuronal circuitry leading to neuroplasticity and aberrant neuronal activity-induced signaling. One potential mechanism underlying the persistent effects of stress on visceral sensitivity could be epigenetic modulation of gene expression. While there are relatively few studies examining epigenetically mediated mechanisms involved in visceral nociception, stress-induced visceral pain has been linked to alterations in DNA methylation and histone acetylation patterns within the brain, leading to increased expression of pro-nociceptive neurotransmitters. This review will discuss the potential neuronal pathways and mechanisms responsible for stress-induced exacerbation of chronic visceral pain. Additionally, we will review the importance of specific experimental models of adult stress and ELS in enhancing our understanding of the basic molecular mechanisms of pain processing.

Divergent functions of the left and right central amygdala in visceral nociception

The left and right central amygdalae (CeA) are limbic regions involved in somatic and visceral pain processing. These 2 nuclei are asymmetrically involved in somatic pain modulation; pain-like responses on both sides of the body are preferentially driven by the right CeA, and in a reciprocal fashion, nociceptive somatic stimuli on both sides of the body predominantly alter molecular and physiological activities in the right CeA. Unknown, however, is whether this lateralization also exists in visceral pain processing and furthermore what function the left CeA has in modulating nociceptive information. Using urinary bladder distension (UBD) and excitatory optogenetics, a pronociceptive function of the right CeA was demonstrated in mice. Channelrhodopsin-2-mediated activation of the right CeA increased visceromotor responses (VMRs), while activation of the left CeA had no effect. Similarly, UBD-evoked VMRs increased after unilateral infusion of pituitary adenylate cyclase-activating polypeptide in the right CeA. To determine intrinsic left CeA involvement in bladder pain modulation, this region was optogenetically silenced during noxious UBD. Halorhodopsin (NpHR)-mediated inhibition of the left CeA increased VMRs, suggesting an ongoing antinociceptive function for this region. Finally, divergent left and right CeA functions were evaluated during abdominal mechanosensory testing. In naive animals, channelrhodopsin-2-mediated activation of the right CeA induced mechanical allodynia, and after cyclophosphamide-induced bladder sensitization, activation of the left CeA reversed referred bladder pain-like behaviors. Overall, these data provide evidence for functional brain lateralization in the absence of peripheral anatomical asymmetries.

Sex-Related Differences in GI Disorders

Epidemiological studies indicate sex-related differences among functional gastrointestinal disorders (FGIDs) wherein females are more likely to receive a diagnosis than their male counterparts. However, the mechanism by which females exhibit an increased vulnerability for development of these pathophysiologies remains largely unknown, and therapeutic treatments are limited. The current chapter focuses on clinical research outlining our current knowledge of factors that contribute to the female predominance among FGID patients such as the menstrual cycle and sex hormones. In addition, we will discuss progress in preclinical research, including animal models, which serve as valuable tools for the investigation of the development and long term manifestation of symptoms observed within the patient population. Although much progress has been made, additional longitudinal studies in both clinical and preclinical research are necessary to identify more specific mechanisms underlying sex-related differences in FGIDs as well as targets for improved therapeutic approaches.

Mapping of Brain Activations to Rectal Balloon Distension Stimuli in Male Patients with Irritable Bowel Syndrome Using Functional Magnetic Resonance Imaging

Background/Aims

Irritable bowel syndrome (IBS) is associated with exaggerated cerebral response including emotional processing following visceral stimulation; though data on this issue is available in female IBS patients, it is scanty among males. Hence, we aimed to study brain response of male IBS patients following rectal balloon distension as compared to healthy controls using functional magnetic resonance imaging (fMRI). Data between diarrhea and constipation predominant IBS (IBS-D and IBS-C) were also compared.

Methods

Rectal balloon distension threshold was assessed in 20 male IBS patients (10 IBS-C and 10 IBS-D) and 10 age-matched male healthy controls. Subsequently, fMRI on all the participants was performed at their respective rectal pain threshold. The fMRI data were analysed using the Statistical Parametric Mapping software.

Results

IBS patients showed greater cerebral activations in insula, middle temporal gyrus, and cerebellum in the left hemisphere compared to healthy controls. Neural activation was found in bilateral precuneus/superior parietal lobules in controls but not in patients with IBS. The brain activation differed among IBS-C and IBS-D patients; while the right mid-cingulate cortex was activated in IBS-C, the left inferior orbito-frontal cortex, left calcarine, and bilateral fusiform gyri were activated among patients with IBS-D following rectal balloon distension.

Conclusions

Brain response to rectal balloon distension differed among male patients with IBS and controls and among patients with IBS-C and IBS-D. Differential activation among patients with IBS-C and IBS-D was seen in the brain regions controlling affective motivation, homeostatic emotions, and autonomic responses to pain.

Efficacy and safety of 5-hydroxytryptamine 3 receptor antagonists in irritable bowel syndrome: A systematic review and meta-analysis of randomized controlled trials

AIM

We assessed the efficacy and safety of 5-hydroxytryptamine (5-HT3) receptor antagonists in adults with non-constipated irritable bowel syndrome (IBS) or diarrhea-predominant IBS (IBS-D).

METHODS

We searched PubMed, MEDLINE, EMBASE, and the Cochrane Controlled Trials Register for randomized controlled trials (RCTs) involving adults with non-constipated IBS or IBS-D that compared 5-HT3 receptor antagonists with placebo or other conventional treatment. Dichotomous symptom data were pooled to obtain the relative risk (RR) and 95% confidence intervals (CIs) for improving global IBS symptoms, abdominal pain and abnormal bowel habits, or stool consistency symptoms after therapy, and adverse events, including constipation. Meta- analysis was performed with Mantel Haenszel method using Revman 5.3 software.

RESULTS

We included 21 RCTs; 16 were high quality (Jadad score ≥ 4). The pooled RR of global IBS symptoms improved by 5-HT3 receptor antagonists versus placebo or mebeverine was 1.56 (95% CI: 1.43-1.71); alosetron, ramosetron, and cilansetron had similar treatment effects. The pooled RR of abdominal pain relieved by 5-HT3 receptor antagonists versus placebo was 1.33 (95% CI: 1.26-1.39). The pooled RR showed that 5-HT3 receptor antagonists improved abnormal bowel habits or stool consistency symptoms (RR = 1.63, 95% CI: 1.33, 1.99). The pooled RR of adverse events following 5-HT3 receptor antagonist treatment was 1.15 (95% CI: 1.08, 1.22). Subgroup analysis indicated that alosetron had a high rate of adverse effects (RR = 1.16, 95% CI: 1.08, 1.25); adverse events following ramosetron treatment were not statistically significantly different. 5-HT3 receptor antagonists were likelier to cause constipation: the pooled RR of constipation developing with 5-HT3 receptor antagonist versus placebo was 3.71 (95% CI: 2.98-4.61). However, constipation was likelier in patients with non-constipated IBS after taking 5-HT3 receptor antagonists than in patients with IBS-D only (non-constipated IBS and IBS-D: RR = 5.28 [95% CI: 3.93, 7.08] vs. IBS-D only 3.24 [2.54, 4.12]).

CONCLUSIONS

Ramosetron, cilansetron, ondansetron, and alosetron are effective for treating non-constipated IBS and IBS-D. Our systematic review found rare serious adverse events.

Symptoms and the body: Taking the inferential leap

The relationship between the conscious experience of physical symptoms and indicators of objective physiological dysfunction is highly variable and depends on characteristics of the person, the context and their interaction. This relationship often breaks down entirely in the case of "medically unexplained" or functional somatic symptoms, violating the basic assumption in medicine that physical symptoms have physiological causes. In this paper, we describe the prevailing theoretical approach to this problem and review the evidence pertaining to it. We then use the framework of predictive coding to propose a new and more comprehensive model of the body-symptom relationship that integrates existing concepts within a unifying framework that addresses many of the shortcomings of current theory. We describe the conditions under which a close correspondence between the experience of symptoms and objective physiology might be expected, and when they are likely to diverge. We conclude by exploring some theoretical and clinical implications of this new account.

Sex-based differences in brain alterations across chronic pain conditions

Common brain mechanisms are thought to play a significant role across a multitude of chronic pain syndromes. In addition, there is strong evidence for the existence of sex differences in the prevalence of chronic pain and in the neurobiology of pain. Thus, it is important to consider sex when developing general principals of pain neurobiology. The goal of the current Mini-Review is to evaluate what is known about sex-specific brain alterations across multiple chronic pain populations. A total of 15 sex difference and 143 single-sex articles were identified from among 412 chronic pain neuroimaging articles. Results from sex difference studies indicate more prominent primary sensorimotor structural and functional alterations in female chronic pain patients compared with male chronic pain patients: differences in the nature and degree of insula alterations, with greater insula reactivity in male patients; differences in the degree of anterior cingulate structural alterations; and differences in emotional-arousal reactivity. Qualitative comparisons of male-specific and female-specific studies appear to be consistent with the results from sex difference studies. Given these differences, mixed-sex studies of chronic pain risk creating biased data or missing important information and single-sex studies have limited generalizability. The advent of large-scale neuroimaging databases will likely aid in building a more comprehensive understanding of sex differences and commonalities in brain mechanisms underlying chronic pain. © 2016 Wiley Periodicals, Inc.

Functional near-infrared spectroscopy study on tonic pain activation by cold pressor test

Functional near-infrared spectroscopy (fNIRS) has recently been suggested for monitoring cortical hemodynamic response to experimental and clinical acute pain. However, the hemodynamic response to a tonic, noxious cold stimulus, and its relation with subjective pain sensation is not fully characterized. We investigated the relationship between pain threshold and tolerance and the evoked hemodynamic response to cold pressor tests (CPTs) at varying intensities and explored the gender effect. Twenty-one healthy individuals (10 males and 11 females) performed four CPTs at 1°C, 5°C, 10°C, and 15°C. Deoxyhemoglobin (HHb) and oxyhemoglobin ([Formula: see text]) were measured continuously on the forehead by two "far" and two "near" channels in addition to pain scores, threshold, and tolerance. We found a significant within-subject correlation between pain threshold and the immediate [Formula: see text] response at the right frontal region. Gender difference and asymmetrical activation were observed in the "far" channels but not the "near" channels, suggesting a hemispheric preference in response to noxious cold stimuli. No gender difference was found in pain threshold, tolerance, or scores. This research adds to the body of literature suggesting the use of fNIRS for bedside assessment of pain in addition to behavioral and subjective measures for comprehensive, multimodal pain management.

Postprandial Symptoms Felt at the Lower Part of the Epigastrium and a Possible Association of Pancreatic Exocrine Dysfunction with the Pathogenesis of Functional Dyspepsia

Objective In symptom-dependent diseases such as functional dyspepsia (FD), matching the pattern of epigastric symptoms, including severity, kind, and perception site, between patients and physicians is critical. Additionally, a comprehensive examination of the stomach, duodenum, and pancreas is important for evaluating the origin of such symptoms. Methods FD-specific symptoms (epigastric pain, epigastric burning, early satiety, and postprandial fullness) and other symptoms (regurgitation, nausea, belching, and abdominal bloating) as well as the perception site of the above symptoms were investigated in healthy subjects using a new questionnaire with an illustration of the human body. A total of 114 patients with treatment-resistant dyspeptic symptoms were evaluated for their pancreatic exocrine function using N-benzoyl-L-tyrosyl-p-aminobenzoic acid. Results A total of 323 subjects (men:women, 216:107; mean age, 52.1 years old) were initially enrolled. Most of the subjects felt the FD-specific symptoms at the epigastrium, while about 20% felt them at other abdominal sites. About 30% of expressed as epigastric symptoms were FD-nonspecific symptoms. At the epigastrium, epigastric pain and epigastric burning were mainly felt at the upper part, and postprandial fullness and early satiety were felt at the lower part. The prevalence of patients with pancreatic exocrine dysfunction was 71% in the postprandial fullness group, 68% in the epigastric pain group, and 82% in the diarrhea group. Conclusion We observed mismatch in the perception site and expression between the epigastric symptoms of healthy subjects and FD-specific symptoms. Postprandial symptoms were often felt at the lower part of the epigastrium, and pancreatic exocrine dysfunction may be involved in the FD symptoms, especially for treatment-resistant dyspepsia patients.

Neuroimaging of Central Sensitivity Syndromes: Key Insights from the Scientific Literature

Central sensitivity syndromes are characterized by distressing symptoms, such as pain and fatigue, in the absence of clinically obvious pathology. The scientific underpinnings of these disorders are not currently known. Modern neuroimaging techniques promise new insights into mechanisms mediating these postulated syndromes. We review the results of neuroimaging applied to five central sensitivity syndromes: fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, temporomandibular joint disorder, and vulvodynia syndrome. Neuroimaging studies of basal metabolism, anatomic constitution, molecular constituents, evoked neural activity, and treatment effect are compared across all of these syndromes. Evoked sensory paradigms reveal sensory augmentation to both painful and nonpainful stimulation. This is a transformative observation for these syndromes, which were historically considered to be completely of hysterical or feigned in origin. However, whether sensory augmentation represents the cause of these syndromes, a predisposing factor, an endophenotype, or an epiphenomenon cannot be discerned from the current literature. Further, the result from cross-sectional neuroimaging studies of basal activity, anatomy, and molecular constituency are extremely heterogeneous within and between the syndromes. A defining neuroimaging "signature" cannot be discerned for any of the particular syndromes or for an over-arching central sensitization mechanism common to all of the syndromes. Several issues confound initial attempts to meaningfully measure treatment effects in these syndromes. At this time, the existence of "central sensitivity syndromes" is based more soundly on clinical and epidemiological evidence. A coherent picture of a "central sensitization" mechanism that bridges across all of these syndromes does not emerge from the existing scientific evidence.

Sex differences in stress-induced visceral hypersensitivity following early life adversity: a two hit model

BACKGROUND

Early life adversity (ELA) has been indicated as a risk factor for the development of stress axis dysfunction in adulthood, specifically in females. We previously showed that unpredictable ELA induces visceral hyperalgesia in adult female rats. It remains to be determined whether ELA alters visceral nociceptive responses to stress in adulthood. The current study tested the hypothesis that following ELA, exposure to an adulthood stressor, or second hit, serves as a risk factor for exaggerated stress-induced visceral hypersensitivity that is sex-specific.

METHODS

Following ELA, adult stress was induced via a single exposure (acute) or repetitive daily exposure, 1 h/day for 7 days (chronic), to water avoidance stress (WAS).

KEY RESULTS

Acute WAS increased pain behaviors in all adult female rats, however, females that experienced unpredictable ELA exhibited significantly more pain behaviors compared to those exposed to predictable ELA or controls. Following chronic WAS, all adult females exhibited increased pain responses, however, an exaggerated response was observed in rats exposed to unpredictable or predictable ELA compared to controls. Similarly, in adult male rats exposure to acute or chronic WAS increased pain behaviors, however, there were no differences in pain behaviors between ELA groups.

CONCLUSIONS & INFERENCES

This study highlights a novel consequence of ELA on stress-induced visceral nociception in adulthood that is sex-specific. More importantly, our study suggests that ELA not only serves as a risk factor for development of chronic pain in adulthood, but also serves as a predisposition for worsening of visceral pain following adult stress in female rats.

Signs and symptoms of temporomandibular disorders in women and men

INTRODUCTION

Women are more likely to present temporomandibular disorders (TMD); however, studies comparing genders in Brazilian samples are rare.

PURPOSE

To analyze the proportion of men and women, as well as the association between gender and age, problem duration, and TMD symptoms in patients admitted to an university clinic for treatment.

METHODS

Interview and assessment data of protocols from 1,000 patients diagnosed with TMD were collected and analyzed and then divided into two groups, male (n = 177) and female (n = 823). The exploratory analysis was based on contingency tables and χ2 test was carried out. Subsequently, the logistic regression model was used and the odds ratios (OR) concerning the evaluated comparisons were calculated.

RESULTS

Females were more prevalent in the sample, and mean ages and TMD duration were similar between the groups, with higher occurrence in young adults (19 to 40 years old). The OR values showed an association between the female gender and the signs/symptoms of pain in the temporomandibular joint, pain in the facial muscles, neck and shoulders, headache, fatigue in the muscles of mastication, otologic symptoms, and dysphonia. Women had two times higher chances of presenting these symptoms than men.

CONCLUSION

In the sample of Brazilian patients with TMD, the number of women who presented a higher prevalence of painful symptoms was greater, followed by otologic symptoms and complaints of dysphonia. The prevalence of joint noise was similar in both studied groups.