The evolving neurobiology of gut feelings

The gut microbiome and diet in psychiatry: focus on depression

PURPOSE OF REVIEW

With depressive disorders the leading source of disability globally, the identification of new targets for prevention and management is imperative. A rapidly emerging field of research suggests that the microbiome-gut-brain axis is of substantial relevance to mood and behaviour. Similarly, unhealthy diet has recently emerged as a significant correlate of and risk factor for depression. This review provides evidence for the gut microbiota as a key factor mediating the link between diet and depressive illness.

RECENT FINDINGS

The development of new technologies is affording a better understanding of how diet influences gut microbiota composition and activity and how this may, in turn, influence depressive illness. New interventions are also suggesting the possible utility of pre and probiotic formulations and fermented food in influencing mental health.

SUMMARY

Although in its early stages, the emerging field of research focused on the human microbiome suggests an important role for the gut microbiota in influencing brain development, behaviour and mood in humans. The recognition that the gut microbiota interacts bidirectionally with other environmental risk factors, such as diet and stress, suggests promise in the development of interventions targeting the gut microbiota for the prevention and treatment of common mental health disorders.

Neuroscience, power and culture: an introduction

In line with their vast expansion over the last few decades, the brain sciences -- including neurobiology, psychopharmacology, biological psychiatry, and brain imaging -- are becoming increasingly prominent in a variety of cultural formations, from self-help guides and the arts to advertising and public health programmes. This article, which introduces the special issue of "History of the Human Science" on "Neuroscience, Power and Culture," considers the ways that social and historical research can, through empirical investigations grounded in the observation of what is actually happening and has already happened in the sciences of mind and brain, complement speculative discussions of the possible social implications of neuroscience that now appear regularly in the media and in philosophical bioethics. It suggests that the neurosciences are best understood in terms of their lineage within the "psy"-disciplines, and that, accordingly, our analyses of them will be strengthened by drawing on existing literatures on the history and politics of psychology -- particularly those that analyze formations of knowledge, power and subjectivity associated with the discipline and its practical applications. Additionally, it argues against taking today's neuroscientific facts and brain-targetting technologies as starting points for analysis, and for greater recognition of the ways that these are shaped by historical, cultural and political-economic forces.

Update on irritable bowel syndrome and gender differences

Irritable bowel syndrome (IBS) is a chronic functional GI disorder characterized by abdominal pain associated with alterations in defecation or stool frequency and consistency. In Western industrialized countries, women seek health care services for their symptoms more frequently than men. The cause of IBS is likely multifactorial involving altered motility, visceral hypersensitivity, and dysregulation of the autonomic nervous system. Many patients note that their symptoms are exacerbated by diet and stress, and women frequently report menstrual cycle fluctuations in symptoms. Current approaches to IBS management include behavioral management therapies such as dietary intake changes and stress reduction cognitive restructuring. Drug therapies are targeted at altering pain sensitivity, motility, and secretion. This review provides an overview of the pathogenesis of IBS, factors that contribute to gender differences, and current therapeutic approaches for symptom management.

More on Darwin's illness: comment on the final diagnosis of Charles Darwin

Without the possibility of confirmatory exhumation, diagnostic inferences about Darwin's illness must remain speculative. A diagnosis of Darwin's aggregate symptoms must account for not only gastrointestinal distress but also his predominant and excessive retching and the conglomerate of other heterogeneous symptoms. We opine that Crohn's disease, posited as the 'final diagnosis', is not sufficient for subsuming his pleiomorphic symptomatology. An additional proposal is outlined that may help to explain his presentation with heterogeneous symptoms. It incorporates constitutional vulnerabilities, psychosomatic influences and Pavlovian conditioning as explanatory variables.

Autonomic response in the perception of disgust and happiness in depersonalization disorder

Patients with depersonalization disorder have shown attenuated responses to emotional unpleasant stimuli, hence supporting the view that depersonalization is characterised by a selective inhibition on the processing of unpleasant emotions. It was the purpose of this study to establish if autonomic responses to facial emotional expressions also show the same blunting effect. The skin conductance responses (SCRs) of 16 patients with chronic DSM-IV depersonalization disorder, 15 normal controls and 15 clinical controls with DSM-IV anxiety disorders were recorded in response to facial expressions of happiness and disgust. Patients with anxiety disorders were found to have greater autonomic responses than patients with depersonalization, in spite of the fact that both groups had similarly high levels of subjective anxiety as measured by anxiety scales. SCR to happy faces did not vary across groups. The findings of this study provide further support to the idea that patients with depersonalization have a selective impairment in the processing of threatening or unpleasant emotional stimuli.

Impact of bitter taste on gastric motility

BACKGROUND

Unexplained nausea and vomiting is often associated with delayed gastric emptying in patients with functional dyspepsia. We hypothesized that the experience of an unpleasant, nauseating taste could lead to a delay in gastric emptying.

METHODS

Sixteen healthy women consumed a bland liquid test meal on three separate study days. On two of the study days subjects sham fed either a bitter tasting, modified Slim-Fast bar or one with a pleasant strawberry flavour. The time for 50% gastric emptying (GE(50)) was non-invasively assessed by electrical impedance tomography and antral motility by electrogastrography (EGG).

RESULTS

Gastric emptying was significantly delayed by sham feeding the bitter compared with the pleasant bar, GE(50) 24.7+/-3.9 versus 17.2+/-1.8 min, P<0.05. EGG power rose significantly during both the pleasant (basal 1.46+/-0.07 to 2.33+/-0.14 log(10) microV(2)/min, P=0.000) and the bitter sham feed (basal 1.64+/-0.09 to 2.35+/-0.11 log(10) microV(2)/min, P=0.000).

CONCLUSION

An unpleasant bitter taste delays gastric emptying but does not significantly impair antral motility.

Autonomic arousal in an appetitive context in primates: a behavioural and neural analysis

Central to many emotional responses is the accompanying peripheral somatic and autonomic arousal, feedback from which has been hypothesized to enhance emotional memory and to contribute to appraisal processes and decision making, and dysfunction of which may contribute to antisocial behaviour. Whilst peripheral arousal may accompany both positive and negative emotional contexts, its relationship with the former is poorly understood, as are the neural mechanisms underlying such a relationship. The purpose of the present study was to determine the autonomic correlates of anticipation, as well as consumption, of high incentive food, in the freely moving common marmoset and to investigate the contribution of the amygdala to such effects. Blood pressure (BP) and heart rate (HR) were measured remotely by a telemetric device implanted into the descending aorta and behavioural responses were monitored whilst marmosets viewed preferred or non-preferred foods and were then allowed access to eat those foods. A marked rise in blood pressure in unrestrained marmosets was observed in response both to the sight of highly preferred foods (anticipatory period) as well as during the actual consumption of those foods (consummatory period). Excitotoxic lesions of the amygdala abolished the autonomic arousal in the anticipatory period, but spared both the behavioural arousal in the anticipatory period and the autonomic arousal in the consummatory period. Together these data serve as an important step towards understanding the role of autonomic arousal in emotion and its neural underpinnings.

Gut feelings, intuition, and emotions: an exploratory study

OBJECTIVE

Investigate whether the gut feelings of one person, as measured with an electrogastrogram (EGG), respond to the emotions of a distant person.

DESIGN

In a double blind protocol, EGG activity was recorded in an individual relaxing in a heavily shielded chamber while, at a distance, a second person periodically viewed the live video image of the first person along with stimuli designed to evoke positive, negative, calming, or neutral emotions.

SUBJECTS

Twenty-six (26) pairs of healthy adult volunteers.

OUTCOME MEASURES

EGG maximum values recorded while the distant person was exposed to emotional stimuli were compared to similar values recorded during exposure to neutral stimuli.

RESULTS

EGG maximums were significantly larger on average when the distant person was experiencing positive (p = 0.006) and negative (p = 0.0009) emotions, as compared to neutral emotions. Nonparametric bootstrap procedures were employed to evaluate these differences, and the results survive correction for multiple analyses.

CONCLUSIONS

EGG activity increases in response to the emotions of a distant person, beyond the influence of ordinary sensory interactions. Relationships commonly reported between gut feelings and intuitive hunches may share a common, poorly understood, perceptive origin.

Endogenous psychoactive tryptamines reconsidered: an anxiolytic role for dimethyltryptamine

The presence of the potent hallucinogenic psychoactive chemical N,N-dimethyltryptamine (DMT) in the human body has puzzled scientists for decades. Endogenous DMT was investigated in the 1960s and 1970s and it was proposed that DMT was involved in psychosis and schizophrenia. This hypothesis developed from comparisons of the blood and urine of schizophrenic and control subjects. However, much of this research proved inconclusive and conventional thinking has since held that trace levels of DMT, and other endogenous psychoactive tryptamines, are insignificant metabolic byproducts. The recent discovery of a G-protein-coupled, human trace amine receptor has triggered a reappraisal of the role of compounds present in limited concentrations in biological systems. Interestingly enough, DMT and other psychoactive tryptamine hallucinogens elicit a robust response at the trace amine receptor. While it is currently accepted that serotonin 5-HT(2A) receptors play a pivotal role in the activity of hallucinogenic/psychedelic compounds, we propose that the effects induced by exogenous DMT administration, especially at low doses, are due in part to activity at the trace amine receptor. Furthermore, we suggest that endogenous DMT interacts with the TA receptor to produce a calm and relaxed mental state, which may suppress, rather than promote, symptoms of psychosis. This hypothesis may help explain the inconsistency in the early analysis of endogenous DMT in humans. Finally, we propose that amphetamine action at the TA receptor may contribute to the calming effects of amphetamine and related drugs, especially at low doses.

Gastric suction at birth associated with long-term risk for functional intestinal disorders in later life

OBJECTIVE

To test the hypothesis that noxious stimulation at birth may increase the long-term risk for developing psychosomatic or functional disorders during later life.

STUDY DESIGN

Matched case-control study using sibling controls. The birth records were retrieved for the offspring of 494 mothers who, after uncomplicated pregnancies, had delivered two or more children with birth weights at least 2500 g, if at least one child was exposed to a perinatal complication or birth asphyxia. Among their offspring (N=1110), the 108 cases hospitalized for functional intestinal symptoms were identified from nationwide hospital discharge records. Of these, 96 cases were compared with 116 unaffected sibling controls.

RESULTS

Functional intestinal symptoms occurred more commonly among the 1110 subjects (9.5%) than in the general population (3.4%, chi(2)=124, P<10(-6)). Gastric suction at birth occurred more frequently among the cases compared with their siblings (22.9% vs 11.2%). There were no differences in the number of cases and controls exposed to perinatal trauma or birth asphyxia. Multivariate logistic regression analyses showed that gastric suction at birth was associated with functional intestinal disorders during later life (odds ratio, 2.99; 95% confidence interval, 1.32-6.79; P=.009), whereas maternal, perinatal, or other confounding variables were not significant.

CONCLUSIONS

Noxious stimulation caused by gastric suction at birth may promote the development of long-term visceral hypersensitivity and cognitive hypervigilance, leading to an increased prevalence of functional intestinal disorders in later life.

Gastric mucosal mast cells are increased in Helicobacter pylori-negative functional dyspepsia

BACKGROUND & AIMS

Mast cells might be involved in pathogenesis of functional dyspepsia because they can release a wide range of potent mediators, capable of altering gastric nerve and muscle function. This study aimed to determine whether mast cell numbers were increased in the gastric mucosa of patients with functional dyspepsia compared to control subjects.

METHODS

Biopsy samples were taken from the antrum and corpus of 111 patients: 20 asymptomatic control subjects, 62 patients with Rome criteria functional dyspepsia (33 Helicobacter pylori positive, 29 H. pylori negative), and 29 inflammatory control subjects (H. pylori positive). Mast cells were detected immunohistochemically by using a mouse monoclonal antibody specific for tryptase. Quantification was performed with light microscopy, and results were expressed as mast cells/mm(2) +/- standard error of mean.

RESULTS

Mast cells were significantly increased in H. pylori negative functional dyspepsia samples compared to normal control samples in the antrum (230.1 +/- 11.3 vs. 94.8 +/- 8.4, P < 0.001) and corpus (264.1 +/- 27.1 vs. 123.9 +/- 11.5, P = 0.001). Mast cells were also significantly increased in the antrum of patients with H. pylori positive functional dyspepsia compared to asymptomatic control subjects (166.5 +/- 17.0 vs. 94.8 +/- 8.4, P < 0.03). However, there was no significant difference between mast cell numbers in patients with H. pylori positive functional dyspepsia compared to inflammatory control subjects.

CONCLUSIONS

Mast cells are increased in functional dyspepsia, independently of inflammation. This might contribute to the pathogenesis of functional dyspepsia by altering signaling in the brain-gut axis.

Current insights into the pathophysiology of irritable bowel syndrome

Recent reports have emphasized the possible role of mucosal immune activation and inflammation in neuropathic changes in the pathophysiology of irritable bowel syndrome (IBS). However, novel findings using functional brain imaging techniques have underlined the importance of altered perception of visceral stimuli to symptom generation in IBS. These new developments have rekindled an old debate on peripheral versus central mechanisms in the pathophysiology of IBS. In this review we discuss the latest findings in light of these two concepts. In addition, we provide evidence for the hypothesis that, in the absence of alterations in endogenous pain modulation systems and changes in visceral perception, chronic inflammatory mucosal changes in the gut are not a plausible mechanism to explain the presence of chronic abdominal pain, a cardinal IBS symptom.

Childhood autism: a circuit syndrome?

BACKGROUND

Autism is a disorder that can lead to life-long disability. Currently, the etiology of autism is unknown, and although there are treatments for some of the behavioral abnormalities, there is no cure.

REVIEW SUMMARY

While this article will review the clinical, anatomic, and pathologic features seen in autism, the primary focus will be to present a new and provocative unifying theory regarding the underlying mechanisms causing this disorder. Current research advances, some controversial, will be discussed, and a novel definition of autism as a "circuit syndrome" will be presented. The work elaborated here will tie many of the disparate findings together, based on the idea that autism arises from abnormalities of the cerebellolimbic circuitry. Some of the more alternative theories of autism, such as mercury toxicity, linkage to the measles, mumps, and rubella vaccine, and the use of secretin will be discussed. Finally, pharmacologic treatment options will be reviewed.

CONCLUSIONS

Autism is not single disorder but represents dysfunction of the cerebellolimbic circuitry that can arise from many different etiologies.

Prostaglandin E(2) modulates TTX-R I(Na) in rat colonic sensory neurons

This study was performed to determine the impact of the inflammatory mediator prostaglandin E(2) (PGE(2)) on the biophysical properties of tetrodotoxin resistant voltage-gated Na(+) currents (TTX-R I(Na)) in colonic dorsal root ganglion (DRG) neurons. TTX-R I(Na) was studied in DRG neurons from thoracolumbar (TL: T(13)-L(2)) and lumbosacral (LS: L(6)-S(2)) DRG retrogradely labeled following the injection of DiIC(18) (DiI) into the wall of the descending colon of adult male rats. TTX-R I(Na) in colonic DRG neurons had a high threshold for activation [V(0.5) of conductance-voltage (G-V) curve = -3.1 +/- 1.0 (SE) mV] and steady-state availability (V(0.5) for H-infinity curve = -18.4 +/- 1.4 mV), was slowly inactivating (10.6 +/- 1.4 ms at 0 mV), and recovered rapidly from inactivation (83.5 +/- 5.0% of the current recovered with a time constant of 1.3 +/- 0.1 ms at -80 mV). TTX-R I(Na) was present in every colonic DRG neuron studied (n = 62). PGE(2) induced a rapid (<15 s) increase in TTX-R I(Na) that was associated with a hyperpolarizing shift in the G-V curve (3.4 +/- 0.7 mV), an increase in the rate of inactivation (4.21 +/- 0.7 ms at 0 mV), and no change in steady-state availability. There was no statistically significant difference (P > 0.05) between TL and LS colonic DRG neurons with respect to the biophysical properties of TTX-R I(Na), the current density or the magnitude of PGE(2)-induced changes in the current. However, both the proportion of TL and LS neurons in which TTX-R I(Na) was modulated by PGE(2) (16 of 16 TL neurons and 12 of 14 LS neurons) as well as the magnitude of PGE(2)-induced changes in the current were significantly larger in colonic DRG neurons than in the total population of DRG neurons. These results suggest that changes in nociceptive processing associated with inflammation of the colon does not reflect differences between TL and LS neurons with respect to the properties of TTX-R I(Na), distribution of current, or magnitude of inflammatory mediator-induced changes in the current. However, these results do suggest modulation of TTX-R I(Na) in colonic afferents is an underlying mechanism of hyperalgesia and pain associated with inflammation of the colon and that this current constitutes a novel target for therapeutic relief of visceral inflammatory pain.

The relationship between rectal pain, unpleasantness, and urge to defecate in normal subjects

Rectal stimulation under normal or pathological conditions evokes numerous sensations. Previous studies have examined rectal stimulation-evoked pain and urge to defecate, but discrepancies in the findings remain because of the different methodologies used in each study and the reporting of sensations only at the end of or after the applied stimuli. Therefore, we conducted a psychophysical study of various aspects of rectal sensation in normal subjects using a variety of distension stimuli and continuous on-line rating of sensation. Ten normal healthy subjects (eight female and two male) were given rectal distension stimuli delivered by a computer-driven barostat. For some experiments, sensation was continuously monitored and rated on a visual analog scale. Subjects first underwent an ascending series of phasic (30 s) distensions to determine how urge, unpleasantness, and pain intensity varied and interrelated as rectal volume and pressure changed. A second series of distensions examined rectal physiology and perception during short phasic (30 s) or long (300 s) distensions at pressures that elicit either moderate urge or moderate pain and while continuously rating these sensations. The McGill Pain Questionnaire was used to assess the multidimensional aspects of rectal pain with each type of distension. The results of the ascending series revealed significant relationships between sensations as pressure and volume increased. The ratings of urge were double that of pain and unpleasantness, whereas unpleasantness and pain ratings were comparable. Isobaric phasic and tonic distensions were associated with an increase in volume (i.e. accommodation) with time. The magnitude of urge with repetitive short isobaric (30 s) distensions was overall not related to the slight increase in rectal volume, while phasic distensions at moderate pain intensity revealed a significant overall relationship between rectal volume and both unpleasantness and pain intensity. Long isobaric distensions evoked sensations that varied over time despite progressive increases in volume, but less variation in sensation was observed during short phasic distensions which also demonstrated a similar increase in rectal volume. Differences in temporal characteristics of sensations evoked by low-pressure distensions eliciting moderate urge versus high-pressure distensions eliciting moderate pain were illustrated by a significantly longer delay to the diminution of non-painful urge versus pain. Therefore, we conclude (1) Differences in the discrimination and the temporal characteristics of urge at subpainful rectal pressures and of pain at noxious pressures suggest that noxious and non-noxious stimuli are processed differently. (2) The overall unpleasantness and pain correlate with rectal volume during accommodation. However, instantaneous evoked sensations can vary independent of volume changes during constant pressure distension. (3) The reported sensation-related responses to tension and stretch will likely be different depending on the degree of accommodation that is occurring. Moreover, the peripheral receptor mechanisms which contribute to controlling this accommodation will also affect the perception of rectal stimuli. (4) Continuous ratings of rectal sensations are valuable in investigating rectal physiology and the multidimensional nature of rectal symptoms.