Siobhain M. O'Mahony

Early Life Stress Alters Behavior, Immunity, and Microbiota in Rats: Implications for Irritable Bowel Syndrome and Psychiatric Illnesses

BACKGROUND Adverse early life events are associated with a maladaptive stress response system and might increase the vulnerability to disease in later life. Several disorders have been associated with early life stress, ranging from depression to irritable bowel syndrome. This makes the identification of the neurobiological substrates that are affected by adverse experiences in early life invaluable. METHODS The purpose of this study was to assess the effect of early life stress on the brain-gut axis. Male rat pups were stressed by separating them from their mothers for 3 hours daily between postnatal days 2-12. The control group was left undisturbed with their mothers. Behavior, immune response, stress sensitivity, visceral sensation, and fecal microbiota were analyzed. RESULTS The early life stress increased the number of fecal boli in response to a novel stress. Plasma corticosterone was increased in the maternally separated animals. An increase in the systemic immune response was noted in the stressed animals after an in vitro lipopolysaccharide challenge. Increased visceral sensation was seen in the stressed group. There was an alteration of the fecal microbiota when compared with the control group. CONCLUSIONS These results show that this form of early life stress results in an altered brain-gut axis and is therefore an important model for investigating potential mechanistic insights into stress-related disorders including depression and IBS.

Disturbance of the gut microbiota in early-life selectively affects visceral pain in adulthood without impacting cognitive or anxiety-related behaviors in male rats

Disruption of bacterial colonization during the early postnatal period is increasingly being linked to adverse health outcomes. Indeed, there is a growing appreciation that the gut microbiota plays a role in neurodevelopment. However, there is a paucity of information on the consequences of early-life manipulations of the gut microbiota on behavior. To this end we administered an antibiotic (vancomycin) from postnatal days 4-13 to male rat pups and assessed behavioral and physiological measures across all aspects of the brain-gut axis. In addition, we sought to confirm and expand the effects of early-life antibiotic treatment using a different antibiotic strategy (a cocktail of pimaricin, bacitracin, neomycin; orally) during the same time period in both female and male rat pups. Vancomycin significantly altered the microbiota, which was restored to control levels by 8 weeks of age. Notably, vancomycin-treated animals displayed visceral hypersensitivity in adulthood without any significant effect on anxiety responses as assessed in the elevated plus maze or open field tests. Moreover, cognitive performance in the Morris water maze was not affected by early-life dysbiosis. Immune and stress-related physiological responses were equally unaffected. The early-life antibiotic-induced visceral hypersensitivity was also observed in male rats given the antibiotic cocktail. Both treatments did not alter visceral pain perception in female rats. Changes in visceral pain perception in males were paralleled by distinct decreases in the transient receptor potential cation channel subfamily V member 1, the α-2A adrenergic receptor and cholecystokinin B receptor. In conclusion, a temporary disruption of the gut microbiota in early-life results in very specific and long-lasting changes in visceral sensitivity in male rats, a hallmark of stress-related functional disorders of the brain-gut axis such as irritable bowel disorder.

Antipsychotics and the gut microbiome: olanzapine-induced metabolic dysfunction is attenuated by antibiotic administration in the rat

The atypical antipsychotic olanzapine is often associated with serious metabolic side effects including weight gain and increased visceral fat. These adverse events are a considerable clinical problem and the mechanisms underlying them are multifactorial and poorly understood. Growing evidence suggests that the gut microbiota has a key role in energy regulation and disease states such as obesity. Moreover, we recently showed that chronic olanzapine altered the composition of the gut microbiome in the rat. It is thus possible that treatments that alter gut microbiota composition could ameliorate olanzapine-induced weight gain and associated metabolic syndrome. To this end, we investigated the impact of antibiotic-induced alteration of the gut microbiota on the metabolic effects associated with chronic olanzapine treatment in female rats. Animals received vehicle or olanzapine (2 mg kg−1 per day) for 21 days, intraperitoneal injection, two times daily. Animals were also coadministered vehicle or an antibiotic cocktail consisting of neomycin (250 mg kg−1 per day), metronidazole (50 mg kg−1 per day) and polymyxin B (9 mg kg−1 per day) by oral gavage, daily, beginning 5 days before olanzapine treatment. The antibiotic cocktail drastically altered the microbiota of olanzapine-treated rats, and olanzapine alone was also associated with an altered microbiota. Coadministration of the antibiotic cocktail in olanzapine-treated rats attenuated: body weight gain, uterine fat deposition, macrophage infiltration of adipose tissue, plasma free fatty acid levels, all of which were increased by olanzapine alone. These results suggest that the gut microbiome has a role in the cycle of metabolic dysfunction associated with olanzapine, and could represent a novel therapeutic target for preventing antipsychotic-induced metabolic disease.

Priming for health: gut microbiota acquired in early life regulates physiology, brain and behaviour

The infant gut microbiome is dynamic, and radical shifts in composition occur during the first 3 years of life. Disruption of these developmental patterns, and the impact of the microbial composition of our gut on brain and behaviour, has attracted much recent attention. Integrating these observations is an important new research frontier.

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

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

Toll-Like Receptor mRNA Expression Is Selectively Increased in the Colonic Mucosa of Two Animal Models Relevant to Irritable Bowel Syndrome

Background Irritable bowel syndrome (IBS) is largely viewed as a stress-related disorder caused by aberrant brain-gut–immune communication and altered gastrointestinal (GI) homeostasis. Accumulating evidence demonstrates that stress modulates innate immune responses; however, very little is known on the immunological effects of stress on the GI tract. Toll-like receptors (TLRs) are critical pattern recognition molecules of the innate immune system. Activation of TLRs by bacterial and viral molecules leads to activation of NF-kB and an increase in inflammatory cytokine expression. It was our hypothesis that innate immune receptor expression may be changed in the gastrointestinal tract of animals with stress-induced IBS-like symptoms. Methodology/Principal Findings In this study, our objective was to evaluate the TLR expression profile in the colonic mucosa of two rat strains that display colonic visceral hypersensivity; the stress-sensitive Wistar-Kyoto (WKY) rat and the maternally separated (MS) rat. Quantitative PCR of TLR2-10 mRNA in both the proximal and distal colonic mucosae was carried out in adulthood. Significant increases are seen in the mRNA levels of TLR3, 4 & 5 in both the distal and proximal colonic mucosa of MS rats compared with controls. No significant differences were noted for TLR 2, 7, 9 & 10 while TLR 6 could not be detected in any samples in both rat strains. The WKY strain have increased levels of mRNA expression of TLR3, 4, 5, 7, 8, 9 & 10 in both the distal and proximal colonic mucosa compared to the control Sprague-Dawley strain. No significant differences in expression were found for TLR2 while as before TLR6 could not be detected in all samples in both strains. Conclusions These data suggest that both early life stress (MS) and a genetic predisposition (WKY) to stress affect the expression of key sentinels of the innate immune system which may have direct relevance for the molecular pathophysiology of IBS.

Evidence of an enhanced central 5HT response in irritable bowel syndrome and in the rat maternal separation model

Abstract  Efforts to define either a biomarker for irritable bowel syndrome (IBS) or a valid animal model have proven disappointing. The aims of this study were to determine if buspirone stimulates prolactin release through the 5‐hydroxytryptamine (5HT)1a receptor and whether this response is altered in patients with IBS and in the rat maternal separation model. Buspirone (30 mg) was used to stimulate prolactin release in 40 patients with IBS and in 40 healthy controls. In study 1, 10 IBS patients and 10 controls underwent pretreatment with pindolol (5HT1a antagonist) or placebo followed by buspirone. In study 2, 30 patients with IBS and 30 healthy controls had prolactin release stimulated by buspirone. Maternally separated and nonseparated rats were also treated with buspirone and prolactin monitored. Serotonin metabolites were measured together with the expression of the 5HT1a and serotonin transporter (SERT) gene. Pindolol produced a dose‐dependent decrease in the buspirone prolactin response. Patients with IBS and maternally separated rats showed an exaggerated release of prolactin in response to buspirone. In the animal model, an increased turnover of 5HT was found in the brainstem together with a trend toward increased activity of the SERT gene. In conclusion altered central serotonin responses are found in both IBS and in an animal model.

Verapamil in treatment resistant depression: a role for the P-glycoprotein transporter?

Verapamil is a calcium channel blocker that also inhibits the P‐glycoprotein (Pgp) membrane transporter. We have found that administration of verapamil with a recognised antidepressant improves clinical outcome in previously treatment resistant cases despite the fact that verapamil does not possess inherent antidepressant activity. In this study we examined the hypothesis that the antidepressant‐like effects of verapamil are mediated through its blockade of the Pgp transporter in the blood brain barrier (BBB).

Rodent Models of Colorectal Distension

Colorectal distension (CRD) is a widely accepted, reproducible method for assessing visceral sensitivity in both clinical and pre‐clinical studies. Distension of the colon mirrors the human scenario of visceral pain with regard to intensity and referral of pain in patients. There are several readouts that can be applied to the CRD protocol depending on the species being evaluated, two of which are described in this unit. CRD can be used to measure the impact of novel compounds, strain, or genetic differences as well as the effect of physical and psychological stressors on the sensitivity of the colon. Investigation of the impact of a noxious visceral stimulus (CRD) on other systems within the body can also be carried out. Given that visceral pain is a major clinical problem and one of the most common reasons patients seek out medical advice, the ability to assess this type of pain is essential to the discovery of successful treatments. This unit outlines two protocols that describe CRD of rats and mice. Curr. Protoc. Neurosci. 61:9.40.1‐9.40.13.

Early-life stress selectively affects gastrointestinal but not behavioral responses in a genetic model of brain-gut axis dysfunction.

Early‐life stress and a genetic predisposition to display an anxiety‐ and depressive‐like phenotype are associated with behavioral and gastrointestinal (GI) dysfunction. Animals exposed to early‐life stress, and those genetically predisposed to display anxiety or depressive behaviors, have proven useful tools in which to study stress‐related GI disorders, such as irritable bowel syndrome (IBS). IBS is a heterogeneous disorder, and likely a consequence of both genetic and environmental factors. However, the combined effects of early‐life stress and a genetic predisposition to display anxiety‐ and depression‐like behaviors on GI function have not been investigated.