Can you describe how and why you decided to collaborate on your ongoing investigations on the adaptive systems of the body?

JB: I have a longstanding interest and publication record in relation to the role of the enteric nervous system (ENS) and components of the gut immune system, such as mast cells. It was thus a logical step to begin to ask questions about the role of the gut microbiome and visceral pain perception. We found that ingestion by rats of a commensal bacteria (which we refer to as JB-1), was able to completely inhibit visceral pain perception. Subsequently, we began to collaborate, and Wolfgang Kunze showed that a specifi c ion channel was inhibited in enteric neurons by this bacteria. This led us to investigate their effects on the brain and behaviour, and correlate this understanding with the potential treatment of psychiatric disorders.

PF: Scientists have a tendency to work in carefully defi ned areas but, in reality, the major adaptive systems of the body do not operate in isolation; these systems are in constant communication, collaborating and coordinating their actions to maintain optimal physiological functions. Thus, in order to address questions as complex as how microbes in the gut communicate with host systems, including the central nervous system (CNS), you really need a multidisciplinary approach.

In general terms, what are the short- and long-term objectives of your work?

PF: The short-term goals are to understand the mechanisms used by bacteria in the gut to modulate the hosts nervous, immune and endocrine systems which can, in turn, infl uence the brain and behaviour. The long-term goal

is to use this knowledge to develop novel preventive or therapeutic strategies for a range of conditions, including mood disorders.

Could you discuss your approach to identifying how elements of the gut microbiome can modulate the brain and some of its functions related to anxiety, fear and cognition?

PF: We are employing two anthropomorphic behavioural stress paradigms in mice that have been validated as much as possible as models of human mental distress – social defeat and circadian rhythm disruption. These animal models allow us to use both top-down and bottom-up approaches to examine the bidirectional relationship between changes in the gut microbiome and brain function and behaviour. For example, how does stress disrupt the microbiota? How does alteration in gut microbes – through the use of antibiotics, or exposure to specifi c commensal bacteria – infl uence brain chemistry and behaviour associated with stress?

How can the translation of further vagus nerve tests on animal models impact upon clinical treatment?

WK: There is an emerging consensus that the vagus nerve is important in transmitting mood-related stimuli from microbiota to the brain. We have uncovered a key step in this process; namely, that much of this traffi c is gated by the ENS within the wall of the intestine. Furthermore, there appears to be a chemical code that is involved in the therapeutic signalling pathway from microbes to the brain.

Future animal studies, designed to determine if neurotransmitter receptors other than nicotinic are involved, could help to identify yet unknown

benefi cial microbes based on the molecules they make. In addition, vagal stimulation via ingested benefi cial microbes may provide a safer alternative to electrical vagal stimulation as currently practised, since the microbes activate vagal branches below the level of the heart. Mood-improving microbes may also act as an adjunct to current vagal stimulation protocols allowing for a reduction in the intensity or frequency of the stimulation.

What is the correlation between post-traumatic stress disorder (PTSD) and the microbiome?

JB: Stress is a major risk factor for a variety of psychiatric disorders, such as anxiety, major depression and PTSD. We know from our own work that we can ameliorate the hypothalamic-pituitary-adrenal (HPA) axis response to stress by prior treatment with JB-1, and others have shown similar results with other commensal bacteria. We are testing models of stress in pregnancy, postnatally and in adulthood, as well as their long-term effects on gut physiology, ENS and vagal function, neurochemical changes in the CNS and behaviour.

In addition, we are looking at the effects of antibiotics at these various time points and correlating results of deep sequencing of the gut microbiome with outcome data. Clinical data suggest that early life major stress is a signifi cant risk factor for subsequent PTSD.

Having worked together for 10 years on the microbiome-gut-brain axis, Professors John Bienenstock, Paul Forsythe and Wolfgang Kunze highlight their current objectives and studies on how microbes infl uence host systems

Microbes: gut, brain and behaviour

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Researchers at the Brain-Body Institute at McMaster University in Canada are investigating how commensal bacteria affect the function of the enteric nervous system and the brain. Their fi ndings could have signifi cant impact on ensuring healthy gut and brain function

The microbiome-gut-brain axis

THE POPULATION OF microbes that live inside the intestine are collectively known as gut microbiota. It is estimated that there are some 10 trillion microorganisms inside every person. While around one-third of these microorganisms are common to us all, the remaining two-thirds are unique to each individual. However, despite the resident specifi city of microbiota, they all perform the same essential physiological functions, such as ensuring proper digestion and playing an important role in the immune system. Despite the universal acknowledgement of the importance of our gut microbiota, there is still a great deal to be understood.

To address this dearth in knowledge, studies are exploring the microbiome-gut-brain axis, which refers to the biochemical signalling that occurs between the gut microbiota, endocrine, immune and enteric nervous system (ENS), and brain. Because of the relative infancy of the fi eld, large knowledge gaps still exist. Studies have, however, begun to shed light on the important role gut microbes play in human development, maturation and adulthood.

THE COMPLEX NATURE OF COMMENSAL RELATIONSHIPSFor the past decade, three researchers from the Brain-Body Institute (BBI) at McMaster University have collaborated on a range of projects that seek to understand more about the microbiome-gut-brain axis. Professors John Bienenstock, Paul Forsythe and Wolfgang Kunze have dedicated their studies to uncovering how commensal bacteria affect the function of the ENS and the brain, in addition to

exploring the pathways that may be involved in their interactions. Indeed, their major focus is on delineating the mechanisms and pathways of communication between gut microbes and the host, fi ndings that will have signifi cant implications for understanding immune, as well as neurodevelopmental and mood disorders.

One study, funded by the US Offi ce of Naval Research and led by Bienenstock, seeks to understand the positive effects of negative responses to environmental stressors. More specifi cally, the researchers are aiming to identify the pathways and specifi c molecules involved in human mental distress. Using mouse models, the team applies molecular methods to investigate how the complex relationship between the gut microbiome, the brain and behaviour are affected by changes to each system, a combination, or all of them. Ultimately, their fi ndings could enable clinicians to maintain or restore normal brain function. “The molecules involved could be mimicked, or synthetic molecular analogues could be developed as drugs,” elaborates Bienenstock. “It may well be possible to use the specifi c bacteria – or clusters of developed bacteria – to effect changes which promote benefi cial central nervous system (CNS) pathways.”

MAKING THE VAGUS NERVE’S ROLE LESS VAGUEThe team has already achieved signifi cant results and led the discovery that the vagus nerve may be involved in the important transmission of information to the brain from the gut bacteria. Indeed, the researchers have used these fi ndings to treat anxiety- and

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GUT MICROBES AND THE NERVOUS SYSTEM

OBJECTIVETo determine how commensal bacteria affect the function of the enteric nervous system and the brain, as well as the pathways involved.

FUNDINGUS Offi ce of Naval Research, USA

International Development Research Center/Canadian Institutes for Health Research, Canada

Natural Sciences and Engineering Research Council of Canada, Canada

CONTACTJohn Bienenstock

McMaster Brain-Body InstituteSt. Joseph’s Healthcare Hamilton

T +1 905 522 1155 x35171 E bienens@mcmaster.ca

JOHN BIENENSTOCK is internationally known as a physician and mucosal immunologist. He holds the title of Distinguished University Professor at McMaster University, an

Honorary MD (Goteborg, Sweden), is a Fellow of the Royal Society of Canada and a Member of the Order of Canada, and an inductee into The Canadian Medical Hall of Fame. Bienenstock is the Founding Director of the McMaster Brain-Body Institute (BBI) at St. Joseph’s Healthcare Hamilton, a former Chair of Pathology and subsequently Dean and Vice-President of the Faculty of Health Sciences, McMaster University.

PAUL FORSYTHE obtained his BSc (Hons) in Biochemistry, MSc in Laboratory Medicine and PhD in Mast Cell Immunopharmacology from Queen’s University Belfast, Northern

Ireland. Following his PhD, he undertook a postdoctoral fellowship with the Pulmonary Research Group at the University of Alberta (1999-2003). Forsythe continued his postdoctoral training at the BBI, before joining the Faculty of Medicine in 2008.

WOLFGANG KUNZE leads the Gut, Brain and Ageing Laboratory at the BBI. He was educated at Melbourne University (1977-1991), where he studied physiology; he did

postdoctoral work in the Departments of Physiology, and Anatomy and Cell Biology at Melbourne University. He then worked at Tubingen University, Germany, in the Department of General Surgery. He joined McMaster University in 2006.

depression-related behaviour in mice. The US Food and Drug Administration (FDA) has approved vagal nerve stimulation to treat depression. It is clear that commensal bacteria in the intestine can affect the ENS and CNS, but the exact way in which this manifests is not yet known. In unravelling this information, the team has the aim of extrapolating and translating these data into clinical treatments for psychiatric disorders.

Many fi ndings have been documented over the last 10 years reporting the spectrum of the team’s research endeavours. One key fi nding has been the discovery that bacterial microvesicles shed from a commensal bacteria known as JB-1 are able to mediate many of the immunological effects of the parent whole live bacteria, and have found a component of those bacteria that replicate many of those effects. “The exploration of microbial components which mediate biological effects in this manner narrows down both the number of bacterial components that may be involved, but also the fact that the ENS activation is indirect via the epithelium,” explains Bienenstock.

A PLETHORA OF PROJECTSDue to the multifaceted nature of their research on the microbiome-gut-brain axis, the researchers also lead individual studies on specifi c aspects of human development. As the proportion of elderly to young individuals rises in regions across the world, healthy ageing is increasingly becoming a focus of study. It is clear that ageing-related changes in animals are paralleled by alterations in the composition of intestinal microbiota. This understanding has led Kunze’s laboratory to initiate a research study investigating related aspects. “We are studying how the intestinal nervous system and gut-to-brain communication changes during ageing,” says Kunze. “We want to see whether benefi cial bacteria can reverse these changes.”

Forsythe is the lead investigator for the Canadian component of their Israel-Canada collaborative project. As such, he coordinates his laboratory’s efforts with collaborators in Israel, but also in Chile. The project uses Drosophila – a genus of small fl ies – to explore the role of antibiotics in infl uencing the make-up of the microbiome and the consequent effects on the brain. “We will be focusing on the effect of early-life antibiotic treatment on specifi c components of the immune system in mice,” explains Forsythe. “We want to know how these immune changes are related to alterations in brain chemistry and behaviour.” The team’s Israeli collaborators will use the antibiotic-treated Drosophila model to identify potentially novel communication pathways, or the networks of genes linked to microbiota-dependent behaviour. Ultimately, the knowledge garnered from this project will enable the team to look for orthologous systems in mammals.

MOVING THE FIELD FORWARDAcross all their research endeavours,

Bienenstock, Forsythe and Kunze are moving the fi eld of microbiome-gut-brain axis study forward. An understanding of the specifi c interactions between commensal bacteria, the nervous systems and the brain has huge potential for the treatments of a broad range of disorders. Therefore, their fi ndings could inform the development of new drug therapies and provide fascinating evidence for the role those trillions of microorganisms play in the healthy function of us all.

Delineating the mechanisms

and pathways of

communication between gut

microbes and the host will

have signifi cant implications

for understanding nervous and

immune disorders

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