Wolfgang A. Kunze

The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut–brain communication

Background  The probiotic Bifidobacterium longum NCC3001 normalizes anxiety‐like behavior and hippocampal brain derived neurotrophic factor (BDNF) in mice with infectious colitis. Using a model of chemical colitis we test whether the anxiolytic effect of B. longum involves vagal integrity, and changes in neural cell function.

Lactobacillus reuteri enhances excitability of colonic AH neurons by inhibiting calcium-dependent potassium channel opening

Probiotics are live non‐pathogenic commensal organisms that exert therapeutic effects in travellers’ diarrhea, irritable bowel syndrome and inflammatory bowel disease. Little is known about mechanisms of action of commensal bacteria on intestinal motility and motility‐induced pain. It has been proposed that probiotics affect intestinal nerve function, but direct evidence for this has thus far been lacking. We hypothesized that probiotic effects might be mediated by actions on colonic intrinsic sensory neurons. We first determined whether sensory neurons were present in rat colon by their responses to chemical mucosal stimulation and identified them in terms of physiological phenotype and soma morphotype. Enteric neuron excitability and ion channel activity were measured using patch clamp recordings. We fed 109Lactobacillus reuteri (LR) or vehicle control to rats for 9 days. LR ingestion increased excitability (threshold for evoking action potentials) and number of action potentials per depolarizing pulse, decreased calcium‐dependent potassium channel (IKCa) opening and decreased the slow afterhyperpolarization (sAHP) in sensory AH neurons, similar to the IKCa antagonists Tram‐34 and clotrimazole. LR did not affect threshold for action potential generation in S neurons. Our results demonstrate that LR targets an ion channel in enteric sensory nerves through which LR may affect gut motility and pain perception.

Voices from within: gut microbes and the CNS

Recent advances in research have greatly increased our understanding of the importance of the gut microbiota. Bacterial colonization of the intestine is critical to the normal development of many aspects of physiology such as the immune and endocrine systems. It is emerging that the influence of the gut microbiota also extends to modulation of host neural development. Furthermore, the overall balance in composition of the microbiota, together with the influence of pivotal species that induce specific responses, can modulate adult neural function, peripherally and centrally. Effects of commensal gut bacteria in adult animals include protection from the central effects of infection and inflammation as well as modulation of normal behavioral responses. There is now robust evidence that gut bacteria influence the enteric nervous system, an effect that may contribute to afferent signaling to the brain. The vagus nerve has also emerged as an important means of communicating signals from gut bacteria to the CNS. Further understanding of the mechanisms underlying microbiome–gut–brain communication will provide us with new insight into the symbiotic relationship between gut microbiota and their mammalian hosts and help us identify the potential for microbial-based therapeutic strategies to aid in the treatment of mood disorders.

The microbiome is essential for normal gut intrinsic primary afferent neuron excitability in the mouse.

Background  The role of intestinal microbiota in the development and function of host physiology is of high interest, especially with respect to the nervous system. While strong evidence has accrued that intestinal bacteria alter host nervous system function, mechanisms by which this occurs have remained elusive. For this reason, we have carried out experiments examining the electrophysiological properties of neurons in the myenteric plexus of the enteric nervous system (ENS) in germ‐free (GF) mice compared with specific pathogen‐free (SPF) control mice and adult germ‐free mice that have been conventionalized (CONV‐GF) with intestinal bacteria.

Vagal pathways for microbiome-brain-gut axis communication.

There is now strong evidence from animal studies that gut microorganism can activate the vagus nerve and that such activation plays a critical role in mediating effects on the brain and behaviour. The vagus appears to differentiate between non-pathogenic and potentially pathogenic bacteria even in the absence of overt inflammation and vagal pathways mediate signals that can induce both anxiogenic and anxiolytic effects, depending on the nature of the stimulus. Certain vagal signals from the gut can instigate an anti-inflammatory reflex with afferent signals to the brain activating an efferent response, releasing mediators including acetylcholine that, through an interaction with immune cells, attenuates inflammation. This immunomodulatory role of the vagus nerve may also have consequences for modulation of brain function and mood.What is currently lacking are relevant data on the electrophysiology of the system. Certainly, important advances in our understanding of the gut-brain and microbiome- gut-brain axis will come from studies of how distinct microbial and nutritional stimuli activate the vagus and the nature of the signals transmitted to the brain that lead to differential changes in the neurochemistry of the brain and behaviour.Understanding the induction and transmission of signals in the vagus nerve may have important implications for the development of microbial-or nutrition based therapeutic strategies for mood disorders.

Communication between gastrointestinal bacteria and the nervous system

In the past few years, intestinal microbiota has emerged as a novel target for the treatment of gut-brain axis alterations. These include functional gastrointestinal disorders, such as irritable bowel syndrome (IBS), which can be comorbid with stress-related psychiatric conditions. Thus, modulation of the microbiota (e.g. with the use of probiotics) could be proposed as a novel strategy not only for the treatment of IBS but also as an adjuvant for psychiatric treatment of anxiety and depression.

Psychoactive bacteria Lactobacillus rhamnosus (JB-1) elicits rapid frequency facilitation in vagal afferents

Mounting evidence supports the influence of the gut microbiome on the local enteric nervous system and its effects on brain chemistry and relevant behavior. Vagal afferents are involved in some of these effects. We previously showed that ingestion of the probiotic bacterium Lactobacillus rhamnosus (JB-1) caused extensive neurochemical changes in the brain and behavior that were abrogated by prior vagotomy. Because information can be transmitted to the brain via primary afferents encoded as neuronal spike trains, our goal was to record those induced by JB-1 in vagal afferents in the mesenteric nerve bundle and thus determine the nature of the signals sent to the brain. Male Swiss Webster mice jejunal segments were cannulated ex vivo, and serosal and luminal compartments were perfused separately. Bacteria were added intraluminally. We found no evidence for translocation of labeled bacteria across the epithelium during the experiment. We recorded extracellular multi- and single-unit neuronal activity with glass suction pipettes. Within minutes of application, JB-1 increased the constitutive single- and multiunit firing rate of the mesenteric nerve bundle, but Lactobacillus salivarius (a negative control) or media alone were ineffective. JB-1 significantly augmented multiunit discharge responses to an intraluminal distension pressure of 31 hPa. Prior subdiaphragmatic vagotomy abolished all of the JB-1-evoked effects. This detailed exploration of the neuronal spike firing that encodes behavioral signaling to the brain may be useful to identify effective psychoactive bacteria and thereby offer an alternative new perspective in the field of psychiatry and comorbid conditions.

Lactobacillus reuteri ingestion prevents hyperexcitability of colonic DRG neurons induced by noxious stimuli

Lactobacillus species ingestion can decrease autonomic responses and spinal fiber discharge to nociceptive colorectal distension (CRD), even in the absence of inflammation. The present study aimed to determine whether dorsal root ganglion (DRG) somas could be a locus where the antinociceptive probiotic may have an effect. Healthy rats were fed with Lactobacillus reuteri or vehicle control for 9 days whereupon they were anesthetized, and intermittent distal colonic CRD at 80 mmHg distension was either performed for 1 h or not. The animals were immediately euthanized and patch-clamp recordings taken after isolation and overnight culture from those DRG that projected to the distal colon. CRD decreased the threshold for action potential generation and increased the number of spikes discharged during a standard depolarizing test stimulus, and this effect was blocked by prior probiotic ingestion. The increase in excitability was paralleled by an increase in DRG capacitance, which was not altered by Lactobacillus reuteri ingestion. CRD did not increase tissue weight or myeloperoxidase activity. We suggest that the effects of CRD may have been caused by activity-dependent neurotransmission between DRG somas. CRD evoked increases in action potential upstroke speed, which suggests that it may also have led to augmentation of sodium channel conductances. Probiotic ingestion may have interfered with this hypothetical mechanism since it blocked the effect of CRD on the action potential.

Luminal administration ex vivo of a live Lactobacillus species moderates mouse jejunal motility within minutes

Gut commensals modulate host immune, endocrine, and metabolic functions. They also affect peripheral and central neural reflexes and function. We have previously shown that daily ingestion of Lactobacillus reuteri (LR) for 9 d inhibits the pseudoaffective cardiac response and spinal single‐fiber discharge evoked by visceral distension, and decreases intestinal motility and myenteric AH cell slow afterhy‐perpolarization (sAHP) by inhibiting a Ca‐activated K (IKCa) channel. We tested whether luminal LR could acutely decrease motility in an ex vivo perfusion model of naive Balb/c jejunum. Live LR dose dependently decreased motor complex pressure wave amplitudes with 9‐ to 16‐min onset latency and an IC50 of 5 × 107 cells/ml Krebs. Heat‐killed LR or another live commensal, Lactobacillus salivarius, were without effect. The IKCa channel blocker TRAM‐34, but neither the opener (DCEBIO) nor the hyperpolarization‐activated cationic channel inhibitor ZD7288 (5 µM) (or TTX 1 µM), mimicked the LR effect on motility acutely ex vivo. We provide evidence for a rapid, strain‐specific, dose‐dependent action of a live Lactobacillus on small intestinal motility reflexes that recapitulates the long‐term effects of LR ingestion. These observations may be useful as a first step to unraveling the pathways involved in bacteria to the nervous system communication.—Wang, B., Mao, Y.‐K., Diorio, C., Pasyk, M., Wu, R.Y., Bienenstock, J., Kunze, W. A. Luminal administration ex vivo of a live Lactobacillus species moderates mouse jejunal motility within minutes. FASEB J. 24, 4078–4088 (2010). www.fasebj.org

On communication between gut microbes and the brain.

Purpose of review Interest in the microbiota–gut–brain axis is increasing apace and what was, not so long ago, a hypothetical relationship is emerging as a potentially critical factor in the regulation of intestinal and mental health. Studies are now addressing the neural circuitry and mechanisms underlying the influence of gut bacteria on the central nervous system and behavior. Recent findings Gut bacteria influence development of the central nervous systems (CNS) and stress responses. In adult animals, the overall composition of the microbiota or exposure to specific bacterial strains can modulate neural function, peripherally and centrally. Gut bacteria can provide protection from the central effects of infection and inflammation as well as modulate normal behavioral responses. Behavioral effects described to date are largely related to stress and anxiety and an altered hypothalamus–pituitary–adrenal axis response is a common observation in many model systems. The vagus nerve has also emerged as an important means of communicating signals from gut microbes to the CNS. Summary Studies of microbiota–gut–brain communication are providing us with a deeper understanding of the relationship between the gut bacteria and their hosts while also suggesting the potential for microbial-based therapeutic strategies that may aid in the treatment of mood disorders.