The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective.

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

Microbes, oxytocin and stress: Converging players regulating eating behavior.

Oxytocin is a peptide-hormone extensively studied for its multifaceted biological functions and has recently gained attention for its role in eating behavior, through its action as an anorexigenic neuropeptide. Moreover, the gut microbiota is involved in oxytocinergic signaling through the brain-gut axis, specifically in the regulation of social behavior. The gut microbiota is also implicated in appetite regulation and is postulated to play a role in central regulation of hedonic eating. In this review, we provide an overview on oxytocin and its individual links with the microbiome, the homeostatic and non-homeostatic regulation of eating behavior as well as social behavior and stress.

Making Sense of Quorum Sensing at the Intestinal Mucosal Interface.

The gut microbiome can produce metabolic products that exert diverse activities, including effects on the host. Short chain fatty acids and amino acid derivatives have been the focus of many studies, but given the high microbial density in the gastrointestinal tract, other bacterial products such as those released as part of quorum sensing are likely to play an important role for health and disease. In this review, we provide of an overview on quorum sensing (QS) in the gastrointestinal tract and summarise what is known regarding the role of QS molecules such as auto-inducing peptides (AIP) and acyl-homoserine lactones (AHL) from commensal, probiotic, and pathogenic bacteria in intestinal health and disease. QS regulates the expression of numerous genes including biofilm formation, bacteriocin and toxin secretion, and metabolism. QS has also been shown to play an important role in the bacteria-host interaction. We conclude that the mechanisms of action of QS at the intestinal neuro-immune interface need to be further investigated.

The neuroendocrine stress response impairs hippocampal vascular function and memory in male and female rats.

Chronic psychological stress affects brain regions involved in memory such as the hippocampus and accelerates age-related cognitive decline, including in Alzheimer's disease and vascular dementia. However, little is known about how chronic stress impacts hippocampal vascular function that is critically involved in maintaining neurocognitive health that could contribute to stress-related memory dysfunction. Here, we used a novel experimental rat model that mimics the neuroendocrine and cardiovascular aspects of chronic stress to determine how the neuroendocrine components of the stress response affect hippocampal function. We studied both male and female rats to determine potential sex differences in the susceptibility of the hippocampus and its vasculature to neuroendocrine stress-induced dysfunction. We show that activation of neuroendocrine stress pathways impaired the vasoreactivity of hippocampal arterioles to mediators involved in coupling neuronal activity with local blood flow that was associated with impaired memory function. Interestingly, we found more hippocampal arteriolar dysfunction and scarcer hippocampal microvasculature in male compared to female rats that was associated with greater memory impairment, suggesting the male sex may be at increased risk of neuroendocrine-derived hippocampal dysfunction during chronic stress. Overall, this study revealed the therapeutic potential of targeting hippocampal arterioles to prevent or slow memory decline in the setting of prolonged and/or unavoidable stress.

Identification of a Quorum Sensing-Dependent Communication Pathway Mediating Bacteria-Gut-Brain Cross Talk.

Despite recently established contributions of the intestinal microbiome to human health and disease, our understanding of bacteria-host communication pathways with regard to the gut-brain axis remains limited. Here we provide evidence that intestinal neurons are able to "sense" bacteria independently of the host immune system. Using supernatants from cultures of the opportunistic pathogen Staphylococcus aureus (S. aureus) we demonstrate the release of mediators with neuromodulatory properties at high population density. These mediators induced a biphasic response in extrinsic sensory afferent nerves, increased membrane permeability in cultured sensory neurons, and altered intestinal motility and secretion. Genetic manipulation of S. aureus revealed two key quorum sensing-regulated classes of pore forming toxins that mediate excitation and inhibition of extrinsic sensory nerves, respectively. As such, bacterial mediators have the potential to directly modulate gut-brain communication to influence intestinal symptoms and reflex function in vivo, contributing to homeostatic, behavioral, and sensory consequences of infection.