Gut Microbiota-Brain Axis Modulation by a Healthier Microbiological Microenvironment : Facts and Fictions

Abstract

Functions of every organ and system of the body need to be perfectly regulated for the maintenance of the milieu interior; this is performed by a wireless (endocrine) system and a wired (nervous) system in the body. Interestingly, the communication between the brain and the gut is bi-directional; though, the brain controls the gut to a large extent, the gut also influences the brain functions. In recent years, it has been realized that the gut microbiota, which is the largest organ of the human body, influences the brain functions. 1,2 However, this is not entirely a new concept. As early as pre-2nd century CE, in the Charaka Samhita, an Indian book on medicine, it was mentioned that the human being is a microcosmic replica of the universe, 3 and the 3 humors (Vayu or gas, Pitta or bile, and Kapha or mucus) are responsible for most ailments. 4 It is interesting to know how the gastrointestinal tract in general and its microbiota, in particular, is being unraveled by the scientists in recent times.Gut microbial modulation of the brain function is best demonstrated by the well-known effects of gut-microbiota directed antibiotic treatment in patients with hepatic encephalopathy. Moreover, in recent times, several animal and human experiments also demonstrated the role of gut microbiota in influencing brain function. In a study by De Palma et al, 5 germ-free mice were shown to have dysregulated hypothalamic pituitary stress response, altered brainderived neurotrophic factors (BDNF) in the hippocampus, altered neurotransmission, altered tryptophan availability and metabolism, and reduced anxiety. In another experimental study, antibiotic treatment of BALB/c mice resulted in increase in Firmicutes phylum dominated by Lactobacillus, sulfate-reducing bacterial species, and decrease in g-Proteobacteria and Bacteroidetes, which was associated with increase in hippocampal BDNF and autonomic-independent anxiolytic behavior. 6 How does gut microbiota alter brain function? In a study on wild mice separated from their mothers, which is well known to induce anxiety, it was found to be associated with altered gut-microbial colonization, long-lasting hyperactivity of the hypothalamic pituitary-axis, visceral hypersensitivity, altered cholinergic activity in the gut, and increased intestinal permeability. -522-249-4406, Fax: +91-522-2668017, E-mail: udayghoshal@gmail.com Article: Bifidobacterium longum and Lactobacillus helveticus synergistically suppress stress-related visceral hypersensitivity through hypothalamic-pituitary-adrenal axis modulation Ait-Belgnaoui A, Payard I, Rolland C, et al

Gut Microbial Dysbiosis in the Pathogenesis of Gastrointestinal Dysmotility and Metabolic Disorders

“…The endocrine and nervous systems are able to conduct and coordinate with absolute synergy in each organ system in the body in order to maintain homeostasis. 104 The processes between the brain and the gut are bi-directional; as the brain modulates gut physiology, the gut is also able to influence brain function. 105 This bi-directional interaction has been demonstrated through the improvement in patients with hepatic encephalopathy after gut-microbiota directed antibiotic treatment.…”

Gut microbiota dysbiosis in functional gastrointestinal disorders: Underpinning the symptoms and pathophysiology

“…Dysregulation of the gut–brain axis is one of the primary pathophysiological mechanisms in a subset of patients with FGIDs. 4 , 101 Gut microbiota‐regulated alterations in epithelial barrier function triggered by immune system activation resulting in abnormal gut–brain communications. 102 Stress‐related corticotropin‐releasing hormones have an important role in intestinal barrier function.…”

“…The spectrum of FGID symptoms includes abdominal pain/burning, bloating, nausea, fullness, vomiting, and altered bowel habit 3 . The pathophysiology of FGIDs is complex, but mounting studies indicate that gut microbiota plays a central role in the development of FGID and modulation of the symptoms 4 . Understanding of the pathogenesis of FGIDs is evolving with the elucidation of pathophysiological mechanisms at the cellular and molecular levels 5,6 .…”

“… 3 The pathophysiology of FGIDs is complex, but mounting studies indicate that gut microbiota plays a central role in the development of FGID and modulation of the symptoms. 4 Understanding of the pathogenesis of FGIDs is evolving with the elucidation of pathophysiological mechanisms at the cellular and molecular levels. 5 , 6 Not long ago, “functional” conditions, such as FGIDs, were explained as idiopathic, and the patients were suspected by physicians and researchers to be neurotic and/or healthy subjects with an imaginary illness.…”

Imbalanced dietary intake alters the colonic microbial profile in growing rats

“…The balanced gut microbiota composition contributes to health promotion, whereas its abnormal state can result in the mental disorder by adversely affecting the ENS and CNS [ 10 ]. Therefore, the desirable modulation of gut microbiota may prevent, and improve such mental disorders [ 11 ].…”