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The Brain-Gut-Microbiome-Axis / Gut-Brain Axis involves interactions between the enteric nervous system, gut microbiota, and the Central Nervous System (CNS). Several pathways have been identified as crucial to this interaction, including:
The interaction between the gut and the brain is a dynamic and complex process, where changes on one side of this axis can lead to alterations on the other. This communication involves several intricate pathways, including metabolic, immune, neuronal, and endocrine signaling.
Immune Pathway means
Intestinal immune cells produce cytokines that can influence brain activity. These cytokines activate the hypothalamic-pituitary-adrenal (HPA) axis, leading to the release of cortisol, a stress hormone.
Neuronal Pathway means
The vagus nerve is crucial for the bidirectional communication between gut microbes and the brain. It transmits signals from the gut to the brain and vice versa, often through the spinal cord or directly via the vagus nerve, to regulate intestinal functions.
Neurotransmitter production means
Gut microbiota has the ability to release neurotransmitters such as norepinephrine, GABA, serotonin, and dopamine. These neurotransmitters can interact with the brain, influencing mood and behavior.
Endocrine pathway means
Intestinal endocrine cells can secrete hormones that have an impact on brain function, further illustrating the complexity of the gut-brain communication network.
Overall, the gut-brain axis is a sophisticated system of communication that underscores the importance of maintaining a healthy microbiome for optimal brain function.
The gut can interact with the brain through two neuroanatomical pathways:
(1) direct information exchange between the gut and the brain by the Autonomic Nervous System (ANS) and the Parasympathetic Nervous System / Parasympathicus / Vagus in the spinal cord and
(2) bidirectional communication between the gut and the brain through bidirectional communication between the Enteric Nervous System (ENS) in the gut and the Autonomic Nervous System (ANS) and Parasympathetic Nervous System / Parasympathicus / Vagus within the spinal cord
The bidirectional Brain-Gut-Microbiome-Axis / Gut-Brain Axis impact of CNS injury and malignancy resulting in gut microbiome dysregulation and increased intestinal permeability may further drive systemic inflammation and secondary Central Nervous System (CNS) damage
Gut microbiota and the Brain speak directly and indirectly through neural, immune, metabolic, and endocrine pathways
Numerous investigations have proved a relationship between the gut microbiota with normal brain function as well as many brain diseases, in which cognitive dysfunction is a common clinical problem
The term “microbiota-gut-brain axis” was broadened from the “gut-brain axis.”
Mutual interactions between the Central Nervous System and Gut Microbiota that are closely associated with the bidirectional effects of Inflammatory Bowel Disease and Central Nervous System Disorders
Nowadays, the bidirectional relationship between the gastrointestinal microbiota and the nervous system, considered the microbiota-gut-brain axis , is being actively studied
The gut microbiota and the brain communicate with each other via various routes including the immune system, Tryptophan metabolism , the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans
Short-chain fatty acids (SCFAs), which interact with intestinal endocrine cells on the intestinal mucosa to promote the release of intestinal hormones such as Cholecystokinin (CCK), Peptide tyrosine tyrosine (Peptide YY / PYY), and Glucagon Like Peptide 1 (GLP-1). Both probiotics and prebiotics increase the production of Short-chain fatty acids (SCFAs). SCFAs and intestinal hormones can enter the circulation and migrate to the Central Nervous System (CNS) (more SCFAs enter the liver and muscle through blood circulation, while a few enter the CNS). SCFAs and intestinal hormones in the CNS can regulate neurotransmitter delivery and social behavior
After entering the Central Nervous System (CNS) Short-chain fatty acids (SCFAs) interact with satietogenic neurons and regulatory neuropeptides
The gut microbiota is known to communicate to the central nervous system (CNS) via the myenteric systems and the entero-endocrine cells using various neuropeptides (Serotonin (5-HT), Peptide YY and Cholecystokinin) and directly influence behavioural changes and cerebral cortical excitability
Animal studies have clearly demonstrated effects of the gut microbiota on gene expression and neurochemical metabolism impacting behavior and performance
Further understanding of how microbiota influence the brain in nature may be helpful for generating new therapeutic strategies for social disorders in humans, such as autism spectrum disorders (ASDs)
A ‘gut feeling’ or the sensation of ‘butterflies’ in the stomach are common illustrations of how a response in the brain is felt in the gut.
The CNS, using the parasympathetic fibres from the vagus nerve (VN), directly influences the composition of the gut microbiota by either activating anti-inflammatory macrophages (M2) or inhibiting pro-inflammatory macrophages (M1), hence modulating intestinal permeability
The MGBA’s primary function is to connect the brain's emotional centers with peripheral intestinal functions such as the enteric reflex, intestinal permeability, immune activation, and enteroendocrine signaling
Microbiota regulate brain function via the gut microbiome-brain axis, significantly influencing cognitive processes and behavior.
The gut-brain axis includes interactions between
(1) the autonomic nervous system,
(2) the central nervous system,
(3) the stress system (Hypothalamic–pituitary–adrenal axis (HPA axis)),
(4) the (gastrointestinal) corticotropin-releasing factor system, and
(5) the gut response (including the gut barrier, luminal microbiota, and intestinal immune response).
Both vagal and spinal sensory nerve fibers transmit visceral stimuli to the central nervous system and modulate various brain functions
Arguments-Pro
The gut-brain axis imbalance due to gut dysbiosis is associated with a range of neurodegenerative diseases
Components
The intrinsic branches of the enteric nervous system (ENS), the extrinsic vagus nerve, the sympathetic branches of the autonomic nervous system (ANS), the immune, endocrine, and humoral pathways belong to the gut-brain axis
see also:
4-Aminobutyric acid / GABA-producing bacteria
Aging / Senescence & Gut microbiota
Brain & Gut microbiota
Brain-Gut-Microbiome-Axis / Gut-Brain Axis & Neurological Disorders
Central Nervous System (CNS) & Gut microbiota
Cognition & Gut microbiota
Depressive Disorders / Mood & Gut microbiota
Dopamine-producing bacteria
Endobiotics
Gut microbiota
Gut microbiota & Major depressive disorder / Major Depression / Depressive episode (MDD)
Gut microbiota & Traumatic brain injury (TBI)
Hypothalamic–pituitary–adrenal axis (HPA axis)
Immunity & Stress
Lactiplantibacillus plantarum & Morbus Parkinson / Parkinson's Disease (PD)
Norepinephrine-producing bacteria
Serotonin (5-HT) producing bacterial species and strains