Key Takeaways

• The gut-brain axis is a two-way communication network between the gut and the central nervous system.
• It works through neural (vagus nerve, ENS), hormonal, immune and microbial signals.
• The enteric nervous system — the "second brain" — contains hundreds of millions of neurons.
• Key messengers include serotonin, GABA, cortisol, melatonin and BDNF.
• Around 90% of the body’s serotonin is produced in the gut.
• Dysregulation is linked to neurodegenerative, neurodevelopmental and mental-health conditions.

Contents

• What is the Gut-Brain Axis?
• Components of the Gut-Brain Axis
• Gut-Brain Signalling Molecules
• Factors That Influence the Axis
• Dysregulation and Disease
• Frequently Asked Questions

Gut-Brain Axis ELISA Kits

Validated ELISA kits for the neurotransmitters, hormones and inflammatory markers that carry signals along the gut-brain axis.

BDNF

BDNF ELISA Kit

NeurotrophinHuman

Supports neuronal growth and is modulated by the gut microbiome.

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Cortisol

Cortisol ELISA Kit

Stress HormoneMulti-species

The stress hormone that reshapes gut function and microbial balance.

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GABA

GABA ELISA Kit

NeurotransmitterHuman

The main inhibitory neurotransmitter, also produced by gut bacteria.

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SERT

Serotonin Transporter (SERT) ELISA Kit

TransporterHuman

Controls serotonin signalling in gut and brain; the SSRI target.

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Calprotectin

Calprotectin ELISA Kit

Gut InflammationHuman

A faecal marker of intestinal inflammation and barrier disruption.

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Melatonin

Melatonin ELISA Kit

HormoneMulti-species

Regulates circadian rhythm and is produced in the gut as well as the pineal gland.

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What is the Gut-Brain Axis?

The gut-brain axis is a dynamic, bidirectional communication system linking the gastrointestinal tract with the central nervous system. It has become a focal point of neuroscience because it reveals how deeply the gut — and the microbiota within it — influences cognition, emotion and behaviour. Beyond digestion, the gut helps shape neurological processes through neural pathways, hormonal signalling and immune mediators, engaging the brain in a continuous dialogue.

This dialogue runs in both directions: the brain influences gut motility, secretion and immune activity, while the gut sends signals back that affect mood, stress responses and even the risk of neurological disease. Understanding these routes is opening a previously unexplored dimension of human physiology.

Components of the Gut-Brain Axis

Several interconnected systems carry information between gut and brain.

The immune system

Gut-associated immune cells release cytokines that reach the brain, linking intestinal inflammation to changes in mood and cognition.

The neuroendocrine system

This bridge between the nervous and endocrine systems releases hormones such as cortisol and serotonin. Cortisol, produced during stress, alters gut function and microbial balance, while serotonin — abundant in the gut — governs motility and gut-brain signalling.

The enteric nervous system

Often called the "second brain", the enteric nervous system is a vast network of neurons in the gut wall that controls peristalsis and secretion independently, while communicating bidirectionally with the CNS.

The vagus nerve

The vagus nerve is the principal neural highway of the axis, carrying signals directly between the gut and the brainstem.

The gut microbiome

The trillions of microbes in the gut produce neurotransmitters and metabolites that influence brain chemistry, making the microbiome a central player in the axis.

Gut-Brain Signalling Molecules

Communication along the axis is carried by a diverse set of chemical messengers.

Neurotransmitters

Serotonin, GABA and dopamine are produced in or influenced by the gut and shape mood, motility and stress responses; gut bacteria themselves synthesise several of these molecules.

Hormones

Cortisol and melatonin connect the stress and circadian systems to gut physiology, while enteric hormones released by the gut regulate appetite and satiety signals to the brain.

Bioactive compounds

Microbial metabolites such as short-chain fatty acids, along with markers of barrier integrity, modulate inflammation and neuronal signalling throughout the axis.

Factors That Influence the Axis

The state of the gut-brain axis is shaped above all by the composition of the gut microbiome, which is in turn influenced by diet, antibiotics, stress, age and environment. A diverse, balanced microbiome supports healthy signalling, whereas dysbiosis — a loss of that balance — disrupts the production of neuroactive metabolites and weakens the intestinal barrier, allowing inflammatory signals to reach the brain.

Dysregulation and Disease

When gut-brain communication breaks down, the consequences reach well beyond the digestive system.

Neurodegenerative disorders

Altered microbiota and gut inflammation have been linked to Parkinson’s and Alzheimer’s disease, where gut-derived signals may contribute to neurodegeneration.

Neurodevelopmental conditions

Differences in the gut microbiome have been associated with neurodevelopmental conditions such as autism spectrum disorder, highlighting the axis’s role in brain development.

Mental health

Dysregulation of the gut-brain axis is increasingly connected to anxiety and depression, with the microbiome influencing the neurotransmitter and stress-hormone systems that underlie mood.