We’ve known since the time of Pavlov that there’s a connection between our gut and brain; now we know our microbiomes play a role in that game of telephone too!
The gut-brain axis: now with microbes!
If you’re not familiar with Pavlov, he won the Nobel in 1940 for discovering that the smell or sight of food triggers the stomach to secrete all the goodies that are responsible for breaking down the food we eat.
This was the first clear link that our brains and our gut communicated.
But it’s not just a one-way conversation!
Our guts also communicate back to the brain to tell us when we’re full or hungry.
More recently we’ve come to realize that the microbes that live in our gut also participate in these conversations in complex ways.
Our gut harbors the largest of our microbiomes and contains trillions of bacteria, fungi, viruses, and archaea.
Evidence suggests that the composition of this microbiome can affect not only how we digest food but potentially our moods, behavior, or the development of neurological disease!
The gut microbiome can do this through interactions with the gut-brain axis which includes:
Autonomic Nervous System: Controls bodily functions such as breathing and digestion, basically all of our bodily functions that happen without us ‘thinking’ about them.
Enteric Nervous System: Refers to the nerves of the gut that function in digestion and ‘moving’ food and waste through it.
Neuroendocrine System: Uses hormones as signaling molecules to control bodily functions but with respect to the gut these discussions are focused primarily on stress responses through the Hypothalamic-pituitary-adrenal axis.
Immune System: Determines how we respond to and clear infections.
Metabolism: Controls how and what we’re able to digest to produce energy or build the precursors that make up all of the molecules in our cells.
The microbes in our gut can communicate directly through all of these pathways because they produce signaling molecules like neurotransmitters, hormones, immune molecules (chemokines and cytokines), amino acids, and microbial metabolites.
These in turn can influence neuronal cells, the activities of our neuroendocrine system, host immune responses, or metabolism.
They can also travel through our bloodstream to interact with the brain directly!
Recent research has also highlighted the importance of these communication pathways in neurological conditions such as anxiety, autism spectrum disorder, and depression.
Unfortunately, we’re still in the early stages of deciphering cause and effect here!
And important questions about whether certain microbes cause neurological disease, or if individuals with neurological disease establish different microbiomes after onset, still need to be answered.
However, it’s clear that our microbiome and the gut-brain axis are in constant communication.
Now we just need to figure out if we can manipulate those conversations to promote health or prevent disease!
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Brian Krueger