Brain chemicals such as serotonin, dopamine and norepinephrine undoubtedly affect the quality of our day but did you know that we have frogs to thank for the first discovery of neurotransmitters in 1921?
Austrian Nobel prize winner Otto Loewi’s inspiration to set up the groundbreaking experiment that discovered neurotransmitters came to him in a dream. A dream that would lead him to combine two frog hearts to study how nerve cells communicate with each other.[1]
One hundred years later, our knowledge of neurotransmitters has informed many ideas about how the brain communicates with our bodies.
In this article, we will look at neurotransmitters and how they affect your body, specifically your mental and digestive health.
What are neurotransmitters?
Neurotransmitters are the chemicals that allow neurons, or nerve cells, to communicate with each other via the nervous system throughout the body.[2]
Without being too hyperbolic, it’s fair to say that the ability of neurons to communicate chemically like this gives the brain the facility to influence the body in the way it does.
Why are neurotransmitters important in your mental health?
Various neurological illnesses see disturbed neurotransmitter levels, such as Parkinson’s disease, schizophrenia, Alzheimer’s disease, epilepsy, Huntington’s disease and depression.[3]
Changes in neurotransmitter levels aren’t only influential in neurological and mental health conditions.
They influence you every day!
For example, neurotransmitters influence your emotions, thoughts, memories and learning to name a few.
Let’s start with some of the leading players first, the amine group.
Monoamines are a group of neurotransmitters that you’ve most likely heard of. They are critical for our learning, motivation and emotional function.[4]
Monoamines include serotonin (scientifically named 5-hydroxytryptamine), dopamine and norepinephrine. They have been a cornerstone of hypotheses around how depression starts. It’s called the monoamine theory of depression.[5]
When it comes to the gut and connection and how it might relate to IBS, serotonin is a central figure for treatment.
The origin of ninety-five per cent of serotonin is in the gut.[6]
And even though we often associate serotonin with changes in mood and sleep, its effects can be seen in the digestive and cardiovascular systems, along with an ability to influence bone mineral density and metabolism.[7]
For example, serotonin is a critical part of the process that helps food travel through your digestion. This process is called motility.[8]
In the late 1980s, researchers found dysfunctional and slow motility in the digestive system common in IBS patients.[9]
Fast forward to the modern day, and interventions influencing serotonin levels are vital to helping people with small intestinal bacterial overgrowth (SIBO) and IBS.[10]
This altered level of serotonin has been studied further in IBS-D (diarrhoea-dominant IBS) and IBS-C (constipation-dominant IBS). Interestingly, people prone to looser bowel motions as part of their IBS picture had higher serotonin concentrations in their blood and urine.[11]
In the brain, serotonin has a wide range of effects that influences our day.
For example, it influences how we eat, sleep and wake states,[12] mood,[13] decision-making,[14] memory and learning. [15]
Serotonin can also influence our social interactions. A review from 2002 suggested that higher serotonin levels help create more constructive social interactions by reducing aggressive and increasing dominant behaviour.[16]
Currently, only around thirty to forty per cent of people respond to serotonin-oriented drug interventions and find their social anxiety improves.[17]
Needless to say, serotonin governs the quality of our day, but it also affects other neurotransmitters.
Serotonin inhibits dopamine release and influences glutamate and GABA release in different brain regions.[18]
If serotonin rules the body, then it might be fair to say that dopamine governs the central nervous system.
Similar to serotonin, altered dopamine levels can be an origin story for brain-based illnesses such as Parkinson’s disease, Huntingdon’s disease, schizophrenia and drug addiction, or addiction in general.[19]
Dopamine is associated mainly with what’s called reward-motivated behaviour. Reward-motivated behaviour includes approaching and consuming something and potentially even becoming addicted to it.[20]
There are five different types of ways dopamine interacts with the body. They cover the regulation of your kidneys, attention, memory and learning and impulse control.[21]
One study on teenagers found that higher dopamine levels could help control their impulsive responses better when a reward was involved.[22]
This effect ties into another important element of how dopamine affects the quality of our day – delayed gratification.
Delayed gratification is thought of as one of the ways animals survive and thrive in life.
It requires us to be able to balance the benefits and the risks of delaying an available reward. Despite the potential of receiving the reward immediately, the right decisions to continue waiting to favour a better reward in the future need to be made.
A simple experiment done in children perfectly expresses delayed gratification called the Stanford Marshmellow experiment. In the study, psychologist Walter Mischel gave the participants a choice of one marshmallow as an immediate reward or two marshmallows if they waited for some time.[23]
This research, whilst later criticised for being limited in a few ways, is still considered somewhat groundbreaking when looking at non-cognitive “skills” that develop early in life. Skills that could extend to being determinant for later success in life.
What does this have to do with dopamine, you ask?
Maybe you’ve guessed it, but dopamine is involved in nearly all the processes in the brain that assist with delayed gratification. We discussed higher dopamine allowing for better impulse control. It also plays a role in the “hot” system of the brain associated with temptation.[24]
Interestingly, this dopamine system is a focus when it comes to obesity and diet management. So much, so that low dopamine levels are associated with obesity.[25]
Dopamine affects your ability to sustain your focus even when you’re tired.
One study from 2012 found that dopamine was the mediator that allowed people to sustain their motivation despite feeling tired.[26]
This interaction directly affects the executive function that dictates your ability to get through your day. For example, the ability to start and finish things, say yes and no to the “right” things, set goals and work through ways to achieve them.
These skills have been shown to connect dopamine to procrastination, with recommendations showing increasing dopamine via increased dietary protein consumption, for example, may help to curb the tendencies we have to put things off.[27]
Dopamine is also responsible for the creation of another important neurotransmitter, norepinephrine.
I’ve heard a very articulate description of the relationship between dopamine and norepinephrine.
“If dopamine provides the motivation, then norepinephrine helps you get it done.”
I wish I could credit the person I heard that from. Still, it describes perfectly the role in the fight or flight system in the brain that allows us to take action.
Norepinephrine plays a role in our alertness, emotional regulation, memory, learning and attention. [28]
As it relates to your day, epinephrine is the primary driver of your stress response. Most of the focus for stress management looks at cortisol. However, epinephrine increases your cardiac and respiratory rate to begin the stress response, so cortisol may maintain it.
Unfortunately, this ability to get your body primed for action comes with a price. Elevated long-term epinephrine levels contribute to the stress-induced portion of chronic diseases such as cardiovascular disease and maybe even cancer.[29]
Dopamine and epinephrine are also influenced by the bacteria in your digestion.
This interaction is another example of the close relationship between the brain and the gut. Some animal studies have shown that the bacteria in the gut directly influence dopamine and epinephrine to influence reward-based behaviour.[30]
Of course, we don’t get too excited about animal studies. However, it does give extra context to the connection between dopamine and eating behaviour and how the gut may play a role.[31]
So, what do you think?
Over the last hundred years, we’ve come from connecting frogs’ hearts with chemical messages to understanding how deeply these chemicals affect the body and the quality of our day.
Not only this, but it’s clear that when it comes to neurotransmitters and their effects in the body, what happens in Vega doesn’t stay in Vegas, with the gut playing a huge role in affecting the influence of serotonin, dopamine and epinephrine.
Hope this helps xx
References
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We love references!
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More references!
[16] Young SN, Leyton M. The role of serotonin in human mood and social interaction. Insight from altered tryptophan levels. Pharmacol Biochem Behav. 2002;71(4):857-865. doi:10.1016/s0091-3057(01)00670-0
[17] Stein MB, Andrews AM. Serotonin States and Social Anxiety. JAMA Psychiatry. 2015;72(8):845-847. doi:10.1001/jamapsychiatry.2015.0486
[18] Murley AG, Rowe JB. Neurotransmitter deficits from frontotemporal lobar degeneration. Brain. 2018;141(5):1263-1285. doi:10.1093/brain/awx327
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Wow still more references?!
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