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Serotonin vs. Dopamine: Which Neurotransmitter Dominates Gut-Brain Interactions?

Adriano dos Santos

The intricate relationship between the gut and brain is mediated by neurotransmitters, which act as chemical messengers linking these two systems. Among these, serotonin and dopamine play critical roles in regulating a wide range of functions, including mood, motivation, digestion, and immune responses.


Serotonin Dopamine



Table of Contents:

  1. Breaking Down the Neuromodulators: A Gut-Brain Symphony

    • Serotonin: The Mood Regulator

    • Dopamine: The Motivational Driver

  2. Gut Microbes as Key Players

  3. Serotonin vs. Dopamine: A Comparative Analysis



About me


I am Adriano dos Santos, BSc, AFMCP, MBOG, NWP, RSM, ESIM, a Functional Registered Nutritionist, specializing in nutritional therapy for patients with metabolic syndrome, particularly those suffering from digestive issues and sleep disturbances.


Last year, I published a scientific paper titled "The Microbiota–Gut–Brain Axis in Metabolic Syndrome and Sleep Disorders: A Systematic Review," which examines the interaction between gut microbiota composition, metabolic syndrome (MetS), and sleep disorders.


It highlights the shared microbial characteristics of these conditions and discusses how dietary patterns, supplements, and probiotics can influence gut microbiota, potentially improving both MetS and sleep quality.



Introduction: The Gut-Brain Connection


The gut-brain axis serves as a communication highway, with the vagus nerve, microbial metabolites, and neurotransmitters acting as messengers. Research has revealed that this axis influences physiological processes such as the sleep-wake cycle, emotional states, and even immune responses (Dos Santos & Galiè, 2024).



Key Takeaways:

  • Serotonin and dopamine are both produced in the gut and influence brain function.

  • Gut microbes play a crucial role in synthesizing these neurotransmitters.

  • Serotonin leads in regulating gut motility and mood, while dopamine drives motivation and arousal.



Breaking Down the Neuromodulators: A Gut-Brain Symphony


Serotonin: The Mood Regulator

  • Production: Approximately 90% of the body’s serotonin is synthesized in the gut by enterochromaffin cells, with Clostridium sporogenes converting tryptophan to serotonin precursors (Dos Santos & Galiè, 2024).

  • Function: Serotonin regulates gastrointestinal activity, interacts with central nervous system (CNS) pathways, and maintains arousal during wake states (Eban-Rothschild et al., 2017).

  • Sleep-Wake Role: Serotonin modulates arousal by acting on the tuberomammillary nucleus (TMN) and is involved in maintaining wakefulness during quiet states (Eban-Rothschild et al., 2017).

  • Gut Microbe Contribution: Serotonin production is modulated by bacterial metabolites that can cross the blood-brain barrier, influencing mood and cognitive function (Parker et al., 2019).


Dopamine: The Motivational Driver

  • Production: Dopamine production in the gut is influenced by microbial activity, including precursors synthesized by various enteric bacteria (Dos Santos & Galiè, 2024).

  • Function: Dopamine regulates reward-driven behaviors and arousal. It acts on the ventral tegmental area (VTA) and dorsal raphe nucleus (DRN) to maintain wakefulness and respond to salient stimuli (Eban-Rothschild et al., 2017).

  • Sensory Modulation: Dopaminergic neurons in the DRN modulate responses to environmental stimuli, enhancing arousal when required (Dos Santos & Galiè, 2024).

  • Wake-Promoting Role: Dopamine interacts with brain structures like the ventral tegmental area (VTA) to sustain wakefulness in response to environmental stimuli (Eban-Rothschild et al., 2017).



Gut Microbes: The Hidden Architects


Microbes in the gut influence neurotransmitter production and gut-brain communication in several ways:

  • Serotonin Synthesis: Clostridium sporogenes converts tryptophan into serotonin precursors, enhancing inhibitory neuroregulatory effects (Dos Santos & Galiè, 2024).

  • Neurotransmitter Release: Bacterial metabolites, such as short-chain fatty acids, influence neurotransmitter production and modulate the blood-brain barrier's integrity (Parker et al., 2019).

  • Histamine and Beyond: Moraxella morganii and Lactobacillus vaginalis contribute to histamine production, affecting circadian rhythms and autoimmune responses (Dos Santos & Galiè, 2024).



Serotonin vs. Dopamine: Which One Wins?


Serotonin emerges as the more influential neurotransmitter in gut-brain interactions, primarily due to its extensive role in gut motility, mood regulation, and neuroprotection. Nearly 90% of the body’s serotonin is synthesized in the gut, underscoring its dominance in this axis (Dos Santos & Galiè, 2024). This neurotransmitter plays a pivotal role in gastrointestinal motility, as it is directly released by enterochromaffin cells in response to microbial metabolites such as short-chain fatty acids (Parker et al., 2019). Furthermore, serotonin extends its influence to the central nervous system (CNS), where it interacts with the dorsal raphe nucleus (DRN), modulating wakefulness and inhibiting REM sleep (Eban-Rothschild et al., 2017).


The gut microbiota significantly enhances serotonin production. For instance, Clostridium sporogenes converts tryptophan into 5-hydroxytryptophan, a precursor to serotonin, ensuring a continuous supply of this neurotransmitter for both gut and brain functions (Dos Santos & Galiè, 2024). Additionally, serotonin interacts with immune pathways, regulating the release of cytokines and other signaling molecules, further highlighting its multifaceted role in maintaining gut-brain homeostasis (Parker et al., 2019).


Dopamine, on the other hand, plays a vital yet complementary role. While it is crucial for motivation, arousal, and response to salient stimuli, its production in the gut is significantly less than that of serotonin. Dopaminergic neurons in the brain, such as those in the ventral tegmental area (VTA), rely on precursors partially synthesized by gut microbes, illustrating its indirect dependence on gut activity (Dos Santos & Galiè, 2024). However, dopamine’s contributions to gut motility and neuroprotection are relatively limited, emphasizing serotonin’s broader influence.



While both neurotransmitters are essential for the gut-brain axis, serotonin’s dominance is evident. It is indispensable for maintaining gut health, regulating motility, and stabilizing mood, whereas dopamine is primarily associated with arousal, motivation, and sensory responses. Serotonin’s prominence in gut-produced neurotransmitters and its foundational role in gut-brain communication grant it a slight edge over dopamine in this intricate system.



Conclusion


In the battle of serotonin vs. dopamine, serotonin holds a slight edge due to its dominant role in gut-brain interactions. Its high production in the gut, influence on motility, and extensive neuroregulatory functions position it as the key neurotransmitter in this intricate system. Dopamine, while vital for arousal and motivation, plays a complementary role, working alongside serotonin to maintain a balanced gut-brain connection.



References

  1. Dos Santos A, Galiè SJN. (2024) The microbiota–gut–brain axis in metabolic syndrome and sleep disorders: A systematic review. Nutrients 2024, 16(3), 390.

  2. Parker, A.; Fonseca, S.; Carding, S.R. (2019) Gut microbes and metabolites as modulators of blood-brain barrier integrity and brain health. Gut Microbes 2019 Aug 1;11(2):135–157.

  3. Eban-Rothschild, A.; Appelbaum, L.; De Lecea, L. (2017) Neuronal Mechanisms for Sleep/Wake Regulation and Modulatory Drive. Neuropsychopharmacology 43, 937–952.

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