The gut–brain axis is a bidirectional system connecting two primary systems: the intestine and the brain. As in humans, this relationship is also clearly evident in veterinary medicine and plays a key role in the health of our companion animals.
This connection regulates emotions, cognitive functions, and gastrointestinal health. The gut influences mood, while stress directly affects digestive processes. Communication flows in both directions: the brain sends signals to the intestine, influencing motility and secretion, and in turn, the intestine communicates back to the brain.
The microbiota, as in humans, plays a fundamental mediating role. Intestinal bacteria produce neurotransmitters such as serotonin, GABA, and dopamine, which act on the enteric nervous system (ENS), a complex neural network composed of approximately 100 million neurons.
This underscores the importance of maintaining the enteric system in a state of eubiosis to support long-term physical and mental well-being. Conversely, an imbalance (dysbiosis) and reduced production of beneficial compounds, such as short-chain fatty acids, can lead to altered conditions including anxiety, depression, and even epileptic episodes, issues that appear increasingly common in modern dogs and cats, alongside gastrointestinal dysfunction.
The ENS is, in effect, an autonomous neural network located within the digestive tract. Its role in the digestion and absorption of nutrients is essential for survival. Therefore, careful evaluation of diet and supplementation is crucial.
For example, serotonin, a neurotransmitter involved in mood regulation, is produced up to 90% in the intestinal mucosa. It regulates multiple gastrointestinal functions, including:
- Peristalsis
- Secretion
- Vasodilation
- Pain perception
- Nausea and inflammation
Additionally, the intestinal system produces cannabinoid-like compounds (via CB1 and CB2 receptors), contributing to signaling through the vagus nerve and influencing sensations such as satiety, discomfort, and general well-being.
For these reasons, the intestine is increasingly recognized, even in veterinary research, as a central hub of health. Wellness, disease, and aging are all closely linked to this internal ecosystem shared by humans and animals alike.
The intestinal epithelium represents the largest interface between the organism and the external environment, a true bridge between macrocosm and microcosm. It is equipped with sophisticated mechanisms that allow nutrient absorption while preventing the entry of pathogens. Maintaining its integrity is therefore essential for optimal health.
A balanced microbiota is also crucial for supporting an efficient immune system, particularly the innate immune response. Disruptions in this balance can lead to malabsorption of essential nutrients, compromising overall health.
Chronic deficiencies of key nutrients and prolonged malabsorption may result not only in mucosal and immune dysfunction but also in the accumulation of toxins, stagnation of metabolic waste, and the proliferation of pathogenic bacteria, potentially leading to serious diseases.
Contributing factors include not only industrial diets rich in preservatives and additives but also emotional and behavioral states. Intestinal disorders can influence the central nervous system due to the bidirectional nature of the gut–brain axis.
The ENS also interacts closely with:
- The endocrine system, through digestive hormones produced by specialized cells in the gastrointestinal mucosa
- The immune system, approximately 80% of whose cells reside in the digestive tract
Thus, while the enteric nervous system is capable of operating autonomously, it is in constant dialogue with both the external environment (food intake) and the internal state (emotions, stress, and disease).
In conclusion, the microbiome can significantly influence mood and brain function, while the intestinal epithelium serves as a critical interface between the environment, the microbiome, and the organism as a whole, playing a central role in maintaining systemic balance and overall health.
Dr. Monica De Felice
Advanced Training Graduate and Scientific Consultant in Human and Pediatric Microbiome (University of Pavia);
S.I.B.S.;
Popular University of Arezzo – Master in Probiotic Clinical Practice and Microbiome Nutrition;
International School on Microbiota in Digestive Diseases (ESNM – European Society of Neurogastroenterology and Motility);
Animal Naturopathy – AIOC Academy Italy;
Cellular and System Longevity;
C.T.S Daphne Lab