Dear Colleagues,

I hope that this overview of the topic will pique your interest, and I invite you to contribute to this project.

Impressive progress has been made in characterizing the bidirectional interactions between the central nervous system, the enteric nervous system, and the gastrointestinal tract. Several exciting preclinical studies have suggested a prominent role for the gut microbiota in these gut–brain interactions. During the first years of life, the brain is exposed to environmental factors that can shape synaptic connections and neuronal circuits, with subsequent influence on behavior and learning processes; at the same time, the gut microbiota is being established and is under structural and functional development. The identification of the gut–brain axis malfunctioning during early life is of major interest because of its potential consequences. As a matter of fact, the main effects of gut microbiota perturbations on the brain may occur at times of lower diversity and instability of the gut microbiota (in infants and the elderly) and during brain development (in the perinatal and infant periods). Given the important role of perinatal influences (including nutrition) on the developing nervous system and the well-documented effects of adverse early life influences on the gut–brain axis, there is a strong rationale to implicate the gut microbiota in brain development and functioning. Thus, the nutrition–gut–brain axis can be considered to be a modulator of health, growth, and development during early life with long-term consequences until adult life. Based on animal studies, the gut microbiota appears to influence the development of emotional behavior, stress- and pain-modulation systems, and brain neurotransmitter systems; additionally, probiotics and antibiotics can alter microbiota, exerting modulatory effects on some of these neuropsychiatric pathologies. Current evidence suggests that multiple mechanisms, including endocrine and neurocrine pathways, may be involved in gut microbiota-to-brain signaling and that the brain can, in turn, alter microbial composition and behavior via the autonomic nervous system. Limited information is available on how these findings may be translated to healthy humans or to disease states (such as irritable bowel syndrome, autism, anxiety, depression, Parkinson’s disease, mood disorders, eating behavior, and chronic pain) involving the brain or the gut–brain axis and the role of diet in these processes. Diet-induced alterations in microbiota composition seem to contribute to regulating aspects of host energy balance, for instance, lipid absorption and energy harvest. It has been shown that different microbial species in the human gut could modulate fatty acid composition not only in the intestine but also in crucial tissues for host metabolism. During the prenatal period, the developing brain is first exposed to the maternal diet and gut-derived metabolites and may be exposed to intrauterine microbes. The newborn’s gut microbiota is shaped by the maternal vaginal (or skin) microbiota. The possibility that pre- and postnatal influences (including maternal diet, type of feeding, complementary food, etc.) on the microbiota can affect brain development is intriguing. An adequate nutritional and healthy microbial environment during perinatal and early life may provide windows of opportunity to reduce the risk of non-communicable and mental diseases later in life; then, in the near future, the use of targeted and individualized strategies to modulate gut microbiota establishment and functioning to favor optimal growth and neurodevelopment may be a very real possibility.

Prof. Cristina Campoy
Guest Editor

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• Nutrition
• Gut–brain axis
• Neurodevelopment
• Microbiome