Biochemical and Biophysical Foundations of the Microbiome–brain Axis

The gut–brain axis represents a complex and highly dynamic bidirectional communication network that integrates neural, endocrine, immune, and metabolic signaling pathways, enabling continuous interaction between the gastrointestinal tract and the central nervous system (CNS). This integrative system operates through multiple interconnected routes, including the vagus nerve, hypothalamic–pituitary–adrenal (HPA) axis, immune mediators, and circulating microbial metabolites. Recent advances in biophysics and biochemistry have demonstrated that microbial-derived compounds, membrane transport mechanisms, and electrophysiological processes play fundamental roles in modulating CNS function at both cellular and systemic levels. From a biophysical perspective, microbiota influence neuronal excitability by altering ion channel dynamics, membrane potential stability, and synaptic transmission efficiency. Changes in ionic gradients and membrane conductivity, often mediated by microbial metabolites such as short-chain fatty acids, directly affect action potential generation and propagation. In parallel, biochemical mechanisms involve the synthesis and regulation of neuroactive molecules, including neurotransmitters, neuromodulators, and metabolic intermediates that can cross or influence the blood–brain barrier. Furthermore, microbial regulation of host metabolism contributes to energy homeostasis and mitochondrial function in neural cells, thereby impacting ATP-dependent processes essential for maintaining electrochemical gradients. The interaction between microbial products and host signaling pathways also modulates inflammatory responses, which in turn can influence neuronal plasticity and network activity. This study aims to synthesize contemporary findings on the biophysical and biochemical mechanisms underlying microbiome-mediated regulation of neural activity, with particular emphasis on molecular signaling pathways, ion channel modulation, membrane transport processes, and metabolic interactions that collectively shape brain function.