The neurobiotic sense: emerging pathways of microbial detection and gut-brain communication

The gut microbiota, a complex community of bacteria, fungi, viruses, and other microorganisms, plays a critical role in regulating host physiology through the gut-brain axis. The gut microbiota interacts with the central nervous system through a range of interconnected pathways. These include humoral signaling, immune-related mechanisms, sensory afferent pathways, and the modulation of enteric neural circuits. Recent research has uncovered specialized epithelial sensory cells, like neuropod cells, that can directly detect microbial molecules and send signals via vagal afferents. This discovery highlights a previously unknown aspect of communication between the gut and brain. The review investigates the structural and functional diversity of the ENS, highlighting components like mechanosensory and chemosensory neurons, enteroendocrine cells, and neuropods that interact with vagal afferents. Specific focus is placed on pattern recognition receptors such as TLR5, which allow gut epithelial neuropod cells to sense bacterial flagellin and dynamically regulate appetite via PYY release and vagal signaling. Further examination addresses the impact of microbial metabolites including short-chain fatty acids, bile acids, tryptophan derivatives on neuronal excitability, neurotransmitter synthesis, and neuroimmune interactions. These insights underscore the gut as a sensory organ equipped with neural circuits specialized for detecting microbial cues, reimagining traditional concepts of host-microbe communication. By redefining microbial detection as a distinct sense comparable to vision or taste, the neurobiotic sense offers a transformative perspective on how gut microbes influence behavior, feeding patterns, and brain function. This emerging framework holds the potential to drive novel therapeutic strategies for treating metabolic, inflammatory, and neuropsychiatric disorders.