Anatomy and function of efferent and afferent vagal innervation of the stomach

The stomach is one of the major targets of the vagus nerve. Vagal cholinergic parasympathetic (efferent) neurons are located in the dorsal motor nucleus of the vagus (DMV) in the caudal brainstem. They do not directly innervate gastric effector cells, but instead a large portion of enteric neurons located in the myenteric plexus, which act as muscle motor neurons and function-specific pattern generators that can regulate specific motility and secretion programs in coordination with physiological needs and environmental conditions. Vagal sensory (afferent) neurons located in the nodose ganglia (NG) innervate all layers of the stomach wall, where they pick up mechanical and chemical signals to inform the brain and effectuate vago-vagal reflexes. The most abundant terminal structures, intraganglionic laminar endings (IGLEs), are in intimate contact with myenteric plexus neurons. Besides sensing gastric tension, they are likely also chemosensors and provide a link between the enteric nervous system and the brain. Transcriptomic analyses of vagal efferent and afferent neurons allowed making great progress on deciphering their respective coding logic, with a predominantly labeled line organization emerging as the general principle. Because of their distinct molecular fingerprints, separate populations of vagal efferents and afferents with unique morphologies and functions have become experimentally and therapeutically accessible. However, the full coding logic also depends on the organization of the peripheral interface with the enteric nervous system, as well as the central interface represented by 2nd and higher order sensory neurons and pre-autonomic neurons upstream of the DMV, which are only starting to be understood.