Figure 1.

Cytoarchitecture of the dorsal vagal complex. Darkfield photomicrograph of a coronal section of rat brainstem at the level of the area postrema/intermediate level following application of HRP crystals to the subdiaphragmatic vagus. Note the intense labeling of the nucleus tractus solitarius (NTS), dorsal motor nucleus of the vagus (DMV), and nucleus ambiguus (NAmb). An area of the photomicrograph (dotted line) has been expanded into cartoon form to allow a more detailed illustration of the brainstem circuitry of gastrointestinal (GI) vago-vagal reflexes. Note that vagal afferent neurons, whose cell bodies lie in the nodose ganglion, receive sensations from the GI tract. The central terminals of these afferent fibers enter the brainstem via the tractus solitarius and terminate within the NTS, utilizing principally glutamate as their neurotransmitter. These afferent signals are integrated by neurons of the NTS that project to, among other areas, the adjacent DMV using, mainly, glutamate, GABA, or NE as neurotransmitters. Neurons of the DMV are the preganglionic parasympathetic motoneurons that provide the motor output to the GI tract via the efferent vagus, where they release acetylcholine onto their postganglionic target. Postganglionic parasympathetic neurons are either excitatory [cholinergic (ACh)] or inhibitory [nonadrenergic, noncholinergic (NANC)].