Nucleus tractus solitarii
The nucleus tractus solitarii (NTS, nucleus of the solitary tract) is an aggregation of neurons in the caudal brainstem of the mammalian brain. It transmits information from stretch- and chemoreceptors of the cardiovascular, respiratory and gastrointestinal systems, and from taste buds on the tongue.  The NTS includes the A2 cell group of noradrenergic neurons, and projects densely to many regions of the hypothalamus and elsewhere. The nucleus has reciprocal connections with the area postrema, a circumventricular organ at the floor of the fourth cerebral ventricle. The area postrema lacks a blood-brain barrier, and neurons there respond to many blood borne factors.
The NTS receives extensive inputs from afferents of the vagus nerve, and relays densory information to many other parts of the brain, but especially to the limbic system, and in particular the hypothalamus.
Many neurons in the NTS synthesise neuropeptides; the noradrenergic neurons of the A2 cell group synthesize and release several peptides, including enkephalins and galanin. Other non=noradrenergic neurons in the NTS synthesize somatostatin, and prolactin-releasing peptide (PRP).
The NTS has an important role in regulation of appetite, mediating the sensations of satiety that arise from ingestion of food and which influence meal size. Food intake results in gastric distension and the release of peptides including cholecystokinin and glucagon-like peptide from the duodenum and ileum, and these signals activate afferent vagal nerve endings. The afferent vagus transmits this sensory information directly to the NTS via a glutamatergic synapse. NTS neurons integrate this sensory information with inputs from other CNS regions, and convey the integrated response to other nuclei, including the adjacent dorsal motor nucleus of the vagus. The preganglionic neurons in the DMV are the source of the parasympathetic motor response back to the gastrointestinal tract. Other NTS neurons, including the A2 neurones and the PRP neurones project to several hypothalamic nuclei involved in appetite regulation, including the paraventricular nucleus, the arcuate nucleus, and the dorsomedial nucleus. 
- Dean JB, Putnam RW (2010) The caudal solitary complex is a site of central CO(2) chemoreception and integration of multiple systems that regulate expired CO(2) Respir Physiol Neurobiol 173:274-87 Review PMID 20670695
- Browning KN, Travagli RA (2011) Plasticity of vagal brainstem circuits in the control of gastrointestinal function Auton Neurosci 161:6-13 Review PMID 21147043