Why is the neurobiology of nausea and vomiting so important?

Abstract

Nausea and vomiting are important as biological systems for drug side effects, disease co-morbidities, and defenses against food poisoning. Vomiting can serve the function of emptying a noxious chemical from the gut, and nausea appears to play a role in a conditioned response to avoid ingestion of offending substances. The sensory pathways for nausea and vomiting, such as gut and vestibular inputs, are generally defined but the problem of determining the brain's final common pathway and central pattern generator for nausea and vomiting is largely unsolved. A neurophysiological analysis of brain pathways provides an opportunity to more closely determine the neurobiology of nausea and vomiting and its prodromal signs (e.g., cold sweating, salivation).

Fig. 1

Model of neural pathways for nausea and vomiting. Inputs: Afferent input from the cerebral cortex, vestibular system, area postrema (AP), and gut vagal afferent fibers converge on the nucleus of the solitary tract (NTS) in the lower brainstem. Integration: The final common neural pathways and central pattern generator for nausea and vomiting and other prodromal signs are largely unknown. The NTS and region of the retrofacial nucleus are thought to play important integrative roles in nausea and vomiting. Outputs: Prodromal signs usually occur prior to retching and vomiting. Proximal gastric relaxation and a giant retrograde contraction of the intestine, mediated by the vagus, serve to position gastrointestinal contents for expulsion by vomiting. The sequence of muscles engaged in retching are different from those used in vomiting (expulsion). ?, indicates unknown elements in these pathways. Some neural regions are omitted for the sake of simplicity (e.g., hypothalamic pathway for vasopressin release).