Central Aspects of Nausea and Vomiting in GI Disorders

Nausea and vomiting result from continuous interactions among gastrointestinal, central nervous system, and autonomic nervous system. Despite being closely associated, central pathways of nausea and vomiting appear to be at least partly different and nausea is no longer considered only a penultimate step of vomiting. Although our understanding of central pathways of nausea has improved over the last one decade, it is still very basic. Afferent pathways from gastrointestinal tract via vagus, vestibular system, and chemoreceptor trigger zone project to nucleus tractus solitarius which, in turn, relays the signal to central pattern generator initiating multiple downstream pathways. This central nausea pathway appears to be under constant modulation by autonomic nervous system and cerebral cortex. There is also some evidence that central pathway of chronic nausea is different from that of acute nausea and closely resembles that of neuropathic pain. This improved understanding has modified the way we can approach the treatment of acute and chronic nausea. While conventional therapies such as antiemetics (antiserotoninergic, antihistaminic, antidopaminergic) and prokinetics are commonly used to manage acute nausea, they are not as effective in improving chronic nausea. Recently, neuromodulators such as tricyclic antidepressants, gabapentin, olanzapine, benzodiazepines, and cannabinoids have been shown to have antinausea effect. There is a need to study the utility of these drugs in managing chronic functional nausea. Improving our understanding of central and peripheral circuitry of nausea will allow us to better utilize the currently available drugs and develop new therapeutic options.