Phylogenic and neurologic aspects of the vomiting process

Hindbrain morphology is compared in a variety of animals representing species that vomit and those that do not. Special attention is given to the nucleus of the tractus solitarius (NTS) and its synaptic connections with surrounding structures. The role of the area postrema is examined from the standpoints of containing the chemoreceptor trigger zone (CTZ) for vomiting, of its functional relationship to the blood-brain barrier, and of its significance as part of the circumventricular organ system. A survey is made of the manifold behavioral contributions of NTS to cardiovascular and respiratory regulation, appetite control, arousal, water balance, and digestive and neuroendocrine functions. An overview is presented of neurochemical distribution in the brain stem with respect to aminergic, cholinergic, and peptidergic substances. Finally, causes and prevention of vomiting are discussed in light of the above considerations.