History and status of the area postrema.

The history of morphological and functional studies on the area postrema (AP) is traced for significant landmarks from 1896, when its name was conferred by Retzius, to 1960 when the foundation of inquiry had become firmly set. A comparative anatomical survey of the medulla oblongata identifies the AP in mammals and birds but not in amphibians and lower phyla even though other members of the so-called circumventricular organ system are represented in the more ancient creatures. Existence of the AP in reptiles is insufficiently documented. The transition from water- to land-dwelling animal life affords propitious neural remodeling for the emergence of the AP in evolving species. No vital role is known to be served by the AP. Nonetheless, its physical interposition between the blood and cerebrospinal fluid and its shared functions with the nucleus tractus solitarii indicate a capability for widespread somatovisceral influence in response to particular perturbations. It is suggested that the diverse systemic expressions of postremal activation are encompassed in the general syndrome of nausea and vomiting.