Morphology of Emetic Chemoreceptor Trigger Zone in Cat Medulla Oblongata

Abstract

1. A hitherto unidentified structure in the medulla oblongata is described. It is an essentially non-neural zone situated between the ala cinerea and the vestibular complex and is contiguous medially with the area postrema which overlies the ala cinerea. The zone consists largely of fibroblasts and cells resembling protoplasmic astrocytes and astroblasts which have an abundance of vascular feet abutting on a dense network of blood vessels. Numerous nerve endings found in this zone are observed to connect with a loose fiber bundle which passes towards the nucleus of the fasciculus solitarius. 2. Experimental studies made with the ablation technic have yielded evidence that this structure is the anatomical framework of the medullary chemoreceptor trigger mechanism for the emetic center. Destruction of this chemoreceptor trigger zone in cats makes the animals refractory to the emetic effect of the intravenously administered cardiac glycosides-lanatoside C, scillaren A and ouabain-in doses which are known to be effective in intact animals.