The cerebral ventricles of the dog. II. Evidence of a hematogenous origin of supraependymal cells during the inflammatory response.

The present investigation examined the ependymal linings of the choroid plexus and cerebral ventricles of the dog following a single intracisternal injection of viable, bacillus Calmette-Guerin (BCG). One or 3 days following the injection of BCG, animals were perfused with buffered aldehydes. The choroid plexus of each cerebral ventricle as well as samples of the ependyma from the caudate nucleus, interthalamic adhesion, and median sulcus were removed and prepared for transmission electron microscopy. Following injection of BCG, leukocytic cells are found in association with the following structures and areas of the subependyma and choroid plexus: the endothelium of small blood vessels and capillaries; the walls of small blood vessels; the subependymal neuropil; the choroid plexus stroma; the single layer of ependyma bordering the luminal surfaces of the choroid plexi and ventricles; and the free, luminal surfaces of the choroid plexus and ventricular ependyma. The population of leukocytic cells included monocytes, macrophages, neutrophils, lymphoblasts, and plasma cells. The results of the present study suggest that the supraependymal leukocyte population of infected animals reaches the cerebral ventricular linings by migrating from the choroidal and subependymal vasculature.