The cerebral ventricles of the dog. I. Ultrastructural features of supraependymal cells during the inflammatory response.

The present investigation examined the ependymal linings of the cerebral ventricles of the dog following a single intracisternal injection of the viable antigen, bacillus Calmette-Guerin (BCG). One or 3 days following the injection of BCG, animals were perfused with buffered aldehydes. Portions of the linings of the lateral, third and fourth cerebral ventricles were removed and routinely prepared for scanning and transmission electron microscopy. Following BCG injection, a tremendous increase in the number of supraependymal cells is apparent throughout the entire cerebral ventricular system. Especially high concentrations of cells were observed on the ependyma overlying the following regions; the caudate nucleus, in the lateral ventricles; the interthalamic adhesion, lateral walls and floor of the third ventricle; lateral margin of the floor, lateral apertures and median sulcus of the fourth ventricle. The supraependymal cell population of infected animals was composed of macrophages, B lymphocytes, neutrophils, and lymphoblasts. Macrophages were found in highest concentration within these supraependymal cell populations. Furthermore, large aggregates of macrophages were observed on the ependyma overlying the interthalamic adhesion of the third ventricle and median sulcus of the fourth ventricle. It was suggested that these clusters may represent the early development of epithelioid granulomas.