The fine structure of stratified ependyma in the ventricular wall of N-ethyl-N-nitrosourea-treated rats

Regional analysis of the ependyma of the third ventricle of rat by light and electron microscopy

Ependymal lining of cerebral ventricles lies at the interface between the ventricular cavities and the brain parenchyma. Ependymal cells are involved in various functions within the brain and play a major role in the production of the chemical principals of the cerebrospinal fluid. Histological studies on the regional variation of the third ventricular ependyma and the subependyma of adult rats were carried out by light and electron microscopic methods. For light microscopic analysis, methacrylate sections were used. In addition to the routine haematoxylin and eosin (H and E) staining for histological studies, the sections were stained with toluidine blue, cresyl violet and periodic acid Schiff's reagent (PAS). A regional analysis of the ependyma of the third ventricle showed that in most regions the ependyma was monolayered. The sidewalls and floor of the ventral portion of the third ventricle showed a multilayered ependyma. For descriptive purposes at the light microscopic level, the ependymal cells were classified, based on the cell shape (flat, cuboidal or columnar), presence or absence of cilia and the number of cytoplasmic granules present in the cells. Studies of transmission electron microscope have shown that these granules represent the cell organelles of the ependyma. The subependyma also showed a regional morphological variation, and, in most instances, contained glial and neuronal elements. In regions of specific brain nuclei, neurons were the major cell type of the subependyma. PAS staining did not show any positive granules in the ependymal cytosol. Characteristic supraependymal elements were present at the ependymal surface of the third ventricle.

Mixed ependymoma-astrocytoma (subependymoma?) of the cerebral cortex

Tumors of mixed glial origin may present as low-grade neoplasms with distinct cell populations or as polymorphic malignant gliomas. Such cell populations are usually appropriate to the location of the tumor. A mixed tumor, with a cell population inappropriate to tumor location, is presented to discuss theories of glial differentiation and cellular heterogeneity. This mixed ependymoma-astrocytoma of the parietal cortex, ultrastructurally similar to subependymoma but anatomically separate from the subependymal cell matrix or ventricular surface, gives evidence for neoplastic differentiation into ependymal and astrocytic cell lines. This supports the idea of a common progenitor cell, the ependymoglia or tanycyte, in human cerebral cortex.

Morphological maturation of tumor cells induced by ethylnitrosourea (ENU) in rat brains. I. On the tumors by administration of ENU in the late gestational stage

Sequential changes in the development of ethylnitrosourea (ENU)-induced rat brain tumors were examined histologically, immunohistochemically, electron microscopically and autoradiographically. In 47 Sprague-Dawley rats transplacentally administered ENU, 95 brain tumors developed, including 76 microtumors less than 1mm in diameter. Microtumors were found mainly in the paraventricular area, but some were found in the peripheral brain tissue. They were composed of small tumor cells which had round dark nuclei and scanty cytoplasm immunohistochemically negative for Leu 7 and glial fibrillary acidic protein (GFAP). The 19 macrotumors were mature gliomas, 3 of which histologically corresponded to oligodendrogliomas and 16 to mixed gliomas. The tumor cells of the former had small round nuclei with distinct perinuclear halos and a small amount of cytoplasm positive for Leu 7. The latter were chiefly composed of polygonal cells having large round nuclei and rich cytoplasm positive for GFAP. An autoradiographic study using 3H-thymidine revealed that the labeling index of the tumor cells was high in mixed gliomas and microtumors, but low in oligodendrogliomas. It may be concluded that the constituent cells of microtumors correspond to glioblasts or migrating neuroglias, which gradually mature to form oligodendrogliomas or astrocytomas.

Morphology of early stages of ENU-induced brain tumors in rats

Tumors were induced in experimental animals in order to investigate early tumor growth with conventional histology and gliofibrillary acid protein (GFAP) demonstration with the peroxidase-antiperoxidase (PAP) method. In one experiment, the animals were killed after transplacental ENU administration, when microtumors were suspected; in the second experiment, the animals were followed up to their natural death and microtumors found at random were used for analysis. Conventional histology revealed 3 types of microtumors: growth restricted to the subventricular matrix, growth in the neighbourhood of the ventricles with obvious or probable connection to the ventricular zones and small tumors observed exclusively in the white matter. The latter tumors by conventional staining were composed of small round cells, considered to be oligodendrocytes. They did not contain GFA-protein positive cells within the tumor. The tumor in presumable and visible connection with the ventricular lining did contain GFAP-positive astrocytes. In the very small subventricular tumors, the small round cells (oligodendrocytes) were in continuous contact with the identical interfascicular glial cells, while GFAP positive astrocytes seemed to stem from the subventricular astrocytes (tanycytes, ependymoglia). The ependyma itself was always preserved. A twofold origin of these experimental tumors with probable development into one common cytological glial type is assumed.

Changes in the central canal area of immature rats following spinal cord injury

A small, unilateral, penetrating wound was placed in the dorsolateral portion of the lumbosacral spinal cord in immature rats. Although this wound did not extend into the central canal area, some cells forming the walls of this canal underwent proliferative activity as demonstrated by [3H]thymidine autoradiography. The uniform, regular cellular arrangement of these walls was lost and portions of the walls thickened and became multilayered in appearance.