Scanning electron microscopic observations of the ependymal cell and the subependymal layer of the third brain ventricle in the rat.
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This investigation was undertaken to clarify the three dimensional ultrastructure of the subependymal layer in relation with the ependymal cell layer in rat brain using the scanning electron microscope (SEM). The subependymal layer existing below the ependyma of the third ventricle in the brain of mature albino rats was examined with S E M. The hypothalamus freshly excised after median sagittal section was treated by collagenase with or without trypsin for a short while to remove the ependymal cells at the ventricular wall. After the enzymatic pretreatment of the specimen, many ependymal cells were removed and the subependymal layer was partially exposed. Most of the ciliated ependymal cells remaining at the ventricular wall extended long, single basal processes which then penetrated into the subependymal layer. The subependymal layer was composed of a delicate framework of thin processes of glial cells, ependymal cells and, in addition nerve cells. Scattered among the neuropil just beneath the ependymal cell layer, there were relatively small, globular subependymal cells. Occasionally, there were large bundles of unmyelinated nerve fibres in the subependymal layer. The individual nerve fibres distinctly showed many axonal varicosities within the fibres. Intermingled with the nerve fibres, glial processes of various forms were present. The structure of the ependymal cells and the subependymal layer was compared with the findings already reported in the studies using light and transmission electron microscope.Keywords:
Subependymal zone
Ependyma
Ependymal Cell
Neuropil
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The subventricular zone of the striatal wall of adult rodents is an active neurogenic region for life. Cubic multiciliated ependyma separates the subventricular zone from the cerebrospinal fluid (CSF) and is involved in the control of adult neurogenesis. By injecting neuraminidase from Clostridium perfringens into the right lateral ventricle of the rat, we provoked a partial detachment of the ependyma in the striatal wall. The contralateral ventricle was never affected and was used as the experimental control. Neuraminidase caused widening of the intercellular spaces among some ependymal cells and their subsequent detachment and disintegration in the CSF. Partial ependymal denudation was followed by infiltration of the CSF with macrophages and neutrophils from the local choroid plexus, which ependymal cells never detached after neuraminidase administration. Inflammation extended toward the periventricular parenchyma. The ependymal cells that did not detach and remained in the ventricle wall never proliferated. The lost ependyma was never recovered, and ependymal cells never behaved as neural stem cells. Instead, a scar formed by overlapping astrocytic processes sealed those regions devoid of ependyma. Some ependymal cells at the border of the denudated areas lost contact with the ventricle and became located under the glial layer. Concomitantly with scar formation, some subependymal cells protruded toward the ventricle through the ependymal breaks, proliferated, and formed clusters of rounded ventricular cells that expressed the phenotype of neuroblasts. Ventricular clusters of neuroblasts remained in the ventricle up to 90 days after injection. In the subventricular zone, adult neurogenesis persisted.
Ependyma
Ependymal Cell
Subependymal zone
Neuroblast
Neuropil
Lateral ventricles
Subarachnoid space
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This investigation was undertaken to clarify the three dimensional ultrastructure of the subependymal layer in relation with the ependymal cell layer in rat brain using the scanning electron microscope (SEM). The subependymal layer existing below the ependyma of the third ventricle in the brain of mature albino rats was examined with S E M. The hypothalamus freshly excised after median sagittal section was treated by collagenase with or without trypsin for a short while to remove the ependymal cells at the ventricular wall. After the enzymatic pretreatment of the specimen, many ependymal cells were removed and the subependymal layer was partially exposed. Most of the ciliated ependymal cells remaining at the ventricular wall extended long, single basal processes which then penetrated into the subependymal layer. The subependymal layer was composed of a delicate framework of thin processes of glial cells, ependymal cells and, in addition nerve cells. Scattered among the neuropil just beneath the ependymal cell layer, there were relatively small, globular subependymal cells. Occasionally, there were large bundles of unmyelinated nerve fibres in the subependymal layer. The individual nerve fibres distinctly showed many axonal varicosities within the fibres. Intermingled with the nerve fibres, glial processes of various forms were present. The structure of the ependymal cells and the subependymal layer was compared with the findings already reported in the studies using light and transmission electron microscope.
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Ependymal Cell
Neuropil
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SUMMARY In its simplest form, the ependyma of the third ventricle consists of a single layer of cuboidal cells. Although these typical mural cells constitute the greater part of the lining of the ventricle, a specialized variety of ependymal cell (the tanycyte) can also be distinguished within circumscribed areas of the ventricular wall. Although such cells are found scattered throughout the dorsoventral extent of the third ventricle, they are particularly numerous along the ventrolateral walls and floor. The regional variation in the surface morphology of the ventricle walls as evident with the scanning electron microscope is consistent with this pattern of tanycyte distribution. Ultrastructural studies have established that the tanycyte is a fundamentally distinct cell with a long basal process extending into the subjacent neuropil and frequently directed toward a capillary wall. This unique morphology conforms closely to its three-dimensional appearance as demonstrated with the scanning electron microscope. The significance of ependymal tanycytes particularly of the third ventricle derives largely from the connections they establish between the ventricular lumen and vasculature of the median eminence. This intriguing structural relationship has led to the suggestion that ependymal cells and cerebrospinal fluid of the third ventricle may be involved in the regulation of adenohypophysial activity. Evidence indicating the functional involvement of specialized ependymal cells in the neuroendocrine control of pituitary activity is reviewed.
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The postnatal development of the zonation and the glial cells of the median eminence (EM) was investigated in male rats. On the 1st day of life, the ME is mostly undifferentiated. In contrast to adult animals, only the ependymal, subependymal and palisade layer can be observed. The remaining area is almost unorganized. A more distinct zonation of the EM exists about the 10th day of life. Ependymal and subependymal layer are reduced to a monolayer of cells; in addition, the reticular layer appears. The adult structure of the EM is seen for the first time about the 14th day of life. The development of the zonation of the EM is finished at the 3rd week of life. Mature microglial cells occur in the median eminence at the 1st day of live. Ependymal cells, tanycytes and astrocytic tanycytes (Zaborszky and Schiebler 1978), which can be found in a greatter amount as an individual cell type, are relatively immature. Protoplasmatic astrocytes occur at the 4th, and fibrous astrocytes at the 14th day of life. The development of glial cells may be finished at the end of the 4th week of life together with the maturation of oligodendrocytes. The opening of the 3rd ventricle needs 2 weeks, that of the recessus infundibularis is finished after the 3rd week of live. On the basis of their lipid granules and the synaptic contacts with neurosecretory axons it is presumed that the tanycytic and astrocytic tanycytes have regulatory functions in connection with neurosecretory processes.
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Using the peroxidase-antiperoxidase method a study was made of the cells immunoreactive to glial fibrillary acidic protein (GFAP) anti-serum in the ependyma of the third ventricle of the rat at different stages of growth. Most of the ependymal cells of the third ventricle were seen to be unreactive to this protein; however, it was sometimes possible to observe some GFAP-immunoreactive ependymocytes and occasionally other immunoreactive cellular types, such as tanycytes and supraependymal cells. Despite this, the most frequent localization of the elements immunoreactive to the protein adopted the shape of an immunoreactive subependymal band situated parallel to the ventricular wall. As the weights of the animals increased an increase in the elements immunoreactive to this protein could be observed in all the zones considered, there being no differences between the male and female animals.
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Abstract An intraventricular neuronal complex has been identified with scanning and transmission electron microscopy at the base of the lamina terminalis of the mouse. The raspberry‐shaped complex protudes from a thickened bulge on the ependymal surface of the lamina terminalis or adjacent rostral floor of the third ventricle. Neurons and occasional ependymal cells cover the surface of the complex. Its core is made up of neurons, ependymal cells, and neuronal processes, which are usually compactly arranged. The core is continuous, through a breach in the ependymal layers, with the subependymal neuropil of the lamina terminalis. Within the core of the complex are large numbers of axodentritic synapses. Axonal varicosities and synaptic terminals are filled with vesicles and mitochondia. Synaptic endings have one of two populations of vesicles: exclusively clear, small, round or flattened vesicles. In view of the known structural and functional characteristics of the lamina terminalis, it is possible that the neuronal complex may participate in neurohormonal regulatory systems of the hypothalamus and hypophysis or in the network of circumventricular organs mediating angiotensin effects.
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Objective:To observe the morphology and dis tribution o f nitric oxide synthase(NOS) positive cerebrospinal fluid(CSF) contacting neuro ns in the surrounding region of the third ventricle in the rat. Methods: NADPH diaphorase histochemistry method was used to investi ga te the distribution of NOS positive CSF contacting neurons in the surrounding r egion of the third ventricle in the rat. Results:NOS positive CSF contacting neurons were scattered at the s ur rounding region of the third ventricle, from anterior ventral area to posterior d orsal area. These neurons could be classified in four types. They were located i n the ependymal layer, subependymal layer. Some of them were located where there was some distance to the ependyma, but they had some processes protruded into t he third ventricle. In the anterior parts of posterior magnocellar paraventricular nuclei and medial magnocellar paraventricular nuclei, there were a large number of NOS positive fibers extending to the third ventricle, mixing with or contacti ng processes of NOS positive CSF contacting neurons. Conclusion: NO S positive CSF contacting neurons in the surrounding re gion of the third ventricle were very close to the CSF. So, we suggested that th ese neurons may acquire information from the CSF and release NO into the CSF, an d play an important role in neurohumoral regulation.
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Cerebral ventricle
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NOS positive CSF-contacting neurons were scattered at the surrounding region of the third ventricle,from anterior ventral area to posterior dorsal area.These neurons could be classified in four types.They were located in the ependymal layer,subependymal layer.Some of them were located where there was some distance to the ependyma,but they had some processes protruded into the third ventricle.In the anterior parts of posterior magnocellar paraventricular nuclei and medial magnocellar paraventricular nuclei,there were a large number of NOS positive fibers extending to the third ventricle,mixing with or contacting processes of NOS positive CSF-contacting neurons.
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Cerebral ventricle
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An infant of 43 weeks gestational age with severe congenital hydrocephalus was operated on for removal of a subependymal astrocytoma in the region of the foramen of Monro. A biopsy of periventricular tissue was taken from the lateral ventricle for examination by scanning and transmission electron microscopy. The ependyma was largely denuded, with glial cell processes forming most of the ventricular lining. Many of the attenuated ependymal cells, however, had intact junctional complexes at areas of contact with other ependymal cells. Club-shaped unipolar cells, believed to be a previously undescribed form of immature ependymal cells, were found in the ventricular lining. Cerebrospinal fluid edema was present in the neuropil up to 60 microns from the ventricular lumen, but there was no obvious axonal pathology in the tissues examined.
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Subependymal zone
Ependymal Cell
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