A Correlative Developmental Study of Structures Involved in the Production, Circulation and Removal of Cerebrospinal Fluid

Neurosciences, Developmental biology, Morphology

Mohamed, Abdelrahman Abdelaziz

University:University of Glasgow

关键词: Neurosciences, Developmental biology, Morphology;   

Others  :  http://theses.gla.ac.uk/77994/1/11003339.pdf

来源: University of Glasgow

【 摘 要 】

The development of the choroid plexus, the IVth ventricular foramina and subarachnoid space has been studied by optical microscopy and morphometric analysis of semi-thin plastic sections and by TEM and SEM in a series of CBA mouse embryos from 11th day p. c. to newborn. 1. Choroid plexus of the IVth ventricle At the 11th day p. c. the choroid epithelial cells were already recognisable in SEM by their bulging apices and relatively abundant microvilli; their lateral plasma membranes, as shown by TEM, were straight and simple. The tela choroidea was more vascular in relation to this specialised epithelium but invagination into the ventricle had not yet begun. By the 13 th day p. c. important qualitative changes had taken place: The apical surfaces of choroid epithelial cells were densely covered by microvilli and their basilateral plasma membranes showed complex infoldings and interdigitations. These two features together with cytoplasmic organelles (mitochondria, rough endoplasmic reticulum, Golgi complex) were essentially similar between 13th day p. c. and birth. Although there was an apparent increase in the size of the choroid plexus from the time of its first appearance, no significant progressive changes were found in the volume densities of its components (epithelium, blood vessels and connective tissue) during prenatal development. The structural evidence is consistent with functional secretory capacity of the plexus from the 13th day p. c. SEM showed the IVth ventricular choroidal "capillaries" to be sinusoidal in nature, and clearly different from those of adjacent subependymal cerebral capillaries, and also surprisingly, those of the lateral ventricle choroid plexus. Although they remain sinusoidal until birth, their endothelial lining was shown by TEM to become progressively and uniformly thinner and to contain an increasing number of fenestrae as development progressed. The endothelial basement membrane was ill-defined and poorly developed throughout development. The choroidal capillaries also became more intimately related to the epithelium as development proceeded. All these features of endothelium would facilitate the movement of substances across the capillary wall. 2. Foramina of the IVth ventricle Although the caudal part of the roof of the IVth ventricle remained extremely attenuated throughout development, no foramina or interependymal pores were found. The ependymal lining of the lateral recesses started to attenuate by the 17th day p. c. but lateral foramina did not appear until birth. The lateral foramina seemed to arise as the result of an active developmental process and not merely through the rupture of the ependymal wall by the CSF pressure. The ventricular cavity was therefore an anatomically closed one until the appearance of the lateral foramina at birth when bulk flow of CSF from the ventricular cavity into the subarachnoid space was first established. 3. The subarachnoid space At the 11th day p. c. , a vascular cellular mesenchyme occupied the entire interval between the neuroepithelium and the future epidermis. At the 13th day p. c. , the small, spindle-shaped mesenchymal cells were becoming widely separated, in some symmetrically placed areas around the brain, by abundant intercellular matrix. Definite "spaces", presumably fluid-filled, were first seen at the 14th day p. c. , particularly over the lateral, ventral and dorsolateral aspects of the hind brain, but not on the dorsal aspect, adjacent to the thin roof of the IVth ventricle. The appearance of the subarachnoid spaces coincided with the appearance of a large number of macrophages in these spaces. The significance of this association is discussed. Contrary to previously held views, it was concluded that bulk flow of CSF does not initiate the development of the subarachnoid space. 4. Arachnoid villi Arachnoid villi were not present in the mouse, but the supporting dura was found to be a thin layer with loosely and randomly oriented fibres. This thin supporting dural layer is apparently adequate for the support of the small size mouse brain and at the same time allows CSF to percolate through from the subarachnoid space to reach the venous sinuses without the need for arachnoid villi.