Analysis of the three dimensional organization of glia cell processes by X-ray- and high voltage electron -microscopy

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Taking advantage of the merits of X-ray- and high voltage electron-microscopy, I examined details of the three dimensional organization of glia cell processes in various parts of the rat central nervous system.With the X-ray microscope one can observe very thick specimens of over 100 in thickness and even in water, and with the high voltage electron microscope, a high resolution observation of rather thick specimens of up to 5mum in thickness is possible. In addition , stereo observation can be done because the depth of focus of the X-ray microscope and electron microscope is very large, and in this way the information obtained from the depth of the specimens can be analyzed.Several important new findings were obtained with the aid of high voltage electron microscopy. 1) The protoplasmic astrocyte in the gray matter formed a dense three dimensional network in which terminal branches of axons and dendrites, and their synapses were embedded. The network was composed of thin leaflets or r … More ibbon-like structures of less than 50 nm in thickness. These fine branches arose directly from large branches and cell soma. They abutted on the outer surface of the capillary and fused to form a thin glial sheet in addition to that formed by rather thick astrocytic processes generally called capillary end feet. 2) The surfaces of the neurons studded with many nerve terminals are covered by astrocytic processes which formed networks covering the somata and large dendrites as seen with the light microscope. The sizes of the mesh roughly coincide with those of nerve terminals. High voltage electron microscopy revealed a layer consisting of polygonal compartments or cells which covered the soma and large dendrites. The walls of cells were consisted of a very thin astrocytic process. Each of these cells was supposed to wrap around a nerve terminal. It is interesting to note that the shapes of the processes other than those on the nerve cell somata resemble to those of the Bergmann glia cell in the cerebellum and Muller cell in the retina which are thought to originate from the radial glia cells. 3) Although global shapes of the fibrous astrocytes in the gray matter and white matter differed to each other and differed from those of the protoplasmic astrocytes, the shapes of their terminal branches were similar in principle, thin and fine leaflets or ribbonlike, and they seemed to adapt themselves to the shapes of neighboring neuronal or vascular structures.It was found that high voltage electron microscope stereoscopy of thick Golgi stained materials was the most effective and reliable method of examining the detail of the three dimensional organization of glia cell processes in the central nervous system at present.Golgi staining also gave enough contrast to glia cell processes for X-ray microscopy. Capability of observing over 100 mum thick specimen in one good focused image was a large merit of the X-ray microscope, however it's two dimensional resolution was about the same to that of the light microscope and was not high enough to resolve the details of fine terminal processes of the astrocytes. Improvement in practical resolution of the X-ray microscope is highly requested. X-ray microscopy of wet preparation will be an useful technique in glia cell morphology in the future. Less