Young dogs of both sexes were used in this study. Transmission and scanning electron microscopy were utilized for the examination of the spinal cord and choroid plexus with emphasis on the study of free cells. These procedures were modified so that, in certain cases, the same cells observed in scanning electron microscopy could be analyzed internally by transmission electron microscopy. One half of the animals were injected under anesthesia with horseradish peroxidase for observation of phagocytosis. This study confirms that the free cells observed in the subarachnoid space with the scanning and transmission electron microscopes are identical. The internal morphology of these cells corresponds to that of macrophages. This is further substantiated by the ability of these cells to localize horseradish peroxidase in discrete vacuoles within their cytoplasms. Both pial macrophages and epiplexus cells localize peroxidase in an identical manner in the same animal after one injection. In addition macrophages on the surface of the pia mater respond to extravasated red blood cells in a characteristic manner including phagocytosis. The plentiful population of macrophages on the surface of the pia mater supports the concept that these cells are of major importance in maintaining asepsis in the subarachnoid space.
Young dogs were perfused with buffered aldehydes. For scanning electron microscopy MICROFIL was injected to help prevent vascular collapse. The dura-arachnoid was exposed leaving the nerve exits and rootlets intact. These were identified according to level and dissected free. Selected specimens were photographed at low magnification. Others were embedded in Epon 812 and sectioned for light and transmission electron microscopy. Similar specimens were prepared by critical point drying and palladium-gold coating for scanning electron microscopy.Nerve roots pierce the dura through single exits (upper cervical, lower lumbar, sacral), or by exits separate for dorsal and ventral roots (lower cervical, thoracic, lumbar), or by multiple exits (cervical). Scanning electron microscopy reveals complicated tissue relationships chiefly involving arachnoid trabeculae. A t the point of nerve root exits the arachnoid gives rise to numerous arachnoid trabeculae which form highly fenestrated sheets. These attach to blood vessels and nerve roots. A lateral recess occurs between dorsal and ventral roots (cervical, lumbar). Numerous macrophages are present on the various surfaces studied.
The connective tissue cells of the dentinal pulp of unerupted dog teeth possess occasional cilia. Internally there are 4 to 8 peripheral doublets and one central doublet. Nine peripheral doublets are observed only close to or near the basal body.
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