Observations on neurons and neuroglia from the area of the reticular formation in tissue culture

Brain macrophages: questions of origin and interrelationship

Brain tissue appears to contain several distinct types of macrophages. An effort is made here to present a description of the complete cohort of macrophages and sources of phagocytic activity in this tissue. Initially, the criteria and methods used for the identification of tissue macrophages in general are considered. These include some morphological and ultrastructural features, assessment of phagocytic activity, and histochemistry for intracellular and surface components. Each of these methods or criteria has certain advantages but also associated problems and limitations; all have been applied in various instances to brain tissue. In a final analysis, the most reliable means of identification of tissue macrophages involves a combination of all of these approaches. The identification and characterization of macrophages have been rendered extremely confusing in the brain because of so many different sources of these cells, both intrinsic and blood-derived. The classes of macrophages or phagocytic cells in brain tissue are microglia, supraependymal cells, epiplexus cells, meningeal macrophages, pericytes, and direct blood-derived macrophages. The morphology, location, and functional properties of each of these classes is described. In an overall view, brain tissue is very well protected by intrinsic macrophages, and the locations and distribution of these cells are consistent with other tissues. Finally, in a consideration of origin and interrelationship, the idea is presented that the most likely source for all or most brain macrophages is monocytic blood cells. The latter cells appear to migrate into the tissue from several sites during embryogenesis and may continue to enter, at least from blood vessels, in the adult state.

Features and distribution of intracerebrally injected peritoneal macrophages

Radioactively labeled macrophages were injected intracerebrally in order to acquire additional criteria for the identity of certain intracerebral cell types with cells of the monocyte-macrophage series. The intracerebral distribution of the labeled cells, their reactive ability following silver impregnation, and the formation of processes were considered as indications for ameboid motility. The localization, reactive ability, and structure of the cells were similar to that found in cells inside the brain which are considered to be monocyte derivatives, i.e., intraventricular cells such as epiplexus cells and supraependymal cells, progressive microglia, free subarachnoidal cells, and perivascular cells of intracerebral vessels. A survival time of 2 months was assumed for the cells since isolated, intracerebrally administered, peritoneal macrophages can still be demonstrated inside the subarachnoid space 2 months after the injection.

In vitro morphological study of cochlear epithelium

1. The mammalian cochlear epithelium was successfully kept alive in long-term tissue cultures. The Na and K concentration of the culture medium was similar to that of perilymph. 2. The most vulnerable cells in the culture epithelium were the outer and inner hair cells followed by the inner zones cells and the interdental cells of the spiral limbus. The difference in disintegration time between the outer and inner hair cells was about 48 hrs under the same culture conditions. The same phenomenon was noted between the rows of outer hair cells. 3. When the outer hair cells were not supported by Deiters' cells or when the cochlear epithelium was separated between Deiters' cells and Hensens cells, the outer hair cells degenerated quickly. 4. The interdental cells appeared to be relatively highly differentiated and showed much activity. No evidence of secretory function of interdental cells could be obtained. 5. The inner sulcus cells, Hensens cells, Claudius' cells and Reissners membrane cells were flattened and arranged like covering epithelium.