A further note on the presence of the endogenous macrophages in the developing cerebellum.

Abstract

In the developing cerebellum of 5- and 10-day-old rats 20 mul of ENU solution was injected. At the site of injection a cavity filled with erythrocytes was seen, and this was lined with hematogenous macrophages. They made their appearance 2 days after injection, and were seen present even after 75 days following the experimental treatment, long after all the degenerative and phagocytic processes were completed. At a distance from the cavity reactive macrophages were seen in the external granular layer, where the cells were killed following an exposure to ENU. They were endogenous macrophages, and they also appeared within 2 days after the injection. After the phagocytosis of the debris the endogenous macrophages, unlike the hematogenous macrophages of the cavity, could not be seen. Presumably they have reverted to their resting state. It is suggested that in the normal developing cerebellum macrophages are present endogenously, and that under the conditions of lesions they participate in phagocytosis.