A transient phase of cell death in the developing medial forebrain of the perinatal ferret

Abstract

A transient bilateral population of cells immediately rostral to the ferret corpus callosum was examined at weekly intervals between embryonic day 28 and postnatal day 7. This region is tentatively identified as the medial forebrain apoptosis zone (MFAZ) because of the specific nature of cell death, and the limited area or zone in which it was observed. No other region within the brain or retina exhibited a similar pattern or amount of cell death. Only scattered apoptotic cells were found throughout the remainder of the brain-including the cerebral cortical plate, subplate, and white matter-with the exception of the ventricular zone of the lateral ventricles which contained a significant population of apoptotic cells. This study addressed three questions about apoptosis in the MFAZ: (1) does apoptotic cell death in this region signal the appearance of phagocytic macrophages, (2) does cell degeneration and phagocytosis in this region lead to the formation of an extracellular space analogous to the cavum septi pellucidi of rodents, and (3) what is the duration of degeneration, or clearance rate, of cell death in this defined region. The MFAZ was first found to contain apoptotic nuclei and macrophages late in gestation, at E34. Numbers of apoptotic nuclei and macrophages peaked one week later at birth in this area, but disappeared early in postnatal life. During this period, formation of a space rostral to the corpus callosum due to the removal of apoptotic cells was not observed. Finally, presence of apoptotic cells in the MFAZ over a period of > or = 9 days suggests a clearance rate of many hours. The close spatiotemporal correlation of the distribution of apoptotic cells and their removal by macrophages suggests that these are interrelated, and perhaps interdependent events.