ACTIVATION OF MICROGLIA IN HEMORRHAGE MICROZONES IN HUMAN EMBRYONIC CORTEX - AN ULTRASTRUCTURAL DESCRIPTION

We have noted the presence within parietal cortex of microzones of hae morrhage in two 14 week gestation fetuses. These were obtained from mo thers with no clinical history indicative of infection or other pathol ogical developmental data. The microzones of haemorrhage were complica ted by degenerative changes in adjacent neurones and activation of put ative microglial cells while other surrounding regions of developing c ortex showed no signs of destructive alterations. This indicates that these zones are not simply the result of the termination procedure. Mi croglia associated with these haemorrhagic microzones showed increased vacuolization, phagocytic activity and abundant phagosomes. Although the cause of the microzones of haemorrhage is unknown, these observati ons ave of interest since they are the first demonstration of possible activation of microglia in such an early stage of human development. This finding suggests that the presence of microhaemorrhage and associ ated neuronal death may provide an inducible stimulus of microglial ce lls during early brain development, even before programmed neuronal de ath occurs.