Distribution and Morphological Features of Microglia in the Developing Cerebral Cortex of Gyrencephalic Mammals

Microglia have been attracting much attention because of their fundamental importance in both the mature brain and the developing brain. Though important roles of microglia in the developing cerebral cortex of mice have been uncovered, their distribution and roles in the developing cerebral cortex in gyrencephalic higher mammals have remained elusive. Here we examined the distribution and morphology of microglia in the developing cerebral cortex of gyrencephalic carnivore ferrets. We found that a number of microglia were accumulated in the germinal zones (GZs), especially in the outer subventricular zone (OSVZ), which is a GZ found in higher mammals. Furthermore, we uncovered that microglia extended their processes tangentially along inner fiber layer (IFL)-like fibers in the developing ferret cortex. The OSVZ and the IFL are the prominent features of the cerebral cortex of higher mammals. Our findings indicate that microglia may play important roles in the OSVZ and the IFL in the developing cerebral cortex of higher mammals.