Capability for reactive gliosis develops prenatally in the diencephalon but not in the cortex of rats

In this study, the glial reactions to stab wounds were investigated on a large population of newborn (PO) and fetal rats, by the immunohistochemical staining of the glial fibrillary acidic protein. The lesions penetrated both the cortex and the diencephalon. The fetuses were lesioned in utero from the 17th embryonic day (E17) and mere born on E22 or E23 in the natural way. In the cortex usually no reactive gliosis developed although definitive tissue destructions remained after the lesion. Weak and incomplete glial reactions were observed in a few cases of E20 or P0 lesions only. In the diencephalon, however, the same stabbings provoked massive glial reactions. The timing and the morphology of this reaction were similar to those found in adult animals. At E17 the lesion did not result in reactive gliosis even in the diencephalon. Our study highlights two phenomena: (i) depending on the brain area severe glial reactions can already follow fetal lesions, and (ii) the appearance of the capability for glial reactions may be a stage of the local tissue maturation in every brain area and cannot be considered as a function of brain development in general. Probably, the capability for glial reactions can take place only when certain histogenetic processes (e.g., cell migration, axon growth, apoptosis) have been at least mostly accomplished, but which of the local development events are the determining ones remains to be investigated. (C) 1997 Academic Press.