Microgyria can be induced in otherwise normal rat neocortex by a freezing injury to the cortical plate before the completion of neuronal migration. We had previously reported radial glial like-immunoreactive fibers in the area of the microgyria in 32-day-old rats. Here we demonstrate that these glial fibers, which are immunoreactive to Rat-401, vimentin, and glial fibrillary acidic protein (GFAP) antibodies, are seen in adult rats. The appearance of these fibers is hypothesized to result from the release of a trophic factor during the recovery from neonatal injury which acts to either (1) halt the transformation of radial glia to astrocytes and/or dedifferentiate already committed astrocytes, (2) create a hybrid cell, or (3) induce increased proliferation of glia.