Inner and outer SVZ in the developing rat cortex.

<p>(<b>a, c, e</b>) Nissl-stained sections of somatosensory or visual cortex from the E18 rat. (<b>b, d, e</b>) Higher magnification images taken from the sections shown in (<b>a</b>), (<b>c</b>) and (<b>e</b>). The inner fiber layer and outer fiber layer are not apparent in any cortical areas of rat cortex. At late stages of rat cortical development, such as E18 or E21, the boundary between the inner subventricular zone (iSVZ) and outer SVZ (oSVZ) can be discriminated based on differences in cell density. At E17 and younger ages Tbr2 immunostaining is required to visualize the location of dense inner band of Tbr2+ cells to localize the iSVZ and oSVZ. The oSVZ is characterized by a stippled or striated appearance created by oblique and tangential clusters of cells that appear to stream across the oSVZ. At E21, the oSVZ has expanded compared to earlier stages of cortical development. Dotted line indicates the upper boundary of the oSVZ. AC, anterior commissure; IC, internal capsule; VZ, ventricular zone; CP, cortical plate. Scale bar below (<b>f</b>) applies to (<b>b, d, f</b>).