Figure 4.

Strong staining of PV started to appear at P13 in layer 4 somatosensory cortex. A, Three consecutive thalamocortical sections stained with cytochrome oxidase (CO), PV, or CB antibody at various stages of the development. The PV-positive cells first appeared in lower layer 4 at P9–P10. In contrast, heavily labeled CB-immunoreactive nonpyramidal cells are found even at P4 in all cortical layers but then dramatically decreased in number around the second postnatal week. Arabic numerals denote cortical layers. Squares show higher-magnification view. B, Histogram showing the density of PV+ (black bars) and CB+ (gray bars) cells in the BDNF(+/+) mice at different postnatal ages constructed from immunohistological staining of these chemical markers as shown in A.