The POA is shown at 4× magnification at the level of the AVPV and MePO (panels A, C) and the MPN (panels B, D) of a representative old male rat. Sections shown in A and C were adjacent, as were B and D. Sections were labeled for AR immunoreactivity (top row) or ERα immunoreactivity (bottom row), and counterstained by Nissl labeling. The contours of the AVPV, MePO and MPN are drawn based on Nissl staining and in comparison to Swanson's rat brain atlas (1998). [Note that during the actual stereological analysis, contours were drawn according to the Nissl staining which is out of focus in the figure.] Scale bar = 500 μm.