Photomicrographs of AR immunoreactivity in the AVPV (left) and MPN (right) of young and middle-aged rats are shown. Rats were perfused at the completion of the two post-tests, 17 days after castration and hormone (testosterone or vehicle) treatment. Representative sections are shown for the AVPV and MPN, respectively, of young-T (A, E), young-V (B, F), middle-aged-T (C, G) and middle-aged-V (D, H) male rats. The contours of the AVPV or MPN are drawn based on Nissl staining and according to Swanson's rat brain atlas (1998). Scale bar = 200 μm. Abbreviations: MA, middle-aged; T, testosterone; V, vehicle; 3V, third ventricle.