The experimental model used to study effects of age, timing, and duration of hormone treatment is shown. OVX surgery, and vehicle (VEH) or E2 capsule implantation were performed at age 4–5 and 11–12 months. Groups 1–6 included MAT and AG rats given VEH or E2 for 3 or 6 months. Groups 7 and 8 involved switching the hormone treatment given to AG rats 3 months after the OVX time point and allowing rats to age for another 3 months. Age effects were compared in groups 1–4 (2 variables, age and hormone). Duration of hormone effect was compared in groups 3–6 (2 variables, hormone and 3 or 6 months of duration). Effects of timing of hormone treatment were compared in groups 5–8.