Estradiol did not induce neuroprogesterone synthesis in reproductively senescent, 9 month old Long-Evans female rats exhibiting continuous cornified vaginal smears) for 30 days (indicating they were in constant estrous (CE)). CE rats were ovx/adx and subsequently subcutaneously injected with estradiol (50 µg EB) or the safflower oil vehicle. Brain tissue was examined for neuroprogesterone 45 hr after EB. Unlike young animals, estradiol treatment had no effect on hypothalamic, progesterone levels (2 way ANOVA (2,23), F = 2.237, p = 0.15) or serum levels (t-test df = 6, t = 1.34, p = 0.23 (Fig 4).Values are means ± SEM of at least 9 animals per group. Abbreviations: CRB: cerebellum; HYPO: hypothalamus; CTX: cortex.