Materials and Methods

Eighty female rats were employed in groups of ten that were placed individually into activity cages with a 4" x 4" x 10" living space and a wire wheel 4" in width and 30'in circumference attached to the side. The rats were initially placed in the cages as weanlings, and only those showing high daily activity were used in hormone experiments. At TO ROdays of age, experimental animals were ovariectomized. At approximately 90-95 days of age, most of the animals received bilateral intracerebral implants of stainless steel tubing containing different ratios of estrogen (estradiol benzoate, EB) to cholesterol (Ch). The implants were aimed at various hypothalamic loci. Vaginal smears were taken at various times throughout the study to check for systemic spread of estrogen from the implants. The diameter of the uterus and the weights of the adrenal glands were recorded at autopsy.