The Rodent Core performs ovariectomies, castrations and determines the stage of the estrus cycle in rats and mice. The Rodent Core will also manage hormone replacement regiments by daily injections, sialastic implants or implantation of pellets containing vehicle or sex steroids. These animal surgeries and treatments will be performed in various animal models including aging models (e.g., the F344 Fischer rat) and disease models (e.g., the diabetic rat). The Core will facilitate CSD investigator studies on sex differences by performing the surgeries, treatments and maintaining the animals. For example, the diabetic rat may require frequent insulin injections, which will be managed by the Core. By performing the surgeries and animal care components of CSD investigator projects, the Rodent Core will facilitate investigations into the ways sex differences alter physiological states and pathophysiological conditions. In addition, the Core will also maintain a database and coordinate members who use identical animal models but study different tissues so animals can be shared. Blood will also be drawn under appropriate conditions and sent to the Hormone Assay Core to determine sex steroid levels in these animals.