The program project is aimed at understanding how diets high in fat lead to increased levels of defended body weight. To do so, requires exploring a single model of dietary obesity from a number of perspective. The Animal/Physiology Core will centralize the production of obese rats and their various control groups for each of the specific projects. This core will generate EVERY animal that will be used in each of the specific projects and thereby assure that each experiment will come form animals that have been treated in an identical manner. There are four primary goals for this core. 1) To generate animals for the individual project in the five dietary groups that are described in detain in the introductory section to the proposal. These groups include rats on a low-fat semi-purified diet (LF), rats on a matched high-fat semi purified diet (HF), rats receiving the HF diet but with calories matched (pair-fed) to intake of the LF rats (PF- HF), rats receiving the LF diet and food-restricted by the same amount as the HF pair fed rats (PF-LF), and rats with pelleted chow (CHOW). 2) To develop rat surgical techniques as required by each of the individual projects. 3) To carry out carcass analysis for body lipid content on subjects from each of the individual projects. 3) To carry out carcass analysis for body lipid content on subjects from each of the individual projects. The Animal/Physiology Core personnel have already carried out all of the experiments to date that characterize the model and consequently the personnel are already well-trained and the protocols are all in place to efficient accomplish the goals of this essential core.