The long-range goal of this project is to conduct systematic studies on the effects of housing enrichment and common husbandry and experimental procedures on the normal cardiovascular and endocrine physiology of rats using state-of-the-art methodologies. It is anticipated that the results will greatly assist Institutional Animal Care and Use Committees in their determination of what procedures can or cannot be conducted in rodent housing areas and whether or not enrichment of the housing environment significantly reduces stress in rodents. The specific aims are: (1) To evaluate several levels of enrichment of the housing environment on distress (or lack of distress) in rats and (2) To evaluate the level of distress in animals undergoing common husbandry or experimental procedures or "witnessing" these procedures being done on other animals. These studies will be conducted on 3-, 6- or 12-month old male and female rats of four commonly used outbred strains obtained from commercial vendors. Animals will be "instrumented" with a radio-telemetry transmitter to continuously monitor arterial blood pressures and heart rate or with a chronic, indwelling venous catheter to obtain sequential blood samples for the determination of plasma levels of stress related hormones (catecholamines, corticosterone and prolactin). Additional variables (weight gain, food and water consumption and estrous cyclicity) will also be monitored to gauge the physiologic status of the rats. The housing conditions to be evaluated are: isolated (single) housing, paired (double) housing, isolated housing with "chew" and "climbing/hiding" "toys" and isolated housing with access to a very enriched environment for a short period each day. Adaptation to the environmental housing conditions will also be evaluated. Common husbandry and experimental manipulations to which animals are to be exposed or witness being done on other animals will include: removal to a new cage, hand restraint and a s.c. injection, placement in a rodent restrainer for a short period with a tail vein injection, witnessing the decapitation of other animals and witnessing a tissue harvest from other animals. Although this project is a descriptive one and not hypothesis driven, it should provide very practical and important results that can be used by local IACUCs as they review animal protocols and by national organizations such as the PHS, AAALAC, ILAR and USDA as they promulgate requirements, guidelines and regulations in this area.