A major objective of the overall research program is to elucidate the basis of neurocognitive aging in behaviorally characterized healthy aged rats. The Animal Resource Core (Core B) is an essential component of the research program in its study of neurocognitive aging to provide young and aged rats to each of the Projects. The overall research program further exploits the feature of individual differences in neurocognitive aging, a phenomenon that is well-documented in humans and captured in the animal model used in this research. The many years of work with this outbred model of male Long Evans have established that a subpopulation at older ages exhibit impaired performance while other rats in the aged cohort maintain preserved performance on a par with young adults. These well-characterized individual differences have been used successfully to examine neurobiological variations in the medial temporal lobe that are closely coupled to cognitive outcomes. Core B under this application will add female Long Evans rats to the resource for studies of individual differences with sex considered as a biological variable in accordance with NIH guidelines. The Animal Resource (Core B) maintains the colony of pathogen-free Long-Evans rats, which are additionally screened for disability and physiological impairment. Under a standardized protocol reproductive status is obtained for all female rats and maintained in the data archive. All rats in the Animal Resource undergo assessment of cognitive function in a standardized protocol for “place” and “cue” learning in a water maze apparatus. The Animal Resource together with the Data Management (Core C) provides routine analysis of these results to characterize presence/severity of impairment. The Animal Resource compiles records on animal health, inventory, and analysis of the behavioral assessments, all in an archived form maintained by Core C (Data Management and Statistics). Animals from the resource are then made available to the Projects for further studies including any Project- specific procedures assigned to Core B, with assignments under the supervision of the Administrative Core (Core A). In many instances live animals are transferred from the Resource to projects for further in vivo analysis (i.e., electrophysiological recording, additional behavioral assessment) or to provide fresh tissue as needed for in vitro studies. In addition to providing rodent material for current projects, Core B also banks tissue specimens (dissected brain regions, peripheral organ tissues, blood samples) to be used at a later date by project investigators or outside scientists. Specimens from both male and female rats will be provided for comparison to STARRRs (NOT-AG-19-017) as described in the narrative. The resource sharing activity is managed and coordinated by the Administrative Core (Core A).