Age-Related Changes in Sympathetic-Adrenal Medullary Function: Relationship toAge-Related Deficits in Learning and Memory

摘要

This dissertation examined the contribution of age-related changes in sympathetic-adrenal medullary (SAM) functioning to age-related deficits in cognitive processes. Two experiments involved parametric studies within a stimulus class to characterize more fully age-related differences in plasma catecholamine (CA) responses to acute stress. Results from the footshock experiment revealed that aged male F-344 rats have potentiated plasma CA responses to handling and transfer during placement in an inhibitory (passive) avoidance testing apparatus. Aged rats may exhibit decrements in retention because the saliency of low intensity footshock is masked by the effects of handling and transfer immediately before and after the training experience. Aged rats had potentiated plasma CA responses and delayed returns to basal levels compared to young adults to higher footshock intensities. Aged rats displayed altered SAM responsiveness to swim stress in a temperature-dependent manner. Aged rats exhibited comparable SAM responsiveness to swim stress at 35 deg C. Similar peak responsiveness for rats of both ages was also found at 20 deg C; however, aged animals exhibited a prolonged recovery to basal values. At intermediate temperatures, aged animals had both potentiated peak plasma EPI responses and a prolonged recovery to basal values.