The objective of the present research plan is to determine how advancing age, and the transition from a healthy aged state to senescence, alters central neural mechanisms regulating SND under basal conditions and in response to acute physical stress. These findings will exert a sustained and powerful influence on the field by establishing new frontiers relating the effect of advancing age on mechanisms regulating the SNS, and by providing insight and direction for determining relationships between chronic disease development and age-associated changes in SNS function.