CHRONIC STRESS AND SYMPATHETIC RESPONSES

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In this proposal, I have outlined a program of research which focuses on homeostatic regulation of the sympathetic nervous system of laboratory rats during chronic exposure to stressful stimulation. The stress concept was first introduced by Hans Selye nearly 50 years ago. In spite of extensive research on the stress responses of animals and humans over the years, there remains a glaring absence of a soundly developed and widely accepted theoretical framework for this field of research. In this proposal, several experiments are described which will clarify the underlying adaptive responses of the sympathetic nervous system to acute versus chronic exposure to stressful stimulation. In the first experiment, adult male laboratory rats will be stressed 30 minutes per day for 0, 1, 7, 14, or 28 consecutive days in one of the following conditions: immobilization (IM), exposure to intermittent, inescapable footshock (FS), or immersion in 18 degrees C water (CI). To control for the element of predictability, another group of rats will be exposed randomly to 1 of the 3 stressors for 7, 14, or 28 consecutive days. Plasma levels of norepinephrine and epinephrine will be measured in blood samples taken before, during, and after stressful stimulation as an index of sympathetic-adrenal medullary activity. In addition, the effects of these stress regimens on catecholamine biosynthetic enzyme activities and catecholamine content of several sympathetically innervated tissues will be quantified. In a second series of "Cross-over" experiments, rats will be stressed chronically in one condition and then acutely in another (i.e. chronic IM-acute FS; chronic FS-acute CI; chronic CI-acute IM) to examine the sympathetic responsiveness of a chronically stressed animal to a novel stressor. The results of this research will provide an extensive empirical base for refining and extending the conceptualization of stress. In addition, it will serve as a foundation for directing the research efforts of my laboratory toward the study of central neuronal adaptations to stressful stimulation in laboratory animals. These findings will be of direct relevance to several stress-related disorders in humans, including peptic ulcer disease, hypertension, depression and coronary artery disease.