[Stressor controllability and brain noradrenaline turnover in rats]

A series of experiments examined the effects of a purely psychological factor in a stressful situation (i.e., the ability to manage a stressor or inability to do so) on noradrenergic metabolism in regional rat brains. In Experiment 1, uncontrollable rats which could not escape and avoid electric shock developed more gastric ulceration than did controllable rats which had exactly the same shock but could exert control over the shock. In Experiment 2, the uncontrollable rats displayed sustained increases in noradrenaline (NA) turnover in various brain regions regardless of stress durations. After the controllable rats had firmly mastered the coping response, excess NA utilization at the earlier stage of stress was reduced in many brain regions. These findings suggested that noradrenergic neuronal activity in some specific brain regions, such as the hypothalamus and limbic areas, might be involved in the coping processes under a stressful situation. This hypothesis was supported by the results of Experiment 3 showing that the effects of stressor controllability on regional brain NA turnover were covaried with the complexity of coping task required. Taken together, it is concluded that the degree of behavioral control (the ability to alter the termination or duration) that an organism has over a stressor modulates the physiological and neurochemical impact of that stressor, and that brain NA is implicated in the learning process where an organism copes with a stressor.