Multisystem Regulation of Performance Deficits Induced by Stressors: An Animal Model of Depression

When an organism is exposed to a stressor, a series of behavioral changes occur that are thought to be of adaptive value. Among other things, the response style of an organism will narrow to those innate responses highest in the animal’s defensive repertoire (see belles, 1970) or to responses previously acquired in aversive situations. In addition, several neurochemical changes occur that may blunt the physical or psychological impact of the stressor, increase arousal or vigilance, or increase the animal’s ability to initiate and sustain defensive responses (see reviews in Zacharko and Anisman, 1989; Maier and Seligman, 1976; Weiss and Simson, 1985). However, there maybe occasions where these responses may have adverse consequences. For instance, when the response required to escape from the stressor is not part of the organism’s repertoire, the persistent adoption of these response styles may be counterproductive. Likewise, excessive utilization may reduce neurotransmitter stores, rendering the animal less able to deal with environmental demands. It has been our contention that many of the behavioral and physiological disturbances associated with acute and chronic uncontrollable stressors stem from the failure of adaptive neurochemical mechanisms. This chapter will outline some of the biochemical and behavioral consequences of stressors, particularly as they relate to an animal model of depression.