Responding for brain stimulation: stress and desmethylimipramine.

Stressors influence the activity of biogenic amines and provoke a variety of behavioral disturbances which have been considered as models of human depression. To evaluate the effects of stressors on reward processes, responding for electrical brain stimulation was assessed after acute or chronic shock, and the modification of performance by desmethylimipramine was determined. While escapable shock did not affect performance, inescapable shock reduced responding from the nucleus accumbens and medial forebrain bundle, but not from the substantia nigra. These deficits were were antagonized by repeated stressor application or by desmethylimipramine. Uncontrollable stressors may influence motivational processes subserved by some brain regions, and may thus influence affective state. Chronic stress or desmethylimipramine may induce adaptive neurochemical changes, thereby preventing the behavioral disturbances otherwise produced by stressors.