Stress, norepinephrine and depression

Experimental and clinical evidence implicates stress as a major predisposing factor in depression and other severe psychiatric disorders. In this review, evidence is presented to show how the impact of stress on the central sympathetic system leads to changes in the endocrine, immune and neurotransmitter axes which underlie the main clinical symptoms of depression. Thus it can be shown that the noradrenergic system is dysfunctional in depression, a situation which reflects the chronic hypersecretion of glucocorticoids and inflammatory mediators within the brain in addition to an enhanced activity of the locus ceruleus. With regard to the actions of antidepressants in modulating the stress response and alleviating depression it is now evident that, irrespective of the presumed specificity of the antidepressants for the noradrenergic or serotonergic systems, they all normalize noradrenergic function. This action is due partly to the regulation of tyrosine hydroxylase activity in the locus ceruleus but also enhances neuronal sprouting which counteracts the neurodegenerative effects of chronic stress.