Intracellular mechanisms of antidepressant drug action.

The action of antidepressant drugs on monoamines such as norepinephrine and serotonin has been described for three decades. However, more-recent research has looked beyond cell surface receptors to transductional cascades and gene expression. Antidepressant drug therapies seem to share several mechanisms involved in either activating the adenylyl cyclase-protein kinase A cascade or inhibiting the phospholipase C-protein kinase C mechanisms. These effects, ultimately, combine to regulate the expression of target genes. Several specific genes are known to be activated or inhibited by antidepressant therapies. Steady-state levels of mRNA for glucocorticoid and mineralocorticoid receptors, brain-derived neurotrophic factor and its receptor trkB, and preproenkephalin are enhanced, whereas those for corticotropin-releasing hormone, c-fos,N-methyl-D-aspartate receptor subunits, and nerve-growth factor 1A are reduced. New molecular genetic methods for identifying differentially expressed genes will aid in the development of targets for wholly new generations of antidepressant drug therapies.