MECHANISM OF ACTIONS OF ANTIDEPRESSANTS: BEYOND THE RECEPTORS

Since the discovery of first antidepressants-monoamine oxidase inhibitors- a half century passed. There are now almost twodozen antidepressant agents that work by nine distinct pharmacological mechanisms at the receptor level. However, opposite to the divergence in their pharmacological mechanisms at the receptor level, antidepressant drugs probably stimulate similar pathways in subcellular level. These subcellular events or so called beyond receptor effects are named neuroplasticity, and the mechanism may be called as adaptation. These after-receptor processes, through their effects on synaptic transmission, and gene expression are indeed capable of altering many molecular events in the brain. In this article, the mechanisms of actions of antidepressants at- and beyond- the receptors are discussed by documenting some of the evidence indicating such long-term alterations. Accordingly, the well-known effects of antidepressants on the receptor level are initiating events of antidepressant drug action, which enhance and prolong the actions of norepinephrine and/or serotonin and/or dopamine. Only if an adequate dose of an antidepressant is taken chronically, the increase in the synaptic norepinephrine and/or serotonin and/or dopamine stresses or perturbs the nervous system and the therapeutic response results from the adaptations that occur as a consequence of these chronic perturbations.