The several weeks latency in onset of the therapeutic actions of antidepressants contributes to distress and clinical risk for those with severe depression. In the search for treatments of more rapid onset, great effort has gone into trying to understand the delay in efficacy of current antidepressants. All current ideas posit that antidepressant-induced increases in synaptic monoamine concentrations cause slowly accumulating adaptive changes in target neurons. Two broad classes of theories have emerged: (1) Changes in protein phosphorylation, gene expression, and protein translation occur in target neurons that ultimately alter synaptic structure or function in a way that relieves symptoms; and (2) antidepressant-induced neurogenesis in the hippocampus and the incorporation of those new neurons into functional circuits is a required step in the therapeutic response. Before considering specific hypotheses, however, it is important to discuss obstacles in relating research in animal models to human depression."}},"i":0}}]}" id="mwEjY">Malenka RC, Nestler EJ, Hyman SE (2009). "Chapter 14:Neuropharmacology of Neural Systems and Disorders". In Sydor A, Brown RY (eds.). Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nded.). New York: McGraw-Hill Medical. pp.355–360. ISBN978-0-07-148127-4. Pharmacologic observations such as these led to a simple hypothesis: depression is the result of inadequate monoamine neurotransmission, and clinically effective antidepressants work by increasing the availability of monoamines. Yet this hypothesis has failed to explain the observation that weeks of treatment with antidepressants are required before clinical efficacy becomes apparent, despite the fact that the inhibitory actions of these agents—whether in relation to reuptake or monoamine oxidase—are immediate. This delay in therapeutic effect eventually led investigators to theorize that long-term adaptations in brain function, rather than increases in synaptic norepinephrine and serotonin per se, most likely underlie the therapeutic effects of antidepressant drugs. Consequently, the focus of research on antidepressants has shifted from the study of their immediate effects to the investigation of effects that develop more slowly. The anatomic focus of research on antidepressants also has shifted. Although monoamine synapses are believed to be the immediate targets of antidepressant drugs, more attention is given to the target neurons of monoamines, where chronic alterations in monoaminergic inputs caused by antidepressant drugs presumably lead to long-lasting adaptations that underlie effective treatment of depression. The identification of molecular and cellular adaptations that occur in response to antidepressants, and the location of the cells and circuits in which they occur, are the chief goals that guide current research. The work described toward the beginning of the chapter on mood-regulating circuits that involve the subgenual cingulate gyrus, for instance, represent a significant advance over a narrow focus on monoamine neuron function.... The several weeks latency in onset of the therapeutic actions of antidepressants contributes to distress and clinical risk for those with severe depression. In the search for treatments of more rapid onset, great effort has gone into trying to understand the delay in efficacy of current antidepressants. All current ideas posit that antidepressant-induced increases in synaptic monoamine concentrations cause slowly accumulating adaptive changes in target neurons. Two broad classes of theories have emerged: (1) Changes in protein phosphorylation, gene expression, and protein translation occur in target neurons that ultimately alter synaptic structure or function in a way that relieves symptoms; and (2) antidepressant-induced neurogenesis in the hippocampus and the incorporation of those new neurons into functional circuits is a required step in the therapeutic response. Before considering specific hypotheses, however, it is important to discuss obstacles in relating research in animal models to human depression.
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