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      Novel rapid-acting antidepressants: molecular and cellular signaling mechanisms

      review-article
      ,
      Neuronal Signaling
      Portland Press Ltd.
      AMPAR, GABAR, Major Depressive Disorder, mGluR, neural circuits

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          Abstract

          Depression is a chronic, debilitating, and common illness. Currently available pharmacotherapies can be helpful but have several major drawbacks, including substantial rates of low or no response and a long therapeutic time lag. In pursuit of better treatment options, recent research has focussed on rapid-acting antidepressants, including the N-methyl- d-aspartate (NMDA) receptor (NMDAR) antagonist ketamine, which affects a range of signaling pathways in ways that are distinct from the mechanisms of typical antidepressants. Because ketamine and similar drugs hold the promise of dramatically improving treatment options for depressed patients, there has been considerable interest in developing new ways to understand how these compounds affect the brain. Here, we review the current understanding of how rapid-acting antidepressants function, including their effects on neuronal signaling pathways and neural circuits, and the research techniques being used to address these questions.

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          Most cited references53

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          NMDA Receptor Blockade at Rest Triggers Rapid Behavioural Antidepressant Responses

          Clinical studies consistently demonstrate that a single sub-psychomimetic dose of ketamine, an ionotropic glutamatergic n-methyl-d-aspartate receptor (NMDAR) antagonist, produces fast-acting antidepressant responses in patients suffering from major depressive disorder (MDD), although the underlying mechanism is unclear 1-3 . Depressed patients report alleviation of MDD symptoms within two hours of a single low-dose intravenous infusion of ketamine with effects lasting up to two weeks 1-3 , unlike traditional antidepressants (i.e. serotonin reuptake inhibitors), which take weeks to reach efficacy. This delay is a major drawback to current MDD therapies, leaving a need for faster acting antidepressants particularly for suicide-risk patients 3 . Ketamine's ability to produce rapidly acting, long-lasting antidepressant responses in depressed patients provides a unique opportunity to investigate underlying cellular mechanisms. We show that ketamine and other NMDAR antagonists produce fast-acting behavioural antidepressant-like effects in mouse models that depend on rapid synthesis of brain-derived neurotrophic factor (BDNF). We find that ketamine-mediated NMDAR blockade at rest deactivates eukaryotic elongation factor 2 (eEF2) kinase (also called CaMKIII) resulting in reduced eEF2 phosphorylation and desuppression of BDNF translation. Furthermore, we find inhibitors of eEF2 kinase induce fast-acting behavioural antidepressant-like effects. Our findings suggest that protein synthesis regulation by spontaneous neurotransmission may serve as a viable therapeutic target for fast-acting antidepressant development.
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            NMDAR inhibition-independent antidepressant actions of ketamine metabolites

            Major depressive disorder afflicts ~16 percent of the world population at some point in their lives. Despite a number of available monoaminergic-based antidepressants, most patients require many weeks, if not months, to respond to these treatments, and many patients never attain sustained remission of their symptoms. The non-competitive glutamatergic N-methyl-D-aspartate receptor (NMDAR) antagonist, (R,S)-ketamine (ketamine), exerts rapid and sustained antidepressant effects following a single dose in depressed patients. Here we show that the metabolism of ketamine to (2S,6S;2R,6R)-hydroxynorketamine (HNK) is essential for its antidepressant effects, and that the (2R,6R)-HNK enantiomer exerts behavioural, electroencephalographic, electrophysiological and cellular antidepressant actions in vivo. Notably, we demonstrate that these antidepressant actions are NMDAR inhibition-independent but they involve early and sustained α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor activation. We also establish that (2R,6R)-HNK lacks ketamine-related side-effects. Our results indicate a novel mechanism underlying ketamine’s unique antidepressant properties, which involves the required activity of a distinct metabolite and is independent of NMDAR inhibition. These findings have relevance for the development of next generation, rapid-acting antidepressants.
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              Synaptic plasticity and depression: new insights from stress and rapid-acting antidepressants.

              Depression is a common, devastating illness. Current pharmacotherapies help many patients, but high rates of a partial response or no response, and the delayed onset of the effects of antidepressant therapies, leave many patients inadequately treated. However, new insights into the neurobiology of stress and human mood disorders have shed light on mechanisms underlying the vulnerability of individuals to depression and have pointed to novel antidepressants. Environmental events and other risk factors contribute to depression through converging molecular and cellular mechanisms that disrupt neuronal function and morphology, resulting in dysfunction of the circuitry that is essential for mood regulation and cognitive function. Although current antidepressants, such as serotonin-reuptake inhibitors, produce subtle changes that take effect in weeks or months, it has recently been shown that treatment with new agents results in an improvement in mood ratings within hours of dosing patients who are resistant to typical antidepressants. Within a similar time scale, these new agents have also been shown to reverse the synaptic deficits caused by stress.
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                Author and article information

                Journal
                ppneurosig
                NS
                Neuronal Signal.
                Neuronal Signaling
                Neuronal Signal.
                Portland Press Ltd.
                2059-6553
                17 August 2017
                05 September 2017
                22 December 2017
                : 1
                : 4
                : NS20170010
                Affiliations
                Department of Psychiatry, Yale University, New Haven, CT 06508, U.S.A.
                Author notes
                Correspondence: Ronald S. Duman ( ronald.duman@ 123456yale.edu )
                Article
                10.1042/NS20170010
                6051536
                30034823
                486ea81a-1345-462e-ae87-608d5a71e61c
                © 2017 The Author(s).

                This is an open access article published by Portland Press Limited on behalf of the Biochemical Society and distributed under the Creative Commons Attribution License 4.0 (CC BY).

                History
                : 30 May 2017
                : 14 August 2017
                : 17 August 2017
                Page count
                Pages: 10
                Categories
                Review Articles
                Review Article
                47

                Neurology,Molecular medicine,Molecular biology,Neurosciences
                AMPAR,neural circuits,mGluR,GABAR,Major Depressive Disorder

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