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      The chronic mild stress (CMS) model of depression: History, evaluation and usage

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          Abstract

          Now 30 years old, the chronic mild stress (CMS) model of depression has been used in >1300 published studies, with a year-on-year increase rising to >200 papers in 2015. Data from a survey of users show that while a variety of names are in use (chronic mild/unpredictable/varied stress), these describe essentially the same procedure. This paper provides an update on the validity and reliability of the CMS model, and reviews recent data on the neurobiological basis of CMS effects and the mechanisms of antidepressant action: the volume of this research may be unique in providing a comprehensive account of antidepressant action within a single model. Also discussed is the use of CMS in drug discovery, with particular reference to hippocampal and extra-hippocampal targets. The high translational potential of the CMS model means that the neurobiological mechanisms described may be of particular relevance to human depression and mechanisms of clinical antidepressant action.

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          Antidepressant effects of ketamine in depressed patients.

          A growing body of preclinical research suggests that brain glutamate systems may be involved in the pathophysiology of major depression and the mechanism of action of antidepressants. This is the first placebo-controlled, double-blinded trial to assess the treatment effects of a single dose of an N-methyl-D-aspartate (NMDA) receptor antagonist in patients with depression. Seven subjects with major depression completed 2 test days that involved intravenous treatment with ketamine hydrochloride (.5 mg/kg) or saline solutions under randomized, double-blind conditions. Subjects with depression evidenced significant improvement in depressive symptoms within 72 hours after ketamine but not placebo infusion (i.e., mean 25-item Hamilton Depression Rating Scale scores decreased by 14 +/- SD 10 points vs. 0 +/- 12 points, respectively during active and sham treatment). These results suggest a potential role for NMDA receptor-modulating drugs in the treatment of depression.
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            Glutamate N-methyl-D-aspartate receptor antagonists rapidly reverse behavioral and synaptic deficits caused by chronic stress exposure.

            Despite widely reported clinical and preclinical studies of rapid antidepressant actions of glutamate N-methyl-D-aspartate (NMDA) receptor antagonists, there has been very little work examining the effects of these drugs in stress models of depression that require chronic administration of antidepressants or the molecular mechanisms that could account for the rapid responses. We used a rat 21-day chronic unpredictable stress (CUS) model to test the rapid actions of NMDA receptor antagonists on depressant-like behavior, neurochemistry, and spine density and synaptic function of prefrontal cortex neurons. The results demonstrate that acute treatment with the noncompetitive NMDA channel blocker ketamine or the selective NMDA receptor 2B antagonist Ro 25-6981 rapidly ameliorates CUS-induced anhedonic and anxiogenic behaviors. We also found that CUS exposure decreases the expression levels of synaptic proteins and spine number and the frequency/amplitude of synaptic currents (excitatory postsynaptic currents) in layer V pyramidal neurons in the prefrontal cortex and that these deficits are rapidly reversed by ketamine. Blockade of the mammalian target of rapamycin protein synthesis cascade abolishes both the behavioral and biochemical effects of ketamine. The results indicate that the structural and functional deficits resulting from long-term stress exposure, which could contribute to the pathophysiology of depression, are rapidly reversed by NMDA receptor antagonists in a mammalian target of rapamycin dependent manner. Copyright © 2011 Society of Biological Psychiatry. Published by Elsevier Inc. All rights reserved.
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              Dopamine neurons modulate neural encoding and expression of depression-related behaviour.

              Major depression is characterized by diverse debilitating symptoms that include hopelessness and anhedonia. Dopamine neurons involved in reward and motivation are among many neural populations that have been hypothesized to be relevant, and certain antidepressant treatments, including medications and brain stimulation therapies, can influence the complex dopamine system. Until now it has not been possible to test this hypothesis directly, even in animal models, as existing therapeutic interventions are unable to specifically target dopamine neurons. Here we investigated directly the causal contributions of defined dopamine neurons to multidimensional depression-like phenotypes induced by chronic mild stress, by integrating behavioural, pharmacological, optogenetic and electrophysiological methods in freely moving rodents. We found that bidirectional control (inhibition or excitation) of specified midbrain dopamine neurons immediately and bidirectionally modulates (induces or relieves) multiple independent depression symptoms caused by chronic stress. By probing the circuit implementation of these effects, we observed that optogenetic recruitment of these dopamine neurons potently alters the neural encoding of depression-related behaviours in the downstream nucleus accumbens of freely moving rodents, suggesting that processes affecting depression symptoms may involve alterations in the neural encoding of action in limbic circuitry.
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                Author and article information

                Contributors
                Journal
                Neurobiol Stress
                Neurobiol Stress
                Neurobiology of Stress
                Elsevier
                2352-2895
                24 August 2016
                February 2017
                24 August 2016
                : 6
                : 78-93
                Affiliations
                [1]Dept. of Psychology, Swansea University, Swansea, SA2 8PP, UK
                Article
                S2352-2895(16)30017-0
                10.1016/j.ynstr.2016.08.002
                5314424
                28229111
                844e9812-6101-406b-9858-179f9809d6a2
                © 2016 The Author

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                History
                : 3 June 2016
                : 19 August 2016
                : 20 August 2016
                Categories
                Article

                depression,chronic mild stress,validity,reliability,neurobiology of stress,antidepressant,hippocampus,prefrontal cortex

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