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The role of serotonin in human behaviour is informed by approaches which allow in vivo modification of synaptic serotonin. However, characterising the effects of increased serotonin signalling in human models of behaviour is challenging given the limitations of available experimental probes, notably selective serotonin reuptake inhibitors. Here we use a now-accessible approach to directly increase synaptic serotonin in humans (a selective serotonin releasing agent) and examine its influence on domains of behaviour historically considered core functions of serotonin. Computational techniques, including reinforcement learning and drift diffusion modelling, explain participant behaviour at baseline and after week-long intervention. Reinforcement learning models reveal that increasing synaptic serotonin reduces sensitivity for outcomes in aversive contexts. Furthermore, increasing synaptic serotonin enhances behavioural inhibition, and shifts bias towards impulse control during exposure to aversive emotional probes. These effects are seen in the context of overall improvements in memory for neutral verbal information. Our findings highlight the direct effects of increasing synaptic serotonin on human behaviour, underlining its role in guiding decision-making within aversive and more neutral contexts, and offering implications for longstanding theories of central serotonin function. Serotonin is involved in aversive processing, but how serotonin shapes behavior remains unclear. Here, the authors show that directly enhancing synaptic serotonin in humans reduces outcome sensitivity and increases behavioral inhibition in aversive contexts. [ABSTRACT FROM AUTHOR]

Clinical depression is a common, debilitating and heterogenous disorder. Existing treatments for depression are inadequate for a significant minority of patients and new approaches are urgently needed. A wealth of evidence implicates the serotonin 1A (5-HT1A) receptor in the pathophysiology of depression. Stimulation of the 5-HT1A receptor is an existing therapeutic target for treating depression and anxiety, using drugs such as buspirone and tandospirone. However, activation of 5-HT1A raphe autoreceptors has also been suggested to be responsible for the delay in the therapeutic action of conventional antidepressants such as selective serotonin reuptake inhibitors (SSRIs). This narrative review provides a brief overview of the 5-HT1A receptor, the evidence implicating it in depression and in the effects of conventional antidepressant treatment. We highlight that pre- and post-synaptic 5-HT1A receptors may have divergent roles in the pathophysiology and treatment of depression. To date, developing this understanding to progress therapeutic discovery has been limited, partly due to a paucity of specific pharmacological probes suitable for use in humans. The development of 5-HT1A 'biased agonism', using compounds such as NLX-101, offers the opportunity to further elucidate the roles of pre- and post-synaptic 5-HT1A receptors. We describe how experimental medicine approaches can be helpful in profiling the effects of 5-HT1A receptor modulation on the different clinical domains of depression, and outline some potential neurocognitive models that could be used to test the effects of 5-HT1A biased agonists. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tips.2008.05.004 Byline: Philip J. Cowen Abstract: The notion that impaired serotonin (5-HT) function can lead to clinical depression has a long history but is still controversial. Some have argued that the 5-HT hypothesis has been misused by the pharmaceutical industry to promote a simplistic biological model of depression to market selective serotonin reuptake inhibitors (SSRIs) to medical practitioners and the public. By contrast, there is now substantial evidence that unmedicated depressed patients have abnormalities in brain 5-HT function; however, the relation of these abnormalities to the clinical syndrome is unclear. The best evidence that 5-HT contributes to the pathophysiology of depression comes from studies of tryptophan depletion, which show that lowering brain 5-HT levels can induce acute symptomatic relapse in recovered depressed patients. Clarification of the mechanism of this effect will enable an understanding of how impaired 5-HT activity contributes to the subjective experience of depression. Author Affiliation: Neurosciences Building, Warneford Hospital, Old Road, Headington, Oxford OX3 7JX, UK

Animal experimental studies suggest that 5-HT4 receptor activation holds promise as a novel target for the treatment of depression and cognitive impairment. 5-HT4 receptors are post-synaptic receptors that are located in striatal and limbic areas known to be involved in cognition and mood. Consistent with this, 5-HT4 receptor agonists produce rapid antidepressant effects in a number of animal models of depression, and pro-cognitive effects in tasks of learning and memory. These effects are accompanied by molecular changes, such as the increased expression of neuroplasticity-related proteins that are typical of clinically useful antidepressant drugs. Intriguingly, these antidepressant-like effects have a fast onset of their action, raising the possibility that 5-HT4 receptor agonists may be a particularly useful augmentation strategy in the early stages of SSRI treatment. Until recently, the translation of these effects to humans has been challenging. Here, we review the evidence from animal studies that the 5-HT4 receptor is a promising target for the treatment of depression and cognitive disorders, and outline a potential pathway for the efficient and cost-effective translation of these effects into humans and, ultimately, to the clinic. [ABSTRACT FROM AUTHOR]

Controversy continues with regard to antidepressants and withdrawal. Recent debates have focused on the prevalence and length of withdrawal, and some continue to state that withdrawal from these compounds constitutes 'addiction'. In this editorial we examine the evidence underlying these recent debates. We acknowledge gaps in knowledge, and make suggestions for how the field can progress. [ABSTRACT FROM AUTHOR]

Background Identification of biomarkers predicting therapeutic outcome of antidepressant treatment is one of the most important tasks in current research because it may transform the lengthy process of finding the right treatment for a given individual with depression. In the current study, we explored the potential of pretreatment pregenual anterior cingulate cortex activity as a putative biomarker of treatment response. Methods Thirty-two medication-free patients with depression were treated for 6 weeks with a selective serotonin reuptake inhibitor, escitalopram. Before treatment began, patients underwent an fMRI scan testing response to brief, masked, presentations of facial expression depicting sadness and happiness. Results After 6 weeks of treatment, there were 20 selective serotonin reuptake inhibitor responders and 12 nonresponders. Increased pretreatment pregenual anterior cingulate cortex activity to sad vs happy faces was observed in responders relative to nonresponders. A leave-one-out analysis suggested that activity in the anterior cingulate cortex was able to predict response status at the level of the individual participant. Conclusions The study supports the notion of pregenual anterior cingulate cortex as a promising predictor of antidepressant response. [ABSTRACT FROM AUTHOR]

Persistent major depression that does not respond to adequate first- or second-line treatment is a common problem in psychiatry. This article updates evidence on recommended treatment strategies and reviews the prospects of more experimental approaches. The main pharmacological development in recent years has been the demonstration that several atypical antipsychotic drugs are effective adjunctive agents in improving symptoms in depression unresponsive to selective serotonin reuptake inhibitors, although their adverse effect burden is high. There is optimism about novel pharmacological strategies based on glutamatergic and anti-inflammatory mechanisms. It is important to combine drug and psychological treatments whenever possible. With persistent therapeutic engagement, the majority of patients remit eventually, but subsequent relapse remains a problem. Clinicians should pursue an active and collaborative treatment plan that makes use of all effective therapeutic modalities and continues into the relapse-prevention phase. LEARNING OBJECTIVES • Be aware of the concept of treatment-resistant depression as a staged condition and of the limitations of this concept • Update knowledge of the efficacy of recommended treatments for resistant depression, including new pharmacological and brain stimulation approaches • Be aware of the need for persistent therapeutic engagement and time-limited treatment trials to achieve remission and prevent relapse DECLARATION OF INTEREST P.J.C. has been a member of a Lundbeck advisory board. I.M.A. has been a member of advisory boards to Lundbeck, Servier and Alkermes. [ABSTRACT FROM AUTHOR]

A number of concerns have been raised about the possible future use of pharmaceuticals designed to enhance cognitive, affective, and motivational processes, particularly where the aim is to produce morally better decisions or behavior. In this article, we draw attention to what is arguably a more worrying possibility: that pharmaceuticals currently in widespread therapeutic use are already having unintended effects on these processes, and thus on moral decision making and morally significant behavior. We review current evidence on the moral effects of three widely used drugs or drug types: (i) propranolol, (ii) selective serotonin reuptake inhibitors, and (iii) drugs that effect oxytocin physiology. This evidence suggests that the alterations to moral decision making and behavior caused by these agents may have important and difficult-to-evaluate consequences, at least at the population level. We argue that the moral effects of these and other widely used pharmaceuticals warrant further empirical research and ethical analysis. [ABSTRACT FROM AUTHOR]

The fact that selective serotonin reuptake inhibitors (SSRIs) have antidepressant effects in some patients supports the notion that serotonin plays a role in the mode of action of antidepressant drugs. However, neither the way in which serotonin may alleviate depressed mood nor the reason why several weeks needs to elapse before the full antidepressant effect of treatment is expressed is known. Here, we propose a neuropsychological theory of SSRI antidepressant action based on the ability of SSRIs to produce positive biases in the processing of emotional information. Both behavioural and neuroimaging studies show that SSRI administration produces positive biases in attention, appraisal and memory from the earliest stages of treatment, well before the time that clinical improvement in mood becomes apparent. We suggest that the delay in the clinical effect of SSRIs can be explained by the time needed for this positive bias in implicit emotional processing to become apparent at a subjective, conscious level. This process is likely to involve the re-learning of emotional associations in a new, more positive emotional environment. This suggests intriguing links between the effect of SSRIs to promote synaptic plasticity and neurogenesis, and their ability to remediate negative emotional biases in depressed patients. [ABSTRACT FROM AUTHOR]

Background: Antidepressant prescribing is widespread. Nonetheless, response to antidepressants is variable. If it was possible to predict response to medication and thus tailor treatment accordingly, this would not only improve patient outcomes but may also have economic benefits.Aims: To test the hypothesis that individuals with more severe depression would benefit more from noradrenaline reuptake inhibitors (NARIs) than selective serotonin reuptake inhibitors (SSRIs) compared with individuals with less severe depression.Method: Individuals recruited from UK primary care who met ICD-10 criteria for a depressive episode and scored 15 or more on the Beck Depression Inventory (BDI) were randomised to either an SSRI (citalopram 20 mg daily) or a NARI (reboxetine 4 mg twice daily). Randomisation was by means of a remote automated telephone system. The main outcome was depressive symptoms measured by the BDI total score 6 weeks after randomisation. (Trial Registration: ISRCTN31345163.)Results: In total, 601 participants were randomised (citalopram: n = 298, reboxetine: n = 303). Ninety-one per cent were followed up at 6 weeks (citalopram: n = 274, reboxetine: n = 272). There was little evidence to support an interaction between treatment and severity of depression (interaction term: 0.02, 95% CI -0.59 to 0.62, P = 0.96). Adjustment for potential confounders (age, gender, employment status, history of depression, number of life events and social support) did not affect the findings (interaction term: 0.06, 95% CI -0.54 to 0.66, P = 0.85).Conclusions: Treatment with NARIs does not confer any advantage over SSRI treatment for outcome in those with more severe depressive illness presenting in primary care. [ABSTRACT FROM AUTHOR]

Background: Selective serotonin reuptake inhibitors (SSRIs) are typically thought to have a delay of several weeks in the onset of their clinical effects. However, recent reports suggest they may have a much earlier therapeutic onset. A reduction in amygdala responsivity has been implicated in the therapeutic action of SSRIs.Aims: To investigate the effect of a single dose of an SSRI on the amygdala response to emotional faces.Method: Twenty-six healthy volunteers were randomised to receive a single oral dose of citalopram (20 mg) or placebo. Effects on the processing of facial expressions were assessed 3 h later using functional magnetic resonance imaging.Results: Volunteers treated with citalopram displayed a significantly reduced amygdala response to fearful facial expressions compared with placebo.Conclusions: Such an immediate effect of an SSRI on amygdala responses to threat supports the idea that antidepressants have an earlier onset of therapeutically relevant effects than conventionally thought. [ABSTRACT FROM AUTHOR]

Objective: The authors used magnetic resonance spectroscopy (MRS) to assess the effect of acute administration of the selective serotonin reuptake inhibitor (SSRI) citalopram on cortical levels of γ-aminobutyric acid (GABA). Method: Ten healthy volunteers received either intravenous citalopram (10 mg) or saline in a randomized, double-blind, crossover design. The occipital GABA/creatine ratio was measured with a proton MR spectral editing technique. Results: In comparison with saline, citalopram produced a mean increase of 35% in relative brain GABA concentration in the occipital cortex. Conclusions: These findings extend previous work showing that SSRI treatment increases cortical GABA in depressed patients and suggest that this results from an action of SSRIs on GABA neurons rather than as a secondary consequence of mood improvement. [ABSTRACT FROM AUTHOR]

A letter to the editor is presented in response to the article "Serotonin and Depression," by D. Healy in the April 21, 2015 issue.

Background: Selective serotonin reuptake inhibitors (SSRIs) are popular medications for anxiety and depression, but their effectiveness, particularly in patients with prominent symptoms of loss of motivation and pleasure, has been questioned. There are few studies of the effect of SSRIs on neural reward mechanisms in humans. Methods: We studied 45 healthy participants who were randomly allocated to receive the SSRI citalopram, the noradrenaline reuptake inhibitor reboxetine, or placebo for 7 days in a double-blind, parallel group design. We used functional magnetic resonance imaging to measure the neural response to rewarding (sight and/or flavor of chocolate) and aversive stimuli (sight of moldy strawberries and/or an unpleasant strawberry taste) on the final day of drug treatment. Results: Citalopram reduced activation to the chocolate stimuli in the ventral striatum and the ventral medial/orbitofrontal cortex. In contrast, reboxetine did not suppress ventral striatal activity and in fact increased neural responses within medial orbitofrontal cortex to reward. Citalopram also decreased neural responses to the aversive stimuli conditions in key “punishment” areas such as the lateral orbitofrontal cortex. Reboxetine produced a similar, although weaker effect. Conclusions: Our findings are the first to show that treatment with SSRIs can diminish the neural processing of both rewarding and aversive stimuli. The ability of SSRIs to decrease neural responses to reward might underlie the questioned efficacy of SSRIs in depressive conditions characterized by decreased motivation and anhedonia and could also account for the experience of emotional blunting described by some patients during SSRI treatment. [Copyright &y& Elsevier]

The timely selection of the optimal treatment for depressed patients is critical to improve remission rates. The detection of pre-treatment variables able to predict differential treatment response may provide novel approaches for treatment selection. Selective serotonin reuptake inhibitors (SSRIs) modulate the fronto-limbic functional response and connectivity, an effect preceding the overt clinical antidepressant effects. Here we investigated whether the cortico-limbic connectivity associated with emotional bias measured before SSRI administration predicts the efficacy of antidepressant treatment in MDD patients. fMRI and Dynamic Causal Modeling (DCM) were combined to study if effective connectivity might differentiate healthy controls (HC) and patients affected by major depression who later responded (RMDD, n =21), or failed to respond (nRMDD, n =12), to 6 weeks of escitalopram administration. Sixteen DCMs exploring connectivity between anterior cingulate cortex (ACC), ventrolateral prefrontal cortex (VLPFC), Amygdala (Amy), and fusiform gyrus (FG) were constructed. Analyses revealed that nRMDD had reduced endogenous connectivity from Amy to VLPFC and to ACC, with an increased connectivity and modulation of the ACC to Amy connectivity when processing of fearful emotional stimuli compared to HC. RMDD and HC did not significantly differ among themselves. Pre-treatment effective connectivity in fronto-limbic circuitry could be an important factor affecting antidepressant response, and highlight the mechanisms which may be involved in recovery from depression. These results suggest that fronto-limbic connectivity might provide a neural biomarker to predict the clinical outcome to SSRIs administration in major depression. [ABSTRACT FROM AUTHOR]

Background: The amygdala is believed to play a key role in processing emotionally salient, threat-relevant, events that require further online processing by cortical regions. Emotional disorders such as depression and anxiety have been associated with hyperactivity of the amygdala, but it is unknown whether antidepressant treatment directly affects amygdala responses to emotionally significant information. Methods: The current study assessed the effects of 7 days administration of the selective serotonin reuptake inhibitor (SSRI), citalopram, on amygdala responses to masked presentations of fearful and happy facial expressions in never-depressed volunteers using blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging. A double-blind, between-groups design was used with volunteers randomized to 20 mg/day citalopram versus placebo. Results: Volunteers receiving citalopram showed decreased amygdala responses to masked presentations of threat compared with those receiving placebo. Citalopram also reduced responses within the hippocampus and medial prefrontal cortex (mPFC) specifically during the fear-relevant stimuli. These neural differences were accompanied by decreased recognition of fearful facial expressions assessed after the scan. By contrast, there was no effect of citalopram on the neural or behavioral response to the happy facial expressions. Conclusions: These results suggest a direct effect of serotonin potentiation on amygdala response to threat-relevant stimuli in humans. Such effects may be important in the therapeutic actions of antidepressants in depression and anxiety. [Copyright &y& Elsevier]