Serotonin-related pathways and developmental plasticity: relevance for psychiatric disorders

Risk for adult psychiatric disorders is partially determined by early-life alterations occurring during neural circuit formation and maturation. In this perspective, recent data show that the serotonin system regulates key cellular processes involved in the construction of cortical circuits. Translational data for rodents indicate that early-life serotonin dysregulation leads to a wide range of behavioral alterations, ranging from stress-related phenotypes to social deficits. Studies in humans have revealed that serotonin-related genetic variants interact with early-life stress to regulate stress-induced cortisol responsiveness and activate the neural circuits involved in mood and anxiety disorders. Emerging data demonstrate that early-life adversity induces epigenetic modifications in serotonin-related genes. Finally, recent findings reveal that selective serotonin reuptake inhibitors can reinstate juvenile-like forms of neural plasticity, thus allowing the erasure of long-lasting fear memories. These approaches are providing new insights on the biological mechanisms and clinical application of antidepressants.     

Pharmacogenomics in depression and antidepressants

Genetic factors are believed to play a major role in the variation of treatment response and the incidence of adverse effects to medication. The aim of pharmacogenetics is to elucidate this variability according to hereditary differences. Considering current hypotheses for the mechanisms of action of antidepressants, most investigations to date have concentrated on mutations in genes coding either for the pathways in the serotonergic and noradrenergic systems or for drug-metabolizing enzymes. Recent studies shifted the emphasis on the main mechanism of drug action from changes in neurotransmitter concentration or receptor function toward long-lasting adaptive processes within the neurons. Although the results are controversial, many studies support the hypothesis that psychopharmacogenetics will help predict an individual's drug response, while minimizing the side effects. The inclusion of functional genomics, which investigates the complex gene and/or protein expression in response to a given drug, may lead to the development of novel and safer drugs.     

Towards achieving remission in the treatment of depression

The burden of depressive illness constitutes a major public health issue. Despite real progress and better tolerance of new antidepressant medications, a significant number of depressed patients still suffer from rather severe residual depressive symptoms.This relative lack of efficacy clearly interferes with their psychosocial functioning and their quality of life. In addition, it is now well-recognized that the failure to reach full clinical remission after antidepressant treatment involves a high risk of relapse or recurrence in patients suffering from major depression. This paper reviews the concept of remission across different definitions, and the potential risk factors associated with the failure to reach clinical remission. The identification of specific residual symptoms in nonremitted patients is also of great importance, in order to assess the predictive value of those symptoms in relation to relapse and recurrence. Some methodological issues are also discussed, as well as various therapeutic strategies aimed at relieving residual depressive symptoms. Clinical remission remains a qold standard and a primary objective of modem antidepressant therapy.     

Treatment of depression in late life

This paper updates the 1996 review of treatment approaches published in the Am J Geriatr Psychiatry (1996;4[suppl 1]:S51-S65 [see ref33]) and a chapter in A Guide to Treatments that Work (Nathan PE, Gorman JM, eds), Oxford University Press, New York, 1998 [see ref 54]:. The major focus is on psychophannacoiogy with attention also to the évidence for the efficacy of psychotherapeutic and somatic approaches.     

Antidepressant chronotherapeutics for bipolar depression

Chronotherapeutics refers to treatments based on the principles of circadian rhythm organization and sleep physiology, which control the exposure to environmental stimuli that act on biological rhythms, in order to achieve therapeutic effects in the treatment of psychiatric conditions. It includes manipulations of the sleep-wake cycle such as sleep deprivation and sleep phase advance, and controlled exposure to light and dark. The antidepressant effects of chronotherapeutics are evident in difficult-to-treat conditions such as bipolar depression, which has been associated with extremely low success rates of antidepressant drugs in naturalistic settings and with stable antidepressant response to chronotherapeutics in more than half of the patients. Recent advances in the study of the effects of chronotherapeutics on neurotransmitter systems, and on the biological clock machinery, allow us to pinpoint its mechanism of action and to transform it from a neglected or “orphan” treatment to a powerful clinical instrument in everyday psychiatric practice.     

Structural plasticity of the adult brain: how animal models help us understand brain changes in depression and systemic disorders related to depression

The brain interprets experiences and translates them into behavioral and physiological responses. Stressful events are those which are threatening or, at the very least, unexpected and surprising, and the physiological and behavioral responses are intended to promote adaptation via a process called "allostasis. " Chemical mediators of allostasis include cortisol and adrenalin from the adrenal glands, other hormones, and neurotransmitters, the parasympathetic and sympathetic nervous systems, and cytokines and chemokines from the immune system. Two brain structures, the amygdala and hippocampus, play key roles in interpreting what is stressful and determining appropriate responses. The hippocampus, a key structure for memories of events and contexts, expresses receptors that enable it to respond to glucocorticoid hormones in the blood, it undergoes atrophy in a number of psychiatric disorders; it also responds to stressors with changes in excitability, decreased dendritic branching, and reduction in number of neurons in the dentate gyrus. The amygdala, which is important for "emotional memories, " becomes hyperactive in posttraumatic stress disorder and depressive illness, in animal models of stress, there is evidence for growth and hypertrophy of nerve cells in the amygdala. Changes in the brain after acute and chronic stressors mirror the pattern seen in the metabolic, cardiovascular, and immune systems, that is, short-term adaptation (allostasis) followed by long-term damage (allostatic load), eg, atherosclerosis, fat deposition obesity, bone demineralization, and impaired immune function. Allostatic load of this kind is seen in major depressive illness and may also be expressed in other chronic anxiety and mood disorders.     

Traumatic stress: effects on the brain

Brain areas implicated in the stress response include the amygdala, hippocampus, and prefrontal cortex. Traumatic stress can be associated with lasting changes in these brain areas. Traumatic stress is associated with increased cortisol and norepinephrine responses to subsequent stressors. Antidepressants have effects on the hippocampus that counteract the effects of stress. Findings from animal studies have been extended to patients with post-traumatic stress disorder (PTSD) showing smaller hippocampal and anterior cingulate volumes, increased amygdala function, and decreased medial prefrontal/anterior cingulate function. In addition, patients with PTSD show increased cortisol and norepinephrine responses to stress. Treatments that are efficacious for PTSD show a promotion of neurogenesis in animal studies, as well as promotion of memory and increased hippocampal volume in PTSD.     

Optimizing the treatment of mood disorders in the perinatal period

The perinatal period is a time of high risk for women with unipolar and bipolar mood disorders. We discuss treatment considerations for perinatal mood disorders, including unipolar and bipolar depression as well as postpartum psychosis. We further explore the unique issues faced by women and their families across the full trajectory of the perinatal period from preconception planning through pregnancy and following childbirth. Treatment of perinatal mood disorders requires a collaborative care approach between obstetrics practitioners and mental health providers, to ensure that a thoughtful risk : benefit analysis is conducted. It is vital to consider the risks of the underlying illness versus risks of medication exposure during pregnancy or lactation. When considering medication treatment, attention must be paid to prior medication trials that were most efficacious and best tolerated. Lastly, it is important to assess the impact of individual psychosocial stressors and lifestyle factors on treatment response.     

Dose-response relationship of recent antidepressants in the short-term treatment of depression

Antidepressant drugs are widely recommended for the treatment of depressive disorders, and finding the "right dose for the right patient" is an important issue. Whatever antidepressant is prescribed, a proportion of adult patients with major depression fail to respond satisfactorily to adequate first-line treatment. A frequent strategy for patients with insufficient response to an initial antidepressant dose is to increase the dose. This review is about this strategy, ie, the possible benefits of prescribing higher doses of recent antidepressants. The results show that a flat dose-response curve is a class phenomenon for selective serotonin reuptake inhibitors (SSRIs), according to randomized, controlled, fixed-dose clinical trials. For the serotonin and noradrenaline reuptake inhibitors (SNRIs), the strategy of dose increase may be relevant for venlafaxine, in order to increase the number of responders. Thus, the subgroup of patients for whom high doses of SSRIs could be useful remains to be defined.     

Pathophysiology of depression and mechanisms of treatment

Major depression is a serious disorder of enormous sociological and clinical relevance. The discovery of antidepressant drugs in the 1950s led to the first biochemical hypothesis of depression, which suggested that an impairment in central monoaminergic function was the major lesion underlying the disorder. Basic research in all fields of neuroscience (including genetics) and the discovery of new antidepressant drugs have revolutionized our understanding of the mechanisms underlying depression and drug action. There is no doubt that the monoaminergic system is one of the cornerstones of these mechanisms, but multiple interactions with other brain systems and the regulation of central nervous system function must also be taken into account In spite of all the progress achieved so far, we must be aware that many open questions remain to be resolved in the future.     

Challenges in the diagnosis and treatment of pediatric bipolar depression

There has been great public and academic interest in the diagnosis and treatment of bipolar disorders (BD) in children and adolescents over the past decade, originally in the US, but now extending internationally. Much of the interest in pediatric BD has focused on the unique manifestation of mania in younger populations. Depression is often overlooked, both as a topic, and as a clinical reality, in these children. While it is becoming clear that adults with BD spend the majority of their symptomatic time in depressive rather than manic episodes, less is known about the pediatric experience of bipolar depression. However, children and adolescents with BD clearly do experience significant depressive symptoms as well as depressive episodes, and therefore early recognition and treatment is necessary. This review addresses what is known about the prevalence, presentation, and treatment of depressive symptoms and episodes in youth with BD, and includes a discussion about the recognition and treatment of bipolar depressive episodes that occur before the first manic episode.     

Light treatment of mood disorders

In 1981, seven patients with nonseasonal depression were treated with bright white light in 1982, bright artificial light was used to treat a manic-depressive patient with a seasonal mood cycle. In the last 20 years, a plethora of studies have further defined the depressive populations, who are responsive to light treatment; the optimal timing, intensity, spectral frequency, and duration of treatment; its comparison with other pharmacological interventions; predictors of response; side-effect profiles; viable placebo-control conditions; alternative devices and forms of administration; potential mechanisms and anatomical pathways mediating light's physiological effects; and its application to other disorders and subsyndromaI states. These studies have been conducted across multiple countries with surprisingly consistent results. Further work is needed, as highlighted in this review, to clarify the specific mechanism of action in subtypes of depressive disorders and differential age and gender effects. Although the majority of work in this area is relatively new, it behooves the reader to remember that Solomon, almost 3000 years ago, wrote in Ecclesiastes: "Truly the light is sweet and a pleasant thing it is for the eyes to behold the sun" (11:7).     

Epigenetic alterations in depression and antidepressant treatment

Epigenetic modifications control chromatin structure and function, and thus mediate changes in gene expression, ultimately influencing protein levels. Recent research indicates that environmental events can induce epigenetic changes and, by this, contribute to long-term changes in neural circuits and endocrine systems associated with altered risk for stress-related psychiatric disorders such as major depression. In this review, we describe recent approaches investigating epigenetic modifications associated with altered risk for major depression or response to antidepressant drugs, both on the candidate gene levels as well as the genome-wide level. In this review we focus on DNA methylation, as this is the most investigated epigenetic change in depression research.     

Cellular abnormalities in depression: evidence from postmortem brain tissue

During the past two decades, in vivo neuroimaging studies have permitted significant insights into the general location of dysfunctional brain regions in depression. In parallel and often intersecting ways, neuroanatomical, pharmacological, and biochemical studies of postmortem brain tissue are permitting new insights into the pathophysiology of depression. In addition to long-recognized neurochemical abnormalities in depression, novel studies at the microscopic level support the contention that mood disorders are associated with abnormalities in cell morphology and distribution. In the past 6 years, cell-counting studies have identified changes in the density and size of both neurons and glia in a number of frontolimbic brain regions, including dorsolateral prefrontal, orbitofrontal, and anterior cingulate cortex, and the amygdala and hippocampus. Convergence of cellular changes at the microscopic level with neuroimaging changes detected in vivo provides a compelling integration of clinical and basic research for disentangling the pathophysiology of depression. The ultimate integration of these two research approaches will occur with premortem longitudinal clinical studies on well-characterized patients linked to postmortem studies of the same subjects.     

Challenges in the development of clinical trials for major depressive disorder: lessons learned from trials in minor depression

This paper reviews some of the challenges faced by individuals who design and implement clinical trials of potential antidepressant medications. Particular emphasis is placed on questioning the validity of some of the theoretical assumptions that form the underpinnings of most conventional trials. Work from our group developing clinical trial methodology for minor depression is used as an example of how alternate constructs may be helpful to differentiate drug-placebo differences.     

Cognitive neuroscience and brain imaging in bipolar disorder

Bipolar disorder is characterized by a combination of state-related changes in psychological function that are restricted to illness episodes, coupled with trait-related changes that persist through periods of remission, irrespective of symptom status. This article reviews studies that have investigated the brain systems involved in these state- and trait-related changes, using two techniques: (i) indirect measures of neurocognitive function, and (ii) direct neuroimaging measures of brain function during performance of a cognitive task. Studies of neurocognitive function in bipolar disorder indicate deficits in three core domains: attention, executive function, and emotional processing. Functional imaging studies implicate pathophysiology in distributed neural circuitry that includes the prefrontal and anterior cingulate cortices, as well as subcortical limbic structures including the amygdala and the ventral striatum. Whilst there have been clear advances in our understanding of brain changes in bipolar disorder, there are limited data in bipolar depression, and there is limited understanding of the influence of clinical variables including medication status, illness severity, and specific symptom dimensions.     

Increased DNA methylation in the suicide brain

Clinical studies find that childhood adversity and stress-ful life events in adulthood increase the risk for major depression and for suicide. The predispositions to either major depression or suicide are thought to depend on genetic risk factors or epigenetic effects. We investigated DNA methylation signatures postmortem in brains of suicides with diagnosis of major depressive disorder. DNA methylation levels were determined at single C-phosphate-G (CpG) resolution sites within ventral prefrontal cortex of 53 suicides and nonpsychiatric controls, aged 16 to 89 years. We found that DNA methylation increases throughout the lifespan. Suicides showed an 8-fold greater number of methylated CpG sites relative to controls (P<2.2x10-16), with greater DNA methylation changes over and above the increased methylation observed in normal aging. This increased DNA methylation may be a significant contributor to the neuropathology and psychopathology underlying the risk of suicide in depression.     

Behavioral control, the medial prefrontal cortex, and resilience

The degree of control that an organism has over a stressor potently modulates the impact of the stressor, with uncontrollable stressors producing a constellation of outcomes that do not occur if the stressor is behaviorally controllable. It has generally been assumed that this occurs because uncontrollability actively potentiates the effects of stressors. Here it will be suggested that in addition, or instead, the presence of control actively inhibits the impact of stressors. At least in part, this occurs because (i) the presence of control is detected by regions of the ventral medial prefrontal cortex (mPFCv); and (ii) detection of control activates mPFCv output to stress-responsive brain stem and limbic structures that actively inhibit stress-induced activation of these structures. Furthermore, an initial experience with control over stress alters the mPFCv response to subsequent stressors so that mPFCv output is activated even if the subsequent stressor is uncontrollable, thereby making the organism resilient. The general implications of these results for understanding resilience in the face of adversity are discussed.     

Psychopharmacology of anxiety disorders

Exposure of the general population to a 1:4 lifetime risk of disabling anxiety has inspired generations of fundamental and clinical psychopharmacologists, from the era of the earliest benzodiazepines (BZ) to that of the selective serotonin reuptake inhibitors (SSRIs) and related compounds, eg, the serotonin and norepinephrine reuptake inhibitors (SNRIs). This comprehensive practical review summarizes current therapeutic research across the spectrum of individual disorders: generalized anxiety disorder (GAD), panic disorder (PD) and agoraphobia (social anxiety disorder), compulsive disorder (OCD), phobic disorder (including social phobia), and posttraumatic stress disorder (PTSD). Specific diagnosis is a precondition to successful therapy: despite substantial overlap, each disorder responds preferentially to specific pharmacotherapy. Comorbidity with depression is common; hence the success of the SSRIs, which were originally designed to treat depression. Assessment (multidomain measures versus individual end points) remains problematic, as-frequently-do efficacy and tolerability The ideal anxiolytic remains the Holy Grail of worldwide psychopharmacologic research.