Neural plasticity to stress and antidepressant treatment

Preclinical models: status of basic research in depression

Approximately one half-century ago several classes of medications, discovered by serendipity, were introduced for the treatment of depression and bipolar disorder. These highly effective medications revolutionized our approach to mood disorders and helped launch the modern era of psychiatry. Yet our progress since those serendipitous discoveries has been disappointing. We still do not understand with certainty how those medications produce their desired clinical effects. We have not introduced newer medications with fundamentally different mechanisms of action than the older agents. We have not identified the genetic and neurobiological mechanisms underlying depression and mania, nor do we understand the mechanisms by which nongenetic factors influence these disorders. We have only a rudimentary understanding of the circuits in the brain responsible for the normal regulation of mood and affect, and of those circuits that function abnormally in mood disorders. In approaching these gaps in our knowledge, this workgroup highlighted four major areas for future investment. These include developing better animal models of mood disorders; identifying genetic determinants of normal and abnormal mood in humans and animals; discovering novel targets and biomarkers of mood disorders and treatments; and increasing the recruitment of investigators from diverse backgrounds to mood disorders research.

Changes in synaptic plasticity in the rat hippocampo-medial prefrontal cortex pathway induced by repeated treatments with fluvoxamine

The present studies were conducted to examine the effects of single and repeated treatments with fluvoxamine, which is a selective serotonin reuptake inhibitor (SSRI), on the synaptic efficacy and synaptic plasticity in the rat hippocampo-medial prefrontal cortex (mPFC) pathway in vivo. It has been reported that the projections arising from the hippocampal structures to the mPFC are involved in the execution of higher cognitive functions in rats. The evoked potentials were recorded in the mPFC by stimulation of the CA1/subicular region of the ventral hippocampus in halothane-anesthetized rats. Single administration of fluvoxamine (10 and 30 mg/kg, i.p.) enhanced synaptic efficacy in the hippocampo-mPFC pathway in a dose-dependent manner. Although repeated treatments with fluvoxamine (30 mg/kg, i.p. after 30 mg/kg/dayx21 days, p.o.) caused an enhancement of synaptic efficacy, there was no significant difference between single and repeated treatments. The input/output characteristics showed hypersensitivity to stimulation intensity in the group with repeated fluvoxamine treatments. The establishment of long-term potentiation (LTP) in the hippocampo-mPFC pathway after a single administration of fluvoxamine was not different from that in the saline-injected group. On the other hand, the hippocampo-mPFC LTP was significantly augmented by repeated treatments with fluvoxamine when compared to a single treatment. These findings suggest that the serotonergic system could modulate the synaptic plasticity at hippocampal-mPFC synapses. The present study, furthermore, suggests that the enhancement of LTP in the hippocampo-mPFC pathway produced by repeated treatments with fluvoxamine may be implicated in the SSRI-induced therapeutic effect on psychiatric disorders.

Delayed pharmacological effects of antidepressants

Although antidepressants may not be primary mood stabilizers, they are efficacious in the prophylaxis of recurrent depressive illnesses, as well as in the treatment of acute episodes. Pharmacological effects that may contribute to the prophylactic effects of these drugs are not understood. Studies have been carried out in which antidepressants have been given to laboratory animals, such as rats, for periods of up to 3-4 weeks. Data obtained in such studies are thought to be important for their beneficial effects in depressive episodes, but also may be relevant to their prophylactic effects. Results are presented showing that when selective inhibitors of serotonin or norepinephrine uptake are given for such time periods, they still produce selective effects on serotonergic or noradrenergic parameters. For example, long-term administration of selective norepinephrine reuptake inhibitors causes a down-regulation of beta(1) adrenoceptors. Selective serotonin reuptake inhibitors do not produce this effect. Long-term administration of selective serotonin reuptake inhibitors causes down-regulation of the serotonin transporter, but not the norepinephrine transporter. In contrast, selective norepinephrine reuptake inhibitors down-regulate the norepinephrine transporter but not the serotonin transporter. Substantial loss of serotonin transporter binding sites takes 15 days to occur and is accompanied by a marked reduction of serotonin transporter function in vivo.

Glutamate and GABA systems as targets for novel antidepressant and mood-stabilizing treatments

Glutamate and gamma-amino butyric acid (GABA) systems are emerging as targets for development of medications for mood disorders. There is increasing preclinical and clinical evidence that antidepressant drugs directly or indirectly reduce N-methyl-D-aspartate glutamate receptor function. Drugs that reduce glutamatergic activity or glutamate receptor-related signal transduction may also have antimanic effects. Recent studies employing magnetic resonance spectroscopy also suggest that unipolar, but not bipolar, depression is associated with reductions in cortical GABA levels. Antidepressant and mood-stabilizing treatments also appear to raise cortical GABA levels and to ameliorate GABA deficits in patients with mood disorders. The preponderance of available evidence suggests that glutamatergic and GABAergic modulation may be an important property of available antidepressant and mood-stabilizing agents. Future research will be needed to develop and evaluate new agents with specific glutamate and GABA receptor targets in the treatment of mood disorders.

Serotonin clearance in vivo is altered to a greater extent by antidepressant-induced downregulation of the serotonin transporter than by acute blockade of this transporter

Serotonin uptake, mediated by the serotonin transporter (SERT), is blocked acutely by antidepressants such as the selective serotonin reuptake inhibitors (SSRIs), but such blockade does not correlate temporally with the onset of therapeutic improvement. Treatment with SSRIs for 21 d induced downregulation of the SERT (Benmansour et al., 1999). The time course of SERT downregulation as well as the time course for its recovery after cessation of treatment with the SSRI sertraline were investigated using tritiated cyanoimipramine to measure SERT binding sites. To determine if there was a temporal correlation between the time when sertraline induced downregulation of the SERT and when marked alteration in SERT function occurred, clearance of locally applied 5-HT into the CA3 region of hippocampus was achieved using in vivo electrochemistry. After 4 or 10 d treatment with sertraline, SERT binding sites decreased very little (15-30%), and the chronoamperometric signals for serotonin in sertraline-treated rats were comparable with ones obtained in control animals. By contrast, after 15 d of treatment, when SERT binding sites were markedly reduced by 80%, there was robust decrease in the clearance of 5-HT. Moreover, the functional consequences of SERT downregulation as measured by chronoamperometry were significantly greater than those seen after acute blockade of the SERT by SSRIs. SERT binding sites decreases are not a consequence of reduced SERT gene expression, as revealed by in situ hybridization measurements. SSRI-induced downregulation of the SERT may be a key component for the clinical response to SSRIs.

Coping with the catch-22s of depression: a guide for educating patients

The author developed a protocol for educating patients about depression that focuses on the obstacles encountered in the course of recovery. These obstacles are construed as "catch-22s," the gist of which is that all the things patients must do to recover from depression are made difficult by virtue of the symptoms of depression. After describing the evolution of the patient education program and providing an overview of the content of the educational curriculum, the author presents the written material that is given as a handout to the patients in the educational group. A guide to the pertinent literature on depression is also included as an appendix.

Social stress in tree shrews: effects on physiology, brain function, and behavior of subordinate individuals

Social stress is known to be involved in the etiology of central nervous disorders such as depression. In recent years, animal models have been developed that use chronic stress to induce neuroendocrine and central nervous changes that might be similar to those occurring in the course of the development of depressive disorders. The present review gives a summary of observations made in the tree shrew chronic social stress model. During periods of daily social stress, male tree shrews develop symptoms that are known from many depressed patients such as persistent hyperactivities of both the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system, disturbances in sleeping patterns, and reduced motor activity. Moreover, various physiological parameters indicate an acceleration of the over all metabolic rate in socially stressed tree shrews. Some of these parameters can be renormalized by antidepressants thus supporting the view of the tree shrew social stress paradigm as model for major depression. In the brains of socially stressed animals, monoamine receptors show dynamic changes that reflect adaptation to the persistent monoaminergic hyperactivity during periods of chronic stress. In addition to the changes in neurotransmitter systems, there are structural changes in neurons, e.g., retraction of the dendrites of hippocampal pyramidal neurons. Together, these processes are suggested as a cause of behavioral alterations that can be counteracted by antidepressants in this naturalistic social stress model.

Morphological brain changes in depression: can antidepressants reverse them?

Structural neuroimaging and postmortem histopathological studies of the brain have revealed morphological changes in cortical and subcortical regions in individuals diagnosed with depression. Moreover, these regions are known to be functionally altered in mood disorders. This indicates that the morphological changes might be directly involved in the pathophysiology of depression, and implies that antidepressants may be able to regulate or reverse the detected structural abnormalities. Work with animal models has shown that antidepressants are capable of inducing structural alterations in dendrites and axons and changes in the numbers of neural cells. However, there have been no studies in the human brain that have directly addressed whether antidepressant treatment can reverse or regulate the depression-related structural changes. Nevertheless, experience with lithium in bipolar disorder and antipsychotics in schizophrenia suggests that treatment with psychotropic drugs can result in structural changes that are consistent with reversion towards normal values. Clearly, ascertaining the role of the reversal of structural changes in the therapeutic actions of antidepressants will require further longitudinal studies and careful comparisons between those patients with mood disorder who are treated with antidepressants and those who are not.

Circuits and systems in stress. I. Preclinical studies

This paper reviews the preclinical literature related to the effects of stress on neurobiological and neuroendocrine systems. Preclinical studies of stress provide a comprehensive model for understanding neurobiological alterations in post-traumatic stress disorder (PTSD). The pathophysiology of stress reflects long-standing changes in biological stress response systems and in systems involved in stress responsivity, learning, and memory. The neural circuitry involved includes systems mediating hypothalamic-pituitary-adrenal (HPA) axis, norepinephrine (locus coeruleus), and benzodiazepine, serotonergic, dopaminergic, neuropeptide, and central amino acid systems. These systems interact with brain structures involved in memory, including hippocampus, amygdala, and prefrontal cortex. Stress responses are of vital importance in living organisms; however excessive and/or repeated stress can lead to long-lasting alterations in these circuits and systems involved in stress responsiveness. Intensity and duration of the stressor, and timing of the stressor in life, have strong impact in this respect.

The Danish PET/depression project: clinical symptoms and cerebral blood flow. A regions-of-interest analysis

OBJECTIVE

We wanted to explore associations between clinical symptoms of depression and the blood flow to specific regions of the brain. Furthermore, we wanted to compare the regions-of-interest (ROI) method with the functions-of-interest (FOI) approach.

METHOD

The resting blood flow to 42 ROI in the brain was obtained with positron emission tomography (PET) imaging in 42 representative in-patients with major depression and 47 matched healthy controls.

RESULTS

The patients had increased blood flow to hippocampus, cerebellum, anterior cingulate gyrus, and the basal ganglia. A strong negative correlation was found between the degree of psychomotor retardation of the patients and the blood flow to the dorsolateral and supraorbital prefrontal cortices. The total Hamilton score was correlated with the blood flow to the hippocampus.

CONCLUSION

Our findings support the notion that depressed patients have disturbances in the loops connecting the frontal lobes, limbic system, basal ganglia, and cerebellum.

An AMPA receptor potentiator modulates hippocampal expression of BDNF: an in vivo study

AMPA receptor activation has been demonstrated to increase the neuronal expression of brain derived neurotrophic factor (BDNF). In the present study, we investigated the effect of a novel AMPA receptor potentiator (LY404187) and its active isomer (LY451646) on the expression of BDNF protein and mRNA, as well as TrkB mRNA in rat hippocampus. LY404187 administered for 7 days (1 mg/kg) significantly increased the number of BDNF immunopositive cells in the dentate gyrus, but not other hippocampal subfields. Chronic treatment (7 days) with LY451646 (0.5 mg/kg, comparable to 1 mg/kg of LY404187) increased the level of both BDNF and TrkB mRNA expression in the dentate gyrus, CA3 and CA4 of the hippocampus. However, chronic treatment with lower doses of LY451646 (0.125 and 0.25 mg/kg) decreased the level of BDNF and TrkB mRNA in hippocampus, whilst the highest used dose of LY451646 (1 mg/kg) had no effect on BDNF and TrkB mRNA in hippocampus. In contrast, acute treatment with LY451646 produced an increase in BDNF mRNA levels at doses of 0.125 and 0.25 mg/kg in the hippocampus (CA4, CA3 and dentate gyrus, but not in CA1). LY451646 at 0.5 mg/kg had no effect, but at 1.0 mg/kg decreased the level of BDNF mRNA in hippocampus. Acute treatment with LY451646 did not affect the TrkB receptor mRNA levels in hippocampus. Our results demonstrate that biarylpropylsulfonamide AMPA receptor potentiators are capable of modulating the expression of BDNF and TrkB mRNA in a dose- and time-dependent manner. The increase in both BDNF protein and mRNA expression in the dentate gyrus but not in CA1 indicates a specific role of AMPA receptors in the regulation of BDNF expression in this hippocampal subfield. The regulation of BDNF expression by biarylpropylsulfonamids such as LY451646 may have important therapeutical implications for this class of molecule in the treatment of depression and other CNS disorders.

Functional genomics and depression research. Beyond the monoamine hypothesis

Although antidepressants have been used clinically for more than 50 years, no consensus has been reached concerning their precise molecular mechanism of action. Functional genomics is a powerful tool that can be used to identify genes affected by antidepressants or by other effective therapeutic manipulations. Using this tool we have previously identified more than 300 cDNA fragments as antidepressant related genes and from these, original cDNA microarrays were developed. Some of these candidate genes may encode common functional molecules induced by chronic antidepressant treatment. Defining the roles of these genes in drug-induced neural plasticity is likely to transform the course of research on the biological basis of depression. Such detailed knowledge will have profound effects on the diagnosis, prevention, and treatment of depression. Novel biological approaches beyond the "monoamine hypothesis" are expected to evoke paradigm shifts in the future of depression research.

Future pharmacotherapy for post-traumatic stress disorder: prevention and treatment

I have presented two complementary lines of speculation in this article. First, I have presented a public health model of resilience, prevention, acute intervention, and tertiary treatment to inform a pharmacotherapeutic strategy for PTSD in the future. Second, I have proposed a rational rather than an empirical approach to the clinical pharmacology of PTSD. Such an approach suggests that efforts be directed toward the development and testing of new classes of drugs designed to target the unique pathophysiology of PTSD.

Cell pathology in bipolar disorder

OBJECTIVES

The objective of this paper is to review findings of morphometric postmortem studies conducted on tissues from subjects with bipolar disorder (BPD) to demonstrate that impairments of cell morphology and resilience may underlie the neurobiology of BPD.

METHODS

Reports of alterations in number, density and size of neurons and glial cells in BPD are reviewed. Owing to the low number of postmortem studies on cellular pathology in BPD, abstracts of recent symposia are also discussed.

RESULTS AND CONCLUSIONS

In BPD. significant reductions in the volume of several brain regions, as well as region- and layer-specific reductions in the number, density and/or size of neurons and glial cells have been demonstrated. Moreover, the results of recent clinical and preclinical studies investigating the molecular and cellular targets of mood stabilizing and antidepressant medications provide intriguing possibilities that impairments in neuroplasticity and cellular resilience may underlie the neurobiology of BPD. Future studies will likely examine the role of both genetic and environmental factors in the pathogenesis and cellular changes in BPD.

Regulation of adult hippocampal neurogenesis - implications for novel theories of major depression

Major depression, whose biological origins have been difficult to grasp for decades, might result from a disturbance in neuronal plasticity. New theories begin to consider a fundamental role of adult hippocampal neurogenesis in this loss of plasticity. Could depression and other mood disorders therefore be 'stem cell disorders'? In this review, the potential role of adult hippocampal neurogenesis and of neuronal stem or progenitor cells in depression is discussed with regard to those aspects that are brought up by recent research on how adult hippocampal neurogenesis is regulated. What is known about this regulation today are mosaic pieces and indicates that regulation is complex and is modulated on several levels. Accordingly, emphasis is here laid on those regulatory feedback mechanisms and interdependencies that could help to explain how the pathogenic progression from a hypothesized disruptive cause can occur and lead to the complex clinical picture in mood disorders. While the 'neurogenic theory' of depression remains highly speculative today, it might stimulate the generation of sophisticated working hypotheses, useful animal experiments and the first step towards new therapeutic approaches.

Adolescent life events as predictors of adult depression

BACKGROUND

Among adults, life events predict future episodes of major depression as well as a range of anxiety disorders. While studies have begun to examine this issue in adolescents, few studies rely upon prospective epidemiological designs to document relationships between adolescent life events and adult major depression.

METHOD

An epidemiologically-selected sample of 776 young people living in Upstate New York received DSM-based psychiatric assessments and an assessment of life events in 1986. Psychopathology was again assessed in 1992. The current study examined the predictive relationship between life events in 1986 and depression as well as anxiety in 1992, controlling for depression/anxiety in 1986.

RESULTS

Adolescent life events predicted an increased risk for major depression diagnosis in adulthood. When analyzed continuously, an association emerged with symptoms of major depression as well as with symptoms of generalized anxiety disorder. However, this association with generalized anxiety disorder was limited to females.

CONCLUSIONS

Life events in adolescence predict risk for major depression during early adulthood.

The effects of antidepressant drug treatments on activator protein-1 binding activity in the rat brain

Since a long-term administration of antidepressant drugs and mood stabilizers is required in the treatment of mood disorders, the regulation of gene expression by these drugs that is mediated by transcription factors, such as activator protein-1 (AP-1) complex, may play an important role in the therapeutic action. In this study, the authors investigated the influence of lithium, antidepressant drugs and stress on AP-1 binding activity in the rat brain. In addition, we examined pretreatment with these drugs on the expression of AP-1 binding activity in response to stress. A gel shift assay was used to measure the levels of AP-1 binding activity. Our results indicate that neither acute nor chronic treatment with antidepressant drugs affects in AP-1 binding activity in the rat frontal cortex or hippocampus. However, the authors found that acute restraint stress for 90 min upregulated the induction of AP-1 binding activity in the rat frontal cortex. In addition, chronic pretreatment with imipramine, but not lithium or paroxetine, downregulated the induction of AP-1 binding activity in response to acute restraint stress in the frontal cortex. The functional classification of antidepressant drugs based on the downregulation of restraint stress-induced AP-1 binding activity may contribute to the advances in our understanding of the pathogenesis of depression.

Physical activity elicits sustained activation of the cyclic AMP response element-binding protein and mitogen-activated protein kinase in the rat hippocampus

To elucidate molecular mechanisms involved in physical activity-induced beneficial effects on brain function, we studied in rats the influence of voluntary running on the activation in the hippocampus of cyclic AMP response element-binding protein (CREB) and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated protein kinase (ERK). These are signaling molecules that play critical roles in synaptic plasticity, including learning and memory. Exercise resulted in an increase in the level of the activated transcription factor, CREB phosphorylated at Ser-133. The amount of the activated transcription factor about doubled already after 1 night of running and remained elevated for at least a week, although control levels were restored after 1 month of exercise. In addition, binding activity in nuclear extracts to cyclic AMP response element (CRE) motif containing oligonucleotides increased significantly in the hippocampus after 3 nights of exercise, although the total amount of the immunochemically identified CREB remained unaltered. Electrophoretic mobility supershift assays indicated that the increased binding was due to the recruitment of members of this transcription factor family, in addition to the CREB proper. Voluntary running also resulted in an increase in the level of phosphorylated MAPK (both p42 and p44). The time-courses of the increases in the level of the phosphorylated protein kinase and the activated transcription factor were different. In comparison with the activated CREB, the increase in the phosphorylated MAPK was delayed, but lasted longer, being detectable even after 1 month of exercise. These observations are consistent with the view that the relatively long-lasting activation of these signaling molecules participates in the regulation of genes, such as the neurotrophin genes, and contributes to the beneficial effects of physical exercise on brain function.

Stress-induced changes in cerebral metabolites, hippocampal volume, and cell proliferation are prevented by antidepressant treatment with tianeptine

Stress-induced structural remodeling in the adult hippocampus, involving debranching and shortening of dendrites and suppression of neurogenesis, provides a cellular basis for understanding the impairment of neural plasticity in the human hippocampus in depressive illness. Accordingly, reversal of structural remodeling may be a desirable goal for antidepressant therapy. The present study investigated the effect of tianeptine, a modified tricyclic antidepressant, in the chronic psychosocial stress model of adult male tree shrews (Tupaia belangeri), a model with high validity for research on the pathophysiology of major depression. Animals were subjected to a 7-day period of psychosocial stress to elicit stress-induced endocrine and central nervous alterations before the onset of daily oral administration of tianeptine (50 mg/kg). The psychosocial stress continued throughout the treatment period of 28 days. Brain metabolite concentrations were determined in vivo by proton magnetic resonance spectroscopy, cell proliferation in the dentate gyrus was quantified by using BrdUrd immunohistochemistry, and hippocampal volume was measured post mortem. Chronic psychosocial stress significantly decreased in vivo concentrations of N-acetyl-aspartate (-13%), creatine and phosphocreatine (-15%), and choline-containing compounds (-13%). The proliferation rate of the granule precursor cells in the dentate gyrus was reduced (-33%). These stress effects were prevented by the simultaneous administration of tianeptine yielding normal values. In stressed animals treated with tianeptine, hippocampal volume increased above the small decrease produced by stress alone. These findings provide a cellular and neurochemical basis for evaluating antidepressant treatments with regard to possible reversal of structural changes in brain that have been reported in depressive disorders.

Antidepressant drug treatments induce glial cell line-derived neurotrophic factor (GDNF) synthesis and release in rat C6 glioblastoma cells

Modulation of neurotrophic factors to protect neurons from damage is proposed as a novel mechanism for the action of antidepressants. However, the effect of antidepressants on modulation of glial cell line-derived neurotrophic factor (GDNF), which has potent and widespread effects, remains unknown. Here, we demonstrated that long-term use of antidepressant treatment significantly increased GDNF mRNA expression and GDNF release in time- and concentration-dependent manners in rat C6 glioblastoma cells. Amitriptyline treatment also increased GDNF mRNA expression in rat astrocytes. GDNF release continued for 24 h following withdrawal of amitriptyline. Furthermore, following treatment with antidepressants belonging to several different classes (amitriptyline, clomipramine, mianserin, fluoxetine and paroxetine) significantly increased GDNF release, but which did not occur after treatment with non-antidepressant psychotropic drugs (haloperidol, diazepam and diphenhydramine). Amitriptyline-induced GDNF release was inhibited by U0126 (10 microM), a mitogen-activated protein kinase (MAPK)-extracellular signal-related kinase (ERK) kinase (MEK) inhibitor, but was not inhibited by H-89 (1 microM), a protein kinase A inhibitor, calphostin C (100 nM), a protein kinase C inhibitor and PD 169316 (10 microM), a p38 mitogen-activated protein kinase inhibitor. These results suggested that amitriptyline-induced GDNF synthesis and release occurred at the transcriptional level, and may be regulated by MEK/MAPK signalling. The enhanced and prolonged induction of GDNF by antidepressants could promote neuronal survival, and protect neurons from the damaging effects of stress. This may contribute to explain therapeutic action of antidepressants and suggest new strategies of pharmacological intervention.

Performance of heterozygous brain-derived neurotrophic factor knockout mice on behavioral analogues of anxiety, nociception, and depression

Evidence suggests that brain-derived neurotrophic factor (BDNF) may be important in the pathophysiology of depression, in addition to its role as a neurotrophic factor for sensory neurons. The authors conducted a series of experiments examining the behavioral profile of BDNF heterozygous knockout and wild-type mice. The heterozygous and wild-type mice did not differ on measures of activity, exploration, or hedonic sensitivity, or in the forced swim test. When assessed in the learned helplessness paradigm, heterozygous mice were slower to escape after training than were wild-type mice (p = .02). This effect may be accounted for by the fact that these mice demonstrate a reduced sensitivity to centrally mediated pain, apparent on the hot plate and Formalin injection tests of nociception. Overall, heterozygous mice were not more likely to display anxious or depressive-like behaviors and, consequently, may not constitute a murine model of genetic vulnerability to mood and anxiety disorders.

Substance P: a new era, a new role

Substance P has been extensively studied and is considered the prototypic neuropeptide of the more than 50 known neuroactive molecules. The understanding of substance P has evolved beyond the original concept as the pain transmitter of the dorsal horn. Animal and genetic research, recent developments of nonpeptide substance P antagonists, and important changes in the understanding of neurotransmission have each contributed to the current understanding of substance P After 7 decades, the physiologic role of substance P is known as a modulator of nociception, involved in signaling the intensity of noxious or aversive stimuli. Genetic studies in mice and development of substance P antagonists provide more recent results that support the redefinition of the central role of substance P Evidence suggests that this neuropeptide is an integral part of central nervous system pathways involved in psychologic stress.

Role of serotonergic and noradrenergic systems in the pathophysiology of depression and anxiety disorders

There is abundant evidence for abnormalities of the norepinephrine (NE) and serotonin (5HT) neurotransmitter systems in depression and anxiety disorders. The majority of evidence supports underactivation of serotonergic function and complex dysregulation of noradrenergic function, most consistent with overactivation of this system. Treatment for these disorders requires perturbation of these systems. Reproducible increases in serotonergic function and decreases in noradrenergic function accompany treatment with antidepressants, and these alterations may be necessary for antidepressant efficacy. Dysregulation of these systems clearly mediates many symptoms of depression and anxiety. The underlying causes of these disorders, however, are less likely to be found within the NE and 5HT systems, per se. Rather their dysfunction is likely due to their role in modulating, and being modulated by, other neurobiologic systems that together mediate the symptoms of affective illness. Clarification of noradrenergic and serotonergic modulation of various brain regions may yield a greater understanding of specific symptomatology, as well as the underlying circuitry involved in euthymic and abnormal mood and anxiety states. Disrupted cortical regulation may mediate impaired concentration and memory, together with uncontrollable worry. Hypothalamic abnormalities likely contribute to altered appetite, libido, and autonomic symptoms. Thalamic and brainstem dysregulation contributes to altered sleep and arousal states. Finally, abnormal modulation of cortical-hippocampal-amygdala pathways may contribute to chronically hypersensitive stress and fear responses, possibly mediating features of anxiety, anhedonia, aggression, and affective dyscontrol. The continued appreciation of the neural circuitry mediating affective states and their modulation by neurotransmitter systems should further the understanding of the pathophysiology of affective and anxiety disorders.

Role of norepinephrine in the pathophysiology of neuropsychiatric disorders

The concatenation of convergent lines of evidence from basic to clinical research continues to reveal that norepinephrine (NE) is a crucial regulator of a myriad of behaviors ranging from stress response to memory formation. Furthermore, many neuropsychiatric disorders involve neurocircuitry that is directly modulated by NE. This report summarizes the physiological roles of NE, as well as the main findings implicating a role for NE system dysfunction in mood and anxiety disorders, posttraumatic stress disorder, attention-deficit/hyperactivity disorder, and Alzheimer's disease. In each of these disorders, there appears to be a complex dysregulation of NE function, with changes in locus ceruleus firing, NE availability, and both pre- and postsynaptic receptor regulation. Many symptoms of these disorders are attributable to abnormalities within distributed neural circuits regulated by NE. Appreciation of NE's role in modulating the neural circuitry mediating cognition and affect should help elucidate the pathophysiology of a variety of neuropsychiatric disorders and the development of novel treatments.

Protein kinase a in major depression: the link between hypothalamic-pituitary-adrenal axis hyperactivity and neurogenesis

The latest and most generative biological theories of major depression center on two major hypotheses. The first focuses on the concept that hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis leads to many of the pathological changes in the brain that accompany major depression. The second posits that neurogenesis leads to the repair of depression-related injuries. These two hypotheses are complementary: the former alludes to the etiology or consequences of depression, while the latter suggests mechanisms of antidepressant action. Significant crosstalk occurs between these two systems at many levels. Protein kinase A (PKA) may play an important role in this crosstalk at the intracellular level of signaling cascades. PKA is involved in the formation of long-term potentiation and fear conditioning in response to stress. Chronic stress leads to the suppression of hippocampal activity, which may cause the hyperactivity of the HPA axis during melancholic depression. PKA is also involved in the stimulation of hippocampal neurogenesis after antidepressant treatment. In theory, neurogenesis may lead to the restoration of hippocampal function, and this may be the mechanism that leads to antidepressant-mediated normalization of HPA hyperactivity. Thus, PKA is active during processes that potentially lead to depression and other processes that lead to the resolution of the illness. These opposing processes may be mediated by separate PKA isozymes that activate two distinct pathways. This review highlights the dual role of this enzyme in two biological hypotheses pertaining to depression and its treatment.

Current perspectives on the pathophysiology of schizophrenia, depression, and anxiety disorders

This article reviews the rapidly changing concepts related to the pathophysiology of major psychiatric disorders. The current era is an exciting one for psychiatric research and the rapidity with which advances are being made is a source of hope to patients with these disorders and for society.

Expression of the cAMP response element binding protein (CREB) in hippocampus produces an antidepressant effect

BACKGROUND

Recent studies have demonstrated that chronic antidepressant treatment increases the expression of the cyclic amp (cAMP) response element binding protein (CREB) in rat hippocampus. The study presented here was conducted to determine if CREB is a relevant target that produces an antidepressant-like effect.

METHODS

We employed the herpes simplex virus (HSV)-mediated gene transfer technique to overexpress CREB and determined its effect on the learned helplessness and forced swim tests, two established models used for pharmacological screening of antidepressant drugs.

RESULTS

In the learned helplessness model, rats that received bilateral microinjection of HSV-CREB into the dentate gyrus showed significantly fewer escape failures in the subsequent conditioned avoidance test than those injected with control vector (HSV-LacZ). In contrast, microinjection of HSV-CREB in either the CA1 pyramidal cell layer of hippocampus or the prefrontal cortex did not produce an antidepressant response. In the forced swim test, CREB expression in the dentate gyrus resulted in a significantly shorter immobility time than those injected with HSV-LacZ.

CONCLUSIONS

These results demonstrate that over-expression of CREB in hippocampus results in an antidepressant effect and suggest that CREB may serve as a potential molecular target for novel therapeutic agents.

Expanding the horizons of depression: beyond the monoamine hypothesis

The monoamine hypothesis has dominated our understanding of depression and of pharmacological approaches to its management and it has produced several generations of antidepressant agents, ranging from the monoamine oxidase inhibitors (MAOIs), through tricyclics (TCAs) and selective serotonin reuptake inhibitors (SSRIs), to the recently introduced selective noradrenaline reuptake inhibitor (NARI), reboxetine. Greater receptor selectivity has improved tolerability, but not efficacy, when newer compounds are compared with the original tricyclic antidepressants (TCAs) and monoamine oxidase inhibitors. Essentially, the newer antidepressants have the same distinguishing feature as older ones, i.e. acute enhancement of monoaminergic neurotransmission. The monoamine hypothesis cannot conclusively link the acute biochemical action of antidepressants on monoamine levels with their delayed clinical effect of 10-14 days, nor can it explain the mode of action of antidepressants that are effective despite being very weak inhibitors of monoaminergic transmission (e.g. iprindole) or, incongruously, enhancing monoamine uptake (e.g. tianeptine). Compared with other fields of medicine, there has been a lack of progress in understanding the pathophysiology of depression and producing truly novel antidepressant agents. Other biological approaches to depression, such as overactivity of the hypothalamic-pituitary-adrenal axis, hippocampal neural plasticity in response to stress, and the link between the inflammatory response and depression, offer new approaches to finding pharmacological agents, aided by improved techniques for visualising the human brain, better animal models, and increased knowledge of human markers of depression. Copyright 2001 John Wiley & Sons, Ltd.

Imipramine and phenelzine decrease glutamate overflow in the prefrontal cortex--a possible mechanism of neuroprotection in major depression?

Antidepressant drugs have been used for decades, but the neurobiological substrate of their efficacy is not completely understood. Although these drugs have well-established effects on monoamines, evidence is emerging that they may also affect other neurotransmitter systems. It has been shown that treatment with a wide range of antidepressants changes the binding characteristics of the N-methyl-D-aspartate type of glutamate receptor. This change is delayed and occurs only in the cortex. The mechanism that triggers it is unknown. We hypothesized that N-methyl-D-aspartate receptor alterations may be due to changes in the dynamics of cortical excitatory amino acid release. Such changes are of particular interest in areas such as the prefrontal cortex, a region involved in stress responses and affected in major depression. We investigated the effects of two antidepressants with different modes of action, imipramine and phenelzine, on glutamate and aspartate outflow in rat prefrontal cortex and striatum. We showed that antidepressants significantly decreased stimulated glutamate outflow. The effect had a rapid onset, was sustained during chronic administration and was only seen in the prefrontal cortex. This change may initiate receptor alterations. Furthermore, if antidepressants can dampen states of hyperglutamatergic activity and the subsequent excitotoxicity, their chronic use may have a considerable neuroprotective potential in major depression.

Induction of cyclin-dependent kinase 5 in the hippocampus by chronic electroconvulsive seizures: role of [Delta]FosB

The transcription factor DeltaFosB is induced in the hippocampus and other brain regions by repeated electroconvulsive seizures (ECS), an effective antidepressant treatment. The unusually high stability of this protein makes it an attractive candidate to mediate some of the long-lasting changes in the brain caused by ECS treatment. To understand how DeltaFosB might alter brain function, we examined the gene expression profiles in the hippocampus of inducible transgenic mice that express DeltaFosB in this brain region by the use of cDNA expression arrays that contain 588 genes. Of the 430 genes detected, 20 genes were consistently upregulated, and 14 genes were downregulated, by >50%. One of the upregulated genes is cyclin-dependent kinase 5 (cdk5). On the basis of its purported role in regulating neuronal structure, we studied directly whether cdk5 is a true target for DeltaFosB. Upregulation of cdk5 immunoreactivity in the hippocampus was confirmed by Western blotting in the DeltaFosB-expressing transgenic mice as well as in rats treated chronically with ECS. Chronic ECS treatment also increased, in the hippocampus, the phosphorylation state of tau, a microtubule-associated protein that is a known substrate for cdk5. A 1.6 kb fragment of the cdk5 promoter was cloned, and activity of the promoter was found to be increased after overexpression of DeltaFosB in cell culture. Moreover, mutation of the single consensus activator protein-1 site contained within the cdk5 promoter fragment completely abolished activation of the promoter by DeltaFosB. Together, these results suggest that cdk5 is one target by which DeltaFosB produces some of its physiological effects in the hippocampus and thereby mediates certain long-term consequences of chronic ECS treatment.

Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus

Recent studies suggest that stress-induced atrophy and loss of hippocampal neurons may contribute to the pathophysiology of depression. The aim of this study was to investigate the effect of antidepressants on hippocampal neurogenesis in the adult rat, using the thymidine analog bromodeoxyuridine (BrdU) as a marker for dividing cells. Our studies demonstrate that chronic antidepressant treatment significantly increases the number of BrdU-labeled cells in the dentate gyrus and hilus of the hippocampus. Administration of several different classes of antidepressant, but not non-antidepressant, agents was found to increase BrdU-labeled cell number, indicating that this is a common and selective action of antidepressants. In addition, upregulation of the number of BrdU-labeled cells is observed after chronic, but not acute, treatment, consistent with the time course for the therapeutic action of antidepressants. Additional studies demonstrated that antidepressant treatment increases the proliferation of hippocampal cells and that these new cells mature and become neurons, as determined by triple labeling for BrdU and neuronal- or glial-specific markers. These findings raise the possibility that increased cell proliferation and increased neuronal number may be a mechanism by which antidepressant treatment overcomes the stress-induced atrophy and loss of hippocampal neurons and may contribute to the therapeutic actions of antidepressant treatment.

Antidepressants: pharmacological profile and clinical consequences

Three neurotransmitter systems are implicated in the biological basis of depression: the serotonergic system is thought to be a major component in the development of depression and in the efficacy of antidepressant drugs, while the noradrenergic and dopaminergic systems play lesser roles, but are important in the development of antidepressant side-effects. Selective serotonin re-uptake inhibitors (SSRIs) are still the drug treatments of choice in major depressive disorder, but each has a subtly different pharmacological profile, which has implications for pharmacodynamic actions and clinical efficacy and side-effect profiles. Although the precise mechanisms responsible for specific depressive symptoms are not yet well defined, evidence is emerging that some SSRIs may be more effective in combating certain symptoms than others. Fluoxetine appears to be particularly effective in overcoming symptoms of fatigue and low energy, whereas paroxetine or sertraline may be more appropriately used for depressed patients experiencing anxiety. A growing understanding of molecular mechanisms in depression and the unique clinical consequences of each pharmacological agent brings us one step closer to being able to individualize antidepressant treatment on the basis of core presenting symptoms and the needs of the individual patient. ( Int J Psych Clin Pract 2001; 5 (Suppl 1): S19-S28).

Serotonergic gene expression and depression: implications for developing novel antidepressants

The development and configuration of several neural networks is dependent on the actions of serotonin (5-HT) acting through multiple hetero- and autoreceptor subtypes. During early brain development 5-HT modulates morphogenetic activities, such as neural differentiation, axon outgrowth, and synaptic modeling. In the adult brain, midbrain raphe serotonergic neurons project to a variety of brain regions and modulate a wide range of physiological functions. Several lines of evidence indicate that genetically determined variability in serotonergic gene expression, as it has been documented for the 5-HT transporter, influences temperamental traits and may lead to psychopathological conditions with increased anxiety, depression, and aggression. Investigation of the regulation of serotonergic gene transcription and its impact on neuronal development, synaptic plasticity, and neurogenesis spur interest to identify serotonergic gene-related molecular factors underlying disease states and to develop more effective antidepressant treatment strategies. Gene targeting strategies have increasingly been integrated into investigations of brain function and along with the fading dogma of a limited capacity of neurons for regeneration and reproducibility, it is realized that gene transfer techniques using efficient viral vectors in conjunction with neuron-selective transcriptional control systems may also be applicable to complex disorders of the brain. Given the fact that the 5-HT system continues to be an important target for drug development and production, novel strategies aiming toward the modification of 5-HT function at the level of gene expression are likely to be exploited by enterprises participating actively in the introduction of alternative therapeutic approaches.

Depresssion--emerging insights from neurobiology

An emerging hypothesis suggests that the pathogenesis and treatment of depression is likely to involve a plasticity of neuronal pathways. The inability of neuronal systems to exhibit appropriate, adaptive plasticity could contribute to the pathogenesis of depression. Antidepressant treatments may exert their therapeutic effects by stimulating appropriate adaptive changes in neuronal systems. Recent studies have demonstrated that chronic antidepressant administration up-regulates the cAMP signal transduction cascade resulting in an increased expression and function of the transcription factor CREB. Enhanced CREB expression leads to an up-regulation of specific target genes, including the neurotrophin BDNF. Chronic antidepressant treatments enhance BDNF expression within hippocampal and cortical neurons and can prevent the stress-induced decrease in BDNF expression. Stress has been shown to: (i) induce neuronal atrophy/death; and (ii) decrease neurogenesis of hippocampal neurons. Clinical studies indicate significant hippocampal damage in cases of major, recurrent depression. It is possible that antidepressant treatments through enhanced expression of growth and survival promoting factors like BDNF may prevent or reverse the atrophy and damage of hippocampal neurons. Indeed, studies have indicated that chronic antidepressant treatments enhance hippocampal neurogenesis, promote neuronal sprouting and prevent atrophy. The molecular mechanisms underlying the effects of antidepressant treatments including adaptations in the cAMP transduction cascade, CREB and BDNF gene expression, and structural neuronal plasticity are discussed.

Protein kinase A and Rap1 levels in platelets of untreated patients with major depression

We have recently reported altered levels of protein kinase A and Rap1 in patients with bipolar disorder. The purpose of the current investigation was to assess the levels of these proteins in platelets from untreated euthymic and depressed patients with major unipolar depression. Platelets were collected from 45 drug-free unipolar patients (13 euthymic and 32 depressed) and 45 healthy subjects. The levels of protein kinase A and Rap1 were assessed by Western blot analysis, immunostaining and computer-assisted imaging. The immunolabeling of the regulatory subunit type II of protein kinase A and that of Rap1 was significantly lower in untreated depressed patients compared with untreated euthymic patients and healthy subjects. No significant differences were found in the immunolabeling of both the regulatory type I and the catalytic subunits of protein kinase A among groups. Levels of the regulatory subunit type II of protein kinase A and Rap1 are altered in platelets of unipolar depressive patients. These findings may provide new insight about the relationship between components of cAMP signaling and affective disorders.

Cellular mechanisms in the vulnerability to depression and response to antidepressants

As a testable heuristic, the concept of stress response and adaptation is highly appealing, and the support for the concept is strong. This explanatory model of depression may account for hitherto apparently discordant facts--contradictory symptoms, antidepressant drugs that act on differing systems, facilitation of antidepressant response by augmentation, and response to psychotherapy and pharmacotherapy. This article has focused narrowly on specific cellular elements of the stress-adaptational mechanisms, including the AC-PKA and PLC-PKC transductional cascades, together with specific response elements, such as the HPA axis, BDNF, and NMDA receptors; however, other important mechanisms, including specific receptor subtypes (e.g., 5-HT1A and NE alpha 2), transmitter systems (e.g., acetylcholine and depamine), and hormones (e.g., thyroid and growth hormones and prolactin), which may be important, have not been discussed. As the complex interactions of these systems gradually yield to investigation, not only will new treatments be developed, but better matching of treatment to patient may become an achievable goal.

Termination of psychotherapy: a training perspective

Given the constraints of the prevailing mental health system in the United States, it has become very challenging for psychiatrists to offer psychotherapy services to patients in need of this modality of treatment. In spite of this situation, the profession has made a consistent effort not only to retain this type of psychiatric care but also to train psychiatric residents in this psychiatric intervention technique and its appropriate indications. In this article, the authors highlight a very important aspect of psychotherapy treatment-the termination phase. They review relevant literature on this subject, discuss some of the most common problems faced by psychiatrists, especially psychiatric residents, when addressing the termination phase of psychotherapy, and then present two cases to illustrate these issues.

Regional metabolic effects of fluoxetine in major depression: serial changes and relationship to clinical response

BACKGROUND

Treatment of major depression with antidepressants is generally associated with a delay in onset of clinical response. Functional brain correlates of this phenomenon have not been previously characterized.

METHODS

Time course of changes in brain glucose metabolism were measured using positron emission tomography in hospitalized unipolar depressed patients treated with fluoxetine. Time-specific and response-specific effects were examined at 1 and 6 weeks of treatment.

RESULTS

Changes were seen over time, and characterized by three distinct patterns: 1) common changes at 1 and 6 weeks, 2) reversal of the 1-week pattern at 6 weeks, and 3) unique changes seen only after chronic treatment. Fluoxetine responders and nonresponders, similar at 1 week, were differentiated by their 6-week pattern. Clinical improvement was uniquely associated with limbic and striatal decreases (subgenual cingulate, hippocampus, insula, and pallidum) and brain stem and dorsal cortical increases (prefrontal, parietal, anterior, and posterior cingulate). Failed response was associated with a persistent 1-week pattern and absence of either subgenual cingulate or prefrontal changes.

CONCLUSIONS

Chronic treatment and clinical response to fluoxetine was associated with a reciprocal pattern of subcortical and limbic decreases and cortical increases. Reversal in the week-1 pattern at 6 weeks suggests a process of adaptation in specific brain regions over time in response to sustained serotonin reuptake inhibition. The inverse patterns in responders and nonresponders also suggests that failure to induce these adaptive changes may underlie treatment nonresponse.

Neuronal plasticity and survival in mood disorders

Studies at the basic and clinical levels demonstrate that neuronal atrophy and cell death occur in response to stress and in the brains of depressed patients. Although the mechanisms have yet to be fully elucidated, progress has been made in characterizing the signal transduction cascades that control neuronal atrophy and programmed cell death and that may be involved in the action of antidepressant treatment. These pathways include the cyclic adenosine monophosphate and neurotrophic factor signal transduction cascades. It is notable that these same pathways have been demonstrated to play a pivotal role in cellular models of neural plasticity. This overlap of plasticity and cell survival pathways, together with studies demonstrating that neuronal activity enhances cell survival, suggests that neuronal atrophy and death could result from a disruption of the mechanisms underlying neural plasticity. The role of these pathways and failure of neuronal plasticity in stress-related mood disorders are discussed.

Neurogenesis in the dentate gyrus of the rat following electroconvulsive shock seizures

Electroconvulsive shock (ECS) seizures provide an animal model of electroconvulsive therapy (ECT) in humans. Recent evidence indicates that repeated ECS seizures can induce long-term structural and functional changes in the brain, similar to those found in other seizure models. We have examined the effects of ECS on neurogenesis in the dentate gyrus of the adult rat using bromodeoxyuridine (BrdU) immunohistochemistry, which identifies newly generated cells. Cells have also been labeled for neuronal nuclear protein (NeuN) to identify neurons. One month following eight ECS seizures, ECS-treated rats had approximately twice as many BrdU-positive cells as sham-treated controls. Eighty-eight percent of newly generated cells colabeled with NeuN in ECS-treated subjects, compared to 83% in sham-treated controls. These data suggest that there is a net increase in neurogenesis within the hippocampal dentate gyrus following ECS treatment. Similar increases have been reported following kindling and kainic acid- or pilocarpine-induced status epilepticus. Increased neurogenesis appears to be a general response to seizure activity and may play a role in the therapeutic effects of ECT.

cAMP response element-mediated gene transcription is upregulated by chronic antidepressant treatment

Regulation of gene transcription via the cAMP-mediated second messenger pathway has been implicated in the actions of antidepressant drugs, but studies to date have not demonstrated such an effect in vivo. To directly study the regulation of cAMP response element (CRE)-mediated gene transcription by antidepressants, transgenic mice with a CRE-LacZ reporter gene construct were administered one of three different classes of antidepressants: a norepinephrine selective reuptake inhibitor (desipramine), a serotonin selective reuptake inhibitor (fluoxetine), or a monoamine oxidase inhibitor (tranylcypromine). Chronic, but not acute, administration of these antidepressants significantly increased CRE-mediated gene transcription, as well as the phosphorylation of CRE binding protein (CREB), in several limbic brain regions thought to mediate the action of antidepressants, including the cerebral cortex, hippocampus, amygdala, and hypothalamus. These results demonstrate that chronic antidepressant treatment induces CRE-mediated gene expression in a neuroanatomically differentiated pattern and further elucidate the molecular mechanisms underlying the actions of these widely used therapeutic agents.