Effect of chronic antidepressant treatment on transcription factor binding activity in rat hippocampus and frontal cortex

The effects of chronic desipramine treatment on neurotrophin-3 in the brain of mice with selective depletion of CREB and CREM in noradrenergic neurons

The disturbances in neurotrophic support are thought to be one of the main causes of depression, which depend not only on the neurotrophins themselves but also on the molecules regulating their synthesis and effector functions. One such molecule is cAMP responsive element binding protein (CREB), which role in depression and antidepressant drugs mechanism of action has been extensively studied. However, CREB's effects vary depending on brain structure, necessitating specific transgenic models for studying its function. Moreover, deletion of CREB enhances cAMP response element modulator (CREM) expression, suspected to compensate for CREB in its absence. Previously, mice lacking CREB in noradrenergic neurons and CREM (Creb1DbhCreCrem-/-) showed to be insensitive to acute desipramine, whereas mice lacking only CREB (Creb1DbhCre) showed similar effects as wild type animals (w/t). As neurotrophic changes require chronic antidepressant treatment, in current study mice (w/t, Creb1DbhCre and Creb1DbhCreCrem-/-; both males and females) were given desipramine for 21 days, to assess the effects of the drug on CREB, neurotrophins and their receptors in the hippocampus and prefrontal cortex. Interestingly, desipramine had no effect on CREB in neither of studied groups. However, both male and female mice lacking CREB and CREM displayed alterations in neurotrophin-3 (NTF3) expression or protein levels, modulated by desipramine. These findings suggest NTF3 is connected with inhibited response to acute and probably chronic desipramine administration in Creb1DbhCreCrem-/- mice, although in w/t chronic desipramine had no effect on NTF3. Nevertheless, our findings give insight into the role of non-BDNF neurotrophins in the mechanism of antidepressant drugs.

The MAOA rs979605 Genetic Polymorphism Is Differentially Associated with Clinical Improvement Following Antidepressant Treatment between Male and Female Depressed Patients

Major depressive disorder (MDD) is the leading cause of disability worldwide. Treatment with antidepressant drugs (ATD), which target monoamine neurotransmitters including serotonin (5HT), are only modestly effective. Monoamine oxidase (MAO) metabolizes 5HT to 5-hydroxy indoleacetic acid (5HIAA). Genetic variants in the X-chromosome-linked MAO-encoding genes, MAOA and MAOB, have been associated with clinical improvement following ATD treatment in depressed patients. Our aim was to analyze the association of MAOA and MAOB genetic variants with (1) clinical improvement and (2) the plasma 5HIAA/5HT ratio in 6-month ATD-treated depressed individuals. Clinical (n = 378) and metabolite (n = 148) data were obtained at baseline and up to 6 months after beginning ATD treatment (M6) in patients of METADAP. Mixed-effects models were used to assess the association of variants with the Hamilton Depression Rating Scale (HDRS) score, response and remission rates, and the plasma 5HIAA/5HT ratio. Variant × sex interactions and dominance terms were included to control for X-chromosome-linked factors. The MAOA rs979605 and MAOB rs1799836 polymorphisms were analyzed. The sex × rs979605 interaction was significantly associated with the HDRS score (p = 0.012). At M6, A allele-carrying males had a lower HDRS score (n = 24, 10.9 ± 1.61) compared to AA homozygous females (n = 14, 18.1 ± 1.87; p = 0.0067). The rs1799836 polymorphism was significantly associated with the plasma 5HIAA/5HT ratio (p = 0.018). Overall, CC/C females/males had a lower ratio (n = 44, 2.18 ± 0.28) compared to TT/T females/males (n = 60, 2.79 ± 0.27; p = 0.047). The MAOA rs979605 polymorphism, associated with the HDRS score in a sex-dependent manner, could be a useful biomarker for the response to ATD treatment.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Anxiety and depression with neurogenesis defects in exchange protein directly activated by cAMP 2-deficient mice are ameliorated by a selective serotonin reuptake inhibitor, Prozac

Intracellular cAMP and serotonin are important modulators of anxiety and depression. Fluoxetine, a selective serotonin reuptake inhibitor (SSRI) also known as Prozac, is widely used against depression, potentially by activating cAMP response element-binding protein (CREB) and increasing brain-derived neurotrophic factor (BDNF) through protein kinase A (PKA). However, the role of Epac1 and Epac2 (Rap guanine nucleotide exchange factors, RAPGEF3 and RAPGEF4, respectively) as potential downstream targets of SSRI/cAMP in mood regulations is not yet clear. Here, we investigated the phenotypes of Epac1 (Epac1(-/-)) or Epac2 (Epac2(-/-)) knockout mice by comparing them with their wild-type counterparts. Surprisingly, Epac2(-/-) mice exhibited a wide range of mood disorders, including anxiety and depression with learning and memory deficits in contextual and cued fear-conditioning tests without affecting Epac1 expression or PKA activity. Interestingly, rs17746510, one of the three single-nucleotide polymorphisms (SNPs) in RAPGEF4 associated with cognitive decline in Chinese Alzheimer's disease (AD) patients, was significantly correlated with apathy and mood disturbance, whereas no significant association was observed between RAPGEF3 SNPs and the risk of AD or neuropsychiatric inventory scores. To further determine the detailed role of Epac2 in SSRI/serotonin/cAMP-involved mood disorders, we treated Epac2(-/-) mice with a SSRI, Prozac. The alteration in open field behavior and impaired hippocampal cell proliferation in Epac2(-/-) mice were alleviated by Prozac. Taken together, Epac2 gene polymorphism is a putative risk factor for mood disorders in AD patients in part by affecting the hippocampal neurogenesis.

A Review of Biomarkers in Mood and Psychotic Disorders: A Dissection of Clinical vs. Preclinical Correlates

Despite significant research efforts aimed at understanding the neurobiological underpinnings of mood (depression, bipolar disorder) and psychotic disorders, the diagnosis and evaluation of treatment of these disorders are still based solely on relatively subjective assessment of symptoms as well as psychometric evaluations. Therefore, biological markers aimed at improving the current classification of psychotic and mood-related disorders, and that will enable patients to be stratified on a biological basis into more homogeneous clinically distinct subgroups, are urgently needed. The attainment of this goal can be facilitated by identifying biomarkers that accurately reflect pathophysiologic processes in these disorders. This review postulates that the field of psychotic and mood disorder research has advanced sufficiently to develop biochemical hypotheses of the etiopathology of the particular illness and to target the same for more effective disease modifying therapy. This implies that a "one-size fits all" paradigm in the treatment of psychotic and mood disorders is not a viable approach, but that a customized regime based on individual biological abnormalities would pave the way forward to more effective treatment. In reviewing the clinical and preclinical literature, this paper discusses the most highly regarded pathophysiologic processes in mood and psychotic disorders, thereby providing a scaffold for the selection of suitable biomarkers for future studies in this field, to develope biomarker panels, as well as to improve diagnosis and to customize treatment regimens for better therapeutic outcomes.

Mice genetically depleted of brain serotonin do not display a depression-like behavioral phenotype

Reductions in function within the serotonin (5HT) neuronal system have long been proposed as etiological factors in depression. Selective serotonin reuptake inhibitors (SSRIs) are the most common treatment for depression, and their therapeutic effect is generally attributed to their ability to increase the synaptic levels of 5HT. Tryptophan hydroxylase 2 (TPH2) is the initial and rate-limiting enzyme in the biosynthetic pathway of 5HT in the CNS, and losses in its catalytic activity lead to reductions in 5HT production and release. The time differential between the onset of 5HT reuptake inhibition by SSRIs (minutes) and onset of their antidepressant efficacy (weeks to months), when considered with their overall poor therapeutic effectiveness, has cast some doubt on the role of 5HT in depression. Mice lacking the gene for TPH2 are genetically depleted of brain 5HT and were tested for a depression-like behavioral phenotype using a battery of valid tests for affective-like disorders in animals. The behavior of TPH2(-/-) mice on the sucrose preference test, tail suspension test, and forced swim test and their responses in the unpredictable chronic mild stress and learned helplessness paradigms was the same as wild-type controls. While TPH2(-/-) mice as a group were not responsive to SSRIs, a subset responded to treatment with SSRIs in the same manner as wild-type controls with significant reductions in immobility time on the tail suspension test, indicative of antidepressant drug effects. The behavioral phenotype of the TPH2(-/-) mouse questions the role of 5HT in depression. Furthermore, the TPH2(-/-) mouse may serve as a useful model in the search for new medications that have therapeutic targets for depression that are outside of the 5HT neuronal system.

Increased hippocampal neurogenesis and accelerated response to antidepressants in mice with specific deletion of CREB in the hippocampus: role of cAMP response-element modulator τ

The transcription factor cAMP response element-binding protein (CREB) has been implicated in the pathophysiology of depression as well as in the efficacy of antidepressant treatment. However, altering CREB levels appears to have differing effects on anxiety- and depression-related behaviors, depending on which brain region is examined. Furthermore, many manipulations of CREB lead to corresponding changes in other CREB family proteins, and the impact of these changes has been largely ignored. To further investigate the region-specific importance of CREB in depression-related behavior and antidepressant response, we used Creb(loxP/loxP) mice to localize CREB deletion to the hippocampus. In an assay sensitive to chronic antidepressant response, the novelty-induced hypophagia procedure, hippocampal CREB deletion, did not alter the response to chronic antidepressant treatment. In contrast, mice with hippocampal CREB deletion responded to acute antidepressant treatment in this task, and this accelerated response was accompanied by an increase in hippocampal neurogenesis. Upregulation of the CREB-family protein cAMP response-element modulator (CREM) was observed after CREB deletion. Viral overexpression of the activator isoform of CREM, CREMτ, in the hippocampus also resulted in an accelerated response to antidepressants as well as increased hippocampal neurogenesis. This is the first demonstration of CREMτ within the brain playing a role in behavior and specifically in behavioral outcomes following antidepressant treatment. The current results suggest that activation of CREMτ may provide a means to accelerate the therapeutic efficacy of current antidepressant treatment.

The involvement of ERK/CREB/Bcl-2 in depression-like behavior in prenatally stressed offspring rats

A number of studies reveal that prenatal stress (PS) may induce an increased vulnerability to depression in offspring. Some evidences indicate that extracellular signal-regulated kinase (ERK)-cyclic AMP responsive element binding protein (CREB) signal system may play an important role in the molecular mechanism of depression. In the present study, we examined the effects of prenatal restraint stress on depression-like behavior in one-month offspring Sprague-Dawley rats and expression of ERK2, CREB, B-cell lymphoma-2 (Bcl-2) mRNA in the hippocampus, prefrontal cortex and striatum to explore the potential role of ERK-CREB pathway in mediating the behavioral effects of PS exposure. Our findings demonstrated that PS increased immobility time in forced swimming test and decreased expression of ERK2, CREB, Bcl-2 mRNA in the hippocampus and prefrontal cortex of juvenile offspring rats except for CREB in hippocampus of male offspring. Changes induced by PS were partly prevented by MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist. These findings suggested that the ERK-CREB system might be related with the depression-like behavior in juvenile offspring rats subjected to PS, in which NMDA receptors might be involved.

Gender-specific effects of fluoxetine on hippocampal glucocorticoid receptor phosphorylation and behavior in chronically stressed rats

Chronic psychosocial isolation stress (CPSI) modulates glucocorticoid receptor (GR) functioning in Wistar male rat hippocampus (HIPPO) through alteration of nuclear GR phosphorylation and its upstream kinases signaling, which parallels animal depressive-like behavior. The current study investigated potential gender specificities regarding the effect of chronic therapy by an antidepressant fluoxetine (FLU) on GR signaling in HIPPO and depressive-like behavior in CPSI animals. FLU was administrated to female and male naïve or CPSI rats for 21 days and GR protein, its phosphorylation status and upstream kinases, as well as GR and BDNF mRNA were followed in HIPPO together with animal serum corticosterone (CORT) and depressive-like behavior. The results showed that CPSI increased immobility in males versus hyperactivity in females and disrupted nuclear pGR232-Cdk5 pathway and JNK signaling in a gender-specific way. In contrast, in both genders CPSI increased the nuclear levels of GR and pGR246 but decreased CORT and mRNA levels of GR and BDNF. Concomitant FLU normalized the depressive-like behavior and altered the nuclear pGR232-Cdk5 signaling in a gender-specific manner. In both females and males, FLU reversed the nuclear levels of GR and pGR246 without affecting CORT and GR mRNA levels. In contrast, FLU exhibited gender-specific effect on BDNF mRNA in CPSI animals, by increasing it in females, but not in males. In spite of normalization the total nuclear GR level upon FLU treatment in both gender, down-regulation of GR mRNA is possibly maintained through prevalence of pGR232 isoform only in males. The gender-specific alterations of pGR232-Cdk5 signaling and BDNF gene expression in HIPPO and normalization of depressive-like behavior upon FLU treatment distinguishes this signaling pathway as potential future antidepressant target for gender-specific therapy of stress related mood disorders.

Maprotiline treatment differentially influences cardiac β-adrenoreceptors expression under normal and stress conditions

Alterations in cardiac function were observed in antidepressants treated patients and published in several clinical reports. These detected changes could be either a consequence of the treatment or of depression itself, which has already been proved to be a risk factor in heart diseases. In order to determine a possible influence of chronic treatment with norepinephrinergic reuptake inhibitor, maprotiline, on the heart, we investigated gene expression of cardiac β-adrenoceptors both in controls and in animals with signs of depression. The rats were divided into two groups, unstressed controls and those exposed to chronic unpredictable mild stress (CUMS). The groups were further divided into two subgroups, one receiving daily intraperitoneal injections of vehicle (sterile water) and another one maprotiline (10 mg/kg) for four weeks. Tissue samples were collected after the last application. Gene expression of cardiac β1- and β2-adrenoceptor was determined using Real-time RT-PCR analysis. Our results show that in control animals expression of both adrenoreceptors was decreased in the right atria after 4 weeks of maprotiline application. Contrary, the same treatment led to a significant increase in expression of cardiac β1-adrenoceptor in the stressed rats, with no change in the characteristics of β2-adrenoceptor. Our findings might reflect the that molecular mechanisms are underlying factors involved in the development of cardiovascular diseases linked with antidepressant treatment.

Analysis of region-specific changes in gene expression upon treatment with citalopram and desipramine reveals temporal dynamics in response to antidepressant drugs at the transcriptome level

RATIONALE

The notion that the onset of action of antidepressant drugs (ADs) takes weeks is widely accepted; however, the sequence of events necessary for therapeutic effects still remains obscure.

OBJECTIVE

We aimed to evaluate a time-course of ADs-induced alterations in the expression of 95 selected genes in 4 regions of the rat brain: the prefrontal and cingulate cortices, the dentate gyrus of the hippocampus, and the amygdala.

METHODS

We employed RT-PCR array to evaluate changes during a time-course (1, 3, 7, 14, and 21 days) of treatments with desipramine (DMI) and citalopram (CIT). In addition to repeated treatment, we also conducted acute treatment (a single dose of drug followed by the same time intervals as the repeated doses).

RESULTS

Time-dependent and structure-specific changes in gene expression patterns allowed us to identify spatiotemporal differences in the molecular action of two ADs. Singular value decomposition analysis revealed differences in the global gene expression profiles between treatment types. The numbers of characteristic modes were generally smaller after CIT treatment than after DMI treatment. Analysis of the dynamics of gene expression revealed that the most significant changes concerned immediate early genes, whose expression was also visualized by in situ hybridization. Transcription factor binding site analysis revealed an over-representation of serum response factor binding sites in the promoters of genes that changed upon treatment with both ADs.

CONCLUSIONS

The observed gene expression patterns were highly dynamic, with oscillations and peaks at various time points of treatment. Our study also revealed novel potential targets of antidepressant action, i.e., Dbp and Id1 genes.

Antidepressants increase human hippocampal neurogenesis by activating the glucocorticoid receptor

Antidepressants increase adult hippocampal neurogenesis in animal models, but the underlying molecular mechanisms are unknown. In this study, we used human hippocampal progenitor cells to investigate the molecular pathways involved in the antidepressant-induced modulation of neurogenesis. Because our previous studies have shown that antidepressants regulate glucocorticoid receptor (GR) function, we specifically tested whether the GR may be involved in the effects of these drugs on neurogenesis. We found that treatment (for 3-10 days) with the antidepressant, sertraline, increased neuronal differentiation via a GR-dependent mechanism. Specifically, sertraline increased both immature, doublecortin (Dcx)-positive neuroblasts (+16%) and mature, microtubulin-associated protein-2 (MAP2)-positive neurons (+26%). This effect was abolished by the GR-antagonist, RU486. Interestingly, progenitor cell proliferation, as investigated by 5'-bromodeoxyuridine (BrdU) incorporation, was only increased when cells were co-treated with sertraline and the GR-agonist, dexamethasone, (+14%) an effect which was also abolished by RU486. Furthermore, the phosphodiesterase type 4 (PDE4)-inhibitor, rolipram, enhanced the effects of sertraline, whereas the protein kinase A (PKA)-inhibitor, H89, suppressed the effects of sertraline. Indeed, sertraline increased GR transactivation, modified GR phosphorylation and increased expression of the GR-regulated cyclin-dependent kinase-2 (CDK2) inhibitors, p27(Kip1) and p57(Kip2). In conclusion, our data suggest that the antidepressant, sertraline, increases human hippocampal neurogenesis via a GR-dependent mechanism that requires PKA signaling, GR phosphorylation and activation of a specific set of genes. Our data point toward an important role for the GR in the antidepressant-induced modulation of neurogenesis in humans.

Transgenic elimination of high-affinity antidepressant and cocaine sensitivity in the presynaptic serotonin transporter

Serotonin [i.e., 5-hydroxytryptamine (5-HT)]-targeted antidepressants are in wide use for the treatment of mood disorders, although many patients do not show a response or experience unpleasant side effects. Psychostimulants, such as cocaine and 3,4-methylenedioxymethamphetamine (i.e., "ecstasy"), also impact 5-HT signaling. To help dissect the contribution of 5-HT signaling to the actions of these and other agents, we developed transgenic mice in which high-affinity recognition of multiple antidepressants and cocaine is eliminated. Our animals possess a modified copy of the 5-HT transporter (i.e., SERT, slc6a4) that bears a single amino acid substitution, I172M, proximal to the 5-HT binding site. Although the M172 substitution does not impact the recognition of 5-HT, this mutation disrupts high-affinity binding of many competitive antagonists in transfected cells. Here, we demonstrate that, in M172 knock-in mice, basal SERT protein levels, 5-HT transport rates, and 5-HT levels are normal. However, SERT M172 mice display a substantial loss of sensitivity to the selective 5-HT reuptake inhibitors fluoxetine and citalopram, as well as to cocaine. Through a series of biochemical, electrophysiological, and behavioral assays, we demonstrate the unique properties of this model and establish directly that SERT is the sole protein responsible for selective 5-HT reuptake inhibitor-mediated alterations in 5-HT clearance, in 5-HT1A autoreceptor modulation of raphe neuron firing, and in behaviors used to predict the utility of antidepressants.

Antidepressant imipramine induces human astrocytes to differentiate into cells with neuronal phenotype

Several recent studies have expanded our conception of the role of astrocytes in neurogenesis, proposing that these cells may contribute to this phenomenon not only as a source of trophic substances, but also as stem cells themselves. We recently observed in vitro that human mature astrocytes can be induced to differentiate into cells with a neuronal phenotype. Antidepressant drugs have been shown to increase neurogenesis in the adult rodent hippocampus. In order to better understand the role of astroglia in antidepressant-induced neurogenesis, primary astrocyte cultures were treated with the antidepressant imipramine. Cell morphology was rapidly modified by treatment. In fact, whereas untreated astrocytes showed large, flat morphology, after a few hours of treatment cells exhibited a round-shaped cell body with long, thin processes. The expression of neuronal markers was analysed by immunocytochemistry, Western Blot and RT-PCR at different treatment times. Results showed an increase in neuronal markers such as neurofilament and neuron-specific enolase (NSE), whereas glial fibrillary acidic protein (GFAP) and nestin expression were not significantly modified by treatment. Similar results were obtained with fluoxetine and venlafaxine. Hes1 mRNA significantly increased after 2 h of treatment, suggesting involvement of this transcription factor in this process. These results confirm the role of astrocytes in neurogenesis and suggest that these cells may represent one of the targets of antidepressants.

Sexually dimorphic functional alterations of rat hepatic glucocorticoid receptor in response to fluoxetine

Gender-related differences in the expression and functional properties of the hepatic glucocorticoid receptor were studied before and after antidepressant fluoxetine administration to both unstressed and rats exposed to a chronic social isolation stress. Some of the receptor's functional properties, including hormone-binding capacity (B(max)), hormone-binding potency (B(max)/K(D) ratio) and the DNA-binding ability, were found to be sexually dimorphic. Fluoxetine treatment (5mg/kg body mass, 21day, intraperitoneally) induced a decrease in B(max) and in the amount of Hsp70 co-immunoprecipitated with the glucocorticoid receptor only in males, and stimulated the association of the receptor with Hsp90 in females. When applied during the last three weeks of the 6-week isolation, fluoxetine parallelly elevated B(max) and the receptor protein level in female animals, while in males diminished B(max) and inhibited association of the receptor with Hsp70. Binding of dexamethasone-receptor complexes both to DNA-cellulose and to isolated liver nuclei did not appear to be a target for fluoxetine action. The results point to sex-related differences in the glucocorticoid receptor functioning and in its response to fluoxetine, and suggest that these differences may contribute to well known sexual dimorphism in the sensitivity to stress, to stress-related disorders and to antidepressant treatment.

Bipolar disorder and mechanisms of action of mood stabilizers

Bipolar disorder (BD) is a major medical and social burden, whose cause, pathophysiology and treatment are not agreed on. It is characterized by recurrent periods of mania and depression (Bipolar I) or of hypomania and depression (Bipolar II). Its inheritance is polygenic, with evidence of a neurotransmission imbalance and disease progression. Patients often take multiple agents concurrently, with incomplete therapeutic success, particularly with regard to depression. Suicide is common. Of the hypotheses regarding the action of mood stabilizers in BD, the "arachidonic acid (AA) cascade" hypothesis is presented in detail in this review. It is based on evidence that chronic administration of lithium, carbamazepine, sodium valproate, or lamotrigine to rats downregulated AA turnover in brain phospholipids, formation of prostaglandin E(2), and/or expression of AA cascade enzymes, including cytosolic phospholipase A(2), cyclooxygenase-2 and/or acyl-CoA synthetase. The changes were selective for AA, since brain docosahexaenoic or palmitic acid metabolism, when measured, was unaffected, and topiramate, ineffective in BD, did not modify the rat brain AA cascade. Downregulation of the cascade by the mood stabilizers corresponded to inhibition of AA neurotransmission via dopaminergic D(2)-like and glutamatergic NMDA receptors. Unlike the mood stabilizers, antidepressants that increase switching of bipolar depression to mania upregulated the rat brain AA cascade. These observations suggest that the brain AA cascade is a common target of mood stabilizers, and that bipolar symptoms, particularly mania, are associated with an upregulated cascade and excess AA signaling via D(2)-like and NMDA receptors. This review presents ways to test these suggestions.

Targeted electrode-based modulation of neural circuits for depression

During the last 20 years of neuroscience research, we have witnessed a fundamental shift in the conceptualization of psychiatric disorders, with the dominant psychological and neurochemical theories of the past now complemented by a growing emphasis on developmental, genetic, molecular, and brain circuit models. Facilitating this evolving paradigm shift has been the growing contribution of functional neuroimaging, which provides a versatile platform to characterize brain circuit dysfunction underlying specific syndromes as well as changes associated with their successful treatment. Discussed here are converging imaging findings that established a rationale for testing a targeted neuromodulation strategy, deep brain stimulation, for treatment-resistant major depression.

Repeated unpredictable stress and antidepressants differentially regulate expression of the bcl-2 family of apoptotic genes in rat cortical, hippocampal, and limbic brain structures

Apoptosis has been proposed as a contributing cellular mechanism to the structural alterations that have been observed in stress-related mood disorders. Antidepressants, on the other hand, are hypothesized to exert trophic and/or neuroprotective actions. The present study examined the regulation of the major antiapoptotic (Bcl-2, Bcl-xl) and proapoptotic (Bax) genes by repeated unpredictable stress (an animal model of depression) and antidepressant treatments (ADT). In adult rats, exposure to unpredictable stress reduced Bcl-2 mRNA levels in the central nucleus of the amygdala (CeA), cingulate (Cg), and frontal (Fr) cortices. Bcl-xl mRNA was significantly decreased in hippocampal subfields. In contrast, chronic administration of clinically effective antidepressants from four different classes, ie fluoxetine, reboxetine, tranylcypromine, and electroconvulsive seizures (ECS) upregulated Bcl-2 mRNA expression in the Cg, Fr, and CeA. Reboxetine, tranylcypromine, and ECS selectively increased Bcl-xl, but not Bcl-2 mRNA expression in the hippocampus. Chemical ADT but not ECS, robustly enhanced Bcl-2 expression in the medial amygdaloid nucleus and ventromedial hypothalamus. Fluoxetine did not influence Bcl-xl expression in the hippocampus, but it was the only ADT that decreased Bax expression in this region. In the CeA, again in direct contrast to the stress effects, exposure to all classes of ADTs significantly increased Bcl-2 mRNA. The selective regulation of Bcl-xl and Bax in hippocampal subfields and of Bcl-2 in the Cg cortex, amygdala, and hypothalamus suggests that these cellular adaptations contribute to the long-term neural plastic adaptations to stress and ADTs in cortical, hypothalamic, and limbic brain structures.

Stress, depression, and neuroplasticity: a convergence of mechanisms

Increasing evidence demonstrates that neuroplasticity, a fundamental mechanism of neuronal adaptation, is disrupted in mood disorders and in animal models of stress. Here we provide an overview of the evidence that chronic stress, which can precipitate or exacerbate depression, disrupts neuroplasticity, while antidepressant treatment produces opposing effects and can enhance neuroplasticity. We discuss neuroplasticity at different levels: structural plasticity (such as plastic changes in spine and dendrite morphology as well as adult neurogenesis), functional synaptic plasticity, and the molecular and cellular mechanisms accompanying such changes. Together, these studies elucidate mechanisms that may contribute to the pathophysiology of depression. Greater appreciation of the convergence of mechanisms between stress, depression, and neuroplasticity is likely to lead to the identification of novel targets for more efficacious treatments.

Citalopram influences mGlu7, but not mGlu4 receptors' expression in the rat brain hippocampus and cortex

Earlier studies showed that chronic electroconvulsive shock (ECS) or imipramine treatment induced a sub-sensitivity of group I metabotropic glutamate receptors (mGluRs) in the hippocampus as well as an increase in the receptor protein level in this structure. In the present study, the effects of chronic imipramine (10 mg/kg, 21 days) or citalopram (10 mg/kg, 21 days) treatment on the mGlu4 or mGlu7 receptors' protein levels in the frontal cortex and hippocampus of the rat brain were examined using the Western blot analysis. We also examined the influence of these drugs' administration on forskolin-stimulated cAMP formation. A non-selective agonist of all receptors belonging to the III group of mGluRs, ACPT-1, was used to establish their effects on the cAMP production. It was found that mGluR7-immunoreactivity both in the hippocampus and in the cerebral cortex was decreased after citalopram, but not imipramine treatment. No changes were observed in the mGluR4-immunoreactivity. Prolonged treatment with these two drugs failed to change the action of group III mGluR agonist, ACPT-1, on the forskolin-stimulated cAMP accumulation. Our results suggest that the mGluR7 receptor is influenced by prolonged treatment of the antidepressant drug citalopram in the brain regions that are considered to be implicated in the clinical response to antidepressant therapy whilst the mGlu4 receptor is not.

Pharmacologically diverse antidepressants rapidly activate brain-derived neurotrophic factor receptor TrkB and induce phospholipase-Cgamma signaling pathways in mouse brain

Previous studies suggest that brain-derived neurotrophic factor and its receptor TrkB are critically involved in the therapeutic actions of antidepressant drugs. We have previously shown that the antidepressants imipramine and fluoxetine produce a rapid autophosphorylation of TrkB in the rodent brain. In the present study, we have further examined the biochemical and functional characteristics of antidepressant-induced TrkB activation in vivo. We show that all the antidepressants examined, including inhibitors of monoamine transporters and metabolism, activate TrkB rapidly in the rodent anterior cingulate cortex and hippocampus. Furthermore, the results indicate that acute and long-term antidepressant treatments induce TrkB-mediated activation of phospholipase-Cgamma1 (PLCgamma1) and increase the phosphorylation of cAMP-related element binding protein, a major transcription factor mediating neuronal plasticity. In contrast, we have not observed any modulation of the phosphorylation of TrkB Shc binding site, phosphorylation of mitogen-activated protein kinase or AKT by antidepressants. We also show that in the forced swim test, the behavioral effects of specific serotonergic antidepressant citalopram, but not those of the specific noradrenergic antidepressant reboxetine, are crucially dependent on TrkB signaling. Finally, brain monoamines seem to be critical mediators of antidepressant-induced TrkB activation, as antidepressants reboxetine and citalopram do not produce TrkB activation in the brains of serotonin- or norepinephrine-depleted mice. In conclusion, our data suggest that rapid activation of the TrkB neurotrophin receptor and PLCgamma1 signaling is a common mechanism for all antidepressant drugs.

Modulation of stress consequences by hippocampal monoaminergic, glutamatergic and nitrergic neurotransmitter systems

Several findings relate the hippocampal formation to the behavioural consequences of stress. It contains a high concentration of corticoid receptors and undergoes plastic modifications, including decreased neurogenesis and cellular remodelling, following stress exposure. Various major neurotransmitter systems in the hippocampus are involved in these effects. Serotonin (5-HT) seems to exert a protective role in the hippocampus and attenuates the behavioural consequences of stress by activating 5-HT1A receptors in this structure. These effects may mediate the therapeutic actions of several antidepressants. The role of noradrenaline is less clear and possibly depends on the specific hippocampal region (dorsal vs. ventral). The deleterious modifications induced in the hippocampus by stress might involve a decrease in neurotrophic factors such as brain derived neurotrophic factor (BDNF) following glutamate N-methyl-D-aspartate (NMDA) receptor activation. In addition to glutamate, nitric oxide (NO) could also be related to these effects. Systemic and intra-hippocampal administration of nitric oxide synthase (NOS) inhibitors attenuates stress-induced behavioural consequences. The challenge for the future will be to integrate results related to these different neurotransmitter systems in a unifying theory about the role of the hippocampus in mood regulation, depressive disorder and antidepressant effects.

Altered glucocorticoid receptor signaling cascade in lymphocytes of bipolar disorder patients

Bipolar disorder (BD) is characterized by hypothalamic pituitary adrenal (HPA) axis hyperactivity, glucocorticoid insensitivity and alterations in serotonin and inflammatory mediators. The glucocorticoid receptor (GR), activator protein-1 (AP-1), nuclear factor-kappa B (NF-kappaB) and c-jun N-terminal kinase (JNK) regulate the above mentioned processes; we therefore assessed their role in BD. Fifteen bipolar depressed patients under multiple anti-depressant therapy, 15 bipolar euthymics under lithium monotherapy and 25 matched controls were studied. Whole cell and nuclear extracts from lymphocytes were immunoblotted for GR, c-fos, JNK and NF-kappaB and nuclear aliquots were submitted to electrophoretic mobility shift assay for GR, AP-1 and NF-kappaB. Associations with the anti-depressant therapy and the state of the disease were also sought. Results, expressed as percentage of pooled protein standard sample intergraded optical density (IOD) (mean +/- SD), revealed: (a) depressed patients had significantly higher GR levels than controls in whole cell (82.63 +/- 6.18 versus 76.27 +/- 4.21%, P < 0.01) and nuclear extracts (86.66 +/- 3.81 versus 81.72 +/- 2.71%, P < 0.001) but lower GR-DNA binding (68.75 +/- 7.91 versus 81.84 +/- 4.25%, P < 0.05). Euthymics had normalized whole cell GR content (73.64 +/- 5.95%) and GR-DNA binding activity (76.82 +/- 7.29%) but higher nuclear GR content (86.89+/-3.96%, P<0.01) than controls; (b) nuclear c-fos content and AP-1-DNA-binding were significantly lower in depressed patients than controls (80.49 +/- 2.03 versus 84.82 +/- 3.48%, P < 0.05 and 78.46 +/- 4.17 versus 84.80 +/- 5.79%, P < 0.05, respectively). Euthymics however, showed similar nuclear c-fos and AP-1-DNA-binding to controls (85.48 +/- 2.71 and 87.78 +/- 3.54%, respectively) but lower whole cell c-fos than in controls (81.18 +/- 3.87 versus 87.01 +/- 4.22%, P < 0.001); (c) depressed patients had significantly lower whole cell and nuclear JNK than controls (67.01 +/- 4.29 versus 72.00 +/- 3.68%, P < 0.05 and 80.10 +/- 2.53 versus 86.96 +/- 2.49%, P < 0.001) whereas euthymics showed lower nuclear JNK (83.27 +/- 1.93%, P < 0.01); (d) whole cell NF-kB was higher in the depressed patients than in controls (67.30 +/- 5.00 versus 63.63 +/- 3.3%, P < 0.05). Concluding, intracellular signaling of GR, AP-1 and JNK are altered in BD and may underly disease aetiopathogenesis and/or reflect the effect of the anti-depressants.

The role of CREB in depression and antidepressant treatment

Major depressive disorder is a severe clinical problem across the globe, with a lifetime risk of 10%-30% for women and 7%-15% for men. The World Health Organization ranks major depression at the top of the list in terms of disease burden, and this burden is expected to rise in the next decade as the prevalence of the disorder grows. Since the late 1950s, a wide range of antidepressant medications targeting the monoamine systems has been available to alleviate the symptoms of major depressive disorder. Although widely prescribed, such antidepressant medications are accompanied by a delay in effectiveness, as well as varied side effects. Therefore, further characterization of the biological mechanisms behind their function is crucial for the development of new and more effective treatments. One protein that could serve as a convergence point for multiple classes of antidepressant drugs is the transcription factor CREB (cyclic adenosine monophosphate response element binding protein). CREB is upregulated by chronic antidepressant treatment, and increasing CREB levels in rodent models results in antidepressant-like behaviors. Furthermore, postmortem studies indicate that CREB levels are increased in subjects taking antidepressants at the time of death. However, not all antidepressants increase CREB levels and/or activity, and reducing CREB levels in some brain regions also results in antidepressant-like behaviors. This review attempts to consolidate the information relevant to the structure and function of the CREB protein and describe how this relates to the mechanism of antidepressant drugs. Animal models in which CREB function is enhanced, by overexpression of the protein, or reduced, by expression of mutant forms of the protein or through gene deletion experiments, are summarized in terms of identifying a role for CREB in behavioral responses in depression tests that were originally designed to evaluate antidepressant efficacy. Human postmortem and genetic studies that implicate CREB in depression and antidepressant efficacy are also discussed.

Signaling pathways regulating gene expression, neuroplasticity, and neurotrophic mechanisms in the action of antidepressants: a critical overview

Regulation of gene expression represents a major component in antidepressant drug action. The effect of antidepressant treatments on the function of cAMP-responsive element binding protein (CREB), a transcription factor that regulates expression of several genes involved in neuroplasticity, cell survival, and cognition, has been extensively studied. Although there is general agreement that chronic antidepressants stimulate CREB function, conflicting results suggest that different effects may depend on drug type, drug dosage, and different experimental paradigms. CREB function is activated by a vast array of physiological stimuli, conveyed through a number of signaling pathways acting in concert, but thus far the effects of antidepressants on CREB have been analyzed mostly with regard to the cAMP-protein kinase A pathway. A growing body of data shows that other major pathways, such as the calcium/calmodulin-dependent kinase and the mitogen-activated kinase cascades, are involved in activity-dependent regulation of gene expression and may also be implicated in the mechanism of action of antidepressants. In this article the available evidence is reviewed with an attempt to identify the reasons for experimental discrepancies and possible directions for future research. Particularemphasis is given to the regulation of brain-derived neurotrophic factor (BDNF), a CREB-regulated gene, which has been implicated in both the pathophysiology and pharmacology of mood disorders. The array of different results obtained by various groups is analyzed with an eye on recent advancements in the regulation of BDNF transcription, in an attempt to understand better the mechanisms of drug action and dissect molecular requirements for faster and more efficient antidepressant treatment.

Antidepressants and prolonged stress in rats modulate CAM-L1, laminin, and pCREB, implicated in neuronal plasticity

Previously, we reported an ability of NE to promote processes of plasticity in neuroblastoma cells, as observed by morphological changes such as an elongated granule-rich cell body and neuritegenesis, in addition to a progressive decrease in the pluripotent marker Oct4 and an increase in the growth cone marker GAP-43. This was accompanied by the induction of three plasticity genes forming a functional cluster, the cell adhesion molecule L1 (CAM-L1), laminin, and CREB, all involved in neuronal plasticity and neurite outgrowth. In the present study, we hypothesized that the regulation of CAM-L1, laminin, and CREB/pCREB by NE could mediate processes of plasticity in the mode of action of antidepressants, as well as in the long-term effects of stress, in rats, given the association of both with NE alterations and neuronal plasticity. In the first experiment, rats were chronically administered with antidepressants (21 days). In the second experiment, rats were exposed to chronic stress and examined 4 months later, a model shown to exhibit behavioral indices of stress. We found brain region-specific alterations in mRNA and protein levels of CAM-L1, laminin, and pCREB in rats chronically treated with the noradrenergic antidepressant desipramine and, to a lesser extent, in those treated with fluoxetine. Stressed rats presented a decrease in CAM-L1, laminin, and pCREB, specifically in brain areas implicated in stress. Our findings suggest that noradrenergic-regulated plasticity genes such as CAM-L1, laminin, and CREB play an important role both in stress and in the treatment of depression.

Antidepressant-elicited changes in gene expression: remodeling of neuronal circuits as a new hypothesis for drug efficacy

Although antidepressants have been used clinically for more than 50 years, no consensus has been reached concerning their precise molecular mechanism of action. Pharmacogenomics is a powerful tool that can be used to identify genes affected by antidepressants or by other effective therapeutic manipulations. Using this tool, others and we have identified as candidate molecular targets several genes or expressed sequence tags (ESTs) that are induced by chronic antidepressant treatment. In this article, we review antidepressant-elicited changes in gene expression, focusing especially on the remodeling of neuronal circuits that results. This refocusing motivates our hypothesis that this plasticity represents the mechanism for drug efficacy, and thus a causal event for clinical improvement. Defining the roles of these molecules in drug-induced neural plasticity is likely to transform the course of research on the biological basis of antidepressants. Such detailed knowledge will have profound effects on the diagnosis, prevention, and treatment of depression. Consideration of novel biological approaches beyond the "monoamine hypothesis" of depression is expected to evoke paradigm shifts in the future of antidepressant research.

Changes in signaling pathways regulating neuroplasticity induced by neurokinin 1 receptor knockout

Neurokinin 1 (NK-1) receptor knockout mice showed behavioral responses similar to animals chronically treated with antidepressants. The aim of this study was to analyse, in NK-1 receptor knockout, the molecular modifications of signaling pathways involved in the pathophysiology of depression and antidepressant mechanism. We found, in total cell cytosol from the prefrontal/frontal cortex, hippocampus and striatum, a marked up-regulation of Ca(2+)-independent enzymatic activity and Thr(286) autophosphorylation of Ca(2+)/calmodulin-dependent protein kinase (CaMK) II. Similar changes in CaMKII regulation were previously observed in rats chronically treated with antidepressants. In striatum, up-regulation of the activity and phosphorylation of CaMKII was also found in the homogenate and synaptosomes. No major changes were observed in the Ca(2+)-dependent kinase activity, with the exception of homogenate from the prefrontal/frontal cortex. We also analysed the expression and phosphorylation of presynaptic proteins, which modulate synaptic vesicle trafficking and exocytosis, and found a marked decrease in synapsin I total expression and basal phosphorylation of Ser(603) (the phosphorylation site for CaMKII) in the prefrontal/frontal cortex. Accordingly, the Ca(2+)/calmodulin-dependent posthoc endogenous phosphorylation of synapsin I in the same area was increased. The knockout of NK-1 receptor had no consequences on the expression or phosphorylation levels of the transcription factor cAMP-responsive element-binding protein and its regulating kinase CaMKIV. However, phosphorylation of ERK1/2-mitogen-activated protein kinases was reduced in the hippocampus and striatum, again resembling an effect previously observed in antidepressant-treated rats. These results show similarities between NK-1 knockouts and animals chronically treated with antidepressants and support the putative antidepressant activity of NK-1 receptor antagonists.

Identification and Expression of Frizzled-3 Protein in Rat Frontal Cortex After Antidepressant and Electroconvulsive Treatment

The biological basis for the therapeutic mechanisms of depression are still unknown. While performing EST (expressed sequence tag) analysis to identify some molecular machinery responsible for the antidepressant effect, we determined the full-length nucleotide sequence of rat frizzled-3 protein (Frz3) cDNA. Interestingly, Northern blot analysis demonstrated that elevated levels of Frz3 were expressed continually from embryonic day 20.5 to postnatal 4 weeks in developing rat brain. In adult rat brain, Frz3 mRNA was expressed predominantly in the cerebral cortex and hypothalamus and moderately in the hippocampus. Using real-time quantitative PCR, we demonstrated that chronic treatment with two different classes of antidepressants, imipramine and sertraline, reduced Frz3 mRNA expression significantly in rat frontal cortex. Electroconvulsive treatment (ECT) also reduced Frz3 expression. In contrast, antidepressants and ECT failed to reduce Frz2 expression. Additionally, chronic treatment with the antipsychotic drug haloperidol did not affect Frz3 expression. Recently, the Frz/Wingless protein pathway has been proposed to direct a complex behavioral phenomenon. In conclusion, the Frz3-mediated signaling cascade may be a component of the molecular machinery targeted by therapeutics commonly used to treat depression.

Selective phosphorylation of nuclear CREB by fluoxetine is linked to activation of CaM kinase IV and MAP kinase cascades

Regulation of gene expression is purported as a major component in the long-term action of antidepressants. The transcription factor cAMP-response element-binding protein (CREB) is activated by chronic antidepressant treatments, although a number of studies reported different effects on CREB, depending on drug types used and brain areas investigated. Furthermore, little is known as to what signaling cascades are responsible for CREB activation, although cAMP-protein kinase A (PKA) cascade was suggested to be a central player. We investigated how different drugs (fluoxetine (FLX), desipramine (DMI), reboxetine (RBX)) affect CREB expression and phosphorylation of Ser(133) in the hippocampus and prefrontal/frontal cortex (PFCX). Acute treatments did not induce changes in these mechanisms. Chronic FLX increased nuclear phospho-CREB (pCREB) far more markedly than pronoradrenergic drugs, particularly in PFCX. We investigated the function of the main signaling cascades that were shown to phosphorylate and regulate CREB. PKA did not seem to account for the selective increase of pCREB induced by FLX. All drug treatments markedly increased the enzymatic activity of nuclear Ca2+/calmodulin (CaM) kinase IV (CaMKIV), a major neuronal CREB kinase, in PFCX. Activation of this kinase was due to increased phosphorylation of the activatory residue Thr196, with no major changes in the expression levels of alpha- and beta-CaM kinase kinase, enzymes that phosphorylate CaMKIV. Again in PFCX, FLX selectively increased the expression level of MAP kinases Erk1/2, without affecting their phosphorylation. Our results show that FLX exerts a more marked effect on CREB phosphorylation and suggest that CaMKIV and MAP kinase cascades are involved in this effect.

Increased CRE-binding activity and tryptophan hydroxylase mRNA expression induced by 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") in the rat frontal cortex but not in the hippocampus

A single administration of either 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") or p-chloroamphetamine (PCA) produced a rapid and marked reduction of serotonin (5-HT) content in rat frontal cortex and hippocampus. In the cortex of MDMA-treated rats, 5-HT levels returned to control values 48 h after drug administration. This recovery was correlated with an induction of CRE-binding activity and an enhanced expression of tryptophan hydroxylase (TPH) mRNA, the rate-limiting enzyme in 5-HT biosynthesis, suggesting that MDMA may up-regulate the TPH gene through a CREB-dependent mechanism. In the cortex of PCA-treated rats, neither a recovery of 5-HT levels nor changes in DNA-binding or TPH mRNA were found at the same time point. In the hippocampus of rats receiving either PCA or MDMA a decrease in TPH mRNA levels was found at all times, along with a reduced CRE-binding at the 8-h time point. The results show region-specific effects of MDMA. In the frontal cortex, the increased TPH expression suggests a compensatory response to MDMA-induced loss of serotonergic function.

Effects of rolipram, a phosphodiesterase 4 inhibitor, in combination with imipramine on depressive behavior, CRE-binding activity and BDNF level in learned helplessness rats

The brain cAMP regulating system and its downstream elements play a pivotal role in the therapeutic effects of antidepressants. We previously reported the increase in activities of phosphodiesterase 4, a major phosphodiesterase isozyme hydrolyzing cAMP, in the frontal cortex and hippocampus of learned helplessness rats, an animal model for depression. The present study was undertaken to examine the combination of effects of rolipram, a phosphodiesterase 4 inhibitor, with imipramine, a typical tricyclic antidepressant, on depressive behavior in learned helplessness rats. Concurrently, cAMP-response element (CRE)-binding activity and brain-derived neurotrophic factor (BDNF) levels related to the therapeutic effects of antidepressants were determined. Repeated administration of imipramine (1.25-10 mg/kg, i.p.) or rolipram (1.25 mg/kg, i.p.) reduced the number of escape failures in learned helplessness rats. Imipramine could not completely ameliorate the escape behavior to a level similar to that of non-stressed rats even at 10 mg/kg. However, repeated coadministration of rolipram with imipramine (1.25 and 2.5 mg/kg, respectively) almost completely eliminated the escape failures in learned helplessness rats. The reduction of CRE-binding activities and BDNF levels in the frontal cortex or hippocampus in learned helplessness rats were ameliorated by treatment with imipramine or rolipram alone. CRE-binding activities and/or BDNF levels of the frontal cortex and hippocampus were significantly increased by treatment with a combination of rolipram and imipramine compared to those in imipramine-treated rats. These results indicated that coadministration of phosphodiesterase type 4 inhibitors with antidepressants may be more effective for depression therapy and suggest that elevation of the cAMP signal transduction pathway is involved in the antidepressive effects.

Different regulation of adenylyl cyclase and rolipram-sensitive phosphodiesterase activity on the frontal cortex and hippocampus in learned helplessness rats

The present study examined the activities of adenylyl cyclase (AC) and rolipram-sensitive phosphodiesterase (PDE4) on brain regions in learned helplessness rat in order to clarify the cyclic AMP (cAMP) regulation system in the depressive state. Rats exposed to inescapable footshocks once a day for 3 days exhibited a significant increase in escape failure on Day 1 (the day after the last inescapable shock day) and Day 7. The plasma corticosterone level in rats subjected to inescapable shocks was significantly higher than that of nonstressed control rats on Days 1 and 7. The PDE4 activity of the frontal cortex was significantly lower than that of nonstressed control rats on Day 1. However, on Day 7, the PDE4 and [3H]-rolipram binding activities were significantly increased in the frontal cortex and hippocampus of learned helplessness rats compared with those of nonstressed control rats. Forskolin-stimulated AC activity was significantly decreased in the frontal cortex, hippocampus and striatum of learned helplessness rats on Day 1, but not on Day 7. Thus, a decrease in both AC and PDE4 activities was noted in the acute depressive state. In contrast, increase of PDE4 activity was noted in the delayed depressive phase, although no change of AC activity was observed. Gel shift assays also showed the decrease of cAMP-response element (CRE)-binding activity relating to cAMP activity in the frontal cortex and hippocampus of learned helplessness rats on Days 1 and 7. These findings indicated a delayed increase in PDE4 activity leading to hypofunction of the cAMP-dependent signal transduction system in the frontal cortex and hippocampus of learned helplessness rats, suggesting that up-regulation of the cAMP-degradation system by PDE4 may play a pivotal role in pathological states of chronic depression.

Long-term treatment with paroxetine increases verbal declarative memory and hippocampal volume in posttraumatic stress disorder

BACKGROUND

Animal studies have shown that stress is associated with damage to the hippocampus, inhibition of neurogenesis, and deficits in hippocampal-based memory dysfunction. Studies in patients with posttraumatic stress disorder (PTSD) found deficits in hippocampal-based declarative verbal memory and smaller hippocampal volume, as measured with magnetic resonance imaging (MRI). Recent preclinical evidence has shown that selective serotonin reuptake inhibitors promote neurogenesis and reverse the effects of stress on hippocampal atrophy. This study assessed the effects of long-term treatment with paroxetine on hippocampal volume and declarative memory performance in PTSD.

METHODS

Declarative memory was assessed with the Wechsler Memory Scale-Revised and Selective Reminding Test before and after 9-12 months of treatment with paroxetine in PTSD. Hippocampal volume was measured with MRI. Of the 28 patients who started the protocol, 23 completed the full course of treatment and neuropsychological testing. Twenty patients were able to complete MRI imaging.

RESULTS

Patients with PTSD showed a significant improvement in PTSD symptoms with treatment. Treatment resulted in significant improvements in verbal declarative memory and a 4.6% increase in mean hippocampal volume.

CONCLUSIONS

These findings suggest that long-term treatment with paroxetine is associated with improvement of verbal declarative memory deficits and an increase in hippocampal volume in PTSD.

Effects of cholinergic lesions produced by infusions of 192 IgG-saporin on glucocorticoid receptor mRNA expression in hippocampus and medial prefrontal cortex of the rat

Principal neurons in the hippocampus and prefrontal cortex of the rat have been identified as targets for glucocorticoids involved in the hypothalamic-pituitary-adrenocortical stress response. Alterations in mRNA expression for glucocorticoid receptors in each of these regions have been shown to affect the negative feedback response to corticosterone following an acute stressor. Both decreases in forebrain glucocorticoid receptors and in the efficiency of adrenocortical feedback have been observed in normal aging, and have been selectively induced with experimental lesions or manipulations in neurotransmitter systems. The current study investigated the possibility that a loss of cholinergic support from cells in the basal forebrain, a hallmark of aging, contributes to the selective age-related loss of glucocorticoid receptor mRNA expression at cholinoceptive target sites that include the hippocampus and medial prefrontal cortex. Lesions of the basal forebrain cholinergic system in young adult rats were made by microinjections of the immunotoxin 192 IgG-saporin into the medial septum/vertical limb of the diagonal band and substantia innominata/nucleus basalis. Basal levels of circulating glucocorticoids were unaffected by the lesions. Analysis of both mineralocorticoid and glucocorticoid receptor mRNA expression revealed a significant decrease in glucocorticoid receptor mRNA in the hippocampus and medial prefrontal cortex, with spared expression at subcortical sites and no detectable change in mineralocorticoid receptor mRNA in any of the examined regions. Thus, rats with lesions of the basal forebrain cholinergic system recapitulate some of the detrimental effects of aging associated with glucocorticoid-mediated stress pathways in the brain.

Antidepressants and neuroplasticity

OBJECTIVE

We review the literature on the cellular changes that underlie the structural impairments observed in brains of animals exposed to stress and in subjects with depressive disorders. We discuss the molecular, cellular and structural adaptations that underlie the therapeutic responses of different classes of antidepressants and contribute to the adaptive plasticity induced in the brain by these drugs.

METHODS

We review results from various clinical and basic research studies.

RESULTS

Studies demonstrate that chronic antidepressant treatment increases the rate of neurogenesis in the adult hippocampus. Studies also show that antidepressants up-regulate the cyclic adenosine monophosphate (cAMP) and the neurotrophin signaling pathways involved in plasticity and survival. In vitro and in vivo data provide direct evidence that the transcription factor, cAMP response element-binding protein (CREB) and the neurotrophin, brain derived-neurotrophic factor (BDNF) are key mediators of the therapeutic response to antidepressants.

CONCLUSIONS

These results suggest that depression maybe associated with a disruption of mechanisms that govern cell survival and neural plasticity in the brain. Antidepressants could mediate their effects by increasing neurogenesis and modulating the signaling pathways involved in plasticity and survival.

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.

Effect of chronic imipramine or electroconvulsive shock on the expression of mGluR1a and mGluR5a immunoreactivity in rat brain hippocampus

Previous studies showed that chronic electroconvulsive shock (ECS) or imipramine treatment induced a subsensitivity of group I metabotropic glutamate receptors (mGluR) in hippocampus. In the present study effects of antidepressant treatment on the expression of mGluR1a and mGluR5a, belonging to the group I mGluR, were investigated in rat brain hippocampus using immunohistochemical and Western blot methods, respectively. Male Wistar rats were treated singly or chronically for 21 days with imipramine, 10 mg/kg, twice daily; with ECS (90 mA, 50 Hz, 0.5 s) every second day; or with haloperidol, 1.2 mg/kg, once daily. Appropriate controls were injected with saline. Rats were sacrificed 24 h after the last treatment and their hippocampi were taken out for analysis. It was found that the mGluR1a-immunoreactivity expression increased significantly in Ammon's horn (CA) regions after chronic ECS. The most pronounced effect was observed in the CA3. No significant effects were found after single treatment or after haloperidol. The expression of mGluR5a increased significantly after chronic imipramine in the CA1 and after chronic ECS in the CA3 region. The results obtained indicate an influence of antidepressant treatment on group I mGluR. This increase in the receptor protein level may be a compensatory mechanism developing after chronic treatment.

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.

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.

Signaling and gene expression in the neuron-glia unit during brain function and dysfunction: Holger Hydén in memoriam

Holger Hydén demonstrated almost 40 years ago that learning changes the base composition of nuclear RNA, i.e. induces an alteration in gene expression. An equally revolutionary observation at that time was that a base change occurred in both neurons and glia. From these findings, Holger Hydén concluded that establishment of memory is correlated with protein synthesis, and he demonstrated de novo synthesis of several high-molecular protein species after learning. Moreover, the protein, S-100, which is mainly found in glial cells, was increased during learning, and antibodies towards this protein inhibited memory consolidation. S-100 belongs to a family of Ca(2+)-binding proteins, and Holger Hydén at an early point realized the huge importance of Ca(2+) in brain function. He established that glial cells show more marked and earlier changes in RNA composition in Parkinson's disease than neurons. Holger Hydén also had the vision and courage to suggest that "mental diseases could as well be thought to depend upon a disturbance of processes in glia cells as in the nerve cells", and he showed that antidepressant drugs cause profound changes in glial RNA. The importance of Holger Hydén's findings and visions can only now be fully appreciated. His visionary concepts of the involvement of glia in neurological and mental illness, of learning being associated with changes in gene expression, and of the functional importance of Ca(2+)-binding proteins and Ca(2+) are presently being confirmed and expanded by others. This review briefly summarizes highlights of Holger Hydén's work in these areas, followed by a discussion of recent research, confirming his findings and expanding his visions. This includes strong evidence that glial dysfunction is involved in the development of Parkinson's disease, that drugs effective in mood disorders alter gene expression and exert profound effects on astrocytes, and that neuronal-astrocytic interactions in glutamate signaling, NO synthesis, Ca(2+) signaling, beta-adrenergic activity, second messenger production, protein kinase activities, and transcription factor phosphorylation control the highly programmed events that carry the memory trace through the initial, signal-mediated short-term and intermediate memory stages to protein synthesis-dependent long-term memory.

Induction of cysteine string protein after chronic antidepressant treatment in rat frontal cortex

We have previously identified 204 partial cDNA fragments (ADRG1-204) as antidepressant related genes/expressed sequence tags. Then, we developed our original cDNA microarrays, on which the 194 clones out of ADRG1-204 were spotted. With this ADRG microarray, we found that the expression of a spot, ADRG55, which representing cysteine string protein (CSP), was significantly increased in rat brain after chronic treatment with a selective serotonin reuptake inhibitor, sertraline. In the present study, reverse transcription-polymerase chain reaction analysis confirmed the induction of CSP at mRNA levels in rat frontal cortex after chronic treatment with two different classes of antidepressants, imipramine or sertraline. Western blot analysis also revealed that CSP-immunoreactivity was increased after antidepressant treatment. In conclusion, our data suggest that CSP is one of the common functional molecules induced after chronic antidepressant treatment.

Identification of a novel gene with RING-H2 finger motif induced after chronic antidepressant treatment in rat brain

Previously, we have identified 200 cDNA fragments as antidepressant related genes/ESTs. In this study, using these cDNAs, we developed our original cDNA microarray for rapid secondary screening of candidate genes as the novel therapeutic targets. With this microarray, we found that the expression of a novel gene, ADRG34, was significantly increased in rat hippocampus which had been chronically treated with a selective serotonin reuptake inhibitor antidepressant, sertraline. RT-PCR analysis also demonstrated the induction of ADRG34 at mRNA levels in rat hippocampus and the frontal cortex. This cDNA encoded 685 amino acid residues containing a RING-H2 finger motif at the carboxy-terminal. Sequence analysis of ADRG34 with the EMBL/GenBank database showed significant homology to mouse and human kf-1 gene. Our data suggest that ADRG34, a possible rat homologue of kf-1, may be one of the common functional molecules induced after chronic antidepressant treatment.

Antidepressants: past, present and future

Since the discovery of first antidepressants in mid-1950's, the field has been intensively studied. Several new classes of compounds emerged and several hypotheses on the mechanism of their action were proposed. The novel antidepressants are either selective and reversible monoamine oxidase inhibitors, (e.g., moclobemide), or selective serotonin reuptake inhibitors (e.g., citalopram or paroxetine), or serotonin and noradrenaline reuptake inhibitors (e.g. , venlafaxine). Recently neuropeptides (e.g., thyrotropin-releasing hormone,TRH) or antagonists of neuropeptide receptors (e.g., tachykinin NK(1) receptor) undergo clinical tests. Several hypotheses proposed the predominant involvement of one or few neurotransmitter receptors in the mechanism of antidepressant action, but it is now assumed that several distinct receptor mechanisms' trigger different but converging intracellular signal cascades that activate transcription factors, which, in turn, promote the expression of genes encoding for proteins, that play a crucial role in restoring of neuronal functions involved in mood regulation.

Antidepressant drugs inhibit glucocorticoid receptor-mediated gene transcription - a possible mechanism

1. Antidepressant drugs are known to inhibit some changes evoked by glucocorticoids, as well as a hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis, often observed in depression. 2. The aim of present study was to investigate effects of various antidepressant drugs on the glucocorticoid-mediated gene transcription in fibroblast cells, stably transfected with an MMTV promoter (LMCAT cells). 3. The present study have shown that antidepressants (imipramine, amitriptyline, desipramine, fluoxetine, tianeptine, mianserin and moclobemide), but not cocaine, inhibit the corticosterone-induced gene transcription in a concentration- and a time-dependent manner. 4. Drugs which are known to augment clinical effects of medication in depressed patients (lithium chloride, amantadine, memantine), do not affect the inhibitory effects of imipramine on the glucocorticoid receptor (GR)-mediated gene transcription. 5. Inhibitors of phospholipase C (PLC), protein kinase C (PKC), Ca(2+)/calmodulin-dependent protein kinase (CaMK) and antagonists of the L-type Ca(2+) channel also inhibit the corticosterone-induced gene transcription. 6. Inhibitors of protein kinase A (PKA) and protein kinase G (PKG) are without effect on the GR-induced gene transcription. 7. Phorbol ester (an activator of PKC) attenuates the inhibitory effect of imipramine on the GR-induced gene transcription. 8. Imipramine decreases binding of corticosterone-receptor complex to DNA. 9. It is concluded that antidepressant drugs inhibit the corticosterone-induced gene transcription, and that the inhibitory effect of imipramine depends partly on the PLC/PKC pathway.

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.

A "theory of relativity" for cognitive elasticity of time and modality dimensions supporting constant working memory capacity: involvement of harmonics among ultradian clocks?

1. The capacity of working memory (WM) for about 7+/-2 ("the magical number") serially organized simple verbal items may represent a fundamental constant of cognition. Indeed, there is the same capacity for sense of familiarity of a number of recently encountered places, observed in radial maze performance both of lab rats and of humans. 2. Moreover, both species show a peculiar capacity for retaining WM of place over delays. The literature also describes paradoxes of extended time duration in certain human verbal recall tasks. Certain bird species have comparable capacity for delayed recall of about 4 to 8 food caches in a laboratory room. 3. In addition to these paradoxes of the time dimension with WM (still sometimes called "short-term" memory) there are another set of paradoxes of dimensionality for human judgment of magnitudes, noted by Miller in his classic 1956 paper on "the magical number." We are able to reliably refer magnitudes to a rating scale of up to about seven divisions. Remarkably, that finding is largely independent of perceptual modality or even of the extent of a linear interval selected within any given modality. 4. These paradoxes suggest that "the magical number 7+/2" depends on fundamental properties of mammalian brains. 5. This paper theorizes that WM numerosity is conserved as a fundamental constant, by means of elasticity of cognitive dimensionality, including the temporal pace of arrival of significant items of cognitive information. 6. A conjectural neural code for WM item-capacity is proposed here, which extends the hypothetical principle of binding-by-synchrony. The hypothesis is that several coactive frequencies of brain electrical rhythms each mark a WM item. 7. If, indeed, WM does involve a brain wave frequency code (perhaps within the gamma frequency range that has often been suggested with the binding hypothesis) mathematical considerations suggest additional relevance of harmonic relationships. That is, if copresent sinusoids bear harmony-like ratios and are confined within a single octave, then they have fast temporal properties, while avoiding spurious difference rhythms. Therefore, if the present hypothesis is valid, it implies a natural limit on parallel processing of separate items in organismic brains. 8. Similar logic of periodic signals may hold for slower ultradian rhythms, including hypothetical ones that contribute to time-tagging and fresh sense of familiarity of a day's event memories. Similar logic may also hold for spatial periodic functions across brain tissue that, hypothetically, represent cognitive information. Thus, harmonic transitions among temporal and spatial periodic functions are a possible vehicle for the cognitive dimensional elasticity that conserves WM capacity. 9. Supporting roles are proposed of (a) basal ganglia, as a high-capacity cache for traces of recent experience temporarily suspended from active task-relevant processing and (b) of hippocampus as a phase and interval comparator for oscillating signals, whose spatiotemporal dynamics are topologically equivalent to a toroidal grid.