Differential expression of VAMP2/synaptobrevin-2 after antidepressant and electroconvulsive treatment in rat frontal cortex

Serum amyloid P component (SAP) modulates antidepressant effects through promoting membrane insertion of the serotonin transporter

Serum amyloid P component (SAP) is a universal constituent of human amyloid deposits including those in Alzheimer's disease. SAP has been observed to be elevated in patients with depression, and higher SAP levels are associated with better response to the antidepressant escitalopram. The mechanisms underlying these clinical observations remain unclear. We examined the effect of SAP on serotonin transporter (SERT) expression and localization using Western blot, confocal microscopy, and positron emission tomography with the radioligand [11C]DASB. We also investigated the effect of SAP on treatment response to escitalopram in mice with the forced swim test (FST), a classical behaviour paradigm to assess antidepressant effects. SAP reduced [11C]DASB binding as an index of SERT levels, consistent with Western blots showing decreased total SAP protein because of increased protein degradation. In conjunction with the global decrease in SERT levels, SAP also promotes VAMP-2 mediated SERT membrane insertion. SAP levels are correlated with behavioural despair and SSRI treatment response in mice with FST. In MDD patients, the SAP and membrane SERT levels are correlated with response to SSRI treatment. SAP has complex effects on SERT levels and localization, thereby modulating the effect of SSRIs, which could partially explain clinical variability in antidepressant treatment response. These results add to our understanding of the mechanism for antidepressant drug action, and with further work could be of clinical utility.

Human-Relevant Sensitivity of iPSC-Derived Human Motor Neurons to BoNT/A1 and B1

The application of botulinum neurotoxins (BoNTs) for medical treatments necessitates a potency quantification of these lethal bacterial toxins, resulting in the use of a large number of test animals. Available alternative methods are limited in their relevance, as they are based on rodent cells or neuroblastoma cell lines or applicable for single toxin serotypes only. Here, human motor neurons (MNs), which are the physiological target of BoNTs, were generated from induced pluripotent stem cells (iPSCs) and compared to the neuroblastoma cell line SiMa, which is often used in cell-based assays for BoNT potency determination. In comparison with the mouse bioassay, human MNs exhibit a superior sensitivity to the BoNT serotypes A1 and B1 at levels that are reflective of human sensitivity. SiMa cells were able to detect BoNT/A1, but with much lower sensitivity than human MNs and appear unsuitable to detect any BoNT/B1 activity. The MNs used for these experiments were generated according to three differentiation protocols, which resulted in distinct sensitivity levels. Molecular parameters such as receptor protein concentration and electrical activity of the MNs were analyzed, but are not predictive for BoNT sensitivity. These results show that human MNs from several sources should be considered in BoNT testing and that human MNs are a physiologically relevant model, which could be used to optimize current BoNT potency testing.

Dysfunction of the SNARE complex in neurological and psychiatric disorders

The communication between neurons constitutes the basis of all neural activities, and synaptic vesicle exocytosis is the fundamental biological event that mediates most communication between neurons in the central nervous system. The SNARE complex is the core component of the protein machinery that facilitates the fusion of synaptic vesicles with presynaptic terminals and thereby the release of neurotransmitters. In synapses, each release event is dependent on the assembly of the SNARE complex. In recent years, basic research on the SNARE complex has provided a clearer understanding of the mechanism underlying the formation of the SNARE complex and its role in vesicle formation. Emerging evidence indicates that abnormal expression or dysfunction of the SNARE complex in synapse physiology might contribute to abnormal neurotransmission and ultimately to synaptic dysfunction. Clinical research using postmortem tissues suggests that SNARE complex dysfunction is correlated with various neurological diseases, and some basic research has also confirmed the important role of the SNARE complex in the pathology of these diseases. Genetic and pharmacogenetic studies suggest that the SNARE complex and individual proteins might represent important molecular targets in neurological disease. In this review, we summarize the recent progress toward understanding the SNARE complex in regulating membrane fusion events and provide an update of the recent discoveries from clinical and basic research on the SNARE complex in neurodegenerative, neuropsychiatric, and neurodevelopmental diseases.

Transcriptional evidence for the role of chronic venlafaxine treatment in neurotrophic signaling and neuroplasticity including also Glutamatergic [corrected] - and insulin-mediated neuronal processes

OBJECTIVES

Venlafaxine (VLX), a serotonine-noradrenaline reuptake inhibitor, is one of the most commonly used antidepressant drugs in clinical practice for the treatment of major depressive disorder (MDD). Despite being more potent than its predecessors, similarly to them, the therapeutical effect of VLX is visible only 3-4 weeks after the beginning of treatment. Furthermore, recent papers show that antidepressants, including also VLX, enhance the motor recovery after stroke even in non depressed persons. In the present, transcriptomic-based study we looked for changes in gene expressions after a long-term VLX administration.

METHODS

Osmotic minipumps were implanted subcutaneously into Dark Agouti rats providing a continuous (40 mg/kg/day) VLX delivery for three weeks. Frontal regions of the cerebral cortex were isolated and analyzed using Illumina bead arrays to detect genes showing significant chances in expression. Gene set enrichment analysis was performed to identify specific regulatory networks significantly affected by long term VLX treatment.

RESULTS

Chronic VLX administration may have an effect on neurotransmitter release via the regulation of genes involved in vesicular exocytosis and receptor endocytosis (such as Kif proteins, Myo5a, Sv2b, Syn2 or Synj2). Simultaneously, VLX activated the expression of genes involved in neurotrophic signaling (Ntrk2, Ntrk3), glutamatergic transmission (Gria3, Grin2b and Grin2a), neuroplasticity (Camk2g/b, Cd47), synaptogenesis (Epha5a, Gad2) and cognitive processes (Clstn2). Interestingly, VLX increased the expression of genes involved in mitochondrial antioxidant activity (Bcl2 and Prdx1). Additionally, VLX administration also modulated genes related to insulin signaling pathway (Negr1, Ppp3r1, Slc2a4 and Enpp1), a mechanism that has recently been linked to neuroprotection, learning and memory.

CONCLUSIONS

Our results strongly suggest that chronic VLX treatment improves functional reorganization and brain plasticity by influencing gene expression in regulatory networks of motor cortical areas. These results are consonant with the synaptic (network) hypothesis of depression and antidepressant-induced motor recovery after stroke.

The endogenous and reactive depression subtypes revisited: integrative animal and human studies implicate multiple distinct molecular mechanisms underlying major depressive disorder

BACKGROUND

Traditional diagnoses of major depressive disorder (MDD) suggested that the presence or absence of stress prior to onset results in either 'reactive' or 'endogenous' subtypes of the disorder, respectively. Several lines of research suggest that the biological underpinnings of 'reactive' or 'endogenous' subtypes may also differ, resulting in differential response to treatment. We investigated this hypothesis by comparing the gene-expression profiles of three animal models of 'reactive' and 'endogenous' depression. We then translated these findings to clinical samples using a human post-mortem mRNA study.

METHODS

Affymetrix mouse whole-genome oligonucleotide arrays were used to measure gene expression from hippocampal tissues of 144 mice from the Genome-based Therapeutic Drugs for Depression (GENDEP) project. The study used four inbred mouse strains and two depressogenic 'stress' protocols (maternal separation and Unpredictable Chronic Mild Stress) to model 'reactive' depression. Stress-related mRNA differences in mouse were compared with a parallel mRNA study using Flinders Sensitive and Resistant rat lines as a model of 'endogenous' depression. Convergent genes differentially expressed across the animal studies were used to inform candidate gene selection in a human mRNA post-mortem case control study from the Stanley Brain Consortium.

RESULTS

In the mouse 'reactive' model, the expression of 350 genes changed in response to early stresses and 370 in response to late stresses. A minimal genetic overlap (less than 8.8%) was detected in response to both stress protocols, but 30% of these genes (21) were also differentially regulated in the 'endogenous' rat study. This overlap is significantly greater than expected by chance. The VAMP-2 gene, differentially expressed across the rodent studies, was also significantly altered in the human study after correcting for multiple testing.

CONCLUSIONS

Our results suggest that 'endogenous' and 'reactive' subtypes of depression are associated with largely distinct changes in gene-expression. However, they also suggest that the molecular signature of 'reactive' depression caused by early stressors differs considerably from that of 'reactive' depression caused by late stressors. A small set of genes was consistently dysregulated across each paradigm and in post-mortem brain tissue of depressed patients suggesting a final common pathway to the disorder. These genes included the VAMP-2 gene, which has previously been associated with Axis-I disorders including MDD, bipolar depression, schizophrenia and with antidepressant treatment response. We also discuss the implications of our findings for disease classification, personalized medicine and case-control studies of MDD.

Effects of chronic fluoride exposure on object recognition memory and mRNA expression of SNARE complex in hippocampus of male mice

This study aimed to investigate the effects of long-term fluoride exposure on object recognition memory and mRNA expression of soluble N-ethylmaleimidesensitive fusion protein attachment protein receptors (SNARE) complex (synaptosome-associated protein of 25 kDa (SNAP-25), vesicle-associated membrane protein 2 (VAMP-2), and syntaxin 1A) in the hippocampus of male mice. Sixty sexually matured male Kunming mice were randomly divided into four groups: control group (given distilled water), low F group (25 mg/L NaF, corresponding to 11 mg/L F(-)), medium F group (50 mg/L NaF, corresponding to 22 mg/L F(-)), and high F group (100 mg/L NaF, corresponding to 45 mg/L F(-)). After 180 days, the spontaneous locomotor behavior and object recognition memory were detected by open field test and novel object recognition (NOR) test. Results showed that compared with the control group, frequency in each zone, total distance, and line crosses were significantly increased in low F and medium F groups, suggesting fluoride enhanced excitement of mice, while there were no marked changes in high F group. Twenty-four hours after training, a deficit of long-term memory (LTM) occurred only in high F group (P < 0.05), but there was no significant change of short-term memory (STM) 1.5 h later. The mRNA expression levels of SNAP-25, VAMP-2, and syntaxin 1A were detected by real-time quantitative RT-PCR, which revealed that the mRNA expression of VAMP-2 was significantly increased in medium F and high F groups (P < 0.01). Taken together, these results indicated that long-term fluoride administration can enhance the excitement of male mice, impair recognition memory, and upregulate VAMP-2 mRNA expression, which are involved in the adverse effects of fluoride on the object recognition memory of nervous system.

Temporal gene expression profile after acute electroconvulsive stimulation in the rat

Electroconvulsive therapy (ECT) remains one of the most effective treatments of major depression. It has been suggested that the mechanisms of action involve gene expression. In recent decades there have been several investigations of gene expression following both acute and chronic electroconvulsive stimulation (ECS). These studies have focused on several distinct gene targets but have generally included only few time points after ECS for measuring gene expression. Here we measured gene expression of three types of genes: Immediate early genes, synaptic proteins, and neuropeptides at six time points following an acute ECS. We find significant increases for c-Fos, Egr1, Neuritin 1 (Nrn 1), Bdnf, Snap29, Synaptotagmin III (Syt 3), Synapsin I (Syn 1), and Psd95 at differing time points after ECS. For some genes these changes are prolonged whereas for others they are transient. Npy expression significantly increases whereas the gene expression of its receptors Npy1r, Npy2r, and Npy5r initially decreases. These decreases are followed by a significant increase for Npy2r, suggesting anticonvulsive adaptations following seizures. In summary, we find distinct changes in mRNA quantities that are characteristic for each gene. Considering the observed transitory and inverse changes in expression patterns, these data underline the importance of conducting measurements at several time points post-ECS.

Stress susceptibility-specific phenotype associated with different hippocampal transcriptomic responses to chronic tricyclic antidepressant treatment in mice

Background

The effects of chronic treatment with tricyclic antidepressant (desipramine, DMI) on the hippocampal transcriptome in mice displaying high and low swim stress-induced analgesia (HA and LA lines) were studied. These mice displayed different depression-like behavioral responses to DMI: stress-sensitive HA animals responded to DMI, while LA animals did not.

Results

To investigate the effects of DMI treatment on gene expression profiling, whole-genome Illumina Expression BeadChip arrays and qPCR were used. Total RNA isolated from hippocampi was used. Expression profiling was then performed and data were analyzed bioinformatically to assess the influence of stress susceptibility-specific phenotypes on hippocampal transcriptomic responses to chronic DMI. DMI treatment affected the expression of 71 genes in HA mice and 41 genes in LA mice. We observed the upregulation of Igf2 and the genes involved in neurogenesis (HA: Sema3f, Ntng1, Gbx2, Efna5, and Rora; LA: Otx2, Rarb, and Drd1a) in both mouse lines. In HA mice, we observed the upregulation of genes involved in neurotransmitter transport, the termination of GABA and glycine activity (Slc6a11, Slc6a9), glutamate uptake (Slc17a6), and the downregulation of neuropeptide Y (Npy) and corticotropin releasing hormone-binding protein (Crhbp). In LA mice, we also observed the upregulation of other genes involved in neuroprotection (Ttr, Igfbp2, Prlr) and the downregulation of genes involved in calcium signaling and ion binding (Adcy1, Cckbr, Myl4, Slu7, Scrp1, Zfp330).

Conclusions

Several antidepressant treatment responses are similar in individuals with different sensitivities to stress, including the upregulation of Igf2 and the genes involved in neurogenesis. However, the findings also reveal that many responses to antidepressant treatments, involving the action of individual genes engaged in neurogenesis, neurotransmitter transport and neuroprotection, depend on constitutive hippocampal transcriptomic profiles and might be genotype dependent. The results suggest that, when and if this becomes feasible, antidepressant treatment should take into consideration individual sensitivity to stress.

Ketamine regulates the presynaptic release machinery in the hippocampus

In the search for new drug targets, that may help point the way to develop fast-acting treatments for mood disorders, we have explored molecular pathways regulated by ketamine, an NMDA receptor antagonist, which has consistently shown antidepressant response within a few hours of administration. Using Sprague-Dawley rats we investigated the effects of ketamine on the presynaptic release machinery responsible for neurotransmitter release at 1, 2 and 4 h as well as 7 days after administration of a single subanesthetic dose of ketamine (15 mg/kg). A large reduction in the accumulation of SNARE complexes was observed in hippocampal synaptic membranes after 1, 2 and 4 h of ketamine administration. In parallel, we found a selective reduction in the expression of the synaptic vesicle protein synaptotagmin I and an increase in the levels of synapsin I in hippocampal synaptosomes suggesting a mechanism by which ketamine reduces SNARE complex formation, in part, by regulating the number of synaptic vesicles in the nerve terminals. Moreover, ketamine reduced Thr(286)-phosphorylated αCaMKII and its interaction with syntaxin 1A, which identifies CaMKII as a potential target for second messenger-mediated actions of ketamine. In addition, despite previous reports of ketamine-induced inhibition of GSK-3, we were unable to detect regulation of its activity after ketamine administration. Our findings demonstrate that ketamine rapidly induces changes in the hippocampal presynaptic machinery similar to those that are obtained only with chronic treatments with traditional antidepressants. This suggests that reduction of neurotransmitter release in the hippocampus has possible relevance for the rapid antidepressant effect of ketamine.

Altered expression of synapse and glutamate related genes in post-mortem hippocampus of depressed subjects

Major depressive disorder (MDD) has been linked to changes in function and activity of the hippocampus, one of the central limbic regions involved in regulation of emotions and mood. The exact cellular and molecular mechanisms underlying hippocampal plasticity in response to stress are yet to be fully characterized. In this study, we examined the genetic profile of micro-dissected subfields of post-mortem hippocampus from subjects diagnosed with MDD and comparison subjects matched for sex, race and age. Gene expression profiles of the dentate gyrus and CA1 were assessed by 48K human HEEBO whole genome microarrays and a subgroup of identified genes was confirmed by real-time polymerase chain reaction (qPCR). Pathway analysis revealed altered expression of several gene families, including cytoskeletal proteins involved in rearrangement of neuronal processes. Based on this and evidence of hippocampal neuronal atrophy in MDD, we focused on the expression of cytoskeletal, synaptic and glutamate receptor genes. Our findings demonstrate significant dysregulation of synaptic function/structure related genes SNAP25, DLG2 (SAP93), and MAP1A, and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor subunit genes GLUR1 and GLUR3. Several of these human target genes were similarly dysregulated in a rat model of chronic unpredictable stress and the effects reversed by antidepressant treatment. Together, these studies provide new evidence that disruption of synaptic and glutamatergic signalling pathways contribute to the pathophysiology underlying MDD and provide interesting targets for novel therapeutic interventions.

Differential expression of synaptic proteins after chronic restraint stress in rat prefrontal cortex and hippocampus

Prolonged stress has been associated with altered synaptic plasticity but little is known about the molecular components and mechanisms involved in the stress response. In this study, we examined the effect of chronic restraint stress (CRS) on the expression of genes associated with synaptic vesicle exocytosis in rat prefrontal cortex and hippocampus. Rats were stressed daily using a 21day restraint stress paradigm, with durations of half an hour or 6h. RNA and protein were extracted from the same tissue sample and used for real-time quantitative polymerase chain reaction (real-time qPCR) and immunoblotting, respectively. Focusing on the SNARE complex, we investigated the expression of the SNARE core components syntaxin 1A, SNAP-25, and VAMP2 at both transcriptional and protein levels. In addition, the expression of 10 SNARE regulatory proteins was investigated at the transcriptional level. Overall, the prefrontal cortex was more sensitive to CRS compared to the hippocampus. In prefrontal cortex, CRS induced increased mRNA levels of VAMP2, VAMP1, syntaxin 1A, snapin, synaptotagmins I and III, and synapsins I and II, whereas SNAP-25 was down-regulated after CRS. Immunoblotting demonstrated equivalent changes in protein levels of VAMP2, syntaxin 1A, and SNAP-25. In hippocampus, we found increased mRNA levels of VAMP2 and SNAP-29 and a decrease in VAMP1 levels. Immunoblotting revealed decreased VAMP2 protein levels despite increased mRNA levels. Changes in the expression of synaptic proteins may accompany or contribute to the morphological, functional, and behavioral changes observed in experimental models of stress and may have relevance to the pathophysiology of stress-related disorders.

Profiling of hypothalamic and hippocampal gene expression in chronically stressed rats treated with St. John's wort extract (STW 3-VI) and fluoxetine

RATIONALE

Hypericum perforatum L., known as St. John's wort (SJW), is used as a phytotherapeutic agent for the treatment of mild to moderate forms of depression.

OBJECTIVES

The aim of the present study was to evaluate the effect of SJW extract (STW 3-VI; 250 and 500 mg/kg; p.o.) and fluoxetine (10 mg/kg, p.o.) on genes involved in the pathogenesis of depression using a chronic restraint stress (CRS) model in rats. Of particular interest was the assessment of similarities and differences between SJW extract and fluoxetine on the gene expression level in two different brain regions.

RESULTS

Hypothalamic and hippocampal tissues were analyzed using the Affymetrix gene chip Rat Genome 230 2.0 Array, which comprises more than 30,000 rat transcripts. Limma program and PANTHER database were used to evaluate the microarray data. Genes involved in the pathways of inflammatory processes (Mapk8), oxidative stress (Gpx3, Gstm3, Sod3) or Alzheimer's disease (Sncb, Apbb1ip) were altered by both fluoxetine and SJW extract. For all groups, several signaling pathways were identified which could provide a link between the various hypotheses of depression.

CONCLUSION

In conclusion, microarray analysis proved to be a valuable tool to identify a large number of genes and resulting pathways that may serve as novel drug targets or predict drug responsiveness for SJW or fluoxetine. Based on our comprehensive analysis, it was possible to identify similarities and differences between SJW and fluoxetine which may help to better understand their molecular action and, in addition, help to find novel treatment strategies for stress-related depression.

Fluoxetine treatment induces EAAT2 expression in rat brain

Synaptic pathology and disturbed glutamatergic neurotransmission contribute to the neurobiology of depression. Reduced expression of glutamate transporters, most importantly excitatory amino acid transporter (EAAT2), was reported in human studies and animal models. We therefore assessed the effects of antidepressant treatment upon EAAT2 expression. Male Sprague-Dawley rats received daily intraperitoneal injections of the antidepressants desipramine (DES, N = 7), fluoxetine (FLU, N = 7), tranylcypromine (TRAN, N = 5) or a saline control (CON, N = 5) for a period of 14 days. The expression of the major glial glutamate transporter EAAT2 was evaluated by semi-quantitative in situ hybridizations using a (35)S-labeled cRNA probe. Treatment with FLU significantly induced EAAT2 expression in hippocampal and cortical regions in comparison with saline injections, while DES and TRAN-applications did not exert significant effects. It can be postulated that increased expression of EAAT2 may counterbalance the tonus of glutamatergic neurotransmission. Our findings are in concert with human post-mortem findings, valid animal models of depression, antidepressive effects of NMDA-antagonists, and the glutamatergic theory of depression. Further studies should examine the effects of antidepressant treatments upon EAAT2 expression in rodent models of depression to further elucidate the underlying molecular mechanisms.

Region and diagnosis-specific changes in synaptic proteins in schizophrenia and bipolar I disorder

Aberrant regulation of synaptic function is thought to play a role in the aetiology of psychiatric disorders, including schizophrenia and bipolar disorder. Normal neurotransmitter release is dependent on a complex group of presynaptic proteins that regulate synaptic vesicle docking, membrane fusion and fission, including synaptophysin, syntaxin, synaptosomal-associated protein-25 (SNAP-25), vesicle-associated membrane protein (VAMP), alpha-synuclein and dynamin I. In addition, structural and signalling proteins such as neural cell adhesion molecule (NCAM) maintain the integrity of the synapse. We have assessed the levels of these important synaptic proteins using Western blots, in three cortical regions (BA10, 40 and 46) obtained post-mortem from subjects with bipolar 1 disorder, schizophrenia or no history of a psychiatric disorder. In bipolar 1 disorder cortex (parietal; BA40), we found a significant increase in the expression of SNAP-25, and a significant reduction in alpha-synuclein compared with controls. These changes in presynaptic protein expression are proposed to inhibit synaptic function in bipolar 1 disorder. In schizophrenia, a significant reduction in the ratio of the two major membrane-bound forms of NCAM (180 and 140) was observed in BA10. The distinct functions of these two NCAM forms suggest that changes in the comparative levels of these proteins could lead to a destabilisation of synaptic signalling. Our data support the notion that there are complex and region-specific alterations in presynaptic proteins that may lead to alterations in synaptic activity in both schizophrenia and bipolar disorder.

Neuroserpin is expressed in early stage of neurogenesis in adult rat hippocampus

In the adult rat hippocampal formation, neurogenesis occurs in the dentate gyrus subgranular zone (SGZ). We used laser capture microdissection and an antidepressant-related genes microarray to analyze gene expression profiles of cells from the SGZ and from the outermost granule cell layer. Of the differentially expressed genes in the SGZ, we focused on neuroserpin, which is highly expressed in the adult rat SGZ. Neuroserpin immunoreactivity was present in cells positive for NeuN (postmitotic cell marker) and Tuj1 (immature neuron marker) but not in cells positive for calbindin (mature neuron marker). Although neuroserpin is expressed during late stage of neurogenesis in development, our results suggest that neuroserpin may play some roles in early stage of neurogenesis in adult rat hippocampus.

Neuropeptide Y modulates the antidepressant activity of imipramine in olfactory bulbectomized rats: involvement of NPY Y1 receptors

Since long-term treatment with imipramine increases the neuropeptide Y (NPY) levels in the frontal cortex and hypothalamus, the possibility exists that the antidepressant action of imipramine may be mediated via the NPY Y1 receptors. Bilateral olfactory bulbectomy (OBX) resulted in hyperactivity (increased number of ambulation, rearing and grooming episodes) in open field test (OFT) suggesting a depression-like condition. Chronic (14 days) administration of NPY, NPY Y1/Y5 receptor agonist [Leu(31), Pro(34)]-NPY (intracerebroventricular, i.c.v.) or tricyclic antidepressant imipramine (intraperitoneal) to OBX rats dose-dependently resulted in decreased hyperactivity in OFT, while selective NPY Y1 receptor antagonist BIBP3226 (i.c.v.) produced opposite effects. The antidepressant actions of imipramine were enhanced by co-administration of NPY or [Leu(31), Pro(34)]-NPY, and antagonized by BIBP3226 given at sub-effective doses. The data suggest that NPY, acting via NPY Y1 receptors, may be involved in antidepressant action of imipramine in OBX rats.

Downregulation of Ccnd1 and Hes6 in rat hippocampus after chronic exposure to the antidepressant paroxetine

OBJECTIVE

The mechanism of action of antidepressant drugs is not fully understood. Application of genomic methods enables the identification of biochemical pathways that are regulated by antidepressants, and this may provide novel clues to the molecular and cellular actions of these drugs. The present study examined gene expression profiles in the hippocampus of rats exposed to chronic antidepressant treatment.

METHODS

Animals were treated for 12 days with the selective serotonin reuptake inhibitor paroxetine; then, hippocampal ribonucleic acid was recovered, and changes in gene expression were assessed by microarray analysis.

RESULTS

A total of 160 genes that showed differential expression after paroxetine exposure were identified. Using functional relevance and observed fold change as selection criteria, the expression changes in a subset of these genes were confirmed by quantitative polymerase chain reaction.

CONCLUSION

Of this subset, only two genes, cyclin D1 (Ccnd1) and hairy and enhancer of split 6 (Hes6), showed robust and consistent changes in expression. Both genes were downregulated by paroxetine, and both have been previously implicated in neurogenesis. Further investigation of these two genes may provide new insight into the mechanism of action of antidepressants.

Association study between vesicle-associated membrane protein 2 gene polymorphisms and fluvoxamine response in Japanese major depressive patients

BACKGROUND

Vesicle-associated membrane protein 2 (VAMP2) is a key component of the synaptic vesicle docking/fusion machinery and its mRNA reportedly increases in the frontal cortex of rats following chronic antidepressant and electroconvulsive treatment. VAMP2 is therefore thought to be involved in the mechanism of action of antidepressants and may alter their efficacy. The purpose of this study was to investigate whether the VAMP2 gene is associated with clinical responses to a specific antidepressant, fluvoxamine.

METHODS

A total of 106 patients with major depressive disorder were given fluvoxamine (50-200 mg/day) for 8 weeks and assessed for severity of depression using the Semi-Structured Interview Guide of the Hamilton Depressive Scale (SIGH-D; 17 items) at 0 and 8 weeks. We defined a clinical response as more than a 50% reduction in baseline SIGH-D within 8 weeks, and defined clinical remission as a SIGH-D score of less than 7 at 8 weeks. Genotyping was performed by PCR-RFLP.

RESULTS

Analysis of haplotype tagging single nucleotide polymorphisms as well as haplotype analysis did not reveal any significant associations.

CONCLUSION

Our results suggest that the VAMP2 gene is unlikely to play a major role in the efficacy of fluvoxamine.

Electroconvulsive seizure-induced gene expression profile of the hippocampus dentate gyrus granule cell layer

Electroconvulsive shock (ECS) is the most effective treatment for depression, but the mechanism underlying the therapeutic action of this treatment is still unknown. To better understand the molecular changes that may be necessary for the clinical effectiveness of ECS we have combined the technologies of gene expression profiling using cDNA microarrays with T7-based RNA amplification and laser microdissection to identify regulated genes in the dentate gyrus granule cell layer of the hippocampus. We have identified genes previously reported to be up-regulated following ECS, including brain-derived neurotrophic factor, neuropeptide Y, and thyrotrophin releasing hormone, as well as several novel genes. Notably, we have identified additional genes that are known to be involved in neuroprotection, such as growth arrest DNA damage inducible beta (Gadd45beta), and the excitatory amino acid transporter-1 (EAAC1/Slc1A1). In addition, via in situ hybridization we show that EAAC1 is specifically up-regulated in the dentate gyrus, but not in other hippocampal subfields. This study demonstrates the utility of microarray analysis of microdissected subregions of limbic brain regions and identifies novel ECS-regulated genes.

ROCK inhibition produces anxiety-related behaviors in mice

RATIONALE

The role of Rho/Rho-associated kinase (ROCK) in regulating dendritic and axonal morphology during development has gained much attention. Very little is known, however, about the role of the Rho/ROCK pathway in emotional behavior.

OBJECTIVE

To investigate the role of ROCK in emotional behaviors. We examined how the ROCK inhibitor Y27632 affects the performance of mice on three behavioral tests that measure anxiety-related behaviors.

RESULTS

In the elevated plus-maze test, Y27632 (10 nmol, intracerebroventricular) induced a significant decrease in the percentage of time spent in the open arms and in the percentage of entries into open arms. In the fear conditioning test, Y27632-treated mice froze significantly more often and longer than did saline-treated mice. In the hole-board test, Y27632 significantly suppressed head-dipping behavior in Y27632-treated mice than in saline-treated mice. On the other hand, Y27632 did not produce on spontaneous alteration performance in the Y-maze test. These results indicate that ROCK inhibition increased anxiety-related behaviors.

CONCLUSION

Our findings suggest that the ROCK pathway is involved in the expression of anxiety- and fear-related behaviors. Furthermore, we propose that if the Rho/ROCK pathway plays an important role in mediating anxiety-related behaviors in humans, it may prove to be a novel system for anxiolytics to target.

Chronic antidepressants reduce depolarization-evoked glutamate release and protein interactions favoring formation of SNARE complex in hippocampus

Glutamate neurotransmission was recently implicated in the action of stress and in antidepressant mechanisms. We report that chronic (not acute) treatment with three antidepressants with different primary mechanisms (fluoxetine, reboxetine, and desipramine) markedly reduced depolarization-evoked release of glutamate, stimulated by 15 or 25 mm KCl, but not release of GABA. Endogenous glutamate and GABA release was measured in superfused synaptosomes, freshly prepared from hippocampus of drug-treated rats. Interestingly, treatment with the three drugs only barely changed the release of glutamate (and of GABA) induced by ionomycin. In synaptic membranes of chronically treated rats we found a marked reduction in the protein-protein interaction between syntaxin 1 and Thr286-phosphorylated alphaCaM kinase II (alpha-calcium/calmodulin-dependent protein kinase II) (an interaction previously proposed to promote neurotransmitter release) and a marked increase in the interaction between syntaxin 1 and Munc-18 (an interaction proposed to reduce neurotransmitter release). Furthermore, we found a selective reduction in the expression level of the three proteins forming the core SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex. These findings suggest that antidepressants work by stabilizing glutamate neurotransmission in the hippocampus and that they may represent a useful tool for the study of relationship between functional and molecular processes in nerve terminals.

Antidepressants differentially affect expression of complexin I and II RNA in rat hippocampus

Disturbance of synaptic transmission is currently viewed as an important pathophysiological mechanism and therapeutic target of mood disorders. Amongst other lines of evidence this theory is based on human post-mortem investigations showing differential expression of complexins. In order to discriminate between molecular correlates of the disease itself and effects of psychotropic drugs given to patients, we performed an animal trial using subchronic antidepressant treatment. Cohorts of adult male Sprague-Dawley rats were treated over a period of 14 days with intraperitoneal injections of either saline (0.9%, n=8), desipramine (15 mg/kg, n=7), fluoxetine (10 mg/kg, n=8), or tranylcypromine (10 mg/kg, n=5). Brain slices were used for in situ hybridizations with 35S labelled RNA probes of the genes complexin I, complexin II and syntaxin 1 A, the SNARE complex protein interacting with the complexins, and assessed semi-quantitatively for region-specific expression levels. Expression of complexin I was induced only in habenular nuclei after treatment with fluoxetine. In contrast, complexin II was significantly induced by desipramine and tranylcypromine, but not fluoxetine, in several brain regions. All treatment groups, but most significantly fluoxetine-treated animals, showed higher expression levels of syntaxin 1A. Antidepressants differentially affect expression levels of complexin I and more prominently complexin II and syntaxin 1A. The induction of complexin II and syntaxin 1A might strengthen the synaptic transmission at axo-dendritic or axo-axonal synapses. Previous post-mortem findings reporting on downregulation of complexins cannot be explained as mere effects of psychotropic drug treatment.

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.

Repetitive transcranial magnetic stimulation induces kf-1 expression in the rat brain

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive approach used for stimulating the brain, and has proven effective in the treatment of depression, however the mechanism of its antidepressant action is unknown. Recently, we have reported the induction of kf-1 in rat frontal cortex and hippocampus after chronic antidepressant treatment and repeated electroconvulsive treatment (ECT). In this study, we demonstrated the induction of kf-1 after rTMS in the rat frontal cortex and hippocampus, but not in hypothalamus. Our data suggest that kf-1 may be a common functional molecule that is increased after antidepressant treatment, ECT and rTMS. In conclusion, it is proposed that induction of kf-1 may be associated with the treatment induced adaptive neural plasticity in the brain, which is a long-term target for their antidepressant action.

The response of synaptophysin and microtubule-associated protein 1 to restraint stress in rat hippocampus and its modulation by venlafaxine

As part of our continuing study of neural plasticity in rat hippocampus, we examined two structural proteins involved in neuronal plasticity, synaptophysin (SYP) and microtubule-associated protein 1 (MAP1) for their response to repeated restraint stress and modulation of such response by the antidepressant drug venlafaxine. This drug has the pharmacological action of inhibiting the reuptake of serotonin and norepinephrine in nerve terminals. We subjected the rats to restraint stress for 4 h per day for three days, and then injected the animals intraperitoneally (i.p.) with vehicle or 5 mg/kg/day of venlafaxine for various time periods. In all, eight groups of 10 rats each were used. The expression of these two proteins in hippocampal tissue of the rats was examined by means of western blot and immunohistochemical staining techniques. We found that restraint stress decreased the expression of SYP in the rat hippocampus by 50% (p < 0.01), and increased the expression of MAP1 by 60% (p < 0.01). SYP returned to the pre-stress levels in three weeks and MAP1 in two weeks. In animals treated with venlafaxine post-stress, SYP returned to pre-stress levels after 2 weeks and MAP1 after 1 week. These findings enhance our understanding of the compromise of the hippocampus by stressful assaults, and may be relevant to the action of venlafaxine in the treatment of patients with major depression, a mental disease thought to be related to the mal-adaptation of subjects to environmental stressors.

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.

Differential regulation of synaptic vesicle proteins by antidepressant drugs

Synaptic vesicle proteins (SVP) play a critical role in neurotransmitter release and neural plasticity, and have been implicated in the pathophysiology of psychiatric disorders such as depression. Antidepressant drugs not only alter the level of neurotransmitters, but also modulate de novo gene transcription and synthesis of proteins involved in neural plasticity. In order to investigate the effects of antidepressant compounds on SVP-mRNA levels, the expressions of synaptophysin, synaptotagmin, VAMP, and synapsin-I were analysed by in situ hybridization in rats which had been treated with desipramine, fluoxetine, tranylcypromine, or saline. The results demonstrate that chronic treatment with fluoxetine and tranylcypromine leads to an increased expression of synaptophysin, but decreased expression of synaptotagmin and VAMP in the hippocampus and cerebral cortex. Additionally, synapsin I-mRNA levels in the hippocampus and cerebral cortex are significantly reduced in tranylcypromine-treated animals. This identifies SVP genes as target genes of antidepressant treatment.

Effects of antidepressant drug imipramine on gene expression in rat prefrontal cortex

We have investigated gene expression changes produced by acute and chronic daily treatment with a prototypical antidepressant, imipramine, using DNA microarrays. The analysis of similarities in gene expression patterns among functionally related genes revealed four expression profile cluster areas that showed a highly significant overrepresentation of several functional classes. Genes encoding for proteins involved in cAMP metabolism, postsynaptic membrane proteins, and proto-oncogenes were overrepresented in different cluster areas. Furthermore, we found that serine proteases as a group were similarly regulated by chronic antidepressant treatment. Our data suggest that cAMP metabolism, synaptic function, and protein processing by serine proteases may be important targets of antidepressant treatment and potential objects for antidepressant drug development.

St John's wort and imipramine-induced gene expression profiles identify cellular functions relevant to antidepressant action and novel pharmacogenetic candidates for the phenotype of antidepressant treatment response

Both the prototypic tricyclic antidepressant imipramine (IMI) and the herbal product St John's wort (SJW) can be effective in the treatment of major depressive disorder. We studied hypothalamic gene expression in rats treated with SJW or IMI to test the hypothesis that chronic antidepressant treatment by various classes of drugs results in shared patterns of gene expression that may underlie their therapeutic effects. Individual hypothalami were hybridized to individual Affymetrix chips; we studied three arrays per group treatment. We constructed 95% confidence intervals for expression fold change for genes present in at least one treatment condition and we considered genes to be differentially expressed if they had a confidence interval excluding 1 (or -1) and had absolute difference in expression value of 10 or greater. SJW treatment differentially regulated 66 genes and expression sequence tags (ESTs) and IMI treatment differentially regulated 74 genes and ESTs. We found six common transcripts in response to both treatments. The likelihood of this occurring by chance is 1.14 x 10(-23). These transcripts are relevant to two molecular machines, namely the ribosomes and microtubules, and one cellular organelle, the mitochondria. Both treatments also affected different genes that are part of the same cell function processes, such as glycolytic pathways and synaptic function. We identified single-nucleotide polymorphisms in the human orthologs of genes regulated both treatments, as those genes may be novel candidates for pharmacogenetic studies. Our data support the hypothesis that chronic antidepressant treatment by drugs of various classes may result in a common, final pathway of changes in gene expression in a discrete brain region.

From monoamines to genomic targets: a paradigm shift for drug discovery in depression

Depression, a complex psychiatric disorder that affects approximately 15% of the population, has an enormous social cost. Although the disorder is thought to be the outcome of gene-environmental interactions, the causative genes and environmental factors underlying depression remain to be identified. All the antidepressant drugs now in use--the forerunner of which was discovered serendipitously 50 years ago--modulate monoamine neurotransmission, and take six to eight weeks to exert their effects, but each drug is efficacious in only 60-70% of patients. A conceptually novel antidepressant that acted rapidly and safely in a high proportion of patients would almost certainly become the world's bestselling drug. Yet such a drug is not on the horizon. Here, we cover the different phases of antidepressant drug discovery in the past, present and future, and comment on the challenges and opportunities for antidepressant research.