Regulation of activity-regulated cytoskeleton protein (Arc) mRNA after acute and chronic electroconvulsive stimulation in the rat

dotdotdot: an automated approach to quantify multiplex single molecule fluorescent in situ hybridization (smFISH) images in complex tissues

Multiplex single-molecule fluorescent in situ hybridization (smFISH) is a powerful method for validating RNA sequencing and emerging spatial transcriptomic data, but quantification remains a computational challenge. We present a framework for generating and analyzing smFISH data in complex tissues while overcoming autofluorescence and increasing multiplexing capacity. We developed dotdotdot (https://github.com/LieberInstitute/dotdotdot) as a corresponding software package to quantify RNA transcripts in single nuclei and perform differential expression analysis. We first demonstrate robustness of our platform in single mouse neurons by quantifying differential expression of activity-regulated genes. We then quantify spatial gene expression in human dorsolateral prefrontal cortex (DLPFC) using spectral imaging and dotdotdot to mask lipofuscin autofluorescence. We lastly apply machine learning to predict cell types and perform downstream cell type-specific expression analysis. In summary, we provide experimental workflows, imaging acquisition and analytic strategies for quantification and biological interpretation of smFISH data in complex tissues.

Electroconvulsive treatment prevents chronic restraint stress-induced atrophy of the hippocampal formation-A stereological study

INTRODUCTION

Electroconvulsive therapy (ECT) is one of the most efficient treatments of major depressive disorder (MDD), although the underlying neurobiology remains poorly understood. There is evidence that ECT and MDD exert opposing effects on the hippocampal formation with respect to volume and number of neurons. However, there has been a paucity of quantitative data in experimental models of ECT and MDD.

METHODS

Using design-based stereology, we have measured the effects of a stress-induced depression model (chronic restraint stress, CRS) and ECS on the morphology of the hippocampus by estimating the volume and total number of neurons in the hilus, CA1, and CA2/3, as well as in the entire hippocampus.

RESULTS

We find that CRS induces a significant decrease in volume exclusively of the hilus and that ECS (CRS + ECS) blocks this reduction. Furthermore, ECS alone does not change the volume or total number of neurons in the entire hippocampus or any hippocampal subdivision in our rat model.

Neuroadaptive changes and behavioral effects after a sensitization regime of MDPV

3,4-methylenedioxypyrovalerone (MDPV) is a synthetic cathinone with cocaine-like properties. In a previous work, we exposed adolescent mice to MDPV, finding sensitization to cocaine effects, and a higher vulnerability to cocaine abuse in adulthood. Here we sought to determine if such MDPV schedule induces additional behavioral-neuronal changes that could explain such results. After MDPV treatment (1.5 mg kg^-1, twice daily, 7 days), mice were behaviorally tested. Also, we investigated protein changes in various brain regions. MDPV induced aggressiveness and anxiety, but also contributed to a faster habituation to the open field. This feature co-occurred with an induction of ΔFosB in the orbitofrontal cortex that was higher than its expression in the ventral striatum. Early after treatment, D2R:D1R ratio pointed to a preponderance of D1R but, upon withdrawal, the ratio recovered. Increased expression of Arc, CDK5 and TH, and decrease in DAT protein levels persisted longer after withdrawal, pointing to a neuroplastic lasting effect similar to that involved in cocaine addiction. The implication of the hyperdopaminergic condition in the MDPV-induced aggressiveness cannot be ruled out. We also found an initial oxidative effect of MDPV, without glial activation. Moreover, although initially the dopaminergic signal induced by MDPV resulted in increased ΔFosB, we did not observe any change in NFκB or GluA2 expression. Finally, the changes observed after MDPV treatment could not be explained according to the autoregulatory loop between ΔFosB and the epigenetic repressor G9a described for cocaine. This provides new knowledge about the neuroadaptive changes involved in the vulnerability to psychostimulant addiction.

Activity-Regulated Cytoskeleton-Associated Protein Accumulates in the Nucleus in Response to Cocaine and Acts as a Brake on Chromatin Remodeling and Long-Term Behavioral Alterations

BACKGROUND

Addiction relies on persistent alterations of neuronal properties, which depends on gene regulation. Activity-regulated cytoskeleton-associated protein (Arc) is an immediate early gene that modulates neuronal plasticity underlying learning and memory. Its role in cocaine-induced neuronal and behavioral adaptations remains elusive.

METHODS

Acute cocaine-treated mice were used for quantitative reverse-transcriptase polymerase chain reaction, immunocytochemistry, and confocal imaging from striatum. Live imaging and transfection assays for Arc overexpression were performed from primary cultures. Molecular and behavioral adaptations to cocaine were studied from Arc-deficient mice and their wild-type littermates.

RESULTS

Arc messenger RNA and proteins are rapidly induced in the striatum after acute cocaine administration, via an extracellular-signal regulated kinase-dependent de novo protein synthesis. Although detected in dendrites, Arc accumulates in the nucleus in active zones of transcription, where it colocalizes with phospho-Ser10-histone H3, an important component of nucleosomal response. In vitro, Arc overexpression downregulates phospho-Ser10-histone H3 without modifying extracellular-signal regulated kinase phosphorylation in the nucleus. In vivo, Arc-deficient mice display decreased heterochromatin domains, a high RNA-polymerase II activity and enhanced c-Fos expression. These mice presented an exacerbated psychomotor sensitization and conditioned place preference induced by low doses of cocaine.

CONCLUSIONS

Cocaine induces the rapid induction of Arc and its nuclear accumulation in striatal neurons. Locally, it alters the nucleosomal response, and acts as a brake on chromatin remodeling and gene regulation. These original observations posit Arc as a major homeostatic modulator of molecular and behavioral responses to cocaine. Thus, modulating Arc levels may provide promising therapeutic approaches in drug addiction.

A critical evaluation of the activity-regulated cytoskeleton-associated protein (Arc/Arg3.1)'s putative role in regulating dendritic plasticity, cognitive processes, and mood in animal models of depression

Major depressive disorder (MDD) is primarily conceptualized as a mood disorder but cognitive dysfunction is also prevalent, and may limit the daily function of MDD patients. Current theories on MDD highlight disturbances in dendritic plasticity in its pathophysiology, which could conceivably play a role in the production of both MDD-related mood and cognitive symptoms. This paper attempts to review the accumulated knowledge on the basic biology of the activity-regulated cytoskeleton-associated protein (Arc or Arg3.1), its effects on neural plasticity, and how these may be related to mood or cognitive dysfunction in animal models of MDD. On a cellular level, Arc plays an important role in modulating dendritic spine density and remodeling. Arc also has a close, bidirectional relationship with postsynaptic glutamate neurotransmission, since it is stimulated by multiple glutamatergic receptor mechanisms but also modulates α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor internalization. The effects on AMPA receptor trafficking are likely related to Arc's ability to modulate phenomena such as long-term potentiation, long-term depression, and synaptic scaling, each of which are important for maintaining proper cognitive function. Chronic stress models of MDD in animals show suppressed Arc expression in the frontal cortex but elevation in the amygdala. Interestingly, cognitive tasks depending on the frontal cortex are generally impaired by chronic stress, while those depending on the amygdala are enhanced, and antidepressant treatments stimulate cortical Arc expression with a timeline that is reminiscent of the treatment efficacy lag observed in the clinic or in preclinical models. However, pharmacological treatments that stimulate regional Arc expression do not universally improve relevant cognitive functions, and this highlights a need to further refine our understanding of Arc on a subcellular and network level.

Epigenetic regulation of Dnmt3a and Arc gene expression after electroconvulsive stimulation in the rat

Electroconvulsive therapy (ECT) remains one of the most effective treatments of major depression. Unfortunately, some patients report side effects, of which the most prominent are memory deficits. The immediate early gene Arc plays a critical role in the maintenance phase of long-term potentiation and consolidation of memory in the rat brain. We recently observed increased methylation of the Arc promoter 24h after acute electroconvulsive stimulation (ECS) in rats, which could cause decreased Arc expression and provide an explanation for the observed memory deficits. In the present study we investigated the methylation and expression changes of Arc at 48h post-ECS and determined the role of de-novo methylation in that process. We initially measured expression of DNA methyltransferases (Dnmt1 and Dnmt3a) and Arc 1, 4, 8, 16, 24, and 48h after a single ECS. Arc expression increased approximately 10-fold at 1 and 4h after ECS, and subsequently decreased below sham levels. Four hours after ECS we also observed a significant increase in Dnmt3a expression, which was attenuated in a second experiment by the use of DNMT inhibitor decitabine (5-aza-2-deoxycytidine). We then investigated Arc gene expression and methylation changes at 48h post-ECS and we found a slightly reduced Arc expression in ECS-treated rats as compared to sham. In animals that received decitabine we observed a significant decrease in Dnmt3a expression and an increase of Arc expression in both ECS and sham groups. The same tendency for reduced Arc expression after ECS, as compared to sham was observed despite the blocking of DNA methylation with decitabine. The DNA methylation as measured by pyrosequencing is decreased 48h post-ECS both in the promoter and intragenic regions as a response to ECS regardless of the treatment with decitabine. Overall the results suggest that DNA methylation is involved in regulating Arc expression but is not the causal mechanism responsible for reducing Arc expression after ECS. We speculate that the decrease is caused by ECS-induced HDAC2 upregulation and decreased H3 acetylation at the Arc promoter.

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.

The Role of Neurotrophins in Major Depressive Disorder

Neurotrophins and other growth factors have been advanced as critical modulators of depressive behavior. Support for this model is based on analyses of knockout and transgenic mouse models, human genetic studies, and screens for gene products that are regulated by depressive behavior and/or antidepressants. Even subtle alteration in the regulated secretion of brain-derived neurotrophic factor (BDNF), for example, due to a single nucleotide polymorphism (SNP)-encoded Val-Met substitution in proBDNF that affects processing and sorting, impacts behavior and cognition. Alterations in growth factor expression result in changes in neurogenesis as well as structural changes in neuronal cytoarchitecture, including effects on dendritic length and spine density, in the hippocampus, nucleus accumbens, and prefrontal cortex. These changes have the potential to impact the plasticity and stability of synapses in the CNS, and the complex brain circuitry that regulates behavior. Here we review the role that neurotrophins play in the modulation of depressive behavior, and the downstream signaling targets they regulate that potentially mediate these behavioral pro-depressant and antidepressant effects.

Long-term decrease in immediate early gene expression after electroconvulsive seizures

Electroconvulsive therapy (ECT) is a well-established psychiatric treatment for severe depression. Despite its clinical utility, post-ECT memory deficits are a common side effect. Neuronal plasticity and memory consolidation are intimately related to the expression of immediate early genes (IEG), such as Egr1, Fos and Arc. Changes in IEG activation have been postulated to underlie long-term neuronal adaptations following electroconvulsive seizures (ECS), an animal model of ECT. To test this hypothesis, we used real-time PCR to examine the effect of acute and chronic ECS (8 sessions, one every other day) on the long-term (>24 h) expression of IEG Egr1, Fos and Arc in the hippocampus, a brain region implicated both in the pathophysiology of depression as well as in memory function. We observed a transient increase in Egr1 and Fos expression immediately after ECS, followed by a long-term decrease of IEG levels after both acute and chronic ECS. A separate group of animals, submitted to the same chronic ECS protocol and then subjected to open field or passive avoidance tasks, confirmed robust memory deficits 2 weeks after the last chronic ECS. The possible role of IEG downregulation on long-term learning deficits observed following ECS are discussed.

Blockade of α2-adrenoceptors induces Arc gene expression in rat brain in a glutamate receptor-dependent manner: a combined qPCR, in situ hybridisation and immunocytochemistry study

Studies of 5-HT-glutamate interactions suggest that activation of brain 5-HT(2A) receptors leads to an AMPA receptor-mediated induction of the immediate early (activity-dependent) gene, Arc (Arg3.1). In this respect, noradrenaline-glutamate interactions are poorly characterised. Here we investigated the influence on regional brain Arc gene expression of selective blockade of α(2)-adrenoceptors in rats. Several complementary techniques were used: qPCR (mRNA, discrete tissue punches), in situ hybridisation (mRNA, sections) and immunocytochemistry. The α(2)-adrenoceptor antagonist, RX 821002, dose-dependently and time-dependently (maximal effect 2 h) increased Arc mRNA levels as demonstrated both by qPCR and in situ hybridisation. The α(2)-adrenoceptor antagonist, atipamezole, also increased Arc mRNA in in situ hybridisation studies. Changes in Arc mRNA after RX 821002 were of similar magnitude in punches and intact tissue sections and region-specific, with effects being most pronounced in parietal cortex and caudate putamen, less robust in frontal cortex, and not detectable in hippocampal sub-regions. Both qPCR and in situ hybridisation studies demonstrated that RX 821002-induced Arc mRNA was blocked by the AMPA antagonist, GYKI 52466. Pretreatment with the NMDA antagonist MK 801 also prevented RX 821002-induced Arc mRNA, as did the mGluR5 antagonist MPEP, whilst the mGluR2/3 antagonist, LY341495, had no effect. Finally, immunocytochemical studies showed that RX 821002 increased Arc-immunoreactivity in cells in close apposition to α(2)-adrenoceptor-positive processes. Thus, employing three complementary techniques, these observations demonstrate that blockade of α(2)-adrenoceptors triggers brain expression of the immediate early gene, Arc, and that this effect involves the recruitment of AMPA, NMDA and mGluR5 but not mGluR2/3 glutamatergic receptors.

Epigenetic regulation of Arc and c-Fos in the hippocampus after acute electroconvulsive stimulation in the rat

Electroconvulsive stimulation (ECS) remains one of the most effective treatments of major depression. However, the underlying molecular changes still remain to be elucidated. Since ECS causes rapid and significant changes in gene expression we have looked at epigenetic regulation of two important immediate early genes that are both induced after ECS: c-Fos and Arc. We examined Arc and c-Fos protein expression and found Arc present over 4 h, in contrast to c-Fos presence lasting only 1 h. Both genes had returned to baseline expression at 24 h post-ECS. Histone H4 acetylation (H4Ac) is one of the important epigenetic marks associated with gene activation. We show increased H4Ac at the c-Fos promoter at 1 h post-ECS. Surprisingly, we also observed a significant increase in DNA methylation of the Arc gene promoter at 24 h post-ECS. DNA methylation, which is responsible for gene silencing, is a rather stable covalent modification. This suggests that Arc expression has been repressed and may consequently remain inhibited for a prolonged period post-ECS. Arc plays a critical role in the maintenance phase of long-term potentiation (LTP) and consolidation of memory in the rat brain. Thus, this study is one of the first to demonstrate DNA methylation as a regulator of ECS-induced gene expression and it provides a molecular link to the memory deficits observed after ECS.

A role for glucocorticoid-signaling in depression-like behavior of gastrin-releasing peptide receptor knock-out mice

Abstract Background. The gastrin-releasing peptide receptor (GRPR) is highly expressed in the limbic system, where it importantly regulates emotional functions and in the suprachiasmatic nucleus, where it is central for the photic resetting of the circadian clock. Mice lacking GRPR presented with deficient light-induced phase shift in activity as well altered emotional learning and amygdala function. The effect of GRPR deletion on depression-like behavior and its molecular signature in the amygdala, however, has not yet been evaluated. Methods. GRPR knock-out mice (GRPR-KO) were tested in the forced-swim test and the sucrose preference test for depression-like behavior. Gene expression in the basolateral nucleus of the amygdala was evaluated by micorarray analysis subsequent to laser-capture microdissection-assisted extraction of mRNA. The expression of selected genes was confirmed by RT-PCR. Results. GRPR-KO mice were found to present with increased depression-like behavior. Microarray analysis revealed down-regulation of several glucocorticoid-responsive genes in the basolateral amygdala. Acute administration of dexamethasone reversed the behavioral phenotype and alterations in gene expression. Discussion. We propose that deletion of GRPR leads to the induction of depression-like behavior which is paralleled by dysregulation of amygdala gene expression, potentially resulting from deficient light-induced corticosterone release in GRPR-KO.

Regulation of brain-derived neurotrophic factor (BDNF) in the chronic unpredictable stress rat model and the effects of chronic antidepressant treatment

Chronic unpredictable stress (CUS) is a widely used animal model of depression. The present study was undertaken to investigate behavioral, physiological and molecular effects of CUS and/or chronic antidepressant treatment (venlafaxine or imipramine) in the same set of animals. Anhedonia, a core symptom of depression, was assessed by measuring consumption of a palatable solution. Exposure to CUS reduced intake of a palatable solution and this effect was prevented by chronic antidepressant treatment. Moreover, chronic antidepressant treatment decreased depressive-like behavior in a modified forced swim test in stressed rats. Present evidence suggests a role for brain-derived neurotrophic factor (BDNF) in depression. BDNF mRNA levels in the ventral and dorsal hippocampus were assessed by in situ hybridization. Exposure to CUS was not correlated with a decrease but rather with an increase in BDNF mRNA expression in both the dentate gyrus of the dorsal hippocampus and the CA3 region of the ventral hippocampus indicating that there is no simple link between depression-like behaviors per se and brain BDNF levels in rats. However, a significant increase in BDNF mRNA levels in the dentate gyrus of the dorsal hippocampus correlated with chronic antidepressant treatment emphasizing a role for BDNF in the mechanisms underlying antidepressant activity.

α7 nicotinic receptor agonism mitigates phencyclidine-induced changes in synaptophysin and Arc gene expression in the mouse prefrontal cortex

Repeated phencyclidine (PCP) administration in mice reproduces several histopathological features of schizophrenia, such as reduced synaptophysin and parvalbumin mRNA expression in the frontal cortex. These changes can be prevented by co-administering the α7 nicotinic acetylcholine receptor (nAChR) agonist SSR180711 with PCP, but it is not known to what extent PCP-induced changes can be normalized once they have already occurred. Here we use semi-quantitative in situ hybridization to show that repeated administration of SSR180711 (3 mg/kg b.i.d. for 5 days) subsequent to repeated PCP administration (10 mg/kg/day for 10 days) is able to mitigate the reduction of synaptophysin mRNA expression induced by PCP in two prefrontal cortical regions, the medial prefrontal cortex (mPFC) and the ventrolateral orbitofrontal cortex (VLO). This effect is accompanied by a normalization of the PCP-induced increase in Arc mRNA expression in the same regions. In contrast, subsequent administration of SSR180711 does not affect PCP-induced decreases in parvalbumin mRNA in the mPFC, and glutamate decarboxylase 67 mRNA in the mPFC or VLO. These data demonstrate that it is possible to restore some, but not all, of the molecular dysregulations induced by repeated PCP administration with an α7 nAChR agonist. They also suggest that the previously demonstrated cognitive improvement with SSR180711 subsequent to PCP treatment does not require normalization of parvalbumin expression, but may instead be related to a restoration of synaptophysin and/or Arc levels in the frontal cortex. These data lend support to the potential for development of α7 nAChR agonists for the treatment of cognitive deficits in schizophrenia.

Repeated administration of alpha7 nicotinic acetylcholine receptor (nAChR) agonists, but not positive allosteric modulators, increases alpha7 nAChR levels in the brain

The alpha7 nicotinic acetylcholine receptor (nAChR) is an important target for treatment of cognitive deficits in schizophrenia and Alzheimer's disease. However, the receptor desensitizes rapidly in vitro, which has led to concern regarding its applicability as a clinically relevant drug target. Here we investigate the effects of repeated agonism on alpha7 nAChR receptor levels and responsiveness in vivo in rats. Using [(125)I]-alpha-bungarotoxin (BTX) autoradiography we show that acute or repeated administration with the selective alpha7 nAChR agonist A-582941 increases the number of alpha7 nAChR binding sites in several brain regions, particularly in the prefrontal cortex. The alpha7 nAChR agonists SSR180711 and PNU-282987 also increase [(125)I]-BTX binding, suggesting that this is a general consequence of alpha7 nAChR agonism. Interestingly, the alpha7 nAChR positive allosteric modulators PNU-120596 and NS1738 do not increase [(125)I]-BTX binding. Furthermore, A-582941-induced increase in Arc and c-fos mRNA expression in the prefrontal cortex is enhanced and unaltered, respectively, after repeated administration, demonstrating that the alpha7 nAChRs remain responsive. Contrarily, A-582941-induced phosphorylation of Erk2 in the prefrontal cortex occurs following acute, but not repeated administration. Our results demonstrate that repeated agonist administration increases the number of alpha7 nAChRs in the brain, and leads to coupling versus uncoupling of specific intracellular signaling pathways. Additionally, our data suggest a fundamental difference between the sequelae of repeated administration with agonists and allosteric modulators of the alpha7 nAChR.

Time-dependent expression of Arc and zif268 after acquisition of fear conditioning

Memory consolidation requires transcription and translation of new protein. Arc, an effector immediate early gene, and zif268, a regulatory transcription factor, have been implicated in synaptic plasticity underlying learning and memory. This study explored the temporal expression profiles of these proteins in the rat hippocampus following fear conditioning. We observed a time-dependent increase of Arc protein in the dorsal hippocampus 30-to-90-minute post training, returning to basal levels at 4 h. Zif268 protein levels, however, gradually increased at 30-minute post training before peaking in expression at 60 minute. The timing of hippocampal Arc and zif268 expression coincides with the critical period for protein synthesis-dependent memory consolidation following fear conditioning. However, the expression of Arc protein appears to be driven by context exploration, whereas, zif268 expression may be more specifically related to associative learning. These findings suggest that altered Arc and zif268 expression are related to neural plasticity during the formation of fear memory.

Opposite effect of phencyclidine on activity-regulated cytoskeleton-associated protein (Arc) in juvenile and adult limbic rat brain regions

The psychotomimetic effect of NMDA antagonists such as phencyclidine (PCP) in humans spurred the hypoglutamatergic theory of schizophrenia. This theory is supported by animal studies demonstrating schizophrenia-like behavioral and molecular changes following PCP administration to adult or neonatal animals. However, schizophrenia is believed to develop in part due to neurodevelopmental dysfunction during adolescence. Therefore, the effects of PCP in juvenile animals may better reflect the pathophysiology of schizophrenia. Here, we compare the effect of PCP (5mg/kg/day for 5 days) on activity-regulated cytoskeleton-associated protein (Arc) and parvalbumin mRNA expression in juvenile and adult rats. Arc is a marker for excitatory neurotransmission. Parvalbumin is a marker for GABAergic neurotransmission, known to be reduced in postmortem brains of schizophrenics. PCP reduced parvalbumin mRNA expression in the medial prefrontal cortex (mPFC), ventrolateral orbitofrontal cortex (VLO) and shell of the nucleus accumbens (ACCshell) in both juvenile and adult rats. Contrarily, PCP produced opposite effects on Arc mRNA expression in the mPFC, VLO and ACCshell, leading to decreased expression in juvenile and increased expression in adult rats. The differential effect of PCP in juvenile and adult rats may be caused by the immature functional state of the prefrontal cortex in juvenile rats. These results demonstrate differences between the effects of PCP in juvenile and adult rats. The decrease in Arc mRNA in juvenile rats corresponds best with the proposed "hypofrontality" in schizophrenia, suggesting the merits of using PCP in juvenile animals as a model for schizophrenia, as this would relate better to the typical onset and clinical features of schizophrenia.

Novel translational control in Arc-dependent long term potentiation consolidation in vivo

Regulation of translation factor activity plays a major role in protein synthesis-dependent forms of synaptic plasticity. We examined translational control across the critical period of Arc synthesis underlying consolidation of long term potentiation (LTP) in the dentate gyrus of intact, anesthetized rats. LTP induction by high frequency stimulation (HFS) evoked phosphorylation of the cap-binding protein eukaryotic initiation factor 4E (eIF4E) and dephosphorylation of eIF2alpha on a protracted time course matching the time-window of Arc translation. Local infusion of the ERK inhibitor U0126 inhibited LTP maintenance and Arc protein expression, blocked changes in eIF4E and eIF2alpha phosphorylation state, and prevented initiation complex (eIF4F) formation. Surprisingly, inhibition of the mTOR protein complex 1 (mTORC1) with rapamycin did not impair LTP maintenance or Arc synthesis nor did it inhibit eIF4F formation or phosphorylation of eIF4E. Rapamycin nonetheless blocked mTOR signaling to p70 S6 kinase and ribosomal protein S6 and inhibited synthesis of components of the translational machinery. Using immunohistochemistry and in situ hybridization, we show that Arc protein expression depends on dual, ERK-dependent transcription and translation. Arc translation is selectively blocked by pharmacological inhibition of mitogen-activated protein kinase-interacting kinase (MNK), the kinase coupling ERK to eIF4E phosphorylation. Furthermore, MNK signaling was required for eIF4F formation. These results support a dominant role for ERK-MNK signaling in control of translational initiation and Arc synthesis during LTP consolidation in the dentate gyrus. In contrast, mTORC1 signaling is activated but nonessential for Arc synthesis and LTP. The work, thus, identifies translational control mechanisms uniquely tuned to Arc-dependent LTP consolidation in live rats.

Genomic analysis of ischemic preconditioning in adult rat hippocampal slice cultures

Understanding endogenous mechanisms of neuroprotection may have important clinical applications. It is well established that brain tissue becomes more resistant to ischemic injury following a sublethal ischemic insult. This process, called ischemic preconditioning (IPC), can be induced in adult rat hippocampal slice cultures by a brief oxygen-glucose deprivation (OGD) [Hassen, G.W., Tian, D., Ding, D., Bergold, P.J., 2004. A new model of ischemic preconditioning using young adult hippocampal slice cultures. Brain Res. Brain Res. Protoc. 13, 135-143]. We have analyzed the changes in gene expression brought about by IPC in this model in order to understand the mechanisms involved. Total RNA was isolated at different time points following a brief OGD (3, 6 and 12 h) and used to probe genome-wide expression microarrays. Genes were identified that were significantly up- or down-regulated relative to controls. We placed genes that were differentially expressed into statistically significant groups based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and gene ontology (GO) terms. Genes involved in signal transduction, transcription, and oxidative phosphorylation are differentially expressed at each time point. The analysis demonstrates that alterations in signaling pathways (TGF-beta, Wnt, MAPK, ErbB, Toll-like receptor, JAK-STAT, VEGF) consistently accompany IPC. RT-PCR was used to confirm that members of these signaling pathways are regulated as predicted by the microarray analysis. We verified that protein translation following OGD is necessary for IPC. We also found that blocking the NMDA receptor during OGD does not significantly inhibit IPC in this model or produce large changes in gene expression. Our data thus suggests that changes in signaling pathways and their down-stream targets play an important role in triggering endogenous neuroprotection.

Selective cognitive deficits and reduced hippocampal brain-derived neurotrophic factor mRNA expression in small-conductance calcium-activated K+ channel deficient mice

Small-conductance calcium-activated K(+) channels 1-3 (SK1-3) are important for neuronal firing regulation and are considered putative CNS drug targets. For instance non-selective SK blockers improve performance in animal models of cognition. The SK subtype(s) involved herein awaits identification and the question is difficult to address pharmacologically due to the lack of subtype-selective SK-channel modulators. In this study, we used doxycycline-induced conditional SK3-deficient (T/T) mice to address the cognitive consequences of selective SK3 deficiency. In T/T mice SK3 protein is near-eliminated from the brain following doxycycline treatment. We tested T/T and wild type (WT) littermate mice in five distinct learning and memory paradigms. In Y-maze spontaneous alternations and five-trial inhibitory avoidance the performance of T/T mice was markedly inferior to WT mice. In contrast, T/T and WT mice performed equally well in passive avoidance, object recognition and the Morris water maze. Thus, some aspects of working/short-term memory are disrupted in T/T mice. Using in situ hybridization, we further found the cognitive deficits in T/T mice to be paralleled by reduced brain-derived neurotrophic factor (BDNF) mRNA expression in the dentate gyrus and CA3 of the hippocampus. BDNF mRNA levels in the frontal cortex were not affected. BDNF has been crucially implicated in many cognitive processes. Hence, the biological substrate for the cognitive impairments in T/T mice could conceivably entail reduced trophic support of the hippocampus.

Basal and stress-induced modulation of activity-regulated cytoskeletal associated protein (Arc) in the rat brain following duloxetine treatment

RATIONALE

Therapeutic efficacy of antidepressant drugs appears to be related to their ability in producing neuroadaptive changes that restore normal brain function. Activity-regulated cytoskeletal associated protein (Arc) is an effector immediate early gene that plays a fundamental role in activity-dependent neural plasticity in corticolimbic brain regions and has been implicated in the modulation of several functions known to be profoundly perturbed in depressive states.

OBJECTIVE

In the present study, we investigated transcriptional and translational changes of Arc in response to acute or chronic treatment with the novel antidepressant duloxetine.

RESULTS

Although a limited increase of Arc messenger RNA (mRNA) levels was found in some structures after acute antidepressant administration, a marked up-regulation of its gene expression was found after chronic treatment, primarily at the level of frontal cortex. The changes observed after prolonged duloxetine administration strongly correlates with those previously reported on brain-derived neurotrophic factor mRNA levels Calabrese et al. (Neuropsychopharmacol 32:2351-2359, 2007). In addition, we found an anatomical-specific influence of chronic duloxetine on stress-dependent Arc modulation, which was limited to the frontal cortex.

CONCLUSIONS

We suggest that these neuroadaptive changes, among others, might contribute to the normalization of neuroplastic defects associated with mood disorders.

Neuropsychological effects and attitudes in patients following electroconvulsive therapy

The current study examined the effects of electroconvulsive therapy (ECT) on neuropsychological test performance. Forty-six patients completed brief neuropsychological and psychological testing before and after receiving ECT for the treatment of recalcitrant and severe depression. Neuropsychological testing consisted of the Levin Selective Reminding Test (Levin) and Wechsler Memory Scale-Revised Edition (WMS-R). Self-report measures included the Beck Depression Inventory (BDI), the Short-Term Memory Questionnaire (STMQ), and several other measures of emotional functioning and patient attitudes toward ECT. The mean number of days between pre-ECT and post-ECT testing was 24. T-test revealed a significant decrease in subjective ratings of depression as rated by the BDI, t(45) = 9.82, P < 0.0001 (Pre-BDI = 27.9 +/- 20.2; post-BDI = 13.5 +/- 9.7). Objective ratings of memory appeared impaired following treatment, and patients' self-report measures of memory confirmed this decline. More specifically, repeated measures MANOVA [Wilks Lambda F(11,30) = 4.3, p < 0.001] indicated significant decreases for measures of immediate recognition memory (p < 0.005), long-term storage (p < 0.05), delayed prose passage recall (p < 0.0001), percent retained of prose passages (p < 0.0001), and percent retained of visual designs (p < 0.0001). In addition, the number of double mentions on the Levin increased (p < 0.02). This study suggests that there may be a greater need to discuss the intermittent cognitive risks associated with ECT when obtaining informed consent prior to treatment. Further that self-reports of cognitive difficulties may persist even when depression has remitted. However, patients may not acknowledge or be aware of changes in their memory functioning, and post-ECT self-reports may not be reliable.

Genome-wide transcriptome profiling of region-specific vulnerability to oxidative stress in the hippocampus

Neurons in the hippocampal CA1 region are particularly sensitive to oxidative stress (OS), whereas those in CA3 are resistant. To uncover mechanisms for selective CA1 vulnerability to OS, we treated organotypic hippocampal slices with duroquinone and compared transcriptional profiles of CA1 vs CA3 cells at various intervals. Gene Ontology and Biological Pathway analyses of differentially expressed genes showed that at all time points, CA1 had higher transcriptional activity for stress/inflammatory response, transition metal transport, ferroxidase, and presynaptic signaling activity, while CA3 had higher GABA-signaling, postsynaptic, and calcium and potassium channel activity. Real-time PCR and immunoblots confirmed the transcriptome data and the induction of OS by duroquinone in both hippocampal regions. Our functional genomics approach has identified in CA1 cells molecular pathways as well as unique genes, such as guanosine deaminase, lipocalin 2, synaptotagmin 4, and latrophilin 2, whose time-dependent induction following the initiation of OS may represent attempts at neurite outgrowth, synaptic recovery, and resistance against OS.

The α7 nicotinic receptor agonist SSR180711 increases activity regulated cytoskeleton protein (Arc) gene expression in the prefrontal cortex of the rat

Nicotinic alpha7 acetylcholine receptors (alpha7 nAChR) have been shown to enhance attentional function and aspects of memory function in experimental models and in man. The protein Arc encoded by the effector immediate early gene arc or arg3.1 has been shown to be strongly implicated in long-term memory function. We have sought to determine if alpha7 nAChR mediate the stimulation of arc gene expression, and if so, where in the brain such activation may occur using semi-quantitative in situ hybridisation. Administration of the novel and selective alpha7 nAChR agonist, SSR180711 (1, 3 and 10 mg/kg) to adolescent rats, produced a dose- and time-dependent increase in the expression of Arc mRNA in the prefrontal cortex and the ventral orbital cortex. By contrast, no change in mRNA levels was detected in the parietal cortex and the CA1 of the hippocampus. These data show that alpha7 nAChR activates a subset of neurons in the rat prefrontal cortex and this activation likely is important for the attentional effects of this new class of drugs.

Expression of brain derived neurotrophic factor, activity-regulated cytoskeleton protein mRNA, and enhancement of adult hippocampal neurogenesis in rats after sub-chronic and chronic treatment with the triple monoamine re-uptake inhibitor tesofensine

The changes of gene expression resulting from long-term exposure to monoamine antidepressant drugs in experimental animals are key to understanding the mechanisms of action of this class of drugs in man. Many of these genes and their products are either relevant biomarkers or directly involved in structural changes that are perhaps necessary for the antidepressant effect. Tesofensine is a novel triple monoamine reuptake inhibitor that acts to increase noradrenaline, serotonin, and dopamine neurotransmission. This study was undertaken to examine the effect of sub-chronic (5 days) and chronic (14 days) administration of Tesofensine on the expression of brain derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton protein (Arc) in the rat hippocampus. Furthermore, hippocampi from the same animals were used to investigate the effect on cell proliferation by means of Ki-67- and NeuroD-immunoreactivity. We find that chronic, but not sub-chronic treatment with Tesofensine increases BDNF mRNA in the CA3 region of the hippocampus (35%), and Arc mRNA in the CA1 of the hippocampus (65%). Furthermore, the number of Ki-67- and neuroD-positive cells increased after chronic, but not sub-chronic treatment. This study shows that Tesofensine enhances hippocampal gene expression and new cell formation indicative for an antidepressant potential of this novel drug substance.

Corticostriatal Up-Regulation of Activity-Regulated Cytoskeletal-Associated Protein Expression after Repeated Exposure to Cocaine

We provide evidence that cocaine evokes short- and long-lasting increases in activity-regulated cytoskeletal-associated protein (Arc) expression after a finely tuned, time-dependent and regional-selective expression profile. Acute experiments revealed that cocaine up-regulates Arc expression primarily in striatum and prefrontal cortex through a dopamine D1-dependent mechanism and a combination of D1- and D2-dependent mechanisms, respectively. Aside from cocaine-dependent Arc elevation, we show for the first time that D1 and D2 receptors tonically regulate basal Arc expression following a regional-selective profile. As opposed to the effects of a single cocaine injection on Arc expression, which dissipate within 24 h, subchronic (five daily injections) or chronic (14 daily injections) cocaine administration, with animals sacrificed hours or days after the last treatment, demonstrated that Arc expression is still up-regulated long after treatment cessation, suggesting that adaptive changes have been set in motion by the prolonged administration of the psychostimulant. In summary, our findings are the first to demonstrate that repeated exposure to cocaine leads to long-lasting dysregulation of Arc expression in the corticostriatal network, thus establishing a molecular basis to explain, at least partially, the impaired synaptic transmission caused by cocaine abuse at this level. Furthermore, given the role exerted by Arc in cytoarchitectural rearrangements, it is conceivable to speculate that it mediates changes in synaptic connectivity brought about by cocaine. Our findings thus pinpoint this molecule as a neuropathological underpinning and molecular bridge that connects short- and long-term neuronal modifications associated with cocaine abuse.

Effects of stress and adrenalectomy on activity-regulated cytoskeleton protein (Arc) gene expression

Activity-regulated cytoskeletal-associated protein (Arc) is an effector immediate early gene induced by novelty and involved in consolidation of long-term memory. Since activation of glucocorticoid receptors is a prerequisite for memory consolidation, we therefore aimed to study the effect of acute restraint stress on Arc gene expression in adrenalectomized rats. Acute stress produced a significant increase in Arc gene expression in the medial prefrontal cortex, but not in the parietal cortex or in the pyramidal cell layer of the hippocampus. The basal level of Arc mRNA in adrenalectomized animals was high in the medial prefrontal cortex and unaffected by acute stress in these animals. These data are consistent with the role of Arc as an integrative modulator of synaptic plasticity by emphasizing the potential role of stress and glucocorticoids in the control of Arc gene expression.