D-Cycloserine enhances the bidirectional range of NMDAR-dependent hippocampal synaptic plasticity.

The partial N-methyl-D-aspartate receptor (NMDAR) agonist D-Cycloserine (DCS) has been evaluated for the treatment of a wide variety of psychiatric disorders, including dementia, schizophrenia, depression and for the augmentation of exposure-based psychotherapy. Most if not all of the potential psychiatric applications of DCS target an enhancement or restitution of cognitive functions, learning and memory. Their molecular correlate is long-term synaptic plasticity; and many forms of synaptic plasticity depend on the activation of NMDA receptors. Here, we comprehensively examined the modulation of different forms of synaptic plasticity in the hippocampus by DCS and its mechanism. We found that DCS positively modulates NMDAR-dependent forms of long-term synaptic plasticity (long-term synaptic potentiation, LTP, and long-term synaptic depression, LTD) in hippocampal brain slices of juvenile rats without affecting basal synaptic transmission. DCS binds to the D-serine/glycine binding site of the NMDAR. Pharmacological inhibition of this site prevented the induction of LTP, whereas agonism at the D-serine/glycine binding site augmented LTP and could functionally substitute for weak LTP induction paradigms. The most probable origin of endogenous D-serine are astrocytes, and its exocytosis is regulated by astrocytic metabotropic glutamate receptors (mGluR1). Functional eradication of astrocytes, inhibition of mGluR1 receptors and G-protein signaling in astrocytes adjacent to postsynaptic neurons prevented the induction of NMDAR-dependent forms of LTP and LTD. Our results support the enhancement of a bidirectional range of NMDAR-dependent hippocampal synaptic plasticity by DCS and D-serine-mediated gliotransmission. Therefore, the D-serine/glycine-binding site in NMDAR is a major target for psychopharmacological interventions targeting plasticity-related disorders.

Delaying circadian sleep phase under ultradian light cycle causes time-of-day-dependent alteration of cognition and mood.

Light exerts powerful and pervasive effects on physiology and behaviour. These effects can be indirect, through clock synchronization and phase adjustment of circadian rhythms, or direct, independent of the circadian process. Exposure to light at inappropriate times, as commonly experienced in today's society, leads to increased prevalence of circadian, sleep and mood disorders as well as cognitive impairments. In mice, exposure to an ultradian 3.5 h light/3.5 h dark cycle (T7) for several days has been shown to impair behaviour through direct, non-circadian, photic effects, a claim we challenge here. We first confirmed that T7 cycle induces a lengthening of the circadian period resulting in a day by day phase-delay of both activity and sleep rhythms. Spatial novelty preference test performed at different circadian time points in mice housed under T7 cycle demonstrated that cognitive deficit was restrained to the subjective night. Mice under the same condition also showed a modification of stress-induced despair-like behaviour in the forced swim test. Therefore, our data demonstrate that ultradian light cycles cause time-of-day-dependent alteration of cognition and mood through clock period lengthening delaying circadian sleep phase, and not through a direct photic influence. These results are of critical importance for the clinical applications of light therapy in the medical field and for today's society to establish lighting recommendations for shift work, schools, hospitals and homes.

A Pattern to Link Adenosine Signaling, Circadian System, and Potential Final Common Pathway in the Pathogenesis of Major Depressive Disorder.

Several studies have reported separate roles of adenosine receptors and circadian clockwork in major depressive disorder. While less evidence exists for regulation of the circadian clock by adenosine signaling, a small number of studies have linked the adenosinergic system, the molecular circadian clock, and mood regulation. In this article, we review relevant advances and propose that adenosine receptor signaling, including canonical and other alternative downstream cellular pathways, regulates circadian gene expression, which in turn may underlie the pathogenesis of mood disorders. Moreover, we summarize the convergent point of these signaling pathways and put forward a pattern by which Homer1a expression, regulated by both cAMP-response element binding protein (CREB) and circadian clock genes, may be the final common pathogenetic mechanism in depression.

Optogenetic stimulation of ventral tegmental area dopaminergic neurons in a female rodent model of depression: The effect of different stimulation patterns.

Major depressive disorder is one of the most common mental disorders, and more than 300 million of people suffer from depression worldwide. Recent clinical trials indicate that deep brain stimulation of the superolateral medial forebrain bundle (mfb) can have rapid and long-term antidepressant effects in patients with treatment-resistant depression. However, the mechanisms of action are elusive. In this study, using female rats, we demonstrate the antidepressant effects of selective optogenetic stimulation of the ventral tegmental area's dopaminergic (DA) neurons passing through the mfb and compare different stimulation patterns. Chronic mild unpredictable stress (CMUS) induced depressive-like, but not anxiety-like phenotype. Short-term and long-term stimulation demonstrated antidepressant effect (OSST) and improved anxiolytic effect (EPM), while long-term stimulation during CMUS induction prevented depressive-like behavior (OSST and USV) and improved anxiolytic effect (EPM). The results highlight that long-term accumulative stimulation on DA pathways is required for antidepressant and anxiolytic effect.

Animal Models of Depression - Chronic Despair Model (CDM).

Major depressive disorder is one of the most prevalent forms of mental illnesses and causes tremendous individual suffering and socioeconomic burden. Despite its importance, current pharmacological treatment is limited, and novel treatment options are urgently needed. One key factor in the search for potential new drugs is evaluating their anti-depressive potency in appropriate animal models. The classical Porsolt forced swim test was used for this purpose for decades to induce and assess a depressive-like state. It consists of two short periods of forced swimming: the first to induce a depressed state and the second on the following day to evaluate the antidepressant effect of the agent given in between the two swim sessions. This model might be suitable as a screening tool for potential antidepressive agents but ignores the delayed onset of action of many antidepressants. The CDM was recently established and represented a modification of the classical test with notable differences. Mice are forced to swim for 5 consecutive days, following the idea that in humans, depression is induced by chronic rather than by acute stress. In a resting period of several days (1-3 weeks), animals develop sustained behavioral despair. The standard read-out method is the measurement of immobility time in an additional delayed swim session, but several alternative methods are proposed to get a broader view of the mood status of the animal. Multiple analysis tools can be used targeting behavioral, molecular, and electrophysiological changes. The depressed phenotype is stable for at least 4 weeks, providing a time window for rapid but also subchronic antidepressant treatment strategies. Furthermore, alterations in the development of a depressive-like state can be addressed using this approach. CDM, therefore, represents a useful tool to better understand depression and to develop novel treatment interventions.

The "missing heritability"-Problem in psychiatry: Is the interaction of genetics, epigenetics and transposable elements a potential solution?

Psychiatric disorders exhibit an enormous burden on the health care systems worldwide accounting for around one-third of years lost due to disability among adults. Their etiology is largely unknown and diagnostic classification is based on symptomatology and course of illness and not on objective biomarkers. Most psychiatric disorders are moderately to highly heritable. However, it is still unknown what mechanisms may explain the discrepancy between heritability estimates and the present data from genetic analysis. In addition to genetic differences also epigenetic modifications are considered as potentially relevant in the transfer of susceptibility to psychiatric diseases. Though, whether or not epigenetic alterations can be inherited for many generations is highly controversial. In the present article, we will critically summarize both the genetic findings and the results from epigenetic analyses, including also those of noncoding RNAs. We will argue that one possible solution to the "missing heritability" problem in psychiatry is a potential role of retrotransposons, the exploration of which is presently only in its beginnings.

Antidepressant drugs act by directly binding to TRKB neurotrophin receptors.

It is unclear how binding of antidepressant drugs to their targets gives rise to the clinical antidepressant effect. We discovered that the transmembrane domain of tyrosine kinase receptor 2 (TRKB), the brain-derived neurotrophic factor (BDNF) receptor that promotes neuronal plasticity and antidepressant responses, has a cholesterol-sensing function that mediates synaptic effects of cholesterol. We then found that both typical and fast-acting antidepressants directly bind to TRKB, thereby facilitating synaptic localization of TRKB and its activation by BDNF. Extensive computational approaches including atomistic molecular dynamics simulations revealed a binding site at the transmembrane region of TRKB dimers. Mutation of the TRKB antidepressant-binding motif impaired cellular, behavioral, and plasticity-promoting responses to antidepressants in vitro and in vivo. We suggest that binding to TRKB and allosteric facilitation of BDNF signaling is the common mechanism for antidepressant action, which may explain why typical antidepressants act slowly and how molecular effects of antidepressants are translated into clinical mood recovery.

Antidepressant treatment is associated with epigenetic alterations of Homer1 promoter in a mouse model of chronic depression.

BACKGROUND: Understanding the neurobiology of depression and the mechanism of action of therapeutic measures is currently a research priority. We have shown that the expression of the synaptic protein Homer1a correlates with depression-like behavior and its induction is a common mechanism of action of different antidepressant treatments. However, the mechanism of Homer1a regulation is still unknown. METHODS: We combined the chronic despair mouse model (CDM) of chronic depression with different antidepressant treatments. Depression-like behavior was characterized by forced swim and tail suspension tests, and via automatic measurement of sucrose preference in IntelliCage. The Homer1 mRNA expression and promoter DNA methylation were analyzed in cortex and peripheral blood by qRT-PCR and pyrosequencing. RESULTS: CDM mice show decreased Homer1a and Homer1b/c mRNA expression in cortex and blood samples, while chronic treatment with imipramine and fluoxetine or acute ketamine application increases their level only in the cortex. The quantitative analyses of the methylation of 7 CpG sites, located on the Homer1 promoter region containing several CRE binding sites, show a significant increase in DNA methylation in the cortex of CDM mice. In contrast, antidepressant treatments reduce the methylation level. LIMITATIONS: Homer1 expression and promotor methylation were not analyzed in different blood cell types. Other CpG sites of Homer1 promoter should be investigated in future studies. Our experimental approach does not distinguish between methylation and hydroxymethylation. CONCLUSIONS: We demonstrate that stress-induced depression-like behavior and antidepressant treatments are associated with epigenetic alterations of Homer1 promoter, providing new insights into the mechanism of antidepressant treatment.

Enhanced adenosine A1 receptor and Homer1a expression in hippocampus modulates the resilience to stress-induced depression-like behavior.

Resilience to stress is critical for the development of depression. Enhanced adenosine A1 receptor (A1R) signaling mediates the antidepressant effects of acute sleep deprivation (SD). However, chronic SD causes long-lasting upregulation of brain A1R and increases the risk of depression. To investigate the effects of A1R on mood, we utilized two transgenic mouse lines with inducible A1R overexpression in forebrain neurons. These two lines have identical levels of A1R increase in the cortex, but differ in the transgenic A1R expression in the hippocampus. Switching on the transgene promotes robust antidepressant and anxiolytic effects in both lines. The mice of the line without transgenic A1R overexpression in the hippocampus (A1Hipp-) show very strong resistance towards development of stress-induced chronic depression-like behavior. In contrast, the mice of the line in which A1R upregulation extends to the hippocampus (A1Hipp+), exhibit decreased resilience to depression as compared to A1Hipp-. Similarly, automatic analysis of reward behavior of the two lines reveals that depression resistant A1Hipp-transgenic mice exhibit high sucrose preference, while mice of the vulnerable A1Hipp + line developed stress-induced anhedonic phenotype. The A1Hipp + mice have increased Homer1a expression in hippocampus, correlating with impaired long-term potentiation in the CA1 region, mimicking the stressed mice. Furthermore, virus-mediated overexpression of Homer1a in the hippocampus decreases stress resilience. Taken together our data indicate for first time that increased expression of A1R and Homer1a in the hippocampus modulates the resilience to stress-induced depression and thus might potentially mediate the detrimental effects of chronic sleep restriction on mood.

Enhanced mGlu5 Signaling in Excitatory Neurons Promotes Rapid Antidepressant Effects via AMPA Receptor Activation.

Conventional antidepressants have limited efficacy and many side effects, highlighting the need for fast-acting and specific medications. Induction of the synaptic protein Homer1a mediates the effects of different antidepressant treatments, including the rapid action of ketamine and sleep deprivation (SD). We show here that mimicking Homer1a upregulation via intravenous injection of cell-membrane-permeable TAT-Homer1a elicits rapid antidepressant effects in various tests. Similar to ketamine and SD, in vitro and in vivo application of TAT-Homer1a enhances mGlu5 signaling, resulting in increased mTOR pathway phosphorylation, and upregulates synaptic AMPA receptor expression and activity. The antidepressant action of SD and Homer1a induction depends on mGlu5 activation specifically in excitatory CaMK2a neurons and requires enhanced AMPA receptor activity, translation, and trafficking. Moreover, our data demonstrate a pronounced therapeutic potential of different TAT-fused peptides that directly modulate mGlu5 and AMPA receptor activity and thus might provide a novel strategy for rapid and effective antidepressant treatment.

The role of adenosine receptors in mood and anxiety disorders.

Adenosine receptor subtypes, first described 40 years ago, are known to regulate diverse biological functions and have a role in various conditions, such as cerebral and cardiac ischemia, immune and inflammatory disorders and cancer. In the brain, they limit potentially dangerous over excitation, but also regulate mechanisms essential in sleep and psychiatric disorders. In this review, we discuss the role of adenosine receptors in mood and anxiety disorders. Activation of A2A receptors is associated with increased depression-like symptoms, while increased A1 receptors signaling elicits rapid antidepressant effects. Indeed, several lines of evidence demonstrate that the therapeutic effects of different non-pharmacological treatments of depression, like sleep deprivation and electroconvulsive therapy are mediated by A1 receptor up-regulation or activation. In addition, A1 receptors may also play a role in the antidepressant effects of transcranial direct current stimulation and deep brain stimulation. As a potential downstream mechanism, which facilitates the antidepressant effects of A1 receptors, we propose a crosstalk between adenosinergic and glutamatergic systems mediated via synaptic plasticity protein Homer1a and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors. Moreover, adenosine receptors are also involved in the control of circadian rhythms, sleep homeostasis and some neuro-immunological mechanisms, all of them implicated in mood regulation. Antagonists of adenosine receptors such as caffeine have general anxiogenic effects. In particular, A2A receptors appear to have an important role in the pathophysiology of anxiety disorders. Taken together, the results discussed here indicate that the adenosinergic system is involved in both the etiology and the treatment of mood and anxiety disorders.

Neuroprotective Effect of AM404 Against NMDA-Induced Hippocampal Excitotoxicity.

Different studies have demonstrated that inflammation and alterations in glutamate neurotransmission are two events contributing to the pathophysiology of neurodegenerative or neurological disorders. There are evidences that N-arachidonoylphenolamine (AM404), a cannabinoid system modulator and paracetamol metabolite, modulates inflammation and exerts neuroprotective effects on Huntington's (HD) and Parkinson's diseases (PD), and ischemia. However, the effects of AM404 on the production of inflammatory mediators and excitotoxicity in brain tissue stimulated with N-methyl-D-aspartic acid (NMDA) are not elucidated. In this present study, we investigated the effects of AM404 on the production of inflammatory mediators and neuronal cell death induced by NMDA in organotypic hippocampal slices cultures (OHSC) using qPCR, western blot (WB), and immunohistochemistry. Moreover, to comprehend the mechanism of excitotoxicity, we evaluated the effects of AM404 on glutamate release in hippocampal synaptosomes and the NMDA-induced calcium responses in acute hippocampal slices. Our results showed that AM404 led to a significant decrease in cell death induced by NMDA, through a mechanism possibly involving the reduction of glutamate release and the calcium ions responses. Furthermore, it decreased the expression of the interleukin (IL)-1ß. This study provides new significant insights about the anti-inflammatory and neuroprotection effects of AM404 on NMDA-induced excitotoxicity. To understand the effects of AM404 in these processes might contribute to the therapeutic potential of AM404 in diseases with involvement of neuroinflammation and neurodegeneration and might lead to a possible future treatment of neurodegenerative diseases.

Recent insights into antidepressant therapy: Distinct pathways and potential common mechanisms in the treatment of depressive syndromes.

There is an urgent, unmet clinical need for faster and more efficient antidepressant drugs with higher response rates. In animal models of depression it was shown in the last few years that inhibition of three signaling molecules (BDNF, p11 and Homer1a) prevents efficacy of antidepressant therapy. These data not only show the crucial role of these factors for the treatment of depression, but may also point towards a better understanding of the molecular changes responsible for successful antidepressant therapy. Reviewing the literature concerning BNDF, p11 and Homer1a we here describe a molecular network in which these molecules interact with each other finally leading to facilitation of AMPA receptor signaling and plasticity, corroborating the current idea of AMPA receptors being a promising drug target in depression.

Antidepressants Rescue Stress-Induced Disruption of Synaptic Plasticity via Serotonin Transporter-Independent Inhibition of L-Type Calcium Channels.

BACKGROUND: Long-term synaptic plasticity is a basic ability of the brain to dynamically adapt to external stimuli and regulate synaptic strength and ultimately network function. It is dysregulated by behavioral stress in animal models of depression and in humans with major depressive disorder. Antidepressants have been shown to restore disrupted synaptic plasticity in both animal models and humans; however, the underlying mechanism is unclear. METHODS: We examined modulation of synaptic plasticity by selective serotonin reuptake inhibitors (SSRIs) in hippocampal brain slices from wild-type rats and serotonin transporter (SERT) knockout mice. Recombinant voltage-gated calcium (Ca2+) channels in heterologous expression systems were used to determine the modulation of Ca2+ channels by SSRIs. We tested the behavioral effects of SSRIs in the chronic behavioral despair model of depression both in the presence and in the absence of SERT. RESULTS: SSRIs selectively inhibited hippocampal long-term depression. The inhibition of long-term depression by SSRIs was mediated by a direct block of voltage-activated L-type Ca2+ channels and was independent of SERT. Furthermore, SSRIs protected both wild-type and SERT knockout mice from behavioral despair induced by chronic stress. Finally, long-term depression was facilitated in animals subjected to the behavioral despair model, which was prevented by SSRI treatment. CONCLUSIONS: These results showed that antidepressants protected synaptic plasticity and neuronal circuitry from the effects of stress via a modulation of Ca2+ channels and synaptic plasticity independent of SERT. Thus, L-type Ca2+ channels might constitute an important signaling hub for stress response and for pathophysiology and treatment of depression.

Ras Activity Tunes the Period and Modulates the Entrainment of the Suprachiasmatic Clock.

The small GTPase Ras is a universal eukaryotic cytoplasmic membrane-anchored protein, which regulates diverse downstream signal transduction pathways that play an important role in the proper functioning of neurons. Ras activity is a central regulator of structural and functional synaptic plasticity in the adult nervous system, where it channels neuronal responses to various extracellular cues allowing the organism to adapt to complex environmental stimuli. The suprachiasmatic nucleus (SCN) is the principle pacemaker of the circadian clock, and the circadian and photic regulation of Ras activity in the SCN is an important modulator of the clockwork. We have generated transgenic mouse expressing constitutively active V12-H-Ras selectively in neurons via a synapsin I promoter (synRas mice), which serves as a suitable model to study the role of neuronal Ras signaling. Modulation of Ras activity affects ERK1,2/CREB signaling and glycogen synthase kinase-3 beta expression in the SCN, which in turn modify the photoentrainment of the clock and the fine tuning the circadian period length. The main focus of this review is to offer an overview of the function of Ras signaling in the circadian rhythm and its potential role in learning and memory consolidation.

Signaling pathways regulating Homer1a expression: implications for antidepressant therapy.

Homer1a is upregulated by several different antidepressant measures, including non-pharmacological treatments, like sleep deprivation (SD) and electroconvulsive therapy (ECT) and antidepressant drugs, such as imipramine, fluoxetine and ketamine. Homer1a induction might thus be a crucial joint mechanism for antidepressant therapy in general. However, the upstream signaling pathways that regulate or induce Homer1a expression are still not well understood. The main focus of the present review is to offer an overview of the current knowledge about the potential role of Homer1a in depression and the signaling pathways responsible for Homer1a regulation. It is suggested here that a detailed characterization of the signaling mechanisms leading to Homer1a expression might provide novel therapeutic targets for antidepressant drug development.

Ras Activity Oscillates in the Mouse Suprachiasmatic Nucleus and Modulates Circadian Clock Dynamics.

Circadian rhythms, generated in the mouse suprachiasmatic nucleus (SCN), are synchronized to the environmental day-night changes by photic input. The activation of the extracellular signal-regulated kinases 1 and 2 (ERK1,2) and cAMP response element-binding protein (CREB)-mediated transcription play a critical role in this photoentrainment. The small GTPase Ras is one of the major upstream regulators of the ERK1,2/CREB pathway. In contrast to the well-described role of Ras in structural and functional synaptic plasticity in the adult mouse brain, the physiological regulation of Ras by photic sensory input is yet unknown. Here, we describe for the first time a circadian rhythm of Ras activity in the mouse SCN. Using synRas transgenic mice, expressing constitutively activated V12-Ha-Ras selectively in neurons, we demonstrate that enhanced Ras activation causes shortening of the circadian period length. We found upregulated expression and decreased inhibitory phosphorylation of the circadian period length modulator, glycogen synthase kinase-3 beta (GSK3ß), in the SCN of synRas mice. Conversely, downregulation of Ras activity by blocking its function with an antibody in oscillating cell cultures reduced protein levels and increased phosphorylation of GSK3ß and lengthened the period of BMAL1 promoter-driven luciferase activity. Furthermore, enhanced Ras activity in synRas mice resulted in a potentiation of light-induced phase delays at early subjective night, and increased photic induction of pERK1,2/pCREB and c-Fos. In contrast, at late subjective night, photic activation of Ras/ERK1,2/CREB in synRas mice was not sufficient to stimulate c-Fos protein expression and phase advance the clock. Taken together, our results demonstrate that Ras activity fine tunes the period length and modulates photoentrainment of the circadian clock.

Increased Signaling via Adenosine A1 Receptors, Sleep Deprivation, Imipramine, and Ketamine Inhibit Depressive-like Behavior via Induction of Homer1a.

Major depressive disorder is among the most commonly diagnosed disabling mental diseases. Several non-pharmacological treatments of depression upregulate adenosine concentration and/or adenosine A1 receptors (A1R) in the brain. To test whether enhanced A1R signaling mediates antidepressant effects, we generated a transgenic mouse with enhanced doxycycline-regulated A1R expression, specifically in forebrain neurons. Upregulating A1R led to pronounced acute and chronic resilience toward depressive-like behavior in various tests. Conversely, A1R knockout mice displayed an increased depressive-like behavior and were resistant to the antidepressant effects of sleep deprivation (SD). Various antidepressant treatments increase homer1a expression in medial prefrontal cortex (mPFC). Specific siRNA knockdown of homer1a in mPFC enhanced depressive-like behavior and prevented the antidepressant effects of A1R upregulation, SD, imipramine, and ketamine treatment. In contrast, viral overexpression of homer1a in the mPFC had antidepressant effects. Thus, increased expression of homer1a is a final common pathway mediating the antidepressant effects of different antidepressant treatments.

P2X7-dependent, but differentially regulated release of IL-6, CCL2, and TNF-α in cultured mouse microglia.

ATP is an important regulator of microglia and its effects on microglial cytokine release are currently discussed as important contributors in a variety of brain diseases. We here analyzed the effects of ATP on the production of six inflammatory mediators (IL-6, IL-10, CCL2, IFN-γ, TNF-α, and IL-12p70) in cultured mouse primary microglia. Stimulation of P2X7 receptor by ATP (1 mM) or BzATP (500 µM) evoked the mRNA expression and release of proinflammatory cytokines IL-6, TNF-α, and the chemokine CCL2 in WT cells but not in P2X7(-/-) cells. The effects of ATP and BzATP were inhibited by the nonselective P2 receptor antagonists PPADs and suramin. Various selective P2X7 receptor antagonists blocked the P2X7-dependent release of IL-6 and CCL2, but, surprisingly, had no effect on BzATP-induced release of TNF-α in microglia. Calcium measurements confirmed that P2X7 is the main purine receptor activated by BzATP in microglia and showed that all P2X7 antagonists were functional. It is also presented that pannexin-1 hemichannel function and potential P2X4/P2X7 heterodimers are not involved in P2X7-dependent release of IL-6, CCL2, and TNF-α in microglia. How P2X7-specific antagonists only affect P2X7-dependent IL-6 and CCL2 release, but not TNF-α release is at the moment unclear, but indicates that the P2X7-dependent release of cytokines in microglia is differentially regulated.

Genetically controlled upregulation of adenosine A(1) receptor expression enhances the survival of primary cortical neurons.

Adenosine has a key endogenous neuroprotective role in the brain, predominantly mediated by the adenosine A(1) receptor (A(1)R). This has been mainly explored using pharmacological tools and/or receptor knockout mice strains. It has long been suggested that the neuroprotective effects of A(1)R are increased following receptor upregulation, thus attenuating neuronal damage in pathological conditions. We have previously shown that the neuroprotective and neuromodulatory actions of the cytokines IL-6 and oncostatin M are mediated by induction of neuronal A(1)R expression. In order to investigate the direct effects of A(1)R upregulation in neurons, we have generated a tetracycline-regulated expression system with a bidirectional promoter, directing the simultaneous expression of the mouse A(1)R and GFP/mCherry reporter genes. In a first step, we tested the efficacy of the system in transiently transfected human embryonic kidney 293 cells. In addition, we confirmed the functional integrity of the expressed A(1)R by whole-cell patch clamp recordings. We demonstrated that A(1)R-transfected primary neurons show enhanced survival against N-methyl-D-aspartate-induced excitotoxicity. Pretreatment with an A(1)R-selective agonist additionally strongly decreased neuronal cell death, while an A(1)R antagonist completely abolished the neuroprotective effects of A(1)R upregulation. The presented data provide for the first time direct evidence that the upregulation of A(1)R enhances neuronal survival.