Reduced levels of serotonin 2A receptors underlie resistance of Egr3-deficient mice to locomotor suppression by clozapine

Acute sleep deprivation upregulates serotonin 2A receptors in the frontal cortex of mice via the immediate early gene Egr3

Serotonin 2A receptors (5-HT_2ARs) mediate the hallucinogenic effects of psychedelic drugs and are a key target of the leading class of medications used to treat psychotic disorders. These findings suggest that dysfunction of 5-HT_2ARs may contribute to the symptoms of schizophrenia, a mental illness characterized by perceptual and cognitive disturbances. Indeed, numerous studies have found that 5-HT_2ARs are reduced in the brains of individuals with schizophrenia. However, the mechanisms that regulate 5-HT_2AR expression remain poorly understood. Here, we show that a physiologic environmental stimulus, sleep deprivation, significantly upregulates 5-HT_2AR levels in the mouse frontal cortex in as little as 6-8 h (for mRNA and protein, respectively). This induction requires the activity-dependent immediate early gene transcription factor early growth response 3 (Egr3) as it does not occur in Egr3 deficient (-/-) mice. Using chromatin immunoprecipitation, we show that EGR3 protein binds to the promoter of Htr2a, the gene that encodes the 5-HT_2AR, in the frontal cortex in vivo, and drives expression of in vitro reporter constructs via two EGR3 binding sites in the Htr2a promoter. These results suggest that EGR3 directly regulates Htr2a expression, and 5-HT_2AR levels, in the frontal cortex in response to physiologic stimuli. Analysis of publicly available post-mortem gene expression data revealed that both EGR3 and HTR2A mRNA are reduced in the prefrontal cortex of schizophrenia patients compared to controls. Together these findings suggest a mechanism by which environmental stimuli alter levels of a brain receptor that may mediate the symptoms, and treatment, of mental illness.

Chemogenetics drives paradigm change in the investigation of behavioral circuits and neural mechanisms underlying drug action

Recent developments in chemogenetic approaches to the investigation of brain function have ushered in a paradigm change in the strategy for drug and behavior research and clinical drug-based medications. As the nature of the drug action is based on humoral regulation, it is a challenge to identify the neuronal mechanisms responsible for the expression of certain targeted behavior induced by drug application. The development of chemogenetic approaches has allowed researchers to control neural activities in targeted neurons through a toolbox, including engineered G protein-coupled receptors or ligand-gated ion channels together with exogenously inert synthetic ligands. This review provides a brief overview of the chemogenetics toolbox with an emphasis on the DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) technique used in rodent models, which is applicable to the investigation of how specific neural circuits regulate behavioral processes. The use of chemogenetics has had a significant impact on basic neuroscience for a better understanding of the relationships between brain activity and the expression of behaviors with cell- and circuit-specific orders. Furthermore, chemogenetics is potentially a useful tool to deconstruct the neuropathological mechanisms of mental diseases and its regulation by drug, and provide us with transformative therapeutics with medication. We also review recent findings in the use of chemogenetic techniques to uncover functional circuit connections of serotonergic neurons in rodent models.

Peripheral Blood Leukocyte RNA-Seq Identifies a Set of Genes Related to Abnormal Psychomotor Behavior Characteristics in Patients with Schizophrenia

BACKGROUND Schizophrenia is a multigene disease with a complex etiology and different clinical manifestations. It is of great significance to understand the etiology and pathogenesis of schizophrenia patients from different clinical dimensions and to interpret the potential molecular changes of schizophrenia patients from different clinical dimensions. MATERIAL AND METHODS RNA-Seq was performed on peripheral blood leukocytes of 50 patients with schizophrenia and 50 healthy controls. Phenotypic information of patients with schizophrenia was collected during blood sampling. Differentially expressed genes (DEGs) were screened by the edgeR package of R software. To better analyze the correlation between DEG expression values, explore the potential association between differential genes and clinical dimensions of schizophrenia, and identify hub genes, we constructed a DEG co-expression network using weighted gene co-expression network analysis (WGCNA). RESULTS We provide the transcription profiles of peripheral blood leukocytes in patients with schizophrenia and found a gene module (including 89 genes) closely related to the clinical dimension of abnormal psychomotor behavior in schizophrenia. CONCLUSIONS The findings enhance our understanding of the biological processes of schizophrenia, enabling us to identify specific clinical dimensions of genes for diagnosis and prognostic markers and possibly for targeted therapy.

Serotonin 5-HT1A, 5-HT2A and dopamine D2 receptors strongly influence prefronto-hippocampal neural networks in alert mice: Contribution to the actions of risperidone

Atypical antipsychotic drugs (APDs) used to treat positive and negative symptoms in schizophrenia block serotonin receptors 5-HT_2AR and dopamine receptors D₂R and stimulate 5-HT_1AR directly or indirectly. However, the exact cellular mechanisms mediating their therapeutic actions remain unresolved. We recorded neural activity in the prefrontal cortex (PFC) and hippocampus (HPC) of freely-moving mice before and after acute administration of 5-HT_1AR, 5-HT_2AR and D₂R selective agonists and antagonists and atypical APD risperidone. We then investigated the contribution of the three receptors to the actions of risperidone on brain activity via statistical modeling and pharmacological reversal (risperidone + 5-HT_1AR antagonist WAY-100635, risperidone + 5-HT_2A/2CR agonist DOI, risperidone + D₂R agonist quinpirole). Risperidone, 5-HT_1AR agonism with 8-OH-DPAT, 5-HT_2AR antagonism with M100907, and D₂R antagonism with haloperidol reduced locomotor activity of mice that correlated with a suppression of neural spiking, power of theta and gamma oscillations in PFC and HPC, and reduction of PFC-HPC theta phase synchronization. By contrast, activation of 5-HT_2AR with DOI enhanced high-gamma oscillations in PFC and PFC-HPC high gamma functional connectivity, likely related to its hallucinogenic effects. Together, power changes, regression modeling and pharmacological reversals suggest an important role of 5-HT_1AR agonism and 5-HT_2AR antagonism in risperidone-induced alterations of delta, beta and gamma oscillations, while D₂R antagonism may contribute to risperidone-mediated changes in delta oscillations. This study provides novel insight into the neural mechanisms for widely prescribed psychiatric medication targeting the serotonin and dopamine systems in two regions involved in the pathophysiology of schizophrenia.

Identifying the In Vivo Cellular Correlates of Antipsychotic Drugs

GPCRs such as 5-HT_2A and D2 are implicated in the therapeutic and the side effects of antipsychotics. However, the pattern of brain activity that leads to the behavioral effects of antipsychotics is poorly understood. To address this question, we used the transgenic ‘FosTRAP’ mice (Mus musculus), where a fluorescent reporter marks the cells responsive to the stimulus of interest. Here, the stimulus was an administration of various antipsychotic drugs. In case of typical antipsychotics such as Haloperidol, the c-fos active cells were predominantly found in the striatum, whereas in case of the atypical antipsychotics (Clozapine and Olanzapine), c-fos-induced cells were more numerous in the cortical regions, e.g., orbital cortex, piriform cortex. Curiously, we also observed ependymal cells to be a novel cellular target of atypical antipsychotics. 5-HT_2A is considered to be a major target for atypical antipsychotics. Therefore, we bred ‘FosTRAP’ mice with 5-HT_2A knock-out (KO) mice and tested their response to the prototype of atypical antipsychotics, Clozapine. Interestingly, the absence of 5-HT_2A did not significantly affect the number of c-fos-induced cells in the cortical regions. However, the ependymal cells showed a dramatically reduced response to Clozapine in the absence of 5-HT_2A. In summary, the TRAP system has allowed us to identify various region-specific activity induced by antipsychotics and novel cellular targets of the antipsychotics. These results serve as a “proof of principle” study that can be extended to explore the biochemical and physiological changes brought about by antipsychotics and specifically identify antipsychotic-responsive cells in the live tissue.

Influence of Schizophrenia-Associated Gene Egr3 on Sleep Behavior and Circadian Rhythms in Mice

Up to 80% of people meeting DSM-IV definitions for schizophrenia will exhibit difficulties with sleep, along with a breakdown in circadian entrainment and rhythmicity. The changes to the sleep and circadian systems in this population are thought to be interdependent, as evidenced by the frequent use of the combined term "sleep and circadian rhythm disruption" or "SCRD" to describe their occurrence. To understand links between sleep and circadian problems in the schizophrenia population, we analyzed the duration and rhythmicity of sleep behavior in mice lacking function of the immediate early gene early growth response 3 ( Egr3). EGR3 has been associated with schizophrenia risk in humans, and Egr3-deficient (-/-) mice display various features of schizophrenia that are responsive to antipsychotic treatment. While Egr3-/- mice slept less than their wildtype (WT) littermates, they showed no evidence of circadian disorganization; in fact, circadian rhythms of activity were more robust in these mice compared with WT, as measured by time series analysis and the relative amplitude index of Van Someren's suite of non-parametric circadian rhythm analyses. Differences in circadian robustness were maintained when the animals were transferred to several weeks of housing under constant darkness or constant light. Together, our results suggest that Egr3-/- mice retain control over the circadian timekeeping of sleep and wake, while showing impaired sleep. The findings are compatible with those from a surprising array of mouse models of schizophrenia and raise the possibility that SCRD may be 2 separate disorders in the schizophrenia population requiring different treatment strategies.

State-Dependent Modulation of Visual Evoked Potentials in a Rodent Genetic Model of Electroencephalographic Instability

Despite normal sleep timing and duration, Egr3-deficient (Egr3^−/−) mice exhibit electroencephalographic (EEG) characteristics of reduced arousal, including elevated slow wave (1–4 Hz) activity during wakefulness. Here we show that these mice exhibit state-dependent instability in the EEG. Intermittent surges in EEG power were found in Egr3^−/− mice during wakefulness and rapid eye movement sleep, most prominently in the beta (15–35 Hz) range compared to wild type (Egr3^+/+) mice. Such surges did not coincide with sleep onset, as the surges were not associated with cessation of electromyographic tone. Cortical processing of sensory information by visual evoked responses (VEP) were found to vary as a function of vigilance state, being of higher magnitude during slow wave sleep (SWS) than wakefulness and rapid eye movement sleep. VEP responses were significantly larger during quiet wakefulness than active wakefulness, in both Egr3^−/− mice and Egr3^+/+ mice. EEG synchronization in the beta range, previously linked to the accumulation of sleep need over time, predicted VEP magnitude. Egr3^−/− mice not only displayed elevated beta activity, but in quiet wake, this elevated beta activity coincides with an elevated evoked response similar to that of animals in SWS. These data confirm that (a) VEPs vary as a function of vigilance state, and (b) beta activity in the EEG is a predictor of state-dependent modulation of visual information processing. The phenotype of Egr3^−/− mice indicates that Egr3 is a genetic regulator of these phenomena.

The Immediate Early Gene Egr3 Is Required for Hippocampal Induction of Bdnf by Electroconvulsive Stimulation

Early growth response 3 (Egr3) is an immediate early gene (IEG) that is regulated downstream of a cascade of genes associated with risk for psychiatric disorders, and dysfunction of Egr3 itself has been implicated in schizophrenia, bipolar disorder, and depression. As an activity-dependent transcription factor, EGR3 is poised to regulate the neuronal expression of target genes in response to environmental events. In the current study, we sought to identify a downstream target of EGR3 with the goal of further elucidating genes in this biological pathway relevant for psychiatric illness risk. We used electroconvulsive stimulation (ECS) to induce high-level expression of IEGs in the brain, and conducted expression microarray to identify genes differentially regulated in the hippocampus of Egr3-deficient (-/-) mice compared to their wildtype (WT) littermates. Our results replicated previous work showing that ECS induces high-level expression of the brain-derived neurotrophic factor (Bdnf) in the hippocampus of WT mice. However, we found that this induction is absent in Egr3-/- mice. Quantitative real-time PCR (qRT-PCR) validated the microarray results (performed in males) and replicated the findings in two separate cohorts of female mice. Follow-up studies of activity-dependent Bdnf exons demonstrated that ECS-induced expression of both exons IV and VI requires Egr3. In situ hybridization demonstrated high-level cellular expression of Bdnf in the hippocampal dentate gyrus following ECS in WT, but not Egr3-/-, mice. Bdnf promoter analysis revealed eight putative EGR3 binding sites in the Bdnf promoter, suggesting a mechanism through which EGR3 may directly regulate Bdnf gene expression. These findings do not appear to result from a defect in the development of hippocampal neurons in Egr3-/- mice, as cell counts in tissue sections stained with anti-NeuN antibodies, a neuron-specific marker, did not differ between Egr3-/- and WT mice. In addition, Sholl analysis and counts of dendritic spines in golgi-stained hippocampal sections revealed no difference in dendritic morphology or synaptic spine density in Egr3-/-, compared to WT, mice. These findings indicate that Egr3 is required for ECS-induced expression of Bdnf in the hippocampus and suggest that Bdnf may be a downstream gene in our previously identified biologically pathway for psychiatric illness susceptibility.

The 5α-reductase inhibitor finasteride increases suicide-related aggressive behaviors and blocks clozapine-induced beneficial effects in an animal model of schizophrenia

Death by suicide is 5 times higher among schizophrenia patients than in the general population. There is now compelling evidence suggesting that the pathophysiology of suicide in schizophrenia does not involve central serotonergic neurotransmission disturbances, as has been shown in other contexts. We recently developed and characterized a murine Two-Hit Model of Suicide-related behavior in a schizophrenia-like context (THMS) (gestational inflammation with polyI:C at gestational day 12 followed by post-weaning social isolation). In this THMS model, we have recently shown that the atypical antipsychotic clozapine normalized the prepulse inhibition (PPI) deficits as well suicide-related, impulsive aggressive and anxiety-like behaviors. While the mechanisms underlying the suicide-reducing benefits of clozapine in schizophrenic patients are not well understood, previous works have revealed that clozapine alters brain levels of neurosteroids, such as allopregnanolone. In the present study, we thus investigated the role of endogenous neurosteroids in clozapine action by evaluating whether the 5α-reductase inhibitor finasteride could overturn the ability of clozapine to reduce suicide-related behaviors. We found that clozapine significantly improved the PPI deficits in THMS mice, which could not be reversed by finasteride treatment. However, finasteride counteracted the ability of clozapine to decrease the exploratory behaviors in the open-field test. In the resident-intruder test, THMS mice showed exacerbated aggressiveness and impulsivity following finasteride alone. In this resident-intruder paradigm, clozapine alone effectively blocked the finasteride-enhanced effects on aggression and impulsivity. Altogether, these findings support the existence of a complex interaction between clozapine and neurosteroids in THMS mice. Further investigations are now required to clarify the details of the molecular mechanisms involved.

Immediate Early Genes Anchor a Biological Pathway of Proteins Required for Memory Formation, Long-Term Depression and Risk for Schizophrenia

While the causes of myriad medical and infectious illnesses have been identified, the etiologies of neuropsychiatric illnesses remain elusive. This is due to two major obstacles. First, the risk for neuropsychiatric disorders, such as schizophrenia, is determined by both genetic and environmental factors. Second, numerous genes influence susceptibility for these illnesses. Genome-wide association studies have identified at least 108 genomic loci for schizophrenia, and more are expected to be published shortly. In addition, numerous biological processes contribute to the neuropathology underlying schizophrenia. These include immune dysfunction, synaptic and myelination deficits, vascular abnormalities, growth factor disruption, and N-methyl-D-aspartate receptor (NMDAR) hypofunction. However, the field of psychiatric genetics lacks a unifying model to explain how environment may interact with numerous genes to influence these various biological processes and cause schizophrenia. Here we describe a biological cascade of proteins that are activated in response to environmental stimuli such as stress, a schizophrenia risk factor. The central proteins in this pathway are critical mediators of memory formation and a particular form of hippocampal synaptic plasticity, long-term depression (LTD). Each of these proteins is also implicated in schizophrenia risk. In fact, the pathway includes four genes that map to the 108 loci associated with schizophrenia: GRIN2A, nuclear factor of activated T-cells (NFATc3), early growth response 1 (EGR1) and NGFI-A Binding Protein 2 (NAB2); each of which contains the "Index single nucleotide polymorphism (SNP)" (most SNP) at its respective locus. Environmental stimuli activate this biological pathway in neurons, resulting in induction of EGR immediate early genes: EGR1, EGR3 and NAB2. We hypothesize that dysfunction in any of the genes in this pathway disrupts the normal activation of Egrs in response to stress. This may result in insufficient electrophysiologic, immunologic, and neuroprotective, processes that these genes normally mediate. Continued adverse environmental experiences, over time, may thereby result in neuropathology that gives rise to the symptoms of schizophrenia. By combining multiple genes associated with schizophrenia susceptibility, in a functional cascade triggered by neuronal activity, the proposed biological pathway provides an explanation for both the polygenic and environmental influences that determine the complex etiology of this mental illness.

EGR3 Immediate Early Gene and the Brain-Derived Neurotrophic Factor in Bipolar Disorder

Bipolar disorder (BD) is a severe psychiatric illness with a consistent genetic influence, involving complex interactions between numerous genes and environmental factors. Immediate early genes (IEGs) are activated in the brain in response to environmental stimuli, such as stress. The potential to translate environmental stimuli into long-term changes in brain has led to increased interest in a potential role for these genes influencing risk for psychiatric disorders. Our recent finding using network-based approach has shown that the regulatory unit of early growth response gene 3 (EGR3) of IEGs family was robustly repressed in postmortem prefrontal cortex of BD patients. As a central transcription factor, EGR3 regulates an array of target genes that mediate critical neurobiological processes such as synaptic plasticity, memory and cognition. Considering that EGR3 expression is induced by brain-derived neurotrophic factor (BDNF) that has been consistently related to BD pathophysiology, we suggest a link between BDNF and EGR3 and their potential role in BD. A growing body of data from our group and others has shown that peripheral BDNF levels are reduced during mood episodes and also with illness progression. In this same vein, BDNF has been proposed as an important growth factor in the impaired cellular resilience related to BD. Taken together with the fact that EGR3 regulates the expression of the neurotrophin receptor p75NTR and may also indirectly induce BDNF expression, here we propose a feed-forward gene regulatory network involving EGR3 and BDNF and its potential role in BD.

Precision medicine for suicidality: from universality to subtypes and personalization

Suicide remains a clear, present and increasing public health problem, despite being a potentially preventable tragedy. Its incidence is particularly high in people with overt or un(der)diagnosed psychiatric disorders. Objective and precise identification of individuals at risk, ways of monitoring response to treatments and novel preventive therapeutics need to be discovered, employed and widely deployed. We sought to investigate whether blood gene expression biomarkers for suicide (that is, a 'liquid biopsy' approach) can be identified that are more universal in nature, working across psychiatric diagnoses and genders, using larger cohorts than in previous studies. Such markers may reflect and/or be a proxy for the core biology of suicide. We were successful in this endeavor, using a comprehensive stepwise approach, leading to a wealth of findings. Steps 1, 2 and 3 were discovery, prioritization and validation for tracking suicidality, resulting in a Top Dozen list of candidate biomarkers comprising the top biomarkers from each step, as well as a larger list of 148 candidate biomarkers that survived Bonferroni correction in the validation step. Step 4 was testing the Top Dozen list and Bonferroni biomarker list for predictive ability for suicidal ideation (SI) and for future hospitalizations for suicidality in independent cohorts, leading to the identification of completely novel predictive biomarkers (such as CLN5 and AK2), as well as reinforcement of ours and others previous findings in the field (such as SLC4A4 and SKA2). Additionally, we examined whether subtypes of suicidality can be identified based on mental state at the time of high SI and identified four potential subtypes: high anxiety, low mood, combined and non-affective (psychotic). Such subtypes may delineate groups of individuals that are more homogenous in terms of suicidality biology and behavior. We also studied a more personalized approach, by psychiatric diagnosis and gender, with a focus on bipolar males, the highest risk group. Such a personalized approach may be more sensitive to gender differences and to the impact of psychiatric co-morbidities and medications. We compared testing the universal biomarkers in everybody versus testing by subtypes versus personalized by gender and diagnosis, and show that the subtype and personalized approaches permit enhanced precision of predictions for different universal biomarkers. In particular, LHFP appears to be a strong predictor for suicidality in males with depression. We also directly examined whether biomarkers discovered using male bipolars only are better predictors in a male bipolar independent cohort than universal biomarkers and show evidence for a possible advantage of personalization. We identified completely novel biomarkers (such as SPTBN1 and C7orf73), and reinforced previously known biomarkers (such as PTEN and SAT1). For diagnostic ability testing purposes, we also examined as predictors phenotypic measures as apps (for suicide risk (CFI-S, Convergent Functional Information for Suicidality) and for anxiety and mood (SASS, Simplified Affective State Scale)) by themselves, as well as in combination with the top biomarkers (the combination being our a priori primary endpoint), to provide context and enhance precision of predictions. We obtained area under the curves of 90% for SI and 77% for future hospitalizations in independent cohorts. Step 5 was to look for mechanistic understanding, starting with examining evidence for the Top Dozen and Bonferroni biomarkers for involvement in other psychiatric and non-psychiatric disorders, as a mechanism for biological predisposition and vulnerability. The biomarkers we identified also provide a window towards understanding the biology of suicide, implicating biological pathways related to neurogenesis, programmed cell death and insulin signaling from the universal biomarkers, as well as mTOR signaling from the male bipolar biomarkers. In particular, HTR2A increase coupled with ARRB1 and GSK3B decreases in expression in suicidality may provide a synergistic mechanistical corrective target, as do SLC4A4 increase coupled with AHCYL1 and AHCYL2 decrease. Step 6 was to move beyond diagnostics and mechanistical risk assessment, towards providing a foundation for personalized therapeutics. Items scored positive in the CFI-S and subtypes identified by SASS in different individuals provide targets for personalized (psycho)therapy. Some individual biomarkers are targets of existing drugs used to treat mood disorders and suicidality (lithium, clozapine and omega-3 fatty acids), providing a means toward pharmacogenomics stratification of patients and monitoring of response to treatment. Such biomarkers merit evaluation in clinical trials. Bioinformatics drug repurposing analyses with the gene expression biosignatures of the Top Dozen and Bonferroni-validated universal biomarkers identified novel potential therapeutics for suicidality, such as ebselen (a lithium mimetic), piracetam (a nootropic), chlorogenic acid (a polyphenol) and metformin (an antidiabetic and possible longevity promoting drug). Finally, based on the totality of our data and of the evidence in the field to date, a convergent functional evidence score prioritizing biomarkers that have all around evidence (track suicidality, predict it, are reflective of biological predisposition and are potential drug targets) brought to the fore APOE and IL6 from among the universal biomarkers, suggesting an inflammatory/accelerated aging component that may be a targetable common denominator.

Antipsychotic-induced Hdac2 transcription via NF-κB leads to synaptic and cognitive side effects

Antipsychotic drugs remain the standard for schizophrenia treatment. Despite their effectiveness in treating hallucinations and delusions, prolonged exposure to antipsychotic medications leads to cognitive deficits in both schizophrenia patients and animal models. The molecular mechanisms underlying these negative effects on cognition remain to be elucidated. Here we demonstrate that chronic antipsychotic drug exposure increases nuclear translocation of NF-κB in both mouse and human frontal cortex, a trafficking event triggered via 5-HT_2A-receptor-dependent downregulation of the NF-κB repressor IκBα. This upregulation of NF-κB activity led to its increased binding at the Hdac2 promoter, thereby augmenting Hdac2 transcription. Deletion of HDAC2 in forebrain pyramidal neurons prevented the negative effects of antipsychotic treatment on synaptic remodeling and cognition. Conversely, virally mediated activation of NF-κB signaling decreased cortical synaptic plasticity via HDAC2. Together, these observations may aid in developing therapeutic strategies to improve the outcome of schizophrenia treatment.

Reward Network Immediate Early Gene Expression in Mood Disorders

Over the past three decades, it has become clear that aberrant function of the network of interconnected brain regions responsible for reward processing and motivated behavior underlies a variety of mood disorders, including depression and anxiety. It is also clear that stress-induced changes in reward network activity underlying both normal and pathological behavior also cause changes in gene expression. Here, we attempt to define the reward circuitry and explore the known and potential contributions of activity-dependent changes in gene expression within this circuitry to stress-induced changes in behavior related to mood disorders, and contrast some of these effects with those induced by exposure to drugs of abuse. We focus on a series of immediate early genes regulated by stress within this circuitry and their connections, both well-explored and relatively novel, to circuit function and subsequent reward-related behaviors. We conclude that IEGs play a crucial role in stress-dependent remodeling of reward circuitry, and that they may serve as inroads to the molecular, cellular, and circuit-level mechanisms of mood disorder etiology and treatment.

Sedative effect of Clozapine is a function of 5-HT2A and environmental novelty

Antipsychotic drugs are the mainstay in the treatment of schizophrenia and bipolar disorder. However, antipsychotics often exhibit sedation or activity suppression among many other side effects, and the factors that influence them remain poorly understood. We now show, using a 5-HT_2A knockout (Htr2a^-/-) mouse, that environmental circumstances can affect suppression of activity induced by the atypical antipsychotic- Clozapine. We observed that Htr2a^-/- mice were more resistant to Clozapine-induced suppression of activity (CISA) and this behaviour was dependent on the environment being 'novel'. In their 'home' environment, at identical doses the mice exhibited CISA. Interestingly, the effect of genotype and environmental novelty on CISA could not be extended to the other antipsychotics that were tested, i.e. Haloperidol and Risperidone. Haloperidol-induced activity suppression was independent of context and genotype. Whereas context affected Risperidone-induced activity suppression only in the Htr2a^+/+ mice. Furthermore, we observed that caffeine, a stimulant, elicited resistance to CISA similar to that seen in the 'novel' context. Our study establishes a previously unknown interaction between the environmental context, 5-HT_2A and CISA and emphasises the role of non-pharmacological factors such as environment on the effects of the drug, which seem antipsychotic-specific. Our findings should advance the understanding of the side effects of individual antipsychotics and the role of environment to overcome side effects such as sedation.

Sleep Homeostatic and Waking Behavioral Phenotypes in Egr3-Deficient Mice Associated with Serotonin Receptor 5-HT2 Deficits

STUDY OBJECTIVE

The expression of the immediate early gene early growth response 3 (Egr3) is a functional marker of brain activity including responses to novelty, sustained wakefulness, and sleep. We examined the role of this gene in regulating wakefulness and sleep.

METHODS

Electroencephalogram/electromyogram (EEG/EMG) were recorded in Egr3-/- and wild-type (WT) mice during 24 h baseline, 6 h sleep disruption and 6 h recovery. Serotonergic signaling was assessed with 6 h EEG/EMG recordings after injections of nonselective 5-HT2 antagonist (clozapine), selective 5-HT2 antagonists (5-HT2A; MDL100907 and 5-HT2BC; SB206553) and a cocktail of both selective antagonists, administered in a randomized order to each animal.

RESULTS

Egr3-/- mice did not exhibit abnormalities in the timing of wakefulness and slow wave sleep (SWS); however, EEG dynamics in SWS (suppressed 1-3 Hz power) and in quiet wakefulness (elevated 3-8 Hz and 15-35 Hz power) differed in comparison to WT-mice. Egr3-/- mice showed an exaggerated response to sleep disruption as measured by active wakefulness, but with a blunted increase in homeostatic sleep drive (elevated 1-4 Hz power) relative to WT-mice. Egr3-/-mice exhibit greatly reduced sedative effects of clozapine at the electroencephalographic level. In addition, clozapine induced a previously undescribed dissociated state (low amplitude, low frequency EEG and a stable, low muscle tone) lasting up to 2 h in WT-mice. Egr3-/- mice did not exhibit this phenomenon. Selective 5-HT2A antagonist, alone or in combination with selective 5-HT2BC antagonist, caused EEG slowing coincident with behavioral quiescence in WT-mice but not in Egr3-/- mice.

CONCLUSION

Egr3 has an essential role in regulating cortical arousal, wakefulness, and sleep, presumably by its regulation of 5-HT2 receptors.

Understanding the pathophysiology of schizophrenia: Contributions from the Melbourne Psychiatric Brain Bank

The Melbourne Psychiatric Brain Bank came into existence 25years ago. This review focusses on lines of research that have used tissue from the Brain Bank over periods of time. Hence there is a discussion on the significance of changes in levels of serotonin 2A receptors in the cortex of patients with schizophrenia and the relevance of such changes with regards to the pathophysiology of the disorder. The extensive contribution made by studies using tissue from the Melbourne Psychiatric Brain Bank to understanding the role of muscarinic receptors in the pathophysiology and treatment of schizophrenia is summarised. Finally, findings using brain bank tissue and "omics" technologies are reviewed. In each case, findings using tissue from the Melbourne Psychiatric Brain Bank is placed in context with research carried out on human postmortem CNS in schizophrenia and with findings in other lines of research that can help explain the causes or consequences of changes in CNS molecular cytoarchitecture. This timely review of data from the Melbourne Psychiatric Brain Bank reinforces the challenges faced in trying to increase our understanding of the molecular pathophysiology of schizophrenia. Continuing to increase our understanding of the disorder is important as a precursor to identifying new drug targets that can be exploited to improve the treatment of a disorder where treatment resistance remains a significant problem (Millan et al., 2016).

Differential expression of transcriptional regulatory units in the prefrontal cortex of patients with bipolar disorder: potential role of early growth response gene 3

Bipolar disorder (BD) is a severe mental illness with a strong genetic component. Despite its high degree of heritability, current genetic studies have failed to reveal individual loci of large effect size. In lieu of focusing on individual genes, we investigated regulatory units (regulons) in BD to identify candidate transcription factors (TFs) that regulate large groups of differentially expressed genes. Network-based approaches should elucidate the molecular pathways governing the pathophysiology of BD and reveal targets for potential therapeutic intervention. The data from a large-scale microarray study was used to reconstruct the transcriptional associations in the human prefrontal cortex, and results from two independent microarray data sets to obtain BD gene signatures. The regulatory network was derived by mapping the significant interactions between known TFs and all potential targets. Five regulons were identified in both transcriptional network models: early growth response 3 (EGR3), TSC22 domain family, member 4 (TSC22D4), interleukin enhancer-binding factor 2 (ILF2), Y-box binding protein 1 (YBX1) and MAP-kinase-activating death domain (MADD). With a high stringency threshold, the consensus across tests was achieved only for the EGR3 regulon. We identified EGR3 in the prefrontal cortex as a potential key target, robustly repressed in both BD signatures. Considering that EGR3 translates environmental stimuli into long-term changes in the brain, disruption in biological pathways involving EGR3 may induce an impaired response to stress and influence on risk for psychiatric disorders, particularly BD.

Genomic structure and expression of the human serotonin 2A receptor gene (HTR2A) locus: identification of novel HTR2A and antisense (HTR2A-AS1) exons

Background

The serotonin 2A receptor is widely implicated in genetic association studies and remains an important drug target for psychiatric, neurological, and cardiovascular conditions. RNA sequencing redefined the architecture of the serotonin 2A receptor gene (HTR2A), revealing novel mRNA transcript isoforms utilizing unannotated untranslated regions of the gene. Expression of these untranslated regions is modulated by common single nucleotide polymorphisms (SNPs), namely rs6311. Previous studies did not fully capture the complexity of the sense- and antisense-encoded transcripts with respect to novel exons in the HTR2A gene locus. Here, we comprehensively catalogued exons and RNA isoforms for both HTR2A and HTR2A-AS1 using RNA-Seq from human prefrontal cortex and multiple mouse tissues. We subsequently tested associations between expression of newfound gene features and common SNPs in humans.

Results

We find that the human HTR2A gene spans ~66 kilobases and consists of 7, rather than 4 exons. Furthermore, the revised human HTR2A-AS1 gene spans ~474 kilobases and consists of 18, rather than 3 exons. Three HTR2A exons directly overlap with HTR2A-AS1 exons, suggesting potential for complementary nucleotide interactions. The repertoire of possible mouse Htr2a splice isoforms is remarkably similar to humans and we also find evidence for overlapping sense-antisense transcripts in the same relative positions as the human transcripts. rs6311 and SNPs in high linkage disequilibrium are associated with HTR2A-AS1 expression, in addition to previously described associations with expression of the extended 5’ untranslated region of HTR2A.

Conclusions

Our proposed HTR2A and HTR2A-AS1 gene structures dramatically differ from current annotations, now including overlapping exons on the sense and anti-sense strands. We also find orthologous transcript isoforms expressed in mice, providing opportunities to elucidate the biological roles of the human isoforms using a model system. Associations between rs6311 and expression of HTR2A and HTR2A-AS1 suggest this polymorphism is capable of modulating the expression of the sense or antisense transcripts. Still unclear is whether these SNPs act directly on the expression of the sense or antisense transcripts and whether overlapping exons are capable of interacting through complimentary base-pairing. Additional studies are necessary to determine the extent and nature of interactions between the SNPs and the transcripts prior to interpreting these findings in the context of phenotypes associated with HTR2A.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-015-0325-6) contains supplementary material, which is available to authorized users.

Alcohol enhances the psychostimulant and conditioning effects of mephedrone in adolescent mice; postulation of unique roles of D3 receptors and BDNF in place preference acquisition

BACKGROUND AND PURPOSE

The psychostimulant mephedrone is often consumed in combination with alcohol (EtOH). This kind of drug consumption during adolescence is a matter of concern.

EXPERIMENTAL APPROACH

We studied, in adolescent CD-1 mice, whether EtOH could enhance the psychostimulant (locomotor acivity) and rewarding [conditioned place preference (CPP)] effects of mephedrone. We also determined the transcriptional changes associated with a conditioning treatment with these drugs.

KEY RESULTS

Mephedrone (10 mg·kg(-1)) increased locomotor activity, which was further enhanced by 40% when combined with EtOH (1 g·kg(-1)). This enhancement was blocked by haloperidol. Furthermore, mephedrone (25 mg·kg(-1)) induced CPP, which increased by 70% when administered with a dose of EtOH that was not conditioning by itself (0.75 g·kg(-1)). There was enhanced expression of the D3 dopamine receptor mRNA (Drd3) and Arpc5 in all drug-treated groups. The D3 receptor antagonist SB-277011A and the BDNF receptor antagonist ANA-12 completely prevented CPP as well as the increases in Drd3 in all groups. Accordingly, increased expression of BDNF mRNA in medial prefrontal cortex was detected at 2 and 4 h after mephedrone administration.

CONCLUSIONS AND IMPLICATIONS

If translated to humans, the enhancement of mephedrone effects by ethanol could result in increased abuse liability. D3 receptors and BDNF play a key role in the establishment of CPP by mephedrone, although an accompanying increase in other synaptic plasticity-related genes may also be necessary.

Htr2a Expression Responds Rapidly to Environmental Stimuli in an Egr3-Dependent Manner

Pharmacologic and genetic findings have implicated the serotonin 2A receptor (5-HT2AR) in the etiology of schizophrenia. Recent studies have shown reduced 5-HT2AR levels in schizophrenia patients, yet the cause of this difference is unknown. Environmental factors, such as stress, also influence schizophrenia risk, yet little is known about how environment may affect this receptor. To determine if acute stress alters 5-HT2AR expression, we examined the effect of sleep deprivation on cortical Htr2a mRNA in mice. We found that 6 h of sleep deprivation induces a twofold increase in Htr2a mRNA, a more rapid effect than has been previously reported. This effect requires the immediate early gene early growth response 3 (Egr3), as sleep deprivation failed to induce Htr2a expression in Egr3-/- mice. These findings provide a functional link between two schizophrenia candidate genes and an explanation of how environment may influence a genetic predisposition for schizophrenia.

Clozapine acts as an agonist at serotonin 2A receptors to counter MK-801-induced behaviors through a βarrestin2-independent activation of Akt

The G protein-coupled serotonin 2A receptor (5-HT2AR) is a prominent target for atypical antipsychotic drugs, such as clozapine. Although clozapine is known to inhibit 5-HT2AR signaling through G protein-dependent mechanisms, it differs from classic GPCR antagonists, in that it also induces 5-HT2AR internalization and activates Akt signaling via a 5-HT2AR-mediated event. In this regard, clozapine may also be considered a functionally selective agonist. The cognate neurotransmitter at the 5-HT2AR, serotonin, also induces 5-HT2AR internalization and Akt phosphorylation. Serotonin promotes interactions with the scaffolding and regulatory protein, βarrestin2, which results in the recruitment and activation of Akt. These interactions prove to be critical for serotonin-induced, 5-HT2AR-mediated behavioral responses in mice. Herein, we sought to determine whether clozapine also utilizes βarrestin2-mediated mechanisms to induce 5-HT2AR signaling, and whether this interaction contributes to its behavioral effects in mice. We demonstrate that unlike serotonin, clozapine-mediated 5-HT2AR internalization and Akt phosphorylation is independent of receptor interactions with βarrestin2. Moreover, clozapine-mediated suppression of MK-801 and phencyclidine (PCP)-induced hyperlocomotion is βarrestin2 independent, although it is dependent upon Akt. These results demonstrate that pharmacologically oppositional ligands, serotonin and clozapine, utilize differential mechanisms to achieve the same 5-HT2AR-meadiated downstream events: Akt phosphorylation and receptor internalization. Although βarrestin2 has no effect on clozapine's actions in vivo, Akt phosphorylation is required for clozapine's efficacy in blocking MK-801- and PCP-induced models of schizophrenic behaviors in mice.

Gpm6b deficiency impairs sensorimotor gating and modulates the behavioral response to a 5-HT2A/C receptor agonist

The neuronal tetraspan proteins, M6A (Gpm6a) and M6B (Gpm6b), belong to the family of proteolipids that are widely expressed in the brain. We recently reported Gpm6a deficiency as a monogenetic cause of claustrophobia in mice. Its homolog proteolipid, Gpm6b, is ubiquitously expressed in neurons and oligodendrocytes. Gpm6b is involved in neuronal differentiation and myelination. It interacts with the N-terminal domain of the serotonin transporter (SERT) and decreases cell-surface expression of SERT. In the present study, we employed Gpm6b null mutant mice (Gpm6b(-/-)) to search for behavioral functions of Gpm6b. We studied male and female Gpm6b(-/-) mice and their wild-type (WT, Gpm6b(+/+)) littermates in an extensive behavioral test battery. Additionally, we investigated whether Gpm6b(-/-) mice exhibit changes in the behavioral response to a 5-HT2A/C receptor agonist. We found that Gpm6b(-/-) mice display completely normal sensory and motor functions, cognition, as well as social and emotionality-like (anxiety, depression) behaviors. On top of this inconspicuous behavioral profile, Gpm6b(-/-) mice of both genders exhibit a selective impairment in prepulse inhibition of the acoustic startle response. Furthermore, in contrast to WT mice that show the typical locomotion suppression and increase in grooming activity after intraperitoneal administration of DOI [(±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride], Gpm6b(-/-) mice demonstrate a blunted behavioral response to this 5-HT2A/C receptor agonist. To conclude, Gpm6b deficiency impairs sensorimotor gating and modulates the behavioral response to a serotonergic challenge.

A novel aminotetralin-type serotonin (5-HT) 2C receptor-specific agonist and 5-HT2A competitive antagonist/5-HT2B inverse agonist with preclinical efficacy for psychoses

Development of 5-HT2C agonists for treatment of neuropsychiatric disorders, including psychoses, substance abuse, and obesity, has been fraught with difficulties, because the vast majority of reported 5-HT2C selective agonists also activate 5-HT2A and/or 5-HT2B receptors, potentially causing hallucinations and/or cardiac valvulopathy. Herein is described a novel, potent, and efficacious human 5-HT2C receptor agonist, (-)-trans-(2S,4R)-4-(3'[meta]-bromophenyl)-N,N-dimethyl-1,2,3,4-tetrahydronaphthalen-2-amine (-)-MBP), that is a competitive antagonist and inverse agonist at human 5-HT2A and 5-HT2B receptors, respectively. (-)-MBP has efficacy comparable to the prototypical second-generation antipsychotic drug clozapine in three C57Bl/6 mouse models of drug-induced psychoses: the head-twitch response elicited by [2,5]-dimethoxy-4-iodoamphetamine; hyperlocomotion induced by MK-801 [(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (dizocilpine maleate)]; and hyperlocomotion induced by amphetamine. (-)-MBP, however, does not alter locomotion when administered alone, distinguishing it from clozapine, which suppresses locomotion. Finally, consumption of highly palatable food by mice was not increased by (-)-MBP at a dose that produced at least 50% maximal efficacy in the psychoses models. Compared with (-)-MBP, the enantiomer (+)-MBP was much less active across in vitro affinity and functional assays using mouse and human receptors and also translated in vivo with comparably lower potency and efficacy. Results indicate a 5-HT2C receptor-specific agonist, such as (-)-MBP, may be pharmacotherapeutic for psychoses, without liability for obesity, hallucinations, heart disease, sedation, or motoric disorders.

Locomotor hyperactivity in 14-3-3ζ KO mice is associated with dopamine transporter dysfunction

Dopamine (DA) neurotransmission requires a complex series of enzymatic reactions that are tightly linked to catecholamine exocytosis and receptor interactions on pre- and postsynaptic neurons. Regulation of dopaminergic signalling is primarily achieved through reuptake of extracellular DA by the DA transporter (DAT) on presynaptic neurons. Aberrant regulation of DA signalling, and in particular hyperactivation, has been proposed as a key insult in the presentation of schizophrenia and related neuropsychiatric disorders. We recently identified 14-3-3ζ as an essential component of neurodevelopment and a central risk factor in the schizophrenia protein interaction network. Our analysis of 14-3-3ζ-deficient mice now shows that baseline hyperactivity of knockout (KO) mice is rescued by the antipsychotic drug clozapine. 14-3-3ζ KO mice displayed enhanced locomotor hyperactivity induced by the DA releaser amphetamine. Consistent with 14-3-3ζ having a role in DA signalling, we found increased levels of DA in the striatum of 14-3-3ζ KO mice. Although 14-3-3ζ is proposed to modulate activity of the rate-limiting DA biosynthesis enzyme, tyrosine hydroxylase (TH), we were unable to identify any differences in total TH levels, TH localization or TH activation in 14-3-3ζ KO mice. Rather, our analysis identified significantly reduced levels of DAT in the absence of notable differences in RNA or protein levels of DA receptors D1-D5. Providing insight into the mechanisms by which 14-3-3ζ controls DAT stability, we found a physical association between 14-3-3ζ and DAT by co-immunoprecipitation. Taken together, our results identify a novel role for 14-3-3ζ in DA neurotransmission and provide support to the hyperdopaminergic basis of pathologies associated with schizophrenia and related disorders.

Preclinical models of antipsychotic drug action

One of the main obstacles faced by translational neuroscience is the development of animal models of psychiatric disorders. Behavioural pharmacology studies indicate that psychedelic drugs, such as lysergic acid diethylamide (LSD) and dissociative drugs, such as phencyclidine (PCP), induce in healthy human volunteers psychotic and cognitive symptoms that resemble some of those observed in schizophrenia patients. Serotonin 5-HT2A and metabotropic glutamate 2 receptors have been involved in the mechanism of action of psychedelic and dissociative drugs. Here we review recent advances using LSD-like and PCP-like drugs in rodent models that implicate these receptors in the neurobiology of schizophrenia and its treatment.

Association of decreased prefrontal hemodynamic response during a verbal fluency task with EGR3 gene polymorphism in patients with schizophrenia and in healthy individuals

The early growth response 3 (EGR3) gene is an immediate early gene that is expressed throughout the brain and has been suggested as a potential susceptibility gene for schizophrenia (SZ). EGR3 impairment is associated with various neurodevelopmental dysfunctions, and some animal studies have reported a role for EGR3 function in the prefrontal cortex. Therefore, EGR3 genotype variation may be reflected in prefrontal function. By using multi-channel near-infrared spectroscopy (NIRS) in an imaging genetics approach, we tested for an association between the EGR3 gene polymorphism and prefrontal hemodynamic response during a cognitive task in patients with SZ. We assessed 73 chronic patients with SZ and 73 age-, gender-, and genotype-matched healthy controls (HC) who provided written informed consent. We used NIRS to measure changes in prefrontal oxygenated hemoglobin concentration (oxyHb) during the letter version of a verbal fluency task (VFT). Statistical comparisons were performed among EGR3 genotype subgroups (rs35201266, GG/GA/AA). The AA genotype group showed significantly smaller oxyHb increases in the left dorsolateral prefrontal cortex (DLPFC) during the VFT than the GG and GA genotype groups; this was true for both patients with SZ and HC. Our findings provide in vivo human evidence of a significant influence of EGR3 polymorphisms on prefrontal hemodynamic activation level in healthy adults and in patients with SZ. Genetic variation in EGR3 may affect prefrontal function through neurodevelopment. This study illustrates the usefulness of NIRS in imaging genetics investigations on psychiatric disorders.

Animal models of serotonergic psychedelics

The serotonin 5-HT(2A) receptor is the major target of psychedelic drugs such as lysergic acid diethylamide (LSD), mescaline, and psilocybin. Serotonergic psychedelics induce profound effects on cognition, emotion, and sensory processing that often seem uniquely human. This raises questions about the validity of animal models of psychedelic drug action. Nonetheless, recent findings suggest behavioral abnormalities elicited by psychedelics in rodents that predict such effects in humans. Here we review the behavioral effects induced by psychedelic drugs in rodent models, discuss the translational potential of these findings, and define areas where further research is needed to better understand the molecular mechanisms and neuronal circuits underlying their neuropsychological effects.

Clozapine-induced locomotor suppression is mediated by 5-HT2A receptors in the forebrain

The need for safer, more effective therapeutics for the treatment of schizophrenia is widely acknowledged. To optimally target novel pharmacotherapies, in addition to establishing the mechanisms responsible for the beneficial effects of antipsychotics, the pathways underlying the most severe side effects must also be elucidated. Here we investigate the role of serotonin 2A (5-HT(2A)), serotonin 2C (5-HT(2C)), and dopamine 2 receptors (D₂) in mediating adverse effects associated with canonical first- and second-generation antipsychotic drugs in mice. Wild-type (WT) and 5-HT(2A) knockout (KO) mice treated with haloperidol, clozapine, and risperidone were assessed for locomotor activity and catalepsy. WT mice showed a marked reduction in locomotor activity following acute administration of haloperidol and high-dose risperidone, which was most likely secondary to the severe catalepsy caused by these compounds. Clozapine also dramatically reduced locomotor activity, but in the absence of catalepsy. Interestingly, 5-HT(2A) KO mice were cataleptic following haloperidol and risperidone, but did not respond to clozapine's locomotor-suppressing effects. Restoration of 5-HT(2A) expression to cortical glutamatergic neurons re-instated the locomotor-suppressing effects of clozapine in the open field. In sum, we confirm that haloperidol and risperidone caused catalepsy in rodents, driven by strong antagonism of D₂. We also demonstrate that clozapine decreases locomotor activity in a 5-HT(2A)-dependent manner, in the absence of catalepsy. Moreover, we show that it is the cortical population of 5-HT(2A) that mediate the locomotor-suppressing effects of clozapine.