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Persistent transcriptional events in ventral tegmental area (VTA) and other reward relevant brain regions contribute to enduring behavioral adaptations that characterize substance use disorder. Recent data from our laboratory indicate that aberrant accumulation of the newly discovered histone post-translational modification (PTM), H3 dopaminylation at glutamine 5 (H3Q5dop), contributes significantly to cocaine-seeking behavior following prolonged periods of abstinence. It remained unclear, however, whether this modification is important for relapse vulnerability in the context of other drugs of abuse, such as opioids. Here, we showed that H3Q5dop plays a critical role in heroin-mediated transcriptional plasticity in midbrain regions, particularly the VTA. In rats undergoing abstinence from heroin self-administration (SA), we found acute and persistent accumulation of H3Q5dop in VTA. Attenuation of H3Q5dop during abstinence induced persistent changes in gene expression programs associated with neuronal signaling and dopaminergic function in heroin abstinence and led to reduced heroin-seeking behavior. Interestingly, the observed changes in molecular pathways after heroin SA showed significant yet reversed overlap with the same genes altered in cocaine SA. These findings establish an essential role for H3Q5dop, and its downstream transcriptional consequences, in heroin-induced functional plasticity in VTA.

More than a normal neurotransmitter The molecular mechanisms underlying the persistence of addiction remain largely unclear. Lepack et al. found that, with cocaine exposure, there is an intracellular accumulation of dopamine in neurons of a brain region called the ventral tegmental area (see the Perspective by Girault). Dopamine associates with chromatin to initiate a previously unknown form of epigenetic regulation called dopaminylation. This modification has an impact on ventral tegmental area function and, consequently, on dopaminergic action potentials. The result is aberrant dopamine signaling in the ventral striatum during periods of drug seeking. Science , this issue p. 197 ; see also p. 134

Understanding the transcriptional changes that are engaged in stress resilience may reveal novel antidepressant targets. Here we use gene co-expression analysis of RNA-sequencing data from brains of resilient mice to identify a gene network that is unique to resilience. Zfp189, which encodes a previously unstudied zinc finger protein, is the highest-ranked key driver gene in the network, and overexpression of Zfp189 in prefrontal cortical neurons preferentially activates this network and promotes behavioral resilience. The transcription factor CREB is a predicted upstream regulator of this network and binds to the Zfp189 promoter. To probe CREB-Zfp189 interactions, we employ CRISPR-mediated locus-specific transcriptional reprogramming to direct CREB or G9a (a repressive histone methyltransferase) to the Zfp189 promoter in prefrontal cortex neurons. Induction of Zfp189 with site-specific CREB is pro-resilient, whereas suppressing Zfp189 expression with G9a increases susceptibility. These findings reveal an essential role for Zfp189 and CREB-Zfp189 interactions in mediating a central transcriptional network of resilience.

Chemical modifications of histones can mediate diverse DNA-templated processes, including gene transcription1–3. Here we provide evidence for a class of histone post-translational modification, serotonylation of glutamine, which occurs at position 5 (Q5ser) on histone H3 in organisms that produce serotonin (also known as 5-hydroxytryptamine (5-HT)). We demonstrate that tissue transglutaminase 2 can serotonylate histone H3 tri-methylated lysine 4 (H3K4me3)-marked nucleosomes, resulting in the presence of combinatorial H3K4me3Q5ser in vivo. H3K4me3Q5ser displays a ubiquitous pattern of tissue expression in mammals, with enrichment observed in brain and gut, two organ systems responsible for the bulk of 5-HT production. Genome-wide analyses of human serotonergic neurons, developing mouse brain and cultured serotonergic cells indicate that H3K4me3Q5ser nucleosomes are enriched in euchromatin, are sensitive to cellular differentiation and correlate with permissive gene expression, phenomena that are linked to the potentiation of TFIID4–6 interactions with H3K4me3. Cells that ectopically express a H3 mutant that cannot be serotonylated display significantly altered expression of H3K4me3Q5ser-target loci, which leads to deficits in differentiation. Taken together, these data identify a direct role for 5-HT, independent from its contributions to neurotransmission and cellular signalling, in the mediation of permissive gene expression. In serotonin-rich tissues, tissue transglutaminase 2 is able to attach serotonin to a glutamine residue in histone H3; this modification mediates permissive gene expression in these tissues.

Persistent transcriptional events in ventral tegmental area (VTA) and other reward relevant brain regions contribute to enduring behavioral adaptations that characterize substance use disorder. Recent data from our laboratory indicate that aberrant accumulation of the newly discovered histone post-translational modification (PTM), H3 dopaminylation at glutamine 5 (H3Q5dop), contributes significantly to cocaine-seeking behavior following prolonged periods of abstinence. It remained unclear, however, whether this modification is important for relapse vulnerability in the context of other drugs of abuse, such as opioids. Here, we showed that H3Q5dop plays a critical role in heroin-mediated transcriptional plasticity in midbrain regions, particularly the VTA. In rats undergoing abstinence from heroin self-administration (SA), we found acute and persistent accumulation of H3Q5dop in VTA. Attenuation of H3Q5dop during abstinence induced persistent changes in gene expression programs associated with neuronal signaling and dopaminergic function in heroin abstinence and led to reduced heroin-seeking behavior. Interestingly, the observed changes in molecular pathways after heroin SA showed significant yet reversed overlap with the same genes altered in cocaine SA. These findings establish an essential role for H3Q5dop, and its downstream transcriptional consequences, in heroin-induced functional plasticity in VTA.

Persistent transcriptional eventsamples were incubated on ice for 30 min and then centrifugeds in ventral tegmental area (VTA) and other reward relevant brain regions contribute to enduring behavioral adaptations that characterize substance use disorder (SUD). Recent data from our laboratory indicate that aberrant accumulation of the newly discovered histone post-translational modification (PTM), H3 dopaminylation at glutamine 5 (H3Q5dop), contributes significantly to cocaine-seeking behavior following prolonged periods of abstinence. It remained unclear, however, whether this modification is important for relapse vulnerability in the context of other drugs of abuse, such as opioids. Here, we showed that H3Q5dop plays a critical role in heroin-mediated transcriptional plasticity in midbrain. In rats undergoing abstinence from heroin self-administration (SA), we found acute and persistent accumulation of H3Q5dop in VTA. By attenuating H3Q5dop during abstinence, we both altered gene expression programs associated with heroin withdrawal and reduced heroin-primed reinstatement behavior. These findings thus establish an essential role for H3Q5dop, and its downstream transcriptional consequences, in opioid-induced plasticity in VTA.SIGNIFICANCE STATEMENTOpioid addiction is a chronically relapsing disorder defined by pathological drug-seeking behavior. Persistent relapse vulnerability is hypothesized to reflect a functional “rewiring” of reward-processing circuitry in the brain. This phenomenon is precipitated by drug-induced alterations in transcriptional plasticity of midbrain dopamine neurons, indicating an important role for epigenetic regulatory mechanisms in opioid dependence. We found that the newly discovered histone modification, H3 dopaminylation at glutamine 5 (H3Q5dop), was increased in ventral tegmental area (VTA) during periods of abstinence. H3Q5dop accumulation was found to regulate transcriptional programs associated with chronic heroin exposure. Using viral-mediated gene therapy to reduce H3Q5dop accumulation during abstinence resulted in attenuated heroin-primed seeking behaviors. Together, our results indicate that H3Q5dop plays an abstinence-specific role in regulating heroin-induced behavioral plasticity during prolonged abstinence.

With an incidence of ~1 in 800 births, Down syndrome (DS) is the most common chromosomal condition linked to intellectual disability worldwide. While the genetic basis of DS has been identified as a triplication of chromosome 21 (HSA21), the genes encoded from HSA21 that directly contribute to cognitive deficits remain incompletely understood. Here, we found that the HSA21-encoded chromatin effector, BRWD1, was upregulated in neurons derived from iPS cells from an individual with Down syndrome and brain of trisomic mice. We showed that selective copy number restoration of Brwd1 in trisomic animals rescued deficits in hippocampal LTP, cognition and gene expression. We demonstrated that Brwd1 tightly binds the BAF chromatin remodeling complex, and that increased Brwd1 expression promotes BAF genomic mistargeting. Importantly, Brwd1 renormalization rescued aberrant BAF localization, along with associated changes in chromatin accessibility and gene expression. These findings establish BRWD1 as a key epigenomic mediator of normal neurodevelopment and an important contributor to DS-related phenotypes.

Background Brain-derived neurotrophic factor (BDNF) plays a key role in the pathophysiology and treatment of depression. Recent clinical studies demonstrate that scopolamine, a nonselective muscarinic acetylcholine receptor antagonist, produces rapid antidepressant effects in patients with depression. Rodent studies demonstrate that scopolamine increases glutamate transmission and synaptogenesis in the medial prefrontal cortex (mPFC). Here we tested the hypothesis that activity-dependent BDNF release within the mPFC is necessary for the antidepressant actions of scopolamine. Methods Behavioral effects of scopolamine were assessed in BDNF Val/Met knock-in mice, in which BDNF processing and release are impaired. In addition, intra-mPFC infusion of a BDNF-neutralizing antibody was performed to test the necessity of BDNF release in driving scopolamine-induced behavioral responses. Further in vivo and in vitro experiments were performed to delineate BDNF-dependent mechanisms underlying the effects of scopolamine. Results We found that BDNF Met/Met mice have attenuated responses to scopolamine and that anti-BDNF antibody infusions into the mPFC prevented the antidepressant-like behavioral effects of scopolamine. In vitro experiments show that scopolamine rapidly stimulates BDNF release and tropomyosin receptor kinase B–extracellular signal-regulated kinase signaling. Moreover, these effects require alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor activation and are blocked by neuronal silencing. Importantly, pretreatment with verapamil prevented scopolamine-induced behavioral responses and BDNF–tropomyosin receptor kinase B signaling, suggesting that these effects are dependent on activation of voltage-dependent calcium channels. Conclusions The results identify an essential role for activity-dependent BDNF release in the rapid antidepressant effects of scopolamine. Attenuation of responses in BDNF Met mice indicates that patients with the Met allele may be less responsive to scopolamine.

Recent preclinical and clinical studies demonstrate that three functionally different compounds, the NMDA receptor channel blocker ketamine, mGlu2/3 receptor antagonist LY341495, and NMDA receptor glycine site agent GLYX-13 produce rapid and long lasting antidepressant effects. Furthermore, these agents are reported to stimulate ERK and mTORC1 signaling in brain. Here we used rat primary cortical culture neurons to further examine the cellular actions of these agents. The results demonstrate that low concentrations of all three compounds rapidly increase levels of the phosphorylated and activated forms of ERK and a downstream target of mTORC1, p70S6 kinase, in a concentration and time dependent manner. In addition, each compound rapidly increases BDNF release into the culture media. Further studies demonstrate that induction of BDNF release, as well as stimulation of phospho-ERK is blocked by incubation with an AMPA receptor antagonist. The requirement for AMPA receptor stimulation suggests that the effects of these rapid agents are activity dependent. This possibility is supported by studies demonstrating that neuronal silencing, via incubation with the GABAA receptor agonist muscimol, completely blocks phospho-ERK and BDNF release by each agent. Finally, incubation with each drug for 24 hr increases the number and length of neuronal branches. Together, the results demonstrate that these three different rapid acting antidepressant agents increase ERK signaling and BDNF release in an activity dependent manner that leads to increased neuronal complexity. Further studies will be required to determine the exact mechanisms underlying these effects in cultured neurons and in rodent models.

Proteasomal-regulated chromatin remodeler mediates cocaine relapse during abstinence., Neuroadaptations in the nucleus accumbens (NAc) underlie cue-induced cocaine craving that intensifies (“incubates”) during abstinence and is believed to contribute to persistent relapse vulnerability. Changes in gene expression often govern perpetual behavioral abnormalities, but epigenetic plasticity during prolonged abstinence from drug exposure is poorly understood. We examined how E3 ubiquitin ligase TRIM3 dysregulates chromatin remodeler INO80 to mediate cocaine craving during prolonged abstinence. We found that INO80 expression increased in the NAc on abstinence day 30 (AD30) but not on AD1 following cocaine self-administration. Furthermore, TRIM3, which mediates degradation of INO80, was reduced on AD30, along with TRIM3-INO80 interaction. Viral-mediated gene transfer of INO80 or TRIM3 governed cocaine craving during prolonged abstinence. Lastly, chromatin immunoprecipitation followed by massively parallel DNA sequencing identified INO80-mediated transcriptional regulation of predicted pathways associated with cocaine plasticity. Together, these results demonstrate a novel ubiquitin-proteasomal-epigenetic mechanism by which TRIM3-INO80 mediates cocaine craving during prolonged abstinence.

Human major depressive disorder (MDD), along with related mood disorders, is among the world's greatest public health concerns; however, its pathophysiology remains poorly understood. Persistent changes in gene expression are known to promote physiological aberrations implicated in MDD. More recently, histone mechanisms affecting cell type- and regional-specific chromatin structures have also been shown to contribute to transcriptional programs related to depressive behaviors, as well as responses to antidepressants. Although much emphasis has been placed in recent years on roles for histone posttranslational modifications and chromatin-remodeling events in the etiology of MDD, it has become increasingly clear that replication-independent histone variants (e.g., H3.3), which differ in primary amino acid sequence from their canonical counterparts, similarly play critical roles in the regulation of activity-dependent neuronal transcription, synaptic connectivity, and behavioral plasticity. Here, we demonstrate a role for increased H3.3 dynamics in the nucleus accumbens (NAc)-a key limbic brain reward region-in the regulation of aberrant social stress-mediated gene expression and the precipitation of depressive-like behaviors in mice. We find that molecular blockade of these dynamics promotes resilience to chronic social stress and results in a partial renormalization of stress-associated transcriptional patterns in the NAc. In sum, our findings establish H3.3 dynamics as a critical, and previously undocumented, regulator of mood and suggest that future therapies aimed at modulating striatal histone dynamics may potentiate beneficial behavioral adaptations to negative emotional stimuli.

SummaryStress resilience involves numerous brain-wide transcriptional changes. Determining the organization and orchestration of these transcriptional events may reveal novel antidepressant targets, but this remains unexplored. Here, we characterize the resilient transcriptome with co-expression analysis and identify a single transcriptionally-active uniquely-resilient gene network. Zfp189, a previously unstudied zinc finger protein, is the top network key driver and its overexpression in prefrontal cortical (PFC) neurons preferentially activates this network, alters neuronal activity and promotes behavioral resilience. CREB, which binds Zfp189, is the top upstream regulator of this network. To probe CREB-Zfp189 interactions as a network regulatory mechanism, we employ CRISPR-mediated locus-specific transcriptional reprogramming to direct CREB selectively to the Zfp189 promoter. This single molecular interaction in PFC neurons recapitulates the pro-resilient Zfp189-dependent downstream effects on gene network activity, electrophysiology and behavior. These findings reveal an essential role for Zfp189 and a CREB-Zfp189 regulatory axis in mediating a central transcriptional network of resilience.

Behavioral coping strategies are critical for active resilience to stress and depression; here we describe a role for neuroligin-2 (NLGN-2) in the nucleus accumbens (NAc). Neuroligins (NLGN) are a family of neuronal postsynaptic cell adhesion proteins that are constituents of the excitatory and inhibitory synapse. Importantly, NLGN-3 and NLGN-4 mutations are strongly implicated as candidates underlying the development of neuropsychiatric disorders with social disturbances such as autism, but the role of NLGN-2 in neuropsychiatric disease states is unclear. Here we show a reduction in NLGN-2 gene expression in the NAc of patients with major depressive disorder. Chronic social defeat stress in mice also decreases NLGN-2 selectively in dopamine D1-positive cells, but not dopamine D2-positive cells, within the NAc of stress-susceptible mice. Functional NLGN-2 knockdown produces bidirectional, cell-type-specific effects: knockdown in dopamine D1-positive cells promotes subordination and stress susceptibility, whereas knockdown in dopamine D2-positive cells mediates active defensive behavior. These findings establish a behavioral role for NAc NLGN-2 in stress and depression; provide a basis for targeted, cell-type specific therapy; and highlight the role of active behavioral coping mechanisms in stress susceptibility.

Clinical studies demonstrate that scopolamine, a non-selective muscarinic acetylcholine receptor (mAchR) antagonist, produces rapid therapeutic effects in depressed patients, and preclinical studies report that the actions of scopolamine require glutamate receptor activation and the mechanistic target of rapamycin complex 1 (mTORC1). The present study extends these findings to determine the role of the medial prefrontal cortex (mPFC) and specific muscarinic acetylcholine receptor (M-AchR) subtypes in the actions of scopolamine. The administration of scopolamine increases the activity marker Fos in the mPFC, including the infralimbic (IL) and prelimbic (PrL) subregions. Microinfusions of scopolamine into either the IL or the PrL produced significant antidepressant responses in the forced swim test, and neuronal silencing of IL or PrL blocked the antidepressant effects of systemic scopolamine. The results also demonstrate that the systemic administration of a selective M1-AChR antagonist, VU0255035, produced an antidepressant response and stimulated mTORC1 signaling in the PFC, similar to the actions of scopolamine. Finally, we used a chronic unpredictable stress model as a more rigorous test of rapid antidepressant actions and found that a single dose of scopolamine or VU0255035 blocked the anhedonic response caused by CUS, an effect that requires the chronic administration of typical antidepressants. Taken together, these findings indicate that mPFC is a critical mediator of the behavioral actions of scopolamine and identify the M1-AChR as a therapeutic target for the development of novel and selective rapid-acting antidepressants.

Background Cariprazine, a D3-preferring dopamine D2/D3 receptor partial agonist, is a new antipsychotic drug recently approved in the United States for the treatment of schizophrenia and bipolar mania. We recently demonstrated that cariprazine also has significant antianhedonic-like effects in rats subjected to chronic stress; however, the exact mechanism of action for cariprazine’s antidepressant-like properties is not known. Thus, in this study we examined whether the effects of cariprazine are mediated by dopamine D3 receptors. Methods Wild-type and D3-knockout mice were exposed to chronic unpredictable stress for up to 26 days, treated daily with vehicle, imipramine (20 mg/kg), aripiprazole (1 and 5 mg/kg), or cariprazine (0.03, 0.1, 0.2, and 0.4 mg/kg), and tested in behavioral assays measuring anhedonia and anxiety-like behaviors. Results Results showed that cariprazine significantly attenuated chronic unpredictable stress-induced anhedonic-like behavior in wild-type mice, demonstrating potent antidepressant-like effects comparable with aripiprazole and the tricyclic antidepressant imipramine. This antianhedonic-like effect of cariprazine was not observed in D3-knockout mice, suggesting that the cariprazine antidepressant-like activity is mediated by dopamine D3 receptors. Moreover, cariprazine significantly reduced drinking latency in the novelty-induced hypophagia test in wild-type mice, further confirming its antianhedonic-like effect and showing that it also has anxiolytic-like activity. Conclusions In combination with previous studies, these results suggest that cariprazine has a unique pharmacological profile and distinct dopamine D3 receptor-dependent mechanism of action that may be beneficial in the treatment of schizophrenia, bipolar disorder, and major depressive disorder.

A single dose of the short-acting NMDA antagonist ketamine produces rapid and prolonged antidepressant effects in treatment-resistant patients with major depressive disorder (MDD), which are thought to occur via restoration of synaptic connectivity. However, acute dissociative side effects and eventual fading of antidepressant effects limit widespread clinical use of ketamine. Recent studies in medial prefrontal cortex (mPFC) show that the synaptogenic and antidepressant-like effects of a single standard dose of ketamine in rodents are dependent upon activation of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) signaling pathway together with inhibitory phosphorylation of glycogen synthase kinase-3 (GSK-3), which relieves its inhibitory in influence on mTOR. Here, we found that the synaptogenic and antidepressant-like effects of a single otherwise subthreshold dose of ketamine were potentiated when given together with a single dose of lithium chloride (a nonselective GSK-3 inhibitor) or a preferential GSK-3β inhibitor; these effects included rapid activation of the mTORC1 signaling pathway, increased inhibitory phosphorylation of GSK-3β, increased synaptic spine density/diameter, increased excitatory postsynaptic currents in mPFC layer V pyramidal neurons, and antidepressant responses that persist for up to 1 week in the forced-swim test model of depression. The results demonstrate that low, subthreshold doses of ketamine combined with lithium or a selective GSK-3 inhibitor are equivalent to higher doses of ketamine, indicating the pivotal role of the GSK-3 pathway in modulating the synaptogenic and antidepressant responses to ketamine. The possible mitigation by GSK-3 inhibitors of the eventual fading of ketamine's antidepressant effects remains to be explored.

Previous imaging and postmortem studies have reported a lower brain volume and a smaller size and density of neurons in the dorsolateral prefrontal cortex (dlPFC) of subjects with major depressive disorder (MDD). These findings suggest that synapse number and function are decreased in the dlPFC of patients with MDD. However, there has been no direct evidence reported for synapse loss in MDD, and the gene expression alterations underlying these effects have not been identified. Here we use microarray gene profiling and electron microscopic stereology to reveal lower expression of synaptic-function–related genes (CALM2, SYN1, RAB3A, RAB4B and TUBB4) in the dlPFC of subjects with MDD and a corresponding lower number of synapses. We also identify a transcriptional repressor, GATA1, expression of which is higher in MDD and that, when expressed in PFC neurons, is sufficient to decrease the expression of synapse-related genes, cause loss of dendritic spines and dendrites, and produce depressive behavior in rat models of depression.

Disruptions in the development of the neocortex are associated with cognitive deficits in humans and other mammals. Several genes contribute to neocortical development, and research into the behavioral phenotype associated with specific gene manipulations is advancing rapidly. Findings include evidence that variants in the human gene DYX1C1 may be associated with an increased risk of developmental dyslexia. Concurrent research has shown that the rat homolog for this gene modulates critical parameters of early cortical development, including neuronal migration. Moreover, recent studies have shown auditory processing and spatial learning deficits in rats following in utero transfection of an RNA interference (RNAi) vector of the rat homolog Dyx1c1 gene. The current study examined the effects of in utero RNAi of Dyx1c1 on working memory performance in Sprague-Dawley rats. This task was chosen based on the evidence of short-term memory deficits in dyslexic populations, as well as more recent evidence of an association between memory deficits and DYX1C1 anomalies in humans. Working memory performance was assessed using a novel match-to-place radial water maze task that allows the evaluation of memory for a single brief (∼4-10 seconds) swim to a new goal location each day. A 10-min retention interval was used, followed by a test trial. Histology revealed migrational abnormalities and laminar disruption in Dyx1c1 RNAi-treated rats. Dyx1c1 RNAi-treated rats exhibited a subtle, but significant and persistent impairment in working memory as compared to Shams. These results provide further support for the role of Dyx1c1 in neuronal migration and working memory.

Current treatments for major depressive disorder (MDD) have a time lag and are ineffective for a large number of patients. Development of novel pharmacological therapies requires a comprehensive understanding of the molecular events that contribute to MDD pathophysiology. Recent evidence points toward aberrant activity of synaptic proteins as a critical contributing factor. In the present studies, we used viral-mediated gene transfer to target a key mediator of activity-dependent synaptic protein synthesis downstream of mechanistic target of rapamycin complex 1 (mTORC1) known as p70 S6 kinase 1 (S6K1). Targeted delivery of two mutants of S6K1, constitutively active or dominant-negative, to the medial prefrontal cortex (mPFC) of rats allowed control of the mTORC1/S6K1 translational pathway. Our results demonstrate that increased expression of S6K1 in the mPFC produces antidepressant effects in the forced swim test without altering locomotor activity. Moreover, expression of active S6K1 in the mPFC blocked the anhedonia caused by chronic stress, resulting in a state of stress resilience. This antidepressant response was associated with increased neuronal complexity caused by enhanced S6K1 activity. Conversely, expression of dominant-negative S6K1 in the mPFC resulted in prodepressive behavior in the forced swim test and was sufficient to cause anhedonia in the absence of chronic stress exposure. Together, these data demonstrate a critical role for S6K1 activity in depressive behaviors, and suggest that pathways downstream of mTORC1 may underlie the pathophysiology and treatment of MDD.

Background Evidence continues to build suggesting that the GABAergic neurotransmitter system is altered in brains of patients with major depressive disorder. However, there is little information available related to the extent of these changes or the potential mechanisms associated with these alterations. As stress is a well-established precipitant to depressive episodes, we sought to explore the impact of chronic stress on GABAergic interneurons. Methods Using western blot analyses and quantitative real-time polymerase chain reaction, we assessed the effects of five-weeks of chronic unpredictable stress exposure on the expression of GABA-synthesizing enzymes (GAD65 and GAD67), calcium-binding proteins (calbindin, parvalbumin, and calretinin), and neuropeptides co-expressed in GABAergic neurons (somatostatin, neuropeptide Y, vasoactive intestinal peptide, and cholecystokinin) in the prefrontal cortex and hippocampus of rats. We also investigated the effects of corticosterone and dexamethasone exposure on these markers in vitro in primary cortical and hippocampal cultures. Results We found that chronic unpredictable stress induced significant reductions of GAD67 protein levels in both the prefrontal cortex and hippocampus of chronic unpredictable stress-exposed rats but did not detect changes in GAD65 protein expression. Similar protein expression changes were found in vitro in cortical neurons. In addition, our results provide clear evidence of reduced markers of interneuron population(s), namely somatostatin and neuropeptide Y, in the prefrontal cortex, suggesting these cell types may be selectively vulnerable to chronic stress. Conclusion Together, this work highlights that chronic stress induces regional and cell type-selective effects on GABAergic interneurons in rats. These findings provide additional supporting evidence that stress-induced GABA neuron dysfunction and cell vulnerability play critical roles in the pathophysiology of stress-related illnesses, including major depressive disorder.

Background Depression is a prevalent neuropsychiatric disorder that affects an estimated 350 million people worldwide. Currently available treatments for depression are lacking in both speed of onset and efficacy. Recent pharmacological efforts have targeted the glutamatergic neurotransmitter system using the N-methyl-D-aspartate (NMDA) receptor antagonist ketamine to produce rapid and robust antidepressant effects, however the widespread clinical use of ketamine is limited due to side effects and abuse liability. More recently, work evaluating metabotropic mGluR2/3 receptor antagonists has demonstrated many similarities with ketamine. Methods Male, Sprague–Dawley rats were exposed to a chronic unpredictable stress paradigm, which produces decreased sucrose preference, a measure of anhedonia. Rats were then treated with vehicle or a single injection of the mGluR2/3 antagonist LY341495 (3 mg/kg, i.p.) and tested at 24 hrs, 48 hrs or 10 days after a single treatment. Results We demonstrate that a single treatment with LY341495 produces a rapid (within 1–2 days) and long-lasting (10 days) reversal of anhedonia caused by chronic unpredictable stress in rats. This model provides a rigorous test of rapid-acting agents as typical antidepressants require several weeks of treatment to produce a response. Conclusions These data suggest that LY341495 has the ability to produce rapid and robust antidepressant effects similar to ketamine. Together, the results highlight the potential for similar compounds to produce rapid and lasting efficacy for the treatment of depression.

Decreased neuronal dendrite branching and plasticity of the hippocampus, a limbic structure implicated in mood disorders, is thought to contribute to the symptoms of depression. However, the mechanisms underlying this effect, as well as the actions of antidepressant treatment, remain poorly characterized. Here, we show that hippocampal expression of neuritin, an activity-dependent gene that regulates neuronal plasticity, is decreased by chronic unpredictable stress (CUS) and that antidepressant treatment reverses this effect. We also show that viral-mediated expression of neuritin in the hippocampus produces antidepressant actions and prevents the atrophy of dendrites and spines, as well as depressive and anxiety behaviors caused by CUS. Conversely, neuritin knockdown produces depressive-like behaviors, similar to CUS exposure. The ability of neuritin to increase neuroplasticity is confirmed in models of learning and memory. Our results reveal a unique action of neuritin in models of stress and depression, and demonstrate a role for neuroplasticity in antidepressant treatment response and related behaviors.

Recent studies demonstrate that ketamine, a fast-acting antidepressant, rapidly activates the mammalian target of rapamycin (mTOR) and increases synaptogenesis in the prefrontal cortex (PFC). Because of the side effect and abuse potential of ketamine we are investigating alternative agents that produce similar effects. Here we demonstrate that a single dose of LY341495, an mGluR2/3 antagonist, produces ketamine-like biochemical and behavioral effects. LY341495 administration rapidly (1 hr) activates the mTOR pathway (mTOR, p70S6K, 4E-BP1) and subsequently (24 hrs) increases levels of synaptic proteins (PSD-95, GluR1 and Synapsin I) 24 hrs later, similar to the effects of ketamine. Finally, the antidepressant effects of LY341495 in the rat forced swim test are completely blocked by the mTOR inhibitor, rapamycin. The results indicate that the antidepressant actions of LY341495 are mediated by activation of mTOR and suggest that this and other mGluR2/3 antagonists could produce rapid antidepressant effects in depressed patients.

Background: Recent studies demonstrate that the rapid antidepressant ketamine increases spine number and function in the medial prefrontal cortex (mPFC), and that these effects are dependent on activation of glutamate α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and brain-derived neurotrophic factor (BDNF). In vitro studies also show that activation of AMPA receptors stimulates BNDF release via activation of L-type voltage-dependent calcium channels (VDCC). Methods: Based on this evidence, we examined the role of BDNF release and the impact of L-type VDCCs on the behavioral actions of ketamine. Results: The results demonstrate that infusion of a neutralizing BDNF antibody into the mPFC blocks the behavioral effects of ketamine in the forced swim test (FST). In addition, we show that pretreatment with nifedipine or verapamil, two structurally-different L-type calcium channel antagonists, blocks the behavioral effects of ketamine in the FST. Finally, we show that ketamine treatment stimulates BDNF release in primary cortical neurons and that this effect is blocked by inhibition of AMPA receptors or L-type VDCCs. Conclusions: Taken together, these results indicate that the antidepressant effects of ketamine are mediated by activation of L-type VDCCs and the release of BDNF. They further elucidate the cellular mechanisms underlying this novel rapid-acting antidepressant.