HDAC inhibitors restore the capacity of aged mice to respond to haloperidol through modulation of histone acetylation

Antipsychotic drugs are widely prescribed to elderly patients for the treatment of a variety of psychopathological conditions, including psychosis and the behavioral disturbances associated with dementia. However, clinical experience suggests that these drugs may be less efficacious in the elderly individuals than in the young. Recent studies suggest that aging may be associated with epigenetic changes and that valproic acid (VPA), a histone deacetylase inhibitor, may reverse such changes. However, it is not yet known whether HDAC inhibitors can modulate age-related epigenetic changes that may impact antipsychotic drug action. In this study, we analyzed conditioned avoidance response (CAR) and c-Fos expression patterns to elucidate the effect of HDAC inhibitors VPA and entinostat (MS-275) on behavioral and molecular markers of the effects of haloperidol (HAL) in aged mice. Our results showed that HAL administration failed to suppress the avoidance response during the CAR test, suggesting an age-related decrease in drug efficacy. In addition, HAL-induced c-Fos expression in the nucleus accumbens shell and prefrontal cortex was significantly lower in aged mice as compared with young mice. Pretreatment with VPA and MS-275 significantly improved HAL effects on the CAR test in aged mice. Also, VPA and MS-275 pretreatment restored HAL-induced increases in c-Fos expression in the nucleus accumbens shell and prefrontal cortex of aged mice to levels comparable with those observed in young mice. Lastly, but most importantly, increases in c-Fos expression and HAL efficacy in the CAR test of the HAL+VPA and HAL+MS-275 groups were correlated with elevated histone acetylation at the c-fos promoter region in aged mice. These findings suggest that pretreatment with VPA or MS-275 increases the behavioral and molecular effects of HAL in aged mice and that these effects occur via modulation of age-related histone hypoacetylation in the nucleus accumbens shell and prefrontal cortex.

Long-term reduction of cocaine self-administration in rats treated with adenoviral vector-delivered cocaine hydrolase: evidence for enzymatic activity

A new pharmacokinetic approach treating cocaine addiction involves rapidly metabolizing cocaine before it reaches brain reward centers using mutated human butyrylcholinesterase (BChE) or cocaine hydrolase (CocH). Recent work has shown that helper-dependent adenoviral (hdAD) vector-mediated plasma CocH reduced the locomotor-activating effects of cocaine and prevented reinstatement of cocaine-seeking behavior up to 6 months in rats. The present study investigated whether hdAD-CocH could decrease ongoing intravenous cocaine (0.4 mg/kg) self-administration. The hdAD-CocH vector was injected into self-administering rats, and after accumulation of plasma CocH, there was a dramatic reduction in cocaine infusions earned under a fixed ratio 1 schedule of reinforcement that lasted for the length of the study (>2 months). Pretreatment with the selective BChE and CocH inhibitor iso-OMPA (1.5 mg/kg) restored cocaine intake; therefore, the decline in self-administration was likely due to rapid CocH-mediated cocaine metabolism. Direct measurements of cocaine levels in plasma and brain samples taken after the conclusion of behavioral studies provided strong support for this conclusion. Further, rats injected with hdAD-CocH did not experience a deficit in operant responding for drug reinforcement and self-administered methamphetamine (0.05 mg/kg) at control levels. Overall, these outcomes suggest that viral gene transfer can yield plasma CocH levels that effectively diminish long-term cocaine intake and may have potential treatment implications for cocaine-dependent individuals seeking to become and remain abstinent.

Enkephalin knockdown in the basolateral amygdala reproduces vulnerable anxiety-like responses to chronic unpredictable stress

The endogenous enkephalins (ENKs) are potential candidates participating in the naturally occurring variations in coping styles and determining the individual capacities for adaptation during chronic stress exposure. Here we demonstrate that there is a large variance in individual behavioral, as well as in physiological outcomes, in a population of Sprague-Dawley rats subjected to 3 weeks of chronic unpredictable stress (CUS). Separation of resilient and vulnerable subpopulations reveals specific long-term neuroadaptation in the ENKergic brain circuits. ENK mRNA expression was greatly reduced in the posterior basolateral nucleus of amygdala (BLAp) in vulnerable individuals. In contrast, ENK mRNA levels were similar in resilient and control (unstressed) individuals. Another group of rats were used for lentiviral-mediated knockdown of ENK to assess whether a decrease of ENK expression in the BLAp reproduces the behavioral disturbances found in vulnerable individuals. ENK knockdown specifically located in the BLAp was sufficient to increase anxiety in the behavioral tests, such as social interaction and elevated plus maze when compared with control individuals. These results show that specific neuroadaptation mediated by the ENKergic neurotransmission in the BLAp is a key regulator of resilience, whereas a decrease of the ENK in the BLAp is a maladaptation mechanism, which mediates the behavioral dichotomy observed between vulnerable and resilient following 3 weeks of CUS.

Protein kinase D1-dependent phosphorylation of dopamine D1 receptor regulates cocaine-induced behavioral responses

The dopamine (DA) D1 receptor (D1R) is critically involved in reward and drug addiction. Phosphorylation-mediated desensitization or internalization of D1R has been extensively investigated. However, the potential for upregulation of D1R function through phosphorylation remains to be determined. Here we report that acute cocaine exposure induces protein kinase D1 (PKD1) activation in the rat striatum, and knockdown of PKD1 in the rat dorsal striatum attenuates cocaine-induced locomotor hyperactivity. Moreover, PKD1-mediated phosphorylation of serine 421 (S421) of D1R promotes surface localization of D1R and enhances downstream extracellular signal-regulated kinase signaling in D1R-transfected HEK 293 cells. Importantly, injection of the peptide Tat-S421, an engineered Tat fusion-peptide targeting S421 (Tat-S421), into the rat dorsal striatum inhibits cocaine-induced locomotor hyperactivity and injection of Tat-S421 into the rat hippocampus or the shell of the nucleus accumbens (NAc) also inhibits cocaine-induced conditioned place preference (CPP). However, injection of Tat-S421 into the rat NAc shell does not establish CPP by itself and injection of Tat-S421 into the hippocampus does not influence spatial learning and memory. Thus, targeting S421 of D1R represents a promising strategy for the development of pharmacotherapeutic treatments for drug addiction and other disorders that result from DA imbalances.

N-Glycosylation of GABAA receptor subunits is altered in Schizophrenia

The molecular mechanisms of schizophrenia have been under investigation for decades; however, the exact causes of this debilitating neuropsychiatric disorder are still unknown. Previous studies have identified multiple affected neurotransmitter systems, brain regions, and cell types, each making a unique contribution to symptom presentation and pathophysiology. Numerous studies have identified gene and protein expression changes in schizophrenia, but the role of post-translational modifications, specifically N-glycosylation, has only recently become a target of investigation. N-glycosylation of molecules associated with glutamatergic neurotransmission is disrupted in schizophrenia, but it was unknown if these alterations are exclusive to the glutamatergic system or due to a more generalized deficit.In normal human cortex, we found evidence for N-glycosylation of the α1, β1, and β2 γ-aminobutyric type A receptor (GABAAR) subunits using deglycosylation protein shift assays. This was confirmed with lectin affinity assays that revealed glycan attachment on the α1, α4, and β1-3 GABAAR subunits. Examining GABAAR subunit N-glycosylation in matched pairs of schizophrenia (N=14) and comparison (N=14) of superior temporal gyrus revealed a smaller molecular mass of immature N-glycans on the α1 subunit, more immature N-glycosylation of the 49-kDa β1 subunit isoform, and altered total N-glycosylation of the β2 GABAAR subunit in schizophrenia. Measures of altered N-glycosylation of the β1 and β2 subunits were confounded by an increased apparent molecular mass of all β1 and β2 subunit isoforms in schizophrenia. Although N-glycosylation of α1, β1, and β2 were all changed in schizophrenia, the concentrations of GABAAR subunits themselves were unchanged. These findings suggest that disruptions of N-glycosylation in schizophrenia are not exclusive to glutamate and may indicate a potential disruption of a central cell signaling process in this disorder.

STAT1 negatively regulates spatial memory formation and mediates the memory-impairing effect of Aβ

Signal transducer and activator of transcription-1 (STAT1) has an important role in inflammation and the innate immune response, but its role in the central nervous system is less well understood. Here, we examined the role of STAT1 in spatial learning and memory, and assessed the involvement of STAT1 in mediating the memory-impairing effect of amyloid-beta (Aβ). We found that water maze training downregulated STAT1 expression in the rat hippocampal CA1 area, and spatial learning and memory function was enhanced in Stat1-knockout mice. Conversely, overexpression of STAT1 impaired water maze performance. STAT1 strongly upregulated the expression of the extracellular matrix protein laminin β1 (LB1), which also impaired water maze performance in rats. Furthermore, Aβ impaired spatial learning and memory in association with a dose-dependent increase in STAT1 and LB1 expression, but knockdown of STAT1 and LB1 both reversed this effect of Aβ. This Aβ-induced increase in STAT1 and LB1 expression was also associated with a decrease in the expression of the N-methyl-D-aspartate receptor (NMDAR) subunits, NR1, and NR2B. Overexpression of NR1 or NR2B or exogenous application of NMDA reversed Aβ-induced learning and memory deficits as well as Aβ-induced STAT1 and LB1 expression. Our results demonstrate that STAT1 negatively regulates spatial learning and memory through transcriptional regulation of LB1 expression. We also identified a novel mechanism for Aβ pathogenesis through STAT1 induction. Notably, impairment of spatial learning and memory by this STAT1-mediated mechanism is independent of cAMP responsive element-binding protein signaling.

Chronic administration of the methylxanthine propentofylline impairs reinstatement to cocaine by a GLT-1-dependent mechanism

In recent years, interactions between neurons and glia have been evaluated as mediators of neuropsychiatric diseases, including drug addiction. In particular, compounds that increase expression of the astroglial glutamate transporter GLT-1 (N-acetylcysteine and ceftriaxone) can decrease measures of drug seeking. However, it is unknown whether the compounds that influence broad measures of glial physiology can influence behavioral measures of drug relapse, nor is it clear whether the upregulated GLT-1 is functionally important for suppressing of drug seeking. To address these questions, we sought to determine whether the glial modulator and neuroprotective agent propentofylline (PPF) modifies drug seeking in rats using a reinstatement model of cocaine relapse. We found that 7 days of chronic (but not acute) administration of PPF significantly decreased both cue- and cocaine-induced reinstatement of cocaine seeking. We next determined whether the effect of systemic PPF on reinstatement depended upon its ability to restore expression of GLT-1 in the nucleus accumbens. PPF restored the cocaine-induced decrease in GLT-1 in the accumbens core; then, using an antisense strategy against glutamate transporter GLT-1, we found that restored transporter expression was necessary for PPF to inhibit cue-primed cocaine seeking. These findings indicate that modulating glial physiology with atypical xanthine derivatives like PPF is a potential avenue for developing new medications for cocaine abuse, and support the hypothesis that neuron-glial interactions contribute to mechanisms of psychostimulant addiction, particularly via expression and function of astroglial glutamate transporters.

Small-volume analysis of cell-cell signaling molecules in the brain

Modern science is characterized by integration and synergy between research fields. Accordingly, as technological advances allow new and more ambitious quests in scientific inquiry, numerous analytical and engineering techniques have become useful tools in biological research. The focus of this review is on cutting edge technologies that aid direct measurement of bioactive compounds in the nervous system to facilitate fundamental research, diagnostics, and drug discovery. We discuss challenges associated with measurement of cell-to-cell signaling molecules in the nervous system, and advocate for a decrease of sample volumes to the nanoliter volume regimen for improved analysis outcomes. We highlight effective approaches for the collection, separation, and detection of such small-volume samples, present strategies for targeted and discovery-oriented research, and describe the required technology advances that will empower future translational science.

Proteomic approaches and identification of novel therapeutic targets for alcoholism

Recent studies have shown that gene regulation is far more complex than previously believed and does not completely explain changes at the protein level. Therefore, the direct study of the proteome, considerably different in both complexity and dynamicity to the genome/transcriptome, has provided unique insights to an increasing number of researchers. During the past decade, extraordinary advances in proteomic techniques have changed the way we can analyze the composition, regulation, and function of protein complexes and pathways underlying altered neurobiological conditions. When combined with complementary approaches, these advances provide the contextual information for decoding large data sets into meaningful biologically adaptive processes. Neuroproteomics offers potential breakthroughs in the field of alcohol research by leading to a deeper understanding of how alcohol globally affects protein structure, function, interactions, and networks. The wealth of information gained from these advances can help pinpoint relevant biomarkers for early diagnosis and improved prognosis of alcoholism and identify future pharmacological targets for the treatment of this addiction.

Integrative biological analysis for neuropsychopharmacology

Although advances in psychotherapy have been made in recent years, drug discovery for brain diseases such as schizophrenia and mood disorders has stagnated. The need for new biomarkers and validated therapeutic targets in the field of neuropsychopharmacology is widely unmet. The brain is the most complex part of human anatomy from the standpoint of number and types of cells, their interconnections, and circuitry. To better meet patient needs, improved methods to approach brain studies by understanding functional networks that interact with the genome are being developed. The integrated biological approaches--proteomics, transcriptomics, metabolomics, and glycomics--have a strong record in several areas of biomedicine, including neurochemistry and neuro-oncology. Published applications of an integrated approach to projects of neurological, psychiatric, and pharmacological natures are still few but show promise to provide deep biological knowledge derived from cells, animal models, and clinical materials. Future studies that yield insights based on integrated analyses promise to deliver new therapeutic targets and biomarkers for personalized medicine.

An integrated quantitative proteomics and systems biology approach to explore synaptic protein profile changes during morphine exposure

Morphine is a classic analgesic for the treatment of chronic pain. However, its repeated use is known to produce tolerance, physical dependence, and addiction; these properties limit its long-term therapeutic use and this has led to a quest for therapeutics without these unwanted side effects. Understanding the molecular changes in response to long-term use of morphine is likely to aid in the development of novel therapeutics for the treatment of pain. Studies examining the effects of chronic morphine administration have reported alterations in gene expression, synapse morphology, and synaptic transmission implying changes in synaptic protein profile. To fully understand the changes in protein profiles, proteomic techniques have been used. Studies using two-dimensional gel electrophoresis of various brain regions combined with mass spectrometry have found alterations in the levels of a number of proteins. However, neither the changes in brain regions relevant to morphine effects nor changes in the abundance of synaptic proteins have been clearly delineated. Recent studies employing subcellular fractionation to isolate the striatal synapse, combined with quantitative proteomics and graph theory-inspired network analyses, have begun to quantify morphine-regulated changes in synaptic proteins and facilitate the generation of networks that could serve as targets for the development of novel therapeutics for the treatment of chronic pain. Thus, an integrated quantitative proteomics and systems biology approach can be useful to identify novel targets for the treatment of pain and other disorders of the brain.

Heteromeric dopamine receptor signaling complexes: emerging neurobiology and disease relevance

The pharmacological modification of dopamine transmission has long been employed as a therapeutic tool in the treatment of many mental health disorders. However, as many of the pharmacotherapies today are not without significant side effects, or they alleviate only a particular subset of symptoms, the identification of novel therapeutic targets is imperative. In light of these challenges, the recognition that dopamine receptors can form heteromers has significantly expanded the range of physiologically relevant signaling complexes as well as potential drug targets. Furthermore, as the physiology and disease relevance of these receptor heteromers is further understood, their ability to exhibit pharmacological and functional properties distinct from their constituent receptors, or modulate the function of endogenous homomeric receptor complexes, may allow for the development of alternate therapeutic strategies and provide new avenues for drug design. In this review, we describe the emerging neurobiology of the known dopamine receptor heteromers, their physiological relevance in brain, and discuss the potential role of these receptor complexes in neuropsychiatric disease. We highlight their value as targets for future drug development and discuss innovative research strategies designed to selectively target these dopamine receptor heteromers in the search for novel and clinically efficacious pharmacotherapies.

Regenerative therapies for central nervous system diseases: a biomaterials approach

The central nervous system (CNS) has a limited capacity to spontaneously regenerate following traumatic injury or disease, requiring innovative strategies to promote tissue and functional repair. Tissue regeneration strategies, such as cell and/or drug delivery, have demonstrated promising results in experimental animal models, but have been difficult to translate clinically. The efficacy of cell therapy, which involves stem cell transplantation into the CNS to replace damaged tissue, has been limited due to low cell survival and integration upon transplantation, while delivery of therapeutic molecules to the CNS using conventional methods, such as oral and intravenous administration, have been limited by diffusion across the blood-brain/spinal cord-barrier. The use of biomaterials to promote graft survival and integration as well as localized and sustained delivery of biologics to CNS injury sites is actively being pursued. This review will highlight recent advances using biomaterials as cell- and drug-delivery vehicles for CNS repair.

Biomarkers for the development of new medications for cocaine dependence

There has been significant progress in personalized drug development. In large part, this has taken place in the oncology field and been due to the ability of researchers/clinicians to discover and develop novel drug development tools (DDTs), such as biomarkers. In cancer treatment research, biomarkers have permitted a more accurate pathophysiological characterization of an individual patient, and have enabled practitioners to target mechanistically the right drug, to the right patient, at the right time. Similar to cancer, patients with substance use disorders (SUDs) present clinically with heterogeneous symptomatology and respond variably to therapeutic interventions. If comparable biomarkers could be identified and developed for SUDs, significant diagnostic and therapeutic advances could be made. In this review, we highlight current opportunities and difficulties pertaining to the identification and development of biomarkers for SUDs. We focus on cocaine dependence as an example. Putative diagnostic, pharmacodynamic (PD), and predictive biomarkers for cocaine dependence are discussed across a range of methodological approaches. A possible cocaine-dependent clinical outcome assessment (COA)--another type of defined DDT--is also discussed. At present, biomarkers for cocaine dependence are in their infancy. Much additional research will be needed to identify, validate, and qualify these putative tools prior to their potential use for medications development and/or application to clinical practice. However, with a large unmet medical need and an estimated market size of several hundred million dollars per year, if developed, biomarkers for cocaine dependence will hold tremendous value to both industry and public health.

Postmortem brain: an underutilized substrate for studying severe mental illness

We propose that postmortem tissue is an underutilized substrate that may be used to translate genetic and/or preclinical studies, particularly for neuropsychiatric illnesses with complex etiologies. Postmortem brain tissues from subjects with schizophrenia have been extensively studied, and thus serve as a useful vehicle for illustrating the challenges associated with this biological substrate. Schizophrenia is likely caused by a combination of genetic risk and environmental factors that combine to create a disease phenotype that is typically not apparent until late adolescence. The complexity of this illness creates challenges for hypothesis testing aimed at understanding the pathophysiology of the illness, as postmortem brain tissues collected from individuals with schizophrenia reflect neuroplastic changes from a lifetime of severe mental illness, as well as treatment with antipsychotic medications. While there are significant challenges with studying postmortem brain, such as the postmortem interval, it confers a translational element that is difficult to recapitulate in animal models. On the other hand, data derived from animal models typically provide specific mechanistic and behavioral measures that cannot be generated using human subjects. Convergence of these two approaches has led to important insights for understanding molecular deficits and their causes in this illness. In this review, we discuss the problem of schizophrenia, review the common challenges related to postmortem studies, discuss the application of biochemical approaches to this substrate, and present examples of postmortem schizophrenia studies that illustrate the role of the postmortem approach for generating important new leads for understanding the pathophysiology of severe mental illness.

Mass spectrometry imaging, an emerging technology in neuropsychopharmacology

Mass spectrometry imaging is a powerful tool for directly determining the distribution of proteins, peptides, lipids, neurotransmitters, metabolites and drugs in neural tissue sections in situ. Molecule-specific imaging can be achieved using various ionization techniques that are suited to different applications but which all yield data with high mass accuracies and spatial resolutions. The ability to simultaneously obtain images showing the distributions of chemical species ranging from metal ions to macromolecules makes it possible to explore the chemical organization of a sample and to correlate the results obtained with specific anatomical features. The imaging of biomolecules has provided new insights into multiple neurological diseases, including Parkinson's and Alzheimer's disease. Mass spectrometry imaging can also be used in conjunction with other imaging techniques in order to identify correlations between changes in the distribution of important chemical species and other changes in the properties of the tissue. Here we review the applications of mass spectrometry imaging in neuroscience research and discuss its potential. The results presented demonstrate that mass spectrometry imaging is a useful experimental method with diverse applications in neuroscience.

Asymmetrical synaptic cooperation between cortical and thalamic inputs to the amygdale

Fear conditioning, a form of associative learning is thought to involve the induction of an associative long-term potentiation of cortical and thalamic inputs to the lateral amygdala. Here, we show that stimulation of the thalamic input can reinforce a transient form of plasticity (E-LTP) induced by weak stimulation of the cortical inputs. This synaptic cooperation occurs within a time window of 30 min, suggesting that synaptic integration at amygdala synapses can occur within large time windows. Interestingly, we found that synaptic cooperation is not symmetrical. Reinforcement of a thalamic E-LTP by subsequent cortical stimulation is only observed within a shorter time window. We found that activation of endocannabinoid CB1 receptors is involved in the time restriction of thalamic and cortical synaptic cooperation in an activity-dependent manner. Our results support the hypothesis that synaptic cooperation can underlie associative learning and that synaptic tagging and capture is a general mechanism in synaptic plasticity.

Role of a hippocampal SRC-family kinase-mediated glutamatergic mechanism in drug context-induced cocaine seeking

Glutamatergic neurotransmission in the dorsal hippocampus (DH) is necessary for drug context-induced reinstatement of cocaine-seeking behavior in an animal model of drug relapse. Furthermore, in vitro studies suggest that the Src family of tyrosine kinases critically regulates glutamatergic cellular functions within the DH. Thus, Src-family kinases in the DH may similarly control contextual cocaine-seeking behavior. To test this hypothesis, rats were trained to lever press for un-signaled cocaine infusions in a distinct context followed by extinction training in a different context. Cocaine-seeking behavior (non-reinforced active lever pressing) was then assessed in the previously cocaine-paired and extinction contexts after AP5 (N-methyl-D-aspartate glutamate (NMDA) receptor (NMDAR) antagonist; 0.25 or 2.5 μg/0.5 μl/hemisphere), PP2 (Src-family kinase inhibitor; 6.25 or 62.5 ng/0.5 μl/hemisphere), Ro25-6981 (NR2B subunit-containing NMDAR antagonist; 0.2 or 2 μg/0.5 μl/hemisphere), or vehicle administration into the DH. Administration of AP5, PP2, or Ro25-6981 into the DH dose-dependently impaired drug context-induced reinstatement of cocaine-seeking behavior relative to vehicle, without altering instrumental behavior in the extinction context or food-reinforced instrumental responding and general motor activity in control experiments. Cocaine-seeking behavior during the first 20 min of the test session in the cocaine-paired context was associated with an increase in NR2B subunit activation, and intra-DH PP2 pretreatment disrupted this relationship. Together, these findings suggest that Src-family kinase activation, NMDAR stimulation, and likely Src-family kinase-mediated NR2B subunit-containing NMDAR activation in the DH are necessary for incentive motivational and/or memory processes that promote contextual cocaine-seeking behavior.

Viral-mediated knockdown of mGluR7 in the nucleus accumbens mediates excessive alcohol drinking and increased ethanol-elicited conditioned place preference in rats

Whether metabotropic glutamate 7 (mGluR7) -activation enhances or diminishes the reinforcing properties of psychostimulants remains unclear. We have previously shown that systemic mGluR7 activation reduced alcohol consumption and preference as well as locomotor-stimulating and rewarding properties of ethanol. In this study, we further examined the contribution of mGluR7 on the effect of ethanol within the nucleus accumbens (NAcc), a neural target for many drugs of abuse. Using short hairpin RNA (shRNA)-expressing lentiviral vectors (LV) to alter locally the activity of mGluR7 in male rats, we have shown that blocking mGluR7 expression increased ethanol consumption and preference in a two-bottle choice drinking paradigm with no effect either on saccharin or on quinine used for taste discrimination. In addition, mGluR7 knockdown increases preference for environments previously paired with low doses of ethanol in the conditioned place preference (CPP) test, as it shifted the dose-response curve for ethanol CPP to the left, indicating alterations in the rewarding effects of alcohol. More importantly, mGluR7 blockade in the dorsal striatum (DS) neither affected ethanol consumption nor ethanol-elicited CPP. These results show that levels of mGluR7 in the NAcc regulate responsiveness to alcohol. Taken together, these findings clearly demonstrate that mGluR7 signaling within the NAcc is a key modulator of functional responses to ethanol and offer an important target for regulating the addictive effects of alcohol.

Increased hippocampal neurogenesis and p21 expression in depression: dependent on antidepressants, sex, age, and antipsychotic exposure

The mammalian hippocampus continues to generate new neurons throughout life. The function of adult-generated neurons remains controversial, but adult neurogenesis in the hippocampus is related to depression. Studies show that neurogenesis in the hippocampus is regulated by antidepressants in both humans and rodents, but no studies have examined the effects of age, sex, or antipsychotic exposure on the relationship between depression, antidepressant exposure, and hippocampal neurogenesis in humans. Hippocampal sections were obtained from the Stanley Medical Research Institute and were immunohistochemically labeled for the immature neuron marker doublecortin and the cell cycle arrest marker p21. We compared the number of cells in the granule cell layer and subgranular zone that expressed these proteins in brains from control subjects (n=12), patients with major depressive disorder (MDD) without psychotic symptoms (n=12), and patients with MDD and psychotic symptoms (n=12). We show here that the density of doublecortin/NeuN expression was increased in MDD patients compared with controls and MDD patients with psychosis, with the effect greater in women. Further, we show that older depressed patients without psychosis had higher levels of p21/NeuN expression and that depressed individuals prescribed antidepressants had higher levels of p21/NeuN expression, but only in older women. We show for the first time that changes in neurogenesis due to prescribed antidepressants or depression are dependent on age, sex, and the presence of antipsychotics or psychotic symptoms.

BDNF overexpression in the ventral tegmental area prolongs social defeat stress-induced cross-sensitization to amphetamine and increases ΔFosB expression in mesocorticolimbic regions of rats

Social defeat stress induces persistent cross-sensitization to psychostimulants, but the molecular mechanisms underlying the development of cross-sensitization remain unclear. One candidate is brain-derived neurotrophic factor (BDNF). The present research examined whether ventral tegmental area (VTA) BDNF overexpression would prolong the time course of cross-sensitization after a single social defeat stress, which normally produces transient cross-sensitization lasting <1 week. ΔFosB, a classic molecular marker of addiction, was also measured in mesocorticolimbic terminal regions. Separate groups of intact male Sprague-Dawley rats underwent a single episode of social defeat stress or control handling, followed by amphetamine (AMPH) challenge 3 or 14 days later. AMPH cross-sensitization was apparent 3, but not 14, days after stress. Intra-VTA infusion of adeno-associated viral (AAV-BDNF) vector resulted in a twofold increase of BDNF level in comparison to the group receiving the control virus (AAV-GFP), which lasted at least 45 days. Additionally, overexpression of BDNF in the VTA alone increased ΔFosB in the nucleus accumbens (NAc) and prefrontal cortex. Fourteen days after viral infusions, a separate group of rats underwent a single social defeat stress or control handling and were challenged with AMPH 14 and 24 days after stress. AAV-BDNF rats exposed to stress showed prolonged cross-sensitization and facilitated sensitization to the second drug challenge. Immunohistochemistry showed that the combination of virally enhanced VTA BDNF, stress, and AMPH resulted in increased ΔFosB in the NAc shell compared with the other groups. Thus, elevation of VTA BDNF prolongs cross-sensitization, facilitates sensitization, and increases ΔFosB in mesocorticolimbic terminal regions. As such, elevated VTA BDNF may be a risk factor for drug sensitivity.

GSK-3 inhibition potentiates the synaptogenic and antidepressant-like effects of subthreshold doses of ketamine

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.

Exercise and sodium butyrate transform a subthreshold learning event into long-term memory via a brain-derived neurotrophic factor-dependent mechanism

We demonstrate that exercise enables hippocampal-dependent learning in conditions that are normally subthreshold for encoding and memory formation, and depends on hippocampal induction of brain-derived neurotrophic factor (BDNF) as a key mechanism. Using a weak training paradigm in an object location memory (OLM) task, we show that sedentary mice are unable to discriminate 24 h later between familiar and novel object locations. In contrast, 3 weeks of prior voluntary exercise enables strong discrimination in the spatial memory task. Cognitive benefits of exercise match those attained with post-training sodium butyrate (NaB), a histone deacetylase (HDAC) inhibitor previously shown to enable subthreshold learning. We demonstrate that the enabling effects of exercise and NaB on subthreshold OLM learning are dependent on hippocampal BDNF upregulation, and are blocked by hippocampal infusion of BDNF short-interfering RNA. Exercise and NaB increased bdnf transcripts I and IV, and the increases were associated with BDNF promoter acetylation on H4K8 but not H4K12. These data provide support for the concept that exercise engages epigenetic control mechanisms and serves as a natural stimulus that operates in part like NaB and potentially other HDAC inhibitors, placing the brain into a state of readiness for plasticity.

Dysfunction of the ubiquitin proteasome and ubiquitin-like systems in schizophrenia

Protein expression abnormalities have been implicated in the pathophysiology of schizophrenia, but the underlying cause of these changes is not known. We sought to investigate ubiquitin and ubiquitin-like (UBL) systems (SUMOylation, NEDD8ylation, and Ufmylation) as putative mechanisms underlying protein expression abnormalities seen in schizophrenia. For this, we performed western blot analysis of total ubiquitination, free ubiquitin, K48- and K63-linked ubiquitination, and E1 activases, E2 conjugases, and E3 ligases involved in ubiquitination and UBL post-translational modifications in postmortem brain tissue samples from persons with schizophrenia (n=13) and comparison subjects (n=13). We studied the superior temporal gyrus (STG) of subjects from the Mount Sinai Medical Center brain collection that were matched for age, tissue pH, and sex. We found an overall reduction of protein ubiquitination, free ubiquitin, K48-linked ubiquitination, and increased K63 polyubiquitination in schizophrenia. Ubiquitin E1 activase UBA (ubiquitin activating enzyme)-6 and E3 ligase Nedd (neural precursor cell-expressed developmentally downregulated)-4 were decreased in this illness, as were E3 ligases involved in Ufmylation (UFL1) and SUMOylation (protein inhibitor of activated STAT 3, PIAS3). NEDD8ylation was also dysregulated in schizophrenia, with decreased levels of the E1 activase UBA3 and the E3 ligase Rnf7. This study of ubiquitin and UBL systems in schizophrenia found abnormalities of ubiquitination, Ufmylation, SUMOylation, and NEDD8ylation in the STG in this disorder. These results suggest a novel approach to the understanding of schizophrenia pathophysiology, where a disruption in homeostatic adaptation of the cell underlies discreet changes seen at the protein level in this illness.

Hyposensitivity to gamma-aminobutyric acid in the ventral tegmental area during alcohol withdrawal: reversal by histone deacetylase inhibitors

Putative dopaminergic (pDAergic) ventral tegmental area (VTA) neurons have an important role in alcohol addiction. Acute ethanol increases the activity of pDAergic neurons, and withdrawal from repeated ethanol administration produces a decreased sensitivity of pDAergic VTA neurons to GABA. Recent studies show that behavioral changes induced by chronic alcohol are reversed by inhibitors of histone deacetylases (HDACs). Whether HDAC-induced histone modifications regulate changes in GABA sensitivity of VTA pDAergic neurons during withdrawal is unknown. Here, we investigated modulation of withdrawal-induced changes in GABA sensitivity of pDAergic VTA neurons by HDAC inhibitors (HDACi), and also measured the levels of HDAC2, histone (H3-K9) acetylation, and GABA-Aα1 receptor (GABA (A-α1) R) subunit in VTA during ethanol withdrawal. Mice were injected intraperitoneally (ip) with either ethanol (3.5 g/kg) or saline twice daily for 3 weeks. In recordings from pDAergic VTA neurons in brain slices from ethanol-withdrawn mice, sensitivity to GABA (50-500 μM) was reduced. In brain slices from ethanol-withdrawn mice incubated with the HDACi SAHA (vorinostat) or trichostatin A (TSA) for 2 h, the hyposensitivity of pDAergic VTA neurons to GABA was significantly attenuated. There was no effect of TSA or SAHA on GABA sensitivity of pDAergic VTA neurons from saline-treated mice. In addition, ethanol withdrawal was associated with an increase in levels of HDAC2 and a decrease in histone (H3-K9) acetylation and levels of GABA (A-α1) R subunits in the VTA. Therefore, blockade of upregulation of HDAC2 by HDACi normalizes GABA hyposensitivity of pDAergic neurons developed during withdrawal after chronic ethanol treatment, which suggests the possibility that inhibition of HDACs can reverse ethanol-induced neuroadaptational changes in reward circuitry.

Predictable chronic mild stress in adolescence increases resilience in adulthood

Stress in adolescence has been widely demonstrated to have a lasting impact in humans and animal models. Developmental risk and protective factors play an important role in the responses to stress in adulthood. Mild-to-moderate stress in adolescence may resist the negative impacts of adverse events in adulthood. However, little research on resilience has been conducted. In this study, we used a predictable chronic mild stress (PCMS) procedure (5 min of daily restraint stress for 28 days) in adolescent rats (postnatal days (PNDs) 28-55) to test the resilience effect of PCMS on depressive-like behavior in the sucrose preference test and forced swim test and anxiety-like behavior in the novelty-suppressed feeding test and elevated plus maze in adulthood. We also investigated the role of mammalian target of rapamycin (mTOR) signaling in the brain during the PCMS procedure in adolescence. Moreover, we investigated the effect of PCMS in adolescence on subsequent responses to chronic unpredictable stress (CUS; PNDs 63-83) in adulthood. The results demonstrated that PCMS during adolescence produced antidepressant- and anxiolytic-like effects and increased mTOR signaling activity in the prefrontal cortex in early adulthood. Either systemic administration or intra-PFC infusion of the mTOR inhibitor rapamycin completely blocked the behavioral effects produced by PCMS in adolescence. PCMS during adolescence resisted depressive- and anxiety-like behavior caused by CUS in adulthood. These findings indicate that PCMS in adolescence can contribute to resilience against depression and anxiety caused by stress in adulthood.

Hippocampal granule neuron number and dentate gyrus volume in antidepressant-treated and untreated major depression

Smaller hippocampal volume is reported in major depressive disorder (MDD). We hypothesize that it may be related to fewer granule neurons (GN) in the dentate gyrus (DG), a defect possibly reversible with antidepressants. We studied age-, sex-, and postmortem interval-matched groups: no major psychopathology (controls); unmedicated-MDD; and MDD treated with serotonin reuptake inhibitors (MDD*SSRI) or tricyclics (MDD*TCA). Frozen right hippocampi were fixed, sectioned (50 μm), immunostained with neuronal nuclear marker (NeuN), and counterstained with hematoxylin. GN and glial number, and DG and granule cell layer (GCL) volumes were stereologically estimated. Fewer GNs in the anterior DG were present in unmedicated-MDDs compared with controls (p=0.013). Younger age of MDD onset correlated with fewer GNs (p=0.021). Unmedicated-MDDs had fewer mid-DG GNs than MDD*SSRIs (p=0.028) and controls (p=0.032). Anterior GCL glial number did not differ between groups. Anterior/mid GCL volume was smaller in unmedicated-MDDs vs controls (p=0.008) and larger in MDD*SSRIs vs unmedicated-MDDs (p<0.001), MDD*TCAs (p<0.001), and controls (p<0.001). Anterior GCL volume and GN number (r=0.594, p=0.001), and mid DG volume and GN number (r=0.398, p=0.044) were correlated. Anterior DG capillary density correlated with GN number (p=0.027), and with GCL (p=0.024) and DG (r=0.400, p=0.047) volumes. Posterior DG volume and GN number did not differ between groups. Fewer GNs in unmedicated-MDD without fewer neuronal progenitor cells, as previously reported, suggests a cell maturation or survival defect, perhaps related to MDD duration. This may contribute to a smaller hippocampus and is potentially reversed by SSRIs. Postmortem studies are correlative and animal studies are needed to test implied causal relationships.

Extracellular signal-regulated kinase in the basolateral amygdala, but not the nucleus accumbens core, is critical for context-response-cocaine memory reconsolidation in rats

The reconsolidation of cocaine memories following retrieval is necessary for the sustained ability of a cocaine-paired environmental context to elicit cocaine seeking. Extracellular signal-regulated kinase (ERK) is an intracellular signaling molecule involved in nucleus accumbens core (NACc)-mediated reconsolidation of Pavlovian cocaine memories. Here, we used a rodent model of drug context-elicited relapse to test the hypothesis that ERK would be similarly required for the reconsolidation of context-response-cocaine memories that underlie drug context-induced reinstatement of instrumental cocaine-seeking behavior, with a focus on the NACc and on the basolateral amygdala (BLA), another important locus for the reconsolidation of cocaine memories. We show that the mitogen-activated protein kinase (MEK)/ERK1/2 inhibitor, U0126 (1.0 μg/0.5 μl/hemisphere), microinfused bilaterally into the BLA--but not the NACc--immediately after brief re-exposure to a previously cocaine-paired context (that is, cocaine-memory reactivation), significantly attenuated subsequent drug context-induced cocaine seeking relative to vehicle (VEH). This effect in the BLA was associated with a transient inhibition of ERK1/2 phosphorylation, and it depended on memory reactivation given that U0126 administered following exposure to a novel context did not alter subsequent cocaine seeking. Furthermore, similar to U0126, baclofen+muscimol-induced (B+M; 106.8/5.7 ng/0.5 μl/hemisphere) neural inactivation of the NACc, following cocaine-memory reactivation, failed to alter subsequent cocaine seeking. These findings demonstrate that ERK activation in the BLA, but not the NACc, is required for the reconsolidation of context-response-cocaine associative memories. Together with prior research, these results suggest that contextual drug-memory reconsolidation in Pavlovian and instrumental settings involves distinct neuroanatomical mechanisms.

A Gαs DREADD mouse for selective modulation of cAMP production in striatopallidal neurons

Here, we describe a newly generated transgenic mouse in which the Gs DREADD (rM3Ds), an engineered G protein-coupled receptor, is selectively expressed in striatopallidal medium spiny neurons (MSNs). We first show that in vitro, rM3Ds can couple to Gαolf and induce cAMP accumulation in cultured neurons and HEK-T cells. The rM3Ds was then selectively and stably expressed in striatopallidal neurons by creating a transgenic mouse in which an adenosine2A (adora2a) receptor-containing bacterial artificial chromosome was employed to drive rM3Ds expression. In the adora2A-rM3Ds mouse, activation of rM3Ds by clozapine-N-oxide (CNO) induces DARPP-32 phosphorylation, consistent with the known consequence of activation of endogenous striatal Gαs-coupled GPCRs. We then tested whether CNO administration would produce behavioral responses associated with striatopallidal Gs signaling and in this regard CNO dose-dependently decreases spontaneous locomotor activity and inhibits novelty induced locomotor activity. Last, we show that CNO prevented behavioral sensitization to amphetamine and increased AMPAR/NMDAR ratios in transgene-expressing neurons of the nucleus accumbens shell. These studies demonstrate the utility of adora2a-rM3Ds transgenic mice for the selective and noninvasive modulation of Gαs signaling in specific neuronal populations in vivo.This unique tool provides a new resource for elucidating the roles of striatopallidal MSN Gαs signaling in other neurobehavioral contexts.

fosB-null mice display impaired adult hippocampal neurogenesis and spontaneous epilepsy with depressive behavior

Patients with epilepsy are at high risk for major depression relative to the general population, and both disorders are associated with changes in adult hippocampal neurogenesis, although the mechanisms underlying disease onset remain unknown. The expression of fosB, an immediate early gene encoding FosB and ΔFosB/Δ2ΔFosB by alternative splicing and translation initiation, is known to be induced in neural progenitor cells within the subventricular zone of the lateral ventricles and subgranular zone of the hippocampus, following transient forebrain ischemia in the rat brain. Moreover, adenovirus-mediated expression of fosB gene products can promote neural stem cell proliferation. We recently found that fosB-null mice show increased depressive behavior, suggesting impaired neurogenesis in fosB-null mice. In the current study, we analyzed neurogenesis in the hippocampal dentate gyrus of fosB-null and fosB(d/d) mice that express ΔFosB/Δ2ΔFosB but not FosB, in comparison with wild-type mice, alongside neuropathology, behaviors, and gene expression profiles. fosB-null but not fosB(d/d) mice displayed impaired neurogenesis in the adult hippocampus and spontaneous epilepsy. Microarray analysis revealed that genes related to neurogenesis, depression, and epilepsy were altered in the hippocampus of fosB-null mice. Thus, we conclude that the fosB-null mouse is the first animal model to provide a genetic and molecular basis for the comorbidity between depression and epilepsy with abnormal neurogenesis, all of which are caused by loss of a single gene, fosB.

The synaptic adhesion molecule SynCAM 1 contributes to cocaine effects on synapse structure and psychostimulant behavior

Drugs of abuse have acute and persistent effects on synapse structure and addiction-related behaviors. Trans-synaptic interactions can control synapse development, and synaptic cell adhesion molecule (SynCAM) proteins (also named nectin-like molecules) are immunoglobulin adhesion proteins that span the synaptic cleft and induce excitatory synapses. Our studies now reveal that the loss of SynCAM 1 in knockout (KO) mice reduces excitatory synapse number in nucleus accumbens (NAc). SynCAM 1 additionally contributes to the structural remodeling of NAc synapses in response to the psychostimulant cocaine. Specifically, we find that cocaine administration increases the density of stubby spines on medium spiny neurons in NAc, and that maintaining this increase requires SynCAM 1. Furthermore, mushroom-type spines on these neurons are structurally more plastic when SynCAM 1 is absent, and challenging drug-withdrawn mice with cocaine shortens these spines in SynCAM 1 KO mice. These effects are correlated with changes on the behavioral level, where SynCAM 1 contributes to the psychostimulant effects of cocaine as measured after acute and repeated administration, and in drug-withdrawn mice. Together, our results provide evidence that the loss of a synapse-organizing adhesion molecule can modulate cocaine effects on spine structures in NAc and increases vulnerability to the behavioral actions of cocaine. SynCAM-dependent pathways may therefore represent novel points of therapeutic intervention after exposure to drugs of abuse.

Disrupted-in-schizophrenia-1 Gln31Leu polymorphism results in social anhedonia associated with monoaminergic imbalance and reduction of CREB and β-arrestin-1,2 in the nucleus accumbens in a mouse model of depression

Disrupted-in-schizophrenia-1 (DISC1) is associated with mental disorders, including major depression. We previously showed that DISC1-Q31L mutant mice have depression-like behaviors and can therefore be used to study neurobiological mechanisms of depression and antidepressant (AD) medication action. First, we found reduced levels of dopamine, serotonin and norepinephrine in the nucleus accumbens (NAC) of DISC1-Q31L mutants. Next, we assessed social-conditioned place preference as a reward-dependent task and the capacity of distinct ADs to correct impaired social behavior in DISC1-Q31L mice. Bupropion, but not fluoxetine or desipramine, was able to correct deficient social facilitation, social reward, and social novelty in DISC1-Q31L mutants, whereas all three ADs were able to improve social motivation and behavioral despair in DISC1-Q31L mutants. Furthermore, we sought to correlate social anhedonia with molecular and cellular features including dendritic spine density, β-arrestin-1,2, and cAMP-response-element-binding protein (CREB) in the NAC as biomarkers related to depression and the DISC1 pathway. DISC1-Q31L mutants showed reduced levels of β-arrestin-1,2, CREB, and spine density in the NAC, further supporting the construct validity of the genetic model. Bupropion induced the greatest effect on CREB in DISC1-Q31L mutants, whereas all studied ADs corrected the reduced levels of β-arrestin-1,2 and modestly ameliorated deficient spine density in this brain region. Overall, we find neurobiological changes accompanying social anhedonia in the NAC of DISC1-Q31L mutant mice, consistent with a role for DISC1 in regulating social reward as an endophenotype of depression.

Ghrelin increases GABAergic transmission and interacts with ethanol actions in the rat central nucleus of the amygdala

The neural circuitry that processes natural rewards converges with that engaged by addictive drugs. Because of this common neurocircuitry, drugs of abuse have been able to engage the hedonic mechanisms normally associated with the processing of natural rewards. Ghrelin is an orexigenic peptide that stimulates food intake by activating GHS-R1A receptors in the hypothalamus. However, ghrelin also activates GHS-R1A receptors on extrahypothalamic targets that mediate alcohol reward. The central nucleus of the amygdala (CeA) has a critical role in regulating ethanol consumption and the response to ethanol withdrawal. We previously demonstrated that rat CeA GABAergic transmission is enhanced by acute and chronic ethanol treatment. Here, we used quantitative RT-PCR (qRT-PCR) to detect Ghsr mRNA in the CeA and performed electrophysiological recordings to measure ghrelin effects on GABA transmission in this brain region. Furthermore, we examined whether acute or chronic ethanol treatment would alter these electrophysiological effects. Our qRT-PCR studies show the presence of Ghsr mRNA in the CeA. In naive animals, superfusion of ghrelin increased the amplitude of evoked inhibitory postsynaptic potentials (IPSPs) and the frequency of miniature inhibitory postsynaptic currents (mIPSCs). Coapplication of ethanol further increased the ghrelin-induced enhancement of IPSP amplitude, but to a lesser extent than ethanol alone. When applied alone, ethanol significantly increased IPSP amplitude, but this effect was attenuated by the application of ghrelin. In neurons from chronic ethanol-treated (CET) animals, the magnitude of ghrelin-induced increases in IPSP amplitude was not significantly different from that in naive animals, but the ethanol-induced increase in amplitude was abolished. Superfusion of the GHS-R1A antagonists D-Lys3-GHRP-6 and JMV 3002 decreased evoked IPSP and mIPSC frequency, revealing tonic ghrelin activity in the CeA. D-Lys3-GHRP-6 and JMV 3002 also blocked ghrelin-induced increases in GABAergic responses. Furthermore, D-Lys3-GHRP-6 did not affect ethanol-induced increases in IPSP amplitude. These studies implicate a potential role for the ghrelin system in regulating GABAergic transmission and a complex interaction with ethanol at CeA GABAergic synapses.

Molecular, cellular, and structural mechanisms of cocaine addiction: a key role for microRNAs

The rewarding properties of cocaine play a key role in establishing and maintaining the drug-taking habit. However, as exposure to cocaine increases, drug use can transition from controlled to compulsive. Importantly, very little is known about the neurobiological mechanisms that control this switch in drug use that defines addiction. MicroRNAs (miRNAs) are small non-protein coding RNA transcripts that can regulate the expression of messenger RNAs that code for proteins. Because of their highly pleiotropic nature, each miRNA has the potential to regulate hundreds or even thousands of protein-coding RNA transcripts. This property of miRNAs has generated considerable interest in their potential involvement in complex psychiatric disorders such as addiction, as each miRNA could potentially influence the many different molecular and cellular adaptations that arise in response to drug use that are hypothesized to drive the emergence of addiction. Here, we review recent evidence supporting a key role for miRNAs in the ventral striatum in regulating the rewarding and reinforcing properties of cocaine in animals with limited exposure to the drug. Moreover, we discuss evidence suggesting that miRNAs in the dorsal striatum control the escalation of drug intake in rats with extended cocaine access. These findings highlight the central role for miRNAs in drug-induced neuroplasticity in brain reward systems that drive the emergence of compulsive-like drug use in animals, and suggest that a better understanding of how miRNAs control drug intake will provide new insights into the neurobiology of drug addiction.

Epigenetic mechanisms in stroke and epilepsy

Epigenetic remodeling and modifications of chromatin structure by DNA methylation and histone modifications represent central mechanisms for the regulation of neuronal gene expression during brain development, higher-order processing, and memory formation. Emerging evidence implicates epigenetic modifications not only in normal brain function, but also in neuropsychiatric disorders. This review focuses on recent findings that disruption of chromatin modifications have a major role in the neurodegeneration associated with ischemic stroke and epilepsy. Although these disorders differ in their underlying causes and pathophysiology, they share a common feature, in that each disorder activates the gene silencing transcription factor REST (repressor element 1 silencing transcription factor), which orchestrates epigenetic remodeling of a subset of 'transcriptionally responsive targets' implicated in neuronal death. Although ischemic insults activate REST in selectively vulnerable neurons in the hippocampal CA1, seizures activate REST in CA3 neurons destined to die. Profiling the array of genes that are epigenetically dysregulated in response to neuronal insults is likely to advance our understanding of the mechanisms underlying the pathophysiology of these disorders and may lead to the identification of novel therapeutic strategies for the amelioration of these serious human conditions.

The role of histone acetylation in cocaine-induced neural plasticity and behavior

How do drugs of abuse, such as cocaine, cause stable changes in neural plasticity that in turn drive long-term changes in behavior? What kind of mechanism can underlie such stable changes in neural plasticity? One prime candidate mechanism is epigenetic mechanisms of chromatin regulation. Chromatin regulation has been shown to generate short-term and long-term molecular memory within an individual cell. They have also been shown to underlie cell fate decisions (or cellular memory). Now, there is accumulating evidence that in the CNS, these same mechanisms may be pivotal for drug-induced changes in gene expression and ultimately long-term behavioral changes. As these mechanisms are also being found to be fundamental for learning and memory, an exciting new possibility is the extinction of drug-seeking behavior by manipulation of epigenetic mechanisms. In this review, we critically discuss the evidence demonstrating a key role for chromatin regulation via histone acetylation in cocaine action.

Random and non-random monoallelic expression

Monoallelic expression poses an intriguing problem in epigenetics because it requires the unequal treatment of two segments of DNA that are present in the same nucleus and which can have absolutely identical sequences. This review will consider different known types of monoallelic expression. For all monoallelically expressed genes, their respective allele-specific patterns of expression have the potential to affect brain function and dysfunction.

Epigenetics of the depressed brain: role of histone acetylation and methylation

Major depressive disorder is a chronic, remitting syndrome involving widely distributed circuits in the brain. Stable alterations in gene expression that contribute to structural and functional changes in multiple brain regions are implicated in the heterogeneity and pathogenesis of the illness. Epigenetic events that alter chromatin structure to regulate programs of gene expression have been associated with depression-related behavior, antidepressant action, and resistance to depression or 'resilience' in animal models, with increasing evidence for similar mechanisms occurring in postmortem brains of depressed humans. In this review, we discuss recent advances in our understanding of epigenetic contributions to depression, in particular the role of histone acetylation and methylation, which are revealing novel mechanistic insight into the syndrome that may aid in the development of novel targets for depression treatment.

Histone regulation in the CNS: basic principles of epigenetic plasticity

Postmitotic neurons are subject to a vast array of environmental influences that require the nuclear integration of intracellular signaling events to promote a wide variety of neuroplastic states associated with synaptic function, circuit formation, and behavioral memory. Over the last decade, much attention has been paid to the roles of transcription and chromatin regulation in guiding fundamental aspects of neuronal function. A great deal of this work has centered on neurodevelopmental and adulthood plasticity, with increased focus in the areas of neuropharmacology and molecular psychiatry. Here, we attempt to provide a broad overview of chromatin regulation, as it relates to central nervous system (CNS) function, with specific emphasis on the modes of histone posttranslational modifications, chromatin remodeling, and histone variant exchange. Understanding the functions of chromatin in the context of the CNS will aid in the future development of pharmacological therapeutics aimed at alleviating devastating neurological disorders.

The dynamics of DNA methylation in schizophrenia and related psychiatric disorders

Major psychiatric disorders such as schizophrenia (SZ) and bipolar disorder (BP) with psychosis (BP+) express a complex symptomatology characterized by positive symptoms, negative symptoms, and cognitive impairment. Postmortem studies of human SZ and BP+ brains show considerable alterations in the transcriptome of a variety of cortical structures, including multiple mRNAs that are downregulated in both inhibitory GABAergic and excitatory pyramidal neurons compared with non-psychiatric subjects (NPS). Several reports show increased expression of DNA methyltransferases in telencephalic GABAergic neurons. Accumulating evidence suggests a critical role for altered DNA methylation processes in the pathogenesis of SZ and related psychiatric disorders. The establishment and maintenance of CpG site methylation is essential during central nervous system differentiation and this methylation has been implicated in synaptic plasticity, learning, and memory. Atypical hypermethylation of candidate gene promoters expressed in GABAergic neurons is associated with transcriptional downregulation of the corresponding mRNAs, including glutamic acid decarboxylase 67 (GAD67) and reelin (RELN). Recent reports indicate that the methylation status of promoter proximal CpG dinucleotides is in a dynamic balance between DNA methylation and DNA hydroxymethylation. Hydroxymethylation and subsequent DNA demethylation is more complex and involves additional proteins downstream of 5-hydroxymethylcytosine, including members of the base excision repair (BER) pathway. Recent advances in our understanding of altered CpG methylation, hydroxymethylation, and active DNA demethylation provide a framework for the identification of new targets, which may be exploited for the pharmacological intervention of the psychosis associated with SZ and possibly BP+.

DNA methylation and its basic function

In the mammalian genome, DNA methylation is an epigenetic mechanism involving the transfer of a methyl group onto the C5 position of the cytosine to form 5-methylcytosine. DNA methylation regulates gene expression by recruiting proteins involved in gene repression or by inhibiting the binding of transcription factor(s) to DNA. During development, the pattern of DNA methylation in the genome changes as a result of a dynamic process involving both de novo DNA methylation and demethylation. As a consequence, differentiated cells develop a stable and unique DNA methylation pattern that regulates tissue-specific gene transcription. In this chapter, we will review the process of DNA methylation and demethylation in the nervous system. We will describe the DNA (de)methylation machinery and its association with other epigenetic mechanisms such as histone modifications and noncoding RNAs. Intriguingly, postmitotic neurons still express DNA methyltransferases and components involved in DNA demethylation. Moreover, neuronal activity can modulate their pattern of DNA methylation in response to physiological and environmental stimuli. The precise regulation of DNA methylation is essential for normal cognitive function. Indeed, when DNA methylation is altered as a result of developmental mutations or environmental risk factors, such as drug exposure and neural injury, mental impairment is a common side effect. The investigation into DNA methylation continues to show a rich and complex picture about epigenetic gene regulation in the central nervous system and provides possible therapeutic targets for the treatment of neuropsychiatric disorders.

Candesartan, an angiotensin II AT₁-receptor blocker and PPAR-γ agonist, reduces lesion volume and improves motor and memory function after traumatic brain injury in mice

Traumatic brain injury (TBI) results in complex pathological reactions, the initial lesion worsened by secondary inflammation and edema. Angiotensin II (Ang II) is produced in the brain and Ang II receptor type 1 (AT₁R) overstimulation produces vasoconstriction and inflammation. Ang II receptor blockers (ARBs) are neuroprotective in models of stroke but little is known of their effect when administered in TBI models. We therefore performed controlled cortical impact (CCI) injury on mice to investigate whether the ARB candesartan would mitigate any effects of TBI. We administered candesartan or vehicle to mice 5 h before CCI injury. Candesartan treatment reduced the lesion volume after CCI injury by approximately 50%, decreased the number of dying neurons, lessened the number of activated microglial cells, protected cerebral blood flow (CBF), and reduced the expression of the cytokine TGFβ1 while increasing expression of TGFβ3. Candesartan-treated mice also showed better motor skills on the rotarod 3 days after injury, and improved performance in the Morris water maze 4 weeks after injury. These results indicate that candesartan is neuroprotective, reducing neuronal injury, decreasing lesion volume and microglial activation, protecting CBF and improving functional behavior in a mouse model of TBI. Co-treatment with a peroxisome proliferator-activated receptor-gamma (PPARγ) antagonist significantly reduced some of the beneficial effects of candesartan after CCI, suggesting that PPARγ activation may contribute to part or to all of the neuroprotective effect of candesartan. Overall, our data suggest that ARBs with dual AT₁R-blocking and PPARγ activation properties may have therapeutic value in treating TBI.

The SSRI citalopram affects fetal thalamic axon responsiveness to netrin-1 in vitro independently of SERT antagonism

Serotonin (5-hydroxytryptamine, 5-HT) signaling is thought to modulate nervous system development. Genetic and pharmacological studies support the idea that altered 5-HT signaling during development can have enduring consequences on brain function and behavior. Recently, we discovered that 5-HT can modulate thalamic axon guidance in vitro and in vivo. Embryonic thalamic axons transiently express the 5-HT transporter (SERT; Slc6a4) and accumulate 5-HT, suggesting that the SERT activity of these axons may regulate 5-HT-modulated guidance cues. We tested whether pharmacologically blocking SERT using selective 5-HT reuptake inhibitors (SSRIs) would impact the action of 5-HT on thalamic axon responses to netrin-1 in vitro. Surprisingly, we observed that two high-affinity SSRIs, racemic citalopram ((RS)-CIT) and paroxetine, affect the outgrowth of embryonic thalamic axons, but differ with respect to their dependence on SERT blockade. Using a recently developed 'citalopram insensitive' transgenic mouse line and in vitro pharmacology, we show that the effect of (RS)-CIT effect is SERT independent, but rather arises from R-CIT activation of the orphan sigma-1 receptor(σ1, Oprs1). Our results reveal a novel σ1 activity in modulating axon guidance and a 5-HT independent action of a widely prescribed SSRI. By extension, (RS)-CIT and possibly other structurally similar SSRIs may have other off-target actions that can impact neural development and contribute to therapeutic efficacy or side effects.

A novel mechanism of cocaine to enhance dopamine d2-like receptor mediated neurochemical and behavioral effects. An in vivo and in vitro study

Recent in vitro results suggest that cocaine may exert direct and/or indirect allosteric enhancing actions at dopamine (DA) D(2) receptors (D(2)Rs). In the present paper we tested the hypothesis that cocaine in vivo can enhance the effects of the D(2)-likeR agonist quinpirole in rats by using microdialysis and pharmacological behavioral studies. Furthermore, in vitro D(2)-likeR binding characteristics and Gα(i/o)-protein coupling, in the absence and in the presence of cocaine, have been investigated in rat striatal membranes. Intra-nucleus accumbens perfusion of the D(2)-likeR agonist quinpirole (10 μM) reduced local dialysate glutamate levels, whereas cocaine (10 and 100 nM) was ineffective. At a low concentration (100 nM), cocaine significantly enhanced quinpirole-induced reduction of accumbal extracellular glutamate levels. The behavioral experiments showed that cocaine (0.625 mg/kg), but not the DA uptake blocker GBR 12783 (1.25 mg/kg), enhanced quinpirole (1 mg/kg)-induced hyperlocomotion. Finally, cocaine (100 nM), but not GBR 12783 (200 nM), produced a small, but significant increase in the efficacy of DA to stimulate binding of GTPγS to striatal D(2)-likeRs, whereas the D(2)-likeR binding characteristics were unchanged in striatal membranes by cocaine in the nM range. The significant increase in the maximal response to DA-stimulated GTPγS binding to D(2)-likeRs by 100 nM cocaine remained in the presence of GBR 12783. The observed cocaine-induced enhancement of the Gα(i/o)-protein coupling of D(2)Rs may be in part because of allosteric direct and/or indirect enhancing effects of cocaine at these receptors. These novel actions of cocaine may have relevance for understanding the actions of cocaine upon accumbal DA, and/or glutamate transmission and thus its rewarding as well as relapsing effects.

Physical exercise and antidepressants enhance BDNF targeting in hippocampal CA3 dendrites: further evidence of a spatial code for BDNF splice variants

Brain-derived neurotrophic factor (BDNF) is encoded by multiple BDNF transcripts, whose function is unclear. We recently showed that a subset of BDNF transcripts can traffic into distal dendrites in response to electrical activity, while others are segregated into the somatoproximal domains. Physical exercise and antidepressant treatments exert their beneficial effects through upregulation of BDNF, which is required to support survival and differentiation of newborn dentate gyrus (DG) neurons. While these DG processes are required for the antidepressant effect, a role for CA1 in antidepressant action has been excluded, and the effect on CA3 neurons remains unclear. Here, we show for the first time that physical exercise and antidepressants induce local increase of BDNF in CA3. Voluntary physical exercise for 28 consecutive days, or 2-week treatment with 10 mg/kg per day fluoxetine or reboxetine, produced a global increase of BDNF mRNA and protein in the neuronal somata of the whole hippocampus and a specific increase of BDNF in dendrites of CA3 neurons. This increase was accounted for by BDNF exon 6 variant. In cultured hippocampal neurons, application of serotonin or norepinephrine (10-50 μM) induced increase in synaptic transmission and targeting of BDNF mRNA in dendrites. The increased expression of BDNF in CA3 dendrites following antidepressants or exercise further supports the neurotrophin hypothesis of antidepressants action and confirms that the differential subcellular localization of BDNF mRNA splice variants provides a spatial code for a selective expression of BDNF in specific subcellular districts. This selective expression may be exploited to design more specific antidepressants.

Increased Kv1 channel expression may contribute to decreased sIPSC frequency following chronic inhibition of NR2B-containing NMDAR

Numerous studies have documented the effects of chronic N-methyl-D-aspartate receptor (NMDAR) blockade on excitatory circuits, but the effects on inhibitory circuitry are not well studied. NR2A- and NR2B-containing NMDARs play differential roles in physiological processes, but the consequences of chronic NR2A- or NR2B-containing NMDAR inhibition on glutamatergic and GABAergic neurotransmission are unknown. We investigated altered GABAergic neurotransmission in dentate granule cells and interneurons following chronic treatment with the NR2B-selective antagonist, Ro25,6981, the NR2A-prefering antagonist, NVP-AAM077, or the non-subunit-selective NMDAR antagonist, D-APV, in organotypic hippocampal slice cultures. Electrophysiological recordings revealed large reductions in spontaneous inhibitory postsynaptic current (sIPSC) frequency in both granule cells and interneurons following chronic Ro25,6981 treatment, which was associated with minimally altered sIPSC amplitude, miniature inhibitory postsynaptic current (mIPSC) frequency, and mIPSC amplitude, suggesting diminished action potential-dependent GABA release. Chronic NVP-AAM077 or D-APV treatment had little effect on these measures. Reduced sIPSC frequency did not arise from downregulated GABA(A)R, altered excitatory or inhibitory drive to interneurons, altered interneuron membrane properties, increased failure rate, decreased action potential-dependent release probability, or mGluR/GABA(B) receptor modulation of GABA release. However, chronic Ro25,6981-mediated reductions in sIPSC frequency were occluded by the K+ channel blockers, dendrotoxin, margatoxin, and agitoxin, but not dendrotoxin-K or XE991. Immunohistochemistry also showed increased Kv1.2, Kv1.3, and Kv1.6 in the dentate molecular layer following chronic Ro25,6981 treatment. Our findings suggest that increased Kv1 channel expression/function contributed to diminished action potential-dependent GABA release following chronic NR2B-containing NMDAR inhibition and that these Kv1 channels may be heteromeric complexes containing Kv1.2, Kv1.3, and Kv1.6.

Dexamethasone stimulated gene expression in peripheral blood is a sensitive marker for glucocorticoid receptor resistance in depressed patients

Although gene expression profiles in peripheral blood in major depression are not likely to identify genes directly involved in the pathomechanism of affective disorders, they may serve as biomarkers for this disorder. As previous studies using baseline gene expression profiles have provided mixed results, our approach was to use an in vivo dexamethasone challenge test and to compare glucocorticoid receptor (GR)-mediated changes in gene expression between depressed patients and healthy controls. Whole genome gene expression data (baseline and following GR-stimulation with 1.5 mg dexamethasone p.o.) from two independent cohorts were analyzed to identify gene expression pattern that would predict case and control status using a training (N=18 cases/18 controls) and a test cohort (N=11/13). Dexamethasone led to reproducible regulation of 2670 genes in controls and 1151 transcripts in cases. Several genes, including FKBP5 and DUSP1, previously associated with the pathophysiology of major depression, were found to be reliable markers of GR-activation. Using random forest analyses for classification, GR-stimulated gene expression outperformed baseline gene expression as a classifier for case and control status with a correct classification of 79.1 vs 41.6% in the test cohort. GR-stimulated gene expression performed best in dexamethasone non-suppressor patients (88.7% correctly classified with 100% sensitivity), but also correctly classified 77.3% of the suppressor patients (76.7% sensitivity), when using a refined set of 19 genes. Our study suggests that in vivo stimulated gene expression in peripheral blood cells could be a promising molecular marker of altered GR-functioning, an important component of the underlying pathology, in patients suffering from depressive episodes.

Exogenous and endogenous cannabinoids suppress inhibitory neurotransmission in the human neocortex

Activation of CB(1) receptors on axon terminals by exogenous cannabinoids (eg, Δ(9)-tetrahydrocannabinol) and by endogenous cannabinoids (endocannabinoids) released by postsynaptic neurons leads to presynaptic inhibition of neurotransmission. The aim of this study was to characterize the effect of cannabinoids on GABAergic synaptic transmission in the human neocortex. Brain slices were prepared from neocortical tissues surgically removed to eliminate epileptogenic foci. Spontaneous GABAergic inhibitory postsynaptic currents (sIPSCs) were recorded in putative pyramidal neurons using patch-clamp techniques. To enhance the activity of cannabinoid-sensitive presynaptic axons, muscarinic receptors were continuously stimulated by carbachol. The synthetic cannabinoid receptor agonist WIN55212-2 decreased the cumulative amplitude of sIPSCs. The CB(1) antagonist rimonabant prevented this effect, verifying the involvement of CB(1) receptors. WIN55212-2 decreased the frequency of miniature IPSCs (mIPSCs) recorded in the presence of tetrodotoxin, but did not change their amplitude, indicating that the neurotransmission was inhibited presynaptically. Depolarization of postsynaptic pyramidal neurons induced a suppression of sIPSCs. As rimonabant prevented this suppression, it is very likely that it was due to endocannabinods acting on CB(1) receptors. This is the first demonstration that an exogenous cannabinoid inhibits synaptic transmission in the human neocortex and that endocannabinoids released by postsynaptic neurons suppress synaptic transmission in the human brain. Interferences of cannabinoid agonists and antagonists with synaptic transmission in the cortex may explain the cognitive and memory deficits elicited by these drugs.

Abnormal activity of the MAPK- and cAMP-associated signaling pathways in frontal cortical areas in postmortem brain in schizophrenia

Recent evidence suggests that schizophrenia may result from alterations of integration of signaling mediated by multiple neurotransmitter systems. Abnormalities of associated intracellular signaling pathways may contribute to the pathophysiology of schizophrenia. Proteins and phospho-proteins comprising mitogen activated protein kinase (MAPK) and 3'-5'-cyclic adenosine monophosphate (cAMP)-associated signaling pathways may be abnormally expressed in the anterior cingulate (ACC) and dorsolateral prefrontal cortex (DLPFC) in schizophrenia. Using western blot analysis we examined proteins of the MAPK- and cAMP-associated pathways in these two brain regions. Postmortem samples were used from a well-characterized collection of elderly patients with schizophrenia (ACC=36, DLPFC=35) and a comparison (ACC=33, DLPFC=31) group. Near-infrared intensity of IR-dye labeled secondary antisera bound to targeted proteins of the MAPK- and cAMP-associated signaling pathways was measured using LiCor Odyssey imaging system. We found decreased expression of Rap2, JNK1, JNK2, PSD-95, and decreased phosphorylation of JNK1/2 at T183/Y185 and PSD-95 at S295 in the ACC in schizophrenia. In the DLPFC, we found increased expression of Rack1, Fyn, Cdk5, and increased phosphorylation of PSD-95 at S295 and NR2B at Y1336. MAPK- and cAMP-associated molecules constitute ubiquitous intracellular signaling pathways that integrate extracellular stimuli, modify receptor expression and function, and regulate cell survival and neuroplasticity. These data suggest abnormal activity of the MAPK- and cAMP-associated pathways in frontal cortical areas in schizophrenia. These alterations may underlie the hypothesized hypoglutamatergic function in this illness. Together with previous findings, these data suggest that abnormalities of intracellular signaling pathways may contribute to the pathophysiology of schizophrenia.

Cerebrospinal fluid biomarkers for major depression confirm relevance of associated pathophysiology

Individual characteristics of pathophysiology and course of depressive episodes are at present not considered in diagnostics. There are no biological markers available that can assist in categorizing subtypes of depression and detecting molecular variances related to disease-causing mechanisms between depressed patients. Identification of such differences is important to create patient subgroups, which will benefit from medications that specifically target the pathophysiology underlying their clinical condition. To detect characteristic biological markers for major depression, we analyzed the cerebrospinal fluid (CSF) proteome of depressed vs control persons, using two-dimensional polyacrylamide gel electrophoresis and time-of-flight (TOF) mass spectrometry peptide profiling. Proteins of interest were identified by matrix-assisted laser desorption ionization TOF mass spectrometry (MALDI-TOF-MS). Validation of protein markers was performed by immunoblotting. We found 11 proteins and 144 peptide features that differed significantly between CSF from depressed patients and controls. In addition, we detected differences in the phosphorylation pattern of several CSF proteins. A subset of the differentially expressed proteins implicated in brain metabolism or central nervous system disease was validated by immunoblotting. The identified proteins are involved in neuroprotection and neuronal development, sleep regulation, and amyloid plaque deposition in the aging brain. This is one of the first hypothesis-free studies that identify characteristic protein expression differences in CSF of depressed patients. Proteomic approaches represent a powerful tool for the identification of disease markers for subgroups of patients with major depression.