The role of NMDA receptors in the signal attenuation rat model of obsessive-compulsive disorder

Smo-Shh Agonist Purmorphamine Prevents Neurobehavioral and Neurochemical Defects in 8-OH-DPAT-Induced Experimental Model of Obsessive-Compulsive Disorder

Obsessive-compulsive disorder is a mental disorder characterized by repetitive, unwanted thoughts and behavior due to abnormal neuronal corticostriatal-thalamocortical pathway and other neurochemical changes. Purmorphamine is a smoothened-sonic-hedgehog agonist that has a protective effect against many neurological diseases due to its role in maintaining functional connectivity during CNS development and its anti-inflammatory and antioxidant properties. As part of our current research, we investigated the neuroprotective effects of PUR against behavioral and neurochemical changes in 8-hydroxy-2-(di-n-propylamino)-tetralin-induced obsessive-compulsive disorder in rats. Additionally, the effect of PUR was compared with the standard drug for OCD, i.e., fluvoxamine. The intra-dorsal raphe-nucleus injection of 8-OH-DPAT in rats for seven days significantly showed OCD-like repetitive and compulsive behavior along with increased oxidative stress, inflammation, apoptosis, as well as neurotransmitter imbalance. These alterations were dose-dependently attenuated by long-term purmorphamine treatment at 5 mg/kg and 10 mg/kg i.p. In this study, we assessed the level of various neurochemical parameters in different biological samples, including brain homogenate, blood plasma, and CSF, to check the drug’s effect centrally and peripherally. These effects were comparable to the standard oral treatment withfluvoxamine at 10 mg/kg. However, when fluvoxamine was given in combination with purmorphamine, there was a more significant restoration of these alterations than the individualtreatmentswithfluvoxamine and purmorphamine. All the above findings demonstrate that the neuroprotective effect of purmorphamine in OCD can be strong evidence for developing a new therapeutic target for treating and managing OCD.

Memantine augmentation of sertraline in the treatment of symptoms and executive function among patients with obsessive-compulsive disorder: A double-blind placebo-controlled, randomized clinical trial

BACKGROUND

Medications currently recommended for the treatment of Obsessive-Compulsive Disorder (OCD) usually decrease the severity of the symptoms by 20-30%; however, 40-60% of OCD patients do not achieve a satisfactory response. Our main objective was to investigate the effectiveness of memantine, a non-competitive N-Methyl-D-aspartate (NMDA) receptor antagonist, as an adjunct therapy to sertraline, a selective serotonin reuptake inhibitor (SSRI), to improve severity of symptoms and executive function among patients with obsessive-compulsive disorder.

METHODS

Seventy patients with OCD according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria, and a Yale-Brown obsessive compulsive scale (Y-BOCS) score of more than 21 were recruited to the study. They received sertraline (100 mg daily initially followed by 200 mg daily after week 4) and either memantine (10 mg twice daily) or placebo in a placebo controlled, double-blinded, parallel-group, clinical trial of 12 weeks. The primary outcome was OCD symptoms measured by the Y-BOCS. Moreover, executive function of participants was measured by the Wisconsin Card Sorting Test (WCST).

RESULTS

The total score, and obsession and compulsion subscales of Y-BOCS significantly dropped in both groups with no significant difference between the two groups. However, memantine group showed a greater response in the number of completed categories subscale of the WCST (p value<0.001). We did not observe any major adverse effects in any of the groups.

CONCLUSION

Memantine has an acceptable safety and tolerability in patients with OCD and might have a positive effect on their executive function. Nevertheless, the current results don`t support the efficacy of memantine as an adjunctive agent to sertraline for symptoms in patients with OCD.

TRIAL REGISTRATION

The trial was registered at the Iranian Registry of Clinical Trials on 04/10/2019 ( www.irct.ir ; IRCT ID: IRCT20170123032145N4).

Antiglutamatergic agents for obsessive-compulsive disorder: Where are we now and what are possible future prospects?

Recent data suggest that obsessive-compulsive disorder (OCD) is driven by an imbalance among the habit learning system and the goal-directed system. The frontostriatal loop termed cortico-striatal-thalamo-cortical (CSTC) circuitry loop is involved in habits and their dysfunction plays an important role in OCD. Glutamatergic neurotransmission is the principal neurotransmitter implicated in the CSTC model of OCD. Hyperactivity in the CSTC loop implies a high level of glutamate in the cortical-striatal pathways as well as a dysregulation of GABAergic transmission, and could represent the pathophysiology of OCD. Moreover, the dysregulation of glutamate levels can lead to neurotoxicity, acting as a neuronal excitotoxin. The hypothesis of a role of neurotoxicity in the pathophysiology of OCD clinically correlates to the importance of an early intervention for patients. Indeed, some studies have shown that a reduction of duration of untreated illness is related to an earlier onset of remission. Although robust data supporting a progression of such brain changes are not available so far, an early intervention could help interrupt damage from neurotoxicity. Moreover, agents targeting glutamate neurotransmission may represent promising therapeutical option in OCD patients.

Effects of Morphine and Maternal Care on Behaviors and Protein Expression of Male Offspring

Genes and environment interact during development to alter gene expression and behavior. Parental morphine exposure before conception has devastating effects on the offspring. In the present study, we evaluated the role of maternal care in the intergenerational effect of maternal morphine exposure. Female rats received morphine or saline for ten days and were drugfree for another ten days. Thereafter, they were allowed to mate with drug-naïve male rats. When pups were born, they were cross-fostered to assess the contribution of maternal care versus morphine effects on the offspring. Adult male offspring were examined for anxiety-like behavior, spatial memory, and obsessive-compulsive-like behavior. To determine the mechanisms underlying the observed behavioral changes, protein levels of acetylated histone H3, BDNF, Trk-B, NMDA subunits, p-CREB, and 5-HT₃R were measured in the brain. Our results indicate that maternal caregiving is impaired in morphine-abstinent mothers. Interestingly, maternal care behaviors were also affected in drug-naïve mothers that raised offspring of morphine-exposed mothers. In addition, the offspring of morphine abstinent and non-drug dependent mothers, when raised by morphine abstinent mothers, exhibited more anxiety, obsessive-compulsive behaviors and impaired spatial memory. These altered behaviors were associated with alterations in the levels of the above-mentioned proteins. These data illustrate the intergenerational effects of maternal morphine exposure on offspring behaviors. Moreover, exposure to morphine before gestation not only affects maternal care and offspring behavior, but also has negative consequences on behaviors and protein expression in adoptive mothers of affected offspring.

Exploring genetic variants in obsessive compulsive disorder severity: A GWAS approach

BACKGROUND

The severity of Obsessive-Compulsive Disorder (OCD) varies significantly among probands. No study has specifically investigated the genetic base of OCD severity. A previous study from our group found an OCD polygenic risk score to predict pre- and post-treatment severity. This study explores the genomic bases of OCD severity.

METHODS

We administered the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) to 401 patients at their first visit to our clinic to measure their OCD severity. Genotyping data was collected by using the Infinium PsychArray-24 BeadChip kit (Illumina). We analyzed genetic association with OCD severity in a linear regression analysis at single-nucleotide polymorphism (SNP)- and gene-levels, this last also considering rare variants. Enrichment analyses were performed from gene-based analyses' results.

RESULTS

No SNP reached significant association (p < 10^-8) with the YBOCS. Six markers showed suggestive association (p < 10^-5). The top SNP was an intergenic variant in chromosome 2: rs7578149 (p < 1.89 × 10^-6), located in a region suggestively associated with MDD. Linkage disequilibrium was found for two clusters of SNPs located between SLC16A14 and SP110 in chromosome 2, all of them forming one peak of association. Enrichment analyses revealed OCD genes to be associated with porin activity (FDR = 0.01) and transmembrane structure (FDR = 0.04).

LIMITATIONS

The size of the sample and the transversal nature of the severity measure are limitations of this study.

CONCLUSION

This study contributes to better characterize OCD at an individual level, helping to know more about the prognosis of the disorder and develop more individualized treatments.

The hippocampus encodes delay and value information during delay-discounting decision making

The hippocampus, a region critical for memory and spatial navigation, has been implicated in delay discounting, the decline in subjective reward value when a delay is imposed. However, how delay information is encoded in the hippocampus is poorly understood. Here, we recorded from CA1 of mice performing a delay-discounting decision-making task, where delay lengths, delay positions, and reward amounts were changed across sessions, and identified subpopulations of CA1 neurons that increased or decreased their firing rate during long delays. The activity of both delay-active and -suppressed cells reflected delay length, delay position, and reward amount; but manipulating reward amount differentially impacted the two populations, suggesting distinct roles in the valuation process. Further, genetic deletion of the N-methyl-D-aspartate (NMDA) receptor in hippocampal pyramidal cells impaired delay-discount behavior and diminished delay-dependent activity in CA1. Our results suggest that distinct subclasses of hippocampal neurons concertedly support delay-discounting decisions in a manner that is dependent on NMDA receptor function.

Investigating the Role of Glutamate in Obsessive-Compulsive Disorder: Current Perspectives

Glutamate is a ubiquitous excitatory neurotransmitter, which is involved in normal physiology, a variety of central nervous system (CNS) functions, including excitotoxicity and neuronal migration. It is implicated in the pathogenesis of various neuropsychiatric disorders including epilepsy, Parkinson's disease, Alzheimer's dementia, schizophrenia and obsessive compulsive disorder (OCD). Over the years, a growing body of evidence has helped researchers understand the mechanisms underlying glutamatergic involvement in the pathogenesis of these disorders. In this review, we attempt to elucidate the role of glutamate in OCD, which is a chronic psychiatric condition with significant morbidity. This article provides current perspectives on the role played by glutamate in the pathogenesis, clinical symptoms and treatment response in OCD, a critical analysis of existing and emerging evidence, both clinical and preclinical, followed by a summary and future directions.

A systematic review and meta-analysis: Memantine augmentation in moderate to severe obsessive-compulsive disorder

A considerable proportion of obsessive-compulsive disorder (OCD) patients receiving first-line pharmacological therapy, fail to fully respond to treatment and continue to exhibit significant symptoms. In this systematic review, we evaluate the efficacy of memantine, as a glutamate-modulating agent, in moderate to severe OCD. Single and double blinded as well as open-label trials of memantine augmentation in adults with OCD were considered. Yale-Brown Obsessive Compulsive Scale (Y-BOCS) scores were the primary outcome measure. The electronic databases of PubMed, Scopus, Embase and Google Scholar were searched for relevant trials using keywords 'obsessive-compulsive disorder OR OCD' AND 'memantine'. The meta-analysis of eight studies involving 125 OCD subjects receiving memantine augmentation exhibited a significant overall mean reduction of 11.73 points in Y-BOCS scores. The categorical analysis of treatment response (a minimum of 35% reduction in Y-BOCS) in four double-blind placebo-controlled studies indicated that OCD patients receiving memantine augmentation were 3.61 times more likely to respond to treatment than those receiving placebo. We found that 20 mg/day memantine augmentation to first-line pharmacological treatment for a period of at least 8 weeks is a safe and effective intervention for moderate to severe OCD.

A Psycho-Behavioral Perspective on Modelling Obsessive-Compulsive Disorder (OCD) in Animals: The Role of Context

Obsessive-compulsive disorder is a heterogeneous and debilitating condition, characterized by intrusive thoughts and compulsive repetition. Animal models of OCD are important tools that have the potential to contribute significantly to our understanding of the condition. Although there is consensus that pre-clinical models are valuable in elucidating the underlying neurobiology in psychiatric disorders, the current paper attempts to prompt ideas on how interpretation of animal behavior can be expanded upon to more effectively converge with the human disorder. Successful outcomes in psychopharmacology involve rational design and synthesis of novel compounds and their testing in well-designed animal models. As part of a special journal issue on OCD, this paper will 1) review the psychobehavioral aspects of OCD that are of importance on how the above ideas can be articulated, 2) briefly elaborate on general issues that are important for the development of animal models of OCD, with a particular focus on the role and importance of context, 3) propose why translational progress may often be less than ideal, 4) highlight some of the significant contributions afforded by animal models to advance understanding, and 5) conclude by identifying novel behavioral constructs for future investigations that may contribute to the face, predictive and construct validity of OCD animal models. We base these targets on an integrative approach to face and construct validity, and note that the issue of treatment-resistance in the clinical context should receive attention in current animal models of OCD.

Increased Fear Memory and Glutamatergic Modulation in Compulsive Drinker Rats Selected by Schedule-Induced Polydipsia

Compulsive behavior is observed in several neuropsychiatric disorders such as obsessive-compulsive disorder (OCD), anxiety, depression, phobia, and schizophrenia. Thus, compulsivity has been proposed as a transdiagnostic symptom with a highly variable pharmacological treatment. Recent evidence shows that glutamate pharmacotherapy may be of benefit in impaired inhibitory control. The purpose of the present study was: first, to test the comorbidity between compulsivity and other neuropsychiatric symptoms on different preclinical behavioral models; second, to assess the therapeutic potential of different glutamate modulators in a preclinical model of compulsivity. Long Evans rats were selected as either high (HD) or low (LD) drinkers corresponding with their water intake in schedule-induced polydipsia (SIP). We assessed compulsivity in LD and HD rats by marble burying test (MBT), depression by forced swimming test (FST), anxiety by elevated plus maze (EPM) and fear behavior by fear conditioning (FC) test. After that, we measured the effects of acute administration (i.p.) of glutamatergic drugs: N-Acetylcysteine (NAC; 25, 50, 100 and 200 mg/kg), memantine (3.1 and 6.2 mg/kg) and lamotrigine (15 and 30 mg/kg) on compulsive drinking on SIP. The results obtained showed a relation between high compulsive drinking on SIP and a higher number of marbles partially buried in MBT, as well as a higher percentage of freezing on the retrieval day of FC test. We did not detect any significant differences between LD and HD rats in FST, nor in EPM. The psychopharmacological study of glutamatergic drugs revealed that memantine and lamotrigine, at all doses tested, decreased compulsive water consumption in HD rats compared to LD rats on SIP. NAC did not produce any significant effect on SIP. These results indicate that the symptom clusters of different forms of compulsivity and phobia might be found in the compulsive phenotype of HD rats selected by SIP. The effects of memantine and lamotrigine in HD rats point towards a dysregulation in the glutamatergic signaling as a possible underlying mechanism in the vulnerability to compulsive behavior on SIP. Further studies on SIP, could help to elucidate the therapeutic role of glutamatergic drugs as a pharmacological strategy on compulsive spectrum disorders.

In Vivo Preclinical Molecular Imaging of Repeated Exposure to an N-methyl-d-aspartate Antagonist and a Glutaminase Inhibitor as Potential Glutamatergic Modulators

Glutamate is the principal excitatory neurotransmitter in the brain and is at the base of a wide variety of neuropathologies, including epilepsy, autism, Fragile X, and obsessive compulsive disorder. Glutamate has also become the target for novel drugs in treatment and in fundamental research settings. However, much remains unknown on the working mechanisms of these drugs and the effects of chronic administration on the glutamatergic system. This study investigated the chronic effects of two glutamate-modulating drugs with imaging techniques to further clarify their working mechanisms for future research opportunities. Animals were exposed to saline (1 ml/kg), (5S,10R)-(+)-5-Methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) (0.3 mg/kg), or ebselen (10 mg/kg) for 7 consecutive days. At the sixth injection, animals underwent a positron emission tomography (PET)/computed tomography (CT) with (3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-O-11C-methyl-oxime) (ABP-688) to visualize the metabotropic G protein-coupled glutamate receptor 5 (mGluR5). After the seventh injection, animals underwent a magnetic resonance spectroscopy (MRS) scan to visualize glutamate and glutamine content. Afterward, results were verified by mGluR5 immunohistochemistry (IHC). PET/CT analysis revealed that animals receiving chronic MK-801 or ebselen had a significant (P < 0.05) higher binding potential (2.90 ± 0.47 and 2.87 ± 0.46, respectively) when compared with saline (1.97 ± 0.39) in the caudate putamen. This was confirmed by mGluR5 IHC, with 60.83% ± 6.30% of the area being highlighted for ebselen and 57.14% ± 9.23% for MK-801 versus 50.21% ± 5.71% for the saline group. MRS displayed significant changes on the glutamine level when comparing chronic ebselen (2.20 ± 0.40 µmol/g) to control (2.72 ± 0.34 µmol/g). Therefore, although no direct effects on glutamate were visualized, the changes in glutamine suggest changes in the total glutamate-glutamine pool. This highlights the potential of both drugs to modulate glutamatergic pathologies.

D-cycloserine augmentation in behavioral therapy for obsessive-compulsive disorder: a meta-analysis

OBJECTIVE

To evaluate the overall effect of D-cycloserine (DCS) augmentation on exposure and response prevention (ERP) therapy for obsessive-compulsive disorder (OCD).

METHODS

Clinical studies on the effect of DCS augmentation on ERP therapy for OCD compared to placebo were included for meta analysis. The primary outcome was the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS). Meta-analyses were performed with a random-effect model or a fixed-effect model using the Cochrane Review Manager (RevMan, version 5.2) to calculate the odds ratio and the mean difference, with their corresponding 95% confidence intervals.

RESULTS

A total of six studies was included in the current meta-analyses, and their data were extracted. Among them, four were for analyses of DCS and Y-BOCS at midtreatment, six for analysis at posttreatment, and four at 3-month follow-up. Besides, three of the six eligible studies were included in the meta-analysis of the DCS and Clinical Global Impression-Severity Scale at posttreatment, and three in the meta-analysis of DCS and proportions of treatment responders and of subjects attaining clinical remission status criteria at posttreatment. Our meta-analyses do not reveal a significant effect of DCS augmentation in ERP therapy for OCD patients, except when measured at midtreatment. Compared to the placebo group, DCS augmentation did show a trend toward significantly lower/decreased Y-BOCS; when measured at posttreatment and in the subpopulation of DCS taken before some of the ERP sessions, DCS augmentation showed a trend toward significantly lower/decreased Y-BOCS.

CONCLUSION

Our result suggested that with the careful optimization of DCS-augmented ERP therapy by fine-tuning timing and dosing of DCS administration and number and frequency of ERP sessions, DCS may enhance the efficacy of ERP therapy in reducing the symptomatic severity of OCD patients, especially at early stage of the treatment; therefore, DCS augmentation could possibly reduce treatment cost, reduce treatment drop and refusal rate, and help to improve access to the limited number of experienced therapists.

A selective review of glutamate pharmacological therapy in obsessive-compulsive and related disorders

Glutamate, an excitatory central nervous system neurotransmitter, is emerging as a potential alternative pharmacological treatment when compared to gamma-aminobutyric acid (GABA)-, dopamine-, and serotonin-modulating treatments for neuropsychiatric conditions. The pathophysiology, animal models, and clinical trials of glutamate modulation are explored in disorders with underlying inhibitory deficits (cognitive, motor, behavioral) including obsessive–compulsive disorder, attention deficit hyperactivity disorder, Tourette syndrome, trichotillomania, excoriation disorder, and nail biting. Obsessive–compulsive disorder, attention deficit hyperactivity disorder, and grooming disorders (trichotillomania and excoriation disorder) have emerging positive data, although only scarce controlled trials are available. The evidence is less supportive for the use of glutamate modulators in Tourette syndrome. Glutamate-modulating agents show promise in the treatment of disorders of inhibition.

Are 5-HT3 antagonists effective in obsessive-compulsive disorder? A systematic review of literature

OBJECTIVE

The purpose of this literature database search-based review was to critically consider and evaluate the findings of literature focusing on efficacy and safety of 5-HT3 antagonists in the treatment of obsessive-compulsive disorder (OCD), so as to test whether preclinical data match clinical therapeutic trials.

DESIGN

The PubMed database has been searched for papers on 5-HT3 antagonists and OCD in humans and for animal models of OCD and 5-HT3 receptors.

RESULTS

Of the clinically tested 5-HT3 receptor antagonists, ondansetron has been used to treat OCD in five therapeutic studies, whereas granisetron only in one recent trial. Both showed some efficacy in open studies and superiority to placebo in double-blind studies, along with fair safety. No animal OCD model directly implicated 5-HT3 receptors.

CONCLUSIONS

Overall, results indicate some utility, but the available literature is too scanty to allow for valid conclusions to be drawn. The mismatch between animal models of obsessive-compulsive disorder and clinical data with 5-HT3 antagonists needs more clinical data to ensure that it is not an artefact.

Signal attenuation as a rat model of obsessive compulsive disorder

In the signal attenuation rat model of obsessive-compulsive disorder (OCD), lever-pressing for food is followed by the presentation of a compound stimulus which serves as a feedback cue. This feedback is later attenuated by repeated presentations of the stimulus without food (without the rat emitting the lever-press response). In the next stage, lever-pressing is assessed under extinction conditions (i.e., no food is delivered). At this stage rats display two types of lever-presses, those that are followed by an attempt to collect a reward, and those that are not. The latter are the measure of compulsive-like behavior in the model. A control procedure in which rats do not experience the attenuation of the feedback cue serves to distinguish between the effects of signal attenuation and of extinction. The signal attenuation model is a highly validated model of OCD and differentiates between compulsive-like behaviors and behaviors that are repetitive but not compulsive. In addition the measures collected during the procedure eliminate alternative explanations for differences between the groups being tested, and are quantitative, unbiased and unaffected by inter-experimenter variability. The major disadvantages of this model are the costly equipment, the fact that it requires some technical know-how and the fact that it is time-consuming compared to other models of OCD (11 days). The model may be used for detecting the anti- or pro-compulsive effects of pharmacological and non-pharmacological manipulations and for studying the neural substrate of compulsive behavior.

Animal models of obsessive-compulsive disorder: utility and limitations

Obsessive-compulsive disorder (OCD) is a disabling and common neuropsychiatric condition of poorly known etiology. Many attempts have been made in the last few years to develop animal models of OCD with the aim of clarifying the genetic, neurochemical, and neuroanatomical basis of the disorder, as well as of developing novel pharmacological and neurosurgical treatments that may help to improve the prognosis of the illness. The latter goal is particularly important given that around 40% of patients with OCD do not respond to currently available therapies. This article summarizes strengths and limitations of the leading animal models of OCD including genetic, pharmacologically induced, behavioral manipulation-based, and neurodevelopmental models according to their face, construct, and predictive validity. On the basis of this evaluation, we discuss that currently labeled "animal models of OCD" should be regarded not as models of OCD but, rather, as animal models of different psychopathological processes, such as compulsivity, stereotypy, or perseverance, that are present not only in OCD but also in other psychiatric or neurological disorders. Animal models might constitute a challenging approach to study the neural and genetic mechanism of these phenomena from a trans-diagnostic perspective. Animal models are also of particular interest as tools for developing new therapeutic options for OCD, with the greatest convergence focusing on the glutamatergic system, the role of ovarian and related hormones, and the exploration of new potential targets for deep brain stimulation. Finally, future research on neurocognitive deficits associated with OCD through the use of analogous animal tasks could also provide a genuine opportunity to disentangle the complex etiology of the disorder.

Comorbid Obsessive-Compulsive Symptoms in Schizophrenia: Insight into Pathomechanisms Facilitates Treatment

Insight into the biological pathomechanism of a clinical syndrome facilitates the development of effective interventions. This paper applies this perspective to the important clinical problem of obsessive-compulsive symptoms (OCS) occurring during the lifetime diagnosis of schizophrenia. Up to 25% of schizophrenia patients suffer from OCS and about 12% fulfil the diagnostic criteria of obsessive-compulsive disorder (OCD). This is accompanied by marked subjective burden of disease, high levels of anxiety, depression and suicidality, increased neurocognitive impairment, less favourable levels of social and vocational functioning, and greater service utilization. Comorbid patients can be assigned to heterogeneous subgroups. It is assumed that second generation antipsychotics (SGAs), most importantly clozapine, might aggravate or even induce second-onset OCS. Several epidemiological and pharmacological arguments support this assumption. Specific genetic risk factors seem to dispose patients with schizophrenia to develop OCS and risk-conferring polymorphisms has been defined in SLC1A1, BDNF, DLGAP3, and GRIN2B and in interactions between these individual genes. Further research is needed with detailed characterization of large samples. In particular interactions between genetic risk constellations, pharmacological and psychosocial factors should be analysed. Results will further define homogeneous subgroups, which are in need for differential causative interventions. In clinical practise, schizophrenia patients should be carefully monitored for OCS, starting with at-risk mental states of psychosis and longitudinal follow-ups, hopefully leading to the development of multimodal therapeutic interventions.

Obsessive compulsive disorder and the glutamatergic system

PURPOSE OF REVIEW

Evidence-based pharmacological interventions for obsessive compulsive disorder (OCD) are targeted mainly at the serotonergic and dopaminergic pathways, and are not always effective. It is timely to review the growing evidence from animal models and clinical research (e.g., brain imaging, genetics) on the role of the glutamatergic system in OCD.

RECENT FINDINGS

Emerging evidence from both animal models and clinical research (including brain imaging, neurogenetics) supports the glutamatergic system as a potential target for pharmacotherapy in OCD. Although there have been relatively few randomized controlled trials of glutamatergic agents in pediatric or adult OCD to date, there is some work on riluzole, memantine, ketamine, topiramate, lamotrigine, N-acetylcysteine, and D-cycloserine.

SUMMARY

Given the need for more efficacious treatments in OCD, and given emergent findings on the role of the glutamatergic system in this disorder, there is a need for additional pharmacotherapy trials on glutamatergic agents in OCD. Possible research designs for such trials might include stand-alone approaches, pharmacotherapy augmentation, or psychotherapy augmentation.

The role of the cholinergic system in the signal attenuation rat model of obsessive-compulsive disorder

RATIONALE

In comparison to studies of the involvement of the serotonergic, dopaminergic, and glutamatergic systems in the pathophysiology of obsessive-compulsive disorder (OCD), research on the involvement of the cholinergic system in this disorder has remained sparse.

OBJECTIVES

The aim of this study was to test the role of the cholinergic system in compulsive behavior using the signal attenuation rat model of OCD. In this model, "compulsive" behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food.

METHODS

The acetylcholinesterase inhibitor physostigmine (0.05, 0.10, and 0.15 mg/kg), the nicotinic agonist nicotine (0.03, 0.06, 0.10, 0.30, 0.60, and 1.00 mg/kg), the nicotinic antagonist mecamylamine (1, 3, 5, and 8 mg/kg), the muscarinic agonist oxotremorine (0.0075, 0.0150, and 0.0300 mg/kg), and the muscarinic antagonist scopolamine (0.15, 0.50, 1.00, and 1.50 mg/kg) were acutely administered to rats just before assessing their lever-press responding following signal attenuation (experiments 1, 3, 5, 7, and 9, respectively). Because the effects of signal attenuation are assessed under extinction conditions, drug doses that were effective in the above experiments were also tested in an extinction session of lever-press responding that was not preceded by signal attenuation (experiments 2, 4, 6, 8, and 10).

RESULTS

Acute systemic administration of the cholinergic agents did not exert a selective anti- or pro-compulsive effect in the signal attenuation model.

CONCLUSIONS

Acetylcholine does not seem to play a role in the signal attenuation rat model of OCD.

Comorbid obsessive-compulsive symptoms in schizophrenia: contributions of pharmacological and genetic factors

A large subgroup of around 25% of schizophrenia patients suffers from obsessive-compulsive symptoms (OCS) and about 12% fulfill the diagnostic criteria of an obsessive-compulsive disorder (OCD). The additional occurrence of OCS is associated with high subjective burden of disease, additional neurocognitive impairment, poorer social and vocational functioning, greater service utilization and high levels of anxiety and depression. Comorbid patients can be assigned to heterogeneous subgroups. One hypothesis assumes that second generation antipsychotics (SGAs), most importantly clozapine, might aggravate or even induce second-onset OCS. Several arguments support this assumption, most importantly the observed chronological order of first psychotic manifestation, start of treatment with clozapine and onset of OCS. In addition, correlations between OCS-severity and dose and serum levels and duration of clozapine treatment hint toward a dose-dependent side effect. It has been hypothesized that genetic risk-factors dispose patients with schizophrenia to develop OCS. One study in a South Korean sample reported associations with polymorphisms in the gene SLC1A1 (solute carrier family 1A1) and SGA-induced OCS. However, this finding could not be replicated in European patients. Preliminary results also suggest an involvement of polymorphisms in the BDNF gene (brain-derived neurotrophic factor) and an interaction between markers of SLC1A1 and the gene DLGAP3 (disc large associated protein 3) as well as GRIN2B (N-methyl-D-aspartate receptor subunit 2B). Further research of well-defined samples, in particular studies investigating possible interactions of genetic risk-constellations and pharmacodynamic properties, are needed to clarify the assumed development of SGA-induced OCS. Results might improve pathogenic concepts and facilitate the definition of at risk populations, early detection and monitoring of OCS as well as multimodal therapeutic interventions.

A review of the interplay between tuberculosis and mental health

AIMS

Tuberculosis and mental illness share common risk factors including homelessness, HIV positive serology, alcohol/substance abuse and migrant status leading to frequent comorbidity. We sought to generate a comprehensive literature review that examines the complex relationship between tuberculosis and mental illness.

METHODS

A literature search was conducted in MedLine, Ovid and Psychinfo, with further examination of the references of these articles. In total 316 articles were identified. It was not possible to conduct a formal meta-analysis due to the absence of randomised controlled data.

RESULTS

Rates of mental illness of up to 70% have been identified in tuberculosis patients. Medications used in the treatment of common mental illnesses, such as depression, may have significant interactions with anti-tuberculosis agents, especially isoniazid and increasingly linezolid. Many medications used in the treatment of tuberculosis can have significant adverse psychiatric effects and some medications such as rifampicin may reduce the effective doses of anti-psychotics y their enzyme induction actions. Treatment with agents such as cycloserine has been associated with depression, and there have been reported cases of psychosis with most anti-tuberculous agents. Mental illness and substance abuse may also affect compliance with treatment, with attendant public health concerns.

CONCLUSIONS

As a result of the common co-morbidity of mental illness and tuberculosis, it is probable that physicians will encounter previously undiagnosed mental illness among patients with tuberculosis. Similarly, psychiatrists are likely to meet tuberculosis among their patients. It is important that both psychiatrists and physicians are aware of the potential for interactions between the drugs used to treat tuberculosis and psychiatric conditions.

Polymorphisms in the glutamate transporter gene SLC1A1 and obsessive-compulsive symptoms induced by second-generation antipsychotic agents

BACKGROUND

A large subgroup of schizophrenic patients develops obsessive-compulsive symptoms (OCS) during treatment with second-generation antipsychotics (SGA). A genetic risk factor for these secondary OCS was recently described in the gene SLC1A1 encoding the neuronal glutamate transporter excitatory amino acid carrier 1. The aim of this study was to replicate these findings in a European sample.

METHODS

A total of 103 schizophrenic patients treated with SGAs were included. Three single nucleotide polymorphisms in SLC1A1 (rs2228622, rs3780412 and rs3780413), which had been associated with SGA-induced OCS, were investigated. Single marker and haplotype analyses were tested with logistic regressions using age, sex and medication type as covariates.

RESULTS

Treatment with markedly antiserotonergic SGAs such as clozapine was more prevalent in the subgroup of patients with comorbid OCS (P<0.001). The dosage and duration of clozapine treatment correlated significantly with the severity of OCS. In contrast to the Asian sample, no genetic associations were found with OCS.

CONCLUSION

Larger samples are necessary to unravel the interplay of pharmacological and genetic risk factors for OCS in schizophrenia.

The role of glutamate signaling in the pathogenesis and treatment of obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a common and often debilitating neuropsychiatric condition characterized by persistent intrusive thoughts (obsessions), repetitive ritualistic behaviors (compulsions) and excessive anxiety. While the neurobiology and etiology of OCD has not been fully elucidated, there is growing evidence that disrupted neurotransmission of glutamate within corticalstriatal-thalamocortical (CSTC) circuitry plays a role in OCD pathogenesis. This review summarizes the findings from neuroimaging, animal model, candidate gene and treatment studies in the context of glutamate signaling dysfunction in OCD. First, studies using magnetic resonance spectroscopy are reviewed demonstrating altered glutamate concentrations in the caudate and anterior cingulate cortex of patients with OCD. Second, knockout mouse models, particularly the DLGAP3 and Sltrk5 knockout mouse models, display remarkably similar phenotypes of compulsive grooming behavior associated with glutamate signaling dysfunction. Third, candidate gene studies have identified associations between variants in glutamate system genes and OCD, particularly for SLC1A1 which has been shown to be associated with OCD in five independent studies. This converging evidence for a role of glutamate in OCD has led to the development of novel treatment strategies involving glutamatergic compounds, particularly riluzole and memantine. We conclude the review by outlining a glutamate hypothesis for OCD, which we hope will inform further research into etiology and treatment for this severe neuropsychiatric condition.

Glutamate abnormalities in obsessive compulsive disorder: neurobiology, pathophysiology, and treatment

Obsessive compulsive disorder is prevalent, disabling, incompletely understood, and often resistant to current therapies. Established treatments consist of specialized cognitive-behavioral psychotherapy and pharmacotherapy with medications targeting serotonergic and dopaminergic neurotransmission. However, remission is rare, and more than a quarter of OCD sufferers receive little or no benefit from these approaches, even when they are optimally delivered. New insights into the disorder, and new treatment strategies, are urgently needed. Recent evidence suggests that the ubiquitous excitatory neurotransmitter glutamate is dysregulated in OCD, and that this dysregulation may contribute to the pathophysiology of the disorder. Here we review the current state of this evidence, including neuroimaging studies, genetics, neurochemical investigations, and insights from animal models. Finally, we review recent findings from small clinical trials of glutamate-modulating medications in treatment-refractory OCD. The precise role of glutamate dysregulation in OCD remains unclear, and we lack blinded, well-controlled studies demonstrating therapeutic benefit from glutamate-modulating agents. Nevertheless, the evidence supporting some important perturbation of glutamate in the disorder is increasingly strong. This new perspective on the pathophysiology of OCD, which complements the older focus on monoaminergic neurotransmission, constitutes an important focus of current research and a promising area for the ongoing development of new therapeutics.

Nutraceuticals in the treatment of obsessive compulsive disorder (OCD): a review of mechanistic and clinical evidence

Obsessive-compulsive disorder (OCD) is a debilitating mental illness which has a significant impact on quality of life. First-line SSRI treatments for OCD typically are of limited benefit to only 40-60% of patients, and are associated with a range of adverse side effects. Current preclinical research investigating nutraceuticals (natural products) for OCD, reveals encouraging novel activity in modulating key pathways suggested to be involved in the pathogenesis of OCD (glutamatergic and serotonergic pathway dysregulation). Emerging clinical evidence also appears to tentatively support certain nutrients and plant-based interventions with known active constituents which modulate these pathways: N-acetlycysteine, myo-inositol, glycine, and milk thistle (Silybum marianum). The serotonin precursor tryptophan is unlikely to be of use in treating OCD while 5-HTP may possibly be a more effective precursor strategy. However, there is currently no clinical evidence to test the efficacy of either of these substances. Currently the balance of clinical evidence does not support the use of St. John's wort (Hypericum perforatum) in OCD. While clinical research in this area is in its infancy, further research into nutraceuticals is warranted in light of the promising preclinical data regarding their mechanisms of action and their favourable side effect profiles in comparison to current SSRI treatments. It is recommended that future clinical trials of nutraceutical treatments for OCD utilize randomized placebo-controlled study designs and considerably larger sample sizes in order to properly test for efficacy.

Animal models of obsessive-compulsive disorder: exploring pharmacology and neural substrates

During the last 30 years there have been many attempts to develop animal models of obsessive-compulsive disorder (OCD). Most models have not been studied further following the original publication, and in the past few years, most papers present studies employing a few established animal models, exploring the neural basis of compulsive behavior and developing new treatment strategies. Here we summarize findings from the five most studied animal models of OCD: 8-OHDPAT (8-hydroxy-2-(di-n-propylamino)-tetralin hydrobromide) induced decreased alternation, quinpirole-induced compulsive checking, marble burying, signal attenuation and spontaneous stereotypy in deer mice. We evaluate each model's face validity, derived from similarity between the behavior in the model and the specific symptoms of the human condition, predictive validity, derived from similarity in response to treatment (pharmacological or other), and construct validity, derived from similarity in the mechanism (physiological or psychological) that induces behavioral symptoms and in the neural systems involved. We present ideas regarding future clinical research based on each model's findings, and on this basis, also emphasize possible new approaches for the treatment of OCD.