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

Comparing the 'When' and the 'Where' of Electrocortical Activity in Patients with Tourette Syndrome, Body-Focused Repetitive Behaviors, and Obsessive Compulsive Disorder

Background/Objectives: Tourette Syndrome (TS), Obsessive Compulsive Disorder (OCD), and Body-Focused Repetitive Behaviors (BFRB) are three disorders that share many similarities in terms of phenomenology, neuroanatomy, and functionality. However, despite the literature pointing toward a plausible spectrum of these disorders, only a few studies have compared them. Studying the neurocognitive processes using Event-Related Potentials (ERPs) offers the advantage of assessing brain activity with excellent temporal resolution. The ERP components can then reflect specific processes known to be potentially affected by these disorders. Our first goal is to characterize 'when' in the processing stream group differences are the most prominent. The second goal is to identify 'where' in the brain the group discrepancies could be. Methods: Participants with TS (n = 24), OCD (n = 18), and BFRB (n = 16) were matched to a control group (n = 59) and were recorded with 58 EEG electrodes during a visual counting oddball task. Three ERP components were extracted (i.e., P200, N200, and P300), and generating sources were modelized with Standardized Low-Resolution Electromagnetic Tomography. Results: We showed no group differences for the P200 and N200 when controlling for anxiety and depressive symptoms, suggesting that the early cognitive processes reflected by these components are relatively intact in these populations. Our results also showed a decrease in the later anterior P300 oddball effect for the TS and OCD groups, whereas an intact oddball effect was observed for the BFRB group. Source localization analyses with sLORETA revealed activations in the lingual and middle occipital gyrus for the OCD group, distinguishing it from the other two clinical groups and the controls. Conclusions: It seems that both TS and OCD groups share deficits in anterior P300 activation but reflect distinct brain-generating source activations.

Targeting inflammatory signaling in obsessive compulsive disorder: a promising approach

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder. Approximately, around 2% to 3% percent of the general population experience symptoms of OCD over the course of their lifetime. OCD can lead to economic burden, poor quality of life, and disability. The characteristic features exhibited generally in OCD are continuous intrusive thoughts and periodic ritualized behaviours. Variations in genes, pathological function of Cortico-Striato-Thalamo-Cortical (CSTC) circuits and dysregulation in the synaptic conduction have been the major factors involved in the pathological progression of OCD. However, the basic mechanisms still largely unknown. Current therapies for OCD largely target monoaminergic neurotransmitters (NTs) in specific dopaminergic and serotonergic circuits. However, such therapies have limited efficacy and tolerability. Drug resistance has been one of the important reasons reported to critically influence the effectiveness of the available drugs. Inflammation has been a crucial factor which is believed to have a significant importance in OCD progression. A significant number of proinflammatory cytokines have been reportedly amplified in patients with OCD. Mechanisms of drug treatment involve attenuation of the symptoms via modulation of inflammatory signalling pathways, modification in brain structure, and synaptic plasticity. Hence, targeting inflammatory signaling may be considered as a suitable approach in the treatment of OCD. The present review focuses mainly on the significant findings from the animal and human studies conducted in this area, that targets inflammatory signaling in neurological conditions. In addition, it also focusses on the therapeutic approaches that target OCD via modification of the inflammatory signaling pathways.

Use of Post-mortem Brain Tissue in Investigations of Obsessive- Compulsive Disorder: A Systematic Review

BACKGROUND

Post-mortem examination of the brain is a key strategy to increase our understanding of the neurobiology of mental disorders. While extensive post-mortem research has been undertaken on some mental disorders, others appear to have been relatively neglected.

OBJECTIVE

The objective of the study was to conduct a systematic review of post-mortem research on obsessive-compulsive disorder (OCD).

METHODS

A systematic review was performed in accordance with PRISMA guidelines to provide an overview of quantitative, qualitative, or mixed methods primary research studies on OCD. Search platforms included NCBI Pubmed, SCOPUS, and Web of Science.

RESULTS

A total of 52 publications were found, and after the removal of works not meeting the inclusion criteria, six (6) peer-reviewed publications remained. These post-mortem studies have provided data on DNA methylation, cellular and molecular alterations, and gene expression profiling in brain areas associated with OCD.

DISCUSSION AND CONCLUSION

Included studies highlight the potential value of post-mortem brains from well-characterized individuals with OCD and suggest the need for additional work in this area.

Pathway-specific alterations in striatal excitability and cholinergic modulation in a SAPAP3 mouse model of compulsive motor behavior

Deletion of the obsessive-compulsive disorder (OCD)-associated gene SAP90/PSD-95-associated protein 3 (Sapap3), which encodes a postsynaptic anchoring protein at corticostriatal synapses, causes OCD-like motor behaviors in mice. While corticostriatal synaptic dysfunction is central to this phenotype, the striatum efficiently adapts to pathological changes, often in ways that expand upon the original circuit impairment. Here, we show that SAPAP3 deletion causes non-synaptic and pathway-specific alterations in dorsolateral striatum circuit function. While somatic excitability was elevated in striatal projection neurons (SPNs), dendritic excitability was exclusively enhanced in direct pathway SPNs. Layered on top of this, cholinergic modulation was altered in opposing ways: striatal cholinergic interneuron density and evoked acetylcholine release were elevated, while basal muscarinic modulation of SPNs was reduced. These data describe how SAPAP3 deletion alters the striatal landscape upon which impaired corticostriatal inputs will act, offering a basis for how pathological synaptic integration and unbalanced striatal output underlying OCD-like behaviors may be shaped.

A closer look to neural pathways and psychopharmacology of obsessive compulsive disorder

The intricate neural pathways involved in obsessive-compulsive disorder (OCD) affect areas of our brain that control executive functioning, organization, and planning. OCD is a chronic condition that can be debilitating, afflicting millions of people worldwide. The lifetime prevalence of OCD in the US is 2.3%. OCD is predominantly characterized by obsessions consisting of intrusive and unwanted thoughts, often with impulses that are strongly associated with anxiety. Compulsions with OCD encompass repetitive behaviors or mental acts to satisfy their afflicted obsessions or impulses. While these factors can be unique to each individual, it has been widely established that the etiology of OCD is complex as it relates to neuronal pathways, psychopharmacology, and brain chemistry involved and warrants further exploration.

Compulsive-like Behaviors in Amyloid-β 1-42-Induced Alzheimer's Disease in Mice Are Associated With Hippocampo-cortical Neural Circuit Dysfunction

Background

In addition to memory deficits, patients with Alzheimer's disease (AD) experience neuropsychiatric disturbances. Recent studies have suggested the association of obsessive-compulsive disorder with the early stages of AD. However, there is a lack of understanding of the neurobiological underpinnings of compulsive-like behaviors at the neuronal circuit level and their relationship with AD.

Methods

We have addressed this issue in an amyloid-β 1-42-induced mouse model of AD by studying compulsive-like behaviors. Next, we compared the hippocampal and medial prefrontal cortex (mPFC) local field potential pattern and coherence between these regions of control and AD mice. We also assessed the expression pattern of acetylcholine and glutamatergic signaling in these regions, using quantitative polymerase chain reaction.

Results

Our findings show that AD mice exhibit compulsive-like behaviors, as evidenced by enhanced marble burying, nest building, and burrowing. Furthermore, AD mice exhibited hippocampo-cortical circuit dysfunction demonstrated by decreased power of rhythmic oscillations at the theta (4-12 Hz) and gamma (25-50 Hz) frequencies in the hippocampus and mPFC, two functionally interconnected brain regions involved both in AD and compulsive behaviors. Importantly, coherence between the hippocampus and mPFC in the theta band of AD animals was significantly reduced. Furthermore, we found reduced cholinergic and glutamatergic neurotransmission in the hippocampus and mPFC of AD mice.

Conclusions

We conclude that the hippocampo-cortical functional alterations may play a significant role in mediating the compulsive-like behaviors observed in AD mice. These findings may help in understanding the underlying circuit mechanisms of obsessive-compulsive disorder-like phenotypes associated with AD.

L-theanine combination therapy with fluvoxamine in moderate-to-severe obsessive-compulsive disorder: A placebo-controlled, double-blind, randomized trial

AIM

The main aim of this study was to investigate the additional effects of L-theanine, an amino acid in tea and an analog of glutamate with neuroprotective and anti-depressant properties, on obsessive-compulsive disorder (OCD) symptoms in combination with fluvoxamine.

METHODS

Patients from either sex aged between 18 and 60 years diagnosed with OCD, based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), who had a Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score of more than 21 were enrolled in a double-blinded, parallel-group, placebo-controlled, clinical trial of 10 weeks to receive either L-theanine (100 mg twice daily) and fluvoxamine (100 mg daily initially followed by 200 mg daily after week 5) or placebo and fluvoxamine. The primary outcome of interest in this study was the Y-BOCS total score decrease from baseline.

RESULTS

From a total of 95 evaluated patients, 50 completed our study; 30 were randomly assigned to each group. Multivariate analysis (ANOVA) showed a significant effect of time× $$ \times $$ treatment for L-theanine in obsession subscale (F = 5.51, P = 0.008) of the Y-BOCS score but not in the total and compulsion scores. Our results showed significantly more improvement in obsession subscale scores in L-theanine compared to placebo group (P = 0.007, Cohen's d = 0.82). Also, total Y-BOCS scores were lower in L-theanine compared to placebo group at week 5 (P = 0.039, Cohen's d = 0.60) and 10 (P = 0.008, Cohen's d = 0.80). However, there was no significant between-group differences in compulsion subscale scores. Complete response was also more frequent in the L-theanine group (P = 0.0001).

CONCLUSION

Findings in this study suggest L-theanine as a relatively safe and effective adjuvant therapy for moderate to severe OCD.

Clinical Effectiveness of N-Methyl-D-Aspartate (NMDA) Receptor Antagonists in Adult Obsessive-Compulsive Disorder (OCD) Treatment: A Systematic Review

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder that affects approximately 2% of the human population. Traditional treatment of OCD includes selective serotonin reuptake inhibitor (SSRI) or serotonin reuptake inhibitor (SRI) treatment along with cognitive behavioral therapy (CBT). Nearly 25%-30% of OCD patients do not respond to SSRIs. Glutamatergic agents are currently being studied for the treatment of OCD due to the glutamatergic pathway in the brain, related to OCD, and the role of the cortico-striato-thalamic circuit (CSTC). This review assesses the clinical effectiveness of N-methyl-D-aspartate (NMDA) antagonists, ketamine/esketamine, memantine, and amantadine, for adult patients with OCD. Inclusion criteria include human studies published within the last 15 years, with patients diagnosed with OCD, aged over 18 years, with only psychiatric comorbidities, and full-text articles. Papers that included interventions other than CBT, exposure with response prevention (ERP), and SSRI/SRI were excluded. Articles were searched for using PubMed, PubMed Central, Medical Literature Analysis and Retrieval System Online, GeorgiA LIbrary LEarning Online, EBSCO Information Services, OpenAthens, Multidisciplinary Digital Publishing Institute, and Google Scholar databases, last searched on December 2, 2022. The risk of bias was assessed using Cochrane Risk of Bias tools, the Scale for the Assessment of Narrative Review Articles (SANRA) checklist for literature reviews, and the Joanna Briggs Institute (JBI) Critical Appraisal Checklist for quasi-experimental studies. Results were presented and synthesized by Excel spreadsheet analysis. The database search yielded 4,221 articles, which was cut down to 18 articles by inclusion/exclusion criteria, including duplications. 80% of the ketamine studies resulted in a significant reduction of obsessions and compulsions based on the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), and each of the memantine and amantadine studies displayed clinical effectiveness, also. Limitations include the small number of amantadine studies and the limited availability of other NMDA receptor (NMDAR) antagonist-focused studies. This systematic review shows that ketamine is an effective drug for the treatment of non-refractory, mild to moderate OCD, and memantine and amantadine are effective augmentation agents for the treatment of mild to severe OCD.

Correlations between single nucleotide polymorphisms in obsessive-compulsive disorder with the clinical features or response to therapy

Obsessive-compulsive disorder (OCD) is a debilitating neuropsychiatric disorder, in which the patient endures intrusive thoughts or is compelled to perform repetitive or ritualized actions. Many cases of OCD are considered to be familial or heritable in nature. It has been shown that a variety of internal and external risk factors are involved in the pathogenesis of OCD. Among the internal factors, genetic modifications play a critical role in the pathophysiological process. Despite many investigations performed to determine the candidate genes, the precise genetic factors involved in the disease remain largely undetermined. The present review summarizes the single nucleotide polymorphisms that have been proposed to be associated with OCD symptoms, early onset disease, neuroimaging results, and response to therapy. This information could help us to draw connections between genetics and OCD symptoms, better characterize OCD in individual patients, understand OCD prognosis, and design more targeted personalized treatment approaches.

Body Focused Repetitive Behavior Disorders: Behavioral Models and Neurobiological Mechanisms

OBJECTIVE

Body Focused Repetitive Behaviors (BFRB) is an umbrella term for undesirable, repetitive motor activities such as Trichotillomania (TTM), Skin Picking Disorder (SPD), nail biting, cheek chewing, lip biting, finger sucking, finger cracking and teeth grinding. Such behaviors are engaged in to eliminate a part of the body and may result in impaired functionality. The frequency of presentation to clinicians is low since BFRB are defined as harmless, although the number of studies on this condition has increased rapidly recently, including those making a clear determination of epidemiological data, those investigating the etiopathogenesis and those providing treatment guidelines, although they remain inadequate. The present study provides a review of studies investigating the etiology of BFRB to date.

METHOD

Articles published between 1992 and 2021 stored in the Pubmed, Medline, Scopus and Web of Science databases were reviewed, and the prominent research studies of the condition identified were included in the evaluation.

RESULTS

Studies investigating the etiopathogenesis of BFRB were found in most cases to investigate adult populations, and were hampered by such confounding factors as clinical heterogeneity, high rates of comorbid psychiatric diseases and small sample sizes. The identified studies reveal that attempts have been made to explain BFRB based on behavioral models, and that the condition is inherited at a high rate. Treatment planning is mostly associated with monoamine systems (especially glutamate and dopamine) and interventions were directed to addiction elements. Furthermore, cognitive flexibility and motor inhibition defects in neurocognitive area and cortico-striato-thalamocortical cycle abnormalities in neuroimaging studies have been reported.

CONCLUSION

Studies investigating the clinical features, incidence, etiopathogenesis and treatment of BFRB, which holds a controversial place in psychiatric classification systems, would contribute to a better understanding of the disease and a more appropriate definition of the condition.

Antiseizure medication-induced obsessive-compulsive disorder and tic disorder: a pragmatic review

INTRODUCTION

With a lifetime prevalence of 2.3%, obsessive compulsive disorder is a chronic, disabling condition that is associated with significant social and occupational impairment. Up to 30% of individuals with obsessive-compulsive disorder have a lifetime diagnosis of tic disorders. Antiseizure medication is increasingly used for a variety of physical and psychiatric illnesses. Clarification of the relationship between these symptoms/disorders and use of antiseizure medication is critically important for diagnostic and treatment purposes.

AREAS COVERED

Studies on antiseizure-induced obsessive-compulsive disorder and tic disorders are reviewed. The literature search strategy identified 89 articles. Twenty-nine articles were included in the final results. Of these, 24 are case reports or case studies, 2 cross-sectional studies, 1 chart review, 1 population-based case-control study and 1 observational prospective study assessing lamotrigine, levetiracetam, topiramate, zonisamide, and carbamazepine.

EXPERT OPINION

This study highlighted the temporal relationship of antiseizure medication use and onset of obsessive-compulsive symptoms and tics. Monitoring for medication-induced obsessive compulsions or tics should be undertaken when prescribing antiseizure medication for treatment of mood disorders or epilepsy. Further research identifying the causal relationship between antiseizure medication and de novo onset of obsessive-compulsive symptoms, obsessive-compulsive disorder and tic disorder is required.

Back to the Future: The Role of Infections in Psychopathology. Focus on OCD

OBJECTIVE

Recently, there has been a resurgence of interest in the relationship between infections and psychopathology, given the increasing data on the neurotropism and neurological/psychiatric morbidity of the SARS-COV2 virus, responsible for the current worldwide pandemic. Although the majority of observations were those obtained in mood and schizophrenic disorders, a few data are also available on the presence of bacterial or viral infections in patients suffering from obsessive-compulsive disorder (OCD). Therefore, given the limited information, the present paper aimed at reviewing the most updated evidence of infections in neuropsychiatric disorders and their possible mechanisms of actions, with a narrow focus on microbes in OCD.

METHOD

This paper is a narrative review. The databases of PubMed, Scopus, Embase, PsycINFO and Google Scholar were accessed to research and collect English language papers published between 1 January 1980 and 31 December 2021. The data on PANDAS/PANS and those observed during severe brain infections were excluded.

RESULTS

Several pathogens have been associated with an increased risk to develop a broad spectrum of neuropsychiatric conditions, such as schizophrenia, mood disorders, autism, attention-deficit/hyperactivity disorder, anorexia nervosa, and post-traumatic stress disorder. Some evidence supported a possible role of infections also in the pathophysiology of OCD. Infections from Herpes simplex virus 1, Borna disease virus, Group A-Beta Hemolytic Streptococcus, Borrelia spp., and Toxoplasma gondii were actually found in patients with OCD. Although different mechanisms have been hypothesized, all would converge to trigger functional/structural alterations of specific circuits or immune processes, with cascade dysfunctions of several other systems.

CONCLUSIONS

Based on the current evidence, a possible contribution of different types of microbes has been proposed for different neuropsychiatric disorders including OCD. However, the currently available literature is meager and heterogeneous in terms of sample characteristics and methods used. Therefore, further studies are needed to better understand the impact of infectious agents in neuropsychiatric disorders. Our opinion is that deeper insights in this field might contribute to a better definition of biological underpinnings of specific clinical pictures, as well as to promote psychiatric precision medicine, with treatments based on altered pathological pathways of single patients. This might be particularly relevant in OCD, a disorder with a high proportion of patients who are resistant or do not respond to conventional therapeutic strategies.

Quantification of Metabotropic Glutamate Receptor 5 Availability With Both [11C]ABP688 and [18F]FPEB Positron Emission Tomography in the Sapap3 Knockout Mouse Model for Obsessive-Compulsive-like Behavior

BACKGROUND

This study provides a first direct comparison between positron emission tomography radioligands targeting the allosteric site of the metabotropic glutamate receptor 5 (mGluR5): [¹¹C]ABP688 and [¹⁸F]FPEB. A blocking paradigm was set up to substantiate the common binding site of both radioligands. Second, both radioligands were applied in Sapap3 knockout (KO) mice showing compulsive-like behavior characterized by a lower in vivo mGluR5 availability.

METHODS

First, wild-type mice (n = 7) received four position emission tomography/computed tomography scans: a [¹¹C]ABP688 scan, a [¹⁸F]FPEB scan, and two blocking scans using cold FPEB and cold ABP688, respectively. A second experiment compared both radioligands in wild-type (n = 7) and KO (n = 10) mice. The simplified reference tissue model was used to calculate the nondisplaceable binding potential representing the in vivo availability of mGluR5 in the brain.

RESULTS

Using cold FPEB as a blocking compound for [¹¹C]ABP688 micro-positron emission tomography and vice versa, we observed averaged global reductions in mGluR5 availability of circa 98% for [¹¹C]ABP688 and 82%-96% for [¹⁸F]FPEB. For KOs, the [¹¹C]ABP688 nondisplaceable binding potential was on average 25% lower compared with wild-type control mice (p < .0001-.001), while this was about 17% for [¹⁸F]FPEB (p < .05).

CONCLUSIONS

The current findings substantiate a common binding site and suggest a strong relationship between mGluR5 availability levels measured with both radioligands. In Sapap3 KO mice, a reduced mGluR5 availability could therefore be demonstrated with both radioligands. With [¹¹C]ABP688, higher significance levels were achieved in more brain regions. These findings suggest [¹¹C]ABP688 as a preferable radiotracer to quantify mGluR5 availability, as exemplified here in a model for compulsive-like behavior.

The Potential of N-Acetylcysteine for Treatment of Trichotillomania, Excoriation Disorder, Onychophagia, and Onychotillomania: An Updated Literature Review

BACKGROUND

Trichotillomania (TTM), excoriation disorder, onychophagia, and onychotillomania are categorized as body focused repetitive behavior (BFRB) disorders, causing damage to the skin, hair, and/or nails with clinically significant psychosocial consequences. Currently, there are no standardized treatments for these compulsive, self-induced disorders. Studies on treatment of these disorders using psychotropic drugs (i.e., selective serotonin reuptake inhibitors, tricyclic antidepressants, anticonvulsants) have shown variable efficacy. Recently, there is a growing interest in N-acetylcysteine (NAC) for treating BFRBs. NAC is a glutamate modulator that has shown promise in successfully reducing the compulsive behaviors in BFRB disorders. This article provides an updated review of the literature on the use of NAC in TTM, excoriation disorder, onychophagia, and onychotillomania.

METHODS

Relevant articles were searched in the PubMed/MEDLINE database.

RESULTS

Twenty-four clinical trials, retrospective cohort studies, and case reports assessing the efficacy of NAC in TTM, excoriation disorder, and onychophagia were included. No studies for onychotillomania were found in our search.

CONCLUSIONS

Although NAC has proven successful for treatment of BFRB disorders, data is derived from few clinical trials and case reports assessing small numbers of patients. Larger studies with longer durations are needed to fully establish the efficacy of NAC in these disorders.

Possible actions of cannabidiol in obsessive-compulsive disorder by targeting the WNT/β-catenin pathway

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder characterized by recurrent and distinctive obsessions and/or compulsions. The etiologies remain unclear. Recent findings have shown that oxidative stress, inflammation, and glutamatergic pathways play key roles in the causes of OCD. However, first-line therapies include cognitive-behavioral therapy but only 40% of the patients respond to this first-line therapy. Research for new treatment is mandatory. This review focuses on the potential effects of cannabidiol (CBD), as a potential therapeutic strategy, on OCD and some of the presumed mechanisms by which CBD provides its benefit properties. CBD medication downregulates GSK-3β, the main inhibitor of the WNT/β-catenin pathway. The activation of the WNT/β-catenin could be associated with the control of oxidative stress, inflammation, and glutamatergic pathway and circadian rhythms dysregulation in OCD. Future prospective clinical trials could focus on CBD and its different and multiple interactions in OCD.

Mechanistic insights into the efficacy of memantine in treating certain drug addictions

The deleterious effects of the drug addiction epidemic are compounded by treatment strategies that are only marginally efficacious. Memantine is a unique glutamatergic medication with proven ability to attenuate drug addiction in preclinical models. However, clinical translational studies are inconsistent. In this review, we summarize preclinical evidences and clinical trials that investigated the efficacy of memantine in treating patients with alcohol, opiate, cocaine, and nicotine use disorders and discuss the results from a mechanistic point of view. Memantine has shown efficacy in reducing alcohol and opiate craving, consumption, and withdrawal severity. However, in cocaine and nicotine use disorders, memantine did not have significant effect on cravings or consumption. Additionally, memantine was associated with increased subjective effects of alcohol, cocaine, and nicotine. We discuss possible mechanisms behind this variability. Since memantine transiently blocks NMDA receptors and protects neurons from overstimulation by excessive synaptic glutamate, its efficacy should be observed in drug phases that cause hyperglutamatergic states, while hypoglutamatergic drug use states would not resolve with blocking NMDA receptors. Second, memantine pharmacokinetic studies have been done in rodents and healthy volunteers, but not in patients with substance use disorder. Memantine, opiates, cocaine, and nicotine share the same transporter family at the blood brain barrier. This shared transport mechanism could impact brain concentrations of memantine and its effects. In conclusion, memantine remains an intriguing compound in our pharmacopeia with controversial results in treating certain aspects of drug addiction. Further studies are needed to understand the clinical and biological correlates of its efficacy.

Astroglia and Obsessive Compulsive Disorder

Obsessive compulsive disorder (OCD) has a prevalence rate of 1-3% in the general population and has been ranked as one of the top ten leading causes of illness-related disability (American Psychiatric Association 2013; Kessler et al. 2005). OCD is characterized by persistent intrusive thoughts (obsessions) and repetitive behaviors (compulsions) (Leckman et al. 1997). There are various OCD-related disorders, including Tourette syndrome (TS), grooming disorders (e.g., skin-picking, trichotillomania), and autism spectrum disorders (ASD) that share considerable overlapping features with OCD (Browne et al. 2014). Although the neurobiological basis of OCD still remains obscure, neuroimaging studies in patients with OCD and OCD-related disorders have consistently identified hyperactivity in orbitofrontal cortex and striatum (Cerliani et al. 2015; Hou et al. 2014; Jung et al. 2017; Neuner et al. 2014). However, the cellular and synaptic abnormalities underlying this hyperactivity are unclear. The most prominent theory regarding the underlying mechanisms of OCD and OCD-related disorders is an increased excitation to inhibition (E/I) ratio due to increased glutamatergic excitation or reduced GABAergic inhibition (Albin and Mink 2006; Rubenstein and Merzenich 2003; Wu et al. 2012). A proper E/I ratio is achieved by factors expressed in neuron and glia. In astrocytes, both the glutamate transporter GLT1 and GABA transporter GAT-3 are critical for regulating the E/I balance (Aida et al. 2015; Aizawa et al. 2020; Boddum et al. 2016; Cui et al. 2014; Kersanté et al. 2013; Kiryk et al. 2008; Matos et al. 2018; Scimemi 2014; Sugimoto et al. 2018; Sugiyama et al. 2017; Tanaka et al. 1997; Zhao et al. 2018). Although astrocyte dysfunction has not been directly explored in OCD patients, several animal studies have found that astrocytes are involved in the pathophysiology of OCD. In this chapter, I highlight recent studies in which astrocyte dysfunction contributed to E/I imbalance, leading to pathological repetitive behaviors shared between patients with OCD, TS, and ASD.

Glutamatergic medications as adjunctive therapy for moderate to severe obsessive-compulsive disorder in adults: a systematic review and meta-analysis

BACKGROUND

Obsessive-compulsive disorder (OCD) is among the most disabling neuropsychiatric conditions characterized by the presence of repetitive intrusive thoughts, impulses, or images (obsessions) and/or ritualized mental or physical acts (compulsions). Serotonergic medications, particularly Selective Serotonin Reuptake Inhibitors (SSRIs), are the first-line treatments for patients with OCD. Recently, dysregulation of glutamatergic system has been proposed to be involved in the etiology of OCD. We designed this systematic review and meta-analysis to evaluate clinical efficacy of glutamatergic medications in patients with OCD, according to the guidelines of Cochrane collaboration.

METHOD

We searched Medline, Scopus, and Cochrane library without applying any language filter. Two of the authors independently reviewed search results for irrelevant and duplicate studies and extracted data and assessed methodological quality of the studies. We transformed data into a common rubric and calculated a weighted treatment effect across studies using Review Manager.

RESULTS

We found 476 references in 3 databases, and after exclusion of irrelevant and duplicate studies, 17 studies with total number of 759 patients with OCD were included. In the present review we found evidence for several drugs such as memantine, N-acetylcysteine (NAC), Minocycline, L-carnosine and riluzole. Glutamaterigic drug plus SSRIs were superior to SSRI+ Placebo with regard to Y-BOCS scale [standardized mean difference (SMD = - 3.81 95% CI = - 4.4, - 3.23).

CONCLUSION

Augmentation of glutamatergic medications with SSRIs are beneficial in obsessive-compulsive patients, no harmful significant differences in any safety outcome were found between the groups.

Pharmacotherapy for Neuropsychiatric Symptoms in Frontotemporal Dementia

Despite significant progress in the understanding of the frontotemporal dementias (FTDs), there remains no disease-modifying treatment for these conditions, and limited effective symptomatic treatment. Behavioural variant frontotemporal dementia (bvFTD) is the most common FTD syndrome, and is characterized by severe impairments in behaviour, personality and cognition. Neuropsychiatric symptoms are common features of bvFTD but are present in the other FTD syndromes. Current treatment strategies therefore focus on ameliorating the neuropsychiatric features. Here we review the rationale for current treatments related to each of the main neuropsychiatric symptoms forming the diagnostic criteria for bvFTD relevant to all FTD subtypes, and two additional symptoms not currently part of the diagnostic criteria: lack of insight and psychosis. Given the paucity of effective treatments for these symptoms, we highlight how contributing mechanisms delineated in cognitive neuroscience may inform future approaches to clinical trials and more precise symptomatic treatments for FTDs.

Bidirectional Behavioral Selection in Mice: A Novel Pre-clinical Approach to Examining Compulsivity

Obsessive-compulsive disorder (OCD) and related disorders (OCRD) is one of the most prevalent neuropsychiatric disorders with no definitive etiology. The pathophysiological attributes of OCD are driven by a multitude of factors that involve polygenic mechanisms, gender, neurochemistry, physiological status, environmental exposures and complex interactions among these factors. Such complex intertwining of contributing factors imparts clinical heterogeneity to the disorder making it challenging for therapeutic intervention. Mouse strains selected for excessive levels of nest- building behavior exhibit a spontaneous, stable and predictable compulsive-like behavioral phenotype. These compulsive-like mice exhibit heterogeneity in expression of compulsive-like and other adjunct behaviors that might serve as a valuable animal equivalent for examining the interactions of genetics, sex and environmental factors in influencing the pathophysiology of OCD. The current review summarizes the existing findings on the compulsive-like mice that bolster their face, construct and predictive validity for studying various dimensions of compulsive and associated behaviors often reported in clinical OCD and OCRD.

Elevated levels of neutrophil gelatinase-associated lipocalin among OCD patients: an exploratory study

BACKGROUND

Obsessive-compulsive disorder (OCD) is a debilitating psychiatric disease that is characterized by its clinical heterogeneity and complex pathophysiology. This complexity comes from the diversity of pathophysiological factors that have been proposed to be involved in the natural history of the disorder. Many theories on OCD pathology support inflammation as a pathophysiological factor, although studies are not consistent on the presence of a pro-inflammatory state among OCD patients. However, some pre-clinical animal studies suggest lipocalin-2 (LCN2), an analogous form of the acute-phase pro-inflammatory protein neutrophil gelatinase-associated lipocalin (NGAL), may be involved in in the regulation of the stress response, which is thought to be disrupted in OCD.

METHODS

Twenty-one OCD patients and 19 healthy subjects participated in this exploratory study. Levels of NGAL were assessed in the peripherous blood of all participants. Severity of disease was assessed using the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS).

RESULTS

OCD patients exhibited significantly higher levels of NGAL when compared to healthy control subjects. No correlation was found between elevated levels of NGAL and severity of symptoms.

CONCLUSIONS

This is the first study to report elevated levels of NGAL among OCD patients, adding evidence for a possible role of immune dysregulation in the pathophysiology of OCD.

Lithium and Atypical Antipsychotics: The Possible WNT/β Pathway Target in Glaucoma

Glaucoma is a progressive neurodegenerative disease that represents the major cause of irreversible blindness. Recent findings have shown which oxidative stress, inflammation, and glutamatergic pathway have main roles in the causes of glaucoma. Lithium is the major commonly used drug for the therapy of chronic mental illness. Lithium therapeutic mechanisms remain complex, including several pathways and gene expression, such as neurotransmitter and receptors, circadian modulation, ion transport, and signal transduction processes. Recent studies have shown that the benefits of lithium extend beyond just the therapy of mood. Neuroprotection against excitotoxicity or brain damages are other actions of lithium. Moreover, recent findings have investigated the role of lithium in glaucoma. The combination of lithium and atypical antipsychotics (AAPs) has been the main common choice for the treatment of bipolar disorder. Due to the possible side effects gradually introduced in therapy. Currently, no studies have focused on the possible actions of AAPs in glaucoma. Recent studies have shown a down regulation of the WNT/β-catenin pathway in glaucoma, associated with the overactivation of the GSK-3β signaling. The WNT/β-catenin pathway is mainly associated with oxidative stress, inflammation and glutamatergic pathway. Lithium is correlated with upregulation the WNT/β-catenin pathway and downregulation of the GSK-3β activity. Thus, this review focuses on the possible actions of lithium and AAPs, as possible therapeutic strategies, on glaucoma and some of the presumed mechanisms by which these drugs provide their possible benefit properties through the WNT/β-catenin pathway.

Lithium: a potential therapeutic strategy in obsessive-compulsive disorder by targeting the canonical WNT/β pathway

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder characterized b-y recurrent and distinctive obsessions and/or compulsions. The etiologies remain unclear. Recent findings have shown that oxidative stress, inflammation, and the glutamatergic pathway play key roles in the causes of OCD. However, first-line therapies include cognitive-behavioral therapy but only 40% of the patients respond to this first-line therapy. Research for a new treatment is mandatory. This review focuses on the potential effects of lithium, as a potential therapeutic strategy, on OCD and some of the presumed mechanisms by which lithium provides its benefit properties. Lithium medication downregulates GSK-3β, the main inhibitor of the WNT/β-catenin pathway. The activation of the WNT/β-catenin could be associated with the control of oxidative stress, inflammation, and glutamatergic pathway. Future prospective clinical trials could focus on lithium and its different and multiple interactions in OCD.

Cannabidiol and the Canonical WNT/β-Catenin Pathway in Glaucoma

Glaucoma is a progressive neurodegenerative disease which constitutes the main frequent cause of irreversible blindness. Recent findings have shown that oxidative stress, inflammation and glutamatergic pathway play key roles in the causes of glaucoma. Recent studies have shown a down regulation of the WNT/β-catenin pathway in glaucoma, associated with overactivation of the GSK-3β signaling. WNT/β-catenin pathway is mainly associated with oxidative stress, inflammation and glutamatergic pathway. Cannabidiol (CBD) is a non-psychotomimetic phytocannabinoid derived from Cannabis sativa plant which possesses many therapeutic properties across a range of neuropsychiatric disorders. Since few years, CBD presents an increased interest as a possible drug in anxiolytic disorders. CBD administration is associated with increase of the WNT/β-catenin pathway and decrease of the GSK-3β activity. CBD has a lower affinity for CB1 but can act through other signaling in glaucoma, including the WNT/β-catenin pathway. CBD downregulates GSK3-β activity, an inhibitor of WNT/β-catenin pathway. Moreover, CBD was reported to suppress pro-inflammatory signaling and neuroinflammation, oxidative stress and glutamatergic pathway. Thus, this review focuses on the potential effects of cannabidiol, as a potential therapeutic strategy, on glaucoma and some of the presumed mechanisms by which this phytocannabinoid provides its possible benefit properties through the WNT/β-catenin pathway.

Neural Mechanisms Underlying Repetitive Behaviors in Rodent Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is comprised of several conditions characterized by alterations in social interaction, communication, and repetitive behaviors. Genetic and environmental factors contribute to the heterogeneous development of ASD behaviors. Several rodent models display ASD-like phenotypes, including repetitive behaviors. In this review article, we discuss the potential neural mechanisms involved in repetitive behaviors in rodent models of ASD and related neuropsychiatric disorders. We review signaling pathways, neural circuits, and anatomical alterations in rodent models that display robust stereotypic behaviors. Understanding the mechanisms and circuit alterations underlying repetitive behaviors in rodent models of ASD will inform translational research and provide useful insight into therapeutic strategies for the treatment of repetitive behaviors in ASD and other neuropsychiatric disorders.

Lower Ventromedial Prefrontal Cortex Glutamate Levels in Patients With Obsessive-Compulsive Disorder

Background: Recent studies using magnetic resonance spectroscopy (¹H-MRS) indicate that patients with obsessive-compulsive disorder (OCD) present abnormal levels of glutamate (Glu) and gamma aminobutyric acid (GABA) in the frontal and striatal regions of the brain. These abnormalities could be related to the hyperactivation observed in cortico-striatal circuits of patients with OCD. However, most of the previous ¹H-MRS studies were not capable of differentiating the signal from metabolites that overlap in the spectrum, such as Glu and glutamine (Gln), and referred to the detected signal as the composite measure-Glx (sum of Glu and Gln). In this study, we used a two-dimensional JPRESS ¹H-MRS sequence that allows the discrimination of overlapping metabolites by observing the differences in J-coupling, leading to higher accuracy in the quantification of all metabolites. Our objective was to identify possible alterations in the neurometabolism of OCD, focusing on Glu and GABA, which are key neurotransmitters in the brain that could provide insights into the underlying neurochemistry of a putative excitatory/inhibitory imbalance. Secondary analysis was performed including metabolites such as Gln, creatine (Cr), N-acetylaspartate, glutathione, choline, lactate, and myo-inositol. Methods: Fifty-nine patients with OCD and 42 healthy controls (HCs) underwent 3T ¹H-MRS in the ventromedial prefrontal cortex (vmPFC, 30 × 25 × 25 mm³). Metabolites were quantified using ProFit (version 2.0) and Cr as a reference. Furthermore, Glu/GABA and Glu/Gln ratios were calculated. Generalized linear models (GLMs) were conducted using each metabolite as a dependent variable and age, sex, and gray matter fraction (fGM) as confounding factors. GLM analysis was also used to test for associations between clinical symptoms and neurometabolites. Results: The GLM analysis indicated lower levels of Glu/Cr in patients with OCD (z = 2.540; p = 0.011). No other comparisons reached significant differences between groups for all the metabolites studied. No associations between metabolites and clinical symptoms were detected. Conclusions: The decreased Glu/Cr concentrations in the vmPFC of patients with OCD indicate a neurochemical imbalance in the excitatory neurotransmission that could be associated with the neurobiology of the disease and may be relevant for the pathophysiology of OCD.

Magnetic Resonance Spectroscopy (MRS) and Positron Emission Tomography (PET) Imaging in Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is characterised by structural and functional deficits in the cortico-striato-thalamic-cortical (CSTC) circuitry and abnormal neurochemical changes are thought to modulate these deficits. The hypothesis that an imbalanced concentration of the brain neurotransmitters, in particular glutamate (Glu) and gamma-amino-butyric acid (GABA), could impair the normal functioning of the CSTC, thus leading to OCD symptoms, has been tested in humans using magnetic resonance spectroscopy (MRS) and positron emission tomography (PET). This chapter summarises these neurochemical findings and represents an attempt to condense such scattered literature. We also discuss potential challenges in the field that may explain the inconsistent findings and suggest ways to overcome them. There is some convergent research from MRS pointing towards abnormalities in the brain concentration of neurometabolite markers of neuronal integrity, such as N-acetylaspartate (NAA) and choline (Cho). Lower NAA levels have been found in dorsal and rostral ACC of OCD patients (as compared to healthy volunteers), which increase after CBT and SSRI treatment, and higher Cho concentration has been reported in the thalamus of the OCD brain. However, findings for other neurometabolites are very inconsistent. Studies have reported abnormalities in the concentrations of creatine (Cr), GABA, glutamate (Glu), glutamine (Gln), Ins (myo-inositol), and serotonin (5-HT), but most of the results were not replicated. The question remains whether the NAA and Cho findings are genuinely the only neurochemical abnormalities in OCD or whether the lack of consistent findings for the other neurometabolites is caused by the lower magnetic field (1-3 Tesla (T)) used by the studies conducted so far, their small sample sizes or a lack of proper control for medication effects. To answer these questions and to further inform the biological underpinning of the symptoms and the cognitive problems at the basis of OCD we need better controlled studies using clear medicated vs unmedicated groups, larger sample sizes, stronger magnetic fields (e.g. at 7 T), and more consistency in the definition of the regions of interest.

Pharmacogenetics of Obsessive-Compulsive Disorder: An Evidence-Update

Pharmacogenetics has become increasingly important in the treatment of psychiatric disorders because approximately 50% of individuals who take psychotropic medications do not typically respond to them. Obsessive-compulsive disorder (OCD) is one such chronic and often debilitating mental illness with significant non-response to even the first-line medication, serotonin reuptake inhibitors. Precision medicine utilizing genetic testing panels has received significant attention based on the evidence that the variability of antidepressant response and adverse effects is partly due to the variability in an individual's genome. Thus, extensive research has investigated the role of genetic factors on antidepressant response in major depressive disorder (MDD) and their utility for guiding antidepressant treatment to significantly improving outcomes in individuals with MDD. However, limited progress remains in the pharmacogenetics of OCD. This chapter will provide an overview of the recent findings in the pharmacogenetics of OCD. Promising results with limited replications have been reported for the cytochrome P450 liver metabolism genes in addition to several serotonergic and glutamatergic system genes, which may play an important role in antidepressant response in the treatment of OCD.

The Psychopharmacology of Obsessive-Compulsive Disorder: A Preclinical Roadmap

This review evaluates current knowledge about obsessive-compulsive disorder (OCD), with the goal of providing a roadmap for future directions in research on the psychopharmacology of the disorder. It first addresses issues in the description and diagnosis of OCD, including the structure, measurement, and appropriate description of the disorder and issues of differential diagnosis. Current pharmacotherapies for OCD are then reviewed, including monotherapy with serotonin reuptake inhibitors and augmentation with antipsychotic medication and with psychologic treatment. Neuromodulatory therapies for OCD are also described, including psychosurgery, deep brain stimulation, and noninvasive brain stimulation. Psychotherapies for OCD are then reviewed, focusing on behavior therapy, including exposure and response prevention and cognitive therapy, and the efficacy of these interventions is discussed, touching on issues such as the timing of sessions, the adjunctive role of pharmacotherapy, and the underlying mechanisms. Next, current research on the neurobiology of OCD is examined, including work probing the role of various neurotransmitters and other endogenous processes and etiology as clues to the neurobiological fault that may underlie OCD. A new perspective on preclinical research is advanced, using the Research Domain Criteria to propose an adaptationist viewpoint that regards OCD as the dysfunction of a normal motivational system. A systems-design approach introduces the security motivation system (SMS) theory of OCD as a framework for research. Finally, a new perspective on psychopharmacological research for OCD is advanced, exploring three approaches: boosting infrastructure facilities of the brain, facilitating psychotherapeutic relearning, and targeting specific pathways of the SMS network to fix deficient SMS shut-down processes. SIGNIFICANCE STATEMENT: A significant proportion of patients with obsessive-compulsive disorder (OCD) do not achieve remission with current treatments, indicating the need for innovations in psychopharmacology for the disorder. OCD may be conceptualized as the dysfunction of a normal, special motivation system that evolved to manage the prospect of potential danger. This perspective, together with a wide-ranging review of the literature, suggests novel directions for psychopharmacological research, including boosting support systems of the brain, facilitating relearning that occurs in psychotherapy, and targeting specific pathways in the brain that provide deficient stopping processes in OCD.

Pharmacological Treatment for Comorbid Bipolar Disorder and Obsessive-Compulsive Disorder in Adults

Comorbidity between bipolar disorder (BD) and obsessive-compulsive disorder (OCD) is fairly common, and the treatment of these conditions when comorbid is challenging. Serotonin reuptake inhibitors, the first option for treatment of OCD, can worsen BD symptoms, and mood stabilizers are generally not efficacious for OCD. Our goal in this article is to assess the clinical effectiveness of pharmacotherapies for comorbid BD-OCD in adults. We searched the Medline, Embase, and Cochrane Central Register of Controlled Trials databases on April 30, 2017, and we also searched the reference lists of identified articles. Studies published beginning January 1, 2007 were included, without language restrictions. Narrative and systematic reviews, letters to the editor, and book chapters were excluded. Two authors independently assessed the quality of the studies and extracted data. Seven studies met our inclusion criteria. Findings from double-blind, randomized, placebo-controlled trials were pooled for analysis. Findings from this pooled analysis indicated that augmentation of mood-stabilizer treatment with glutamate modulator agents (topiramate or memantine) may favor full response of obsessive-compulsive symptoms (risk ratio: 2.62, 95% confidence interval: 1.45-4.74) in patients with BD type I and OCD in the manic phase, and that it does not significantly induce adverse effects (risk ratio: 1.26, 95% confidence interval: 0.53-3.01). Results of a narrative synthesis of observational studies indicated greater efficacy of mood-stabilizer treatment, with serotonin reuptake inhibitors less used. Findings from studies employing different designs were not compared, and our results should be interpreted cautiously.

Pregabalin augmentation for resistant obsessive-compulsive disorder: a double-blind placebo-controlled clinical trial

BACKGROUND AND OBJECTIVE

Glutamate dysfunction has been shown to be associated with pathophysiology of obsessive-compulsive disorder (OCD). Our objective is to survey the effects of pregabalin (a glutamate-modulating agent) as an augmenting treatment for resistant OCD.

PATIENTS AND METHODS

In this 12-week double-blind placebo-controlled clinical trial, 56 patients with resistant OCD were randomly allocated to receive either pregabalin or placebo plus their current medication (sertraline). Yale-Brown Obsessive Compulsive Scale (Y-BOCS) was used to evaluate the outcomes. Adverse effects were also registered.

RESULTS

Of the 56 patients with resistant OCD who were randomly allocated in 2 groups of pregabalin (n = 28) and placebo group (n = 28), 42 patients (22 in pregabalin group and 20 in placebo group) completed the trial. Throughout the trial, the mean score decreased from 26.13± 7.03 to 8.81 ± 3.47 in the pregabalin group (p < 0) and from 26.85 ± 4.34 to 17.63 ± 4.22 in the placebo group (p < 0). At the end of trial, 16 (57.14%) patients in the pregabalin group and 2 (7.14%) patients in the placebo group showed more than 35% decline in YBOCS (p < .01). The pregabalin group showed good tolerability and safety.

CONCLUSIONS

Our study revealed that pregabalin, as an augmenting medication, is more effective than placebo in the treatment of patients with resistant OCD.

A single nucleotide polymorphism in SLC1A1 gene is associated with age of onset of obsessive-compulsive disorder

Different genetic polymorphisms in the SLC1A1 have been shown to be associated with obsessive-compulsive disorder. Rs301430 is a T/C functional polymorphism affecting the gene expression and extrasynaptic glutamate concentration.We observed that Rs301430 influence age at onset in obsessive-compulsive disorder.

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.

Blood glutamate scavenging as a novel glutamate-based therapeutic approach for post-stroke depression

Post-stroke depression (PSD) is a major complication of stroke that significantly impacts functional recovery and quality of life. While the exact mechanism of PSD is unknown, recent attention has focused on the association of the glutamatergic system in its etiology and treatment. Minimizing secondary brain damage and neuropsychiatric consequences associated with excess glutamate concentrations is a vital part of stroke management. The blood glutamate scavengers, oxaloacetate and pyruvate, degrade glutamate in the blood to its inactive metabolite, 2-ketoglutarate, by the coenzymes glutamate-oxaloacetate transaminase (GOT) and glutamate-pyruvate transaminase (GPT), respectively. This reduction in blood glutamate concentrations leads to a subsequent shift of glutamate down its concentration gradient from the blood to the brain, thereby decreasing brain glutamate levels. Although there are not yet any human trials that support blood glutamate scavengers for clinical use, there is increasing evidence from animal research of their efficacy as a promising new therapeutic approach for PSD. In this review, we present recent evidence in the literature of the potential therapeutic benefits of blood glutamate scavengers for reducing PSD and other related neuropsychiatric conditions. The evidence reviewed here should be useful in guiding future clinical trials.

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.

Altered frequencies of Th17 and Treg cells in children and adolescents with obsessive-compulsive disorder

OBJECTIVE

Obsessive-compulsive disorder (OCD) is a debilitating neuropsychiatric disorder with an etiopathophysiology that seems to include immune alterations. Previous studies have suggested that variations in the levels of circulating T cell subpopulations may be involved in psychiatric diseases. However, the role of these cells in OCD remains unexplored. Hence, the present study aimed to examine the levels of T helper 1 (Th1), Th2, Th17 and regulatory T (Treg) cells in patients with early-onset OCD and healthy controls.

METHODS

The assessment was performed in 99 children and adolescents with OCD and 46 control subjects. The percentages of circulating Th1, Th2, Th17 and Treg cells were evaluated using flow cytometry.

RESULTS

OCD patients had significantly higher levels of Th17 cells and lower percentages of Treg cells than healthy controls (p = 0.001 and p = 0.005, respectively). Furthermore, levels of Th17 cells progressively increased with the duration (p = 0.005) and severity of OCD (p = 0.008), whereas the percentages of Treg cells significantly declined with the duration of the disorder (p = 1.8 × 10^-5).

CONCLUSIONS

These results provide more evidence of the involvement of immune dysregulation, specifically an imbalance in the levels of circulating T helper and regulatory T cells, in the pathophysiology of early-onset OCD.

New Directions in the Use of Brain Stimulation Interventions in Patients with Obsessive-Compulsive Disorder

Obsessive-Compulsive Disorder (OCD) is a highly disabling condition with early onset and chronic course in most of the affected patients. In addition, OCD may show high comorbidity and suicide attempt rates, which worsen the overall burden of the disease for patients and their caregivers. First-line treatments for OCD consist of pro-serotonergic compounds and cognitive-behavioral therapy. Nonetheless, many patients show only limited benefit from such interventions and require additional "next-step" interventions, including augmentative antipsychotics and glutamate-modulating agents. Based on the knowledge about altered neurocircuitry in OCD, brain stimulation techniques, including transcranial magnetic and electrical stimulations (TMS and tDCS) and deep brain stimulation (DBS), have been increasingly investigated over the last decade, revealing positive results for otherwise intractable and treatment-refractory patients. Available evidence in the field is in continuous evolution and professionals actively involved in the management of OCD patients, psychiatrists in particular, need to be updated about latest developments. Through the analysis of controlled studies, meta-analyses, and International treatment guidelines, the present article is aimed at providing the state of the art on the use of brain stimulation techniques for the treatment of OCD.

The Glutamate and the Immune Systems: New Targets for the Pharmacological Treatment of OCD

BACKGROUND

In the last decades the pharmacological treatment of obsessivecompulsive disorder (OCD) has been significantly promoted by the effectiveness of selective serotonin (5-HT) reuptake inhibitors (SSRIs) and the subsequent development of the 5-HT hypothesis of OCD. However, since a large majority of patients (between 40% and 60 %) do not respond to SSRIs or strategies based on the modulation of the 5-HT system, it is now essential to search for other possible therapeutic targets.

AIMS

The aim of this paper was to review current literature through a PubMed and Google Scholar search of novel hypotheses and related compounds for the treatment of OCD, with a special focus on the glutammate and the immune systems.

DISCUSSION

The literature indicates that glutamate, the main excitatory neurotransmitter, might play an important role in the pathophysiology of OCD. In addition, a series of clinical studies also supports the potential efficacy of drugs modulating the glutamate system. The role of the immune system alterations in OCD in both children and adults needs to be more deeply elucidated. In children, a subtype of OCD has been widely described resulting from infections driven by group A streptococcus β-hemolitic and belonging to the so-called "pediatric autoimmune neuropsychiatric disorders associated with streptococcus" (PANDAS). In adults, available findings are meager and controversial, although interesting.

CONCLUSION

The glutamate and the immune systems represent two intriguing topics of research that hold promise for the development of open novel treatment strategies in OCD.

Lamotrigine-induced obsessive-compulsive disorder in patients with bipolar disorder

IntroductionLamotrigine is a commonly used drug in the treatment of bipolar disorder. Although there are reports of its effectiveness in the management of bipolar disorder and comorbid obsessive-compulsive disorder (OCD), lamotrigine has also been associated with obsessionality in patients with bipolar disorder.

METHODS

Charts of 8 patients with bipolar disorder who had de novo onset of obsessions and compulsions after the use of lamotrigine were reviewed. The Naranjo scale was used to assess the likelihood of patients developing OCD due to lamotrigine use.

RESULTS

Two to 8 months after the initiation of lamotrigine, patients with no such prior history developed obsessions and compulsions meeting the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) diagnostic criteria for medication-induced OCD. In all except 1 patient, the symptoms resolved within a month of lamotrigine discontinuation.

CONCLUSIONS

Some patients with bipolar disorder may develop OCD after initiation of lamotrigine. Due to the inherent limitations of a case series, the findings should be interpreted with caution.

A CASE OF PERIPARTUM OBSESSIVE-COMPULSIVE DISORDER: The Potential Role of Corticosteroids, Gonadal Steroids, and the Neuropeptide Oxytocin in its Pathogenesis

The perinatal period represents a time of increased vulnerability to psychiatric disorders, including the largely understudied obsessive-compulsive disorder (OCD). In contrast to the gradual onset of typical OCD, postpartum OCD appears to be characterized by the rapid onset of obsessional symptoms after the birth, with onset as early as the second postpartum day with a mean time to onset of 2.2 to 3.7 weeks. We present a case of a patient with prepartum generalized anxiety disorder (GAD) and new-onset postpartum OCD. The patient's ego-dystonic obsessions were aggressive in nature ("harm to newborn") with pathological checking compulsions requiring reassurance that she would not engage in this activity. Neurobiologically, there has been speculation that changes in estrogen and progesterone in the puerperium might alter serotoninergic function, placing some women at risk for this subtype of OCD. Some research studies have found evidence to suggest that oxytocin is associated with OCD. We review the growing evidence that suggests oxytocin and gonadal steroids might play a role in the pathogenesis of some forms of OCD.

Amantadine as adjuvant therapy in the treatment of moderate to severe obsessive-compulsive disorder: A double-blind randomized trial with placebo control

AIM

The role of the glutamatergic system in the pathogenesis of obsessive-compulsive disorder (OCD) has been shown by numerous studies. The aim of the present randomized, double-blind, placebo-controlled, 12-week trial was to assess the efficacy and tolerability of amantadine as an adjuvant to fluvoxamine in the treatment of patients with moderate to severe OCD.

METHODS

One hundred patients diagnosed with moderate to severe OCD were randomized into two parallel groups to receive fluvoxamine (100 mg twice a day) plus placebo or fluvoxamine (100 mg twice a day) plus amantadine (100 mg daily) for 12 weeks. All patients received 100 mg/day fluvoxamine for 28 days followed by 200 mg/day for the rest of the trial, regardless of their treatment groups. Patients were evaluated for response to treatment using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS) at baseline and at Weeks 4, 10, and 12. The main outcome measure was to assess the efficacy of amantadine in improving the OCD symptoms.

RESULTS

Repeated-measure analysis of variance showed a significant effect for Time × Treatment interaction (Greenhouse-Geisser corrected: F = 3.84, d.f. = 1.50, P = 0.03) in the Y-BOCS total score and a significant effect for Time × Treatment interaction (Greenhouse-Geisser corrected: F = 5.67, d.f. = 1.48, P < 0.01) in the Y-BOCS Obsession subscale score between the two groups.

CONCLUSION

The results of this study suggest that amantadine may be effective as an augmentative agent in the treatment of moderate-to-severe OCD.

The right thalamic glutamate level correlates with functional connectivity with right dorsal anterior cingulate cortex/middle occipital gyrus in unmedicated obsessive-compulsive disorder: A combined fMRI and 1H-MRS study

OBJECTIVE

The imbalance in neurotransmitter and neuronal metabolite concentration within cortico-striato-thalamo-cortical (CSTC) circuit contributes to obsessive-compulsive disorder's (OCD) onset. Previous studies showed that glutamate mediated upregulation of resting-state activity in healthy people. However, there have been few studies investigating the correlational features between functional and neurochemical alterations in OCD.

METHODS

We utilize a combined resting-state functional magnetic resonance imaging (rs-fMRI) and proton magnetic resonance spectroscopy (¹H-MRS) approach to investigate the altered functional connectivity (FC) in association with glutamatergic dysfunction in OCD pathophysiology. Three regions of interest are investigated, i.e., medial prefrontal cortex and bilateral thalamus, for seed-based whole-brain FC analysis as well as MRS data acquisition. There are 23 unmedicated adult OCD patients and 23 healthy controls recruited for brain FC analysis. Among them, 12 OCD and 8 controls are performed MRS data acquisition.

RESULTS

Besides abnormal FC within CSTC circuit, we also find altered FCs in large-scale networks outside CSTC circuit, including occipital area and limbic and motor systems. The decreased FC between right thalamus and right middle occipital gyrus (MOG) is correlated with glutamatergic signal within right thalamus in OCD patients. Moreover, the FC between right thalamus and right dorsal anterior cingulate cortex (dACC) is associated with glutamate level in right thalamus, specifically in patient's group. Finally, the FC between right thalamus and right MOG is correlated with patient's Yale-Brown Obsessive Compulsive Scale (YBOCS) compulsion and total scores, while the right thalamic glutamatergic signal is associated with YBOCS-compulsion score.

CONCLUSION

Our findings showed that the coupled intrinsic functional-biochemical alterations existed both within CSTC circuit and from CSTC to occipital lobe in OCD pathophysiology.

Gene variations in PBX1, LMX1A and SLITRK1 are associated with obsessive-compulsive disorder and its clinical features

Genetic factors probably influence OCD development and a current hypothesis proposes that genes involved in the development of the central nervous system (CNS) are related to OCD. The aim of this study was to analyze six Single Nucleotide Polymorphisms (SNPs) in five genes with functions related to neurodevelopment in OCD. A total of 203 patient and 203 control samples were genotyped using the TaqMan® methodology. Statistically significant associations between OCD and PBX1 (rs2275558) in total sample (P = 0.002) and in males (P = 0.0003) were observed. Concerning symptom dimensions, the expression of neutralization showed a statistical significant association with LMX1A (rs4657411, P = 0.004) in total sample. We also observed significant association between LMX1A (rs4657411) and washing dimension in females (P = 0.01). Additionally, SLITRK1 (rs9593835) was significantly associated with checking dimension in male patients (P = 0.04). Our results indicate an important influence of neurodevelopment genes in the OCD susceptibility. Additional studies with larger samples are needed to confirm these results.

No effect of riluzole and memantine on learning deficit following quinpirole sensitization - An animal model of obsessive-compulsive disorder

RATIONALE

Chronic quinpirole (QNP) sensitization is an established animal model relevant to obsessive-compulsive disorder (OCD) that has been previously shown to induce several OCD-like behavioral patterns, such as compulsive-like checking and increased locomotion.

OBJECTIVES

In current study we explored the effect of antiglutamatergic drugs, memantine and riluzole, on cognitive and behavioral performance of QNP sensitized rats.

METHODS

During habituation phase, the rats (N = 56) were injected with QNP (0.25 mg/kg) or saline solution (every other day up to 10 injections) and placed into rotating arena without foot shocks for 50-min exploration. Active place avoidance task in rotating arena with unmarked to-be-avoided shock sector was used during acquisition phase. Rats were injected with memantine (1 mg/kg or 5 mg/kg), riluzole (1 mg/kg or 5 mg/kg) or saline solution 30 min before the trial and with QNP (0.25 mg/kg) or saline right before they were placed inside the rotating arena with 60° unmarked shock sector. Locomotion and number of entrances into the shock sector were recorded.

RESULTS

QNP sensitization led to a robust deficit in place learning. However, neither memantine nor riluzole did reverse or alleviate the deficit induced by QNP. Contrarily, memantine significantly aggravated QNP induced deficit.

CONCLUSIONS

The exacerbation of cognitive deficit following antiglutamatergic agents could be mediated by decreased glutamate concentration in nucleus accumbens and decreased hippocampal activation in the QNP sensitization model.

Glutamate transporter gene polymorphisms and obsessive-compulsive disorder: A case-control association study

The etiology of obsessive-compulsive disorder (OCD) is largely unknown, but family, twin, neuroimaging, and pharmacological studies suggest that glutamatergic system plays a significant role on its underlying pathophysiology. We performed an association analysis of six Single Nucleotide Polymorphisms (SNPs) within SLC1A1 gene (rs12682807, rs2075627, rs3780412, rs301443, rs301430, rs301434) in a group of 199 patients and 200 healthy controls. Symptom profiles were evaluated using the Florida Obsessive-Compulsive Inventory (FOCI) and the Obsessive-Compulsive Inventory-Revised (OCI-R). SNPs were analyzed by Taqman® methodology (Thermo Fisher, Brazil). The genotype distributions were in Hardy-Weinberg equilibrium. The A-A-G (rs301434-rs3780412-rs301443) haplotype was twice as common in OCD as in controls (P = 0.02). We also found significant differences between male patients and controls for rs301443 in a dominant model (P = 0.04) and a protective effect of GG genotype of rs2072657 in women (P = 0.02). Regarding clinical characteristics, the G-A (rs301434-rs3780412) haplotype was almost twice more common in patients with vs. without hoarding (P = 0.04). Further analyses showed significant associations between hoarding and rs301434 (P = 0.04) and rs3780412 (P = 0.04) in women, both in a dominant model. A dominant effect was also observed on ordering dimension for rs301434 (P = 0.01, in women) and rs301443 (P = 0.04). Finally, the rs2072657 showed a recessive effect on neutralization (P = 0.04) and checking (P = 0.03, in men). These preliminary results demonstrated that the SLC1A1 may contribute to some extent the susceptibility to OCD and its symptoms. However, additional studies are still needed.

Genetics of obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) has been seen to run in families and genetics help to understand its heritability. In this review, we summarize older studies which focused on establishing the familial nature of OCD, including its various dimensions of symptoms, and we focus on recent findings from studies using both the candidate gene approach and genome-wide association study (GWAS) approach. The family studies and twin studies establish the heritability of OCD. Candidate gene approaches have implicated genes in the serotonergic, glutamatergic, and dopaminergic pathways. GWAS has not produced significant results possibly due to the small sample size. Newer techniques such as gene expression studies in brain tissue, stem cell technology, and epigenetic studies may shed more light on the complex genetic basis of OCD.

Glutamatergic augmentation strategies in obsessive-compulsive disorder

Proven treatment strategies for obsessive-compulsive disorder (OCD) include pharmacotherapy with serotonin reuptake inhibitors and cognitive behavior therapy (CBT). A significant proportion of patients (25%-30%) fail to respond to these treatment options, necessitating the need for additional treatment options to improve treatment outcomes and quality of life in patients with OCD. Augmentation strategies using various glutamatergic agents have been explored, with diverse outcomes. The aim of this review is to give an overview of the glutamatergic system in the brain with a focus on glutamatergic abnormalities in OCD and to review the existing evidence for various glutamatergic agents used for augmentation.