Neurobiology of obsessive-compulsive disorder: insights into neural circuitry dysfunction through mouse genetics

Neurobiology of Obsessive-Compulsive Disorder from Genes to Circuits: Insights from Animal Models

Obsessive-compulsive disorder (OCD) is a chronic, severe psychiatric disorder that has been ranked by the World Health Organization as one of the leading causes of illness-related disability, and first-line interventions are limited in efficacy and have side-effect issues. However, the exact pathophysiology underlying this complex, heterogeneous disorder remains unknown. This scenario is now rapidly changing due to the advancement of powerful technologies that can be used to verify the function of the specific gene and dissect the neural circuits underlying the neurobiology of OCD in rodents. Genetic and circuit-specific manipulation in rodents has provided important insights into the neurobiology of OCD by identifying the molecular, cellular, and circuit events that induce OCD-like behaviors. This review will highlight recent progress specifically toward classic genetic animal models and advanced neural circuit findings, which provide theoretical evidence for targeted intervention on specific molecular, cellular, and neural circuit events.

Similarities and differences between eating disorders and obsessive-compulsive disorder in childhood and adolescence: a systematic review

Background

The developmental age, comprising childhood and adolescence, constitutes an extremely important phase of neurodevelopment during which various psychiatric disorders can emerge. Obsessive-Compulsive Disorder (OCD) and Eating Disorders (ED) often manifest during this critical developmental period sharing similarities but also differences in psychopathology, neurobiology, and etiopathogenesis. The aim of this study is to focus on clinical, genetic and neurobiological similarities and differences in OCD and ED.

Methods

This study is based on a PubMed/MEDLINE and Cochrane Central Register for Controlled Trial (CENTRAL). The research adhered to the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

Results

The aforementioned search yielded an initial collection of 335 articles, published from 1968 to September 2023. Through the application of inclusion and exclusion criteria, a total of 324 articles were excluded, culminating in a final selection of 10 articles.

Conclusions

Our findings showed both differences and similarities between OCD and ED. Obsessive-compulsive (OC) symptoms are more prevalent in ED characterized by a binge/purge profile than in those with a restrictive profile during developmental age. OC symptomatology appears to be a common dimension in both OCD and ED. When presents, OC symptomatology, exhibits transversal characteristic alterations in the anterior cingulate cortex and poorer cognitive flexibility. These correlations could be highlighted by genetic overlaps between disorders. A comprehensive definition, integrating psychopathological and neurobiological aspects could significantly aid treatment selection and thereby influence the prognosis of these patients.

Opening new vistas on obsessive-compulsive disorder with the observing response task

Obsessive-compulsive disorder (OCD), a highly prevalent and debilitating disorder, is incompletely understood in terms of underpinning behavioural, psychological, and neural mechanisms. This is attributable to high symptomatic heterogeneity; cardinal features comprise obsessions and compulsions, including clinical subcategories. While obsessive and intrusive thoughts are arguably unique to humans, dysfunctional behaviours analogous to those seen in clinical OCD have been examined in nonhuman animals. Genetic, ethological, pharmacological, and neurobehavioural approaches all contribute to understanding the emergence and persistence of compulsive behaviour. One behaviour of particular interest is maladaptive checking, whereby human patients excessively perform checking rituals despite these serving no purpose. Dysfunctional and excessive checking is the most common symptom associated with OCD and can be readily operationalised in rodents. This review considers animal models of OCD, the neural circuitries associated with impairments in habit-based and goal-directed behaviour, and how these may link to the compulsions observed in OCD. We further review the Observing Response Task (ORT), an appetitive instrumental learning procedure that distinguishes between functional and dysfunctional checking, with translational application in humans and rodents. By shedding light on the psychological and neural bases of compulsive-like checking, the ORT has potential to offer translational insights into the underlying mechanisms of OCD, in addition to being a platform for testing psychological and neurochemical treatment approaches.

Striatal insights: a cellular and molecular perspective on repetitive behaviors in pathology

Animals often behave repetitively and predictably. These repetitive behaviors can have a component that is learned and ingrained as habits, which can be evolutionarily advantageous as they reduce cognitive load and the expenditure of attentional resources. Repetitive behaviors can also be conscious and deliberate, and may occur in the absence of habit formation, typically when they are a feature of normal development in children, or neuropsychiatric disorders. They can be considered pathological when they interfere with social relationships and daily activities. For instance, people affected by obsessive-compulsive disorder, autism spectrum disorder, Huntington's disease and Gilles de la Tourette syndrome can display a wide range of symptoms like compulsive, stereotyped and ritualistic behaviors. The striatum nucleus of the basal ganglia is proposed to act as a master regulator of these repetitive behaviors through its circuit connections with sensorimotor, associative, and limbic areas of the cortex. However, the precise mechanisms within the striatum, detailing its compartmental organization, cellular specificity, and the intricacies of its downstream connections, remain an area of active research. In this review, we summarize evidence across multiple scales, including circuit-level, cellular, and molecular dimensions, to elucidate the striatal mechanisms underpinning repetitive behaviors and offer perspectives on the implicated disorders. We consider the close relationship between behavioral output and transcriptional changes, and thereby structural and circuit alterations, including those occurring through epigenetic processes.

Serotonergic agonism and pharmacologically-induced adolescent stress cause operant-based learning deficits in mice

BACKGROUND

The interplay between environmental stress and genetic factors is thought to play an important role in the pathogenesis and maintenance of obsessive-compulsive disorder (OCD). However, the relative contribution of these causative antecedents in the manifestation of cognitive inflexibility-a phenotype often seen in obsessive-compulsive (OC)- spectrum disorders-is not fully understood.

METHOD

In this study, we treated mice with 50 mg/L corticosterone (CORT, a glucocorticoid stress hormone) in their drinking water during adolescence. In adulthood, we assessed anxiety-like behaviour and locomotor activity; along with operant-based discrimination and reversal learning. RU-24969, a selective serotonin receptor 5-HT1A/1B receptor agonist, was used as an acute pharmacological model of OC-like behaviour. RU-24969 (5 mg/kg) was administered prior to each reversal learning testing session.

RESULTS

We found that acute treatment with 5 mg/kg RU-24969 induced stereotyped hyperlocomotion in vehicle- and CORT-treated mice. Furthermore, pre-treatment with CORT in adolescence produced subtle anxiety-like behaviour in adult mice, and also resulted in an impairment to late-stage discrimination learning and alterations to reversal learning. Finally, acute treatment with 5 mg/kg RU-24969 caused an impairment to early-stage reversal learning.

CONCLUSION

Whilst we revealed dissociable detrimental effects of adolescent CORT treatment and acute 5-HT1A/1B receptor agonism on discrimination and reversal learning, respectively, we did not find evidence of additive deleterious effects of these two treatments. We therefore suggest that while disrupted serotonergic signalling is likely to be involved in the cognitive phenotype of OC-spectrum disorders, distinct neuropathological pathways may be at play in mediating the role of stress as an antecedent in OCD and related illnesses.

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.

Acute administration of the NMDA receptor antagonists ketamine and MK-801 reveals dysregulation of glutamatergic signalling and sensorimotor gating in the Sapap3 knockout mouse model of compulsive-like behaviour

Obsessive-compulsive disorder (OCD) is characterised by excessive intrusive thoughts that may cause an individual to engage in compulsive behaviours. Frontline pharmacological treatments (i.e., selective serotonin reuptake inhibitors (SSRIs)) leave approximately 40% of patients refractory to treatment. To investigate the possibility of novel pharmacological therapies for OCD, as well as the potential mechanisms underlying its pathology, we used the Sapap3 knockout (KO) mouse model of OCD, which exhibits increased anxiety and compulsive grooming behaviours. Firstly, we investigated whether administration of the NMDA receptor (NMDAR) antagonist ketamine (30 mg/kg), would reduce anxiety and grooming behaviour in Sapap3 KO mice. Anxiety-like behaviour was measured via time spent in the light component of the light-dark box test. Grooming behaviour was recorded and scored in freely moving mice. In line with previous works conducted in older animals (i.e. typically between 6 and 9 months of age), we confirmed here that Sapap3 KO mice exhibit an anxious, compulsive grooming, hypolocomotive and reduced body weight phenotype even at a younger age (i.e., 2-3 months of age). However, we found that acute administration of ketamine did not cause a reduction in anxiety or grooming behaviour. We then investigated in vivo glutamatergic function via the administration of a different NMDAR antagonist, MK-801 (0.25 mg/kg), prior to locomotion and prepulse inhibition assays. We found evidence of altered functional NMDAR activity, as well as sexually dimorphic prepulse inhibition, a measure of sensorimotor gating, in Sapap3 KO mice. These results are suggestive of in vivo glutamatergic dysfunction and their functional consequences, enabling future research to further investigate novel treatments for OCD.

Intersectin deficiency impairs cortico-striatal neurotransmission and causes obsessive-compulsive behaviors in mice

The generation of appropriate behavioral responses involves dedicated neuronal circuits. The cortico-striatal-thalamo-cortical loop is especially important for the expression of motor routines and habits. Defects in this circuitry are closely linked to obsessive stereotypic behaviors, hallmarks of neuropsychiatric diseases including autism spectrum disorders (ASDs) and obsessive-compulsive disorders (OCDs). However, our knowledge of the essential synaptic machinery required to maintain balanced neurotransmission and plasticity within the cortico-striatal circuitry remains fragmentary. Mutations in the large synaptic scaffold protein intersectin1 (ITSN1) have been identified in patients presenting with ASD symptoms including stereotypic behaviors, although a causal relationship between stereotypic behavior and intersectin function has not been established. We report here that deletion of the two closely related proteins ITSN1 and ITSN2 leads to severe ASD/OCD-like behavioral alterations and defective cortico-striatal neurotransmission in knockout (KO) mice. Cortico-striatal function was compromised at multiple levels in ITSN1/2-depleted animals. Morphological analyses showed that the striatum of intersectin KO mice is decreased in size. Striatal neurons exhibit reduced complexity and an underdeveloped dendritic spine architecture. These morphological abnormalities correlate with defects in cortico-striatal neurotransmission and plasticity as well as reduced N-methyl-D-aspartate (NMDA) receptor currents as a consequence of postsynaptic NMDA receptor depletion. Our findings unravel a physiological role of intersectin in cortico-striatal neurotransmission to counteract ASD/OCD. Moreover, we delineate a molecular pathomechanism for the neuropsychiatric symptoms of patients carrying intersectin mutations that correlates with the observation that NMDA receptor dysfunction is a recurrent feature in the development of ASD/OCD-like symptoms.

Obsessive-compulsive disorder: Etiology, neuropathology, and cognitive dysfunction

BACKGROUND

This review provides an overview of obsessive-compulsive disorder (OCD) symptoms, including the four partially distinct subtypes of the disorder, current diagnostic criteria, and common comorbidities. Critically, it focuses on the etiology of OCD, including its underlying neuropathology, and examines cognitive dysfunction in OCD.

METHODS

This review study was conducted by library method.

RESULTS

We show how dysfunction in cortico-striato-thalamo-cortical (CSTC) circuits may underpin symptoms; and shed light on the putative neurochemistry within these loops such as the role of serotonin, dopamine, and glutamate systems. We also show how OCD is characterized by cognitive dysfunction including problems in cognitive flexibility, visuospatial memory, response inhibition, and goal-directed behavior, linked to aberrant activity within CSTC circuits.

CONCLUSIONS

In brief, research questions we shed light on include (1) what are the symptoms in OCD; (2) what is the etiology of the disorder and do existing models explain OCD; and (3) what are key cognitive deficits in OCD and do these improve with treatment?

Memantine for Refractory Obsessive-Compulsive Disorder: Protocol for a Pragmatic, Double-blind, Randomized, Parallel-Group, Placebo-Controlled, Monocenter Trial

BACKGROUND

Obsessive-compulsive disorder (OCD) is a psychiatric syndrome characterized by unwanted and repetitive thoughts and repeated ritualistic compulsions for decreasing distress. Symptoms can cause severe distress and functional impairment. OCD affects 2% to 3% of the population and is ranked within the 10 leading neuropsychiatric causes of disability. Cortico-striatal-thalamo-cortical circuitry dysfunction has been implicated in OCD, including altered brain activation and connectivity. Complex glutamatergic signaling dysregulation within cortico-striatal circuitry has been proposed in OCD. Data obtained by several studies indicate reduced glutamatergic concentrations in the anterior cingulate cortex, combined with overactive glutamatergic signaling in the striatum and orbitofrontal cortex. A growing number of randomized controlled trials have assessed the utility of different glutamate-modulating drugs as augmentation medications or monotherapies for OCD, including refractory OCD. However, there are relevant variations among studies in terms of patients' treatment resistance, comorbidity, age, and gender. At present, 4 randomized controlled trials are available on the efficacy of memantine as an augmentation medication for refractory OCD.

OBJECTIVE

Our study's main purpose is to conduct a double-blind, randomized, parallel-group, placebo-controlled, monocenter trial to assess the efficacy and safety of memantine as an augmentative agent to a selective serotonin reuptake inhibitor in the treatment of moderate to severe OCD. The study's second aim is to evaluate the effect of memantine on cognitive functions in patients with OCD. The third aim is to investigate if responses to memantine are modulated by variables such as gender, symptom subtypes, and the duration of untreated illness.

METHODS

Investigators intend to conduct a double-blind, randomized, parallel-group, placebo-controlled, monocenter trial to assess the efficacy and safety of memantine as an augmentative agent to a selective serotonin reuptake inhibitor in the treatment of patients affected by severe refractory OCD. Participants will be rated via the Yale-Brown Obsessive Compulsive Scale at baseline and at 2, 4, 6, 8, 10, and 12 months. During the screening period and T4 and T6 follow-up visits, all participants will undergo an extensive neuropsychological evaluation. The 52-week study duration will consist of 4 distinct periods, including memantine titration and follow-up periods.

RESULTS

Recruitment has not yet started. The study will be conducted from June 2023 to December 2024. Results are expected to be available in January 2025. Throughout the slow-titration period, we will observe the minimum effective dose of memantine, and the follow-up procedure will detail its residual efficacy after drug withdrawal.

CONCLUSIONS

The innovation of this research proposal is not limited to the evaluation of the efficacy and safety of memantine as an augmentation medication for OCD. We will also test if memantine acts as a pure antiobsessive medication or if memantine's ability to improve concentration and attention mimics an antiobsessive effect.

TRIAL REGISTRATION

ClinicalTrials.gov NCT05015595; https://clinicaltrials.gov/ct2/show/NCT05015595.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

PRR1-10.2196/39223.

Striatal adenosine A2A receptor involvement in normal and large nest building deer mice: perspectives on compulsivity and anxiety

Obsessive-compulsive disorder (OCD) is characterized by recurring obsessive thoughts and repetitive behaviors that are often associated with anxiety and perturbations in cortico-striatal signaling. Given the suboptimal response of OCD to current serotonergic interventions, there is a need to better understand the psychobiological mechanisms that may underlie the disorder. In this regard, investigations into adenosinergic processes might be fruitful. Indeed, adenosine modulates both anxiety- and motor behavioral output. Thus, we aimed to explore the potential associations between compulsive-like large nest building (LNB) behavior in deer mice, anxiety and adenosinergic processes. From an initial pool of 120 adult deer mice, 34 normal nest building (NNB)- and 32 LNB-expressing mice of both sexes were selected and exposed to either a normal water (wCTRL) or vehicle control (vCTRL), lorazepam (LOR) or istradefylline (ISTRA) for 7- (LOR) or 28 days after which nesting assessment was repeated and animals screened for anxiety-like behavior in an anxiogenic open field. Mice were then euthanized, the striatal tissue removed on ice and the adenosine A_2A receptor expression quantified. Our findings indicate that NNB and LNB behavior are not distinctly associated with measures of generalized anxiety and that ISTRA-induced changes in nesting expression are dissociated from changes in anxiety scores. Further, data from this investigation show that nesting in deer mice is directly related to striatal adenosine signaling, and that LNB is founded upon a lower degree of adenosinergic A_2A stimulation.

Transcranial Magnetic Stimulation in Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) patients need novel therapeutic interventions since most experience residual symptoms despite treatment. Converging evidence suggest that OCD involves dysfunction of limbic cortico-striato-thalamo-cortical loops, including the medial prefrontal cortex (mPFC) and dorsal anterior cingulate cortex (dACC), that tends to normalize with successful treatment. Recently, three repetitive transcranial magnetic stimulation (rTMS) coils were FDA-cleared for treatment-refractory OCD. This review presents on-label and off-label clinical evidence and relevant physical characteristics of the three coils. The Deep TMS™ H7 Coil studies' point to efficacy of mPFC-dACC stimulation, while no clear target stems from the small heterogenous D-B80 and figure-8 coils studies.

The Sapap3-/- mouse reconsidered as a comorbid model expressing a spectrum of pathological repetitive behaviours

Symptom comorbidity is present amongst neuropsychiatric disorders with repetitive behaviours, complicating clinical diagnosis and impeding appropriate treatments. This is of particular importance for obsessive-compulsive disorder (OCD) and Tourette syndrome. Here, we meticulously analysed the behaviour of Sapap3 knockout mice, the recent rodent model predominantly used to study compulsive-like behaviours, and found that its behaviour is more complex than originally and persistently described. Indeed, we detected previously unreported elements of distinct pathologically repetitive behaviours, which do not form part of rodent syntactic cephalo-caudal self-grooming. These repetitive behaviours include sudden, rapid body and head/body twitches, resembling tic-like movements. We also observed that another type of repetitive behaviour, aberrant hindpaw scratching, might be responsible for the flagship-like skin lesions of this mouse model. In order to characterise the symptomatological nature of observed repetitive behaviours, we pharmacologically challenged these phenotypes by systemic aripiprazole administration, a first-line treatment for tic-like symptoms in Tourette syndrome and trichotillomania. A single treatment of aripiprazole significantly reduced the number of head/body twitches, scratching, and single-phase grooming, but not syntactic grooming events. These observations are in line with the high comorbidity of tic- and compulsive-like symptoms in Tourette, OCD and trichotillomania patients.

Disruption of Astrocyte-Dependent Dopamine Control in the Developing Medial Prefrontal Cortex Leads to Excessive Grooming in Mice

BACKGROUND

Astrocytes control synaptic activity by modulating perisynaptic concentrations of ions and neurotransmitters including dopamine (DA) and, as such, could be involved in the modulating aspects of mammalian behavior.

METHODS

We produced a conditional deletion of the vesicular monoamine transporter 2 (VMAT2) specifically in astrocytes (aVMTA2cKO mice) and studied the effects of the lack of VMAT2 in prefrontal cortex (PFC) astrocytes on the regulation of DA levels, PFC circuit functions, and behavioral processes.

RESULTS

We found a significant reduction of medial PFC (mPFC) DA levels and excessive grooming and compulsive repetitive behaviors in aVMAT2cKO mice. The mice also developed a synaptic pathology, expressed through increased relative AMPA versus NMDA receptor currents in synapses of the dorsal striatum receiving inputs from the mPFC. Importantly, behavioral and synaptic phenotypes were rescued by re-expression of mPFC VMAT2 and L-DOPA treatment, showing that the deficits were driven by mPFC astrocytes that are critically involved in developmental DA homeostasis. By analyzing human tissue samples, we found that VMAT2 is expressed in human PFC astrocytes, corroborating the potential translational relevance of our observations in mice.

CONCLUSIONS

Our study shows that impairment of the astrocytic control of DA in the mPFC leads to symptoms resembling obsessive-compulsive spectrum disorders such as trichotillomania and has a profound impact on circuit function and behaviors.

Fentanyl-induced changes in brain activity in awake nonhuman primates at 9.4 Tesla

Functional magnetic resonance imaging (fMRI) has been used to study the influence of opioids on neural circuitry implicated in opioid use disorder, such as the cortico-striatal-thalamo-cortical (CSTC) circuit. Given the increase in fentanyl-related deaths, this study was conducted to characterize the effects of fentanyl on patterns of brain activation in awake nonhuman primates. Four squirrel monkeys were acclimated to awake scanning procedures conducted at 9.4 Tesla. Subsequently, test sessions were conducted in which a dose of fentanyl that reliably maintains intravenous (IV) self-administration behavior in monkeys, 1 μg/kg, was administered and the effects on patterns of brain activity were assessed using: (1) a pharmacological regressor to elucidate fentanyl-induced patterns of neural activity, and (2) seed-based approaches targeting bilateral anterior cingulate, thalamus, or nucleus accumbens (NAc) to determine alterations in CSTC functional connectivity. Results showed a functional inhibition of BOLD signal in brain regions that mediate behavioral effects of opioid agonists, such as cingulate cortex, striatum and midbrain. Functional connectivity between each of the seed regions and areas involved in motoric, sensory and cognition-related behavior generally decreased. In contrast, NAc functional connectivity with other striatal regions increased. These results indicate that fentanyl produces changes within CSTC circuitry that may reflect key features of opioid use disorder (e.g. persistent drug-taking/seeking) and thereby contribute to long-term disruptions in behavior and addiction. They also indicate that fMRI in alert nonhuman primates can detect drug-induced changes in neural circuits and, in turn, may be useful for investigating the effectiveness of medications to reverse drug-induced dysregulation.

Genetics and neurobiology of eating disorders

Eating disorders (anorexia nervosa, bulimia nervosa and binge-eating disorder) are a heterogeneous class of complex illnesses marked by weight and appetite dysregulation coupled with distinctive behavioral and psychological features. Our understanding of their genetics and neurobiology is evolving thanks to global cooperation on genome-wide association studies, neuroimaging, and animal models. Until now, however, these approaches have advanced the field in parallel, with inadequate cross-talk. This review covers overlapping advances in these key domains and encourages greater integration of hypotheses and findings to create a more unified science of eating disorders. We highlight ongoing and future work designed to identify implicated biological pathways that will inform staging models based on biology as well as targeted prevention and tailored intervention, and will galvanize interest in the development of pharmacologic agents that target the core biology of the illnesses, for which we currently have few effective pharmacotherapeutics.

Neurobiological outcomes of cognitive behavioral therapy for obsessive-compulsive disorder: A systematic review

INTRODUCTION

Obsessive-compulsive disorder (OCD) is characterized by recurrent distressing thoughts and repetitive behaviors, or mental rituals performed to reduce anxiety. Recent neurobiological techniques have been particularly convincing in suggesting that cortico-striatal-thalamic-cortico (CSTC) circuits, including orbitofrontal cortex (OFC) and striatum regions (caudate nucleus and putamen), are responsible for mediation of OCD symptoms. However, it is still unclear how these regions are affected by OCD treatments in adult patients. To address this yet open question, we conducted a systematic review of all studies examining neurobiological changes before and after first-line psychological OCD treatment, i.e., cognitive-behavioral therapy (CBT).

METHODS

Studies were included if they were conducted in adults with OCD and they assessed the neurobiological effects of CBT before and after treatment. Two databases were searched: PsycINFO and PubMed for the time frame up to May 2022.

RESULTS

We obtained 26 pre-post CBT treatment studies performed using different neurobiological techniques, namely functional magnetic resonance imaging (fMRI), Positron emission tomography (PET), regional cerebral blood flow (rCBF), 5-HT concentration, magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), Electroencephalography (EEG). Neurobiological data show the following after CBT intervention: (i) reduced activations in OFC across fMRI, EEG, and rCBF; (ii) decreased activity in striatum regions across fMRI, rCBF, PET, and MRI; (iii) increased activations in cerebellum (CER) across fMRI and MRI; (iv) enhanced neurochemical concentrations in MRS studies in OFC, anterior cingulate cortex (ACC) and striatum regions. Most of these neurobiological changes are also accompanied by an improvement in symptom severity as assessed by a reduction in the Y-BOCS scores.

CONCLUSION

Cognitive-behavioral therapy seems to be able to restructure, modify, and transform the neurobiological component of OCD, in addition to the clinical symptoms. Nevertheless, further studies are necessary to frame the OCD spectrum in a dimensional way.

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.

Changes of Serum Homocysteine and Vitamin B12, but Not Folate Are Correlated With Obsessive-Compulsive Disorder: A Systematic Review and Meta-Analysis of Case-Control Studies

BACKGROUND

Obsessive-compulsive disorder (OCD) a complex neuropsychiatric disorder, is characterized by irresistible obsessive thinking and compulsive behavior. Folate is a member of water-soluble vitamins in the human body and sustains many normal daily activities (e.g., exercise, sleep, and memory). Homocysteine, a sulfur-containing non-essential amino acid, has been investigated in numerous psychiatric disorders (e.g., OCD). Vitamin B12 is a type of complex organic compound with cobalt contained. Moreover, vitamin B12 and folate deficiency and high levels of homocysteine were found to have an effect on brain functions and also lead to non-specific psychiatric symptoms.

OBJECTIVES

This study aimed to confirm the epidemiological evidence of OCD and investigate whether vitamin B12, folate, and homocysteine have an effect on the etiology of OCD.

METHODS

A systematic search was conducted on eight databases (i.e., PubMed, Embase, Web of Science, the Cochrane Library, China Biology Medicine disc, China National Knowledge Infrastructure, Wanfang Database, China Science and Technology Journal Database), and the retrieval time was up to March 2021. The available articles involving patients with OCD with/without abnormal serum levels of vitamin B12, folate, and homocysteine were comprehensively reviewed and analyzed.

RESULTS

A total of 5 studies involving 309 patients were included in this meta-analysis, including 172 cases in the experimental group and 137 in the control group. The content of folate in the OCD group was not significantly different from that in the control group (SMD = -0.089, 95%CI -0.755 to 0.577, p = 0.794). And serum homocysteine was significantly higher in the patients with OCD (SMD = 1.132, 95%CI 0.486 to 1.778, p = 0.001). Vitamin B12 was significantly lower in patients with OCD (SMD = -0.583, 95%CI -0.938 to -0.229, p = 0.001).

CONCLUSIONS

This meta-analysis shows serum high levels of homocysteine, low levels of vitamin B12, and normal folate level are closely correlated with OCD. However, high-quality case-control studies should be further conducted to explore the correlation between serum levels of vitamin B12, folate, homocysteine, and OCD.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021262161; PROSPERO (Number CRD#42021262161).

The prefrontal cortex and neurosurgical treatment for intractable OCD

Over the past two decades, circuit-based neurosurgical procedures have gained increasing acceptance as a safe and efficacious approach to the treatment of the intractable obsessive-compulsive disorder (OCD). Lesions and deep brain stimulation (DBS) of the longitudinal corticofugal white matter tracts connecting the prefrontal cortex with the striatum, thalamus, subthalamic nucleus (STN), and brainstem implicate orbitofrontal, medial prefrontal, frontopolar, and ventrolateral cortical networks in the symptoms underlying OCD. The highly parallel distributed nature of these networks may explain the relative lack of adverse effects observed following surgery. Additional pre-post studies of cognitive tasks in more surgical patients are needed to confirm the role of these networks in OCD and to define therapeutic responses to surgical intervention.

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.

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.

Therapeutic Potentials of Ketamine and Esketamine in Obsessive-Compulsive Disorder (OCD), Substance Use Disorders (SUD) and Eating Disorders (ED): A Review of the Current Literature

The obsessive–compulsive spectrum refers to disorders drawn from several diagnostic categories that share core features related to obsessive–compulsive disorder (OCD), such as obsessive thoughts, compulsive behaviors and anxiety. Disorders that include these features can be grouped according to the focus of the symptoms, e.g., bodily preoccupation (i.e., eating disorders, ED) or impulse control (i.e., substance use disorders, SUD), and they exhibit intriguing similarities in phenomenology, etiology, pathophysiology, patient characteristics and clinical outcomes. The non-competitive N-methyl-D-aspartate receptor (NMDAr) antagonist ketamine has been indicated to produce remarkable results in patients with treatment-resistant depression, post-traumatic stress disorder and OCD in dozens of small studies accrued over the past decade, and it appears to be promising in the treatment of SUD and ED. However, despite many small studies, solid evidence for the benefits of its use in the treatment of OCD spectrum and addiction is still lacking. Thus, the aim of this perspective article is to examine the potential for ketamine and esketamine in treating OCD, ED and SUD, which all involve recurring and intrusive thoughts and generate associated compulsive behavior. A comprehensive and updated overview of the literature regarding the pharmacological mechanisms of action of both ketamine and esketamine, as well as their therapeutic advantages over current treatments, are provided in this paper. An electronic search was performed, including all papers published up to April 2021, using the following keywords (“ketamine” or “esketamine”) AND (“obsessive” OR “compulsive” OR “OCD” OR “SUD” OR “substance use disorder” OR “addiction” OR “craving” OR “eating” OR “anorexia”) NOT review NOT animal NOT “in vitro”, on the PubMed, Cochrane Library and Web of Science online databases. The review was conducted in accordance with preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. The use and efficacy of ketamine in SUD, ED and OCD is supported by glutamatergic neurotransmission dysregulation, which plays an important role in these conditions. Ketamine’s use is increasing, and preliminary data are optimistic. Further studies are needed in order to better clarify the many unknowns related to the use of both ketamine and esketamine in SUD, ED and OCD, and to understand their long-term effectiveness.

Involvement of GABAA Receptors in the Anxiolytic-Like Effect of Hydroxycitronellal

Hydroxycitronellal (HC) is a monoterpene present in essential oils of aromatic plants of different species, obtained from semisynthesis of citronellal, and is widely used as a fragrance in cosmetics. The objective of this work was to evaluate the possible anxiolytic-like activity of HC and its possible mechanism of action using in vivo and in silico methodologies. Swiss male mice (Mus musculus) were treated with HC (12.5, 25, and 50 mg/kg, i.p.) and subjected to the rota rod, elevated plus maze, and open field tests. No significant impairments were observed in the rota rod tests for the motor activity of the animals treated with HC at 12.5, 25, and 50 mg/kg, i.p., indicating no myo-relaxing or sedative effects. In the elevated plus maze, HC (in the three doses) induced significant increases in the percentage of entries (respectively, 34.8%, 33.8%, and 38.6%) and in the length of stay (respectively, 49.9%, 56.1%, and 57.0%) in the open arms of the EPM, as well as the number of crossings in the open field tests. The mechanism of action of the compound's anxiolytic-like activity can be attributed to the involvement of GABA_A receptors, and this interaction was observed in in vivo and in silico studies. For HC, the results suggest anxiolytic-like effects, possibly via modulation of the GABAergic system. The use of natural products to treat anxiety can become an alternative to existing synthetic products.

Gray Matter Abnormalities of Orbitofrontal Cortex and Striatum in Drug-Naïve Adult Patients With Obsessive-Compulsive Disorder

Objective: This study examined whether obsessive-compulsive disorder (OCD) patients have gray matter abnormalities in regions related to executive function, and whether such abnormalities are associated with impaired executive function. Methods: Multiple scales were administered to 27 first-episode drug-naïve OCD patients and 29 healthy controls. Comprehensive brain morphometric indicators of orbitofrontal cortex (OFC) and three striatum areas (caudate, putamen, and pallidum) were determined. Hemisphere lateralization index was calculated for each region of interest. Correlations between lateralization index and psychological variables were examined in OCD group. Results: The OCD group had greater local gyrification index for the right OFC and greater gray matter volumes of the bilateral putamen and left pallidum than healthy controls. They also had weaker left hemisphere superiority for local gyrification index of the OFC and gray matter volume of the putamen, but stronger left hemisphere superiority for gray matter volume of the pallidum. Patients' lateralization index for local gyrification index of the OFC correlated negatively with Yale-Brown Obsessive Compulsive Scale and Dysexecutive Questionnaire scores, respectively. Conclusion: Structural abnormalities of the bilateral putamen, left pallidum, and right OFC may underlie OCD pathology. Abnormal lateralization in OCD may contribute to the onset of obsessive-compulsive symptoms and impaired executive function.

Lost in translation: no effect of repeated optogenetic cortico-striatal stimulation on compulsivity in rats

The orbitofrontal cortex-ventromedial striatum (OFC-VMS) circuitry is widely believed to drive compulsive behavior. Hyperactivating this pathway in inbred mice produces excessive and persistent self-grooming, which has been considered a model for human compulsivity. We aimed to replicate these findings in outbred rats, where there are few reliable compulsivity models. Male Long-Evans rats implanted with optical fibers into VMS and with opsins delivered into OFC received optical stimulation at parameters that produce OFC-VMS plasticity and compulsive grooming in mice. We then evaluated rats for compulsive self-grooming at six timepoints: before, during, immediately after, and 1 h after each stimulation, 1 and 2 weeks after the ending of a 6-day stimulation protocol. To further test for effects of OFC-VMS hyperstimulation, we ran animals in three standard compulsivity assays: marble burying, nestlet shredding, and operant attentional set-shifting. OFC-VMS stimulation did not increase self-grooming or induce significant changes in nestlet shredding, marble burying, or set-shifting in rats. Follow-on evoked potential studies verified that the stimulation protocol altered OFC-VMS synaptic weighting. In sum, although we induced physiological changes in the OFC-VMS circuitry, we could not reproduce in a strongly powered study in rats a model of compulsive behavior previously reported in mice. This suggests possible limitations to translation of mouse findings to species higher on the phylogenetic chain.

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.

Stimulant use in patients presenting with psychocutaneous disorders

BACKGROUND

Psychocutaneous disorders are often attributed to stimulant medications, yet this relationship has never been fully elucidated. Literature on psychocutaneous disorders largely focuses on clinical presentation and treatment rather than disease etiology or exacerbation.

OBJECTIVE

To determine whether patients presenting with psychocutaneous disorders display high rates of stimulant use and psychiatric comorbidity.

METHODS

We undertook a retrospective cohort study of patients with psychocutaneous disorders presenting to a single center. It was hypothesized that these patients would have high rates of stimulant use and psychiatric comorbidity. Following analysis of baseline demographics, the patients were assigned to 1 of 2 groups: those with a psychotic disorder and those with a neurotic disorder.

RESULTS

Sixty percent of the patients (n = 317) with psychocutaneous disease had recently used a stimulant and more than 80% (270 of 317) carried an additional psychiatric diagnosis. The neurotic disorder group (n = 237) was younger and had higher rates of stimulant use. The psychotic disorder group (n = 80) had higher rates of psychosis, medical comorbidity, and illicit stimulant drug use.

LIMITATIONS

The predominantly Caucasian population may limit generalizability of findings as may the retrospective nature.

CONCLUSIONS

Patients with psychocutaneous disease have high rates of stimulant use and most have at least 1 psychiatric comorbidity.

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.

Harmonizing the Neurobiology and Treatment of Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a common, chronic, and oftentimes disabling disorder. The only established first-line treatments for OCD are exposure and response prevention, and serotonin reuptake inhibitor medications (SRIs). However, a subset of patients fails to respond to either modality, and few experience complete remission. Beyond SRI monotherapy, antipsychotic augmentation is the only medication approach for OCD with substantial empirical support. Our incomplete understanding of the neurobiology of OCD has hampered efforts to develop new treatments or enhance extant interventions. This review focuses on several promising areas of research that may help elucidate the pathophysiology of OCD and advance treatment. Multiple studies support a significant genetic contribution to OCD, but pinpointing the specific genetic determinants requires additional investigation. The preferential efficacy of SRIs in OCD has neither led to discovery of serotonergic abnormalities in OCD nor to development of new serotonergic medications for OCD. Several lines of preclinical and clinical evidence suggest dysfunction of the glutamatergic system in OCD, prompting testing of several promising glutamate modulating agents. Functional imaging studies in OCD show consistent evidence for increased activity in brain regions that form a cortico-striato-thalamo-cortical (CSTC) loop. Neuromodulation treatments with either noninvasive devices (e.g., transcranial magnetic stimulation) or invasive procedures (e.g., deep brain stimulation) provide further support for the CSTC model of OCD. A common substrate for various interventions (whether drug, behavioral, or device) may be modulation (at different nodes or connections) of the CSTC circuit that mediates the symptoms of OCD.

Invasive and Non-invasive Neurostimulation for OCD

It becomes increasingly clear that (non-)invasive neurostimulation is an effective treatment for obsessive-compulsive disorder (OCD). In this chapter we review the available evidence on techniques and targets, clinical results including a meta-analysis, mechanisms of action, and animal research. We focus on deep brain stimulation (DBS), but also cover non-invasive neurostimulation including transcranial magnetic stimulation (TMS). Data shows that most DBS studies target the ventral capsule/ventral striatum (VC/VS), with an overall 76% response rate in treatment-refractory OCD. Also TMS holds clinical promise. Increased insight in the normalizing effects of neurostimulation on cortico-striatal-thalamic-cortical (CSTC) loops - through neuroimaging and animal research - provides novel opportunities to further optimize treatment strategies. Advancing clinical implementation of neurostimulation techniques is essential to ameliorate the lives of the many treatment-refractory OCD patients.

Deep Brain Stimulation for Alzheimer's Disease: Tackling Circuit Dysfunction

OBJECTIVES

Treatments for Alzheimer's disease are urgently needed given its enormous human and economic costs and disappointing results of clinical trials targeting the primary amyloid and tau pathology. On the other hand, deep brain stimulation (DBS) has demonstrated success in other neurological and psychiatric disorders leading to great interest in DBS as a treatment for Alzheimer's disease.

MATERIALS AND METHODS

We review the literature on 1) circuit dysfunction in Alzheimer's disease and 2) DBS for Alzheimer's disease. Human and animal studies are reviewed individually.

RESULTS

There is accumulating evidence of neural circuit dysfunction at the structural, functional, electrophysiological, and neurotransmitter level. Recent evidence from humans and animals indicate that DBS has the potential to restore circuit dysfunction in Alzheimer's disease, similarly to other movement and psychiatric disorders, and may even slow or reverse the underlying disease pathophysiology.

CONCLUSIONS

DBS is an intriguing potential treatment for Alzheimer's disease, targeting circuit dysfunction as a novel therapeutic target. However, further exploration of the basic disease pathology and underlying mechanisms of DBS is necessary to better understand how circuit dysfunction can be restored. Additionally, robust clinical data in the form of ongoing phase III clinical trials are needed to validate the efficacy of DBS as a viable treatment.

Sapap3 deletion causes dynamic synaptic density abnormalities: a longitudinal [11C]UCB-J PET study in a model of obsessive-compulsive disorder-like behaviour

Background

Currently, the evidence on synaptic abnormalities in neuropsychiatric disorders—including obsessive–compulsive disorder (OCD)—is emerging. The newly established positron emission tomography (PET) ligand ((R)-1-((3-((11)C-methyl-(11)C)pyridin-4-yl)methyl)-4-(3,4,5-trifluorophenyl)pyrrolidin-2-one) ([¹¹C]UCB-J) provides the opportunity to visualize synaptic density changes in vivo, by targeting the synaptic vesicle protein 2A (SV2A). Here, we aim to evaluate such alterations in the brain of the SAP90/PSD-95-associated protein 3 (Sapap3) knockout (ko) mouse model, showing an abnormal corticostriatal neurotransmission resulting in OCD-like behaviour.

Methods

Longitudinal [¹¹C]UCB-J µPET/CT scans were acquired in Sapap3 ko and wildtype (wt) control mice (n = 9/group) to study SV2A availability. Based on the Logan reference method, we calculated the volume of distribution (V_T(IDIF)) for [¹¹C]UCB-J. Both cross-sectional (wt vs. ko) and longitudinal (3 vs. 9 months) volume-of-interest-based statistical analysis and voxel-based statistical parametric mapping were performed. Both [¹¹C]UCB-J ex vivo autoradiography and [³H]UCB-J in vitro autoradiography were used for the validation of the µPET data.

Results

At the age of 3 months, Sapap3 ko mice are already characterized by a significantly lower SV2A availability compared to wt littermates (i.a. cortex − 12.69%, p < 0.01; striatum − 14.12%, p < 0.001, thalamus − 13.11%, p < 0.001, and hippocampus − 12.99%, p < 0.001). Healthy ageing in control mice was associated with a diffuse and significant (p < 0.001) decline throughout the brain, whereas in Sapap3 ko mice this decline was more confined to the corticostriatal level. A strong linear relationship (p < 0.0001) was established between the outcome parameters of [¹¹C]UCB-J µPET and [¹¹C]UCB-J ex vivo autoradiography, while such relationship was absent for [³H]UCB-J in vitro autoradiography.

Conclusions

[¹¹C]UCB-J PET is a potential marker for synaptic density deficits in the Sapap3 ko mouse model for OCD, parallel to disease progression. Our data suggest that [¹¹C]UCB-J ex vivo autoradiography is a suitable proxy for [¹¹C]UCB-J PET data in mice.

Shank3 mutation in a mouse model of autism leads to changes in the S-nitroso-proteome and affects key proteins involved in vesicle release and synaptic function

Mutation in the SHANK3 human gene leads to different neuropsychiatric diseases including Autism Spectrum Disorder (ASD), intellectual disabilities and Phelan-McDermid syndrome. Shank3 disruption in mice leads to dysfunction of synaptic transmission, behavior, and development. Protein S-nitrosylation, the nitric oxide (NO^•)-mediated posttranslational modification (PTM) of cysteine thiols (SNO), modulates the activity of proteins that regulate key signaling pathways. We tested the hypothesis that Shank3 mutation would generate downstream effects on PTM of critical proteins that lead to modification of synaptic functions. SNO-proteins in two ASD-related brain regions, cortex and striatum of young and adult InsG3680(+/+) mice (a human mutation-based Shank3 mouse model), were identified by an innovative mass spectrometric method, SNOTRAP. We found changes of the SNO-proteome in the mutant compared to WT in both ages. Pathway analysis showed enrichment of processes affected in ASD. SNO-Calcineurin in mutant led to a significant increase of phosphorylated Synapsin1 and CREB, which affect synaptic vesicle mobilization and gene transcription, respectively. A significant increase of 3-nitrotyrosine was found in the cortical regions of the adult mutant, signaling both oxidative and nitrosative stress. Neuronal NO^• Synthase (nNOS) was examined for levels and localization in neurons and no significant difference was found in WT vs. mutant. S-nitrosoglutathione concentrations were higher in mutant mice compared to WT. This is the first study on NO^•-related molecular changes and SNO-signaling in the brain of an ASD mouse model that allows the characterization and identification of key proteins, cellular pathways, and neurobiological mechanisms that might be affected in ASD.

Central norepinephrine transmission is required for stress-induced repetitive behavior in two rodent models of obsessive-compulsive disorder

RATIONALE

Obsessive-compulsive disorder (OCD) is characterized by repetitive behaviors exacerbated by stress. Many OCD patients do not respond to available pharmacotherapies, but neurosurgical ablation of the anterior cingulate cortex (ACC) can provide symptomatic relief. Although the ACC receives noradrenergic innervation and expresses adrenergic receptors (ARs), the involvement of norepinephrine (NE) in OCD has not been investigated.

OBJECTIVE

To determine the effects of genetic or pharmacological disruption of NE neurotransmission on marble burying (MB) and nestlet shredding (NS), two animal models of OCD.

METHODS

We assessed NE-deficient (Dbh -/-) mice and NE-competent (Dbh +/-) controls in MB and NS tasks. We also measured the effects of anti-adrenergic drugs on NS and MB in control mice and the effects of pharmacological restoration of central NE in Dbh -/- mice. Finally, we compared c-fos induction in the locus coeruleus (LC) and ACC of Dbh -/- and control mice following both tasks.

RESULTS

Dbh -/- mice virtually lacked MB and NS behaviors seen in control mice but did not differ in the elevated zero maze (EZM) model of general anxiety-like behavior. Pharmacological restoration of central NE synthesis in Dbh -/- mice completely rescued NS behavior, while NS and MB were suppressed in control mice by anti-adrenergic drugs. Expression of c-fos in the ACC was attenuated in Dbh -/- mice after MB and NS.

CONCLUSION

These findings support a role for NE transmission to the ACC in the expression of stress-induced compulsive behaviors and suggest further evaluation of anti-adrenergic drugs for OCD is warranted.

Progression of obsessive compulsive disorder-like grooming in Sapap3 knockout mice: A longitudinal [11C]ABP688 PET study

We aimed to evaluate [3-(6-methyl-pyridin-2-ylethynyl)-cyclohex-2-enone-0-¹¹C-methyloxime] ([¹¹C]ABP688) small animal positron emission tomography (μPET) as a biomarker to visualize possible longitudinal changes in metabotropic glutamate receptor 5 (mGluR5) availability in the brain of SAP90/PSD-95 associated protein 3 (Sapap3) knockout (ko) mice, showing obsessive compulsive disorder (OCD)-like behavior.

METHODS

Alongside the assessment of grooming, we performed [¹¹C]ABP688 μPET/CT imaging in wildtype (wt; n=10) and ko (n=11) mice both at 3 and 9 months. Using the simplified reference tissue method (SRTM), the nondisplaceable binding potential (BP_ND) was calculated representing the in vivo availability of the metabotropic glutamate receptor 5 (mGluR5) in the brain with the cerebellum as a reference region. Longitudinal voxel-based statistical parametric mapping (SPM) was performed on BP_ND images. Results were verified using [¹¹C]ABP688 ex vivo autoradiography, [³H]ABP688 in vitro autoradiography, and mGluR5 immunohistochemistry.

RESULTS

Cross-sectional comparisons revealed significantly increased grooming parameters in ko animals, at both time points. A significant longitudinal increase in % grooming duration (+268.25%; p<0.05) reflected aggravation of this behavior in ko mice. [¹¹C]ABP688 μPET revealed significantly lower mGluR5 availability in the cortex, striatum, hippocampus, and amygdala of ko mice at both ages. A significant longitudinal BP_ND decline was present for ko mice (p<0.01: cortex -17.14%, striatum -19.82%, amygdala -23.57%; p<0.05: hippocampus -15.53%), which was confirmed by SPM (p<0.01).

CONCLUSION

Sapap3 ko mice show a decline in mGluR5 availability in OCD relevant brain regions parallel to the worsening of OCD-like behavior. This demonstrates a potential role for [¹¹C]ABP688 PET as a biomarker to monitor disease progression in vivo.

Use of EEG for Predicting Treatment Response to Transcranial Magnetic Stimulation in Obsessive Compulsive Disorder

Aim. In this study we assessed the predictive power of quantitative EEG (qEEG) for the treatment response to right frontal transcranial magnetic stimulation (TMS) in obsessive compulsive disorder (OCD) using a machine learning approach. Method. The study included 50 OCD patients (35 responsive to TMS, 15 nonresponsive) who were treated with right frontal low frequency stimulation and identified retrospectively from Uskudar Unversity, NPIstanbul Brain Hospital outpatient clinic. All patients were diagnosed with OCD according to the DSM-IV-TR and DSM-5 criteria. We first extracted pretreatment band powers for patients. To explore the prediction accuracy of pretreatment EEG, we employed machine learning methods using an artificial neural network model. Results. Among 4 EEG bands, theta power successfully discriminated responsive from nonresponsive patients. Responsive patients had more theta powers for all electrodes as compared to nonresponsive patients. Discussion. qEEG could be helpful before deciding about treatment strategy in OCD. The limitations of our study are moderate sample size and limited number of nonresponsive patients and that treatment response was defined by clinicians and not by using a formal symptom measurement scale. Future studies with larger samples and prospective design would show the role of qEEG in predicting TMS response better.

Altered response to risky decisions and reward in patients with obsessive–compulsive disorder

BACKGROUND

Patients with obsessive–compulsive disorder (OCD) employ ritualistic behaviours to reduce or even neutralize the anxiety provoked by their obsessions. The presence of excessive rumination and indecision has motivated the view of OCD as a disorder of decision-making. Most studies have focused on the “cold,” cognitive aspects of decision-making. This study expands current understanding of OCD by characterizing the abnormalities associated with affective, or “hot” decision-making.

METHODS

We performed a functional MRI study in a sample of 34 patients with OCD and 33 sex- and age-matched healthy controls, during which participants made 2-choice gambles taking varying levels of risk.

RESULTS

During risky decisions, patients showed significantly reduced task-related activation in the posterior cingulum, lingual gyrus and anterior cingulate cortex. We identified significant group × risk interactions in the calcarine cortex, precuneus, amygdala and anterior cingulate cortex. During the outcome phase, patients with OCD showed stronger activation of the orbitofrontal cortex, anterior cingulate cortex and putamen in response to unexpected losses.

LIMITATIONS

The group of patients not receiving medication was very small (n = 5), which precluded us from assessing the effect of medication on risk-taking behaviour in these patients.

CONCLUSION

Obsessive–compulsive disorder is associated with abnormal brain activity patterns during risky decision-making in a set of brain regions that have been consistently implicated in the processing of reward prediction errors. Alterations in affective “hot” processes implicated in decision-making may contribute to increased indecisiveness and intolerance to uncertainty in patients with OCD.

How obsessive-compulsive and bipolar disorders meet each other? An integrative gene-based enrichment approach

BACKGROUND

The novel approaches to psychiatric classification assume that disorders, contrary to what was previously thought, are not completely separate phenomena. In this regard, in addition to symptom-based criteria, disturbances are also considered on the basis of lower level components. With this viewpoint, identifying common biochemical markers would be beneficial in adopting a comprehensive strategy for prevention, diagnosis and treatment.

MAIN BODY

One of the problematic areas in clinical settings is the coexistence of both obsessive-compulsive disorder (OCD) and bipolar disorder (BD) that is challenging and difficult to manage. In this study, using a system biologic approach we aimed to assess the interconnectedness of OCD and BD at different levels. Gene Set Enrichment Analysis (GSEA) method was used to identify the shared biological network between the two disorders. The results of the analysis revealed 34 common genes between the two disorders, the most important of which were CACNA1C, GRIA1, DRD2, NOS1, SLC18A1, HTR2A and DRD1. Dopaminergic synapse and cAMP signaling pathway as the pathways, dopamine binding and dopamine neurotransmitter receptor activity as the molecular functions, dendrite and axon part as the cellular component and cortex and striatum as the brain regions were the most significant commonalities.

SHORT CONCLUSION

The results of this study highlight the role of multiple systems, especially the dopaminergic system in linking OCD and BD. The results can be used to estimate the disease course, prognosis, and treatment choice, particularly in the cases of comorbidity. Such perspectives, going beyond symptomatic level, help to identify common endophenotypes between the disorders and provide diagnostic and therapeutic approaches based on biological in addition to the symptomatic level.

Factors associated with obsessive-compulsive symptoms in people with epilepsy

PURPOSE

Obsessive-compulsive disorder (OCD) is a common but underrecognized psychiatric condition comorbid with epilepsy. We thus investigated clinical factors associated with obsessive-compulsive symptoms (OCS) in adults with epilepsy.

METHODS

This was a cross-sectional multicenter study in Republic of Korea. Obsessive-compulsive symptoms were assessed using the Obsessive-Compulsive Inventory-Revised (OCI-R). Clinical factors that were assessed included age, sex, seizure-related variables, and the number and use of antiepileptic drugs (AEDs) prescribed. Data were analyzed by stepwise linear regression and adjusted according to anxiety and depressive symptoms as assessed by Hospital Anxiety Depression Scale (HADS).

RESULTS

The study population comprised 221 adults with epilepsy (42.1% male, 39.7 ± 11.9 years of age). The mean OCI-R score was 18.0 (standard deviation, 12.7), and an OCI-R score of ≥21 was obtained for 40.3% of the study sample. On a stepwise linear regression analysis, epilepsy severity, temporal lobe seizures, the use of topiramate, and the use of lamotrigine were identified as independent factors associated with OCI-R score after adjusting for anxiety according to the HADS. All factors except topiramate usage were positively associated with OCS. The total explained variance was 37.3%.

CONCLUSIONS

Obsessive-compulsive symptoms are common in persons with epilepsy and are associated with severe epilepsy, temporal lobe seizures, and the use of topiramate and lamotrigine. Specifically, the use of lamotrigine may aggravate OCS, whereas the use of topiramate may have beneficial effects on OCS.

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.

Behavioral flexibility in a mouse model for obsessive-compulsive disorder: Impaired Pavlovian reversal learning in SAPAP3 mutants

Obsessive-compulsive disorder (OCD) is characterized by obsessive thinking, compulsive behavior and anxiety, and is often accompanied by cognitive deficits. The neuropathology of OCD involves dysregulation of cortical-striatal circuits. Similar to OCD patients, SAPAP3 knockout mice 3 (SAPAP3-/- ) exhibit compulsive behavior (grooming), anxiety and dysregulated cortical-striatal function. However, it is unknown whether SAPAP3-/- display cognitive deficits and how these different behavioral traits relate to one another. SAPAP3-/- and wild-type (WT) littermates were trained in a Pavlovian conditioning task pairing visual cues with the delivery of sucrose solution. After mice learned to discriminate between a reward-predicting conditioned stimulus (CS+) and a non-reward stimulus (CS-), contingencies were reversed (CS+ became CS- and vice versa). Additionally, we assessed grooming, anxiety and general activity. SAPAP3-/- acquired Pavlovian approach behavior similarly to WT, albeit less vigorously and with a different strategy. However, unlike WT, SAPAP3-/- were unable to adapt their behavior after contingency reversal, exemplified by a lack of re-establishing CS+ approach behavior (sign tracking). Surprisingly, such behavioral inflexibility, decreased vigor, compulsive grooming and anxiety were unrelated. This study shows that SAPAP3-/- are capable of Pavlovian learning, but lack flexibility to adapt associated conditioned approach behavior. Thus, SAPAP3-/- not only display compulsive-like behavior and anxiety, but also cognitive deficits, confirming and extending the validity of SAPAP3-/- as a suitable model for the study of OCD. The observation that compulsive-like behavior, anxiety and behavioral inflexibility were unrelated suggests a non-causal relationship between these traits and may be of clinical relevance for the treatment of OCD.

The Effect of ASIC3 Knockout on Corticostriatal Circuit and Mouse Self-grooming Behavior

Stereotypic and/or repetitive behavior is one of the major symptoms of autism spectrum disorder (ASD). Increase of self-grooming behavior is a behavioral phenotype commonly observed in the mouse models for ASD. Previously, we have shown that knockout of acid-sensing ion channel 3 (ASIC3) led to the increased self-grooming behavior in resident-intruder test. Given the facts that ASIC3 is mainly expressed in the peripheral dorsal root ganglion (DRG) and conditional knockout of ASIC3 in the proprioceptors induced proprioception deficits. We speculate a hypothesis that stereotypic phenotype related to ASD, pararalled with striatal dysfunction, might be caused by proprioception defect in the peripheral sensory neuron origin. Herein, we investigate in depth whether and how ASIC3 is involved in the regulation of self-grooming behavior. First, we observed that Asic3 null mutant mice exhibited increased self-grooming in social interaction during juvenile stage. Similarly, they displayed increased self-grooming behavior in a novel cage in the absence of cagemate. To further understand the mechanism by which ASIC3 affects grooming behavior, we analyzed neurochemical, neuropathological and electrophysiological features in the dorsal striatum of Asic3 null mutant mice. Knockout of Asic3 increased dopamine (DA) activity and phospho-ERK immunoreactivities in the dorsal striatum. Furthermore, we detected a lower paired-pulse ratio (PPR) and impaired long-term potentiation (LTP) in corticostriatal circuits in Asic3 null mutant mice as compared with wild-type (WT) littermates. Moreover, knockout of Asic3 altered the medial spiny neurons in the striatum with defects in presynaptic function and decrease of dendritic spines. Lastly, genetic ablation of Asic3 specifically in parvalbumin-positive (PV+) cells resulted in the increase of self-grooming behavior in mice. These findings suggest knockout of Asic3 in the PV+ neurons alters grooming behavior by co-opting corticostriatal circuits.

Basolateral amygdala input to the medial prefrontal cortex controls obsessive-compulsive disorder-like checking behavior

Obsessive-compulsive disorder (OCD) affects ∼1 to 3% of the world's population. However, the neural mechanisms underlying the excessive checking symptoms in OCD are not fully understood. Using viral neuronal tracing in mice, we found that glutamatergic neurons from the basolateral amygdala (BLA^Glu) project onto both medial prefrontal cortex glutamate (mPFC^Glu) and GABA (mPFC^GABA) neurons that locally innervate mPFC^Glu neurons. Next, we developed an OCD checking mouse model with quinpirole-induced repetitive checking behaviors. This model demonstrated decreased glutamatergic mPFC microcircuit activity regulated by enhanced BLA^Glu inputs. Optical or chemogenetic manipulations of this maladaptive circuitry restored the behavioral response. These findings were verified in a mouse functional magnetic resonance imaging (fMRI) study, in which the BLA-mPFC functional connectivity was increased in OCD mice. Together, these findings define a unique BLA^Glu→mPFC^GABA→Glu circuit that controls the checking symptoms of OCD.

A high-refined carbohydrate diet facilitates compulsive-like behavior in mice through the nitric oxide pathway

Obesity is characterized by abnormal adipose tissue expansion and is associated with chronic inflammation. Obesity itself may induce several comorbidities, including psychiatric disorders. It has been previously demonstrated that proinflammatory cytokines are able to up-regulate inducible nitric oxide synthase (iNOS) and nitric oxide (NO) release, which both have a role in compulsive related behaviors.

OBJECTIVE

To evaluate whether acute or chronic consumption of a high-refined carbohydrate-containing (HC) diet will modify burying-behavior in the Marble Burying Test (MBT) through augmentation of NO signaling in the striatum, a brain region related to the reward system. Further, we also verified the effects of chronic consumption of a HC diet on the reinforcing effects induced by cocaine in the Conditioned Place Preference (CPP) test.

METHODS

Male BALB/c mice received a standard diet (control diet) or a HC diet for 3 days or 12 weeks.

RESULTS

An increase in burying behavior occurred in the MBT after chronic consumption of a HC diet that was associated with an increase of nitrite levels in the striatum. The pre-treatment with Aminoguanidine (50 mg/kg), a preferential inhibitor of iNOS, prevented such alterations. Additionally, a chronic HC diet also induced a higher expression of iNOS in this region and higher glutamate release from striatal synaptosomes. Neither statistical differences were observed in the expression levels of the neuronal isoform of NOS nor in microglia number and activation. Finally, the reinforcing effects induced by cocaine (15 mg/kg, i.p.) during the expression of the conditioned response in the CPP test were not different between the chronically HC diet fed mice and the control group. However, HC diet-feeding mice presented impairment of cocaine-preference extinction.

CONCLUSION

Altogether, our results suggest that the chronic consumption of a HC diet induces compulsive-like behavior through a mechanism possibly associated with NO activation in the striatum.

How can preclinical mouse models be used to gain insight into prefrontal cortex dysfunction in obsessive-compulsive disorder?

Obsessive-compulsive disorder is a debilitating psychiatric disorder that is characterised by perseverative thoughts and behaviours. Cognitive and affective disturbances play a central role in this illness, and it is therefore not surprising that clinical neuroimaging studies have demonstrated widespread alterations in prefrontal cortex functioning in patients. Preclinical mouse experimental systems provide the opportunity to gain mechanistic insight into the neurobiological changes underlying prefrontal cortex dysfunction through new technologies that allow measurement and manipulation of activity in discrete neural populations in awake, behaving mice. However, recent preclinical research has focused on striatal dysfunction, and has therefore provided relatively little insight regarding the role of the prefrontal cortex in obsessive-compulsive disorder–relevant behaviours. Here, we will discuss a number of translational prefrontal cortex–dependent paradigms, including obsessive-compulsive disorder–relevant tasks that produce compulsive responding, and how they can be leveraged in this context. Drawing on recent examples that have led to mechanistic insight about specific genes, cell types and circuits that mediate prefrontal cortex contributions to distinct aspects of cognition, we will provide a framework for applying similar strategies to identify neural mechanisms underlying obsessive-compulsive disorder–relevant behavioural domains. We propose that research using clinically relevant paradigms will accelerate translation of findings from preclinical mouse models, thus supporting the development of novel therapeutics targeted to specific pathophysiological mechanisms.