Hoxb8 is required for normal grooming behavior in mice

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.

The genetics of trichotillomania and excoriation disorder: A systematic review

BACKGROUND

Trichotillomania (TTM) and excoriation disorder (ED) are impairing obsessive-compulsive related disorders that are common in the general population and for which there are no clear first-line medications, highlighting the need to better understand the underlying biology of these disorders to inform treatments. Given the importance of genetics in obsessive-compulsive disorder (OCD), evaluating genetic factors underlying TTM and ED may advance knowledge about the pathophysiology of these body-focused repetitive behaviors.

AIM

In this systematic review, we summarize the available evidence on the genetics of TTM and ED and highlight gaps in the field warranting further research.

METHOD

We systematically searched Embase, PsycInfo, PubMed, Medline, Scopus, and Web of Science for original studies in genetic epidemiology (family or twin studies) and molecular genetics (candidate gene and genome-wide) published up to June 2023.

RESULTS

Of the 3536 records identified, 109 studies were included in this review. These studies indicated that genetic factors play an important role in the development of TTM and ED, some of which may be shared across the OCD spectrum, but there are no known high-confidence specific genetic risk factors for either TTM or ED.

CONCLUSIONS

Our review underscores the need for additional genome-wide research conducted on the genetics of TTM and ED, for instance, genome-wide association and whole-genome/whole-exome DNA sequencing studies. Recent advances in genomics have led to the discovery of risk genes in several psychiatric disorders, including related conditions such as OCD, but to date, TTM and ED have remained understudied.

Optogenetic stimulation of mouse Hoxb8 microglia in specific regions of the brain induces anxiety, grooming, or both

Previously, we have shown that either disruption of the Hoxb8 gene or ablation of a microglial subpopulation, Hoxb8 microglia, results in mice exhibiting both chronic anxiety and OCSD-like behavior, compulsive pathological hair pulling (trichotillomania), to the point of showing lesions at the sites of overgrooming. Herein we show, that optogenetic stimulation of Hoxb8 microglia in specific regions of the brain induces elevated anxiety, grooming or both. Optogenetic stimulation of Hoxb8 microglia within the dorsomedial striatum (DMS) or the medial prefrontal cortex (mPFC) induces grooming, whereas stimulation of Hoxb8 microglia in the basolateral amygdala (BLA) or central amygdala (CeA) produces elevated anxiety. Optogenetic stimulation of Hoxb8 microglia in the ventral CA1 region of the hippocampus (vCA1) induces both behaviors as well as freezing. In vitro we directly demonstrate that optogenetic stimulation of Hoxb8 microglia in specific regions of the brain activate neighboring neural activity through the induction of the c-fos-immediate early response. These experiments connect outputs from optogenetically stimulated Hoxb8 microglia, within specific regions of the brain, to the activation of neurons and neural circuits that in turn enable induction of these behaviors. These experiments suggest that Hoxb8 microglia are likely to be among, or the main, first responders to signals that evoke these behaviors. The same regions of the brain (DMS, mPFC, BLA, CeA and vCA1) have previously been defined at the neuronal level, by optogenetics, to control anxiety in mice. Intriguingly, the optogenetic experiments in microglia suggest that the two populations of microglia, canonical non-Hoxb8 and Hoxb8 microglia, function in opposition rather than in parallel to each other, providing a biological reason for the presence of two microglial subpopulations in mice.

From compulsivity to compulsion: the neural basis of compulsive disorders

Compulsive behaviour, an apparently irrational perseveration in often maladaptive acts, is a potential transdiagnostic symptom of several neuropsychiatric disorders, including obsessive-compulsive disorder and addiction, and may reflect the severe manifestation of a dimensional trait termed compulsivity. In this Review, we examine the psychological basis of compulsions and compulsivity and their underlying neural circuitry using evidence from human neuroimaging and animal models. Several main elements of this circuitry are identified, focused on fronto-striatal systems implicated in goal-directed behaviour and habits. These systems include the orbitofrontal, prefrontal, anterior cingulate and insular cortices and their connections with the basal ganglia as well as sensoriomotor and parietal cortices and cerebellum. We also consider the implications for future classification of impulsive-compulsive disorders and their treatment.

Programmed Grooming after 30 Years of Study: A Review of Evidence and Future Prospects

In 1992, an evolutionary model for the endogenous regulation of parasite-defense grooming was first proposed for African antelope by Ben and Lynette Hart. Known as the programmed grooming model, it hypothesized that a central control mechanism periodically evokes grooming so as to remove ectoparasites before they blood feed. The programmed grooming model contrasts with a stimulus-driven mechanism, in which grooming is stimulated by direct peripheral irritation from ectoparasite bites. In the 30+ years since the seminal 1992 paper, 26 studies have provided robust support for the programmed grooming model in ungulate hosts and ticks. In addition, multiple studies from unaffiliated investigators have evaluated the predictions of the model in different host systems (including rodents and primates) and in a variety of other ectoparasites (fleas, lice, and keds). I conducted a tricennial review of these studies to assess the current evidence and arrived at the following three conclusions: (1) tests of the programmed grooming predictions should use a similar methodology to the well-established protocol, so that the results are comparable and can be properly assessed; (2) the predictions used to test the model should be tailored to the biology of the host taxa under investigation; and (3) the predictions should likewise be tailored to the biology of the ectoparasites involved, bearing in mind that grooming has varying degrees of effectiveness, depending on the parasite. Further research is warranted to enhance our understanding of the role of grooming in maintaining the health of wild animals in the face of parasite attacks.

Persistent enhancement of basolateral amygdala-dorsomedial striatum synapses causes compulsive-like behaviors in mice

Compulsive behaviors are observed in a range of psychiatric disorders, however the neural substrates underlying the behaviors are not clearly defined. Here we show that the basolateral amygdala-dorsomedial striatum (BLA-DMS) circuit activation leads to the manifestation of compulsive-like behaviors. We revealed that the BLA neurons projecting to the DMS, mainly onto dopamine D1 receptor-expressing neurons, largely overlap with the neuronal population that responds to aversive predator stress, a widely used anxiogenic stressor. Specific optogenetic activation of the BLA-DMS circuit induced a strong anxiety response followed by compulsive grooming. Furthermore, we developed a mouse model for compulsivity displaying a wide spectrum of compulsive-like behaviors by chronically activating the BLA-DMS circuit. In these mice, persistent molecular changes at the BLA-DMS synapses observed were causally related to the compulsive-like phenotypes. Together, our study demonstrates the involvement of the BLA-DMS circuit in the emergence of enduring compulsive-like behaviors via its persistent synaptic changes.

Mechanisms of pathogenesis and environmental moderators in preclinical models of compulsive-like behaviours

Obsessive-compulsive and related disorders (OCRD) is an emergent class of psychiatric illnesses that contributes substantially to the global mental health disease burden. In particular, the prototypical illness, obsessive-compulsive disorder (OCD), has a profoundly deleterious effect on the quality of life of those with lived experience. Both clinical and preclinical studies have investigated the genetic and environmental influences contributing to the pathogenesis of obsessive-compulsive and related disorders. Significant progress has been made in recent years in our understanding of the genetics of OCD, along with the critical role of common environmental triggers (e.g., stress). Some of this progress can be attributed to the sophistication of rodent models used in the field, particularly genetic mutant models, which demonstrate promising construct, face, and predictive validity. However, there is a paucity of studies investigating how these genetic and environmental influences interact to precipitate the behavioural, cellular, and molecular changes that occur in OCD. In this review, we assert that preclinical studies offer a unique opportunity to carefully manipulate environmental and genetic factors, and in turn to interrogate gene-environment interactions and relevant downstream sequelae. Such studies may serve to provide a mechanistic framework to build our understanding of the pathogenesis of complex neuropsychiatric disorders such as OCD. Furthermore, understanding gene-environment interactions and pathogenic mechanisms will facilitate precision medicine and other future approaches to enhance treatment, reduce side-effects of therapeutic interventions, and improve the lives of those suffering from these devastating disorders.

A new Hoxb8FlpO mouse line for intersectional approaches to dissect developmentally defined adult sensorimotor circuits

Improvements in the speed and cost of expression profiling of neuronal tissues offer an unprecedented opportunity to define ever finer subgroups of neurons for functional studies. In the spinal cord, single cell RNA sequencing studies support decades of work on spinal cord lineage studies, offering a unique opportunity to probe adult function based on developmental lineage. While Cre/Flp recombinase intersectional strategies remain a powerful tool to manipulate spinal neurons, the field lacks genetic tools and strategies to restrict manipulations to the adult mouse spinal cord at the speed at which new tools develop. This study establishes a new workflow for intersectional mouse-viral strategies to dissect adult spinal function based on developmental lineages in a modular fashion. To restrict manipulations to the spinal cord, we generate a brain-sparing Hoxb8FlpO mouse line restricting Flp recombinase expression to caudal tissue. Recapitulating endogenous Hoxb8 gene expression, Flp-dependent reporter expression is present in the caudal embryo starting day 9.5. This expression restricts Flp activity in the adult to the caudal brainstem and below. Hoxb8FlpO heterozygous and homozygous mice do not develop any of the sensory or locomotor phenotypes evident in Hoxb8 heterozygous or mutant animals, suggesting normal developmental function of the Hoxb8 gene and protein in Hoxb8FlpO mice. Compared to the variability of brain recombination in available caudal Cre and Flp lines, Hoxb8FlpO activity is not present in the brain above the caudal brainstem, independent of mouse genetic background. Lastly, we combine the Hoxb8FlpO mouse line with dorsal horn developmental lineage Cre mouse lines to express GFP in developmentally determined dorsal horn populations. Using GFP-dependent Cre recombinase viruses and Cre recombinase-dependent inhibitory chemogenetics, we target developmentally defined lineages in the adult. We show how developmental knock-out versus transient adult silencing of the same ROR𝛃 lineage neurons affects adult sensorimotor behavior. In summary, this new mouse line and viral approach provides a blueprint to dissect adult somatosensory circuit function using Cre/Flp genetic tools to target spinal cord interneurons based on genetic lineage.

Distinct regions of Praja-1 E3 ubiquitin-protein ligase selectively bind to docosahexaenoic acid-containing phosphatidic acid and diacylglycerol kinase δ

1-Stearoyl-2-docosahexaenoyl (18:0/22:6)-phosphatidic acid (PA) interacts with and activates Praja-1 E3 ubiquitin-protein ligase (full length: 615 aa) to ubiquitinate and degrade the serotonin transporter (SERT). SERT modulates serotonergic system activity and is a therapeutic target for depression, autism, obsessive-compulsive disorder, schizophrenia and Alzheimer's disease. Moreover, diacylglycerol kinase (DGK) δ2 (full length: 1214 aa) interacts with Praja-1 in addition to SERT and generates 18:0/22:6-PA, which binds and activates Praja-1. In the present study, we investigated the interaction of Praja-1 with 18:0/22:6-PA and DGKδ2 in more detail. We first found that the N-terminal one-third region (aa 1-224) of Praja-1 bound to 18:0/22:6-PA and that Lys141 in the region was critical for binding to 18:0/22:6-PA. In contrast, the C-terminal catalytic domain of Praja-1 (aa 446-615) interacted with DGKδ2. Additionally, the N-terminal half of the catalytic domain (aa 309-466) of DGKδ2 intensely bound to Praja-1. Moreover, the N-terminal region containing the pleckstrin homology and C1 domains (aa 1-308) and the C-terminal half of the catalytic domain (aa 762-939) of DGKδ2 weakly associated with Praja-1. Taken together, these results reveal new functions of the N-terminal (aa 1-224) and C-terminal (aa 446-615) regions of Praja-1 and the N-terminal half of the catalytic region (aa 309-466) of DGKδ2 as regulatory domains. Moreover, it is likely that the DGKδ2-Praja-1-SERT heterotrimer proximally arranges the 18:0/22:6-PA-producing catalytic domain of DGKδ2, the 18:0/22:6-PA-binding regulatory domain of Praja-1, the ubiquitin-protein ligase catalytic domain of Praja-1 and the ubiquitination acceptor site-containing SERT C-terminal region.

Genomics of Obsessive-Compulsive Disorder and Related Disorders: What the Clinician Needs to Know

A wealth of evidence has shown that genetics plays a major role in susceptibility to obsessive-compulsive disorder (OCD) and all of its related disorders. Several large-scale, collaborative efforts using modern genomic methods are beginning to reveal the genetic architecture of these traits and identify long-sought risk genes. In this article, we summarize current OCD and related disorder genomic knowledge and explain how to communicate this information to patients and their families. The article concludes with a discussion of how genomic discovery in OCD and related disorders can inform our understanding of disease etiology and provide novel targets for therapeutic development.

Streptococcus pyogenes vaccine candidates do not induce autoimmune responses in a rheumatic heart disease model

We have developed a candidate vaccine to protect against multiple strains of Streptococcus pyogenes infections. The candidate vaccine contains two synthetic peptides derived from S. pyogenes proteins: the M-protein epitope, p*17 and the IL-8 degrading S. pyogenes Cell-Envelope Proteinase (SpyCEP) epitope, K4S2. In this study we utilise a rat autoimmune valvulitis model that displays both the cardiac and neurobehavioural pathology associated with post-streptococcal sequelae, to assess if the vaccine candidate antigens induce autoimmune complications and inflammatory pathology. Each antigen was conjugated to carrier protein diphtheria toxoid (DT) and independently assessed for potential to induce autoimmune pathology in female Lewis rats. Rats were administered three subcutaneous doses, and one intranasal dose over a four-week study with a two-week recovery period. A positive control group received recombinant S. pyogenes M5 (rM5) protein, and the negative control group received PBS. Rats that received rM5 developed significant cardiac and neurological pathologies. There was no evidence of these pathologies in the PBS control group, or the rats administered either P*17-DT or K4S2-DT. This study provides further preclinical evidence of the safety of the vaccine candidates p*17 and K4S2 and their appropriateness as candidates in human clinical trials.

Adolescent self-administration of the synthetic cannabinoid receptor agonist JWH-018 induces neurobiological and behavioral alterations in adult male mice

RATIONALE

The use of synthetic cannabinoid receptor agonists (SCRAs) is growing among adolescents, posing major medical and psychiatric risks. JWH-018 represents the reference compound of SCRA-containing products.

OBJECTIVES

This study was performed to evaluate the enduring consequences of adolescent voluntary consumption of JWH-018.

METHODS

The reinforcing properties of JWH-018 were characterized in male CD1 adolescent mice by intravenous self-administration (IVSA). Afterwards, behavioral, neurochemical, and molecular evaluations were performed at adulthood.

RESULTS

Adolescent mice acquired operant behavior (lever pressing, Fixed Ratio 1-3; 7.5 µg/kg/inf); this behavior was specifically directed at obtaining JWH-018 since it increased under Progressive Ratio schedule of reinforcement, and was absent in vehicle mice. JWH-018 IVSA was reduced by pretreatment of the CB1-antagonist/inverse agonist AM251. Adolescent exposure to JWH-018 by IVSA increased, at adulthood, both nestlet shredding and marble burying phenotypes, suggesting long-lasting repetitive/compulsive-like behavioral effects. JWH-018 did not affect risk proclivity in the wire-beam bridge task. In adult brains, there was an increase of ionized calcium binding adaptor molecule 1 (IBA-1) positive cells in the caudate-putamen (CPu) and nucleus accumbens (NAc), along with a decrease of glial fibrillary acidic protein (GFAP) immunoreactivity in the CPu. These glial alterations in adult brains were coupled with an increase of the chemokine RANTES and a decrease of the cytokines IL2 and IL13 in the cortex, and an increase of the chemokine MPC1 in the striatum.

CONCLUSIONS

This study suggests for the first time that male mice self-administer the prototypical SCRA JWH-018 during adolescence. The adolescent voluntary consumption of JWH-018 leads to long-lasting behavioral and neurochemical aberrations along with glia-mediated inflammatory responses in adult brains.

WNT/β-catenin pathway and circadian rhythms in obsessive-compulsive disorder

The neuropsychiatric disease named obsessive-compulsive disorder is composed by obsessions and/or compulsions. Obsessive-compulsive disorder etiologies are undefined. However, numerous mechanisms in several localizations are implicated. Some studies showed that both glutamate, inflammatory factors and oxidative stress could have main functions in obsessive-compulsive disorder. Glycogen synthase kinase-3β, the major negative controller of the WNT/β-catenin pathway is upregulated in obsessive-compulsive disorder. In obsessive-compulsive disorder, some studies presented the actions of the different circadian clock genes. WNT/β-catenin pathway and circadian clock genes appear to be intricate. Thus, this review focuses on the interaction between circadian clock genes and the WNT/β-catenin pathway in obsessive-compulsive disorder.

Effects of low doses of different nitric oxide (NO) donors in rat models of obsessive-compulsive disorder (OCD) and posttraumatic stress disorder (PTSD)

Several lines of evidence suggest that the intra- and inter-cellular messenger nitric oxide (NO) is critically involved in anxiety. Contrasting findings are reported, however, regarding the effects of NO donors in preclinical models of anxiety. Previous research has shown that challenge with a low dose range of the NO donors sodium nitroprusside (SNP) and molsidomine induce anti-anxiety-like effects in rodents. There is poor information concerning the effects of these NO donors on preclinical models mimicking the obsessive-compulsive disorder (OCD) and the post-traumatic stress disorder (PTSD). The present research was designed to investigate this issue in the rat. To this end, the mCPP-induced excessive self-grooming and the contextual fear conditioning (CFC) test which are behavioural paradigms resembling OCD and PTSD respectively in rodents were used. Acute administration of SNP (1 mg/kg) and molsidomine (4 mg/kg) attenuated excessive self-grooming induced by the 5-HT_2C receptor agonist mCPP (0.6 mg/kg). Further, at the same dosage, both these NO donors reduced freezing behaviour evidenced in the CFC test. The present results suggest that NO donors are efficacious in attenuating abnormal behaviours revealed in animal models of OCD and PTSD which are among the most severe pathologies of anxiety.

The therapeutic potential of bone marrow-derived macrophages in neurological diseases

Circulating monocytes are precursors of both tissue macrophages and dendritic cells, and they can infiltrate the central nervous system (CNS) where they transform into bone marrow-derived macrophages (BMDMs). BMDMs play essential roles in various CNS diseases, thus modulating BMDMs might be a way to treat these disorders because there are currently no efficient therapeutic methods available for most of these neurological diseases. Moreover, BMDMs can serve as promising gene delivery vehicles following bone marrow transplantation for otherwise incurable genetic CNS diseases. Understanding the distinct roles that BMDMs play in CNS diseases and their potential as gene delivery vehicles may provide new insights and opportunities for using BMDMs as therapeutic targets or delivery vehicles. This review attempts to comprehensively summarize the neurological diseases that might be treated by modulating BMDMs or by delivering gene therapies via BMDMs after bone marrow transplantation.

BDNF Alleviates Microglial Inhibition and Stereotypic Behaviors in a Mouse Model of Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a severe mental illness characterized by obsessions and compulsions. However, its underlying mechanisms remain to be elucidated. Recent studies have suggested that neuroimmune dysregulation is involved in the pathogenesis of OCD. To investigate the role of microglia in this disorder, we established a pharmacological mouse model by using the serotonin (5-HT) 1A/1B receptor agonist RU24969 to mimic monoamine dysregulation in OCD, and we examined the morphological and functional alterations of microglia in this model. We found that RU24969 treatment led to compulsive circling behavior in mice. Strikingly, we found that the density and mobility of microglia in the prelimbic cortex were much lower in RU24969-treated mice than in control mice. Moreover, the expression of cytokines and chemokines, including BDNF, IL-1β, IL-6, TNFα, CD80, CD86, MHC-I, and MHC-II, also decreased in RU24969-treated mice. Importantly, we found that injection of BDNF or induction of BDNF expression by trehalose completely reversed microglial dysfunction and reduced stereotypic behavior. These results indicate that microglial dysfunction is closely related to stereotypic behaviors in our mouse model of OCD and that BDNF could be an effective treatment for stereotypic behaviors.

Case Report: Novel CSF1R Variant in a Patient With Behavioral Variant Frontotemporal Dementia Syndrome With Prodromal Repetitive Scratching Behavior

CSF1R-related leukoencephalopathy is an autosomal dominant neurodegenerative disease caused by mutations in the tyrosine kinase domain of the colony stimulating factor 1 receptor (CSF1R). Several studies have found that hematogenic stem cell transplantation is an effective disease modifying therapy however the literature regarding prodromal and early symptoms CSF1R-related leukoencephalopathy is limited. We describe a 63-year-old patient with 4 years of repetitive scratching and skin picking behavior followed by 10 years of progressive behavioral, cognitive, and motor decline in a pattern suggesting behavioral variant of frontotemporal dementia. Brain MRI demonstrated prominent frontal and parietal atrophy accompanied by underlying bilateral patchy white matter hyperintensities sparing the U fibers and cavum septum pellucidum. Whole-exome sequencing revealed a novel, predicted deleterious missense variant in a highly conserved amino acid in the tyrosine kinase domain of CSF1R (p.Gly872Arg). Given this evidence and the characteristic clinical and radiological findings this novel variant was classified as likely pathogenic according to the American College of Medical Genetics standard guidelines. Detailed description of the prodromal scratching and skin picking behavior and possible underlying mechanisms in this case furthers knowledge about early manifestations of CSF1R-related leukoencephalopathy with the hope that early detection and timely administration of disease modifying therapies becomes possible.

Optogenetic inhibition of indirect pathway neurons in the dorsomedial striatum reduces excessive grooming in Sapap3-knockout mice

Excessive grooming of Sapap3-KO mice has been used as a model of obsessive-compulsive disorder (OCD). Previous studies suggest that dysregulation of cortico-striatal circuits is critically important in the generation of compulsive behaviors, and it has been proposed that the alteration in the activity patterns of striatal circuitry underlies the excessive grooming observed in Sapap3-KO mice. To test this hypothesis, we used in-vivo calcium imaging of individual cells to record striatal activity in these animals and optogenetic inhibition to manipulate this activity. We identified striatal neurons that are modulated during grooming behavior and found that their proportion is significantly larger in Sapap3-KO mice compared to wild-type littermates. Inhibition of striatal cells in Sapap3-KO mice increased the number of grooming episodes observed. Remarkably, the specific inhibition of indirect pathway neurons decreased the occurrence of grooming events. Our results indicate that there is striatal neural activity related to excessive grooming engagement in Sapap3-KO mice. We also demonstrate, for the first time, that specific inhibition of striatal indirect pathway neurons reduces this compulsive phenotype, suggesting that treatments that alleviate compulsive symptoms in OCD patients may exert their effects through this specific striatal population.

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.

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.

The effect of dexketoprofen trometamol on WAG/Rij rats with absence epilepsy (dexketoprofen in absence epilepsy)

AIM

Epilepsy is one of the most common neurological diseases. Dexketoprofen (DEX) is a nonselective nonsteroidal anti-inflammatory drug that is used as an analgesic. The present study aimed to assess the efficiency of DEX on WAG/Rij rats by electrophysiologically and behaviorally.

MATERIAL AND METHODS

Twenty-eight male WAG/Rij rats were used. The effects of acute treatment with DEX (5, 25, and 50 mg/kg, i.p) on absence-like seizures, and related psychiatric comorbidity were assessed. The ECoG recording was taken for 180 min before and after drug injection. After drug injection and EcoG recording, anxiety-depression-like behavior was tested with the open field test for 5 min.

RESULTS

The 5 mg/kg DEX significantly reduced the number and duration of SWDs percentage (p < 0.05) between 120 and 180 min, but 25 and 50 mg/kg DEX significantly increased the number and duration of SWDs percentage between 0 and 30 min (p < 0.05), and after 30 min the increase stopped (p > 0.05). And also, the 5 mg/kg DEX decreased the number and duration of SWDs percentage (p < 0.05) for 180 min (p < 0.05), but 25 and 50 mg/kg DEX administration did not alter (p > 0.05). The 5, 25, and 50 mg/kg doses of DEX significantly increased the duration of grooming (p < 0.05) but did not change the number of squares crossed (p > 0.05).

CONCLUSION

Low dose DEX reduced absence-like seizures, but care should be taken when using high doses in absence epilepsy. Also, it may be beneficial for painful diseases accompanied by anxiety-depression.

Stereotypies in the Autism Spectrum Disorder: Can We Rely on an Ethological Model?

BACKGROUND

Stereotypic behaviour can be defined as a clear behavioural pattern where a specific function or target cannot be identified, although it delays on time. Nonetheless, repetitive and stereotypical behaviours play a key role in both animal and human behaviour. Similar behaviours are observed across species, in typical human developmental phases, and in some neuropsychiatric conditions, such as Autism Spectrum Disorder (ASD) and Intellectual Disability. This evidence led to the spread of animal models of repetitive behaviours to better understand the neurobiological mechanisms underlying these dysfunctional behaviours and to gain better insight into their role and origin within ASD and other disorders. This, in turn, could lead to new treatments of those disorders in humans.

METHOD

This paper maps the literature on repetitive behaviours in animal models of ASD, in order to improve understanding of stereotypies in persons with ASD in terms of characterization, pathophysiology, genomic and anatomical factors.

RESULTS

Literature mapping confirmed that phylogenic approach and animal models may help to improve understanding and differentiation of stereotypies in ASD. Some repetitive behaviours appear to be interconnected and mediated by common genomic and anatomical factors across species, mainly by alterations of basal ganglia circuitry. A new distinction between stereotypies and autotypies should be considered.

CONCLUSIONS

Phylogenic approach and studies on animal models may support clinical issues related to stereotypies in persons with ASD and provide new insights in classification, pathogenesis, and management.

Group A streptococcal antigen exposed rat model to investigate neurobehavioral and cardiac complications associated with post-streptococcal autoimmune sequelae

Background

The neuropsychiatric disorders due to post-streptococcal autoimmune complications such as Sydenham's chorea (SC) are associated with acute rheumatic fever and rheumatic heart disease (ARF/RHD). An animal model that exhibits characteristics of both cardiac and neurobehavioral defects in ARF/RHD would be an important adjunct for future studies. Since age, gender, strain differences, and genotypes impact on the development of autoimmunity, we investigated the behavior of male and female Wistar and Lewis rat strains in two age cohorts (<6 weeks and >12 weeks) under normal husbandry conditions and following exposure to group A streptococcus (GAS).

Methods

Standard behavioral assessments were performed to determine the impairments in fine motor control (food manipulation test), gait and balance (beam walking test), and obsessive-compulsive behavior (grooming and marble burying tests). Furthermore, electrocardiography, histology, and behavioral assessments were performed on male and female Lewis rats injected with GAS antigens.

Results

For control Lewis rats there were no significant age and gender dependent differences in marble burying, food manipulation, beam walking and grooming behaviors. In contrast significant age-dependent differences were observed in Wistar rats in all the behavioral tests except for food manipulation. Therefore, Lewis rats were selected for further experiments to determine the effect of GAS. After exposure to GAS, Lewis rats demonstrated neurobehavioral abnormalities and cardiac pathology akin to SC and ARF/RHD, respectively.

Conclusion

We have characterised a new model that provides longitudinal stability of age-dependent behavior, to simultaneously investigate both neurobehavioral and cardiac abnormalities associated with post-streptococcal complications.

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.

Distinct behavioral traits and associated brain regions in mouse models for obsessive-compulsive disorder

BACKGROUND

Obsessive-compulsive disorder (OCD) is a mental disease with heterogeneous behavioral phenotypes, including repetitive behaviors, anxiety, and impairments in cognitive functions. The brain regions related to the behavioral heterogeneity, however, are unknown.

METHODS

We systematically examined the behavioral phenotypes of three OCD mouse models induced by pharmacological reagents [RU24969, 8-hydroxy-DPAT hydrobromide (8-OH-DPAT), and 1-(3-chlorophenyl) piperazine hydrochloride-99% (MCPP)], and compared the activated brain regions in each model, respectively.

RESULTS

We found that the mouse models presented distinct OCD-like behavioral traits. RU24969-treated mice exhibited repetitive circling, anxiety, and impairments in recognition memory. 8-OH-DPAT-treated mice exhibited excessive spray-induced grooming as well as impairments in recognition memory. MCPP-treated mice showed only excessive self-grooming. To determine the brain regions related to these distinct behavioral traits, we examined c-fos expression to indicate the neuronal activation in the brain. Our results showed that RU24969-treated mice exhibited increased c-fos expression in the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), prelimbic cortex (PrL), infralimbic cortex (IL), nucleus accumbens (NAc), hypothalamus, bed nucleus of the stria terminalis, lateral division, intermediate part (BSTLD), and interstitial nucleus of the posterior limb of the anterior commissure, lateral part (IPACL), whereas in 8-OH-DPAT-treated mice showed increased c-fos expression in the ACC, PrL, IL, OFC, NAc shell, and hypothalamus. By contrast, MCPP did not induce higher c-fos expression in the cortex than control groups.

CONCLUSION

Our results indicate that different OCD mouse models exhibited distinct behavioral traits, which may be mediated by the activation of different brain regions.

Social contact behaviors are associated with infection status for Trichuris sp. in wild vervet monkeys (Chlorocebus pygerythrus)

Social grooming in the animal kingdom is common and serves several functions, from removing ectoparasites to maintaining social bonds between conspecifics. We examined whether time spent grooming with others in a highly social mammal species was associated with infection status for gastrointestinal parasites. Of six parasites detected, one (Trichuris sp.) was associated with social grooming behaviors, but more specifically with direct physical contact with others. Individuals infected with Trichuris sp. spent significantly less time grooming conspecifics than those not infected, and time in direct contact with others was the major predictor of infection status. One model correctly predicted infection status for Trichuris sp. with a reliability of 95.17% overall when the variables used were time spent in direct contact and time spent grooming others. This decrease in time spent grooming and interacting with others is likely a sickness behavior displayed by individuals with less energy or motivation for non-essential behaviors. This study emphasizes the possible links between host behavior and parasitic infections and highlights the need for an understanding of a study population’s parasitic infections when attempting to interpret animal behavior.

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.

Immunological Dysfunction in Tourette Syndrome and Related Disorders

Chronic tic disorder and Tourette syndrome are common childhood-onset neurological diseases. However, the pathophysiology underlying these disorders is unclear, and most studies have focused on the disinhibition of the corticostriatal–thalamocortical circuit. An autoimmune dysfunction has been proposed in the pathogenetic mechanism of Tourette syndrome and related neuropsychiatric disorders such as obsessive–compulsive disorder, autism, and attention-deficit/hyperactivity disorder. This is based on evidence from animal model studies and clinical findings. Herein, we review and give an update on the clinical characteristics, clinical evidence, and genetic studies in vitro as well as animal studies regarding immune dysfunction in Tourette syndrome.

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.

Animal Models for OCD Research

OCD has lagged behind other psychiatric illnesses in the identification of molecular treatment targets, due in part to a lack of significant findings in genome-wide association studies. However, while progress in this area is being made, OCD's symptoms of obsessions, compulsions, and anxiety can be deconstructed into distinct neural functions that can be dissected in animal models. Studies in rodents and non-human primates have highlighted the importance of cortico-basal ganglia-thalamic circuits in OCD pathophysiology, and emerging studies in human post-mortem brain tissue point to glutamatergic synapse abnormalities as a potential cellular substrate for observed dysfunctional behaviors. In addition, accumulated evidence points to a potential role for neuromodulators including serotonin and dopamine in both OCD pathology and treatment. Here, we review current efforts to use animal models for the identification of molecules, cell types, and circuits relevant to OCD pathophysiology. We start by describing features of OCD that can be modeled in animals, including circuit abnormalities and genetic findings. We then review different strategies that have been used to study OCD using animal model systems, including transgenic models, circuit manipulations, and dissection of OCD-relevant neural constructs. Finally, we discuss how these findings may ultimately help to develop new treatment strategies for OCD and other related disorders.

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.

The role of neuroglia in autism spectrum disorders

Neuroglia are a large class of neural cells of ectodermal (astroglia, oligodendroglia, and peripheral glial cells) and mesodermal (microglia) origin. Neuroglial cells provide homeostatic support, protection, and defense to the nervous tissue. Pathological potential of neuroglia has been acknowledged since their discovery. Research of the recent decade has shown the key role of all classes of glial cells in autism spectrum disorders (ASD), although molecular mechanisms defining glial contribution to ASD are yet to be fully characterized. This narrative conceptualizes recent findings of the broader roles of glial cells, including their active participation in the control of cerebral environment and regulation of synaptic development and scaling, highlighting their putative involvement in the etiopathogenesis of ASD.

Dopaminergic and serotonergic modulation of social reward appraisal in zebrafish (Danio rerio) under circumstances of motivational conflict: Towards a screening test for anti-compulsive drug action

Cognitive flexibility, shown to be impaired in patients presenting with compulsions, is dependent on balanced dopaminergic and serotonergic interaction. Towards the development of a zebrafish (Danio rerio) screening test for anti-compulsive drug action, we manipulated social reward appraisal under different contexts by means of dopaminergic (apomorphine) and serotonergic (escitalopram) intervention. Seven groups of zebrafish (n = 6 per group) were exposed for 24 days (1 h per day) to either control (normal tank water), apomorphine (50 or 100 μg/L), escitalopram (500 or 1000 μg/L) or a combination (A100/E500 or A100/E1000 μg/L). Contextual reward appraisal was assessed over three phases i.e. Phase 1 (contingency association), Phase 2 (dissociative testing), and Phase 3 (re-associative testing). We demonstrate that 1) sight of social conspecifics is an inadequate motivational reinforcer under circumstances of motivational conflict, 2) dopaminergic and serotonergic intervention lessens the importance of an aversive stimulus, increasing the motivational valence of social reward, 3) while serotoninergic intervention maintains reward directed behavior, high-dose dopaminergic intervention bolsters cue-directed responses and 4) high-dose escitalopram reversed apomorphine-induced behavioral inflexibility. The results reported here are supportive of current dopamine-serotonin opponency theories and confirm the zebrafish as a potentially useful species in which to investigate compulsive-like behaviors.

Microglia and sexual differentiation of the developing brain: A focus on ontogeny and intrinsic factors

Sexual differentiation of the brain during early development likely underlies the strong sex biases prevalent in many neurological conditions. Mounting evidence indicates that microglia, the innate immune cells of the central nervous system, are intricately involved in these sex-specific processes of differentiation. In this review, we synthesize literature demonstrating sex differences in microglial number, morphology, transcriptional state, and functionality throughout spatiotemporal development as well as highlight current literature regarding ontogeny of microglia. Along with vanRyzin et al. in this issue, we explore the idea that differences in microglia imparted by chromosomal or ontogeny-related programming can influence microglial-driven sexual differentiation of the brain, as well as the idea that extrinsic differences in the male and female brain microenvironment may in turn impart sex differences in microglia.

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

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

Animal models of OCD-relevant processes: an RDoC perspective

Animal models have been invaluable tools in deciphering pathophysiology in many branches of medicine. Their application in the study of complex neuropsychiatric conditions such as obsessive-compulsive disorder (OCD), however, raises vexing interpretative challenges. The Research Domain Criteria (RDoC) approach of identifying dimensions of function and dysfunction that cut across syndromic diagnoses provides one potential path forward. We review some of the domains in the current RDoC matrix that may inform our understanding of patients with obsessions and compulsions, and how work in animal model systems is helping us to understand them. We focus on three specific RDoC constructs that may be particularly informative for our understanding of OCD: potential threat, habit, and cognitive control. In each case we review selected recent studies in animal models and their potential contribution to our understanding of OCD, and suggest directions for future research, informed by the animal studies. Such mechanistic work in animal models, in parallel with clinical studies refining our understanding of the relationship between these dimensional constructs and the symptomatology of particular groups of patients, may over time help us to generate a more comprehensive understanding of the pathogenesis and complexity of obsessions and compulsions.

A Proximal Perspective on Disgust

The functional basis of disgust in disease avoidance is widely accepted; however, there is disagreement over what disgust is. This is a significant problem, as basic questions about disgust require knowing if single/multiple forms/processes exist. We address this issue with a new model with one form of disgust generated by multiple processes: (a) pure disgust experienced during gastrointestinal illness; (b) somatosensory disgust elicited by specific cues that activate the pure disgust state; (c) anticipatory disgust elicited by associations between distance cues for somatosensory disgust and requiring threat evaluation; (d) simulated disgusts elicited by imagining somatosensory and anticipatory disgust and frequently involving other emotions. Different contamination processes interlink (a–d). The implications of our model for fundamental questions about disgust (e.g., emotion status; continuation into animals) are examined.

Synaptic Wiring of Corticostriatal Circuits in Basal Ganglia: Insights into the Pathogenesis of Neuropsychiatric Disorders

The striatum is a key hub in the basal ganglia for processing neural information from the sensory, motor, and limbic cortices. The massive and diverse cortical inputs entering the striatum allow the basal ganglia to perform a repertoire of neurological functions ranging from basic level of motor control to high level of cognition. The heterogeneity of the corticostriatal circuits, however, also renders the system susceptible to a repertoire of neurological diseases. Clinical and animal model studies have indicated that defective development of the corticostriatal circuits is linked to various neuropsychiatric disorders, including attention-deficit hyperactivity disorder (ADHD), Tourette syndrome, obsessive-compulsive disorder (OCD), autism spectrum disorder (ASD), and schizophrenia. Importantly, many neuropsychiatric disease-risk genes have been found to form the molecular building blocks of the circuit wiring at the synaptic level. It is therefore imperative to understand how corticostriatal connectivity is established during development. Here, we review the construction during development of these corticostriatal circuits at the synaptic level, which should provide important insights into the pathogenesis of neuropsychiatric disorders related to the basal ganglia and help the development of appropriate therapies for these diseases.

Human-leukocyte antigen class II genes in early-onset obsessive-compulsive disorder

Objective: The exact aetiology of obsessive-compulsive disorder (OCD) is unknown, although there is evidence to suggest a gene-environment interaction model. Several lines of evidence support a possible role of the immune system in this model. Methods: The present study explores the allele variability in HLA genes of class II (HLA-DRB1, HLA-DQB1) in a sample of 144 early-onset OCD compared with reference samples of general population in the same geographical area. Results: None of the 39 alleles identified (allele frequency >1%) showed significant differences between OCD and reference populations. Pooling the different alleles that comprised HLA-DR4 (including DRB1*04:01, DRB1*04:04 and DRB1*04:05 alleles) we observed a significantly higher frequency (X²₁ = 5.53, P = 0.018; OR = 1.64, 95% CI 1.08-2.48) of these alleles in the early-onset OCD sample (10.8%) than in the reference population (6.8%). Conclusions: Taking into account the role of HLA class II genes in the central nervous system, the results presented here support a role of the immune system in the pathophysiological model of OCD.

Trichotillomania (hair pulling disorder)

Trichotillomania is characterized by the repetitive pulling out of one's own hair leading to hair loss and possibly functional impairment. Trichotillomania has been documented in the medical literature since the 19^th century. Prevalence studies suggest that trichotillomania is a common disorder (point prevalence estimates of 0.5%-2.0%). Although grouped with the obsessive-compulsive disorder (OCD) in the diagnostic and statistical manual of mental disorders-5, trichotillomania is distinct from OCD in many respects. For example, the treatment of trichotillomania generally employs habit reversal therapy and medication (n-acetylcysteine or olanzapine), both of which are quite different from those used to treat OCD. Conversely, some first-line treatments used for OCD (e.g., selective serotonin reuptake inhibitors) appear ineffective for trichotillomania. This article presents what is known about trichotillomania and the evidence for a variety of treatment interventions.

Auto-Reactive Th17-Cells Trigger Obsessive-Compulsive-Disorder Like Behavior in Mice With Experimental Autoimmune Encephalomyelitis

Th17-lymphocytes are well known for their deleterious role in autoimmunity. But does the notoriety of this repertoire extend beyond autoimmunity? In the present study we employed experimental autoimmune encephalomyelitis as model system to study the role auto-reactive Th17 cells in neuropsychiatric disorders. The mice with experimental autoimmune encephalomyelitis exhibited exaggerated grooming activity. The observed behavioral anomaly resembled obsessive compulsive disorder (OCD) upon analysis of grooming microstructure, induced grooming, marble burying and nestlet shredding. The observed OCD like behavior was relieved upon Th17 cell depletion; alternatively, it could alone be induced by adoptive transfer of myelin oligodendrocyte glycoprotein (35-55) reactive Th17 in B6.Rag1^−/− mice. The observed OCD like behavior was also alleviated upon treatment with a selective serotonin reuptake inhibitor, fluoxetine.

Corticostriatal circuit defects in Hoxb8 mutant mice

Hoxb8 mutant mice exhibit compulsive grooming and hair removal dysfunction similar to humans with the obsessive-compulsive disorder (OCD)-spectrum disorder, trichotillomania. As, in the mouse brain, the only detectable cells that label with Hoxb8 cell lineage appear to be microglia, we suggested that defective microglia cause the neuropsychiatric disorder. Does the Hoxb8 mutation in microglia lead to neural circuit dysfunctions? We demonstrate that Hoxb8 mutants contain corticostriatal circuit defects. Golgi staining, ultra-structural and electrophysiological studies of mutants reveal excess dendritic spines, pre- and postsynaptic structural defects, long-term potentiation and miniature postsynaptic current defects. Hoxb8 mutants also exhibit hyperanxiety and social behavioral deficits similar to mice with neuronal mutations in Sapap3, Slitrk5 and Shank3, reported models of OCD and autism spectrum disorders (ASDs). Long-term treatment of Hoxb8 mutants with fluoxetine, a serotonin reuptake inhibitor, reduces excessive grooming, hyperanxiety and social behavioral impairments. These studies provide linkage between the neuronal defects induced by defective Hoxb8-microglia and neuronal dysfunctions directly generated by mutations in synaptic components that result in mice, which display similar pathological grooming, hyperanxiety and social impairment deficits. Our results shed light on Hoxb8 microglia-driven circuit-specific defects and therapeutic approaches that will become essential to developing novel therapies for neuropsychiatric diseases such as OCD and ASDs with Hoxb8-microglia being the central target.

Genetic susceptibility in obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is present in 1.5-2.5% of the population and can result in substantial lifelong disability. It is characterized by intrusive thoughts, sensations, and urges and by repetitive behaviors that are difficult to control despite, in most cases, preserved insight as to their excessive or irrational nature. The causes and underlying pathophysiology of OCD are not well understood, which has limited the development of new treatments and interventions. Despite evidence for a substantial genetic contribution to disease risk, identification and replication of genetic variants associated with OCD have been challenging. Decades of candidate gene association studies have provided little insight. They are now being supplanted by modern genomewide approaches to discover both common and rare sequence and structural variants. Studies to date suggest potential novel therapeutic avenues such as modulators of glutamatergic and immune pathways; however, individual genetic findings are not yet statistically robust or replicated. Further efforts are clearly needed to identify specific risk variants and to confirm vulnerable pathways by studying much larger cohorts of patients with comprehensive variant discovery approaches. Mouse knockout models have already made notable inroads into our understanding of OCD pathology; their utility will only increase as specific risk alleles are identified.