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

Free operant observing in humans: a translational approach to compulsive certainty seeking

Excessive checking is reported in non-clinical populations and is a pervasive symptom in obsessive compulsive disorder (OCD). We implemented a free-operant task in humans, previously used in rats, wherein participants can "check" to reduce uncertainty. Participants can press an observing key to ascertain which of two main keys will, if pressed, currently lead to rewards. Over a series of experiments, we found that punishment robustly increased observing in non-clinical participants and that observing persisted long after punishment was removed. Moreover, participants appeared insensitive to the initial costs of checking, and a threefold increase in the effort required to observe served to deter participants only to a limited degree. We also assessed observing in OCD patients with no known comorbidities. The patients observed more than control participants and were abnormally insensitive to the introduction of punishment. These findings support the translational value of the task, with similar behaviours in humans and rodents. This paradigm may serve as a unifying platform, promoting interaction between different approaches to analyse adaptive and maladaptive certainty seeking behaviours. Specifically, we demonstrate how seemingly disparate theoretical and empirical approaches can be reconciled synergistically to promote a combined behavioural and cognitive account of certainty seeking.

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.

Peromyscus maniculatus bairdii as a naturalistic mammalian model of obsessive-compulsive disorder: current status and future challenges

Obsessive-compulsive disorder (OCD) is a prevalent and debilitating condition, characterized by intrusive thoughts and repetitive behavior. Animal models of OCD arguably have the potential to contribute to our understanding of the condition. Deer mice (Permomyscus maniculatus bairdii) are characterized by stereotypic behavior which is reminiscent of OCD symptomology, and which may serve as a naturalistic animal model of this disorder. Moreover, a range of deer mouse repetitive behaviors may be representative of different compulsive-like phenotypes. This paper will review work on deer mouse behavior, and evaluate the extent to which this serves as a valid and useful model of OCD. We argue that findings over the past decade indicate that the deer mouse model has face, construct and predictive validity.

Subthalamic Nucleus Deep Brain Stimulation: Basic Concepts and Novel Perspectives

Over the last decades, extensive basic and clinical knowledge has been acquired on the use of subthalamic nucleus (STN) deep brain stimulation (DBS) for Parkinson's disease (PD). It is now clear that mechanisms involved in the effects of this therapy are far more complex than previously anticipated. At frequencies commonly used in clinical practice, neural elements may be excited or inhibited and novel dynamic states of equilibrium are reached. Electrode contacts used for chronic DBS in PD are placed near the dorsal border of the nucleus, a highly cellular region. DBS may thus exert its effects by modulating these cells, hyperdirect projections from motor cortical areas, afferent and efferent fibers to the motor STN. Advancements in neuroimaging techniques may allow us to identify these structures optimizing surgical targeting. In this review, we provide an update on mechanisms and the neural elements modulated by STN DBS.

Methoxetamine affects brain processing involved in emotional response in rats

BACKGROUND AND PURPOSE

Methoxetamine (MXE) is a novel psychoactive substance that is emerging on the Internet and induces dissociative effects and acute toxicity. Its pharmacological effects have not yet been adequately investigated.

EXPERIMENTAL APPROACH

We examined a range of behavioural effects induced by acute administration of MXE (0.5-5 mg·kg^-1 ; i.p.) in rats and whether it causes rapid neuroadaptive molecular changes.

KEY RESULTS

MXE (0.5-5 mg·kg^-1 ) affected motor activity in a dose- and time-dependent manner, inducing hypermotility and hypomotility at low and high doses respectively. At low and intermediate doses (0.5 and 1 mg·kg^-1 ), MXE induced anxious and/or obsessive-compulsive traits (marble burying test), did not significantly increase sociability (social interaction test) or induce spatial anxiety (elevated plus maze test). At a high dose (5 mg·kg^-1 ), MXE induced transient analgesia (tail-flick and hot-plate test), decreased social interaction time (social interaction test) and reduced immobility time while increasing swimming activity (forced swim test), suggesting an antidepressant effect. Acute MXE administration did not affect self-grooming behaviour at any dose tested. Immunohistochemical analysis showed that behaviourally active doses of MXE (1 and 5 mg·kg^-1 ) increased phosphorylation of ribosomal protein S6 in the medial prefrontal cortex and hippocampus.

CONCLUSIONS AND IMPLICATIONS

MXE differentially affected motor activity, behaviour and emotional states in rats, depending on the dose tested. As reported for ketamine, phosphorylation of the ribosomal protein S6 was increased in MXE-treated animals, thus providing a 'molecular snapshot' of rapid neuroadaptive molecular changes induced by behaviourally active doses of MXE.

Preclinical molecular imaging of glutamatergic and dopaminergic neuroreceptor kinetics in obsessive compulsive disorder

BACKGROUND

Molecular neuroimaging was applied in the quinpirole rat model for compulsive checking in OCD to visualize the D2- and mGluR5-receptor occupancy with Raclopride and ABP-688 microPET/CT.

METHODS

Animals (n=48) were exposed to either saline (CTRL; 1mL/kg) or quinpirole (QP; dopamine D2-agonist, 0.5mg/kg) in a single injection (RAC and ABP acute groups) or twice-weekly during 7weeks (chronic group). Animals underwent PET/CT after the 1st injection (acute) or before initial exposure and following the 10th injection in week 5 (chronic). For the latter, each injection was paired with an open field test and video tracking.

RESULTS

The QP animals displayed a strong increase in visiting frequency (checking) in the chronic group (+699.29%) compared to the control animals. Acute administration of the drug caused significant (p<0.01) decreases in D2R occupancy in the CP (-42.03%±4.01%). Chronical exposure resulted in significantly stronger decreases in the CP (-52.29%±3.79%). Furthermore significant increases in mGluR5 occupancy were found in the CP (10.36%±4.09%), anterior cingulate cortex (13.26%±4.01%), amygdala (24.36%±6.86%), entorhinal cortex (18.49%±5.14%) and nucleus accumbens (13.8%±4.87%) of the chronic group, not present after acute exposure.

CONCLUSIONS

Compared to acute exposure, sensitisation to QP as a model for OCD differs both on a dopaminergic and glutamateric level, indicating involvement of processes such as receptor internalization and changes in extracellular availability of both neurotransmitters.

Exploring the Validity of Proposed Transgenic Animal Models of Attention-Deficit Hyperactivity Disorder (ADHD)

Attention-deficit/hyperactivity disorder (ADHD) is a common, behavioral, and heterogeneous neurodevelopmental condition characterized by hyperactivity, impulsivity, and inattention. Symptoms of this disorder are managed by treatment with methylphenidate, amphetamine, and/or atomoxetine. The cause of ADHD is unknown, but substantial evidence indicates that this disorder has a significant genetic component. Transgenic animals have become an essential tool in uncovering the genetic factors underlying ADHD. Although they cannot accurately reflect the human condition, they can provide insights into the disorder that cannot be obtained from human studies due to various limitations. An ideal animal model of ADHD must have face (similarity in symptoms), predictive (similarity in response to treatment or medications), and construct (similarity in etiology or underlying pathophysiological mechanism) validity. As the exact etiology of ADHD remains unclear, the construct validity of animal models of ADHD would always be limited. The proposed transgenic animal models of ADHD have substantially increased and diversified over the years. In this paper, we compiled and explored the validity of proposed transgenic animal models of ADHD. Each of the reviewed transgenic animal models has strengths and limitations. Some fulfill most of the validity criteria of an animal model of ADHD and have been extensively used, while there are others that require further validation. Nevertheless, these transgenic animal models of ADHD have provided and will continue to provide valuable insights into the genetic underpinnings of this complex disorder.

Obsessive-compulsive disorder: Insights from animal models

Research with animal models of obsessive-compulsive disorder (OCD) shows the following: (1) Optogenetic studies in mice provide evidence for a plausible cause-effect relation between increased activity in cortico-basal ganglia-thalamo-cortical (CBGTC) circuits and OCD by demonstrating the induction of compulsive behavior with the experimental manipulation of the CBGTC circuit. (2) Parallel use of several animal models is a fruitful paradigm to examine the mechanisms of treatment effects of deep brain stimulation in distinct OCD endophenotypes. (3) Features of spontaneous behavior in deer mice constitute a rich platform to investigate the neurobiology of OCD, social ramifications of a compulsive phenotype, and test novel drugs. (4) Studies in animal models for psychiatric disorders comorbid with OCD suggest comorbidity may involve shared neural circuits controlling expression of compulsive behavior. (5) Analysis of compulsive behavior into its constitutive components provides evidence from an animal model for a motivational perspective on OCD. (6) Methods of behavioral analysis in an animal model translate to dissection of compulsive rituals in OCD patients, leading to diagnostic tests.

Atomoxetine for hoarding disorder: A pre-clinical and clinical investigation

Despite several studies suggested that inattention and impulsivity-compulsivity could represent two core dimensions of hoarding disorder (HD), only a small case series study investigated the effectiveness of attention-deficit-hyperactivity-disorder (ADHD) medications in HD. The aim of the present study was to target attentional and inhibitory control networks in HD patients through the ADHD medication atomoxetine, moving from a preclinical investigation on an animal model of compulsive-like behavior (marble burying test) to a clinical investigation on both medicated and unmedicated patients with a primary diagnosis of HD without ADHD. Our preclinical investigation showed that acute administration of atomoxetine significantly reduced the compulsive-like behaviours of mice in the marble burying test without affecting neither locomotor activity and coordination nor exploration behaviours. When compared, atomoxetine and fluoxetine showed similar effects on the marble burying test. However, fluoxetine impaired both locomotor and exploratory activity. In our clinical investigation 12 patients were enrolled and 11 patients completed an open trial with atomoxetine at flexible dose (40-80 mg) for 12 weeks. At the endpoint the mean UCLA Hoarding Severity Scale score decreased by 41.3% for the whole group (p = 0003). Six patients were classified as full responders (mean symptom reduction of 57.2%) and three patients as partial responders (mean symptom reduction of 27.3%). Inattentive and impulsivity symptoms showed a significant mean score reduction of 18.5% from baseline to the endpoint (F (1,9) = 20.9, p = 0.0013). Hoarding symptoms improvement was correlated to reduction of patients' disability and increased in their global functioning. These preclinical and clinical data suggest that atomoxetine may be effective for HD and therefore should be considered for future controlled trials.

Strain and sex based characterization of behavioral expressions in non-induced compulsive-like mice

There is currently a lack of understanding how genetic background and sex differences attribute to the heterogeneity of obsessive-compulsive disorder (OCD). An animal model of compulsive-like behaviors has been developed through bidirectional selection of house mice (Mus musculus) for high (big cotton nests; BIG mice) and low levels (small nests; SMALL mice) of nest-building behavior. The BIG male strains have predictive and face validity as a spontaneous animal model of OCD. Here, we evaluated compulsive-, anxiety-, cognitive-, and depression-like behaviors among male and proestrus female replicate strains each of BIG (BIG1, BIG2) and SMALL (SML1, SML2) nest-builders, and randomly-bred Controls (C1, C2). BIG1 and BIG2 males and females had higher nesting scores when compared to SMALL and Control strains. Male BIG1 and BIG2 strains showed more compulsive-like nesting than BIG1 and BIG2 proestrus females, which was not observed among the other strains. Nesting scores were also different between BIG replicate male strains. A similar pattern was observed in the compulsive-like marble burying behavior with BIG strains burying more marbles than SMALL and Control strains. Significant replicate and sex differences were also observed in marble burying among the BIG strains. The open field test revealed replicate effects while the BIG strains showed less anxiety-like behavior in the elevated plus maze test compared to the SMALL strains. For novel object recognition only the Control strains showed replicate and sex differences. In the depression-like forced swim test proestrus females demonstrated less depression-like behavior than males. BIG and SMALL nest-building strains had a higher corticosterone stress response than the Control strains. Together these results indicate a strong interplay of genetic background and sex in influencing expression of behaviors in our compulsive-like mouse model. These results are in congruence with the clinical heterogeneity of OCD.

5α-reduced progestogens ameliorate mood-related behavioral pathology, neurotoxicity, and microgliosis associated with exposure to HIV-1 Tat

Human immunodeficiency virus (HIV) is associated with motor and mood disorders, likely influenced by reactive microgliosis and subsequent neural damage. We have recapitulated aspects of this pathology in mice that conditionally express the neurotoxic HIV-1 regulatory protein, trans-activator of transcription (Tat). Progestogens may attenuate Tat-related behavioral impairments and reduce neurotoxicity in vitro, perhaps via progesterone's 5α-reductase-dependent metabolism to the neuroprotective steroid, allopregnanolone. To test this, ovariectomized female mice that conditionally expressed (or did not express) central HIV-1 Tat were administered vehicle or progesterone (4mg/kg), with or without pretreatment of a 5α-reductase inhibitor (finasteride, 50mg/kg). Tat induction significantly increased anxiety-like behavior in an open field, elevated plus maze and a marble burying task concomitant with elevated protein oxidation in striatum. Progesterone administration attenuated anxiety-like effects in the open field and elevated plus maze, but not in conjunction with finasteride pretreatment. Progesterone also attenuated Tat-promoted protein oxidation in striatum, independent of finasteride pretreatment. Concurrent experiments in vitro revealed Tat (50nM)-mediated reductions in neuronal cell survival over 60h, as well as increased neuronal and microglial intracellular calcium, as assessed via fura-2 AM fluorescence. Co-treatment with allopregnanolone (100nM) attenuated neuronal death in time-lapse imaging and blocked the Tat-induced exacerbation of intracellular calcium in neurons and microglia. Lastly, neuronal-glial co-cultures were labeled for Iba-1 to reveal that Tat increased microglial numbers in vitro and co-treatment with allopregnanolone attenuated this effect. Together, these data support the notion that 5α-reduced pregnane steroids exert protection over the neurotoxic effects of HIV-1 Tat.

Sustained lentiviral-mediated overexpression of microRNA124a in the dentate gyrus exacerbates anxiety- and autism-like behaviors associated with neonatal isolation in rats

Autism spectrum disorders (ASD) are highly disabling psychiatric disorders. Despite a strong genetic etiology, there are no efficient therapeutic interventions that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of microRNA (miR) machinery may contribute to the underlying molecular mechanisms involved in ASD. Here, we report a stress model demonstrating that neonatal isolation-induced long-lasting hippocampal elevation of miR124a was associated with reduced expression of its target BDNF mRNA. In addition, we investigated the impact of lentiviral-mediated overexpression of miR124a into the dentate gyrus (DG) on social interaction, repetitive- and anxiety-like behaviors in the neonatal isolation (Iso) model of autism. Rats isolated from the dams on PND 1 to PND 11 were assessed for their social interaction, marble burying test (MBT) and repetitive self-grooming behaviors as adults following miR124a overexpression. Also, anxiety-like behavior and locomotion were evaluated in the elevated plus maze (EPM) and open-field (OF) tests. Results show that, consistent with previously published reports, Iso rats displayed decreased social interaction contacts but increased repetitive- and anxiety-like behaviors. Interestingly, across both autism- and anxiety-like behavioral assays, miR124a overexpression in the DG significantly exacerbated repetitive behaviors, social impairments and anxiety with no effect on locomotor activity. Our novel findings attribute neonatal isolation-inducible cognitive impairments to induction of miR124a and consequently suppressed BDNF mRNA, opening venues for intercepting these miR124a-mediated damages. They also highlight the importance of studying microRNAs in the context of ASD and identify miR124a as a novel potential therapeutic target for improving mood disorders.

Compulsivity in obsessive-compulsive disorder and addictions

Compulsive behaviors are driven by repetitive urges and typically involve the experience of limited voluntary control over these urges, a diminished ability to delay or inhibit these behaviors, and a tendency to perform repetitive acts in a habitual or stereotyped manner. Compulsivity is not only a central characteristic of obsessive-compulsive disorder (OCD) but is also crucial to addiction. Based on this analogy, OCD has been proposed to be part of the concept of behavioral addiction along with other non-drug-related disorders that share compulsivity, such as pathological gambling, skin-picking, trichotillomania and compulsive eating. In this review, we investigate the neurobiological overlap between compulsivity in substance-use disorders, OCD and behavioral addictions as a validation for the construct of compulsivity that could be adopted in the Research Domain Criteria (RDoC). The reviewed data suggest that compulsivity in OCD and addictions is related to impaired reward and punishment processing with attenuated dopamine release in the ventral striatum, negative reinforcement in limbic systems, cognitive and behavioral inflexibility with diminished serotonergic prefrontal control, and habitual responding with imbalances between ventral and dorsal frontostriatal recruitment. Frontostriatal abnormalities of compulsivity are promising targets for neuromodulation and other interventions for OCD and addictions. We conclude that compulsivity encompasses many of the RDoC constructs in a trans-diagnostic fashion with a common brain circuit dysfunction that can help identifying appropriate prevention and treatment targets.

The BDNF Valine 68 to Methionine Polymorphism Increases Compulsive Alcohol Drinking in Mice That Is Reversed by Tropomyosin Receptor Kinase B Activation

BACKGROUND

The valine 66 to methionine (Met) polymorphism within the brain-derived neurotrophic factor (BDNF) sequence reduces activity-dependent BDNF release and is associated with psychiatric disorders in humans. Alcoholism is one of the most prevalent psychiatric diseases. Here, we tested the hypothesis that this polymorphism increases the severity of alcohol abuse disorders.

METHODS

We generated transgenic mice carrying the mouse homolog of the human Met66BDNF allele (Met68BDNF) and used alcohol-drinking paradigms in combination with viral-mediated gene delivery and pharmacology.

RESULTS

We found that Met68BDNF mice consumed excessive amounts of alcohol and continued to drink despite negative consequences, a hallmark of addiction. Importantly, compulsive alcohol intake was reversed by overexpression of the wild-type valine68BDNF allele in the ventromedial prefrontal cortex of the Met68BDNF mice or by systemic administration of the tropomyosin receptor kinase B agonist, LM22A-4.

CONCLUSIONS

Our findings suggest that carrying this BDNF allele increases the risk of developing uncontrolled and excessive alcohol drinking that can be reversed by directly activating the BDNF receptor, tropomyosin receptor kinase B. Importantly, this work identifies a potential therapeutic strategy for the treatment of compulsive alcohol drinking in humans carrying the Met66BDNF allele.

Social behavior in deer mice as a novel interactive paradigm of relevance for obsessive-compulsive disorder (OCD)

Greater obsessive-compulsive (OC) symptom severity may be associated with poor social adjustment. Rather than possessing deficits in social skill per se, OCD patients may be more socially isolative in the presence of normal controls. We aimed to apply a novel social interaction challenge (SIC) to an established animal model of OCD, viz., the deer mouse, to assess complex social behavior in animals by investigating group sociability and its response to chronic escitalopram treatment (50 mg/kg/day × 28 days), both within and between non (N)- (viz., normal) and high (H)- (viz., OCD-like) stereotypical cohorts. Using automated screening, we scored approach behavior, episodes of proximity, duration of proximity, and relative net weighted movement. H animals socialized more with one another within cohort in all of the above parameters compared to the within-cohort behavior of N animals. Furthermore, the social behavior of H animals toward one another, both within and between cohort demonstrated significant improvements following chronic escitalopram treatment. However, the study also demonstrates that the social interaction between H and N animals remain poor even after chronic escitalopram treatment. To conclude, findings from the current investigation support clinical data demonstrating altered sociability in patients with OCD.

A Framework for Understanding the Emerging Role of Corticolimbic-Ventral Striatal Networks in OCD-Associated Repetitive Behaviors

Significant interest in the mechanistic underpinnings of obsessive-compulsive disorder (OCD) has fueled research on the neural origins of compulsive behaviors. Converging clinical and preclinical evidence suggests that abnormal repetitive behaviors are driven by dysfunction in cortico-striatal-thalamic-cortical (CSTC) circuits. These findings suggest that compulsive behaviors arise, in part, from aberrant communication between lateral orbitofrontal cortex (OFC) and dorsal striatum. An important body of work focused on the role of this network in OCD has been instrumental to progress in the field. Disease models focused primarily on these regions, however, fail to capture an important aspect of the disorder: affective dysregulation. High levels of anxiety are extremely prevalent in OCD, as is comorbidity with major depressive disorder. Furthermore, deficits in processing rewards and abnormalities in processing emotional stimuli are suggestive of aberrant encoding of affective information. Accordingly, OCD can be partially characterized as a disease in which behavioral selection is corrupted by exaggerated or dysregulated emotional states. This suggests that the networks producing OCD symptoms likely expand beyond traditional lateral OFC and dorsal striatum circuit models, and highlights the need to cast a wider net in our investigation of the circuits involved in generating and sustaining OCD symptoms. Here, we address the emerging role of medial OFC, amygdala, and ventral tegmental area projections to the ventral striatum (VS) in OCD pathophysiology. The VS receives strong innervation from these affect and reward processing regions, and is therefore poised to integrate information crucial to the generation of compulsive behaviors. Though it complements functions of dorsal striatum and lateral OFC, this corticolimbic-VS network is less commonly explored as a potential source of the pathology underlying OCD. In this review, we discuss this network's potential role as a locus of OCD pathology and effective treatment.

Stress-related regulation of the kynurenine pathway: Relevance to neuropsychiatric and degenerative disorders

The kynurenine pathway (KP), which is activated in times of stress and infection has been implicated in the pathophysiology of neurodegenerative and psychiatric disorders. Activation of this tryptophan metabolising pathway results in the production of neuroactive metabolites which have the potential to interfere with normal neuronal functioning which may contribute to altered neuronal transmission and the emergence of symptoms of these brain disorders. This review investigates the involvement of the KP in a range of neurological disorders, examining recent in vitro, in vivo and clinical discoveries highlights evidence to indicate that the KP is a potential therapeutic target in both neurodegenerative and stress-related neuropsychiatric disorders. Furthermore, this review identifies gaps in our knowledge with regard to this field which are yet to be examined to lead to a more comprehensive understanding of the role of KP activation in brain health and disease. This article is part of the Special Issue entitled 'The Kynurenine Pathway in Health and Disease'.

Autism-Like Behavior and Epigenetic Changes Associated with Autism as Consequences of In Utero Exposure to Environmental Pollutants in a Mouse Model

We tested the hypothesis that in utero exposure to heavy metals increases autism-like behavioral phenotypes in adult animals and induces epigenetic changes in genes that have roles in the etiology of autism. Mouse dams were treated with cadmium, lead, arsenate, manganese, and mercury via drinking water from gestational days (E) 1–10. Valproic acid (VPA) injected intraperitoneally once on (E) 8.5 served as a positive control. Young male offspring were tested for behavioral deficits using four standardized behavioral assays. In this study, in utero exposure to heavy metals resulted in multiple behavioral abnormalities that persisted into adulthood. VPA and manganese induced changes in perseverative/impulsive behavior and social dominance behavior, arsenic caused changes only in perseverative/impulsive behavior, and lead induced abnormalities in social interaction in comparison to the control animals. Brain samples from Mn, Pb, and VPA treated and control animals were evaluated for changes in CpG island methylation in promoter regions and associated changes in gene expression. The Chd7 gene, essential for neural crest cell migration and patterning, was found to be hypomethylated in each experimental animal tested compared to water-treated controls. Furthermore, distinct patterns of CpG island methylation yielded novel candidate genes for further investigation.

Different physiological and behavioural effects of e-cigarette vapour and cigarette smoke in mice

Nicotine is the primary addictive substance in tobacco smoke and electronic cigarette (e-cig) vapour. Methodological limitations have made it difficult to compare the role of the nicotine and non-nicotine constituents of tobacco smoke. The aim of this study was to compare the effects of traditional cigarette smoke and e-cig vapour containing the same amount of nicotine in male BALB/c mice exposed to the smoke of 21 cigarettes or e-cig vapour containing 16.8 mg of nicotine delivered by means of a mechanical ventilator for three 30-min sessions/day for seven weeks. One hour after the last session, half of the animals were sacrificed for neurochemical analysis, and the others underwent mecamylamine-precipitated or spontaneous withdrawal for the purposes of behavioural analysis. Chronic intermittent non-contingent, second-hand exposure to cigarette smoke or e-cig vapour led to similar brain cotinine and nicotine levels, similar urine cotinine levels and the similar up-regulation of α4β2 nicotinic acetylcholine receptors in different brain areas, but had different effects on body weight, food intake, and the signs of mecamylamine-precipitated and spontaneous withdrawal episodic memory and emotional responses. The findings of this study demonstrate for the first time that e-cig vapour induces addiction-related neurochemical, physiological and behavioural alterations. The fact that inhaled cigarette smoke and e-cig vapour have partially different dependence-related effects indicates that compounds other than nicotine contribute to tobacco dependence.

Reduced dopamine and glutamate neurotransmission in the nucleus accumbens of quinpirole-sensitized rats hints at inhibitory D2 autoreceptor function

Dopamine from the ventral tegmental area and glutamate from several brain nuclei converge in the nucleus accumbens (NAc) to drive motivated behaviors. Repeated activation of D2 receptors with quinpirole (QNP) induces locomotor sensitization and compulsive behaviors, but the mechanisms are unknown. In this study, in vivo microdialysis and fast scan cyclic voltammetry in adult anesthetized rats were used to investigate the effect of repeated QNP on dopamine and glutamate neurotransmission within the NAc. Following eight injections of QNP, a significant decrease in phasic and tonic dopamine release was observed in rats that displayed locomotor sensitization. Either a systemic injection or the infusion of QNP into the NAc decreased dopamine release, and the extent of this effect was similar in QNP-sensitized and control rats, indicating that inhibitory D2 autoreceptor function is maintained despite repeated activation of D2 receptors and decreased dopamine extracellular levels. Basal extracellular levels of glutamate in the NAc were also significantly lower in QNP-treated rats than in controls. Moreover, the increase in NAc glutamate release induced by direct stimulation of medial prefrontal cortex was significantly lower in QNP-sensitized rats. Together, these results indicate that repeated activation of D2 receptors disconnects NAc from medial prefrontal cortex and ventral tegmental area. Repeated administration of the dopamine D2 receptor agonist quinpirole (QNP) induces locomotor sensitization. We found that the NAc of QNP-sensitized rats has reduced glutamate levels coming from prefrontal cortex together with a decreased phasic and tonic dopamine neurotransmission but a conserved presynaptic D2 receptor function. We suggest that locomotor sensitization is because of increased affinity state of D2 post-synaptic receptors.

Anxiolytic-like effects of ursolic acid in mice

Ursolic acid is a pentacyclic triterpenoid that possesses several biological and neuropharmacological effects including antidepressant-like activity. Anxiety disorders represent common and disability psychiatric conditions that are often associated with depressive symptoms. This work investigated the anxiolytic-like effects of ursolic acid administration in different behavioral paradigms that evaluate anxiety in mice: open field test, elevated plus maze test, light/dark box test and marble burying test. To this end, mice were administered with ursolic acid (0.1, 1 and 10mg/kg, p.o.) or diazepam (2mg/kg, p.o.), positive control, and submitted to the behavioral tests. The results show that ursolic acid (10mg/kg) elicited an anxiolytic-like effect observed by the increased total time in the center and decreased number of rearings responses in the open field test and an increased percentage of entries and total time spent in the open arms of elevated plus maze, similarly to diazepam. No significant effects of ursolic acid were shown in the light/dark box and marble burying test. These data indicate that ursolic acid exhibits anxiolytic-like effects in the open field and elevated plus maze test, but not in the light/dark box and marble burying test, showing the relevance of testing several behavioral paradigms in the evaluation of anxiolytic-like actions. Of note, the results extend the understanding on the effects of ursolic acid in the central nervous system and suggest that it may be a novel approach for the management of anxiety-related disorders.

Rats with differential self-grooming expression in the elevated plus-maze do not differ in anxiety-related behaviors

Individual differences are important biological predictors for reactivity to stressful stimulation. The extent to which trait differences underlie animal's reactions to conditioned and unconditioned fear stimuli, for example, is still to be clarified. Although grooming behavior has been associated with some aspects of the obsessive-compulsive disorder in humans, its relation with other anxiety disorders is still unknown. Given that grooming behavior could be a component of the whole spectrum of these disorders, in the present study we allocated male Wistar rats in low, intermediate and high self-grooming groups according to the duration of such behavior in the elevated plus-maze (EPM). These groups were then evaluated in unconditioned fear tests, such as the EPM and the open-field, and in conditioned fear tests, such as fear-potentiated startle and fear extinction retention. Additionally, we studied the expression of unconditioned behaviors in marble burying test and the sensorimotor gate function with prepulse inhibition test. Neurochemicals and neuroendocrine parameters were also evaluated, with the quantification of basal corticosterone in the plasma, and dopamine, serotonin and their metabolites in brain structures involved with fear processing. In general, rats classified according to grooming expression showed similar performance in all behavioral tests. Accordingly, corticosterone and monoamine concentrations were similar among groups. Thus, despite grooming expression elicited by different approaches--especially pharmacological ones--has been related with some aspects of anxiety disorders, rats with different expression of spontaneous self-grooming in the EPM do not differ in anxiety-like behaviors nor in neurochemical and neuroendocrine parameters generally associated with anxiety disorders.

Marble-burying is enhanced in 3xTg-AD mice, can be reversed by risperidone and it is modulable by handling

Translational research on behavioural and psychological symptoms of dementia (BPSD) is relevant to the study the neuropsychiatric symptoms that strongly affect the quality of life of the human Alzheimer's disease (AD) patient and caregivers, frequently leading to early institutionalization. Among the ethological behavioural tests for rodents, marble burying is considered to model the spectrum of anxiety, psychotic and obsessive-compulsive like symptoms. The present work was aimed to study the behavioural interactions of 12 month-old male 3xTg-AD mice with small objects using the marble-burying test, as compared to the response elicited in age-matched non-transgenic (NTg) mice. The distinction of the classical 'number of buried marbles' but also those left 'intact' and those 'changed' of position of marbles or partially buried (the transitional level of interaction) provided new insights into the modelling of BPSD-like alterations in this AD model. The analysis revealed genotype differences in the behavioural patterns and predominant behaviors. In the NTg mice, predominance was shown in the 'changed or partially buried', while interactions with marble were enhanced in 3xTg-AD mice resulting in an increase of marble burying. Besides, genotype-dependent meaningful correlations were found, with the marble test pattern of 3xTg-AD mice being directly related to neophobia in the corner tests. In both genotypes, the increase of burying was reversed by chronic treatment with risperidone (1mg/kg, s.c.). In 3xTg-AD mice, the repetitive handling of animals during the treatment also exerted modulatory effects. These distinct patterns further characterize the modelling of BPSD-like symptoms in the 3xTg-AD mice, and provide another behavioural tool to assess the benefits of preventive and/or therapeutic strategies, as well as the potential action of risk factors for AD, in this animal model.

Analytical strategies for the marble burying test: avoiding impossible predictions and invalid p-values

Background

The marble burying test is used to measure repetitive and anxiety-related behaviour in rodents. The number of marbles that animals bury are count data (non-negative integers), which are bounded below by zero and above by the number of marbles present. Count data are often analysed using normal linear models, which include the t-test and analysis of variance (ANOVA) as special cases. Linear models assume that the data are unbounded and that the variance is constant across groups. These requirements are rarely met with count data, leading to 95% confidence intervals that include impossible values (less than zero or greater than the number of marbles present), misleading p-values, and impossible predictions. Transforming the data or using nonparametric methods are common alternatives but transformations do not perform well when many zero values are present and nonparametric methods have several drawbacks.

Findings

The problems with using normal linear models to analyse marble burying data are demonstrated and generalised linear models (GLMs) are introduced as more appropriate alternatives.

Conclusions

GLMs have been specifically developed to deal with count and other types of non-Gaussian data, are straightforward to use and interpret, and will lead to more sensible inferences.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1062-7) contains supplementary material, which is available to authorized users.

Clinical Outcome and Mechanisms of Deep Brain Stimulation for Obsessive-Compulsive Disorder

Clinical outcome of deep brain stimulation (DBS) for obsessive-compulsive disorder (OCD) shows robust effects in terms of a mean Yale-Brown Obsessive-Compulsive Scale (YBOCS) reduction of 47.7 % and a mean response percentage (minimum 35 % YBOCS reduction) of 58.2 %. It appears that most patients regain a normal quality of life (QoL) after DBS. Reviewing the literature of the last 4 years, we argue that the mechanisms of action of DBS are a combination of excitatory and inhibitory as well as local and distal effects. Evidence from DBS animal models converges with human DBS EEG and imaging findings, in that DBS may be effective for OCD by reduction of hyperconnectivity between frontal and striatal areas. This is achieved through reduction of top-down-directed synchrony and reduction of frontal low-frequency oscillations. DBS appears to counteract striatal dysfunction through an increase in striatal dopamine and through improvement of reward processing. DBS affects anxiety levels through reduction of stress hormones and improvement of fear extinction.

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

OBJECTIVE

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

DESIGN

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

RESULTS

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

CONCLUSIONS

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

Nucleus accumbens core and pathogenesis of compulsive checking

To investigate the role of the nucleus accumbens core (NAc) in the development of quinpirole-induced compulsive checking, rats received an excitotoxic lesion of NAc or sham lesion and were injected with quinpirole (0.5 mg/kg) or saline; development of checking behavior was monitored for 10 biweekly tests. The results showed that even after the NAc lesion, quinpirole still induced compulsive checking, suggesting that the pathogenic effects produced by quinpirole lie outside the NAc. Although the NAc lesion did not prevent the induction of compulsive checking, it altered how quickly it develops, suggesting that the NAc normally contributes toward the induction of compulsive checking. Saline-treated rats with an NAc lesion were hyperactive, but did not develop compulsive checking, indicating that hyperactivity by itself is not sufficient for the pathogenesis of compulsive checking. It is proposed that compulsive checking is the exaggerated output of a security motivation system and that the NAc serves as a neural hub for coordinating the orderly activity of neural modules of this motivational system. Evidence is considered suggesting that the neurobiological condition for the pathogenesis of compulsive checking is two-fold: activation of dopamine D2/D3 receptors without concurrent stimulation of D1-like receptors and long-term plastic changes related to quinpirole-induced sensitization.

Signal attenuation as a rat model of obsessive compulsive disorder

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

Translatable and Back-Translatable Measurement of Impulsivity and Compulsivity: Convergent and Divergent Processes

Impulsivity and compulsivity have emerged as important dimensional constructs that challenge traditional psychiatric classification systems. Both are present in normal healthy populations where the need to act quickly and repeatedly without hesitation can be highly advantageous. However, when excessively expressed, impulsive and compulsive behavior can lead to adverse consequences and spectrum disorders exemplified by attention-deficit/hyperactivity disorder (ADHD), obsessive compulsive disorder (OCD), autism, and drug addiction. Impulsive individuals have difficulty in deferring gratification and are inclined to 'jump the gun' and respond prematurely before sufficient information is gathered. Compulsivity involves repetitive behavior often motivated by the need to reduce or prevent anxiety, thus leading to the maladaptive perseveration of behavior. Defined in this way, impulsivity and compulsivity could be viewed as separate entities or 'traits' but overwhelming evidence indicates that both may be present in the same disorder, either concurrently or even separately at different time points. Herein we discuss the neural and cognitive heterogeneity of impulsive and compulsive endophenotypes. These constructs map onto distinct fronto-striatal neural and neurochemical structures interacting both at nodal convergent points and as opponent processes highlighting both the heterogeneity and the commonalities of function. We focus on discoveries made using both translational research methodologies and studies exclusively in humans, and implications for treatment intervention in disorders in which impulsive and compulsive symptoms prevail. We emphasize the relevance of these constructs for understanding dimensional psychiatry.

Animal models of obsessive-compulsive disorder: utility and limitations

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

Crazy like a fox. Validity and ethics of animal models of human psychiatric disease

Animal models of human disease play a central role in modern biomedical science. Developing animal models for human mental illness presents unique practical and philosophical challenges. In this article we argue that (1) existing animal models of psychiatric disease are not valid, (2) attempts to model syndromes are undermined by current nosology, (3) models of symptoms are rife with circular logic and anthropomorphism, (4) any model must make unjustified assumptions about subjective experience, and (5) any model deemed valid would be inherently unethical, for if an animal adequately models human subjective experience, then there is no morally relevant difference between that animal and a human.

Striatal circuits, habits, and implications for obsessive-compulsive disorder

Increasing evidence implicates abnormalities in corticostriatal circuits in the pathophysiology of obsessive-compulsive disorder (OCD) and OC-spectrum disorders. Parallels between the emergence of repetitive, compulsive behaviors and the acquisition of automated behaviors suggest that the expression of compulsions could in part involve loss of control of such habitual behaviors. The view that striatal circuit dysfunction is involved in OC-spectrum disorders is strengthened by imaging and other evidence in humans, by discovery of genes related to OCD syndromes, and by functional studies in animal models of these disorders. We highlight this growing concordance of work in genetics and neurobiology suggesting that frontostriatal circuits, and their links with basal ganglia, thalamus and brainstem, are promising candidates for therapeutic intervention in OCD.

Anxiety- and depression-like phenotype of hph-1 mice deficient in tetrahydrobiopterin

Decreased tetrahydrobiopterin (BH4) biosynthesis has been implicated in the pathophysiology of anxiety and depression. The aim of this study was therefore to characterise the phenotype of homozygous hph-1 (hph) mice, a model of BH4 deficiency, in behavioural tests of anxiety and depression as well as determine hippocampal monoamine and plasma nitric oxide levels. In the elevated zero maze test, hph mice displayed increased anxiety-like responses compared to wild-type mice, while the marble burying test revealed decreased anxiety-like behaviour. This was particularly observed in male mice. In the tail suspension test, hph mice of both sexes displayed increased depression-like behaviours compared to wild-type counterparts, whereas the forced swim test showed a trend towards increased depression-like behaviours in male hph mice, but significant decrease in depression-like behaviours in female mice. This study provides the first evidence that congenital BH4 deficiency regulates anxiety- and depression-like behaviours. The altered responses observed possibly reflect decreased hippocampal serotonin and dopamine found in hph mice compared to wild-type mice, but also reduced nitric oxide formation. We propose that the hph-1 mouse may be a novel tool to investigate the role of BH4 deficiency in anxiety and depression.

Autistic-like syndrome in mu opioid receptor null mice is relieved by facilitated mGluR4 activity

The etiology of Autism Spectrum Disorders (ASDs) remains largely unknown. Identifying vulnerability genes for autism represents a major challenge in the field and allows the development of animal models for translational research. Mice lacking the mu opioid receptor gene (Oprm1(-/-)) were recently proposed as a monogenic mouse model of autism, based on severe deficits in social behavior and communication skills. We confirm this hypothesis by showing that adult Oprm1(-/-) animals recapitulate core and multiple comorbid behavioral symptoms of autism and also display anatomical, neurochemical, and genetic landmarks of the disease. Chronic facilitation of mGluR4 signaling, which we identified as a novel pharmacological target in ASDs in these mice, was more efficient in alleviating behavioral deficits than the reference molecule risperidone. Altogether, our data provide first evidence that disrupted mu opioid receptor signaling is sufficient to trigger a comprehensive autistic syndrome, maybe through blunted social reward processes, and this mouse model opens promising avenues for therapeutic innovation.

Sex differences in animal models of psychiatric disorders

Psychiatric disorders are characterized by sex differences in their prevalence, symptomatology and treatment response. Animal models have been widely employed for the investigation of the neurobiology of such disorders and the discovery of new treatments. However, mostly male animals have been used in preclinical pharmacological studies. In this review, we highlight the need for the inclusion of both male and female animals in experimental studies aiming at gender-oriented prevention, diagnosis and treatment of psychiatric disorders. We present behavioural findings on sex differences from animal models of depression, anxiety, post-traumatic stress disorder, substance-related disorders, obsessive-compulsive disorder, schizophrenia, bipolar disorder and autism. Moreover, when available, we include studies conducted across different stages of the oestrous cycle. By inspection of the relevant literature, it is obvious that robust sex differences exist in models of all psychiatric disorders. However, many times results are conflicting, and no clear conclusion regarding the direction of sex differences and the effect of the oestrous cycle is drawn. Moreover, there is a lack of considerable amount of studies using psychiatric drugs in both male and female animals, in order to evaluate the differential response between the two sexes. Notably, while in most cases animal models successfully mimic drug response in both sexes, test parameters and treatment-sensitive behavioural indices are not always the same for male and female rodents. Thus, there is an increasing need to validate animal models for both sexes and use standard procedures across different laboratories.

Anxiety-like behavior of mice produced by conditional central expression of the HIV-1 regulatory protein, Tat

RATIONALE

Human immunodeficiency virus (HIV) infection is associated with substantial increases in generalized anxiety. The HIV regulatory protein, transactivator of transcription (Tat), has been implicated in the neuropathogenesis related to HIV-1 infection. However, direct examination of the effect of Tat on behavioral measures of anxiety has not been demonstrated.

OBJECTIVE

To identify whether expression of the Tat1-86 protein exerts dose-dependent and persistent anxiety-like effects in a whole animal model, the GT-tg bigenic mouse.

METHODS

GT-tg mice and C57BL/6J controls were administered doxycycline in a dose- (0, 50, 100, or 125 mg/kg, i.p., for 7 days) or duration- (100 mg/kg, i.p., for 0, 1, 3, 5, or 14 days) dependent manner to induce Tat1-86 in brain. Mice were assessed for anxiety-like behavior in an open field, social interaction, or marble burying task 0, 7, and/or 14 days later. Central expression of Tat1-86 protein was verified with Western blot analyses.

RESULTS

Doxycycline produced no effects on C57BL/6J controls that lacked the Tat1-86 transgene. Among GT-tg mice, doxycycline (100 mg/kg for 3, 5, or 7 days) significantly increased anxiety-like behavior in all tasks, commensurate with enhanced Western blot labeling of Tat1-86 protein in brain, displaying optimal effects with the 7-day regimen. Greater exposure to doxycycline (either 125 mg/kg for 7 days or 100 mg/kg for 14 days) impaired locomotor behavior; whereas lower dosing (below 100 mg/kg) produced only transient increases in anxiety-like behavior.

CONCLUSIONS

Expression of HIV-1-Tat1-86 in GT-tg mouse brain produces exposure-dependent, persistent increases in anxiety-like behavior.

Atomoxetine decreases vulnerability to develop compulsivity in high impulsive rats

BACKGROUND

The factors contributing to the development and severity of obsessive-compulsive spectrum disorders such as obsessive-compulsive disorder, Tourette's syndrome, pathological gambling, and addictions remain poorly understood, limiting the development of therapeutic and preventive strategies. Recent evidence indicates that impulse-control deficits may contribute to the severity of compulsivity in several of these disorders. This suggests that impulsivity may be a transnosological endophenotype of vulnerability to compulsivity. However, the precise nature of the link between impulsivity and compulsivity in anxiety-related compulsive disorders remains unknown.

METHODS

We investigated the relationship between impulsivity and the development of a compulsive behavior in rats, which captures the hallmarks of compulsivity as defined in the DSM-IV--namely, that it is maladaptive, excessive, repetitive, and anxiolytic.

RESULTS

We demonstrate that a high-impulsivity trait, as measured in the five-choice serial reaction time task, predicts an increased propensity to develop compulsivity as measured in a schedule-induced polydipsia procedure. Trait impulsivity and compulsivity were nonlinearly related. This impulsivity-compulsivity relationship was lost after the development of compulsivity or under chronic treatment with atomoxetine, a noradrenergic reuptake inhibitor used to treat attention-deficit/hyperactivity disorder. Atomoxetine treatment both decreased impulsivity and prevented the development of compulsivity in high-impulsive animals.

CONCLUSIONS

These observations provide insight into the reciprocal influence of impulsivity and compulsivity in compulsive disorders and suggest that atomoxetine may be a useful treatment for patients suffering from obsessive-compulsive spectrum disorders with high impulsivity.

The dopamine D2/D3 receptor agonist quinpirole increases checking-like behaviour in an operant observing response task with uncertain reinforcement: a novel possible model of OCD

Excessive checking is a common, debilitating symptom of obsessive-compulsive disorder (OCD). In an established rodent model of OCD checking behaviour, quinpirole (dopamine D2/3-receptor agonist) increased checking in open-field tests, indicating dopaminergic modulation of checking-like behaviours. We designed a novel operant paradigm for rats (observing response task (ORT)) to further examine cognitive processes underpinning checking behaviour and clarify how and why checking develops. We investigated i) how quinpirole increases checking, ii) dependence of these effects on D2/3 receptor function (following treatment with D2/3 receptor antagonist sulpiride) and iii) effects of reward uncertainty. In the ORT, rats pressed an 'observing' lever for information about the location of an 'active' lever that provided food reinforcement. High- and low-checkers (defined from baseline observing) received quinpirole (0.5mg/kg, 10 treatments) or vehicle. Parametric task manipulations assessed observing/checking under increasing task demands relating to reinforcement uncertainty (variable response requirement and active-lever location switching). Treatment with sulpiride further probed the pharmacological basis of long-term behavioural changes. Quinpirole selectively increased checking, both functional observing lever presses (OLPs) and non-functional extra OLPs (EOLPs). The increase in OLPs and EOLPs was long-lasting, without further quinpirole administration. Quinpirole did not affect the immediate ability to use information from checking. Vehicle and quinpirole-treated rats (VEH and QNP respectively) were selectively sensitive to different forms of uncertainty. Sulpiride reduced non-functional EOLPs in QNP rats but had no effect on functional OLPs. These data have implications for treatment of compulsive checking in OCD, particularly for serotonin-reuptake-inhibitor treatment-refractory cases, where supplementation with dopamine receptor antagonists may be beneficial.

Spatial Navigation: Implications for Animal Models, Drug Development and Human Studies

Spatial navigation and memory is considered to be a part of the declarative memory system and it is widely used as an animal model of human declarative memory. However, spatial tests typically involve only static settings, despite the dynamic nature of the real world. Animals, as well as people constantly need to interact with moving objects, other subjects or even with entire moving environments (flowing water, running stairway). Therefore, we design novel spatial tests in dynamic environments to study brain mechanisms of spatial processing in more natural settings with an interdisciplinary approach including neuropharmacology. We also translate data from neuropharmacological studies and animal models into development of novel therapeutic approaches to neuropsychiatric disorders and more sensitive screening tests for impairments of memory, thought, and behavior.

Animal models of obsessive-compulsive spectrum disorders

Obsessive-compulsive disorder (OCD) and related conditions (trichotillomania, pathological skin-picking, pathological nail-biting) are common and disabling. Current treatment approaches fail to help a significant proportion of patients. Multiple tiers of evidence link these conditions with underlying dysregulation of particular cortico-subcortical circuitry and monoamine systems, which represent targets for treatment. Animal models designed to capture aspects of these conditions are critical for several reasons. First, they help in furthering our understanding of neuroanatomical and neurochemical underpinnings of the obsessive-compulsive (OC) spectrum. Second, they help to account for the brain mechanisms by which existing treatments (pharmacotherapy, psychotherapy, deep brain stimulation) exert their beneficial effects on patients. Third, they inform the search for novel treatments. This article provides a critique of key animal models for selected OC spectrum disorders, beginning with initial work relating to anxiety, but moving on to recent developments in domains of genetic, pharmacological, cognitive, and ethological models. We find that there is a burgeoning literature in these areas with important ramifications, which are considered, along with salient future lines of research.

Antidepressant-like properties of novel HDAC6-selective inhibitors with improved brain bioavailability

HDAC inhibitors have been reported to produce antidepressant and pro-cognitive effects in animal models, however, poor brain bioavailability or lack of isoform selectivity of current probes has limited our understanding of their mode of action. We report the characterization of novel pyrimidine hydroxyl amide small molecule inhibitors of HDAC6, brain bioavailable upon systemic administration. We show that two compounds in this family, ACY-738 and ACY-775, inhibit HDAC6 with low nanomolar potency and a selectivity of 60- to 1500-fold over class I HDACs. In contrast to tubastatin A, a reference HDAC6 inhibitor with similar potency and peripheral activity, but more limited brain bioavailability, ACY-738 and ACY-775 induce dramatic increases in α-tubulin acetylation in brain and stimulate mouse exploratory behaviors in novel, but not familiar environments. Interestingly, despite a lack of detectable effect on histone acetylation, we show that ACY-738 and ACY-775 share the antidepressant-like properties of other HDAC inhibitors, such as SAHA and MS-275, in the tail suspension test and social defeat paradigm. These effects of ACY-738 and ACY-775 are directly attributable to the inhibition of HDAC6 expressed centrally, as they are fully abrogated in mice with a neural-specific loss of function of HDAC6. Furthermore, administered in combination, a behaviorally inactive dose of ACY-738 markedly potentiates the anti-immobility activity of a subactive dose of the selective serotonin reuptake inhibitor citalopram. Our results validate new isoform-selective probes for in vivo pharmacological studies of HDAC6 in the CNS and reinforce the viability of this HDAC isoform as a potential target for antidepressant development.

Mouse models of neurodevelopmental disease of the basal ganglia and associated circuits

This chapter focuses on neurodevelopmental diseases that are tightly linked to abnormal function of the striatum and connected structures. We begin with an overview of three representative diseases in which striatal dysfunction plays a key role--Tourette syndrome and obsessive-compulsive disorder, Rett's syndrome, and primary dystonia. These diseases highlight distinct etiologies that disrupt striatal integrity and function during development, and showcase the varied clinical manifestations of striatal dysfunction. We then review striatal organization and function, including evidence for striatal roles in online motor control/action selection, reinforcement learning, habit formation, and action sequencing. A key barrier to progress has been the relative lack of animal models of these diseases, though recently there has been considerable progress. We review these efforts, including their relative merits providing insight into disease pathogenesis, disease symptomatology, and basal ganglia function.

Marble burying and nestlet shredding as tests of repetitive, compulsive-like behaviors in mice

Obsessive-compulsive disorder (OCD) and autism spectrum disorders (ASD) are serious and debilitating psychiatric conditions and each constitutes a significant public health concern, particularly in children. Both of these conditions are highlighted by the repeated expression of meaningless behaviors. Individuals with OCD often show checking, frequent hand washing, and counting. Children with ASDs also engage in repetitive tapping, arm or hand flapping, and rocking. These behaviors can vary widely in intensity and frequency of expression. More intense forms of repetitive behaviors can even result in injury (e.g. excessive grooming, hand washing, and self-stimulation). These behaviors are therefore very disruptive and make normal social discourse difficult. Treatment options for repetitive behaviors in OCD and ASDs are somewhat limited and there is great interest in developing more effective therapies for each condition. Numerous animal models for evaluating compulsive-like behaviors have been developed over the past three decades. Perhaps the animal models with the greatest validity and ease of use are the marble burying test and the nestlet shredding test. Both tests take advantage of the fact that the target behaviors occur spontaneously in mice. In the marble burying test, 20 marbles are arrayed on the surface of clean bedding. The number of marbles buried in a 30 min session is scored by investigators blind to the treatment or status of the subjects. In the nestlet shredding test, a nestlet comprised of pulped cotton fiber is preweighed and placed on top of cage bedding and the amount of the nestlet remaining intact after a 30 min test session is determined. Presently, we describe protocols for and show movie documentation of marble burying and nestlet shredding. Both tests are easily and accurately scored and each is sensitive to small changes in the expression of compulsive-like behaviors that result from genetic manipulations, disease, or head injury.

Dopaminergic control of cognitive flexibility in humans and animals

Striatal dopamine (DA) is thought to code for learned associations between cues and reinforcers and to mediate approach behavior toward a reward. Less is known about the contribution of DA to cognitive flexibility—the ability to adapt behavior in response to changes in the environment. Altered reward processing and impairments in cognitive flexibility are observed in psychiatric disorders such as obsessive compulsive disorder (OCD). Patients with this disorder show a disruption of functioning in the frontostriatal circuit and alterations in DA signaling. In this review we summarize findings from animal and human studies that have investigated the involvement of striatal DA in cognitive flexibility. These findings may provide a better understanding of the role of dopaminergic dysfunction in cognitive inflexibility in psychiatric disorders, such as OCD.

Prefrontal cortical dysfunction after overexpression of histone deacetylase 1

BACKGROUND

Postmortem brain studies have shown that HDAC1-a lysine deacetylase with broad activity against histones and nonhistone proteins-is frequently expressed at increased levels in prefrontal cortex (PFC) of subjects diagnosed with schizophrenia and related disease. However, it remains unclear whether upregulated expression of Hdac1 in the PFC could affect cognition and behavior.

METHODS

Using adeno-associated virus, an Hdac1 transgene was expressed in young adult mouse PFC, followed by behavioral assays for working and long-term memory, repetitive activity, and response to novelty. Prefrontal cortex transcriptomes were profiled by microarray. Antipsychotic drug effects were explored in mice treated for 21 days with haloperidol or clozapine.

RESULTS

Hdac1 overexpression in PFC neurons and astrocytes resulted in robust impairments in working memory, increased repetitive behaviors, and abnormal locomotor response profiles in novel environments. Long-term memory remained intact. Over 300 transcripts showed subtle but significant changes in Hdac1-overexpressing PFC. Major histocompatibility complex class II (MHC II)-related transcripts, including HLA-DQA1/H2-Aa, HLA-DQB1/H2-Ab1, and HLA-DRB1/H2-Eb1, located in the chromosome 6p21.3-22.1 schizophrenia and bipolar disorder risk locus, were among the subset of genes with a more robust (>1.5-fold) downregulation in expression. Hdac1 levels declined during the course of normal PFC development. Antipsychotic drug treatment, including the atypical clozapine, did not affect Hdac1 levels in PFC but induced expression of multiple MHC II transcripts.

CONCLUSIONS

Excessive HDAC1 activity, due to developmental defects or other factors, is associated with behavioral alterations and dysregulated expression of MHC II and other gene transcripts in the PFC.