Spontaneous alternation behavior: an animal model for obsessive-compulsive disorder?

Early and transitory hypoactivity and olfactory alterations after chronic atrazine exposure in female Sprague-Dawley rats

Several studies have shown that chronic exposure to the herbicide atrazine (ATR) causes alterations in locomotor activity and markers of the dopaminergic systems of male rats. However, few studies have evaluated the sex-dependent effects of atrazine exposure. The aim of the present study was to evaluate whether chronic ATR exposure causes alterations in behavioral performance and dopaminergic systems of female rats. At weaning, two groups of rats were exposed to 1 or 10 mg ATR/kg body weight daily thorough the food, while the control group received food without ATR for 14 months. Spontaneous locomotor activity was evaluated monthly for 12 months, while anxiety, egocentric and spatial memory, motor coordination, and olfactory function tasks were evaluated between 13 and 14 months of ATR exposure. Tyrosine hydroxylase (TH) and monoamine content in brain tissue were assessed at the end of ATR treatment. Female rats treated with 1 or 10 mg ATR showed vertical hypoactivity compared to the control group only in the first month of ATR exposure. Impairments in olfactory functions were found due to ATR exposure. Nevertheless, no alterations in anxiety, spatial and egocentric memory, or motor coordination tasks were observed, while the levels of TH and dopamine and its metabolites in brain tissue were similar among groups. These results suggest that female rats could present greater sensitivity to the neurotoxic effects of ATR on spontaneous locomotor activity in the early stages of development. However, they are unaffected by chronic ATR exposure later in life compared to male rats. More studies are necessary to unravel the sex-related differences observed after chronic ATR exposure.

Acetyl-11-keto-beta boswellic acid(AKBA) modulates CSTC-pathway by activating SIRT-1/Nrf2-HO-1 signalling in experimental rat model of obsessive-compulsive disorder: Evidenced by CSF, blood plasma and histopathological alterations

Obsessive-Compulsive disorder (OCD) is a long-term and persistent mental illness characterised by obsessive thoughts and compulsive behaviours. Numerous factors can contribute to the development or progression of OCD. These factors may result from the dysregulation of multiple intrinsic cellular pathways, including SIRT-1, Nrf2, and HO-1. Inhibitors of selective serotonin reuptake (SSRIs) are effective first-line treatments for OCD. In our ongoing research, we have investigated the role of SIRT-1, Nrf2, and HO-1, as well as the neuroprotective potential of Acetyl-11-keto-beta boswellic acid (AKBA) against behavioural and neurochemical changes in rodents treated with 8-OH-DPAT. In addition, the effects of AKBA were compared to those of fluvoxamine (FLX), a standard OCD medication. Injections of 8-OH-DPAT into the intra-dorso raphe nuclei (IDRN) of rats for seven days induced repetitive and compulsive behaviour accompanied by elevated oxidative stress, inflammatory processes, apoptosis, and neurotransmitter imbalances in CSF, blood plasma, and brain samples. Chronic administration of AKBA at 50 mg/kg and 100 mg/kg p.o. restored histopathological alterations in the cortico-striatal-thalamo-cortical (CSTC) pathway, including the cerebral cortex, striatum, and hippocampal regions. Our investigation revealed that when AKBA and fluvoxamine were administered together, the alterations were restored to a greater degree than when administered separately. These findings demonstrate that the neuroprotective effect of AKBA can serve as an effective basis for developing a novel OCD treatment.

Specifics of Experimental Modeling 8-OH-DPAT-Induced Perseverative Behavior in Mice

The effect of 5-HT_1A receptor agonist 8-OH-DPAT (intraperitoneal injection in doses of 1, 2, and 4 mg/kg) on spontaneous alternation behavior of mice in Y-maze was studied without and with habituation procedure and food reward. In the first case, 8-OH-DPAT administration led to a decrease in spontaneous alternation and locomotor activity in mice. At the same time, 8-OH-DPAT treatment after habituation and food deprivation increased repeated choices of goal arms without affecting locomotor activity, which was consistent with perseverative behavior. 8-OH-DPAT-induced decrease in spontaneous alternation behavior in Y-maze in mice with habituation and food reward is the most suitable procedure for experimental modeling of the perseverative behavior and studying the anticompulsive activity of new substances.

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.

Animal Behavior in Psychedelic Research

Psychedelic-assisted psychotherapy holds great promise in the treatment of mental health disorders. Research into 5-hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelic compounds has increased dramatically over the past two decades. In humans, these compounds produce drastic effects on consciousness, and their therapeutic potential relates to changes in the processing of emotional, social, and self-referential information. The use of animal behavior to study psychedelics is under debate, and this review provides a critical perspective on the translational value of animal behavior studies in psychedelic research. Acute activation of 5-HT_2ARs produces head twitches and unique discriminative cues, disrupts sensorimotor gating, and stimulates motor activity while inhibiting exploration in rodents. The acute treatment with psychedelics shows discrepant results in conventional rodent tests of depression-like behaviors but generally induces anxiolytic-like effects and inhibits repetitive behavior in rodents. Psychedelics impair waiting impulsivity but show discrepant effects in other tests of cognitive function. Tests of social interaction also show conflicting results. Effects on measures of time perception depend on the experimental schedule. Lasting or delayed effects of psychedelics in rodent tests related to different behavioral domains appear to be rather sensitive to changes in experimental protocols. Studying the effects of psychedelics on animal behaviors of relevance to effects on psychiatric symptoms in humans, assessing lasting effects, publishing negative findings, and relating behaviors in rodents and humans to other more translatable readouts, such as neuroplastic changes, will improve the translational value of animal behavioral studies in psychedelic research. SIGNIFICANCE STATEMENT: Psychedelics like LSD and psilocybin have received immense interest as potential new treatments of psychiatric disorders. Psychedelics change high-order consciousness in humans, and there is debate about the use of animal behavior studies to investigate these compounds. This review provides an overview of the behavioral effects of 5-HT_2AR agonist psychedelics in laboratory animals and discusses the translatability of the effects in animals to effects in humans. Possible ways to improve the utility of animal behavior in psychedelic research are discussed.

Spontaneous alternation and stereotypical behaviour in deer mice: response to escitalopram and levetiracetam

Obsessive-compulsive disorder is varyingly associated with cognitive impairment, that is, deficits in spatial working memory, although it seems unlikely that this is generalised across all domains of functioning. Further, it is unclear whether symptoms will respond to potentially novel, non-serotonergic drugs that have shown promise as so-called cognitive enhancers. Here, we studied low (Norm-N; n = 31) and compulsive-like high (Comp-H; n = 34) stereotypical deer mice (Peromyscus maniculatus bairdii) to establish (1) whether there is a relationship between stereotypical intensity and working memory ability as measured by spontaneous T-maze arm alternation and (2) if and how stereotypy and its association with changes in working memory, would respond to the known anti-compulsive agent, escitalopram, and the proposed cognitive enhancer, levetiracetam. After assessing the stereotypical and alternation behaviour of all animals at baseline, they were divided into three socially housed drug exposure groups, that is, water control (n = 11 per phenotype), escitalopram 50 mg/kg/d (n = 11 per phenotype) and levetiracetam 75 mg/kg/d (Norm-N: n = 9; Comp-H: n = 12). Drugs were administered for 28 days before stereotypy and alternation assessment were repeated. The present data indicate a weak negative relationship between stereotypical intensity and spontaneous alternation. While levetiracetam increased the time spent engaging in normal rodent activity by Comp-H, but not Norm-N animals, neither of the interventions affected the expression of Comp-H behaviour or the alternation behaviour of deer mice. In conclusion, this work points to some degree of cognitive involvement in Comp-H expression, which should be explored to further our understanding of compulsive-like stereotypy.

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

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

Memantine and Riluzole Exacerbate, Rather Than Ameliorate Behavioral Deficits Induced by 8-OH-DPAT Sensitization in a Spatial Task

Chronic sensitization to serotonin 1A and 7 receptors agonist 8-OH-DPAT induces compulsive checking and perseverative behavior. As such, it has been used to model obsessive-compulsive disorder (OCD)-like behavior in mice and rats. In this study, we tested spatial learning in the 8-OH-DPAT model of OCD and the effect of co-administration of memantine and riluzole—glutamate-modulating agents that have been shown to be effective in several clinical trials. Rats were tested in the active place avoidance task in the Carousel maze, where they learned to avoid the visually imperceptible shock sector. All rats were subcutaneously injected with 8-OH-DPAT (0.25 mg/kg) or saline (control group) during habituation. During acquisition, they were pretreated with riluzole (1 mg/kg), memantine (1 mg/kg), or saline solution 30 min before each session and injected with 8-OH-DPAT (“OH” groups) or saline (“saline” groups) right before the experiment. We found that repeated application of 8-OH-DPAT during both habituation and acquisition significantly increased locomotion, but it impaired the ability to avoid the shock sector. However, the application of 8-OH-DPAT in habituation had no impact on the learning process if discontinued in acquisition. Similarly, memantine and riluzole did not affect the measured parameters in the “saline” groups, but in the “OH” groups, they significantly increased locomotion. In addition, riluzole increased the number of entrances and decreased the maximum time avoided of the shock sector. We conclude that monotherapy with glutamate-modulating agents does not reduce but exacerbates cognitive symptoms in the animal model of OCD.

Stereotypy and spontaneous alternation in deer mice and its response to anti-adenosinergic intervention

Repetitive behavioral phenotypes are a trait of several neuropsychiatric disorders, including obsessive-compulsive disorder (OCD). Such behaviors are typified by complex interactions between cognitive and neurobiological processes which most likely contribute to the suboptimal treatment responses often observed. To this end, exploration of the adenosinergic system may be useful, since adenosine-receptor modulation has previously shown promise to restore control over voluntary behavior and improve cognition in patients presenting with motor repetition. Here, we employed the deer mouse (Peromyscus maniculatus bairdii) model of compulsive-like behavioral persistence, seeking to investigate possible associations between stereotypic motor behavior and cognitive flexibility as measured in the T-maze continuous alternation task (T-CAT). The effect of istradefylline, a selective adenosine A_2A receptor antagonist at two doses (10 and 20 mg kg^-1  day^-1 ) on the expression of stereotypy and T-CAT performance in high (H) and non-(N) stereotypical animals, was investigated in comparison to a control intervention (six groups; n = 8 or 9 per group). No correlation between H behavior and T-CAT performance was found. However, H but not N animals presented with istradefylline-sensitive spontaneous alternation and stereotypy, in that istradefylline at both doses significantly improved the spontaneous alternation scores and attenuated the stereotypical expression of H animals. Thus, evidence is presented that anti-adenosinergic drug action improves repetitive behavior and spontaneous alternation in stereotypical deer mice, putatively pointing to a shared psychobiological construct underlying naturalistic stereotypy and alterations in cognitive flexibility in deer mice.

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.

New Era of Diacylglycerol Kinase, Phosphatidic Acid and Phosphatidic Acid-Binding Protein

Diacylglycerol kinase (DGK) phosphorylates diacylglycerol (DG) to generate phosphatidic acid (PA). Mammalian DGK consists of ten isozymes (α–κ) and governs a wide range of physiological and pathological events, including immune responses, neuronal networking, bipolar disorder, obsessive-compulsive disorder, fragile X syndrome, cancer, and type 2 diabetes. DG and PA comprise diverse molecular species that have different acyl chains at the sn-1 and sn-2 positions. Because the DGK activity is essential for phosphatidylinositol turnover, which exclusively produces 1-stearoyl-2-arachidonoyl-DG, it has been generally thought that all DGK isozymes utilize the DG species derived from the turnover. However, it was recently revealed that DGK isozymes, except for DGKε, phosphorylate diverse DG species, which are not derived from phosphatidylinositol turnover. In addition, various PA-binding proteins (PABPs), which have different selectivities for PA species, were recently found. These results suggest that DGK–PA–PABP axes can potentially construct a large and complex signaling network and play physiologically and pathologically important roles in addition to DGK-dependent attenuation of DG–DG-binding protein axes. For example, 1-stearoyl-2-docosahexaenoyl-PA produced by DGKδ interacts with and activates Praja-1, the E3 ubiquitin ligase acting on the serotonin transporter, which is a target of drugs for obsessive-compulsive and major depressive disorders, in the brain. This article reviews recent research progress on PA species produced by DGK isozymes, the selective binding of PABPs to PA species and a phosphatidylinositol turnover-independent DG supply pathway.

Large nest building and high marble-burying: Two compulsive-like phenotypes expressed by deer mice (Peromyscus maniculatus bairdii) and their unique response to serotoninergic and dopamine modulating intervention

This study aimed to further dissect the deer mouse (Peromyscus maniculatus bairdii) model of compulsive-like behavior with respect to two persistent-like behavioral phenotypes viz. large nest building (LNB) and high marble-burying (HMB), which may be relevant to understanding the neurobiology of different symptom dimensions in obsessive-compulsive and related disorders. Since LNB is sensitive to chronic, high dose escitalopram intervention but HMB is not, we assessed whether the two behaviors could be further distinguished based on their response to 4 weeks of uninterrupted serotoninergic intervention (i.e. escitalopram; ESC; 50 mg/kg/day), dopaminergic antagonism, i.e. flupentixol; FLU; 0.9 mg/kg/day), dopaminergic potentiation (i.e. rasagiline; RAS; 5 mg/kg/day), and their respective combinations with escitalopram (ESC/FLU and ESC/RAS). Here we show LNB to be equally responsive to chronic ESC and ESC/FLU. HMB was insensitive to either of these interventions but was responsive to ESC/RAS. Additionally, we report that scoring preoccupied interaction with marbles over several trials is an appropriate measure of compulsive-like behavioral persistence in addition to the standard marble burying test. Taken together, these data provide further evidence that LNB and HMB in deer mice have distinctive neurobiological underpinnings. Thus, the naturally occurring compulsive-like behaviors expressed by deer mice may be useful in providing a platform to test unique treatment targets for different symptom dimensions of OCD and related disorders.

A critical inquiry into marble-burying as a preclinical screening paradigm of relevance for anxiety and obsessive-compulsive disorder: Mapping the way forward

Rodent marble-burying behavior in the marble-burying test (MBT) is employed as a model or measure to study anxiety- and compulsive-like behaviors or anxiolytic and anticompulsive drug action. However, the test responds variably to a range of pharmacological interventions, and little consensus exists regarding specific methodologies for its execution. Regardless, the test is widely applied to investigate the effects of pharmacological, genetic, and behavioral manipulations on purported behaviors related to the said neuropsychiatric constructs. Therefore, in the present review we attempt to expound the collective translational significance of the MBT. We do this by (1) reviewing burying behavior as a natural behavioral phenotype, (2) highlighting key aspects of anxiety and obsessive-compulsive disorder from a translational perspective, (3) reviewing the history and proof of concept of the MBT, (4) critically appraising potential methodological confounds in execution of the MBT, and (5) dissecting responses of the MBT to various pharmacological interventions. We conclude by underlining that the collective translational value of the MBT will be strengthened by contextually valid experimental designs and objective reporting of data.

CUL3 Deficiency Causes Social Deficits and Anxiety-like Behaviors by Impairing Excitation-Inhibition Balance through the Promotion of Cap-Dependent Translation

Autism spectrum disorders (ASD) are a group of neurodevelopmental disorders with symptoms including social deficits, anxiety, and communication difficulties. However, ASD pathogenic mechanisms are poorly understood. Mutations of CUL3, which encodes Cullin 3 (CUL3), a component of an E3 ligase complex, are thought of as risk factors for ASD and schizophrenia (SCZ). CUL3 is abundant in the brain, yet little is known of its function. Here, we show that CUL3 is critical for neurodevelopment. CUL3-deficient mice exhibited social deficits and anxiety-like behaviors with enhanced glutamatergic transmission and neuronal excitability. Proteomic analysis revealed eIF4G1, a protein for Cap-dependent translation, as a potential target of CUL3. ASD-associated cellular and behavioral deficits could be rescued by pharmacological inhibition of the eIF4G1 function and chemogenetic inhibition of neuronal activity. Thus, CUL3 is critical to neural development, neurotransmission, and excitation-inhibition (E-I) balance. Our study provides novel insight into the pathophysiological mechanisms of ASD and SCZ.

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.

Marble-burying behavior test as a murine model of compulsive-like behavior

Object burying by rodents is a popular screening tool for anxiolytic agents. However, modulation of marble-burying by serotonin reuptake inhibitors prompted its link to obsessive-compulsive disorder/compulsive-like behavior. The Marble-burying behavior test is an acute test; however, some investigators incorporate the sub-acute treatment regimen as an essential component for screening anti-compulsive agents. The test exhibits between-laboratory methodological differences and demonstrates positive treatment responses to an array of pharmacotherapies, creating doubts about its predictive validity and construct validity. Numerous reviews are available on marble-burying behavior test, which incorporates the test as a part of anti-compulsive behavior-like screens, but none has made it a sole subject-matter for discussion. This review attempts to provide a comprehensive account of the marble-burying test as a model of compulsive-like disorders. It envisages the model's scientific origins, the preclinical research done and its correlation with the clinical research outcomes, and a detailed discussion about its validity. In conclusion, there appears a need to address the issue of construct and predictive validity of the model authoritatively; or the paradigm may remain squandered in the field of obsessive-compulsive disorder research.

The Neuronal Glutamate Transporter EAAT3 in Obsessive-Compulsive Disorder

Obsessive compulsive disorder (OCD) is a heterogeneous psychiatric disorder affecting 1%–3% of the population worldwide. About half of OCD afflicted individuals do not respond to currently available pharmacotherapy, which is mainly based on serotonin reuptake inhibition. Therefore, there is a critical need to search novel and improved therapeutic targets to treat this devastating disorder. In recent years, accumulating evidence has supported the glutamatergic hypothesis of OCD, and particularly pointing a potential role for the neuronal glutamate transporter EAAT3. This mini-review summarizes recent findings regarding the neurobiological basis of OCD, with an emphasis on the glutamatergic neurotransmission and EAAT3 as a key player in OCD etiology.

The 5-hydroxytryptamine 2A receptor agonists DOI and 25CN-NBOH decrease marble burying and reverse 8-OH-DPAT-induced deficit in spontaneous alternation

5-Hydroxytryptamine 2A receptor (5-HT_2AR) agonist psychedelics are increasingly recognized as potentially useful treatments of psychiatric disorders, such as obsessive-compulsive disorder, depression, anxiety, and drug dependence. There is limited understanding of the way they exert their therapeutic action, but inhibition of rigid behavior and cognition has been suggested as a key factor. To examine the role of 5-HT_2ARs in modulating repetitive behavior, we tested two 5-HT_2AR agonists, DOI, and the selective 25CN-NBOH, in two mouse tests of compulsive-like behavior. Using adult C57BL/6JOlaHsd male mice, we examined the effects of the two compounds on digging behavior in the marble burying test and on 8-OH-DPAT-disrupted spontaneous alternation behavior in the Y-maze. Both compounds dose-dependently decreased digging behavior in the marble burying test, indicating anti-compulsivity effects, which were not related to non-specific locomotor inhibition. Both 5-HT_2AR agonists also reversed 8-OH-DPAT-reduced alternation ratio in the spontaneous alternation behavior test, although the effects were less pronounced than in the marble burying test. This suggests that the 5-HT_2AR promotes exploratory behavior, but that the deficit produced by 8-OH-DPAT is too excessive to be fully reversed by 5-HT_2AR agonists. This study shows that agonism of 5-HT_2AR reduces repetitive behavioral patterns, supporting the theory that this is a potential new treatment approach to disorders of cognitive or behavioral inflexibility. This article is part of the special issue entitled 'Serotonin Research: Crossing Scales and Boundaries'.

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.

Converging evidence points towards a role of insulin signaling in regulating compulsive behavior

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder with childhood onset, and is characterized by intrusive thoughts and fears (obsessions) that lead to repetitive behaviors (compulsions). Previously, we identified insulin signaling being associated with OCD and here, we aim to further investigate this link in vivo. We studied TALLYHO/JngJ (TH) mice, a model of type 2 diabetes mellitus, to (1) assess compulsive and anxious behaviors, (2) determine neuro-metabolite levels by 1 H magnetic resonance spectroscopy (MRS) and brain structural connectivity by diffusion tensor imaging (DTI), and (3) investigate plasma and brain protein levels for molecules previously associated with OCD (insulin, Igf1, Kcnq1, and Bdnf) in these subjects. TH mice showed increased compulsivity-like behavior (reduced spontaneous alternation in the Y-maze) and more anxiety (less time spent in the open arms of the elevated plus maze). In parallel, their brains differed in the white matter microstructure measures fractional anisotropy (FA) and mean diffusivity (MD) in the midline corpus callosum (increased FA and decreased MD), in myelinated fibers of the dorsomedial striatum (decreased FA and MD), and superior cerebellar peduncles (decreased FA and MD). MRS revealed increased glucose levels in the dorsomedial striatum and increased glutathione levels in the anterior cingulate cortex in the TH mice relative to their controls. Igf1 expression was reduced in the cerebellum of TH mice but increased in the plasma. In conclusion, our data indicates a role of (abnormal) insulin signaling in compulsivity-like behavior.

8-OH-DPAT Induces Compulsive-like Deficit in Spontaneous Alternation Behavior: Reversal by MDMA but Not Citalopram

Rodents exhibit natural exploratory behaviors, which can be measured by the spontaneous alternation behavior (SAB) test. Perseverance in this test induced by the 5-hydroxytryptamine 1A receptor (5-HT_1AR) agonist, 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT), resembles compulsive behaviors observed in humans and manifests as reduced alternation ratio. This study characterized 8-OH-DPAT-induced perseverance in the SAB test in C57BL/6JOlaHsd male mice by coadministration of WAY100635, citalopram and the 5-HT releasing agent, 3,4-methylenedioxymethamphetamine (MDMA), to deepen the understanding of 5-HT-dependent mechanisms. The 5-HT_1AR mechanism of 8-OH-DPAT (1.0 mg/kg, p < 0.01) on perseverance was confirmed by coadministration of the 5-HT_1AR antagonist, WAY100635 (2.0 mg/kg, p < 0.05), which attenuated the effects of 8-OH-DPAT. Such effects could also be reversed by MDMA (1.0 mg/kg, p < 0.05; 10.0 mg/kg, p < 0.001) but not citalopram. These findings confirm the importance of 5-HT in regulating perseverative behavior. Future investigations are required to determine the predictive validity of the 8-OH-DPAT-disrupted SAB test as an inducible mouse model of compulsivity.

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

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

Disease-modifying effects of ganglioside GM1 in Huntington's disease models

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor, cognitive and psychiatric problems. Previous studies indicated that levels of brain gangliosides are lower than normal in HD models and that administration of exogenous ganglioside GM1 corrects motor dysfunction in the YAC128 mouse model of HD In this study, we provide evidence that intraventricular administration of GM1 has profound disease-modifying effects across HD mouse models with different genetic background. GM1 administration results in decreased levels of mutant huntingtin, the protein that causes HD, and in a wide array of beneficial effects that include changes in levels of DARPP32, ferritin, Iba1 and GFAP, modulation of dopamine and serotonin metabolism, and restoration of normal levels of glutamate, GABA, L-Ser and D-Ser. Treatment with GM1 slows down neurodegeneration, white matter atrophy and body weight loss in R6/2 mice. Motor functions are significantly improved in R6/2 mice and restored to normal in Q140 mice, including gait abnormalities that are often resistant to treatments. Psychiatric-like and cognitive dysfunctions are also ameliorated by GM1 administration in Q140 and YAC128 mice. The widespread benefits of GM1 administration, at molecular, cellular and behavioural levels, indicate that this ganglioside has strong therapeutic and disease-modifying potential in HD.

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.

Adult zebrafish in CNS disease modeling: a tank that's half-full, not half-empty, and still filling

The zebrafish (Danio rerio) is increasingly used in a broad array of biomedical studies, from cancer research to drug screening. Zebrafish also represent an emerging model organism for studying complex brain diseases. The number of zebrafish neuroscience studies is exponentially growing, significantly outpacing those conducted with rodents or other model organisms. Yet, there is still a substantial amount of resistance in adopting zebrafish as a first-choice model system. Studies of the repertoire of zebrafish neural and behavioral functions continue to reveal new opportunities for understanding the pathobiology of various CNS deficits. Although some of these models are well established in zebrafish, including models for anxiety, depression, and addiction, others are less recognized, for example, models of autism and obsessive-compulsive states. However, mounting data indicate that a wide spectrum of CNS diseases can be modeled in adult zebrafish. Here, we summarize recent findings using zebrafish CNS assays, discuss model limitations and the existing challenges, as well as outline future directions of research in this field.

Postpartum Lactation-Mediated Behavioral Outcomes and Drug Responses in a Spontaneous Mouse Model of Obsessive-Compulsive Disorder

Using a spontaneous mouse model of obsessive-compulsive disorder (OCD), the current study evaluated the influence of postpartum lactation on the expression of compulsive-like behaviors, SSRI effectiveness, and the putative role of oxytocin and dopamine in mediating these lactation specific behavioral outcomes. Compulsive-like lactating mice were less compulsive-like in nest building and marble burying and showed enhanced responsiveness to fluoxetine (50 mg/kg) in comparison to compulsive-like nonlactating and nulliparous females. Lactating mice exhibited more anxiety-like behavior in the open field test compared to the nulliparous females, while chronic fluoxetine reduced anxiety-like behaviors. Blocking the oxytocin receptor with L368-899 (5 mg/kg) in the lactating mice exacerbated the compulsive-like and depression-like behaviors. The dopamine D2 receptor (D2R) agonist bromocriptine (10 mg/kg) suppressed marble burying, nest building, and central entries in the open field, but because it also suppressed overall locomotion in the open field, activation of the D2R receptor may have inhibited overall activity nonspecifically. Lactation- and fluoxetine-mediated behavioral outcomes in compulsive-like mice, therefore, appear to be partly regulated by oxytocinergic mechanisms. Serotonin immunoreactivity and serum levels were higher in lactating compulsive-like mice compared to nonlactating and nulliparous compulsive-like females. Together, these results suggest behavioral modulation, serotonergic alterations, and changes in SSRI effectiveness during lactation in compulsive-like mice. This warrants further investigation of postpartum events in OCD patients.

Complete Disruption of the Kainate Receptor Gene Family Results in Corticostriatal Dysfunction in Mice

Kainate receptors are members of the glutamate receptor family that regulate synaptic function in the brain. They modulate synaptic transmission and the excitability of neurons; however, their contributions to neural circuits that underlie behavior are unclear. To understand the net impact of kainate receptor signaling, we generated knockout mice in which all five kainate receptor subunits were ablated (5ko). These mice displayed compulsive and perseverative behaviors, including over-grooming, as well as motor problems, indicative of alterations in striatal circuits. There were deficits in corticostriatal input to spiny projection neurons (SPNs) in the dorsal striatum and correlated reductions in spine density. The behavioral alterations were not present in mice only lacking the primary receptor subunit expressed in adult striatum (GluK2 KO), suggesting that signaling through multiple receptor types is required for proper striatal function. This demonstrates that alterations in striatal function dominate the behavioral phenotype in mice without kainate receptors.

Validity of Quinpirole Sensitization Rat Model of OCD: Linking Evidence from Animal and Clinical Studies

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder with 1–3% prevalence. OCD is characterized by recurrent thoughts (obsessions) and repetitive behaviors (compulsions). The pathophysiology of OCD remains unclear, stressing the importance of pre-clinical studies. The aim of this article is to critically review a proposed animal model of OCD that is characterized by the induction of compulsive checking and behavioral sensitization to the D2/D3 dopamine agonist quinpirole. Changes in this model have been reported at the level of brain structures, neurotransmitter systems and other neurophysiological aspects. In this review, we consider these alterations in relation to the clinical manifestations in OCD, with the aim to discuss and evaluate axes of validity of this model. Our analysis shows that some axes of validity of quinpirole sensitization model (QSM) are strongly supported by clinical findings, such as behavioral phenomenology or roles of brain structures. Evidence on predictive validity is contradictory and ambiguous. It is concluded that this model is useful in the context of searching for the underlying pathophysiological basis of the disorder because of the relatively strong biological similarities with OCD.

Rodent models of obsessive compulsive disorder: Evaluating validity to interpret emerging neurobiology

Obsessive Compulsive Disorder (OCD) is a common neuropsychiatric disorder with unknown molecular underpinnings. Identification of genetic and non-genetic risk factors has largely been elusive, primarily because of a lack of power. In contrast, neuroimaging has consistently implicated the cortico-striatal-thalamo-cortical circuits in OCD. Pharmacological treatment studies also show specificity, with consistent response of OCD symptoms to chronic treatment with serotonin reuptake inhibitors; although most patients are left with residual impairment. In theory, animal models could provide a bridge from the neuroimaging and pharmacology data to an understanding of pathophysiology at the cellular and molecular level. Several mouse models have been proposed using genetic, immunological, pharmacological, and optogenetic tools. These experimental model systems allow testing of hypotheses about the origins of compulsive behavior. Several models have generated behavior that appears compulsive-like, particularly excessive grooming, and some have demonstrated response to chronic serotonin reuptake inhibitors, establishing both face validity and predictive validity. Construct validity is more difficult to establish in the context of a limited understanding of OCD risk factors. Our current models may help us to dissect the circuits and molecular pathways that can elicit OCD-relevant behavior in rodents. We can hope that this growing understanding, coupled with developing technology, will prepare us when robust OCD risk factors are better understood.

Influence of Long-Term Zinc Administration on Spatial Learning and Exploratory Activity in Rats

Animal brain contains a significant amount of zinc, which is a cofactor for more than 300 enzymes. Moreover, it provides the basis for functioning of more than 2000 transcription factors, and it is necessary for memory formation and learning processes in the brain. The aim of this study was to investigate the effect of zinc supplementation on behavior in 3-month-old rats. For this purpose, the Morris water maze paradigm, hole-board, and T-maze were used. Wistar rats received a solution of ZnSO4 in drinking water at the doses of 16 mg/kg (Zn16 group) and 32 mg/kg (Zn32 group). In rats pretreated with the lower dose of zinc, the improvement of the mean escape latency was observed in comparison to the control group and Zn32 group. During memory task, both ZnSO4-supplemented groups showed an increase in crossings over the previous platform position. Furthermore, the exploratory activity in Zn16 group was improved in comparison to Zn32 and control group. In the brains of zinc-supplemented rats, we observed the higher content of zinc, both in the hippocampus and the prefrontal cortex. Hippocampal zinc level correlated positively with the mean annulus crossings of the Zn16 group during the probe trial. These findings show that the long-term administration of ZnS04 can improve learning, spatial memory, and exploratory activity in rats. Graphical Abstract Improvement of spatial learning, memory, and exploratory behavior.

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.

Mice repeatedly exposed to Group-A β-Haemolytic Streptococcus show perseverative behaviors, impaired sensorimotor gating, and immune activation in rostral diencephalon

Repeated exposure to Group-A β-Haemolytic Streptococcus (GAS) may constitute a vulnerability factor in the onset and course of pediatric motor disturbances. GAS infections/colonization can stimulate the production of antibodies, which may cross the blood brain barrier, target selected brain areas (e.g. basal ganglia), and exacerbate motor alterations. Here, we exposed developing SJL male mice to four injections with a GAS homogenate and evaluated the following domains: motor coordination; general locomotion; repetitive behaviors; perseverative responses; and sensorimotor gating (pre-pulse inhibition, PPI). To demonstrate that behavioral changes were associated with immune-mediated brain alterations, we analyzed, in selected brain areas, the presence of infiltrates and microglial activation (immunohistochemistry), monoamines (HPLC), and brain metabolites (in vivo Magnetic Resonance Spectroscopy). GAS-exposed mice showed increased repetitive and perseverative behaviors, impaired PPI, and reduced concentrations of serotonin in prefrontal cortex, a brain area linked to the behavioral domains investigated, wherein they also showed remarkable elevations in lactate. Active inflammatory processes were substantiated by the observation of infiltrates and microglial activation in the white matter of the anterior diencephalon. These data support the hypothesis that repeated GAS exposure may elicit inflammatory responses in brain areas involved in motor control and perseverative behavior, and result in phenotypic abnormalities.

Brain and behavioral perturbations in rats following Western diet access

Energy dense "Western" diets (WD) are known to cause obesity as well as learning and memory impairments, blood-brain barrier damage, and psychological disturbances. Impaired glucose (GLUT1) and monocarboxylate (MCT1) transport may play a role in diet-induced dementia development. In contrast, ketogenic diets (KD) have been shown to be neuroprotective. We assessed the effect of 10, 40 and 90 days WD, KD and Chow maintenance on spontaneous alternation (SA) and vicarious trial and error (VTE) behaviors in male rats, then analyzed blood glucose, insulin, and ketone levels; and hippocampal GLUT1 and MCT1 mRNA. Compared to Chow and KD, rats fed WD had increased 90 day insulin levels. SA was decreased in WD rats at 10, but not 40 or 90 days. VTE was perturbed in WD-fed rats, particularly at 10 and 90 days, indicating hippocampal deficits. WD rats had lower hippocampal GLUT1 and MCT1 expression compared to Chow and KD, and KD rats had increased 90 day MCT1 expression compared to Chow and WD. These data suggest that WD reduces glucose and monocarboxylate transport at the hippocampus, which may result in learning and memory deficits. Further, KD consumption may be useful for MCT1 transporter recovery, which may benefit cognition.

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.

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.

Separate mechanisms for development and performance of compulsive checking in the quinpirole sensitization rat model of obsessive-compulsive disorder (OCD)

RATIONALE

Acute administration of serotonergic agonist, meta-chlorophenylpiperazine (mCPP), attenuates performance of compulsive checking in an animal model of obsessive-compulsive disorder (OCD). It is not known whether mCPP has a similar effect on development of compulsive checking.

OBJECTIVES

The objective of the study was to examine whether similar mechanisms mediate the development versus the performance of compulsive checking in the rat model.

METHODS

Four groups of male rats (N = 14/group) were tested: two experimental groups co-injected with D2/D3 dopamine agonist quinpirole (0.25 mg/kg) and mCPP (0.625 mg/kg or 1.25 mg/kg), and two control groups, one co-injected with quinpirole and saline, the other receiving injections of saline. The time course of development of compulsive checking across injections 1 to 10 in quinpirole-treated rats was compared to rats co-injected with quinpirole and mCPP.

RESULTS

Results showed that during the course of chronic treatment, mCPP (1.25 mg/kg) significantly attenuated performance of checking behavior. However, when these rats were retested for expression of compulsive checking (that is, with an injection of quinpirole only), their profile of compulsive checking was no different from the control rats treated throughout with quinpirole only.

CONCLUSIONS

Findings show that mCPP inhibits performance of compulsive checking but does not block quinpirole from inducing the neural substrate underlying this compulsive behavior. Hence, a separate mechanism underlies the induction of compulsive checking and the performance of it. It is suggested that development of the OCD endophenotype reflects neuroplastic changes produced by repeated dopamine D2/D3 receptor stimulation, while stimulation of serotonergic receptors mediates a negative feedback signal that shuts down the motor performance of checking.

Performance of compulsive behavior in rats is not a unitary phenomenon - validation of separate functional components in compulsive checking behavior

A previous analysis of the quinpirole sensitisation rat model of obsessive-compulsive disorder revealed that the behavioral phenotype of compulsive checking consists of three constitutive components – vigor of checking performance, focus on the task of checking, and satiety following a bout of checking. As confirmation of this analysis, the aim of the present study was to reconstitute, without quinpirole treatment, each of the putative components, with the expectation that these would self-assemble into compulsive checking. To reconstitute vigor and satiety, the employed treatment was a bilateral lesion of the nucleus accumbens core (NAc), as this treatment was shown previously to exaggerate these components. To reconstitute focus, the employed treatment was a low dose of the serotonin-1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin hydrochloride (DPAT) (0.0625 mg/kg), as high doses of this drug induce compulsive behavior and exacerbate focus. Results showed that injection of DPAT to NAc lesion rats did yield compulsive checking. Neither the drug alone nor the NAc lesion by itself produced compulsive checking. The demonstrated synthesis of compulsive checking by the combined treatment of low-dose DPAT and NAc lesion strengthened the previous fractionation of the model obsessive-compulsive disorder phenotype into three constitutive components, and suggested a role for serotonin-1A receptors outside the NAc in enhanced focus on the task of checking.

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.

Emerging drugs to treat obsessive-compulsive disorder

INTRODUCTION

Obsessive-compulsive disorder (OCD) is a chronic and disabling neuropsychiatric disorder with a lifetime prevalence of approximately 1 - 2% and a rate of treatment resistance of 40%. Other disorders have been related to OCD and have been grouped together in a separate DSM-5 chapter, hypothesizing the existence of an 'OC spectrum', showing a paradigm shift in the conceptualization of the disorder.

AREAS COVERED

A review of the most important and recent neurobiological findings that sustain the hypothesis of a more sophisticated model of the disorder is provided, together with a brief overview of the most relevant pharmacological animal models of OCD and its first-line treatments. Current research goals, new compounds tested and the rationale behind the development of these new pharmacologic agents are then explained and reviewed.

EXPERT OPINION

In the past years, no effective novel compounds have emerged for the treatment of OCD, even if many efforts has been made in the study of its neurobiological underpinnings. Relevant changes in the conceptualization of the disorder, suggested by interesting new neurobiological evidences, may result helpful in the development of new treatments.

Sex- and endocrine-stage-differences in middle-aged rats in an animal model of OCD

Various clinical studies suggest that many features of OCD are influenced by sex, age and fluctuations in hormonal levels. Animal models have confirmed these differences, and suggest they are mediated by the serotonergic system. We compared the perseveration behavior in a T-maze after the administration of the 5-HT1A agonist, 8-OH-DPAT (2.0 mg/kg) and the preventive action of subchronic fluoxetine (10 mg/kg, 3 times) in middle-aged (11-14 months) males and female rats in two endocrine states: irregular cycles (tested in diestrus) or persistent diestrus. After 8-OH-DPAT, females with persistent diestrus presented higher perseveration scores than males and females with irregular cycles. Fluoxetine produced an anticompulsive-like effect only in females with persistent diestrus. Females in persistent diestrus showed higher estradiol levels than those in irregular cycles or males. In all groups 8-OH-DPAT increased ambulation and fluoxetine did not modify this action. In males, the combined administration of fluoxetine and 8-OH-DPAT impaired motor coordination. Data are discussed on the basis of estradiol levels and sex differences.