Animal Models for Obsessive-Compulsive Disorder

A virtual library for behavioral performance in standard conditions-rodent spontaneous activity in an open field during repeated testing and after treatment with drugs or brain lesions

BACKGROUND

Beyond their specific experiment, video records of behavior have future value-for example, as inputs for new experiments or for yet unknown types of analysis of behavior-similar to tissue or blood sample banks in life sciences where clinically derived or otherwise well-described experimental samples are stored to be available for some unknown potential future purpose.

FINDINGS

Research using an animal model of obsessive-compulsive disorder employed a standardized paradigm where the behavior of rats in a large open field was video recorded for 55 minutes on each test. From 43 experiments, there are 19,976 such trials that amount to over 2 years of continuous recording. In addition to videos, there are 2 video-derived raw data objects: XY locomotion coordinates and plots of animal trajectory. To motivate future use, the 3 raw data objects are annotated with a general schema-one that abstracts the data records from their particular experiment while providing, at the same time, a detailed list of independent variables bearing on behavioral performance. The raw data objects are deposited as 43 datasets but constitute, functionally, a library containing 1 large dataset.

CONCLUSIONS

Size and annotation schema give the library high reuse potential: in applications using machine learning techniques, statistical evaluation of subtle factors, simulation of new experiments, or as educational resource. Ultimately, the library can serve both as the seed and as the test bed to create a machine-searchable virtual library of linked open datasets for behavioral performance in defined conditions.

An Interdisciplinary Approach for Compulsive Behavior in Dogs: A Case Report

Compulsive disorder is a debilitating condition affecting both humans and animals, characterized by intrusive thoughts and recurring out-of-place behaviors. Among them, tail chasing might represent one of the most common traits in compulsive dogs. Herein, we reported the case of a 7-year-old intact male German Shepherd mixed-breed dog, presenting with tail chasing behavior. He underwent a first behavioral evaluation 1 year before (at the age of 6), when he injured himself with severe wounds at level of the tail and left thigh. To avoid any specific suffering and increase his physical health, of course, the study was carried out through an interdisciplinary approach, employing a veterinary behaviorist and a rehabilitating dog instructor. Three months after pharmacological treatment with fluoxetine and α-s1 casozepine, associated with a behavioral recovery program, the owner reported an improvement of compulsive events in his dog, in terms of intensity and frequency. Interestingly, over the following 3 months, the dog did not experience any new tail chasing episodes.

Changes in gut microbiota during development of compulsive checking and locomotor sensitization induced by chronic treatment with the dopamine agonist quinpirole

Long-term treatment of rats with the D2/D3 dopamine agonist quinpirole induces compulsive checking (proposed as animal model of obsessive-compulsive disorder) and locomotor sensitization. The mechanisms by which long-term use of quinpirole produces those behavioral transformations are not known. Here we examined whether changes in gut microbiota play a role in these behavioral phenomena, by monitoring the development of compulsive checking and locomotor sensitization at the same time as measuring the response of gut microbiota to chronic quinpirole injections. Two groups of rats received nine injections of saline (n=16) or quinpirole (n=15; 0.25 mg/kg), at weekly intervals for the first 5 weeks and then two injections per week until the end of treatment. After each injection, rats were placed on a large open field for 55 min, and their behavior was video recorded for subsequent analysis. Fecal matter was collected after each trial and frozen for bacterial community profiling of the 16S rRNA gene, using paired-end reads of the V3 region. The results indicated that the induction of locomotor sensitization and compulsive checking was accompanied by changes in several communities of bacteria belonging to the order Clostridiales (class Clostridia, phylum Firmicutes), and predominantly in Lachnospiraceae and Ruminococcaceae families of bacteria. It is suggested that changes in these microbes may serve to support the energy use requirements of compulsive checking and obsessive-compulsive 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.

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.

Effects of the serotonergic agonist mCPP on male rats in the quinpirole sensitization model of obsessive-compulsive disorder (OCD)

RATIONALE

The serotonergic agonist, meta-chlorophenylpiperazine (mCPP), produces inconsistent effects on obsessive-compulsive disorder (OCD) symptoms, perhaps because clinical studies have not utilized a homogenous OCD subgroup of patients.

OBJECTIVES

This study aimed to evaluate mCPP effects on functional components of compulsive checking, using the quinpirole sensitization rat model of OCD.

METHODS

In study 1, the effects of mCPP were evaluated in quinpirole rats with compulsive checking. Two experimental groups were co-injected with quinpirole (0.125 mg/kg) and mCPP (0.625 or 1.25 mg/kg), while one control group was co-injected with quinpirole (0.125 mg/kg) and saline and the other control group received co-injections of saline. In study 2, mCPP (0, 0.3125, 0.625, and 1.25 mg/kg) was administered repeatedly to naïve rats and induction of compulsive checking evaluated.

RESULTS

mCPP significantly attenuated quinpirole-induced compulsive checking behavior by reducing vigor of checking (indexed by frequency of checking and length of check) and increasing rest after a bout of checking (indexed by time to the next checking bout), but it did not affect focus on the task of checking (indexed by recurrence time of checking and number of stops before returning to check). In naïve rats, mCPP did not induce compulsive behavior, but the highest dose reduced vigor of checking performance compared to saline controls.

CONCLUSIONS

mCPP did not exacerbate or induce compulsive checking behavior. Instead, it ameliorated compulsive checking by reducing vigor of checking and increasing post-checking satiety, without affecting focus on checking. Ameliorative effects of mCPP may involve 5HT2A/2C receptors in substantia nigra pars reticulata that inhibit expression of motor vigor.

Environmental effects on compulsive tail chasing in dogs

Obsessive Compulsive Disorder (OCD) is a neuropsychiatric disorder observed both in humans and animals. Examples of Canine Compulsive Disorder (CD) include excessive tail chasing (TC), light/shadow chasing and flank sucking. We performed a questionnaire survey to investigate the characteristics of compulsive (TC) and its possible associations with environmental correlates and personality in a pet population of 368 dogs from four dog breeds. We observed an early onset of TC at 3–6 months of age and a large variation in TC frequency in all breeds, with an overrepresentation of milder cases. Almost half of the TC dogs showed lowered responsiveness during bouts and displayed also other types of compulsions more often than the controls. Interestingly, dogs that received dietary supplements, especially vitamins and minerals, expressed less TC compared to dogs that did not receive any supplements. Neutered females had less TC, suggesting an influence of ovarian hormones on TC. Tail chasers were shyer and had separated earlier from their mothers than the controls. Finally, our genetic study did not find an association between TC and CDH2, a locus previously associated with the canine flank sucking compulsion. In conclusion, the early-onset and the variable nature of the repetitive behaviour, which is affected by environmental factors such as micronutrients, neutering and maternal care, share several similar components between canine and human compulsions and supports canine TC as a model for human OCD.

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

During the last 30 years there have been many attempts to develop animal models of obsessive-compulsive disorder (OCD). Most models have not been studied further following the original publication, and in the past few years, most papers present studies employing a few established animal models, exploring the neural basis of compulsive behavior and developing new treatment strategies. Here we summarize findings from the five most studied animal models of OCD: 8-OHDPAT (8-hydroxy-2-(di-n-propylamino)-tetralin hydrobromide) induced decreased alternation, quinpirole-induced compulsive checking, marble burying, signal attenuation and spontaneous stereotypy in deer mice. We evaluate each model's face validity, derived from similarity between the behavior in the model and the specific symptoms of the human condition, predictive validity, derived from similarity in response to treatment (pharmacological or other), and construct validity, derived from similarity in the mechanism (physiological or psychological) that induces behavioral symptoms and in the neural systems involved. We present ideas regarding future clinical research based on each model's findings, and on this basis, also emphasize possible new approaches for the treatment of OCD.

Predictive validity of a non-induced mouse model of compulsive-like behavior

A key to advancing the understanding of obsessive-compulsive disorder (OCD)-like symptoms is the development of spontaneous animal models. Over 55 generations of bidirectional selection for nest-building behavior in house mice, Mus musculus, resulted in a 40-fold difference in the amount of cotton used for a nest in high (BIG) and low (SMALL) selected lines. The nesting behavior of BIG mice appears to be compulsive-like and has initial face validity as an animal model for OCD in humans. Compulsive-like digging behavior was assessed; BIG male mice buried about three times as many marbles as SMALL male mice, strengthening face validity. Using the open field and elevated plus maze, SMALL male mice showed higher levels of anxiety/fear-like behavior than BIG male mice, indicating that compulsive-like and not anxiety-like behavior was measured. To establish predictive validity, chronic (4 weeks) oral administration of fluoxetine (30, 50 and 100mg/kg/day) and clomipramine (80 mg/kg/day), both effective in treating OCD, significantly reduced compulsive-like nest-building behavior in BIG male mice. Compulsive-like digging behavior was also significantly reduced by chronic oral fluoxetine (30 and 80 mg/kg/day) treatment in BIG male mice. General locomotor activity was not affected by chronic oral fluoxetine (30 and 80 mg/kg/day) treatment; chronic oral treatment with desipramine (30 mg/kg/day), an antidepressant not effective in treating OCD, had no effect on nesting behavior of BIG male mice, strengthening predictive validity. Together, the results indicate that these mice have good face and predictive validity as a non-induced mouse model of compulsive-like behavior relevant to OCD.

The mouse who couldn't stop washing: pathologic grooming in animals and humans

The basic science literature is replete with descriptions of naturally occurring or experimentally induced pathological grooming behaviors in animals, which are widely considered animal models of obsessive-compulsive disorder (OCD). These animal models rely largely on observed similarities between animal behaviors and human OCD behaviors, and on studies of animal pathological grooming disorders that respond to serotonin enhancing drugs. However, current limitations in assessment of complex cognition and affect in animals precludes the field's ability to match the driving primary processes behind observable phenomenology in animal "OCD" with human behavioral disorders. We propose that excessive grooming behaviors in animals may eventually prove to be equally, or possibly more relevant to, other conditions in humans that involve pathological grooming or grooming-like behaviors, such as trichotillomania, body dysmorphic disorder, olfactory reference syndrome, compulsive skin-picking, and onychophagia. Research is needed to better understand pathological grooming behaviors in both humans and animals, as animal models have the potential to elucidate pathogenic mechanisms and inform the treatment of these psychiatric conditions in humans.

High-frequency stimulation of the nucleus accumbens core and shell reduces quinpirole-induced compulsive checking in rats

Electrical deep brain stimulation (DBS) is currently studied in the treatment of therapy-refractory obsessive compulsive disorders (OCDs). The variety of targeted brain areas and the inconsistency in demonstrating anti-compulsive effects, however, highlight the need for better mapping of brain regions in which stimulation may produce beneficial effects in OCD. Such a goal may be advanced by the assessment of DBS in appropriate animal models of OCD. Currently available data on DBS of the nucleus accumbens (NAc) on OCD-like behavior in rat models of OCD are contradictory and partly in contrast to clinical data and theoretical hypotheses about how the NAc might be pathophysiologically involved in the manifestation of OCD. Consequently, the present study investigates the effects of DBS of the NAc core and shell in a quinpirole rat model of OCD. The study demonstrates that electrical modulation of NAc core and shell activity via DBS reduces quinpirole-induced compulsive checking behavior in rats. We therefore conclude that both, the NAc core and shell constitute potential target structures in the treatment of OCD.

High frequency stimulation and temporary inactivation of the subthalamic nucleus reduce quinpirole-induced compulsive checking behavior in rats

Obsessive-compulsive disorder (OCD) represents a highly prevalent and impairing psychiatric disorder. Functional and structural imaging studies implicate the involvement of basal ganglia-thalamo-cortical circuits in the pathophysiology of this disorder. In patients remaining resistant to pharmaco- and behavioral therapy, modulation of these circuits may consequently reverse clinical symptoms. High frequency stimulation (HFS) of the subthalamic nucleus (STN), an important station of the basal ganglia-thalamo-cortical circuits, has been reported to reduce obsessive-compulsive symptoms in a few Parkinson's disease patients with comorbid OCD. The present study tested the effects of bilateral HFS of the STN and of bilateral pharmacological inactivation of the STN (via intracranial administration of the GABA agonist muscimol) on checking behavior in the quinpirole rat model of OCD. We demonstrate that both HFS and pharmacological inactivation of the STN reduce quinpirole-induced compulsive checking behavior. We conclude that functional inhibition of the STN can alleviate compulsive checking, and suggest the STN as a potential target structure for HFS in the treatment of OCD.

Animal models of obsessive-compulsive disorder: rationale to understanding psychobiology and pharmacology

Animal models have shown progressive development and have undoubtedly proven their supportive value in OCD research. Thus, various animal models have confirmed the importance of the 5-HT [72-74] and dopamine systems [104,111] in the neurobiology and treatment of OCD. Given the neurochemical, emotional, and cognitive complexity of the disorder, how-ever, animal models are being used to investigate more and more complicated neurochemical and behavioral theories purported to underlie OCD. The lever-press model, for example, has implicated deficient response feed-back in a neural system that regulates operant behavior [74]. Studies on stereotypic movement disorder [89] have opened a new avenue of investigation into the neurobiology of stereotypy that may be applicable to more complex syndromes such as OCD. Models that have focused on specific neuropsychologic aspects of OCD such as reward [74], displacement behavior[63,101], perseveration and indecisiveness [73,102], and spontaneous stereotypy [90,94] are important in their attempt to unify the diverse behavioral manifestations of this disorder. It is clear that for a deeper, more holistic understanding of OCD, multiple animal models will be needed to allow investigation of the various aspects of the disorder and to provide convergent validation of the research findings. The heterogeneous nature of OCD, the various subtypes that exist within the disorder, and the range of obsessive-compulsive spectrum disorders suggest that particular questions regarding OCD may be addressed best by us-ing a particular ethologic model, whereas other questions might require a pharmacologic model or a combination of both for meaningful results[62,115]. Genetic models will be extremely useful for studying the genetics of pathologic behavior and for relating these findings to neuroanatomic and neurochemical changes in the model (eg, DICT-7 mice as a model for Tourette's syndrome and OCD). Neither ethologic nor pharmacologic models, however, can assess whether the "compulsive" behavior is a response to an "obsessive" anxiety or fear. Perhaps the symptoms seen in patients who have OCD, which may be exacerbated by everyday stress, are analogous to displacement behaviors in animals and also reflect some form of anxiety or stress [98]. In this regard, the bank vole model [116]has provided evidence that previously developed stereotypies increase markedly after acute stress and argues that healthy individuals "habituate" to everyday stress, whereas patients who have OCD do not. Interindividual variation in behavioral response and attempts to replicate studies in different laboratories often is the nemesis of the behavioral scientist. Small within- and between-subject variability is usually desirable, how-ever, because there are cases in which the study of the variability of the model could lead to a better understanding of the disorder. Variability can-not always be considered an error; it is possible that previously disregarded neuronal systems may have a place in the observed variation and, indeed, in the pathophysiology of OCD. In this regard, SRIs are not always effective for OCD [6,29,30] such that a lack of effect in a model may reflect an un-known neurobiological basis for compulsive behavior in a sub-group of SRI refractory patients. Similarly, separating the afflicted (ie, working with animals that show greater behavioral change in a model and/or after drug treatment) would have distinct benefits. To increase successful implementation of an ethologic animal model, especially when reinforcement models or signal attenuation models are used,the laboratory must be equipped with the essential behavioral testing apparatus as well as the operant chambers/rooms in which to conduct the train-ing and data collection. Quantification of certain stereotypy behaviors also requires experienced or trained observers. An illustration of the difficulty in measuring behavioral changes is that in the rewarded alternation model,a good response to behavioral treatment (alternation training) may lead to a floor effect [73] which, after successful drug treatment of the animal,produces no residual persistence (ie, measurable behavioral change) on which a drug treatment can be tested. Clearly, the choice of ethologic, pharmacologic, or genetic models should be considered carefully. A well-validated model may quell many of the limitations and considerations described previously. Noninvasive neuroimaging(eg, the use of small-animal single-photon emission CT) to explore the neuroanatomic basis of OCD offers an exciting future challenge, especially if combined with pharmacologic or ethologic models, and could confirm or ex-tend knowledge of the neuroanatomy of OCD. Although studies to investigate further the interactive role of 5-HT, dopamine, GABA, and glutamate are still needed, the role of neuroactive peptides such as cholecystokinin, corticotrophin-releasing factor, neuropeptide Y, tachykinins (ie, substance P),and natriuretic peptides in OCD should also be considered. Genetically engineered animal models will become increasingly valuable in combination with new technologies such as gene-chip microarrays, RNA interference, and advanced proteomics that will help further the understanding of OCD. Animal models of OCD are poised to play a vital role in extending the knowledge of the disorder now and in the future.

Current animal models of obsessive compulsive disorder: a critical review

During the last 30 years there have been many attempts to develop animal models of obsessive compulsive disorder (OCD), in the hope that they may provide a route for furthering our understanding and treatment of this disorder. The present paper reviews current genetic, pharmacological and behavioral animal models of OCD, and evaluates their face validity (derived from phenomenological similarity between the behavior in the animal model and the specific symptoms of the human condition), predictive validity (derived from similarity in response to treatment) and construct validity (derived from similarity in the underlying mechanisms--physiological or psychological).

Development and temporal organization of compulsive checking induced by repeated injections of the dopamine agonist quinpirole in an animal model of obsessive-compulsive disorder

Rats treated chronically with the dopamine D2/D3 receptor agonist quinpirole develop locomotor sensitization and exhibit compulsive checking of specific places in an open-field arena, a behavioral profile that may represent an animal model of obsessive-compulsive disorder. However, it is not known how compulsive checking develops across quinpirole injections nor whether checking behavior possesses a particular temporal structure. Male rats received quinpirole (0.5mg/kg, twice weekly x 10) or an equivalent regimen of saline and were placed in a large open field for 55 min where their behavior was digitally tracked for subsequent analysis of checking behavior using existing and newly developed computer software. Results showed that the measures of compulsive checking did not follow a singular profile across injections: some remained constant and others changed monotonically reaching their near-maximum levels after about 5-7 quinpirole injections. Moreover, results showed that checking behavior was organized into bouts of checking, with the number of bouts, as well as the rate of checking within a bout, increasing across injections to reach near maximal levels after about 5-7 administrations of quinpirole. Finally, quinpirole-treated rats showed a paucity of long inter-bout intervals. These results suggest that (a) compulsive checking emerges from the operation of at least two underlying processes: a regulated process and a process of sensitization that intensifies the performance of checking behavior; and (b) quinpirole treatment may attenuate a sense of satiety that could underlie the compulsive nature of checking. Finally, because key variables measured using the newly developed algorithms showed the expected profile, the present study provides validation for the use of this methodology for the analysis of checking behavior.

Rituals, stereotypy and compulsive behavior in animals and humans

From a survey of the behavior of animals in the wild, in captivity, under the influence of psychoactive drugs and in a model of obsessive-compulsive disorder (OCD), we identify that the behavioral repertoire invariably includes motor rituals, and that such rituals are performed at a few specific locations/objects in the environment with an orderly transition amongst locations/objects. The concept and parameters of this stable organization of rituals in time and space were used to analyze rituals of OCD patients, compared with control individuals performing the same actions (e.g. car locking). It was found that human rituals also converged to a few places/objects where repetitive acts were performed in a regular order, with the acts in OCD patients overlapping with those of control individuals. Across a very diverse range of animals and conditions, motor rituals are thus characterized by their close linkage to a few environmental locations and the repeated performance of relatively few acts. Such similarity in form may reflect a similarity in the mechanisms that control motor rituals in both animals and humans.

Psychostimulant-induced behavior as an animal model of obsessive-compulsive disorder: an ethological approach to the form of compulsive rituals

Rats treated chronically with the D2/D3 dopamine receptor agonist quinpirole show a pattern of behavior that meets a set of ethologically derived criteria of compulsive behavior in obsessive-compulsive disorder (OCD). Moreover, in both quinpirole-treated rats and OCD patients, the structure of compulsive rituals appear similar in being composed of relatively few motor acts that are organized in a flexible yet recurrent manner. In addition, the development of compulsive behavior in quinpirole-treated rats is attenuated by the OCD pharmacotherapeutic drug clomipramine. These similarities support the validity of quinpirole-treated rats as a psychostimulant-induced animal model of OCD. Considering that the induction of compulsive behavior in the rat model involves chronic hyperstimulation of dopamine receptors, this raises the possibility that dopaminergic mechanisms may play a role in OCD, at least in some subtypes of this disorder.