Reappraisal of spontaneous stereotypy in the deer mouse as an animal model of obsessive-compulsive disorder (OCD): response to escitalopram treatment and basal serotonin transporter (SERT) density

Adult Offspring of Deer Mouse Breeding Pairs Selected for Normal and Compulsive-Like Large Nesting Expression Invariably Show the Same Behavior Without Prior In-Breeding

Obsessive-compulsive disorder is a neuropsychiatric condition with notable genetic involvement. Against this background, laboratory-housed deer mice of both sexes varyingly present with excessive and persistent large nesting behavior (LNB), which has been validated for its resemblance of clinical compulsivity. Although LNB differs from normal nesting behavior (NNB) on both a biological and cognitive level, it is unknown to what extent the expression of LNB and NNB is related to familial background. Here, we randomly selected 14 NNB- and 14 LNB-expressing mice (equally distributed between sexes) to constitute 7 breeding pairs of each phenotype. Pairs were allowed to breed two successive generations of offspring, which were raised until adulthood (12 weeks) and assessed for nesting expression. Remarkably, our findings show that offspring from LNB-expressing pairs build significantly larger nests compared to offspring from NNB-expressing pairs and the nesting expression of the offspring of each breeding pair, irrespective of parental phenotype or litter, is family specific. Collectively, the results of this investigation indicate that LNB can be explored for its potential to shed light on heritable neurocognitive mechanisms that may underlie the expression of specific persistent behavioral phenotypes.

Differential impact of pegfilgrastim, a recombinant human granulocyte colony stimulating factor, on the neutrophil count of male and female deer mice (Peromyscus maniculatus bairdii)

BACKGROUND

An increasing body of research implicates inflammatory processes, including alterations in the neutrophil-lymphocyte ratio (NLR), in the pathophysiology of psychiatric illness. The deer mouse (Peromyscus maniculatus bairdii) is commonly studied for its naturalistic expression of compulsive-like behaviour. Towards future efforts to gain an understanding of how innate and adaptive immune processes might be involved in this model, we aimed to study the effects of pegfilgrastim, a pegylated recombinant human granulocyte colony-stimulating factor (g-CSF) analogue, on the NLR of both male and female deer mice.

METHODS

Briefly, 54 deer mice (equally distributed between sexes) were exposed to a single injection with either control or pegfilgrastim (0.1 or 1 mg/kg) (n = 18 per group). Six mice of each group (three per sex) were euthanized on days two, four and seven post-administration, their blood collected and the NLR calculated. Data were analysed by means of ordinary three-way ANOVA, followed by Bonferroni post-hoc testing.

RESULTS

Irrespective of dose, pegfilgrastim resulted in higher NLR values in mice of both sexes at days four and seven of testing. However, female mice exposed to the higher dose, presented with significantly higher NLR values irrespective of time, compared to male mice exposed to the same.

CONCLUSION

The data generated from this work highlight important dose- and sex-specific aspects of pegfilgrastim with female mice showing heighted elevation of the NLR in response to high-dose pegfilgrastim administration only. Since the innate immune components of male and female deer mice is differentially sensitive to g-CSF stimulation, our results provide a useful basis for further study of sex-specific immunological processes in deer mice.

Towards zebrafish models to unravel translational insights of obsessive-compulsive disorder: A neurobehavioral perspective

Obsessive-compulsive disorder (OCD) is a chronic and debilitating illness that has been considered a polygenic and multifactorial disorder, challenging effective therapeutic interventions. Although invaluable advances have been obtained from human and rodent studies, several molecular and mechanistic aspects of OCD etiology are still obscure. Thus, the use of non-traditional animal models may foster innovative approaches in this field, aiming to elucidate the underlying mechanisms of disease from an evolutionary perspective. The zebrafish (Danio rerio) has been increasingly considered a powerful organism in translational neuroscience research, especially due to the intrinsic features of the species. Here, we outline target mechanisms of OCD for translational research, and discuss how zebrafish-based models can contribute to explore neurobehavioral aspects resembling those found in OCD. We also identify possible advantages and limitations of potential zebrafish-based models, as well as highlight future directions in both etiological and therapeutic research. Lastly, we reinforce the use of zebrafish as a promising tool to unravel the biological basis of OCD, as well as novel pharmacological therapies in the field.

Large nesting expression in deer mice remains stable under conditions of visual deprivation despite heightened limbic involvement: Perspectives on compulsive-like behavior

Visual stimuli and limbic activation varyingly influence obsessive-compulsive symptom expression and so impact treatment outcomes. Some symptom phenotypes, for example, covert repugnant thoughts, are likely less sensitive to sensory stimuli compared to symptoms with an extrinsic focus, that is, symptoms related to contamination, safety, and "just-right-perceptions." Toward an improved understanding of the neurocognitive underpinnings of obsessive-compulsive psychobiology, work in naturalistic animal model systems is useful. Here, we explored the impact of visual feedback and limbic processes on 24 normal (NNB) and large (LNB) nesting deer mice, respectively (as far as possible, equally distributed between sexes). Briefly, after behavioral classification into either the NNB or LNB cohorts, mice of each cohort were separated into two groups each and assessed for nesting expression under either standard light conditions or conditions of complete visual deprivation (VD). Nesting outcomes were assessed in terms of size and neatness. After nesting assessment completion, mice were euthanized, and samples of frontal-cortical and hippocampal tissues were collected to determine serotonin and noradrenaline concentrations. Our results show that LNB, as opposed to NNB, represents an inflexible and excessive behavioral phenotype that is not dependent on visually guided action-outcome processing, and that it associates with increased frontal-cortical and hippocampal noradrenaline concentrations, irrespective of lighting condition. Collectively, the current results are informing of the neurocognitive underpinnings of nesting behavior. It also provides a valuable foundation for continued investigations into the noradrenergic mechanisms that may influence the development and promulgation of excessive, rigid, and inflexible behaviors.

Rhesus monkeys exhibiting spontaneous ritualistic behaviors resembling obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a chronic and debilitating psychiatric disorder that affects ∼2%-3% of the population globally. Studying spontaneous OCD-like behaviors in non-human primates may improve our understanding of the disorder. In large rhesus monkey colonies, we found 10 monkeys spontaneously exhibiting persistent sequential motor behaviors (SMBs) in individual-specific sequences that were repetitive, time-consuming and stable over prolonged periods. Genetic analysis revealed severely damaging mutations in genes associated with OCD risk in humans. Brain imaging showed that monkeys with SMBs had larger gray matter (GM) volumes in the left caudate nucleus and lower fractional anisotropy of the corpus callosum. The GM volume of the left caudate nucleus correlated positively with the daily duration of SMBs. Notably, exposure to a stressor (human presence) significantly increased SMBs. In addition, fluoxetine, a serotonergic medication commonly used for OCD, decreased SMBs in these monkeys. These findings provide a novel foundation for developing better understanding and treatment of OCD.

Associations between nesting, stereotypy, and working memory in deer mice: response to levetiracetam

BACKGROUND

Some deer mice (Peromyscus maniculatus bairdii) exhibit various phenotypes of persistent behaviors. It remains unknown if and how said phenotypes associate with early-life and adult cognitive perturbations, and whether potentially cognitive enhancing drugs might modify such associations. Here, we explored the longitudinal relationship between early-life behavioral flexibility and the expression of persistent behavior in adulthood. We also investigated how said phenotypes might associate with working memory in adulthood, and how this association might respond to chronic exposure to the putative cognitive enhancer, levetiracetam (LEV).

METHODS

76 juvenile deer mice were assessed for habit-proneness in the Barnes maze (BM) and divided into two exposure groups (n = 37-39 per group), i.e., control and LEV (75 mg/kg/day). After 56 days of uninterrupted exposure, mice were screened for nesting and stereotypical behavior, and then assessed for working memory in the T-maze.

RESULTS

Juvenile deer mice overwhelmingly utilize habit-like response strategies, regardless of LNB and HS behavior in adulthood. Further, LNB and HS are unrelated in terms of their expression, while LEV reduces the expression of LNB, but bolsters CR (but not VA). Last, an increased level of control over high stereotypical expression may facilitate improved working memory performance.

CONCLUSION

LNB, VA and CR, are divergent in terms of their neurocognitive underpinnings. Chronic LEV administration throughout the entire rearing period may be of benefit to some phenotypes, e.g., LNB, but not others (CR). We also show that an increased level of control over the expression of stereotypy may facilitate improved working memory performance.

Behavioral restriction, lorazepam, and escitalopram uniquely influence the expression of naturalistic stereotypy in deer mice: perspectives on anxiety- and compulsive-like behavior

Introduction: Stereotypical expression in laboratory-housed rodents can be explained by different motivational, coping, and motor dysfunction theories. Here, we aimed to explore the neurocognitive underpinnings of high stereotypical (HS) expression in deer mice (Peromyscus maniculatus bairdii), previously proposed as a model system of compulsive-like behavioral persistence. Specifically, we aimed to establish whether HS behavior is related to an underlying escape-related trigger. Methods: One-hundred and sixteen deer mice were classified as either non-stereotypical (NS) or HS. Mice of each cohort were further subdivided and exposed to either sub-acute (3-day) or chronic (25-day) behavioral restriction (R), and high-dose escitalopram (ESC), lorazepam (LOR), alone and in combination with R (ESC+R and LOR+R, respectively). Mice were reassessed for stereotypical behavior at both time points. Results: Our results indicate that HS behavior is likely not temporally and functionally related to an anxiogenic trigger, i.e., R, but rather that HS is associated with parallel changes in anxiogenic feedback processing. We also show that chronic R alone significantly decreased the time spent in expressing HS behavior in animals of the HS, but not NS phenotype. Discussion: This points to the possibility that HS-expressing mice represent a subgroup of P. maniculatus bairdii in which unique interactions between neurobiology and processes of gradual behavioral organization, may contribute to the expression of the typical behaviors observed in this cohort. Collectively, our findings highlight the value of the deer mouse model system to investigate the potential neurocognitive mechanisms that may underlie the development of persistent phenotypes that can likely not be explained entirely by current theories.

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.

An acute dose-ranging evaluation of the antidepressant properties of Sceletium tortuosum (Zembrin®) versus escitalopram in the Flinders Sensitive Line rat

ETHNOPHARMACOLOGICAL RELEVANCE

Sceletium tortuosum (L.) N.E.Br. (ST) has been used by the Khoisan people of South Africa as a mood elevator. Its various pharmacological mechanisms of action suggest distinct potential as an antidepressant. Clinical studies in healthy individuals suggest beneficial effects on mood, cognition, and anxiety.

AIM OF THE STUDY

To obtain a chromatographic fingerprint of a standardized extract of S. tortuosum (Zembrin®), and to evaluate the acute antidepressant-like properties of Zembrin® versus the reference antidepressant, escitalopram, in the Flinders Sensitive Line (FSL) rat, a genetic rodent model of depression.

MATERIALS AND METHODS

The chemical profile of Zembrin® was determined by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) chromatogram method using alkaloid standards. Twelve saline treated FSL and six Flinders Resistant Line (FRL) control rats were used to confirm face validity of the FSL model using the forced swim test (FST). Thereafter, FSL rats (n = 10) received either 5, 10, 25, 50 or 100 mg/kg of Zembrin®, or 5, 10 or 20 mg/kg escitalopram oxalate (ESC), both via oral gavage, and subjected to the open field test (OFT) and FST.

RESULTS

Four main ST alkaloids were identified and quantified in Zembrin® viz. mesembrenone, mesembrenol, mesembrine, and mesembranol (47.9%, 32%, 13.2%, and 6.8% of the total alkaloids, respectively). FSL rats showed significantly decreased swimming and climbing (coping) behaviours, and significantly increased immobility (despair), versus FRL controls. ESC 5 mg/kg and Zembrin® 25 mg/kg and 50 mg/kg showed significant dose-dependent reversal of immobility in FSL rats and variable effects on coping behaviours. Zembrin® 50 mg/kg was the most effective antidepressant dose, showing equivalence to ESC 5.

CONCLUSIONS

Zembrin® (25 and 50 mg/kg) and ESC (5 mg/kg) are effective antidepressants after acute treatment in the FST, as assessed in FSL rats. Moreover, Zembrin® 50 mg/kg proved equivalent to ESC 5. Further long-term bio-behavioural studies on the antidepressant properties of Zembrin® are warranted.

Cerebellin-2 regulates a serotonergic dorsal raphe circuit that controls compulsive behaviors

Cerebellin-1 (Cbln1) and cerebellin-2 (Cbln2) are secreted glycoproteins that are expressed in distinct subsets of neurons throughout the brain. Cbln1 and Cbln2 simultaneously bind to presynaptic neurexins and postsynaptic GluD1 and GluD2, thereby forming trans-synaptic adhesion complexes. Genetic associations link cerebellins, neurexins and GluD's to neuropsychiatric disorders involving compulsive behaviors, such as Tourette syndrome, attention-deficit hyperactivity disorder (ADHD), and obsessive-compulsive disorder (OCD). Extensive evidence implicates dysfunction of serotonergic signaling in these neuropsychiatric disorders. Here, we report that constitutive Cbln2 KO mice, but not Cbln1 KO mice, display robust compulsive behaviors, including stereotypic pattern running, marble burying, explosive jumping, and excessive nest building, and exhibit decreased brain serotonin levels. Strikingly, treatment of Cbln2 KO mice with the serotonin precursor 5-hydroxytryptophan or the serotonin reuptake-inhibitor fluoxetine alleviated compulsive behaviors. Conditional deletion of Cbln2 both from dorsal raphe neurons and from presynaptic neurons synapsing onto dorsal raphe neurons reproduced the compulsive behaviors of Cbln2 KO mice. Finally, injection of recombinant Cbln2 protein into the dorsal raphe of Cbln2 KO mice largely reversed their compulsive behaviors. Taken together, our results show that Cbln2 controls compulsive behaviors by regulating serotonergic circuits in the dorsal raphe.

An auto real-time jump tagging system for exploring stereotyped jumping behavior in mice

The jump is one of the common stereotyped behavior in rodents which can be found in certain types of disease models, such as addiction. It can be easily identified by the human eye. However, it is difficult to be tagged in real-time by manual operation, which limits the detailed exploration of its neural mechanisms with the new techniques, such as fiber photometry recording. Here we introduced an auto real-time jump tagging system (Art-JT system) to record the jump based on online monitoring the pressure changes of the floor in which the mouse is free exploring. Meanwhile, the Art-JT system can send the digital signal of the jump timing to the external device for tagging the events in the fiber photometry system. We tested it with the mice induced by Naloxone precipitated withdrawal jumping and found that it could accurately record the jump events and provide several detailed parameters of the jump. We also confirmed that the jump was correlated with the medial prefrontal cortex and primary motor cortex neuronal activities by combining the Art-JT system, GCaMP6 mice, and fiber photometry system. Our results suggested that the Art-JT system may be a powerful tool for recording and analyzing jumps efficiently and helping us to understand stereotyped behavior.

Escitalopram and lorazepam differentially affect nesting and open field behaviour in deer mice exposed to an anxiogenic environment

Large nest building behaviour (LNB), as expressed by a subpopulation of laboratory housed deer mice (Peromyscus maniculatus bairdii), is persistent and repetitive. However, the response of LNB to an anxiogenic environment has not yet been investigated. Here, we employed LNB and normal nesting (NNB) expressing mice, subdivided into three drug-exposed groups per cohort, i.e. water (28 days), escitalopram (50 mg/kg/day, 28 days) and lorazepam (2 mg/kg/day; 4 days) to investigate this theme. During the last 4 days of drug exposure, mice were placed inside anxiogenic open field arenas which contained a separate enclosed and dark area for 4 consecutive nights during which open field and/or nest building assessments were performed. We show that LNB behaviour in deer mice is stable, irrespective of the anxiety-related context in which it is assessed, and that LNB mice find an open field arena to be less aversive compared to NNB mice. Escitalopram and lorazepam differentially affected the nesting and open field behaviour of LNB expressing mice, confirming deer mouse LNB as a repetitive behavioural phenotype that is related to a compulsive-like process which is regulated by the serotonergic system.

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.

The neurobiology of environmentally induced stereotypic behaviours in captive animals: assessing the basal ganglia pathways and cortico-striatal-thalamo-cortical circuitry hypotheses

The neurobiology of environmentally induced stereotypic behaviours (SBs) (e.g., pacing in zoo carnivores, crib-biting in horses, tail chasing in dogs) is hypothesized to involve altered functioning within the basal ganglia (‘Basal Ganglia (BG) Pathways Hypotheses’) and/or between the basal ganglia and cortex (‘Cortico-Striatal-Thalamo-Cortical (CSTC) Circuits Hypotheses’). We review four decades of relevant studies, critically assessing support for both hypotheses. Currently no BG Pathways or CSTC Circuits hypothesis is fully supported. While some results are partially consistent with some hypotheses (decreased subthalamic nucleus activity in deer mice and C58 mice); others (nucleus accumbens activity in mink and C57 mice) seem to reflect individual differences in SB, but not environmental effects. Yet others can be tentatively rejected: neither elevated striatal dopamine nor the cortico-striatal connection of the sensorimotor circuit seem to be involved for most species studied to date. Further research is now important for understanding the impact of captivity on animals’ functioning.

Neural Mechanisms Underlying Repetitive Behaviors in Rodent Models of Autism Spectrum Disorders

Autism spectrum disorder (ASD) is comprised of several conditions characterized by alterations in social interaction, communication, and repetitive behaviors. Genetic and environmental factors contribute to the heterogeneous development of ASD behaviors. Several rodent models display ASD-like phenotypes, including repetitive behaviors. In this review article, we discuss the potential neural mechanisms involved in repetitive behaviors in rodent models of ASD and related neuropsychiatric disorders. We review signaling pathways, neural circuits, and anatomical alterations in rodent models that display robust stereotypic behaviors. Understanding the mechanisms and circuit alterations underlying repetitive behaviors in rodent models of ASD will inform translational research and provide useful insight into therapeutic strategies for the treatment of repetitive behaviors in ASD and other neuropsychiatric disorders.

The Psychopharmacology of Obsessive-Compulsive Disorder: A Preclinical Roadmap

This review evaluates current knowledge about obsessive-compulsive disorder (OCD), with the goal of providing a roadmap for future directions in research on the psychopharmacology of the disorder. It first addresses issues in the description and diagnosis of OCD, including the structure, measurement, and appropriate description of the disorder and issues of differential diagnosis. Current pharmacotherapies for OCD are then reviewed, including monotherapy with serotonin reuptake inhibitors and augmentation with antipsychotic medication and with psychologic treatment. Neuromodulatory therapies for OCD are also described, including psychosurgery, deep brain stimulation, and noninvasive brain stimulation. Psychotherapies for OCD are then reviewed, focusing on behavior therapy, including exposure and response prevention and cognitive therapy, and the efficacy of these interventions is discussed, touching on issues such as the timing of sessions, the adjunctive role of pharmacotherapy, and the underlying mechanisms. Next, current research on the neurobiology of OCD is examined, including work probing the role of various neurotransmitters and other endogenous processes and etiology as clues to the neurobiological fault that may underlie OCD. A new perspective on preclinical research is advanced, using the Research Domain Criteria to propose an adaptationist viewpoint that regards OCD as the dysfunction of a normal motivational system. A systems-design approach introduces the security motivation system (SMS) theory of OCD as a framework for research. Finally, a new perspective on psychopharmacological research for OCD is advanced, exploring three approaches: boosting infrastructure facilities of the brain, facilitating psychotherapeutic relearning, and targeting specific pathways of the SMS network to fix deficient SMS shut-down processes. SIGNIFICANCE STATEMENT: A significant proportion of patients with obsessive-compulsive disorder (OCD) do not achieve remission with current treatments, indicating the need for innovations in psychopharmacology for the disorder. OCD may be conceptualized as the dysfunction of a normal, special motivation system that evolved to manage the prospect of potential danger. This perspective, together with a wide-ranging review of the literature, suggests novel directions for psychopharmacological research, including boosting support systems of the brain, facilitating relearning that occurs in psychotherapy, and targeting specific pathways in the brain that provide deficient stopping processes in OCD.

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.

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.

Effect of Escitalopram on Serum GDNF and BDNF Levels and 5-HT Level of Brain Tissue of Obsessive-Compulsive Disorder Rats

The present study aims to discuss the effect of escitalopram in glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF) levels, and 5-Hydroxytryptamine (5-HT) in obsessive-compulsive disorder rats. A total of 42 rats were divided into three groups randomly: control group (n = 14), model group (n = 14) (obsessive-compulsive disorder group), and escitalopram group (n = 14) (model + obsessive-compulsive disorder group + escitalopram treatment). The open-field method was used to test the rat behavior, enzyme-linked immunosorbent assay (ELISA) was used to determine the serum GDNF and BDNF levels. In addition, Western blot was used to determine the brain tissue protein levels of GDNF and BDNF and high-performance liquid chromatography + electrochemistry method to determine the 5-HT level of brain tissue. Visiting place was changed, rotational frequency and fixed duration enhanced in escitalopram group compared to model group (P < 0.05). Besides, GDNF and BDNF levels of serum and brain tissue were decreased in model group and escitalopram group compared to control group (P < 0.05), while GDNF and BDNF levels of serum and brain tissue were increased in escitalopram group compared to model group (P < 0.05). Moreover, the 5-HT level of brain tissue in escitalopram group was higher than that in model group (P < 0.05). Escitalopram could increase GDNF and BDNF levels and 5-HT content in serum and brain tissue in obsessive-compulsive disorder rats, which contributes to a function on the treatment of obsessive-compulsive disorder.

Cortical endogenous opioids and their role in facilitating repetitive behaviors in deer mice

Deer mice provide a non-pharmacologically induced model for the study of repetitive behaviors. In captivity, these animals develop frequent jumping and rearing that resemble clinical symptoms of obsessive-compulsive behavior (OCB), autism spectrum disorder (ASD), complex motor stereotypies (CMS), and Tourette's syndrome (TS). In this study, we pursue the mechanism of repetitive behaviors by performing stereological analyses and liquid chromatography/ mass spectrometry (LC-MS/MS) measurements of glutamate (Glut), GABA, 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), leu-enkephalin (leu-enk), and dynorphin-A (dyn-A) in frontal cortex (FC), prefrontal cortex (PFC), and basal ganglia. The only significant stereological alteration was a negative correlation between repetitive behaviors and the cell count in the ventromedial striatum (VMS). Neurochemical analyses demonstrated a significant negative correlation between repetitive behaviors and endogenous opioids (leu-enk and dyn-A) in the FC - the site of origin of habitual behaviors and cortical projections to striatal MSNs participating in direct and indirect pathways. The precise neurochemical process by which endogenous opioids influence synaptic neurotransmission is unknown. One postulated cortical mechanism, supported by our findings, is an opioid effect on cortical interneuron GABA release and a consequent effect on glutamatergic cortical pyramidal cells. Anatomical changes in the VMS could have a role in repetitive behaviors, recognizing that this region influences goal-directed and habitual behaviors.

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.

Btbd3 expression regulates compulsive-like and exploratory behaviors in mice

BTB/POZ domain-containing 3 (BTBD3) was identified as a potential risk gene in the first genome-wide association study of obsessive-compulsive disorder (OCD). BTBD3 is a putative transcription factor implicated in dendritic pruning in developing primary sensory cortices. We assessed whether BTBD3 also regulates neural circuit formation within limbic cortico-striato-thalamo-cortical circuits and behaviors related to OCD in mice. Behavioral phenotypes associated with OCD that are measurable in animals include compulsive-like behaviors and reduced exploration. We tested Btbd3 wild-type, heterozygous, and knockout mice for compulsive-like behaviors including cage-mate barbering, excessive wheel-running, repetitive locomotor patterns, and reduced goal-directed behavior in the probabilistic learning task (PLT), and for exploratory behavior in the open field, digging, and marble-burying tests. Btbd3 heterozygous and knockout mice showed excessive barbering, wheel-running, impaired goal-directed behavior in the PLT, and reduced exploration. Further, chronic treatment with fluoxetine, but not desipramine, reduced barbering in Btbd3 wild-type and heterozygous, but not knockout mice. In contrast, Btbd3 expression did not alter anxiety-like, depression-like, or sensorimotor behaviors. We also quantified dendritic morphology within anterior cingulate cortex, mediodorsal thalamus, and hippocampus, regions of high Btbd3 expression. Surprisingly, Btbd3 knockout mice only showed modest increases in spine density in the anterior cingulate, while dendritic morphology was unaltered elsewhere. Finally, we virally knocked down Btbd3 expression in whole, or just dorsal, hippocampus during neonatal development and assessed behavior during adulthood. Whole, but not dorsal, hippocampal Btbd3 knockdown recapitulated Btbd3 knockout phenotypes. Our findings reveal that hippocampal Btbd3 expression selectively modulates compulsive-like and exploratory behavior.

Neurophysiological correlates of stereotypic behaviour in a model carnivore species

Stereotypic behaviour (SB) is common in animals housed in farm, zoo or laboratory conditions, including captive Carnivora (e.g. wild ursids and felids). Neurobiological data on housing-induced SBs come from four species (macaques, two rodent species, and horses), and suggest basal ganglia (BG) dysfunction. We investigated whether similar patterns occur in Carnivora via a model, American mink, because their SB is distinctive in form and timing. We raised 32 males in non-enriched (NE) or enriched (E) cages for 2 years, and assessed two forms of SB: 1) Carnivora-typical locomotor-and-whole-body ('loco') SBs (e.g. pacing, weaving); 2) scrabbling with the forepaws. Neuronal activity was analysed via cytochrome oxidase (CO) staining of the dorsal striatum (caudate; putamen), globus pallidus (externus, GPe; internus, GPi), STN, and nucleus accumbens (NAc); and the GPe:GPi ratio (GPr) calculated to assess relative activation of direct and indirect pathways. NE mink stereotyped more, and had lower GPr CO-staining indicating relatively lower indirect pathway activation. However, no single BG area was affected by housing and nor did GPr values covary with SB. Independent of housing, elevated NAc CO-staining predicted more loco SB, while scrabbling, probably because it negatively correlated with loco SB, negatively covaried with NAc CO-staining in NE subjects. These results thus implicate the NAc in individual differences in mink SB. However, because they cannot explain why NE subjects showed more SB, they provide limited support for the BG dysfunction hypothesis for this species' housing-induced SB. More research is therefore needed to understand how barren housing causes SB in captive Carnivora.

Abnormal repetitive behaviors in zebrafish and their relevance to human brain disorders

Abnormal repetitive behaviors (ARBs) are a prominent symptom of numerous human brain disorders and are commonly seen in rodent models as well. While rodent studies of ARBs continue to dominate the field, mounting evidence suggests that zebrafish (Danio rerio) also display ARB-like phenotypes and may therefore be a novel model organism for ARB research. In addition to clear practical research advantages as a model species, zebrafish share high genetic and physiological homology to humans and rodents, including multiple ARB-related genes and robust behaviors relevant to ARB. Here, we discuss a wide spectrum of stereotypic repetitive behaviors in zebrafish, data on their genetic and pharmacological modulation, and the overall translational relevance of fish ARBs to modeling human brain disorders. Overall, the zebrafish is rapidly emerging as a new promising model to study ARBs and their underlying mechanisms.

MicroRNA-200a Targets Cannabinoid Receptor 1 and Serotonin Transporter to Increase Visceral Hyperalgesia in Diarrhea-predominant Irritable Bowel Syndrome Rats

Background/Aims

MicroRNAs (miRNAs) were reported to be responsible for intestinal permeability in diarrhea-predominant irritable bowel syndrome (IBS-D) rats in our previous study. However, whether and how miRNAs regulate visceral hypersensitivity in IBS-D remains largely unknown.

Methods

We established the IBS-D rat model and evaluated it using the nociceptive visceral hypersensitivity test, myeloperoxidase activity assay, restraint stress-induced defecation, and electromyographic (EMG) activity. The distal colon was subjected to miRNA microarray analysis followed by isolation and culture of colonic epithelial cells (CECs). Bioinformatic analysis and further experiments, including dual luciferase assays, quantitative real-time polymerase chain reaction, western blot, and enzyme-linked immunosorbent assay, were used to detect the expression of miRNAs and how it regulates visceral hypersensitivity in IBS-D rats.

Results

The IBS-D rat model was successfully established. A total of 24 miRNAs were differentially expressed in the distal colon of IBS-D rats; 9 were upregulated and 15 were downregulated. Among them, the most significant upregulation was miR-200a, accompanied by downregulation of cannabinoid receptor 1 (CNR1) and serotonin transporter (SERT). MiR-200a mimic markedly inhibited the expression of CNR1/SERT. Bioinformatic analysis and luciferase assay confirmed that CNR1/SERT are direct targets of miR-200a. Rescue experiments that overexpressed CNR1/SERT significantly abolished the inhibitory effect of miR-200a on the IBS-D rats CECs.

Conclusions

This study suggests that miR-200a could induce visceral hyperalgesia by targeting the downregulation of CNR1 and SERT, aggravating or leading to the development and progression of IBS-D. MiR-200a may be a regulator of visceral hypersensitivity, which provides potential targets for the treatment of IBS-D.

Back to basics: A methodological perspective on marble-burying behavior as a screening test for psychiatric illness

Animal models of human psychiatric illness are valuable frameworks to investigate the etiology and neurobiology underlying the human conditions. Accurate behavioral measures that can be used to characterize animal behavior, thereby contributing to a model's validity, are crucial. One such measure, i.e. the rodent marble-burying test (MBT), is often applied as a measure of anxiety- and compulsive-like behaviors. However, the test is characterized by noteworthy between-laboratory methodological differences and demonstrates positive treatment responses to an array of pharmacotherapies that are often of little translational value. Therefore, using a naturalistic animal model of obsessive-compulsive disorder, i.e. the deer mouse (Peromyscus maniculatus bairdii), the current investigation attempted to illuminate the discrepancies reported in literature by means of a methodological approach to the MBT. Five key aspects of the test that vary between laboratories, viz. observer/scoring, burying substrate, optional avoidance, the use of repeated testing, and determinations of locomotor activity, have been investigated. Following repeated MB tests in four different burying substrates and in two zone configurations, we have demonstrated that 1) observer bias may contribute to the significant differences in findings reported, 2) MB seems to be a natural exploratory response to a novel environment, rather than being triggered by aberrant cognition, 3) burying substrates with a small particle size and higher density deliver the most accurate results with respect to the burying phenotype, and 4) to exclude the influence of normal exploratory behavior on the number of marbles being covered, assessments of marble-burying should be based on pre-occupation with the objects itself.

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.

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.

Excessive nest building is a unique behavioural phenotype in the deer mouse model of obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a phenotypically heterogeneous condition characterised by time-consuming intrusive thoughts and/or compulsions. Irrespective of the symptom type diagnosed, the severity of OCD is characterised by heterogeneity in symptom presentation that complicates diagnosis and treatment. Heterogeneity of symptoms would be invaluable in an animal model. Nest building behaviour forms part of the normal behavioural repertoire of rodents and demonstrates profound between-species differences. However, it has been proposed that within-species differences in nest building behaviour (i.e. aberrant vs. normal nest building) may resemble obsessive-compulsive-like symptoms. In an attempt to investigate whether other obsessive-compulsive-like behaviours are present in an animal model of OCD, or if aberrant nest building behaviour may represent a unique obsessive-compulsive phenotype in such a model, the current study assessed nest building behaviour in high (H, viz obsessive-compulsive) and non (N, viz normal) stereotypical deer mice. Subsequently, 12 N and H animals, respectively, were provided with an excess of cotton wool daily for one week prior to and following four weeks of high-dose oral escitalopram treatment (50 mg/kg/day). Data from the current investigation demonstrate daily nesting activity to be highly variable in deer mice, with stereotypy and nest building being independent behaviours. However, we identified unique aberrant large nest building behaviour in 30% of animals from both cohorts that was attenuated by escitalopram to pre-treatment nesting scores of the larger group. In summary, behavioural and drug-treatment evidence confirms that deer mouse behaviour does indeed resemble symptom heterogeneity related to OCD, and as such expands its face and predictive validity for the disorder.

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

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

Neuronal mechanisms and circuits underlying repetitive behaviors in mouse models of autism spectrum disorder

Autism spectrum disorder (ASD) refers to a broad spectrum of neurodevelopmental disorders characterized by three central behavioral symptoms: impaired social interaction, impaired social communication, and restricted and repetitive behaviors. However, the symptoms are heterogeneous among patients and a number of ASD mouse models have been generated containing mutations that mimic the mutations found in human patients with ASD. Each mouse model was found to display a unique set of repetitive behaviors. In this review, we summarize the repetitive behaviors of the ASD mouse models and variations found in their neural mechanisms including molecular and electrophysiological features. We also propose potential neuronal mechanisms underlying these repetitive behaviors, focusing on the role of the cortico-basal ganglia-thalamic circuits and brain regions associated with both social and repetitive behaviors. Further understanding of molecular and circuitry mechanisms of the repetitive behaviors associated with ASD is necessary to aid the development of effective treatments for these disorders.

A review of animal models of obsessive-compulsive disorder: a focus on developmental, immune, endocrine and behavioral models

INTRODUCTION

Obsessive-compulsive disorder (OCD) is a neuropsychiatric condition characterized by intrusive thoughts (obsessions) and/or repetitive behaviors (compulsions). Several models of OCD exist, many which employ behaviors such as over-grooming or hoarding as correlates for compulsive behaviors - often using a response to serotonergic agents as evidence for their validity. Recent discoveries in the genetics of OCD and the identification of aberrancies of glutamatergic, hormonal, and immune pathways in the OCD phenotype highlight a need to review existing of animal models of OCD. The focus of attention to these pathways may lead to possible new targets for drug discovery.

AREAS COVERED

In this review, the authors describe frameworks for animal models in OCD conceptualized as either biological (e.g., developmental, genetic, and endocrine pathways), or behavioral (e.g., repetitive grooming, and stereotypies). In addition, the authors give special attention to the emerging role of glutamate in OCD.

EXPERT OPINION

While many animal models for OCD demonstrate pathologic repetitive behavior phenotypes, which are relieved by serotoninergic agents, animal models based on reversal learning, perseverative responding, and neurodevelopmental mechanisms represent robust new paradigms. Glutamatergic influences in these new animal models suggest that drug discovery using neuroprotective approaches may represent a new stage for pharmacologic developments in OCD.

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

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