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

Brain structural abnormalities in Doberman pinschers with canine compulsive disorder

Obsessive compulsive disorder (OCD) is a debilitating condition, the etiology of which is poorly understood, in part because it often remains undiagnosed/untreated for a decade or more. Characterizing the etiology of compulsive disorders in animal models may facilitate earlier diagnosis and intervention. Doberman pinschers have a high prevalence of an analogous behavioral disorder termed canine compulsive disorder (CCD), which in many cases responds to treatments used for OCD. Thus, studies of CCD may help elucidate the etiology of compulsive disorders. We compared brain structure in Dobermans with CCD (N=8) and unaffected controls (N=8) to determine whether CCD is associated with structural abnormalities comparable to those reported in humans with OCD. We obtained 3 Tesla magnetic resonance structural and diffusion images from anesthetized Dobermans and subjected images to segmentation, voxel based morphometry, and diffusion tensor analyses. CCD dogs exhibited higher total brain and gray matter volumes and lower dorsal anterior cingulate cortex and right anterior insula gray matter densities. CCD dogs also had higher fractional anisotropy in the splenium of the corpus callosum, the degree of which correlated with the severity of the behavioral phenotype. Together, these findings suggest that CCD is associated with structural abnormalities paralleling those identified in humans with OCD. Accordingly, the CCD model, which has a number of advantages over other animal models of OCD, may assist in establishing the neuroanatomical basis for and etiology of compulsive disorders, which could lead to earlier diagnosis of and new treatments for humans and animals with these disorders.

Effects of the 5HT2C antagonist SB242084 on the pramipexole-induced potentiation of water contrafreeloading, a putative animal model of compulsive behavior

RATIONALE

In rats, quinpirole, a dopaminergic D2/D3 receptor agonist, elicits both hyperdipsia and water "contrafreeloading" (CFL), a putative model of compulsivity. The role of D3 receptors in this effect remains unclear. Clomipramine (CIM) was found to contrast both hyperdipsia and CFL, but the role of serotonin in this effect requires further investigation.

OBJECTIVES

We studied the effects of the preferential D3 agonist pramipexole (PPX) in both models. Furthermore, we tested the sensitivity of PPX-induced CFL to CIM and to the 5HT2c antagonist SB242084.

METHODS

In experiment 1, drinking was measured at 2 and 5 h after eight daily injections of PPX (0 to 1.0 mg/kg intraperitoneally). In the CFL study, every other third lever press, the rat was reinforced by the delivery of water. On days 1-6, water was only available upon lever pressing. On days 7-15, choice between response-contingent and free access was provided. PPX doses as in the experiment 1 were given. In two further experiments, PPX (0.5 mg/kg) was administered alone or in combination with CIM (5 or 10 mg/kg) or SB242084 (0.3 or 1.0 mg/kg).

RESULTS

PPX did not produce hyperdipsia but enhanced spontaneous CFL. SB242084 attenuated PPX-induced CFL more effectively than CIM, restoring the preference for free access to water.

CONCLUSIONS

CFL, but not polydipsia, was induced by preferential D3 activation, an effect prevented by 5HT2c receptor blockade. Since PPX interferes with decision making and 5HT2c receptor supersensitivity is involved in the expression of compulsive behaviors, this study supports the compulsive nature of dopaminergic-induced CFL.

Hair pulling disorder (trichotillomania): genes, neurobiology, and a model for understanding impulsivity and compulsivity

Hair pulling disorder (trichotillomania) affects at least 3.7 million people in the United States and results in marked functional impairment. This article reviews empirical research investigating the genetics and neurobiology of hair pulling disorder (HPD). We also discuss recent advances in the characterization of this phenotype which have led to evidence supporting the existence of at least two disparate pulling styles-automatic and focused pulling. These pulling styles exhibit facets of behavioral processes, impulsivity and compulsivity, characteristic of several classes of disorders (e.g., obsessive-compulsive spectrum disorders, impulse control disorders). Available genetic, neurobiological, and clinical data support the importance of impulsivity for conceptualizing HPD. Impulsivity alone is insufficient to fully understand this complex phenotype. Characterizations of both automatic and focused pulling as well as preliminary findings from affective neuroscience across species highlight the importance of compulsivity for understanding HPD. Opposing and complementary aspects to impulsivity-compulsivity provide a more comprehensive conceptualization of HPD and supports HPD's potential importance for advancing scientific inquiry in relation to the pathogenesis and treatment of related phenotypes. This review concludes with a description of areas-phenotype, neurobiology, and genes-in need of further study.

Comprehensive neurocognitive endophenotyping strategies for mouse models of genetic disorders

There is a need for refinement of the current behavioral phenotyping methods for mouse models of genetic disorders. The current approach is to perform a behavioral screen using standardized tasks to define a broad phenotype of the model. This phenotype is then compared to what is known concerning the disorder being modeled. The weakness inherent in this approach is twofold: First, the tasks that make up these standard behavioral screens do not model specific behaviors associated with a given genetic mutation but rather phenotypes affected in various genetic disorders; secondly, these behavioral tasks are insufficiently sensitive to identify subtle phenotypes. An alternate phenotyping strategy is to determine the core behavioral phenotypes of the genetic disorder being studied and develop behavioral tasks to evaluate specific hypotheses concerning the behavioral consequences of the genetic mutation. This approach emphasizes direct comparisons between the mouse and human that facilitate the development of neurobehavioral biomarkers or quantitative outcome measures for studies of genetic disorders across species.

D1 and D2 dopamine receptor antagonists decrease behavioral bout duration, without altering the bout's repeated behavioral components, in a naturalistic model of repetitive and compulsive behavior

Nest building behavior in the pregnant female rabbit (Oryctolagus cuniculus) is a model for compulsive behavior in Obsessive Compulsive Disorder (OCD). This behavior comprises a cycle of repeated, stereotyped components (collecting straw, entering nest box and depositing the straw there, returning to collect more straw), which itself is repeated 80+ times in a single bout that lasts approximately 50min. The bout, in turn, is repeated if necessary, according to the rabbit's perception of whether or not the nest is finished. We administered SCH23390 (5-100μg/kg; D1/D5 antagonist) or raclopride (0.05-1.0mg/kg; D2/D3 antagonist), subcutaneously to day 28 pregnant female rabbits, 30 or 60min before placing straw inside their home cage. At doses that minimally affected ambulatory behavior in open field (5-12.5μg/kg SCH23390, 0.5-1.0mg/kg raclopride), both antagonists dramatically reduced bout duration while not significantly affecting the initiation of straw carrying behavior, the sequential performance of the individual cycle components, maximum cycle frequency, or the total number of bouts performed. These results point to an important role for dopamine neurotransmission for the prolonged expression of a normal, repetitive and compulsive-like behavior. Moreover, the finding that dopamine receptor antagonists decrease the time spent engaged in repetitive behavior (without significantly altering the form of the repetitive behavior itself) suggests a possible explanation for why neuroleptics can be clinically effective for treating OCD.

Essential role for orbitofrontal serotonin 1B receptors in obsessive-compulsive disorder-like behavior and serotonin reuptake inhibitor response in mice

BACKGROUND

Perseveration and sensorimotor gating deficits are core features of obsessive-compulsive disorder (OCD). Serotonin 1B receptor (5-HT1BR) agonists exacerbate OCD symptoms in patients and induce perseveration and sensorimotor gating deficits in mice. Serotonin reuptake inhibitors (SRIs), but not noradrenaline reuptake inhibitors (NRIs), reduce OCD symptoms following 4 to 8 weeks of treatment. Using mice, we compared the effects of chronic SRI versus NRI treatment on 5-HT1BR-induced OCD-like behavior and 5-HT1BR sensitivity in orbitofrontal-subcortical OCD circuits. Furthermore, we localized the 5-HT1BR population that mediates OCD-like behavior.

METHODS

Mice chronically received the SRI clomipramine or the NRI desipramine and were examined for 5-HT1BR-induced OCD-like behavior or 5-HT1BR binding and G-protein coupling in caudate putamen, nucleus accumbens, and orbitofrontal cortex. Separate mice were tested for OCD- or depression-like behavior following 4, 14, 21, 28, or 56 days of SRI treatment. Finally, OCD-like behavior was assessed following intra-orbitofrontal 5-HT1BR agonist infusion or intra-orbitofrontal 5-HT1BR antagonist infusion coupled with systemic 5-HT1BR agonist treatment.

RESULTS

Effective, but not ineffective, OCD treatments reduced OCD-like behavior in mice with a time course that parallels the delayed therapeutic onset in OCD patients and downregulated 5-HT1BR expression in the orbitofrontal cortex. Intra-orbitofrontal 5-HT1BR agonist infusion induced OCD-like behavior, and intra-orbitofrontal 5-HT1BR antagonist infusion blocked OCD-like effects of systemic 5-HT1BR agonist treatment.

CONCLUSIONS

These results indicate that orbitofrontal 5-HT1BRs are necessary and sufficient to induce OCD-like behavior in mice and that SRI pharmacotherapy reduces OCD-like behavior by desensitizing orbitofrontal 5-HT1BRs. Our findings suggest an essential role for orbitofrontal 5-HT1BRs in OCD pathophysiology and treatment.