Selective alleviation of compulsive lever-pressing in rats by D1, but not D2, blockade: possible implications for the involvement of D1 receptors in obsessive-compulsive disorder

Computational insights on asymmetrical D1 and D2 receptor-mediated chunking: implications for OCD and Schizophrenia

Repetitive thoughts and motor programs including perseveration are bridge symptoms characteristic of obsessive compulsive disorder (OCD), schizophrenia and in the co-morbid overlap of these conditions. The above pathologies are sensitive to altered activation and kinetics of dopamine D 1 and D 2 receptors that differently influence sequence learning and recall. Recognizing start and stop elements of motor and cognitive behaviors has crucial importance. During chunking, frequent components of temporal strings are concatenated into single units. We extended a published computational model (Asabuki et al. 2018), where two populations of neurons are connected and simulated in a reservoir computing framework. These neural pools were adopted to represent D1 and D2 striatal neuronal populations. We investigated how specific neural and striatal circuit parameters can influence start/stop signaling and found that asymmetric intra-network connection probabilities, synaptic weights and differential time constants may contribute to signaling of start/stop elements within learned sequences. Asymmetric coupling between the striatal D 1 and D 2 neural populations was also demonstrated to be beneficial. Our modeling results predict that dynamical differences between the two dopaminergic striatal populations and the interaction between them may play complementary roles in chunk boundary signaling. Start and stop dichotomies can arise from the larger circuit dynamics as well, since neural and intra-striatal connections only partially support a clear division of labor.

Feed tossing behaviour of Holstein cows: evaluation of physiological stress state and rumen fermentation function

Background

Abnormal or stereotyped behaviours in dairy cows are common in large-scale indoor farms and are usually accompanied by high physiological stress levels. Feed tossing is an abnormal behaviour commonly seen in cows while being fed, making farm management difficult. However, the reasons behind this behaviour have not been sufficiently reported. The objective of this study was to explore the changes in rumen fermentation, serum indicators, inflammatory conditions and the performance of cows with feed tossing behaviour. Holstein cows with similar lactation stages in the same barn were subjected to behaviour observations two times per day for 21 consecutive days. Ten cows with feed tossing behaviour (FT) and ten cows without abnormal behaviours (CON) were selected for further sampling. Plasma samples, rumen fluid, milk yield data of cows, and an indoor environment temperature-humidity index (THI) were collected.

Results

There was no significant difference in average daily milk yield during the observation period between feed-tossing cows (n = 68) and the other cows (n = 112). The number of cows showing FT behaviour had a moderately strong negative linear correlation with the THI of the environment. Compared to the CON cows, the FT cows had higher cortisol, norepinephrine and urea nitrogen levels in plasma, as well as higher plasma levels of inflammatory indicators, including total protein, lactate dehydrogenase, albumin, aspartate aminotransferase levels, and the ratio of aspartate aminotransferase to alanine aminotransferase. The FT cows had no significant variations from the CON cows regarding their rumen fermentation indicators, such as pH, ammonia nitrogen, and volatile fatty acids. In addition, 16S rRNA analysis revealed that there might be no clear association between the diversity and abundance of rumen bacteria and feed tossing behaviour.

Conclusions

Our findings suggested that cows might have suffered from high levels of physiological stress and immune state for a long period when they exhibited FT behaviour. The environmental THI could affect the FT behaviour of cows; as the THI increases, the willingness of cows to throw decreases. This work provided the first evidence that feed tossing might be a response associated with high levels of physiological stress and immune. It also explored our insights into a commonly observed behavioural response to cow welfare traits.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03469-0.

Assessment of Repetitive and Compulsive Behaviors Induced by Pramipexole in Rats: Effect of Alpha-Synuclein-Induced Nigrostriatal Degeneration

Treatment with dopamine agonists in Parkinson’s disease (PD) is associated with debilitating neuropsychiatric side-effects characterized by impulsive and compulsive behaviors. The vulnerability to develop such impairments is thought to involve interactions between individual vulnerability traits, types of antiparkinsonian medications, and the neurodegenerative process. We investigated the effect of the dopamine D3/D2 agonist pramipexole (PPX) and selective nigrostriatal degeneration achieved by viral-mediated expression of alpha-synuclein on the expression of repetitive and compulsive-like behaviors in rats. In a task assessing spontaneous food hoarding behavior, PPX increased the time spent interacting with food pellets at the expense of hoarding. This disruption of hoarding behavior was identical in sham and lesioned rats. In an operant post-training signal attenuation task, the combination of nigrostriatal lesion and PPX decreased the number of completed trials and increased the number of uncompleted trials. The lesion led to an increased compulsive behavior after signal attenuation, and PPX shifted the overall behavioral output towards an increased proportion of compulsive lever-presses. Given the magnitude of the behavioral effects and the lack of strong interaction between PPX and nigral degeneration, these results suggest that extra-nigral pathology may be critical to increase the vulnerability to develop compulsive behaviors following treatment with D3/D2 agonists.

Stereotypies in the Autism Spectrum Disorder: Can We Rely on an Ethological Model?

BACKGROUND

Stereotypic behaviour can be defined as a clear behavioural pattern where a specific function or target cannot be identified, although it delays on time. Nonetheless, repetitive and stereotypical behaviours play a key role in both animal and human behaviour. Similar behaviours are observed across species, in typical human developmental phases, and in some neuropsychiatric conditions, such as Autism Spectrum Disorder (ASD) and Intellectual Disability. This evidence led to the spread of animal models of repetitive behaviours to better understand the neurobiological mechanisms underlying these dysfunctional behaviours and to gain better insight into their role and origin within ASD and other disorders. This, in turn, could lead to new treatments of those disorders in humans.

METHOD

This paper maps the literature on repetitive behaviours in animal models of ASD, in order to improve understanding of stereotypies in persons with ASD in terms of characterization, pathophysiology, genomic and anatomical factors.

RESULTS

Literature mapping confirmed that phylogenic approach and animal models may help to improve understanding and differentiation of stereotypies in ASD. Some repetitive behaviours appear to be interconnected and mediated by common genomic and anatomical factors across species, mainly by alterations of basal ganglia circuitry. A new distinction between stereotypies and autotypies should be considered.

CONCLUSIONS

Phylogenic approach and studies on animal models may support clinical issues related to stereotypies in persons with ASD and provide new insights in classification, pathogenesis, and management.

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.

Mesolimbic dopamine projections mediate cue-motivated reward seeking but not reward retrieval in rats

Efficient foraging requires an ability to coordinate discrete reward-seeking and reward-retrieval behaviors. We used pathway-specific chemogenetic inhibition to investigate how rats’ mesolimbic and mesocortical dopamine circuits contribute to the expression and modulation of reward seeking and retrieval. Inhibiting ventral tegmental area dopamine neurons disrupted the tendency for reward-paired cues to motivate reward seeking, but spared their ability to increase attempts to retrieve reward. Similar effects were produced by inhibiting dopamine inputs to nucleus accumbens, but not medial prefrontal cortex. Inhibiting dopamine neurons spared the suppressive effect of reward devaluation on reward seeking, an assay of goal-directed behavior. Attempts to retrieve reward persisted after devaluation, indicating they were habitually performed as part of a fixed action sequence. Our findings show that complete bouts of reward seeking and retrieval are behaviorally and neurally dissociable from bouts of reward seeking without retrieval. This dichotomy may prove useful for uncovering mechanisms of maladaptive behavior.

The Effect of Atorvastatin on Obsessive-compulsive Symptoms of Refractory Obsessive-compulsive Disorder (Add-on Therapy)

Background

Considering the effect of statins on the regulation of dopamine neurotransmitters and glutamates and importance of the treatment of obsessive-compulsive disorder (OCD) due to its relatively high prevalence and disability of available drugs in treatment of many patients, we came to the point to examine effectiveness of statins in patients with OCD.

Materials and Methods

This study is a double-blind randomized clinical trial, which is done in OCD clinic of Isfahan Shariati in 2014 for 1 year. The target population consists of 64 patients with OCD; one group is given a daily 40 mg atorvastatin tablets and the other group receives placebo. At baseline, 4- and 8-week severities of obsessive-compulsive symptoms are measured using Yale-Brown scale and compared in the two groups.

Results

The study results show a statistically significant difference between the two groups of intervention and control (P < 0.001). Furthermore, the results show the intervention effect at the end of the 4^th week and 8^th week (P < 0.001) that this change is evident in the 4^th week but remained almost constant in the 8^th week.

Conclusion

Overall, the evidences obtained from the study declare the effects of adding statins to treat obsessive-compulsive symptoms.

Effect of Religious Cognitive Behavioral Therapy on Religious Obsessive-compulsive Disorder (3 and 6 months Follow-up)

Background:

Obsessive-compulsive disorder (OCD) is a chronic disorder that strongly affects one's life and social, emotional, and occupational functioning. Due to the effect of religious beliefs on phenomenology of OCD, in this paper, we assess the effectiveness of religious cognitive behavioral therapy (CBT) within 3 and 6 months follow-up.

Materials and Methods:

This study is a clinical trial with follow-ups which last 2 months consisting eight sessions of 1.5 h of religious CBT. The research is conducted in a group of 40, with pre- and post-test after 3 and 6 months. Used Yale-Brown OCD symptom scale, before, the end, after 3 months and after 6 months of intervention. Treatment is carried out by a psychiatrist and a clergyman through religious CBT. The trial is held in OCD clinic affiliated with Noor Hospital. Results are analyzed by ANOVA repeated measure with SPSS18.

Results:

The results showed a considerable decrease in OCD symptoms which remained almost persistent after 3 and 6 months (F = 3/54. P = 0/024). It also shows that religious CBT can leave substantial effect on OCD symptoms; permanency of this intervention after 3 and 6 months is noticeable (P < 0/001). In Conclusion this therapy could be helpful for OCD patients with religious content.

Conclusion:

RCBT have a positive effect on people with religious obsessive -compulsive.

Chronic pramipexole treatment induces compulsive behavior in rats with 6-OHDA lesions of the substantia nigra and ventral tegmental area

Dopamine replacement therapy (DRT) reduces motor symptoms in Parkinson's disease (PD), but also induces impulsive-compulsive behavior (ICB) in up to 25% of PD patients. These non-motor side effects of DRT generally follow a gradual transition from impulsive to compulsive-like-i.e. repetitive, compelled, and non-pleasurable-behavior. Here, we investigated the effect of chronic pramipexole (PPX) treatment on the onset of compulsive-like behavior, measured via the post-training signal attenuation (PTSA) procedure, in rats with dopaminergic lesions. Accordingly, we aimed to mimic chronic DRT in a PD context, and obtain data on the brain regions that potentially sustain this type of compulsive behavior pattern in rats. We observed that the lesion or treatment alone did not induce compulsive lever pressing in rats. However, rats with lesions of the substantia nigra and ventral tegmental area as well as with chronic PPX treatment developed strong compulsive lever-pressing behavior, as measured via PTSA. Furthermore, when chronic PPX treatment was discontinued before the PTSA test, the lesioned rats showed the same level of compulsive behavior as sham-operated rats. In fact, lesioned, treated, and compulsive-like rats showed significantly higher Fos expression in the orbitofrontal cortex and dorsal striatum. Thus, chronic PPX treatment in PD rats induced a strong compulsive-like behavior. Furthermore, Fos expression mapping suggests that the behavior was sustained via the activation of the orbitofrontal cortex and dorsal striatum.

Striatopallidal dysfunction underlies repetitive behavior in Shank3-deficient model of autism

The postsynaptic scaffolding protein SH3 and multiple ankyrin repeat domains 3 (SHANK3) is critical for the development and function of glutamatergic synapses. Disruption of the SHANK3-encoding gene has been strongly implicated as a monogenic cause of autism, and Shank3 mutant mice show repetitive grooming and social interaction deficits. Although basal ganglia dysfunction has been proposed to underlie repetitive behaviors, few studies have provided direct evidence to support this notion and the exact cellular mechanisms remain largely unknown. Here, we utilized the Shank3B mutant mouse model of autism to investigate how Shank3 mutation may differentially affect striatonigral (direct pathway) and striatopallidal (indirect pathway) medium spiny neurons (MSNs) and its relevance to repetitive grooming behavior in Shank3B mutant mice. We found that Shank3 deletion preferentially affects synapses onto striatopallidal MSNs. Striatopallidal MSNs showed profound defects, including alterations in synaptic transmission, synaptic plasticity, and spine density. Importantly, the repetitive grooming behavior was rescued by selectively enhancing the striatopallidal MSN activity via a Gq-coupled human M3 muscarinic receptor (hM3Dq), a type of designer receptors exclusively activated by designer drugs (DREADD). Our findings directly demonstrate the existence of distinct changes between 2 striatal pathways in a mouse model of autism and indicate that the indirect striatal pathway disruption might play a causative role in repetitive behavior of Shank3B mutant mice.

Compulsivity in obsessive-compulsive disorder and addictions

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

From Thought to Action: How the Interplay Between Neuroscience and Phenomenology Changed Our Understanding of Obsessive-Compulsive Disorder

The understanding of obsessive-compulsive disorder (OCD) has evolved with the knowledge of behavior, the brain, and their relationship. Modern views of OCD as a neuropsychiatric disorder originated from early lesion studies, with more recent models incorporating detailed neuropsychological findings, such as perseveration in set-shifting tasks, and findings of altered brain structure and function, namely of orbitofrontal corticostriatal circuits and their limbic connections. Interestingly, as neurobiological models of OCD evolved from cortical and cognitive to sub-cortical and behavioral, the focus of OCD phenomenology also moved from thought control and contents to new concepts rooted in animal models of action control. Most recently, the proposed analogy between habitual action control and compulsive behavior has led to the hypothesis that individuals suffering from OCD may be predisposed to rely excessively on habitual rather than on goal-directed behavioral strategies. Alternatively, compulsions have been proposed to result either from hyper-valuation of certain actions and/or their outcomes, or from excessive uncertainty in the monitoring of action performance, both leading to perseveration in prepotent actions such as washing or checking. In short, the last decades have witnessed a formidable renovation in the pathophysiology, phenomenology, and even semantics, of OCD. Nevertheless, such progress is challenged by several caveats, not least psychopathological oversimplification and overgeneralization of animal to human extrapolations. Here we present an historical overview of the understanding of OCD, highlighting converging studies and trends in neuroscience, psychiatry and neuropsychology, and how they influenced current perspectives on the nosology and phenomenology of this disorder.

Signal attenuation as a rat model of obsessive compulsive disorder

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

Animal models of obsessive-compulsive disorder: utility and limitations

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

Dopaminergic control of cognitive flexibility in humans and animals

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

The role of the cholinergic system in the signal attenuation rat model of obsessive-compulsive disorder

RATIONALE

In comparison to studies of the involvement of the serotonergic, dopaminergic, and glutamatergic systems in the pathophysiology of obsessive-compulsive disorder (OCD), research on the involvement of the cholinergic system in this disorder has remained sparse.

OBJECTIVES

The aim of this study was to test the role of the cholinergic system in compulsive behavior using the signal attenuation rat model of OCD. In this model, "compulsive" behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food.

METHODS

The acetylcholinesterase inhibitor physostigmine (0.05, 0.10, and 0.15 mg/kg), the nicotinic agonist nicotine (0.03, 0.06, 0.10, 0.30, 0.60, and 1.00 mg/kg), the nicotinic antagonist mecamylamine (1, 3, 5, and 8 mg/kg), the muscarinic agonist oxotremorine (0.0075, 0.0150, and 0.0300 mg/kg), and the muscarinic antagonist scopolamine (0.15, 0.50, 1.00, and 1.50 mg/kg) were acutely administered to rats just before assessing their lever-press responding following signal attenuation (experiments 1, 3, 5, 7, and 9, respectively). Because the effects of signal attenuation are assessed under extinction conditions, drug doses that were effective in the above experiments were also tested in an extinction session of lever-press responding that was not preceded by signal attenuation (experiments 2, 4, 6, 8, and 10).

RESULTS

Acute systemic administration of the cholinergic agents did not exert a selective anti- or pro-compulsive effect in the signal attenuation model.

CONCLUSIONS

Acetylcholine does not seem to play a role in the signal attenuation rat model of OCD.

Comparison of the MK-801-induced increase in non-rewarded appetitive responding with dopamine agonists and locomotor activity in rats

Systemic administration of the noncompetitive N-methyl-D-aspartate (NMDA)- receptor antagonist, MK-801, has been proposed to model cognitive deficits similar to those seen in patients with schizophrenia. Evidence has shown that MK-801 increases the probability of operant responding during extinction, possibly modeling perseveration, as would be seen in patients with schizophrenia. This MK-801-induced behavioral perseveration is reversed by dopamine receptor antagonism. To further explore the role of dopamine in this behavioral change, the current study sought to determine if the MK-801-induced increase in non-rewarded operant responding could be mimicked by dopamine agonism and determine how it was related to locomotor activity. Male Long Evans rats were treated systemically with MK-801, cocaine, GBR12909 or apomorphine (APO) and given a single trial operant extinction session, followed by a separate assessment of locomotor activity. Both MK-801 (0.05 mg/kg) and cocaine (10 mg/kg) significantly increased responding during the extinction session and both increased horizontal locomotor activity. No dose of GBR-12909 (5, 10 or 20 mg/kg) was found to effect non-rewarded operant responding or locomotor activity. APO (0.05, 0.5, 2 or 5 mg/kg) treatment produced a dose-dependent decrease in both operant responding and locomotor activity. These results suggest the possibility that, rather than a primary influence of increased dopamine concentration on elevating bar-pressing responses during extinction, other neurotransmitter systems may be involved.

Evaluation of animal models of obsessive-compulsive disorder: correlation with phasic dopamine neuron activity

Obsessive compulsive disorder (OCD) is a psychiatric condition defined by intrusive thoughts (obsessions) associated with compensatory and repetitive behaviour (compulsions). However, advancement in our understanding of this disorder has been hampered by the absence of effective animal models and correspondingly analysis of the physiological changes that may be present in these models. To address this, we have evaluated two current rodent models of OCD; repeated injection of dopamine D2 agonist quinpirole and repeated adolescent injection of the tricyclic agent clomipramine in combination with a behavioural paradigm designed to produce compulsive lever pressing. These results were then compared with their relative impact on the state of activity of the mesolimbic dopaminergic system using extracellular recoding of spontaneously active dopamine neurons in the ventral tegmental area (VTA). The clomipramine model failed to exacerbate compulsive lever pressing and VTA dopamine neurons in clomipramine-treated rats had mildly diminished bursting activity. In contrast, quinpirole-treated animals showed significant increases in compulsive lever pressing, which was concurrent with a substantial diminution of bursting activity of VTA dopamine neurons. Therefore, VTA dopamine activity correlated with the behavioural response in these models. Taken together, these data support the view that compulsive behaviours likely reflect, at least in part, a disruption of the dopaminergic system, more specifically by a decrease in baseline phasic dopamine signalling mediated by burst firing of dopamine neurons.

Outlining new frontiers for the comprehension of obsessive-compulsive disorder: a review of its relationship with fear and anxiety

Anxiety is an important component of the psychopathology of the obsessive-compulsive disorder (OCD). So far, most interventions that have proven to be effective for treating OCD are similar to those developed for other anxiety disorders. However, neurobiological studies of OCD came to conclusions that are not always compatible with those previously associated with other anxiety disorders.

OBJECTIVES

The aim of this study is to review the degree of overlap between OCD and other anxiety disorders phenomenology and pathophysiology to support the rationale that guides research in this field.

RESULTS

Clues about the neurocircuits involved in the manifestation of anxiety disorders have been obtained through the study of animal anxiety models, and structural and functional neuroimaging in humans. These investigations suggest that in OCD, in addition to dysfunction in cortico-striatal pathways, the functioning of an alternative neurocircuitry, which involves amygdalo-cortical interactions and participates in fear conditioning and extinction processes, may be impaired.

CONCLUSION

It is likely that anxiety is a relevant dimension of OCD that impacts on other features of this disorder. Therefore, future studies may benefit from the investigation of the expression of fear and anxiety by OCD patients according to their type of obsessions and compulsions, age of OCD onset, comorbidities, and patterns of treatment response.

Facilitation of extinction of operant behaviour in C57Bl/6 mice by chlordiazepoxide and D-cycloserine

RATIONALE AND OBJECTIVE

Effects on the extinction of GABAergic drug, chlordiazepoxide (CDP), and glutamatergic drug, D: -cycloserine (DCS), in C57BL/6 mice were compared.

MATERIALS AND METHODS

Following a palatability test (Experiment 1), Experiments 2-6 involved food-reinforced lever press training followed by extinction sessions at 1- or 4-day intervals. The effects of drugs were examined. Experiment 7 involved a two-lever task.

RESULTS

CDP did not affect food palatability (Experiment 1), but facilitated extinction when administered prior to extinction sessions via intracerebral (Experiment 2) or peripheral administration at 1-day (Experiments 3-7) or 4-day intervals (Experiment 6). Reducing the amount of training prior to extinction reduced the delay in the effect of CDP typically seen, and CDP had a larger effect in early sessions on mice that had received less training (Experiment 3). There was some evidence that CDP could be blocked by flumazenil (Experiment 4), and CDP withdrawal reversed extinction facilitation (Experiments 5 and 7). With 4-day intervals, DCS administered immediately following extinction sessions, or pre-session CDP, facilitated extinction with 48-trial sessions (experiment 6B). With six-trial sessions, the co-administration of post-session DCS enhanced facilitation produced by pre-session CDP (experiment 6A). Finally, CDP facilitated extinction in a dose-related fashion following training on a two-lever food-reinforced task (Experiment 7).

CONCLUSIONS

The findings are consistent with the hypotheses that two neurotransmitter systems have different roles in operant extinction and that glutamatergic systems are involved in extinction learning and GABAergic systems involved in the expression of that learning. This parallels findings with extinction following Pavlovian conditioning, which has been more extensively investigated.

Behavioral, pharmacological, and immunological abnormalities after streptococcal exposure: a novel rat model of Sydenham chorea and related neuropsychiatric disorders

Group A streptococcal (GAS) infections and autoimmunity are associated with the onset of a spectrum of neuropsychiatric disorders in children, with the prototypical disorder being Sydenham chorea (SC). Our aim was to develop an animal model that resembled the behavioral, pharmacological, and immunological abnormalities of SC and other streptococcal-related neuropsychiatric disorders. Male Lewis rats exposed to GAS antigen exhibited motor symptoms (impaired food manipulation and beam walking) and compulsive behavior (increased induced-grooming). These symptoms were alleviated by the D2 blocker haloperidol and the selective serotonin reuptake inhibitor paroxetine, respectively, drugs that are used to treat motor symptoms and compulsions in streptococcal-related neuropsychiatric disorders. Streptococcal exposure resulted in antibody deposition in the striatum, thalamus, and frontal cortex, and concomitant alterations in dopamine and glutamate levels in cortex and basal ganglia, consistent with the known pathophysiology of SC and related neuropsychiatric disorders. Autoantibodies (IgG) of GAS rats reacted with tubulin and caused elevated calcium/calmodulin-dependent protein kinase II signaling in SK-N-SH neuronal cells, as previously found with sera from SC and related neuropsychiatric disorders. Our new animal model translates directly to human disease and led us to discover autoantibodies targeted against dopamine D1 and D2 receptors in the rat model as well as in SC and other streptococcal-related neuropsychiatric disorders.

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.

Cortico-striatal oxidative status, dopamine turnover and relation with stereotypy in the deer mouse

The deer mouse presents with spontaneous stereotypic movements that resemble the repetitive behaviours of obsessive-compulsive disorder (OCD), and demonstrates a selective response to serotonin reuptake inhibitors. OCD has been linked to altered redox status and since increased dopamine signalling can promote stereotypies as well as oxidative stress, we investigated whether the severity of deer mouse stereotypy may be associated with altered dopamine turnover and cortico-striatal redox status. Deer mice were separated into high (HSB), low (LSB) and non-stereotypy (NS) groups. Frontal cortical and striatal dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), as well as superoxide dismutase (SOD) activity, reduced (GSH) and oxidised (GSSG) glutathione and glutathione redox index, were analysed as markers for regional dopamine turnover and oxidative stress, respectively. Dopamine and its metabolites and SOD activity did not differ across the stereotypy groups. Significantly reduced GSH and GSSG and increased glutathione redox index were only observed in the frontal cortex of HSB animals. Frontal cortical GSH and GSSG were inversely correlated while glutathione redox index was positively correlated with stereotypy. Deer mouse stereotypy is thus characterised by a deficient glutathione system in the frontal cortex but not striatum, and provides a therapeutic rationale for using glutathione-active antioxidants in OCD. The evidence for a primary frontal lesion has importance for future OCD research.

Dopamine, but not serotonin, regulates reversal learning in the marmoset caudate nucleus

Studies of visual discrimination reversal learning have revealed striking neurochemical dissociations at the level of the orbitofrontal cortex (OFC) with serotoninergic, but not dopaminergic, integrity being important for successful reversal learning. These findings have considerable implications for disorders such as obsessive compulsive disorder and schizophrenia, in which reversal learning is impaired, and which are primarily treated with drugs targeting the dopaminergic and serotoninergic systems. Dysfunction in such disorders however, is not limited to the OFC and extends subcortically to other structures implicated in reversal learning, such as the medial caudate nucleus. Therefore, because the roles of the serotonin and dopamine within the caudate nucleus are poorly understood, this study compared the effects of selective serotoninergic or selective dopaminergic depletions of the marmoset medial caudate nucleus on serial discrimination reversal learning. All monkeys were able to learn novel stimulus-reward associations but, unlike control monkeys and monkeys with selective serotoninergic medial caudate depletions, dopamine-depleted monkeys were markedly impaired in their ability to reverse this association. This impairment was not perseverative in nature. These findings are the opposite of those seen in the OFC and provide evidence for a neurochemical double dissociation between the OFC and medial caudate in the regulation of reversal learning. Although the specific contributions of these monoamines within the OFC-striatal circuit remain to be elucidated, these findings have profound implications for the development of drugs designed to remediate some of the cognitive processes underlying impaired reversal learning.

Towards a comprehensive model of stereotypy: integrating operant and neurobiological interpretations

The predominant models on the emergence and maintenance of stereotypy in individuals with developmental disabilities are based on operant and neurobiological interpretations of the behavior. Although the proponents of the two models maintain largely independent lines of research, operant and neurobiological interpretations of stereotypy are not mutually exclusive. The paper reviews the two models of stereotypy and proposes an integrated model using recent findings on the neurobiology of reinforcement. The dopaminergic system and the basal ganglia are both involved in stereotypy and in reinforcement, which provides a potential link between the models. Implications of the integrated model for future research are discussed in terms of improving the assessment and treatment of stereotypy in individuals with developmental disabilities.

High but not low frequency stimulation of both the globus pallidus and the entopeduncular nucleus reduces 'compulsive' lever-pressing in rats

The anti-compulsive effects of high and low frequency stimulation (LFS, HFS) of the entopeduncular nucleus and globus pallidus (the rat's equivalent, respectively, of the primate's internal and external segments of the globus pallidus) were assessed in the signal attenuation rat model of obsessive-compulsive disorder (OCD). HFS, but not LFS, of the two nuclei exerted an anti-compulsive effect, suggesting that HFS of either segment of the globus pallidus may provide an additional therapeutic strategy for OCD.

N-methyl d-aspartate receptors are involved in the induction, but not expression stage of amphetamine sensitization in schedule-induced polydipsia in rats

1. The aim of the present study was to examine the role of dopaminergic and glutamatergic receptors on different stages of the amphetamine (AMPH) sensitized effect in schedule-induced polydipsia (SIP) in rats. 2. Three experiments were designed to evaluate the roles of DAD2 receptor antagonist haloperidol (HAL) and glutamatergic N-methyl d-aspartate receptor antagonist MK-801 on both the induction and the expression stage of AMPH sensitization in SIP rats. First, the induction of AMPH sensitization in the SIP model was tested again to confirm previous findings. Second, HAL or MK-801 was co-administered with AMPH on five consecutive days and their effect on induction was examined 14 days after withdrawal. Finally, HAL or MK-801 was co-administered with AMPH on the final day of testing in SIP rats in which AMPH sensitization had been established previously. 3. The present results showed that HAL and MK-801 affected the effect of AMPH differently during the process of sensitization. Whereas HAL influenced the sensitization during both the induction and the expression phases, MK-801 affected only the induction phase; thus, once the sensitization had been established, MK-801 had no further influence. 4. These results suggest that the SIP model could be considered useful for the study of sensitization. In addition, the induction and expression of AMPH sensitization is influenced differently by the dopaminergic and glutamatergic systems.

The role of NMDA receptors in the signal attenuation rat model of obsessive-compulsive disorder

RATIONALE

In recent years, an increasing body of evidence points to the involvement of the glutamatergic system and specifically the glutamatergic ionotropic N-methyl-D-aspartate (NMDA) receptor in the pathophysiology of obsessive-compulsive disorder (OCD).

OBJECTIVES

To test the role of NMDA receptors in compulsive behavior using the signal attenuation rat model of OCD. In this model, 'compulsive' behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food.

METHODS

The NMDA antagonist, MK 801 (0.025-0.100 mg/kg) and the partial NMDA agonist, D-cycloserine (3-100 mg/kg) were administered to rats just before assessing their lever-press responding following signal attenuation (Experiments 1 and 2, respectively). Because the effects of signal attenuation are assessed under extinction conditions, drug doses that were effective in Experiments 1 and 2 were also tested in an extinction session of lever-press responding that was not preceded by signal attenuation (Experiment 3).

RESULTS

Systemic administration of D: -cycloserine (15 mg/kg) selectively decreased compulsive lever pressing, whereas systemic administration of MK 801 did not affect compulsive lever-pressing but dramatically increased resistance to extinction.

CONCLUSIONS

Activation of NMDA receptors may have an anti-compulsive effect in OCD patients.

The role of the striatum in compulsive behavior in intact and orbitofrontal-cortex-lesioned rats: possible involvement of the serotonergic system

In the signal attenuation rat model of obsessive-compulsive disorder (OCD), 'compulsive' behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food. We have recently found that lesions to the rat orbitofrontal cortex (OFC) led to an increase in compulsive lever-pressing that was prevented by systemic administration of the selective serotonin reuptake inhibitor paroxetine, and paralleled by an increase in the density of the striatal serotonin transporter. This study further explored the interaction between the OFC, the striatum, and the serotonergic system in the production of compulsive lever-pressing. Experiment 1 revealed that OFC lesions decrease the content of serotonin, dopamine, glutamate, and GABA in the striatum. Experiment 2 showed that intrastriatal administration of paroxetine blocked OFC lesion-induced increased compulsivity, but did not affect compulsive responding in intact rats. Experiments 3 and 4 found that pre-training striatal lesions had no effect on compulsive lever-pressing, whereas post-training striatal inactivation exerted an anticompulsive effect. These results strongly implicate the striatum in the expression of compulsive lever-pressing in both intact and OFC-lesioned rats. Furthermore, the results support the possibility that in a subpopulation of OCD patients a primary pathology of the OFC leads to a dysregulation of the striatal serotonergic system, which is manifested in compulsive behavior, and that antiobsessional/anticompulsive drugs exerts their effects, in these patients, by normalizing the dysfunctional striatal serotonergic system.

The neurobiology of repetitive behavior: of mice…

Repetitive and stereotyped behavior is a prominent element of both animal and human behavior. Similar behavior is seen across species, in diverse neuropsychiatric disorders and in key phases of typical development. This raises the question whether these similar classes of behavior are caused by similar neurobiological mechanisms or whether they are neurobiologically unique? In this paper we discuss fundamental animal research and translational models. Imbalances in corticostriatal function often result in repetitive behavior, where different classes of behavior appear to be supported by similar neural mechanisms. Although the exact nature of these imbalances are not yet fully understood, synthesizing the literature in this area provides a framework for studying the neurobiological systems involved in repetitive behavior.

Obsessive-compulsive disorder and related disorders: a comprehensive survey

Our aim was to present a comprehensive, updated survey on obsessive-compulsive disorder (OCD) and obsessive-compulsive related disorders (OCRDs) and their clinical management via literature review, critical analysis and synthesis. Information on OCD and OCRD current nosography, clinical phenomenology and etiology, may lead to a better comprehension of their management. Clinicians should become familiar with the broad spectrum of OCD disorders, since it is a pivotal issue in current clinical psychiatry.

Dopamine D1 receptor binding in the striatum of patients with obsessive-compulsive disorder

BACKGROUND

Obsessive-compulsive disorder (OCD) is a chronic anxiety disorder of unknown aetiology. Psychopharmacological studies have suggested a role for the neurotransmitter serotonin however further evidence for serotonin in the aetiology of OCD is conflicted. The authors used positron emission tomography (PET) to examine the binding of the dopamine D(1) receptor antagonist [(11)C]-SCH23390 to D(1) receptors in the striatum of drug-free OCD patients compared with healthy controls.

METHODS

Seven drug-free patients (two drug naïve) with OCD and seven age, gender and education matched healthy controls underwent positron emission tomography with [(11)C]-SCH23390. Binding Potentials (BP) at D(1) receptors were calculated for the caudate nucleus and putamen. Correlations between BP values for basal ganglia regions and clinical measures were performed in OCD patients.

RESULTS

The BP for [(11)C]-SCH23390 at D(1) receptors in OCD patients was significantly reduced in both caudate nucleus (0.59+/-0.06 vs 0.88+/-0.06, p<0.05) and putamen (0.89+/-0.06 vs 1.14+/-0.06, p<0.05) compared with healthy controls. No correlations were found between D(1) BP and symptom measures.

LIMITATIONS

The main limitations of this study are the small sample size and the PET methodology which does not allow for disaggregation of Bmax and Kd values for D(1) receptor binding of [(11)C]-SCH23390.

CONCLUSIONS

The finding of downregulation of D(1) receptors in the striatum of OCD patients suggests increased nigrostriatal dopaminergic drive in OCD. If confirmed, this finding provides support for trials of novel treatments in OCD based on dopaminergic system blockade.

Ovarian hormones modulate 'compulsive' lever-pressing in female rats

Life events related to the female hormonal cycle may trigger the onset of obsessive-compulsive disorder (OCD) or exacerbate symptoms in women already suffering from it. These observations suggest a possible role for ovarian hormones in the course of this disorder. Yet, the mechanisms that may subserve the modulatory effect of ovarian hormones are currently unknown. The aim of the present study was therefore to test the role of ovarian hormones in the signal attenuation rat model of OCD. Experiment 1 compared the behavior of pre-pubertal and adult male and female rats in the model, and found no age and sex differences in compulsive responding. Experiment 2 found that compulsive responding fluctuates along the estrous cycle, being highest during late diestrous and lowest during estrous. Acute administration of estradiol to pre-pubertal female rats was found to attenuate compulsive behavior (Experiment 3), and withdrawal from chronic administration of estradiol was shown to increase this behavior (Experiment 4). These findings extend the use of the signal attenuation model of OCD to female rats, and by demonstrating that the model is sensitive to the levels of ovarian hormones, provide the basis for using the model to study the role of ovarian hormones in OCD. In addition, the present findings support the hypothesis that the increased risk of onset and exacerbation of OCD in women post-partum may be a result of the decrease in the level of estradiol, which was elevated during pregnancy.

Facilitation of extinction of operant behaviour in mice by D-cycloserine

RATIONALE AND OBJECTIVE

The N-methyl-D-aspartate receptor agonist D-cycloserine (DCS) facilitates extinction following Pavlovian fear conditioning or conditioned place preference in rats, but its effects on extinction following operant conditioning are not previously established. We studied the effects of DCS on operant extinction with mice, previously shown to be facilitated by GABAergic potentiators including chlordiazepoxide.

MATERIALS AND METHODS

Following training of lever pressing by C57Bl/6 male mice on a discrete-trial fixed-ratio food reinforcement schedule with six reinforcers per session, 48-trial extinction sessions were conducted at 3- (Experiment 1) or 4-day intervals (Experiment 2). Effects of DCS (15 or 30 mg/kg, i.p.) administered immediately after 48-trial extinction sessions were compared with those of saline injections.

RESULTS

With 3-day intervals between extinction sessions, post-session administration of DCS facilitated extinction, and this effect was stronger with 4-day intervals between extinction sessions. Facilitation of extinction by post-session drug administration persisted over a number of extinction sessions.

CONCLUSIONS

Operant extinction in mice can be facilitated by DCS, a glutamatergic agonist, as well as by GABAergic potentiators. The relationship between glutamatergic and GABAergic processes in operant extinction is yet to be established. These findings strengthen the basis for clinical uses of DCS.

Dopaminergic and serotonergic modulation of persistent behaviour in the reinforced spatial alternation model of obsessive-compulsive disorder

RATIONALE

We have proposed rewarded T-maze alternation as a model of obsessive-compulsive disorder (OCD): the serotonin agonist m-chlorophenylpiperazine (mCPP) increments persistence therein, while chronic pretreatment with selective serotonin reuptake inhibitor (SSRI fluoxetine) but not benzodiazepine or desipramine abolishes mCPP effects. However, we noted that acute SSRI administration also causes transient persistence increase, counteracted by mCPP pretreatment.

OBJECTIVES

This study (a) further explores the cross-tolerance between fluoxetine and mCPP and (b) extends the model by investigating its sensitivity to dopaminergic manipulations (D2, 3 agonism--quinpirole).

MATERIALS AND METHODS

In both experiments, baseline and drug testing were carried out under daily T-maze alternation training. Exp. 1: Matched group (n = 8) pairs of rats received one of the following 20-day pretreatments (daily intraperitoneal administration): (1) saline, (2) low-dose fluoxetine (2.5 mg/kg), (3) low-dose mCPP (0.5 mg/kg) or (4) combined fluoxetine + mCPP. One group per pretreatment then received a 4-day challenge with high-dose fluoxetine (10 mg/kg), the other with high-dose mCPP (2.5 mg/kg). Exp. 2: One group (n = 12) of rats received 20-day treatment with saline, another with quinpirole (0.5 mg/kg).

RESULTS

Exp. 1: Saline and low-dose mCPP- or fluoxetine-pretreated animals showed significant persistence increases under both challenges, while combined low-dose fluoxetine + mCPP pretreatment afforded full protection from either challenge. Exp. 2: Quinpirole significantly increased directional persistence after 13 administration days.

CONCLUSIONS

These results establish the sensitivity of the rewarded alternation OCD model to D2, 3 receptor activation, thereby extending its profile of pharmacological isomorphism with OCD. Furthermore, they suggest a common mechanism of action of an SSRI and a serotonin agonist in the control of directional persistence.

High frequency stimulation and pharmacological inactivation of the subthalamic nucleus reduces 'compulsive' lever-pressing in rats

In recent years there have been several attempts to establish high frequency stimulation (HFS) as an additional treatment strategy for obsessive-compulsive disorder (OCD). Two studies reported that bilateral HFS of the subthalamic nucleus (STN) dramatically alleviated compulsions and improved obsessions in three patients with co-morbid Parkinson's disease and OCD. A recent study reported that HFS as well as pharmacological inactivation of the STN alleviate compulsive checking in the quinpirole rat model of OCD. As the quinpirole model is based on a dopaminergic manipulation, the aim of the present study was to test whether HFS and pharmacological inactivation of the STN exert an anti-compulsive effect also in the drug-naive brain, using the signal attenuation rat model of OCD. The main finding of the present study is that both HFS and pharmacological inactivation of the STN exerted an anti-compulsive effect, although the two manipulations differed in their effects on other behavioral measures. These findings support the possibility that HFS of the STN may provide an additional therapeutic strategy for OCD.

Strain differences in ‘compulsive’ lever-pressing

In the signal attenuation rat model of obsessive-compulsive disorder, 'compulsive' behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food. In recent years several studies have reported that Lewis rats, an inbred strain derived from the Sprague Dawley strain, exhibit addictive and/or compulsive tendencies. The aim of the present study was thus to test whether Lewis rats will also show increased compulsivity in the signal attenuation model. Because the model has been developed and validated using Wistar rats only, the present study compared the behavioral response to signal attenuation of Lewis, Sprague Dawley and Wistar rats, and assessed the effects of the anti-compulsive drug paroxetine on compulsive behavior in Lewis and Sprague Dawley rats. The results show that Lewis rats are more 'compulsive' than Sprague Dawley and Wistar rats in terms of both higher levels of compulsive lever-pressing and higher resistance to the anti-compulsive effect of paroxetine. The possibility that these strain differences are related to strain differences in the serotonergic and dopaminergic systems are discussed in light of current knowledge of the pathophysiology and pharmacotherapy of OCD.

The signal attenuation rat model of obsessive-compulsive disorder: a 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 a recently developed rat model of OCD, namely, signal attenuation. Results of pharmacological and lesion studies are presented and evaluated with respect to the pharmacology and pathophysiology of OCD. It is argued that signal attenuation is a rat model of OCD with construct (derived from similarity in the underlying mechanisms), predictive (derived from similarity in response to treatment), and face (derived from phenomenological similarity between "compulsive" behavior in the model and compulsions in OCD patients) validity.

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).

Maternal age at the birth of the first child as an epistatic factor in polygenic disorders

The identification of the genes for complex, polygenic disorders has proven difficult. This is due to the small effect size of each gene and genetic heterogeneity. An additional important factor could be the presence of unidentified epistatic factors. In the broad definition of epistasis, the effect of one unit is not predicable unless the value of another unit is known and one of the units may not be a gene. We have previously identified maternal age as an epistatic factor for the effect of the LEP gene on the age of onset of menarche. We report here the effect of maternal age and the age of the mother at the birth of her first child (maternal age 1st) as epistatic factors for the interaction of the dopamine D1 gene (DRD1) with obsessive-compulsive behaviors and with stuttering. The epistatic effects of maternal age 1st were stronger than maternal age. This type of epistatic factor may be generalizable to many other gene-trait interactions.

‘Compulsive’ lever pressing in rats is enhanced following lesions to the orbital cortex, but not to the basolateral nucleus of the amygdala or to the dorsal medial prefrontal cortex

In a new rat model of obsessive-compulsive disorder (OCD), 'compulsive' behaviour is induced by attenuating a signal indicating that a lever-press response was effective in producing food. We have recently found that compulsive lever pressing is increased following lesions to the rat orbital cortex, in accordance with several lines of evidence implicating the orbitofrontal cortex in the pathophysiology of OCD. In view of the functional similarities between the orbital cortex, the basolateral nucleus of the amygdala and the medial prefrontal cortex, the present study compared the effects of lesions to these three regions. The present study replicated the finding that lesions to the rat orbital cortex enhance compulsive lever pressing. In contrast, lesions to the dorsal medial prefrontal cortex and to the basolateral amygdala did not affect compulsive lever pressing. A comparison of these findings to current knowledge regarding similarities and differences in the functioning of the three regions sheds light on the mechanism by which signal attenuation induces compulsive lever pressing and on the role played by the orbital cortex in compulsive behaviour.

Role of the orbital cortex and of the serotonergic system in a rat model of obsessive compulsive disorder

The serotonergic system and the orbitofrontal cortex have been consistently implicated in the pathophysiology of obsessive compulsive disorder. Yet, the relations between these two systems and the ways they interact in producing obsessions and compulsions are poorly understood. The present study tested the hypothesis that pathology of the orbitofrontal cortex leads to a dysregulation of the serotonergic system which is manifested in compulsive behavior, using a new rat model of this disorder. In the model, 'compulsive' behavior is induced by attenuating a signal indicating that a lever-press response was effective in producing food. We found that lesion to the rat orbital cortex led to a selective increase in compulsive lever-pressing that was prevented by the serotonin re-uptake inhibitor, paroxetine, and was paralleled by an increase in the density of the striatal serotonin transporter, assessed using high affinity [3H]imipramine binding. These results suggest that the serotonergic system is involved in orbital lesion-induced compulsivity, and provide a possible account for the observed association between obsessions and compulsions and dysfunction of the orbitofrontal cortex and of the serotonergic system in obsessive compulsive disorder.