Increased schedule-induced polydipsia in the rat following subchronic treatment with MK-801

Orexin deficiency modulates the dipsogenic effects of angiotensin II in a sex-dependent manner

The orexin (hypocretin) neuropeptide system is an important regulator of ingestive behaviors, i.e., it promotes food and water intake. Here, we investigated the role of orexin in drinking induced by the potent dipsogen angiotensin II (ANG II). Specifically, male and female orexin-deficient mice received intracerebroventricular (ICV) injections of ANG II, followed by measuring their water intake within 15 min. We found that lower doses of ANG II (100 ng) significantly stimulated drinking in males but not in females, indicating a general sex-dependent effect that was not affected by orexin deficiency. However, higher doses of ANG II (500 ng) were sufficient to induce drinking in female wild-type mice, while female orexin-deficient mice still did not respond to the dipsogenic properties of ANG II. In conclusion, these results suggest sex-dependent effects in ANG II-induced drinking and further support the sexual dimorphism of orexin system functions.

Differential Neurobiological Markers in Phenotype-stratified Rats Modeling High or Low Vulnerability to Compulsive Behavior: A Narrative Review

Compulsivity is a key manifestation of inhibitory control deficit and a cardinal symptom in different neuropsychopathological disorders such as obsessive-compulsive disorder, schizophrenia, addiction, and attention-deficit hyperactivity disorder. Schedule-induced polydipsia (SIP), is an animal model to study compulsivity. In this procedure, rodents develop excessive and persistent drinking behavior under different food-reinforcement schedules, that are not related to homeostatic or regulatory requirements. However, there are important individual differences that support the role of high-drinker HD rats as a compulsive phenotype, characterized in different paradigms by inhibitory response deficit, cognitive inflexibility, and resistant to extinction behavior; with significant differences in response to pharmacological challenges, and relevant neurobiological alterations in comparison with the control group, the non-compulsive low drinker LD group on SIP. The purpose of this review is to collate and update the main findings on the neurobiological bases of compulsivity using the SIP model. Specifically, we reviewed preclinical studies on SIP, that have assessed the effects of serotonergic, dopaminergic, and glutamatergic drugs; leading to the description of the neurobiological markers, such as the key role of the serotonin 5-HT2A receptor and glutamatergic signaling in a phenotype vulnerable to compulsivity as high drinker HD rats selected by SIP. The review of the main findings of HD rats on SIP helps in the characterization of the preclinical compulsive phenotype, disentangles the underlying neurobiological, and points toward genetic hallmarks concerning the vulnerability to compulsivity.

Negative valence system as a relevant domain in compulsivity: review in a preclinical model of compulsivity

Compulsive behavior is observed in different neuropsychiatric disorders such as Obsessive-Compulsive Disorder (OCD), anxiety, phobia, schizophrenia and addiction. Compulsivity has been proposed as a transdiagnostic symptom, where the Research Domain Criteria (RDoC) strategy could help to understand its neuropsychological basis for a better understanding, and development of therapeutic and preventive strategies. However, research on compulsivity has been focused on the cognitive control domain, and the contribution of an altered negative valence system has been less considered. In this review, we collate the main findings in an animal model of compulsivity, the high drinker (HD) rats selected by Schedule-Induced Polydipsia (SIP) regarding these two research domains. This preclinical model of compulsivity has shown a phenotype characterized by a lack of behavioral inhibition, impulsive decision-making and cognitive inflexibility. Moreover, the results in compulsive HD rats, suggests that there is also a relevant alteration in the emotional dimension, linked to the negative valence system domain, as for example by: the increased perseverative responses in a withdrawal condition, associated with the behavioral construct of frustrative non-reward; and an inhibition or extinction deficit in memory retrieval associated with an alteration in the behavioral response to sustained threat. However, the precise nature of the link between these shared altered domains, cognitive control and negative valence system, remains unknown. These results point towards relevant behavioral aspects of the compulsive phenotype that should be taken into account when studying the vulnerability to compulsivity that could help in the development of a better transdiagnostic assessment, preventive and therapeutic strategies.

Dietary tryptophan depletion alters the faecal bacterial community structure of compulsive drinker rats in schedule-induced polydipsia

RATIONALE

Compulsive behaviour, present in different psychiatric disorders such as obsessive-compulsive disorder, schizophrenia and drug abuse, is associated with altered levels of serotonin (5-hydroxytryptamine, 5-HT). The gut microbiota regulates tryptophan (TRP) metabolism and may affect global 5-H synthesis in the enteric and central nervous systems, suggesting a possible involvement of gut microbiota in compulsive spectrum disorders.

OBJECTIVES

The present study investigated whether chronic TRP depletion by diet alters the faecal bacterial community profiles of compulsive versus non-compulsive rats in schedule-induced polydipsia (SIP). Peripheral plasma 5-HT and brain-derived neurotrophic factor (BDNF) levels were evaluated.

METHODS

Wistar rats were selected as High Drinkers (HD) or Low Drinkers (LD) according to their SIP behaviour and were fed for 14 days with either a TRP-free diet (T-) or a TRP-supplemented diet (T+). The faecal bacterial community structure was investigated with 16S rRNA gene-targeted denaturing gradient gel electrophoresis (DGGE) fingerprinting analysis.

RESULTS

Compulsive HD rats showed a lower bacterial diversity than LD rats, irrespectively of the diet. The TRP-depleted HD rats, the only group increasing compulsive licking in SIP, showed a reduction of bacterial evenness and a highly functionally organized community compared with the other groups, indicating that this bacterial community is more fragile to external changes due to the dominance of a low number of species. The chronic TRP depletion by diet effectively reduced peripheral plasma 5-HT levels in both HD and LD rats, while plasma BDNF levels were not altered.

CONCLUSIONS

These results highlight the possible implication of reduced microbial diversity in compulsive behaviour and the involvement of the serotonergic system in modulating the gut brain-axis in compulsive spectrum disorders.

The Bed Nucleus of the Stria Terminalis, Homeostatic Satiety, and Compulsions: What Can We Learn From Polydipsia?

A compulsive phenotype characterizes several neuropsychiatric illnesses - including but not limited to - schizophrenia and obsessive compulsive disorder. Because of its perceived etiological heterogeneity, it is challenging to disentangle the specific neurophysiology that precipitates compulsive behaving. Using polydipsia (or non-regulatory water drinking), we describe candidate neural substrates of compulsivity. We further postulate that aberrant neuroplasticity within cortically projecting structures [i.e., the bed nucleus of the stria terminalis (BNST)] and circuits that encode homeostatic emotions (thirst, hunger, satiety, etc.) underlie compulsive drinking. By transducing an inaccurate signal that fails to represent true homeostatic state, cortical structures cannot select appropriate and adaptive actions. Additionally, augmented dopamine (DA) reactivity in striatal projections to and from the frontal cortex contribute to aberrant homeostatic signal propagation that ultimately biases cortex-dependent behavioral selection. Responding becomes rigid and corresponds with both erroneous, inflexible encoding in both bottom-up structures and in top-down pathways. How aberrant neuroplasticity in circuits that encode homeostatic emotion result in the genesis and maintenance of compulsive behaviors needs further investigation.

Behavioral and biological markers for predicting compulsive-like drinking in schedule-induced polydipsia

Schedule-induced polydipsia (SIP), characterized by the development of persistent and excessive drinking under intermittent food-reinforcement schedules, is an animal model of compulsive behavior that can differentiate two populations: high drinkers (HD) and low drinkers (LD). The aim of the present study was to identify behavioral and biological markers to predict the vulnerability to developing compulsive-like drinking in SIP. Adult male Wistar rats were first trained in a spatial-discrimination serial reversal-learning task and in a reinforcer devaluation task to measure behavioral flexibility and habit formation, respectively. Subsequently, the rats were tested using the SIP protocol and identified as HD or LD based on their drinking rates. The performance of HD and LD rats in the two previous tasks was then analyzed. Before and after SIP exposure, blood glucose and plasma corticosterone (CORT) levels were measured. Additionally, serum electrolyte levels, including sodium, potassium, and chloride, were analyzed after SIP. HD rats showed higher behavioral inflexibility by exhibiting increased perseverative responses in the reversal-learning task and insensitivity to reinforcer devaluation during extinction under selective satiation. After SIP exposure, HD rats exhibited increased basal plasma CORT levels, indicating that this vulnerable group might have a dysregulation of the HPA axis. Although HD and LD rats had blood glucose levels within normal range, the HD group showed lower levels. The HD group did not exhibit hyponatremia (i.e., reduced serum sodium levels) when compared to LD rats after 20 daily SIP sessions. The results of the present study demonstrated that HD rats exhibit behavioral inflexibility and greater habitual-like behavior before SIP. Moreover, these results highlight the importance of measuring different behavioral and biological markers for predicting the vulnerability to developing compulsivity, and for enhancing the understanding of the pathophysiology of compulsive spectrum disorders.

Do psychoactive drugs have a therapeutic role in compulsivity? Studies on schedule-induced polydipsia

RATIONALE

Clinical studies have shown that some psychoactive recreational drugs have therapeutic applications in anxiety, depression, and schizophrenia. However, to date, there are few studies on the therapeutic potential efficacy of recreational drugs in compulsive neuropsychiatric disorders.

OBJECTIVES

We explored the therapeutic potential of different psychoactive and psychedelic drugs in a preclinical model of compulsive behavior.

METHODS

Outbred male Wistar rats were selected as either high (HD) or low (LD) drinkers according to their behavior in schedule-induced polydipsia (SIP). Subsequently, we assessed the effects of acute administration of scopolamine (0.125, 0.25, and 0.5 mg/kg), methamphetamine (0.25, 0.5, 1.25, and 2.5 mg/kg), ketamine (1.25, 2.5, 5, and 10 mg/kg), cannabidiol (1 and 3 mg/kg), WIN21255-2 (0.5, 075, and 1 mg/kg), and AM404 (0.25 and 0.5 mg/kg) on compulsive drinking in SIP.

RESULTS

Scopolamine reduced dose-dependent compulsive drinking in HD compared with LD rats in SIP. Methamphetamine induced a dose-dependent inverted U-curve effect in both groups, in which lower doses increased and higher doses reduced compulsive drinking in SIP. Ketamine, cannabidiol, WIN21255-2, and AM404 did not have any relevant effects in SIP.

CONCLUSIONS

These data provide new evidence that low doses of scopolamine and intermediate doses of methamphetamine might therapeutically reduce compulsive behaviors and suggest that there is not a direct participation of the endocannabinoid system in compulsive behavior on SIP. The research in the underlying neurochemical mechanisms of these psychoactive drugs might provide an additional insight on new therapeutic targets in compulsive neuropsychiatric disorders.

Behavioral Biomarkers of Schizophrenia in High Drinker Rats: A Potential Endophenotype of Compulsive Neuropsychiatric Disorders

Psychogenic polydipsia, which is compulsive, non-regulatory fluid consumption, is present in 6%-20% of chronic psychiatric patients and frequently associated with the schizophrenia diagnosis. In the present study, we investigated the relation between schizophrenia-like symptoms and biomarkers with a compulsive drinking behavior phenotype in rats. Rats that were selected for low drinking vs high drinking behavior following schedule-induced polydipsia (SIP) were assessed in a latent inhibition (LI) paradigm using tone and electrical foot shock and in a spatial reversal learning task to evaluate behavioral inflexibility. We also analyzed the myelin basic protein in different brain areas of high drinker (HD) and low drinker (LD) rats. The HD rats, which were characterized by a compulsive drinking behavior on SIP, had a reduced level of LI effect and increased behavioral inflexibility in the spatial reversal learning task in comparison to the LD group. Moreover, HD rats showed less myelination in the center of the corpus callosum, striatum, and amygdala in comparison to LD rats. These findings strengthen the validity of HD rats that were selected by SIP as a possible phenotype of compulsive neuropsychiatric disorders, as evidenced by the existence of behaviors and biological markers that are related to schizophrenia and obsessive-compulsive disorder, including a reduced LI effect, behavioral inflexibility and reduced brain myelination. Future studies could contribute to the elucidation of the mechanisms underlying the compulsive phenotype of HD rats and its relation to vulnerability to schizophrenia.

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.

Tryptophan depletion affects compulsive behaviour in rats: strain dependent effects and associated neuromechanisms

RATIONALE

Compulsive behaviour, present in different psychiatric disorders, such as obsessive-compulsive disorder, schizophrenia and drug abuse, is associated with altered levels of monoamines, particularly serotonin (5-hydroxytryptamine) and its receptor system.

OBJECTIVES

The present study investigated whether 5-HT manipulation, through a tryptophan (TRP) depletion by diet in Wistar and Lister Hooded rats, modulates compulsive drinking in schedule-induced polydipsia (SIP) and locomotor activity in the open-field test. The levels of dopamine, noradrenaline, serotonin and its metabolite were evaluated, as well as the 5-HT_2A and 5-HT_1A receptor binding, in different brain regions.

METHODS

Wistar rats were selected as high (HD) or low (LD) drinkers according to their SIP behaviour, while Lister hooded rats did not show SIP acquisition. Both strains were fed for 14 days with either a TRP-free diet (T-) or a TRP-supplemented diet (T+) RESULTS: The TRP depletion diet effectively reduced 5-HT levels in the frontal cortex, amygdala and hippocampus in both strains of rats. The TRP-depleted HD Wistar rats were more sensitive to 5-HT manipulation, exhibiting more licks on SIP than did the non-depleted HD Wistar rats, while the LD Wistar and the Lister Hooded rats did not exhibit differences in SIP. In contrast, the TRP-depleted Lister Hooded rats increased locomotor activity compared to the non-depleted rats, while no differences were found in the Wistar rats. Serotonin 2A receptor binding in the striatum was significantly reduced in the TRP-depleted HD Wistar rats.

CONCLUSIONS

These results suggest that alterations of the serotonergic system could be involved in compulsive behaviour in vulnerable populations.

A response strategy predicts acquisition of schedule-induced polydipsia in rats

Schedule-induced polydipsia (SIP) is excessive, non-regulatory drinking. We aimed to identify phenotypic learning traits representative of neural circuitry that underlies SIP and hypothesized that rats that are response-learners will be more susceptible in developing compulsive water drinking. Using the Y-maze, the rats were characterized as either place- or response-learners. They were exposed to the SIP protocol for a period of 21days. Subsequent histological staining for FosB/ΔFosB examined neuronal activation associated with SIP in several brain regions. The rats with a preference for a response-learning strategy were more likely to develop SIP than the rats using a place-learning strategy. Furthermore amphetamine sensitization, observed to increase SIP, also shifted learning strategy to a response-learning strategy. No differences were observed in FosB/ΔFosB expression between SIP and non-SIP rats in the dorsolateral striatum (DLS) and CA1 region of the hippocampus. However, SIP rats had greater FosB/ΔFosB expression in prefrontal cortex regions. The rats that develop SIP have a preference for response-learning strategies and increased neuronal activation in frontal cortical regions associated with habit formation and compulsion.

Activation of serotonin 5-HT2A receptors inhibits high compulsive drinking on schedule-induced polydipsia

RATIONALE

Schedule-induced polydipsia (SIP) is an established model for studying compulsive behaviour in rats. Serotoninergic drugs effectively reduce compulsive drinking on SIP, and high compulsive drinker rats selected by SIP have shown differences in serotoninergic brain activity. However, the specific serotoninergic receptors that modulate compulsive SIP remain unclear.

OBJECTIVE

We investigated the functional role of serotonin 5-hydroxytryptamine 2A or C (5-HT2A/C) receptors in compulsive SIP behaviour.

METHODS

Rats were selected for low (LD) versus high drinking (HD) behaviour on SIP. The effects of the systemic administration of the selective serotonin reuptake inhibitor citalopram, selective norepinephrine reuptake inhibitor atomoxetine, serotonin 5-HT2A/C receptor agonist DOI hydrochloride ((±)-2,5-dimethoxy-4-iodoamphetamine), serotonin 5-HT2C receptor antagonist SB242084, serotonin 5-HT2A receptor antagonist ketanserin and M100907 were assessed on SIP. Subsequently, the effects of DOI were tested after the pre-administration of SB242084, ketanserin and M100907 on SIP.

RESULTS

Citalopram and DOI reduced compulsive drinking in HD compared with LD rats on SIP. In contrast, SB242084 increased compulsive drinking in HD compared with LD rats on SIP. Atomoxetine, ketanserin and M100907 had no effect on SIP. The reduction in water intake produced by DOI was blocked by ketanserin and M100907, but not by SB242084 administration, in HD rats.

CONCLUSIONS

These findings highlight the contribution of serotoninergic 5-HT2A/C receptors compared with noradrenergic mechanisms on SIP and reveal the "therapeutic" activation of serotonin 5-HT2A in the inhibition of the compulsive drinking behaviour in HD rats. Thus, it may represent a potentially new marker of vulnerability and provides additional insight for potential treatments on compulsive behaviours in neuropsychiatric populations.

The amphetamine sensitization model of schizophrenia symptoms and its effect on schedule-induced polydipsia in the rat

RATIONALE

Amphetamine enhances dopamine (DA) transmission and induces psychotic states or exacerbates psychosis in at-risk individuals. Amphetamine sensitization of the DA system has been proposed as a rodent model of schizophrenia-like symptoms. In humans, excessive nonphysiologic drinking or primary polydipsia is significantly associated with a diagnosis of schizophrenia. In rodents, nonphysiologic drinking can be induced by intermittent presentation of food in the presence of a drinking spout to a hungry animal; this phenomenon is termed, "schedule-induced polydipsia" (SIP).

OBJECTIVE

This study aims to determine the effects of amphetamine sensitization on SIP.

METHODS

We injected rats with amphetamine (1.5 mg/kg) daily for 5 days. Following 4 weeks of withdrawal, animals were food restricted and exposed to the SIP protocol (noncontingent fixed-time 1-min food schedule) for daily 2-h sessions for 24 days.

RESULTS

Results showed that previously amphetamine-injected animals drank more in the SIP protocol and drank more than controls when the intermittent food presentation schedule was removed.

CONCLUSIONS

These findings suggest that hyperdopaminergia associated with schizophrenia may contribute to the development of polydipsia in this population. Whether animals that develop SIP have DA dysfunction or aberrant activity of other circuits that modulate DA activity has yet to be clearly defined.

Increased drinking following social isolation rearing: implications for polydipsia associated with schizophrenia

Primary polydipsia, excessive drinking without known medical cause, is especially associated with a diagnosis of schizophrenia. We used animal models of schizophrenia-like symptoms to examine the effects on schedule-induced polydipsia: post-weaning social isolation rearing, subchronic MK-801 treatment (an NMDA-receptor antagonist) or the two combined. Male, Sprague-Dawley rats reared in groups or in isolation beginning at postnatal day 21 were further divided to receive subchronic MK-801 (0.5 mg/kg twice daily) or saline for 7 days beginning on postnatal day 62. Following a 4-day withdrawal period, all groups were trained on a schedule-induced polydipsia paradigm. Under food-restriction, animals reared in isolation and receiving food pellets at 1-min intervals developed significantly more drinking behavior than those reared with others. The addition of subchronic MK-801 treatment did not significantly augment the amount of water consumed. These findings suggest a predisposition to polydipsia is a schizophrenia-like behavioral effect of post-weaning social isolation.

Differential behavioral profiling of stimulant substances in the rat using the LABORAS™ system

Preclinical testing requires rapid and reliable evaluation of the main in vivo effects of novel test substances usually in rodents. Nevertheless, the techniques primarily used up to now involve either automated measurement of motor activity or direct observation of behavioral effects by extensively trained investigators. The advantages of these approaches are respectively high-throughput and comprehensive behavioral assessment. Nevertheless, motor activity is only one aspect of animal behavior and it cannot predict the full neurobehavioral profile of a substance, whereas direct observation is time-consuming. There is thus a need for novel approaches that combine the advantages of both automatic detection and comprehensive behavioral analysis. In the present study, we used the LABORAS™ system to analyze motor and non-motor behavior in rats administered various stimulant substances with or without known psychotomimetic properties or abuse liability (amphetamine, cocaine dizocilpine (MK-801), ketamine, modafinil and nicotine). The data show that LABORAS™ clearly detects the stimulating effects on motor behaviors of amphetamine, cocaine, dizocilpine and ketamine in a dose- and time-dependent manner. Differential effects of these test substances on non-motor behaviors, such as grooming, eating and drinking could also be detected. Nicotine displayed only slight stimulating effects on locomotion, whereas modafinil was virtually without effect on the behaviors evaluated by the system. These data with different stimulant substances suggest that LABORAS™ presents an advantage over classical methods performing automated measurements restricted to locomotion. Furthermore, the procedure is considerably more rapid than behavioral observation procedures. Characterization of the behavioral profile of test substances using LABORAS™ should therefore accelerate preclinical studies. In addition, the multi-faceted parameters measured by LABORAS™ permit a more detailed comparison of the behavioral profiles of novel substances with standard reference substances, thereby providing important indicators for orienting further substance evaluation and supporting drug development.

Schedule-induced polydipsia as a model of compulsive behavior: neuropharmacological and neuroendocrine bases

BACKGROUND

Schedule-induced polydipsia (SIP), characterized by the development of excessive drinking under intermittent food-reinforcement schedules, has been proposed as a successful model for obsessive-compulsive disorder (OCD), schizophrenia, and alcohol abuse.

OBJECTIVES

The purpose of this study was to review the main findings and current thinking regarding the use of SIP for compulsivity assessment and evaluate its contribution to improving our knowledge of the neurobehavioral mechanisms underlying the excessive behavior manifested in SIP relevant to compulsive behavior disorders.

METHODS

The literature reviews SIP procedure and surveys main findings about its neurobehavioral basis and pharmacology relevant to its possible status as a model for compulsive disorders. Specifically, we reviewed effects of antipsychotics and serotoninergic drugs used in the treatment of OCD and schizophrenia. We also considered individual differences in SIP and its relevance as a possible compulsivity endophenotype.

CONCLUSIONS

SIP represents an animal model of non-regulatory and excessive drinking that may be valid for studying the psychopharmacology of the compulsive phenotype and modeling different psychopathologies from compulsivity spectrum disorders.

Poor inhibitory control and neurochemical differences in high compulsive drinker rats selected by schedule-induced polydipsia

RATIONALE

Schedule-induced polydipsia (SIP), characterized by the development of excessive drinking under intermittent food reinforcement schedules, has been proposed as a model for obsessive-compulsive disorder, schizophrenia and drug abuse.

OBJECTIVES

The purpose of this study is to investigate if individual differences in SIP reflect psychopathological behavioural traits related to lack of inhibitory control and reactivity to novelty, and if these differences have neurochemical correlates.

METHODS

Outbred Wistar rats were selected for being either high (HD) or low (LD) drinkers according to their SIP behaviour. We tested locomotor reactivity to a novel environment and inhibitory control on the five-choice serial reaction time task (5-CSRTT), under baseline vs. extinction conditions and following challenge with D: -amphetamine (saline, 0.5 or 1 mg/kg). Post-mortem analyses of the monoaminergic levels in different brain regions were also analysed.

RESULTS

Compared to LD animals, HD rats exhibiting SIP acquisition showed no differences in spontaneous locomotor reactivity to novelty. On the 5-CSRTT, HD rats showed a greater increase in perseverative responses under extinction, a trend towards elevated premature responses on baseline, and a significantly greater elevation of premature responses to D: -amphetamine 0.5 mg/kg. The HD animals also exhibited increased serotonin activity in the amygdala, and correlational analyses between the rate of drinking on SIP and monoamine levels also revealed altered dopaminergic mesolimbic function.

CONCLUSIONS

These findings show that HD rats selected by SIP exhibit compulsive and impulsive behaviour based on measures of performance on the five-choice serial reaction time task and associated with changes in monoaminergic systems in limbic-striatal circuitry.