Increased Fear Memory and Glutamatergic Modulation in Compulsive Drinker Rats Selected by Schedule-Induced Polydipsia

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

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

Sex differences in the anticompulsive-like effect of memantine: Involvement of nitric oxide pathway but not AMPA receptors

Memantine, an N-Methyl-D-Aspartate (NMDA) antagonist, has been examined as a potential treatment for Obsessive-Compulsive Disorder (OCD). Yet, there is limited knowledge regarding how it works to reduce compulsive behaviour and whether it has different effects on individuals based on their sex. Herein, we investigated if there are sex differences in the anticompulsive-like effect of memantine in adult Swiss mice. Additionally, we explored whether the nitric oxide (NO) pathway and α-amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (AMPA) receptors play a role in memantine's effects. To start, we assessed the impact of a single intraperitoneal dose of memantine (at 3, 5, and 10 mg/kg) on behaviours exhibited in the open field test (OFT) and the marble-burying test (MBT), the latter being a predictive test for anticompulsive effects. All doses of memantine reduced marble-burying behaviour in both male and female mice without affecting their locomotor activity in the OFT. This anticompulsive-like effect was also confirmed in another predictive test, the nest-building test, with the highest memantine dose (10 mg/kg) reducing nest-building behaviour without significant differences between male and female mice. We observed that pre-treatment with L-arginine, a NO precursor, mitigated the anticompulsive-like effect of memantine in male mice but had no effect in female mice in the MBT. Finally, NBQX, an AMPA receptor antagonist, did not block the anticompulsive-like effect of memantine. In summary, our study suggests that the anticompulsive-like effect of memantine does not appear to be sex-specific, does not depend on AMPA receptors, and involves the NO pathway primarily in male mice.

Reduced Expression of the Htr2a, Grin1, and Bdnf Genes and Cognitive Inflexibility in a Model of High Compulsive Rats

Compulsivity is a core symptom in different psychopathological disorders, characterized by excessive behaviors and behavioral inflexibility. The selection of high drinker (HD) versus low drinker (LD) rats by schedule-induced polydipsia (SIP) is a valid model for studying the compulsive phenotype. The compulsive HD rats showed cognitive inflexibility and reduced serotonin 2A (5-HT2A) receptor binding levels in the frontal cortex (FC). According to that, we hypothesize that compulsive HD rats might have an alteration in the cognitive control domain regarding inflexibility, assessed by spatial memory on the Morris Water Maze (MWM), working and reference memory by the Radial Arm Maze, and behavioral deficits in stimulus processing by the Novel Object Recognition test. The possible underlying mechanisms might be linked to the brain gene expression of 5HT2A, 5HT2C, glutamate NMDA receptors, and brain-derived neurotrophic factor (BDNF) in FC, hippocampus, and amygdala. HD rats confirmed a cognitive inflexibility profile on the reversal condition in the MWM compared to LD rats, while no differences were observed on stimulus processing, spatial, and working memory. Moreover, HD rats showed a reduced expression of the Htr2a, Grin1, and Bdnf genes in FC. Furthermore, there was a negative correlation between the relative expression of the Htr2a, Grin1, and Bdnf genes in FC and the level of compulsive water intake in HD rats on SIP. These data reveal that cognitive inflexibility may not be associated with a memory or stimulus processing deficit in compulsive individuals but may result by a region-specific alteration of the Htr2a, Grin1, and Bdnf gene expression in FC.

Behavioral domains in compulsive rats: implications for understanding compulsive spectrum disorders

Introduction

Compulsive behavior has been proposed as a transdiagnostic trait observed in different neuropsychiatric disorders, such as obsessive-compulsive disorder, autism, and schizophrenia. Research Domain Criteria (RDoC) strategy could help to disentangle the neuropsychological basis of compulsivity for developing new therapeutic and preventive approaches. In preclinical research, the selection of high-drinker (HD) vs. low-drinker (LD) animals by schedule-induced polydipsia (SIP) is considered a putative model of compulsivity, which includes a well-differentiated behavioral pattern.

Methods

The purpose of this research was to assess the cognitive control and the negative valence system domains in a phenotype of compulsive HD rats. After the selection of animals as HD or LD, we assessed behavioral inflexibility by probabilistic spatial reversal learning (PSRL), motor and cognitive impulsivity by variable delay-to-signal (VDS), and risky decision-making by rodent gambling task (rGT).

Results

HD rats performed fewer reversals and showed less probability of pressing the same lever that was previously reinforced on PSRL, more premature responses after the exposure to longer delays on VDS, and more disadvantageous risky choices on rGT. Moreover, HD animals performed more perseverative responses under the punishment period on rGT.

Discussion

These results highlight that HD compulsive phenotype exhibits behavioral inflexibility, insensitivity to positive feedback, waiting impulsivity, risky decision-making, and frustrative non-reward responsiveness. Moreover, these findings demonstrate the importance of mapping different behavioral domains to prevent, treat, and diagnose compulsive spectrum disorders correctly.

The development of compulsive coping behaviour is associated with a downregulation of Arc in a Locus Coeruleus neuronal ensemble

Some compulsive disorders have been considered to stem from the loss of control over coping strategies, such as displacement. However, the cellular mechanisms involved in the acquisition of coping behaviours and their subsequent compulsive manifestation in vulnerable individuals have not been elucidated. Considering the role of the locus coeruleus (LC) noradrenaline-dependent system in stress and related excessive behaviours, we hypothesised that neuroplastic changes in the LC may be associated with the acquisition of an adjunctive polydipsic water drinking, a prototypical displacement behaviour, and the ensuing development of compulsion in vulnerable individuals. Thus, male Sprague Dawley rats were characterised for their tendency, or not, to develop compulsive polydipsic drinking in a schedule-induced polydipsia (SIP) procedure before their fresh brains were harvested. A new quantification tool for RNAscope assays revealed that the development of compulsive adjunctive behaviour was associated with a low mRNA copy number of the plasticity marker Arc in the LC which appeared to be driven by specific adaptations in an ensemble of tyrosine hydroxylase (TH)+, zif268- neurons. This ensemble was specifically engaged by the expression of compulsive adjunctive behaviour, not by stress, because its functional recruitment was not observed in individuals that no longer had access to the water bottle before sacrifice, while it consistently correlated with the levels of polydipsic water drinking only when it had become compulsive. Together these findings suggest that downregulation of Arc mRNA levels in a population of a TH+/zif268- LC neurons represents a signature of the tendency to develop compulsive coping behaviours.

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.

Socioemotional deficit and HPA axis time response in high compulsive rats selected by schedule-induced polydipsia

Compulsivity is a failure to stop an ongoing behavior that has become inappropriate to the situation and is recognized as a transdiagnostic trait present in different neuropsychiatric disorders. The implication of motivation and emotion, as well as the stress response in compulsive population has not been fully understood. We assessed the motivation to reward and cues, the emotional response in different contexts and the hypothalamic-pituitary-adrenal (HPA) axis response in rats selected by a preclinical model of compulsive behavior. Firstly, high (HD) or low (LD) drinkers were selected according to their drinking behavior on schedule-induced polydipsia (SIP). Then, we assessed motivation by the propensity to attribute incentive salience to rewards on Pavlovian Conditioned Approach (PavCA) and motivation to gain reward on Progressive Ratio Schedule of Reinforcement (PRSR). Emotion was measured by Social Dominance on the Tube Test (SDTT) and emotional memory on Passive Avoidance (PA). Plasma corticosterone (CORT) levels in response to SIP were assessed. HD rats showed a socioemotional deficit by fewer victories on the SDTT, and an increased latency to enter the dark compartment on the PA. No differences were found between groups regarding to motivational assessment. Moreover, HD rats revealed a blunted time response in the increase of CORT levels at 45 min after SIP compared to LD rats. The findings show that the compulsive phenotype of HD rats exhibit less social dominance, more resistance to extinction and a differential CORT time response to SIP. These findings may contribute to highlight the relevance of assessing socioemotional behaviors and stress response for a better characterization of the vulnerability to compulsive spectrum disorders.

NMR-based Metabolomics and Fatty Acid Profiles to Unravel Biomarkers in Preclinical Animal Models of Compulsive Behavior

Compulsivity is a key manifestation of inhibitory control deficit and a cardinal symptom of psychopathological conditions such as obsessive-compulsive and attention-deficit hyperactivity disorders, in which metabolic alterations have raised attention as putative biomarkers for early identification. The present study assessed the metabolic profile in a preclinical model of a compulsive phenotype of rats. We used the schedule-induced polydipsia (SIP) method to classify male Wistar rats into high drinkers (HDs) or low drinkers (LDs) according to their compulsive drinking rate developed by exposure to a fixed-time 60 s (FT-60) schedule of reinforcement with water available ad libitum during 20 sessions. Before and after SIP, blood samples were collected for subsequent serum analysis by nuclear magnetic resonance spectroscopy coupled to multivariate analysis. Although no differences existed in the pre-SIP set, the compulsive drinking behavior induced remarkable metabolic alterations: HD rats selected by SIP exhibited a hyperlipidemic, hypoglycemic, and hyperglutaminergic profile compared with their low-compulsive counterparts. Interestingly, these alterations were not attributable to the mere exposure to reward pellets because a control experiment did not show differences between HDs and LDs after 20 sessions of pellet consumption without intermittent reinforcement. Our results shed light toward the implication of dietary and metabolic factors underpinning the vulnerability to compulsive behaviors.

Neurochemical substrates linked to impulsive and compulsive phenotypes in addiction: A preclinical perspective

Drug compulsion manifests in some but not all individuals and implicates multifaceted processes including failures in top-down cognitive control as drivers for the hazardous pursuit of drug use in some individuals. As a closely related construct, impulsivity encompasses rash or risky behaviour without foresight and underlies most forms of drug taking behaviour, including drug use during adverse emotional states (i.e., negative urgency). While impulsive behavioural dimensions emerge from drug-induced brain plasticity, burgeoning evidence suggests that impulsivity also predates the emergence of compulsive drug use. Although the neural substrates underlying the apparently causal relationship between trait impulsivity and drug compulsion are poorly understood, significant advances have come from the interrogation of defined limbic cortico-striatal circuits involved in motivated behaviour and response inhibition, together with chemical neuromodulatory influences from the ascending neurotransmitter systems. We review what is presently known about the neurochemical mediation of impulsivity, in its various forms, and ask whether commonalities exist in the neurochemistry of compulsive drug-motivated behaviours that might explain individual risk for addiction.

N-acetylcysteine as a new prominent approach for treating psychiatric disorders

N-acetylcysteine (NAC) is a well-known and safe mucolytic agent, also used in patients with paracetamol overdose. In addition to these effects, recent preclinical and clinical studies have shown that NAC exerts beneficial effects on different psychiatric disorders. Many potential mechanisms have been proposed to underlie the therapeutic effects of NAC, including the regulation of several neurotransmitters, oxidative homeostasis, and inflammatory mediators. In this paper, we summarize the current knowledge on the ability of NAC to ameliorate symptoms and neuropathologies related to different psychiatric disorders, including attention deficit hyperactivity disorder, anxiety, bipolar disorder, depression, obsessive-compulsive disorder, obsessive-compulsive-related disorder, posttraumatic stress disorder, and schizophrenia. Although preclinical studies have shown a positive effect of NAC on animal models of psychiatric disorders, the clinical efficacy of NAC is not fully established. NAC remains a strong candidate for adjunct treatment for many psychiatric disorders, but additional preclinical and clinical studies are needed.

Dietary Nutrients and Prevention of Alzheimer's disease

Alzheimer's disease is an irrevocable, progressive brain disorder that gradually destroys memory and cognitive skills. One of the extensively studied method of preventing Alzheimer's disease (AD) disease progression is by providing nutritional diet. Several reports have shown that intake of nutritional elements as huperzine A, ursolic acid, vitamins etc. can directly influence pathogenesis of AD. Surprisingly, occurrence of metabolic disorders due to unhealthy diet has been known to be a major environmental causes for AD. It has been noted that AD disease severity can be controlled by supplementing dietary supplements containing huge amounts of health-promoting ingredients. These elements promote cell health, regeneration, and the anti-aging process that specifically interrupt the pathogenic pathways in AD development. Fortunately, incorporating changes in the nutritional content is inexpensive, easy, acceptable, safe, effective, and in most cases free from major adverse events. Many nutritional phytoconstituents such as flavonoids, alkaloids, and terpenoids are still being evaluated in the hope of identifying a successful therapy for AD. This review discusses the therapeutical potential of several key nutrients that have been researched for treating AD treatment and the method of their neuroprotective intervention.

Efficacy and safety of riluzole for depressive disorder: A systematic review and meta-analysis of randomized placebo-controlled trials

Glutamatergic modulators may have therapeutic potential in the treatment of depressive disorder (DD), riluzole, as a modulating drug of the glutamatergic system, its antidepressant efficacy and safety of riluzole for DD are inconsistent. This meta-analysis was performed to determine the efficacy and safety of riluzole used for DD. A systematic literature search was performed using PubMed, Embase, Cochrane Library, Web of Science, VIP and other databases from 1980 to 2019. The primary outcome was change in depression severity and meta-analysis was performed using comprehensive meta-analysis software. Seven randomized controlled trials (RCTs) were included. There was some difference in depression severity change in riluzole-citalopram therapy. No significant differences were observed in response rate, remission rate, relapse rate and adverse events, while, the relapse time in riluzole group was longer than placebo group. In this meta-analysis riluzole showed no antidepressant efficacy compared to placebo in monotherapy or riluzole-ketamine combined therapy, while it might relieve depression severity to some extent in riluzole-citalopram therapy. Furthermore, riluzole showed favorable safety for DD. The longer relapse time of riluzole group might have clinical significance to some extent, although this had no statistical difference. More studies are needed to clarify the potential association between riluzole and DD.