Effects of agents targeting glutamatergic systems on marble-burying behavior

Combinatorial therapy with sub-effective Ro25-6981 and ZL006 ameliorates depressive-like behavior in single or combined stressed male mice

Major depression is a severe neuropsychiatric disorder that poses a significant challenge to health. However, development of an effective therapy for the disease has long been difficult. Here, we investigate the efficacy of a novel combinatorial treatment employing sub-effective doses of Ro25-6981, an antagonist targeting GluN2B-containing NMDA receptors, in conjunction with ZL006, an inhibitor of the PSD95/nNOS, on mouse models of depression. We employed social isolation, chronic restraint stress, or a combination of both to establish a depressed mouse model. Treatment with the drug combination reduced depressive-like behaviors without affecting locomotor activity in mice subjected to social isolation or chronic restraint stress. Furthermore, the combination therapy ameliorated depressive-like behaviors induced by combined stress of chronic restraint followed by social isolation. Mechanistic studies revealed that the combined treatment downregulated the hippocampal nitric oxide level. However, the therapeutic benefits of this combination were negated by the activation of NMDA receptors with a low dose of NMDA or by increasing nitric oxide levels with l-arginine. Moreover, the combinatorial treatment had negligible effects on object memory and contextual fear memory. Our data establish a combined therapy paradigm, providing a potential strategy targeting major depression.

L-theanine combination therapy with fluvoxamine in moderate-to-severe obsessive-compulsive disorder: A placebo-controlled, double-blind, randomized trial

AIM

The main aim of this study was to investigate the additional effects of L-theanine, an amino acid in tea and an analog of glutamate with neuroprotective and anti-depressant properties, on obsessive-compulsive disorder (OCD) symptoms in combination with fluvoxamine.

METHODS

Patients from either sex aged between 18 and 60 years diagnosed with OCD, based on the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), who had a Yale-Brown Obsessive Compulsive Scale (Y-BOCS) score of more than 21 were enrolled in a double-blinded, parallel-group, placebo-controlled, clinical trial of 10 weeks to receive either L-theanine (100 mg twice daily) and fluvoxamine (100 mg daily initially followed by 200 mg daily after week 5) or placebo and fluvoxamine. The primary outcome of interest in this study was the Y-BOCS total score decrease from baseline.

RESULTS

From a total of 95 evaluated patients, 50 completed our study; 30 were randomly assigned to each group. Multivariate analysis (ANOVA) showed a significant effect of time× $$ \times $$ treatment for L-theanine in obsession subscale (F = 5.51, P = 0.008) of the Y-BOCS score but not in the total and compulsion scores. Our results showed significantly more improvement in obsession subscale scores in L-theanine compared to placebo group (P = 0.007, Cohen's d = 0.82). Also, total Y-BOCS scores were lower in L-theanine compared to placebo group at week 5 (P = 0.039, Cohen's d = 0.60) and 10 (P = 0.008, Cohen's d = 0.80). However, there was no significant between-group differences in compulsion subscale scores. Complete response was also more frequent in the L-theanine group (P = 0.0001).

CONCLUSION

Findings in this study suggest L-theanine as a relatively safe and effective adjuvant therapy for moderate to severe OCD.

A critical inquiry into marble-burying as a preclinical screening paradigm of relevance for anxiety and obsessive-compulsive disorder: Mapping the way forward

Rodent marble-burying behavior in the marble-burying test (MBT) is employed as a model or measure to study anxiety- and compulsive-like behaviors or anxiolytic and anticompulsive drug action. However, the test responds variably to a range of pharmacological interventions, and little consensus exists regarding specific methodologies for its execution. Regardless, the test is widely applied to investigate the effects of pharmacological, genetic, and behavioral manipulations on purported behaviors related to the said neuropsychiatric constructs. Therefore, in the present review we attempt to expound the collective translational significance of the MBT. We do this by (1) reviewing burying behavior as a natural behavioral phenotype, (2) highlighting key aspects of anxiety and obsessive-compulsive disorder from a translational perspective, (3) reviewing the history and proof of concept of the MBT, (4) critically appraising potential methodological confounds in execution of the MBT, and (5) dissecting responses of the MBT to various pharmacological interventions. We conclude by underlining that the collective translational value of the MBT will be strengthened by contextually valid experimental designs and objective reporting of data.

A Psycho-Behavioral Perspective on Modelling Obsessive-Compulsive Disorder (OCD) in Animals: The Role of Context

Obsessive-compulsive disorder is a heterogeneous and debilitating condition, characterized by intrusive thoughts and compulsive repetition. Animal models of OCD are important tools that have the potential to contribute significantly to our understanding of the condition. Although there is consensus that pre-clinical models are valuable in elucidating the underlying neurobiology in psychiatric disorders, the current paper attempts to prompt ideas on how interpretation of animal behavior can be expanded upon to more effectively converge with the human disorder. Successful outcomes in psychopharmacology involve rational design and synthesis of novel compounds and their testing in well-designed animal models. As part of a special journal issue on OCD, this paper will 1) review the psychobehavioral aspects of OCD that are of importance on how the above ideas can be articulated, 2) briefly elaborate on general issues that are important for the development of animal models of OCD, with a particular focus on the role and importance of context, 3) propose why translational progress may often be less than ideal, 4) highlight some of the significant contributions afforded by animal models to advance understanding, and 5) conclude by identifying novel behavioral constructs for future investigations that may contribute to the face, predictive and construct validity of OCD animal models. We base these targets on an integrative approach to face and construct validity, and note that the issue of treatment-resistance in the clinical context should receive attention in current animal models of OCD.

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

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

Methoxetamine affects brain processing involved in emotional response in rats

BACKGROUND AND PURPOSE

Methoxetamine (MXE) is a novel psychoactive substance that is emerging on the Internet and induces dissociative effects and acute toxicity. Its pharmacological effects have not yet been adequately investigated.

EXPERIMENTAL APPROACH

We examined a range of behavioural effects induced by acute administration of MXE (0.5-5 mg·kg^-1 ; i.p.) in rats and whether it causes rapid neuroadaptive molecular changes.

KEY RESULTS

MXE (0.5-5 mg·kg^-1 ) affected motor activity in a dose- and time-dependent manner, inducing hypermotility and hypomotility at low and high doses respectively. At low and intermediate doses (0.5 and 1 mg·kg^-1 ), MXE induced anxious and/or obsessive-compulsive traits (marble burying test), did not significantly increase sociability (social interaction test) or induce spatial anxiety (elevated plus maze test). At a high dose (5 mg·kg^-1 ), MXE induced transient analgesia (tail-flick and hot-plate test), decreased social interaction time (social interaction test) and reduced immobility time while increasing swimming activity (forced swim test), suggesting an antidepressant effect. Acute MXE administration did not affect self-grooming behaviour at any dose tested. Immunohistochemical analysis showed that behaviourally active doses of MXE (1 and 5 mg·kg^-1 ) increased phosphorylation of ribosomal protein S6 in the medial prefrontal cortex and hippocampus.

CONCLUSIONS AND IMPLICATIONS

MXE differentially affected motor activity, behaviour and emotional states in rats, depending on the dose tested. As reported for ketamine, phosphorylation of the ribosomal protein S6 was increased in MXE-treated animals, thus providing a 'molecular snapshot' of rapid neuroadaptive molecular changes induced by behaviourally active doses of MXE.

The role of GluN2B-containing NMDA receptors in short- and long-term fear recall

N-methyl-d-aspartate (NMDA) receptors are crucial synaptic elements in long-term memory formation, including the associative learning of fearful events. Although NMDA blockers were consistently shown to inhibit fear memory acquisition and recall, the clinical use of general NMDA blockers is hampered by their side effects. Recent studies revealed significant heterogeneity in the distribution and neurophysiological characteristics of NMDA receptors with different GluN2 (NR2) subunit composition, which may have differential role in fear learning and recall. To investigate the specific role of NMDA receptor subpopulations with different GluN2 subunit compositions in the formation of lasting traumatic memories, we contrasted the effects of general NMDA receptor blockade with GluN2A-, GluN2B-, and GluN2C/D subunit selective antagonists (MK-801, PEAQX, Ro25-6981, PPDA, respectively). To investigate acute and lasting consequences, behavioral responses were investigated 1 and 28days after fear conditioning. We found that MK-801 (0.05 and 0.1mg/kg) decreased fear recall at both time points. GluN2B receptor subunit blockade produced highly similar effects, albeit efficacy was somewhat smaller 28days after fear conditioning. Unlike MK-801, Ro25-6981 (3 and 10mg/kg) did not affect locomotor activity in the open-field. In contrast, GluN2A and GluN2C/D blockers (6 and 20mg/kg PEAQX; 3 and 10mg/kg PPDA, respectively) had no effect on conditioned fear recall at any time point and dose. This sharp contrast between GluN2B- and other subunit-containing NMDA receptor function indicates that GluN2B receptor subunits are intimately involved in fear memory formation, and may provide a novel pharmacological target in post-traumatic stress disorder or other fear-related disorders.

Minocycline combination therapy with fluvoxamine in moderate-to-severe obsessive-compulsive disorder: A placebo-controlled, double-blind, randomized trial

AIM

Several lines of evidence implicate glutamatergic dysfunction in the pathophysiology of obsessive-compulsive disorder (OCD), presenting this neurotransmitter as a target for the development of novel pharmacotherapy. The objective of this study was to assess the efficacy of minocycline as an augmentative agent to fluvoxamine in the treatment of patients with OCD.

METHODS

One hundred and two patients with the diagnosis of moderate-to-severe OCD were recruited to this study. A randomized double-blind trial was designed and patients received either L-carnosine or placebo as adjuvant to fluvoxamine for 10 weeks. The patients randomly received either minocycline 100 mg twice per day or placebo for 10 weeks. All patients received fluvoxamine (100 mg/day) for the first 4 weeks, followed by 200 mg/day for the rest of the trial, regardless of their treatment groups. Participants were evaluated using the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). The main outcome measure was to assess the efficacy of minocycline in improving the OCD symptoms.

RESULTS

General linear model repeated measures demonstrated significant effect for time × treatment interaction on the Y-BOCS total scores, F(1.49, 137.93) = 7.1, P  = 0.003, and Y-BOCS Obsession subscale score, F(1.54, 141.94) = 9.72, P = 0.001, and near significant effect for the Y-BOCS Compulsion subscale score, F(1.27, 117.47) = 2.92, P  = 0.08. A significantly greater rate of partial and complete response was observed in the minocycline group (P < 0.001). The frequency of side-effects was not significantly different between the treatment arms.

CONCLUSION

The results of this study suggest that minocycline could be a tolerable and effective adjuvant in the management of patients with OCD.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

cGMP-dependent protein kinase type II knockout mice exhibit working memory impairments, decreased repetitive behavior, and increased anxiety-like traits

Neuronal activity regulates AMPA receptor trafficking, a process that mediates changes in synaptic strength, a key component of learning and memory. This form of plasticity may be induced by stimulation of the NMDA receptor which, among its activities, increases cyclic guanosine monophosphate (cGMP) through the nitric oxide synthase pathway. cGMP-dependent protein kinase type II (cGKII) is ultimately activated via this mechanism and AMPA receptor subunit GluA1 is phosphorylated at serine 845. This phosphorylation contributes to the delivery of GluA1 to the synapse, a step that increases synaptic strength. Previous studies have shown that cGKII-deficient mice display striking spatial learning deficits in the Morris Water Maze compared to wild-type littermates as well as lowered GluA1 phosphorylation in the postsynaptic density of the prefrontal cortex (Serulle et al., 2007; Wincott et al., 2013). In the current study, we show that cGKII knockout mice exhibit impaired working memory as determined using the prefrontal cortex-dependent Radial Arm Maze (RAM). Additionally, we report reduced repetitive behavior in the Marble Burying task (MB), and heightened anxiety-like traits in the Novelty Suppressed Feeding Test (NSFT). These data suggest that cGKII may play a role in the integration of information that conveys both anxiety-provoking stimuli as well as the spatial and environmental cues that facilitate functional memory processes and appropriate behavioral response.

Antidepressant- and anticompulsive-like effects of purinergic receptor blockade: involvement of nitric oxide

Activation of purinergic receptors by ATP (P2R) modulates glutamate release and the activation of post-synaptic P2R is speculated to induce nitric oxide (NO) synthesis. Increased glutamatergic and nitrergic signaling have been involved in the neurobiology of stress-related psychiatric disorders such as anxiety and depression. Therefore, the aim of this study was to test the effects of two P2R antagonists (PPADS and iso-PPADS) in animals submitted to models predictive of antidepressant-, anxiolytic- and anticompulsive-like effects. Swiss mice receiving PPADS at 12.5mg/kg showed reduced immobility time in the forced swimming test (FST) similarly to the prototype antidepressant imipramine (30mg/kg). This dose was also able to decrease the number of buried marbles in the marble-burying test (MBT), an anticompulsive-like effect. However, no effect was observed in animals submitted to the elevated plus maze (EPM) and to the open field test. The systemic administration of iso-PPADS, a preferential P2XR antagonist, also reduced the immobility time in FST, which was associated to a decrease in NOx levels in the prefrontal cortex. In addition, P2X7 receptor was found co-immunoprecipitated with neuronal nitric oxide synthase (NOS1) in the prefrontal cortex. These results suggest that P2X7, possibly coupled to NOS1, could modulate behavioral responses associated to stress-related disorders and it could be a new target for the development of more effective treatments for affective disorders.

Multiple mechanisms involved in the large-spectrum therapeutic potential of cannabidiol in psychiatric disorders

Cannabidiol (CBD) is a major phytocannabinoid present in the Cannabis sativa plant. It lacks the psychotomimetic and other psychotropic effects that the main plant compound Δ(9)-tetrahydrocannabinol (THC) being able, on the contrary, to antagonize these effects. This property, together with its safety profile, was an initial stimulus for the investigation of CBD pharmacological properties. It is now clear that CBD has therapeutic potential over a wide range of non-psychiatric and psychiatric disorders such as anxiety, depression and psychosis. Although the pharmacological effects of CBD in different biological systems have been extensively investigated by in vitro studies, the mechanisms responsible for its therapeutic potential are still not clear. Here, we review recent in vivo studies indicating that these mechanisms are not unitary but rather depend on the behavioural response being measured. Acute anxiolytic and antidepressant-like effects seem to rely mainly on facilitation of 5-HT1A-mediated neurotransmission in key brain areas related to defensive responses, including the dorsal periaqueductal grey, bed nucleus of the stria terminalis and medial prefrontal cortex. Other effects, such as anti-compulsive, increased extinction and impaired reconsolidation of aversive memories, and facilitation of adult hippocampal neurogenesis could depend on potentiation of anandamide-mediated neurotransmission. Finally, activation of TRPV1 channels may help us to explain the antipsychotic effect and the bell-shaped dose-response curves commonly observed with CBD. Considering its safety profile and wide range of therapeutic potential, however, further studies are needed to investigate the involvement of other possible mechanisms (e.g. inhibition of adenosine uptake, inverse agonism at CB2 receptor, CB1 receptor antagonism, GPR55 antagonism, PPARγ receptors agonism, intracellular (Ca(2+)) increase, etc.), on CBD behavioural effects.

AMPAKINE enhancement of social interaction in the BTBR mouse model of autism

Autism is a neurodevelopmental disorder in which the first diagnostic symptom is unusual reciprocal social interactions. Approximately half of the children diagnosed with an autism spectrum disorder also have intellectual impairments. General cognitive abilities may be fundamental to many aspects of social cognition. Cognitive enhancers could conceivably be of significant benefit to children and adults with autism. AMPAKINE compounds are a novel class of pharmacological agents that act as positive modulators of AMPA receptors to enhance excitatory glutamatergic neurotransmission. This class of compounds was reported to improve learning and memory in several rodent and non-human primate tasks, and to normalize respiratory abnormalities in a mouse model of Rett syndrome. Here we evaluate the actions of AMPA compounds in adult male and female BTBR mice, a well characterized mouse model of autism. Acute treatment with CX1837 and CX1739 reversed the deficit in sociability in BTBR mice on the most sensitive parameter, time spent sniffing a novel mouse as compared to time spent sniffing a novel object. The less sensitive parameter, time in the chamber containing the novel mouse versus time in the chamber containing the novel object, was not rescued by CX1837 or CX1739 treatment. Preliminary data with CX546, in which β-cyclodextrin was the vehicle, revealed behavioral effects of the acute intraperitoneal and oral administration of vehicle alone. To circumvent the artifacts introduced by the vehicle administration, we employed a novel treatment regimen using pellets of peanut butter for drug delivery. Absence of vehicle treatment effects when CX1837 and CX1739 were given in the peanut butter pellets, to multiple cohorts of BTBR and B6 control mice, confirmed that the pharmacologically-induced improvements in sociability in BTBR were not confounded by the administration procedures. The highest dose of CX1837 improved the cognitive deficit in novel object recognition in BTBR. No drug effects were detected on the high levels of repetitive self-grooming in BTBR. In open field tests, CX1837 and CX1739 did not induce hyperactivity or sedation in either strain. It is interesting to speculate that the ability of CX1837 and CX1739 to restore aspects of sociability in BTBR mice could utilize synaptic mechanisms regulating social cognition, suggesting a potential pharmacological target for interventions to treat symptoms of autism. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Anxiolytic effects and neuroanatomical targets of estrogen receptor-β (ERβ) activation by a selective ERβ agonist in female mice

The dichotomous anxiogenic and anxiolytic properties of estrogens have been reported to be mediated by two distinct neural estrogen receptors (ER), ERα and ERβ, respectively. Using a combination of pharmacological and genetic approaches, we confirmed that the anxiolytic actions of estradiol are mediated by ERβ and extended and these observations to demonstrate the neuroanatomical targets involved in ERβ activation in these behavioral responses. We examined the effects of the biologically active S-enantiomer of diarylpropionitrile (S-DPN) on anxiety-related behavioral measures, the corresponding stress hormonal response to hypothalamo-pituitary-adrenal axis reactivity, and potential sites of neuronal activation in mutant female mice carrying a null mutation for ERβ gene (βERKO). S-DPN administration significantly reduced anxiety-like behaviors in the open field, light-dark exploration, and the elevated plus maze (EPM) in ovariectomized wild-type (WT) mice, but not in their βERKO littermates. Stress-induced corticosterone (CORT) and ACTH were also attenuated by S-DPN in the WT mice but not in the βERKO mice. Using c-fos induction after elevated plus maze, as a marker of stress-induced neuronal activation, we identified the anterodorsal medial amygdala and bed nucleus of the stria terminalis as the neuronal targets of S-DPN action. Both areas showed elevated c-fos mRNA expression with S-DPN treatment in the WT but not βERKO females. These studies provide compelling evidence for anxiolytic effects mediated by ERβ, and its neuroanatomical targets, that send or receive projections to/from the paraventricular nucleus, providing potential indirect mode of action for the control of hypothalamo-pituitary-adrenal axis function and behaviors.

Facilitation of CB1 receptor-mediated neurotransmission decreases marble burying behavior in mice

Obsessive-compulsive disorder (OCD) is a common psychiatric disorder characterized by the occurrence of obsessions and compulsions. Glutamatergic abnormalities have been related to the pathophysiology of OCD. Cannabinoids inhibit glutamate release in the central nervous system, but the involvement of drugs targeting the endocannabinoid system has not yet been tested in animal models of repetitive behavior. Thus, the aim of the present study was to verify the effects of the CB1 receptor agonist WIN55,212-2, the inhibitor of anandamide uptake AM404 and the anandamide hydrolysis inhibitor URB597, on compulsive-associate behavior in male C57BL/6J mice submitted to the marble burying test (MBT), an animal model used for anti-compulsive drug screening. WIN55,212-2 (1 and 3 mg/kg), AM404 (1 and 3 mg/kg) and URB597 (0.1, 0.3 and 1 mg/kg) induced a significant decrease in the number of buried marbles compared to controls. Pretreatment with the CB1 receptor antagonist, AM251, prevented both WIN55,212-2 and URB597 effects. These results suggest a potential role for drugs acting on the cannabinoid system in modulating compulsive behavior.