Effects of novel antipsychotics with mixed D(2) antagonist/5-HT(1A) agonist properties on PCP-induced social interaction deficits in the rat

Clozapine prevented social interaction deficits and reduced c-Fos immunoreactivity expression in several brain areas of rats exposed to acute restraint stress

In the present study, we evaluate the effect of acute restraint stress (15 min) of male Wistar rats on social interaction measurements and c-Fos immunoreactivity (c-Fos-ir) expression, a marker of neuronal activity, in areas involved with the modulation of acute physical restraint in rats, i.e., the paraventricular nucleus of the hypothalamus (PVN), median raphe nucleus (MnR), medial prefrontal cortex (mPFC), cingulate prefrontal cortex (cPFC), nucleus accumbens (NaC), hippocampus (CA3), lateral septum (LS) and medial amygdala (MeA). We considered the hypothesis that restraint stress exposure could promote social withdrawal induced by the activation of the hypothalamic-pituitary-adrenocortical (HPA) axis, and increase c-Fos expression in these limbic forebrain areas investigated. In addition, we investigated whether pretreatment with the atypical antipsychotic clozapine (5 mg/kg; I.P.) could attenuate or block the effects of restraint on these responses. We found that restraint stress induced social withdrawal, and increased c-Fos-ir in these areas, demonstrating that a single 15 min session of physical restraint of rats effectively activated the HPA axis, representing an effective tool for the investigation of neuronal activity in brain regions sensitive to stress. Conversely, pretreatment with clozapine, prevented social withdrawal and reduced c-Fos expression. We suggest that treatment with clozapine exerted a preventive effect in the social interaction deficit, at least in part, by blocking the effect of restraint stress in brain regions that are known to regulate the HPA-axis, including the cerebral cortex, hippocampus, hypothalamus, septum and amygdala. Further experiments will be done to confirm this hypothesis.

N-Acetylcysteine and Aripiprazole Improve Social Behavior and Cognition and Modulate Brain BDNF Levels in a Rat Model of Schizophrenia

Treatment of negative symptoms and cognitive disorders in patients with schizophrenia is still a serious clinical problem. The aim of our study was to compare the efficacy of chronic administration of the atypical antipsychotic drug aripiprazole (7-{4-[4-(2,3-dichlorophenyl)-1-piperazinyl] butoxy}-3,4-dihydro-2(1H)-quinolinone; ARI) and the well-known antioxidant N-acetylcysteine (NAC) both in alleviating schizophrenia-like social and cognitive deficits and in reducing the decreases in the levels of the brain-derived neurotrophic factor (BDNF) in the prefrontal cortex (PFC) and hippocampus (HIP) of adult Sprague-Dawley rats, that have been induced by chronic administration of the model compound L-buthionine-(S, R)-sulfoximine (BSO) during the early postnatal development (p5–p16). ARI was administered at doses of 0.1 and 0.3 mg/kg while NAC at doses of 10 and 30 mg/kg, alone or in combination. Administration of higher doses of ARI or NAC alone, or co-treatment with lower, ineffective doses of these drugs significantly improved social and cognitive performance as assessed in behavioral tests. Both doses of NAC and 0.3 mg/kg of ARI increased the expression of BDNF mRNA in the PFC, while all doses of these drugs and their combinations enhanced the levels of BDNF protein in this brain structure. In the HIP, only 0,3 mg/kg ARI increased the levels of both BDNF mRNA and its protein. These data show that in the rat BSO-induced neurodevelopmental model of schizophrenia, ARI and NAC differently modulated BDNF levels in the PFC and HIP.

Sustained NMDA receptor hypofunction impairs brain-derived neurotropic factor signalling in the PFC, but not in the hippocampus, and disturbs PFC-dependent cognition in mice

BACKGROUND

Cognitive deficits profoundly impact on the quality of life of patients with schizophrenia. Alterations in brain derived neurotrophic factor (BDNF) signalling, which regulates synaptic function through the activation of full-length tropomyosin-related kinase B receptors (TrkB-FL), are implicated in the aetiology of schizophrenia, as is N-methyl-D-aspartate receptor (NMDA-R) hypofunction. However, whether NMDA-R hypofunction contributes to the disrupted BDNF signalling seen in patients remains unknown.

AIMS

The purpose of this study was to characterise BDNF signalling and function in a preclinical rodent model relevant to schizophrenia induced by prolonged NMDA-R hypofunction.

METHODS

Using the subchronic phencyclidine (PCP) model, we performed electrophysiology approaches, molecular characterisation and behavioural analysis.

RESULTS

The data showed that prolonged NMDA-R antagonism, induced by subchronic PCP treatment, impairs long-term potentiation (LTP) and the facilitatory effect of BDNF upon LTP in the medial prefrontal cortex (PFC) of adult mice. Additionally, TrkB-FL receptor expression is decreased in the PFC of these animals. By contrast, these changes were not present in the hippocampus of PCP-treated mice. Moreover, BDNF levels were not altered in the hippocampus or PFC of PCP-treated mice. Interestingly, these observations are paralleled by impaired performance in PFC-dependent cognitive tests in mice treated with PCP.

CONCLUSIONS

Overall, these data suggest that NMDA-R hypofunction induces dysfunctional BDNF signalling in the PFC, but not in the hippocampus, which may contribute to the PFC-dependent cognitive deficits seen in the subchronic PCP model. Additionally, these data suggest that targeting BDNF signalling may be a mechanism to improve PFC-dependent cognitive dysfunction in schizophrenia.

Experimental Serotonergic Agents for the Treatment of Schizophrenia

Schizophrenia remains one of the most chronic and highly disabling mental disorder. To date, the pathomechanism of schizophrenia is not fully understood and current treatments are characterized by some limitations. First- and second-generation antipsychotics have shown clinical efficacy in treating positive symptoms, while are poorly effective on both negative symptoms and cognitive deficits. Moreover, they can involve many metabolic and neurological side effects, leading to low therapeutic compliance. Many evidence suggested that serotonin may play a complex role in the neurobiology of schizophrenia. Therefore, new drugs targeting 5-HT receptors (5-HTRs) have become an important area of research in schizophrenia in the hope that treatment efficacy may be improved without inducing side effects observed with currently available antipsychotics. Research using the main database sources was conducted to obtain an overview of preclinical and clinical pharmacological 5-HTR-targeted therapies in patients with schizophrenia. We identified 17 experimental serotonergic agents, under study for their potential use in schizophrenia treatment. Particularly, AVN-211, LuAF-35700 and Brilaroxazine are currently under clinical development. Moreover, some compounds showed some pro-cognitive and antipsychotic-like properties in animal models, while other agents showed contradictory effects in improving symptoms and were removed from the development program. Although some serotonergic drugs seem promising for improving the treatment of schizophrenia, further studies regarding the pathophysiological mechanisms of schizophrenia and novel compounds as well as high-quality trials are necessary in order to improve schizophrenia outcomes.

1MeTIQ and olanzapine, despite their neurochemical impact, did not ameliorate performance in fear conditioning and social interaction tests in an MK-801 rat model of schizophrenia

Background

The aim of the present study was to evaluate the effect of 1MeTIQ on fear memory and social interaction in an MK-801-induced model of schizophrenia. The results obtained after administration of 1MeTIQ were compared with those obtained with olanzapine, an antipsychotic drug.

Methods

Sprague–Dawley rats received a single injection of MK-801 to induce behavioral disorders. 1MeTIQ was given either acutely in a single dose or chronically for 7 consecutive days. Olanzapine was administered once. In groups receiving combined treatments, 1MeTIQ or olanzapine was administered 20 min before MK-801 injection. Contextual fear conditioning was used to assess disturbances in fear memory (FM), and the sociability of the rats was measured in the social interaction test (SIT). Biochemical analysis was carried out to evaluate monoamine levels in selected brain structures after treatment.

Results

Our results are focused mainly on data obtained from neurochemical studies, demonstrating that 1MeTIQ inhibited the MK-801-induced reduction in dopamine levels in the frontal cortex and increased the 5-HT concentration. The behavioral tests revealed that acute administration of MK-801 caused disturbances in both the FM and SIT tests, while neither 1MeTIQ nor olanzapine reversed these deficits.

Conclusion

1MeTIQ, although pharmacologically effective (i.e., it reverses MK-801-induced changes in monoamine activity), did not influence MK-801-induced social and cognitive deficits. Thus, our FM tests and SIT did not support the main pharmacological hypotheses that focus on dopamine system stabilization and dopamine–serotonin system interactions as probable mechanisms for inhibiting the negative symptoms of schizophrenia.

International Union of Basic and Clinical Pharmacology. CX. Classification of Receptors for 5-hydroxytryptamine; Pharmacology and Function

5-HT receptors expressed throughout the human body are targets for established therapeutics and various drugs in development. Their diversity of structure and function reflects the important role 5-HT receptors play in physiologic and pathophysiological processes. The present review offers a framework for the official receptor nomenclature and a detailed understanding of each of the 14 5-HT receptor subtypes, their roles in the systems of the body, and, where appropriate, the (potential) utility of therapeutics targeting these receptors. SIGNIFICANCE STATEMENT: This review provides a comprehensive account of the classification and function of 5-hydroxytryptamine receptors, including how they are targeted for therapeutic benefit.

The Role of Zebrafish and Laboratory Rodents in Schizophrenia Research

Schizophrenia is a severe disorder characterized by positive, negative and cognitive symptoms, which are still not fully understood. The development of efficient antipsychotics requires animal models of a strong validity, therefore the aims of the article were to summarize the construct, face and predictive validity of schizophrenia models based on rodents and zebrafish, to compare the advantages and disadvantages of these models, and to propose future directions in schizophrenia modeling and indicate when it is reasonable to combine these models. The advantages of rodent models stem primarily from the high homology between rodent and human physiology, neurochemistry, brain morphology and circuitry. The advantages of zebrafish models stem in the high fecundity, fast development and transparency of the embryo. Disadvantages of both models originate in behavioral repertoires not allowing specific symptoms to be modeled, even when the models are combined. Especially modeling the verbal component of certain positive, negative and cognitive symptoms is currently impossible.

Effect of combined treatment with aripiprazole and antidepressants on the MK-801-induced deficits in recognition memory in novel recognition test and on the release of monoamines in the rat frontal cortex

According to preclinical and clinical studies, the antidepressant-induced increase in the activity of atypical antipsychotics may efficiently improve the treatment of negative and some cognitive symptoms of schizophrenia. In the present study, we aimed to evaluate the effects of the antidepressants escitalopram and mirtazapine and the atypical antipsychotic drug aripiprazole, administered separately or in combination, on the MK-801-induced deficits in the recognition memory test and on the extracellular levels of monoamines and their metabolites in the rat frontal cortex. Based on the results of the behavioral tests, co-treatment with an ineffective dose of aripiprazole (0.1 mg/kg) and escitalopram (2.5 and 5 mg/kg) or mirtazapine (5 mg/kg) abolished the deficits evoked by MK-801 in the novel object recognition test, and those effects were blocked by the 5-HT_1A receptor antagonist (WAY 100,635) or the dopamine D₁ receptor antagonist (SCH 23,390). Moreover, co-treatment with aripiprazole (0.3 mg/kg) and escitalopram (5 mg/kg) significantly increased the levels of noradrenaline and serotonin, decreased the level of its metabolite, and did not alter level of dopamine, but decreased the levels of its metabolites. In addition, co-treatment with aripiprazole (0.3 mg/kg) and mirtazapine (10 mg/kg) significantly increased the level of noradrenaline, did not change the levels of dopamine and serotonin, but increased the levels of their metabolites. Based on these results, the increase in the extracellular levels of noradrenaline or serotonin in the cortex induced by co-treatment with an antidepressant and aripiprazole may be very important for the pharmacotherapy of negative and some cognitive symptoms of schizophrenia.

Cannabidiol attenuates behavioral changes in a rodent model of schizophrenia through 5-HT1A, but not CB1 and CB2 receptors

Preclinical and clinical data indicate that cannabidiol (CBD), a non-psychotomimetic compound from the Cannabis sativa plant, can induce antipsychotic-like effects. In an animal model of schizophrenia based on the antagonism of NMDA receptors, the behavioral and molecular changes induced by repeated treatment with the NMDA receptor antagonist MK-801 were prevented when CBD was co-administered with MK-801. It is unknown, however, if CBD would reverse these changes once they have been established. Thus, in the present study we used male C57BL/6J mice, 6 weeks old, to evaluate whether daily CBD injection for seven days, starting after the end of the repeated treatment with MK-801 for 14 days, would reverse MK-801-induced deficits in the social interaction (SI) and novel object recognition (NOR) tests, which have been used to investigate the negative and cognitive symptoms of schizophrenia, respectively. We also assessed whether CBD effects would be blocked by pretreatment with AM251, a CB1 receptor antagonist, AM630, a CB2 receptor antagonist, or WAY100635, a 5-HT1A receptor antagonist. CBD and the second-generation antipsychotic clozapine, used as a positive control, attenuated the impairments in the SI and NOR tests induced by repeated administered MK-801. CBD effects were blocked by WAY100635, but not by AM251 or AM630. These data suggest that CBD induces antipsychotic-like effects by activating 5-HT1A receptors and indicate that this compound could be an interesting alternative for the treatment of negative and cognitive symptoms of schizophrenia.

The Role of the N-Methyl-D-Aspartate Receptors in Social Behavior in Rodents

The appropriate display of social behaviors is essential for the well-being, reproductive success and survival of an individual. Deficits in social behavior are associated with impaired N-methyl-D-aspartate (NMDA) receptor-mediated neurotransmission. In this review, we describe recent studies using genetically modified mice and pharmacological approaches which link the impaired functioning of the NMDA receptors, especially of the receptor subunits GluN1, GluN2A and GluN2B, to abnormal social behavior. This abnormal social behavior is expressed as impaired social interaction and communication, deficits in social memory, deficits in sexual and maternal behavior, as well as abnormal or heightened aggression. We also describe the positive effects of pharmacological stimulation of the NMDA receptors on these social deficits. Indeed, pharmacological stimulation of the glycine-binding site either by direct stimulation or by elevating the synaptic glycine levels represents a promising strategy for the normalization of genetically-induced, pharmacologically-induced or innate deficits in social behavior. We emphasize on the importance of future studies investigating the role of subunit-selective NMDA receptor ligands on different types of social behavior to provide a better understanding of the underlying mechanisms, which might support the development of selective tools for the optimized treatment of disorders associated with social deficits.

Co-treatment with antidepressants and aripiprazole reversed the MK-801-induced some negative symptoms of schizophrenia in rats

BACKGROUND

Schizophrenia is a chronic, most devastating psychiatric illness that impairs mental and social functioning. A few clinical reports have suggested that antidepressant drugs are able to augment the activity of atypical antipsychotic drugs, thus effectively improving treatment of some negative symptoms of schizophrenia.

METHODS

The aim of the present study was to investigate the effect of the antidepressant escitalopram or mirtazapine and aripiprazole (an atypical antipsychotic), given separately or jointly, on the deficits induced by MK-801(a noncompetitive N-methyl-d-aspartate receptor antagonist) in the social interaction test in male Sprague-Dawley rats. The social interaction was measured for 10 min, starting 4 h after MK-801 (0.1 mg/kg) administration. Antidepressants and aripiprazole were given 60 and 30 min before the test, respectively. WAY 100635 (a 5-HT1A antagonist) and SCH 23390 (a dopamine D1 antagonist) were give 20 min before the tests.

RESULTS

The present results showed that MK-801 (0.1 mg/kg)-induced deficits in the social interaction test. Aripiprazole (0.1 and 0.3 mg/kg) reversed those effects. Co-treatment with an ineffective dose of aripiprazole (0.03 mg/kg) and escitalopram (5 and 10 mg/kg) or mirtazapine (5 mg/kg) abolished the deficits evoked by MK-801, and those effects were especially blocked by a 5-HT1A receptor antagonist (WAY 100635) or partly by dopamine D1 receptor antagonist (SCH 23390).

CONCLUSIONS

The obtained results suggest that amelioration of the antipsychotic-like effect of aripiprazole by antidepressants in the MK-801-induced some negative symptoms of schizophrenia in rats may be associated with serotonin 5-HT1A and to a lesser degree with dopamine D1 receptors.

Impact of Chronic Risperidone Use on Behavior and Survival of 3xTg-AD Mice Model of Alzheimer's Disease and Mice With Normal Aging

Psychosis and/or aggression are common problems in dementia, and when severe or persistent, cause considerable patient distress and disability, caregiver stress, and early institutionalization. In 2005, the Food and Drug Administration (FDA) determined that atypical antipsychotics were associated with a significantly greater mortality risk compared to placebo, which prompted the addition of an FDA black-box warning. The American College of Neuropsychopharmacology (ACNP) White Paper, 2008, reviewed this issue and made clinical and research recommendations regarding the use of antipsychotics in dementia patients with psychosis and/or agitation. Increased mortality risk has also been described in cerebrovascular adverse events in elderly users of antipsychotics. In the present work, at the translational level, we used male 3xTg-AD mice (PS1M146V, APPSwe, tauP301L) at advanced stages of the disease reported to have worse survival than females, to study the behavioral effects of a low chronic dose of risperidone (0.1 mg/kg, s.c., 90 days, from 13 to 16 months of age) and its impact on long-term survival, as compared to mice with normal aging. Animals were behaviorally assessed for cognitive and BPSD (behavioral and psychological symptoms of dementia)-like symptoms in naturalistic and experimental conditions (open-field test, T-maze, social interaction, Morris water maze, and marble test) before and after treatment. Weight, basal glucose levels, and IPGTT (i.p. glucose tolerance test) were also recorded. Neophobia in the corner test was used for behavioral monitoring. Survival curves were recorded throughout the experiment until natural death. The benefits of risperidone were limited, both at cognitive and BPSD-like level, and mostly restricted to burying, agitation/vibrating tail, and other social behaviors. However, the work warns about a clear early mortality risk window during the treatment and long-lasting impact on survival. Reduced life expectancy and life span were observed in the 3xTg-AD mice, but total lifespan (36 months) recorded in C57BL/6 × 129Sv counterparts with normal aging was also truncated to 28 months in those with treatment. Sarcopenia at time of death was found in all groups, but was more severe in wild-type animals treated with risperidone. Therefore, the 3xTg-AD mice and their non-transgenic counterparts can be useful to delimitate critical time windows and for studying the physio-pathogenic factors and underlying causal events involved in this topic of considerable public health significance.

Selective adrenergic alpha2C receptor antagonist ameliorates acute phencyclidine-induced schizophrenia-like social interaction deficits in rats

RATIONALE

Social withdrawal is a core feature of the negative symptoms of schizophrenia. Currently available pharmacotherapies have only limited efficacy towards the negative symptoms, i.e., there is a significant unmet medical need in the treatment of these symptoms.

OBJECTIVE

We wanted to confirm whether selective adrenergic α_2C receptor (AR) antagonist therapy could ameliorate acute phencyclidine (PCP)-induced schizophrenia-like social interaction deficits in rats, and to compare the effects of an α_2C AR antagonist to another putative therapeutic alternative, an α₇ nicotinic acetylcholine receptor (nAChR) partial agonist, as well against three commonly used atypical antipsychotics.

METHODS

Here, we used acute PCP administration and modified a protocol for testing social interaction deficits in male Wistar rats and then used this model to compare the effects of an α_2C AR antagonist (ORM-13070 0.3 and 1.0 mg/kg s.c.) with an α₇ nAChR partial agonist (EVP-6124 0.3 mg/kg s.c.) and three atypical antipsychotics (clozapine 2.5 mg/kg i.p., risperidone 0.04 and 0.08 mg/kg s.c., olanzapine 0.125 and 0.5 mg/kg s.c.) on social interaction behavior.

RESULTS

Acute PCP (1.5 mg/kg s.c.) produced robust and reproducible deficits in social interaction behavior without affecting locomotor activity. The selective α_2C AR antagonist significantly ameliorated PCP-induced social interaction deficits. In contrast, neither the partial α₇ nAChR agonist nor any of the three atypical antipsychotics were able to reverse the behavioral deficits at the selected doses.

CONCLUSION

Our findings confirm that α_2C AR antagonism is a potential mechanism for the treatment of the negative symptoms of schizophrenia.

Cystine/Glutamate Antiporter and Aripiprazole Compensate NMDA Antagonist-Induced Dysfunction of Thalamocortical L-Glutamatergic Transmission

To explore pathophysiology of schizophrenia, this study analyzed the regulation mechanisms that are associated with cystine/glutamate antiporter (Sxc), group-II (II-mGluR), and group-III (III-mGluR) metabotropic glutamate-receptors in thalamo-cortical glutamatergic transmission of MK801-induced model using dual-probe microdialysis. L-glutamate release in medial pre-frontal cortex (mPFC) was increased by systemic- and local mediodorsal thalamic nucleus (MDTN) administrations of MK801, but was unaffected by local administration into mPFC. Perfusion into mPFC of activators of Sxc, II-mGluR, and III-mGluR, and into the MDTN of activators of Sxc, II-mGluR, and GABA_A receptor inhibited MK801-evoked L-glutamate release in mPFC. Perfusion of aripiprazole (APZ) into MDTN and mPFC also inhibited systemic MK801-evoked L-glutamate release in mPFC. Inhibition of II-mGluR in mPFC and MDTN blocked inhibitory effects of Sxc-activator and APZ on MK801-evoked L-glutamate release; however, their inhibitory effects were blocked by the inhibition of III-mGluR in mPFC but not in MDTN. These results indicate that reduced activation of the glutamate/NMDA receptor (NMDAR) in MDTN enhanced L-glutamate release in mPFC possibly through GABAergic disinhibition in MDTN. Furthermore, MDTN-mPFC glutamatergic transmission receives inhibitory regulation of Sxc/II-mGluR/III-mGluR functional complex in mPFC and Sxc/II-mGluR complex in MDTN. Established antipsychotic, APZ inhibits MK801-evoked L-glutamate release through the activation of Sxc/mGluRs functional complexes in both MDTN and mPFC.

Hunting for the high-affinity state of G-protein-coupled receptors with agonist tracers: Theoretical and practical considerations for positron emission tomography imaging

The concept of the high‐affinity state postulates that a certain subset of G‐protein‐coupled receptors is primarily responsible for receptor signaling in the living brain. Assessing the abundance of this subset is thus potentially highly relevant for studies concerning the responses of neurotransmission to pharmacological or physiological stimuli and the dysregulation of neurotransmission in neurological or psychiatric disorders. The high‐affinity state is preferentially recognized by agonists in vitro. For this reason, agonist tracers have been developed as tools for the noninvasive imaging of the high‐affinity state with positron emission tomography (PET). This review provides an overview of agonist tracers that have been developed for PET imaging of the brain, and the experimental paradigms that have been developed for the estimation of the relative abundance of receptors configured in the high‐affinity state. Agonist tracers appear to be more sensitive to endogenous neurotransmitter challenge than antagonists, as was originally expected. However, other expectations regarding agonist tracers have not been fulfilled. Potential reasons for difficulties in detecting the high‐affinity state in vivo are discussed.

Male rats treated with subchronic PCP show intact olfaction and enhanced interest for a social odour in the olfactory habituation/dishabituation test

The olfactory system participates in many sensory processes, and olfactory endophenotypes appear in a variety of neurological disorders such as Alzheimer's and Parkinson's disease, depression and schizophrenia. Social withdrawal is a core negative symptom of schizophrenia and animal models have proven to be invaluable for studying the neurobiological mechanisms and cognitive processes behind the formation of social relationships. The subchronic phencyclidine (PCP) rat model is a validated model for negative symptoms of schizophrenia, such as impaired sociability. However, the complete range of social behaviour and deficits in the model are still not fully understood. Intact rodent olfaction is essential for a wide range of social behaviour and disrupted olfactory function could have severe effects on social communication and recognition. In order to examine the olfactory ability of male rats treated with subchronic PCP, we conducted an olfactory habituation/dishabituation test including both non-social and social odours. The subchronic PCP-treated rats successfully recognized and discriminated among the odours, indicative of intact olfaction. Interestingly, the subchronic PCP-treated rats showed greater interest for a novel social odour compared to the saline-treated rats and the rationale remains to be elucidated. Our data indicate that subchronic PCP treatment does not disrupt olfactory function in male rats. By ruling out impaired olfaction as cause for the poor social interaction performance in subchronic PCP-treated rats, our data supports the use of NMDA receptor antagonists to model the negative symptoms of schizophrenia.

Effects of 2-bromoterguride, a dopamine D2 receptor partial agonist, on cognitive dysfunction and social aversion in rats

RATIONALE

2-Bromoterguride, a dopamine D₂ receptor partial agonist with antagonist properties at serotonin 5-HT_2A receptors and α_2C-adrenoceptors, meets the prerequisites of a putative atypical antipsychotic drug (APD). We recently showed that 2-bromoterguride is effective in tests of positive symptoms of schizophrenia in rats without inducing extrapyramidal side effects or metabolic changes.

OBJECTIVE

In continuation of our recent work, we now investigated the effect of 2-bromoterguride on apomorphine and phencyclidine (PCP)-induced disruptions of prepulse inhibition (PPI) of the acoustic startle response, a measure of sensory gating. In addition, we used subchronic PCP treatment to produce cognitive deficits and social aversion, and assessed the effect of 2-bromoterguride on the performance in the novel object recognition (NOR) task (model for studying cognitive deficit symptoms of schizophrenia) and the social interaction test (model for studying negative symptoms of schizophrenia). Finally, we extended the side effect profile of 2-bromoterguride by measuring the prolactin response to systemic administration of the drug in rats.

RESULTS

Treatment with 2-bromoterguride (0.1 and 0.3 mg/kg) reversed PPI deficits induced by apomorphine and PCP, respectively. Subchronic PCP induced impairments in object memory and social interaction behavior which were ameliorated by 2-bromoterguride but not by clozapine and aripiprazole, respectively. Prolactin concentration in blood serum was not elevated at 1, 2, or 4 h post-2-bromoterguride treatment, which further supports the safe and effective use of this drug.

CONCLUSIONS

Our data support 2-bromoterguride as a promising APD candidate due to its beneficial effect on cognitive impairments and negative symptoms of schizophrenia.

Aripiprazole, A Drug that Displays Partial Agonism and Functional Selectivity

BACKGROUND

The treatment of schizophrenia is challenging due to the wide range of symptoms (positive, negative, cognitive) associated with the disease. Typical antipsychotics that antagonize D2 receptors are effective in treating positive symptoms, but extrapyramidal side-effects (EPS) are a common occurrence. Atypical antipsychotics targeting 5-HT2A and D2 receptors are more effective at treating cognitive and negative symptoms compared to typical antipsychotics, but these drugs also result in side-effects such as metabolic syndromes.

OBJECTIVE

To identify evidence in the literature that elucidates the pharmacological profile of aripiprazole.s.

METHODS

We searched PubMed for peer reviewed articles on aripiprazole and its clinical efficacy, side-effects, pharmacology, and effects in animal models of schizophrenia symptoms.

RESULTS

Aripiprazole is a newer atypical antipsychotic that displays a unique pharmacological profile, including partial D2 agonism and functionally selective properties. Aripiprazole is effective at treating the positive symptoms of schizophrenia and has the potential to treat negative and cognitive symptoms at least as well as other atypical antipsychotics. The drug has a favorable side-effect profile and has a low propensity to result in EPS or metabolic syndromes. Animal models of schizophrenia have been used to determine the efficacy of aripiprazole in symptom management. In these instances, aripiprazole resulted in the reversal of deficits in extinction, pre-pulse inhibition, and social withdrawal. Because aripiprazole requires a greater than 90% occupancy rate at D2 receptors to be clinically active and does not produce EPS, this suggests a functionally selective effect on intracellular signaling pathways.

CONCLUSION

A combination of factors such as dopamine system stabilization via partial agonism, functional selectivity at D2 receptors, and serotonin-dopamine system interaction may contribute to the ability of aripiprazole to successfully manage schizophrenia symptoms. This review examines these mechanisms of action to further clarify the pharmacological actions of aripiprazole.

Oral haloperidol or olanzapine intake produces distinct and region-specific increase in cannabinoid receptor levels that is prevented by high fat diet

Clinical studies show higher levels of cannabinoid CB1 receptors (CB1R) in the brain of schizophrenic patients while preclinical studies report a significant functional interaction between dopamine D2 receptors and CB1Rs as well as an upregulation of CB1Rs after antipsychotic treatment. These findings prompted us to study the effects of chronic oral intake of a first and a second generation antipsychotic, haloperidol and olanzapine, on the levels and distribution of CB1Rs in the rat brain. Rats consumed either regular chow or high-fat food and drank water, haloperidol drinking solution (1.5mg/kg), or olanzapine drinking solution (10mg/kg) for four weeks. Motor and cognitive functions were tested at the end of treatment week 3 and upon drug discontinuation. Two days after drug discontinuation, rats were euthanized and brains were processed for in vitro receptor autoradiography. In chow-fed animals, haloperidol and olanzapine increased CB1R levels in the basal ganglia and the hippocampus, in a similar, but not identical pattern. In addition, olanzapine had unique effects in CB1R upregulation in higher order cognitive areas, in the secondary somatosensory cortex, in the visual and auditory cortices and the geniculate nuclei, as well as in the hypothalamus. High fat food consumption prevented antipsychotic-induced increase in CB1R levels in all regions examined, with one exception, the globus pallidus, in which they were higher in haloperidol-treated rats. The results point towards the hypothesis that increased CB1R levels could be a confounding effect of antipsychotic medication in schizophrenia that is circumveneted by high fat feeding.

Short- and long-term behavioral analysis of social interaction, ultrasonic vocalizations and social motivation in a chronic phencyclidine model

Phencyclidine (PCP) has been suggested to induce symptoms of schizophrenia. However, animal models using PCP administration have produced ambiguous results thus far. It seems that acute effects are similar to symptoms of schizophrenia, however, it is not clear if PCP can induce permanent behavioral changes that reflect schizophrenic-like symptoms. Therefore, we assessed the ability of chronic PCP administration (3mg/kg, 14 days) to induce short or long lasting behavioral changes in rats. Social behavior, including ultrasonic vocalizations and motivation for social contact were investigated at different time points, up to 29-36 days, after cessation of PCP treatment. During a social separation test, performed at 5 and 36 days, PCP treated rats spent less time near the divider that separates them from their familiar cage mate compared with saline (SAL) treated rats. Further, at short term, PCP was able to induce a decrease in social behavior. In contrast, at long-term, PCP treated animals spent more time in contact when exposed to an unfamiliar partner as compared to SAL treated rats. But, this difference was not observed when exposed to a familiar partner. We did not find any difference in ultrasonic vocalizations at all time points. The results of our study indicate that PCP is unable to induce overt long term deficits in social interaction behavior. Rather, it seems that PCP diminishes motivation for social contact. The long-term consequences of chronic PCP administration on social behavior in rodent models remain complex, and future studies addressing this are still needed.

Adjunctive Aripiprazole in Bipolar I Depression

Background:

Aripiprazole has demonstrated efficacy in treatment of bipolar mania, as well as in the maintenance treatment of bipolar disorder. There has been only one report supporting a role for this agent in the depressed phase of the illness.

Objective:

To evaluate the effectiveness of adjunctive aripiprazole in bipolar I depressed patients who are nonresponders to standard therapy.

Methods:

Chart records were reviewed for all patients with bipolar I depression, diagnosed by Diagnostic and Statistical Manual of Mental Disorders, 4th revision, criteria between June 2004 and January 2006 from the Long Beach Veterans Affairs Mood Disorders Clinic. Included subjects had experienced moderate to marked depressive symptoms (Clinical Global Impression–Bipolar Depression ≥4) despite at least 2 months of treatment with adequate doses of at least one mood stabilizer. In addition, all subjects had been treated subsequently with aripiprazole 15–30 mg/day added to the existing regimen. Detailed chart notes were used to retrospectively rate symptoms. The presence or absence of each symptom was recorded before and after aripiprazole augmentation. Based on these data, Clinical Global Impression bipolar severity (CGI-BP-S) ratings and CGI-BP improvement scores for bipolar I depression were assigned.

Results:

Ten subjects met study criteria. Adjunctive aripiprazole given for 21–110 days resulted in significant improvements in CGI-BP-S depression ratings. Seven of 10 patients were assigned CGI-BP improvement ratings of much or very much improved. Adverse events were mild and included akathisia, nausea, and insomnia. Dose adjustments of aripiprazole or the addition of drugs to treat adverse effects excluded subjects from further data collection. No patient stopped aripiprazole due to adverse effects.

Conclusions:

This study adds to a previous report indicating beneficial effects of adjunctive aripiprazole in treatment of bipolar I depression. Double-blind, placebo-controlled investigations are needed to confirm these findings.

MK-801-induced deficits in social recognition in rats: reversal by aripiprazole, but not olanzapine, risperidone, or cannabidiol

Deficiencies in social activities are hallmarks of numerous brain disorders. With respect to schizophrenia, social withdrawal belongs to the category of negative symptoms and is associated with deficits in the cognitive domain. Here, we used the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801) for induction of social withdrawal in rats and assessed the efficacy of several atypical antipsychotics with different pharmacological profiles as putative treatment. In addition, we reasoned that the marijuana constituent cannabidiol (CBD) may provide benefit or could be proposed as an adjunct treatment in combination with antipsychotics. Hooded Lister rats were tested in the three-chamber version for social interaction, with an initial novelty phase, followed after 3 min by a short-term recognition memory phase. No drug treatment affected sociability. However, distinct effects on social recognition were revealed. MK-801 reduced social recognition memory at all doses (>0.03 mg/kg). Predosing with aripiprazole dose-dependently (2 or 10 mg/kg) prevented the memory decline, but doses of 0.1 mg/kg risperidone or 1 mg/kg olanzapine did not. Intriguingly, CBD impaired social recognition memory (12 and 30 mg/kg) but did not rescue the MK-801-induced deficits. When CBD was combined with protective doses of aripiprazole (CBD-aripiprazole at 12 :  or 5 : 2 mg/kg) the benefit of the antipsychotic was lost. At the same time, activity-related changes in behaviour were excluded as underlying reasons for these pharmacological effects. Collectively, the combined activity of aripiprazole on dopamine D2 and serotonin 5HT1A receptors appears to provide a significant advantage over risperidone and olanzapine with respect to the rescue of cognitive deficits reminiscent of schizophrenia. The differential pharmacological properties of CBD, which are seemingly beneficial in human patients, did not back-translate and rescue the MK-801-induced social memory deficit.

Improvement of ketamine-induced social withdrawal in rats: the role of 5-HT7 receptors

Social withdrawal, one of the core negative symptoms of schizophrenia, can be modelled in the social interaction (SI) test in rats using N-methyl-D-aspartate receptor glutamate receptor antagonists. We have recently shown that amisulpride, an antipsychotic with a high affinity for serotonin 5-HT7 receptors, reversed ketamine-induced SI deficits in rats. The aim of the present study was to further elucidate the potential involvement of 5-HT7 receptors in the prosocial action of amisulpride. Acute administration of amisulpride (3 mg/kg) and SB-269970 (1 mg/kg), a 5-HT7 receptor antagonist, reversed ketamine-induced social withdrawal, whereas sulpiride (20 or 30 mg/kg) and haloperidol (0.2 mg/kg) were ineffective. The 5-HT7 receptor agonist AS19 (10 mg/kg) abolished the prosocial efficacy of amisulpride (3 mg/kg). The coadministration of an inactive dose of SB-269970 (0.2 mg/kg) showed the prosocial effects of inactive doses of amisulpride (1 mg/kg) and sulpiride (20 mg/kg). The anxiolytic chlordiazepoxide (2.5 mg/kg) and the antidepressant fluoxetine (2.5 mg/kg) were ineffective in reversing ketamine-induced SI deficits. The present study suggests that the antagonism of 5-HT7 receptors may contribute towards the mechanisms underlying the prosocial action of amisulpride. These results may have therapeutic implications for the treatment of negative symptoms in schizophrenia and other disorders characterized by social withdrawal.

The phytocannabinoid, Δ⁹-tetrahydrocannabivarin, can act through 5-HT₁A receptors to produce antipsychotic effects

BACKGROUND AND PURPOSE

This study aimed to address the questions of whether Δ(9)-tetrahydrocannabivarin (THCV) can (i) enhance activation of 5-HT1 A receptors in vitro and (ii) induce any apparent 5-HT₁A receptor-mediated antipsychotic effects in vivo.

EXPERIMENTAL APPROACH

In vitro studies investigated the effect of THCV on targeting by 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) of 5-HT₁A receptors in membranes obtained from rat brainstem or human 5-HT₁A CHO cells, using [(35)S]-GTPγS and 8-[(3)H]-OH-DPAT binding assays. In vivo studies investigated whether THCV induces signs of 5-HT₁A receptor-mediated antipsychotic effects in rats.

KEY RESULTS

THCV (i) potently, albeit partially, displaced 8-[(3) H]-OH-DPAT from specific binding sites in rat brainstem membranes; (ii) at 100 nM, significantly enhanced 8-OH-DPAT-induced activation of receptors in these membranes; (iii) produced concentration-related increases in 8-[(3)H]-OH-DPAT binding to specific sites in membranes of human 5-HT₁A receptor-transfected CHO cells; and (iv) at 100 nM, significantly enhanced 8-OH-DPAT-induced activation of these human 5-HT₁A receptors. In phencyclidine-treated rats, THCV, like clozapine (i) reduced stereotyped behaviour; (ii) decreased time spent immobile in the forced swim test; and (iii) normalized hyperlocomotor activity, social behaviour and cognitive performance. Some of these effects were counteracted by the 5-HT₁A receptor antagonist, WAY100635, or could be reproduced by the CB₁ antagonist, AM251.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that THCV can enhance 5-HT₁A receptor activation, and that some of its apparent antipsychotic effects may depend on this enhancement. We conclude that THCV has therapeutic potential for ameliorating some of the negative, cognitive and positive symptoms of schizophrenia.

Dopamine Targeting Drugs for the Treatment of Schizophrenia: Past, Present and Future

Schizophrenia is a chronic and debilitating neuropsychiatric disorder affecting approximately 1% of the world's population. This disease is associated with considerable morbidity placing a major financial burden on society. Antipsychotics have been the mainstay of the pharmacological treatment of schizophrenia for decades. The traditional typical and atypical antipsychotics demonstrate clinical efficacy in treating positive symptoms, such as hallucinations and delusions, while are largely ineffective and may worsen negative symptoms, such as blunted affect and social withdrawal, as well as cognitive function. The inability to treat these latter symptoms may contribute to social function impairment associated with schizophrenia. The dysfunction of multiple neurotransmitter systems in schizophrenia suggests that drugs selectively targeting one neurotransmission pathway are unlikely to meet all the therapeutic needs of this heterogeneous disorder. Often, however, the unintentional engagement of multiple pharmacological targets or even the excessive engagement of intended pharmacological targets can lead to undesired consequences and poor tolerability. In this article, we will review marketed typical and atypical antipsychotics and new therapeutic agents targeting dopamine receptors and other neurotransmitters for the treatment of schizophrenia. Representative typical and atypical antipsychotic drugs and new investigational drug candidates will be systematically reviewed and compared by reviewing structure-activity relationships, pharmacokinetic properties, drug metabolism and safety, pharmacological properties, preclinical data in animal models, clinical outcomes and associated side effects.

Glutamatergic agents for schizophrenia: current evidence and perspectives

Suboptimal outcomes in schizophrenia are a consequence of lacking insight into the etiology, biomarkers and treatment-relevant subgroups, the therapeutic restriction to dopaminergic-modulating antipsychotics that fail to significantly improve negative and cognitive symptoms, non-adherence, and, in the case of treatment-resistance, the underutilization of clozapine. Evidence suggests additional, extra-dopaminergic abnormalities in amino acid neurotransmission, particularly the glutamatergic system. Antidopaminergic antipsychotics modulate this system on several levels, as do mood stabilizers, including lamotrigine, topiramate and pregabaline. Recently, agonists at metabotropic glutamate receptors and glycine uptake inhibitors failed in large placebo-controlled trials for schizophrenia. Problems to overcome for successfully leveraging glutamatergic agents for schizophrenia are patient selection, focus on positive symptoms and late disease stages, and dose-response relationships. Because glutamate guides processes of brain development and maturation, clinical research should focus on the at-risk mental state or first-episode psychosis, address cognition and negative symptoms and use monotherapy designs in parallel to augmentation strategies.

Behavioral effects of phencyclidine on nicotine self-administration and reinstatement in the presence or absence of a visual stimulus in rats

RATIONALE

Tobacco use is a serious health problem in the USA, and this problem is potentiated in patients with schizophrenia. The reward system is implicated in schizophrenia and may contribute to the high comorbidity between nicotine use and schizophrenia, but very little research has been done on the topic. The reward-enhancement effect of nicotine has been shown to be important in nicotine use, but there have been no studies on this effect in animal models of schizophrenia.

OBJECTIVES

This study was designed to determine the effects of phencyclidine, used to model negative symptoms of schizophrenia, on self-administration of nicotine with or without a co-occurring sensory reinforcer [i.e., visual stimulus (VS)] in rats.

METHODS

Phencyclidine (2.0 mg/kg) was administered before each of seven nicotine self-administration sessions (0.01 mg/kg/inf) after which rats (n = 8-9 per group) were given 7 days of extinction without phencyclidine pretreatment. Reinstatement using phencyclidine (2.0 mg/kg), nicotine (0.2 mg/kg), and yohimbine (1.25 mg/kg, a pharmacological stressor) was tested after extinction to determine if previous exposure to phencyclidine would alter reinstatement of active lever pressing.

RESULTS

Phencyclidine initially decreased nicotine self-administration but only in the groups with a concurrent VS. This decrease in self-administration dissipated after 5 days. During reinstatement, rats that had previously received phencyclidine during self-administration with a VS were more sensitive to stress-induced reinstatement than any other group.

CONCLUSIONS

These results show a transitory effect of phencyclidine on nicotine self-administration. Phencyclidine may induce a potential sensitivity to pharmacological stressors contributing to reinstatement of nicotine.

HTR1A Gene Polymorphisms and 5-HT1A Receptor Partial Agonist Antipsychotics Efficacy in Schizophrenia

Individual differences in serotonin 1A (5-HT1A) receptor may result in variable response to antipsychotics with 5-HT1A receptor partial agonism. We investigated the relationship between 5-HT1A receptor gene (HTR1A) single nucleotide polymorphisms (SNPs) and efficacy of antipsychotics with 5-HT1A receptor partial agonism in Japanese patients with schizophrenia. Perospirone or aripiprazole was administered to 100 patients with schizophrenia in a randomized controlled study. Candidate SNPs were rs6295 (which affects HTR1A expression and function), rs1364043, rs878567, and rs10042486. Efficacy at week 12 of treatment was evaluated using the Positive and Negative Syndrome Scale (PANSS) 5-factor subscales (excitement/hostility, depression/anxiety, cognition, positive, and negative). Rs1364043 T allele was correlated with the percent change in the PANSS 5-factor negative score (P < 0.01). Haplotype analysis showed that the rs10042486-rs6295-rs1364043 T-C-G haplotype was correlated with worse negative score improvement (haplotype frequency, 0.675; P = 0.014), and the relatively rare T-G-T haplotype correlated with better efficacy (haplotype frequency, 0.05; P = 0.031). This is the first study to show that rs10042486-rs6295-rs1364043 HTR1A variants may be correlated with the improvement of the PANSS 5-factor negative score during treatment with 5-HT1A partial agonist antipsychotics. Studies with larger sample sizes and in different ethnic groups are warranted.

Improvement of dizocilpine-induced social recognition deficits in mice by brexpiprazole, a novel serotonin-dopamine activity modulator

Cognitive impairment, including impaired social cognition, is largely responsible for the deterioration in social life suffered by patients with psychiatric disorders, such as schizophrenia and major depressive disorder (MDD). Brexpiprazole (7-{4-[4-(1-benzothiophen-4-yl)piperazin-1-yl]butoxy}quinolin-2(1H)-one), a novel serotonin-dopamine activity modulator, was developed to offer efficacious and tolerable therapy for different psychiatric disorders, including schizophrenia and adjunctive treatment of MDD. In this study, we investigated whether brexpiprazole could improve social recognition deficits (one of social cognition deficits) in mice, after administration of the N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 (dizocilpine). Dosing with dizocilpine (0.1mg/kg) induced significant impairment of social recognition in mice. Brexpiprazole (0.01, 0.03, 0.1mg/kg, p.o.) significantly ameliorated dizocilpine-induced social recognition deficits, without sedation or a reduction of exploratory behavior. In addition, brexpiprazole alone had no effect on social recognition in untreated control mice. By contrast, neither risperidone (0.03mg/kg, p.o.) nor olanzapine (0.03mg/kg, p.o.) altered dizocilpine-induced social recognition deficits. Finally, the effect of brexpiprazole on dizocilpine-induced social recognition deficits was antagonized by WAY-100,635, a selective serotonin 5-HT1A antagonist. These results suggest that brexpiprazole could improve dizocilpine-induced social recognition deficits via 5-HT1A receptor activation in mice. Therefore, brexpiprazole may confer a beneficial effect on social cognition deficits in patients with psychiatric disorders.

Aripiprazole: from pharmacological profile to clinical use

Clinical experience with aripiprazole has confirmed the effectiveness and the safety of this novel antipsychotic drug in patients with schizophrenia as well as for the treatment of mania in type I bipolar disorder. However the generalization of the results from clinical trials requires further effort in order to address some issues and to overcome incorrect and partial interpretation of the clinical evidence. This article provides some straightforward guidance that may help clinical psychiatrists to translate the mechanism of action of aripiprazole into clinical setting, thus improving the appropriate use of the drug through rational application of its pharmacological profile. Examples of paradigmatic clinical situations are presented and discussed, suggesting possible intervention strategies, which may contribute to achieving the most appropriate use of the pharmacological properties of aripiprazole in real life settings.

Update on the Mechanism of Action of Aripiprazole: Translational Insights into Antipsychotic Strategies Beyond Dopamine Receptor Antagonism

Dopamine partial agonism and functional selectivity have been innovative strategies in the pharmacological treatment of schizophrenia and mood disorders and have shifted the concept of dopamine modulation beyond the established approach of dopamine D2 receptor (D2R) antagonism. Despite the fact that aripiprazole was introduced in therapy more than 12 years ago, many questions are still unresolved regarding the complexity of the effects of this agent on signal transduction and intracellular pathways, in part linked to its pleiotropic receptor profile. The complexity of the mechanism of action has progressively shifted the conceptualization of this agent from partial agonism to functional selectivity. From the induction of early genes to modulation of scaffolding proteins and activation of transcription factors, aripiprazole has been shown to affect multiple cellular pathways and several cortical and subcortical neurotransmitter circuitries. Growing evidence shows that, beyond the consequences of D2R occupancy, aripiprazole has a unique neurobiology among available antipsychotics. The effect of chronic administration of aripiprazole on D2R affinity state and number has been especially highlighted, with relevant translational implications for long-term treatment of psychosis. The hypothesized effects of aripiprazole on cell-protective mechanisms and neurite growth, as well as the differential effects on intracellular pathways [i.e. extracellular signal-regulated kinase (ERK)] compared with full D2R antagonists, suggest further exploration of these targets by novel and future biased ligand compounds. This review aims to recapitulate the main neurobiological effects of aripiprazole and discuss the potential implications for upcoming improvements in schizophrenia therapy based on dopamine modulation beyond D2R antagonism.

Antipsychotic treatment modulates glutamate transport and NMDA receptor expression

Schizophrenia patients often suffer from treatment-resistant cognitive and negative symptoms, both of which are influenced by glutamate neurotransmission. Innovative therapeutic strategies such as agonists at metabotropic glutamate receptors or glycin reuptake inhibitors try to modulate the brain's glutamate network. Interactions of amino acids with monoamines have been described on several levels, and first- and second-generation antipsychotic agents (FGAs, SGAs) are known to exert modulatory effects on the glutamatergic system. This review summarizes the current knowledge on effects of FGAs and SGAs on glutamate transport and receptor expression derived from pharmacological studies. Such studies serve as a control for molecular findings in schizophrenia brain tissue and are clinically relevant. Moreover, they may validate animal models for psychosis, foster basic research on antipsychotic substances and finally lead to a better understanding of how monoaminergic and amino acid neurotransmissions are intertwined. In the light of these results, important differences dependent on antipsychotic substances, dosage and duration of treatment became obvious. While some post-mortem findings might be confounded with multifold drug effects, others are unlikely to be influenced by antipsychotic treatment and could represent important markers of schizophrenia pathophysiology. In similarity to the convergence of toxic and psychotomimetic effects of dopaminergic, serotonergic and anti-glutamatergic substances, the therapeutic mechanisms of SGAs might merge on a yet to be defined molecular level. In particular, serotonergic effects of SGAs, such as an agonism at 5HT1A receptors, represent important targets for further clinical research.

Analysis of sociability and preference for social novelty in the acute and subchronic phencyclidine rat

Both acute and sub-chronic phencyclidine administration produce behavioural and pathophysiological changes that resemble some features of schizophrenia. The present study aimed to determine if acute and sub-chronic phencyclidine treatment in male rats produces deficits in sociability and social novelty preference, which may reflect aspects of the negative symptomatology observed in schizophrenia. Rats were treated with phencyclidine acutely (2 or 5 mg/kg) or subchronically (2 or 5 mg/kg bi-daily for one week followed by a one week wash-out period) or vehicle. Social affiliative behaviour was assessed using the sociability and preference for social novelty paradigm where social interaction time was measured in (a) a chamber containing an unfamiliar conspecific vs an empty chamber (sociability), or (b) a chamber containing an unfamiliar conspecific vs a chamber containing a familiar conspecific (preference for social novelty). Results showed that acute administration of phencyclidine produced a reduction in measures of sociability but had no effect on preference for social novelty while sub-chronic administration of phencyclidine had no effect on sociability or social novelty. This study provides further evidence for the usefulness of phencyclidine models in modelling the symptomatology of schizophrenia.

Design, synthesis and evaluation of benzo[a]thieno[3,2-g]quinolizines as novel l-SPD derivatives possessing dopamine D1, D2 and serotonin 5-HT1A multiple action profiles

A novel scaffold derived from l-SPD with a substituted thiophene group in the D ring were designed, synthesized, and evaluated for their binding affinities at dopamine (D1, D2 and D3) and serotonin (5-HT1A and 5-HT2A) receptors. Most of the tetracyclic compounds exhibited higher affinities for D2 and 5-HT1A receptors than l-SPD, while compound 23 e showed the highest Ki value of 7.54 nM at D2 receptor which was 14 times more potent than l-SPD. Additionally, compounds 23 d and 23 e were more potent than l-SPD at D3 receptor. According to the functional assays, 23 d and 23 e were demonstrated as full antagonists at D1 and D2 receptors and full agonists at 5-HT1A receptor. Since the combination of D2 antagonism and 5-HT1A agonism is considered effective in treating both the positive and negative symptoms of schizophrenia, these novel compounds are implicated as potential therapeutic agents.

Acute and chronic effects of NMDA receptor antagonists in rodents, relevance to negative symptoms of schizophrenia: a translational link to humans

Negative symptoms of schizophrenia remain an unmet clinical need as they are common, persistent, respond poorly to existing treatments and lead to disability. Blunted affect, alogia, asociality, anhedonia and avolition are regarded as key negative symptoms despite DSM-IV-TR specifying a more limited range. The key to development of improved therapies is improved animal models that mimic the human condition in terms of behaviour and pathology and that predict efficacy of novel treatments in patients. Accumulating evidence shows that NMDA receptor (NMDAR) antagonists mimic cognitive deficits of relevance to schizophrenia in animals, along with associated pathological changes. This review examines evidence for the ability of NMDAR antagonists to mimic anhedonia and asociality, two negative symptoms of schizophrenia, in animals. The use of various species, paradigms and treatment regimens are reviewed. We conclude that sub-chronic treatment with NMDAR antagonists, typically PCP, induces social withdrawal in animals but not anhedonia. NMDAR antagonists have further effects in paradigms such as motivational salience that may be useful for mimicking other aspects of negative symptoms but these require further development. Sub-chronic treatment regimens of NMDAR antagonists also have some neurobiological effects of relevance to negative symptoms. It is our view that a sub-chronic treatment regime with NMDAR antagonists, particularly PCP, with animals tested following a wash-out period and in a battery of tests to assess certain behaviours of relevance to negative symptoms and social withdrawal (the animal equivalent of asociality) is valuable. This will enhance our understanding of the psycho and neuropathology of specific negative symptom domains and allow early detection of novel pharmacological targets.

Social interaction and social withdrawal in rodents as readouts for investigating the negative symptoms of schizophrenia

Negative symptoms (e.g., asociality and anhedonia) are a distinct symptomatic domain that has been found to significantly affect the quality of life in patients diagnosed with schizophrenia. Additionally, the primary negative symptom of asociality (i.e., withdrawal from social contact that derives from indifference or lack of desire to have social contact) is a major contributor to poor psychosocial functioning and has been found to play an important role in the course of the disorder. Nonetheless, the pathophysiology underlying these symptoms is unknown and currently available treatment options (e.g., antipsychotics and cognitive-behavioral therapy) fail to reliably produce efficacious benefits. Utilizing rodent paradigms that measure social behaviors (e.g., social withdrawal) to elucidate the neurobiological substrates that underlie social dysfunction and to identify novel therapeutic targets may be highly informative and useful to understand more about the negative symptoms of schizophrenia. Accordingly, the purpose of this review is to provide an overview of the behavioral tasks for assessing social functioning that may be translationally relevant for investigating negative symptoms associated with schizophrenia.

Quinoline- and isoquinoline-sulfonamide analogs of aripiprazole: novel antipsychotic agents?

The introduction of typical antipsychotics over six decades ago signaled an important milestone in psychiatry. However, second-generation antipsychotics ameliorated the positive symptoms of schizophrenia but displayed limited effectiveness for the negative and cognitive symptoms. In addition, while the newer antipsychotics produced fewer motor side effects, the atypical antipsychotics still induced weight gain and endocrinopathies. In recent years, a third generation of antipsychotics was identified. Aripiprazole was the first approved drug acting as a D2 partial agonist/functionally selective ligand. This review presents the state of the development of novel antipsychotic dopaminergic and non-dopaminergic agents, supported by an overview of the compounds evaluated under advanced preclinical and clinical development (e.g., cariprazine and brexpiprazole). In line with the recent trends in the development of modern atypical antipsychotics, we present our strategic development of long-chain arylpiperazine-derived quinoline- and isoquinoline-sulfonamide displaying a multireceptor binding profile and partial D2 receptor agonism.

Effects of the selective 5-HT7 receptor antagonist SB-269970 and amisulpride on ketamine-induced schizophrenia-like deficits in rats

A wide body of evidence suggests that 5-HT7 receptors are implicated in a variety of central nervous system functions, including control of learning and memory processes. According to recent preclinical data, the selective blockade of these receptors may be a potential target for cognitive improvement in schizophrenia. The first aim of the present study was to evaluate the effects of the selective 5-HT7 receptor antagonist, SB-269970, and the antipsychotic drug with a high affinity for 5-HT7 receptors, amisulpride, on ketamine-induced deficits in attentional set-shifting and novel object recognition tasks in rats. Because the role of 5-HT7 receptor blockade in ameliorating positive and negative symptoms of schizophrenia remains equivocal, the second aim of these experiments was to examine the effectiveness of SB-269970 and amisulpride in reversing ketamine-induced deficits in prepulse inhibition of the startle reflex and in social interaction test in rats. The study revealed that acute administration of SB-269970 (1 mg/kg) or amisulpride (3 mg/kg) ameliorated ketamine-induced cognitive inflexibility and novel object recognition deficit in rats. Both compounds were also effective in attenuating ketamine-evoked disruption of social interactions. In contrast, neither SB-269970 nor amisulpride affected ketamine-disrupted prepulse inhibition or 50 kHz USVs accompanying social behaviour. In conclusion, antagonism of 5-HT7 receptors may represent a useful pharmacological approach in the treatment of cognitive deficits and some negative symptoms of schizophrenia.

Synthesis and dual D2 and 5-HT1A receptor binding affinities of 5-piperidinyl and 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones

A series of new 5-piperidinyl and 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones have been synthesized and evaluated for dual D2 and 5-HT1A receptor binding affinities. The synthesized ligands are structurally related to bifeprunox, a potential atypical antipsychotic, having potent D2 receptor antagonist and 5-HT1A receptor agonist properties. The Suzuki-Miyaura reaction of cyclic vinyl boronate with appropriate aryl halide yielded arylpiperidine, which was eventually transformed to piperidinyl-1H-benzo[d]imidazol-2(3H)-one. The reductive amination of the latter with appropriate biarylaldehdyes rendered the synthesis of 5-piperidinyl-1H-benzo[d]imidazol-2(3H)-ones. Likewise, the Buchwald-Hartwig coupling reactions of 1-boc-piperazine with appropriate aryl halide and subsequent removal of the boc group rendered arylpiperazine. The reductive amination of the latter with appropriate biarylaldehdyes accomplished the synthesis of 5-piperazinyl-1H-benzo[d]imidazol-2(3H)-ones. The structure-activity relationship studies showed that cyclopentenylpyridine and cyclopentenylbenzyl groups contribute significantly to the dual D2 and 5-HT1A receptor binding affinities of these compounds.

Effects of chronic oral treatment with aripiprazole on the expression of NMDA receptor subunits and binding sites in rat brain

RATIONALE

The glutamatergic theory of schizophrenia proposes a dysfunction of ionotropic N-methyl-D: -aspartate receptors (NMDA-R). Several therapeutic strategies address NMDA-R function and the effects of antipsychotic agents on NMDA-R expression have been described. Within the second-generation antipsychotics, the partial dopaminergic and serotonergic agonist aripiprazole (APZ) was able to counteract the behavioral effects of NMDA-R antagonists.

OBJECTIVES

This study aims to investigate the effects of APZ on NMDA-R subunit expression and binding.

METHODS

We treated Sprague-Dawley rats for 4 weeks or 4 months with APZ in daily oral doses of 10 and 40 mg per kilogram of body weight. Gene expression of the NMDA-R subunits NR1, NR2A, NR2B, NR2C, and NR2D, respectively, was assessed by semiquantitative radioactive in situ hybridization and in parallel receptor binding using (3)H-MK-801 receptor autoradiography.

RESULTS

Increased expression levels of NR1 (4 weeks), NR2A (4 weeks), NR2C (4 weeks and 4 months), and NR2D (4 months) were observed in several hippocampal and cortical brain regions. The parallel reduced expression of NR2B mRNAs (4 months) resulted in a relative increase of the NR2A/NR2B ratio. Marked differences between specific brain regions, the doses of APZ, and the time points of assessment became obvious. On the receptor level, increased MK-801-binding was found after 4 weeks in the 40-mg group and after 4 months in the 10-mg group.

CONCLUSIONS

The effects of APZ converge in enhanced NMDA receptor expression and a shift of subunit composition towards adult-type receptors. Our results confirm the regulatory connections between dopaminergic, serotonergic, and glutamatergic neurotransmissions with relevance for cognitive and negative symptoms of schizophrenia.

Comparative pharmacology of antipsychotics possessing combined dopamine D2 and serotonin 5-HT1A receptor properties

RATIONALE

There is increasing interest in antipsychotics intended to manage positive symptoms via D(2) receptor blockade and improve negative symptoms and cognitive deficits via 5-HT(1A) activation. Such a strategy reduces side-effects such as the extrapyramidal syndrome (EPS), weight gain, and autonomic disturbance liability.

OBJECTIVE

This study aims to review pharmacological literature on compounds interacting at both 5-HT(1A) and D(2) receptors (as well as at other receptors), including aripiprazole, perospirone, ziprasidone, bifeprunox, lurasidone and cariprazine, PF-217830, adoprazine, SSR181507, and F15063.

METHODS

We examine data on in vitro binding and agonism and in vivo tests related to (1) positive symptoms (e.g., psychostimulant-induced hyperactivity or prepulse inhibition deficit), (2) negative symptoms (e.g., phencyclidine-induced social interaction deficits and cortical dopamine release), and (3) cognitive deficits (e.g., phencyclidine or scopolamine-induced memory deficits). EPS liability is assessed by measuring catalepsy and neuroendocrine impact by determining plasma prolactin, glucose, and corticosterone levels.

RESULTS

Compounds possessing "balanced" 5-HT(1A) receptor agonism and D(2) antagonism (or weak partial agonism) and, in some cases, combined with other beneficial properties, such as 5-HT(2A) receptor antagonism, are efficacious in a broad range of rodent pharmacological models yet have a lower propensity to elicit EPS or metabolic dysfunction.

CONCLUSIONS

Recent compounds exhibiting combined 5-HT(1A)/D(2) properties may be effective in treating a broader range of symptoms of schizophrenia and be better tolerated than existing antipsychotics. Nevertheless, further investigations are necessary to evaluate recent compounds, notably in view of their differing levels of 5-HT(1A) affinity and efficacy, which can markedly influence activity and side-effect profiles.