Blockade of phencyclidine-induced effects by a nitric oxide donor

Meta-correlation of the effect of ketamine and psilocybin induced subjective effects on therapeutic outcome

There is some evidence that the subjective effects of ketamine and other psychedelics like psilocybin are crucial for their therapeutic outcomes, such as treatment of depression or substance use disorder (SUD). We performed a meta-analysis and systematic review on the correlation of subjective symptoms and dissociation versus ketamine-induced therapeutic outcomes in patients with depression or SUD. A similar analysis was conducted for psilocybin-induced therapeutic improvement. We retrieved 23 papers studying ketamine (21 on depression, 2 on SUD) in 471 patients and 8 papers studying psilocybin (6 on depression, 2 on SUD) in 183 patients. Our study demonstrated a modest role for subjective effects mediating therapeutic outcomes, with R2-values ranging from 5-10% for ketamine and for psilocybine the R2 was 24%. A greater mediating effect for psilocybin compared to ketamine was detected, particularly when restricting the analysis to depression. Additionally there is a greater mediating effect in SUD than depression, irrespective of treatment.

Nitric Oxide Donor Sodium Nitroprusside Reduces Racemic Ketamine-But Not Esketamine-Induced Pain Relief

The anesthetic, analgesic and antidepressant drug ketamine produces dissociation with symptoms of psychosis and anxiety, an effect attributed to neuronal nitric oxide depletion following N-methyl-d-aspartate blockade. There is evidence that dissociation induced by racemic ketamine, containing both ketamine enantiomers (S- and R-ketamine) but not esketamine (the S-isomer) is inhibited by nitric oxide (NO) donor sodium nitroprusside (SNP). We tested whether a similar intervention would reduce racemic and esketamine-induced analgesia in a randomized double-blind placebo-controlled trial. Seventeen healthy volunteers were treated with 0.5 μg.kg-1.min-1 SNP or placebo during a 3-h infusion of escalating doses of racemic ketamine (total dose 140 mg) or esketamine (70 mg). Pain pressure threshold (PPT) and arterial blood samples for measurement of S- and R-ketamine and their metabolites, S- and R-norketamine, were obtained. The data were analyzed with a population pharmacokinetic-pharmacodynamic model that incorporated the measured S- and R- ketamine and S- and R-norketamine isomers as input and PPT as output to the model. The potency of the 2 formulations in increasing PPT from baseline by 100% was 0.47 ± 0.12 (median ± standard error of the estimate) nmol/mL for esketamine and 0.62 ± 0.19 nmol/mL for racemic ketamine, reflecting the 52 ± 27% lower analgesic potency of R-ketamine versus S-ketamine. Modeling showed that SNP had no effect on S-ketamine potency but abolished the R-ketamine analgesic effect. Similar observations were made for S- and R-norketamine. Since SNP had no effect on S-ketamine analgesia, we conclude that SNP interacts on R-ketamine nociceptive pathways, possibly similar to its effects on R-ketamine activated dissociation pathways.

P2X7 purinergic receptor modulates dentate gyrus excitatory neurotransmission and alleviates schizophrenia-like symptoms in mouse

ATP-gated P2X7 receptors (P2X7Rs) play a crucial role in brain disorders. However, how they affect normal and pathological synaptic transmission is still largely unclear. Here, by using whole-cell patch-clamp technique to record AMPA- and NMDA receptor-mediated excitatory postsynaptic currents (s/mEPSCs) in dentate gyrus granule cells (DG GCs), we revealed a modulation by P2X7Rs of presynaptic sites, especially originated from entorhinal cortex (EC)-GC path but not the mossy cell (MC)-GC path. The involvement of P2X7Rs was confirmed using a pharmacological approach. Additionally, the acute activation of P2X7Rs directly elevated calcium influx from EC-GC terminals. In postnatal phencyclidine (PCP)-induced mouse model of schizophrenia, we observed that P2X7R deficiency restored the EC-GC synapse alteration and alleviated PCP-induced symptoms. To summarize, P2X7Rs participate in the modulation of GC excitatory neurotransmission in the DG via EC-GC pathway, contributing to pathological alterations of neuronal functions leading to neurodevelopmental disorders.

The Nitric Oxide (NO) Donor Molsidomine Counteract Social Withdrawal and Cognition Deficits Induced by Blockade of the NMDA Receptor in the Rat

The deficiency of the gaseous molecule nitric oxide (NO) seems to be critically involved in the pathogenesis of schizophrenia. Thus, molecules that can normalize NO levels, as are NO donors, might be of utility for the medication of this psychiatric disease. The aim of the present study was to detect the ability of the NO donor molsidomine to reduce schizophrenia-like impairments produced by the blockade of the N-methyl-D-aspartate (NMDA) receptor in rats. Molsidomine's ability to attenuate social withdrawal and spatial recognition memory deficits induced by the NMDA receptor antagonist ketamine were assessed using the social interaction and the object location test, respectively. Further, the efficacy of the combination of sub-effective doses of molsidomine with sub-effective doses of the atypical antipsychotic clozapine in alleviating non-spatial recognition memory deficits was evaluated utilizing the object recognition task. Molsidomine (2 and 4 mg/kg) attenuated social withdrawal and spatial recognition memory deficits induced by ketamine. Co-administration of inactive doses of molsidomine (1 mg/kg) and clozapine (0.1 mg/kg) counteracted delay-dependent and ketamine-induced non-spatial recognition memory deficits. The current findings suggest that molsidomine is sensitive to glutamate hypofunction since it attenuated behavioral impairments in animal models mimicking the negative symptoms and cognitive deficits of schizophrenia. Additionally, the present results support the potential of molsidomine as an adjunctive drug for the therapy of schizophrenia.

The efficacy and safety of sodium nitroprusside in the treatment of schizophrenia: Protocol for an updated systematic review and meta-analysis

BACKGROUND

Schizophrenia is a chronic persistent disease with high recurrence rate and high disability rate in the field of psychiatry. Sodium nitroprusside is a nitric oxide (NO) donor and considered a promising new compound for the treatment of schizophrenia. New high-quality clinical trials of sodium nitroprusside in the treatment of schizophrenia have been published in recent years. It is necessary to re-conduct the meta-analysis after the inclusion of these new clinical trials. Our study will conduct a systematic review and meta-analysis of the relevant literature in this field, so as to lay an evidence-based medicine foundation for the efficacy of sodium nitroprusside in the treatment of schizophrenia.

METHODS AND ANALYSIS

Randomized controlled trials (RCTs) of sodium nitroprusside in the treatment of schizophrenia were searched through English databases (PubMed, Web of Science, Embase, and Cochrane Library) and Chinese databases (China Biology Medicine disc, VIP, WanFang Data, and CNKI). The extracted data will be inputted into Review Manager 5.3 for Meta-analysis. The included literature will be assessed for bias risk according to the bias risk assessment tools in the Cochrane Handbook for Systematic Reviews of Interventions. Funnel plots will be used to assess possible publication bias. Heterogeneity is tested by I2 and χ2 tests, and the existence of heterogeneity is defined as I2 ≥50% and P ≤0.1. If heterogeneity exists, the random-effect model will be used, and sensitivity analysis or subgroup analysis will be performed to further determine the source of heterogeneity.

PROSPERO REGISTRATION NUMBER

CRD42022341681.

The Nitric Oxide (NO) Donor Sodium Nitroprusside (SNP) and Its Potential for the Schizophrenia Therapy: Lights and Shadows

Schizophrenia is a severe psychiatric disorder affecting up to 1% of the worldwide population. Available therapy presents different limits comprising lack of efficiency in attenuating negative symptoms and cognitive deficits, typical features of schizophrenia and severe side effects. There is pressing requirement, therefore, to develop novel neuroleptics with higher efficacy and safety. Nitric oxide (NO), an intra- and inter-cellular messenger in the brain, appears to be implicated in the pathogenesis of schizophrenia. In particular, underproduction of this gaseous molecule is associated to this mental disease. The latter suggests that increment of nitrergic activity might be of utility for the medication of schizophrenia. Based on the above, molecules able to enhance NO production, as are NO donors, might represent a class of compounds candidates. Sodium nitroprusside (SNP) is a NO donor and is proposed as a promising novel compound for the treatment of schizophrenia. In the present review, we intended to critically assess advances in research of SNP for the therapy of schizophrenia and discuss its potential superiority over currently used neuroleptics.

Treatment-resistant schizophrenia - A RCT on the effectiveness of repeated-dose sodium nitroprusside

OBJECTIVES

Sodium nitroprusside (SNP) has shown efficacy in schizophrenia in early stages of the disease in a previous study, but in more recent studies it has not shown efficacy in patients with longer disease duration. In present study, we evaluated the efficacy of repeated-dose SNP in treatment-resistant schizophrenia.

METHODS

This was a double-blind, randomized, placebo-controlled trial. Twenty DSM-IV schizophrenia subjects, aged 18-60 years, with a history of nonresponse to ≥2 trials of antipsychotics of adequate dose and duration (≥6 weeks) were enrolled. Participants received SNP or placebo 4-hour infusions at 0.5 μg/kg/min. A total of 4 infusions and 4 follow-up evaluations, with an interval of 2 weeks, were performed. Severity of symptoms were assessed by using Positive and Negative Syndrome Scale (PANSS), Brief Psychiatric Rating Scale (BPRS-18) and Clinical Global Impression (CGI) scales.

RESULTS

SNP and placebo groups did not differ at baseline or in change from baseline for PANSS-total (F = 0.525; p = 0.841), PANSS-positive (F = 0.32; p = 0.958), PANSS-negative (F = 1.05; p = 0.483), BPRS (F = 0.615; p = 0.734), or CGI-S (F = 1.11; p = 0.416) scores. SNP was well tolerated and showed a good safety profile.

CONCLUSION

Although preliminary, the present findings suggest that SNP is not efficacious in TRS, reinforcing previous studies that have not demonstrated symptom improvement in chronic schizophrenia subjects. At this time, it is conceivable to speculate that efficacy of SNP might be restricted to early stages of disease.

New insights on nitric oxide: Focus on animal models of schizophrenia

Schizophrenia is a devastating complex disorder characterised by a constellation of behavioral deficits with the underlying mechanisms not fully known. Nitric oxide (NO) has emerged as a key signaling molecule implicated in schizophrenia. Three nitric oxide sinthases (NOS), endothelial, neuronal, and inducible, release NO within the cell. Animal models of schizophrenia are grouped in four groups, neurovedelopmental, glutamatergic, dopaminergic and genetic. In this review, we aim to evaluate changes in NO levels in animal models of schizophrenia and the resulting long-lasting behavioral and neural consequences. In particular, NO levels are substantially modified, region-specific, in various neurodevelopmental models, e.g. bilateral excitotoxic lesion of the ventral hippocampus (nVHL), maternal immune activation and direct NO manipulations early in development, among others. In regards to glutamatergic models of schizophrenia, phencyclidine (PCP) administration increases NO levels in the prefrontal cortex (PFC) and ventral hippocampus. As far as genetic models are concerned, neuronal NOS knock-out mice display schizophrenia-related behaviors. Administration of NO donors can reverse schizophrenia-related behavioral deficits. While most modifications in NO are derived from neuronal NOS, recent evidence indicates that PCP treatment increases NO from the inducible NOS isoform. From a pharmacological perspective, treatment with various antipsychotics including clozapine, haloperidol and risperidone normalize NO levels in the PFC as well as improve behavioral deficits in nVHL rats. NO induced from the neuronal and inducible NOS is relevant to schizophrenia and warrants further research.

Glyceryl trinitrate in first-episode psychosis unmedicated with antipsychotics: A randomised controlled pilot study

BACKGROUND

There is a pressing need for new classes of treatment for psychosis. A key therapeutic target for novel compounds is the NMDA receptor, which may be modulated by nitric oxide donors such as sodium nitroprusside (SNP). Recent studies of SNP in patients with psychosis have mixed results, and the drug has to be administered intravenously. Glyceryl trinitrate (GTN) is a well-established cardiovascular medicine that is also a nitric oxide donor, and can be given orally.

AIMS

We explored the safety and potential effects of GTN in unmedicated patients with a first episode of psychosis.

METHODS

This was a single-centre, randomised, double-blind, placebo-controlled trial from December 2016 to April 2019 (ClinicalTrials.gov identifier: NCT02906553). Patients received 3 × sprays of GTN or placebo for three consecutive days, and were re-assessed on Days 1, 2, 3 and 7. The primary outcome was cognition (Jumping to Conclusions task), secondary outcomes were symptoms (Positive and Negative Syndrome Scale (PANSS)), verbal memory (Hopkins Verbal Learning task), and mood (Bond-Lader Visual Analogue Scales).

RESULTS

Nineteen patients were randomised, and 13 participants were included in the analyses. Compared with placebo, GTN was well tolerated, but was not associated with significant effects on cognition, symptoms, or mood. Bayesian statistics indicate that our results were 2× more likely under the null hypothesis than the alternative hypothesis, providing anecdotal evidence that GTN does not improve psychotic symptoms.

CONCLUSIONS

We found no indication of an effect of GTN on symptoms of psychosis or cognition.

Association Analysis of Neuronal Nitric Oxide Synthase 1 Gene Polymorphism With Psychopathological Symptoms in Chronic Ketamine Users

Objective: We previously found that chronic ketamine usages were associated with various psychotic and cognitive symptoms mimicking schizophrenia. The blockade of the NMDA receptor and subsequent nitric oxide synthase 1 (NOS1) dysfunction were found to be closely correlated with schizophrenia including NOS1 gene polymorphisms. We examined the allelic variants of the gene coding neuronal nitric oxide synthase 1 (NOS1) in chronic ketamine users in the Chinese population and analyzed the association between NOS1 gene polymorphism and psychopathological symptoms in chronic ketamine users. The association between the NOS1 polymorphism and ketamine use characteristics was also examined. Methods: One hundred ninety seven male chronic ketamine users and 82 controls were recruited. Four common SNPs of the NOS1 gene, rs6490121, rs41279104, rs3782206, and rs3782219, were examined by real-time PCR with the TaqMan® assay system. Psychopathological symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS), Beck Depression Inventory (BDI), and the Beck Anxiety Inventory (BAI). Results: The genotype distribution of rs6490121 and rs41279104 in chronic ketamine users was significantly different from that in the control (p = 0.0001 and p = 0.002). The G allele frequency of rs6490121 in ketamine users was higher than that in the control (p = 2.23 * 10^-6, OR = 3.07, 95% CI = 1.93-4.90). The T allele frequency of rs41279104 in chronic ketamine users was higher than that in the control (p = 0.01, OR = 1.76, 95% CI = 1.14-2.72). The BAI score was significantly different among the three genotypic groups of rs6490121 (F = 6.21, p = 0.002) in ketamine users; subjects of genotype AG and GG had a lower score than subjects of genotype AA. The score of the negative symptom subscale of PANSS was significantly different among the three genotypic groups of rs41279104 (F = 5.39, p = 0.005); in ketamine users, subjects of genotype CT and TT had a higher score than subjects of genotype CC. There was no difference in drug use characteristics in different genotypes of the four NOS1 gene polymorphisms tested in ketamine users (p > 0.05).

An electrochemical investigation into the effects of local and systemic administrations of sodium nitroprusside in brain extracellular fluid of mice

Sodium nitroprusside (SNP) is a nitric oxide (NO)-donor drug used clinically to treat severe hypertension, however, there are limitations associated with its mechanism of action that prevent widespread adoption. In particular, its impact on cerebral hemodynamics is controversial and direct evidence on its effects are lacking. Electrochemical methods provide an attractive option to undertake real time neurochemical measurements in situ using selective microsensors. Herein, we report the novel application of an existing platinum (Pt)-Nafion® sensor to measure the release of NO from SNP under in vitro and in vivo conditions. Initially, the temporal release of NO was measured and the effect of the reducing agent, ascorbic acid (AA), was elucidated in vitro. A combined microdialysis/NO sensor construct was implanted into the striatum of anaesthetised mice and the local perfusion of 10 mM SNP with/without AA resulted in increased NO concentration detected using the Pt-Nafion® sensor. Subsequently, the NO sensor, coupled with carbon paste electrodes (CPEs) for the electrochemical measurement of O₂, were applied to investigate SNP effects in freely moving mice. A complex mechanism of action was identified that infers NO inhibition and biphasic O₂ dynamics. The preliminary findings within support a strong cerebrovascular effect of systemic SNP administration that warrants careful consideration for clinical use.

Enhancement of the antipsychotic effect of risperidone by sodium nitroprusside in rats

Recently, a single injection of the nitric oxide donor sodium nitroprusside (SNP) was found to induce a rapid and sustained antipsychotic effect in treatment-resistant schizophrenia (TRS). Moreover, a single i.p. injection of SNP in rats was found to generate both rapid and persisting changes in brain synaptic plasticity, including enhanced excitatory postsynaptic current responses and spine morphology in layer V pyramidal cells in the medial prefrontal cortex (mPFC) brain slices. Here we used the conditioned avoidance response (CAR) test in rats to investigate the antipsychotic-like efficacy of SNP in combination with low-dose risperidone. In addition, we performed microdialysis experiments in freely moving rats to measure neurotransmitter efflux in the mPFC and the nucleus accumbens (NAc). Risperidone caused only 20% suppression of CAR, which is far below the degree of CAR suppression required to predict a significant clinical antipsychotic effect. Addition of a low dose of SNP to risperidone dramatically enhanced the antipsychotic-like effect to a clinically relevant level. SNP significantly enhanced the risperidone-induced dopamine output in the mPFC but not in the NAc. The increased prefrontal dopamine release induced by the drug combination may also improve cognition as indicated by previous preclinical and clinical studies and, furthermore, via enhanced synaptic spine function and morphology in mPFC generate a both rapid and prolonged antipsychotic and pro-cognitive effect. Our results delineate SNP as a promising new treatment option for schizophrenia, including TRS, when added to currently available antipsychotic medication in order to improve efficacy at maintained or even reduced dosage.

Effects of sodium nitroprusside in the acute dizocilpine (MK-801) animal model of schizophrenia

Schizophrenia treatment remains a major challenge, especially the associated cognitive impairments, as these are not consistently alleviated by conventional antipsychotics. Recent animal and clinical studies suggest that the nitric oxide (NO) donor sodium nitroprusside (SNP) reduces the psychiatric symptoms and cognitive deficits of schizophrenia. The present study was designed to investigate the efficacy of SNP against schizophrenia-like behavioral and cognitive deficits in the dizocilpine (MK-801) rat model. We used the rotarod and open field tests to identify the SNP dose which had no adverse effects on rat's exploratory and motor behavior, then established the schizophrenia model by injecting adult Sprague-Dawley rats intraperitoneally with MK-801 (0.4 mg/kg) with or without SNP pre-treatment. Behavioral changes were examined after 10 min. Prepulse inhibition (PPI) and the Y maze tests were conducted to assess cognitive deficits, and elevated plus maze and open field tests to assess anxiety-like behaviors. Preliminary rotarod and open field tests demonstrated that 2.5 mg/kg SNP had no effect on motor performance. Acute MK-801 treatment induced both cognitive deficits and anxiety. Co-administration of SNP (2.5 mg/kg) failed to improve these schizophrenia-like abnormalities. Sodium nitroprusside appears unable to improve schizophrenia-like symptoms and cognitive deficits induced by MK-801, inconsistent with the effectiveness of SNP as an adjunct therapy for anxiety disorders and working memory impairments in schizophrenia patients. Future studies are required to define an effective dose range for SNP monotherapy and adjunct therapy in different rodent models.

An Overview of Animal Models Related to Schizophrenia

Schizophrenia is a heterogeneous psychiatric disorder that is poorly treated with current therapies. In this brief review, we provide an update regarding the use of animal models to study schizophrenia in an attempt to understand its aetiology and develop novel therapeutic strategies. Tremendous progress has been made developing and validating rodent models that replicate the aetiologies, brain pathologies, and behavioural abnormalities associated with schizophrenia in humans. Here, models are grouped into 3 categories-developmental, drug induced, and genetic-to reflect the heterogeneous risk factors associated with schizophrenia. Each of these models is associated with varied but overlapping pathophysiology, endophenotypes, behavioural abnormalities, and cognitive impairments. Studying schizophrenia using multiple models will permit an understanding of the core features of the disease, thereby facilitating preclinical research aimed at the development and validation of better pharmacotherapies to alter the progression of schizophrenia or alleviate its debilitating symptoms.

Sodium nitroprusside treatment for psychotic symptoms and cognitive deficits of schizophrenia: A randomized, double-blind, placebo-controlled trial

Schizophrenia presents with a broad range of negative, positive, and cognitive symptoms, and comprehensive treatment is still a challenge. Sodium nitroprusside (SNP) has been reported to rapidly reduce psychotic symptoms and improve cognitive functions in patients with schizophrenia, providing a new possible direction for treatment. In this study, we tested whether SNP can improve psychotic symptoms and cognitive function in schizophrenia patients with longer disease history. This was a randomized, double-blind, placebo-controlled trial conducted between May 2016 and April 2017. Forty-two schizophrenia patients aged 18-45 years were recruited from Henan Province Mental Hospital. Baseline psychiatric symptoms were measured using the Positive and Negative Syndrome Scale (PANSS), and baseline cognitive functions were measured using the Wechsler Adult Intelligence Scale. Patients received two SNP or placebo infusions (0.5 μg/kg per min for 4 h) at a one-week interval. We reassessed psychiatric symptoms and cognitive functions using the same tests shortly after the first and second infusions and 4 weeks after the second infusion. We did not find any significant effect of SNP over placebo on psychotic symptoms or cognitive functions, although SNP was relatively well tolerated with a good safety profile.

The role of striatum and prefrontal cortex in the prevention of amphetamine-induced schizophrenia-like effects mediated by nitric oxide compounds

Pharmacological manipulation of nitric oxide (NO) has been suggested as a promising treatment for schizophrenia symptoms. A single infusion of sodium nitroprusside, a NO donor with short half-life, was found to improve schizophrenia symptoms. However, an increasing number of preclinical studies have demonstrated the potential beneficial effects of both NO donors and inhibitors. We investigated the potential synergistic effect of sub-effective doses of the NO donor sodium nitroprusside or the NO inhibitor 7-Nitroindazole (7NI) combined with clozapine, a standard atypical antipsychotic, on counteracting amphetamine or MK-801-induced psychosis-like behaviors. The impact of sodium nitroprusside and 7NI on cAMP regulation in the prefrontal cortex and striatum was also evaluated. Confirming previous results, we found that both NO donors and inhibitors prevented amphetamine-induced effects (prepulse inhibition [PPI] disruption and hyperlocomotion). In addition, we observed a synergistic effect of sodium nitroprusside and clozapine on antagonizing the disruptive effects of amphetamine, but not MK-801, in the PPI test. The sub-effective dose of 7NI tested did not prevent amphetamine or MK-induced PPI effects when combined with clozapine. Interestingly, cAMP levels were significantly decreased in the prefrontal cortex after treatment with sodium nitroprusside. In the striatum, both sodium nitroprusside and 7NI blocked the amphetamine-induced increase of cAMP. Our data corroborate previous findings on the dopaminergic mechanisms involved in the action of sodium nitroprusside. It is likely that the differential effects of sodium nitroprusside are related to its ability to modify cAMP levels in the prefrontal cortex.

Anticonvulsant effect of minocycline on pentylenetetrazole-induced seizure in mice: involvement of nitric oxide and N-methyl-d-aspartate receptor

Anticonvulsant effects of minocycline have been explored recently. This study was designed to examine the anticonvulsant effect of acute administration of minocycline on pentylenetetrazole-induced seizures in mouse considering the possible role of the nitric oxide/N-methyl-d-aspartate (NMDA) pathway. We induced seizure using intravenous administration of pentylenetetrazole. Our results showed that acute administration of minocycline increased the seizure threshold. Furthermore, co-administration of subeffective doses of the nonselective nitric oxide synthase (NOS) inhibitor NG-l-arginine methyl ester (10 mg/kg) and the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg) enhanced the anticonvulsant effect of subeffective doses of minocycline (40 mg/kg). We found that inducible NOS inhibitor aminoguanidine (100 mg/kg) had no effect on the antiseizure effect of minocycline. Moreover, l-arginine (60 mg/kg), as a NOS substrate, reduced the anticonvulsant effect of minocycline. We also demonstrated that pretreatment with the NMDA receptor antagonists ketamine (0.5 mg/kg) and MK-801 (0.05 mg/kg) increased the anticonvulsant effect of subeffective doses of minocycline. Results showed that minocycline significantly decreased the hippocampal nitrite level. Furthermore, co-administration of a neuronal NOS inhibitor like NMDA receptor antagonists augmented the effect of minocycline on the hippocampal nitrite level. In conclusion, we revealed that anticonvulsant effect of minocycline might be, at least in part, due to a decline in constitutive hippocampal nitric oxide activity as well as inhibition of NMDA receptors.

Sodium nitroprusside is effective in preventing and/or reversing the development of schizophrenia-related behaviors in an animal model: The SHR strain

AIMS

The treatment of schizophrenia with antipsychotics is still unsatisfactory. Therefore, the search for new treatments and prevention is crucial, and animal models are fundamental tools for this objective. Preclinical and clinical data evidence the antipsychotic profile of sodium nitroprusside (SNP), a nitric oxide (NO) donor. We aimed to investigate SNP in treating and/or preventing the schizophrenia-related behaviors presented by the spontaneously hypertensive rats (SHR) strain.

METHODS

Wistar rats (WR) and SHRs were submitted to two schemes of treatment: (i) a single injection of SNP or vehicle in adulthood; (ii) a long-term early treatment from 30 to 60 postnatal day with SNP or vehicle. The following behaviors were evaluated 24 hours after the acute treatment or 30 days after the long-term treatment: locomotion, social interaction, and contextual fear conditioning.

RESULTS

Spontaneously hypertensive rats presented hyperlocomotion, decreased social interaction, and impaired contextual fear conditioning. Single injection of SNP decreased social interaction in both strains and induced a deficit in contextual fear conditioning in WR. Oppositely, early treatment with SNP prevented the behavioral abnormalities in adult SHRs without promoting any effects in WR.

CONCLUSION

Our preclinical data point to SNP as a preventive and safe strategy with a broad range of effectiveness to the positive, negative, and cognitive symptoms of schizophrenia.

The antipsychotic landscape: dopamine and beyond

Until recently, the actions of antipsychotic and pro-psychotic drugs have largely been evaluated in the framework of neuronal doctrine - namely, that neurons communicate by releasing transmitters, and that psychiatric disorders are caused by neurotransmitter imbalances. Moreover, the majority of studies have focused on single transmitter systems - neglecting the fact that in the nervous system, different transmitter systems work in concert and impact on not only their immediate receptors but also downstream pathways that shape structural plasticity. In this review, we discuss the history of understanding the antipsychotic and pro-psychotic actions of drugs, recent developments and future perspectives.

Multidimensional Connectomics and Treatment-Resistant Schizophrenia: Linking Phenotypic Circuits to Targeted Therapeutics

Schizophrenia is a very complex syndrome that involves widespread brain multi-dysconnectivity. Neural circuits within specific brain regions and their links to corresponding regions are abnormal in the illness. Theoretical models of dysconnectivity and the investigation of connectomics and brain network organization have been examined in schizophrenia since the early nineteenth century. In more recent years, advancements have been achieved with the development of neuroimaging tools that have provided further clues to the structural and functional organization of the brain and global neural networks in the illness. Neural circuitry that extends across prefrontal, temporal and parietal areas of the cortex as well as limbic and other subcortical brain regions is disrupted in schizophrenia. As a result, many patients have a poor response to antipsychotic treatment and treatment failure is common. Treatment resistance that is specific to positive, negative, and cognitive domains of the illness may be related to distinct circuit phenotypes unique to treatment-refractory disease. Currently, there are no customized neural circuit-specific and targeted therapies that address this neural dysconnectivity. Investigation of targeted therapeutics that addresses particular areas of substantial regional dysconnectivity is an intriguing approach to precision medicine in schizophrenia. This review examines current findings of system and circuit-level brain dysconnectivity in treatment-resistant schizophrenia based on neuroimaging studies. Within a connectome context, on-off circuit connectivity synonymous with excitatory and inhibitory neuronal pathways is discussed. Mechanistic cellular, neurochemical and molecular studies are included with specific emphasis given to cell pathology and synaptic communication in glutamatergic and GABAergic systems. In this review we attempt to deconstruct how augmenting treatments may be applied within a circuit context to improve circuit integration and treatment response. Clinical studies that have used a variety of glutamate receptor and GABA interneuron modulators, nitric oxide-based therapies and a variety of other strategies as augmenting treatments with antipsychotic drugs are included. This review supports the idea that the methodical mapping of system-level networks to both on (excitatory) and off (inhibitory) cellular circuits specific to treatment-resistant disease may be a logical and productive approach in directing future research toward the advancement of targeted pharmacotherapeutics in schizophrenia.

MK-801-induced impairments on the trial-unique, delayed nonmatching-to-location task in rats: effects of acute sodium nitroprusside

RATIONALE

The cognitive symptoms observed in schizophrenia are not consistently alleviated by conventional antipsychotics. Following a recent pilot study, sodium nitroprusside (SNP) has been identified as a promising adjunct treatment to reduce the working memory impairments experienced by schizophrenia patients.

OBJECTIVE

The present experiments were designed to explore the effects of SNP on the highly translatable trial-unique, delayed nonmatching-to-location (TUNL) task in rats with and without acute MK-801 treatment.

METHODS

SNP (0.5, 1.0, 2.0, 4.0, and 5.0 mg/kg) and MK-801 (0.05, 0.075, and 0.1 mg/kg) were acutely administered to rats trained on the TUNL task.

RESULTS

Acute MK-801 treatment impaired TUNL task accuracy. Administration of SNP (2.0 mg/kg) with MK-801 (0.1 mg/kg) failed to rescue performance on TUNL. SNP (5.0 mg/kg) administration nearly 4 h prior to MK-801 (0.05 mg/kg) treatment had no preventative effect on performance impairments. SNP (2.0 mg/kg) improved performance on a subset of trials.

CONCLUSION

These results suggest that SNP may possess intrinsic cognitive-enhancing properties but is unable to block the effects of acute MK-801 treatment on the TUNL task. These results are inconsistent with the effectiveness of SNP as an adjunct therapy for working memory impairments in schizophrenia patients. Future studies in rodents that assess SNP as an adjunct therapy will be valuable in understanding the mechanisms underlying the effectiveness of SNP as a treatment for schizophrenia.

Potential role of amino acids in pathogenesis of schizophrenia

Schizophrenia is a syndrome of inconclusive etiopathogenesis with a prevalence of about 1% in general population. Underlying factors include genetic predisposition and defected neurodevelopment in early stages of life. The role of amino acids has been indicated in some reports. However, very few workers have detailed the effect of each amino acid in the pathophysiology of schizophrenia. Thus, in the present review, we aimed to provide an insight into the potential role of amino acids levels during schizophrenia. Any single amino acid defect cannot lead to the development of the disease. Higher concentration of glycine, serine, glutamate, homocysteine, and arginine are reported by many scientists in blood samples of patients of schizophrenia. Levels of rest of the amino acids show inconsistent results. Involvement of glutamate in pathophysiology of schizophrenia was hypothesized as early as the 1980s. It was demonstrated that dissociative anesthetics which are N-methyl-D-aspartate (NMDA) receptor antagonists can produce all negative, psychotic, cognitive, and physiological features of schizophrenia in healthy controls. This led to the development of hypothesis of NMDA receptor hypofunctioning in the pathophysiology of schizophrenia. Later on, it was also found that agents enhancing functioning of NMDA receptor at glycine modulatory site, improved symptoms in patients of schizophrenia receiving antipsychotic medications. Thus, the relationship of perturb amino acid levels with the biological basis and pathophysiology of schizophrenia is an important area to be further explored for effective management of schizophrenic patients.

The effect of sodium nitroprusside on psychotic symptoms and spatial working memory in patients with schizophrenia: a randomized, double-blind, placebo-controlled trial

BACKGROUND

Sodium nitroprusside (SNP) has been reported to rapidly reduce psychotic symptoms in patients with schizophrenia. This has the potential to revolutionize treatment for schizophrenia. In this study, we tested the hypothesis that SNP leads to a reduction in psychotic symptoms and an improvement in spatial working memory (SWM) performance in patients with schizophrenia.

METHOD

This was a single-centre, randomized, double-blind, placebo-controlled trial performed from 27 August 2014 to 10 February 2016 (clinicaltrials.gov identifier: NCT02176044). Twenty patients with schizophrenia aged 18-60 years with a diagnosis of schizophrenia or schizoaffective disorder were recruited from psychiatric outpatient clinics in the South London and Maudsley NHS Trust, London, UK. Baseline symptoms were measured using the Positive and Negative Syndrome Scale (PANSS) and the 18-item Brief Psychiatric Rating Scale (BPRS-18), and SWM was assessed using the CANTAB computerized test. Participants received either an infusion of SNP (0.5 μg/kg per min for 4 h) or placebo and were re-assessed for symptoms and SWM performance immediately after the infusion, and 4 weeks later.

RESULTS

SNP did not lead to any reduction in psychotic symptoms or improvement in SWM performance compared to placebo.

CONCLUSIONS

Although this study was negative, it is possible that the beneficial effects of SNP may occur in patients with a shorter history of illness, or with more acute exacerbation of symptoms.

Cytoarchitecture of nitrergic neurons in the human striatum and subthalamic nucleus

BACKGROUND

Nitric oxide (NO) is a gaseous molecule that modulates several physiological processes, including signal transmission in the central nervous system. There is evidence supporting NO as a major neurotransmitter involved in motor and emotion/behavior control. We investigated the distribution and morphology of nitrergic neurons in the two main input structures of the basal ganglia of human brain: the striatum and subthalamic nucleus.

METHODS

We studied samples of striatum (caudate and putamen) and subthalamic nucleus of 20 human brains from subjects without neurological/psychiatric diseases. The tissues were stained by histochemistry for nicotinamide adenine dinucleotide phosphate diaphorase activity and by immunohistochemistry for neuronal NO synthase (nNOS). Subsequently, we analyzed the nitrergic neuronal profile and its morphometric parameters.

RESULTS

Our data corroborate that approximately 2% of neurons in striatum express nNOS and these exhibited morphology characteristic of interneurons. Posterior regions of the striatum have a higher nitrergic neuronal profile than anterior regions of this nucleus suggesting an anteroposterior gradient of nitrergic neurons. Posterior limbic-associated areas of the striatum have a higher nitrergic neuronal profile compared to other functional subdivisions. Also, approximately 90% of neurons in the subthalamic nucleus express nNOS.

CONCLUSIONS

A remarkable presence of nitrergic neurons in the human striatum and subthalamic nucleus suggests that NO may play a critical role in the physiology of these nuclei.

The nitric oxide donor sodium nitroprusside attenuates recognition memory deficits and social withdrawal produced by the NMDA receptor antagonist ketamine and induces anxiolytic-like behaviour in rats

RATIONALE

Experimental evidence indicates that the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist ketamine impairs cognition and can mimic certain aspects of positive and negative symptoms of schizophrenia in rodents. Nitric oxide (NO) is considered as an intracellular messenger in the brain, and its abnormalities have been linked to schizophrenia.

OBJECTIVES

The present study was designed to investigate the ability of the NO donor sodium nitroprusside (SNP) to counteract schizophrenia-like behavioural deficits produced by ketamine in rats.

METHODS

The ability of SNP to reverse ketamine-induced memory deficits and social withdrawal were assessed using the novel object recognition task (NORT) and the social interaction test, respectively. Furthermore, since anxiety disorders are noted to occur commonly in schizophrenics, the effects of SNP on anxiety-like behaviour were examined using the light/dark test. Locomotor activity was also assessed as an independent measure of the potential motoric effects of this NO donor.

RESULTS

SNP (0.3 and 1 mg/kg) reversed ketamine (3 mg/kg)-induced short-term recognition memory deficits. SNP (1 mg/kg) counteracted the ketamine (8 mg/kg)-induced social isolation in the social interaction test. The anxiolytic-like effects in the light/dark test of SNP (1 mg/kg) cannot be attributed to changes in locomotor activity.

CONCLUSIONS

Our findings illustrate a functional interaction between the nitrergic and glutamatergic system that may be of relevance for schizophrenia-like behavioural deficits. The data also suggest a role of NO in anxiety.

Role of the nitric oxide donor sodium nitroprusside in the antidepressant effect of ketamine in mice

Ketamine may represent an efficient alternative antidepressant with rapid therapeutic onset; however, the clinical use of ketamine is hampered by psychosis-like side-effects. Recent studies suggest that the nitric oxide (NO) donor sodium nitroprusside (SNP) prevents psychosis-like abnormalities triggered by ketamine or another NMDA receptor (NMDAR) antagonist, phencyclidine (PCP) in rats. SNP was shown to elicit antipsychotic effects also in humans. Considering the tight interrelation between NMDAR activation and neuronal NO synthesis, we evaluated the effect of pre-treatment with SNP on the antidepressant action of ketamine. We found that SNP (0.5-1mg/kg, i.p.) did not alter the antidepressant effect of ketamine (30 mg/kg) in the Porsolt Forced Swim Test (FST) in mice. Additionally, SNP by itself produced no effect in the FST or in the openfield. This suggests indirectly a differential involvement of the nitrinergic system in the antidepressant vs. psychotomimetic effect of ketamine, although an influence of species-specific differences cannot be excluded in this interpretation.

Neurodevelopmental Animal Models Reveal the Convergent Role of Neurotransmitter Systems, Inflammation, and Oxidative Stress as Biomarkers of Schizophrenia: Implications for Novel Drug Development

Schizophrenia is a life altering disease with a complex etiology and pathophysiology, and although antipsychotics are valuable in treating the disorder, certain symptoms and/or sufferers remain resistant to treatment. Our poor understanding of the underlying neuropathological mechanisms of schizophrenia hinders the discovery and development of improved pharmacological treatment, so that filling these gaps is of utmost importance for an improved outcome. A vast amount of clinical data has strongly implicated the role of inflammation and oxidative insults in the pathophysiology of schizophrenia. Preclinical studies using animal models are fundamental in our understanding of disease development and pathology as well as the discovery and development of novel treatment options. In particular, social isolation rearing (SIR) and pre- or postnatal inflammation (PPNI) have shown great promise in mimicking the biobehavioral manifestations of schizophrenia. Furthermore, the "dual-hit" hypothesis of schizophrenia states that a first adverse event such as genetic predisposition or a prenatal insult renders an individual susceptible to develop the disease, while a second insult (e.g., postnatal inflammation, environmental adversity, or drug abuse) may be necessary to precipitate the full-blown syndrome. Animal models that emphasize the "dual-hit" hypothesis therefore provide valuable insight into understanding disease progression. In this Review, we will discuss SIR, PPNI, as well as possible "dual-hit" animal models within the context of the redox-immune-inflammatory hypothesis of schizophrenia, correlating such changes with the recognized monoamine and behavioral alterations of schizophrenia. Finally, based on these models, we will review new therapeutic options, especially those targeting immune-inflammatory and redox pathways.

Effects of nitric oxide-related compounds in the acute ketamine animal model of schizophrenia

Background

Better treatments for schizophrenia are urgently needed. The therapeutic use of the nitric oxide (NO)-donor sodium nitroprusside (SNP) in patients with schizophrenia has shown promising results. The role of NO in schizophrenia is still unclear, and NO modulation is unexplored in ketamine (KET) animal models to date. In the present study, we compared the behavioral effects of pre- and post-treatment with SNP, glyceryl trinitrate (GTN), and methylene blue (MB) in the acute KET animal model of schizophrenia.

The present study was designed to test whether acute SNP, GTN, and MB treatment taken after (therapeutic effect) or before (preventive effect) a single KET injection would influence the behavior of rats in the sucrose preference test, object recognition task and open field.

Results

The results showed that KET induced cognitive deficits and hyperlocomotion. Long- term memory improvement was seen with the therapeutic GTN and SNP treatment, but not with the preventive one. MB pretreatment resulted in long-term memory recovery. GTN pre-, but not post-treatment, tended to increase vertical and horizontal activity in the KET model. Therapeutic and preventive SNP treatment consistently decreased KET-induced hyperlocomotion.

Conclusion

NO donors – especially SNP – are promising new pharmacological candidates in the treatment of schizophrenia. In addition, we showed that the potential impact of NO-related compounds on KET-induced behavioral changes may depend on the temporal window of drug administration.

Nitroprusside single-dose prevents the psychosis-like behavior induced by ketamine in rats for up to one week

Recently, we found a rapid and long-lasting improvement of symptoms in schizophrenic patients on antipsychotics after a single four-hour infusion of sodium nitroprusside (SNP), a nitric oxide (NO) donor with a short half-life. This improvement persisted for up to 4weeks. Because these patients remained on antipsychotics after infusion of SNP was finished, the question arises about whether this improvement was due to SNP itself. We have now investigated whether SNP, alone, can produce preventive antipsychotic effects in rats treated with ketamine (KET). 56 adult rats divided into 7 groups were infused with SNP 4mg/kg, KET 25mg/kg, or saline as follows: group1 - saline, group2 - SNP, group3 - KET, group4 - KET 12h after SNP, group5 - KET 1day after SNP, group6 - KET 2days after SNP, and group7 - KET 1week after SNP. The animals were filmed in an open field arena for 30min and the videos were later analyzed by ANY-Maze software to measure activity and stereotypy. SNP significantly prevented the emergence of hyperactivity induced by KET when it was administered for up to 1week before KET, and prevented the emergence of stereotypies when it was administered for up to 1day before KET. These findings in rats, which have an even faster metabolic rate than humans, suggest that the long-lasting effects observed in our clinical trial with SNP in humans could have been due to SNP itself, and indicate for the first time that SNP may present preventive antipsychotic effects.

Enhanced dopamine-dependent hippocampal plasticity after single MK-801 application

Dopaminergic hyperfunction and N-methyl-D-aspartate receptor (NMDAR) hypofunction have both been implicated in psychosis. Dopamine-releasing drugs and NMDAR antagonists replicate symptoms associated with psychosis in healthy humans and exacerbate symptoms in patients with schizophrenia. Though hippocampal dysfunction contributes to psychosis, the impact of NMDAR hypofunction on hippocampal plasticity remains poorly understood. Here, we used an NMDAR antagonist rodent model of psychosis to investigate hippocampal long-term potentiation (LTP). We found that single systemic NMDAR antagonism results in a region-specific, presynaptic LTP at hippocampal CA1-subiculum synapses that is induced by activation of D1/D5 dopamine receptors and modulated by L-type voltage-gated Ca(2+) channels. Thereby, our findings may provide a cellular mechanism how NMDAR antagonism can lead to an enhanced hippocampal output causing activation of the hippocampus-ventral tegmental area-loop and overdrive of the dopamine system.

Anti-N-methyl-d-aspartate receptor encephalitis: review of clinical presentation, diagnosis and treatment

Anti-N-methyl-d-aspartate (NMDA) receptor encephalitis is a form of encephalitis occurring primarily in women and associated with antibodies against NR1 or NR2 subunits of the NMDA receptor. As a potentially treatable differential for symptoms and signs seen in neurology and psychiatric clinics, clinicians practising across the lifespan should be aware of this form of encephalitis. Common clinical features include auditory and visual hallucinations, delusions, behavioural change (frequently with agitation), impaired consciousness, motor disturbance (ranging from dyskinesia to catatonia), seizures, and autonomic dysfunction. We present a review of the literature on the disorder, including its clinical presentation, differential diagnosis, epidemiology, treatment and prognosis.

Glutamate and dopamine in schizophrenia: an update for the 21st century

The glutamate and dopamine hypotheses are leading theories of the pathoaetiology of schizophrenia. Both were initially based on indirect evidence from pharmacological studies supported by post-mortem findings, but have since been substantially advanced by new lines of evidence from in vivo imaging studies. This review provides an update on the latest findings on dopamine and glutamate abnormalities in schizophrenia, focusing on in vivo neuroimaging studies in patients and clinical high-risk groups, and considers their implications for understanding the biology and treatment of schizophrenia. These findings have refined both the dopamine and glutamate hypotheses, enabling greater anatomical and functional specificity, and have been complemented by preclinical evidence showing how the risk factors for schizophrenia impact on the dopamine and glutamate systems. The implications of this new evidence for understanding the development and treatment of schizophrenia are considered, and the gaps in current knowledge highlighted. Finally, the evidence for an integrated model of the interactions between the glutamate and dopamine systems is reviewed, and future directions discussed.

Role of nitric oxide in the regulation of motor function. An overview of behavioral, biochemical and histological studies in animal models

A compelling body of evidence suggests that nitric oxide (NO), a unique gaseous neurotransmitter and neuromodulator plays a key role in the regulation of motor function. Recently, the interest of researchers concentrates on the NO - soluble guanylyl cyclase (sGC) - cyclic GMP (cGMP) signaling pathway in the striatum as a new target for the treatment of Parkinson's disease (PD). The aim of the study is to review the available literature referring to the role of NO in the integration of basal ganglia functions. First, attention has been focused on behavioral effects of NO donors and neuronal nitric oxide synthase (nNOS) inhibitors in the modulation of motor behavior. Then, disturbances in the nitrergic neurotransmission in PD and its 6-OHDA animal model have been presented. Moreover, the most current data demonstrating the contribution of both dopamine and glutamate to the regulation of NO biosynthesis in the striatum have been analyzed. Finally, the role of NO in the tonic and phasic dopamine release as well as in the regulation of striatal output pathways also has been discussed.

Animal Models of Psychosis: Current State and Future Directions

Psychosis is an abnormal mental state characterized by disorganization, delusions and hallucinations. Animal models have become an increasingly important research tool in the effort to understand both the underlying pathophysiology and treatment of psychosis. There are multiple animal models for psychosis, with each formed by the coupling of a manipulation and a measurement. In this manuscript we do not address the diseases of which psychosis is a prominent comorbidity. Instead, we summarize the current state of affairs and future directions for animal models of psychosis. To accomplish this, our manuscript will first discuss relevant behavioral and electrophysiological measurements. We then provide an overview of the different manipulations that are combined with these measurements to produce animal models. The strengths and limitations of each model will be addressed in order to evaluate its cross-species comparability.

Critical role of nitric oxide in the modulation of prepulse inhibition in Swiss mice

RATIONALE

Nitric oxide (NO) modulates the dopamine uptake and release processes and appears to be implicated in dopamine-related pathologies, such as schizophrenia. However, it is unclear whether there is excess or deficient NO synthesis in schizophrenia pathophysiology. Analyses of the intracellular pathways downstream of NO system activation have identified the cyclic nucleotide cyclic guanosine monophosphate (cGMP) as a possible target for drug development. Defects in the sensorimotor gating of the neural mechanism underlying the integration and processing of sensory information have been detected across species through prepulse inhibition (PPI).

OBJECTIVES

The aim of this study was to investigate the effects of NO/cGMP increase on sensorimotor gating modulation during dopamine hyperfunction.

METHODS

Mice were treated with NO donors and subjected to the PPI test. Treatment with the NO donor sodium nitroprusside was preceded by pretreatment with a soluble guanylate cyclase (sGC) inhibitor. Additionally, the mice were treated with NO donors and phosphodiesterases inhibitors prior to amphetamine treatment.

RESULTS

Pretreatment with the NO donors enhanced the PPI response and attenuated the amphetamine-disruptive effects on the PPI. The sGC inhibitor did not modify the sodium nitroprusside effects. Additionally, the cGMP increase induced by a specific phosphodiesterase inhibitor did not modify the amphetamine-disruptive effect.

CONCLUSIONS

This study provides the first demonstration that an increase in NO can improve the PPI response and block the amphetamine-disruptive effects on the PPI response. Our data are consistent with recent clinical results. However, these effects do not appear to be related to an increase in cGMP levels, and further investigation is thus required.

Doxycycline restrains glia and confers neuroprotection in a 6-OHDA Parkinson model

Neuron-glia interactions play a key role in maintaining and regulating the central nervous system. Glial cells are implicated in the function of dopamine neurons and regulate their survival and resistance to injury. Parkinson's disease is characterized by the loss of dopamine neurons in the substantia nigra pars compacta, decreased striatal dopamine levels and consequent onset of extrapyramidal motor dysfunction. Parkinson's disease is a common chronic, neurodegenerative disorder with no effective protective treatment. In the 6-OHDA mouse model of Parkinson's disease, doxycycline administered at a dose that both induces/represses conditional transgene expression in the tetracycline system, mitigates the loss of dopaminergic neurons in the substantia nigra compacta and nerve terminals in the striatum. This protective effect was associated with: (1) a reduction of microglia in normal mice as a result of doxycycline administration per se; (2) a decrease in the astrocyte and microglia response to the neurotoxin 6-OHDA in the globus pallidus and substantia nigra compacta, and (3) the astrocyte reaction in the striatum. Our results suggest that doxycycline blocks 6-OHDA neurotoxicity in vivo by inhibiting microglial and astrocyte expression. This action of doxycycline in nigrostriatal dopaminergic neuron protection is consistent with a role of glial cells in Parkinson's disease neurodegeneration. The neuroprotective effect of doxycycline may be useful in preventing or slowing the progression of Parkinson's disease and other neurodegenerative diseases linked to glia function.

Information processing deficits and nitric oxide signalling in the phencyclidine model of schizophrenia

RATIONALE

Schizophrenia-like cognitive deficits induced by phencyclidine (PCP), a drug commonly used to model schizophrenia in experimental animals, are attenuated by nitric oxide (NO) synthase inhibitors. Furthermore, PCP increases NO levels and sGC/cGMP signalling in the prefrontal cortex in rodents. Hence, a cortical NO/sGC/cGMP signalling pathway may constitute a target for novel pharmacological therapies in schizophrenia.

OBJECTIVES

The objective of this study was to further investigate the role of NO signalling for a PCP-induced deficit in pre-attentive information processing.

MATERIALS AND METHODS

Male Sprague-Dawley rats were surgically implanted with NO-selective amperometric microsensors aimed at the prefrontal cortex, ventral hippocampus or nucleus accumbens, and NO levels and prepulse inhibition (PPI) were simultaneously assessed.

RESULTS

PCP treatment increased NO levels in the prefrontal cortex and ventral hippocampus, but not in the nucleus accumbens. The increase in NO levels was not temporally correlated to the deficit in PPI induced by PCP. Furthermore, pretreatment with the neuronal NO synthase inhibitor N-propyl-L-arginine dose-dependently attenuated both the increase in prefrontal cortex NO levels and the deficit in PPI.

CONCLUSIONS

These findings support a demonstrated role of NO in the behavioural and neurochemical effects of PCP. Furthermore, this effect is brain region-specific and mainly involves the neuronal isoform of NOS. However, a temporal correlation between a PCP-induced disruption of PPI and an increase in prefrontal cortex NO levels was not demonstrated, suggesting that the interaction between PCP and the NO system is more complex than previously thought.

GLT-1 expression and Glu uptake in rat cerebral cortex are increased by phencyclidine

Using western blottings, microdialysis, and functional assays we tested the hypothesis that phencyclidine (PCP) modifies the expression and function of glutamate (Glu) transporters in the rat frontal cortex. Western blotting studies revealed that administration of PCP (10 mg/kg/day; 7 days) increased significantly the expression of the astrocytic Glu transporter GLT-1/EAAT2. Functional studies showed that PCP increased significantly Na+-dependent Glu uptake in slices and in neuron/astrocyte co-cultures, and microdialysis studies evidenced that PCP treatment reduced basal Glu output. In our experimental conditions, PCP did not induce toxicity. These studies show that PCP increases the expression of GLT-1 in the cerebral cortex, thereby increasing Glu uptake and reducing extracellular [Glu].