Recovery of neuropsychological functions during reduction in use of phencyclidine

The effect of phencyclidine-mediated blockade of NMDA receptors in the early postnatal period on glutathione and sulfur amino acid levels in the rat brain as a potential causative factor of schizophrenia-like behavior in adulthood

BACKGROUND

Phencyclidine, an NMDA receptor antagonist, is frequently used to model behavioral and neurochemical changes correlated with schizophrenia in laboratory animals. The present study aimed to examine the effects of repeated administration of phencyclidine during early postnatal development on the contents of glutathione and sulfur-containing amino acids, as well as the activity of antioxidant enzymes in the brain of 12-day-old rats, and schizophrenia-like symptoms in adulthood.

METHODS

Male Sprague-Dawley pups were administered phencyclidine (10 mg/kg) or saline subcutaneously on the postnatal days p2, p6, p9 and p12. In 12-day-old pups, 4 h after the last dose of phencyclidine, the levels of glutathione, cysteine, methionine, and homocysteine, and the enzymatic activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR) were measured in the frontal cortex, hippocampus, and striatum. In 70-72-day-old rats, schizophrenia-like symptoms were assessed using behavioral tests.

RESULTS

Biochemical data showed that perinatal phencyclidine treatment significantly reduced glutathione and cysteine levels in all brain structures studied, methionine was diminished in the striatum, and homocysteine in both the frontal cortex and striatum. GR activity was increased in the frontal cortex while SODactivity was decreased in the hippocampus. Behaviorally, perinatal phencyclidine induced long-term deficits in social and cognitive function and a decrease in locomotor activity assessed as the time of walking. Finally, perinatal treatment with phencyclidine resulted in a significant reduction in body weight gain over time.

CONCLUSION

Our research provides further evidence for the usefulness of the phencyclidine-induced neurodevelopmental model of schizophrenia for studying the pathogenesis of schizophrenia.

Phencyclidine-Like Abuse Liability and Psychosis-Like Neurocognitive Effects of Novel Arylcyclohexylamine Drugs of Abuse in Rodents

Abuse of novel arylcyclohexylamines (ACX) poses risks for toxicities, including adverse neurocognitive effects. In vivo effects of ring-substituted analogs of phencyclidine (PCP), eticyclidine (PCE), and ketamine are understudied. Adult male National Institutes of Health Swiss mice were used to assess locomotor effects of PCP and its 3-OH, 3-MeO, 3-Cl, and 4-MeO analogs, PCE and its 3-OH and 3-MeO analogs, and ketamine and its deschloro and 2F-deschloro analogs, in comparison with those of methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA), and two benzofuran analogs of MDMA. PCP-like interoceptive effects for all of these ACXs were determined using a food-reinforced drug discrimination procedure in adult male Sprague Dawley rats. A novel operant assay of rule-governed behavior incorporating aspects of attentional set-shifting was used to profile psychosis-like neurocognitive effects of PCP and 3-Cl-PCP in rats, in comparison with cocaine and morphine. PCP-like ACXs were more effective locomotor stimulants than the amphetamines, PCE-like ACXs were as effective as the amphetamines, and ketamine-like ACXs were less effective than the amphetamines. Addition of -Cl, -OH, or -OMe at the 3-position on the aromatic ring did not impact locomotor effectiveness, but addition of -OMe at the 4-position reduced locomotor effectiveness. Lethal effects were induced by drugs with -OH at the 3-position or -OMe at the 3- or 4-position. All novel ACXs substituted at least partially for PCP, and PCP and 3-Cl-PCP elicited dose-dependent psychosis-like neurocognitive deficits in the rule-governed behavior task not observed with cocaine or morphine. Novel ACXs exhibit substantial abuse liability and toxicities not necessarily observed with their parent drugs. SIGNIFICANCE STATEMENT: Novel arylcyclohexylamine analogs of PCP, PCE, and ketamine are appearing on the illicit market, and abuse of these drugs poses risks for toxicities, including adverse neurocognitive effects. These studies demonstrate that the novel ACXs exhibit PCP-like abuse liability in the drug discrimination assay, elicit varied locomotor stimulant and lethal effects in mice, and induce psychosis-like neurocognitive effects in rats.

Use of Quantitative Electroencephalography to Inform Age- and Sex-Related Differences in NMDA Receptor Function Following MK-801 Administration

Sex- and age-related differences in symptom prevalence and severity have been widely reported in patients with schizophrenia, yet the underlying mechanisms contributing to these differences are not well understood. N-methyl-D-aspartate (NMDA) receptor hypofunction contributes to schizophrenia pathology, and preclinical models often use NMDA receptor antagonists, including MK-801, to model all symptom clusters. Quantitative electroencephalography (qEEG) represents a translational approach to measure neuronal activity, identify targetable biomarkers in neuropsychiatric disorders and evaluate possible treatments. Abnormalities in gamma power have been reported in patients with schizophrenia and correspond to psychosis and cognitive impairment. Further, as gamma power reflects cortical glutamate and GABA signaling, it is highly sensitive to changes in NMDA receptor function, and NMDA receptor antagonists aberrantly increase gamma power in rodents and humans. To evaluate the role of sex and age on NMDA receptor function, MK-801 (0.03-0.3 mg/kg, SC) was administered to 3- and 9-month-old male and female Sprague-Dawley rats that were implanted with wireless EEG transmitters to measure cortical brain function. MK-801-induced elevations in gamma power were observed in 3-month-old male and female and 9-month-old male rats. In contrast, 9-month-old female rats demonstrated blunted maximal elevations across a wide dose range. Importantly, MK-801-induced hyperlocomotor effects, a common behavioral screen used to examine antipsychotic-like activity, were similar across all groups. Overall, sex-by-age-related differences in gamma power support using qEEG as a translational tool to evaluate pathological progression and predict treatment response across a heterogeneous population.

A Kpna1-deficient psychotropic drug-induced schizophrenia model mouse for studying gene-environment interactions

KPNA1 is a mediator of nucleocytoplasmic transport that is abundantly expressed in the mammalian brain and regulates neuronal differentiation and synaptic function. De novo mutations in Kpna1 have been identified using genome-wide association studies in humans with schizophrenia; however, it remains unclear how KPNA1 contributes to schizophrenia pathogenesis. Recent studies have suggested a complex combination of genetic and environmental factors that are closely related to psychiatric disorders. Here, we found that subchronic administration of phencyclidine, a psychotropic drug, induced vulnerability and behavioral abnormalities consistent with the symptoms of schizophrenia in Kpna1-deficient mice. Microarray assessment revealed that the expression levels of dopamine d1/d2 receptors, an RNA editing enzyme, and a cytoplasmic dynein component were significantly altered in the nucleus accumbens brain region in a gene-environment (G × E) interaction-dependent manner. Our findings demonstrate that Kpna1-deficient mice may be useful as a G × E interaction mouse model for psychiatric disorders and for further investigation into the pathogenesis of such diseases and disorders.

Subchronic PCP effects on DNA methylation and protein expression of NMDA receptor subunit genes in the prefrontal cortex and hippocampus of female rats

BACKGROUND

N-methyl-d-aspartate receptor (NMDAR) dysfunction is implicated in schizophrenia, and NMDAR antagonists, such as phencyclidine (PCP), can induce behaviours that mimic aspects of the disorder.

AIMS

We investigated DNA methylation of Grin1, Grin2a and Grin2b promoter region and NR1 and NR2 protein expression in the prefrontal cortex (PFC) and hippocampus of adult female Lister-hooded rats following subchronic PCP (scPCP) administration. We also determined whether any alterations were tissue-specific.

METHODS

Rats were divided into two groups that received vehicle (0.9% saline) or 2 mg/kg PCP twice a day for 7 days (n = 10 per group). After behavioural testing (novel object recognition), to confirm a cognitive deficit, brains were dissected and NMDAR subunit DNA methylation and protein expression were analysed by pyrosequencing and ELISA. Line-1 methylation was determined as a measure of global methylation. Data were analysed using Student's t-test and Pearson correlation.

RESULTS

The scPCP administration led to Grin1 and Grin2b hypermethylation and reduction in NR1 protein in both PFC and hippocampus. No significant differences were observed in Line-1 or Grin2a methylation and NR2 protein.

CONCLUSIONS

The scPCP treatment resulted in increased DNA methylation at promoter sites of Grin1 and Grin2b NMDAR subunits in two brain areas implicated in schizophrenia, independent of any global change in DNA methylation, and are similar to our observations in a neurodevelopmental animal model of schizophrenia - social isolation rearing post-weaning. Moreover, these alterations may contribute to the changes in protein expression for NMDAR subunits demonstrating the potential importance of epigenetic mechanisms in schizophrenia.

Dysregulation of Epigenetic Control Contributes to Schizophrenia-Like Behavior in Ebp1+/- Mice

Dysregulation of epigenetic machinery can cause a variety of neurological disorders associated with cognitive abnormalities. In the hippocampus of postmortem Schizophrenia (SZ) patients, the most notable finding is the deregulation of GAD67 along with differential regulation of epigenetic factors associated with glutamate decarboxylase 67 (GAD67) expression. As we previously reported, ErbB3-binding protein 1 (EBP1) is a potent epigenetic regulator. EBP1 can induce repression of Dnmt1, a well-studied transcriptional repressor of GAD67. In this study, we investigated whether EBP1 contributes to the regulation of GAD67 expression in the hippocampus, controlling epigenetic machinery. In accordance with SZ-like behaviors in Ebp1^(+/−) mice, heterozygous deletion of EBP1 led to a dramatic reduction of GAD67 expression, reflecting an abnormally high level of Dnmt1. Moreover, we found that EBP1 binds to the promoter region of HDAC1, which leads to histone deacetylation of GAD67, and suppresses histone deacetylase 1 (HDAC1) expression, inversely mirroring an unusually high level of HDAC1 in Ebp1^(+/−) mice. However, EBP1 mutant (p.Glu 183 Ter) found in SZ patients did not elevate the expression of GAD67, failing to suppress Dnmt1 and/or HDAC1 expression. Therefore, this data supports the hypothesis that a reduced amount of EBP1 may contribute to an etiology of SZ due to a loss of transcriptional inhibition of epigenetic repressors, leading to a decreased expression of GAD67.

NMDAR Hypofunction Animal Models of Schizophrenia

The N-methyl-d-aspartate receptor (NMDAR) hypofunction hypothesis has been proposed to help understand the etiology and pathophysiology of schizophrenia. This hypothesis was based on early observations that NMDAR antagonists could induce a full range of symptoms of schizophrenia in normal human subjects. Accumulating evidence in humans and animal studies points to NMDAR hypofunctionality as a convergence point for various symptoms of schizophrenia. Here we review animal models of NMDAR hypofunction generated by pharmacological and genetic approaches, and how they relate to the pathophysiology of schizophrenia. In addition, we discuss the limitations of animal models of NMDAR hypofunction and their potential utility for therapeutic applications.

Serotonin and Glutamate Interactions in Preclinical Schizophrenia Models

The serotonergic and glutamatergic neurotransmitter systems have both been implicated in the pathophysiology of schizophrenia, and there are multiple lines of evidence to demonstrate that they can interact in a functionally relevant manner. Particularly, it has been demonstrated that serotonin (5-hydroxytryptamine) 2A (5-HT_2A) receptors and metabotropic glutamate type 2 (mGlu2) receptors can assemble into a functional heteromeric complex and modulate each other's function. This heteromeric complex has been implicated in the mechanism of action of hallucinogens as well as antipsychotic agents, and its role has been demonstrated in both in vitro and in vivo systems. Additionally, the difference in the changes in G_i/o and G_q/11 protein activity when a ligand binds to the heteromeric complex can be used as an index to predict the pro- or antipsychotic properties of an agent. Signaling via the heteromer is dysregulated in postmortem human brain samples of schizophrenia subjects, which may be linked to altered cortical functions. Alternative routes for the functional crosstalk between mGlu2 and 5-HT_2A receptors include synaptic and epigenetic mechanisms. This Review highlights the advances made over the past few years in elucidating the structural and functional mechanisms underlying crosstalk between 5-HT_2A and mGlu2 receptors in preclinical models of schizophrenia.

Chronic phencyclidine treatment impairs spatial working memory in rhesus monkeys

RATIONALE

Phencyclidine (PCP) could induce schizophrenia (Sz) like behavior in both humans and animals, therefore, has been widely utilized to establish Sz animal models. It induced cognitive deficits, the core symptom of Sz, mainly through influencing frontal dopaminergic function. Nonhuman primate (NHP) studies demonstrated impaired object retrieval detour (ORD) and spatial delayed response (SDR) task performance by acute or chronic PCP treatment. However, NHP investigations, continually monitoring SDR performance before, during and after PCP treatment, are lacking.

OBJECTIVES

Present study investigated the long-term influence of chronic PCP treatment on SDR performance and the possible increase of SDR deficit severity and duration by the incremental dosing procedure in rhesus monkeys.

METHODS

SDR task was performed repeatedly up to eight weeks after constant dosing procedure (i.m., 0.3 mg/kg, day 12-25), during which drug effects on locomotor activity and blood cortisol concentration were assessed. Incremental dosing procedure (starting dose 0.3 mg/kg, day 6-19) began five months later.

RESULTS

Constant dosing procedure induced differential level of hyperactivity across testing days, without significant influence on blood cortisol concentration. It reduced SDR performance, until occurrence of the first and worst impairment on day 15 and 23 respectively. The impaired performance recovered to pretreatment level over one week after drug cessation. In contrast, incremental dosing procedure impaired SDR performance on the first treatment day, which recovered within treatment period.

CONCLUSION

Results suggested increase of SDR deficit severity by repeated PCP administrations, whereas the incremental dosing procedure did not increase SDR deficit severity and duration.

DARK Classics in Chemical Neuroscience: Phencyclidine (PCP)

Phencyclidine (PCP, "angel dust", an arylcyclohexylamine) was the first non-natural, man-made illicit drug of abuse, and was coined 'the most dangerous drug in America" in the late 1970s (amidst sensational horror stories of the drug's effects); however, few other illicit drugs have had such a significant and broad impact on society-both good and bad. Originally developed as a new class of anesthetic, PCP-derived psychosis gave way to the PCP hypothesis of schizophrenia (later coined the NMDA receptor hypofunction hypothesis or the glutamate hypothesis of schizophrenia), which continues to drive therapeutic discovery for schizophrenia today. PCP also led to the discovery of ketamine (and a new paradigm for the treatment of major depression), as well as other illicit, designer drugs, such as methoxetamine (MXE) and a new wave of Internet commerce for illicit drugs (sold as research chemicals, or RCs). Furthermore, PCP is a significant contaminant/additive of many illegal drugs sold today, due to its ease of preparation by clandestine chemists. Here, we will review the history, importance, synthesis (both legal and clandestine), pharmacology, drug metabolism, and folklore of PCP, a true DARK classic in chemical neuroscience.

Deconstructing Schizophrenia: Advances in Preclinical Models for Biomarker Identification

Schizophrenia is considered to develop as a consequence of genetic and environmental factors impacting on brain neural systems and circuits during vulnerable neurodevelopmental periods, thereby resulting in symptoms in early adulthood. Understanding of the impact of schizophrenia risk factors on brain biology and behaviour can help in identifying biologically relevant pathways that are attractive for informing clinical studies and biomarker development. In this chapter, we emphasize the importance of adopting a reciprocal forward and reverse translation approach that is iteratively updated when additional new information is gained, either preclinically or clinically, for offering the greatest opportunity for discovering panels of biomarkers for the diagnosis, prognosis and treatment of schizophrenia. Importantly, biomarkers for identifying those at risk may inform early intervention strategies prior to the development of schizophrenia.Given the emerging nature of this approach in the field, this review will highlight recent research of preclinical biomarkers in schizophrenia that show the most promise for informing clinical needs with an emphasis on relevant imaging, electrophysiological, cognitive behavioural and biochemical modalities. The implementation of this reciprocal translational approach is exemplified firstly by the production and characterization of preclinical models based on the glutamate hypofunction hypothesis, genetic and environmental risk factors for schizophrenia (reverse translation), and then the recent clinical recognition of the thalamic reticular thalamus (TRN) as an important locus of brain dysfunction in schizophrenia as informed by preclinical findings (forward translation).

Glutamatergic Dysfunction and Glutamatergic Compounds for Major Psychiatric Disorders: Evidence From Clinical Neuroimaging Studies

Excessive glutamate release has been linked to stress and many neurodegenerative diseases. Evidence indicates abnormalities of glutamatergic neurotransmission or glutamatergic dysfunction as playing an important role in the development of many major psychiatric disorders (e.g., schizophrenia, bipolar disorder, and major depressive disorder). Recently, ketamine, an N-methyl-d-aspartate antagonist, has been demonstrated to have promisingly rapid antidepressant efficacy for treatment-resistant depression. Many compounds that target the glutamate system have also become available that possess potential in the treatment of major psychiatric disorders. In this review, we update evidence from recent human studies that directly or indirectly measured glutamatergic neurotransmission and function in major psychiatric disorders using modalities such as magnetic resonance spectroscopy, positron emission tomography/single-photon emission computed tomography, and paired-pulse transcranial magnetic stimulation. The newer generation of antidepressants that target the glutamatergic system developed in human clinical studies is also reviewed.

Altered cortico-striatal crosstalk underlies object recognition memory deficits in the sub-chronic phencyclidine model of schizophrenia

The neural mechanisms underlying cognitive deficits in schizophrenia are poorly understood. Sub-chronic treatment with the NMDA antagonist phencyclidine (PCP) produces cognitive abnormalities in rodents that reliably model aspects of the neurocognitive alterations observed in schizophrenia. Given that network activity across regions encompassing medial prefrontal cortex (mPFC) and nucleus accumbens (NAc) plays a significant role in motivational and cognitive tasks, we measured activity across cortico-striatal pathways in PCP-treated rats to characterize neural enabling and encoding of task performance in a novel object recognition task. We found that PCP treatment impaired task performance and concurrently (1) reduced tonic NAc neuronal activity, (2) desynchronized cross-activation of mPFC and NAc neurons, and (3) prevented the increase in mPFC and NAc neural activity associated with the exploration of a novel object in relation to a familiar object. Taken together, these observations reveal key neuronal and network-level adaptations underlying PCP-induced cognitive deficits, which may contribute to the emergence of cognitive abnormalities in schizophrenia.

Glutamatergic regulation of cognition and functional brain connectivity: insights from pharmacological, genetic and translational schizophrenia research

The pharmacological modulation of glutamatergic neurotransmission to improve cognitive function has been a focus of intensive research, particularly in relation to the cognitive deficits seen in schizophrenia. Despite this effort, there has been little success in the clinical use of glutamatergic compounds as procognitive drugs. Here, we review a selection of the drugs used to modulate glutamatergic signalling and how they impact on cognitive function in rodents and humans. We highlight how glutamatergic dysfunction, and NMDA receptor hypofunction in particular, is a key mechanism contributing to the cognitive deficits observed in schizophrenia and outline some of the glutamatergic targets that have been tested as putative procognitive targets for this disorder. Using translational research in this area as a leading exemplar, namely, models of NMDA receptor hypofunction, we discuss how the study of functional brain network connectivity can provide new insight into how the glutamatergic system impacts on cognitive function. Future studies characterizing functional brain network connectivity will increase our understanding of how glutamatergic compounds regulate cognition and could contribute to the future success of glutamatergic drug validation. Linked Articles This article is part of a themed section on Pharmacology of Cognition: a Panacea for Neuropsychiatric Disease? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.19/issuetoc.

Prolonged deficits of associative motor learning in cynomolgus monkeys after long-term administration of phencyclidine

Phencyclidine (PCP) is a potent drug of abuse that induces sustained schizophrenia-like symptoms in humans by blocking neurotransmission at N-methyl-d-aspartate (NMDA)-type glutamate receptors. Alterations in NMDA receptor function have been linked to numerous behavioral deficits and cognitive dysfunction. Classical eye-blink conditioning (EBC), including delay (dEBC) and trace (tEBC) paradigms, provides an effective means to study the neurobiology of associative motor learning in rodents, mammals and primates. To assess whether administration of low-dosage PCP for extended periods has prolonged effect to alter associative motor learning, in this study 19 adult cynomolgus monkeys were administered PCP (0.3mg/kg, intramuscularly) or saline twice a day for 14days. Twelve-fifteen months after PCP or saline injection, monkeys received dEBC, tEBC, or pseudo-paired training for 6 or 12 successive daily sessions, respectively. The results of this study show that percentage of conditioned response (CR) in dEBC increased as a function of training sessions in both PCP-treated and control monkeys and there was no significant CR% difference between the two groups. However, the CR timing in dEBC of PCP-treated monkeys was significantly impaired, as manifested by shorter CR peak latencies than those of the control group. PCP-treated animals showed significantly lower percentage of CR in tEBC compared to controls. PCP-treated animals were also more sensitive to outside stimuli in tEBC because the UR peak latency of PCP-treated group was significantly lower than the control group. These results indicated that cynomolgus monkeys manifested prolonged deficits in associative motor learning after long-term administration of phencyclidine.

Targeting metabotropic glutamate receptors for novel treatments of schizophrenia

Support for the N-methyl-D-aspartate receptor (NMDAR) hypofunction hypothesis of schizophrenia has led to increasing focus on restoring proper glutamatergic signaling as an approach for treatment of this devastating disease. The ability of metabotropic glutamate (mGlu) receptors to modulate glutamatergic neurotransmission has thus attracted considerable attention for the development of novel antipsychotics. Consisting of eight subtypes classified into three groups based on sequence homology, signal transduction, and pharmacology, the mGlu receptors provide a wide range of targets to modulate NMDAR function as well as glutamate release. Recently, allosteric modulators of mGlu receptors have been developed that allow unprecedented selectivity among subtypes, not just groups, facilitating the investigation of the effects of subtype-specific modulation. In preclinical animal models, positive allosteric modulators (PAMs) of the group I mGlu receptor mGlu5 have efficacy across all three symptom domains of schizophrenia (positive, negative, and cognitive). The discovery and development of mGlu5 PAMs that display unique signal bias suggests that efficacy can be retained while avoiding the neurotoxic effects of earlier compounds. Interestingly, mGlu1 negative allosteric modulators (NAMs) appear efficacious in positive symptom models of the disease but are still in early preclinical development. While selective group II mGlu receptor (mGlu2/3) agonists have reached clinical trials but were unsuccessful, specific mGlu2 or mGlu3 receptor targeting still hold great promise. Genetic studies implicated mGlu2 in the antipsychotic effects of group II agonists and mGlu2 PAMs have since entered into clinical trials. Additionally, mGlu3 appears to play an important role in cognition, may confer neuroprotective effects, and thus is a promising target to alleviate cognitive deficits in schizophrenia. Although group III mGlu receptors (mGlu4/6/7/8) have attracted less attention, mGlu4 agonists and PAMs appear to have efficacy across all three symptoms domains in preclinical models. The recent discovery of heterodimers comprising mGlu2 and mGlu4 may explain the efficacy of mGlu4 selective compounds but this remains to be determined. Taken together, compounds targeting mGlu receptors, specifically subtype-selective allosteric modulators, provide a compelling alternative approach to fill the unmet clinical needs for patients with schizophrenia.

Synapse pathology and translational applications for schizophrenia

Schizophrenia is a chronic, severe, and disabling brain disorder, with an estimated lifetime prevalence of 0.7%. Despite its relatively low prevalence, the onset of schizophrenia usually occurs early in life, resulting in a severe lifelong disability for patients and increasing the economic and care burden on their families. This makes schizophrenia one of the most catastrophic mental illnesses. Although the etiology of schizophrenia remains poorly understood, clinical, genetic, and pharmacological studies have indicated that its pathophysiology involves synaptic disturbances. Here, I review the evidence suggesting synaptic disturbance as the causal pathophysiology of schizophrenia and discuss the possible application of synaptic intervention as a novel therapeutic strategy for schizophrenia.

REVIEW ■ : Long-lasting Effects of Recreational Drugs of Abuse on the Central Nervous System

Although a wealth of knowledge exists regarding the acute pharmacological effects of recreational drugs on the CNS, much less is known about the long-term toxic effects of recreational drugs on the CNS. Recent findings in nonhuman primates treated with amphetamine analogs, such as ±3,4-methylenedioxymetham phetamine (MDMA), indicate that these drugs can produce long-lasting, probably permanent, changes in brain serotonin innervation. Similarly, animals treated with phencyclidine (PCP) and related drugs develop neurodegenerative changes in selected brain regions. It seems clear, then, that some psychoactive drugs have the potential to produce persistent changes in CNS structure and, possibly, function. The goal of this article is to summarize current knowledge regarding the long-term effects of several popular recreational drugs, including MDMA and related amphetamine analogs, cocaine, marijuana, alcohol, PCP, lysergic acid (LSD), and opiates. Gaps in the current knowledge base are identified, and areas ripe for future research efforts are suggested. NEUROSCIENTIST 3:399-411, 1997

Dopamine D1 receptor activation improves PCP-induced performance disruption in the 5C-CPT by reducing inappropriate responding

Attentional deficits contribute significantly to the functional disability of schizophrenia patients. The 5-choice continuous performance test (5C-CPT) measures attention in mice, rats, and humans, requiring the discrimination of trial types that either require a response or the inhibition of a response. The 5C-CPT, one version of human continuous performance tests (CPT), enables attentional testing in rodents in a manner consistent with humans. Augmenting the prefrontal cortical dopaminergic system has been proposed as a therapeutic target to attenuate the cognitive disturbances associated with schizophrenia. Using translational behavioural tasks in conjunction with inducing conditions relevant to schizophrenia pathophysiology enable the assessment of pro-attentive properties of compounds that augment dopaminergic activity. Here, using a repeated phencyclidine (PCP) treatment regimen and the 5C-CPT paradigm, we assess the pro-attentive properties of SKF 38393, a dopamine D1 receptor agonist, in rats. We show that repeated PCP treatment induces robust deficits in 5C-CPT performance indicative of impaired attention. Pre-treatment with SKF 38393 partially attenuates the PCP-induced deficits in 5C-CPT performance by reducing false alarm responding and increasing response accuracy. Impaired target detection was still evident in SKF 38393-treated rats however. Thus, augmentation of the dopamine D1 system improves PCP-induces deficits in 5C-CPT performance by selectively reducing aspects of inappropriate responding. These findings provide evidence to support the hypothesis that novel therapies targeting the dopamine D1 receptor system could improve aspects of attentional deficits in schizophrenia patients.

The subchronic phencyclidine rat model: relevance for the assessment of novel therapeutics for cognitive impairment associated with schizophrenia

RATIONALE

Current treatments for schizophrenia have modest, if any, efficacy on cognitive dysfunction, creating a need for novel therapies. Their development requires predictive animal models. The N-methyl-D-aspartate (NMDA) hypothesis of schizophrenia indicates the use of NMDA antagonists, like subchronic phencyclidine (scPCP) to model cognitive dysfunction in adult animals.

OBJECTIVES

The objective of this study was to assess the scPCP model by (1) reviewing published findings of scPCP-induced neurochemical changes and effects on cognitive tasks in adult rats and (2) comparing findings from a multi-site study to determine scPCP effects on standard and touchscreen cognitive tasks.

METHODS

Across four research sites, the effects of scPCP (typically 5 mg/kg twice daily for 7 days, followed by at least 7-day washout) in adult male Lister Hooded rats were studied on novel object recognition (NOR) with 1-h delay, acquisition and reversal learning in Morris water maze and touchscreen-based visual discrimination.

RESULTS

Literature findings showed that scPCP impaired attentional set-shifting (ASST) and NOR in several labs and induced a variety of neurochemical changes across different labs. In the multi-site study, scPCP impaired NOR, but not acquisition or reversal learning in touchscreen or water maze. Yet, this treatment regimen induced locomotor hypersensitivity to acute PCP until 13-week post-cessation.

CONCLUSIONS

The multi-site study confirmed that scPCP impaired NOR and ASST only and demonstrated the reproducibility and usefulness of the touchscreen approach. Our recommendation, prior to testing novel therapeutics in the scPCP model, is to be aware that further work is required to understand the neurochemical changes and specificity of the cognitive deficits.

Hippocampal Proteomic and Metabonomic Abnormalities in Neurotransmission, Oxidative Stress, and Apoptotic Pathways in a Chronic Phencyclidine Rat Model

Schizophrenia is a neuropsychiatric disorder affecting 1% of the world's population. Due to both a broad range of symptoms and disease heterogeneity, current therapeutic approaches to treat schizophrenia fail to address all symptomatic manifestations of the disease. Therefore, disease models that reproduce core pathological features of schizophrenia are needed for the elucidation of pathological disease mechanisms. Here, we employ a comprehensive global label-free liquid chromatography-mass spectrometry proteomic (LC-MS(E)) and metabonomic (LC-MS) profiling analysis combined with the targeted proteomics (selected reaction monitoring and multiplex immunoassay) of serum and brain tissues to investigate a chronic phencyclidine (PCP) rat model in which glutamatergic hypofunction is induced through noncompetitive NMDAR-receptor antagonism. Using a multiplex immunoassay, we identified alterations in the levels of several cytokines (IL-5, IL-2, and IL-1β) and fibroblast growth factor-2. Extensive proteomic and metabonomic brain tissue profiling revealed a more prominent effect of chronic PCP treatment on both the hippocampal proteome and metabonome compared to the effect on the frontal cortex. Bioinformatic pathway analysis confirmed prominent abnormalities in NMDA-receptor-associated pathways in both brain regions, as well as alterations in other neurotransmitter systems such as kainate, AMPA, and GABAergic signaling in the hippocampus and in proteins associated with neurodegeneration. We further identified abundance changes in the level of the superoxide dismutase enzyme (SODC) in both the frontal cortex and hippocampus, which indicates alterations in oxidative stress and substantiates the apoptotic pathway alterations. The present study could lead to an increased understanding of how perturbed glutamate receptor signaling affects other relevant biological pathways in schizophrenia and, therefore, support drug discovery efforts for the improved treatment of patients suffering from this debilitating psychiatric disorder.

Dietary Intake of Sulforaphane-Rich Broccoli Sprout Extracts during Juvenile and Adolescence Can Prevent Phencyclidine-Induced Cognitive Deficits at Adulthood

Oxidative stress and inflammation play a role in cognitive impairment, which is a core symptom of schizophrenia. Furthermore, a hallmark of the pathophysiology of this disease is the dysfunction of cortical inhibitory γ-aminobutyric acid (GABA) neurons expressing parvalbumin (PV), which is also involved in cognitive impairment. Sulforaphane (SFN), an isothiocyanate derived from broccoli, is a potent activator of the transcription factor Nrf2, which plays a central role in the inducible expressions of many cytoprotective genes in response to oxidative stress. Keap1 is a cytoplasmic protein that is essential for the regulation of Nrf2 activity. Here, we found that pretreatment with SFN attenuated cognitive deficits, the increase in 8-oxo-dG-positive cells, and the decrease in PV-positive cells in the medial prefrontal cortex and hippocampus after repeated administration of phencyclidine (PCP). Furthermore, PCP-induced cognitive deficits were improved by the subsequent subchronic administration of SFN. Interestingly, the dietary intake of glucoraphanin (a glucosinolate precursor of SFN) during the juvenile and adolescence prevented the onset of PCP-induced cognitive deficits as well as the increase in 8-oxo-dG-positive cells and the decrease in PV-positive cells in the brain at adulthood. Moreover, the NRF2 gene and the KEAP1 gene had an epistatic effect on cognitive impairment (e.g., working memory and processing speed) in patients with schizophrenia. These findings suggest that SFN may have prophylactic and therapeutic effects on cognitive impairment in schizophrenia. Therefore, the dietary intake of SFN-rich broccoli sprouts during the juvenile and adolescence may prevent the onset of psychosis at adulthood.

Altered functional brain network connectivity and glutamate system function in transgenic mice expressing truncated Disrupted-in-Schizophrenia 1

Considerable evidence implicates DISC1 as a susceptibility gene for multiple psychiatric diseases. DISC1 has been intensively studied at the molecular, cellular and behavioral level, but its role in regulating brain connectivity and brain network function remains unknown. Here, we utilize a set of complementary approaches to assess the functional brain network abnormalities present in mice expressing a truncated Disc1 gene (Disc1tr Hemi mice). Disc1tr Hemi mice exhibited hypometabolism in the prefrontal cortex (PFC) and reticular thalamus along with a reorganization of functional brain network connectivity that included compromised hippocampal-PFC connectivity. Altered hippocampal-PFC connectivity in Disc1tr Hemi mice was confirmed by electrophysiological analysis, with Disc1tr Hemi mice showing a reduced probability of presynaptic neurotransmitter release in the monosynaptic glutamatergic hippocampal CA1-PFC projection. Glutamate system dysfunction in Disc1tr Hemi mice was further supported by the attenuated cerebral metabolic response to the NMDA receptor (NMDAR) antagonist ketamine and decreased hippocampal expression of NMDAR subunits 2A and 2B in these animals. These data show that the Disc1 truncation in Disc1tr Hemi mice induces a range of translationally relevant endophenotypes underpinned by glutamate system dysfunction and altered brain connectivity.

Impaired limbic cortico-striatal structure and sustained visual attention in a rodent model of schizophrenia

BACKGROUND

N-methyl-d-aspartate receptor (NMDAR) dysfunction is thought to contribute to the pathophysiology of schizophrenia. Accordingly, NMDAR antagonists such as phencyclidine (PCP) are used widely in experimental animals to model cognitive impairment associated with this disorder. However, it is unclear whether PCP disrupts the structural integrity of brain areas relevant to the profile of cognitive impairment in schizophrenia.

METHODS

Here we used high-resolution magnetic resonance imaging and voxel-based morphometry to investigate structural alterations associated with sub-chronic PCP treatment in rats.

RESULTS

Sub-chronic exposure of rats to PCP (5mg/kg twice daily for 7 days) impaired sustained visual attention on a 5-choice serial reaction time task, notably when the attentional load was increased. In contrast, sub-chronic PCP had no significant effect on the attentional filtering of a pre-pulse auditory stimulus in an acoustic startle paradigm. Voxel-based morphometry revealed significantly reduced grey matter density bilaterally in the hippocampus, anterior cingulate cortex, ventral striatum, and amygdala. PCP-treated rats also exhibited reduced cortical thickness in the insular cortex.

CONCLUSIONS

These findings demonstrate that sub-chronic NMDA receptor antagonism is sufficient to produce highly-localized morphological abnormalities in brain areas implicated in the pathogenesis of schizophrenia. Furthermore, PCP exposure resulted in dissociable impairments in attentional function.

Subanesthetic ketamine treatment promotes abnormal interactions between neural subsystems and alters the properties of functional brain networks

Acute treatment with subanesthetic ketamine, a non-competitive N-methyl-D-aspartic acid (NMDA) receptor antagonist, is widely utilized as a translational model for schizophrenia. However, how acute NMDA receptor blockade impacts on brain functioning at a systems level, to elicit translationally relevant symptomatology and behavioral deficits, has not yet been determined. Here, for the first time, we apply established and recently validated topological measures from network science to brain imaging data gained from ketamine-treated mice to elucidate how acute NMDA receptor blockade impacts on the properties of functional brain networks. We show that the effects of acute ketamine treatment on the global properties of these networks are divergent from those widely reported in schizophrenia. Where acute NMDA receptor blockade promotes hyperconnectivity in functional brain networks, pronounced dysconnectivity is found in schizophrenia. We also show that acute ketamine treatment increases the connectivity and importance of prefrontal and thalamic brain regions in brain networks, a finding also divergent to alterations seen in schizophrenia. In addition, we characterize how ketamine impacts on bipartite functional interactions between neural subsystems. A key feature includes the enhancement of prefrontal cortex (PFC)-neuromodulatory subsystem connectivity in ketamine-treated animals, a finding consistent with the known effects of ketamine on PFC neurotransmitter levels. Overall, our data suggest that, at a systems level, acute ketamine-induced alterations in brain network connectivity do not parallel those seen in chronic schizophrenia. Hence, the mechanisms through which acute ketamine treatment induces translationally relevant symptomatology may differ from those in chronic schizophrenia. Future effort should therefore be dedicated to resolve the conflicting observations between this putative translational model and schizophrenia.

Preclinical models of antipsychotic drug action

One of the main obstacles faced by translational neuroscience is the development of animal models of psychiatric disorders. Behavioural pharmacology studies indicate that psychedelic drugs, such as lysergic acid diethylamide (LSD) and dissociative drugs, such as phencyclidine (PCP), induce in healthy human volunteers psychotic and cognitive symptoms that resemble some of those observed in schizophrenia patients. Serotonin 5-HT2A and metabotropic glutamate 2 receptors have been involved in the mechanism of action of psychedelic and dissociative drugs. Here we review recent advances using LSD-like and PCP-like drugs in rodent models that implicate these receptors in the neurobiology of schizophrenia and its treatment.

Ontogenetic influence on rat susceptibility to lindane seizure after pretreatment with phencyclidine

The aim of the study was to determine the effects of early postnatal PCP treatment on the sensitivity of pubertal and adult rats to lindane proepileptogenic effects. Rat pups were treated with NaCl (0.9%) or PCP (10 mg/kg) at postnatal days 2, 6, 9 and 12. One control (NaCl-35) and one experimental (PCP-35) group have received lindane (4 mg/kg) at postnatal day 35, while others received lindane at postnatal day 65 (NaCl-65 and PCP-65). One week prior to lindane treatment three gold-plated EEG electrodes were implanted. Pubertal rats had significantly shorter latency time. After lindane, a prompt increase in power spectral density seen in PCP-treated groups vs. control was evident earlier in PCP-65 rats. The theta waves were significantly increased in PCP-35 and alpha rhythm in PCP-65 rats, when compared with corresponding controls. Postnatal PCP treatment increases the synchronization of brain electrical activity, thus contributing to the increased susceptibility to lindane.

Sustained NMDA receptor hypofunction induces compromised neural systems integration and schizophrenia-like alterations in functional brain networks

Compromised functional integration between cerebral subsystems and dysfunctional brain network organization may underlie the neurocognitive deficits seen in psychiatric disorders. Applying topological measures from network science to brain imaging data allows the quantification of complex brain network connectivity. While this approach has recently been used to further elucidate the nature of brain dysfunction in schizophrenia, the value of applying this approach in preclinical models of psychiatric disease has not been recognized. For the first time, we apply both established and recently derived algorithms from network science (graph theory) to functional brain imaging data from rats treated subchronically with the N-methyl-D-aspartic acid (NMDA) receptor antagonist phencyclidine (PCP). We show that subchronic PCP treatment induces alterations in the global properties of functional brain networks akin to those reported in schizophrenia. Furthermore, we show that subchronic PCP treatment induces compromised functional integration between distributed neural systems, including between the prefrontal cortex and hippocampus, that have established roles in cognition through, in part, the promotion of thalamic dysconnectivity. We also show that subchronic PCP treatment promotes the functional disintegration of discrete cerebral subsystems and also alters the connectivity of neurotransmitter systems strongly implicated in schizophrenia. Therefore, we propose that sustained NMDA receptor hypofunction contributes to the pathophysiology of dysfunctional brain network organization in schizophrenia.

Risperidone reverses phencyclidine induced decrease in glutathione levels and alterations of antioxidant defense in rat brain

Perinatal phencyclidine (PCP) administration to rats represents one of the actual animal models of schizophrenia. Numerous data suggest redox dysregulation in this disease. We have previously demonstrated decreased content of the reduced glutathione (GSH) and complex disbalance of antioxidant enzymes in the brain of rats perinatally treated with PCP. The aim of this study was to elucidate whether chronic risperidone treatment can reverse these changes. The Wistar rats were perinatally treated with either PCP (10mg/kg; PCP, two groups) or saline (0.9% NaCl, two groups). At postnatal day (PN) 35, two groups of rats one NaCl and one PCP have started to receive risperidone in drinking water for nine weeks (NaCl-RSP and PCP-RSP groups). Animals were sacrificed on PN100 and the levels of GSH, the activities of γ-glutamate cysteine ligase (GCL), glutathione peroxidase (GPx), glutathione reductase (GR) and superoxide dismutase (SOD), as well as, the concentration of lipid peroxides were determined in the different brain structures. Risperidone restored decreased GSH levels, as well as decreased γ-GCL activity in cortex and hippocampus of animals perinatally treated with PCP. Alterations in GPx and GR activities caused by perinatal PCP treatment were also reversed by risperidone in most investigated brain structures. Furthermore, chronic risperidone treatment caused the decrease in SOD activity both in control and in PCP perinatally treated groups. Increased levels of lipid peroxides noticed in hippocampus and thalamus were reversed after chronic risperidone treatment. The results of the present study demonstrate that risperidone treatment restores GSH levels and to great measure reverses antioxidant defense alterations in the brain of perinatally PCP treated rats. Further studies are necessary in order to clarify the significance of risperidone influence on oxidative stress parameters in schizophrenia.

Direct and indirect interactions of the dopamine D₃ receptor with glutamate pathways: implications for the treatment of schizophrenia

This article, based on original data as well as on previously reported preclinical and clinical data that are reviewed, describes direct and indirect interactions of the D(3) receptor with N-methyl-D-aspartate receptor (NMDA) signaling and their functional consequences and therapeutic implications for schizophrenia. D(3) receptor immunoreactivity at ultrastructural level with electron microscopy was identified at presumably glutamatergic, asymmetric synapses of the medium-sized spiny neurons of the nucleus accumbens. This finding supports the existence of a direct interaction of the D(3) receptor with glutamate, in line with previously described interactions with NMDA signaling involving Ca(2+)/calmodulin-dependent protein kinase II at post-synaptic densities (Liu et al. 2009). Indirect interactions of the D(3) receptor with glutamate could involve a negative control exerted by the D(3) receptor on mesocortical dopamine neurons and the complex regulation of the glutamatergic pyramidal cells by dopamine in the prefrontal cortex. This could be exemplified here by the regulation of pyramidal cell activity in conditions of chronic NMDA receptor blockade with dizocilpine (MK-801). BP897, a D(3) receptor-selective partial agonist, reversed the dysregulation of cortical c-fos mRNA expression and pyramidal cell hyperexcitability, as measured by paired-pulse electrophysiology. At the behavioral level, blockade of the D(3) receptor, by known D(3) receptor antagonists or the novel D(3) receptor-selective antagonist F17141, produces antipsychotic-like effects in reversing hyperactivity and social interaction deficits induced by NMDA receptor blockade by MK-801 in mice. The glutamate-D(3) receptor interactions described here offer a conceptual framework for developing new D(3) receptor-selective drugs, which may appear as an original, efficacious, and safe way to potentially indirectly target glutamate in schizophrenia.

Modafinil reverses phencyclidine-induced deficits in cognitive flexibility, cerebral metabolism, and functional brain connectivity

OBJECTIVE

In the present study, we employ mathematical modeling (partial least squares regression, PLSR) to elucidate the functional connectivity signatures of discrete brain regions in order to identify the functional networks subserving PCP-induced disruption of distinct cognitive functions and their restoration by the procognitive drug modafinil.

METHODS

We examine the functional connectivity signatures of discrete brain regions that show overt alterations in metabolism, as measured by semiquantitative 2-deoxyglucose autoradiography, in an animal model (subchronic phencyclidine [PCP] treatment), which shows cognitive inflexibility with relevance to the cognitive deficits seen in schizophrenia.

RESULTS

We identify the specific components of functional connectivity that contribute to the rescue of this cognitive inflexibility and to the restoration of overt cerebral metabolism by modafinil. We demonstrate that modafinil reversed both the PCP-induced deficit in the ability to switch attentional set and the PCP-induced hypometabolism in the prefrontal (anterior prelimbic) and retrosplenial cortices. Furthermore, modafinil selectively enhanced metabolism in the medial prelimbic cortex. The functional connectivity signatures of these regions identified a unifying functional subsystem underlying the influence of modafinil on cerebral metabolism and cognitive flexibility that included the nucleus accumbens core and locus coeruleus. In addition, these functional connectivity signatures identified coupling events specific to each brain region, which relate to known anatomical connectivity.

CONCLUSIONS

These data support clinical evidence that modafinil may alleviate cognitive deficits in schizophrenia and also demonstrate the benefit of applying PLSR modeling to characterize functional brain networks in translational models relevant to central nervous system dysfunction.

Models of aspects of schizophrenia: behavioral sensitization induced by subchronic phencyclidine administration

Presented in this unit is a protocol using subchronically administered phencyclidine (PCP) for establishing a behavioral sensitization model of aspects of schizophrenia. This model is validated using haloperidol and risperidone. The end-point of the assay is locomotor hyperactivity, which is induced by PCP challenge following subchronic treatment with this NMDA receptor antagonist. The antipsychotics haloperidol, risperidone, and quetiapine all reduce hyperactivity in a dose-dependent and selective manner. While the effects of other antipsychotics such as clozapine, olanzapine, and ziprasidone are similar to haloperidol, the interpretation of responses to them is often confounded by nonspecific effects during habituation.

Rats tested after a washout period from sub-chronic PCP administration exhibited impaired performance in the 5-Choice Continuous Performance Test (5C-CPT) when the attentional load was increased

It is well documented that schizophrenia patients exhibit dysfunction in various cognitive domains, including attention/vigilance, as demonstrated by impaired performance in the myriad of Continuous Performance Tests (CPTs). NMDA receptor antagonists provide a pharmacological model in animals of the cognitive disruption presented in the disorder. We therefore examined the effects of a sub-chronic PCP treatment regimen (5.0mg/kg 7-days bi-daily) in the recently developed rodent test of vigilance, the 5-Choice Continuous Performance Test (5C-CPT). We assessed the effects of this regimen after at least a 7-day washout period on both baseline performance and when the attentional load was increased. Sub-chronic PCP treatment impaired 5C-CPT performance in a manner consistent with impaired vigilance in patients with schizophrenia, with reduced hit rate and impaired signal sensitivity. These effects were only evident when performance was challenged following parameter manipulations. These data demonstrate that attention/vigilance is sensitive to disruption following sub-chronic PCP treatment in a pre-clinical task that may demonstrate increased analogy to human vigilance tasks. Although the PCP-induced attentional deficits are not as large as those deficits observed in other domains, these data provide evidence that this pharmacological model can affect multiple cognitive domains and may be useful for assessing putative pro-cognitive therapeutics for schizophrenia.

Possible long-term effects of γ-hydroxybutyric acid (GHB) due to neurotoxicity and overdose

In several countries, including the Netherlands, the use of GHB seems to be rising. GHB is regarded by recreational users as an innocent drug without any side effects. Recently, the number of patients in treatment due to GHB addiction sharply increased. In addition, various studies report incidents following risky GHB use or GHB overdosing. Other sedative drugs, like ketamine and alcohol have been shown to result in unintended neurotoxic harm at the level of memory and cognitive function. As outlined in the present review, GHB and ketamine have a common mode of action, which suggests that GHB may also lead to similar neurotoxicity as ketamine. GHB overdosing, as well as binge drinking (and high ketamine doses), induce profound coma which is probably neurotoxic for the brain especially in the maturing brain of young adults. It is therefore advocated to investigate possible long-term neurotoxic effects in recreational GHB users e.g. by studying the residual effects on cognition and memory.

The role of energy metabolism dysfunction and oxidative stress in schizophrenia revealed by proteomics

Schizophrenia is a psychiatric illness that affects approximately 30 million people worldwide. Converging lines of evidence suggest that mitochondrial function may be compromised in this disorder, and this can lead to perturbations in calcium buffering, oxidative phosphorylation, increased production of reactive oxygen species, and apoptotic factors, which can, in turn, affect neuronal processes such as neurotransmitter synthesis and synaptic plasticity. Proteomics studies in brain and peripheral tissues of schizophrenia patients have provided considerable evidence and identified biomarker fingerprints corresponding to such pathways. Here we review the results of these studies with a focus on the biomarker pattern depicting alterations in energy metabolism and oxidative stress in this debilitating illness.

Animal models of schizophrenia

Developing reliable, predictive animal models for complex psychiatric disorders, such as schizophrenia, is essential to increase our understanding of the neurobiological basis of the disorder and for the development of novel drugs with improved therapeutic efficacy. All available animal models of schizophrenia fit into four different induction categories: developmental, drug-induced, lesion or genetic manipulation, and the best characterized examples of each type are reviewed herein. Most rodent models have behavioural phenotype changes that resemble 'positive-like' symptoms of schizophrenia, probably reflecting altered mesolimbic dopamine function, but fewer models also show altered social interaction, and learning and memory impairment, analogous to negative and cognitive symptoms of schizophrenia respectively. The negative and cognitive impairments in schizophrenia are resistant to treatment with current antipsychotics, even after remission of the psychosis, which limits their therapeutic efficacy. The MATRICS initiative developed a consensus on the core cognitive deficits of schizophrenic patients, and recommended a standardized test battery to evaluate them. More recently, work has begun to identify specific rodent behavioural tasks with translational relevance to specific cognitive domains affected in schizophrenia, and where available this review focuses on reporting the effect of current and potential antipsychotics on these tasks. The review also highlights the need to develop more comprehensive animal models that more adequately replicate deficits in negative and cognitive symptoms. Increasing information on the neurochemical and structural CNS changes accompanying each model will also help assess treatments that prevent the development of schizophrenia rather than treating the symptoms, another pivotal change required to enable new more effective therapeutic strategies to be developed.

Phencyclidine-induced loss of asymmetric spine synapses in rodent prefrontal cortex is reversed by acute and chronic treatment with olanzapine

Enduring cognitive deficits exist in schizophrenic patients, long-term abusers of phencyclidine (PCP), as well as in animal PCP models of schizophrenia. It has been suggested that cognitive performance and memory processes are coupled with remodeling of pyramidal dendritic spine synapses in prefrontal cortex (PFC), and that reduced spine density and number of spine synapses in the medial PFC of PCP-treated rats may potentially underlie, at least partially, the cognitive dysfunction previously observed in this animal model. The present data show that the decrease in number of asymmetric (excitatory) spine synapses in layer II/III of PFC, previously noted at 1-week post PCP treatment also occurs, to a lesser degree, in layer V. The decrease in the number of spine synapses in layer II/III was sustained and persisted for at least 4 weeks, paralleling the observed cognitive deficits. Both acute and chronic treatment with the atypical antipsychotic drug, olanzapine, starting at 1 week after PCP treatment at doses that restore cognitive function, reversed the asymmetric spine synapse loss in PFC of PCP-treated rats. Olanzapine had no significant effect on spine synapse number in saline-treated controls. These studies demonstrate that the effect of PCP on asymmetric spine synapse number in PFC lasts at least 4 weeks in this model. This spine synapse loss in PFC is reversed by acute treatment with olanzapine, and this reversal is maintained by chronic oral treatment, paralleling the time course of the restoration of the dopamine deficit, and normalization of cognitive function produced by olanzapine.

Similarities in the behavior and molecular deficits in the frontal cortex between the neurotensin receptor subtype 1 knockout mice and chronic phencyclidine-treated mice: relevance to schizophrenia

Much evidence suggests that targeting the neurotensin (NT) system may provide a novel and promising treatment for schizophrenia. Our recent work shows that: NTS1 knockout (NTS1(-/-)) mice may provide a potential animal model for studying schizophrenia by investigating the effect of deletion NTS1 receptor on amphetamine-induced hyperactivity and neurochemical changes. The data indicate a hyper-dopaminergic state similar to the excessive striatal DA activity reported in schizophrenia. The present study was done to determine if NTS1(-/-) mice also have similar changes in behavior, in prefrontal neurotransmitters, and in protein expression, as observed in wild type (WT) mice treated with the psychotomimetic phencylclidine (PCP), an animal model for schizophrenia. Our results showed many similarities between untreated NTS1(-/-) mice and WT mice chronically treated with PCP (as compared with untreated WT mice): 1) lower PCP-induced locomotor activity; 2) similar avolition-like behavior in forced-swim test and tail suspension test; 3) lower prefrontal glutamate levels; 4) less PCP-induced dopamine release in medial prefrontal cortex (mPFC); and 5) down-regulation of mRNA and protein for DA D(1), DA D(2), and NMDAR2A in mPFC. Therefore, these data strengthen the hypothesis that the NTS1(-/-) mouse is an animal model of schizophrenia, particularly for the dysfunction of the prefrontal cortex. In addition, after chronic PCP administration, the DA D(1) receptor was up-regulated in NTS1(-/-) mice, results which suggest a possible interaction of NTS1/DA D(1) in mPFC contributing to chronic PCP-induced schizophrenia-like signs.

Disruption of performance in the five-choice serial reaction time task induced by administration of N-methyl-D-aspartate receptor antagonists: relevance to cognitive dysfunction in schizophrenia

Schizophrenia patients suffer from cognitive impairments that are not satisfactorily treated by currently available medications. Cognitive dysfunction in schizophrenia encompasses deficits in several cognitive modalities that can be differentially responsive to different medications and are likely to be mediated by different neurobiological substrates. Translational animal models of cognitive deficits with relevance to schizophrenia are critical for gaining insights into the mechanisms underlying these impairments and developing more effective treatments. The five-choice serial reaction time task (5-CSRTT) is a cognitive task used in rodents that allows simultaneous assessment of several cognitive modalities, including attention, response inhibition, cognitive flexibility, and processing speed. Administration of N-methyl-D-aspartate (NMDA) glutamate receptor antagonists disrupts multiple 5-CSRTT performance measures in a way that mirrors various cognitive deficits exhibited by schizophrenia patients. Some of these disruptions are partially attenuated by antipsychotic medications that exhibit partial effectiveness on cognitive dysfunction in schizophrenia, suggesting that the model has predictive validity. Examination of the effects of pharmacological manipulations on 5-CSRTT performance disruptions induced by NMDA antagonists have implicated a range of brain regions, neurotransmitter systems, and specific receptor subtypes in schizophrenia-like impairment of different cognitive modalities. Thus, disruption of 5-CSRTT performance by NMDA antagonists represents a valuable tool for exploring the neurobiological bases of cognitive dysfunction in schizophrenia.

Animal models of schizophrenia

Schizophrenia may well represent one of the most heterogenous mental disorders in human history. This heterogeneity encompasses (1) etiology; where numerous putative genetic and environmental factors may contribute to disease manifestation, (2) symptomatology; with symptoms characterized by group; positive--behaviors not normally present in healthy subjects (e.g. hallucinations), negative--reduced expression of normal behaviors (e.g. reduced joy), and cognitive--reduced cognitive capabilities separable from negative symptoms (e.g. impaired attention), and (3) individual response variation to treatment. The complexity of this uniquely human disorder has complicated the development of suitable animal models with which to assay putative therapeutics. Moreover, the development of animal models is further limited by a lack of positive controls because currently approved therapeutics only addresses psychotic symptoms, with minor negative symptom treatment. Despite these complexities however, many animal models of schizophrenia have been developed mainly focusing on modeling individual symptoms. Validation criteria have been established to assay the utility of these models, determining the (1) face, (2) predictive, (3) construct, and (4) etiological validities, as well as (5) reproducibility of each model. Many of these models have been created following the development of major hypotheses of schizophrenia, including the dopaminergic, glutamatergic, and neurodevelopmental hypotheses. The former two models have largely consisted of manipulating these neurotransmitter systems to produce behavioral abnormalities with some relevance to symptoms or putative etiology of schizophrenia. Given the serotonergic link to hallucinations and cholinergic link to attention, other models have manipulated these systems also. Finally, there has also been a drive toward creating mouse models of schizophrenia utilizing transgenic technology. Thus, there are opportunities to combine both environmental and genetic factors to create more suitable models of schizophrenia. More sophisticated animal tasks are also being created with which to ascertain whether these models produce behavioral abnormalities consistent with patients with schizophrenia. While animal models of schizophrenia continue to be developed, we must be cognizant that (1) validating these models are limited to the degree by which Clinicians can provide relevant information on the behavior of these patients, and (2) any putative treatments that are developed are also likely to be given with concurrent antipsychotic treatment. While our knowledge of this devastating disorder increases and our animal models and tasks with which to measure their behaviors become more sophisticated, caution must still be taken when validating these models to limit complications when introducing putative therapeutics to human trials.

Effects of antipsychotic drugs on MK-801-induced attentional and motivational deficits in rats

BACKGROUND

Attentional deficits that accompany schizophrenia are not effectively treated by available antipsychotic medications. Disruption of NMDA receptor function is often used to model aspects of this disorder in rodents. We used the 5-choice serial reaction time task (5CSRTT) to characterize attentional deficits caused by acute administration or withdrawal from chronic administration of the NMDA receptor antagonist MK-801, and determine if they are ameliorated by haloperidol or clozapine.

METHODS

Acute studies involved tests in the presence of MK-801: rats were administered haloperidol (0.008-0.125 mg/kg, SC) or clozapine (0.16-2.5 mg/kg, SC) in combination with MK-801 (0.25 mg/kg, IP) prior to daily test sessions. Chronic studies involved tests in the absence of MK-801: following daily tests, rats were administered MK-801 (0.5 mg/kg, IP) and tested 24 h later in the absence or presence of haloperidol or clozapine.

RESULTS

Acute MK-801 disrupted performance: it decreased accuracy while increasing omissions, premature responses, and magazine entries. Haloperidol reduced disruptive effects associated with increased activation, whereas it exacerbated other deficits. Clozapine dose-dependently attenuated several of the MK-801-induced performance deficits. Withdrawal from chronic MK-801 progressively increased omissions and response latencies and decreased premature responding, suggesting an amotivational state. Neither haloperidol nor clozapine ameliorated these performance deficits.

DISCUSSION

Acute administration and withdrawal from chronic MK-801 administration produced distinct behavioral profiles in the 5CSRTT. Acute MK-801 impaired attention and impulse control whereas chronic MK-801 withdrawal caused signs consistent with amotivation. Haloperidol and clozapine were more effective at attenuating deficits caused by acute MK-801 administration.

An Evaluation of Phencyclidine (PCP) Psychosis: A Retrospective Analysis at a State Facility

It has been reported in the literature that phencyclidine (PCP) psychosis recovery may take up to 4-6 weeks. This retrospective review sought to determine whether patients with a new onset of PCP psychosis have a longer hospitalization than those patients with new onset functional psychosis. The PCP arm (N = 20) was found to have a significantly shorter hospitalization than those with a new onset functional psychosis (N = 20)-mean 4.8 days (range 1-9) versus 13.6 days (range 3-41), p < .05. In addition, patients with psychosis related to PCP use were treated more aggressively with conventional antipsychotics than patients with a new onset functional psychosis at this facility.

Ultrasonic vocalisations explain unexpected effects on pre-pulse inhibition responses in rats chronically pre-treated with phencyclidine

Deficits in pre-pulse inhibition (PPI-indicative of psychosis in humans) can be replicated in rats using the NMDA receptor antagonist phencyclidine (PCP). Ultrasonic vocalisations (USVs) produced by rats in response to acoustic startle are indicative of heightened anxiety; here we tested the predictive validity of USVs as an indicator of PPI. Male juvenile Sprague-Dawley rats (n=10) were treated for 14 days with either PCP (5mg/kg i.p.) or saline controls (1 ml/kg i.p.). PPI responses and USVs were recorded on days 16 and 19. PCP-treated rats showed decreased PPI performance on day 16 compared to controls; an observation that was unexpectedly reversed on day 19. Call parameters indicated that both treatment groups experienced similar levels of anxiety in response to the PPI paradigm on day 16. On day 19, the controls showed increased call duration and latency to onset (LtO) of calling, but decreased in the total number of calls produced compared to day 16. The calling period was significantly reduced compared to PCP-treated animals on say 19, whilst the LtO and duration were significantly increased. These changes were considered indicative of heightened levels of anxiety, most likely due to inadvertent fear conditioning (supported by reduced PPI performance) acquired during PPI testing. In contrast, the stability of USV characteristics emitted by PCP treated animals likely signified the detrimental effects of chronic PCP treatment on working memory. These results suggest that USVs are a valuable additional measure during PPI testing, helping to explain the unexpected results from our control group.

Subchronic and chronic PCP treatment produces temporally distinct deficits in attentional set shifting and prepulse inhibition in rats

RATIONALE

We have previously demonstrated that subchronic (five daily administrations of 2.6 mg/kg PCP) and chronic intermittent administration of 2.6 mg/kg PCP to rats produces hypofrontality and other neurochemical changes akin to schizophrenia pathology (Cochran et al., Neuropsychopharmacology, 28:265-275, 2003).

OBJECTIVES

We sought to determine whether behavioral alterations related to discrete aspects of schizophrenia are also induced by these PCP treatment regimes.

MATERIALS AND METHODS

Following administration of vehicle or PCP according to the protocols described above, rats were assessed for attentional set shifting ability, prepulse inhibition (PPI), or social interaction and the locomotor response to a challenge dose of amphetamine.

RESULTS

Ability to shift attentional set was impaired 72 h after the last PCP administration following the subchronic and chronic intermittent treatment regimes. PPI was disrupted after each acute administration of PCP in animals under the subchronic treatment regime. However, PPI deficits were not sustained 72 h after the last of five daily administrations. In subchronic and chronic PCP treated animals, no change was found in social interaction behavior, and there was little change in baseline or amphetamine-stimulated locomotor activity, employed as an indicator of dopaminergic hyperfunction.

CONCLUSIONS

The temporally distinct behavioral effects of these PCP treatment regimes suggest that PPI deficits relate directly to acute NMDA receptor antagonism, whereas the more enduring set shifting deficits relate to the longer term consequences of NMDA receptor blockade. Therefore, these subchronic and chronic PCP treatment regimes produce hypofrontality (Cochran et al., Neuropsychopharmacology, 28:265-275, 2003) and associated prefrontal cortex-dependent deficits in behavioral flexibility which mirror core deficits in schizophrenia.

Phencyclidine animal models of schizophrenia: Approaches from abnormality of glutamatergic neurotransmission and neurodevelopment

In humans, phencyclidine (PCP), a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, reproduces a schizophrenia-like psychosis including positive symptoms, negative symptoms and cognitive dysfunction. Thus, the glutamatergic neuronal dysfunction hypothesis is one of the main explanatory hypotheses and PCP-treated animals have been utilized as an animal model of schizophrenia. The adult rodents treated with PCP repeatedly exhibit hyperlocomotion as an index of positive symptoms, a social behavioral deficit in a social interaction test and enhanced immobility in a forced swimming test as indices of negative symptoms. They also show a sensorimotor gating deficits and cognitive dysfunctions in several learning and memory tests. Some of these behavioral changes endure after withdrawal from repeated PCP treatment. Furthermore, repeated PCP treatment induces some neurochemical and neuroanatomical changes. On the other hand, the exposure to viral or environmental insult in the second trimester of pregnancy increases the probability of subsequently developing schizophrenia as an adult. NMDA receptor has been implicated in controlling the structure and plasticity of developing brain circuitry. Based on neurodevelopment hypothesis of schizophrenia, schizophrenia model rats treated with PCP at the perinatal stage is developed. Perinatal PCP treatment impairs neuronal development and induces long-lasting schizophrenia-like behaviors in adult period. Many findings suggest that these PCP animal models would be useful for evaluating novel therapeutic candidates and for confirming pathological mechanisms of schizophrenia.

Chronic phencyclidine treatment increases dendritic spine density in prefrontal cortex and nucleus accumbens neurons

We examined whether repeated exposure to the noncompetitive NMDA receptor antagonist phencyclidine (PCP) produces enduring changes in dendritic structure in a manner similar to the stimulants cocaine and amphetamine. Adult rats were treated with i.p. injections of PCP (5 mg/kg) or saline, twice a day, for 5 consecutive days, for a total of 4 weeks. One month after the last injection, their brains were removed and processed for Golgi-Cox staining. Prior exposure to PCP increased dendritic spine density in the mPFC and NAcc core, but not in the parietal cortex. These findings, which are similar to those observed after chronic treatment with cocaine and amphetamine, raise the possibility that, despite differences in their mechanisms of action, PCP and stimulant drugs may induce some of their enduring effects via common processes.

Acute and chronic effects of ketamine upon human memory: a review

INTRODUCTION

Ketamine is attracting increasing research interest not only because of its powerful amnestic effects but also as a putative model of schizophrenia and as a substance with an expanding following of recreational users.

OBJECTIVE

This article reviews the existing literature on the effects of acute ketamine on the memory of healthy volunteers and of repeated doses of ketamine in recreational users.

CURRENT TRENDS

Although there have been relatively few, often methodologically diverse, studies to date of the mnemonic effects of ketamine, there is an emerging consensus that an acute dose of the drug impairs the manipulation of information in working memory and produces decrements in the encoding of information into episodic memory. Preliminary evidence suggests that ketamine may differ from other classic amnestic drugs in impairing aspects of semantic memory. Acute-on-chronic effects in ketamine users generally mimic the pattern seen in controlled studies with healthy volunteers. However, chronic ketamine use may be associated with a more specific pattern of memory decrements and with episodic memory impairment, which might not abate following cessation of use.

FUTURE TRENDS

An important aim of future research should be to detail the specificity of ketamine's amnestic effects on both a neuropharmacological and a cognitive level.

Clozapine but not haloperidol treatment reverses sub-chronic phencyclidine-induced disruption of conditional discrimination performance

Abusers of phencyclidine (PCP) often present with a symptom profile similar to that exhibited by schizophrenic patients. Animal models utilising such psychotomimetics are currently informing research into the condition. Accumulating evidence suggests that a central cognitive deficit in schizophrenia is the inability to use task-setting cues to guide goal directed behaviour and that this ability is mediated by prefrontal dopamine (DA). The current study used the non-competitive NMDA antagonist phencyclidine (PCP) and Haloperidol (typical antipsychotic) and Clozapine (atypical antipsychotic) in order to further investigate the influence of DAergic manipulation on a task that requires the use of conditional information to inform goal-directed performance. An instrumental conditional discrimination task was employed in which rats learn to respond appropriately according to the presence of specific auditory conditional stimuli. Probe test 1 showed impaired conditional discrimination performance following sub-chronic PCP administration (seven twice-daily injection protocol) compared to control which was reversed by acute treatment with clozapine (5 mg/kg) but not haloperidol (0.1 mg/kg) both administered 60 min pre-test. Probe test 2 (8 days post-treatment) showed enduring deficits to conditional discrimination performance that were again reversed by clozapine but not haloperidol (injection procedures as above). These results show that tasks dependent upon conditional relationships are particularly sensitive to manipulation of DAergic systems as prolonged treatment with PCP has been shown to selectively reduce prefrontal cortex (PFC) DA activity and treatment with clozapine (known to ameliorate cognitive deficits) but not haloperidol has been shown to selectively restore PFC DA levels.