Cost-effectiveness of psilocybin-assisted therapy for severe depression: exploratory findings from a decision analytic model

BACKGROUND

There is growing evidence to support the use of the psychedelic drug psilocybin for difficult-to-treat depression. This paper compares the cost-effectiveness of psilocybin-assisted psychotherapy (PAP) with conventional medication, cognitive behavioural therapy (CBT), and the combination of conventional medication and CBT.

METHODS

A decision model simulated patient events (response, remission, and relapse) following treatment. Data on probabilities, costs and quality-adjusted life years (QALYs) were derived from previous studies or from best estimates. Expected healthcare and societal costs and QALYs over a 6-month time period were calculated. Sensitivity analyses were used to address uncertainty in parameter estimates.

RESULTS

The expected healthcare cost of PAP varied from £6132 to £7652 depending on the price of psilocybin. This compares to £3528 for conventional medication alone, £4250 for CBT alone, and £4197 for their combination. QALYs were highest for psilocybin (0.310), followed by CBT alone (0.283), conventional medication alone (0.278), and their combination (0.287). Psilocybin was shown to be cost-effective compared to the other therapies when the cost of therapist support was reduced by 50% and the psilocybin price was reduced from its initial value to £400 to £800 per person. From a societal perspective, psilocybin had improved cost-effectiveness compared to a healthcare perspective.

CONCLUSIONS

Psilocybin has the potential to be a cost-effective therapy for severe depression. This depends on the level of psychological support that is given to patients receiving psilocybin and the price of the drug itself. Further data on long-term outcomes are required to improve the evidence base.

Handling prevents and reverses cognitive deficits induced by sub-chronic phencyclidine in a model for schizophrenia in rats

Treatments for schizophrenia are not effective in ameliorating cognitive deficits. Therefore, novel therapies are needed to treat cognitive impairments associated with schizophrenia (CIAS), which are modelled in rats through administration of sub-chronic phencyclidine (scPCP). We have previously shown that enrichment via voluntary exercise prevents and reverses impairments in novel object recognition (NOR) in this model. The present study aimed to investigate if handling could prevent delay-induced NOR deficits and prevent and reverse scPCP-induced NOR deficits. Two cohorts of adult female Lister Hooded rats were used. In experiment one, handling (five minutes/day, five days/week for two weeks), took place before scPCP administration (2 mg/kg, i.p. twice-daily for seven days). NOR tests were conducted at two, four, and seven weeks post-handling with a one-minute inter-trial interval (ITI) and at five weeks post-dosing with a six-hour ITI. In experiment two, rats were handled after scPCP administration and tested immediately in the one-minute ITI NOR task and again at two weeks post-handling. In both handling regimens, the scPCP control groups failed to discriminate novelty, conversely the scPCP handled groups significantly discriminated in this task. In the 6 h ITI test, vehicle control and scPCP control failed to discriminate novelty; however, the vehicle handled and scPCP handled groups did significantly discriminate. Handling rats prevented and reversed scPCP-induced deficits and prevented delay-induced NOR deficits. These findings add to evidence that environmental enrichment is a viable treatment for cognitive deficits in rodent tests and models of relevance to schizophrenia, with potential to translate into effective treatments for CIAS.

Oscillatory Deficits in the Sub-Chronic PCP Rat Model for Schizophrenia Are Reversed by mGlu5 Receptor-Positive Allosteric Modulators VU0409551 and VU0360172

The cognitive deficits of schizophrenia are linked to imbalanced excitatory and inhibitory signalling in the prefrontal cortex (PFC), disrupting gamma oscillations. We previously demonstrated that two mGlu5 receptor-positive allosteric modulators (PAMs), VU0409551 and VU0360172, restore cognitive deficits in the sub-chronic PCP (scPCP) rodent model for schizophrenia via distinct changes in PFC intracellular signalling molecules. Here, we have assessed ex vivo gamma oscillatory activity in PFC slices from scPCP rats and investigated the effects of VU0409551 and VU0360172 upon oscillatory power. mGlu5 receptor, protein kinase C (PKC), and phospholipase C (PLC) inhibition were also used to examine ‘modulation bias’ in PAM activity. The amplitude and area power of gamma oscillations were significantly diminished in the scPCP model. Slice incubation with either VU0409551 or VU0360172 rescued scPCP-induced oscillatory deficits in a concentration-dependent manner. MTEP blocked the PAM-induced restoration of oscillatory power, confirming the requirement of mGlu5 receptor modulation. Whilst PLC inhibition prevented the power increase mediated by both PAMs, PKC inhibition diminished the effects of VU0360172 but not VU0409551. This aligns with previous reports that VU0409551 exhibits preferential activation of the phosphatidylinositol-3-kinase (PI3K) signalling pathway over the PKC cascade. Restoration of the excitatory/inhibitory signalling balance and gamma oscillations may therefore underlie the mGluR5 PAM-mediated correction of scPCP-induced cognitive deficits.

Maternal Immune Activation Induces Adolescent Cognitive Deficits Preceded by Developmental Perturbations in Cortical Reelin Signalling

Exposure to maternal immune activation (MIA) in utero significantly elevates the risk of developing schizophrenia and other neurodevelopmental disorders. To understand the biological mechanisms underlying the link between MIA and increased risk, preclinical animal models have focussed on specific signalling pathways in the brain that mediate symptoms associated with neurodevelopmental disorders such as cognitive dysfunction. Reelin signalling in multiple brain regions is involved in neuronal migration, synaptic plasticity and long-term potentiation, and has been implicated in cognitive deficits. However, how regulation of Reelin expression is affected by MIA across cortical development and associated cognitive functions remains largely unclear. Using a MIA rat model, here we demonstrate cognitive deficits in adolescent object-location memory in MIA offspring and reductions in Reln expression prenatally and in the adult prefrontal cortex. Further, developmental disturbances in gene/protein expression and DNA methylation of downstream signalling components occurred subsequent to MIA-induced Reelin dysregulation and prior to cognitive deficits. We propose that MIA-induced dysregulation of Reelin signalling contributes to the emergence of prefrontal cortex-mediated cognitive deficits through altered NMDA receptor function, resulting in inefficient long-term potentiation. Our data suggest a developmental window during which attenuation of Reelin signalling may provide a possible therapeutic target.

Maternal behaviours and adult offspring behavioural deficits are predicted by maternal TNFα concentration in a rat model of neurodevelopmental disorders

Exposure to inflammatory stressors during fetal development is a major risk factor for neurodevelopmental disorders (NDDs) in adult offspring. Maternal immune activation (MIA), induced by infection, causes an acute increase in pro-inflammatory cytokines which can increase the risk for NDDs directly by inducing placental and fetal brain inflammation, or indirectly through affecting maternal care behaviours thereby affecting postnatal brain development. Which of these two potential mechanisms dominates in increasing offspring risk for NDDs remains unclear. Here, we show that acute systemic maternal inflammation induced by the viral mimetic polyinosinic:polycytidylic acid (poly I:C) on gestational day 15 of rat pregnancy affects offspring and maternal behaviour, offspring cognition, and expression of NDD-relevant genes in the offspring brain. Dams exposed to poly I:C elicited an acute increase in the pro-inflammatory cytokine tumour necrosis factor (TNF; referred to here as TNFα), which predicted disruption of key maternal care behaviours. Offspring of poly I:C-treated dams showed early behavioural and adult cognitive deficits correlated to the maternal TNFα response, but, importantly, not with altered maternal care. We also found interacting effects of sex and treatment on GABAergic gene expression and DNA methylation in these offspring in a brain region-specific manner, including increased parvalbumin expression in the female adolescent frontal cortex. We conclude that the MIA-induced elevation of TNFα in the maternal compartment affects fetal neurodevelopment leading to altered offspring behaviour and cognition. Our results suggest that a focus on prenatal pathways affecting fetal neurodevelopment would provide greater insights into the mechanisms underpinning the TNFα-mediated genesis of altered offspring behaviour and cognition following maternal inflammation.

Clustering of cognitive phenotypes identifies susceptible and resilient offspring in a rat model of maternal immune activation and early-life stress

Schizophrenia and other neurodevelopmental disorders often have very heterogeneous symptoms, especially regarding cognition: while some individuals may exhibit deficient cognition, others are relatively unaffected. Studies using developmental animal models often ignore phenotypic heterogeneity in favour of traditional treatment/control comparisons. This may result in resilient or unaffected individuals masking the effects of susceptible individuals if grouped together. Here, we used maternal immune activation and limited bedding and nesting, respectively, as a two-hit neurodevelopmental model for schizophrenia. Both factors reduced cognitive function in a novel object recognition (NOR) task. While we found treatment group effects on cognitive phenotypes, behavioural clustering identified three subpopulations exposed to either insult: those exhibiting ‘typical’ cognitive performance on the NOR, an intermediate phenotype, or a marked deficit. These clusters included offspring from each treatment group, although both intermediate and marked deficit clusters were composed primarily of offspring from treated groups. Clustering allowed stratification within treatment groups into ‘susceptible’ and ‘resilient’ individuals, while also identifying conserved phenotypes across treatment groups. Using unbiased cluster analyses in preclinical models can better characterize phenotypes and enables a better understanding of both face and construct validity of phenotypic heterogeneity. The use of unbiased clustering techniques may help identify potential markers associated with individual susceptibility and resilience in neurodevelopmental disorder models.

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Maternal immune activation and early life stress affect recognition memory.

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New groups were identified using unbiased clustering based on task performance.

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These clusters reflected high-, low-, and intermediary recognition memory.

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Treatment offspring were distributed across all three unbiased clusters.

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These findings suggest some offspring will be resilient to developmental insults.

Inflammation and Brain Structure in Schizophrenia and Other Neuropsychiatric Disorders: A Mendelian Randomization Study

Importance

Previous in vitro and postmortem research suggests that inflammation may lead to structural brain changes via activation of microglia and/or astrocytic dysfunction in a range of neuropsychiatric disorders.

Objective

To investigate the relationship between inflammation and changes in brain structures in vivo and to explore a transcriptome-driven functional basis with relevance to mental illness.

Design, Setting, and Participants

This study used multistage linked analyses, including mendelian randomization (MR), gene expression correlation, and connectivity analyses. A total of 20 688 participants in the UK Biobank, which includes clinical, genomic, and neuroimaging data, and 6 postmortem brains from neurotypical individuals in the Allen Human Brain Atlas (AHBA), including RNA microarray data. Data were extracted in February 2021 and analyzed between March and October 2021.

Exposures

Genetic variants regulating levels and activity of circulating interleukin 1 (IL-1), IL-2, IL-6, C-reactive protein (CRP), and brain-derived neurotrophic factor (BDNF) were used as exposures in MR analyses.

Main Outcomes and Measures

Brain imaging measures, including gray matter volume (GMV) and cortical thickness (CT), were used as outcomes. Associations were considered significant at a multiple testing-corrected threshold of P < 1.1 × 10-4. Differential gene expression in AHBA data was modeled in brain regions mapped to areas significant in MR analyses; genes were tested for biological and disease overrepresentation in annotation databases and for connectivity in protein-protein interaction networks.

Results

Of 20 688 participants in the UK Biobank sample, 10 828 (52.3%) were female, and the mean (SD) age was 55.5 (7.5) years. In the UK Biobank sample, genetically predicted levels of IL-6 were associated with GMV in the middle temporal cortex (z score, 5.76; P = 8.39 × 10-9), inferior temporal (z score, 3.38; P = 7.20 × 10-5), fusiform (z score, 4.70; P = 2.60 × 10-7), and frontal (z score, -3.59; P = 3.30 × 10-5) cortex together with CT in the superior frontal region (z score, -5.11; P = 3.22 × 10-7). No significant associations were found for IL-1, IL-2, CRP, or BDNF after correction for multiple comparison. In the AHBA sample, 5 of 6 participants (83%) were male, and the mean (SD) age was 42.5 (13.4) years. Brain-wide coexpression analysis showed a highly interconnected network of genes preferentially expressed in the middle temporal gyrus (MTG), which further formed a highly connected protein-protein interaction network with IL-6 (enrichment test of expected vs observed network given the prevalence and degree of interactions in the STRING database: 43 nodes/30 edges observed vs 8 edges expected; mean node degree, 1.4; genome-wide significance, P = 4.54 × 10-9). MTG differentially expressed genes that were functionally enriched for biological processes in schizophrenia, autism spectrum disorder, and epilepsy.

Conclusions and Relevance

In this study, genetically determined IL-6 was associated with brain structure and potentially affects areas implicated in developmental neuropsychiatric disorders, including schizophrenia and autism.

Maternal immune activation in rodent models: A systematic review of neurodevelopmental changes in gene expression and epigenetic modulation in the offspring brain

Maternal immune activation (mIA) during pregnancy is hypothesised to disrupt offspring neurodevelopment and predispose offspring to neurodevelopmental disorders such as schizophrenia. Rodent models of mIA have explored possible mechanisms underlying this paradigm and provide a vital tool for preclinical research. However, a comprehensive analysis of the molecular changes that occur in mIA-models is lacking, hindering identification of robust clinical targets. This systematic review assesses mIA-driven transcriptomic and epigenomic alterations in specific offspring brain regions. Across 118 studies, we focus on 88 candidate genes and show replicated changes in expression in critical functional areas, including elevated inflammatory markers, and reduced myelin and GABAergic signalling proteins. Further, disturbed epigenetic markers at nine of these genes support mIA-driven epigenetic modulation of transcription. Overall, our results demonstrate that current outcome measures have direct relevance for the hypothesised pathology of schizophrenia and emphasise the importance of mIA-models in contributing to the understanding of biological pathways impacted by mIA and the discovery of new drug targets.

Standard versus reduced dose of antipsychotics for relapse prevention in multi-episode schizophrenia: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Dose reduction of antipsychotic maintenance treatment in individuals with schizophrenia could be desirable to minimise adverse effects, but evidence for this strategy is unclear. We aimed to compare risks and benefits of reduced versus standard doses of antipsychotics.

METHODS

We searched Embase, Medline, PsycINFO, and the Cochrane Library from database inception until June 17, 2020, for randomised trials in adults with schizophrenia or schizoaffective disorder lasting at least 24 weeks, including individuals clinically stable at baseline, and comparing at least two doses of the same antipsychotic, excluding trials in first-episode psychosis or treatment-resistant schizophrenia. We compared low-dose (within 50-99% of the lower limit of the standard dose) and very-low dose (less than 50% of the lower limit) with standard dose, defined as doses higher than the lower limit of the treatment dose recommended by the International Consensus Study. Data from published reports on number of participants, treatment, sex, age, number of events, and changes in psychopathology scores were extracted independently by at least two authors. Investigators or sponsors were contacted by email to obtain missing information regarding outcomes. Co-primary outcomes were relapse and all-cause discontinuation. Study-level data were meta-analysed using random-effects models, calculating risk ratios (RRs) for dichotomous data, and Hedges' g for continuous data. The protocol was registered with OSF registries.

FINDINGS

7853 references were identified in the database search and one additional reference from a manual review of relevant studies. 5744 abstracts were assessed for eligibility, and 101 references were assessed for full-text review. Of these, 79 were excluded for a variety of reasons, resulting in 22 studies being included in the meta-analysis, reporting on 24 trials and 3282 individuals. Study participants had a median age of 38 years (IQR 36-40) with 2166 (65·9%) males and 1116 (34·0%) females. Compared with standard dose, low dose increased the risk of relapse by 44% (16 trials, 1920 participants; RR 1·44, 95% CI 1·10-1·87; p=0·0076; I²=46%) and the risk of all-cause discontinuation by 12% (16 trials, 1932 participants; RR 1·12, 1·03-1·22; p=0·0085; I²=0%). Very low dose increased the risk of relapse by 72% (13 trials, 2058 participants; RR 1·72, 95% CI 1·29-2·29; p=0·0002; I²=70%) and all-cause discontinuation by 31% (11 trials, 1866 participants; RR 1·31, 1·11-1·54; p=0·0011; I²=63%). Compared with low dose, very low dose did not significantly increase the risk of relapse (five trials, 686 participants; RR 1·31, 95% CI 0·96-1·79; p=0·092; I²=51%) or all-cause discontinuation (five trials 686 participants; RR 1·11, 95% CI 0·95-1·30; p=0·18; I²=43%). Subgroup analyses comparing double-blind versus open-label studies, first-generation versus second-generation antipsychotics, and oral versus long-acting injectable antipsychotics were consistent with the overall results. Most studies were classified as having some concerns in the risk of bias assessment, which was mainly caused by absence of publicly available study registrations.

INTERPRETATION

During maintenance treatment in multi-episode schizophrenia, antipsychotic doses should probably not be reduced below the standard dose range recommended for acute stabilisation, because reducing the dose further is associated with an increased risk of both relapse and all-cause discontinuation.

FUNDING

None.

Poly(I:C) source, molecular weight and endotoxin contamination affect dam and prenatal outcomes, implications for models of maternal immune activation

The viral mimetic polyinosinic:polycytidylic acid (poly(I:C)) is increasingly used to induce maternal immune activation (mIA) to model neurodevelopmental disorders (NDDs). Robust and reproducible phenotypes across studies are essential for the generation of models that will enhance our understanding of NDDs and enable the development of improved therapeutic strategies. However, differences in mIA-induced phenotypes using poly(I:C) have been widely observed, and this has prompted the reporting of useful and much needed methodological guidelines. Here, we perform a detailed investigation of molecular weight and endotoxin variations in poly(I:C) procured from two of the most commonly used suppliers, Sigma and InvivoGen. We demonstrate that endotoxin contamination and molecular weight differences in poly(I:C) composition lead to considerable variability in maternal IL-6 response in rats treated on gestational day (GD)15 and impact on fetal outcomes. Specifically, both endotoxin contamination and molecular weight predicted reductions in litter size on GD21. Further, molecular weight predicted a reduction in placental weight at GD21. While fetal body weight at GD21 was not affected by poly(I:C) treatment, male fetal brain weight was significantly reduced by poly(I:C), dependent on supplier. Our data are in agreement with recent reports of the importance of poly(I:C) molecular weight, and extend this work to demonstrate a key role of endotoxin on relevant phenotypic outcomes. We recommend that the source and batch numbers of poly(I:C) used should always be stated and that molecular weight variability and endotoxin contamination should be minimised for more robust mIA modelling.

Cognitive dysfunction in diabetic rats is prevented by pyridoxamine treatment. A multidisciplinary investigation

OBJECTIVE

The impact of diabetes mellitus on the central nervous system is less widely studied than in the peripheral nervous system, but there is increasing evidence that it elevates the risk of developing cognitive deficits. The aim of this study was to characterize the impact of experimental diabetes on the proteome and metabolome of the hippocampus. We tested the hypothesis that the vitamin B6 isoform pyridoxamine is protective against functional and molecular changes in diabetes.

METHODS

We tested recognition memory using the novel object recognition (NOR) test in streptozotocin (STZ)-induced diabetic, age-matched control, and pyridoxamine- or insulin-treated diabetic male Wistar rats. Comprehensive untargeted metabolomic and proteomic analyses, using gas chromatography-mass spectrometry and iTRAQ-enabled protein quantitation respectively, were utilized to characterize the molecular changes in the hippocampus in diabetes.

RESULTS

We demonstrated diabetes-specific, long-term (but not short-term) recognition memory impairment and that this deficit was prevented by insulin or pyridoxamine treatment. Metabolomic analysis showed diabetes-associated changes in 13/82 identified metabolites including polyol pathway intermediates glucose (9.2-fold), fructose (4.9-fold) and sorbitol (5.2-fold). We identified and quantified 4807 hippocampal proteins; 806 were significantly altered in diabetes. Pathway analysis revealed significant alterations in cytoskeletal components associated with synaptic plasticity, glutamatergic signaling, oxidative stress, DNA damage and FXR/RXR activation pathways in the diabetic rat hippocampus.

CONCLUSIONS

Our data indicate a protective effect of pyridoxamine against diabetes-induced cognitive deficits, and our comprehensive 'omics datasets provide insight into the pathogenesis of cognitive dysfunction enabling development of further mechanistic and therapeutic studies.

Global brain volume reductions in a sub-chronic phencyclidine animal model for schizophrenia and their relationship to recognition memory

BACKGROUND

Cognitive deficits and structural brain changes co-occur in patients with schizophrenia. Improving our understanding of the relationship between these is important to develop improved therapeutic strategies. Back-translation of these findings into rodent models for schizophrenia offers a potential means to achieve this goal.

AIMS

The purpose of this study was to determine the extent of structural brain changes and how these relate to cognitive behaviour in a sub-chronic phencyclidine rat model.

METHODS

Performance in the novel object recognition task was examined in female Lister Hooded rats at one and six weeks after sub-chronic phencyclidine (2 mg/kg intra-peritoneal, n=15) and saline controls (1 ml/kg intra-peritoneal, n=15). Locomotor activity following acute phencyclidine challenge was also measured. Brain volume changes were assessed in the same animals using ex vivo structural magnetic resonance imaging and computational neuroanatomical analysis at six weeks.

RESULTS

Female sub-chronic phencyclidine-treated Lister Hooded rats spent significantly less time exploring novel objects (p<0.05) at both time-points and had significantly greater locomotor activity response to an acute phencyclidine challenge (p<0.01) at 3-4 weeks of washout. At six weeks, sub-chronic phencyclidine-treated Lister Hooded rats displayed significant global brain volume reductions (p<0.05; q<0.05), without apparent regional specificity. Relative volumes of the perirhinal cortex however were positively correlated with novel object exploration time only in sub-chronic phencyclidine rats at this time-point.

CONCLUSION

A sustained sub-chronic phencyclidine-induced cognitive deficit in novel object recognition is accompanied by global brain volume reductions in female Lister Hooded rats. The relative volumes of the perirhinal cortex however are positively correlated with novel object exploration, indicating some functional relevance.

Stabilized Low-n Amyloid-β Oligomers Induce Robust Novel Object Recognition Deficits Associated with Inflammatory, Synaptic, and GABAergic Dysfunction in the Rat

BACKGROUND

With current treatments for Alzheimer's disease (AD) only providing temporary symptomatic benefits, disease modifying drugs are urgently required. This approach relies on improved understanding of the early pathophysiology of AD. A new hypothesis has emerged, in which early memory loss is considered a synapse failure caused by soluble amyloid-β oligomers (Aβo). These small soluble Aβo, which precede the formation of larger fibrillar assemblies, may be the main cause of early AD pathologies.

OBJECTIVE

The aim of the current study was to investigate the effect of acute administration of stabilized low-n amyloid-β1-42 oligomers (Aβo1-42) on cognitive, inflammatory, synaptic, and neuronal markers in the rat.

METHODS

Female and male Lister Hooded rats received acute intracerebroventricular (ICV) administration of either vehicle or 5 nmol of Aβo1-42 (10μL). Cognition was assessed in the novel object recognition (NOR) paradigm at different time points. Levels of inflammatory (IL-1β, IL-6, TNF-α), synaptic (PSD-95, SNAP-25), and neuronal (n-acetylaspartate, parvalbumin-positive cells) markers were investigated in different brain regions (prefrontal and frontal cortex, striatum, dorsal and ventral hippocampus).

RESULTS

Acute ICV administration of Aβo1-42 induced robust and enduring NOR deficits. These deficits were reversed by acute administration of donepezil and rolipram but not risperidone. Postmortem analysis revealed an increase in inflammatory markers, a decrease in synaptic markers and parvalbumin containing interneurons in the frontal cortex, with no evidence of widespread neuronal loss.

CONCLUSION

Taken together the results suggest that acute administration of soluble low-n Aβo may be a useful model to study the early mechanisms involved in AD and provide us with a platform for testing novel therapeutic approaches that target the early underlying synaptic pathology.

Evolution of a maternal immune activation (mIA) model in rats: Early developmental effects

Maternal immune activation (mIA) in rodents is rapidly emerging as a key model for neurodevelopmental disorders such as autism spectrum disorder (ASD) and schizophrenia. Here, we optimise a mIA model in rats, aiming to address certain limitations of current work in this field. Specifically, the lack of clear evidence for methodology chosen, identification of successful induction of mIA in the dams and investigation of male offspring only. We focus on gestational and early juvenile changes in offspring following mIA, as detailed information on these critical early developmental time points is sparse. Following strain (Wistar, Lister Hooded, Sprague Dawley) comparison and selection, and polyriboinosinic-polyribocytidylic acid (poly I:C) dose selection (2.5-15 mg/kg single or once daily for 5 days), mIA was induced in pregnant Wistar rats with 10 mg/kg poly I:C i.p. on gestational day (GD) 15. Early morphometric analysis was conducted in male and female offspring at GD21 and postnatal day (PD) 21, eight dams for each treatment at each time point were used, 32 in total. Subsequent microglia analysis was conducted at PD21 in a small group of offspring. Poly I:C at 10 mg/kg i.p. induced a robust, but variable, plasma IL-6 response 3 h post-injection and reduced body weight at 6 h and 24 h post-injection in two separate cohorts of Wistar rats at GD15. Plasma IL-6 was not elevated at PD21 in offspring or dams. Poly I:C-induced mIA did not affect litter numbers, but resulted in PD21 pup, and GD21 placenta growth restriction. Poly I:C significantly increased microglial activation at PD21 in male hippocampi. We have identified 10 mg/kg poly I:C i.p on GD15 as a robust experimental approach for inducing mIA in Wistar rats and used this to identify early neurodevelopmental changes. This work provides a framework to study the developmental trajectory of disease-relevant, sex-specific phenotypic changes in rats.

Mapping the impact of exposure to maternal immune activation on juvenile Wistar rat brain macro- and microstructure during early post-natal development

Maternal immune activation is consistently associated with elevated risk for multiple psychiatric disorders in the affected offspring. Related to this, an important goal of our work is to explore the impact of maternal immune activation effects across the lifespan. In this context, we recently reported the effects of polyriboinosinic-polyribocytidylic acid-induced maternal immune activation at gestational day 15, immediately prior to birth, at gestational day 21 and again at post-natal day 21, providing a systematic assessment of plasma interleukin 6, body temperature and weight alterations in pregnant rats and preliminary evidence for gross morphological changes and microglial neuropathology in both male and female offsprings at these time points. Here, we sought to complement and extend these data by characterising in more detail the mesoscale impact of gestational polyriboinosinic-polyribocytidylic acid exposure at gestational day 15 on the neuroanatomy of the juvenile (post-natal day 21) rat brain using high-resolution, ex vivo anatomical magnetic resonance imaging in combination with atlas-based segmentation. Our preliminary data suggest subtle neuroanatomical effects of gestational polyriboinosinic-polyribocytidylic acid exposure (n = 10) relative to saline controls (n = 10) at this time-point. Specifically, we found an increase in the relative volume of the diagonal domain in polyriboinosinic-polyribocytidylic acid offspring (p < 0.01 uncorrected), which just failed to pass stringent multiple comparisons correction (actual q = 0.07). No statistically significant microstructural alterations were detectable using diffusion tensor imaging. Further studies are required to map the proximal effects of maternal immune activation on the developing rodent brain from foetal to early post-natal life and confirm our findings herein.

Pharmacology of cognition: a panacea for neuropsychiatric disease?

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.

Dopamine dysregulation in the prefrontal cortex relates to cognitive deficits in the sub-chronic PCP-model for schizophrenia: A preliminary investigation

RATIONALE

Dopamine dysregulation in the prefrontal cortex (PFC) plays an important role in cognitive dysfunction in schizophrenia. Sub-chronic phencyclidine (scPCP) treatment produces cognitive impairments in rodents and is a thoroughly validated animal model for cognitive deficits in schizophrenia. The aim of our study was to investigate the role of PFC dopamine in scPCP-induced deficits in a cognitive task of relevance to the disorder, novel object recognition (NOR).

METHODS

Twelve adult female Lister Hooded rats received scPCP (2 mg/kg) or vehicle via the intraperitoneal route twice daily for 7 days, followed by 7 days washout. In vivo microdialysis was carried out prior to, during and following the NOR task.

RESULTS

Vehicle rats successfully discriminated between novel and familiar objects and this was accompanied by a significant increase in dopamine in the PFC during the retention trial ( p < 0.01). scPCP produced a significant deficit in NOR ( p < 0.05 vs. control) and no PFC dopamine increase was observed.

CONCLUSIONS

These data demonstrate an increase in dopamine during the retention trial in vehicle rats that was not observed in scPCP-treated rats accompanied by cognitive disruption in the scPCP group. This novel finding suggests a mechanism by which cognitive deficits are produced in this animal model and support its use for investigating disorders in which PFC dopamine is central to the pathophysiology.

Modelling the cognitive and neuropathological features of schizophrenia with phencyclidine

Here, Reynolds and Neill describe the studies that preceded and followed publication of this paper, which reported a deficit in parvalbumin (PV), a calcium-binding protein found in GABA interneurons known to be reduced in schizophrenia patients, in conjunction with a deficit in reversal learning in an animal model for schizophrenia. This publication resulted from common research interests: Reynolds in the neurotransmitter pathology of schizophrenia, and Neill in developing animal models for schizophrenia symptomatology. The animal model, using a sub-chronic dosing regimen (sc) with the non-competitive NMDA receptor antagonist PCP (phencyclidine), evolved from previous work in rats (for PCP) and primates (for cognition). The hypothesis of a PV deficit came from emerging evidence for a GABAergic dysfunction in schizophrenia, in particular a deficit in PV-containing GABA interneurons. Since this original publication, a PV deficit has been identified in other animal models for schizophrenia, and the PV field has expanded considerably. This includes mechanistic work attempting to identify the link between oxidative stress and GABAergic dysfunction using this scPCP model, and assessment of the potential of the PV neuron as a target for new antipsychotic drugs. The latter has included development of a molecule targeting KV3.1 channels located on PV-containing GABA interneurons which can restore both PV expression and cognitive deficits in the scPCP model.

Subchronic administration of phencyclidine produces hypermethylation in the parvalbumin gene promoter in rat brain

AIM

A deficit in parvalbumin neurons is found in schizophrenia and several animal models of the disease. In this preliminary study, we determined whether one such model, phencyclidine (PCP) administration, results in changes in DNA methylation in the rat Pvalb promoter.

MATERIALS & METHODS

DNA from hippocampus and prefrontal cortex from rats, which 6 weeks previously received either 2 mg/kg PCP or vehicle for 7 days, underwent bisulphite pyrosequencing to determine methylation.

RESULTS

PCP administration induced significantly greater methylation at one of two Pvalb CpG sites in both prefrontal cortex and hippocampus, while no significant difference was found in long interspersed nucleotide element-1, a global measure of DNA methylation.

CONCLUSION

Subchronic PCP administration results in a specific hypermethylation in the Pvalb promoter which may contribute to parvalbumin deficits in this animal model of psychosis.

Postnatal Phencyclidine (PCP) as a Neurodevelopmental Animal Model of Schizophrenia Pathophysiology and Symptomatology: A Review

Cognitive dysfunction and negative symptoms of schizophrenia remain an unmet clinical need. Therefore, it is essential that new treatments and approaches are developed to recover the cognitive and social impairments that are seen in patients with schizophrenia. These may only be discovered through the use of carefully validated, aetiologically relevant and translational animal models. With recent renewed interest in the neurodevelopmental hypothesis of schizophrenia, postnatal administration of N-methyl-D-aspartate receptor (NMDAR) antagonists such as phencyclidine (PCP) has been proposed as a model that can mimic aspects of schizophrenia pathophysiology. The purpose of the current review is to examine the validity of this model and compare it with the adult subchronic PCP model. We review the ability of postnatal PCP administration to produce behaviours (specifically cognitive deficits) and neuropathology of relevance to schizophrenia and their subsequent reversal by pharmacological treatments. We review studies investigating effects of postnatal PCP on cognitive domains in schizophrenia in rats. Morris water maze and delayed spontaneous alternation tasks have been used for working memory, attentional set-shifting for executive function, social novelty discrimination for selective attention and prepulse inhibition of acoustic startle for sensorimotor gating. In addition, we review studies on locomotor activity and neuropathology. We also include two studies using dual hit models incorporating postnatal PCP and two studies on social behaviour deficits following postnatal PCP. Overall, the evidence we provide supports the use of postnatal PCP to model cognitive and neuropathological disturbances of relevance to schizophrenia. To date, there is a lack of evidence to support a significant advantage of postnatal PCP over the adult subchronic PCP model and full advantage has not been taken of its neurodevelopmental component. When thoroughly characterised, it is likely that it will provide a useful neurodevelopmental model to complement other models such as maternal immune activation, particularly when combined with other manipulations to produce dual or triple hit models. However, the developmental trajectory of behavioural and neuropathological changes induced by postnatal PCP and their relevance to schizophrenia must be carefully mapped out. Overall, we support further development of dual (or triple) hit models incorporating genetic, neurodevelopmental and appropriate environmental elements in the search for more aetiologically valid animal models of schizophrenia and neurodevelopmental disorders (NDDs).

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.

Putative therapeutic targets for symptom subtypes of adult ADHD: D4 receptor agonism and COMT inhibition improve attention and response inhibition in a novel translational animal model

Prefrontal cortical dopamine plays an important role in cognitive control, specifically in attention and response inhibition; the core deficits in ADHD. We have previously shown that methylphenidate and atomoxetine differentially improve these deficits dependent on baseline performance. The present study extends this work to investigate the effects of putative therapeutic targets in our model. A selective dopamine D4 receptor agonist (A-412997) and the catechol-O-methyl-transferase (COMT) inhibitor; tolcapone, were investigated in the combined subtype of adult ADHD (ADHD-C). Adult female rats were trained to criterion in the 5C-CPT (5-Choice Continuous Performance Task) and then separated into subgroups according to baseline levels of sustained attention, vigilance, and response disinhibition. The subgroups included: high-attentive (HA) and low-attentive with high response disinhibition (ADHD-C). The ADHD-C subgroup was selected to represent the combined subtype of adult ADHD. Effects of tolcapone (3.0, 10.0, 15.0mg/kg) and A-412997 (0.1, 0.3, 1.0µmol/kg) were tested by increasing the variable inter-trial-interval (ITI) duration in the 5C-CPT. Tolcapone (15mg/kg) significantly increased sustained attention, vigilance and response inhibition in ADHD-C animals, and impaired attention in HA animals. A-412997 (1.0µmol/kg) significantly increased vigilance and response inhibition in ADHD-C animals only, with no effect in HA animals. This is the first study to use the translational 5C-CPT to model the adult ADHD-C subtype in rats and to study new targets in this model. Both tolcapone and A-412997 increased vigilance and response inhibition in the ADHD-C subgroup. D4 and COMT are emerging as important potential therapeutic targets in adult ADHD that warrant further investigation.

Pay attention to impulsivity: modelling low attentive and high impulsive subtypes of adult ADHD in the 5-choice continuous performance task (5C-CPT) in female rats

Varying levels of attention and impulsivity deficits are core features of the three subtypes of adult attention deficit-hyperactivity disorder (ADHD). To date, little is known about the neurobiological correlates of these subtypes. Development of a translational animal model is essential to improve our understanding and improve therapeutic strategies. The 5-choice continuous performance task (5C-CPT) in rats can be used to examine different forms of attention and impulsivity. Adult rats were trained to pre-set 5C-CPT criterion and subsequently separated into subgroups according to baseline levels of sustained attention, vigilance, premature responding and response disinhibition in the 5C-CPT. The behavioural subgroups were selected to represent the different subtypes of adult ADHD. Consequently, effects of the clinically used pharmacotherapies (methylphenidate and atomoxetine) were assessed in the different subgroups. Four subgroups were identified: low-attentive (LA), high-attentive (HA), high-impulsive (HI) and low-impulsive (LI). Methylphenidate and atomoxetine produced differential effects in the subgroups. Methylphenidate increased sustained attention and vigilance in LA animals, and reduced premature responding in HI animals. Atomoxetine also improved sustained attention and vigilance in LA animals, and reduced response disinhibition and premature responding in HI animals. This is the first study using adult rats to demonstrate the translational value of the 5C-CPT to select subgroups of rats, which may be used to model the subtypes observed in adult ADHD. Our findings suggest that this as an important paradigm to increase our understanding of the neurobiological underpinnings of adult ADHD-subtypes and their response to pharmacotherapy.

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

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

PD168077, a D(4) receptor agonist, reverses object recognition deficits in rats: potential role for D(4) receptor mechanisms in improving cognitive dysfunction in schizophrenia

This study investigated the effects of the dopamine D(4) receptor agonist, PD168077, on recognition memory using a novel object recognition task, which detects disruption and improvement of recognition memory in rats by measuring their ability to discriminate between familiar and novel objects. When acquisition and test were 6 h apart (experiment 1), control rats failed to discriminate between familiar and novel objects at test. Rats given low doses of PD168077 (0.3; 1.0 mg/kg) also failed to discriminate between the objects, while rats given higher doses (3.0; 10.0 mg/kg) explored the novel object more than the familiar object, indicating retained memory of the familiar object. Thus, at higher doses, PD168077 improved recognition memory in rats. Experiment 2 tested whether PD168077 would attenuate deficits in novel object recognition induced by sub-chronic phencyclidine. Testing was 1 min after acquisition, such that vehicle pre-treated rats differentiated between the novel and familiar objects: however, sub-chronic phencyclidine-treated rats failed to discriminate between the two, indicating disruption of recognition memory. PD168077 (10 mg/kg) restored the ability of phencyclidine-treated rats to differentiate between the novel and familiar objects, indicating improved recognition memory. The results suggest that D(4) receptor activation can improve cognitive dysfunction in an animal model relevant to schizophrenia.

Phencyclidine (PCP)-induced disruption in cognitive performance is gender-specific and associated with a reduction in brain-derived neurotrophic factor (BDNF) in specific regions of the female rat brain

Phencyclidine (PCP), used to mimic certain aspects of schizophrenia, induces sexually dimorphic, cognitive deficits in rats. In this study, the effects of sub-chronic PCP on expression of brain-derived neurotrophic factor (BDNF), a neurotrophic factor implicated in the pathogenesis of schizophrenia, have been evaluated in male and female rats. Male and female hooded-Lister rats received vehicle or PCP (n=8 per group; 2 mg/kg i.p. twice daily for 7 days) and were tested in the attentional set shifting task prior to being sacrificed (6 weeks post-treatment). Levels of BDNF mRNA were measured in specific brain regions using in situ hybridisation. Male rats were less sensitive to PCP-induced deficits in the extra-dimensional shift stage of the attentional set shifting task compared to female rats. Quantitative analysis of brain regions demonstrated reduced BDNF levels in the medial prefrontal cortex (p<0.05), motor cortex (p<0.01), orbital cortex (p<0.01), olfactory bulb (p<0.05), retrosplenial cortex (p<0.001), frontal cortex (p<0.01), parietal cortex (p<0.01), CA1 (p<0.05) and polymorphic layer of dentate gyrus (p<0.05) of the hippocampus and the central (p<0.01), lateral (p<0.05) and basolateral (p<0.05) regions of the amygdaloid nucleus in female PCP-treated rats compared with controls. In contrast, BDNF was significantly reduced only in the orbital cortex and central amygdaloid region of male rats (p<0.05). Results suggest that blockade of NMDA receptors by sub-chronic PCP administration has a long-lasting down-regulatory effect on BDNF mRNA expression in the female rat brain which may underlie some of the behavioural deficits observed post PCP administration.

Animal models of cognitive dysfunction and negative symptoms of schizophrenia: focus on NMDA receptor antagonism

Cognitive deficits in schizophrenia remain an unmet clinical need. Improved understanding of the neuro- and psychopathology of these deficits depends on the availability of carefully validated animal models which will assist the development of novel therapies. There is much evidence that at least some of the pathology and symptomatology (particularly cognitive and negative symptoms) of schizophrenia results from a dysfunction of the glutamatergic system which may be modelled in animals through the use of NMDA receptor antagonists. The current review examines the validity of this model in rodents. We review the ability of acute and sub-chronic treatment with three non-competitive NMDA antagonists; phencyclidine (PCP), ketamine and MK801 (dizocilpine) to produce cognitive deficits of relevance to schizophrenia in rodents and their subsequent reversal by first- and second-generation antipsychotic drugs. Effects of NMDA receptor antagonists on the performance of rodents in behavioural tests assessing the various domains of cognition and negative symptoms are examined: novel object recognition for visual memory, reversal learning and attentional set shifting for problem solving and reasoning, 5-Choice Serial Reaction Time for attention and speed of processing; in addition to effects on social behaviour and neuropathology. The evidence strongly supports the use of NMDA receptor antagonists to model cognitive deficit and negative symptoms of schizophrenia as well as certain pathological disturbances seen in the illness. This will facilitate the evaluation of much-needed novel pharmacological agents for improved therapy of cognitive deficits and negative symptoms in schizophrenia.

Effects of subchronic phencyclidine on behaviour of female rats on the elevated plus maze and open field

Female hooded-Lister rats received either subchronic phencyclidine (PCP) (2 mg/kg, n = 20) or vehicle (1 ml/kg, n = 20) intraperitoneally twice daily for 7 days, followed by a 7-day washout period. Rats were challenged with acute PCP or vehicle and tested for locomotor activity to ensure hyperactivity was observed in the subchronic PCP-treated rats. Rats were then tested on the elevated plus maze and in an open field for 10 min. Subchronic PCP did not significantly affect behaviour on the elevated plus maze or in the open field. In conclusion, subchronic PCP does not induce anxiety-like behaviour.

Olanzapine-induced weight gain in the rat: role of 5-HT2C and histamine H1 receptors

INTRODUCTION

Substantial increases in body weight can be induced by several antipsychotic drugs, most notably olanzapine and clozapine. Antagonism at certain receptors, particularly 5-HT2C and histamine H1 receptors, is implicated in this effect.

MATERIALS AND METHODS

We have investigated the contribution of effects at these receptors to olanzapine-induced weight gain occurring over 5 days following daily intraperitoneal drug injections in groups of eight female rats.

RESULTS

Olanzapine (2 mg/kg) and the 5-HT2C antagonist SB 243213 (1 mg/kg), but not the histamine H1 antagonist mepyramine (1 mg/kg), produced significant increases in percentage body weight above vehicle; olanzapine showed a significantly greater effect than SB 243213. Haloperidol (0.1 mg/kg) alone or with mepyramine had no significant effects on weight gain, while with SB 243213 and with both SB 243213 and mepyramine, it showed olanzapine-like increases in weight.

CONCLUSION

These results suggest that 5-HT2C receptor antagonism or inverse agonism, in the presence of D2 receptor antagonism, may contribute to olanzapine-induced weight gain.

Oestradiol attenuates the cognitive deficit induced by acute phencyclidine treatment in mature female hooded-Lister rats

Gender differences in psychiatric research are becoming more widely recognized, and changes in levels of the steroid hormone, oestrogen, over the menstrual or oestrous cycle are becoming increasingly implicated in alterations in cognitive strategies and capacities. The aim of this study is to investigate the interaction between oestrogen, NMDA receptor function and cognitive processing in rats. Forty-five mature female hooded-Lister rats received vehicle, 0.5, 5 or 10 microg/kg of oestradiol benzoate (EB, s.c. in olive oil) 24 h prior to an acute dose of 2 mg/kg phencyclidine (PCP, i.p. in 0.9% w/v saline), or vehicle (0.9% saline). After 30 min following PCP treatment, animals completed the novel object recognition task with a 1 min inter-trial interval to assess object recognition memory. Results show that 5 and 10 microg/kg of EB 24 h prior to 2 mg/kg PCP significantly (P < 0.01 and < 0.001, respectively) protected against the cognitive impairing effect of PCP in contrast to vehicle and 0.5 microg/kg EB plus PCP (not significant). EB may exert a neuromodulatory effect in this animal model leading to attenuation of the PCP-induced impairment in object recognition memory, suggesting an interaction between the gonadal steroids and NMDA receptor-mediated cognitive dysfunction, which is of potential relevance to schizophrenia.

Ziprasidone and aripiprazole attenuate olanzapine-induced hyperphagia in rats

Weight gain induced by some second-generation anti-psychotics such as olanzapine has emerged as a most debilitating side-effect. This study investigates whether co-administration with either ziprasidone or aripiprazole, which have little propensity to induce weight gain, can attenuate the hyperphagic effect of olanzapine. Female hooded-Lister rats (n=8 per group) were treated acutely with either vehicle, olanzapine (1 mg/kg), ziprasidone (1 mg/kg), aripiprazole (2 mg/kg) or olanzapine in combination with ziprasidone or aripiprazole and placed in automated locomotor activity (LMA) boxes with preweighed palatable mash. Food intake and LMA were measured for 60 min postdrug treatment. All olanzapine-treated groups demonstrated significant increases in food intake (P<0.001). This effect was attenuated following co-administration of olanzapine with either ziprasidone or aripiprazole (P<0.001), neither of which affected food intake alone. The lack of hyperphagia induced by aripiprazole and ziprasidone may reflect an inherent pharmacological mechanism preventing weight gain.

Investigation into the influence of a high fat diet on antipsychotic-induced weight gain in female rats

Atypical antipsychotic drug therapy may result in substantial weight gain, increased adiposity and the promotion of metabolic abnormalities. The mechanism(s) which underlie such effects remain unclear. Previous studies in our laboratory have demonstrated significant weight gain in female rats maintained on a standard laboratory diet after sub-chronic administration of olanzapine and risperidone, but not ziprasidone. The aim of this paper is to investigate the effect of antipsychotic drugs on body weight, ingestive behaviour and adiposity in female rats with access to a high fat diet. Adult female rats given free access to a high fat diet received either olanzapine (2 mg/kg), risperidone (0.5 mg/kg), ziprasidone (2.5 mg/kg) or vehicle for 28 days. Body weight, food and water intake in addition to intra-abdominal fat deposition were assessed. Olanzapine initially increased body weight but by the end of the study olanzapine animals appeared to have lost weight compared to the vehicle-treated group. Olanzapine-induced reductions in body weight were accompanied by a significant hypophagia during weeks 3 and 4. Risperidone increased body weight during week 1 only and reduced intake of a high fat diet during weeks 3 and 4. Ziprasidone was without effect on indices of body weight and ingestive behaviour. There were no effects of antipsychotic drugs on intra-abdominal fat deposition. Access to a diet high in fat attenuated weight gain induced by olanzapine and risperidone in female rats.

The distinct effects of subchronic antipsychotic drug treatment on macronutrient selection, body weight, adiposity, and metabolism in female rats

INTRODUCTION

Treatment with some antipsychotic drugs may result in excessive body weight gain which can have detrimental effects on patient compliance, morbidity and mortality. The aim of the present study was to investigate the effect of atypical antipsychotic drugs on dietary macronutrient selection, body weight, body composition and biochemical parameters related to obesity in female rats.

MATERIALS AND METHODS

Forty pair-housed, adult female hooded-Lister rats (250 +/- 5 g) were habituated to three diets containing principally protein, fat, or carbohydrate in a home cage self-selection paradigm. Olanzapine (2 mg/kg), risperidone (0.5 mg/kg), ziprasidone (2.5 mg/kg), or vehicle was injected intraperitoneally once daily for 22 days; food selection, water intake, and body weight were recorded daily, while body composition and plasma hormones (insulin, glucose, nonesterified free fatty acid, total cholesterol, glycerol, triacylglycerol, leptin, and prolactin) were analyzed at the end of the study.

RESULTS

Only olanzapine significantly increased body weight and food intake. Macronutrient selection was significantly altered after olanzapine and risperidone treatment (increased protein and decreased fat preference). Only olanzapine increased carcass fat content. Locomotor activity was significantly reduced in all treatment groups. Both olanzapine and risperidone significantly increased plasma prolactin. Olanzapine was without effect on any other biochemical parameter measured. Ziprasidone significantly reduced plasma leptin and nonsignificantly reduced NEFA, while risperidone significantly reduced fasting plasma glucose.

CONCLUSION

This study supports our previous work demonstrating weight gain and increased feeding behavior induced by olanzapine and could have important implications for enhancing our understanding of the mechanisms by which olanzapine and other atypical antipsychotics induce weight gain in the clinic.

Atypical antipsychotics attenuate a sub-chronic PCP-induced cognitive deficit in the novel object recognition task in the rat

The novel object recognition (NOR) task is a paradigm employed to detect both disruption and improvement of non-spatial memory in rats. PCP (phencyclidine) may be used to model aspects of schizophrenia symptomology in rats, in particular cognitive deficits. The aim of this study was to investigate the ability of typical and atypical antipsychotics to improve a sub-chronic PCP-induced impairment in cognition using the NOR task. Female hooded-Lister rats (195+/-12 g) received either vehicle (0.9% saline twice daily) or PCP (2 mg/kg, twice daily) for 7 days followed by 7-days drug free. Haloperidol (0.05 and 0.075 mg/kg), clozapine (1 and 5mg/kg), risperidone (0.05, 0.1 and 0.2 mg/kg) or vehicle (veh, saline) was administered i.p. 30 min prior to testing. Rats completed an acquisition trial followed by an inter-trial interval of 1 min, then a retention trial. Following sub-chronic vehicle treatment, rats spent significantly (p<0.05) more time exploring the novel compared to the familiar object, an effect that was abolished in the sub-chronic PCP treated animals. Clozapine (1.0 and 5.0 mg/kg) and risperidone (0.2 mg/kg) but not haloperidol significantly attenuated the PCP-induced impairment such that animals again spent significantly more time exploring the novel compared with familiar object (p<0.05). These results support our earlier work showing that acute PCP induces a robust object recognition deficit in female rats. Clozapine and risperidone but not haloperidol showed efficacy to reverse the deficit induced by sub-chronic PCP suggesting that this test may have some validity for assessing efficacy for improvement of cognitive deficit symptoms of schizophrenia.

Sub-chronic psychotomimetic phencyclidine induces deficits in reversal learning and alterations in parvalbumin-immunoreactive expression in the rat

Acute administration of the psychotomimetic phencyclidine (PCP) can mimic some features of schizophrenia, while a repeated treatment regimen of PCP may provide a more effective way to model in animals the enduring cognitive dysfunction observed in many schizophrenic patients. The present study aims to investigate behavioural and neuropathological effects of sub-chronic PCP administration. The cognitive deficit induced by sub-chronic PCP was examined using a previously established operant reversal-learning paradigm. Subsequently, the effect of sub-chronic PCP on parvalbumin-immunoreactive (parvalbumin-IR) neurons was assessed using immunohistochemical techniques. Rats were trained to respond for food in an operant reversal-learning paradigm for approximately 6 weeks, followed by sub-chronic administration of PCP (2mg/kg) or vehicle twice daily for 7 days followed 7 days later by behavioural testing. Six weeks post PCP, brains were analysed using immunohistochemical techniques to determine the size and density of parvalbumin-IR in the frontal cortex and hippocampus. Sub-chronic PCP significantly reduced (p <0.001) percentage correct responding in the reversal phase relative to the initial phase, an effect that persisted throughout the experimental period (4 weeks). The density of parvalbumin-IR neurons was reduced in the hippocampus, with significant reductions in the dentate gyrus and CA2/3 regions (p <0.001). There were significant changes in the frontal cortex, with a reduction (p <0.01) in the M1 (motor area 1) region and increases in the M2 (motor area 2) region and cingulate cortex (p <0.01-p <0.001). These results parallel findings of profound hippocampal and more subtle cortical deficits of parvalbumin-IR neurons in schizophrenia, and provide evidence to suggest that sub-chronic PCP can induce a lasting cognitive deficit, an effect that may be related to the observed neuronal deficits.

Influence of gender on working and spatial memory in the novel object recognition task in the rat

Gender differences in many behavioural tasks have been observed in both humans and laboratory animals. The novel object recognition (NOR) task is increasingly used to investigate drug effects on working memory processes, although, the influence of sexually dimorphic behaviours have not yet been evaluated. In addition, the role of natural fluctuations in the sex steroids during the oestrous cycle has received little attention during object recognition tasks. Therefore, the aim of the current study was to investigate the influence of gender and oestrous cycle phase on working and spatial memory using the NOR task. Animals were tested in the NOR task and the spatial NOR task. Male and female rats completed an acquisition trial followed by an inter-trial interval of a specified length, then a final retention trial. Vaginal cytology enabled the influence of oestrous cycle phase to be determined in both the NOR and spatial NOR, each animal was tested during one phase of their regular oestrous cycle only. It was found that female rats performed significantly better than male rats in the standard NOR paradigm (p<0.05 compared to no significance (NS) at 3h, respectively), while male rats showed improved memory in the spatial NOR paradigm compared with female rats (p<0.05 compared to NS at 3h, respectively). There was no influence of phase of oestrous cycle on the NOR task, however, during the spatial NOR there was a significant improvement in ability when oestrogen and progesterone levels have been shown to be at their lowest (i.e. p<0.05 during oestrous compared to NS at other stages). In conclusion, it is clear that gonadal hormones can influence components of memory and gender is an important consideration in experimental design.

The effect of atypical and classical antipsychotics on sub-chronic PCP-induced cognitive deficits in a reversal-learning paradigm

Phencyclidine (PCP), an NMDA antagonist, has been shown to mimic some aspects of schizophrenia including positive, negative and cognitive symptoms. Previous studies in this laboratory have shown a selective reversal-learning deficit following acute PCP administration, a deficit that is attenuated by atypical, but not classical, antipsychotic treatment. However, acute PCP has limitations for modelling the chronic psychotic illness and persistent cognitive deficits observed in many schizophrenic patients. Therefore, the aim of this study was to examine the cognitive deficit induced by PCP over a longer term using a previously established operant reversal-learning procedure. Moreover, the efficacy of the atypical antipsychotics clozapine, ziprasidone and olanzapine to reverse the sub-chronic PCP deficit was compared with that of the classical antipsychotics, haloperidol and chlorpromazine. Female hooded-Lister rats were trained to respond for food using an operant reversal-learning paradigm. When animals achieved criterion of 90% correct responding they were treated with PCP (2mg/kg) or vehicle twice daily for 7 days, and 7 days later tested for their cognitive ability. PCP induced a significant impairment in the reversal phase relative to the initial phase of the task. Acute ziprasidone (2.5mg/kg), olanzapine (1.5mg/kg) and clozapine (5mg/kg) produced a significant attenuation of the impairment induced by sub-chronic PCP in the reversal phase. In marked contrast to these effects, acute administration of the classical agents haloperidol (0.05 mg/kg) and chlorpromazine (2mg/kg) failed to significantly reverse the PCP-induced cognitive impairment. These data clearly demonstrate that sub-chronic PCP produces enduring and persistent cognitive deficits, effects that are significantly attenuated by atypical but not classical antipsychotics.

Effects of sub-chronic antipsychotic drug treatment on body weight and reproductive function in juvenile female rats

RATIONALE

Weight gain caused by some antipsychotics is not only confined to adults but can also adversely affect both children and adolescents. Indeed, olanzapine and risperidone have been associated with extreme weight gain in adolescents even greater than that reported in adults. We have recently shown substantial weight gain in adult female rats following treatment with olanzapine and risperidone but not ziprasidone.

OBJECTIVES

The aim of the present study was to compare the effects of several antipsychotics on weight gain and reproductive function in juvenile (aged 7 weeks) female hooded Lister rats.

METHODS

Olanzapine (4 mg/kg), risperidone (0.5 mg/kg), ziprasidone (2.5 mg/kg), sulpiride (10 mg/kg), haloperidol (0.5 mg/kg) or vehicle was administered i.p. once per day for 21 days. Body weight, food and water intake were measured daily, in addition to the determination of stage of the oestrous cycle.

RESULTS

Sub-chronic administration of olanzapine, risperidone, sulpiride and haloperidol, but not ziprasidone, significantly increased body weight compared to vehicle-treated animals during weeks 1-3. Sulpiride significantly increased food and water intake. Significantly increased percentage intra-abdominal fat weight was observed in olanzapine, risperidone, sulpiride and haloperidol, but not ziprasidone-treated animals. Marked disruption of the oestrous cycle was observed in all but the ziprasidone-treated group, which continued to have regular 4-day oestrous cycles.

CONCLUSIONS

Weight gain observed in these juvenile animals was 1.5-2 times greater than that previously observed in adult rats. These findings have important implications for the use of antipsychotics in children and adolescent patients.

Investigation of the effects of lamotrigine and clozapine in improving reversal-learning impairments induced by acute phencyclidine and D-amphetamine in the rat

RATIONALE

Phencyclidine (PCP), a glutamate/N-methyl-D-aspartate (NMDA) receptor antagonist, has been shown to induce a range of symptoms similar to those of patients with schizophrenia, while D-amphetamine induces predominantly positive symptoms. Previous studies in our laboratory have shown that PCP can selectively impair the performance of an operant reversal-learning task in the rat. Furthermore, we found that the novel antipsychotic ziprasidone, but not the classical antipsychotic haloperidol, could prevent the PCP-induced deficit.

OBJECTIVES

The aim of the present study was to validate the model further using the atypical antipsychotic clozapine and then to investigate the effects of lamotrigine, a broad-spectrum anticonvulsant that is known to reduce glutamate release in vitro and is able to prevent ketamine-induced psychotic symptoms in healthy human volunteers. A further aim was to compare effects of PCP and D-amphetamine in the test and investigate the effects of the typical antipsychotic haloperidol against the latter.

METHODS

Female hooded-Lister rats were food deprived and trained to respond for food in a reversal-learning paradigm.

RESULTS

PCP at 1.5 mg/kg and 2.0 mg/kg and D-amphetamine at 0.5 mg/kg significantly and selectively impaired performance in the reversal phase of the task. The cognitive deficit induced by 1.5 mg/kg PCP was attenuated by prior administration of lamotrigine (20 mg/kg and 30 mg/kg) or clozapine (5 mg/kg), but not haloperidol (0.05 mg/kg). In direct contrast, haloperidol (0.05 mg/kg), but not lamotrigine (25 mg/kg) or clozapine (5 mg/kg), prevented a similar cognitive impairment produced by D-amphetamine (0.5 mg/kg).

CONCLUSIONS

Our findings provide further data to support the use of PCP-induced disruption of reversal learning in rodents to investigate novel antipsychotic drugs. The results also provide evidence for different mechanisms of PCP and D-amphetamine-induced disruption of performance in the test, and their different sensitivities to typical and atypical antipsychotic drugs.