Luvadaxistat: A Novel Potent and Selective D-Amino Acid Oxidase Inhibitor Improves Cognitive and Social Deficits in Rodent Models for Schizophrenia

N-methyl-D-aspartate (NMDA) receptor hypofunctionality is a well-studied hypothesis for schizophrenia pathophysiology, and daily dosing of the NMDA receptor co-agonist, D-serine, in clinical trials has shown positive effects in patients. Therefore, inhibition of D-amino acid oxidase (DAAO) has the potential to be a new therapeutic approach for the treatment of schizophrenia. TAK-831 (luvadaxistat), a novel, highly potent inhibitor of DAAO, significantly increases D-serine levels in the rodent brain, plasma, and cerebrospinal fluid. This study shows luvadaxistat to be efficacious in animal tests of cognition and in a translational animal model for cognitive impairment in schizophrenia. This is demonstrated when luvadaxistat is dosed alone and in conjunction with a typical antipsychotic. When dosed chronically, there is a suggestion of change in synaptic plasticity as seen by a leftward shift in the maximum efficacious dose in several studies. This is suggestive of enhanced activation of NMDA receptors in the brain and confirmed by modulation of long-term potentiation after chronic dosing. DAAO is highly expressed in the cerebellum, an area of increasing interest for schizophrenia, and luvadaxistat was shown to be efficacious in a cerebellar-dependent associative learning task. While luvadaxistat ameliorated the deficit seen in sociability in two different negative symptom tests of social interaction, it failed to show an effect in endpoints of negative symptoms in clinical trials. These results suggest that luvadaxistat potentially could be used to improve cognitive impairment in patients with schizophrenia, which is not well addressed with current antipsychotic medications.

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.

Dissociating the effects of distraction and proactive interference on object memory through tests of novelty preference

Encoding information into memory is sensitive to distraction while retrieving that memory may be compromised by proactive interference from pre-existing memories. These two debilitating effects are common in neuropsychiatric conditions, but modelling them preclinically to date is slow as it requires prolonged operant training. A step change would be the validation of functionally equivalent but fast, simple, high-throughput tasks based on spontaneous behaviour. Here, we show that spontaneous object preference testing meets these requirements in the subchronic phencyclidine rat model for cognitive impairments associated with schizophrenia. Subchronic phencyclidine rats show clear memory sensitivity to distraction in the standard novel object recognition task. However, due to this, standard novel object recognition task cannot assess proactive interference. Therefore, we compared subchronic phencyclidine performance in standard novel object recognition task to that using the continuous novel object recognition task, which offers minimal distraction, allowing disease-relevant memory deficits to be assessed directly. We first determined that subchronic phencyclidine treatment did not affect whisker movements during object exploration. Subchronic phencyclidine rats exhibited the expected distraction standard novel object recognition task effect but had intact performance on the first continuous novel object recognition task trial, effectively dissociating distraction using two novel object recognition task variants. In remaining continuous novel object recognition task trials, the cumulative discrimination index for subchronic phencyclidine rats was above chance throughout, but, importantly, their detection of object novelty was increasingly impaired relative to controls. We attribute this effect to the accumulation of proactive interference. This is the first demonstration that increased sensitivity to distraction and proactive interference, both key cognitive impairments in schizophrenia, can be dissociated in the subchronic phencyclidine rat using two variants of the same fast, simple, spontaneous object memory paradigm.

Aerobic exercise improves memory and prevents cognitive deficits of relevance to schizophrenia in an animal model

INTRODUCTION AND OBJECTIVES

Cognitive impairment associated with schizophrenia (CIAS) greatly reduces patients' functionality, and remains an unmet clinical need. The sub-chronic phencyclidine (scPCP) rat model is commonly employed in studying CIAS. We have previously shown that voluntary exercise reverses impairments in novel object recognition (NOR) induced by scPCP. However, there has not been a longitudinal study investigating the potential protective effects of exercise in a model of CIAS. This study aimed to investigate the pro-cognitive and protective effects of exercise on CIAS using the translational NOR and attentional set-shifting tasks (ASST).

METHODS

Female Lister Hooded rats were either exercised (wheel running for one hour per day, five days per week, for six weeks; n=20) or not (n=20) and then tested in a natural-forgetting NOR test. Rats in each group were then administered either PCP (2 mg/kg intraperitoneally (i.p.)) or saline solution (1 mL/kg i.p.) for seven days, followed by seven days washout. Three NOR tests were conducted immediately and two and nine weeks after washout, and a natural-forgetting NOR test was carried out again eight weeks post washout. Rats were trained and tested in ASST from week 6 to week 10 post washout.

RESULTS

Non-exercised rats displayed a deficit in both of the natural-forgetting NOR tests, whereas exercised rats did not. The scPCP exercise group did not show the expected deficit in NOR at any time point, and had a significantly ameliorated deficit in the ASST compared to the scPCP control group.

CONCLUSION

Voluntary exercise has long-lasting pro-cognitive and protective effects in two cognitive domains. Exercise improves cognition and could provide protection against CIAS.

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.

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).

Effects of cariprazine, a novel antipsychotic, on cognitive deficit and negative symptoms in a rodent model of schizophrenia symptomatology

Negative symptoms and cognitive impairment associated with schizophrenia are strongly associated with poor functional outcome and reduced quality of life and remain an unmet clinical need. Cariprazine is a dopamine D3/D2 receptor partial agonist with preferential binding to D3 receptors, recently approved by the FDA for the treatment of schizophrenia and manic or mixed episodes associated with bipolar I disorder. The aim of this study is to evaluate effects of cariprazine in an animal model of cognitive deficit and negative symptoms of schizophrenia. Following sub-chronic PCP administration (2mg/kg, IP for 7 days followed by 7 days drug-free), female Lister Hooded rats were administered cariprazine (0.05, 0.1, or 0.25mg/kg, PO) or risperidone (0.16 or 0.1mg/kg, IP) before testing in novel object recognition (NOR), reversal learning (RL), and social interaction (SI) paradigms. As we have consistently demonstrated, sub-chronic PCP significantly impaired behavior in these tests. Deficits were significantly improved by cariprazine, in a dose dependent manner in the operant RL test with efficacy at lower doses in the NOR and SI tests. Locomotor activity was reduced at the highest doses of 0.1mg/kg and 0.25mg/kg in NOR and SI. Risperidone also reversed the PCP-induced deficit in all tests. In conclusion, cariprazine was effective to overcome PCP-induced deficits in cognition and social behavior in a thoroughly validated rat model in tests representing specific symptom domains in schizophrenia patients. These findings support very recent results showing efficacy of cariprazine in the treatment of negative symptoms in schizophrenia patients.

Nicotinic α7 and α4β2 agonists enhance the formation and retrieval of recognition memory: Potential mechanisms for cognitive performance enhancement in neurological and psychiatric disorders

Cholinergic dysfunction has been shown to be central to the pathophysiology of Alzheimer's disease and has also been postulated to contribute to cognitive dysfunction observed in various psychiatric disorders, including schizophrenia. Deficits are found across a number of cognitive domains and in spite of several attempts to develop new therapies, these remain an unmet clinical need. In the current study we investigated the efficacy of donepezil, risperidone and selective nicotinic α7 and α4β2 receptor agonists to reverse a delay-induced deficit in recognition memory. Adult female Hooded Lister rats received drug treatments and were tested in the novel object recognition (NOR) task following a 6h inter-trial interval (ITI). In all treatment groups, there was no preference for the left or right identical objects in the acquisition trial. Risperidone failed to enhance recognition memory in this paradigm whereas donepezil was effective such that rats discriminated between the novel and familiar object in the retention trial following a 6h ITI. Although a narrow dose range of PNU-282987 and RJR-2403 was tested, only one dose of each increased recognition memory, the highest dose of PNU-282987 (10mg/kg) and the lowest dose of RJR-2403 (0.1mg/kg), indicative of enhanced cognitive performance. Interestingly, these compounds were also efficacious when administered either before the acquisition or the retention trial of the task, suggesting an important role for nicotinic receptor subtypes in the formation and retrieval of recognition memory.

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.

PNU-120596, a positive allosteric modulator of α7 nicotinic acetylcholine receptors, reverses a sub-chronic phencyclidine-induced cognitive deficit in the attentional set-shifting task in female rats

The α7 nicotinic acetylcholine receptors (nAChRs) have been highlighted as a target for cognitive enhancement in schizophrenia. Adult female hooded Lister rats received sub-chronic phencyclidine (PCP) (2 mg/kg) or vehicle i.p. twice daily for 7 days, followed by 7 days' washout. PCP-treated rats then received PNU-120596 (10 mg/kg; s.c.) or saline and were tested in the attentional set-shifting task. Sub-chronic PCP produced a significant cognitive deficit in the extra-dimensional shift (EDS) phase of the task (p < 0.001, compared with vehicle). PNU-120596 significantly improved performance of PCP-treated rats in the EDS phase of the attentional set-shifting task (p < 0.001). In conclusion, these data demonstrate that PNU-120596 improves cognitive dysfunction in our animal model of cognitive dysfunction in schizophrenia, most likely via modulation of α7 nACh receptors.

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.

Activation of α7 nicotinic receptors improves phencyclidine-induced deficits in cognitive tasks in rats: implications for therapy of cognitive dysfunction in schizophrenia

RATIONALE

Nicotinic α7 acetylcholine receptors (nAChRs) have been highlighted as a target for cognitive enhancement in schizophrenia.

AIM

To investigate whether the deficits induced by sub-chronic phencyclidine (PCP) in reversal learning and novel object recognition could be attenuated by the selective α7 nAChR full agonist, PNU-282987.

METHODS

Adult female hooded-Lister rats received sub-chronic PCP (2mg/kg) or vehicle i.p. twice daily for 7days, followed by 7 days washout. In cohort 1, PCP-treated rats then received PNU-282987 (5, 10, 20mg/kg; s.c.) or vehicle and were tested in the reversal-learning task. In cohort 2, PCP-treated rats received PNU-282987 (10mg/kg; s.c.) or saline for 15days and were tested in the novel object recognition test on day 1 and on day 15, to test for tolerance.

RESULTS

Sub-chronic PCP produced significant deficits in both cognitive tasks (P<0.01-0.001). PNU-282987 attenuated the PCP-induced deficits in reversal learning at 10mg/kg (P<0.01) and 20mg/kg (P<0.001), and in novel object recognition at 10mg/kg on day 1 (P<0.01) and on day 15 (P<0.001).

CONCLUSIONS

These data show that PNU-282987 has efficacy to reverse PCP-induced deficits in two paradigms of relevance to schizophrenia. Results further suggest that 15-day once daily dosing of PNU-282987 (10mg/kg s.c.) does not cause tolerance in the rat. This study suggests that activation of α7 nAChRs, may represent a suitable strategy for improving cognitive deficits of relevance to schizophrenia.

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.

Isolation rearing impairs novel object recognition and attentional set shifting performance in female rats

It has been suggested that the isolation rearing paradigm models certain aspects of schizophrenia symptomatology. This study aimed to investigate whether isolation rearing impairs rats' performance in two models of cognition: the novel object recognition (NOR) and attentional set-shifting tasks, tests of episodic memory and executive function, respectively. Two cohorts of female Hooded-Lister rats were used in these experiments. Animals were housed in social isolation or in groups of five from weaning, post-natal day 28. The first cohort was tested in the NOR test with inter-trial intervals (ITIs) of 1 min up to 6 h. The second cohort was trained and tested in the attentional set-shifting task. In the NOR test, isolates were only able to discriminate between the novel and familiar objects up to 1-h ITI, whereas socially reared animals remembered the familiar object up to a 4-h ITI. In the attentional set-shifting task, isolates were significantly and selectively impaired in the extra-dimensional shift phase of the task (P < 0.01). Rats reared in isolation show impaired episodic memory in the NOR task and reduced ability to shift attention between stimulus dimensions in the attentional set-shifting task. Because schizophrenic patients show similar deficits in performance in these cognitive domains, these data further support isolation rearing as a putative preclinical model of the cognitive deficits associated with schizophrenia.

Sertindole improves sub-chronic PCP-induced reversal learning and episodic memory deficits in rodents: involvement of 5-HT(6) and 5-HT (2A) receptor mechanisms

AIM

This study examined the efficacy of sertindole in comparison with a selective 5-HT(6) and a 5-HT(2A) receptor antagonist to reverse sub-chronic phencyclidine (PCP)-induced cognitive deficits in female rats.

METHODS

In the first test, adult female hooded Lister rats were trained to perform an operant reversal learning task to 90% criterion. After training, rats were treated with PCP at 2 mg/kg (i.p.) or vehicle twice daily for 7 days, followed by 7 days washout. For the second test, novel object recognition (NOR), a separate batch of rats, had the same sub-chronic PCP dosing regime and washout period. In reversal learning, rats were treated acutely with sertindole, the selective 5-HT(2A) receptor antagonist M100.907 or the selective 5-HT(6) receptor antagonist SB-742457.

RESULTS

The PCP-induced selective reversal learning deficit was significantly improved by sertindole, M100.907 and SB-742457. Sertindole also significantly improved the sub-chronic PCP-induced deficit in NOR, a test of episodic memory following a 1 min and 1 h inter-trial interval. In vivo binding studies showed that the dose-response relationship for sertindole in this study most closely correlates with affinity for 5-HT(6) receptor in vivo binding in striatum, although contribution from binding to 5-HT(2A) receptors in vivo in cortex may also provide an important mechanism.

CONCLUSION

The efficacies of selective 5-HT(2A) and 5-HT(6) receptor antagonists suggest potential mechanisms mediating the effects of sertindole, which has high affinity for these 5-HT receptor subtypes. The sertindole-induced improvement in cognitive function in this animal model suggests relevance for the management of cognitive deficit symptoms in schizophrenia.

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.

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.

Correlation of hyperforin content of Hypericum perforatum (St John's Wort) extracts with their effects on alcohol drinking in C57BL/6J mice: a preliminary study

Extracts of the herb St John's Wort have been shown to reduce alcohol intake in alcohol-preferring rats, but it is not known which of the constituent(s) are responsible for this effect. In this study, the effect of a crude methanolic extract of Hypericum perforatum (negligible hyperforin content) on alcohol drinking in C57BL/6J alcohol-preferring mice was compared with that of a hyperforin-rich extract (45% hyperforin) prepared by extracting the herb with supercritical carbon dioxide. The dose of the hyperforin-rich extract required to significantly reduce 10% ethanol intake (5 mg/kg) was 125-fold less than that required for the crude extract (625 mg/kg), and was comparable to the dose of fluoxetine (10 mg/kg) required to produce a similar effect. None of these agents significantly affected water intake. These results suggest that the effects of H. perforatum extracts on alcohol drinking behaviour are due to the hyperforin content of the herb rather than to other, more polar constituents. Hyperforin is an unstable compound and this study also highlights the effect of different methods of extract preparation on hyperforin content.

Mandibular growth after distraction in patients under 48 months of age

Distraction osteogenesis is an effective technique for reconstruction of the congenitally deficient mandible. However, the age at which it is best performed remains under discussion. Distraction performed at an early age, while possibly allowing the face to develop with a more normal functional matrix, may entail a higher rate of complications. Additionally, it is possible that subsequent asymmetric growth of the mandible may necessitate serial distraction. To address this issue, the clinical records and cephalometric radiographs of all patients less than 48 months of age undergoing mandibular distraction at New York University Medical Center between August of 1989 and August of 1997 were examined. There was a total of 14 patients ranging in age from 19 months to 43 months. Nine patients had a diagnosis of unilateral craniofacial microsomia, three had Treacher Collins syndrome, one had Nager syndrome, and one had bilateral developmental micrognathia. The average amount of distraction was 27 mm (range, 23 to 39 mm) in unilateral cases and 24 mm in bilateral cases (range, 15 to 31 mm). The period of clinical follow-up averaged 32.6 months (range, 12 to 92 months). All patients showed significant improvement in craniofacial appearance, and in four patients, long-term tracheostomy tubes were removed. There were two major complications. In one patient with craniofacial microsomia, there was a relapse in the early postretention phase related to the presence of a dentigerous cyst. This required removal of the cyst and repeat distraction. In the patient with Nager syndrome, a coronoid ankylosis developed requiring surgical release. There were no other major complications. The scars required revision in only two of the patients. Cephalometric analysis of the patients in the study revealed a differential in the rate of growth between the affected and the unaffected side in all cases of craniofacial microsomia. The affected side always grew at a slower rate than the contralateral side after the distraction process was complete. This led to a progressive asymmetry of the rami, clinically expressed by some degree of facial asymmetry and an occlusal cant. For this reason, secondary distraction was required in one patient and is planned in a second. Initial overcorrection of the patient would seem to minimize the likelihood that secondary distraction will be necessary. Distraction osteogenesis for reconstruction of the mandible in this subset of young patients was a safe and effective technique for improving the craniofacial skeletal form and appearance, with minimal associated morbidity. Longer follow-up is necessary to assess the full impact of growth in these cases.

A virtual reality system for bone fragment positioning in multisegment craniofacial surgical procedures

This article reports our clinical experience since 1994 with rigid-motion tracking of bone fragments during craniofacial surgical procedures, using a virtual reality approach. Three noncollinear infrared diodes are fixed to the skull base. A pointer is used to register anatomic features on the patient to those on the computerized tomography-based model of the patient within a computer work station. Three diodes are then attached to each fragment just before the osteotomy is completed. Rigid motions of the fragment are thus tracked and reported to the surgeon by using virtual reality techniques. Errors in fragment positioning are reported both graphically and numerically with respect to a precomputed optimum fragment position. This guidance system allows multisegment midface osteotomies to be performed more precisely. The main problems encountered so far have been devascularization-infection and difficulties in maintaining correct position during application of rigid fixation. Devascularization-infection problems have been addressed by minimizing surgical exposure of the bone. Soft-fixation plates and temporary Kirschner wire fixation have helped with intermediate positioning, but an intraoperative mechanical positioning device would be useful in the future.

Presurgical columellar elongation and primary retrograde nasal reconstruction in one-stage bilateral cleft lip and nose repair

We present a new combined approach to primary bilateral cleft lip, nose, and alveolus repair using presurgical nasoalveolar molding combined with a one-stage lip, nose, and alveolus repair. Presurgical alveolar molding is used to bring the protruding premaxilla back into proper alignment with the lateral segments in the maxillary arch. Presurgical nasal molding produces tissue expansion of the short columella and nasal lining. A coordinated surgical approach involves a one-stage repair of the lip, nose, and alveolus. The nasal repair uses a retrograde approach in which the prolabial flap and columella are reflected over the nasal dorsum by continuing the dissection behind the prolabium up the membranous septum and over the septal angle. Tissues are dissected out from between the tip cartilages, and the domes are sutured together in the midline. This method joins a new class of bilateral cleft repairs that place the primary emphasis on correction of the deformity of the nasal tip cartilages.

The prolabial unwinding flap method for one-stage repair of bilateral cleft lip, nose, and alveolus

This paper describes a one-stage reconstruction of the complete bilateral cleft lip, nose, and alveolus using an asymmetrically designed prolabial flap. The columella of the nose and the central lip are produced by "unwinding" the columellar and labial sections of the prolabium around a small central tab, which is used to center the junction between the lip and columella. Only two scars are produced, both of which run vertically along each philtral column. Accurate preoperative orthopedics without lip adhesion is considered essential to this repair. The principal advantage/disadvantage to the method is its asymmetrical design. If asymmetries result, they have been easily corrected. Eight consecutive cases are presented with follow-up ranging from 1.5 to 6.3 years.

Landmarks in three dimensions: reconstruction from cephalograms versus direct observation

A method for generating three-dimensional landmark locations from routine biplane pairs of cephalograms was previously introduced. In this article we compare the locations thus reconstructed to the same configurations as directly recorded through a redundant network of interpoint distances measured with calipers. Six mandibular landmarks were located by both methods on each of 10 dry skulls. With the caliper distances is associated a standard error that can be estimated without explicit remeasurement by the method of "adjustment of networks" familiar from surveying. These standard errors are consistent with the remeasurement error both of the caliper measurements and of the stereolocation from cephalograms; the methods appear to have the same precision, about 0.4 mm per distance. The bias (systematic shift) of the biplane reconstructions with respect to the points used for laying down the calipers may be estimated by regressions of distance discrepancies on the direction cosines of the separations between pairs of landmarks. The caliper tips placed condylion approximately 10 mm medially and a bit forward of where we chose to reconstruct it from biplane cephalograms. The caliper locations of gonion average about 1.6 mm back of their cephalometric position, while those at menton and lower incisal edge are forward by some 1.4 mm. We conclude that the biplane reconstruction (the "three-dimensional cephalogram") is sufficiently accurate for routine clinical and surgical application.

The three-dimensional cephalogram: theory, technique, and clinical application

The Broadbent-Bolton cephalostat produces intrinsically three-dimensional information about cranial form. Yet in the clinical setting, this information has been used primarily two dimensions at a time in the separate study of lateral or posteroanterior cephalograms. In this article we demonstrate an expedient use of existing cephalostat-based data sets to derive certain analyses of three-dimensional form. The technique is essentially the same as that of the Broadbent-Bolton "Orientator," an exploitation of the geometry of the cephalostat to simulate stereophotogrammetry. The three-dimensional method supports the usual biometrics of landmark locations, and takes advantage of a normative data base that is suited for semiautomatic analysis of syndromic data. The principal drawback of the method is its inability to represent curving form in three dimensions. However, in comparison with computed tomography (CT), it involves low radiation dose, is simpler to obtain, has an available normative data base, and is more practical for quantitative or long-term serial analysis.

Computer-aided planning and evaluation of facial and orthognathic surgery

The desire to apply the scientific method to aesthetic facial surgery is the underpinning of this article, which summarizes the attempts that have been made to apply numeric methods to facial surgery, with particular emphasis on computer methods.

Three-dimensional computer-assisted design of craniofacial surgical procedures: optimization and interaction with cephalometric and CT-based models

A computer program is described which aids the clinician in planning craniofacial surgical procedures. It operates on a three-dimensional landmark data base derived by combining posteroanterior and lateral cephalograms from the patient and from the Bolton normative standards. A three-dimensional surgical simulation program based on computerized tomographic (CT) data is also described which can be linked to the cephalometrically based program. After the clinician has selected the number and type of osteotomies to be performed on the patient, an automated optimization program computes the postoperative positions of these fragments which best fit the appropriate normal cephalometric form. The clinician then interactively modifies the design to account for such variables as bone-graft resorption, relapse tendency, occlusal disparities, and the condition of the overlying soft-tissue matrix. Osteotomy movement specifications are easily transferred between the CT-based and the cephalometrically based surgical simulation programs. This allows the automated positioning step to be performed on the cephalometrically based model while the interactive step is performed using the superior image provided by the CT-based model.

Le Fort III advancement osteotomy in the growing child

A prospective clinical and cephalometric study was conducted on 12 patients under the age of 12 years undergoing Le Fort III advancement with the following findings: 1. There was a remarkable degree of postoperative skeletal stability of the midfacial segment. 2. Disharmony in jaw relationship (anterior crossbite) observed during the period of longitudinal postoperative study could be attributed to expected mandibular development. 3. In some patients, growth and development of the maxilla in a forward and downward direction were documented after Le Fort III advancement. The authors recommend that a Le Fort III advancement can be safely performed at approximately age 4 without a deleterious effect on midfacial development in the patient with craniofacial dysostosis.

Early surgery for craniofacial synostosis: an 8-year experience

A prospective review is presented of 50 patients with one of the craniofacial synostosis syndromes who underwent early interventive craniofacial surgical correction (average age 7.6 months at time of surgery). The study has demonstrated the efficacy and safety of the techniques when employed in the infant. Satisfactory cranio-orbital form was achieved in the majority of the patients, although 10 patients required secondary surgery because of sutural refusion or the development of turricephaly or calvarial contour irregularities. Despite earlier hopes, this surgery did not result in the development of satisfactory occlusal relationships and midfacial form in the craniofacial dysostosis group (Crouzon's, Apert's, etc.). Based on this clinical experience, a surgical treatment plan is presented for the newborn with craniofacial synostosis.

Cephalometric analysis: part I

A protocol for cephalometric analysis is presented to enable the clinician to evaluate the bony face by subdividing it into four components: 1. Vertical facial measurements 2. Horizontal midface measurements 3. Horizontal lower face measurements 4. Dental measurements. The clinician is encouraged to view the components alone and together. Caution is advised in deriving the treatment plans solely from the cephalometric analysis. Emphasis is placed on integrating the data derived from the cephalometric analysis with the clinical picture, history, dental model analysis, soft-tissue analysis, and patient desires.