Exploration of cognitive and neurochemical deficits in an animal model of schizophrenia. Investigation into sub-chronic PCP-induced cognitive deficits using behavioural, neurochemical and electrophysiological techniques; and use of receptor-selective agents to study the pharmacology of antipsychotics in female rats.

Cognitive dysfunction is a core characteristic of schizophrenia, which can often persist when other symptoms, particularly positive symptoms, may be improved with drug treatment. The non-competitive NMDA receptor antagonist, phencyclidine (PCP), is a psychomotor stimulant drug that has been shown to induce symptoms characteristic of schizophrenia in humans and animals. The aim of these studies was to use the sub-chronic PCP model in rats to investigate cognitive dysfunction in behavioural tests which have been highlighted as relevance by the MATRICS initiative (MATRICS.ucla.edu). The main tests used were attentional set-shifting, operant reversal learning, and novel object recognition tasks. The pharmacology of antipsychotics was studied in the reversal learning task using receptor selective compounds. Following this, experiments were carried out using in vitro electrophysiology and in vivo microdialysis in an attempt to investigate the mechanisms underpinning the PCP-induced cognitive deficits. The attentional set-shifting task is a test of executive function, the extra-dimensional shift (EDS) phase relates to the ability to shift attention to a different stimulus dimension; this is impaired in patients with schizophrenia. The studies presented in chapter 2 showed that sub-chronic PCP administration impaired attentional set-shifting performance selectively in the EDS phase, a deficit which was significantly attenuated by sub-chronic administration of clozapine and risperidone, but not haloperidol. The effect of PCP was also shown to be more robust in female rats compared to males. A deficit in set-shifting ability was also observed in isolation reared rats. However, the deficits produced by PCP were more robust than the deficit produced by isolation rearing. The reversal learning task is another test of executive function. Chapter 3 reported that sub-chronic PCP administration impairs reversal learning ability in an operant task, as demonstrated by reduced percent correct responding in the reversal phase of the reversal learning task. It was found that a D1 agonist (SKF-38398), a 5-HT1A partial agonist (buspirone), a 5-HT2C antagonist (SB-243213A) and an agonist and positive allosteric modulator of the alpha 7 nACh receptor (PNU-282987 and PheTQS respectively) are able to reverse the sub-chronic PCP-induced deficit in reversal learning. Although many antipsychotics have affinity for muscarinic M1 and histamine H1 receptors, selective agents at these receptors were not able to improve the PCP-induced deficit. In chapter 4, the atypical antipsychotics, clozapine and risperidone, when given alone to naïve rats had no effect on reversal learning. Haloperidol when given to naïve rats impaired performance at the highest dose. Sub-chronic PCP was again found to impair reversal learning performance. Investigative experiments revealed that the 2 min time-out could be important as a cue. Following a double reversal, olanzapine-treated rats lost the ability to switch between the rules, whereas clozapine and risperidone-treated rats could perform the double reversal. Experiments with the extended (15 min) reversal phase could allow the investigation of the time-course effects of antipsychotics or selective compounds. The studies presented in chapter 5 found a reduction in gamma oscillations in the CA3 region of the hippocampus, following sub-chronic PCP treatment (2-5 weeks post treatment) that was paralleled by a deficit in parvalbumin immunoreactive (IR) cell density, at a similar time point (2 weeks post treatment). In contrast, a time-dependent increase in gamma oscillations was observed (6-8 weeks post treatment), at which point parvalbumin IR cell density was unchanged (8 weeks post treatment). Gamma oscillations were unchanged in the prefrontal cortex (PFC) following the PCP treatment regime. Locomotor activity tests were also carried out to ensure that the sub-chronic PCP treatment was successful. In-vivo microdialysis revealed that vehicle-treated rats show an increase in dopamine in the PFC which is selective for the retention trial of the novel object recognition task. PCP-treated rats were unable to distinguish between the novel and familiar objects and the increase in dopamine observed in vehicle rats was absent. As a control experiment it was also shown that sub-chronic PCP did not induce anxiety-like symptoms in the elevated plus maze and open field tests. These studies suggest that sub-chronic PCP induces cognitive deficits in behavioural tasks, and these deficits may be due to GABAergic mediated processes in the hippocampus and dopaminergic dysfunction in the PFC. These behavioural and neurochemical results are concurrent to findings observed in schizophrenia

Role of 5-HT receptor mechanisms in sub-chronic PCP-induced reversal learning deficits in the rat

YesRationale: 5-HT receptor mechanisms have been suggested to mediate improvements in cognition in schizophrenia. Aim: To investigate the involvement of 5-HT receptor mechanisms in sub-chronic PCP-induced reversal learning deficits in female rats, a task of relevance to schizophrenia. Methods: Adult female hooded-Lister rats were trained to perform an operant reversal learning task and then received sub-chronic PCP (2 mg/kg) or vehicle i.p. twice daily for seven days, followed by 7-days washout. Rats then received an acute dose of the 5-HT7 receptor antagonist SB-269970A (1.0, 3.0, 10.0 mg/kg; i.p.) or vehicle. In experiment 2, PCP-treated rats received the selective 5-HT2C receptor antagonist, SB-243213A acutely (1.0, 3.0, 10.0 mg/kg; i.p.) or vehicle. In experiment 3, PCP-treated rats received the 5-HT1A receptor partial agonist, buspirone (0.15625, 0.3125, 0.625 mg/kg, i.p.) in combination with the selective 5-HT1A receptor antagonist WAY-100635 (0.3, 1.0 mg/kg). Results: In all experiments sub-chronic PCP significantly impaired reversal phase performance (P<0.01-0.001), with no effect in the initial phase. SB-269970A at 3.0 and 10.0 mg/kg significantly improved the PCP-induced deficit (P<0.05). SB-243213A also significantly attenuated the deficit at 10 mg/kg (P<0.05). In experiment 3, buspirone attenuated the deficit with significant effects at 0.3125 mg/kg and 0.625 mg/kg (P<0.05). WAY-100635 at 0.3 and 1.0 mg/kg produced a partial attenuation of buspirone’s effect as buspirone (0.3125 mg/kg) in the presence of WAY-100635 did not significantly reverse the PCP-induced deficit. Conclusions: These studies implicate the role of 5-HT7, 5-HT2C and 5-HT1A receptors in the improvement of cognitive dysfunction of relevance to schizophrenia

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

YesRationale: 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 (2 mg/kg) or vehicle i.p. twice daily for seven days, followed by 7-days washout. In cohort 1, PCP-treated rats then received PNU-282987 (5, 10, 20 mg/kg; s.c.) or vehicle and were tested in the reversal learning task. In cohort 2, PCP-treated rats received PNU-282987 (10 mg/kg; s.c.) or saline for 15 days 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 10 mg/kg (P<0.01) and 20 mg/kg (P<0.001), and in novel object recognition at 10 mg/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 daily dosing of PNU-282987 (10 mg/kg s.c.) does not cause tolerance in rat. This study suggests that activation of α7 nAChRs, may represent a suitable strategy for improving cognitive deficits of relevance to schizophrenia.SL McLean was supported by a joint University of Bradford–GSK postgraduate studentship

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

yesRationale: 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 seven days, followed by seven 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

Feasibility and Clinical Utility of Hand-held Optical Coherence Tomography in Children with Retinoblastoma

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023

A proposal for reducing maximum target doses of drugs for psychosis: Reviewing dose-response literature

YesBackground: Presently, there is limited guidance on the maximal dosing of psychosis drugs that is based on effectiveness rather than safety or toxicity. Current maximum dosing recommendations may far exceed the necessary degree of dopamine D2 receptor blockade required to treat psychosis. This may lead to excess harm through cognitive impairment and side effects. Aims: This analysis aimed to establish guidance for prescribers by optimally dosing drugs for psychosis based on efficacy and benefit. Methods: We used data from two dose–response meta-analyses and reviewed seven of the most prescribed drugs for psychosis in the UK. Where data were not available, we used appropriate comparison techniques based on D2 receptor occupancy to extrapolate our recommendations. Results: We found that the likely threshold dose for achieving remission of psychotic symptoms was often significantly below the currently licensed dose for these drugs. We therefore recommend that clinicians are cautious about exceeding our recommended doses. Individual factors, however, should be accounted for. We outline potentially relevant factors including age, ethnicity, sex, smoking status and pharmacogenetics. Additionally, we recommend therapeutic drug monitoring as a tool to determine individual pharmacokinetic variation. Conclusions: In summary, we propose a new set of maximum target doses for psychosis drugs based on efficacy. Further research through randomised controlled trials should be undertaken to evaluate the effect of reducing doses from current licensing maximums or from doses that are above our recommendations. However, dose reductions should be implemented in a manner that accounts for and reduces the effects of drug withdrawal

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

YesCholinergic 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 6 h 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 6 h 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 (10 mg/kg) and the lowest dose of RJR-2403 (0.1 mg/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.This work was conducted at the University of Bradford and was funded by b-neuro. However all our recent studies mentioned in the discussion section have been conducted at the University of Manchester (UoM), and funded by b-neuro, Autifony, Innovate UK (formerly TSB) and Uo

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

yThe 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) (2mg/kg) or vehicle i.p. twice daily for 7 days, followed by 7 days’ washout. PCP-treated rats then received PNU-120596 (10mg/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.This work was partially funded by Johnson & Johnson Pharmaceutical Research and Development

What Are the Barriers and Enablers to the Implementation of Pharmacogenetic Testing in Mental Health Care Settings?

In psychiatry, the selection of antipsychotics and antidepressants is generally led by a trial-and-error approach. The prescribing of these medications is complicated by sub-optimal efficacy and high rates of adverse drug reactions (ADRs). These both contribute to poor levels of adherence. Pharmacogenetics (PGx) considers how genetic variation can influence an individual’s response to a drug. Pharmacogenetic testing is a tool that could aid clinicians when selecting psychotropic medications, as part of a more personalized approach to prescribing. This may improve the use of and adherence to these medications. Yet to date, the implementation of PGx in mental health environments in the United Kingdom has been slow. This review aims to identify the current barriers and enablers to the implementation of PGx in psychiatry and determine how this can be applied to the uptake of PGx by NHS mental health providers. A systematic searching strategy was developed, and searches were carried out on the PsychInfo, EmBase, and PubMed databases, yielding 11 appropriate papers. Common barriers to the implementation of PGx included cost, concerns over incorporation into current workflow and a lack of knowledge about PGx; whilst frequent enablers included optimism that PGx could lead to precision medicine, reduce ADRs and become a more routine part of psychiatric clinical care. The uptake of PGx in psychiatric care settings in the NHS should consider and overcome these barriers, while looking to capitalize on the enablers identified in this review