A novel touchscreen-automated paired-associate learning (PAL) task sensitive to pharmacological manipulation of the hippocampus: a translational rodent model of cognitive impairments in neurodegenerative disease

Asymptomatic neonatal herpes simplex virus infection in mice leads to long-term cognitive impairment

Neonatal herpes simplex virus (nHSV) is a devastating infection impacting approximately 14,000 newborns globally each year. Infection is associated with high neurologic morbidity and mortality, making early intervention and treatment critical. Clinical outcomes of symptomatic nHSV infections are well-studied, but little is known about the frequency of, or outcomes following, sub-clinical or asymptomatic nHSV. Given the ubiquitous nature of HSV infection and frequency of asymptomatic shedding in adults, subclinical infections are underreported, yet could contribute to long-term neurological damage. To assess potential neurological morbidity associated with subclinical nHSV infection, we developed a low-dose (100 PFU) HSV infection protocol in neonatal C57BL/6 mice. At this dose, HSV DNA was detected in the brain by PCR but was not associated with acute clinical symptoms. However, months after initial inoculation with 100 PFU of HSV, we observed impaired mouse performance on a range of cognitive and memory performance tasks. Memory impairment was induced by infection with either HSV-1 or HSV-2 wild-type viruses, but not by a viral mutant lacking the autophagy-modulating Beclin-binding domain of the neurovirulence gene γ34.5. Retroviral expression of wild type γ34.5 gene led to behavioral pathology in mice, suggesting that γ34.5 expression may be sufficient to cause cognitive impairment. Maternal immunization and HSV-specific antibody treatment prevented offspring from developing neurological sequelae following nHSV-1 infection. Altogether, these results support the idea that subclinical neonatal infections may lead to cognitive decline in adulthood, with possible profound implications for research on human neurodegenerative disorders such as Alzheimer's Disease.

Chronic, Reusable, Multiday Neuropixels Recordings during Free-Moving Operant Behavior

Electrophysiological recording is a powerful technique to examine neuronal substrates underlying cognition and behavior. Neuropixels probes provide a unique capacity to capture neuronal activity across many brain areas with high spatiotemporal resolution. Neuropixels are also expensive and optimized for acute, head-fixed use, both of which limit the types of behaviors and manipulations that can be studied. Recent advances have addressed the cost issue by showing chronic implant, explant, and reuse of Neuropixels probes, but the methods were not optimized for use in free-moving behavior. There were specific needs for improvement in cabling/connection stability. Here, we extend that work to demonstrate chronic Neuropixels recording, explant, and reuse in a rat model during fully free-moving operant behavior. Similar to prior approaches, we house the probe and headstage within a 3D-printed housing that avoids direct fixation of the probe to the skull, enabling eventual explant. We demonstrate innovations to allow chronic headstage connection with protection against environmental factors and a more stable cabling setup to reduce the tension that can interrupt recording. We demonstrate this approach with rats performing two different behavioral tasks, in each case showing: (1) chronic single- or dual-probe recordings in free-moving rats in operant chambers and (2) reusability of Neuropixels 1.0 probes with continued good single-unit yield after retrieval and reimplant. We thus demonstrate the potential for Neuropixels recordings in a wider range of species and preparations.

Open science and data sharing in cognitive neuroscience with MouseBytes and MouseBytes

Open access to rodent cognitive data has lagged behind the rapid generation of large open-access datasets in other areas of neuroscience, such as neuroimaging and genomics. One contributing factor has been the absence of uniform standardization in experiments and data output, an issue that has particularly plagued studies in animal models. Touchscreen-automated cognitive testing of animal models allows standardized outputs that are compatible with open-access sharing. Touchscreen datasets can be combined with different neuro-technologies such as fiber photometry, miniscopes, optogenetics, and MRI to evaluate the relationship between neural activity and behavior. Here we describe a platform that allows deposition of these data into an open-access repository. This platform, called MouseBytes, is a web-based repository that enables researchers to store, share, visualize, and analyze cognitive data. Here we present the architecture, structure, and the essential infrastructure behind MouseBytes. In addition, we describe MouseBytes+, a database that allows data from complementary neuro-technologies such as imaging and photometry to be easily integrated with behavioral data in MouseBytes to support multi-modal behavioral analysis.

Paired associates learning is disrupted after unilateral parietal lobe controlled cortical impact in rats: A trial-by-trial behavioral analysis

Approximately 60-70 million people suffer from traumatic brain injury (TBI) each year. Animal models continue to be paramount in understanding mechanisms of cellular dysfunction and testing new treatments for TBI. Enhancing the translational potential of novel interventions therefore necessitates testing pre-clinical intervention strategies with clinically relevant cognitive assays. This study used a unilateral parietal lobe controlled cortical impact (CCI) model of TBI and tested rats on a touchscreen-based Paired Associates Learning (PAL) task, which is part of the Cambridge Neuropsychological Test Automated Battery. In humans, the PAL task has been used to assess cognitive deficits in the ability to form stimulus-location associations in a multitude of disease states, including TBI. Although the use of PAL in animal models could be important for understanding the clinical severity of cognitive impairment post-injury and throughout intervention, to date, the extent to which a rat model of TBI produces deficits in PAL task performance has not yet been reported. This study details the behavioral consequences of the CCI injury model with a Trial-by-Trial analysis of PAL performance that enables behavioral strategy use to be inferred. Following behavior, the extent of the injury was quantified with histology and staining for the presence of glial fibrillary acid protein and ionized calcium-binding adapter molecule 1. Rats that received unilateral CCI were impaired on the PAL task and showed more aberrant response-driven behavior. The magnitude of PAL impairment was also correlated with Iba1 staining in the thalamus. These observations suggest that PAL could be useful for pre-clinical assessments of novel interventions for treating TBI.

Use of an Automated Mouse Touchscreen Platform for Quantification of Cognitive Deficits After Central Nervous System Injury

Analyzing cognitive performance is an important aspect of assessing physiological deficits after stroke or other central nervous system (CNS) injuries in both humans and in basic science animal models. Cognitive testing on an automated touchscreen operant platform began in humans but is now increasingly popular in preclinical studies as it enables testing in many cognitive domains in a highly reproducible way while minimizing stress to the laboratory animal. Here, we describe the step-by-step setup and application of four operant touchscreen tests used on adult mice. In brief, mice are trained to touch a graphical image on a lit screen and initiate subsequent trials for a reward. Following initial training, mice can be tested on tasks that probe performance in many cognitive domains and thus infer the integrity of brain circuits and regions. There are already many outstanding published protocols on touchscreen cognitive testing. This chapter is designed to add to the literature in two specific ways. First, this chapter provides in a single location practical, behind-the-scenes tips for setup and testing of mice in four touchscreen tasks that are useful to assess in CNS injury models: Paired Associates Learning (PAL), a task of episodic, associative (object-location) memory; Location Discrimination Reversal (LDR), a test for mnemonic discrimination (also called behavioral pattern separation) and cognitive flexibility; Autoshaping (AUTO), a test of Pavlovian or classical conditioning; and Extinction (EXT), tasks of stimulus-response and response inhibition, respectively. Second, this chapter summarizes issues to consider when performing touchscreen tests in mouse models of CNS injury. Quantifying gross and fine aspects of cognitive function is essential to improved treatment for brain dysfunction after stroke or CNS injury as well as other brain diseases, and touchscreen testing provides a sensitive, reliable, and robust way to achieve this.

Touchscreen-Based Cognitive Training Alters Functional Connectivity Patterns in Aged But Not Young Male Rats

Age-related cognitive decline is related to cellular and systems-level disruptions across multiple brain regions. Because age-related cellular changes within different structures do not show the same patterns of dysfunction, interventions aimed at optimizing function of large-scale brain networks may show greater efficacy at improving cognitive outcomes in older adults than traditional pharmacotherapies. The current study aimed to leverage a preclinical rat model of aging to determine whether cognitive training in young and aged male rats with a computerized paired-associates learning (PAL) task resulted in changes in global resting-state functional connectivity. Moreover, seed-based functional connectivity was used to examine resting state connectivity of cortical areas involved in object-location associative memory and vulnerable in old age, namely the medial temporal lobe (MTL; hippocampal cortex and perirhinal cortex), retrosplenial cortex (RSC), and frontal cortical areas (prelimbic and infralimbic cortices). There was an age-related increase in global functional connectivity between baseline and post-training resting state scans in aged, cognitively trained rats. This change in connectivity following cognitive training was not observed in young animals, or rats that traversed a track for a reward between scan sessions. Relatedly, an increase in connectivity between perirhinal and prelimbic cortices, as well as reduced reciprocal connectivity within the RSC, was found in aged rats that underwent cognitive training, but not the other groups. Subnetwork activation was associated with task performance across age groups. Greater global functional connectivity and connectivity between task-relevant brain regions may elucidate compensatory mechanisms that can be engaged by cognitive training.

The extracellular matrix and perineuronal nets in memory

All components of the CNS are surrounded by a diffuse extracellular matrix (ECM) containing chondroitin sulphate proteoglycans (CSPGs), heparan sulphate proteoglycans (HSPGs), hyaluronan, various glycoproteins including tenascins and thrombospondin, and many other molecules that are secreted into the ECM and bind to ECM components. In addition, some neurons, particularly inhibitory GABAergic parvalbumin-positive (PV) interneurons, are surrounded by a more condensed cartilage-like ECM called perineuronal nets (PNNs). PNNs surround the soma and proximal dendrites as net-like structures that surround the synapses. Attention has focused on the role of PNNs in the control of plasticity, but it is now clear that PNNs also play an important part in the modulation of memory. In this review we summarize the role of the ECM, particularly the PNNs, in the control of various types of memory and their participation in memory pathology. PNNs are now being considered as a target for the treatment of impaired memory. There are many potential treatment targets in PNNs, mainly through modulation of the sulphation, binding, and production of the various CSPGs that they contain or through digestion of their sulphated glycosaminoglycans.

Dysregulation of Npas4 and Inhba expression and an altered excitation-inhibition balance are associated with cognitive deficits in DBA/2 mice

Differences in the learning associated transcriptional profiles between mouse strains with distinct learning abilities could provide insight into the molecular basis of learning and memory. The inbred mouse strain DBA/2 shows deficits in hippocampus-dependent memory, yet the transcriptional responses to learning and the underlying mechanisms of the impairments are unknown. Comparing DBA/2J mice with the reference standard C57BL/6N mouse strain we verify an enhanced susceptibility to kainic acid induced seizures, confirm impairments in hippocampus-dependent spatial memory tasks and uncover additional behavioral abnormalities including deficits in hippocampus-independent learning. Surprisingly, we found no broad dysfunction of the DBA/2J strain in immediate early gene (IEG) activation but instead report brain region-specific and gene-specific alterations. The learning-associated IEGs Arc, c-Fos, and Nr4a1 showed no DBA/2J deficits in basal or synaptic activity induced gene expression in hippocampal or cortical primary neuronal cultures or in the CA1, CA3, or retrosplenial cortex following spatial object recognition (SOR) training in vivo. However, the parietal cortex showed reduced and the dentate gyrus showed enhanced SOR-evoked induction of most IEGs. All DBA/2J hippocampal regions exhibited elevated basal expression of inhibin β A (Inhba) and a learning-associated superinduction of the transcription factor neuronal Per-Arnt-Sim domain protein 4 (Npas4) known to regulate the synaptic excitation-inhibition balance. In line with this, CA1 pyramidal neurons of DBA/2J mice showed fewer inhibitory and more excitatory miniature postsynaptic currents but no alteration in most other electrophysiological properties or gross dendritic morphology. The dysregulation of Npas4 and Inhba expression and synaptic connectivity may underlie the cognitive deficits and increased susceptibility to seizures of DBA/2J mice.

Age-related impairments on the touchscreen paired associates learning (PAL) task in male rats

Discovery research in rodent models of cognitive aging is instrumental for identifying mechanisms of behavioral decline in old age that can be therapeutically targeted. Clinically relevant behavioral paradigms, however, have not been widely employed in aged rats. The current study aimed to bridge this translational gap by testing cognition in a cross-species touchscreen-based platform known as paired-associates learning (PAL) and then utilizing a trial-by-trial behavioral analysis approach. This study found age-related deficits in PAL task acquisition in male rats. Furthermore, trial-by-trial analyses and testing rats on a novel interference version of PAL suggested that age-related impairments were not due to differences in vulnerability to an irrelevant distractor, motivation, or to forgetting. Rather, impairment appeared to arise from vulnerability to accumulating, proactive interference, with aged animals performing worse than younger rats in later trial blocks within a single testing session. The detailed behavioral analysis employed in this study provides new insights into the etiology of age-associated cognitive deficits.

Voluntary Exercise Increases Neurogenesis and Mediates Forgetting of Complex Paired Associates Memories

The hippocampus is a critical structure involved in many forms of learning and memory. It is also one of the only regions in the mammalian brain that continues to generate new neurons throughout adulthood. This process of adult neurogenesis may increase the plasticity of the hippocampus which could be beneficial for learning but has also been demonstrated to decrease the stability of previously acquired memories. Here we test whether exposure to voluntary running (which increases the production of new neurons) following the formation of a gradually acquired paired associates task will result in forgetting of this type of memory. We trained mice in a touchscreen-based object/location task and then increased neurogenesis using voluntary running. Our results indicate that running increased neurogenesis and resulted in poor recall of the previously established memory. When subsequently exposed to a reversal task we also show that running reduced the number of correction trials required to acquire the new task contingencies. This suggests that prior forgetting reduces perseveration on the now outdated memory. Together our results add to a growing body of literature which indicates the important role of adult neurogenesis in destabilizing previously acquired memories to allow for flexible encoding of new memories.

Cognitive behavioral markers of neurodevelopmental trajectories in rodents

Between adolescence and adulthood, the brain critically undergoes maturation and refinement of synaptic and neural circuits that shape cognitive processing. Adolescence also represents a vulnerable period for the onset of symptoms in neurodevelopmental psychiatric disorders. Despite the wide use of rodent models to unravel neurobiological mechanisms underlying neurodevelopmental disorders, there is a surprising paucity of rigorous studies focusing on normal cognitive-developmental trajectories in such models. Here, we sought to behaviorally capture maturational changes in cognitive trajectories during adolescence and into adulthood in male and female mice using distinct behavioral paradigms. C57 BL/6J mice (4.5, 6, and 12 weeks of age) were assessed on three behavioral paradigms: drug-induced locomotor hyperactivity, prepulse inhibition, and a novel validated version of a visuospatial paired-associate learning touchscreen task. We show that the normal maturational trajectories of behavioral performance on these paradigms are dissociable. Responses in drug-induced locomotor hyperactivity and prepulse inhibition both displayed a 'U-shaped' developmental trajectory; lower during mid-adolescence relative to early adolescence and adulthood. In contrast, visuospatial learning and memory, memory retention, and response times indicative of motivational processing progressively improved with age. Our study offers a framework to investigate how insults at different developmental stages might perturb normal trajectories in cognitive development. We provide a brain maturational approach to understand resilience factors of brain plasticity in the face of adversity and to examine pharmacological and non-pharmacological interventions directed at ameliorating or rescuing perturbed trajectories in neurodevelopmental and neuropsychiatric disorders.

GPR40 receptor agonist TAK-875 improves cognitive deficits and reduces β-amyloid production in APPswe/PS1dE9 mice

RATIONALE

Alzheimer's disease (AD) is an age-related neurodegenerative disease characterized by progressive cognitive dysfunction and memory impairment. G protein-coupled receptor 40 (GPR40) is expressed in brain in addition to periphery and is associated with cognitive function such as space orientation, memory, and learning. However, the effects and mechanisms of GPR40 agonist in improving the AD progression remain largely unknown.

OBJECTIVES

The present study aimed to investigate the therapeutic effects and mechanisms of a potent and selective GPR40 agonist TAK-875 on the APPswe/PS1dE9 mice.

RESULTS

The results showed that intracerebroventricular administration of TAK-875 significantly rescued cognitive deficits in APPswe/PS1dE9 mice, and these effects may be mediated by the regulation of phospholipase C/protein kinase C signaling pathway, which enhanced α-secretase ADAM10 activity, promoted amyloid precursor protein non-amyloidogenic processing pathway, and reduced β-amyloid production.

CONCLUSIONS

These results suggest that GPR40 may be a potential therapeutic target for AD, and GPR40 agonists may become promising AD drugs in the future.

Partial mGlu5 Negative Allosteric Modulator M-5MPEP Demonstrates Antidepressant-Like Effects on Sleep Without Affecting Cognition or Quantitative EEG

Selective negative allosteric modulators (NAMs) targeting the metabotropic glutamate receptor subtype 5 (mGlu5) demonstrate anxiolytic-like and antidepressant-like effects yet concern regarding adverse effect liability remains. Functional coupling of mGlu5 with ionotropic N-methyl-D-aspartate receptors (NMDARs) represents a potential mechanism through which full inhibition leads to adverse effects, as NMDAR inhibition can induce cognitive impairments and psychotomimetic-like effects. Recent development of "partial" mGlu5 NAMs, characterized by submaximal but saturable levels of blockade, may represent a novel development approach to broaden the therapeutic index of mGlu5 NAMs. This study compared the partial mGlu5 NAM, M-5MPEP, with the full mGlu5 NAM, VU0424238 on sleep, cognition, and brain function alone and in combination with a subthreshold dose of the NMDAR antagonist, MK-801, using a paired-associates learning (PAL) cognition task and electroencephalography (EEG) in rats. M-5MPEP and VU0424238 decreased rapid eye movement (REM) sleep and increased REM sleep latency, both putative biomarkers of antidepressant-like activity. Neither compound alone affected accuracy, but 30 mg/kg VU0424238 combined with MK-801 decreased accuracy on the PAL task. Using quantitative EEG, VU0424238, but not M-5MPEP, prolonged arousal-related elevations in high gamma power, and, in combination, VU0424238 potentiated effects of MK-801 on high gamma power. Together, these studies further support a functional interaction between mGlu5 and NMDARs that may correspond with cognitive impairments. Present data support further development of partial mGlu5 NAMs given their potentially broader therapeutic index than full mGlu5 NAMs and use of EEG as a translational biomarker to titrate doses aligning with therapeutic versus adverse effects.

Ocular measures during associative learning predict recall accuracy

The ability to form associations between stimuli and commit those associations to memory is a cornerstone of human cognition. Dopamine and noradrenaline are critical neuromodulators implicated in a range of cognitive functions, including learning and memory. Eye blink rate (EBR) and pupil diameter have been shown to index dopaminergic and noradrenergic activity. Here, we examined how these ocular measures relate to accuracy in a paired-associate learning task where participants (N = 73) learned consistent object-location associations over eight trials consisting of pre-trial fixation, encoding, delay, and retrieval epochs. In order to examine how within-subject changes and between-subject changes in ocular metrics related to accuracy, we mean centered individual metric values on each trial based on within-person and across-subject means for each epoch. Within-participant variation in EBR was positively related to accuracy in both encoding and delay epochs: faster EBR within the individual predicted better retrieval. Differences in EBR across participants was negatively related to accuracy in the encoding epoch and in early trials of the pre-trial fixation: faster EBR, relative to other subjects, predicted poorer retrieval. Visual scanning behavior in pre-trial fixation and delay epochs was also positively related to accuracy in early trials: more scanning predicted better retrieval. We found no relationship between pupil diameter and accuracy. These results provide novel evidence supporting the utility of ocular metrics in illuminating cognitive and neurobiological mechanisms of paired-associate learning.

Atrx Deletion in Neurons Leads to Sexually Dimorphic Dysregulation of miR-137 and Spatial Learning and Memory Deficits

ATRX gene mutations have been identified in syndromic and non-syndromic intellectual disabilities in humans. ATRX is known to maintain genomic stability in neuroprogenitor cells, but its function in differentiated neurons and memory processes remains largely unresolved. Here, we show that the deletion of neuronal Atrx in mice leads to distinct hippocampal structural defects, fewer presynaptic vesicles, and an enlarged postsynaptic area at CA1 apical dendrite-axon junctions. We identify male-specific impairments in long-term contextual memory and in synaptic gene expression, linked to altered miR-137 levels. We show that ATRX directly binds to the miR-137 locus and that the enrichment of the suppressive histone mark H3K27me3 is significantly reduced upon the loss of ATRX. We conclude that the ablation of ATRX in excitatory forebrain neurons leads to sexually dimorphic effects on miR-137 expression and on spatial memory, identifying a potential therapeutic target for neurological defects caused by ATRX dysfunction.

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Loss of ATRX in neurons has sexually dimorphic effects on long-term spatial memory

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Targeted deletion of neuronal ATRX in mice causes ultrastructural synaptic defects

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ATRX null neurons show sex-specific changes in miR-137 and target synaptic transcripts

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ATRX directly binds and suppresses miR-137 in males via enrichment of H3K27me3

Vortioxetine ameliorates anhedonic-like behaviour and promotes strategic cognitive performance in a rodent touchscreen task

Depression-associated cognitive impairments are among the most prevalent and persistent symptoms during remission from a depressive episode and a major risk factor for relapse. Consequently, development of antidepressant drugs, which also alleviate cognitive impairments, is vital. One such potential antidepressant is vortioxetine that has been postulated to exhibit both antidepressant and pro-cognitive effects. Hence, we tested vortioxetine for combined antidepressant and pro-cognitive effects in male Long-Evans rats exposed to the chronic mild stress (CMS) paradigm. This well-established CMS paradigm evokes cognitive deficits in addition to anhedonia, a core symptom of depression. Learning and memory performance was assessed in the translational touchscreen version of the paired-associates learning task. To identify the mechanistic underpinning of the neurobehavioural results, transcriptional profiling of genes involved in the stress response, neuronal plasticity and genes of broad relevance in neuropsychiatric pathologies were assessed. Vortioxetine substantially relieved the anhedonic-like state in the CMS rats and promoted acquisition of the cognitive test independent of hedonic phenotype, potentially due to an altered cognitive strategy. Minor alterations in gene expression profiling in prefrontal cortex and hippocampus were found. In summary, our findings suggest that vortioxetine exhibits an antidepressant effect as well as behavioural changes in a translational learning task.

Touchscreen cognitive testing: Cross-species translation and co-clinical trials in neurodegenerative and neuropsychiatric disease

Translating results from pre-clinical animal studies to successful human clinical trials in neurodegenerative and neuropsychiatric disease presents a significant challenge. While this issue is clearly multifaceted, the lack of reproducibility and poor translational validity of many paradigms used to assess cognition in animal models are central contributors to this challenge. Computer-automated cognitive test batteries have the potential to substantially improve translation between pre-clinical studies and clinical trials by increasing both reproducibility and translational validity. Given the structured nature of data output, computer-automated tests also lend themselves to increased data sharing and other open science good practices. Over the past two decades, computer automated, touchscreen-based cognitive testing methods have been developed for non-human primate and rodent models. These automated methods lend themselves to increased standardization, hence reproducibility, and have become increasingly important for the elucidation of the neurobiological basis of cognition in animal models. More recently, there have been increased efforts to use these methods to enhance translational validity by developing task batteries that are nearly identical across different species via forward (i.e., translating animal tasks to humans) and reverse (i.e., translating human tasks to animals) translation. An additional benefit of the touchscreen approach is that a cross-species cognitive test battery makes it possible to implement co-clinical trials-an approach developed initially in cancer research-for novel treatments for neurodegenerative disorders. Co-clinical trials bring together pre-clinical and early clinical studies, which facilitates testing of novel treatments in mouse models with underlying genetic or other changes, and can help to stratify patients on the basis of genetic, molecular, or cognitive criteria. This approach can help to determine which patients should be enrolled in specific clinical trials and can facilitate repositioning and/or repurposing of previously approved drugs. This has the potential to mitigate the resources required to study treatment responses in large numbers of human patients.

Differential effects of d- and l-enantiomers of govadine on distinct forms of cognitive flexibility and a comparison with dopaminergic drugs

RATIONALE

There is an urgent need for novel drugs for treating cognitive deficits that are defining features of schizophrenia. The individual d- and l-enantiomers of the tetrahydroprotoberberine (THPB) d,l-govadine have been proposed for the treatment of cognitive deficiencies and positive symptoms of schizophrenia, respectively.

OBJECTIVES

We examined the effects of d-, l-, or d,l-govadine on two distinct forms of cognitive flexibility perturbed in schizophrenia and compared them to those induced by a selective D1 receptor agonist and D2 receptor antagonist.

METHODS

Male rats received d-, l-, or d,l-govadine (0.3, 0.5, and 1.0 mg/kg), D1 agonist SKF81297(0.1, 0.3, and 1.0 mg/kg), or D2 antagonist haloperidol (0.1-0.2 mg/kg). Experiment 1 used a strategy set-shifting task (between-subjects). In experiment 2, well-trained rats were tested on a probabilistic reversal task (within-subjects).

RESULTS

d-Govadine improved set-shifting across all doses, whereas higher doses of l-govadine impaired set-shifting. SKF81297 reduced perseverative errors at the lowest dose. Low/high doses of haloperidol increased/decreased set-shifting errors, the latter "improvement" attributable to impaired retrieval of a previous acquired rule. Probabilistic reversal performance was less affected by these drugs, but d-govadine reduced errors during the first reversal, whereas l-govadine impaired initial discrimination learning. d,l-Govadine had no reliable cognitive effects but caused psychomotor slowing like l-govadine and haloperidol.

CONCLUSIONS

These findings further highlight differences between two enantiomers of d,l-govadine that may reflect differential modulation of D1 and D2 receptors. These preclinical findings give further impetus to formal clinical evaluation of d-govadine as a treatment for cognitive deficiencies related to schizophrenia.

Age affects procedural paired-associates learning in the grey mouse lemur (Microcebus murinus)

The ability to associate memorized objects with their location in space gradually declines during normal aging and can drastically be affected by neurodegenerative diseases. This study investigates object-location paired-associates learning (PAL) in the grey mouse lemur (Microcebus murinus), a nonhuman primate model of brain aging. Touchscreen-based testing of 6 young adults (1–5 years) and 6 old adults (> 7 years) in the procedural rodent dPAL-task revealed significant age-related performance decline, evident in group differences in the percentage of correct decision during learning and the number of sessions needed to reach a predefined criterion. Response pattern analyses suggest decreased susceptibility to relative stimulus-position biases in young animals, facilitating PAL. Additional data from a subset of “overtrained” individuals (n = 7) and challenge sessions using a modified protocol (sPAL) further suggest that learning criteria routinely used in animal studies on PAL can underestimate the endpoint at which a stable performance is reached and that more conservative criteria are needed to improve construct validity of the task. To conclude, this is the first report of an age effect on dPAL and corroborates the role of mouse lemurs as valuable natural nonhuman primate models in aging research.

Translation-Focused Approaches to GPCR Drug Discovery for Cognitive Impairments Associated with Schizophrenia

There are no effective therapeutics for cognitive impairments associated with schizophrenia (CIAS), which includes deficits in executive functions (working memory and cognitive flexibility) and episodic memory. Compounds that have entered clinical trials are inadequate in terms of efficacy and/or tolerability, highlighting a clear translational bottleneck and a need for a cohesive preclinical drug development strategy. In this review we propose hippocampal-prefrontal-cortical (HPC-PFC) circuitry underlying CIAS-relevant cognitive processes across mammalian species as a target source to guide the translation-focused discovery and development of novel, procognitive agents. We highlight several G protein-coupled receptors (GPCRs) enriched within HPC-PFC circuitry as therapeutic targets of interest, including noncanonical approaches (biased agonism and allosteric modulation) to conventional clinical targets, such as dopamine and muscarinic acetylcholine receptors, along with prospective novel targets, including the orphan receptors GPR52 and GPR139. We also describe the translational limitations of popular preclinical cognition tests and suggest touchscreen-based assays that probe cognitive functions reliant on HPC-PFC circuitry and reflect tests used in the clinic, as tests of greater translational relevance. Combining pharmacological and behavioral testing strategies based in HPC-PFC circuit function creates a cohesive, translation-focused approach to preclinical drug development that may improve the translational bottleneck currently hindering the development of treatments for CIAS.

Touchscreen-based location discrimination and paired associate learning tasks detect cognitive impairment at an early stage in an App knock-in mouse model of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive decline with accumulation of amyloid beta (Aβ) and neurofibrillary tangles that usually begins 15–30 years before clinical diagnosis. Rodent models that recapitulate aggressive Aβ and/or the pathology of neurofibrillary tangles are essential for AD research. Accordingly, non-invasive early detection systems in these animal models are required to evaluate the phenotypic changes, elucidate the mechanism of disease progression, and facilitate development of novel therapeutic approaches. Although many behavioral tests efficiently reveal cognitive impairments at the later stage of the disease in AD models, it has been challenging to detect such impairments at the early stage. To address this issue, we subjected 4–6-month-old male App^{NL−G−F/NL−G−F} knock-in (App-KI) mice to touchscreen-based location discrimination (LD), different object–location paired-associate learning (dPAL), and reversal learning tests, and compared the results with those of the classical Morris water maze test. These tests are mainly dependent on the brain regions prone to Aβ accumulation at the earliest stages of the disease. At 4–6 months, considered to represent the early stage of disease when mice exhibit initial deposition of Aβ and slight gliosis, the classical Morris water maze test revealed no difference between groups, whereas touchscreen-based LD and dPAL tasks revealed significant impairments in task performance. Our report is the first to confirm that a systematic touchscreen-based behavioral test battery can sensitively detect the early stage of cognitive decline in an AD-linked App-KI mouse model. This system could be applied in future translational research.

Similar cognitive deficits in mice and humans in the chronic phase post-stroke identified using the touchscreen-based paired-associate learning task

For many chronic stroke survivors, persisting cognitive dysfunction leads to significantly reduced quality of life. Translation of promising therapeutic strategies aimed at improving cognitive function is hampered by existing, disparate cognitive assessments in animals and humans. In this study, we assessed post-stroke cognitive function using a comparable touchscreen-based paired-associate learning task in a cross-sectional population of chronic stroke survivors (≥ 5 months post-stroke, n = 70), age-matched controls (n = 70), and in mice generated from a C57BL/6 mouse photothrombotic stroke model (at six months post-stroke). Cognitive performance of stroke survivors was analysed using linear regression adjusting for age, gender, diabetes, systolic blood pressure and waist circumference. Stroke survivors made significantly fewer correct choices across all tasks compared with controls. Similar cognitive impairment was observed in the mice post-stroke with fewer correct choices compared to shams. These results highlight the feasibility and potential value of analogous modelling of clinically meaningful cognitive impairments in chronic stroke survivors and in mice in chronic phase after stroke. Implementation of validated, parallel cross-species test platforms for cognitive assessment offer the potential of delivering a more useful framework for evaluating therapies aimed at improving long-term cognitive function post-stroke.

New frontiers in translational research: Touchscreens, open science, and the mouse translational research accelerator platform

Many neurodegenerative and neuropsychiatric diseases and other brain disorders are accompanied by impairments in high-level cognitive functions including memory, attention, motivation, and decision-making. Despite several decades of extensive research, neuroscience is little closer to discovering new treatments. Key impediments include the absence of validated and robust cognitive assessment tools for facilitating translation from animal models to humans. In this review, we describe a state-of-the-art platform poised to overcome these impediments and improve the success of translational research, the Mouse Translational Research Accelerator Platform (MouseTRAP), which is centered on the touchscreen cognitive testing system for rodents. It integrates touchscreen-based tests of high-level cognitive assessment with state-of-the art neurotechnology to record and manipulate molecular and circuit level activity in vivo in animal models during human-relevant cognitive performance. The platform also is integrated with two Open Science platforms designed to facilitate knowledge and data-sharing practices within the rodent touchscreen community, touchscreencognition.org and mousebytes.ca. Touchscreencognition.org includes the Wall, showcasing touchscreen news and publications, the Forum, for community discussion, and Training, which includes courses, videos, SOPs, and symposia. To get started, interested researchers simply create user accounts. We describe the origins of the touchscreen testing system, the novel lines of research it has facilitated, and its increasingly widespread use in translational research, which is attributable in part to knowledge-sharing efforts over the past decade. We then identify the unique features of MouseTRAP that stand to potentially revolutionize translational research, and describe new initiatives to partner with similar platforms such as McGill's M3 platform (m3platform.org).

Impact of Hyperhomocysteinemia and Different Dietary Interventions on Cognitive Performance in a Knock-in Mouse Model for Alzheimer's Disease

BACKGROUND

Hyperhomocysteinemia is considered a possible contributor to the complex pathology of Alzheimer's disease (AD). For years, researchers in this field have discussed the apparent detrimental effects of the endogenous amino acid homocysteine in the brain. In this study, the roles of hyperhomocysteinemia driven by vitamin B deficiency, as well as potentially beneficial dietary interventions, were investigated in the novel App^NL-G-F knock-in mouse model for AD, simulating an early stage of the disease.

METHODS

Urine and serum samples were analyzed using a validated LC-MS/MS method and the impact of different experimental diets on cognitive performance was studied in a comprehensive behavioral test battery. Finally, we analyzed brain samples immunohistochemically in order to assess amyloid-β (Aβ) plaque deposition.

RESULTS

Behavioral testing data indicated subtle cognitive deficits in App^NL-G-F compared to C57BL/6J wild type mice. Elevation of homocysteine and homocysteic acid, as well as counteracting dietary interventions, mostly did not result in significant effects on learning and memory performance, nor in a modified Aβ plaque deposition in 35-week-old App^NL-G-F mice.

CONCLUSION

Despite prominent Aβ plaque deposition, the App^NL-G-F model merely displays a very mild AD-like phenotype at the investigated age. Older App^NL-G-F mice should be tested in order to further investigate potential effects of hyperhomocysteinemia and dietary interventions.

A molecular insight into the dissociable regulation of associative learning and motivation by the synaptic protein neuroligin-1

Background

In a changing environment, a challenge for the brain is to flexibly guide adaptive behavior towards survival. Complex behavior and the underlying neural computations emerge from the structural components of the brain across many levels: circuits, cells, and ultimately the signaling complex of proteins at synapses. In line with this logic, dynamic modification of synaptic strength or synaptic plasticity is widely considered the cellular level implementation for adaptive behavior such as learning and memory. Predominantly expressed at excitatory synapses, the postsynaptic cell-adhesion molecule neuroligin-1 (Nlgn1) forms trans-synaptic complexes with presynaptic neurexins. Extensive evidence supports that Nlgn1 is essential for NMDA receptor transmission and long-term potentiation (LTP), both of which are putative synaptic mechanisms underlying learning and memory. Here, employing a comprehensive battery of touchscreen-based cognitive assays, we asked whether impaired NMDA receptor transmission and LTP in mice lacking Nlgn1 does in fact disrupt decision-making. To this end, we addressed two key decision problems: (i) the ability to learn and exploit the associative structure of the environment and (ii) balancing the trade-off between potential rewards and costs, or positive and negative utilities of available actions.

Results

We found that the capacity to acquire complex associative structures and adjust learned associations was intact. However, loss of Nlgn1 alters motivation leading to a reduced willingness to overcome effort cost for reward and an increased willingness to exert effort to escape an aversive situation. We suggest Nlgn1 may be important for balancing the weighting on positive and negative utilities in reward-cost trade-off.

Conclusions

Our findings update canonical views of this key synaptic molecule in behavior and suggest Nlgn1 may be essential for regulating distinct cognitive processes underlying action selection. Our data demonstrate that learning and motivational computations can be dissociated within the same animal model, from a detailed behavioral dissection. Further, these results highlight the complexities in mapping synaptic mechanisms to their behavioral consequences, and the future challenge to elucidate how complex behavior emerges through different levels of neural hardware.

Exploratory relationships between cognitive improvements and training induced plasticity in hippocampus and cingulum in a rat model of mild traumatic brain injury: a diffusion MRI study

Traumatic brain injury (TBI) is a major cause of long-term cognitive deficits, even in mild TBI patients. Computerized cognitive training can help alleviate complaints and improve daily life functioning of TBI patients. However, the underlying biological mechanisms of cognitive training in TBI are not fully understood. In the present study, we utilised for the first time a touchscreen cognitive training system in a rat model of mild TBI. Moreover, we wanted to examine whether the beneficial effects of a cognitive training are task-dependent and selective in their target. Specifically, we examined the effect of two training tasks, i.e. the Paired Associate Learning (PAL) task targeting spatial memory functioning and 5-Choice Continuous Performance (5-CCP) task loading on attention and inhibition control, on the microstructural organization of the hippocampus and cingulum, respectively, using diffusion tensor imaging (DTI). Our findings revealed that the two training protocols induced similar effects on the diffusion MRI metrics. Further, in the TBI groups who received training microstructural organization in the hippocampus and cingulum improved (as denoted by increases in fractional anisotropy), while a worsening (i.e., increases in mean diffusivity and radial diffusivity) was found in the TBI control group. In addition, these alterations in diffusion MRI metrics coincided with improved performance on the training tasks in the TBI groups who received training. Our findings show the potential of DTI metrics as reliable measure to evaluate cognitive training in TBI patients and to facilitate future research investigating further improvement of cognitive training targeting deficits in spatial memory and attention.

Differential effects of post-training scopolamine on spatial and non-spatial learning tasks in mice

Muscarinic antagonist scopolamine has been extensively used to model amnesia in lab rodents, but most studies have focused on the effects of pre-training scopolamine administration. Here, we examined post-training scopolamine administration in C57BL/6JRj mice. Learning was assessed in three different procedures: odour discrimination in a digging paradigm, visual discrimination in a touchscreen-based setup, and spatial learning in the Morris water maze. Scopolamine administration affected performance in the odour discrimination task. More specifically, scopolamine decreased perseverance, which facilitated reversal learning. Similar results were obtained in the visual discrimination task, but scopolamine did not affect performance in the spatial learning task. It is unlikely that these results can be explained by non-memory-related cognitive effects (e.g., attention), non-cognitive behaviours (e.g., locomotor activity) or peripheral side-effects (e.g., mydriasis). They likely relate to the various neuropharmacological actions of scopolamine.

Role of cortical microbleeds in cognitive impairment: In vivo behavioral and imaging characterization of a novel murine model

Cerebral microbleeds (CMBs) could contribute to cognitive impairment in the general population and in patients with dementia. We designed a study to (i) develop a murine model of CMBs, (ii) assess whether CMBs affect cognition in this model and (iii) assess whether this model is sensitive to pharmacological modulation. Male C57Bl6/J mice were stereotactically administered collagenase to induce cortical lesion analysed by MRI at 24 h. CMB-mice were assessed at six weeks post-lesion for cognitive performances (Barnes maze and Touchscreen automated paired-associated learning (PAL) task) and for cerebral metabolism (in vivo PET/CT with fluorodeoxyglucose (FDG)). CMB-model sensitivity to pharmacological modulation was assessed by administering atorvastatin (5 mg/kg/day) over the follow-up period. CMB mice were compared to naïve littermates. Collagenase at 0.8 µU/µl appeared suitable to induce reproducible and reliable CMBs. At six weeks, a decline in learning, spatial and visuospatial memory was significantly observed in CMB-mice. Brain metabolism was impaired in all cortex, striatum and the ipsilateral dentate gyrus. A significant improvement in cognition performances was depicted under atorvastatin. In this novel murine model of CMBs, we validated that CMBs lowered cognitive performances and affected regional metabolism. We also proved that this CMB-model is sensitive to pharmacological modulation.

Adolescent exposure to Δ9-tetrahydrocannabinol delays acquisition of paired-associates learning in adulthood

RATIONALE AND OBJECTIVES

Adolescence is a sensitive period of brain development, during which there may be a heightened vulnerability to the effects of drug use. Despite this, the long-term effects of cannabis use during this developmental period on cognition are poorly understood.

METHODS

We exposed adolescent rats to escalating doses of Δ9-tetrahydrocannabinol (THC)-the primary psychoactive component of cannabis-or vehicle solution during postnatal days (PND) 35-45, a period of development that is analogous to human adolescence (THC doses: PND 35-37, 2.5 mg/kg; PND 38-41, 5 mg/kg; PND 42-45, 10 mg/kg). After a period of abstinence, in adulthood, rats were tested on an automated touchscreen version of a paired-associates learning (PAL) task to assess their ability to learn and recall object-location associations. Prepulse inhibition (PPI) of the startle response was also measured at three time points (5 days, 4 months, and 6 months after exposure) to assess sensorimotor gating, the ability to filter out insignificant sensory information from the environment.

RESULTS

Compared to rats exposed to vehicle alone, rats exposed to THC during adolescence took longer to learn the PAL task when tested in adulthood, even when trials contained visually identical stimuli that differed only in location. Despite this, no differences were observed later in testing, when trials contained visually distinct stimuli in different locations. Rats exposed to THC also displayed impairments in sensorimotor gating, as measured by prepulse inhibition of the startle response, though this deficit did appear to decrease over time.

CONCLUSION

Taken together, THC exposure during adolescence produces long-term deficits in associative learning and sensorimotor gating, though the impact of these deficits seems to diminish with time. Thus, adolescence may represent a period of neurocognitive development that is vulnerable to the harms of cannabis use, though the stability of such harms is uncertain.

A low-cost touchscreen operant chamber using a Raspberry Pi™

The development of a touchscreen platform for rodent testing has allowed new methods for cognitive testing that have been back-translated from clinical assessment tools to preclinical animal models. This platform for cognitive assessment in animals is comparable to human neuropsychological tests such as those employed by the Cambridge Neuropsychological Test Automated Battery, and thus has several advantages compared to the standard maze apparatuses typically employed in rodent behavioral testing, such as the Morris water maze. These include improved translation of preclinical models, as well as high throughput and the automation of animal testing. However, these systems are relatively expensive, which can impede progress for researchers with limited resources. Here we describe a low-cost touchscreen operant chamber based on the single-board computer, Raspberry Pi^TM, which is capable of performing tasks similar to those supported by current state-of-the-art systems. This system provides an affordable alternative for cognitive testing in a touchscreen operant paradigm for researchers with limited funding.

'Real-life' hippocampal-dependent spatial memory impairments in Huntington's disease

Hippocampal-dependent spatial memory impairments are seen in Huntington's disease animal models. Similar impairments were recently reported in Huntington's disease participants on analogous spatial memory tasks (e.g., virtual Morris Water Maze), however, these tasks do not translate well to the range of functions involved in day-to-day spatial cognition. In this study we examined 'real-life' hippocampal-dependent spatial memory in Huntington's disease participants. We studied premanifest Huntington's disease (N = 24), early manifest Huntington's disease (N = 14), and matched healthy controls (N = 33) with a virtual environment, which demanded spatial memory function on three levels: navigation, object location, and plan drawing. To examine the case for hippocampal-dependent spatial memory more closely, we compared the performance of our Huntington's disease participants to that of a group of temporal lobe epilepsy patients (N = 30) who were previously tested on the virtual environment. Spatial memory performance was also compared to two common neuropsychological tests of spatial cognition, the Paired Associates Learning from the Cambridge Neuropsychological Automated Test Battery, and the Rey-Osterrieth Complex Figure Test. People with early manifest Huntington's disease were impaired across all spatial memory tasks. Premanifest Huntington's disease participants were most notably impaired on the object location measure of the virtual environment, which is heavily dependent on hippocampal function, but showed no such impairments on the Paired Associates Learning or the Rey-Osterrieth Complex Figure Test. Object location memory and navigation performance did not differ between people with Huntington's disease and temporal lobe epilepsy. Aligned with studies in Huntington's disease animal models, 'real-life' spatial memory is impaired in people with Huntington's disease prior to clinical diagnosis. This alignment has important implications for testing treatments for Huntington's disease. From the standpoint of neurodegeneration, the dependence of our spatial memory measures on hippocampal function extends the focus of cognitive assessment research in Huntington's disease beyond its primary pathology within the striato-frontal circuit.

Hop-Derived Iso-α-Acids in Beer Improve Visual Discrimination and Reversal Learning in Mice as Assessed by a Touch Panel Operant System

Dementia and cognitive decline have become worldwide health problems due to rapid growth of the aged population in many countries. We previously demonstrated that single or short-term administration of iso-α-acids, hop-derived bitter acids in beer, improves the spatial memory of scopolamine-induced amnesia model mice in the Y-maze and enhances novel object recognition in normal mice via activation of the vagus nerve and hippocampal dopaminergic system. However, these behavioral tests do not replicate the stimulus conditions or response requirements of human memory tests, and so may have poor translational validity. In this report, we investigated the effects of iso-α-acids on visual discrimination (VD) and reversal discrimination (RD) using a touch panel-based operant system similar to that used for human working memory tests. In the VD task, scopolamine treatment reduced correct response rate and prolonged response latency in mice, deficits reversed by prior oral administration of iso-α-acids. In the RD task, administration of iso-α-acids significantly increased correct response rate compared to vehicle administration. Previous studies have reported that dopamine signaling is involved in both VD and RD learning, suggesting that enhancement of dopamine release contributes to improved memory performance in mice treated with iso-α-acids. Taken together, iso-α-acids improve VD and RD learning, which are considered high-order cognitive functions. Given the translational advantages of the touch panel-based operant system, the present study suggests that iso-α-acids could be effective for improvement of working memory in human dementia patients.

Inhibitory control in BALB/c mice sub-strains during extinction learning

Dysregulation of executive function (EF) involves alterations in cognitive flexibility / control and is underscored by learning impairments in neurodevelopmental disorders. Here, we examine cognitive inflexibility in BALB/cJ mice (a mouse model showing diminished sociability, increased anxiety and inattentive behaviour) and closely related "reference" BALB/cByJ mice. We used an appetitive extinction paradigm to investigate if cognitive flexibility measures are different between learning acquisition and extinction. The two BALB/c sub-strains learned to respond to a stimulus in a touchscreen operant chamber, after which the reward was removed and responses should be inhibited. Both mice sub-strains showed a different rate of learning while acquiring the task, in which the BALB/cJ mice were faster learners compared to the BALB/cByJ mice. This was not observed during the extinction phase, in which the BALB/cJ mice were able to extinguish responding to unrewarded stimuli equally. Within the BALB/cJ sub-strain, variation in the ability to inhibit a learnt response was observed when comparing them to similar grouped BALB/cByJ mice: BALB/cJ animals that reached the criterion were more reward driven, while BALB/cJ mice failing to reach the set criterion during extinction processing make more mistakes. Additionally, the changes observed during acquisition, were driven by animals not reaching the extinction criterion. Our results suggest that the BALB/c mice sub-strains may use different strategies to learn during appetitive extinction. This may be useful in the phenotypic dissection of cognitive flexibility in BALB/c sub-strains and their mapping on genetic variance revealed by next-generation sequencing in future studies.

Technology or ecology? New tools to assess cognitive judgement bias in mice

Cognitive judgement bias tests have become important new tools for the assessment of animal emotions. They allow for the inference of an animal's emotional state based on ambiguous cue interpretations. As mice are the predominantly used animal model for cognitive and behavioural neuroscience, research in this field would considerably benefit from the development of suitable judgement bias tests for this species. Against this background, we aimed to implement two different active choice cognitive judgement bias paradigms for mice in a methodological study. For this purpose, two experiments were conducted: in experiment I, an automated, vision-based touchscreen technique was applied, allowing for the direct translation of tasks from rodents to humans and vice versa. Experiment II comprised a task relying on more ecologically relevant cues in form of tunnels of different lengths. While the touchscreen task was characterized by automation-related advantages such as the possibility to present many trials per session and a high convenience for the experimenter, the tunnel task was learned faster by the mice. In both tests, however, the response to the trained and ambiguous conditions resulted in a graded curve, the basic requirement for proving task validity. Thus, both the translational touchscreen task as well as the ecologically more relevant tunnel task could successfully be implemented and provide new tools for the future assessment of cognitive judgement biases in mice.

Impaired Performance of the Q175 Mouse Model of Huntington's Disease in the Touch Screen Paired Associates Learning Task

Cognitive disturbances often predate characteristic motor dysfunction in individuals with Huntington’s disease (HD) and place an increasing burden on the HD patients and caregivers with the progression of the disorder. Therefore, application of maximally translational cognitive tests to animal models of HD is imperative for the development of treatments that could alleviate cognitive decline in human patients. Here, we examined the performance of the Q175 mouse knock-in model of HD in the touch screen version of the paired associates learning (PAL) task. We found that 10–11-month-old heterozygous Q175 mice had severely attenuated learning curve in the PAL task, which was conceptually similar to previously documented impaired performance of individuals with HD in the PAL task of the Cambridge Neuropsychological Test Automated Battery (CANTAB). Besides high rate of errors in PAL task, Q175 mice exhibited considerably lower responding rate than age-matched wild-type (WT) animals. Our examination of effortful operant responding during fixed ratio (FR) and progressive ratio (PR) reinforcement schedules in a separate cohort of similar age confirmed slower and unselective performance of mutant animals, as observed during PAL task, but suggested that motivation to work for nutritional reward in the touch screen setting was similar in Q175 and WT mice. We also demonstrated that pronounced sensorimotor disturbances in Q175 mice can be detected at early touch screen testing stages, (e.g., during “Punish Incorrect” phase of operant pretraining), so we propose that shorter test routines may be utilised for more expedient studies of treatments aimed at the rescue of HD-related phenotype.

Long-Term Stress Disrupts the Structural and Functional Integrity of GABAergic Neuronal Networks in the Medial Prefrontal Cortex of Rats

Clinical and experimental data suggest that fronto-cortical GABAergic deficits contribute to the pathophysiology of major depressive disorder (MDD). To further test this hypothesis, we used a well characterized rat model for depression and examined the effect of stress on GABAergic neuron numbers and GABA-mediated synaptic transmission in the medial prefrontal cortex (mPFC) of rats. Adult male Wistar rats were subjected to 9-weeks of chronic mild stress (CMS) and based on their hedonic-anhedonic behavior they were behaviorally phenotyped as being stress-susceptible (anhedonic) or stress-resilient. Post mortem quantitative histopathology was used to examine the effect of stress on parvalbumin (PV)-, calretinin- (CR), calbindin- (CB), cholecystokinin- (CCK), somatostatin-(SST) and neuropeptide Y-positive (NPY+) GABAergic neuron numbers in all cortical subareas of the mPFC (anterior cingulate (Cg1), prelimbic (PrL) and infralimbic (IL) cortexes). In vitro, whole-cell patch-clamp recordings from layer II–III pyramidal neurons of the ventral mPFC was used to examine GABAergic neurotransmission. The cognitive performance of the animals was assessed in a hippocampal-prefrontal-cortical circuit dependent learning task. Stress exposure reduced the number of CCK-, CR- and PV-positive GABAergic neurons in the mPFC, most prominently in the IL cortex. Interestingly, in the stress-resilient animals, we found higher number of neuropeptide Y-positive neurons in the entire mPFC. The electrophysiological analysis revealed reduced frequencies of spontaneous and miniature IPSCs in the anhedonic rats and decreased release probability of perisomatic-targeting GABAergic synapses and alterations in GABA_B receptor mediated signaling. In turn, pyramidal neurons showed higher excitability. Anhedonic rats were also significantly impaired in the object-place paired-associate learning task. These data demonstrate that long-term stress results in functional and structural deficits of prefrontal GABAergic networks. Our findings support the concept that fronto-limbic GABAergic dysfunctions may contribute to emotional and cognitive symptoms of MDD.

Evaluation of Touchscreen Chambers To Assess Cognition in Adult Mice: Effect of Training and Mild Traumatic Brain Injury

Cognitive impairments are often experienced after a mild traumatic brain injury (mTBI). In the clinical arena, neuropsychological assessments are used frequently to detect cognitive deficits. Animal models of mTBI, however, rely on an assortment of behavioral tasks to assess cognitive outcome. Computer-based touchscreen systems have been developed for rodents and are hypothesized to offer a translational approach to evaluate cognitive function because of the similarities of tasks performed in rodents to those implemented in humans. While these touchscreen systems have been used in pre-clinical models of neurodegenerative diseases and psychiatric disorders, their use in assessing cognitive impairment after mTBI has not been investigated. We hypothesized that mTBI would result in impaired cognitive performance on touchscreen tasks, particularly those with hippocampal-based learning components, including the paired associate learning (PAL) task and the location discrimination (LD) task. Adult male, C57BL/6 mice received a single impact-acceleration mTBI. We found that training mice before injury to perform to criteria is arduous and that performance is sensitive to many environmental variables. Despite extensive optimization and training, mice failed to perform better than chance in the PAL paradigm. Alternatively, mice demonstrated some capacity to learn in the LD paradigm, but only with the easier stages of the task. The mTBI did not affect performance in the LD paradigm, however. Thus, we concluded that under the conditions presented here, the PAL and LD touchscreen tasks are not robust outcome measures for the evaluation of cognitive performance in C57BL/6 mice after a single impact-acceleration mTBI.

Acute stress, but not corticosterone, facilitates acquisition of paired associates learning in rats using touchscreen-equipped operant conditioning chambers

Acute stress influences learning and memory in humans and rodents, enhancing performance in some tasks while impairing it in others. Typically, subjects preferentially employ striatal-mediated stimulus-response strategies in spatial memory tasks following stress, making use of fewer hippocampal-based strategies which may be more cognitively demanding. Previous research demonstrated that the acquisition of rodent paired associates learning (PAL) relies primarily on the striatum, while task performance after extensive training is impaired by hippocampal disruption. Therefore, we sought to explore whether the acquisition of PAL, an operant conditioning task involving spatial stimuli, could be enhanced by acute stress. Male Long-Evans rats were trained to a predefined criterion in PAL and then subjected to either a single session of restraint stress (30 min) or injection of corticosterone (CORT; 3 mg/kg). Subsequent task performance was monitored for one week. We found that rats subjected to restraint stress, but not those rats injected with CORT, performed with higher accuracy and efficiency, when compared to untreated controls. These results suggest that while acute stress enhances the acquisition of PAL, CORT alone does not. This dissociation may be due to differences between these treatments and their ability to produce sufficient catecholamine release in the amygdala, a requirement for stress effects on memory.

Regulation of Cognitive Processing by Hippocampal Cholinergic Tone

Cholinergic dysfunction has been associated with cognitive abnormalities in a variety of neurodegenerative and neuropsychiatric diseases. Here we tested how information processing is regulated by cholinergic tone in genetically modified mice targeting the vesicular acetylcholine transporter (VAChT), a protein required for acetylcholine release. We measured long-term potentiation of Schaffer collateral-CA1 synapses in vivo and assessed information processing by using a mouse touchscreen version of paired associates learning task (PAL). Acquisition of information in the mouse PAL task correlated to levels of hippocampal VAChT, suggesting a critical role for cholinergic tone. Accordingly, synaptic plasticity in the hippocampus in vivo was disturbed, but not completely abolished, by decreased hippocampal cholinergic signaling. Disrupted forebrain cholinergic signaling also affected working memory, a result reproduced by selectively decreasing VAChT in the hippocampus. In contrast, spatial memory was relatively preserved, whereas reversal spatial memory was sensitive to decreased hippocampal cholinergic signaling. This work provides a refined roadmap of how synaptically secreted acetylcholine influences distinct behaviors and suggests that distinct forms of cognitive processing may be regulated in different ways by cholinergic activity.

Impaired object-location learning and recognition memory but enhanced sustained attention in M2 muscarinic receptor-deficient mice

RATIONALE

Muscarinic acetylcholine receptors are known to play key roles in mediating cognitive processes, and impaired muscarinic cholinergic neurotransmission is associated with normal ageing processes and Alzheimer's disease. However, the specific contributions of the individual muscarinic receptor subtypes (M1-M5) to cognition are presently not well understood.

OBJECTIVES

The aim of this study was to investigate the contribution of M2-type muscarinic receptor signalling to sustained attention, executive control and learning and memory.

METHODS

M2 receptor-deficient (M2^-/-) mice were tested on a touchscreen-operated task battery testing visual discrimination, behavioural flexibility, object-location associative learning, attention and response control. Spontaneous recognition memory for real-world objects was also assessed.

RESULTS

We found that M2^-/- mice showed an enhancement of attentional performance, but significant deficits on some tests of learning and memory. Executive control and visual discrimination were unaffected by M2-depletion.

CONCLUSIONS

These findings suggest that M2 activation has heterogeneous effects across cognitive domains, and provide insights into how acetylcholine may support multiple specific cognitive processes through functionally distinct cholinergic receptor subtypes. They also suggest that therapeutics involving M2 receptor-active compounds should be assessed across a broad range of cognitive domains, as they may enhance some cognitive functions, but impair others.

CACNA1C gene regulates behavioral strategies in operant rule learning

Behavioral experiments are usually designed to tap into a specific cognitive function, but animals may solve a given task through a variety of different and individual behavioral strategies, some of them not foreseen by the experimenter. Animal learning may therefore be seen more as the process of selecting among, and adapting, potential behavioral policies, rather than mere strengthening of associative links. Calcium influx through high-voltage-gated Ca²⁺ channels is central to synaptic plasticity, and altered expression of Ca_v1.2 channels and the CACNA1C gene have been associated with severe learning deficits and psychiatric disorders. Given this, we were interested in how specifically a selective functional ablation of the Cacna1c gene would modulate the learning process. Using a detailed, individual-level analysis of learning on an operant cue discrimination task in terms of behavioral strategies, combined with Bayesian selection among computational models estimated from the empirical data, we show that a Cacna1c knockout does not impair learning in general but has a much more specific effect: the majority of Cacna1c knockout mice still managed to increase reward feedback across trials but did so by adapting an outcome-based strategy, while the majority of matched controls adopted the experimentally intended cue-association rule. Our results thus point to a quite specific role of a single gene in learning and highlight that much more mechanistic insight could be gained by examining response patterns in terms of a larger repertoire of potential behavioral strategies. The results may also have clinical implications for treating psychiatric disorders.

To deal with an uncertain and complex world, animals have developed a large repertoire of behavioral heuristics and default strategies that spring into action in unknown situations. Building on this a priori repertoire, animals may find various ways to succeed on a given behavioral task. Therefore, determining the exact behavioral strategy followed during a task may be essential for understanding the cognitive processes involved. Using computational models to analyze behavior, we examined how a genetic variation in a gene that encodes a calcium channel and has been associated with learning deficits influences the way in which animals acted on a task in which a reward was associated with a specific behavior. We found that a knockout of the relevant gene does not lead to a general learning impairment but rather led animals to adopt a behavioral strategy different from the one employed by the control animals. Specifically, knockout animals managed to increase their reward returns by basing their responses more on the previous reward location rather than on reward-indicating stimuli, like the controls did. These findings may prove useful for behavioral therapy in the context of psychiatric disorders associated with this specific gene variation.

Effects of dorsal hippocampus catecholamine depletion on paired-associates learning and place learning in rats

Growing evidence suggests that the catecholamine (CA) neurotransmitters dopamine and noradrenaline support hippocampus-mediated learning and memory. However, little is known to date about which forms of hippocampus-mediated spatial learning are modulated by CA signaling in the hippocampus. Therefore, in the current study we examined the effects of 6-hydroxydopamine-induced CA depletion in the dorsal hippocampus on two prominent forms of hippocampus-based spatial learning, that is learning of object-location associations (paired-associates learning) as well as learning and choosing actions based on a representation of the context (place learning). Results show that rats with CA depletion of the dorsal hippocampus were able to learn object-location associations in an automated touch screen paired-associates learning (PAL) task. One possibility to explain this negative result is that object-location learning as tested in the touchscreen PAL task seems to require relatively little hippocampal processing. Results further show that in rats with CA depletion of the dorsal hippocampus the use of a response strategy was facilitated in a T-maze spatial learning task. We suspect that impaired hippocampus CA signaling may attenuate hippocampus-based place learning and favor dorsolateral striatum-based response learning.

Modeling neurodevelopmental cognitive deficits in tasks with cross-species translational validity

Numerous psychiatric disorders whose cognitive dysfunction links to functional outcome have neurodevelopmental origins including schizophrenia, autism and bipolar disorder. Treatments are needed for these cognitive deficits, which require development using animal models. Models of neurodevelopmental disorders are as varied and diverse as the disorders themselves, recreating some but not all aspects of the disorder. This variety may in part underlie why purported procognitive treatments translated from these models have failed to restore functioning in the targeted patient populations. Further complications arise from environmental factors used in these models that can contribute to numerous disorders, perhaps only impacting specific domains, while diagnostic boundaries define individual disorders, limiting translational efficacy. The Research Domain Criteria project seeks to 'develop new ways to classify mental disorders based on behavioral dimensions and neurobiological measures' in hopes of facilitating translational research by remaining agnostic toward diagnostic borders derived from clinical presentation in humans. Models could therefore recreate biosignatures of cognitive dysfunction irrespective of disease state. This review highlights work within the field of neurodevelopmental models of psychiatric disorders tested in cross-species translational cognitive paradigms that directly inform this newly developing research strategy. By expounding on this approach, the hopes are that a fuller understanding of each model may be attainable in terms of the cognitive profile elicited by each manipulation. Hence, conclusions may begin to be drawn on the nature of cognitive neuropathology on neurodevelopmental and other disorders, increasing the chances of procognitive treatment development for individuals affected in specific cognitive domains.

Hippocampal dysfunction defines disease onset in Huntington's disease

BACKGROUND

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterised by a triad of motor, psychiatric and cognitive deficits with the latter classically attributed to disruption of frontostriatal networks. However, emerging evidence from animal models of HD suggests that some of the early cognitive deficits may have a hippocampal basis. The objective of this study was to link previous rodent findings in this area to clinical practice.

METHODS

In this study, 94 participants included patients with early HD, premanifest HD and age-matched controls underwent hippocampal-based cognitive assessments. These included a virtual reality version of the Morris water maze, a task involved participants having to swim through a virtual pool to find a submerged platform using a joystick, and the Cambridge Neuropsychological Test Automated Battery (CANTAB) paired associates learning task, a test also known to rely on hippocampal integrity.

RESULTS

Patients with early HD showed impaired performance in both the virtual Morris water maze and the CANTAB paired associates learning. Such deficits were also correlated with estimated years to diagnosis in premanifest participants.

CONCLUSIONS

This study highlights the merit of using analogous tests in the laboratory and clinic and demonstrates that hippocampal impairments are an early feature of HD in patients as previously shown in rodent models of the disease. As such, they could be used not only to assist in the diagnosis of disease onset, but may also be useful as an outcome measure in future therapeutic trials.

Assessing the Cognitive Translational Potential of a Mouse Model of the 22q11.2 Microdeletion Syndrome

A chromosomal microdeletion at the 22q11.2 locus is associated with extensive cognitive impairments, schizophrenia and other psychopathology in humans. Previous reports indicate that mouse models of the 22q11.2 microdeletion syndrome (22q11.2DS) may model the genetic basis of cognitive deficits relevant for neuropsychiatric disorders such as schizophrenia. To assess the models usefulness for drug discovery, a novel mouse (Df(h22q11)/+) was assessed in an extensive battery of cognitive assays by partners within the NEWMEDS collaboration (Innovative Medicines Initiative Grant Agreement No. 115008). This battery included classic and touchscreen-based paradigms with recognized sensitivity and multiple attempts at reproducing previously published findings in 22q11.2DS mouse models. This work represents one of the most comprehensive reports of cognitive functioning in a transgenic animal model. In accordance with previous reports, there were non-significant trends or marginal impairment in some tasks. However, the Df(h22q11)/+ mouse did not show comprehensive deficits; no robust impairment was observed following more than 17 experiments and 14 behavioral paradigms. Thus - within the current protocols - the 22q11.2DS mouse model fails to mimic the cognitive alterations observed in human 22q11.2 deletion carriers. We suggest that the 22q11.2DS model may induce liability for cognitive dysfunction with additional "hits" being required for phenotypic expression.

Stimulant drug effects on touchscreen automated paired-associates learning (PAL) in rats

Here we tested in rats effects of the procognitive drugs modafinil and methylphenidate on post-acquisition performance in an object–location paired-associates learning (PAL) task. Modafinil (32; 64 mg/kg) was without effect, while higher (9 mg/kg) but not lower (4.5 mg/kg) doses of methylphenidate impaired PAL performance. Likewise, higher but not lower doses of amphetamine (0.4; 0.8 mg/kg) and MK-801 (0.08; 0.12 mg/kg) decreased PAL performance. Impaired PAL performance induced by methylphenidate, amphetamine, and MK801 most likely reflects compromised cognitive function, e.g., retrieval of learned paired associates. Our data suggest that stimulant drugs such as methylphenidate and modafinil might not facilitate performance in hippocampus-related cognitive tasks.

Cognitive Translation Using the Rodent Touchscreen Testing Approach

The development of novel therapeutic avenues for the treatment of cognitive deficits in psychiatric and neurodegenerative disease is of high importance, yet progress in this field has been slow. One reason for this lack of success may lie in discrepancies between how cognitive functions are assessed in experimental animals and humans. In an attempt to bridge this translational gap, the rodent touchscreen testing platform is suggested as a translational tool. Specific examples of successful cross-species translation are discussed focusing on paired associate learning (PAL), the 5-choice serial reaction time task (5-CSRTT), the rodent continuous performance task (rCPT) and reversal learning. With ongoing research assessing the neurocognitive validity of tasks, the touchscreen approach is likely to become increasingly prevalent in translational cognitive research.

The Paired Associates Learning (PAL) Test: 30 Years of CANTAB Translational Neuroscience from Laboratory to Bedside in Dementia Research

The origins and rationale of the Cambridge Neuropsychological Test Automated Battery (CANTAB) as a cross-species translational instrument suitable for use in human neuropsychopharmacological studies are reviewed. We focus on its use for the early assessment and detection of Alzheimer's disease, in particular the Paired Associates Learning (PAL) test. We consider its psychometric properties, neural validation, and utility, including studies on large samples of healthy volunteers, patients with mild cognitive impairment (MCI), and Alzheimer's disease. We demonstrate how it can be applied in cross-species studies using experimental animals to bridge the cross-species translational 'gap'. We also show how the CANTAB PAL has bridged a second translational 'gap' through its application to the early detection of memory problems in primary care clinics, using iPad technology.