Prefrontal cortex synchronization with the hippocampus and parietal cortex is strategy-dependent during spatial learning

During spatial learning, subjects progressively adjust their navigation strategies as they acquire experience. The medial prefrontal cortex (mPFC) supports this operation, for which it may integrate information from distributed networks, such as the hippocampus (HPC) and the posterior parietal cortex (PPC). However, the mechanism underlying the prefrontal coordination with HPC and PPC during spatial learning is poorly understood. Here we show that during navigation trials, mice displayed two sequential behavioral stages: searching and exploration. Exclusively during searching, mice gradually increased their efficiency by transitioning from non-spatial to spatial strategies. When mice used spatial strategies specifically in searching stage, hippocampal and parietal oscillations synchronized gamma oscillations (60-100 Hz) and neuronal firing in the mPFC. This coincided with an increase in the incidence of gamma and task-stage-related changes in firing patterns in the mPFC. These findings relate the goal-directed organization of behavior during spatial learning to transient task-related prefrontal large-scale synchronization.

Anxiety-like behavior and altered hippocampal activity in a transgenic mouse model of Fabry disease

BACKGROUND

Fabry disease (FD) patients are known to be at high risk of developing neuropsychiatric symptoms such as anxiety, depression and cognitive deficits. Despite this, they are underdiagnosed and inadequately treated. It is unknown whether these symptoms arise from pathological glycosphingolipid deposits or from cerebrovascular abnormalities affecting neuronal functions in the central nervous system. We therefore aimed to fill this knowledge gap by exploring a transgenic FD mouse model with a combination of behavior, transcriptomic, functional and morphological assessments, with a particular focus on the hippocampus.

RESULTS

Male FD mice exhibited increased anxiety-like behavior in the open field test, accompanied by a reduced exploratory drive in the Barnes maze, which could be related to the increased deposition of globotriaosylceramide (Gb3) identified in the dentate gyrus (DG). Hippocampus single-cell sequencing further revealed that Gb3 accumulation was associated with differential gene expression in neuronal and non-neuronal cell populations with granule, excitatory and interneurons, as well as microglia and endothelial cells as the main clusters with the most dysregulated genes. Particularly FD hippocampal neurons showed decreased electrical baseline activity in the DG and increased activity in the CA3 region of acutely dissected hippocampal slices.

CONCLUSIONS

Our study highlights transcriptional and functional alterations in non-neuronal and neuronal cell clusters in the hippocampus of FD mice, which are suggested to be causally related to anxiety-like behavior developing as a consequence of FD pathology in mouse models of the disease and in patients.

Depression-like behavior is associated with deficits in cognition and hippocampal neurogenesis in a subset of spinally contused male, but not female, rats

Depression and cognitive deficits present at higher rates among people with spinal cord injury (SCI) compared to the general population, yet these SCI comorbidities are poorly addressed. Sex and age appear to play roles in depression incidence, but consensus on the direction of their effects is limited. Systemic and cortical inflammation and disruptions in hippocampal neurogenesis have been identified as potential treatment targets, but a comprehensive understanding of these mechanisms remains elusive. We used a rodent SCI model to interrogate these gaps in knowledge. We examined post-injury depression-like behavior and cognitive deficits, as well as the association between affect, cognition, chronic hippocampal inflammation and hippocampal neurogenesis, in young and middle-aged male and female Sprague-Dawley rats. Depression-like behavior manifested in male and female subsets of SCI rats irrespective of age, at rates commensurate with the incidence of clinical depression. Changes in components of behavior were driven by sex and age, and affective outcomes were independent of common post-injury pathophysiological outcomes including locomotor functional deficits and spinal lesion severity. Interestingly, however, only male depression-like SCI rats exhibited deficits in hippocampal-associated spatial cognition. Neurogenesis was also disrupted in only SCI males in regions of the hippocampus responsible for affective outcomes. Decreased neurogenesis among middle-aged male subjects coincided with increases in numbers of the pro-inflammatory markers CD86 and iNOS, while middle-aged females had increased numbers of cells expressing Iba-1 and anti-inflammatory marker CD206. Overall, the present data suggest that post-SCI depression and cognition may be affected, in part, by sex- and age-dependent changes in hippocampal neurogenesis and inflammation. Hippocampal neurogenesis is a potential target to address psychological wellbeing after SCI, but therapeutic strategies must carefully consider sex and age as biological variables.

The effects of locus coeruleus ablation on mouse brain volume and microstructure evaluated by high-field MRI

The locus coeruleus (LC) produces most of the brain's noradrenaline (NA). Among its many roles, NA is often said to be neuroprotective and important for brain upkeep. For this reason, loss of LC integrity is thought to impact brain volume and microstructure as well as plasticity broadly. LC dysfunction is also a suspected driver in the development of neurodegenerative diseases. Nevertheless, the impact of LC dysfunction on the gross structure and microstructure of normal brains is not well-studied. We employed high-field ex vivo magnetic resonance imaging (MRI) to investigate brain volumetrics and microstructure in control (CON) mice and mice with LC ablation (LCA) at two ages, representing the developing brain and the fully matured brain. These whole-brain methods are known to be capable of detecting subtle morphological changes and brain microstructural remodeling. We found mice behavior consistent with histologically confirmed LC ablation. However, MRI showed no difference between CON and LCA groups with regard to brain size, relative regional volumes, or regional microstructural indices. Our findings suggest that LC-NA is not needed for postnatal brain maturation and growth in mice. Nor is it required for maintenance in the normal adult mouse brain, as no atrophy or microstructural aberration is detected after weeks of LC dysfunction. This adds clarity to the often-encountered notion that LC-NA is important for brain "trophic support" as it shows that such effects are likely most relevant to mechanisms related to brain plasticity and neuroprotection in the (pre)diseased brain.

Invisible but Insidious Effects of Microplastics

Increasing evidence on the adverse health impacts of microplastics (MPs) is available, but their associated risks to the well-being of humans and long-term impacts are poorly understood. An indicator of the remote effects of MPs may be their influence on the rate of aging. To assess the effects of MPs on the aging process, we used accelerated senescence OXYS rats that develop a complex of geriatric diseases. We prepared the polyethylene terephthalate MPs (2-6 microns in size) and in OXYS and Wistar (maternal strain) rats assessed the influence of chronic administration of MPs (10 or 100 mg/kg per day from age 1.5 to 3.5 months,) on the hematological and biochemical blood parameters, spatial learning, and memory. In addition, the effects of MPs on the development of cataracts and retinopathy, similar to age-related macular degeneration (AMD), in OXYS rats were assessed. We found that in the absence of significant changes in standard clinical blood parameters, chronic MP administration negatively affected the cognitive functions of both Wistar rats and OXYS rats. Additionally, a dose of 100 mg/kg MPs contributed to cataract and AMD progression in OXYS rats. Our results suggest that MPs may increase the rate of aging and, in the long term, lifespan.

Deep brain stimulation mitigates memory deficits in a rodent model of traumatic brain injury

BACKGROUND

Traumatic brain injury (TBI) is a major life-threatening event. In addition to neurological deficits, it can lead to long-term impairments in attention and memory. Deep brain stimulation (DBS) is an established therapy for movement disorders that has been recently investigated for memory improvement in various disorders. In models of TBI, stimulation delivered to different brain targets has been administered to rodents long after the injury with the objective of treating motor deficits, coordination and memory impairment.

OBJECTIVE

To test the hypothesis that DBS administered soon after TBI may prevent the development of memory deficits and exert neuroprotective effects.

METHODS

Male rats were implanted with DBS electrodes in the anterior nucleus of the thalamus (ANT) one week prior to lateral fluid percussion injury (FPI). Immediately after TBI, animals received active or sham stimulation for 6 h. Four days later, they were assessed in a novel object/novel location recognition test (NOR/NLR) and a Barnes maze paradigm. After the experiments, hippocampal cells were counted. Separate groups of animals were sacrificed at different timepoints after TBI to measure cytokines and brain derived neurotrophic factor (BDNF). In a second set of experiments, TBI-exposed animals receiving active or sham stimulation were injected with the tropomyosin receptor kinase B (TrkB) antagonist ANA-12, followed by behavioural testing.

RESULTS

Rats exposed to TBI given DBS had an improvement in several variables of the Barnes maze, but no significant improvements in NOR/NLR compared to Sham DBS TBI animals or non-implanted controls. Animals receiving stimulation had a significant increase in BDNF levels, as well as in hippocampal cell counts in the hilus, CA3 and CA1 regions. DBS failed to normalize the increased levels of TNFα and the proinflammatory cytokine IL1β in the perilesional cortex and the hippocampus of the TBI-exposed animals. Pharmacological experiments revealed that ANA-12 administered alongside DBS did not counter the memory improvement observed in ANT stimulated animals.

CONCLUSIONS

DBS delivered immediately after TBI mitigated memory deficits, increased the expression of BDNF and the number of hippocampal cells in rats. Mechanisms for these effects were not related to an anti-inflammatory effect or mediated via TrkB receptors.

Levetiracetam Prevents Neurophysiological Changes and Preserves Cognitive Function in the Human Immunodeficiency Virus (HIV)-1 Transactivator of Transcription Transgenic Mouse Model of HIV-Associated Neurocognitive Disorder

Human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND) affects nearly half of the 39 million people living with HIV. HAND symptoms range from subclinical cognitive impairment to dementia; the mechanisms that underlie HAND remain unclear and there is no treatment. The HIV protein transactivator of transcription (TAT) is thought to contribute to HAND because it persists in the central nervous system and elicits neurotoxicity in animal models. Network hyperexcitability is associated with accelerated cognitive decline in neurodegenerative disorders. Here we show that the antiepileptic drug levetiracetam (LEV) attenuated aberrant excitatory synaptic transmission, protected synaptic plasticity, reduced seizure susceptibility, and preserved cognition in inducible TAT (iTAT) transgenic male mice. iTAT mice had an increased frequency of spontaneous excitatory postsynaptic currents in hippocampal slice recordings and impaired long-term potentiation, a form of synaptic plasticity that underlies learning and memory. Two-week administration of LEV by osmotic minipump prevented both impairments. Kainic acid administered to iTAT mice induced a higher maximum behavioral seizure score, longer seizure duration, and shorter latency to first seizure, consistent with a lower seizure threshold. LEV treatment prevented these in vivo signs of hyperexcitability. Lastly, in the Barnes maze, iTAT mice required more time to reach the goal, committed more errors, and received lower cognitive scores relative to iTAT mice treated with LEV. Thus, TAT expression drives functional deficits, suggesting a causative role in HAND. As LEV not only prevented aberrant synaptic activity in iTAT mice but also prevented cognitive dysfunction, it may provide a promising pharmacological approach to the treatment of HAND. SIGNIFICANCE STATEMENT: Approximately half of people living with human immunodeficiency virus (HIV) also suffer from HIV-associated neurocognitive disorder (HAND), for which there is no treatment. The HIV protein transactivator of transcription (TAT) causes toxicity that is thought to contribute to HAND. Here, the antiepileptic drug levetiracetam (LEV) prevented synaptic and cognitive impairments in a TAT-expressing mouse. LEV is widely used to treat seizures and is well-tolerated in humans, including those with HIV. This study supports further investigation of LEV-mediated neuroprotection in HAND.

Cellular and circuit features distinguish dentate gyrus semilunar granule cells and granule cells activated during contextual memory formation

The dentate gyrus is critical for spatial memory formation and shows task related activation of cellular ensembles considered as memory engrams. Semilunar granule cells (SGCs), a sparse dentate projection neuron subtype distinct from granule cells (GCs), were recently reported to be enriched among behaviorally activated neurons. However, the mechanisms governing SGC recruitment during memory formation and their role in engram refinement remains unresolved. By examining neurons labeled during contextual memory formation in TRAP2 mice, we empirically tested competing hypotheses for GC and SGC recruitment into memory ensembles. In support of the proposal that more excitable neurons are preferentially recruited into memory ensembles, SGCs showed greater sustained firing than GCs. Additionally, SGCs labeled during memory formation showed less adapting firing than unlabeled SGCs. Our recordings did not reveal glutamatergic connections between behaviorally labeled SGCs and GCs, providing evidence against SGCs driving local circuit feedforward excitation in ensemble recruitment. Contrary to a leading hypothesis, there was little evidence for individual SGCs or labeled neuronal ensembles supporting lateral inhibition of unlabeled neurons. Instead, pairs of GCs and SGCs within labeled neuronal cohorts received more temporally correlated spontaneous excitatory synaptic inputs than labeled-unlabeled neuronal pairs, validating a role for correlated afferent inputs in neuronal ensemble selection. These findings challenge the proposal that SGCs drive dentate GC ensemble refinement, while supporting a role for intrinsic active properties and correlated inputs in preferential SGC recruitment to contextual memory engrams.

Impact Statement

Evaluation of semilunar granule cell involvement in dentate gyrus contextual memory processing supports recruitment based on intrinsic and input characteristics while revealing limited contribution to ensemble refinement.

Unbiased analysis of spatial learning strategies in a modified Barnes maze using convolutional neural networks

Assessment of spatial learning abilities is central to behavioral neuroscience and a useful tool for animal model validation and drug development. However, biases introduced by the apparatus, environment, or experimentalist represent a critical challenge to the test validity. We have recently developed the Modified Barnes Maze (MBM) task, a spatial learning paradigm that overcomes inherent behavioral biases of animals in the classical Barnes maze. The specific combination of spatial strategies employed by mice is often considered representative of the level of cognitive resources used. Herein, we have developed a convolutional neural network-based classifier of exploration strategies in the MBM that can effectively provide researchers with enhanced insights into cognitive traits in mice. Following validation, we compared the learning performance of female and male C57BL/6J mice, as well as that of Ts65Dn mice, a model of Down syndrome, and 5xFAD mice, a model of Alzheimer's disease. Male mice exhibited more effective navigation abilities than female mice, reflected in higher utilization of effective spatial search strategies. Compared to wildtype controls, Ts65Dn mice exhibited delayed usage of spatial strategies despite similar success rates in completing this spatial task. 5xFAD mice showed increased usage of non-spatial strategies such as Circling that corresponded to higher latency to reach the target and lower success rate. These data exemplify the need for deeper strategy classification tools in dissecting complex cognitive traits. In sum, we provide a machine-learning-based strategy classifier that extends our understanding of mice's spatial learning capabilities while enabling a more accurate cognitive assessment.

Mapping SCA1 regional vulnerabilities reveals neural and skeletal muscle contributions to disease

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by an expanded polyglutamine tract in the widely expressed ataxin-1 (ATXN1) protein. To elucidate anatomical regions and cell types that underlie mutant ATXN1-induced disease phenotypes, we developed a floxed conditional knockin mouse (f-ATXN1146Q/2Q) with mouse Atxn1 coding exons replaced by human ATXN1 exons encoding 146 glutamines. f-ATXN1146Q/2Q mice manifested SCA1-like phenotypes including motor and cognitive deficits, wasting, and decreased survival. Central nervous system (CNS) contributions to disease were revealed using f-ATXN1146Q/2Q;Nestin-Cre mice, which showed improved rotarod, open field, and Barnes maze performance by 6-12 weeks of age. In contrast, striatal contributions to motor deficits using f-ATXN1146Q/2Q;Rgs9-Cre mice revealed that mice lacking ATXN1146Q/2Q in striatal medium-spiny neurons showed a trending improvement in rotarod performance at 30 weeks of age. Surprisingly, a prominent role for muscle contributions to disease was revealed in f-ATXN1146Q/2Q;ACTA1-Cre mice based on their recovery from kyphosis and absence of muscle pathology. Collectively, data from the targeted conditional deletion of the expanded allele demonstrated CNS and peripheral contributions to disease and highlighted the need to consider muscle in addition to the brain for optimal SCA1 therapeutics.

Barnes maze test for spatial memory: A new, sensitive scoring system for mouse search strategies

The Barnes maze is a task used to assess spatial learning and memory in rodents. It requires animals to learn the position of a hole that can be used as an escape from a bright and open arena. The often-used parameters of latency and path length to measure learning and memory do not reflect the different navigation strategies chosen by the animals. Here, we propose an 11-point scoring scheme to classify the search strategies developed by the animals during the initial training as well as after the change of the escape target to a new position. Strategy scores add an important dimension to time and path length to assess the behavior in this popular maze.

The behavioral, pathological and therapeutic features of the triple transgenic Alzheimer's disease (3 × Tg-AD) mouse model strain

As a classic animal model of Alzheimer's disease (AD), the 3 × Tg-AD mouse not only recapitulates most of anatomical hallmarks observed in AD pathology but also displays cognitive alterations in memory and learning tasks. The 3 × Tg-AD can better show the two characteristics of AD, amyloid β (Aβ) and neurofibrillary tangles (NFT). Therefore, 3 × Tg-AD strain is widely used in AD pathogenesis research and new drug development of AD. In this paper, the construction methods, pathological changes, and treatment characteristics of 3 × Tg-AD mouse models commonly used in AD research are summarized and commented, hoping to provide reference for researchers to choose and establish experimental patterns.

High salt induces cognitive impairment via the interaction of the angiotensin II-AT1 and prostaglandin E2-EP1 systems

BACKGROUND AND PURPOSE

High salt (HS) intake has been associated with hypertension and cognitive impairment. It is well known that the angiotensin II (Ang II)-AT1 receptor and prostaglandin E2 (PGE2)-EP1 receptor systems are involved in hypertension and neurotoxicity. However, the involvement of these systems in HS-mediated hypertension and emotional and cognitive impairments remains unclear.

EXPERIMENTAL APPROACH

Mice were loaded with HS solution (2% NaCl drinking water) for 12 weeks, and blood pressure was monitored. Subsequently, effects of HS intake on emotional and cognitive function and tau phosphorylation in the prefrontal cortex (PFC) and hippocampus (HIP) were investigated. The involvement of Ang II-AT1 and PGE2-EP1 systems in HS-induced hypertension and neuronal and behavioural impairments was examined by treatment with losartan, an AT1 receptor blocker (ARB), or EP1 gene knockout.

KEY RESULTS

We demonstrate that hypertension and impaired social behaviour and object recognition memory following HS intake may be associated with tau hyperphosphorylation, decreased phosphorylation of Ca2+ /calmodulin-dependent protein kinase II (CaMKII), and postsynaptic density protein 95 (PSD95) expression in the PFC and HIP of mice. These changes were blocked by pharmacological treatment with losartan or EP1 receptor gene knockout.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that the interaction of Ang II-AT1 receptor and PGE2-EP1 receptor systems could be novel therapeutic targets for hypertension-induced cognitive impairment.

Delineating regional vulnerability in the neurodegenerative disease SCA1 using a conditional mutant ATXN1 mouse

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by an expanded polyglutamine tract in the widely expressed ATXN1 protein. To elucidate anatomical regions and cell types that underlie mutant ATXN1-induced disease phenotypes, we developed a floxed conditional knockout mouse model ( f-ATXN1 146Q/2Q ) having mouse Atxn1 coding exons replaced by human exons encoding 146 glutamines. F-ATXN1 146Q/2Q mice manifest SCA1-like phenotypes including motor and cognitive deficits, wasting, and decreased survival. CNS contributions to disease were revealed using ATXN1 146Q/2Q ; Nestin-Cre mice, that showed improved rotarod, open field and Barnes maze performances. Striatal contributions to motor deficits were examined using f-ATXN1 146Q/2Q ; Rgs9-Cre mice. Mice lacking striatal ATXN1 146Q/2Q had improved rotarod performance late in disease. Muscle contributions to disease were revealed in f-ATXN1 146Q/2Q ; ACTA1-Cre mice which lacked muscle pathology and kyphosis seen in f-ATXN1 146Q/2Q mice. Kyphosis was not improved in f-ATXN1 146Q/2Q ;Nestin - Cre mice. Thus, optimal SCA1 therapeutics will require targeting mutant ATXN1 toxic actions in multiple brain regions and muscle.

Locus coeruleus ablation in mice: protocol optimization, stereology and behavioral impact

The Locus Coeruleus (LC) is in the brainstem and supplies key brain structures with noradrenaline, including the forebrain and hippocampus. The LC impacts specific behaviors such as anxiety, fear, and motivation, as well as physiological phenomena that impact brain functions in general, including sleep, blood flow regulation, and capillary permeability. Nevertheless, the short- and long-term consequences of LC dysfunction remain unclear. The LC is among the brain structures first affected in patients suffering from neurodegenerative diseases such as Parkinson's disease and Alzheimer's Disease, hinting that LC dysfunction may play a central role in disease development and progression. Animal models with modified or disrupted LC function are essential to further our understanding of LC function in the normal brain, the consequences of LC dysfunction, and its putative roles in disease development. For this, well-characterized animal models of LC dysfunction are needed. Here, we establish the optimal dose of selective neurotoxin N-(2-chloroethyl)-N-ethyl-bromo-benzylamine (DSP-4) for LC ablation. Using histology and stereology, we compare LC volume and neuron number in LC ablated (LCA) mice and controls to assess the efficacy of LC ablation with different numbers of DSP-4 injections. All LCA groups show a consistent decrease in LC cell count and LC volume. We then proceed to characterize the behavior of LCA mice using a light-dark box test, Barnes maze test, and non-invasive sleep-wakefulness monitoring. Behaviorally, LCA mice differ subtly from control mice, with LCA mice generally being more curious and less anxious compared to controls consistent with known LC function and projections. We note an interesting contrast in that control mice have varying LC size and neuron count but consistent behavior whereas LCA mice (as expected) have consistently sized LC but erratic behavior. Our study provides a thorough characterization of an LC ablation model, firmly consolidating it as a valid model system for the study of LC dysfunction.

BDNF is altered in a brain-region specific manner and rescues deficits in Spinocerebellar Ataxia Type 1

Spinocerebellar ataxia type 1 (SCA1) is an adult-onset, dominantly inherited neurodegenerative disease caused by the expanded polyQ tract in the protein ATAXIN1 (ATXN1) and characterized by progressive motor and cognitive impairments. There are no disease-modifying treatments or cures for SCA1. Brain-derived neurotrophic factor (BDNF) plays important role in cerebellar physiology and has shown therapeutic potential for cerebellar pathology in the transgenic mouse model of SCA1, ATXN1[82Q] line that overexpress mutant ATXN1 under a cerebellar Purkinje-cell-specific promoter. Here we demonstrate decreased expression of brain derived neurotrophic factor (BDNF) in the cerebellum and medulla of patients with SCA1. Early stages of disease seem most amenable to therapy. Thus, we next quantified Bdnf expression in Atxn1154Q/2Q mice, a knock-in mouse model of SCA1, during the early symptomatic disease stage in four clinically relevant brain regions: cerebellum, medulla, hippocampus and motor cortex. We found that during the early stages of disease, Bdnf mRNA expression is reduced in the hippocampus and cerebellum, while it is increased in the cortex and brainstem. Importantly, we observed that pharmacological delivery of recombinant BDNF improved motor and cognitive performance, and mitigated pathology in the cerebellum and hippocampus of Atxn1154Q/2Q mice. Our findings demonstrate brain-region specific deficiency of BDNF in SCA1 and show that reversal of low BDNF levels offers the potential for meaningful treatment of motor and cognitive deficits in SCA1.

Decreasing mutant ATXN1 nuclear localization improves a spectrum of SCA1-like phenotypes and brain region transcriptomic profiles

Spinocerebellar ataxia type 1 (SCA1) is a dominant trinucleotide repeat neurodegenerative disease characterized by motor dysfunction, cognitive impairment, and premature death. Degeneration of cerebellar Purkinje cells is a frequent and prominent pathological feature of SCA1. We previously showed that transport of ATXN1 to Purkinje cell nuclei is required for pathology, where mutant ATXN1 alters transcription. To examine the role of ATXN1 nuclear localization broadly in SCA1-like disease pathogenesis, CRISPR-Cas9 was used to develop a mouse with an amino acid alteration (K772T) in the nuclear localization sequence of the expanded ATXN1 protein. Characterization of these mice indicates that proper nuclear localization of mutant ATXN1 contributes to many disease-like phenotypes including motor dysfunction, cognitive deficits, and premature lethality. RNA sequencing analysis of genes with expression corrected to WT levels in Atxn1175QK772T/2Q mice indicates that transcriptomic aspects of SCA1 pathogenesis differ between the cerebellum, brainstem, cerebral cortex, hippocampus, and striatum.

Assessing Depression and Cognitive Impairment Following Stroke and Neurotrauma: Behavioral Methods for Quantifying Impairment and Functional Recovery

Rodent models of stroke and neural injury are reliable and useful tools for testing new interventions and therapeutics. In addition to physical (motor) impairment, cognitive deficits and depressive behaviors are often observed due to neurotrauma. Proper experimental design of pre- and post-assessments of these behaviors that reduce or minimize the confounding effects of motor impairment are essential for determining markers of progression of impairment or recovery. This chapter provides step-by-step laboratory protocols for assessing cognition using the Barnes maze and the novel object recognition test (NORT) and depressive-like behaviors using the sucrose preference test, the three-chambered sociability approach test, and the burrowing test.

Impaired hippocampal neurogenesis and cognitive performance in adult DBC1-knock out mice

The protein DBC1 is the main SIRT1 regulator known so far, and by doing so, it is involved in the regulation of energy metabolism, especially in liver and fat adipose tissue. DBC1 also has an important function in cell cycle progression and regulation in cancer cells, affecting tumorigenesis. We recently showed that during quiescence, non-transformed cells need DBC1 in order to re-enter and progress through the cell cycle. Moreover, we showed that deletion of DBC1 affects cell cycle progression during liver regeneration. This novel concept prompted us to evaluate the role of DBC1 during adult neurogenesis, where transition from quiescence to proliferation in neuronal progenitors is key and tightly regulated. Herein, we analyzed several markers of cell cycle expressed in the dentate gyrus of the hippocampus of controls and DBC1 KO adult mice. Our results suggest a reduced number of neuroblasts therein present, probably due to a decline of neuroblast generation or an impairment in neural differentiation. In agreement with this, we also found that adult DBC1 KO mice had a reduction in the volume of the granule cell layer of the dentate gyrus. Interestingly, behavioral analysis of KO and control mice revealed that deletion of DBC1 parallels to specific cognitive impairments, concerning learning and possibly memory formation. Our results show, for the first time, that DBC1 plays an active role in the nervous system. In particular, specific anatomical and behavioral changes are observed when is absent.

Development of an age-dependent cognitive index: relationship between impaired learning and disturbances in circadian timekeeping

Preclinical quantitative models of cognitive performance are necessary for translation from basic research to clinical studies. In rodents, non-cognitive factors are a potential influence on testing outcome and high variability in behavior requires multiple time point testing for better assessment of performance in more sophisticated tests. Thus, these models have limited translational value as most human cognitive tests characterize cognition using single digit scales to distinguish between impaired and unimpaired function. To address these limitations, we developed a cognitive index for learning based on previously described scores for strategies used by mice to escape the Barnes maze. We compared the cognitive index and circadian patterns of light-dark entrainment in young (4-6 months), middle-aged (13-14 months), and aged (18-24 months) mice as cognitive changes during aging are often accompanied by pronounced changes in sleep-wake cycle. Following continuous analysis of circadian wheel-running activity (30-40 days), the same cohorts of mice were tested in the Barnes maze. Aged mice showed significant deficits in the learning and memory portions of the Barnes maze relative to young and middle-aged animals, and the cognitive index was positively correlated to the memory portion of the task (probe) in all groups. Significant age-related alterations in circadian entrainment of the activity rhythm were observed in the middle-aged and aged cohorts. In middle-aged mice, the delayed phase angle of entrainment and increased variability in the daily onsets of activity preceded learning and memory deficits observed in aged animals. Interestingly, learning-impaired mice were distinguished by a positive relationship between the extent of Barnes-related cognitive impairment and variability in daily onsets of circadian activity. While it is unclear whether changes in the sleep-wake cycle or other circadian rhythms play a role in cognitive impairment during aging, our results suggest that circadian rhythm perturbations or misalignment may nevertheless provide an early predictor of age-related cognitive decline.

Comparison of young male mice of two different strains (C57BL/6J and the hybrid B6129SF1/J) in selected behavior tests: a small scale study

Background

All mouse strains are different, before choosing a strain for a large study, a small scale study should be done. In this study, we compared young males of two mouse strains, C57BL/6J and the hybrid B6129SF1/J, and gained knowledge on their performance in three different behavioral tests; open field (OF) test, Barnes maze (BM) test and a restraint stress test.

Results

We found that the young males of the C57BL/6J strain spent more time moving in the OF. In the BM, the hybrid covered less ground before reaching the goal box during the first three sessions, than the C57BL/6J. The hybrid left more fecal pellets than C57BL/6J both in OF and BM. During the stress test, the C57BL/6J had a lower corticosterone response than the hybrid.

Conclusions

Our findings indicate that the C57BL/6J has a presumably higher locomotor activity and/or explorative behavior than the hybrid, while the hybrid appeared more sensitive to stress.

PDZD8 Disruption Causes Cognitive Impairment in Humans, Mice, and Fruit Flies

BACKGROUND

The discovery of coding variants in genes that confer risk of intellectual disability (ID) is an important step toward understanding the pathophysiology of this common developmental disability.

METHODS

Homozygosity mapping, whole-exome sequencing, and cosegregation analyses were used to identify gene variants responsible for syndromic ID with autistic features in two independent consanguineous families from the Arabian Peninsula. For in vivo functional studies of the implicated gene's function in cognition, Drosophila melanogaster and mice with targeted interference of the orthologous gene were used. Behavioral, electrophysiological, and structural magnetic resonance imaging analyses were conducted for phenotypic testing.

RESULTS

Homozygous premature termination codons in PDZD8, encoding an endoplasmic reticulum-anchored lipid transfer protein, showed cosegregation with syndromic ID in both families. Drosophila melanogaster with knockdown of the PDZD8 ortholog exhibited impaired long-term courtship-based memory. Mice homozygous for a premature termination codon in Pdzd8 exhibited brain structural, hippocampal spatial memory, and synaptic plasticity deficits.

CONCLUSIONS

These data demonstrate the involvement of homozygous loss-of-function mutations in PDZD8 in a neurodevelopmental cognitive disorder. Model organisms with manipulation of the orthologous gene replicate aspects of the human phenotype and suggest plausible pathophysiological mechanisms centered on disrupted brain development and synaptic function. These findings are thus consistent with accruing evidence that synaptic defects are a common denominator of ID and other neurodevelopmental conditions.

Compromised Cortical-Hippocampal Network Function From Transient Hypertension: Linking Mid-Life Hypertension to Late Life Dementia Risk

Mid-life hypertension is a major risk factor for developing dementia later in life. While anti-hypertensive drugs restore normotension, dementia risk remains above baseline suggesting that brain damage sustained during transient hypertension is irreversible. The current study characterized a rat model of transient hypertension with an extended period of normotensive recovery: F344 rats were treated with L-NG-Nitroarginine methyl ester (L-NAME) for 1 month to induce hypertension then allowed up to 4 months of recovery. With respect to cognitive deficits, comparison between 1 month and 4 months of recovery identified initial deficits in spatial memory that resolved by 4 months post-hypertension; contrastingly, loss of cognitive flexibility did not. The specific cells and brain regions underlying these cognitive deficits were investigated. Irreversible structural damage to the brain was observed in both the prefrontal cortex and the hippocampus, with decreased blood vessel density, myelin and neuronal loss. We then measured theta-gamma phase amplitude coupling as a readout for network function, a potential link between the observed cognitive and pathological deficits. Four months after hypertension, we detected decreased theta-gamma phase amplitude coupling within each brain region and a concurrent increase in baseline connectivity between the two regions reflecting an attempt to maintain function that may account for the improvement in spatial memory. Our results demonstrate that connectivity between prefrontal cortex and hippocampus is a vulnerable network affected by transient hypertension which is not rescued over time; thus demonstrating for the first time a mechanistic link between the long-term effects of transient hypertension and dementia risk.

Parvalbumin neuroplasticity compensates for somatostatin impairment, maintaining cognitive function in Alzheimer's disease

BACKGROUND

Patient-to-patient variability in the degree to which β-amyloid, tau and neurodegeneration impact cognitive decline in Alzheimer's disease (AD) complicates disease modeling and treatment. However, the underlying mechanisms leading to cognitive resilience are not resolved. We hypothesize that the variability in cognitive function and loss relates to neuronal resilience of the hippocampal GABAergic network.

METHODS

We compared TgF344-AD and non-transgenic littermate rats at 9, 12, and 15 months of age. Neurons, β-amyloid plaques and tau inclusions were quantified in hippocampus and entorhinal cortex. Somatostatin (SST) and parvalbumin (PVB) interneurons were traced to examine hippocampal neuroplasticity and cognition was tested in the Barnes maze.

RESULTS

The 9-month-old TgF344-AD rats exhibited loss of neurons in the entorhinal cortex and hippocampus. Hippocampal neuronal compensation was observed in 12-month TgF344-AD rats, with upregulation of GABAergic interneuronal marker. By 15 months, the TgF344-AD rats had robust loss of excitatory and inhibitory neurons. β-Amyloid and tau pathology accumulated continuously across age. SST interneurons exhibited tau inclusions and atrophy from 9 months, whereas PVB interneurons were resilient until 15 months. The hippocampal PVB circuit underwent neuroplastic reorganization with increased dendritic length and complexity in 9- and 12-month-old TgF344-AD rats, before atrophy at 15 months. Strikingly, 12-month-old TgF344-AD rats were resilient in executive function and cognitive flexibility. Cognitive resilience in TgF344-AD rats occurred as maintenance of function between 9 and 12 months of age despite progressive spatial memory deficits, and was sustained by PVB neuroplasticity.

CONCLUSIONS

Our results demonstrate the inherent neuronal processes leading to cognitive maintenance, and describe a novel finding of endogenous cognitive resilience in an AD model.

Voluntary Wheel Running in Old C57BL/6 Mice Reduces Age-Related Inflammation in the Colon but Not in the Brain

Inflammation is considered a possible cause of cognitive decline during aging. This study investigates the influence of physical activity and social isolation in old mice on their cognitive functions and inflammation. The Barnes maze task was performed to assess spatial learning and memory in 3, 9, 15, 24, and 28 months old male C57BL/6 mice as well as following voluntary wheel running (VWR) and social isolation (SI) in 20 months old mice. Inflammatory gene expression was analyzed in hippocampal and colonic samples by qPCR. Cognitive decline occurs in mice between 15 and 24 months of age. VWR improved cognitive functions while SI had negative effects. Expression of inflammatory markers changed during aging in the hippocampus (Il1a/Il6/S100b/Iba1/Adgre1/Cd68/Itgam) and colon (Tnf/Il6/Il1ra/P2rx7). VWR attenuates inflammaging specifically in the colon (Ifng/Il10/Ccl2/S100b/Iba1), while SI regulates intestinal Il1b and Gfap. Inflammatory markers in the hippocampus were not altered following VWR and SI. The main finding of our study is that both the hippocampus and colon exhibit an increase in inflammatory markers during aging, and that voluntary wheel running in old age exclusively attenuates intestinal inflammation. Based on the existence of the gut-brain axis, our results extend therapeutic approaches preserving cognitive functions in the elderly to the colon.

Inflammatory monocytes and microglia play independent roles in inflammatory ictogenesis

BACKGROUND

The pathogenic contribution of neuroinflammation to ictogenesis and epilepsy may provide a therapeutic target for reduction of seizure burden in patients that are currently underserved by traditional anti-seizure medications. The Theiler's murine encephalomyelitis virus (TMEV) model has provided important insights into the role of inflammation in ictogenesis, but questions remain regarding the relative contribution of microglia and inflammatory monocytes in this model.

METHODS

Female C57BL/6 mice were inoculated by intracranial injection of 2 × 105, 5 × 104, 1.25 × 104, or 3.125 × 103 plaque-forming units (PFU) of the Daniel's strain of TMEV at 4-6 weeks of age. Infiltration of inflammatory monocytes, microglial activation, and cytokine production were measured at 24 h post-infection (hpi). Viral load, hippocampal injury, cognitive performance, and seizure burden were assessed at several timepoints.

RESULTS

The intensity of inflammatory infiltration and the extent of hippocampal injury induced during TMEV encephalitis scaled with the amount of infectious virus in the initial inoculum. Cognitive performance was preserved in mice inoculated with 1.25 × 104 PFU TMEV relative to 2 × 105 PFU TMEV, but peak viral load at 72 hpi was equivalent between the inocula. CCL2 production in the brain was attenuated by 90% and TNFα and IL6 production was absent in mice inoculated with 1.25 × 104 PFU TMEV. Acute infiltration of inflammatory monocytes was attenuated by more than 80% in mice inoculated with 1.25 × 104 PFU TMEV relative to 2 × 105 PFU TMEV but microglial activation was equivalent between groups. Seizure burden was attenuated and the threshold to kainic acid-induced seizures was higher in mice inoculated with 1.25 × 104 PFU TMEV but low-level behavioral seizures persisted and the EEG exhibited reduced but detectable abnormalities.

CONCLUSIONS

The size of the inflammatory monocyte response induced by TMEV scales with the amount of infectious virus in the initial inoculum, despite the development of equivalent peak infectious viral load. In contrast, the microglial response does not scale with the inoculum, as microglial hyper-ramification and increased Iba-1 expression were evident in mice inoculated with either 1.25 × 104 or 2 × 105 PFU TMEV. Inoculation conditions that drive inflammatory monocyte infiltration resulted in robust behavioral seizures and EEG abnormalities, but the low inoculum condition, associated with only microglial activation, drove a more subtle seizure and EEG phenotype.

Morris water maze: a versatile and pertinent tool for assessing spatial learning and memory

Since its development about 40 years ago (1981–2021), Morris water maze has turned into a very popular tool for assessing spatial learning and memory. Its many advantages have ensured its pertinence to date. These include its effectiveness in evaluating hippocampal-dependent learning and memory, exemption from motivational differences across diverse experimental manipulations, reliability in various cross-species studies, and adaptability to many experimental conditions with various test protocols. Nonetheless, throughout its establishment, several experimental and analysis loopholes have galvanized researchers to assess ways in which it could be improved and adapted to fill this gap. Therefore, in this review, we briefly summarize these developments since the early years of its establishment through to the most recent advancements in computerized analysis, offering more comprehensive analysis paradigms. In addition, we discuss the adaptability of the Morris water maze across different test versions and analysis paradigms, providing suggestions with regard to the best paradigms for particular experimental conditions. Hence, the proper selection of the experimental protocols, analysis paradigms, and consideration of the assay’s limitations should be carefully considered. Given that appropriate measures are taken, with various adaptations made, the Morris water maze will likely remain a relevant tool to assess the mechanisms of spatial learning and memory.

Reelin changes hippocampal learning in aging and Alzheimer's disease

The hippocampal formation (HF) is a neuroanatomical region essential for learning and memory. As one of the earliest regions to display the histopathological hallmarks of Alzheimer's disease (AD), determining the specific mechanisms of the HF's vulnerability is of capital importance. Reelin, a glycoprotein crucial in cortical lamination during embryonic neurogenesis, has an uncommon expression pattern within the HF and has been implicated in both learning and AD pathogenesis. We hypothesized that Reelin deficiency would expedite behavioral impairments which accompany normal aging. Additionally, we hypothesized that Reelin deficiency in the presence of mutated human microtubule associated protein tau (MAPT) would further impair hippocampal function. To test our hypothesis, we utilized cohorts of aged mice, aged mice with Reelin conditional knockout (RcKO), and adult mice with both RcKO and MAPT in the Barnes maze and Trace fear conditioning. Consistent with prior literature, increased age in wild-type mice was sufficient to reduce spatial searching in the Barnes maze. Increased age both exacerbated spatial impairments and altered context learning in RcKO mice. Lastly, adult mice with both RcKO and the MAPT transgene displayed both the lowest age-of-onset and most severe spatial learning deficits. In conclusion, Reelin deficiency when combined with AD risk-factors produced consistent impairments in spatial memory tasks. Furthermore, our results further implicate Reelin's importance in both HF homeostasis and AD pathogenesis.

Learning Deficits Accompanied by Microglial Proliferation After the Long-Term Post-Injection of Alzheimer's Disease Brain Extract in Mouse Brains

BACKGROUND

Human tauopathy brain injections into the mouse brain induce the development of tau aggregates, which spread to functionally connected brain regions; however, the features of this neurotoxicity remain unclear. One reason may be short observational periods because previous studies mostly used mutated-tau transgenic mice and needed to complete the study before these mice developed neurofibrillary tangles.

OBJECTIVE

To examine whether long-term incubation of Alzheimer's disease (AD) brain in the mouse brain cause functional decline.

METHODS

We herein used Tg601 mice, which overexpress wild-type human tau, and non-transgenic littermates (NTg) and injected an insoluble fraction of the AD brain into the unilateral hippocampus.

RESULTS

After a long-term (17-19 months) post-injection, mice exhibited learning deficits detected by the Barnes maze test. Aggregated tau pathology in the bilateral hippocampus was more prominent in Tg601 mice than in NTg mice. No significant changes were observed in the number of Neu-N positive cells or astrocytes in the hippocampus, whereas that of Iba-I-positive microglia increased after the AD brain injection.

CONCLUSION

These results potentially implicate tau propagation in functional decline and indicate that long-term changes in non-mutated tau mice may reflect human pathological conditions.

Mir363-3p Treatment Attenuates Long-Term Cognitive Deficits Precipitated by an Ischemic Stroke in Middle-Aged Female Rats

Cognitive impairment and memory loss are commonly seen after stroke and a third of patients will develop signs of dementia a year after stroke. Despite a large number of studies on the beneficial effects of neuroprotectants, few studies have examined the effects of these compounds/interventions on long-term cognitive impairment. Our previous work showed that the microRNA mir363-3p reduced infarct volume and sensory-motor impairment in the acute stage of stroke in middle-aged females but not males. Thus, the present study determined the impact of mir363-3p treatment on stroke-induced cognitive impairment in middle-aged females. Sprague–Dawley female rats (12 months of age) were subjected to middle cerebral artery occlusion (MCAo; or sham surgery) and injected (iv) with mir363-3p mimic (MCAo + mir363-3p) or scrambled oligos (MCAo + scrambled) 4 h later. Sensory-motor performance was assessed in the acute phase (2–5 days after stroke), while all other behaviors were tested 6 months after MCAo (18 months of age). Cognitive function was assessed by the novel object recognition test (declarative memory) and the Barnes maze (spatial memory). The MCAo + scrambled group showed reduced preference for a novel object after the stroke and poor learning in the spatial memory task. In contrast, mir363-3p treated animals were similar to either their baseline performance or to the sham group. Histological analysis showed significant deterioration of specific white matter tracts due to stroke, which was attenuated in mir363-3p treated animals. The present data builds on our previous finding to show that a neuroprotectant can abrogate the long-term effects of stroke.

Cell-type specific knockout of peptidylglycine α-amidating monooxygenase reveals specific behavioral roles in excitatory forebrain neurons and cardiomyocytes

Neuropeptides and peptide hormones play a crucial role in integrating the many factors that affect physiologic and cognitive processes. The potency of many of these peptides requires an amidated amino acid at the C-terminus; a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), catalyzes this modification. Anxiety-like behavior is known to be altered in mice with a single functional Pam allele (Pam^+/- ) and in mice unable to express Pam in excitatory forebrain neurons (Pam^Emx1-cKO/cKO ) or in cardiomyocytes (Pam^Myh6-cKO/cKO ). Examination of PAM-positive and glutamic acid decarboxylase 67 (GAD)-positive cells in the amygdala of Pam^Emx1-cKO/cKO mice demonstrated the absence of PAM in pyramidal neurons and its continued presence in GAD-positive interneurons, suggestive of altered excitatory/inhibitory balance. Additional behavioral tests were used to search for functional alterations in these cell-type specific knockout mice. Pam^Emx1-cKO/cKO mice exhibited a less focused search pattern for the Barnes Maze escape hole than control or Pam^Myh6-cKO/cKO mice. While wildtype mice favor interacting with novel objects as opposed to familiar objects, both Pam^Emx1-cKO/cKO and Pam^Myh6-cKO/cKO mice exhibited significantly less interest in the novel object. Since PAM levels in the central nervous system of Pam^Myh6-cKO/cKO mice are unaltered, the behavioral effect observed in these mice may reflect their inability to produce atrial granules and the resulting reduction in serum levels of atrial natriuretic peptide. In the sociability test, male mice of all three genotypes spent more time with same-sex stranger mice; while control females showed no preference for stranger mice, female Pam^Emx1-cKO/cKO mice showed preference for same-sex stranger mice in all trials.

Social housing enhances acquisition of task set independently of environmental enrichment: A longitudinal study in the Barnes maze

Human studies suggest that healthy social relationships benefit cognition, yet little is known about the underlying neural mechanisms of this protective effect. In rodents, studies on acute isolation and environmental enrichment (EE) confirm the importance of social exposure. Despite the widely recognized importance of sociality, however, rodent models have yet to explore the independent contributions of social housing divorced of other forms of enrichment. This study dissociates the effects of social and physical enrichment on spatial learning and memory from adulthood to old age. Rats were placed in either single or group housing, provided with ample enrichment, and tested at three time points on several phases/versions of the Barnes maze (BM) (standard, retention probes, variable location, and reversal). We found that sustained social housing enhanced cognitive flexibility, as evidenced by superior acquisition of task set (standard BM), adaptability to a new task set (variable BM), and improved reversal learning (reversal BM). Long-term retention (BM retention probes) of spatial memory was unaffected by housing conditions. Recent studies from our lab, including this report, are the first to show that social housing confers cognitive benefits beyond those of physical enrichment. Importantly, our experimental design is ideal for exploring the neural underpinnings of this socially induced cognitive protection. Understanding how sociality influences cognition will be invaluable to translational models of aging, neuropsychiatric disease, and neurological injury.

Regional differences in Alzheimer's disease pathology confound behavioural rescue after amyloid-β attenuation

Failure of Alzheimer’s disease clinical trials to improve or stabilize cognition has led to the need for a better understanding of the driving forces behind cognitive decline in the presence of active disease processes. To dissect contributions of individual pathologies to cognitive function, we used the TgF344-AD rat model, which recapitulates the salient hallmarks of Alzheimer’s disease pathology observed in patient populations (amyloid, tau inclusions, frank neuronal loss, and cognitive deficits). scyllo-Inositol treatment attenuated amyloid-β peptide in disease-bearing TgF344-AD rats, which rescued pattern separation in the novel object recognition task and executive function in the reversal learning phase of the Barnes maze. Interestingly, neither activities of daily living in the burrowing task nor spatial memory in the Barnes maze were rescued by attenuating amyloid-β peptide. To understand the pathological correlates leading to behavioural rescue, we examined the neuropathology and in vivo electrophysiological signature of the hippocampus. Amyloid-β peptide attenuation reduced hippocampal tau pathology and rescued adult hippocampal neurogenesis and neuronal function, via improvements in cross-frequency coupling between theta and gamma bands. To investigate mechanisms underlying the persistence of spatial memory deficits, we next examined neuropathology in the entorhinal cortex, a region whose input to the hippocampus is required for spatial memory. Reduction of amyloid-β peptide in the entorhinal cortex had no effect on entorhinal tau pathology or entorhinal-hippocampal neuronal network dysfunction, as measured by an impairment in hippocampal response to entorhinal stimulation. Thus, rescue or not of cognitive function is dependent on regional differences of amyloid-β, tau and neuronal network dysfunction, demonstrating the importance of staging disease in patients prior to enrolment in clinical trials. These results further emphasize the need for combination therapeutic approaches across disease progression.

The closed-head impact model of engineered rotational acceleration (CHIMERA) as an application for traumatic brain injury pre-clinical research: A status report

Closed-head traumatic brain injury (TBI) is a worldwide concern with increasing prevalence and cost to society. Rotational acceleration is a primary mechanism in TBI that results from tissue strains that give rise to diffuse axonal injury. The Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) was recently introduced as a method for the study of impact acceleration effects in pre-clinical TBI research. This review provides a survey of the published literature implementing the CHIMERA device and describes pathological, imaging, neurophysiological, and behavioral findings. Findings show CHIMERA inflicts damage in white matter tracts as a key area of injury. Behaviorally, repeated studies have shown motor deficits and more chronic cognitive effects after CHIMERA injury. Good progress with model application has been accomplished by investigators attending to what is required for model validation. However, the majority of CHIMERA studies only utilize adult male mice. To further establish this model, more work with female animals and various age groups need to be performed, as well as studies to further establish and standardize methodologies for validation of the models for clinical relevance. Common data elements to standardize the reporting methodology for the CHIMERA literature are suggested.

Role of Kalirin and mouse strain in retention of spatial memory training in an Alzheimer's disease model mouse line

Nontransgenic and 3xTG transgenic mice, which express mutant transgenes encoding human amyloid precursor protein (hAPP) along with Alzheimer's disease-associated versions of hTau and a presenilin mutation, acquired the Barnes Maze escape task equivalently at 3-9 months of age. Although nontransgenics retested at 6 and 9 months acquired the escape task more quickly than naïve mice, 3xTG mice did not. Deficits in Kalirin, a multidomain protein scaffold and guanine nucleotide exchange factor that regulates dendritic spines, has been proposed as a contributor to the cognitive decline observed in Alzheimer's disease. To test whether deficits in Kalirin might amplify deficits in 3xTG mice, mice heterozygous/hemizygous for Kalirin and the 3xTG transgenes were generated. Mouse strain, age and sex affected cortical expression of key proteins. hAPP levels in 3xTG mice increased total APP levels at all ages. Kalirin expression showed strong sex-dependent expression in C57 but not B6129 mice. Decreasing Kalirin levels to half had no effect on Barnes Maze task acquisition or retraining in 3xTG hemizygous mice.

The role of the fornix in human navigational learning

Experiments on rodents have demonstrated that transecting the white matter fibre pathway linking the hippocampus with an array of cortical and subcortical structures - the fornix - impairs flexible navigational learning in the Morris Water Maze (MWM), as well as similar spatial learning tasks. While diffusion magnetic resonance imaging (dMRI) studies in humans have linked inter-individual differences in fornix microstructure to episodic memory abilities, its role in human spatial learning is currently unknown. We used high-angular resolution diffusion MRI combined with constrained spherical deconvolution-based tractography, to ask whether inter-individual differences in fornix microstructure in healthy young adults would be associated with spatial learning in a virtual reality navigation task. To efficiently capture individual learning across trials, we adopted a novel curve fitting approach to estimate a single index of learning rate. We found a statistically significant correlation between learning rate and the microstructure (mean diffusivity) of the fornix, but not that of a comparison tract linking occipital and anterior temporal cortices (the inferior longitudinal fasciculus, ILF). Further, this correlation remained significant when controlling for both hippocampal volume and participant gender. These findings extend previous animal studies by demonstrating the functional relevance of the fornix for human spatial learning in a virtual reality environment, and highlight the importance of a distributed neuroanatomical network, underpinned by key white matter pathways, such as the fornix, in complex spatial behaviour.

Chronic PD-1 Checkpoint Blockade Does Not Affect Cognition or Promote Tau Clearance in a Tauopathy Mouse Model

Programmed cell death protein 1 (PD-1) checkpoint blockade with an antibody has been shown to reduce amyloid-β plaques, associated pathologies and cognitive impairment in mouse models. More recently, this approach has shown effectiveness in a tauopathy mouse model to improve cognition and reduce tau lesions. Follow-up studies by other laboratories did not see similar benefits of this type of therapy in other amyloid-β plaque models. Here, we report a modest increase in locomotor activity but no effect on cognition or tau pathology, in a different more commonly used tauopathy model following a weekly treatment for 12 weeks with the same PD-1 antibody and isotype control as in the original Aβ- and tau-targeting studies. These findings indicate that further research is needed before clinical trials based on PD-1 checkpoint immune blockage are devised for tauopathies.

A modified Barnes maze for an accurate assessment of spatial learning in mice

BACKGROUND

The Morris water maze (MWM) and the Barnes maze (BM) are among the most widely-used paradigms for assessing spatial learning in rodents, with specific advantages and disadvantages for each apparatus. Compared with the intense water-related stress exerted during the MWM, the BM exhibits a milder light-induced stress, while suffering from biasing animals towards non-spatial strategies such as serial search, a heuristic non-spatial search strategy. To overcome this problem, we have developed a modified Barnes maze (MBM) apparatus that recapitulates natural environments more accurately without inducing undesirable exploration strategy bias.

NEW METHOD

Apparatus. A circular 122 cm-wide table with 40 randomly placed holes. One target hole is leading to an escape chamber. Task. Three target locations were examined, varying in their distance from the center. C57BL6/j male mice were given three trials per day to find the target. Following acquisition, a probe test was performed by removing the escape chamber.

RESULTS

Spatial-encoding-depended reduction in latency to reach the target was observed, along with improvement in path efficiency with test progress. Mice tested with peripheral and distal targets outperformed mice tested with a central target. A robust exploration pattern was identified in the probe test.

COMPARISON WITH EXISTING METHOD

The MBM mimics natural environment to a higher degree of accuracy than the BM, without eliciting bias towards non-spatial searching strategies.

CONCLUSIONS

Spatial learning in the MBM is a target-location sensitive process, providing flexibility in task difficulty. Along with overcoming biases towards non-spatial strategies, the MBM represents an improvement over the well-validated BM.

Cerebellar contribution to the cognitive alterations in SCA1: evidence from mouse models

Spinocerebellar ataxia type 1 (SCA1) is a fatal neurodegenerative disease caused by abnormal expansion of glutamine (Q) encoding CAG repeats in the gene Ataxin-1 (ATXN1). Although motor and balance deficits are the core symptoms of SCA1, cognitive decline is also commonly observed in patients. While mutant ATXN1 is expressed throughout the brain, pathological findings reveal severe atrophy of cerebellar cortex in SCA1 patients. The cerebellum has recently been implicated in diverse cognitive functions, yet to what extent cerebellar neurodegeneration contributes to cognitive alterations in SCA1 remains poorly understood. Much of our understanding of the mechanisms underlying pathogenesis of motor symptoms in SCA1 comes from mouse models. Reasoning that mouse models could similarly offer important insights into the mechanisms of cognitive alterations in SCA1, we tested cognition in several mouse lines using Barnes maze and fear conditioning. We confirmed cognitive deficits in Atxn1154Q/2Q knock-in mice with brain-wide expression of mutant ATXN1 and in ATXN1 null mice. We found that shorter polyQ length and haploinsufficiency of ATXN1 do not cause significant cognitive deficits. Finally, ATXN1[82Q ] transgenic mice-with cerebellum limited expression of mutant ATXN1-demonstrated milder impairment in most aspects of cognition compared to Atxn1154Q/2Q mice, supporting the concept that cognitive deficits in SCA1 arise from a combination of cerebellar and extra-cerebellar dysfunctions.

L-Lactate Promotes Adult Hippocampal Neurogenesis

Neurogenesis, the formation of new neurons in the adult brain, is important for memory formation and extinction. One of the most studied external interventions that affect the rate of adult neurogenesis is physical exercise. Physical exercise promotes adult neurogenesis via several factors including brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF). Here, we identified L-lactate, a physical exercise-induced metabolite, as a factor that promotes adult hippocampal neurogenesis. While prolonged exposure to L-lactate promoted neurogenesis, no beneficial effect was exerted on cognitive learning and memory. Systemic pharmacological blocking of monocarboxylate transporter 2 (MCT2), which transports L-lactate to the brain, prevented lactate-induced neurogenesis, while 3,5-dihydroxybenzoic acid (3,5-DHBA), an agonist for the lactate-receptor hydroxycarboxylic acid receptor 1 (HCAR1), did not affect adult neurogenesis. These data suggest that L-lactate partially mediates the effect of physical exercise on adult neurogenesis, but not cognition, in a MCT2-dependent manner.

CHIMERA repetitive mild traumatic brain injury induces chronic behavioural and neuropathological phenotypes in wild-type and APP/PS1 mice

Background

The annual incidence of traumatic brain injury (TBI) in the United States is over 2.5 million, with approximately 3–5 million people living with chronic sequelae. Compared with moderate-severe TBI, the long-term effects of mild TBI (mTBI) are less understood but important to address, particularly for contact sport athletes and military personnel who have high mTBI exposure. The purpose of this study was to determine the behavioural and neuropathological phenotypes induced by the Closed-Head Impact Model of Engineered Rotational Acceleration (CHIMERA) model of mTBI in both wild-type (WT) and APP/PS1 mice up to 8 months post-injury.

Methods

Male WT and APP/PS1 littermates were randomized to sham or repetitive mild TBI (rmTBI; 2 × 0.5 J impacts 24 h apart) groups at 5.7 months of age. Animals were assessed up to 8 months post-injury for acute neurological deficits using the loss of righting reflex (LRR) and Neurological Severity Score (NSS) tasks, and chronic behavioural changes using the passive avoidance (PA), Barnes maze (BM), elevated plus maze (EPM) and rotarod (RR) tasks. Neuropathological assessments included white matter damage; grey matter inflammation; and measures of Aβ levels, deposition, and aducanumab binding activity.

Results

The very mild CHIMERA rmTBI conditions used here produced no significant acute neurological or motor deficits in WT and APP/PS1 mice, but they profoundly inhibited extinction of fear memory specifically in APP/PS1 mice over the 8-month assessment period. Spatial learning and memory were affected by both injury and genotype. Anxiety and risk-taking behaviour were affected by injury but not genotype. CHIMERA rmTBI induced chronic white matter microgliosis, axonal injury and astrogliosis independent of genotype in the optic tract but not the corpus callosum, and it altered microgliosis in APP/PS1 amygdala and hippocampus. Finally, rmTBI did not alter long-term tau, Aβ or amyloid levels, but it increased aducanumab binding activity.

Conclusions

CHIMERA is a useful model to investigate the chronic consequences of rmTBI, including behavioural abnormalities consistent with features of post-traumatic stress disorder and inflammation of both white and grey matter. The presence of human Aβ greatly modified extinction of fear memory after rmTBI.

Electronic supplementary material

The online version of this article (10.1186/s13195-018-0461-0) contains supplementary material, which is available to authorized users.

Restoring microglial and astroglial homeostasis using DNA immunization in a Down Syndrome mouse model

Down Syndrome (DS), the most common cause of genetic intellectual disability, is characterized by over-expression of the APP and DYRK1A genes, located on the triplicated chromosome 21. This chromosomal abnormality leads to a cognitive decline mediated by Amyloid-β (Aβ) overproduction and tau hyper-phosphorylation as early as the age of 40. In this study, we used the Ts65Dn mouse model of DS to evaluate the beneficial effect of a DNA vaccination against the Aβ1-11 fragment, in ameliorating Aβ-related neuropathology and rescue of cognitive and behavioral abilities. Anti-Aβ1-11 vaccination induced antibody production and facilitated clearance of soluble oligomers and small extracellular inclusions of Aβ from the hippocampus and cortex of Ts65Dn mice. This was correlated with reduced neurodegeneration and restoration of the homeostatic phenotype of microglial and astroglial cells. Vaccinated Ts65Dn mice performed better in spatial-learning tasks, exhibited reduced motor hyperactivity typical for this strain, and restored short-term memory abilities. Our findings support the hypothesis that DS individuals may benefit from active immunotherapy against Aβ from a young age by slowing the progression of dementia.