Endogenous anxiety and stress responses in water maze and Barnes maze spatial memory tasks

Morphological and functional evidence of increased excitatory signaling in the prelimbic cortex during ethanol withdrawal

Excessive alcohol consumption in humans induces deficits in decision making and emotional processing, which indicates a dysfunction of the prefrontal cortex (PFC). The present study aimed to determine the impact of chronic intermittent ethanol (CIE) inhalation on mouse medial PFC pyramidal neurons. Data were collected 6-8 days into withdrawal from 7 weeks of CIE exposure, a time point when mice exhibit behavioral symptoms of withdrawal. We found that spine maturity in prelimbic (PL) layer 2/3 neurons was increased, while dendritic spines in PL layer 5 neurons or infralimbic (IL) neurons were not affected. Corroborating these morphological observations, CIE enhanced glutamatergic transmission in PL layer 2/3 pyramidal neurons, but not IL layer 2/3 neurons. Contrary to our predictions, these cellular alterations were associated with improved, rather than impaired, performance in reversal learning and strategy switching tasks in the Barnes maze at an earlier stage of chronic ethanol exposure (5-7 days withdrawal from 3 to 4 weeks of CIE), which could result from the anxiety-like behavior associated with ethanol withdrawal. Altogether, this study adds to a growing body of literature indicating that glutamatergic activity in the PFC is upregulated following chronic ethanol exposure, and identifies PL layer 2/3 pyramidal neurons as a sensitive target of synaptic remodeling. It also indicates that the Barnes maze is not suitable to detect deficits in cognitive flexibility in CIE-withdrawn mice.

Erythropoietin improves object placement recognition memory in a time dependent manner in both, uninjured animals and fimbria-fornix-lesioned male rats

An increasing number of reports sustain a possible role of erythropoietin (EPO) as neuroprotective agent. In two previous articles we have evaluated EPO as plasticity promoting agent, and to contribute the restoration of brain function affected by acquired damage. We have shown that EPO is able to induce an increased synaptic efficacy in vivo along with a plasticity promoting effect. In the Morris water maze EPO administration to fimbria-fornix lesioned male rats induces a significant improvement of their spatial memory, affected by the lesion. Singularly, EPO was only effective when administered shortly after training (10 min) but not after several hours (5 h), suggesting a specific EPO effect on time dependent plasticity process. In the present paper we have expanded this line of evidence using a low stress paradigm of object placement recognition in lesioned and healthy male rats. The memory trace in this model is short-lasting; animals could recognize the change in object position when tested 24 h after, but not 48 or 72 h after the acquisition session. EPO administration 10 min after acquisition significantly prolongs retention to, at least, 72 h in healthy rats. No effect was seen if EPO was administered 5 h after training, suggesting a specific EPO modulatory effect on the consolidation process. Remarkably, early EPO treatment to fimbria fornix lesioned animals reverts the memory deficit caused by the lesion. An increased expression of the plasticity related gene arc, was also confirmed in the hippocampus and the prefrontal cortex, that is likely to be involved in the behavioral improvement observed.

Sex differences and the role of acute stress in the open-field tower maze

Many studies provide evidence that differences in spatial learning exist between males and females. However, it is necessary to consider non-mnemonic factors that may influence these findings. The present experiment investigated acquisition, retention, and the effects of stress on response- and place-learning in male and female rats. Rats were trained in an open-field tower maze. Procedures were used to minimize stress in the rats, and their ability to solve place- or response-learning in the maze was determined by analyzing a response variable (i.e., first choice correct response) that was not influenced by general locomotor activity. The results revealed that male and female rats acquire place- and response-learning at the same rate even though females moved significantly faster in the maze. However, females showed better retrieval of place-, but not response-learning compared to male rats. This effect appeared to be enhanced when the rats were tested immediately following an acute restraint stress. Furthermore, both female and male rats that were exposed to acute restraint stress showed less impairment than controls when subsequently tested in a novel situation. These findings have clinical implications that a mild physiological stress response can make one more cognitively resistant to adversities later in life.

A Comparative Study Evaluating the Impact of Physical Exercise on Disease Progression in a Mouse Model of Alzheimer's Disease

Evidence suggests that physical exercise can serve as a preventive strategy against Alzheimer's disease (AD). In contrast, much less is known about the impact of exercise when it is introduced after cognitive deficits are established. Using the TgCRND8 mouse model of amyloidosis, we compared the effects of exercise as an intervention strategy aimed at altering disease progression. Voluntary running for 1 month or 2 months was introduced in 3-month-old TgCRND8 mice, which exhibit amyloid-beta (Aβ) plaque pathology and cognitive deficits at this age. Specifically, we examined Aβ plaque load, spatial memory, and neurogenesis in the dentate gyrus in the hippocampus. After 1 month of running, TgCRND8 mice spent more time in the novel arm of the Y-maze compared to the familiar arms, indicating improved memory. The levels of doublecortin (a marker of immature neurons) were increased in TgCRND8 mice running for 1 month, but with no significant difference in the number of new mature neurons or plaque burden. As the disease progressed, running prevented further deficits in the Y-maze performance and hippocampal neurogenesis and it reduced plaque load pathology in TgCRND8 mice running for 2 months, compared to non-running transgenics. Therefore, the impact of running on memory, neurogenesis, and amyloid pathology was of greater significance when sustained through later stages of the disease.

Barnes Maze Procedure for Spatial Learning and Memory in Mice

The Barnes maze is a dry-land based rodent behavioral paradigm for assessing spatial learning and memory that was originally developed by its namesake, Carol Barnes. It represents a well-established alternative to the more popular Morris Water maze and offers the advantage of being free from the potentially confounding influence of swimming behavior. Herein, the Barnes maze experimental setup and corresponding procedures for testing and analysis in mice are described in detail.

The impact of early-life stress on the expression of HPA-associated genes in the adult murine brain

Early life is an important period for the development of the nervous system and for the programming of behavioural phenotypes in adulthood. In our study, two types of early-life stress were used: prolonged separation of pups from their mothers (for 3 h/day, maternal separation (MS)) and brief separation (for 15 min/day, handling (HD)). We analysed the effects of early-life stress on behaviour and the expression of HPA-associated genes in the hypothalamus, hippocampus, and frontal cortex of male mice. Adult mice in the MS group demonstrated reduced locomotor activity and deficiencies in spatial long-term memory, while the HD showed no significant changes. Additionally, early-life MS resulted in reduced hippocampal Crhr1 mRNA, increased MR/GR mRNA in the hippocampus and hypothalamus. Both groups, HD and MS, showed increased Avp mRNA in the hypothalamus. Thus, prolonged maternal separation but not brief leads to adverse behavioural changes and influences the expression of HPA-associated genes in a brain region-specific manner.

Working Memory Impairments in Chromosome 22q11.2 Deletion Syndrome: The Roles of Anxiety and Stress Physiology

Stress and anxiety have a negative impact on working memory systems by competing for executive resources and attention. Broad memory deficits, anxiety, and elevated stress have been reported in individuals with chromosome 22q11.2 deletion syndrome (22q11.2DS). We investigated anxiety and physiological stress reactivity in relation to visuospatial working memory impairments in 20 children with 22q11.2DS and 32 typically developing (TD) children ages 7 to 16. Children with 22q11.2DS demonstrated poorer working memory, reduced post-stress respiratory sinus arrhythmia recovery, and overall increased levels of cortisol in comparison to TD children. Anxiety, but not physiological stress responsivity, mediated the relationship between 22q11.2DS diagnosis and visuospatial working memory impairment. Findings indicate that anxiety exacerbates impaired working memory in children with 22q11.2DS.

Somatic Arc protein expression in hippocampal granule cells is increased in response to environmental change but independent of task-specific learning

Activated neurons express immediate-early genes, such as Arc. Expression of Arc in the hippocampal granule cell layer, an area crucial for spatial learning and memory, is increased during acquisition of spatial learning; however, it is unclear whether this effect is related to the task-specific learning process or to nonspecific aspects of the testing procedure (e.g. exposure to the testing apparatus and exploration of the environment). Herein, we show that Arc-positive cells numbers are increased to the same extent in the granule cell layer after both acquisition of a single spatial learning event in the active place avoidance task and exploration of the testing environment, as compared to naïve (i.e. caged) mice. Repeated exposure the testing apparatus and environment did not reduce Arc expression. Furthermore, Arc expression did not correlate with performance in both adult and aged animals, suggesting that exploration of the testing environment, rather than the specific acquisition of the active place avoidance task, induces Arc expression in the dentate granule cell layer. These findings thus suggest that Arc is an experience-induced immediate-early gene.

Cognitive and behavioral evaluation of nutritional interventions in rodent models of brain aging and dementia

Evaluation of behavior and cognition in rodent models underpins mechanistic and interventional studies of brain aging and neurodegenerative diseases, especially dementia. Commonly used tests include Morris water maze, Barnes maze, object recognition, fear conditioning, radial arm water maze, and Y maze. Each of these tests reflects some aspects of human memory including episodic memory, recognition memory, semantic memory, spatial memory, and emotional memory. Although most interventional studies in rodent models of dementia have focused on pharmacological agents, there are an increasing number of studies that have evaluated nutritional interventions including caloric restriction, intermittent fasting, and manipulation of macronutrients. Dietary interventions have been shown to influence various cognitive and behavioral tests in rodents indicating that nutrition can influence brain aging and possibly neurodegeneration.

Inhibition of p75 neurotrophin receptor does not rescue cognitive impairment in adulthood after isoflurane exposure in neonatal mice

BACKGROUND

Isoflurane is widely used for anaesthesia in humans. Isoflurane exposure of rodents prior to post-natal day 7 (PND7) leads to widespread neurodegeneration in laboratory animals. Previous data from our laboratory suggest an attenuation of apoptosis with the p75 neurotrophin receptor (p75NTR) inhibitor TAT-Pep5. We hypothesized that isoflurane toxicity leads to behavioural and cognitive abnormalities and can be rescued with pre-anaesthesia administration of TAT-Pep5.

METHODS

Neonatal mouse pups were pretreated with either TAT-Pep5 (25 μl, 10 μM i.p.) or a scrambled control peptide (TAT-ctrl; 25 μl, 10 μM i.p.) prior to isoflurane exposure (1.4%; 4 h) or control ( n  = 15-26/group). Three to 5 months after exposure, behavioural testing and endpoint assays [brain volume (stereology) and immunoblotting] were performed.

RESULTS

No significant difference was observed in open field, T-maze, balance beam or wire-hanging testing. The Barnes maze revealed a significant effect of isoflurane ( P  = 0.019) in errors to find the escape tunnel during the day 5 probe trial, a finding indicative of impaired short-term spatial memory. No difference was found for brain volumes or protein expression. TAT-Pep5 treatment did not reverse the effects of isoflurane on neurocognitive behaviour.

CONCLUSION

A single isoflurane exposure to early post-natal mice caused a hippocampal-dependent memory deficit that was not prevented by pre-administration of TAT-Pep5, although TAT-Pep5, an inhibitor of p75NTR, has been shown to reduce isoflurane-induced apoptosis. These findings suggest that neuronal apoptosis is not requisite for the development of cognitive deficits in the adults attendant with neonatal anaesthetic exposure.

Spatial learning and memory in male mice with altered growth hormone action

Growth hormone (GH) has a significant influence on cognitive performance in humans and other mammals. To understand the influence of altered GH action on cognition, we assessed spatial learning and memory using a Barnes maze (BM) comparing twelve-month old, male, bovine GH (bGH) and GH receptor antagonist (GHA) transgenic mice and their corresponding wild type (WT) littermates. During the acquisition training period in the BM, bGH mice showed increased latency, traveled longer path lengths and made more errors to reach the target than WT mice, indicating significantly poorer learning. Short-term memory (STM) and long-term memory (LTM) trials showed significantly suppressed memory retention in bGH mice when compared to the WT group. Conversely, GHA mice showed significantly better learning parameters (latency, path length and errors) and increased use of an efficient search strategy than WT mice. Our study indicates a negative impact of GH excess and a beneficial effect of the inhibition of GH action on spatial learning and memory and, therefore, cognitive performance in male mice. Further research to elucidate GH's role in brain function will facilitate identifying therapeutic applications of GH or GHA for neuropathological and neurodegenerative conditions.

Hippocampal neurogenesis and pattern separation: A meta-analysis of behavioral data

The generation of new neurons in the hippocampus of adult mammals has become a widely accepted phenomenon, but the functional significance of the adult neurogenesis in the hippocampus is not fully understood. One of the main hypotheses currently investigated suggests that neurogenesis contributes to pattern separation in the dentate gyrus. Many behavioral studies were conducted aiming to test this hypothesis using rodents as animal model. In those studies, researches ablated neurogenesis in the animals and subsequently evaluate them in tests of behavioral pattern separation, that is, behaviors that are thought to rely on the computational process of pattern separation. The results of these studies are varied, with most supporting a role for neurogenesis in pattern separation, but some others not. To address this controversy we performed a systematic review and meta-analysis of studies evaluating the effect of neurogenesis ablation on behavioral pattern separation. Analysis results indicated that most of the literature in the topic is surprisingly consistent and, although there are two studies with divergent results, the bulk of the literature supports an effect of hippocampal neurogenesis on behavioral pattern separation. We discuss those findings in light of other behavioral effects of hippocampal neurogenesis ablation, limitations of behavioral data and other lines of evidence about the effect of hippocampal neurogenesis in the dentate gyrus.

Efectos de la inactivación sistémica de los receptores GR y MR sobre el daño rápido en la recuperación de la memoria espacial inducido por corticosterona

Estudios previos de nuestro laboratorio han mostrado que la inyección de corticosterona aplicada diez minutos antes de la prueba de recobre afecta la recuperación de la memoria espacial en el laberinto de Barnes. Se ha propuesto que los efectos de esta hormona están mediados por la activación de los receptores clásicos de glucocorticoides; sin embargo la rápida aparición de los efectos permite suponer un mecanismo alternativo de tipo no genómico. El objetivo del presente estudio fue determinar la participación de los receptores de glucocorticoides GR y MR sobre el efecto rápido de la corticosterona en la recuperación de la memoria espacial en el laberinto de Barnes. Treinta y siete ratas Wistar macho fueron entrenadas en la tarea y 24h después recibieron una inyección subcutánea de antagonista GR, antagonista MR o vehículo. Cincuenta minutos después de la inyección, los animales fueron inyectados con corticosterona o vehículo y diez minutos después se evaluó la recuperación de la memoria espacial. Los resultados mostraron que la corticosterona perjudica rápidamente la recuperación de la memoria espacial a largo plazo, pues los animales inyectados presentaron mayores latencias de escape, mayor número de errores, mayor número de exploraciones y mayor distancia recorrida hasta alcanzar la meta. Este efecto sólo fue revertido con la administración del antagonista MR. Este hallazgo concuerda con estudios in vitro donde se muestra que los efectos rápidos de la corticosterona sobre la trasmisión glutamatérgica en el hipocampo están mediados por los receptores MR, posiblemente localizados en la membrana celular.

Cognitive flexibility deficits in a mouse model for the absence of full-length dystrophin

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disorder, caused by mutations in the DMD gene and the resulting lack of dystrophin. The DMD gene has seven promoters, giving rise to multiple full-length and shorter isoforms. Besides the expression of dystrophin in muscles, the majority of dystrophin isoforms is expressed in brain and dystrophinopathy can lead to cognitive deficits, including intellectual impairments and deficits in executive function. In contrast to the muscle pathology, the impact of the lack of dystrophin on the brain is not very well studied. Here, we study the behavioral consequences of a lack of full-length dystrophin isoforms in mdx mice, particularly with regard to domains of executive functions and anxiety. We observed a deficit in cognitive flexibility in mdx mice in the absence of motor dysfunction or general learning impairments using two independent behavioral tests. In addition, increased anxiety was observed, but its expression depended on the context. Overall, these results suggest that the absence of full-length dystrophin in mice has specific behavioral effects that compare well to deficits observed in DMD patients.

Cortical spreading depolarization increases adult neurogenesis, and alters behavior and hippocampus-dependent memory in mice

Cortical spreading depolarizations are an epiphenomenon of human brain pathologies and associated with extensive but transient changes in ion homeostasis, metabolism, and blood flow. Previously, we have shown that cortical spreading depolarization have long-lasting consequences on the brains transcriptome and structure. In particular, we found that cortical spreading depolarization stimulate hippocampal cell proliferation resulting in a sustained increase in adult neurogenesis. Since the hippocampus is responsible for explicit memory and adult-born dentate granule neurons contribute to this function, cortical spreading depolarization might influence hippocampus-dependent cognition. To address this question, we induced cortical spreading depolarization in C57Bl/6 J mice by epidural application of 1.5 mol/L KCl and evaluated neurogenesis and behavior at two, four, or six weeks thereafter. Congruent with our previous findings in rats, we found that cortical spreading depolarization increases numbers of newborn dentate granule neurons. Moreover, exploratory behavior and object location memory were consistently enhanced. Reference memory in the water maze was virtually unaffected, whereas memory formation in the Barnes maze was impaired with a delay of two weeks and facilitated after four weeks. These data show that cortical spreading depolarization produces lasting changes in psychomotor behavior and complex, delay- and task-dependent changes in spatial memory, and suggest that cortical spreading depolarization-like events affect the emotional and cognitive outcomes of associated brain pathologies.

Intranasal Adeno-Associated Virus Mediated Gene Delivery and Expression of Human Iduronidase in the Central Nervous System: A Noninvasive and Effective Approach for Prevention of Neurologic Disease in Mucopolysaccharidosis Type I

Mucopolysaccharidosis type I (MPS I) is a progressive, multi-systemic, inherited metabolic disease caused by deficiency of α-L-iduronidase (IDUA). Current treatments for this disease are ineffective in treating central nervous system (CNS) disease due to the inability of lysosomal enzymes to traverse the blood-brain barrier. A noninvasive and effective approach was taken in the treatment of CNS disease by intranasal administration of an IDUA-encoding adeno-associated virus serotype 9 (AAV9) vector. Adult IDUA-deficient mice aged 3 months were instilled intranasally with AAV9-IDUA vector. Animals sacrificed 5 months post instillation exhibited IDUA enzyme activity levels that were up to 50-fold that of wild-type mice in the olfactory bulb, with wild-type levels of enzyme restored in all other parts of the brain. Intranasal treatment with AAV9-IDUA also resulted in the reduction of tissue glycosaminoglycan storage materials in the brain. There was strong IDUA immunofluorescence staining of tissue sections observed in the nasal epithelium and olfactory bulb, but there was no evidence of the presence of transduced cells in other portions of the brain. This indicates that reduction of storage materials most likely occurred as a result of enzyme diffusion from the olfactory bulb and the nasal epithelium into deeper areas of the brain. At 8 months of age, neurocognitive testing using the Barnes maze to assess spatial navigation demonstrated that treated IDUA-deficient mice were no different from normal control animals, while untreated IDUA-deficient mice exhibited significant learning and navigation deficits. This novel, noninvasive strategy for intranasal AAV9-IDUA instillation could potentially be used to treat CNS manifestations of human MPS I.

Acute ethanol exposure during late mouse neurodevelopment results in long-term deficits in memory retrieval, but not in social responsiveness

OBJECTIVE

Prenatal alcohol exposure can result in neurological changes in affected individuals and may result in the emergence of a broad spectrum of neurobehavioral abnormalities termed fetal alcohol spectrum disorders (FASD). The effects of ethanol exposure during development are both time and dose dependent. Although many animal models of FASD use more chronic ethanol exposure, acute developmental alcohol exposure may also cause long-lasting neuronal changes. Our research employed behavioral measures to assess the effects of a single early postnatal ethanol intoxication event in mice.

MATERIALS AND METHODS

Mice were dosed at postnatal day 6 (a 2.5 g/kg dose of ethanol or a saline control administered twice, 2 hr apart) as a model of third trimester binge drinking in humans. This exposure was followed by behavioral assessment in male mice at 1 month (1M) and at 4 months of age (4M), using the Barnes maze (for learning/memory retrieval), exploratory behavior, and a social responsiveness task.

RESULTS

Ethanol-exposed mice appeared to be less motivated to complete the Barnes maze at 1M, but were able to successfully learn the maze. However, deficits in long-term spatial memory retrieval were observed in ethanol-exposed mice when the Barnes maze recall was measured at 4M. No significant differences were found in open field behavior or social responsiveness at 1M or 4M of age.

CONCLUSIONS

Acute ethanol exposure at P6 in mice leads to mild but long-lasting deficits in long-term spatial memory. Results suggest that even brief acute exposure to high ethanol levels during the third trimester equivalent of human pregnancy may have a permanent negative impact on the neurological functioning of the offspring.

Vibrissal paralysis produces increased corticosterone levels and impairment of spatial memory retrieval

This research was aimed at establishing how the absence of active whisking in rats affects acquisition and recovery of spatial memory. The mystacial vibrissae were irreversibly paralyzed by cutting the facial nerve's mandibular and buccal branches bilaterally in the facial nerve lesion group (N=14); control animals were submitted to sham-surgery (N=15). Sham-operated (N=11) and facial nerve-lesioned (N=10) animals were trained (one session, eight acquisition trials) and tested 24h later in a circular Barnes maze. It was found that facial nerve lesioned-animals adequately acquired the spatial task, but had impaired recovery of it when tested 24h after training as compared to control ones. Plasma corticosterone levels were measured after memory testing in four randomly chosen animals of each trained group and after a single training trial in the maze in additional facial nerve-lesioned (N=4) and sham-operated animals (N=4). Significant differences respecting the elevation of corticosterone concentration after either a single training trial or memory testing indicated that stress response was enhanced in facial nerve-lesioned animals as compared to control ones. Increased corticosterone levels during training and testing might have elicited the observed whisker paralysis-induced spatial memory retrieval impairment.

Otolith dysfunction alters exploratory movement in mice

The organization of rodent exploratory behavior appears to depend on self-movement cue processing. As of yet, however, no studies have directly examined the vestibular system's contribution to the organization of exploratory movement. The current study sequentially segmented open field behavior into progressions and stops in order to characterize differences in movement organization between control and otoconia-deficient tilted mice under conditions with and without access to visual cues. Under completely dark conditions, tilted mice exhibited similar distance traveled and stop times overall, but had significantly more circuitous progressions, larger changes in heading between progressions, and less stable clustering of home bases, relative to control mice. In light conditions, control and tilted mice were similar on all measures except for the change in heading between progressions. This pattern of results is consistent with otoconia-deficient tilted mice using visual cues to compensate for impaired self-movement cue processing. This work provides the first empirical evidence that signals from the otolithic organs mediate the organization of exploratory behavior, based on a novel assessment of spatial orientation.

Similarities in spatial cognition in sister species of the striped mouse Rhabdomys originating from different ecological contexts

Variation in spatial cognition is correlated with differences in the environments where animals originate, such that different environments might select for different cognitive ability. We investigated whether three sister species of the striped mouse genus Rhabdomys differed in their spatial cognition. The species originated from three locations across a rainfall gradient in southern Africa, which vary in habitat complexity. We tested individuals in a modified Barnes maze and asked whether the species had different spatial memory and navigation and whether these differences were related to their geographic location. We showed that the species had similar spatial memory and cue use, differing only when external cues were initially removed and during the first probe test of spatial memory. The similarities suggest that the environment of origin is not associated with spatial cognition in Rhabdomys, and that spatial cognition is phylogenetically constrained or there might be similar selection pressures across the distribution.

Novel application of a Radial Water Tread maze can distinguish cognitive deficits in mice with traumatic brain injury

INTRODUCTION

The use of forced-swim, rat-validated cognition tests in mouse models of traumatic brain injury (TBI) raises methodological concerns; such models are vulnerable to a number of confounding factors including impaired motor function and stress-induced non-compliance (failure to swim). This study evaluated the ability of a Radial Water Tread (RWT) maze, designed specifically for mice, that requires no swimming to distinguish mice with controlled cortical impact (CCI) induced TBI and Sham controls.

METHODS

Ten-week-old, male C57BL6/J mice were randomly assigned to receive either Sham (n=14) or CCI surgeries (n=15). Mice were tested for sensorimotor deficits via Gridwalk test and Noldus CatWalk gait analysis at 1 and 32days post-injury. Mice received RWT testing at either 11days (early time point) or 35days (late time point) post-injury.

RESULTS

Compared to Sham-treated animals, CCI-induced TBI resulted in significant impairment in RWT maze performance. Additionally, CCI injured mice displayed significant deficits on the Gridwalk test at both 1day and 32days post-injury, and impairment in the CatWalk task at 1day, but not 32days, compared to Shams.

CONCLUSIONS

The Radial Water Tread maze capitalizes on the natural tendency of mice to avoid open areas in favor of hugging the edges of an apparatus (thigmotaxis), and replaces a forced-swim model with water shallow enough that the animal is not required to swim, but aversive enough to motivate escape. Our findings indicate the RWT task is a sensitive species-appropriate behavioral test for evaluating spatial memory impairment in a mouse model of TBI.

Perivascular macrophages mediate the neurovascular and cognitive dysfunction associated with hypertension

Hypertension is a leading risk factor for dementia, but the mechanisms underlying its damaging effects on the brain are poorly understood. Due to a lack of energy reserves, the brain relies on continuous delivery of blood flow to its active regions in accordance with their dynamic metabolic needs. Hypertension disrupts these vital regulatory mechanisms, leading to the neuronal dysfunction and damage underlying cognitive impairment. Elucidating the cellular bases of these impairments is essential for developing new therapies. Perivascular macrophages (PVMs) represent a distinct population of resident brain macrophages that serves key homeostatic roles but also has the potential to generate large amounts of reactive oxygen species (ROS). Here, we report that PVMs are critical in driving the alterations in neurovascular regulation and attendant cognitive impairment in mouse models of hypertension. This effect was mediated by an increase in blood-brain barrier permeability that allowed angiotensin II to enter the perivascular space and activate angiotensin type 1 receptors in PVMs, leading to production of ROS through the superoxide-producing enzyme NOX2. These findings unveil a pathogenic role of PVMs in the neurovascular and cognitive dysfunction associated with hypertension and identify these cells as a putative therapeutic target for diseases associated with cerebrovascular oxidative stress.

Combined Treatment With Environmental Enrichment and (-)-Epigallocatechin-3-Gallate Ameliorates Learning Deficits and Hippocampal Alterations in a Mouse Model of Down Syndrome

Intellectual disability in Down syndrome (DS) is accompanied by altered neuro-architecture, deficient synaptic plasticity, and excitation-inhibition imbalance in critical brain regions for learning and memory. Recently, we have demonstrated beneficial effects of a combined treatment with green tea extract containing (-)-epigallocatechin-3-gallate (EGCG) and cognitive stimulation in young adult DS individuals. Although we could reproduce the cognitive-enhancing effects in mouse models, the underlying mechanisms of these beneficial effects are unknown. Here, we explored the effects of a combined therapy with environmental enrichment (EE) and EGCG in the Ts65Dn mouse model of DS at young age. Our results show that combined EE-EGCG treatment improved corticohippocampal-dependent learning and memory. Cognitive improvements were accompanied by a rescue of cornu ammonis 1 (CA1) dendritic spine density and a normalization of the proportion of excitatory and inhibitory synaptic markers in CA1 and dentate gyrus.

Active place avoidance is no more stressful than unreinforced exploration of a familiar environment

Training in the active place avoidance task changes hippocampus synaptic function, the dynamics of hippocampus local field potentials, place cell discharge, and active place avoidance memory is maintained by persistent PKMζ activity. The extent to which these changes reflect memory processes and/or stress responses is unknown. We designed a study to assess stress within the active place avoidance task by measuring serum corticosterone (CORT) at different stages of training. CORT levels did not differ between trained mice that learned to avoid the location of the mild foot shock, and untrained no-shock controls exposed to the same environment for the same amount of time. Yoked mice, that received unavoidable shocks in the same time sequence as the trained mice, had significantly higher CORT levels than mice in the trained and no-shock groups after the first trial. This increase in CORT disappeared by the fourth trial the following day, and levels of CORT for all groups matched that of home cage controls. The data demonstrate that place avoidance training is no more stressful than experiencing a familiar environment. We conclude that changes in neural function as a result of active place avoidance training are likely to reflect learning and memory processes rather than stress. © 2016 Wiley Periodicals, Inc.

Histone deacetylase inhibition abolishes stress-induced spatial memory impairment

Acute stress induced before spatial training impairs memory consolidation. Although non-epigenetic underpinning of such effect has been described, the epigenetic mechanisms involved have not yet been studied. Since spatial training and intense stress have opposite effects on histone acetylation balance, it is conceivable that disruption of such balance may underlie acute stress-induced spatial memory consolidation impairment and that inhibiting histone deacetylases prevents such effect. Trichostatin-A (TSA, a histone deacetylase inhibitor) was used to test its effectiveness in preventing stress' deleterious effect on memory. Male Wistar rats were trained in a spatial task in the Barnes maze; 1-h movement restraint was applied to half of them before training. Immediately after training, stressed and non-stressed animals were randomly assigned to receive either TSA (1mg/kg) or vehicle intraperitoneal injection. Twenty-four hours after training, long-term spatial memory was tested; plasma and brain tissue were collected immediately after the memory test to evaluate corticosterone levels and histone H3 acetylation in several brain areas. Stressed animals receiving vehicle displayed memory impairment, increased plasma corticosterone levels and markedly reduced histone H3 acetylation in prelimbic cortex and hippocampus. Such effects did not occur in stressed animals treated with TSA. The aforementioned results support the hypothesis that acute stress induced-memory impairment is related to histone deacetylation.

The impact of biological sex and sex hormones on cognition in a rat model of early, pre-motor Parkinson's disease

Parkinson's disease (PD) is well known for motor deficits such as bradykinesia. However, patients often experience additional deficits in working memory, behavioral selection, decision-making and other executive functions. Like other features of PD, the incidence and severity of these cognitive symptoms differ in males and females. However, preclinical models have not been used to systematically investigate the roles that sex or sex hormones may play in these complex signs. To address this, we used a Barnes maze spatial memory paradigm to compare the effects of a bilateral nigrostriatal dopamine lesion model of early PD on cognitive behaviors in adult male and female rats and in adult male rats that were gonadectomized or gonadectomized and supplemented with testosterone or estradiol. We found that dopamine lesions produced deficits in working memory and other executive operations, albeit only in male rats where circulating androgen levels were physiological. In males where androgen levels were depleted, lesions produced no additional Barnes maze deficits and attenuated those previously linked to androgen deprivation. We also found that while most measures of Barnes maze performance were unaffected by dopamine lesions in the females, lesions did induce dramatic shifts from their preferred use of thigmotactic navigation to the use of spatially guided place strategies similar to those normally preferred by males. These and other sex- and sex hormone-specific differences in the effects of nigrostriatal dopamine lesions on executive function highlight the potential of gonadal steroids as protective and/or therapeutic for the cognitive symptoms of PD. However, their complexity also indicates the need for a more thorough understanding of androgen and estrogen effects in guiding the development of hormone therapies that might effectively address these non-motor signs.

The water maze paradigm in experimental studies of chronic cognitive disorders: Theory, protocols, analysis, and inference

An instrumental step in assessing the validity of animal models of chronic cognitive disorders is to document disease-related deficits in learning/memory capacity. The water maze (WM) is a popular paradigm because of its low cost, relatively simple protocol and short procedure time. Despite being broadly accepted as a spatial learning task, inference of generalized, bona fide "cognitive" dysfunction can be challenging because task accomplishment is also reliant on non-cognitive processes. We review theoretical background, testing procedures, confounding factors, as well as approaches to data analysis and interpretation. We also describe an extended protocol that has proven useful in detecting early performance deficits in murine models of neuropsychiatric lupus and Alzheimer's disease. Lastly, we highlight the need for standardization of inferential criteria on "cognitive" dysfunction in experimental rodents and exclusion of preparations of a limited scientific merit. A deeper appreciation for the multifactorial nature of performance in WM may also help to reveal other deficits that herald the onset of neurodegenerative brain disorders.

The role of Neuropeptide Y in fear conditioning and extinction

While anxiety disorders are the brain disorders with the highest prevalence and constitute a major burden for society, a considerable number of affected people are still treated insufficiently. Thus, in an attempt to identify potential new anxiolytic drug targets, neuropeptides have gained considerable attention in recent years. Compared to classical neurotransmitters they often have a regionally restricted distribution and may bind to several distinct receptor subtypes. Neuropeptide Y (NPY) is a highly conserved neuropeptide that is specifically concentrated in limbic brain areas and signals via at least 5 different G-protein-coupled receptors. It is involved in a variety of physiological processes including the modulation of emotional-affective behaviors. An anxiolytic and stress-reducing property of NPY is supported by many preclinical studies. Whether NPY may also interact with processing of learned fear and fear extinction is comparatively unknown. However, this has considerable relevance since pathological, inappropriate and generalized fear expression and impaired fear extinction are hallmarks of human post-traumatic stress disorder and a major reason for its treatment-resistance. Recent evidence from different laboratories emphasizes a fear-reducing role of NPY, predominantly mediated by exogenous NPY acting on Y1 receptors. Since a reduction of fear expression was also observed in Y1 receptor knockout mice, other Y receptors may be equally important. By acting on Y2 receptors, NPY promotes fear extinction and generates a long-term suppression of fear, two important preconditions that could support cognitive behavioral therapies in human patients. A similar effect has been demonstrated for the closely related pancreatic polypeptide (PP) when acting on Y4 receptors. Preliminary evidence suggests that NPY modulates fear in particular by activation of Y1 and Y2 receptors in the basolateral and central amygdala, respectively. In the basolateral amygdala, NPY signaling activates inhibitory G protein-coupled inwardly-rectifying potassium channels or suppresses hyperpolarization-induced I(h) currents in a Y1 receptor-dependent fashion, favoring a general suppression of neuronal activity. A more complex situation has been described for the central extended amygdala, where NPY reduces the frequency of inhibitory and excitatory postsynaptic currents. In particular the inhibition of long-range central amygdala output neurons may result in a Y2 receptor-dependent suppression of fear. The role of NPY in processes of learned fear and fear extinction is, however, only beginning to emerge, and multiple questions regarding the relevance of endogenous NPY and different receptor subtypes remain elusive. Y2 receptors may be of particular interest for future studies, since they are the most prominent Y receptor subtype in the human brain and thus among the most promising therapeutic drug targets when translating preclinical evidence to potential new therapies for human anxiety disorders.

Cognitive Deficits in Calsyntenin-2-deficient Mice Associated with Reduced GABAergic Transmission

Calsyntenin-2 has an evolutionarily conserved role in cognition. In a human genome-wide screen, the CLSTN2 locus was associated with verbal episodic memory, and expression of human calsyntenin-2 rescues the associative learning defect in orthologous Caenorhabditis elegans mutants. Other calsyntenins promote synapse development, calsyntenin-1 selectively of excitatory synapses and calsyntenin-3 of excitatory and inhibitory synapses. We found that targeted deletion of calsyntenin-2 in mice results in a selective reduction in functional inhibitory synapses. Reduced inhibitory transmission was associated with a selective reduction of parvalbumin interneurons in hippocampus and cortex. Clstn2(-/-) mice showed normal behavior in elevated plus maze, forced swim test, and novel object recognition assays. However, Clstn2(-/-) mice were hyperactive in the open field and showed deficits in spatial learning and memory in the Morris water maze and Barnes maze. These results confirm a function for calsyntenin-2 in cognitive performance and indicate an underlying mechanism that involves parvalbumin interneurons and aberrant inhibitory transmission.

Age-related changes in behavior in C57BL/6J mice from young adulthood to middle age

Background

Aging is considered to be associated with progressive changes in the brain and its associated sensory, motor, and cognitive functions. A large number of studies comparing young and aged animals have reported differences in various behaviors between age-cohorts, indicating behavioral dysfunctions related to aging. However, relatively little is known about behavioral changes from young adulthood to middle age, and the effect of age on behavior during the early stages of life remains to be understood. In order to investigate age-related changes in the behaviors of mice from young adulthood to middle age, we performed a large-scale analysis of the behavioral data obtained from our behavioral test battery involving 1739 C57BL/6J wild-type mice at 2–12 months of age.

Results

Significant behavioral differences between age groups (2–3-, 4–5-, 6–7-, and 8–12-month-old groups) were found in all the behavioral tests, including the light/dark transition, open field, elevated plus maze, rotarod, social interaction, prepulse inhibition, Porsolt forced swim, tail suspension, Barnes maze, and fear conditioning tests, except for the hot plate test. Compared with the 2–3-month-old group, the 4–5- and 6–7-month-old groups exhibited decreased locomotor activity to novel environments, motor function, acoustic startle response, social behavior, and depression-related behavior, increased prepulse inhibition, and deficits in spatial and cued fear memory. For most behaviors, the 8–12-month-old group showed similar but more pronounced changes in most of these behaviors compared with the younger age groups. Older groups exhibited increased anxiety-like behavior in the light/dark transition test whereas those groups showed seemingly decreased anxiety-like behavior measured by the elevated plus maze test.

Conclusions

The large-scale analysis of behavioral data from our battery of behavioral tests indicated age-related changes in a wide range of behaviors from young adulthood to middle age in C57BL/6J mice, though these results might have been influenced by possible confounding factors such as the time of day at testing and prior test experience. Our results also indicate that relatively narrow age differences can produce significant behavioral differences during adulthood in mice. These findings provide an insight into our understanding of the neurobiological processes underlying brain function and behavior that are subject to age-related changes in early to middle life. The findings also indicate that age is one of the critical factors to be carefully considered when designing behavioral tests and interpreting behavioral differences that might be induced by experimental manipulations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13041-016-0191-9) contains supplementary material, which is available to authorized users.

Role of α4-containing GABAA receptors in limiting synaptic plasticity and spatial learning of female mice during the pubertal period

Expression of α4βδ GABA_A receptors (GABARs) increases at the onset of puberty on dendritic spines of CA1 hippocampal pyramidal cells. These receptors reduce activation of NMDA receptors (NMDARs), impair induction of long-term potentiation (LTP) and reduce hippocampal-dependent spatial learning. These effects are not seen in the δ-/- mouse, implicating α4βδ GABARs. Here we show that knock-out of α4 also restores synaptic plasticity and spatial learning in female mice at the onset of puberty (verified by vaginal opening). To this end, field excitatory post-synaptic potentials (fEPSPs) were recorded from the stratum radiatum of CA1 hippocampus in the slice from +/+ and α4-/- pubertal mice (PND 35-44). Induction of LTP, in response to stimulation of the Schaffer collaterals with theta burst stimulation (TBS), was unsuccessful in the +/+ hippocampus, but reinstated by α4 knock-out (~65% potentiation) but not by blockade of α5-GABARs with L-655,708 (50nM). In order to compare spatial learning in the two groups of mice, animals were trained in an active place avoidance task where the latency to first enter a shock zone is a measure of learning. α4-/- mice had significantly longer latencies by the third learning trial, suggesting better spatial learning, compared to +/+ animals, who did not reach the criterion for learning (120s latency). These findings suggest that knock-out of the GABAR α4 subunit restores synaptic plasticity and spatial learning at puberty and is consistent with the concept that the dendritic α4βδ GABARs which emerge at puberty selectively impair CNS plasticity. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Effects of high-fat diet exposure on learning & memory

The associations between consumption of a high-fat or 'Western' diet and metabolic disorders such as obesity, diabetes, and cardiovascular disease have long been recognized and a great deal of evidence now suggests that diets high in fat can also have a profound impact on the brain, behavior, and cognition. Here, we will review the techniques most often used to assess learning and memory in rodent models and discuss findings from studies assessing the cognitive effects of high-fat diet consumption. The review will then consider potential underlying mechanisms in the brain and conclude by reviewing emerging literature suggesting that maternal consumption of a high-fat diet may have effects on the learning and memory of offspring.

Place and Response Learning in the Open-field Tower Maze

This protocol describes how the Open-field Tower Maze (OFTM) paradigm is used to study spatial learning in rodents. This maze is especially useful for examining how rats learn to use a place- or response-learning to successfully navigate in an open-field arena. Additionally, this protocol describes how the OFTM differs from other behavioral maze paradigms that are commonly used to study spatial learning in rodents. The OFTM described in this article was adapted from the one previously described by Cole, Clipperton, and Walt (2007). Specifically, the OFTM was created to test spatial learning in rodents without the experimenter having to consider how "stress" might play a role as a confounding variable. Experiments have shown that stress-alone can significantly affect cognitive function(1). The representative results section contains data from an experiment that used the OFTM to examine the effects of estradiol treatment on place- and response-learning in adult female Sprague Dawley rats(2). Future studies will be designed to examine the role of the hippocampus and striatum in place- and response-learning in the OFTM.

Cognitive impairment and morphological changes in the dorsal hippocampus of very old female rats

The hippocampus, a medial temporal lobe structure necessary for the formation of spatial memory, is particularly affected by both normal and pathologic aging. In previous studies, we observed a significant age-related increase in dopaminergic neuron loss in the hypothalamus and the substantia nigra of female rats, which becomes more conspicuous at extreme ages. Here, we extend our studies by assessing spatial memory in 4-6 month-old (young), 26-month-old (old) and 29-32-month-old (senile) Sprague-Dawley female rats as well as the age-related histopathological changes in their dorsal hippocampus. Age changes in spatial memory performance were assessed with a modified version of the Barnes maze test. We employed two probe trials (PTs), one and five days after training, respectively, in order to evaluate learning ability as well as short-term and longer-term spatial memory retention. A set of relevant hippocampal cell markers was also quantitated in the animals by means of an unbiased stereological approach. The results revealed that old rats perform better than senile rats in acquisition trials and young rats perform better than both aging groups. However, during short-term PT both aging groups showed a preserved spatial memory while in longer-term PT, spatial memory showed deterioration in both aged groups. Morphological analysis showed a marked decrease (94-97%) in doublecortin neuron number in the dentate gyrus in both aged groups and a reduction in glial fibrillary acidic protein-positive cell number in the stratum radiatum of aging rats. Astroglial process length and branching complexity decreased in aged rats. We conclude that while target-seeking activity and learning ability decrease in aged females, spatial memory only declines in the longer-term tests. The reduction in neuroblast number and astroglial arborescence complexity in the dorsal hippocampus are likely to play a role in the cognitive deficits of aging rats.

Voluntary exercise attenuates LPS-induced reductions in neurogenesis and increases microglia expression of a proneurogenic phenotype in aged mice

Background

Microglia can acquire various phenotypes of activation that mediate their inflammatory and neuroprotective effects. Aging causes microglia to become partially activated towards an inflammatory phenotype. As a result, aged animals display a prolonged neuroinflammatory response following an immune challenge. Currently unknown is whether this persistent neuroinflammation leads to greater reductions in hippocampal neurogenesis. Exercise has been shown to alter microglia activation in aged animals, but the nature of these changes has yet to be fully elucidated. The present study assessed whether aged mice show enhanced reductions in hippocampal neurogenesis following an acute immune challenge with lipopolysaccharide (LPS). Further, we assessed whether voluntary wheel running protects against the effects of LPS.

Methods

Adult (4 months) and aged (22 months) male C57BL6/J mice were individually housed with or without a running wheel for a total of 9 weeks. After 5 weeks, mice received a single intraperitoneal LPS or saline injection in combination with four daily injections of bromodeoxyuridine (BrdU) to label dividing cells. Tissue was collected 4 weeks later and immunohistochemistry was conducted to measure new cell survival, new neuron numbers, and microglia activation.

Results

Data show that LPS reduced the number of new neurons in aged, but not adult, mice. These LPS-induced reductions in neurogenesis in the aged mice were prevented by wheel running. Further, exercise increased the proportion of microglia co-labeled with brain-derived neurotrophic factor (BDNF) in the aged.

Conclusions

Collectively, findings indicate that voluntary wheel running may promote a neuroprotective microglia phenotype and protect against inflammation-induced reductions in hippocampal neurogenesis in the aged brain.

IL-4 Knock Out Mice Display Anxiety-Like Behavior

Inflammation is a recognized antecedent and coincident factor when examining the biology of anxiety. Little is known, however, about how reductions in endogenous anti-inflammatory mediators impact anxiety. Therefore, mood- cognition- and anxiety-associated/like behaviors were examined in IL-4 knock out (KO) mice and wild-type (WT) mice. In comparison to WT mice, IL-4 KO mice demonstrated decreased burrowing and increased social exploration. No differences were seen in forced swim or saccharine preference testing. IL-4 KO mice had similar performance to WT mice in the Morris water maze and during object location and novel object recognition. In the elevated zero-maze, IL-4 KO mice, in comparison to WT mice, demonstrated anxiety-like behavior. Anxiety-like behavior in IL-4 KO mice was not observed, however, during open-field testing. Taken together, these data indicate that IL-4 KO mice display state, but not trait, anxiety suggesting that reductions in endogenous anti-inflammatory bioactives can engender subtypes of anxiety.

The sodium-activated potassium channel Slack is required for optimal cognitive flexibility in mice

Kcnt1 encoded sodium-activated potassium channels (Slack channels) are highly expressed throughout the brain where they modulate the firing patterns and general excitability of many types of neurons. Increasing evidence suggests that Slack channels may be important for higher brain functions such as cognition and normal intellectual development. In particular, recent findings have shown that human Slack mutations produce very severe intellectual disability and that Slack channels interact directly with the Fragile X mental retardation protein (FMRP), a protein that when missing or mutated results in Fragile X syndrome (FXS), the most common form of inherited intellectual disability and autism in humans. We have now analyzed a recently developed Kcnt1 null mouse model in several behavioral tasks to assess which aspects of memory and learning are dependent on Slack. We demonstrate that Slack deficiency results in mildly altered general locomotor activity, but normal working memory, reference memory, as well as cerebellar control of motor functions. In contrast, we find that Slack channels are required for cognitive flexibility, including reversal learning processes and the ability to adapt quickly to unfamiliar situations and environments. Our data reveal that hippocampal-dependent spatial learning capabilities require the proper function of Slack channels.

Effect of cardiac arrest on cognitive impairment and hippocampal plasticity in middle-aged rats

Cardiopulmonary arrest is a leading cause of death and disability in the United States that usually occurs in the aged population. Cardiac arrest (CA) induces global ischemia, disrupting global cerebral circulation that results in ischemic brain injury and leads to cognitive impairments in survivors. Ischemia-induced neuronal damage in the hippocampus following CA can result in the impairment of cognitive function including spatial memory. In the present study, we used a model of asphyxial CA (ACA) in nine month old male Fischer 344 rats to investigate cognitive and synaptic deficits following mild global cerebral ischemia. These experiments were performed with the goals of 1) establishing a model of CA in nine month old middle-aged rats; and 2) to test the hypothesis that learning and memory deficits develop following mild global cerebral ischemia in middle-aged rats. To test this hypothesis, spatial memory assays (Barnes circular platform maze and contextual fear conditioning) and field recordings (long-term potentiation and paired-pulse facilitation) were performed. We show that following ACA in nine month old middle-aged rats, there is significant impairment in spatial memory formation, paired-pulse facilitation n dysfunction, and a reduction in the number of non-compromised hippocampal Cornu Ammonis 1 and subiculum neurons. In conclusion, nine month old animals undergoing cardiac arrest have impaired survival, deficits in spatial memory formation, and synaptic dysfunction.

Vitamin C deficiency in the brain impairs cognition, increases amyloid accumulation and deposition, and oxidative stress in APP/PSEN1 and normally aging mice

Subclinical vitamin C deficiency is widespread in many populations, but its role in both Alzheimer's disease and normal aging is understudied. In the present study, we decreased brain vitamin C in the APPSWE/PSEN1deltaE9 mouse model of Alzheimer's disease by crossing APP/PSEN1(+) bigenic mice with SVCT2(+/-) heterozygous knockout mice, which have lower numbers of the sodium-dependent vitamin C transporter required for neuronal vitamin C transport. SVCT2(+/-) mice performed less well on the rotarod task at both 5 and 12 months of age compared to littermates. SVCT2(+/-) and APP/PSEN1(+) mice and the combination genotype SVCT2(+/-)APP/PSEN1(+) were also impaired on multiple tests of cognitive ability (olfactory memory task, Y-maze alternation, conditioned fear, Morris water maze). In younger mice, both low vitamin C (SVCT2(+/-)) and APP/PSEN1 mutations increased brain cortex oxidative stress (malondialdehyde, protein carbonyls, F2-isoprostanes) and decreased total glutathione compared to wild-type controls. SVCT2(+/-) mice also had increased amounts of both soluble and insoluble Aβ1-42 and a higher Aβ1-42/1-40 ratio. By 14 months of age, oxidative stress levels were similar among groups, but there were more amyloid-β plaque deposits in both hippocampus and cortex of SVCT2(+/-)APP/PSEN1(+) mice compared to APP/PSEN1(+) mice with normal brain vitamin C. These data suggest that even moderate intracellular vitamin C deficiency plays an important role in accelerating amyloid pathogenesis, particularly during early stages of disease development, and that these effects are likely modulated by oxidative stress pathways.

P301L tau expression affects glutamate release and clearance in the hippocampal trisynaptic pathway

Individuals at risk of developing Alzheimer's disease (AD) often exhibit hippocampal hyperexcitability. A growing body of evidence suggests that perturbations in the glutamatergic tripartite synapse may underlie this hyperexcitability. Here, we used a tau mouse model of AD (rTg(TauP301L)4510) to examine the effects of tau pathology on hippocampal glutamate regulation. We found a 40% increase in hippocampal vesicular glutamate transporter, which packages glutamate into vesicles, and has previously been shown to influence glutamate release, and a 40% decrease in hippocampal glutamate transporter 1, the major glutamate transporter responsible for removing glutamate from the extracellular space. To determine whether these alterations affected glutamate regulation in vivo, we measured tonic glutamate levels, potassium-evoked glutamate release, and glutamate uptake/clearance in the dentate gyrus, cornu ammonis 3(CA3), and cornu ammonis 1(CA1) regions of the hippocampus. P301L tau expression resulted in a 4- and 7-fold increase in potassium-evoked glutamate release in the dentate gyrus and CA3, respectively, and significantly decreased glutamate clearance in all three regions. Both release and clearance correlated with memory performance in the hippocampal-dependent Barnes maze task. Alterations in mice expressing P301L were observed at a time when tau pathology was subtle and before readily detectable neuron loss. These data suggest novel mechanisms by which tau may mediate hyperexcitability. Pre-synaptic vesicular glutamate transporters (vGLUTs) package glutamate into vesicles before exocytosis into the synaptic cleft. Once in the extracellular space, glutamate acts on glutamate receptors. Glutamate is removed from the extracellular space by excitatory amino acid transporters, including GLT-1, predominantly localized to glia. P301L tau expression increases vGLUT expression and glutamate release, while also decreasing GLT-1 expression and glutamate clearance.