NMDA Receptor (NMDAR) activity has been strongly implicated in both in-vitro and in-vivo learning models and the decline in cognitive function associated with aging and is linked to a decrease in NMDAR functional expression. GLYX-13 is a tetrapeptide (Thr-Pro-Pro-Thr) which acts as a NMDAR receptor partial agonist at the glycine site. GLYX-13 was administered to young adult (3 month old) and aged (27–32 month old) Fischer 344 X Brown Norway F1 rats (FBNF1), and behavioral learning tested in trace eyeblink conditioning (tEBC), a movable platform version of the Morris water maze (MWM), and alternating t-maze tasks. GLYX-13 (1 mg/kg i.v.) enhanced learning in both young adult and aging animals for MWM and alternating t-maze, and increased tEBC in aging rats. We previously showed optimal enhancement of tEBC in young adult rats given GLYX-13 at the same dose. Of these learning tasks, the MWM showed the most robust age related deficit in learning. In the MWM, GLYX-13 enhancement of learning was greater in the old compared to the young adult animals. Examination of the induction of long-term potentiation (LTP) and depression (LTD) at Schaffer collateral-CA1 synapses in hippocampal slices showed that aged rats showed marked, selective impairment in the magnitude of LTP evoked by a sub-maximal tetanus, and that GLYX-13 significantly enhanced the magnitude of LTP in slices from both young adult and aged rats without affecting LTD. These data, combined with the observation that the GLYX-13 enhancement of learning was greater in old than in young adult animals, suggest that GLYX-13 may be a promising treatment for deficits in cognitive function associated with aging.
learning; memory; aging; rat; hippocampus; eyeblink conditioning, water maze, t-maze, GLYX-13
Impairment of cognitive functions including hippocampus-dependent spatial learning and memory affects nearly half of the aged population. Age-related cognitive decline is associated with synaptic dysfunction that occurs in the absence of neuronal cell loss, suggesting that impaired neuronal signaling and plasticity may underlie age-related deficits of cognitive function. Expression of myelin-associated inhibitors (MAIs) of synaptic plasticity, including the ligands MAG, Nogo-A, and OMgp, and their common receptor, NgR1, was examined in hippocampal synaptosomes and CA1, CA3 and DG subregions derived from adult (12–13 months) and aged (26–28 months) Fischer 344 × Brown Norway rats. Rats were behaviorally phenotyped by Morris water maze testing and classified as aged cognitively intact (n=7–8) or aged cognitively impaired (n=7–10) relative to adults (n=5–7). MAI protein expression was induced in cognitively impaired, but not cognitively intact, aged rats and correlated with cognitive performance in individual rats. Immunohistochemical experiments demonstrated that upregulation of MAIs occurs, in part, in hippocampal neuronal axons and somata. While a number of pathways and processes are altered with brain aging, we report a coordinated induction of myelin-associated inhibitors of functional and structural plasticity only in cognitively impaired aged rats. Induction of MAIs may decrease stimulus-induced synaptic strengthening and structural remodeling, ultimately impairing synaptic mechanisms of spatial learning and memory and resulting in cognitive decline.
myelin-associated glycoprotein; neurite outgrowth inhibitor A; oligodendrocyte myelin glycoprotein; Nogo-66 receptor; Fischer 344 × Brown Norway rat; Morris water maze
The impact of a single seizure on cognition remains controversial. We hypothesized that a single early life seizure (sELS) on rat post-natal day (P) 7 would alter only hippocampal-dependent learning and memory in mature (P60) rats. The Morris Water Maze (MWM), Novel Object and Novel Place Recognition (NOR/NPR) tasks, and Contextual Fear Conditioning (CFC) were used to assess learning and memory associated with hippocampal/prefrontal cortex, perirhinal/hippocampal cortex, and amygdala function, respectively. The Elevated Plus Maze (EPM) and Open Field Test (OFT) were used to assess anxiety associated with the septum. We report that sELS impaired hippocampal-dependent short-term memory but not spatial learning or recall. sELS did not disrupt performance in the NOR/NPR. CFC performance suggested intact amydgala function. sELS did not change anxiety levels as measured by the EPM or OFT. Our data suggests that the long-term cognitive impacts of sELS are largely limited to the hippocampus/prefrontal cortex.
seizure; morris water maze; development; kainate; working memory; hippocampus; pre-frontal cortex; neonate
Age-related changes in the hippocampus increase vulnerability to impaired learning and memory. Our goal is to understand how a genetic vulnerability to cognitive impairment can be modified by aging and sex. Mice with a mutation in the cAMP response element binding (CREB) protein gene (CREBαδ- deficient mice) have a mild cognitive impairment and show test condition-dependent learning and memory deficits. We tested 3 ages of CREBαδ- deficient and wild-type (WT) mice in 2 Morris water maze (MWM) protocols: MWM4 and MWM2. All CREBαδ- deficient mice performed well in the easier MWM4, except for the aged females that performed poorly. In the harder MWM2, young male and female and middle-aged male CREBαδ- deficient mice performed well, but aged male and all middle-aged and aged female CREBαδ- deficient mice were impaired. These results show that mice with a genetic vulnerability to impaired learning and memory exhibit increased vulnerability with age that is most apparent among females. Thus, a genetic predisposition to cognitive impairment may render females more vulnerable than males to such deficits with age.
Aging; Sex Differences; Spatial; Learning; Memory; Morris water maze
±3,4-Methylenedioxymethamphetamine (MDMA) is a recreational drug that causes cognitive deficits in humans. A rat model for learning and memory deficits has not been established, although some cognitive deficits have been reported.
Male Sprague-Dawley rats were treated with MDMA (15 mg/kg × 4 doses) or saline (SAL) (n = 20/treatment group) and tested in different learning paradigms: 1) path integration in the Cincinnati water maze (CWM), 2) spatial learning in the Morris water maze (MWM), and 3) novel object recognition (NOR). One week after drug administration, testing began in the CWM, then four phases of MWM, and finally NOR. Following behavioral testing, monoamine levels were assessed.
±3,4-Methylenedioxymethamphetamine-treated rats committed more CWM errors than did SAL-treated rats. ±3,4-Methylenedioxymethamphetamine-treated animals were further from the former platform position during each 30-second MWM probe trial but showed no differences during learning trials with the platform present. There were no group differences in NOR. ± 3,4-Methylenedioxymethamphetamine depleted serotonin in all brain regions and dopamine in the striatum.
±3,4-Methylenedioxymethamphetamine produced MWM reference memory deficits even after complex learning in the CWM, where deficits in path integration learning occurred. Assessment of path integration may provide a sensitive index of MDMA-induced learning deficits.
MDMA; Morris water maze; Cincinnati water maze; sequential learning; spatial learning
This study determined whether developmental and adult 3,4-methylenedioxymethamphetamine (MDMA) exposures in rats have interactive effects on body temperature, learning, other behaviors, and monoamine concentrations in the hippocampus, prefrontal cortex, and striatum. Learning was assessed in the Cincinnati water maze (CWM), Morris water maze (MWM), and novel object recognition (NOR). On acquisition trials in the MWM, significant differences from developmental MDMA exposure were found on latency, cumulative distance, path length, and angle of first bearing to the goal, but the early and adult MDMA exposure group performed no worse than the developmental-only MDMA group. In the reversal trials, however, an interaction was seen: latency to the goal, cumulative distance, and angle of first bearing were increased in animals treated both developmentally and in adulthood with MDMA compared with those treated only developmentally. Other tests (elevated zero maze, CWM, NOR, and open-field activity) did not show an interaction, nor did hippocampal concentrations of serotonin or dopamine. However, several behavioral tests showed neonatal MDMA effects, including increased errors in the CWM, reduced time spent with a new object in the NOR test, and reduced locomotor activity in the open-field. By contrast, adult MDMA decreased the number of entries into open quadrants of the elevated zero maze. Litter effects were controlled by treating litter as the experimental unit and using mixed models repeated measures analyses. Correlational analyses suggested that the MWM reversal interaction involves multiple monoamine changes. The results indicate that developmental MDMA exposure can interact with adult exposure to interfere with some aspects of learning.
MDMA; development; amphetamines; serotonin; dopamine; spatial learning; preclinical
Background and the purpose of the study
It has been well established that cholinergic pathway plays an important role in learning and memory processes. The present study was designed to evaluate the effects of Morris water maze (MWM) training on spatial memory acquisition and expression of the vesicular acetylcholine transporter (VAChT) in male rats.
In this study, training trials of all groups of animals were conducted in the MWM task. Rats received one training session consisting of four trials per day which continued for another four consecutive days. Controls received visible platform MWM training. The escape latency, the traveled distance and swimming speed for each rat were recorded and used to evaluate the performance of the animal during training period. For evaluation of expression of VAChT protein levels, brain tissues from animals in each experiment were obtained immediately after the last trial on the related experimental day and processed for immunohistochemistry staining and western blotting analysis.
There was a significant difference between animals subjected to one day training and those receiving four days of training in escape latency and travel distance. There were an apparent increase in VAChT immunoreactivity in the medial septal area (MSA) and CA1 region of the hippocampus in one day and four day trained animals compared with controls (visible group). Quantitative immunostaining analysis by optical density measurements in the CA1 region and evaluation of immunopositive neurons in medial septal area of brain sections confirmed qualitative findings. Assessment of VAChT protein level expression in hippocampus by western blotting evaluation showed the same pattern of immunohistochemistry results.
Overall, results of this study reveal changes in cholinergic neuron activity in different stages of training in the MWM task. Data suggest that there is a significant level of cholinergic neuronal activity during early stages of the training especially in the hippocampus region that may contribute to the apparent increase in VAChT expression.
Acquisition phase; Cholinergic markers; Hippocampus; Medial septal area; Immunohistochenistry; Western blottig
The present study aims to evaluate the effect of bone marrow mesenchymal stem cells (MSCs) grafts on cognition deficit in chemically and age-induced Alzheimer's models of rats. In the first experiments aged animals (30 months) were tested in Morris water maze (MWM) and divided into two groups: impaired memory and unimpaired memory. Impaired groups were divided into two groups and cannulated bilaterally at the CA1 of the hippocampus for delivery of mesenchymal stem cells (500 × 103/μL) and PBS (phosphate buffer saline). In the second experiment, Ibotenic acid (Ibo) was injected bilaterally into the nucleus basalis magnocellularis (NBM) of young rats (3 months) and animals were tested in MWM. Then, animals with memory impairment received the following treatments: MSCs (500 × 103/μL) and PBS. Two months after the treatments, cognitive recovery was assessed by MWM in relearning paradigm in both experiments. Results showed that MSCs treatment significantly increased learning ability and memory in both age- and Ibo-induced memory impairment. Adult bone marrow mesenchymal stem cells show promise in treating cognitive decline associated with aging and NBM lesions.
To investigate the neuroprotective effect of Convolvulus pluricaulis aqueous extract (AE) against scopolamine (1 mg/kg body weight (bwt))-induced neurotoxicity in the cerebral cortex of male Wistar rats.
Materials and Methods:
The study was carried out on male Wistar rats (age matched, weight 250 ± 20 g). The present study investigated cognitive-enhancing property of AE using Elevated plus maze (EPM) (transfer latency [TL]) and Morris water maze (MWM). Besides evaluating the effect of extract on neurochemical enzymes, in vivo antioxidant and free radical scavenging activities were also screened. All the measured parameters were compared with rivastigmine tartrate (1 mg/kg bwt) which was taken as standard.
Pretreatment of rats with AE (150 mg/kg bwt) significantly reduced scopolamine-induced increase in the TL in EPM, whereas in MWM, administration of extract improved the impairment of spatial memory induced by scopolamine. The activity of acetylcholinesterase (AChE) was significantly inhibited by extract within the cortex and hippocampus. Reduced activities or contents of glutathione reductase, superoxide dismutase, and reduced glutathione within the cortex and hippocampus induced by scopolamine were elevated by the extract. Taken together, it could be postulated that extract may exert its potent-enhancing activity through both anti-AChE and antioxidant action.
AE possesses neuroprotective potential, thus validating its use in alleviating toxic effects of scopolamine.
Convolvulus pluricaulis; elevated plus maze; Morris water maze; oxidative stress
The use of behavioral testing has become an invaluable tool for assessing the efficacy of therapeutics for a variety of disorders of the central nervous system. This chapter will describe in detail several behavioral paradigms to evaluate the efficacy of PPAR agonists to modulate cognitive impairments in rodent models. When used together as a battery these procedures allow for a global assessment of cognition. These tests are explained in detail below, and include: (1) Novel Object Recognition (NOR), (2) Morris Water Maze (MWM), (3) Delay Match to Place (DMP), and (4) Cue Strategy.
PPAR agonists; Cognition; Novel object recognition; Morris water maze; Delay match to place; Cue strategy
This study was designed to examine the effects of recombinant human growth hormone replacement on somatic growth and cognitive function in hypophysectomized (HYPOX) female Sprague-Dawley rats. Rats (5 per group) were randomized by weight to 3 experimental groups: group 1, administered 200 µg/kg of GH once daily for 9 days; group 2, administered 200 µg/kg of GH twice daily; and group 3, administered saline daily. Somatic growth was evaluated by measurement of body weight daily and of the width of the proximal tibial growth plate of the HYPOX rats. Cognitive function was evaluated using the Morris water maze (MWM) test. The results indicated that GH replacement therapy in HYPOX rats promoted an increase in the body weight and the width of the tibial growth plate in a dose-dependent manner. On the third day of the MWM test, the escape latency in the GH-treated groups 1 and 2 was significantly shorter than that in the control rats (P<0.001 and P=0.032, respectively), suggesting that rhGH improved spatial memory acquisition in the MWM test. Therefore it is concluded that rhGH replacement therapy in HYPOX rats stimulates an increase in somatic growth in a dose-dependent manner and also has beneficial effects on cognitive functions.
Growth Hormone; Hypophysectomized Rat; Somatic Growth; Cognitive Function; Morris Water Maze Test
Traumatic brain injury (TBI) survivors often suffer from a post-traumatic syndrome with deficits in learning and memory. Calcium (Ca2+) has been implicated in the pathophysiology of TBI-induced neuronal death. However, the role of long-term changes in neuronal Ca2+ function in surviving neurons and the potential impact on TBI-induced cognitive impairments are less understood. Here we evaluated neuronal death and basal free intracellular Ca2+ ([Ca2+]i) in acutely isolated rat CA3 hippocampal neurons using the Ca2+ indicator, Fura-2, at seven and thirty days after moderate central fluid percussion injury. In moderate TBI, cognitive deficits as evaluated by the Morris Water Maze (MWM), occur after injury but resolve after several weeks. Using MWM paradigm we compared alterations in [Ca2+]i and cognitive deficits. Moderate TBI did not cause significant hippocampal neuronal death. However, basal [Ca2+]i was significantly elevated when measured seven days post-TBI. At the same time, these animals exhibited significant cognitive impairment (F2,25 = 3.43, p < 0.05). When measured 30 days post-TBI, both basal [Ca2+ ]i and cognitive functions had returned to normal. Pretreatment with MK-801 blocked this elevation in [Ca2+]i and also prevented MWM deficits. These studies provide evidence for a link between elevated [Ca2+]i and altered cognition. Since no significant neuronal death was observed, the alterations in Ca2+ homeostasis in the traumatized, but surviving neurons may play a role in the pathophysiology of cognitive deficits that manifest in the acute setting after TBI and represent a novel target for therapeutic intervention following TBI.
Calcium dynamics; Fura-2; Acute isolation of hippocampal neurons; Morris water maze; Neuronal death; Sprague; Dawley rats
Lifelong dietary restriction (DR) is known to have many potential beneficial effects on brain function as well as delaying the onset of neurological diseases. In the present investigation, the effect of late-onset short-term intermittent fasting dietary restriction (IF-DR) regimen was studied on motor coordination and cognitive ability of ageing male rats. These animals were further used to estimate protein carbonyl content and mitochondrial complex I–IV activity in different regions of brain and peripheral organs, and the degree of age-related impairment and reversion by late-onset short-term IF-DR was compared with their levels in 3-month-old young rats. The results of improvement in motor coordination by rotarod test and cognitive skills by Morris water maze in IF-DR rats were found to be positively correlated with the decline in the oxidative molecular damage to proteins and enhanced mitochondrial complex IV activity in different regions of ageing brain as well as peripheral organs. The work was further extended to study the expression of synaptic plasticity-related proteins, such as synaptophysin, calcineurin and CaM kinase II to explore the molecular basis of IF-DR regimen to improve cognitive function. These results suggest that even late-onset short-term IF-DR regimen have the potential to retard age-associated detrimental effects, such as cognitive and motor performance as well as oxidative molecular damage to proteins.
Intermittent fasting–dietary restriction (IF-DR); Ageing; Synaptic plasticity; Mitochondrial electron transport chain (ETC); Morris water maze (MWM); Protein carbonyl content
Age-related cognitive dysfunction, including impairment of hippocampus-dependent spatial learning and memory, affects approximately half of the aged population. Induction of a variety of neuroinflammatory measures has been reported with brain aging but the relationship between neuroinflammation and cognitive decline with non-neurodegenerative, normative aging remains largely unexplored. This study sought to comprehensively investigate expression of the MHC II immune response pathway and glial activation in the hippocampus in the context of both aging and age-related cognitive decline.
Three independent cohorts of adult (12-13 months) and aged (26-28 months) F344xBN rats were behaviorally characterized by Morris water maze testing. Expression of MHC II pathway-associated genes identified by transcriptomic analysis as upregulated with advanced aging was quantified by qPCR in synaptosomal fractions derived from whole hippocampus and in hippocampal subregion dissections (CA1, CA3, and DG). Activation of astrocytes and microglia was assessed by GFAP and Iba1 protein expression, and by immunohistochemical visualization of GFAP and both CD74 (Ox6) and Iba1.
We report a marked age-related induction of neuroinflammatory signaling transcripts (i.e., MHC II components, toll-like receptors, complement, and downstream signaling factors) throughout the hippocampus in all aged rats regardless of cognitive status. Astrocyte and microglial activation was evident in CA1, CA3 and DG of intact and impaired aged rat groups, in the absence of differences in total numbers of GFAP+ astrocytes or Iba1+ microglia. Both mild and moderate microglial activation was significantly increased in all three hippocampal subregions in aged cognitively intact and cognitively impaired rats compared to adults. Neither induction of MHCII pathway gene expression nor glial activation correlated to cognitive performance.
These data demonstrate a novel, coordinated age-related induction of the MHC II immune response pathway and glial activation in the hippocampus, indicating an allostatic shift toward a para-inflammatory phenotype with advancing age. Our findings demonstrate that age-related induction of these aspects of hippocampal neuroinflammation, while a potential contributing factor, is not sufficient by itself to elicit impairment of spatial learning and memory in models of normative aging. Future efforts are needed to understand how neuroinflammation may act synergistically with cognitive-decline specific alterations to cause cognitive impairment.
hippocampus; cognitive decline; para-inflammation; neuroinflammation; aging; Morris water maze
Developmental lead (Pb) exposure is associated with cognitive impairments in humans and rodents alike. In particular, impaired spatial learning and memory, as assessed using the Morris water maze (MWM), has been noted in developmentally Pb –exposed rats. Although sex and rearing environment can influence MWM performance in normal animals, the interactions of sex and rearing environment on the impact of developmental Pb exposure on hippocampal-dependent processes has not been well characterized. The present study examined the effects of perinatal exposure (i.e., gestation through weaning) to different levels of Pb (250, 750 and 1,500 ppm Pb acetate in food) in males and females raised in a non-enriched environment (standard cage with 3 animals and no toys) or an enriched environment (large cage containing a variety of toys that were changed twice weekly). Testing in the MWM began at postnatal day 55. Behavioral outcomes were influenced by sex and rearing environment, with complex interactions with Pb exposure. In non-Pb exposed control animals, beneficial effects of environmental enrichment on spatial learning and memory were observed in males and females, with greater effects in females. Pb exposure in females mitigated at least some of the benefits of enrichment on learning, particularly at the lowest and highest exposure levels. In males, enrichment conferred a modest learning advantage and for the most part, Pb exposure did not affect this. However, in males with the highest Pb exposure, enrichment did help to overcome detrimental effects of Pb on learning. In females, any potential benefit to reference memory contributed by enrichment was muted by exposure to Pb and for the most part, this was not reproduced in males. Thus, there are complex interactions between sex, environment, and Pb exposure on spatial learning and memory. Environmental manipulation is a potential risk modifier of developmental Pb exposure and interacts with other factors including sex and amount of Pb exposure to affect the functional influences of Pb on the brain.
Lead; Sex; Environment; Learning; Memory
Age-related cognitive decline occurs without frank neurodegeneration and is the most common cause of memory impairment in aging individuals. With increasing longevity, cognitive deficits, especially in hippocampus-dependent memory processes, are increasing in prevalence. Nevertheless, the neurobiological basis of age-related cognitive decline remains unknown. While concerted efforts have led to the identification of neurobiological changes with aging, few age-related alterations have been definitively correlated to behavioral measures of cognitive decline. In this work, adult (12 Months) and aged (28 months) rats were categorized by Morris water maze performance as Adult cognitively Intact, Aged cognitively Intact or Aged cognitively Impaired, and protein expression was examined in hippocampal synaptosome preparations. Previously described differences in synaptic expression of neurotransmission-associated proteins (Dnm1, Hpca, Stx1, Syn1, Syn2, Syp, SNAP25, VAMP2 and 14-3-3 eta, gamma, and zeta) were confirmed between Adult and Aged rats, with no further dysregulation associated with cognitive impairment. Proteins related to synaptic structural stability (MAP2, drebrin, Nogo-A) and activity-dependent signaling (PSD-95, 14-3-3θ, CaMKIIα) were up- and down-regulated, respectively, with cognitive impairment but were not altered with increasing age. Localization of MAP2, PSD-95, and CaMKIIα demonstrated protein expression alterations throughout the hippocampus. The altered expression of activity- and structural stability-associated proteins suggests that impaired synaptic plasticity is a distinct phenomenon that occurs with age-related cognitive decline, and demonstrates that cognitive decline is not simply an exacerbation of the aging phenotype.
Nogo; CamkII; aging; hippocampus; synapse; learning and memory
Disturbed proteostasis as a particular phenotype of the aging organism has been advanced in C. elegans experiments and is also conceived to underlie neurodegenerative diseases in humans. Here, we investigated whether particular changes in non-disease related proteostasis can be identified in the aged mammalian brain, and whether a particular signature of aberrant proteostasis is related to behavioral performance of learning and memory. Young (adult, n = 30) and aged (2 years, n = 50) Wistar rats were tested in the Morris Water Maze (MWM) to distinguish superior and inferior performers. For both young and old rats, the best and worst performers in the MWM were selected and the insoluble proteome, termed aggregome, was purified from the hippocampus as evidence for aberrant proteostasis. Quantitative proteomics (iTRAQ) was performed. The aged inferior performers were considered as a model for spontaneous, age-associated cognitive impairment. Whereas variability of the insoluble proteome increased with age, absolute changes in the levels of insoluble proteins were small compared to the findings in the whole C. elegans insoluble proteome. However, we identified proteins with aberrant proteostasis in aging. For the cognitively impaired rats, we identified a changed molecular circuitry of proteins selectively involved in F-actin remodeling, synapse building and long-term depression: actin related protein 3 (ARP3), neurabin II (NEB2) and IQ motif and SEC7 domain-containing protein 1 (BRAG2). We demonstrate that aberrant proteostasis is a specific phenotype of brain aging in mammals. We identify a distinct molecular circuitry where changes in proteostasis are characteristic for poor learning and memory performance in the wild type, aged rat. Our findings 1. establish the search for aberrant proteostasis as a successful strategy to identify neuronal dysfunction in deficient cognitive behavior, 2. reveal a previously unknown functional network of proteins (ARP3, NEB2, BRAG2) involved in age-associated cognitive dysfunction.
Emotion and spatial cognitive aspects were assessed in adult and middle-aged rats using the elevated T-maze (ETM) and the Morris water maze (MWM) tasks. Both adult and middle-aged rats were able to acquire inhibitory avoidance behaviour, though the middle-aged subjects showed larger latencies along the trials, including the baseline, which was significantly longer than that showed by adult rats. Further, compared to adult rats, middle-aged rats had longer escape latency. In spite of the worse performance in the second session of the spatial cognitive task, the middle-aged rats were able to learn the task and remember the information along the whole probe trial test. Both thalamic serotonin (5-HT) concentration and amygdala serotonergic activity (5-HIAA/5-HT) are significantly correlated, respectively, to escape latency and behavioural extinction in the MWM only for middle-aged rats. A significant correlation between the 5-HIAA/5-HT ratio in the amygdala and behavioural extinction for middle-aged, but not for adult, rats was observed. This result suggests that serotonergic activity in the amygdala may regulate behavioural flexibility in aged animals. In addition, a significant negative correlation was found between hippocampal 5-HIAA/5-HT ratio and the path length at the second training session of the MWM task, although only for adult subjects. This was the only session where a significant difference between the performance of middle-aged and adult rats has occurred. Although the involvement of the hippocampus in learning and memory is well established, the present work shows, for the first time, a correlation between a serotonergic hippocampal parameter and performance of a spatial task, which is lost with ageing.
Serotonergic parameters; Emotion; Cognition; Elevated T-maze; Morris water maze; Ageing; Rats
As deficits in memory and cognition are commonly observed in survivors of traumatic brain injury (TBI), causing reduced quality of life for the patient, a major goal in experimental TBI research is to identify and evaluate cognitive dysfunction. The present study assessed the applicability of the serial Morris water maze (MWM) test to determine cognitive function following experimental TBI in the same group of rats which is particularly important for long-term studies and increasingly valuable for the evaluation of novel treatment strategies.
Male Sprague-Dawley rats (n = 27) were anesthetized and subjected to either sham injury (n = 9) or lateral fluid percussion (FP) brain injury of moderate severity (n = 18). At 4 weeks post-injury, animals were trained in a water maze over 3 days (acquisition/learning phase) to find a submerged platform. At 8 weeks post-injury the hidden platform was then moved to the opposite quadrant, and animals were trained to find the new position of the platform over 3 days. Forty-eight hours later, animals were tested for memory retention in a probe trial in which the platform was not present.
Brain-injured animals had significant learning impairment (p < 0.0001), shifted-learning impairment (p < 0.001) and memory retention deficits (p < 0.01) in comparison to their sham-injured counterparts over the 8 week testing period. Swim speed and distance were not significantly altered by brain injury at any time point.
The validation of this testing paradigm using a clinically relevant experimental brain injury model is an important addition to behavioral outcome testing.
Head injury; water maze; shift learning; reversal learning; multiple time points
In this study, we investigated the effects of long-term (9-month) treatment with pioglitazone (PIO; 20 mg/kg/d) in two animal models of Alzheimer's disease (AD)-related neural dysfunction and pathology: the PS1-KIM146V (human presenilin-1 M146V knock-in mouse) and 3xTg-AD (triple transgenic mouse carrying AD-linked mutations) mice. We also investigated the effects on wild-type (WT) mice. Mice were monitored for body mass changes, fasting glycemia, glucose tolerance, and studied for changes in brain mitochondrial enzyme activity (complexes I and IV) as well as energy metabolism (lactate dehydrogenase (LDH)). Cognitive effects were investigated with the Morris water maze (MWM) test and the object recognition task (ORT). Behavioral analysis revealed that PIO treatment promoted positive cognitive effects in PS1-KI female mice. These effects were associated with normalization of peripheral gluco-regulatory abnormalities that were found in untreated PS1-KI females. PIO-treated PS1-KI females also showed no statistically significant alterations in brain mitochondrial enzyme activity but significantly increased reverse LDH activity.PIO treatment produced no effects on cognition, glucose metabolism, or mitochondrial functioning in 3xTg-AD mice. Finally, PIO treatment promoted enhanced short-term memory performance in WT male mice, a group that did not show deregulation of glucose metabolism but that showed decreased activity of complex I in hippocampal and cortical mitochondria. Overall, these results indicate metabolically driven cognitive-enhancing effects of PIO that are differentially gender-related among specific genotypes.
pioglitazone; neurodegeneration; insulin signaling; glucose metabolism; mitochondrial complex activity; LDH
We found that a single week of exercise enhanced cognitive function on the Morris water maze (MWM), such that exercise animals were significantly better than sedentary controls at learning and recalling the location of the platform. In order to elucidate the role that calcium calmodulin protein kinase II (CAMKII) holds in mediating the exercise-induced enhancement in learning and memory, a specific antagonist of CAMKII, KN-62, was used to block CAMKII in the hippocampus during a 1-week voluntary exercise period. Following, a 2-trial-per-day MWM was performed for 5 consecutive days, succeeded by a probe trial 2 days later. Inhibiting CAMKII action during exercise blocked the ability of exercise to enhance memory retention on the MWM; the recall abilities of exercise animals receiving the CAMKII blocker were significantly worse than those of both sedentary and exercise controls. Conversely, CAMKII may not play a significant role in mediating the effects of exercise on learning acquisition as inhibiting CAMKII failed to block the exercise-induced enhancement in learning acquisition. Our results also show that CAMKII activation early during MWM learning may be counterproductive to learning acquisition, as exercising animals given the CAMKII inhibitor performed significantly (p < 0.001) better than exercising control animals and sedentary controls only on day 2 of the MWM. Inhibiting CAMKII also blocked the exercise-induced upregulation of molecules critical for learning and memory, BDNF and the transcription activator CREB, which is regulated by and downstream to BDNF action. These findings indicate that hippocampal CAMKII may have a refined role in mediating the effects of exercise on cognition, selectively functioning to regulate memory retention.
BDNF; CREB; Morris water maze; learning and memory; exercise
This study focused on the effects of zinc oxide nanoparticles (nano-ZnO) on spatial learning and memory and synaptic plasticity in the hippocampus of young rats, and tried to interpret the underlying mechanism. Rats were randomly divided into four groups. Nano-ZnO and phosphate-buffered saline were administered in 4-week-old rats for 8 weeks. Subsequently, performance in Morris water maze (MWM) was determined, and then long-term potentiation (LTP) and depotentiation were measured in the perforant pathway to dentate gyrus (DG) in anesthetized rats. The data showed that, (1) in MWM, the escape latency was prolonged in the nano-ZnO group and, (2) LTP was significantly enhanced in the nano-ZnO group, while depotentiation was barely influenced in the DG region of the nano-ZnO group. This bidirectional effect on long-term synaptic plasticity broke the balance between stability and flexibility of cognition. The spatial learning and memory ability was attenuated by the alteration of synaptic plasticity in nano-ZnO-treated rats.
zinc oxide nanoparticles; synaptic plasticity; long-term potentiation; depotentiation; spatial learning; memory
We have previously described the transcriptional changes that occur in the hippocampal CA1 field of aged rats following a Morris Water Maze (MWM) training paradigm. In this report we proceed with the analysis of the dentate region from the same animals. Animals were first identified as age learning-impaired or age-superior learners when compared to young rats based on their performance in the MWM. Messenger RNA was isolated from the dentate gyrus of each animal to interrogate Affymetrix RAE 230A rat genome microarrays. Microarray profiling identified 1129 genes that were differentially expressed between aged and young rats as a result of aging, and independent of their behavioral training (p<0.005). We applied Ingenuity Pathway Analysis (IPA) algorithms to identify the significant biological processes underlying age-related changes in the dentate gyrus. The most significant functions, as calculated by IPA, included cell movement, cell growth and proliferation, nervous system development and function, cellular assembly and organization, cell morphology and cell death. These significant processes are consistent with age-related changes in neurogenesis, and the neurogenic markers were generally found to be downregulated in senescent animals. In addition, statistical analysis of the different experimental groups of aged animals recognized 85 genes (p<0.005) that were different in the dentate gyrus of aged rats that had learned the MWM when compared to learning impaired and a number of controls for stress, exercise and non-spatial learning. The list of learning-related genes expressed in the dentate adds to the set of genes we previously described in the CA1 region. This long list of genes constitutes a starting tool to elucidating the molecular pathways involved in learning and memory formation.
aging; hippocampus; learning and memory; Morris water maze; nervous system; gene expression; learning impaired; superior learner; dentate gyrus; microarray; class prediction; pathway analysis; neurogenesis
The present study was undertaken to explore the potential of stevioside in memory dysfunction of rats. Memory impairment was produced by scopolamine (0.5 mg/kg, i.p.) in animals. Morris water maze (MWM) test was employed to assess learning and memory. Brain acetylcholinestrase enzyme (AChE) activity was measured to assess the central cholinergic activity. The levels of brain thiobarbituric acid-reactive species (TBARS) and reduced glutathione (GSH) were estimated to assess the degree of oxidative stress. Scopolamine administration induced significant impairment of learning and memory in rats, as indicated by a marked decrease in MWM performance. Scopolamine administration also produced a significant enhancement of brain AChE activity and brain oxidative stress (increase in TBARS and decrease in GSH) levels. Pretreatment of stevioside (250 mg/kg dose orally) significantly reversed scopolamine-induced learning and memory deficits along with attenuation of scopolamine-induced rise in brain AChE activity and brain oxidative stress levels. It may be concluded that stevioside exerts a memory-preservative effect in cognitive deficits of rats possibly through its multiple actions.
Memory; Morris water-maze; scopolamine; stevioside
Longitudinal hippocampal pathways are needed for seizure synchronization, and there is evidence that their transection may abolish seizures. However, the effect of such transection on memory is unknown. In this study, we investigated the effect of transverse CA3 transections on memory function in Sprague-Dawley rats. Using a stereotactic knife, a single CA3 transection was made unilaterally (n=5) or bilaterally (n=5). Sham surgery was done in another group (n=4). Morris water maze (MWM) and Novel object recognition (NOR) tests were started 18 days later revealing no significant differences between transected animals and controls. Cresyl-violet brain staining confirmed the locations of transections in the CA3 region. We conclude that normal performance in MWM and NOR tests does not appear to require intact transmission throughout the whole length of CA3, supporting the hypothesis that CA3 transections may be used in temporal lobe epilepsy to interrupt seizure circuitry while preserving memory.
Temporal Lobe Epilepsy; Hippocampus; Epilepsy Surgery; Memory Processing