Age-related Spatial Learning Research Articles

A Long-Term Enriched Environment Ameliorates the Accelerated Age-Related Memory Impairment Induced by Gestational Administration of Lipopolysaccharide: Role of Plastic Mitochondrial Quality Control.

Studies have shown that gestational inflammation accelerates age-related memory impairment in mother mice. An enriched environment (EE) can improve age-related memory impairment, whereas mitochondrial dysfunction has been implicated in the pathogenesis of brain aging. However, it is unclear whether an EE can counteract the accelerated age-related memory impairment induced by gestational inflammation and whether this process is associated with the disruption of mitochondrial quality control (MQC) processes. In this study, CD-1 mice received daily intraperitoneal injections of lipopolysaccharide (LPS, 50 μg/kg) or normal saline (CON group) during gestational days 15–17 and were separated from their offspring at the end of normal lactation. The mothers that received LPS were divided into LPS group and LPS plus EE (LPS-E) treatment groups based on whether the mice were exposed to an EE until the end of the experiment. At 6 and 18 months of age, the Morris water maze test was used to evaluate spatial learning and memory abilities. Quantitative reverse transcription polymerase chain reaction and Western blot were used to measure the messenber RNA (mRNA) and protein levels of MQC-related genes in the hippocampus, respectively. The results showed that all the aged (18 months old) mice underwent a striking decline in spatial learning and memory performances and decreased mRNA/protein levels related to mitochondrial dynamics (Mfn1/Mfn2, OPA1, and Drp1), biogenesis (PGC-1α), and mitophagy (PINK1/parkin) in the hippocampi compared with the young (6 months old) mice. LPS treatment exacerbated the decline in age-related spatial learning and memory and enhanced the reduction in the mRNA and protein levels of MQC-related genes but increased the levels of PGC-1α in young mice. Exposure to an EE could alleviate the accelerated decline in age-related spatial learning and memory abilities and the accelerated changes in MQC-related mRNA or protein levels resulting from LPS treatment, especially in aged mice. In conclusion, long-term exposure to an EE can counteract the accelerated age-related spatial cognition impairment modulated by MQC in CD-1 mother mice that experience inflammation during pregnancy.

Dietary fish hydrolysate supplementation containing n-3 LC-PUFAs and peptides prevents short-term memory and stress response deficits in aged mice

Brain aging is characterized by a decline in cognitive functions, which can lead to the development of neurodegenerative pathologies. Age-related spatial learning and memory deficits are associated with a chronic low-grade inflammation. Anxiety disorders and stress response alterations, occurring for a part of the elderly, have also been linked to an increased neuroinflammation and thus, an accelerated cognitive decline. Nutrition is an innovative strategy to prevent age-related cognitive impairments. Among the nutrients, n-3 long chain polyunsaturated fatty acids (LC-PUFAs) and low molecular weight peptides from proteins, especially those from marine resources, are good candidates for their immunomodulatory, anxiolytic and neuroprotective properties. The aim of this study is to determine the combined effect of n-3 LC-PUFAs and low molecular weight peptides on cognitive functions, and their mechanism of action. We are the first to show that a dietary supplementation with a fish hydrolysate containing n-3 LC-PUFAs and low molecular weight peptides prevented the age-related spatial short-term memory deficits and modulated navigation strategies adopted during spatial learning. In addition, the fish hydrolysate displayed anxiolytic activities with the reduction of anxiety-like behaviour in aged mice, restored the plasmatic corticosterone levels similar to adult animals following an acute stress and modulated the hypothalamic stress response. These effects on behaviour can be explained by the immunomodulatory and neuroprotective properties of the fish hydrolysate that limited microgliosis in vivo, decreased LPS-induced expression of pro-inflammatory cytokines and increased the expression of growth factors such as BDNF and NGF in vitro. Thus, n-3 LC-PUFAs and low molecular weight peptides contained in the fish hydrolysate can play an important role in the limitation of neuroinflammation and stress response alterations during aging and represent a potential strategy for the prevention of age-related cognitive decline.

Accelerated Deficits of Spatial Learning and Memory Resulting From Prenatal Inflammatory Insult Are Correlated With Abnormal Phosphorylation and Methylation of Histone 3 in CD-1 Mice.

Gestational infection causes various neurological deficits in offspring, such as age-related spatial learning and memory (SLM) decline. How inflammation causes age-related SLM dysfunction remains unknown. Previous research has indicated that histone modifications, such as phosphorylation of H3S10 (H3S10p) and trimethylation of H3K9 (H3K9me3) may be involved. In our study, pregnant mice received an intraperitoneal injection of lipopolysaccharide (LPS, 50 or 25 μg/kg) or normal saline during gestational days 15–17. After normal parturition, the offspring were randomly separated into 1-, 6-, 12-, 18-, and 22-month-old groups. SLM performance was assessed using a radial six-arm water maze (RAWM). The hippocampal levels of H3S10p and H3K9me3 were detected using an immunohistochemical method. The results indicated that the offspring had significantly impaired SLM, with decreased H3S10p and increased H3K9me3 levels from 12 months onward. Maternal LPS exposure during late gestation significantly and dose-dependently exacerbated the age-related impairment of SLM, with the decrease in H3S10p and increase in H3K9me3 beginning at 12 months in the offspring. The histone modifications (H3S10p and H3K9me3) were significantly correlated with impairment of SLM. Our findings suggest that prenatal exposure to inflammation could exacerbate age-related impairments of SLM and changes in histone modifications in CD-1 mice from 12 months onward, and SLM impairment might be linked to decreased H3S10p and increased H3K9me3.

Water Maze Testing to Identify Compounds for Cognitive Enhancement

The water maze task is widely used to evaluate spatial learning and memory in rodents. The basic paradigm requires an animal to swim in a pool until it finds a hidden escape platform. The animals learn to find the platform using extra-maze cues and, after several training trials, are able to swim directly to it from any starting location. Memory for the platform location is assessed by examining swimming behavior with the platform removed from the maze, while sensory, motor and motivational aspects of the task can be examined by making the platform visible to the animals. Described in this unit is the use of the water maze to identify rats with age-related spatial learning and memory impairments. The efficacy of potential pharmacological treatments for alleviating these deficits is then evaluated. This assay provides a means for studying the neurobiology of spatial learning and memory, and to identify potential pharmacotherapies for treating memory-impaired humans. While the use of aged rats is described in this unit, the protocol can also be employed for compound screening with other rodent models that have spatial learning and memory impairments, such as transgenic mouse models of Alzheimer's disease.

Inhibition of phosphodiesterase-5 rescues age-related impairment of synaptic plasticity and memory

Aging is characterized by a progressive cognitive decline that leads to memory impairment. Because the cyclic nucleotide cascade is essential for the integrity of synaptic function and memory, and it is down-regulated during aging and in neurodegenerative disorders, we investigated whether an increase in cGMP levels might rescue age-related synaptic and memory deficits in mice. We demonstrated that acute perfusion with the phosphodiesterase-5 inhibitor sildenafil (50nM) ameliorated long-term potentiation in hippocampal slices from 26–30-month-old mice. Moreover, chronic intraperitoneal injection of sildenafil (3mg/kg for 3 weeks) improved age-related spatial learning and reference memory as tested by the Morris Water Maze, and recognition memory as tested by the Object Recognition Test. Finally, sildenafil restored central cAMP responsive element-binding protein (CREB) phosphorylation, which is crucial for synaptic plasticity and memory. Our data suggest that inhibition of phosphodiesterase-5 may be beneficial to treat age-related cognitive dysfunction in a physiological mouse model of aging.

Correlation of increased hippocampal Sumo3 with spatial learning ability in old C57BL/6 mice

Age-related impairment of learning and memory is a common phenomenon in humans and animals, yet the underlying mechanism remains unclear. We hypothesize that a small ubiquitin-related modifier (Sumo) might correlate with age-related loss of learning and memory. To test this hypothesis, the present study evaluated age-related spatial learning and memory in C57BL/6 mice (25 aged 7 months and 21 aged 25 months) using a radial six-arm water maze (RAWM). After the behavioral test, the protein expression of Sumo3 was determined in different brain regions using Western blotting. The results showed that the 25-month-old mice had longer latency and a higher number of errors in both learning and memory phases in the RAWM task than the 7-month-old mice. Compared to the latter, the former's level of Sumo3 protein was significantly increased in the dorsal and ventral hippocampus. For the 25-month-old mice, the number of errors and the latency in the learning phase negatively correlated with the Sumo3 level in the dorsal hippocampus. These results suggest that increased Sumo3 in the hippocampus may be correlated with spatial learning ability in old C57BL/6 mice.

Reduced thyroid hormones with increased hippocampal SNAP-25 and Munc18-1 might involve cognitive impairment during aging

The mechanism underlying the decline of age-related learning and memory remains unclear. Brain-region-specific changes of synaptic proteins and decreased thyroid hormones (THs) have been implied involving this decline. During normal aging, however, the relationships among synaptic proteins, THs and abilities of learning and memory remain to be elucidated. In this study, the age-related spatial learning and memory ability of 41 Kunming mice (KM) (14 mice aged 6 months, 13 mice aged 11 months, 14 mice aged 22 months) was measured with radial six-arm water maze. The levels of SNAP-25 and Munc18-1 in brain regions were semi-quantified by Western blotting and the serum THs were detected by radioimmunoassay. Our results showed the old Kunming mice had marked impairment of spatial learning and memory, with decreased serum free triiodothyronine (FT3) and increased SNAP-25 and Munc18-1 in dorsal hippocampus (DH), ventral hippocampus (VH) and frontal lobe (F). The Pearson's correlation test showed the impairment of spatial learning ability positively correlated with SNAP-25 in DH and Munc18-1 in DH and VH. While, the levels of SNAP-25 (DH, VH and F) and Munc18-1 (DH) negatively correlated with the serum FT3 level, and the spatial memory decline marginal negatively correlate with serum THs. These results suggested that increased hippocampal SNAP-25 and Munc18-1 which seemingly result from decreased serum THs might involve the age-related impairment of spatial learning and memory.

Indomethacin enhances learning and memory potential by interacting with CaMKII

The present study examined the effect of indomethacin (IM), a cyclooxygenase inhibitor, on learning and memory functions. IM activated Ca(2+) /calmodulin-dependent protein kinase II (CaMKII) in cultured rat hippocampal neurons. IM (100 µM) significantly increased the rate of spontaneous AMPA receptor-mediated miniature excitatory postsynaptic currents elicited from CA1 pyramidal neurons of rat hippocampal slices, without affecting the amplitude, and enhanced extracellular high K(+) (20 mM)-induced glutamate release from rat hippocampal slices, indicating that IM stimulates presynaptic glutamate release. Those IM effects were clearly inhibited by the CaMKII inhibitor KN-93. IM persistently facilitated synaptic transmission monitored from the CA1 region of rat hippocampal slices in a concentration (1-100 µM)-dependent manner that was also abolished by KN-93. In the water maze test, IM (1 mg/kg, i.p.) enhanced spatial learning and memory ability for normal rats, and ameliorated scopolamine-induced spatial learning and memory impairment or age-related spatial learning and memory deterioration for senescence-accelerated mouse-prone 8 mice. In the test to learn 15 numbers consisting of three patterns of five digit number for healthy human subjects, oral intake with IM (25 mg/kg) significantly raised the scores of correct number arrangements that subjects memorized 5 min and 3 days after the test. The results of the present study indicate that IM could enhance learning and memory potential by facilitating hippocampal synaptic transmission as a result from stimulating presynaptic glutamate release under the control of CaMKII.

Region-specific genetic alterations in the aging hippocampus: implications for cognitive aging.

Aging is associated with cognitive decline in both humans and animals and of all brain regions, the hippocampus appears to be particularly vulnerable to senescence. Age-related spatial learning deficits result from alterations in hippocampal connectivity and plasticity. These changes are differentially expressed in each of the hippocampal fields known as cornu ammonis 1 (CA1), cornu ammonis 3 (CA3), and the dentate gyrus. Each sub-region displays varying degrees of susceptibility to aging. For example, the CA1 region is particularly susceptible in Alzheimer's disease while the CA3 region shows vulnerability to stress and glucocorticoids. Further, in animals, aging is the main factor associated with the decline in adult neurogenesis in the dentate gyrus. This review discusses the relationship between region-specific hippocampal connectivity, morphology, and gene expression alterations and the cognitive deficits associated with senescence. In particular, data are reviewed that illustrate how the molecular changes observed in the CA1, CA3, and dentate regions are associated with age-related learning deficits. This topic is of importance because increased understanding of how gene expression patterns reflect individual differences in cognitive performance is critical to the process of identifying new and clinically useful biomarkers for cognitive aging.

Long-term administration of green tea catechins prevents age-related spatial learning and memory decline in C57BL/6 J mice by regulating hippocampal cyclic amp-response element binding protein signaling cascade

Flavonoid-rich foods have been shown to be effective at reversing age-related deficits in learning and memory in both animals and humans. However, little investigation of the preventative effects of flavonoids on the naturally aged animals was reported. In our study, 14-month-old female C57BL/6 J mice were orally administered 0.025%, 0.05% and 0.1% green tea catechins (GTC, w/v) in drinking water for 6 months; we found that a supplementation with 0.05% or 0.1% GTC prevented age-related spatial learning and memory decline of mice in the Morris water maze. Better performance of GTC-treated mice was associated with increased levels of cAMP-response element binding protein (CREB) phosphorylation in the hippocampus. The expressions of brain-derived neurotrophic factor (BDNF) and Bcl-2, two target genes of CREB which can exhibit long-term regulatory roles in synaptic plasticity and synaptic structure, were also increased. We also found that long-term 0.05% or 0.1% GTC administration prevented age-related reductions of two representative post-synaptic density proteins PSD95 and Ca 2+/calmodulin-dependent protein kinase II, suggesting that synaptic structural changes may be involved. These results demonstrated that long-term 0.05% or 0.1% green tea catechin administration may prevent age-related spatial learning and memory decline of female C57BL/6 J mice by regulating hippocampal CREB signaling cascade.

The chronology of age-related spatial learning impairment in two rat strains, as tested by the Barnes maze.

The Barnes maze offers advantages for cognitive aging studies, because of its relatively unstressful design and its modest physical demands. The authors therefore undertook a detailed chronological investigation of performance against age, for female Sprague-Dawley and male and female Dark Agouti rats. The trial duration was 10 days. Rats were tested at 6, 11, 14, 17, 20, and 26 months of age, but individual rats were tested at one age only. At 6 months of age, all rats reached the criterion. Sprague-Dawley rats performed best at this age. Impairment began at 14 months in Dark Agouti rats and continued to increase up to 26 months of age. Impairment was greater in Dark Agouti than Sprague-Dawley rats and was greater in females than males. At 26 months, 70% of Sprague-Dawley females reached criterion; of the Dark Agoutis, only 33% of females and 57% of males reached criterion. This study confirms the utility of the Barnes maze as a robust vehicle in aged rats. It also highlights major performance differences between strains and genders in aging rats.

The bite-raised condition in aged SAMP8 mice induces dendritic spine changes in the hippocampal region

The present study examined the effect of the bite-raised condition on the number of dendritic spines on hippocampal pyramidal cells in SAMP8 mice and related the results with learning ability in a water maze test. Aged mice in the bite-raised condition had reduced learning ability and a lower number of CA1 pyramidal cell dendritic spines. The results suggest that the bite-raised condition exacerbates the age-related spatial learning impairment, and that this may be due to the degeneration of hippocampal dendritic spines.

Age-related spatial learning impairment is unrelated to spinophilin immunoreactive spine number and protein levels in rat hippocampus

Age-related impairments in hippocampus-dependent learning and memory tasks are not associated with a loss of hippocampal neurons, but may be related to alterations in synaptic integrity. Here we used stereological techniques to estimate spine number in hippocampal subfields using immunostaining for the spine-associated protein, spinophilin, as a marker. Quantification of the immunoreactive profiles was performed using the optical disector/fractionator technique. Aging was associated with a modest increase in spine number in the molecular layer of the dentate gyrus and CA1 stratum lacunosum-moleculare. By comparison, spinophilin protein levels in the hippocampus, measured by Western blot analysis, failed to differ as a function of age. Neither the morphological nor the protein level data were correlated with spatial learning ability across individual aged rats. The results extend current evidence on synaptic integrity in the aged brain, indicating that a substantial loss of dendritic spines and spinophilin protein in the hippocampus are unlikely to contribute to age-related impairment in spatial learning.

Profiling psychomotor and cognitive aging in four-way cross mice

In part due to their genetic uniformity and stable characteristics, inbred rodents or their F1 progeny are frequently used to study brain aging. However, it is recognized that focus on a single genotype could lead to generalizations about brain aging that might not apply to the species as a whole, or to the human population. As a potential alternative to uniform genotypes, genetically heterogeneous (HET) mice, produced by a four-way cross, were tested in the current study to determine if they exhibit age-related declines in cognitive and psychomotor function similar to other rodent models of brain aging. Young (4months) and older (23months) CB6F1 × C3D2F1 mice were administered a variety of tests for cognitive, psychomotor, and sensory/reflexive capacities. Spontaneous locomotion, rearing, and ability to turn in an alley all decreased with age, as did behavioral measures sensitive to muscle strength, balance, and motor coordination. Although no effect of age was found for either startle response amplitude or reaction time to shock stimuli, the old mice reacted with less force to low intensity auditory stimuli. When tested on a spatial swim maze task, the old mice learned less efficiently, exhibited poorer retention after a 66-h delay, and demonstrated greater difficulty learning a new spatial location. In addition, the older mice were less able to learn the platform location when it was identified by a local visual cue. Because there was a significant correlation between spatial and cued discrimination performance in the old mice, it is possible that age-related spatial maze learning deficits could involve visual or motor impairments. Variation among individuals increased with age for most tests of psychomotor function, as well as for spatial swim performance, suggesting that four-way cross mice may be appropriate models of individualized brain aging. However, the analysis of spatial maze learning deficits in older CB6F1 × C3D2F1 mice may have limited applicability in the study of brain aging, because of a confounding with visually cued performance deficits.

Changes in transcription within the CA1 field of the hippocampus are associated with age-related spatial learning impairments

Aged rats display a broad range of behavioral performance in spatial learning. The aim of this study was to identify candidate genes that are associated with learning and memory impairments. We first categorized aged-superior learners and age learning-impaired rats based on their performance in the Morris water maze (MWM) and then isolated messenger RNA from the CA1 hippocampal region of each animal to interrogate Affymetrix microarrays. Microarray analysis identified a set of 50 genes that was transcribed differently in aged-superior learners that had successfully learned the spatial strategy in the MWM compared to aged learning-impaired animals that were unable to learn and a variety of groups designed to control for all non-learning aspects of exposure to the water maze paradigm. A detailed analysis of the navigation patterns of the different groups of animals during acquisition and probe trials of the MWM task was performed. Young animals used predominantly an allocentric (spatial) search strategy and aged-superior learners appeared to use a combination of allocentric and egocentric (response) strategies, whereas aged-learning impaired animals displayed thigmotactic behavior. The significant 50 genes that we identified were tentatively classified into four groups based on their putative role in learning: transcription, synaptic morphology, ion conductivity and protein modification. Thus, this study has potentially identified a set of genes that are responsible for the learning impairments in aged rats. The role of these genes in the learning impairments associated with aging will ultimately have to be validated by manipulating gene expression in aged rats. Finally, these 50 genes were functioning in the context of an aging CA1 region where over 200 genes was found to be differentially expressed compared to a young CA1.

Pilocarpine improves olfactory discrimination and social recognition memory deficits in 24 month-old rats

Muscarinic receptor agonists have been suggested as potential drugs to counteract age-related cognitive decline since critical changes in cholinergic system occur with aging. Recently, we demonstrated that single administration of the non-selective muscarinic receptor agonist pilocarpine prevents age-related spatial learning impairments in rats. In addition, increasing evidence suggests that areas in the central nervous system processing olfactory information are affected at the early stages of age-related diseases, such as Alzheimer's disease, and that specific olfactory testing may represent an important tool in the diagnosis of these diseases. In the present study, olfactory discrimination and short-term social memory of 3 and 24 month-old rats were assessed with the olfactory discrimination and social recognition memory tasks, respectively. The actions of the repeated treatment with pilocarpine (30 mg/kg, i.p.; once per day for 21 days) in relation to age-related effects on olfactory and cognitive functions were also studied. The 24 month-old rats exhibited significantly impaired performance in both models, demonstrating deficits in their odour discrimination and in their ability to recognize a juvenile rat after a short period of time. The treatment with pilocarpine improved in a specific manner these age-related deficits in 24 month-old rats without altering their motor performance. The present results extend the notion of the participation of muscarinic receptors in control of olfactory functions and reinforce the potential of muscarinic receptor agonists for the treatment of age-related cognitive decline.

Differential expression of PSD proteins in age-related spatial learning impairments

Deficits in hippocampus-dependent spatial learning that are typical for a subpopulation of aged rats are not associated with loss of neurons or excitatory synapses but accompanied by significant reduction of postsynaptic density (PSD) area in perforated synapses. Here, we examined whether structural alterations in aged learning-impaired rats correlate with altered content of PSD proteins which are critically involved in normal synaptic function. Spatial memory tasks were used to separate male rats into young, aged learning-unimpaired and impaired groups. Semi-quantitative immunohistochemistry revealed significant alterations in the content of the AMPA receptor GluR1 subunit, PSD-95 and synGAP in the hippocampal formation of aged-learning impaired compared to aged-unimpaired and young rats. While synGAP expression was reduced, GluR1 and PSD95 levels were selectively increased in aged-learning-impaired subjects. These findings suggest that age-induced changes of the PSD protein expression levels are more pronounced in learning-impaired rats compared to unimpaired subjects and that the alterations in synaptic protein content may result in reduced synaptic function, potentially underlying the individual differences in mnemonic functions during aging.

Pilocarpine prevents age-related spatial learning impairments in rats

The cholinergic pathways are intimately involved in the learning and memory process and disruption of this system produces impairments in many learning and memory models. Converging lines of evidence support the idea that there is an age-related decline in learning and memory in animals and this decline is strikingly similar to memory changes that occur when the cholinergic system is compromised. The purpose of this work was to evaluate whether a single administration of the muscarinic receptor agonist Pilocarpine (Pilo) could prevent the age-related learning impairment in rats. Three groups of animals received Pilo (300 mg/kg, i.p.), at 3 months of age, and the animals that did not show Status epilepticus were submitted to the water maze task 1 or 21 months after or once a month from the 4th to 24th month of age. The results showed that Pilo did not interfere with learning abilities 1-month after treatment nor in animals that were submitted to the test once a month. In addition, the animals treated with Pilo and submitted to the task 21 month after performed as well as control young rats in the training and in the testing sessions, while a marked learning impairment was detected in control old rats. These results indicate that a single administration of Pilo might prevent the age-related learning impairments in rats on a spatial task in the water maze.

Effect of age on the radial arm water maze—a test of spatial learning and memory

Aged rats show decrements in performance on cognitive tasks that require the use of spatial learning and memory. We used the 8-arm radial water maze (RAWM) to measure spatial learning as a function of age in young (6 months) and old (21 months) male F344 rats. Rats were placed in the RAWM in different start arms with the same goal arm for 3 days (five trials/day); the goal arm was changed on day 4. Old rats demonstrated spatial impairment as evidenced by increased latencies to find the hidden platform on day 4. Old rats made significantly more errors, both reference and working memory errors, than young rats on all days. It is likely that the old rats utilized non-spatial strategies to solve the task, and therefore were impaired in learning a new platform location. The RAWM is a reliable, sensitive, and powerful additional test to assess age-related spatial learning and memory deficits, combining the advantages of the Morris water maze and the radial arm maze while minimizing the disadvantages.

Hippocampal map realignment and spatial learning.

The spatial selectivity of hippocampal neurons suggests that they contribute to an internal representation of current location. The activity of hippocampal pyramidal cells was recorded while adult (10-13 months old) and aged (24-28 months old) rats performed a task in which two spatial reference frames were put in conflict. Rats attempted to find an unmarked goal whose position was fixed relative to only one of the two reference frames. The ability of a rat's hippocampus to adjust to the conflicting information and use the 'correct' position estimate (hippocampal map 'realignment') was correlated with the rat's ability to find the hidden goal. In addition, aged rats were impaired relative to adult rats in both goal-finding accuracy and map realignment. Thus, changes in the effectiveness with which the hippocampal spatial representation is updated on the basis of external cues may contribute to both within-age-group spatial learning variability and age-related spatial learning deficits.