The influence of APOE and TOMM40 polymorphisms on hippocampal volume and episodic memory in old age

Mitochondrial dysfunction is implicated in neurodegenerative disorders, such as Alzheimer's disease (AD). Translocase of outer mitochondrial membrane 40 (TOMM40) may be influential in this regard by influencing mitochondrial neurotoxicity. Little is known about the influence of the TOMM40 gene on hippocampal (HC) volume and episodic memory (EM), particularly in healthy older adults. Thus, we sought to discern the influence of TOMM40 single nucleotide polymorphisms (SNPs), which have previously been associated with medial temporal lobe integrity (rs11556505 and rs2075650), on HC volume and EM. The study sample consisted of individuals from the Swedish National Study on Aging and Care in Kungsholmen (SNAC-K) who were free of dementia and known neurological disorders, and 60-87 years of age (n = 424). EM was measured by using a 16-item word list with a 2-min free recall period and delineation of the HC was performed manually. The influence of Apolipoprotein E (APOE) and TOMM40 was assessed by 2 × 2 ANOVAs and partial correlations. There was no effect of APOE and TOMM40 on EM performance and HC volume. However, partial correlations revealed that HC volume was positively associated with free recall performance (r = 0.21, p < 0.01, r (2) = 0.04). When further stratified for TOMM40, the observed association between HC volume and free recall in APOE ε4 carriers was present in combination with TOMM40 rs11556505 any T (r = 0.28, p < 0.01, R (2) = 0.08) and rs2075650 any G (r = 0.28, p < 0.01, R (2) = 0.08) "risk" alleles. This pattern might reflect higher reliance on HC volume for adequate EM performance among APOE ε4 carriers with additional TOMM40 "risk" alleles suggesting that the TOMM40 gene cannot merely be considered a marker of APOE genotype. Nevertheless, neither APOE nor TOMM40 influenced HC volume or EM in this population-based sample of cognitively intact individuals over the age of 60.

Impact of negative emotion on the neural correlates of long-term recognition in younger and older adults

Some studies have suggested that the memory advantage for negative emotional information over neutral information (“negativity effect”) is reduced in aging. Besides the fact that most findings are based on immediate retrieval, the neural underpinnings of long-term emotional memory in aging have so far not been investigated. To address these issues, we assessed recognition of neutral and negative scenes after 1- and 3-week retention intervals in younger and older adults using functional magnetic resonance imaging. We further used an event-related design in order to disentangle successful, false, and true recognition. This study revealed four key findings: (1) increased retention interval induced an increased rate of false recognitions for negative scenes, canceling out the negativity effect (present for hit rates only) on discrimination in both younger and older adults; (2) in younger, but not older, adults, reduced activity of the medial temporal lobe was observed over time for neutral scenes, but not for negative scenes, where stable or increased activity was seen; (3) engagement of amygdala (AMG) was observed in older adults after a 3-week delay during successful recognition of negative scenes (hits vs. misses) in comparison with neutral scenes, which may indicate engagement of automatic processes, but engagement of ventrolateral prefrontal cortex was unrelated to AMG activity and performance; and (4) after 3 weeks, but not after 1 week, true recognition of negative scenes was characterized by more activity in left hippocampus and lateral occipito-temporal regions (hits vs. false alarms). As these regions are known to be related to consolidation mechanisms, the observed pattern may indicate the presence of delayed consolidation of true memories. Nonetheless, older adults’ low performance in discrimination of negative scenes could reflect the fact that overall, after long delays of retention, they rely more on general information rather than on perceptual detail in making recognition judgments.

The dimensionality of between-person differences in white matter microstructure in old age

Between-person differences in white matter microstructure may partly generalize across the brain and partly play out differently for distinct tracts. We used diffusion-tensor imaging and structural equation modeling to investigate this issue in a sample of 260 adults aged 60-87 years. Mean fractional anisotropy and mean diffusivity of seven white matter tracts in each hemisphere were quantified. Results showed good fit of a model positing that individual differences in white matter microstructure are structured according to tracts. A general factor, although accounting for variance in the measures, did not adequately represent the individual differences. This indicates the presence of a substantial amount of tract-specific individual differences in white matter microstructure. In addition, individual differences are to a varying degree shared between tracts, indicating that general factors also affect white matter microstructure. Age-related differences in white matter microstructure were present for all tracts. Correlations among tract factors did not generally increase as a function of age, suggesting that aging is not a process with homogenous effects on white matter microstructure across the brain. These findings highlight the need for future research to examine whether relations between white matter microstructure and diverse outcomes are specific or general.

Distinct and shared cognitive functions mediate event- and time-based prospective memory impairment in normal ageing

Prospective memory (PM) is the ability to remember to perform an action at a specific point in the future. Regarded as multidimensional, PM involves several cognitive functions that are known to be impaired in normal ageing. In the present study we set out to investigate the cognitive correlates of PM impairment in normal ageing. Manipulating cognitive load, we assessed event- and time-based PM, as well as several cognitive functions, including executive functions, working memory, and retrospective episodic memory, in healthy participants covering the entire adulthood. We found that normal ageing was characterised by PM decline in all conditions and that event-based PM was more sensitive to the effects of ageing than time-based PM. Whatever the conditions, PM was linked to inhibition and processing speed. However, while event-based PM was mainly mediated by binding and retrospective memory processes, time-based PM was mainly related to inhibition. The only distinction between high- and low-load PM cognitive correlates lies in an additional, but marginal, correlation between updating and the high-load PM condition. The association of distinct cognitive functions, as well as shared mechanisms with event- and time-based PM, confirm that each type of PM relies on a different set of processes.

Local brain atrophy accounts for functional activity differences in normal aging

Functional brain imaging studies of normal aging typically show age-related under- and overactivations during episodic memory tasks. Older individuals also undergo nonuniform gray matter volume (GMv) loss. Thus, age differences in functional brain activity could at least in part result from local atrophy. We conducted a series of voxel-based blood oxygen level-dependent (BOLD)-GMv analyses to highlight whether age-related under- and overrecruitment was accounted for by GMv changes. Occipital GMv loss accounted for underrecruitment at encoding. Efficiency reduction of sensory-perceptual mechanisms underpinned by these areas may partly be due to local atrophy. At retrieval, local GMv loss accounted for age-related overactivation of left dorsolateral prefrontal cortex, but not of left dorsomedial prefrontal cortex. Local atrophy also accounted for age-related overactivation in left lateral parietal cortex. Activity in these frontoparietal regions correlated with performance in the older group. Atrophy in the overrecruited regions was modest in comparison with other regions as shown by a between-group voxel-based morphometry comparison. Collectively, these findings link age-related structural differences to age-related functional under- as well as overrecruitment.

Neurocognitive systems related to real-world prospective memory

Background

Prospective memory (PM) denotes the ability to remember to perform actions in the future. It has been argued that standard laboratory paradigms fail to capture core aspects of PM.

Methodology/Principal Findings

We combined functional MRI, virtual reality, eye-tracking and verbal reports to explore the dynamic allocation of neurocognitive processes during a naturalistic PM task where individuals performed errands in a realistic model of their residential town. Based on eye movement data and verbal reports, we modeled PM as an iterative loop of five sustained and transient phases: intention maintenance before target detection (TD), TD, intention maintenance after TD, action, and switching, the latter representing the activation of a new intention in mind. The fMRI analyses revealed continuous engagement of a top-down fronto-parietal network throughout the entire task, likely subserving goal maintenance in mind. In addition, a shift was observed from a perceptual (occipital) system while searching for places to go, to a mnemonic (temporo-parietal, fronto-hippocampal) system for remembering what actions to perform after TD. Updating of the top-down fronto-parietal network occurred at both TD and switching, the latter likely also being characterized by frontopolar activity.

Conclusion/Significance

Taken together, these findings show how brain systems complementary interact during real-world PM, and support a more complete model of PM that can be applied to naturalistic PM tasks and that we named PROspective MEmory DYnamic (PROMEDY) model because of its dynamics on both multi-phase iteration and the interactions of distinct neurocognitive networks.

Preserved hippocampus activation in normal aging as revealed by fMRI

The hippocampus is deteriorated in various pathologies such as Alzheimer's disease (AD) and such deterioration has been linked to memory impairment. By contrast, the structural and functional effects of normal aging on the hippocampus is a matter of debate, with some findings suggesting deterioration and others providing evidence of preservation. This constitutes a crucial question since many investigations on AD are based on the assumption that the deterioration of the hippocampus is the breaking point between normal and pathological aging. A growing number of fMRI studies specifically aimed at investigating hippocampal engagement in various cognitive tasks, notably memory tasks, but the results have been inconclusive. Here, we optimized the episodic face-name paired-associates task in order to test the functioning of the hippocampus in normal aging. Critically, we found no difference in the activation of the hippocampus between the young and a group of older participants. Analysis of individual patterns of activation substantiated this impression. Collectively, these findings provide evidence of preserved hippocampal functioning in normal aging.

Structural and metabolic correlates of episodic memory in relation to the depth of encoding in normal aging

This study set out to establish the relationship between changes in episodic memory retrieval in normal aging on the one hand and gray matter volume and (18)FDG uptake on the other. Structural MRI, resting-state (18)FDG-PET, and an episodic memory task manipulating the depth of encoding and the retention interval were administered to 46 healthy subjects divided into three groups according to their age (young, middle-aged, and elderly adults). Memory decline was found not to be linear in the course of normal aging: Whatever the retention interval, the retrieval of shallowly encoded words was impaired in both the middle-aged and the elderly, whereas the retrieval of deeply encoded words only declined in the elderly. In middle-aged and elderly subjects, the reduced performance in the shallow encoding condition was mainly related to posterior mediotemporal volume and metabolism. By contrast, the impaired retrieval of deeply encoded words in the elderly group was mainly related to frontal and parietal regions, suggesting the adoption of inefficient strategic processes.

Voxel-based mapping of brain gray matter volume and glucose metabolism profiles in normal aging

With age, the brain undergoes both structural and functional alterations, probably resulting in reported cognitive declines. Relatively few investigations have sought to identify those areas that remain intact with aging, or undergo the least deterioration, which might underlie cognitive preservations. Our aim here was to establish a comprehensive profile of both structural and functional changes in the aging brain, using up-to-date voxel-based methodology (i.e. optimized voxel-based morphometry (VBM) procedure; resting-state (18)FDG-PET with correction for partial volume effects (PVE)) in 45 optimally healthy subjects aged 20-83 years. Negative and positive correlations between age and both gray matter (GM) volume and (18)FDG uptake were assessed. The frontal cortex manifested the greatest deterioration, both structurally and functionally, whereas the anterior hippocampus, the thalamus and (functionally) the posterior cingulate cortex were the least affected. Our results support the developmental theory which postulates that the first regions to emerge phylogenetically and ontogenetically are the most resistant to age effects, and the last ones the most vulnerable. Furthermore, the lesser affected anterior hippocampal region, together with the lesser functional alteration of the posterior cingulate cortex, appear to mark the parting of the ways between normal aging and Alzheimer's disease, which is characterized by early and prominent deterioration of both structures.

Working memory and FDG–PET dissociate early and late onset Alzheimer disease patients

The aims of this study were to determine the influence of the onset of Alzheimer's disease (AD) on 1) memory and cerebral glucose metabolism, 2) the relationships between cognitive performance and cerebral glucose metabolism. Brain metabolism was measured by 18FDG-PET in 12 early onset AD patients (age < 65 years) and 26 late onset ones (> 65), with comparable mean MMSE scores. Working memory, semantic memory and episodic memory were assessed. Cognitivo-metabolic correlations (CMC) and complementary interregional correlations were performed in order to identify specific neurocognitive processes within each group. Both AD groups performed poorly on all tasks, except digit span in the late onset group. The early onset group performed more poorly than the late onset one on both the digit span and Brown-Peterson Paradigm (BPP) tasks. Temporo-parietal hypometabolism was found in both groups, the left hemisphere being more affected than the right, especially in the early onset patients, who also showed specific left frontal hypometabolism. For the BPP task, the CMC principally involved left frontal areas in the early onset group, and the cerebellum in the late onset one. For the digit span task, they involved cerebellar and occipital regions in the latter. Regarding the digit span, the occipital and cerebellar involvement may have reflected an effective compensatory mechanism in the late onset patients, while high left supramarginal gyrus hypometabolism in the early onset patients may have explained their failure in this task. In the BPP task, the lower performance of the early onset group may have been due to a frontal lobe dysfunction, as suggested by 1) the hypometabolism of this region, 2) the CMC results, 3) the interregional correlations, which indicated greater disruption of the antero- posterior loop.

Immunophenotype, ras oncogenes and p53 onco-suppressor gene in benzo(a)pyrene induced malignant soft tissue tumours in Wistar rats

This study was designed to identify the immunophenotypic characteristics of malignant soft tissue tumours, induced experimentally with benzo(a)pyrene (BaP), and to evaluate the immunohistochemical expression of the ras oncogene family and p53 onco-suppressor gene in these tumours, in association with prognostic factors. Seventy-five male Wistar rats were subcutaneous injected, dorsally, with a single dose of 10.08 mgr BaP. A solid, well-circumscribed tumour was formed at the injection site, in 70 of the animals, 80-100 days after the carcinogen's administration. The tumour as well as selected main organs were excised and studied after the animals' death. All the specimens were fixed in formalin 10%, embedded in paraffin and stained with H + E. The immunohistochemical avidin-biotin method was performed in the tumour sections, using the following monoclonal or polyclonal antibodies: vimentin, desmin, muscle specific actin (MSA), a-smooth muscle actin (SMA), myoglobin, smooth muscle myosin, a-1-antitrypsin, a-1-antichymotrypsin, S-100 protein, epithelial membrane antigen (EMA), K-ras, H-ras, Pan-ras and p53. The induced tumours of the animals were almost well-circumscribed, with a partly storiform cut surface. Histologically, their appearance was more conventional with high grade leiomyosarcomas; about half of them showed highly anaplastic areas, resembling other pleomorphic undifferentiated sarcomas. Pulmonary metastatic foci were detected in 37 animals. Immunohistochemically, all the tumours displayed positive expression of vimentin, MSA and SMA. Desmin was positively expressed in 40 tumours, smooth muscle myosin in 57 tumours and EMA in 12 tumours. All the tumours were negative for myoglobin, a-1-antitrypsin, a-1-antichymotrypsin and S-100 protein. In addition, five tumours showed a positive reaction for K-ras p21, 37 for H-ras p21, 41 for Pan-ras p21 and 14 for p53 protein. The overexpression of the oncoproteins H-ras p21 and Pan-ras p21 in these tumours was significantly associated with a non-advanced tumour stage (absence of metastatic focus). In conclusion, the histological as well as the immunophenotypic features of the induced tumours are more conventional with leiomyosarcomas mostly of high grade; many of them are "dedifferentiated". The identification of both ras and p53 gene products in these tumours indicates that alterations of these genes are common but not specific events, implicated in the tumourigenesis, which may become prognostic markers for this subtype of soft tissue sarcomas.

Comparison of the therapeutic effects of two vanadium complexes administered at low dose on benzo[a]pyrene-induced malignant tumors in rats

The antitumor effects of low dose administration of the vanadium(III) complexes with L-cysteine (complex 1) and N-(2-mercaptopropionyl)-glycine (complex 2) were compared on benzo[a]pyrene (BaP)-induced tumors in Wistar rats. Male Wistar rats, injected with 10.0 mg of BaP, were divided into one control (C-G) and two treatment (TR-G) groups of 17 animals each. Animals of the first treatment group were administered complex 2 (TR-2 group) and those of the second group were administered complex 1 (TR-1 group) at doses of 100 microg of vanadium per os daily, starting from the day a palpable tumor was developed till their death. BaP injection induced a 100% tumor (leiomyosarcomas) development in the animals of all groups. Administration of complex 1 to the animals resulted in a significant prolongation of the mean survival time, a complete remission of 17.6% of the tumors developed, a significant reduction of the carcinogenic potency (CP) of BaP and of the tumor growth rate (TGR) in TR-1 group animals, compared to the control and the TR-2 group. In marked contrast, complex 2 failed at the doses administered to exert any significant modulation of the above mentioned parameters. Results indicate that at low (100 micro/day) concentrations of vanadium, complex 1 exerts a significant anticarcinogenic effect on experimentally-induced leiomyosarcomas in rats, whereas complex 2 has no effect when administered at the same low concentrations of vanadium.

Dose-related preventive and therapeutic effects of antioxidants-anticarcinogens on experimentally induced malignant tumors in Wistar rats

A combination of antioxidants-anticarcinogens, consisting of vitamins C and E, selenium and 2-mercaptopropionyl glycine (2-MPG), was administered orally for the prevention (PRG) and treatment (TRG) of benzo(a)pyrene (BaP)-induced malignant tumors (leiomyosarcomas), in Wistar rats. In order to evaluate dose-related effects, a low dose vitamin (0.15 g/kg b.w. per day of vit.C and 0.05 g/kg b.w. per day of vit.E) and a high dose (1.5 g/kg b.w. per day of vit.C and 0.5 g/kg b.w. per day of vit.E) combination was administered, in prevention and treatment groups. Selenium was administered in doses of 2 microg/kg b.w. per day and 2-MPG in 15 mg/kg b.w. per day, in all groups. Daily estimations of 24 h urine volume levels of thiobarbituric acid reacting substances (MDA) were performed in 20 animals, divided into a control group, a BaP-injected group, a tricapryline-injected group and a BaP-injected and treated by the low dose combination group. Results revealed that the low dose combination failed to exert any beneficial effect on mean survival time of animals treated either preventitively or therapeutically. An increased number of animals bearing a second (lung) tumor was, in addition, found in autopsy and histological examination in the low dose combination (PRG and TRG) and the high dose TRG groups. The high dose combination groups manifested a significant prolongation of the mean survival time of animals; complete remission of tumors developed in 16.8% of the animals in the treatment group and a 5.2% prevention of tumor formation in the preventive group, without any evidence of an increased number of double tumor formation in the PRG group. Urine MDA increased significantly in animals injected by BaP during the first 10 days and since the 90th day (formation of palpable tumors) after injection, in relation to control and tricapryline-injected groups. Complete prevention of urine MDA-increased values was obtained in BaP-injected and treated by the low dose combination animals. Results indicate that high doses (megadoses) of the antioxidant-anticarcinogen vitamins C and E in combination with carefully selected other antioxidants possessing supplementary actions, are probably needed in order to achieve a sufficient prevention and treatment of malignant diseases.