Brain plasticity: to what extent do aged animals retain the capacity to coordinate gene activity in response to acute challenges

Clear-headed into old age: Resilience and resistance against brain aging-A PET imaging perspective

With the advances in modern medicine and the adaptation towards healthier lifestyles, the average life expectancy has doubled since the 1930s, with individuals born in the millennium years now carrying an estimated life expectancy of around 100 years. And even though many individuals around the globe manage to age successfully, the prevalence of aging-associated neurodegenerative diseases such as sporadic Alzheimer's disease has never been as high as nowadays. The prevalence of Alzheimer's disease is anticipated to triple by 2050, increasing the societal and economic burden tremendously. Despite all efforts, there is still no available treatment defeating the accelerated aging process as seen in this disease. Yet, given the advances in neuroimaging techniques that are discussed in the current Review article, such as in positron emission tomography (PET) or magnetic resonance imaging (MRI), pivotal insights into the heterogenous effects of aging-associated processes and the contribution of distinct lifestyle and risk factors already have and are still being gathered. In particular, the concepts of resilience (i.e. coping with brain pathology) and resistance (i.e. avoiding brain pathology) have more recently been discussed as they relate to mechanisms that are associated with the prolongation and/or even stop of the progressive brain aging process. Better understanding of the underlying mechanisms of resilience and resistance may one day, hopefully, support the identification of defeating mechanism against accelerating aging.

Occupational Neuroplasticity in the Human Brain: A Critical Review and Meta-Analysis of Neuroimaging Studies

Many studies have revealed the structural or functional brain changes induced by occupational factors. However, it remains largely unknown how occupation-related connectivity shapes the brain. In this paper, we denote occupational neuroplasticity as the neuroplasticity that takes place to satisfy the occupational requirements by extensively professional training and to accommodate the long-term, professional work of daily life, and a critical review of occupational neuroplasticity related to the changes in brain structure and functional networks has been primarily presented. Furthermore, meta-analysis revealed a neurophysiological mechanism of occupational neuroplasticity caused by professional experience. This meta-analysis of functional neuroimaging studies showed that experts displayed stronger activation in the left precentral gyrus [Brodmann area (BA)6], left middle frontal gyrus (BA6), and right inferior frontal gyrus (BA9) than novices, while meta-analysis of structural studies suggested that experts had a greater gray matter volume in the bilateral superior temporal gyrus (BA22) and right putamen than novices. Together, these findings not only expand the current understanding of the common neurophysiological basis of occupational neuroplasticity across different occupations and highlight some possible targets for neural modulation of occupational neuroplasticity but also provide a new perspective for occupational science research.

Vulnerability and resilience to Alzheimer's disease: early life conditions modulate neuropathology and determine cognitive reserve

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a high prevalence among the elderly and a huge personal and societal impact. Recent epidemiological studies have indicated that the incidence and age of onset of sporadic AD can be modified by lifestyle factors such as education, exercise, and (early) stress exposure. Early life adversity is known to promote cognitive decline at a later age and to accelerate aging, which are both primary risk factors for AD. In rodent models, exposure to 'negative' or 'positive' early life experiences was recently found to modulate various measures of AD neuropathology, such as amyloid-beta levels and cognition at later ages. Although there is emerging interest in understanding whether experiences during early postnatal life also modulate AD risk in humans, the mechanisms and possible substrates underlying these long-lasting effects remain elusive.

METHODS

We review literature and discuss the role of early life experiences in determining later age and AD-related processes from a brain and cognitive 'reserve' perspective. We focus on rodent studies and the identification of possible early determinants of later AD vulnerability or resilience in relation to early life adversity/enrichment.

RESULTS

Potential substrates and mediators of early life experiences that may influence the development of AD pathology and cognitive decline are: programming of the hypothalamic-pituitary-adrenal axis, priming of the neuroinflammatory response, dendritic and synaptic complexity and function, overall brain plasticity, and proteins such as early growth response protein 1 (EGR1), activity regulated cytoskeleton-associated protein (Arc), and repressor element-1 silencing transcription factor (REST).

CONCLUSIONS

We conclude from these rodent studies that the early postnatal period is an important and sensitive phase that influences the vulnerability to develop AD pathology. Yet translational studies are required to investigate whether early life experiences also modify AD development in human studies, and whether similar molecular mediators can be identified in the sensitivity to develop AD in humans.

Dance training is superior to repetitive physical exercise in inducing brain plasticity in the elderly

Animal research indicates that a combination of physical activity and sensory enrichment has the largest and the only sustaining effect on adult neuroplasticity. Dancing has been suggested as a human homologue to this combined intervention as it poses demands on both physical and cognitive functions. For the present exploratory study, we designed an especially challenging dance program in which our elderly participants constantly had to learn novel and increasingly difficult choreographies. This six-month-long program was compared to conventional fitness training matched for intensity. An extensive pre/post-assessment was performed on the 38 participants (63-80 y), covering general cognition, attention, memory, postural and cardio-respiratory performance, neurotrophic factors and-most crucially-structural MRI using an exploratory analysis. For analysis of MRI data, a new method of voxel-based morphometry (VBM) designed specifically for pairwise longitudinal group comparisons was employed. Both interventions increased physical fitness to the same extent. Pronounced differences were seen in the effects on brain volumes: Dancing compared to conventional fitness activity led to larger volume increases in more brain areas, including the cingulate cortex, insula, corpus callosum and sensorimotor cortex. Only dancing was associated with an increase in plasma BDNF levels. Regarding cognition, both groups improved in attention and spatial memory, but no significant group differences emerged. The latter finding may indicate that cognitive benefits may develop later and after structural brain changes have taken place. The present results recommend our challenging dance program as an effective measure to counteract detrimental effects of aging on the brain.

Loss of MAP function leads to hippocampal synapse loss and deficits in the Morris Water Maze with aging

Hyperphosphorylation and accumulation of tau aggregates are prominent features in tauopathies, including Alzheimer's disease, but the impact of loss of tau function on synaptic and cognitive deficits remains poorly understood. We report that old (19-20 months; OKO) but not middle-aged (8-9 months; MKO) tau knock-out mice develop Morris Water Maze (MWM) deficits and loss of hippocampal acetylated α-tubulin and excitatory synaptic proteins. Mild motor deficits and reduction in tyrosine hydroxylase (TH) in the substantia nigra were present by middle age, but did not affect MWM performance, whereas OKO mice showed MWM deficits paralleling hippocampal deficits. Deletion of tau, a microtubule-associated protein (MAP), resulted in increased levels of MAP1A, MAP1B, and MAP2 in MKO, followed by loss of MAP2 and MAP1B in OKO. Hippocampal synaptic deficits in OKO mice were partially corrected with dietary supplementation with docosahexaenoic acid (DHA) and both MWM and synaptic deficits were fully corrected by combining DHA with α-lipoic acid (ALA), which also prevented TH loss. DHA or DHA/ALA restored phosphorylated and total GSK3β and attenuated hyperactivation of the tau C-Jun N-terminal kinases (JNKs) while increasing MAP1B, dephosphorylated (active) MAP2, and acetylated α-tubulin, suggesting improved microtubule stability and maintenance of active compensatory MAPs. Our results implicate the loss of MAP function in age-associated hippocampal deficits and identify a safe dietary intervention, rescuing both MAP function and TH in OKO mice. Therefore, in addition to microtubule-stabilizing therapeutic drugs, preserving or restoring compensatory MAP function may be a useful new prevention strategy.

Efficiency, capacity, compensation, maintenance, plasticity: emerging concepts in cognitive reserve

Cognitive reserve (CR) is a concept meant to account for the frequent discrepancy between an individual's measured level of brain pathology and her expected cognitive performance. It is particularly important within the context of aging and dementia, but has wider applicability to all forms of brain damage. As such, it has intimate links to related compensatory and neuroprotective concepts, as well as to the related notion of brain reserve. In this article, we introduce the concept of cognitive reserve and explicate its potential cognitive and neural implementation. We conclude that cognitive reserve is compatible and complementary with many related concepts, but that each much draw sharper conceptual boundaries in order to truly explain preserved cognitive function in the face of aging or brain damage.

Post-stroke depression and the aging brain

Ageing is associated with changes in the function of various organ systems. Changes in the cardiovascular system affect both directly and indirectly the function in a variety of organs, including the brain, with consequent neurological (motor and sensory performance) and cognitive impairments, as well as leading to the development of various psychiatric diseases. Post-stroke depression (PSD) is among the most frequent neuropsychiatric consequences of cerebral ischemia. This review discusses several animal models used for the study of PSD and summarizes recent findings in the genomic profile of the ageing brain, which are associated with age-related disorders in the elderly. Since stroke and depression are diseases with increased incidence in the elderly, great clinical benefit may especially accrue from deciphering and targeting basic mechanisms underlying PSD. Finally, we discuss the relationship between ageing, circadian rhythmicity and PSD.

Structural brain plasticity in adult learning and development

Recent research using magnetic resonance imaging has documented changes in the adult human brain's grey matter structure induced by alterations in experiential demands. We review this research and relate it to models of brain plasticity from related strands of research, such as work on animal models. This allows us to generate recommendations and predictions for future research that may advance the understanding of the function, sequential progression, and microstructural nature of experience-dependent changes in regional brain volumes. Informed by recent evidence on adult age differences in structural brain plasticity, we show how understanding learning-related changes in human brain structure can expand our knowledge about adult development and aging. We hope that this review will promote research on the mechanisms regulating experience-dependent structural plasticity of the adult human brain.

Spatial behavior and seizure-induced changes in c-fos mRNA expression in young and old rats

The subcellular processes of gene induction and expression in the hippocampus are likely to underlie some of the known age-related impairments in spatial learning and memory. It is well established that immediate-early genes are rapidly and transiently induced in response to neuronal activity and this expression is required for stabilization of durable memories. To examine whether age-related memory impairment might be caused, in part, by differences in the level of cellular activation or subcellular processing, c-fos expression in CA1 pyramidal and dentate gyrus granule cells in the dorsal hippocampus of young and old rats was determined using fluorescence in situ hybridization and reverse transcription polymerase chain reaction. No significant age differences were found in the numbers of pyramidal or granule cells that show c-fos expression; however, c-fos mRNA transcripts were altered in these 2 cell types in aged animals. These findings suggest that though the networks of cells that participate in behavior or seizure-induced activity are largely maintained in aged rats, their RNA transcript levels are altered. This might, in part, contribute to cognitive deficits frequently observed with advancing age.

Structural and functional imaging correlates of cognitive and brain reserve hypotheses in healthy and pathological aging

In the field of ageing and dementia, brain- or cognitive reserve refers to the capacity of the brain to manage pathology or age-related changes thereby minimizing clinical manifestations. The brain reserve capacity (BRC) hypothesis argues that this capacity derives from an individual's unique neural profile (e.g., cell count, synaptic connections, brain volume, etc.). Complimentarily, the cognitive reserve (CR) hypothesis emphasizes inter-individual differences in the effective recruitment of neural networks and cognitive processes to compensate for age-related effects or pathology. Despite an abundance of research, there is scarce literature attempting to synthesize the BRC the CR models. In this paper, we will review important aging and dementia studies using structural and functional neuroimaging techniques to investigate and attempt to assimilate both reserve hypotheses. The possibility to conceptualize reserve as reflecting indexes of brain plasticity will be proposed and novel data suggesting an intimate and complex correspondence between active and passive components of reserve will be presented.

'When an old rat smells a cat': A decline in defense-related, but not accessory olfactory, Fos expression in aged rats

Comparisons were made between young (3-6 months) and aged (20-30 months) Wistar rats on locomotor activity, emergence, social interaction and cat odor avoidance. Aged rats were less active and spent less time in the open field during the emergence test than younger rats. Older rats also showed fewer contacts with a novel conspecific in the social interaction test, although total duration of interaction did not differ. There were very few behavioral differences between male and female rats. Older rats were less reactive than younger rats in a test of cat odor avoidance. However, they expressed similar amounts of cat odor-induced Fos in the posterior accessory olfactory bulb, a critical region for processing the predator odor stimulus. Older rats had reduced Fos expression in several defense-related brain regions that are normally activated by predator odors such as the medial amygdala and dorsal premammillary nucleus. These results indicate that aged rats are less reactive than younger rats to predator odors due to decreased responsiveness in defense-related but not necessarily olfactory circuits.

Training-induced brain structure changes in the elderly

It has been suggested that learning is associated with a transient and highly selective increase in brain gray matter in healthy young volunteers. It is not clear whether and to what extent the aging brain is still able to exhibit such structural plasticity. We built on our original study, now focusing on healthy senior citizens. We observed that elderly persons were able to learn three-ball cascade juggling, but with less proficiency compared with 20-year-old adolescents. Similar to the young group, gray-matter changes in the older brain related to skill acquisition were observed in area hMT/V5 (middle temporal area of the visual cortex). In addition, elderly volunteers who learned to juggle showed transient increases in gray matter in the hippocampus on the left side and in the nucleus accumbens bilaterally.

Dietary restriction modulates alpha-synuclein expression in the aging rat cortex and hippocampus

Dietary restriction (DR) is one of the promising environmental interventions known to attenuate aging and decrease risk of age-related neurodegenerative disorders. The aim of this study was to assess the effects of DR on expression of alpha-synuclein, a presynaptic protein involved in pathogenesis of Parkinson's and some other neurodegenerative diseases, in the cortex and hippocampus of adult, middle-aged, late middle-aged, and aged rats. Using Real Time RT-PCR, the authors report that aging regulates the expression of alpha-synuclein in a tissue-specific manner and that long-term DR reverts the late age-related changes of alpha-synuclein expression.

Microtubule-associated protein 1B, a growth-associated and phosphorylated scaffold protein

Microtubule-associated protein 1B, MAP1B, is one of the major growth associated and cytoskeletal proteins in neuronal and glial cells. It is present as a full length protein or may be fragmented into a heavy chain and a light chain. It is essential to stabilize microtubules during the elongation of dendrites and neurites and is involved in the dynamics of morphological structures such as microtubules, microfilaments and growth cones. MAP1B function is modulated by phosphorylation and influences microtubule stability, microfilaments and growth cone motility. Considering its large size, several interactions with a variety of other proteins have been reported and there is increasing evidence that MAP1B plays a crucial role in the stability of the cytoskeleton and may have other cellular functions. Here we review molecular and functional aspects of this protein, evoke its role as a scaffold protein and have a look at several pathologies where the protein may be involved.

Clinical prospects for neural grafting therapy for hippocampal lesions and epilepsy

OBJECTIVE

Hippocampal lesions and epilepsy may be potential clinical targets for neural grafting. We hypothesized that neural grafting could be a restorative therapy either acutely, adding unformed neural elements, or chronically, treating postlesioning epilepsy. The goal of this review was to assess the clinical reality of this hypothesis of neural grafting and to determine the problems that remain to be resolved before grafting can be applied clinically.

METHODS

We quantitatively defined graft integration within the host, on a cellular basis, by directly assessing survival of the transplanted neurons, graft cell dispersion and migration, neuronal differentiation and development, and establishment of appropriate local and long-distance synaptic connectivity.

RESULTS

Embryonic hippocampal suspension grafts demonstrate excellent survival rates (20-80%). Embryonic axons exhibit extensive, appropriate, local and long-distance connectivity, can facilitate reconstruction of excitatory and inhibitory cortical circuitry, and can prevent the formation of aberrant circuitry. Immature neural stem cells demonstrate lesser degrees of integration, likely because of a paucity of positional cues in the lesioned brain for the differentiation of stem cells into region-specific neuronal phenotypes. Labeled grafted cells may be selectively and noninvasively removed from the host with triggerable stealth toxins, for the late treatment of unanticipated graft problems.

CONCLUSION

Neural grafting with appropriate embryonic neurons may provide significant clinical benefits. However, embryonic cell availability is severely limited, and alternative sources of cells, such as stem cells, require significant additional research into the induction and maintenance of neuronal commitment and the ability of the cells to form functional synaptic connections in vivo.

17beta-Estradiol increases, aging decreases, c-Fos expression in the rat accessory olfactory bulb

In the present paper we investigated the c-Fos immunoreactivity in the accessory olfactory bulb (AOB) of juvenile, adult and old rats of both sexes, as well as the effect of 17beta-estradiol on the expression of this immediate early gene. Basal c-Fos expression in the olfactory bulb decreased with age, and estrogen treatment caused an increase in the number of neurons expressing c-Fos in the AOB. The results indicate that both aging and estrogen have roles in the ability of neurons to co-ordinate genetic activity. Our observations may explain the decrease in age-related changes of brain plasticity, and provide data for the understanding of hormonally regulated neuronal plasticity.