Ageing and the brain

Age- and hormone-regulation of opioid peptides and synaptic proteins in the rat dorsal hippocampal formation

Circulating estrogen levels and hippocampal-dependent cognitive functions decline with aging. Moreover, the responses of hippocampal synaptic structure to estrogens differ between aged and young rats. We recently reported that estrogens increase levels of post-synaptic proteins, including PSD-95, and opioid peptides leu-enkephalin and dynorphin in the hippocampus of young animals. However, the influence of ovarian hormones on synaptic protein and opioid peptide levels in the aging hippocampus is understudied. Here, young (3- to 5-month-old), middle-aged (9- to 12-month-old), and aged (about 22-month-old) female rats were ovariectomized and then, 4 weeks later, subcutaneously implanted with a silastic capsule containing vehicle or 17β-estradiol. After 48 h, rats were subcutaneously injected with progesterone or vehicle and sacrificed 1 day later. Coronal sections through the dorsal hippocampus were processed for quantitative peroxidase immunohistochemistry of leu-enkephalin, dynorphin, synaptophysin, and PSD-95. With age, females showed opposing changes in leu-enkephalin and dynorphin levels in the mossy fiber pathway, particularly within the hilus, and regionally specific changes in synaptic protein levels. 17β-estradiol, with or without progesterone, altered leu-enkephalin levels in the dentate gyrus and synaptophysin levels in the CA1 of young but not middle-aged or aged females. Additionally, 17β-estradiol decreased synaptophysin levels in the CA3 of middle-aged females. Our results support and extend previous findings indicating 17β-estradiol modulation of hippocampal opioid peptides and synaptic proteins while demonstrating regional and age-specific effects. Moreover, they lend credence to the "window of opportunity" hypothesis during which hormone replacement can modulate hippocampal structure and circuitry to improve cognitive outcomes.

Proteasome activity and biological properties of normal prion protein: a comparison between young and aged cattle

Atypical bovine spongiform encephalopathy (atypical BSE) has recently been identified in several countries including Japan. Most cases of atypical BSE have been reported in cattle older than 8 years of age. To clarify the association between age and occurrence of atypical BSE, we investigated both the physiological properties and amount of cellular prion protein (PrP(C)) in brain homogenates from young and aged cattle by enzyme-linked immunosorbent assay and immunoblotting. The amount of PrP(C) in the brain homogenates was not significantly different between young and aged cattle, but the amount in the detergent-insoluble fraction in the aged cattle was significantly higher than that of young cattle. Significant differences were observed in neither of the glycosylation forms nor in proteinase K sensitivity in young and aged cattle. Age-related changes included deposition of lipofuscin pigment and a decrease of 33% in proteasome activity in the brains of aged cattle compared to that of young cattle.

Differential protection among fractionated blueberry polyphenolic families against DA-, Abeta(42)- and LPS-induced decrements in Ca(2+) buffering in primary hippocampal cells

It has been postulated that at least part of the loss of cognitive function in aging may be the result of deficits in Ca(2+) recovery (CAR) and increased oxidative/inflammatory (OX/INF) stress signaling. However, previous research showed that aged animals supplemented with blueberry (BB) extract showed fewer deficits in CAR, as well as motor and cognitive functional deficits. A recent subsequent experiment has shown that DA- or Abeta(42)-induced deficits in CAR in primary hippocampal neuronal cells (HNC) were antagonized by BB extract, and (OX/INF) signaling was reduced. The present experiments assessed the most effective BB polyphenol fraction that could protect against OX/INF-induced deficits in CAR, ROS generation, or viability. HNCs treated with BB extract, BB fractions (e.g., proanthocyanidin, PAC), or control medium were exposed to dopamine (DA, 0.1 mM), amyloid beta (Abeta(42), 25 muM) or lipopolysaccharide (LPS, 1 microg/mL). The results indicated that the degree of protection against deficits in CAR varied as a function of the stressor and was generally greater against Abeta(42) and LPS than DA. The whole BB, anthocyanin (ANTH), and PRE-C18 fractions offered the greatest protection, whereas chlorogenic acid offered the lowest protection. Protective capabilities of the various fractions against ROS depended upon the stressor, where the BB extract and the combined PAC (high and low molecular weight) fraction offered the best protection against LPS and Abeta(42) but were less effective against DA-induced ROS. The high and low molecular weight PACs and the ANTH fractions enhanced ROS production regardless of the stressor used, and this reflected increased activation of stress signals (e.g., P38 MAPK). The viability data indicated that the whole BB and combined PAC fraction showed greater protective effects against the stressors than the more fractionated polyphenolic components. Thus, these results suggest that, except for a few instances, the lesser the polyphenolic fractionation, the greater the effects, especially with respect to prevention of ROS and stress signal generation and viability.

Sirtuin activators: designing molecules to extend life span

Resveratrol (RESV) exerts important pharmacological effects on human health: in addition to its beneficial effects on type 2 diabetes and cardiovascular diseases, it also modulates neuronal energy homeostasis and shows antiaging properties. Although it clearly has free radical scavenger properties, the mechanisms involved in these beneficial effects are not fully understood. In this regard, one area of major interest concerns the effects of RESV on the activity of sirtuin 1 (SIRT1), an NAD(+)-dependent histone deacetylase that has been implicated in aging. Indeed, the role of SIRT1 is currently the subject of intense research due to the antiaging properties of RESV, which increases life span in various organisms ranging from yeast to rodents. In addition, when RESV is administered in experimental animal models of neurological disorders, it has similar beneficial effects to caloric restriction. SIRT1 activation could thus constitute a potential strategic target in neurodegenerative diseases and in disorders involving disturbances in glucose homeostasis, as well as in dyslipidaemias or cardiovascular diseases. Therefore, small SIRT1 activators such as SRT501, SRT2104, and SRT2379, which are currently undergoing clinical trials, could be potential drugs for the treatment of type 2 diabetes, obesity, and metabolic syndrome, among other disorders. This review summarises current knowledge about the biological functions of SIRT1 in aging and aging-associated diseases and discusses its potential as a pharmacological target.

Brain injury and recovery following binge ethanol: evidence from in vivo magnetic resonance spectroscopy

BACKGROUND

The binge-drinking model in rodents using intragastric injections of ethanol (EtOH) for 4 days results in argyrophilic corticolimbic tissue classically interpreted as indicating irreversible neuronal degeneration. However, recent findings suggest that acquired argyrophilia can also identify injured neurons that have the potential to recover. The current in vivo magnetic resonance (MR) imaging and spectroscopy study was conducted to test the hypothesis that binge EtOH exposure would injure but not cause the death of neurons as previously ascertained postmortem.

METHODS

After baseline MR scanning, 11 of 19 rats received a loading dose of 5 g/kg EtOH via oral gavage, then a maximum of 3 g/kg every 8 hours for 4 days, for a total average cumulative EtOH dose of 43 +/- 1.2 g/kg and average blood alcohol levels of 258 +/- 12 mg/dL. All animals were scanned after 4 days of gavage (post-gavage scan) with EtOH (EtOH group) or dextrose (control [Con] group) and again after 7 days of abstinence from EtOH (recovery scan).

RESULTS

Tissue shrinkage at the post-gavage scan was reflected by significantly increased lateral ventricular volume in the EtOH group compared with the Con group. At the post-gavage scan, the EtOH group had lower dorsal hippocampal N-acetylaspartate and total creatine and higher choline-containing compounds than the Con group. At the recovery scan, neither ventricular volume nor metabolite levels differentiated the groups.

CONCLUSIONS

Rapid recovery of ventricular volume and metabolite levels with removal of the causative agent argues for transient rather than permanent effects of a single EtOH binge episode in rats.

Diet and age interactions with regards to cholesterol regulation and brain pathogenesis

Cholesterol is an essential molecule for brain homeostasis; yet, hypercholesterolemia and its numerous complications are believed to play a role in promoting multiple aspects of brain pathogenesis. An ever increasing number of individuals in modern Western Society are regularly consuming diets high in fat which promote the development of hypercholesterolemia. Additionally, modern societies are becoming increasingly aged, causing a collision between increased hypercholesterolemia and increased aging, which will likely lead to the development of increased pathological conditions due to hypercholesterolemia, thereby promoting deleterious neurochemical and behavioral changes in the brain. Lastly, while beneficial in controlling cholesterol levels, the long-term use of statins itself may potentially promote adverse effects on brain homeostasis, although specifics on this remain largely unknown. This review will focus on linking the current understanding of diet-induced hypercholesterolemia (as well as statin use) to the development of oxidative stress, neurochemical alterations, and cognitive disturbances in the aging brain.

Ischemic stroke in the elderly: an overview of evidence

Stroke mostly occurs in elderly people and patient outcomes after stroke are highly influenced by age. A better understanding of the causes of stroke in the elderly might have important practical implications not only for clinical management, but also for preventive strategies and future health-care policies. In this Review, we explore the evidence from both human and animal studies relating to the effect of old age-in terms of susceptibility, patient outcomes and response to treatment-on ischemic stroke. Several aging-related changes in the brain have been identified that are associated with an increase in vulnerability to ischemic stroke in the elderly. Furthermore, risk factor profiles for stroke and mechanisms of ischemic injury differ between young and elderly patients. Elderly patients with ischemic stroke often receive less-effective treatment and have poorer outcomes than younger individuals who develop this condition. Neuroprotective agents for ischemic stroke have been sought for decades but none has proved effective in humans. One contributing factor for this translational failure is that most preclinical studies have used young animals. Future research on ischemic stroke should consider age as a factor that influences stroke prevention and treatment, and should focus on the management of acute stroke in the elderly to reduce the incidence and improve outcomes in this vulnerable group.

Elevation of CSF albumin in old sheep: relations to CSF turnover and albumin extraction at blood-CSF barrier

Albumin is the most abundant protein in both CSF and plasma, and albumin quotient is often used to assess the functions of brain barriers especially that of the blood-CSF barrier [i.e. the choroid plexus (CP) which also secretes CSF]. In this study, we took albumin as a model molecule to investigate ageing-related alterations in the CSF-CP system in sheep. We found significant ageing-related increases in the weight of lateral CP [122.4 +/- 14.0 mg in the young, 198.6 +/- 35.4 mg in the middle aged, 286.1 +/- 25.1 mg in the old (p < 0.05)], in the CSF albumin as well as the albumin quotient. Albumin protein spots in old CSF displayed wider on 2D western immunoblotting images, and had higher densities on images of 2D large gels stained with Pro-Q Emerald 488 compared to the young samples, suggesting ageing-related post-translational modification in the albumin. CSF secretion was reduced with age: 0.148 +/- 0.013 mL/min/g in the young, 0.092 +/- 0.02 mL/min/g in the middle aged, 0.070 +/- 0.013 mL/min/g in the old (p < 0.05). The (125)I-BSA extraction was not different among the sheep groups, nor was altered by temperature reduction, monensin, nocodazole, anti-transforming growth factor beta receptor II antibody, as well as unlabelled albumins. In conclusion, elevation of albumin in old CSF is associated with reduced CSF secretion by the CP, which size increases with age. (125)I-BSA extract, reflecting the extracellular space rather than the active albumin uptake in the CP, is not different between ages. These early changes in health ageing may result in the accumulation and modifications of CSF proteins leading to neurotoxicity.

Changes in kinetics of amino acid uptake at the ageing ovine blood-cerebrospinal fluid barrier

Amino acids (AA) in brain are precisely controlled by blood-brain barriers, which undergo a host of changes in both morphology and function during ageing. The effect of these age-related changes on AA homeostasis in brain is not well described. This study investigated the kinetics of four AA (Leu, Phe, Ala and Lys) uptakes at young and old ovine choroid plexus (CP), the blood-cerebrospinal fluid (CSF) barrier (BCB), and measured AA concentrations in CSF and plasma samples. In old sheep, the weight of lateral CP increased, so did the ratio of CP/brain. The expansion of the CP is consistent with clinical observation of thicker leptomeninges in old age. AA concentrations in old CSF, plasma and their ratio were different from the young. Both V(max) and K(m) of Phe and Lys were significant higher compared to the young, indicating higher trans-stimulation in old BCB. Cross-competition and kinetic inhibition studies found the sensitivity and specificity of these transporters were impaired in old BCB. These changes may be the first signs of a compromised barrier system in ageing brain leading increased AA influx into the brain causing neurotoxicity.

Mosaic aging

Although all multicellular organisms undergo structural and functional deterioration with age, senescence is not a uniform process. Rather, each organism experiences a constellation of changes that reflect the heterogeneous effects of age on molecules, cells, organs and systems, an idiosyncratic pattern that we refer to as mosaic aging. Varying genetic, epigenetic and environmental factors (local and extrinsic) contribute to the aging phenotype in a given individual, and these agents influence the type and rate of functional decline, as well as the likelihood of developing age-associated afflictions such as cardiovascular disease, arthritis, cancer, and neurodegenerative disorders. Identifying key factors that drive aging, clarifying their activities in different systems, and in particular understanding how they interact will enhance our comprehension of the aging process, and could yield insights into the permissive role that senescence plays in the emergence of acute and chronic diseases of the elderly.

Observation of the density and size of cells in hippocampus and vascular lesion in thalamus of GFAP-apoE transgenic mice

OBJECTIVE

Apolipoprotein E (apoE) is associated with increased risk of age-related diseases, such as Alzheimer's disease (AD) and cerebrovascular disease (CVD). The present study aims to investigate the age-related general morphological changes of the brain in GFAP-apoE transgenic mice, especially the alterations in number and size of hippocampal pyramidal cells and the microvascular lesions in the thalamus.

METHODS

Nine female apoE4/4 mice were divided into 3 groups (n=3 in each group): 3-4 months (young group), 9-10 months (middle-aged group) and 20-21 months (old group). Age-matched apoE3/3 mice were employed as control group (n=3 in each group). The paraffin sections of brain tissue were stained by 2 conventional staining methods, thionin staining and hematoxylin-esion(HE) staining, the former of which was to observe the hippocampal cells, while the latter was used to examine the brain microvasculature.

RESULTS

There was no apparent difference in the cortical layer between apoE3/3 and apoE4/4 mice, neither any significant difference in the number of cells in hippocampal CA1-CA3 subfields between apoE3/3 and apoE4/4 mice at various age points (P>0.05). However, the mean size of pyramidal cells in CA1 subfield in apoE3/3 and apoE4/4 mice decreased as mice were getting older (P<0.001). At the age of 20-21 months, this cellular atrophy in apoE4/4 mice was more severe than that in old apoE3/3 mice (P<0.05). Furthermore, microvascular lesion in the thalamus was detected in all the 3 old apoE4/4 mice, at varying degrees (5.24%, 1.41% and 3.97%, respectively), while only one apoE3/3 mouse exhibited microvascular lesion in the thalamus, at a low level (0.85%).

CONCLUSION

The current study suggests that the cell size in hippocampal CA1 subfield decreases with aging, irrespective of apoE genotype. Cellular atrophy in CA1 subfield and the microvascular lesion in the thalamus are both more severe in old apoE4/4 mice as compared with those in age-matched apoE3/3 mice. Doubts still exist on whether the decreased cell size in hippocampal CA1 subfield in old apoE4/4 mice is associated with dysfunction in learning and memory and whether the microvascular lesions indicate a higher risk of stroke in human apoE4 allele mice. To clarify these issues, further investigations are needed.

Serial susceptibility weighted MRI measures brain iron and microbleeds in dementia

A new iron sensitive MR sequence (susceptibility weighted imaging - SWI) enabling the simultaneous quantitation of regional brain iron levels and brain microbleeds (BMB) has been acquired serially to study dementia. Cohorts of mildly cognitively impaired (MCI) elderly (n = 73) and cognitively normal participants (n = 33) have been serially evaluated for up to 50 months. SWI phase values (putative iron levels) in 14 brain regions were measured and the number of BMB were counted for each SWI study. SWI phase values showed a left putaminal mean increase of iron (decrease of phase values) over the study duration in 27 participants who progressed to dementia compared to Normals (p = 0.035) and stable MCI (p = 0.01). BMB were detected in 9 out of 26 (38%) MCI participants who progressed to dementia and are a significant risk factor for cognitive failure in MCI participants [risk ratio = 2.06 (95% confidence interval 1.37-3.12)]. SWI is useful to measure regional iron changes and presence of BMB, both of which may be important MR-based biomarkers for neurodegenerative diseases.

Age-related physiologic changes and perioperative management of elderly patients

Aging itself only minimally increases operative risk, but with aging, there is an increase of the prevalence of chronic diseases and a progressive deterioration of organ function. Aging is associated with a progressive decrease in heart, lung and kidney performance. Under normal conditions, these physiologic changes do not produce any problems for the elderly, but when these patients are subjected to the stress of surgery or its complications, there may be inadequate functional reserve. It is very important to know age-related patho-physiological changes in order to be able to better evaluate elderly patients undergoing surgery, and to prevent and manage preoperative complications. In this review we try to identify and to describe the most frequent physiological changes in the elderly, how those impact pharmacodynamic and pharmacokinetic parameters, and how to assess and manage them.

Estrogen therapy: is time of initiation critical for neuroprotection?

According to the 'critical period' hypothesis, which attempts to explain the observed discrepancies in the studies on estrogen and cognition, estrogen therapy effectively decreases cognitive decline in aging women when it is initiated around the time of menopause but not when it is started decades later. Here, I review studies in which the timing of the initiation of estrogen therapy was provided, to determine whether their findings support the 'critical period' hypothesis. The vast majority of the reviewed studies support the idea that early but not late initiation of estrogen therapy might prevent or delay cognitive decline in aging women. Nevertheless, numerous design issues, such as the specific drugs and doses that were used, the possible effects of progestins on cognition, and the failure to administer neuropsychological tests of specific cognitive domains that are sensitive to estrogen therapy confound the extant literature. In view of the reanalyzes of the Women's Health Initiative's data that show a beneficial effect of estrogen therapy on cardiac and breast diseases in women aged 50-59 years, more definitive evidence is needed to confirm that the early initiation of estrogen therapy that is continued for a few years provides enduring protection against cognitive aging 15-20 years later.

Neurophysiological changes with age probed by inverse modeling of EEG spectra

OBJECTIVE

To investigate age-associated changes in physiologically-based EEG spectral parameters in the healthy population.

METHODS

Eyes-closed EEG spectra of 1498 healthy subjects aged 6-86 years were fitted to a mean-field model of thalamocortical dynamics in a cross-sectional study. Parameters were synaptodendritic rates, cortical wave decay rates, connection strengths (gains), axonal delays for thalamocortical loops, and power normalizations. Age trends were approximated using smooth asymptotically linear functions with a single turning point. We also considered sex differences and relationships between model parameters and traditional quantitative EEG measures.

RESULTS

The cross-sectional data suggest that changes tend to be most rapid in childhood, generally leveling off at age 15-20 years. Most gains decrease in magnitude with age, as does power normalization. Axonal and dendritic delays decrease in childhood and then increase. Axonal delays and gains show small but significant sex differences.

CONCLUSIONS

Mean-field brain modeling allows interpretation of age-associated EEG trends in terms of physiological processes, including the growth and regression of white matter, influencing axonal delays, and the establishment and pruning of synaptic connections, influencing gains.

SIGNIFICANCE

This study demonstrates the feasibility of inverse modeling of EEG spectra as a noninvasive method for investigating large-scale corticothalamic dynamics, and provides a basis for future comparisons.

Current Concepts in Vascular Cognitive Impairment and Pharmacotherapeutic Implications

Objective:

To review evolution of the vascular cognitive impairment (VCI) construct, including diagnosis, pharmacotherapeutic implications, and address challenges that will shape future developments.

Data Sources:

Literature retrieval was accessed through PubMed, from 1966 to December 2008, using the terms vascular cognitive impairment, vascular dementia, post-stroke dementia, vascular cognitive disorder, mild cognitive impairment, criteria, disease progression, outcomes, treatment, prevention, biomarkers, and neuroimaging.

Study Selection and Data Extraction:

All articles in published English identified from the data sources were evaluated for inclusion. Regarding pharmacotherapy, prospective double-blind, placebo-controlled studies were included as well as extensions or relevant post hoc analyses.

Data Synthesis:

In the 1970s, “senile dementia due to hardening of the arteries” was used to describe dementia due to vascular causes. This was a narrow view of what is now known to be a common form of cognitive impairment in older people. Multiple infarct dementia (MID) was first proposed to describe dementia attributable to multiple cerebral infarcts, followed by the vascular dementia (VaD) construct, itself meant to be an improvement over MID. The VaD construct had limitations, not the least of which was that, by the time a patient was diagnosed with VaD, the opportunity for prevention was lost. Thus arose the concept of VCI, representing a group of heterogeneous disorders that share presumed vascular causes. The importance of VCI is centered on the fact that vascular risk factors are treatable, and thus should lead to a reduction in the incidence of cognitive impairment due to vascular causes. There is evidence that treatment of hypertension can lead to a reduction in the incidence of cognitive impairment and dementia, and that treatment of VaD with acetylcholinesterase inhibitors may be beneficial.

Conclusions:

Careful attention needs to be given to controlling vascular risk factors in at-risk patients. Pharmacists should play an active role in this important area of geriatric pharmacotherapy.

Immune senescence and brain aging: can rejuvenation of immunity reverse memory loss?

The factors that determine brain aging remain a mystery. Do brain aging and memory loss reflect processes occurring only within the brain? Here, we present a novel view, linking aging of adaptive immunity to brain senescence and specifically to spatial memory deterioration. Inborn immune deficiency, in addition to sudden imposition of immune malfunction in young animals, results in cognitive impairment. As a corollary, immune restoration at adulthood or in the elderly results in a reversal of memory loss. These results, together with the known deterioration of adaptive immunity in the elderly, suggest that memory loss does not solely reflect chronological age; rather, it is an outcome of the gap between an increasing demand for maintenance (age-related risk-factor accumulation) and the reduced ability of the immune system to meet these needs.

The developing and restructuring superior cervical ganglion of guinea pigs (Cavia porcellus var. albina)

Post-natal development comprises both maturation (from newborn to adult) and ageing (from adult to senility) and, during this phase, several adaptive mechanisms occur in sympathetic ganglia, albeit they are not fully understood. Therefore, the present study aimed at detecting whether post-natal development would exert any effect on the size and number of a guinea pig's superior cervical ganglion (SCG) neurons. Twenty right SCGs from male subjects were used at four ages, i.e. newborn (7 days), young (30 days), adult (7 months) and old animals (50 months). Using design-based stereological methods the volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated using the vertical nucleator. The main findings of this study were a combination of post-natal-dependent increases and decreases in some variables: (i) 27% increase in ganglion volume, (ii) 24% and 43% decreases in the total number of mono and binucleate neurons, respectively, and (iii) 27.5% and 40% decreases in the mean perikaryal volume of mono and binucleate neurons, respectively. Despite the fall in neuron numbers found here, post-natal development is not only associated with neuron loss, but also embraces other structural adaptive mechanisms, which are discussed in this paper.

Cognitive performance and age-related changes in the hippocampal proteome

Declining cognitive performance is associated with increasing age, even in the absence of overt pathological processes. We and others have reported that declining cognitive performance is associated with age-related changes in brain glucose utilization, long-term potentiation and paired-pulse facilitation, protein expression, neurotransmitter levels, and trophic factors. However, it is unclear whether these changes are causes or symptoms of the underlying alterations in dendritic and synaptic morphology that occur with age. In this study, we examined the hippocampal proteome for age- and cognition-associated changes in behaviorally stratified young and old rats, using two-dimensional in-gel electrophoresis and MS/MS. Comparison of old cognitively intact with old cognitively impaired animals revealed additional changes that would not have been detected otherwise. Interestingly, not all age-related changes in protein expression were associated with cognitive decline, and distinct differences in protein expression were found when comparing old cognitively intact with old cognitively impaired rats. A large number of protein changes with age were related to the glycolysis/gluconeogenesis pathway. In total, the proteomic changes suggest that age-related alterations act synergistically with other perturbations to result in cognitive decline. This study also demonstrates the importance of examining behaviorally-defined animals in proteomic studies, as comparison of young to old animals regardless of behavioral performance would have failed to detect many cognitive impairment-specific protein expression changes evident when behavioral stratification data were used.

Does senescence give rise to disease?

The distinctions between senescence and disease are blurred in the literature of evolutionary biology, biodemography, biogerontology and medicine. Theories of senescence that have emerged over the past several decades are based on the concepts that organisms are a byproduct of imperfect structural designs built with imperfect materials and maintained by imperfect processes. Senescence is a complex mixture of processes rather than a monolithic process. Senescence and disease have overlapping biological consequences. Senescence gives rise to disease, but disease does not give rise to senescence. Current data indicate that treatment of disease can delay the age of death but there are no convincing data that these interventions alter senescence. An understanding of these basic tenets suggests that there are biological limits to duration of life and the life expectancy of populations and reveal biological domains where the development of interventions and/or treatments may modulate senescence.

Calcium ions in neuronal degeneration

Neuronal Ca(2+) homeostasis and Ca(2+) signaling regulate multiple neuronal functions, including synaptic transmission, plasticity, and cell survival. Therefore disturbances in Ca(2+) homeostasis can affect the well-being of the neuron in different ways and to various degrees. Ca(2+) homeostasis undergoes subtle dysregulation in the physiological ageing. Products of energy metabolism accumulating with age together with oxidative stress gradually impair Ca(2+) homeostasis, making neurons more vulnerable to additional stress which, in turn, can lead to neuronal degeneration. Neurodegenerative diseases related to aging, such as Alzheimer's disease, Parkinson's disease, or Huntington's disease, develop slowly and are characterized by the positive feedback between Ca(2+) dyshomeostasis and the aggregation of disease-related proteins such as amyloid beta, alfa-synuclein, or huntingtin. Ca(2+) dyshomeostasis escalates with time eventually leading to neuronal loss. Ca(2+) dyshomeostasis in these chronic pathologies comprises mitochondrial and endoplasmic reticulum dysfunction, Ca(2+) buffering impairment, glutamate excitotoxicity and alterations in Ca(2+) entry routes into neurons. Similar changes have been described in a group of multifactorial diseases not related to ageing, such as epilepsy, schizophrenia, amyotrophic lateral sclerosis, or glaucoma. Dysregulation of Ca(2+) homeostasis caused by HIV infection or by sudden accidents, such as brain stroke or traumatic brain injury, leads to rapid neuronal death. The differences between the distinct types of Ca(2+) dyshomeostasis underlying neuronal degeneration in various types of pathologies are not clear. Questions that should be addressed concern the sequence of pathogenic events in an affected neuron and the pattern of progressive degeneration in the brain itself. Moreover, elucidation of the selective vulnerability of various types of neurons affected in the diseases described here will require identification of differences in the types of Ca(2+) homeostasis and signaling among these neurons. This information will be required for improved targeting of Ca(2+) homeostasis and signaling components in future therapeutic strategies, since no effective treatment is currently available to prevent neuronal degeneration in any of the pathologies described here.

Asymmetric post-natal development of superior cervical ganglion of paca (Agouti paca)

Functional asymmetry has been reported in sympathetic ganglia. Although there are few studies reporting on body side-related morphoquantitative changes in sympathetic ganglion neurons, none of them have used design-based stereological methods to address this issue during post-natal development. We therefore aimed at detecting possible asymmetry-related effects on the quantitative structure of the superior cervical ganglion (SCG) from pacas during ageing, using very precise design-based stereological methods. Forty (twenty left and twenty right) SCG from twenty male pacas were studied at four different ages, i.e. newborn, young, adult and aged animals. By using design-based stereological methods the total volume of ganglion and the total number of mononucleate and binucleate neurons were estimated. Furthermore, the mean perikaryal volume of mononucleate and binucleate neurons was estimated, using the vertical nucleator. The main findings of this study were: (1) the right SCG from aged pacas has more mononucleate and binucleate neurons than the left SCG in all other combinations of body side and animal age, showing the effect of the interaction between asymmetry (right side) and animal age, and (2) right SCG neurons (mono and binucleate) are bigger than the left SCG neurons (mono and binucleate), irrespective of the animal age. This shows, therefore, the exclusive effect of asymmetry (right side). At the time of writing there is still no conclusive explanation for some SCG quantitative changes exclusively assigned to asymmetry (right side) and those assigned to the interaction between asymmetry (right side) and senescence in pacas. We therefore suggest that forthcoming studies should focus on the functional consequences of SCG structural asymmetry during post-natal development. Another interesting investigation would be to examine the interaction between ganglia and their innervation targets using anterograde and retrograde neurotracers. Would differences in the size of target organs explain ganglia structural asymmetry?

Caloric restriction and brain function

PURPOSE OF REVIEW

In addition to extending lifespan, animal research shows that specific diets benefit brain functioning. Indeed, it has been proven that caloric restriction prevents age-related neuronal damage. What are those mechanisms involved in the effects of caloric restriction on brain functioning? Could caloric restriction be proposed in the future to prevent or treat neurodegenerative disorders such as Alzheimer's disease? Is there a future for caloric restriction interventions in adults?

RECENT FINDINGS

Hypotheses linking caloric restriction to cognitive capability include anti-inflammatory mechanisms, reduction of neural oxidative stress, promotion of synaptic plasticity, induction of various stress and neurotrophic/neuroprotective factors. Caloric restriction may also prevent beta-amyloid neuropathology in Alzheimer transgenic models. Finally, both exercise and caloric restriction enhance neurogenesis via different mechanisms suggesting that their combination may decrease the risk of neurodegenerative disease.

SUMMARY

It is now well established that caloric restriction could be used to promote successful brain aging. Data from randomized controlled trials in humans are limited. No positive effect on cognitive impairment was found probably due to methodological limitations. The long-term effects of caloric restriction in adults must be clarified before engaging in such preventive strategy. Additional animal studies must be conducted in the future to test the effects of 'multidomain' interventions (caloric restriction plus regular exercise) on age-related cognitive decline.

Age-dependent variability in gene expression in male Fischer 344 rat retina

Recent evidence suggests that older adults may be a sensitive population with regard to environmental exposure to toxic compounds. One source of this sensitivity could be an enhanced variability in response. Studies on phenotypic differences have suggested that variation in response does increase with age. However, few reports address the question of variation in gene expression as an underlying cause for increased variability of phenotypic response in the aged. In this study, we utilized global analysis to compare variation in constitutive gene expression in the retinae of young (4 months), middle-aged (11 months), and aged (23 months) Fischer 344 rats. Three hundred and forty transcripts were identified in which variance in expression increased from 4 to 23 months of age, while only 12 transcripts were found for which it decreased. Functional roles for identified genes were clustered in basic biological categories including cell communication, function, metabolism, and response to stimuli. Our data suggest that population stochastically induced variability should be considered in assessing sensitivity due to old age.

Apolipoprotein E and cholesterol in aging and disease in the brain

Cholesterol can be detrimental or vital, and must be present in the right place at the right time and in the right amount. This is well known in the heart and the vascular system. However, in the CNS cholesterol is still an enigma, although several of its fundamental functions in the brain have been identified. Brain cholesterol has attracted additional attention owing to its close connection to ApoE, a key polymorphic transporter of extracellular cholesterol in humans. Indeed, both cholesterol and ApoE are so critical to fundamental activities of the brain, that the brain regulates their synthesis autonomously. Yet, similar control mechanisms of ApoE and cholesterol homeostasis may exist on either sides of the blood-brain barrier. One indication is that the APOE ε4 allele is associated with hypercholesterolemia and a proatherogenic profile on the vascular side and with increased risk of Alzheimer's disease on the CNS side. In this review, we draw attention to the association between cholesterol and ApoE in the aging and diseased brain, and to the behavior of the ApoE4 protein at the molecular level. The attempt to correlate in vivo and in vitro observations is challenging but crucial for developing future strategies to address ApoE-related aberrations in cholesterol metabolism selectively in the brain.

Brain aging modulates the neuroprotective effects of estrogen on selective aspects of cognition in women: a critical review

Although there is now a substantial literature on the putative neuroprotective effects of estrogen on cognitive functioning in postmenopausal women, it is replete with inconsistencies. The critical period hypothesis, posited several years ago, attempts to account for the discrepancies in this literature by positing that estrogen treatment (ET) will protect aspects of cognition in older women only when treatment is initiated soon after the menopause. Indeed, evidence from basic neuroscience and from the animal and human literature reviewed herein provides compelling support for the critical period hypothesis. Although it is not known with certainty why estrogen does not protect cognition and may even cause harm when administered to women over the age of 65years, it is likely that the events that characterize brain aging, such as a reduction in brain volume and in neuronal size, alterations in neurotransmitter systems, and a decrease in dendritic spine numbers, form an unfavorable background that precludes a neuroprotective effects of exogenous estrogen on the brain. Other factors that have likely contributed to the discrepancies in the estrogen-cognition literature include differences in the estrogen compounds used, their route of administration, cyclic versus continuous regimens, and the concomitant use of progestins. This critical analysis attempts to define conditions under which ET may protect aspects of cognition in aging women while also considering the cost/benefit ratio for the treatment of women aged 50-59years. Suggestions for specific future research questions are also addressed.

The pathology of ageing: concepts and mechanisms

The rising numbers and proportion of aged individuals in the population is a global demographic trend. The diseases associated with ageing are becoming more prevalent, and the associated healthcare costs are having a significant economic impact in all countries. With these changes have come great advances in our understanding of the mechanisms of ageing. The mechanisms of cellular ageing at a genetic, protein and organelle level are becoming clearer, as are some of the more complex associations between environment and ageing. System ageing is also becoming better understood, and the potential biological advantages of ageing are being explored. Many of the advances in these fields are opening up the prospect of targeted therapeutic intervention for ageing and age related disease.