[The Role of Circadian Rhythms in Aging and ADHD]

The circadian rhythms coordinates the internal physiology to increase the homeostatic capacity thereby providing both a survival advantage to the system and an optimization of energy budgeting. Because multiple-oscillator circadian mechanisms are likely to play a role in regulating human health, and may contribute to the aging process, we give an overview of the relationship between the central clock in the hypothalamus and peripheral clocks for psychological health and aging.

Monomeric C-reactive protein--a key molecule driving development of Alzheimer's disease associated with brain ischaemia?

Alzheimer’s disease (AD) increases dramatically in patients with ischaemic stroke. Monomeric C-reactive protein (mCRP) appears in the ECM of ischaemic tissue after stroke, associating with microvasculature, neurons and AD-plaques, Aβ, also, being able to dissociate native-CRP into inflammatory, mCRP in vivo. Here, mCRP injected into the hippocampal region of mice was retained within the retrosplenial tract of the dorsal 3rd ventrical and surrounding major vessels. Mice developed behavioural/cognitive deficits within 1 month, concomitant with mCRP staining within abnormal looking neurons expressing p-tau and in beta-amyloid 1-42-plaque positive regions. mCRP co-localised with CD105 in microvessels suggesting angiogenesis. Phospho-arrays/Western blotting identified signalling activation in endothelial cells and neurons through p-IRS-1, p-Tau and p-ERK1/2-which was blocked following pre-incubation with mCRP-antibody. mCRP increased vascular monolayer permeability and gap junctions, increased NCAM expression and produced haemorrhagic angiogenesis in mouse matrigel implants. mCRP induced tau244–372 aggregation and assembly in vitro. IHC study of human AD/stroke patients revealed co-localization of mCRP with Aβ plaques, tau-like fibrils and IRS-1/P-Tau positive neurons and high mCRP-levels spreading from infarcted core regions matched reduced expression of Aβ/Tau. mCRP may be responsible for promoting dementia after ischaemia and mCRP clearance could inform therapeutic avenues to reduce the risk of future dementia.

Vascular cognitive impairment, dementia, aging and energy demand. A vicious cycle

To a great extent, cognitive health depends on cerebrovascular health and a deeper understanding of the subtle interactions between cerebrovascular function and cognition is needed to protect humans from one of the most devastating affliction, dementia. However, the underlying biological mechanisms are still not completely clear. Many studies demonstrated that the neurovascular unit is compromised in cerebrovascular diseases and also in other types of dementia. The hemodynamic neurovascular coupling ensures a strong increase of the cerebral blood flow (CBF) and an acute increase in neuronal glucose uptake upon increased neural activity. Dysfunction of cerebral autoregulation with increasing age along with age-related structural and functional alterations in cerebral blood vessels including accumulation of amyloid-beta (Aβ) in the media of cortical arterioles, neurovascular uncoupling due to astrocyte endfeet retraction, impairs the CBF and increases the neuronal degeneration and susceptibility to hypoxia and ischemia. A decreased cerebral glucose metabolism is an early event in Alzheimer's disease (AD) pathology and may precede the neuropathological Aβ deposition associated with AD. Aβ accumulation in turn leads to further decreases in the CBF closing the vicious cycle. Alzheimer, aging and diabetes are also influenced by insulin/insulin-like growth factor-1 signaling, and accumulated evidence indicates sporadic AD is associated with disturbed brain insulin metabolism. Understanding how vascular and metabolic factors interfere with progressive loss of functional neuronal networks becomes essential to develop efficient drugs to prevent cognitive decline in elderly.

Preclinical models of stroke in aged animals with or without comorbidities: role of neuroinflammation

Age is the principal nonmodifiable risk factor for stroke. Over the past 10 years, suitable models for stroke in aged rats have been established. At genetic and cellular level there are significant differences in behavioral, cytological and genomics responses to injury in old animals as compared with the young ones. Behaviorally, the aged rats have the capacity to recover after cortical infarcts albeit to a lower extent than the younger counterparts. Similarly, the increased vulnerability of the aged brain to stroke, together with a decreased interhemisphere synchrony after stroke, assessed by different experimental methods (MRI, fMRI, in vivo microscopy, EEG) leads to unfavorable recovery of physical and cognitive functions in aged people and may have a prognostic value for the recovery of stroke patients. Furthermore, in elderly, comorbidities like diabetes or arterial hypertension are associated with higher risk of stroke, increased mortality and disability, and poorer functional status and quality of life. Aging brain reacts strongly to ischemia-reperfusion injury with an early inflammatory response. The process of cellular senescence can be an important additional contributor to chronic post-stroke by creating a "primed" inflammatory environment in the brain. Overall, these pro-inflammatory reactions promote early scar formation associated with tissue fibrosis and reduce functional recovery. A better understanding of molecular factors and signaling pathways underlying the contribution of comorbidities to stroke-induced pathological sequelae, may be translated into successful treatment or prevention therapies for age-associated diseases which would improve lifespan and quality of life.

Enabling brain plasticity and neurological recovery in the ischemic brain: effect of age and vascular risk factors as confounders

Cerebral plasticity and neurological recovery can be stimulated in the ischemic brain by exogenous pharmacological and cell-based treatments. Neurons, neuroblasts and endothelial cells synergistically interact with each other as a regenerative triad, creating an environment in which neurological recovery takes place. Developmental genetic programs are reactivated. Brain neurons and capillary cells are enabled to sprout, and glial cells support plasticity processes. Until now, the large majority of studies were performed in young, otherwise healthy animals, which lack the risk factors and co-morbidities associated with human stroke. Recent behavioral, histochemical and molecular biological studies have shown that restorative brain responses may differ between young and old animals, and that they are also modulated by vascular risk factors, such as hyperlipidemia and diabetes, which are highly prevalent in ischemic stroke. We claim that age aspects, vascular risk factors and co-morbidities should more intensively be examined in future experimental studies. Confounding effects of age, risk factors and co-morbidities should carefully be considered in clinical proof-of-concept trials.

Pathophysiology of the vascular wall and its relevance for cerebrovascular disorders in aged rodents

Chronic hypertension and cerebral amyloid angiopathy (CAA) are the main pathologies which can induce the rupture of cerebral vessels and intracerebral hemorrhages, as a result of degenerative changes in the vascular wall. A lot of progress has been made in this direction since the successful creation of the first mouse model for the study of Alzheimer's disease (AD), as the spectrum of AD pathology includes a plethora of changes found in pure cerebrovascular diseases. We describe here some of these mouse models having important vascular changes that parallel human AD pathology, and more importantly, we show how these models have helped us understand more about the mechanisms that lead to CAA formation. An important cellular event associated with reduced structural and functional recovery after stroke in aged animals is the early formation of a scar in the infarcted region that impairs subsequent neural recovery and repair. We review recent evidence showing that the rapid formation of the glial scar following stroke in aged rats is associated with premature cellular proliferation that originates primarily from the walls of capillaries in the corpus callosum adjacent to the infarcted region. After stroke several vascular mechanisms are turned-on immediately to protect the brain from further damage and help subsequent neuroregeneration and functional recovery. Although does occur after stroke, vasculogenesis is overshadowed in its protective/restorative role by the angiogenesis and arteriogenesis. Understanding the basic mechanisms underlying functional recovery after cerebral stroke in aging subjects is likely to yield new insights into the treatment of brain injury in the clinic.

Central nervous system aging and regeneration after injuries. A systematic approach

Aging is associated with a decline of locomotor, sensory and cognitive performance in humans and experimental animals. Mechanistically, organismal senescence is caused by a gradual, lifelong accumulation of multifaceted molecular and cellular damage. Further, the rate and pattern of organismal senescence may be regulated in part by changes in multiple genes involved in multiple processes. While this theory is supported by genetic data in lower organisms, a lack of direct experimental evidence in higher organisms has contributed to a broader acceptance of the "stochastic aging" model, in which accumulating, random damaging biological events play an important role. However, these insults alone cannot account for the inexorable deterioration and loss of function that characterizes old biological systems of higher complexity like humans. Recent advances in unbiased gene expression profiling of the entire genome is a valuable tool for the study of complex biological phenomena such as aging. Using this technology, it is now possible to analyze in detail gene expression at the systems level. In the past decade with the advent of high-throughput technologies, biology has migrated from a descriptive science to a predictive. Most importantly, data from animal models has shown that senescent systems do retain some capacity for regeneration and functional recovery after injuries.

Strategies to improve post-stroke behavioral recovery in aged subjects

Old age is associated with an enhanced susceptibility to stroke and poor recovery from brain injury. Therefore, find therapeutic strategies aimed at improving functional recovery after brain ischemia in aged subjects is of considerable clinical interest. While environmental enrichment has been shown to improve the behavioral outcome of stroke in young animals, the effect of an enriched environment, hypothermia and Granulocyte-Colony Stimulating Factor (G-CSF) on behavioral and neuropathological recovery in aged animals is not known. Focal cerebral ischemia was produced by occlusion of the right middle cerebral artery in 3-month- and 20-month-old male Sprague-Dawley rats. The functional outcome was assessed in neurobehavioral tests conducted over a period of 14-28 days following surgery. Brain tissue then was immunostained for proliferating astrocytes and the infarct and scar tissue volumes were measured. Aged rats showed more severe behavioral impairments and diminished functional recovery compared to young rats. Most infarcted animals had disturbances of sensorimotor function, with recovery beginning later, progressing more slowly, and reaching a lower functional endpoint in aged animals. However, the enriched environment significantly improved the rate and extent of recovery in aged animals. Correlation analysis revealed that the beneficial effect of the enriched environment on recovery, both in young and aged rats, correlated highly with a reduction in infarct size, in the number of proliferating astrocytes, and in the volume of the glial scar. These results suggest that temporally modulating astrocytic proliferation and the ensuing scar formation might be a fruitful approach to improving functional recovery after stroke in aged rats. In aged humans, stroke is a major cause of disability for which no neuroprotective measures are available. A viable alternative to conventional drug-based neuroprotective therapies is brain/body cooling, or hypothermia. In animal studies of focal ischemia, short-term hypothermia consistently reduces infarct size. Nevertheless, efficient neuroprotection requires long-term, regulated lowering of whole body temperature. In this study, we show that two days post-stroke exposure of aged rats to a mixture of air and a mild inhibitor of oxidative phosphorylation, H2S, causes deep hypothermia (27.8+/-0.3 degrees C) and a 50% reduction in infarct size without obvious neurological deficits or physiological side effects. G-CSF treatment after stroke exerted a robust and sustained beneficial effect on survival rate and running function. Transient improvement after G-CSF treatment could be observed for coordinative motor function on the inclined plane test and for working memory in the radial maze test. At cellular level, G-CSF treatment increased the number of proliferating cells in the SVZ and the dentate gyrus and increased the number of newborn neurons in the SVZ, ipsilateral to the lesion. These results suggests that the G-CSF treatment in aged rats has a survival enhancing capacity and a beneficial effect on functional outcome most likely via supportive cellular processes such as neurogenesis.

CONCLUSIONS

These findings are important for the further clinical development of the drug in elderly stroke patients. Future studies should focus on an optimization of treatment schedule to achieve a maximum of post-stroke recovery enhancement in aged subjects.

The genomic response of the ipsilateral and contralateral cortex to stroke in aged rats

Aged rats recover poorly after unilateral stroke, whereas young rats recover readily possibly with the help from the contralateral, healthy hemisphere. In this study we asked whether anomalous, age-related changes in the transcriptional activity in the brains of aged rats could be one underlying factor contributing to reduced functional recovery. We analysed gene expression in the periinfarct and contralateral areas of 3-month- and 18-month-old Sprague Dawley rats. Our experimental end-points were cDNA arrays containing genes related to hypoxia signalling, DNA damage and apoptosis, cellular response to injury, axonal damage and re-growth, cell lineage differentiation, dendritogenesis and neurogenesis. The major transcriptional events observed were: (i) Early up-regulation of DNA damage and down-regulation of anti-apoptosis-related genes in the periinfarct region of aged rats after stroke; (ii) Impaired neurogenesis in the periinfarct area, especially in aged rats; (iii) Impaired neurogenesis in the contralateral (unlesioned) hemisphere of both young and aged rats at all times after stroke and (iv) Marked up-regulation, in aged rats, of genes associated with inflammation and scar formation. These results were confirmed with quantitative real-time PCR. We conclude that reduced transcriptional activity in the healthy, contralateral hemisphere of aged rats in conjunction with an early up-regulation of DNA damage-related genes and pro-apoptotic genes and down-regulation of axono- and neurogenesis in the periinfarct area are likely to account for poor neurorehabilitation after stroke in old rats.

Annexin A3 expression after stroke in the aged rat brain

In an effort to identify new proteins involved in functional recovery after cerebral ischemia, young (3 months) and aged (18 months) male rats were subjected to middle cerebral artery (MCA) occlusion. Brains were harvested at 3- and 14-days post ischemia and proteins from the peri-infarcted and the corresponding contralateral area and total proteins were analyzed by two-dimensional polyacrylamide gel electrophoresis followed by mass spectrometry analysis. Annexin A3 (ANXA3) was identified as one upregulated protein in the post-ischemic rat brain. Using western blotting, real-time PCR and immunohistochemistry, we confirmed that at 3-14 days post-stroke, ANXA3 expression in the peri-infarct area was consistently increased over the corresponding area of control rats. Double staining revealed that ANXA3 is produced by activated microglial cells. We found that aged rats also had more newly proliferating cells expressing ANXA3 than young rats do. Occasionally, ANXA3-immunopositive cells wraped around neurons, suggesting that annexin A3 may be involved in the removal of dying neurons after stroke.

Cellular and molecular mechanisms underlying neurorehabilitation after stroke in aged subjects

Old age is associated with an enhanced susceptibility to stroke and poor recovery from brain injury, but the cellular processes underlying these phenomena are uncertain. Therefore studying the basic mechanism underlying functional recovery after brain ischemia in aged subjected it is of considerable clinical interest. Potential mechanisms include neuroinflammation, changes in brain plasticity-promoting factors, unregulated expression of neurotoxic factors, or differences in the generation of scar tissue that impedes the formation of new axons and blood vessels in the infarcted region. Available data indicate that behaviorally, aged rats were more severely impaired by ischemia than were young rats, and they also showed diminished functional recovery. Further, as compared to young rats, aged rats develop a larger infarct area, as well as a necrotic zone characterized by a higher rate of cellular degeneration, and a larger number of apoptotic cells. In both old and young rats, the early intense proliferative activity following stroke leads to a precipitous formation of growth-inhibiting scar tissue, a phenomenon amplified by the persistent expression of neurotoxic factors. Reduced transcriptional activity in the healthy, contralateral hemisphere in conjunction with an early upregulation of DNA damage related genes and the early induction of proapoptotic genes in the periinfarct area of aged rats are likely to account for poor neurorehabilitation after stroke in aged rats. Finally, the regenerative potential of the rat brain is largely preserved up to 20 months of age but gene expression is temporally displaced, has lower amplitude, and is sometimes of relatively short duration. Most interestingly, it has recently been shown that the human brain can respond to stroke with increased progenitor proliferation in aged patients opening the possibilities to utilize this intrinsic attempt for neuroregeneration of the human brain as a potential therapy for stroke. Given the heterogeneity of stroke, a universal anti-inflammatory solution may be a distant prospect, but probably neuroprotective drug cocktails targeting inflammatory pathways in combination with thrombolysis may be a possibility for acute stroke treatment in the future.

Environmental enrichment improves functional and neuropathological indices following stroke in young and aged rats

PURPOSE

Aging is associated with a temporally dysregulated cellular response to ischemia as well as poor functional recovery. While environmental enrichment has been shown to improve the behavioral outcome of stroke in young animals, the effect of an enriched environment on behavioral and neuropathological recovery in aged animals is not known.

METHODS

Focal cerebral ischemia was produced by electrocoagulation of the right middle cerebral artery in 3 month- and 20 month-old male Sprague-Dawley rats. The functional outcome was assessed in neurobehavioral tests conducted over a period of 28 days following surgery. Brain tissue was then immunostained for proliferating astrocytes and the infarct and scar tissue volumes were measured.

RESULTS

Aged rats showed more severe behavioral impairments and diminished functional recovery compared to young rats. Most infarcted animals had disturbances of sensorimotor function, with recovery beginning later, progressing more slowly, and reaching a lower functional endpoint in aged animals. However, the enriched environment significantly improved the rate and extent of recovery in aged animals. Correlation analysis revealed that the beneficial effect of the enriched environment on recovery, both in young and aged rats, correlated highly with a reduction in infarct size, in the number of proliferating astrocytes, and in the volume of the glial scar.

CONCLUSIONS

These results suggest that temporally modulating astrocytic proliferation and the ensuing scar formation might be a fruitful approach to improving functional recovery after stroke in aged rats.

Modified variant of the Rieske iron-sulfur protein in the hippocampus of kindled rats and human epileptic patients

Kindled seizures are widely used to model epileptogenesis, but the molecular mechanisms underlying the attainment of kindling status are largely unknown. Recently we showed that achievement of kindling status in the Sprague-Dawley rat is associated with a critical developmental interval of 25 +/- 1 days; the identification of this long, well-defined developmental interval for inducing kindling status makes possible a dissection of the cellular and genetic events underlying this phenomenon and its relationship to normal and pathological brain function. Now we report the identification, by proteomics, of a modified variant of the Rieske iron-sulfur protein, a component of the mitochondrial cytochrome bc1 complex, whose isoelectric point is shifted toward more alkaline values in the hippocampus of kindled rats. By immunohistochemistry the Rieske protein is well-expressed in the hippocampus except in the CA1 subfield, a region of selective vulnerability to seizures in humans and animal models. We also noted an asymmetric, selective expression of the Rieske protein in the subgranular neurons of the dorsal dentate gyrus, a region implicated in neurogenesis. Abnormal changes in Rieske protein immunoreactivity also were found in sections obtained from human epileptic patients. These results suggest that the Rieske protein may play a role in the response of neurons to seizure activity and could give important new insights into the molecular pathogenesis of epilepsy.

Differential regulation of transport proteins in the periinfarct region following reversible middle cerebral artery occlusion in rats

Members of various transport protein families including ATP-binding cassette transporters and solute carriers were shown to be expressed in brain capillaries, choroid plexus, astrocytes or neurons, controlling drug and metabolite distribution to and from the brain. However, data are currently very limited on how the expression of these transport systems is affected by damage to the brain such as stroke. Therefore we studied the expression of four selected transporters, P-glycoprotein (Mdr1a/b; Abcb1a/b), Mrp5 (Abcc5), Bcrp (Abcg2), and Oatp2 (Slc21a5) in a rat model for stroke. Transporter expression was analyzed by real-time polymerase chain reaction in the periinfarcted region and protein localization and cellular phenotyping were done by immunohistochemistry and confocal immunofluorescence microscopy. After stroke, P-glycoprotein staining was detected in endothelial cells of disintegrated capillaries and by day 14 in newly generated blood vessels. There was no significant difference, however, in the Mdr1a mRNA amount in the periinfarcted region compared with the contralateral site. For Bcrp, a significant mRNA up-regulation was observed from days 3-14. This up-regulation was followed by the protein as confirmed by quantitative immunohistochemistry. Oatp2, located in the vascular endothelium, was also up-regulated at day 14. For Mrp5, an up-regulation was observed in neurons in the periinfarcted region (day 14). In conclusion, after stroke the transport proteins were up-regulated with a maximum at day 14, a time point that coincides with behavioral recuperation. The study further suggests Bcrp as a pronounced marker for the regenerative process and a possible functional role of Mrp5 in surviving neurons.

Premature cellular proliferation following cortical infarct in aged rats

Old age is associated with an enhanced susceptibility to stroke and poor recovery from brain injury, but the cellular mechanisms underlying such phenomena are not known. Using BrdU-labeling, quantitative immunohistochemistry and 3D-reconstruction of confocal images in a rat model of mild cerebral ischemia, we found that aged rats are highly susceptible to develop an early infarct that is associated with premature cellular proliferation originating from the vascular tree. In aged rats we also found a rapid delimitation of the infarct area by capillary-derived neuroepithelial cells and an early incorporation of these cells into the glial scar. Since most proliferating cells at the infarct site are microglia or nestin-positive cells derived from the vascular wall, we conclude that the vasculature plays a hitherto unrecognized role as a source of proliferating neuroepithelial cells after stroke. Age-associated alterations in the timing and origin of the cytogenic response to cerebral ischemia may underlie the poor functional recovery from stroke. Clarifying the molecular basis of these phenomena could yield novel approaches to enhancing neurorestoration in the elderly. Studies of stroke in experimental animals have demonstrated the neuroprotective efficacy of a variety of interventions, but most of the strategies that have been clinically tested failed to show benefit in aged humans. One possible explanation for this discrepancy between laboratory and clinical investigations is the role that age plays in the recovery of the brain from insult. Although it is well known that aging is a risk factor for stroke (Barnett HJ, 2002), the majority of experimental studies of stroke have been performed on young animals, and therefore may not fully replicate the effects of ischemia on neural tissue in aged subjects (Wang LC et al., 1995; Davies M et al., 1995; Sutherland GR et al., 1996; Popa-Wagner A et al., 1998, 1999a). Hence, the aged post-acute animal model is clinically most relevant to stroke rehabilitation and cellular studies (Lindner MD et al., 2003; Brown AW et al., 2003; Badan I et al., 2003).

Age Influences the Expression of GAP-43 in the Rat Hippocampus following Seizure

BACKGROUND

Normal aging is associated with impairments in learning and memory and motor function. One viable hypothesis is that these changes reflect an age-related decrease in brain plasticity.

OBJECTIVE

The aim of the present study was to identify age-related changes in the time course of expression of the axonal growth associated protein 43 (GAP-43) in a rat model of brain plasticity.

METHODS

We examined by Northern blotting, in situ hybridization, and immunohistochemistry the effects of age on the time course of the expression GAP-43 following pentylenetetrazole-induced seizure in the hippocampus of 3-, 18-, and 28-month-old rats.

RESULTS

In this model of brain plasticity, young rats displayed a decrease in GAP-43 mRNA levels in CA1, CA3, and polymorphic regions, lasting from 10 h to 3 days after seizure. This was followed by recovery, with peak expression between days 10 and 20. The baseline levels of GAP-43 mRNA decreased with age, especially in the CA3 region. Despite lower baseline levels, middle-aged rats showed the same pattern of upregulation of GAP-43 mRNA expression as the young animals. Old rats showed only minimal upregulation, however, and this occurred only in the polymorphic layer. The level GAP-43 protein itself was higher in old control rats than in the other two control groups, a condition that was transiently reversed by seizure activity.

CONCLUSIONS

Middle-aged rats are still capable of a sustained, though diminished, response to seizure activity, while old rats lose this ability. Disruption of the temporal and anatomical coordination of expression of GAP-43 may contribute to the general decline in brain plasticity with age.

Accelerated accumulation of N- and C-terminal beta APP fragments and delayed recovery of microtubule-associated protein 1B expression following stroke in aged rats

The age-related decline in plasticity of the brain may be one factor underlying poor functional recovery after stroke. In the present work we tested the hypothesis that the attenuation of neural plasticity in old age could be the result of an altered temporal relationship between factors promoting brain plasticity [microtubule-associated protein 1B (MAP1B)] and neurotoxic factors such as C-terminal betaAPP. Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague-Dawley rats. The functional outcome was assessed in neurobehavioral tests at 3, 7, 14 and 28 days after surgery. At the indicated timepoints, brains were removed and immunostained for C- and N-terminal betaAPP and MAP1B. At 2 weeks poststroke, we found an age-related increase in the amount of the C-terminal fragment of betaAPP in the peri-infarcted area and the infarct core as well as an early, vigorous incorporation of N-terminal betaAPP into the developing astroglial scar. The recovery of the plasticity-associated protein MAP1B following stroke was delayed in both age groups and became prominent between days 14 and 28. As aged rats showed diminished functional recovery compared with young rats, these results suggest that the accumulation of C-terminal betaAPP, together with the early incorporation of N-terminal betaAPP into the glial scar, may over-ride the beneficial role of plasticity factors such as MAP1B.

Observations on experimental marginal periodontitis in rats

OBJECTIVE

The purpose of this study was to assess periodontal destruction following experimentally induced marginal periodontitis in rats by ligatures over a 60-day observation period. The extent to which the physiological movement of teeth influenced the effect of the ligatures was also examined. In addition, two methods for measuring bone loss in the defleshed jaw were compared.

METHODS

Thirty-five male Sprague-Dawley rats (SD) were divided into five groups. Marginal periodontitis was induced by ligatures on the second maxillary molars. Rats were killed after 15, 30, and 60 days. Rats in the control group were killed on day 1 and day 60. Bone loss was determined with two different methods on the buccal and palatinal surfaces of the defleshed jaw. In the first method, the distance of the cementoenamel junction (CEJ) from the alveolar bone crest (ABC) was measured at different sites; in the second method, the area of the exposed root surface of the molars was measured.

RESULTS

Comparison of the control groups from day 1 and day 60 using both measuring methods showed significant differences in bone loss. In the area where the ligature was located, test rats exhibited significantly greater bone loss than control rats. Comparison of control rats from day 1 with test rats from day 15 showed that the increase in bone loss between the groups within the area of the ligature was significantly greater than outside it. The age-dependent bone loss increases over the entire observation period of 60 days. The ligature-induced bone loss increased most from day 1 to day 15; on days 30 and 60, slighter increases in bone loss were observed.

CONCLUSIONS

The application of this model can only be recommended for short (</=15 days) observation periods. The distance method should be preferred to the area method.

Temporal Dynamics of Degenerative and Regenerative Events Associated with Cerebral Ischemia in Aged Rats

BACKGROUND AND PURPOSE

The age-related decline in plasticity of the brain may be one factor underlying the poor functional recovery after stroke. In the present work we tested the hypothesis that the attenuation of neural plasticity could be the result of an age-related REDUCTION in the upregulation of factors promoting brain plasticity (microtubule-associated protein 1B [MAP1B], beta-amyloid precursor protein [betaAPP]), and an age-related INCREASE in glial reactivity and the accumulation of Abeta, a proteolytic cleavage product of betaAPP with neurotoxic properties.

METHODS

Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague-Dawley rats. The functional outcome was assessed in neurobehavioral tests 3, 7, 14 and 28 days after surgery. At the indicated time points, brains were removed and immunostained for glial cells. Abeta, as well as the markers of brain plasticity, betaAPP and MAP1B.

RESULTS

Histologically, in young rats there was a gradual activation of both microglia and astrocytes that peaked by days 14-28 with the formation of a glial scar. In contrast, aged rats showed an accelerated astrocytic and microglial reaction that peaked in the first week after stroke. The expression patterns of a growth-associated phenotype of betaAPP as well as with MAP1B accumulation in varicosities along axons in cortical areas affected by stroke peaked between days 14 and 28 in young animals. In aged rats their expression was both delayed (28 days) and reduced. In addition the carboxy terminal fragment of betaAPP steadily accumulated over time and reached a maximum by day 14 in aged rats as compared to 28 days in young rats.

CONCLUSIONS

These results suggest that a temporally anomalous gliotic reaction to cerebral ischemia in aged rats in conjunction with a late and limited upregulation of neuronal plasticity proteins as well as a diminished neurogenesis potential lead to the prevalence of scar tissue that impedes functional recovery from stroke.

Accelerated glial reactivity to stroke in aged rats correlates with reduced functional recovery

Following cerebral ischemia, perilesional astrocytes and activated microglia form a glial scar that hinders the genesis of new axons and blood vessels in the infarcted region. Since glial reactivity is chronically augmented in the normal aging brain, the authors hypothesized that postischemic gliosis would be temporally abnormal in aged rats compared to young rats. Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague Dawley rats. The functional outcome was assessed in neurobehavioral tests at 3, 7, 14, and 28 days after surgery. Brain tissue was immunostained for microglia, astrocytes, oligodendrocytes, and endothelial cells. Behaviorally, aged rats were more severely impaired by stroke and showed diminished functional recovery compared with young rats. Histologically, a gradual activation of both microglia and astrocytes that peaked by days 14 to 28 with the formation of a glial scar was observed in young rats, whereas aged rats showed an accelerated astrocytic and microglial reaction that peaked during the first week after stroke. Oligodendrocytes were strongly activated at early stages of infarct development in all rats, but this activation persisted in aged rats. Therefore, the development of the glial scar was abnormally accelerated in aged rats and coincided with the stagnation of recovery in these animals. These results suggest that a temporally anomalous gliotic reaction to cerebral ischemia in aged rats leads to the premature formation of scar tissue that impedes functional recovery after stroke.

Neurofilament expression in the rat brain after cerebral infarction: effect of age

In this study the role of neurofilaments (NFs) in brain plasticity after cerebral infarction in young and middle aged rats was evaluated. Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague-Dawley rats. After 1 week, brains were removed and in situ hybridization and immunostaining was performed for NF-68 kDa, 160 kDa and 200 kDa in different phosphorylation states. After focal cerebral ischemia the levels of gene and protein expression of neurofilament proteins were increased in the border zone of the infarcted area compared with the unaffected contralateral site. Furthermore, the level of gene expression was significant lower in aged as in young animals. Focal cerebral ischemia resulted in a clearly increased number of immunostained axons in the penumbral region in both young and aged rats. On the other hand the immunostained apical dendrites became thicker and vacuolization appeared. Our results suggest that that neurofilament proteins are involved in response of brain to focal ischemia.

Delayed and blunted induction of mRNA for tissue plasminogen activator in the brain of old rats following pentylenetetrazole-induced seizure activity

The ability of the rodent brain to support plasticity-related phenomena declines with increasing age. Here we investigated the extent to which old rats retain the capacity to initiate transcription for immediate early genes, particularly as it relates to brain plasticity, in response to a strong stimulus. The intraperitoneal administration of pentylenetetrazole (PTZ) to rats of various ages evoked tonic-clonic seizures. Using an RNA gel-blot and in situ hybridization analysis, we found that 1 hour after the onset of seizure, messenger RNA (mRNA) for tissue plasminogen activator (TPA) was increased approximately 3.7-fold in the hippocampi of 3-month-old rats. The levels of TPA mRNA in the hippocampi and cortices of 3-month-old rats returned to control levels by 3 hours after PTZ administration. The levels of TPA mRNA increased 2.5-fold in the hippocampi of 18-month-old rats and 1.8-fold in the brains of the 28-month-old-rats at 3 hours and returned to basal levels by 15 hours following PTZ treatment. Quantitatively similar increases were calculated for the cortex. At peak induction the transcripts were localized throughout the cortical layers of the 3-month-old rats, whereas the TPA mRNA expression was restricted to cortical layer V of the older rats. Our results suggest that although the aging brain retains the capacity to respond to chemically induced seizures, the induction of TPA mRNA is temporarily delayed and the levels are diminished with increasing age. Because TPA has been implicated in neuronal plasticity, this finding suggests that immediate early genes are important factors in the limited plasticity of the aging brain.

Anomalous expression of microtubule-associated protein 1B in the hippocampus and cortex of aged rats treated with pentylenetetrazole

The aim of the present study was to assess the age-dependent response of microtubule-associated protein 1B, a plasticity-associated protein deriving from a late gene, following administration of an epileptogenic stimulus. The effect of a single administration of the convulsant pentylenetetrazole on microtubule-associated protein 1B expression in the hippocampal formation and cortex of three-, 18- and 28-month-old rats was assessed using northern blot analysis, in situ hybridization and immunohistochemistry. In three-month-old rats, we detected initial increases in microtubule-associated protein 1B messenger RNA at 15 h following pentylenetetrazole administration in the granule cells of the dentate gyrus, in the CA3 region of the hippocampus and in layers II/III of the entorhinal cortex, and these reached a maximum at 44 h. However, in the hippocampus and cortex of 18-month-old rats, the peak occurred at 15 h, and in the brains of 28-month-old rats a blunted peak was reached at 3 h. Pentylenetetrazole treatment in young rats resulted in a robust induction of microtubule-associated protein 1B immunoreactivity in the granule cells of the dentate gyrus and in layers II/III of the entorhinal cortex, but also produced a large decrease in the retrosplenial cortex. However, following pentylenetetrazole treatment in older rats, the granule cells of the dentate gyrus were nearly devoid of microtubule-associated protein 1B immunoreactivity, whereas the retrosplenial cortex showed no changes at all, and the entorhinal cortex had an expression pattern similar to that of young rats. Aberrant immunolabeling of microtubule-associated protein 1B occurred in cortical layer VI of the aged rats where, unlike in young rats, there was heavy staining of neuronal somata. These results suggest that the regulation of the plasticity-associated protein microtubule-associated protein 1B is altered in the ageing rat brain, with the peak of expression shifted to earlier times in 18-month-old rats and blunted, variable increases at even earlier times in 28-month-old rats.

Upregulation of MAP1B and MAP2 in the rat brain after middle cerebral artery occlusion: effect of age

Although stroke in humans usually afflicts the elderly, most experimental studies on the nature of cerebral ischemia have used young animals. This is especially important when studying restorative processes that are age dependent. To explore the potential of older animals to initiate regenerative processes after cerebral ischemia, the authors studied the expression of the juvenile-specific cytoskeletal protein, microtubule-associated protein (MAP) 1B, and the adult-specific protein, MAP2, in male Sprague-Dawley rats at 3 months and 20 months of age. The levels of MAP1B and MAP2 transcripts and the corresponding proteins declined with increasing age in the hippocampus. In the cortex, the levels of the transcripts did not change significantly with age, but the morphologic features of immunostained fibers were clearly affected by age; that is, cortical MAP1B fibers became thicker, and MAP2 fibers, more diffuse, in aged rats. Focal cerebral ischemia, produced by reversible occlusion of the right middle cerebral artery, resulted in a large decrease in the expression of both MAP1B and MAP2 in the infarct core at the messenger ribonucleic acid and protein levels. However, at 1 week after the stroke, there was vigorous expression of MAP1B and its messenger ribonucleic acid, as well as MAP2 protein, in the border zone adjacent to the infarct of 3-month-old and 20 month-old male Sprague-Dawley rats. The upregulation of these key cytologic elements generally was diminished in aged rats compared with young animals, although the morphologic features of fibers in the infarct border zone were similar in both age groups. These results suggest that the regenerative potential of the aged rat brain appears to be competent, although attenuated, at least with respect to MAP1B and MAP2 expression up to 20 months of age.

beta-Amyloid precursor protein and ss-amyloid peptide immunoreactivity in the rat brain after middle cerebral artery occlusion: effect of age

BACKGROUND AND PURPOSE

Previous studies have shown that the ss-amyloid precursor protein (ssAPP) is upregulated after cerebral ischemia and that the ss-amyloid (Ass) fragment may be toxic to brain cells. Although stroke in humans usually afflicts the elderly, most experimental studies on the nature of cerebral ischemia have used young animals. To test the hypothesis that the upregulation and/or persistence of amyloidogenic proteins is exacerbated in aged rats after cerebral ischemic stroke, we studied the expression of ssAPP and its proteolytic product Ass in the brains of young and old rats 7 days after temporary cerebral ischemia.

METHODS

Focal cerebral ischemia was produced by reversible occlusion of the right middle cerebral artery in 3- and 20-month-old male Sprague-Dawley rats. After 1 week, brains were removed and immunostaining was performed for ssAPP, Ass, and ED1 for macrophages and glial fibrillary acidic protein (GFAP).

RESULTS

Histological staining revealed that the degree of necrotic cavitation in the infarct core was relatively less in aged rats than in young rats, suggesting a slower pace of degenerative change and/or tissue removal in older animals. ssAPP immunoreactivity was robustly increased, primarily in macrophage-like, ED1-positive cells in the infarct core and in the penumbra of both young and aged animals. Ass immunoreactivity was evident in GFAP-positive astrocytic somata and processes, and also in clusters of small spherical structures in the penumbra. These Ass-immunoreactive minispheres were more numerous in aged rats than in young rats.

CONCLUSIONS

The presence of ssAPP and Ass immunoreactivity in the infarct core and penumbra indicates that cerebral ischemia promotes conditions that are favorable to the focal accumulation of ssAPP and its proteolytic fragments, especially in the aged brain.

Increased expression of microtubule-associated protein 1B in the hippocampus, subiculum, and perforant path of rats treated with a high dose of pentylenetetrazole

A single administration of the convulsant pentylenetetrazole (PTZ) initiates a complex pattern of long-term changes in microtubule-associated protein 1B (MAP1B) expression across the hippocampal formation. Using Northern blot and in situ hybridization we show that the first increases in MAP1B mRNA were detected at 15 h following PTZ administration in the granule cells of the dentate gyrus and CA3 region of the hippocampus and reached a maximum at 44 h. The levels of MAP1B mRNA in the subiculum peaked at later times (5 days). At 72 h MAP1B immunoreactivity was mainly localized in the granule-cell bodies and dentate inner and midmolecular layer as well as in neuronal cell bodies and the stratum lucidum, including the mossy fiber pathway of the CA3 region. By 5-10 days the levels of MAP1B in the pyramidal cells in the CA3 region decreased to very low levels; rather, heavy staining of interneuron-like cells and "strings-of-bead" structures all over the hippocampus and at the stratum oriens/alveus border were seen. The levels of MAP1B in the hippocampus returned to control levels by 20 days after PTZ administration. MAP1B immunoreactivity in the alvear path was also evident at 5 days postinjection at the CA1/alveus border. The intensity of MAP1B staining increased gradually in the perforant path starting at 72 h and persisted at high levels until day 35. Our studies show that (i) MAP1B is a temporal and regional marker for rapid and acute epileptic seizures and (ii) long-term increases in MAP1B in the perforant path might play a role in PTZ-induced seizures.

V+ fibronectin mRNA is increased in the brains of aged rats: effect of food restriction

Food restriction increases life-span in rodents. With regard to the central nervous system, underfeeding has been shown to have beneficial effects on synaptic transmission in old rats. However, the molecular events underlying functional changes in the brains of food-restricted rats are largely unknown. In the present study the levels of fibronectin mRNA containing the alternatively spliced segment V (FN-V+) as well as the levels of FN mRNA containing the alternatively spliced segment EIIIB (FN-EIIIB+), were examined by RNA gel blot hybridization in the brains of 3-day-old, 24-day-old, 10-month-old, 18-month-old, 30-month-old ad libitum (AL) fed, 30-month-old food-restricted (FR), and 35-37-month-old, FR rats. The hybridization signal for the FN-EIIIB+ mRNA was relatively abundant at early postnatal stages but very few transcripts were detected in the brains of adult, AL rats. The transcripts coding for FN-V+ mRNA were moderately expressed in the brains of 3-day-old, 24-day-old, 10-month-old, and 18-month-old rats. However, the FN-V+ mRNA signal was then prominently increased (approx. 3-fold) in the brains of the 30-month-old, AL rats vs. 10-month-old, AL rats, and further increased (approx. 2-fold) in the brains of 30-month-old, FR, as compared to 30-month-old, AL rats. However, the levels of FN-V+ mRNA were slightly decreased in the brains of very old (35-37-month) FR rats vs. 30-month-old FR rats. The distribution of fibronectin messenger RNA and protein was also investigated by non-radioactive in situ hybridization and immunohistochemistry, respectively. The most prominent expression of FN-V+ messenger RNA was seen in neurons of the hippocampus, including the granule cells of the dentate gyrus, and in layers III and V of the cortex of 30-month-old, FR rats. FN immunostaining closely paralleled the distribution of FN mRNA and was confined to the neuronal cell periphery. The upregulation of fibronectin gene expression upon exposure to glucocorticoids is well documented. Prolonged food restriction, acting as a stress factor, combined with decreased plasticity of glucocorticoid regulatory responses in the aged rats could cause an increase in the levels of FN mRNA and protein in the brains of old, FR rats. Since FN has been shown to provide an adhesive substrate for extending neurites, we conclude that food restriction may potentiate synaptic plasticity, via glucocorticoid receptor binding elements of the FN gene, in the brains of old rats.

[Alzheimer disease: involvement of the complement system in cell death. Gene expression of C1q and C3 in the frontal cortex of patients with Alzheimer disease and control probands]

Patients with Alzheimer's disease are found to have inflammatory changes in the vicinity of plaques and fibrils, and involvement of the complement system has been confirmed by immunocytochemical studies. In order to confirm these findings on the genetic plane, the prevalence of mRNAs for C1q and C3 complement components were investigated in our laboratory. We were able to show that the hybridization signals for complement C1q-mRNA on Northern blots of deceased Alzheimer patients were about 3.5 times as pronounced as in the case of control persons. In contrast to earlier reports, no difference in the expression of complement C3-mRNA in the brains of decreased Alzheimer patients and control persons was established. On the other hand, with the aid of non-radioactive in situ hybridization with digoxigenin-labelled riboprobes, it has been shown that complement C1q- and C3-mRNA is closely associated with the neurons.

Complement C1q and C3 mRNA expression in the frontal cortex of Alzheimer's patients

The levels and cellular localization of mRNA for complement C1q and C3 were examined by RNA gel blot and nonradioactive in situ hybridization in the frontal cortex of patients with Alzheimer's disease (AD) and age-matched controls. We found that the hybridization signal for C1q mRNA was markedly increased (approx. 3.5-fold) in the frontal cortex of AD patients compared to that in age-matched controls. In contrast to previous reports we also found that the levels of C3 mRNA, although well expressed, did not differ significantly between AD cases and age-matched controls. Nonradioactive in situ hybridization using digoxigenin-labeled ribo-probes revealed that transcripts coding for both C1q and C3 were closely associated with neurons. These results support the hypothesis that complement could play a role in neuronal degeneration which has been observed in the brain of AD patients.

Fibronectin mRNA (FN-V95+) is increased in the liver of old Sprague-Dawley rats: effect of food restriction

Because fibronectin (FN) mRNA has been shown to be increased in the brain of old rats and during in vivo and in vitro aging of both endothelial cells and fibroblasts, it was of interest to determine what effect age and caloric restriction have on the ability of liver cells to express FN mRNA. The prevalence of fibronectin mRNA containing the alternatively spliced variant V95 (FN-V95) was examined by RNA gel blot hybridization in the liver of 10-mo, 18-mo, 30-mo ad lib-fed (AL) and 30-mo food-restricted (FR) rats. The transcripts coding for FN-V95 mRNA were well expressed in the liver of 10-mo and 18-mo-old rats. The hybridization signal then increased (1.3-fold, p < .05) in the liver of 30-mo AL rats vs 10-mo-old rats. However, the prevalence of FN-V95 mRNA was dramatically decreased (approximately 4.5-fold, p < .01) in the liver of 30-mo food-restricted rats as compared to 30-mo-old AL rats. The distribution of FN-V95 mRNA was also investigated by non-radioactive in situ hybridization (ISH) on liver frozen sections. The hybridization signal for FN-V95 mRNA was evenly distributed among liver cells of 10-mo and 18-mo-old rats, while weak hybridization signals were sparsely scattered on liver sections derived from 30-mo-old FR rats. In contrast, strong hybridization signals showing a localized distribution were detected on liver sections obtained from 30-mo-old AL rats. Histologic examination of cryostat sections also revealed a massive accumulation of lipid droplets in the liver of 30-mo-old AL rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pentylenetetrazole-induced seizure up-regulates levels of microtubule-associated protein 1B mRNA and protein in the hippocampus of the rat

Stimuli that evoke seizure are capable of inducing structural changes in the hippocampus. However, late-acting genes related to these changes have not been described. Administration of pentylenetetrazole (PTZ; 50 mg/kg) to rats of various ages evoked tonic-clonic seizures. Using RNA gel blot analysis we found that the level of the mRNA for microtubule-associated protein 1B (MAP1B) was robustly increased in the hippocampus of 3-month-old rats. The levels of MAP1B mRNA in hippocampus peaked at 40 h and began to decline by 72 h following PTZ treatment. Immunoblotting with anti-MAP1B antibody demonstrates the increase in content of immunoreactive proteins 40-72 h after seizure onset in the hippocampus of PTZ-treated rats. These results indicate that MAP1B is a sensitive indicator of hippocampal structural changes occurring in response to PTZ-induced seizure activity.

Decortication and striatal mRNA: increases of mRNA for fibronectin, but not of NCAM or alpha-1 tubulin

Ipsilateral frontal cortex lesions damaged the corticostriatal input. Northern hybridization analysis showed increases in fibronectin (FN) mRNA, but not changes in mRNA for neural cell adhesion molecule (NCAM), neuro-filament-68 (NF-68) or alpha-tubulin (alpha-1T) 72 h post-lesion. In situ hybridization resolved a different spatial-temporal distribution. The superficial cell layer beneath the wound cavity showed transient elevations of FN mRNA that peaked at 72 h post-lesion. However, in the ipsilateral striatum, FN mRNA was maximal at later times than in the wound cavity, at 240 h post-lesion. Changes in NCAM and alpha-tubulin mRNAs in response to decortication occur only around the wound cavity but not in the deafferentated striatum. The different time courses of mRNA revealed by Northern blot analysis and in situ hybridization are most probably due to contamination of the ipsilateral striatum at dissection with superficial tissue adjacent to the wound cavity. These results suggest that cellular responses to ipsilateral decortication consist of two phases: (i) a wound healing process; and (ii) striatal responses to deafferentation.