A chronic physiological rat model of dementia

The Vascular Hypothesis of Alzheimer's Disease: A Key to Preclinical Prediction of Dementia Using Neuroimaging

The vascular hypothesis of Alzheimer's disease (VHAD) was proposed 24 years ago from observations made in our laboratory using aging rats subjected to chronic brain hypoperfusion. In recent years, VHAD has become a mother-lode to numerous neuroimaging studies targeting cerebral hemodynamic changes, particularly brain hypoperfusion in elderly patients at risk of developing Alzheimer's disease (AD). There is a growing consensus among neuroradiologists that brain hypoperfusion is likely involved in the pathogenesis of AD and that disturbed cerebral blood flow (CBF) can serve as a key biomarker for predicting conversion of mild cognitive impairment to AD. The use of cerebral hypoperfusion as a preclinical predictor of AD is becoming decisive in stratifying low and high risk patients that may develop cognitive decline and for assessing the effectiveness of therapeutic interventions. There is currently an international research drive from neuroimaging groups to seek new perspectives that can broaden our understanding of AD and improve lifestyle. Diverse neuroimaging methods are currently being used to monitor normal and dyscognitive brain activity. Some techniques are very powerful and can detect, diagnose, quantify, prognose, and predict cognitive decline before AD onset, even from a healthy cognitive state. Multimodal imaging offers new insights in the treatment and prevention of cognitive decline during advanced aging and better understanding of the functional and structural organization of the human brain. This review discusses the impact the VHAD and CBF are having on the neuroimaging technology that can usher practical strategies to help prevent AD.

Harpagoside Rescues the Memory Impairments in Chronic Cerebral Hypoperfusion Rats by Inhibiting PTEN Activity

Vascular dementia (VaD) is the second most common dementia worldwide. Unlike Alzheimer's disease, VaD does not yet have effective therapeutic drugs. Harpagoside is the most important component extracted from Harpagophytum procumbens, a traditional Chinese medicine that has been widely used. The neuroprotective effects of harpagoside have been studied in Aβ- and MPTP-induced neurotoxicity. However, whether harpagoside is protective against VaD is not clear. In this study, with the use of chronic cerebral hypoperfusion rats, a well-known VaD model, we demonstrated that chronic administration (two months) of harpagoside was able to restore both the spatial learning/memory and fear memory impairments. Importantly, the protective effects of harpagoside were not due to alterations in the physiological conditions, metabolic parameters, or locomotor abilities of the rats. Meanwhile, we found that harpagoside suppressed the overactivation of PTEN induced by CCH by enhancing PTEN phosphorylation. Furthermore, harpagoside elevated the activity of Akt and inhibited the activity of GSK-3β, downstream effectors of PTEN. Overall, our study suggested that harpagoside treatment might be a potential therapeutic drug targeting the cognitive impairments of VaD.

Arginine vasopressin ameliorates spatial learning impairments in chronic cerebral hypoperfusion via V1a receptor and autophagy signaling partially

Chronic cerebral hypoperfusion (CCH) is a major factor contributing to neurological disorders and cognitive decline. Autophagy activation is believed to provide both beneficial and detrimental roles during hypoxic/ischemic cellular injury. Although arginine vasopressin (AVP) has been strongly involved in many behaviors, especially in learning and memory, the effects of AVP on CCH and their molecular mechanisms remain unclear. Here, to investigate whether there was neuroprotective effects of AVP on CCH through V1a receptor (an AVP receptor) signaling, permanent bilateral carotid arteries occlusion (two vessel occlusion, 2VO) was used to establish a rat model of CCH, and hypertonic saline (5.3%) was injected intraperitoneally to induce the secretion of AVP. Results showed that hypertonic saline effectively alleviated spatial learning and memory deficit, enhanced synaptic plasticity of CA3-CA1 hippocampal synapses, upregulated N-methyl-d-aspartate receptor subunit 2B (NR2B) and postsynaptic density protein 95 (PSD-95) surface expressions, reduced oxidative stress and increased Nissl bodies in 2VO model rats. These phenomena were significantly decreased by V1a receptor antagonist SR49059. Interestingly, hypertonic saline also upregulated autophagy in the hippocampus of 2VO rats partly through V1a receptor. These findings imply that AVP has a beneficial role for the treatment of cognitive impairments partly through V1a receptor signaling in CCH, which is possibly related to improving synaptic plasticity by promoting NR2B and PSD-95 externalization and by enhancing autophagy.

Pathophysiological rat model of vascular dementia: magnetic resonance spectroscopy, microimaging and behavioral study

Chronic cerebral hypoperfusion and aging can be related to vascular dementia manifested by the decline in cognitive abilities and memory impairment. The identification of specific biomarkers of vascular disorder in early stages is important for the development of neuroprotective agents. In the present study, a three-vessel occlusion (3-VO) rat model of vascular dementia in the middle-aged rat brain was used to investigate the effect of global cerebral hypoperfusion. A multimodal study was performed using magnetic resonance spectroscopy, MR-microimaging, histology and behavioral tests. Our measurements showed a signal alteration in T2-weighted MR images, the elevation of T2 relaxation times and histologically proven neural cell death in the hippocampal area, as well as mild changes in concentration of proton and phosphorus metabolites. These changes were accompanied by mild behavioral alterations in the open field and slightly decreased habituation. The analysis of the effects of vascular pathology on cognitive functions and neurodegeneration can contribute to the development of new treatment strategies for early stages of neurodegeneration.

[Animal models of neurodegenerative diseases]

Numerous evidences indicate that the phenotype of a neurodegenerative disease and its pathogenetic mechanism are only loosely linked. The phenotype is directly related to the topography of the lesions and is reproduced whatever the mechanism as soon as the same neurons are destroyed or deficient: the symptoms of Parkinson disease are mimicked by any destruction of the neurons of the substantia nigra, caused for instance by the toxin MPTP. This does not mean that idiopathic Parkinson disease is due to MPTP. In the same way, mouse lines such as Reeler, Weaver and Staggerer in which ataxia occurs spontaneously does not help to understand human ataxias: now that mutations responsible for these phenotypes have been identified, it appears that one is responsible for lissencephaly (mutation of the reelin gene) and the other two have no equivalent in man. Therapeutic attempts, however, rely on the understanding of the pathogenetic mechanisms. Introducing a mutated human transgene in the genome of an animal has, in many instances, significantly improved this understanding. Transgenic mice have proven useful in reproducing lesions seen in neurodegenerative disease such as the plaques of Alzheimer disease (in the APP mouse which has integrated the mutated gene of the amyloid protein precursor), the tau glial and neuronal accumulation (seen in cases of frontotemporal dementias due to tau mutation), the nuclear inclusions caused by CAG triplet expansion (seen in the mutation of Huntington disease and autosomal dominant spinocerebellar ataxias). These recent advances have fostered numerous therapeutic attempts. Transgenesis in drosophila and in the worm Caenorhabditis elegans have opened new possibilities in the screening of protein partners, modifier genes, and potential therapeutic molecules. However, it is also becoming clear that introducing a human mutated gene in an animal does not necessarily trigger pathogenetic cascades identical to those seen in the human disease. Human diseases have to be studied in parallel with their animal models to ensure that the model mimic at least a few original mechanisms, on which new therapeutics may be tested.

New magnetic resonance spectroscopy biomarker for monitoring neurodegenerative diseases: animal models

Creatine kinase (CK) plays a central role in energy transfer in cells with high-energy demands, and the enzyme is rather susceptible to oxidative inactivation. The aim of the present study was to investigate whether the rate constant of forward CK reaction (k(for)) is a suitable indicator of alterations in cerebral energy metabolism. We monitored k(for) in the rat brain non-invasively by in vivo phosphorus ((31)P) magnetic resonance spectroscopy (MRS). To alter energy metabolism, we applied following experimental models: Huntington's disease, diabetes mellitus, chronic alcohol intoxication and chronic cerebral hypoperfusion (vascular dementia model). Results of our (31)P MRS experiment confirm importance of creatine kinase/phosphocreatinine (CK/PCr) system in the regulation of brain energy metabolism in vivo because a kinetic parameter k(for) was significantly changed in all above animal models that simulate neurodegenerative diseases or commonly during oxidative stress. Using this method we distinguished vascular dementia (VD) and Huntington disease (HD), because in VD model a kinetic parameter k(for) decreased and in the case HD increased. Considering the importance of CK for the maintenance of energy homeostasis in the brain, it is conceivable that an alteration of this enzyme activity in the brain may be one of the mechanisms by which various neurodegenerative diseases might be monitored just by means saturation transfer method (31)P MRS.

Inhibition of vascular nitric oxide after rat chronic brain hypoperfusion: spatial memory and immunocytochemical changes

An aging rat model of chronic brain hypoperfusion (CBH) that mimics human mild cognitive impairment (MCI) was used to examine the role of nitric oxide synthase (NOS) isoforms on spatial memory function. Rats with CBH underwent bilateral common carotid artery occlusion (2-vessel occlusion (2-VO)) for either 26 or 8 weeks and were compared with nonoccluded sham controls (S-VO). The neuronal and endothelial (nNOS/eNOS) constitutive inhibitor nitro-L-arginine methyl ester (L-NAME) 20 mg/kg was administered after 26 weeks for 3 days to 2-VO and S-VO groups and spatial memory was assessed with a modified Morris watermaze test. Only 2-VO rats worsened their spatial memory ability after L-NAME. Electron microscopic immunocytochemical examination using an antibody against eNOS showed 2-VO rats had significant loss or absence of eNOS-containing positive gold particles in hippocampal endothelium and these changes were associated with endothelial cell compression, mitochondrial damage and heavy amyloid deposition in hippocampal capillaries and perivascular region. In the 8-week study, three groups of 2-VO rats were administered an acute dose of 7-NI, aminoguanidine or L-NIO, the relatively selective inhibitors of nNOS, inducible NOS and eNOS. Only rats administered the eNOS inhibitor L-NIO worsened markedly their watermaze performance (P = 0.009) when compared with S-VO nonoccluded controls. We conclude from these findings that vascular nitric oxide derived from eNOS may play a critical role in spatial memory function during CBH possibly by keeping cerebral perfusion optimal through its regulation of microvessel tone and cerebral blood flow and that disruption of this mechanism can result in spatial memory impairment. These findings may identify therapeutic targets for preventing MCI and treating Alzheimer's disease.

Study of the oxidative stress in a rat model of chronic brain hypoperfusion

A multiple analysis of the cerebral oxidative stress was performed on a physiological model of dementia accomplished by three-vessel occlusion in aged rats. The forward rate constant of creatine kinase, k(for), was studied by saturation transfer (31)P magnetic resonance spectroscopy in adult and aged rat brain during chronic hypoperfusion. In addition, free radicals in aging rat brain homogenates before and/or after occlusion were investigated by spin-trapping electron paramagnetic resonance spectroscopy (EPR). Finally, biochemical measurements of oxidative phosphorylation parameters in the above physiological model were performed. The significant reduction of k(for) in rat brain compared to controls 2 and 10 weeks after occlusion indicates a disorder in brain energy metabolism. This result is consistent with the decrease of the coefficient of oxidative phosphorylation (ADP:O), and the oxidative phosphorylation rate measured in vitro on brain mitochondria. The EPR study showed a significant increase of the ascorbyl free radical concentration in this animal model. Application of alpha-phenyl-N-tert-butylnitrone (PBN) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) spin traps revealed formation of highly reactive hydroxyl radical (.OH) trapped in DMSO as the .CH(3) adduct. It was concluded that the ascorbate as a major antioxidant in brain seems to be useful in monitoring chronic cerebral hypoperfusion.

In vivo NMR studies of neurodegenerative diseases in transgenic and rodent models

In vivo magnetic resonance spectroscopy (MRS) and magnetic resonance imaging (MRI) provide unique quality to attain neurochemical, physiological, anatomical, and functional information non-invasively. These techniques have been increasingly applied to biomedical research and clinical usage in diagnosis and prognosis of diseases. The ability of MRS to detect early yet subtle changes of neurochemicals in vivo permits the use of this technology for the study of cerebral metabolism in physiological and pathological conditions. Recent advances in MR technology have further extended its use to assess the etiology and progression of neurodegeneration. This review focuses on the current technical advances and the applications of MRS and MRI in the study of neurodegenerative disease animal models including amyotrophic lateral sclerosis, Alzheimer's, Huntington's, and Parkinson's diseases. Enhanced MR measurable neurochemical parameters in vivo are described in regard to their importance in neurodegenerative disorders and their investigation into the metabolic alterations accompanying the pathogenesis of neurodegeneration.

Cognitive impairment and chronic cerebral hypoperfusion: what can be learned from experimental models

The relation between chronic cerebral hypoperfusion and cognitive functions has not been completely clarified. The resolution of cerebral hypoperfusion states, such as those induced by arteriovenous malformations or carotid stenosis/occlusion, has been reported to improve mental decline in humans. Subcortical vascular dementia is another human condition supposed to be linked with chronic cerebral hypoxia/ischemia. The extent of this cause/effect relation is, however, difficult to be assessed in humans, where different factors, such as ageing or subtle degenerative processes, can coexist and interact influencing cognitive performances. Experimental studies can help to elucidate this relation because they can use models of pure chronic/moderate cerebral hypoperfusion. An experimental model of chronic ischemia is the bilateral common carotid artery occlusion in the rat. In this paper, we present a review of experimental studies that evaluated cognitive functions in the rat with bilateral common carotid artery occlusion. We then present an experimental model of bilateral common carotid artery occlusion in the rat modified with respect to previous papers regarding both the surgical procedure and the neurocognitive evaluation that is focused on cognitive domains depending on subcortical-frontal circuits. We propose this model to investigate subcortical vascular dementia.

Persistent impairment of gait performances and working memory after bilateral common carotid artery occlusion in the adult Wistar rat

BACKGROUND

The clinical and pathophysiological effects of a chronic reduction of cerebral blood flow in humans are not completely known. We investigated whether rats subjected to bilateral common carotid artery occlusion (bCCA-o) developed focal neurological deficits, gait dysfunction, and working memory alterations.

METHODS

Eighteen male Wistar rats were subjected to bCCA-o, 13 were sham-operated. We assessed sensorimotor functions, gait on a 60 cm-long elevated bridge, and working memory (object recognition and Y maze tests) before and 30, 60, and 90 days after surgery. Histological analysis was performed in a subgroup of 10 rats.

RESULTS

No rat showed sensorimotor alterations after surgery. Although gait performances of both bCCA-o and sham-operated rats declined over time, the differences reached statistical significance only for the bCCA-o group (mean+/-SE: 26.8+/-5.0; 22.4+/-4.9; 24.5+/-5.5 cm at 30, 60, and 90 days, respectively) in comparison with baseline (52.9+/-5.2 cm; P<0.05). At 60 and 90 days, bCCA-o rats in comparison with sham-operated rats showed decreased performances on object recognition (discrimination index: 0.15+/-0.03 vs. 0.29+/-0.05 at 60 days and 0.10+/-0.04 vs. 0.41+/-0.07 at 90 days; P<0.05) and on Y maze test (alternating rats: 9.9 vs. 85.7% at 60 days and 16.6 vs. 100% at 90 days; P<0.01). In none of the animals were cerebral infarcts detected. Selective neuronal necrosis was observed in the cortex and hippocampus of both bCCA-o and sham-operated rats without any obvious difference.

CONCLUSIONS

bCCA-o in the Wistar rat induces persistent and progressive gait and working memory impairment without producing sensorimotor deficit or cerebral infarcts. This model may help to elucidate some physiopathological aspects of neurological impairment associated with states of cerebral chronic ischemia.

Astrocytes degenerate in frontotemporal dementia: possible relation to hypoperfusion

To understand the extent and specificity of astrocyte pathology in sporadic frontotemporal dementia (FTD), we examined several FTD cases for molecular and morphologic characteristics of astrocyte degeneration. We quantified reactive and degenerating astrocytes in sections of frontal, temporal, parietal, and occipital cortex identified using glial fibrillary acidic protein (GFAP) immunoreactivity, terminal deoxynucleotidyl transferase (TdT) labeling, and morphological characteristics and compared them with nondemented, age-matched control brains. Conventional and confocal microscopy revealed that a subpopulation of GFAP(+) astrocytes exhibited positive TdT labeling and beading of their processes in the frontal, temporal, and parietal cortices in 5 of 7 FTD cases that also exhibited gliosis. This morphology was reproduced in cultured astrocytes using ischemic insults. Degenerating astrocytes in FTD correlated inversely with cerebral blood flow as measured by single photon emission computed tomography (SPECT) analysis of (133)Xe inhalation (r = 0.55, p < 0.05). Furthermore, areas of significant astrogliosis corresponded to areas of SPECT hypoperfusion, suggesting that astrocytes may be affected by or perhaps have a causal role in the disturbances of cerebral perfusion in FTD.

Evidence that Alzheimer's disease is a microvascular disorder: the role of constitutive nitric oxide

Evidence is fast accumulating which indicates that Alzheimer's disease is a vascular disorder with neurodegenerative consequences rather than a neurodegenerative disorder with vascular consequences. It is proposed that two factors need to be present for AD to develop: (1) advanced ageing, (2) presence of a condition that lowers cerebral perfusion, such as a vascular-risk factor. The first factor introduces a normal but potentially insidious process that lowers cerebral blood flow in inverse relation to increased ageing; the second factor adds a crucial burden which further lowers brain perfusion and places vulnerable neurons in a state of high energy compromise leading to a cascade of neuronal metabolic turmoil. Convergence of the two factors above will culminate in a critically attained threshold of cerebral hypoperfusion (CATCH). CATCH is a hemodynamic microcirculatory insufficiency that will destabilize neurons, synapses, neurotransmission and cognitive function, creating in its wake a neurodegenerative state characterized by the formation of senile plaques, neurofibrillary tangles, amyloid angiopathy and in some cases, Lewy bodies. Since any of a considerable number of vascular-related conditions must be present in the ageing individual for cognition to be disturbed, CATCH identifies an important aspect of the heterogeneic disease profile assumed to be present in the AD syndrome. It is proposed that CATCH initiates AD by distorting regional brain capillary structure involving endothelial cell shape changes and impairment of nitric oxide (NO) release which affect signaling between the immune, cardiovascular and nervous systems. Evidence is presented that in many tissues there is a basal level of NO being produced and that the actions of several signaling molecules may initiate increases in basal NO levels. Moreover, these temporary increases in basal NO levels exert inhibitory cellular actions, via cellular conformational changes. Findings indicate that (a) constitutive NO is responsible for a basal or 'tonal' level of NO; (b) this NO keeps particular types of cells in a state of inhibition and (c) activation of these cells occurs through disinhibition. Consequently, tissues not maintaining a basal NO level are more prone to excitatory, immune, vascular and neural influences. Under such circumstances, these tissues cannot be down-regulated to normal basal levels, thus prolonging their excitatory state. Thus, the clinical convergence of advanced ageing in the presence of a chronic, pre-morbid vascular risk factor, can, in time, contribute to an endotheliopathy involving basal NO deficit, to the degree where regional metabolic dysfunction leads to cognitive meltdown and to progressive neurodegeneration characteristic of Alzheimer's disease.

A study of creatine kinase reaction in rat brain under chronic pathological conditions-chronic ischemia and ethanol intoxication

Creatine kinase reaction rates were measured by the magnetisation transfer technique in brains of healthy adult and aged rats and in rats with chronic cerebral ischemia and chronic ethanol intoxication. These measurements indicated that the rate constant of the creatine kinase reaction is significantly reduced in the case of severe chronic cerebral ischemia in aged rats. In the adult rats, during chronic ethanol intoxication after 3 weeks of administration of 3 ml of 30% ethanol once a day via a gastric tube, a significant decrease in the pseudo first-order rate constant k(for) of the creatine kinase reaction was also found. In contrast, mild chronic cerebral ischemia in adult rats produced an increase in the reaction rate 4 weeks after occlusion. At the same time, corresponding conventional phosphorus magnetic resonance spectra showed negligible changes in signal intensities.

Chronic cerebrovascular ischemia in aged rats: effects on brain metabolic capacity and behavior

The objective of this study was to model one of the risk factors for the development of late-onset Alzheimer's disease, decreased cerebral blood flow. Aging rats were tested for visuospatial behavioral deficits after permanent surgical occlusion of both carotid arteries. This was followed after 4 weeks by quantitative cytochrome oxidase histochemical mapping of metabolic capacity throughout the brain. The brain regions affected were related to observed deficits in spatial memory (CA1 and posterior parietal cortex), visually guided movements (superior colliculus and secondary visual cortex), motor coordination (red nucleus), and escape behavior (central gray). The results suggest that deficits in visuospatial learning are not exclusively the result of hippocampal dysfunction, but may be directly correlated with altered oxidative energy metabolism in other integrative visuomotor regions identified in this study. It was concluded that chronic cerebrovascular ischemia in this aged rat model produces neurometabolic and behavioral alterations that may be relevant for an increased risk for the development of Alzheimer's disease.

Critically attained threshold of cerebral hypoperfusion: the CATCH hypothesis of Alzheimer's pathogenesis

This review discusses the experimental and clinical data which indicate that chronic cerebral hypoperfusion can affect metabolic, anatomic, and cognitive function adversely. In aged but not young animals, chronic brain hypoperfusion results in regional pre- and post-synaptic changes, protein synthesis abnormalities, energy metabolic dysregulation, reduced glucose utilization, cholinergic receptor loss, and visuo-spatial memory deficits. Additionally, aging animals that are kept for prolonged periods of time after chronic brain hypoperfusion, also develop brain capillary degeneration in CA1 hippocampus and neuronal damage extending from the hippocampal region to the temporo-parietal cortex where neurodegenerative tissue atrophy eventually forms. All these pathologic events occur in rodents in the absence of senile plaques and neurofibrillary tangles. Alzheimer brains reveal similar biochemical and structural changes as those experimentally induced in aging animals. Moreover, regional cerebral hypoperfusion is one of the earlier (if not the earliest) clinical manifestations in both the sporadic and familial forms of Alzheimer's disease. In addition, therapy that improves or increases cerebral perfusion is generally of some benefit to Alzheimer patients. Conversely, a variety of disorders with different etiologies that impair or diminish cerebral perfusion are reported to be risk factors for this dementia. These findings have prompted us to propose the concept that advanced aging in the presence of a vascular risk factor can converge to create a critically attained threshold of cerebral hypoperfusion (CATCH) that triggers regional brain microcirculatory disturbances and impairs optimal delivery of energy substrates needed for normal brain cell function. The outcome of this defect generates a chain of events leading to the progressive evolution of brain metabolic, cognitive and tissue pathology that characterize Alzheimer's disease. The possible role of CATCH in familial and early onset Alzheimer's disease is briefly discussed from a theoretical vantagepoint. The growing and most recent evidence in support of the CATCH concept is the focus of this review.

Adverse psychological impact, glutamatergic dysfunction, and risk factors for Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cell loss and pathological changes in neuronal transmission. In particular, malfunction in glutamatergic activity may be associated with the impairment of memory seen in Alzheimer patients. Both hypoactivation and hyperactivation of glutamatergic systems seem to cause impeded cognitive processing in animals. Rats subjected to rearing in isolation display reduced levels of glutamate in temporal regions accompanied by impaired learning and memory. Similar cognitive deficits are also seen in animals exposed to behavioral stress. Stress appears to have deleterious effects on cognition caused by glutamate neurotoxicity leading to attenuated synaptic activity. It is suggested that stress may represent a potential risk factor for AD. The known risk factors for AD (age, heredity, head trauma, low education, depression) may all be related to glutamatergic dysfunction. Some difficulties with pharmacological approaches based on glutamatergic agonists are discussed. It is suggested that optimal glutamate-mediated neurotransmission throughout life may prevent the occurrence of mental decline associated with AD.

Creatine kinase reaction rates in rat brain during chronic ischemia

Creatine kinase reaction rates were measured by magnetisation transfer technique in the brain of healthy adult and aged rats and in the rats with mild or severe chronic cerebral ischemia. These measurements indicated that the rate constant of the creatine kinase reaction is significantly reduced in the case of chronic brain ischemia in aged rats. In contrast, occlusion of both carotid arteries in adult rats produced a slight increase in the reaction rate 4 weeks after occlusion. At the same time, corresponding conventional phosphorus magnetic resonance spectra showed negligible changes in signal intensities.

Chronic cerebral hypoperfusion disrupts discriminative behavior in acquired-learning rats

We describe an 'acquired-learning' rat model that was used to investigate the effects of chronic cerebral hypoperfusion on the maintenance of previously acquired discriminative behavior using the discriminating learning task. Male Wistar rats, aged 11 weeks, were trained to discriminate between lamp-on and lamp-off states under an operant-type learning procedure. After 30 sessions, we selected 'acquired-learning' rats with an average discrimination ratio higher than 75% recorded during the last three sessions. Chronic hypoperfusion was then induced by permanent ligation of both common carotid arteries under pentobarbital anesthesia. The rats were tested after surgery over a period of 12 weeks and brain tissue was analyzed for muscarinic acetylcholine receptor (mACh-R) binding. Cerebral hypoperfusion resulted in a significant reduction in the discrimination ratio throughout the observation period, compared with sham-operated rats. However, chronic hypoperfusion would not affect on motor function. The maximum number of mACh-R examined 12 weeks after the operation was significantly reduced in the frontal cortex and hippocampus in the hypoperfusion group. Impaired discrimination learning was associated with a reduction in mACh-R. Our findings suggest that chronic cerebral hypoperfusion in acquired-learning rats is a useful model for investigating the pathophysiology of dementia and that cortical and/or hippocampal cholinergic systems contributes to learning impairment, at least, in our learning task.

Reversal of ischemic-induced chronic memory dysfunction in aging rats with a free radical scavenger-glycolytic intermediate combination

Rats were subjected to bilateral carotid artery occlusion (2-VO) or sham occlusion (No-VO) and tested 12 weeks for visuo-spatial memory (VSM) function. After 14 weeks, 2-VO rats (N = 4) showing severe visuo-spatial memory impairment were given dimethyl sulfoxide (DMSO)-fructose 1,6-diphosphate (FDP) i.p. for seven days and retested on the water maze. After DMSO-FDP, a 54% improvement in their VSM was seen which nearly reached control No-VO values. Untreated 2-VO (N = 4) and No-VO (N = 8) rats showed no significant changes in their VSM. DMSO-FDP treatment was discontinued and rats were retested on the water maze but improvement was lost and VSM function regressed to pretreatment levels. Immunohistochemical examination showed minimal neuronal damage in all 2-VO rats and slight loss of microtubule associated protein-2. Glial fibrillary acidic protein immunostaining increase was observed only in untreated 2-VO rats. The results indicate that a DMSO-FDP combination improves VSM secondary to chronic brain hypoperfusion.

Reduced cytochrome oxidase and memory dysfunction after chronic brain ischemia in aged rats

The effects of chronic cerebrovascular ischemia on memory function and cytochrome oxidase (CO) activity were investigated. Cerebrovascular insufficiency was induced by permanent bilateral carotid artery ligation (2-VO) in 19 month old rats. Sham surgery in no-vessel occlusion (no-VO) rats were used for controls. Memory function was tested 1 week prior to surgery and then weekly for 21 days using the Morris water maze. Regional brain activity of CO was measured 4 weeks after surgery by quantitative histochemistry. Histologic examination of brain slices was used to evaluate any neuropathology present. Results showed that 2-VO rats were significantly impaired in the water maze task at each testing period with respect to no-VO controls. In addition, CO activity in 2-VO rats was markedly reduced only in the dorsal CA1 region of the hippocampus and in the posterior parietal cortex. These brain regions are involved in visuo-spatial memory mechanisms. Analysis of other brain regions in 2-VO rats did not reveal further CO activity changes. There were no damaged or loss of neurons in 2-VO or no-VO groups in any region examined, including CA1 and posterior parietal cortex. The CA1 region however, is known to undergo neuronal loss 25 weeks after chronic 2-VO suggesting that this vascular insult can induce a slowly-evolving cascade consisting of neuronal damage, atrophy and death. The present findings indicate that reduced CO activity in CA1 and posterior parietal regions can predict neural damage and atrophy prior to structural perikaryal pathology following chronic brain ischemia. In addition, the data shows that neuronal energy metabolic deficiency may initiate visuo-spatial memory impairment in this aging rat model.

Correlates between nuclear magnetic resonance spectroscopy, diffusion weighted imaging, and CA1 morphometry following chronic brain ischemia

Chronic brain ischemia (CBI) was induced in aging (13 month) rats by ligating the left subclavian artery and placing temporary occluders in each common carotid artery [three-vessel occlusion (3-VO)]. Carotid artery occluders were removed after 1, 2, or 3 weeks following brain ischemia or maintained for 9 weeks. Two rats were kept with their occluders in place for 25 weeks. On weeks 3 and 9 after CBI, 31P-/1H-nuclear magnetic resonance (NMR) spectroscopy and high resolution diffusion weighted imaging were performed in vivo, non-invasively for detection of hippocampal high energy phosphates, lactate, intracellular pH, N-acetyl-aspartate, choline, glutamate, creatine, and structural alterations of the brain following CBI. Brains were histologically processed for morphometry of glial fibrillary acidic protein (GFAP) and CA1 damaged neurons 9 weeks after CBI. 31P-/1H-NMR spectroscopy showed that high energy substrates remained normal in ischemic animals when compared to non-ischemic controls except for an elevation of phosphomonesters in the hippocampal region. Rats deoccluded 1 and 2 weeks after initiation of CBI had no NMR spectroscopic or imaging changes. Rats kept ischemic for 9 weeks showed high signal intensities in the parietal cortex detected by diffusion weighted imaging as well as CA1 damage and increased GFAP density but no cortical atrophy or neuronal damage could be detected histologically. Rats kept ischemic for 25 weeks showed extensive cortical atrophy which corresponded to the high signal intensity observed with diffusion weighted imaging in the group kept ischemic for 9 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)