Learning deficit in immature rabbits with aluminum-induced neurofibrillary changes

Naproxen as a potential candidate for promoting rivastigmine anti-Alzheimer activity against aluminum chloride-prompted Alzheimer's-like disease in rats; neurogenesis and apoptosis modulation as a possible underlying mechanism

BACKGROUND AND AIM

Alzheimer's disease (AD) is one of the leading causes of dependence and disability among the elderly worldwide. The traditional anti-Alzheimer medication, rivastigmine, one of the cholinesterase inhibitors (ChEIs), fails to achieve a definitive cure. We tested the hypothesis that naproxen administration to the rivastigmine-treated aluminum chloride (AlCl3) Alzheimer's rat model could provide an additive neuroprotective effect compared to rivastigmine alone.

MATERIALS AND METHODS

The studied groups were control (Cont), AlCl3 treated (Al), rivastigmine treated (RIVA), naproxen treated (Napro), and combined rivastigmine and naproxen treated (RIVA + Napro). Rats' memory, spatial learning, and cognitive behavior were assessed followed by evaluation of hippocampal acetylcholinesterase (AChE) activity. Hippocampal and cerebellar histopathology were thoroughly examined. Activated caspase-3 and the neuroepithelial stem cells marker; nestin expressions were immunohistochemically assayed.

RESULTS

AD rats displayed significantly impaired memory and cognitive function, augmented hippocampal AChE activity; massive neurodegeneration associated with enhanced astrogliosis, apoptosis, and impaired neurogenesis. Except for the enhancement of neurogenesis and suppression of apoptosis, the combination therapy had no additional neuroprotective benefit over rivastigmine-only therapy.

CONCLUSION

Naproxen's efficacy was established by its ability to function at the cellular level, improved neurogenesis, and decreased, apoptosis without having an additional mitigating impact on cognitive impairment in rivastigmine-treated AD rats.

EGCG Nanoparticles Attenuate Aluminum Chloride Induced Neurobehavioral Deficits, Beta Amyloid and Tau Pathology in a Rat Model of Alzheimer's Disease

Rational: Alzheimer's disease (AD) is a neurodegenerative pathology characterized by the presence of neuritic plaques and neurofibrillary tangles. Aluminum has been reported to play an important role in the etiology and pathogenesis of this disease. Hence, the present study aimed to evaluate the neuroprotective role of epigallocatechin-gallate (EGCG) loaded nanoparticles (nanoEGCG) against aluminum chloride (AlCl3) induced neurobehavioral and pathological changes in AD induced rats. Method: 100 mg/kg body weight AlCl3 was administered orally for 60 days, which was followed by 10 mg/kg body weight free EGCG and nanoEGCG treatment for 30 days. Morris water maze, open field and novel object recognition tests were employed for neurobehavioral assessment of the rats. This was followed by histopathological assessment of the cortex and the hippocampus in the rat brain. For further validation biochemical, immunohistochemistry and western blot assays were carried out. Result: Aluminum exposure reduced the exploratory and locomotor activities in open field and significantly reduced the memory and learning curve of rats in Morris water maze and novel object recognition tests. These neurobehavioral impairments were significantly attenuated in nanoEGCG treated rats. Histopathological assessment of the cortex and hippocampus of AlCl3 induced rat brains showed the presence of both neuritic plaques and neurofibrillary tangles. In nanoEGCG treated rats this pathology was absent. Significant increase in biochemical, immunohistochemical and protein levels was noted in AlCl3 induced rats. While these levels were greatly reduced in nanoEGCG treated rats. Conclusion: In conclusion, this study strengthens the hypothesis that EGCG nanoparticles can reverse memory loss, neuritic plaque and neurofibrillary tangles formation.

Multiple pharmacological activities of Caesalpinia crista against aluminium-induced neurodegeneration in rats: Relevance for Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia and mainly affects cognitive function of the aged populations. Aluminium, a neurotoxic metal, has been suggested as a contributing factor of AD. Caesalpinia crista is a medicinal plant known for its anti-microbial, anti-inflammatory and anti-oxidant properties. The present study was conducted in order to evaluate the neuroprotective effects of methanolic extracts of C. crista (MECC) on aluminium-induced neurodegeneration in rats. Co-administration with MECC significantly and dose dependently ameliorated the aluminium-dependent cognitive impairment, AChE hyperactivity and oxidative stress in the hippocampus and in the frontal cortex of rat brain. Moreover, MECC reduced the neuronal injury induced by aluminium as shown by the diminution of neuron loss and pyknosis in the CA1 and CA3 regions of the hippocampus. From this study, it is inferred that MECC protect against aluminium-induced behavioral alterations, cognitive function, oxidative stress and neuroinflammation in vivo. Therefore, this plant may serve as a source of natural products having multiple functions and could be utilized as an anti-AD preparation.

Aluminium oxide nanoparticles compromise spatial learning and memory performance in rats

Recently, the biosafety and potential influences of nanoparticles on central nervous system have received more attention. In the present study, we assessed the effect of aluminium oxide nanoparticles (Al2O3-NPs) on spatial cognition. Male Wistar rats were intravenously administered Al2O3-NP suspension (20 mg/kg body weight/day) for four consecutive days, after which they were assessed. The results indicated that Al2O3-NPs impaired spatial learning and memory ability. An increment in malondialdehyde levels with a concomitant decrease in superoxide dismutase activity confirmed the induction of oxidative stress in the hippocampus. Additionally, our findings showed that exposure to Al2O3-NPs resulted in decreased acetylcholinesterase activity in the hippocampus. Furthermore, Al2O3-NPs enhanced aluminium (Al) accumulation and disrupted mineral element homoeostasis in the hippocampus. However, they did not change the morphology of the hippocampus. Our results show a connection among oxidative stress, disruption of mineral element homoeostasis, and Al accumulation in the hippocampus, which leads to spatial memory deficit in rats treated with Al2O3-NPs.

Astaxanthin ameliorates aluminum chloride-induced spatial memory impairment and neuronal oxidative stress in mice

Aluminum chloride induces neurodegenerative disease in animal model. Evidence suggests that aluminum intake results in the activation of glial cells and generation of reactive oxygen species. By contrast, astaxanthin is an antioxidant having potential neuroprotective activity. In this study, we investigate the effect of astaxanthin on aluminum chloride-exposed behavioral brain function and neuronal oxidative stress (OS). Male Swiss albino mice (4 months old) were divided into 4 groups: (i) control (distilled water), (ii) aluminum chloride, (iii) astaxanthin+aluminum chloride, and (iv) astaxanthin. Two behavioral tests; radial arm maze and open field test were conducted, and OS markers were assayed from the brain and liver tissues following 42 days of treatment. Aluminum exposed group showed a significant reduction in spatial memory performance and anxiety-like behavior. Moreover, aluminum group exhibited a marked deterioration of oxidative markers; lipid peroxidation (MDA), nitric oxide (NO), glutathione (GSH) and advanced oxidation of protein products (AOPP) in the brain. To the contrary, co-administration of astaxanthin and aluminum has shown improved spatial memory, locomotor activity, and OS. These results indicate that astaxanthin improves aluminum-induced impaired memory performances presumably by the reduction of OS in the distinct brain regions. We suggest a future study to determine the underlying mechanism of astaxanthin in improving aluminum-exposed behavioral deficits.

Protective effect of selenium against aluminum chloride-induced Alzheimer's disease: behavioral and biochemical alterations in rats

In present study, selenium was selected for evaluating effect of selenium on aluminum chloride (AlCl3)-induced Alzheimer's disease in rats. Thirty Wistar rats were divided into five groups of six in each. Group I (control) received distilled water, group II-AlCl3 (100 mg/kg, p.o.), group III-selenium (1 mg/kg, p.o.), group IV-AlCl3 + vitamin E (100 mg/kg, p.o. + 100 mg/kg, p.o.), and group V-AlCl3 + selenium (100 mg/kg, p.o. + 1 mg/kg, p.o.) for 21 days. At end of experiment, various behavioral, biochemical, and histopathological assessments were carried out. The animals showed increase in time to reach platform in Morris water maze and decreased step-down latencies in passive avoidance test indicating learning and memory impairment in aluminum chloride-treated group, but administration of selenium decreased time to reach platform in Morris water maze, increased step-down latencies, and strengthened its memory action in drug-treated animals. There was decrease in muscle strength measured by rotarod test indicating motor incoordination and decrease in locomotor activity assessed by actophotometer test in AlCl3 control group, whereas in selenium-AlCl3 group, there was improvement in muscle strength and locomotion. Biochemical analysis of the brain revealed that chronic administration of AlCl3 significantly increased lipid peroxidation and decreased levels of acetyl cholinesterase, catalase, reduced glutathione and glutathione reductase, an index of oxidative stress process. Administration of selenium attenuated lipid peroxidation and ameliorated the biochemical changes. There were marked changes at subcellular level observed by histopathology studies in AlCl3 group, and better improvement in these changes was observed in selenium + AlCl3group. Therefore, this study strengthens the hypothesis that selenium helps to combat oxidative stress produced by accumulation of AlCl3 in the brain and helps in prophylaxis of Alzheimer's diseases.

Systematic review of potential health risks posed by pharmaceutical, occupational and consumer exposures to metallic and nanoscale aluminum, aluminum oxides, aluminum hydroxide and its soluble salts

Abstract Aluminum (Al) is a ubiquitous substance encountered both naturally (as the third most abundant element) and intentionally (used in water, foods, pharmaceuticals, and vaccines); it is also present in ambient and occupational airborne particulates. Existing data underscore the importance of Al physical and chemical forms in relation to its uptake, accumulation, and systemic bioavailability. The present review represents a systematic examination of the peer-reviewed literature on the adverse health effects of Al materials published since a previous critical evaluation compiled by Krewski et al. (2007) . Challenges encountered in carrying out the present review reflected the experimental use of different physical and chemical Al forms, different routes of administration, and different target organs in relation to the magnitude, frequency, and duration of exposure. Wide variations in diet can result in Al intakes that are often higher than the World Health Organization provisional tolerable weekly intake (PTWI), which is based on studies with Al citrate. Comparing daily dietary Al exposures on the basis of "total Al"assumes that gastrointestinal bioavailability for all dietary Al forms is equivalent to that for Al citrate, an approach that requires validation. Current occupational exposure limits (OELs) for identical Al substances vary as much as 15-fold. The toxicity of different Al forms depends in large measure on their physical behavior and relative solubility in water. The toxicity of soluble Al forms depends upon the delivered dose of Al(+3) to target tissues. Trivalent Al reacts with water to produce bidentate superoxide coordination spheres [Al(O2)(H2O4)(+2) and Al(H2O)6 (+3)] that after complexation with O2(•-), generate Al superoxides [Al(O2(•))](H2O5)](+2). Semireduced AlO2(•) radicals deplete mitochondrial Fe and promote generation of H2O2, O2 (•-) and OH(•). Thus, it is the Al(+3)-induced formation of oxygen radicals that accounts for the oxidative damage that leads to intrinsic apoptosis. In contrast, the toxicity of the insoluble Al oxides depends primarily on their behavior as particulates. Aluminum has been held responsible for human morbidity and mortality, but there is no consistent and convincing evidence to associate the Al found in food and drinking water at the doses and chemical forms presently consumed by people living in North America and Western Europe with increased risk for Alzheimer's disease (AD). Neither is there clear evidence to show use of Al-containing underarm antiperspirants or cosmetics increases the risk of AD or breast cancer. Metallic Al, its oxides, and common Al salts have not been shown to be either genotoxic or carcinogenic. Aluminum exposures during neonatal and pediatric parenteral nutrition (PN) can impair bone mineralization and delay neurological development. Adverse effects to vaccines with Al adjuvants have occurred; however, recent controlled trials found that the immunologic response to certain vaccines with Al adjuvants was no greater, and in some cases less than, that after identical vaccination without Al adjuvants. The scientific literature on the adverse health effects of Al is extensive. Health risk assessments for Al must take into account individual co-factors (e.g., age, renal function, diet, gastric pH). Conclusions from the current review point to the need for refinement of the PTWI, reduction of Al contamination in PN solutions, justification for routine addition of Al to vaccines, and harmonization of OELs for Al substances.

Modeling Alzheimer's disease with non-transgenic rat models

Alzheimer's disease (AD), for which there is no cure, is the most common form of dementia in the elderly. Despite tremendous efforts by the scientific community, the AD drug development pipeline remains extremely limited. Animal models of disease are a cornerstone of any drug development program and should be as relevant as possible to the disease, recapitulating the disease phenotype with high fidelity, to meaningfully contribute to the development of a successful therapeutic agent. Over the past two decades, transgenic models of AD based on the known genetic origins of familial AD have significantly contributed to our understanding of the molecular mechanisms involved in the onset and progression of the disease. These models were extensively used in AD drug development. The numerous reported failures of new treatments for AD in clinical trials indicate that the use of genetic models of AD may not represent the complete picture of AD in humans and that other types of animal models relevant to the sporadic form of the disease, which represents 95% of AD cases, should be developed. In this review, we will discuss the evolution of non-transgenic rat models of AD and how these models may open new avenues for drug development.

Naringin protects memory impairment and mitochondrial oxidative damage against aluminum-induced neurotoxicity in rats

Aluminum has been indicated in neurodegenerative disorders and naringin, a bioflavonoid has been used to reduce neurotoxic effects of aluminum against aluminum chloride-induced rats. Therefore, present study has been designed to explore the possible role of naringin against aluminum-induced cognitive dysfunction and oxidative damage in rats. Aluminum (100 mg/kg) and naringin (40 and 80 mg/kg) drug treatment were administered orally for six weeks to male wistar rats. Various behavioral performance tasks, biochemical, mitochondrial oxidative parameters, and aluminum concentration in the brain were assessed. Aluminum chloride treatment significantly caused cognitive dysfunction and mitochondria oxidative damage as compared to vehicle treated control group. Besides, aluminum chloride treatment significantly increased acetyl cholinesterase activity and aluminum concentration in the brain as compared to sham. Chronic administration of naringin significantly improved cognitive performance and attenuated mitochondria oxidative damage, acetyl cholinesterase activity, and aluminum concentration in aluminum-treated rats as compared to control rats. Results of the study demonstrate neuroprotective potential of naringin against aluminum chloride-induced cognitive dysfunction and mitochondrial oxidative damage.

Potential therapeutic effect of nanobased formulation of rivastigmine on rat model of Alzheimer's disease

Background

To sustain the effect of rivastigmine, a hydrophilic cholinesterase inhibitor, nanobased formulations were prepared. The efficacy of the prepared rivastigmine liposomes (RLs) in comparison to rivastigmine solution (RS) was assessed in an aluminium chloride (AlCl₃)-induced Alzheimer’s model.

Methods

Liposomes were prepared by lipid hydration (F1) and heating (F2) methods. Rats were treated with either RS or RLs (1 mg/kg/day) concomitantly with AlCl₃ (50 mg/kg/day).

Results

The study showed that the F1 method produced smaller liposomes (67.51 ± 14.2 nm) than F2 (528.7 ± 15.5 nm), but both entrapped the same amount of the drug (92.1% ± 1.4%). After 6 hours, 74.2% ± 1.5% and 60.8% ± 2.3% of rivastigmine were released from F1 and F2, respectively. Both RLs and RS improved the deterioration of spatial memory induced by AlCl₃, with RLs having a superior effect. Further biochemical measurements proved that RS and RLs were able to lower plasma C-reactive protein, homocysteine and asymmetric dimethy-larginine levels. RS significantly attenuated acetylcholinesterase (AChE) activity, whereas Na⁺/K⁺-adenosine triphosphatase (ATPase) activity was enhanced compared to the AlCl₃-treated animals; however, RLs succeeded in normalization of AChE and Na⁺/K⁺ ATPase activities. Gene-expression profile showed that cotreatment with RS to AlCl₃-treated rats succeeded in exerting significant decreases in BACE1, AChE, and IL1B gene expression. Normalization of the expression of the aforementioned genes was achieved by coadministration of RLs to AlCl₃-treated rats. The profound therapeutic effect of RLs over RS was evidenced by nearly preventing amyloid plaque formation, as shown in the histopathological examination of rat brain.

Conclusion

RLs could be a potential drug-delivery system for ameliorating Alzheimer’s disease.

Aluminium and Alzheimer's disease

The hypothesis that aluminium (Al) is a cause of (or a risk factor in) the development of beta-amyloid plaques and neurofibrillary tangles (NFT) and dementia in Alzheimer's disease (AD) is based on studies by Wisniewski et al, Klatzo et al and Terry & Peña in 1965 that showed that injection of experimental animals with Al compounds induces the formation of NFT. Other publications revealed that Al affects cognitive functions in experimental animals and humans undergoing dialysis for renal failure. Electron probe and laser microprobe mass analysis (LAMMA) studies have demonstrated the presence of Al in NFT and cores of amyloid stars and nuclei of neurons in AD patients. Other studies have indicated the association between amyotrophic lateral sclerosis/Guam parkinsonism-dementia complex and Al in the environment. A recent report suggests that the chelating agent desferrioxamine slows the rate of cognitive decline in AD patients. Extensive studies of the pathology of AD and Al-induced encephalopathy by our group and others indicate that Al does not cause Alzheimer's disease neuropathology. However, under certain conditions, cognition can be affected when Al enters the brain. Therefore, for individuals with renal failure or undergoing dialysis or individuals with a damaged blood-brain barrier, the intake of Al should be controlled.

Cerebellar Granule Cell Death Induced by Aluminum

Using flow cytometry of acutely isolated cerebellar granule cell neurons, we have determined the effects of Al (III) on viability, membrane potential, intracellular calcium concentration and generation of reactive oxygen species (ROS). Al (III) killed granule cells in a time- and concentration-dependent fashion when monitored by use of the DNA-binding dye, propidium iodide. The threshold concentration was about 50 micromolar, and cell death at 100 micromolar was apparent after 30 min exposure and increased over time. Cell death was accompanied by cell swelling and a decrease in membrane potential, and was not dependent on external calcium concentration. While exposure to Al (III) was accompanied by an increase in ROS and an elevation of intracellular calcium concentration, calcium chelators and ROS scavengers did not reduce cell death. The action of Al (III) was not accompanied by activation of caspase-3 or an increase in annexin-V binding, both indicators of apoptosis. In the presence of intracellular O,O'-bis(2-aminophenyl)ethyleneglycol-N,N,N',N'-tetraacetic acid (BAPTA) and absence of extracellular calcium there was still a fluo-3 signal, which likely reflects an accumulation of intracellular Al (III). These observations suggest that the cell death is subsequent to intracellular accumulation of Al (III) and subsequent perturbation of cellular metabolism.

Aluminum complexing enhances amyloid β protein penetration of blood–brain barrier

A significant co-morbidity of Alzheimer's disease and cerebrovascular impairment suggests that cerebrovascular dysregulation is an important feature of dementia. Amyloid beta protein (Abeta), a relevant risk factor in Alzheimer's disease, has neurotoxic properties and is thought to play a critical role in the cognitive impairments. Previously, we demonstrated that the 42mer of Abeta (Abeta42) complexed with aluminum (Al-Abeta42) is much more cytotoxic than non-complexed Abeta42. The level of Abeta in the brain is a balance between synthesis, degradation, and fluxes across the blood-brain barrier (BBB). In the present paper, we determined whether complexing with aluminum affected the ability of radioactively iodinated Abeta to cross the in vivo BBB. We found that the rates of uptake of Al-Abeta42 and Abeta42 were similar, but that Al-Abeta42 was sequestered by brain endothelial cells much less than Abeta42 and so more readily entered the parenchymal space of the brain. Al-Abeta42 also had a longer half-life in blood and had increased permeation at the striatum and thalamus. Brain-to-blood transport was similar for Al-Abeta42 and Abeta42. In conclusion, complexing with aluminum affects some aspects of blood-to-brain permeability so that Al-Abeta42 would have more ready access to brain cells than Abeta42.

A new insight on Al-maltolate-treated aged rabbit as Alzheimer's animal model

Lack of an adequate animal model for Alzheimer's disease (AD) has limited an understanding of the pathogenesis of the disease and the development of therapeutic agents targeting key pathophysiological processes. There are undoubtedly few satisfactory animal models for exploring therapies targeting at amyloid beta (Abeta) secretion, deposition, aggregation, and probably the inflammatory response. However, an understanding of the complex events--tau, Abeta, oxidative stress, redox active iron, etc.--involved in the neuronal cell loss is still unclear due to the lack of a suitable animal model system. The use of neurotoxic agents particularly aluminum-organic complexes, especially Al-maltolate, expands the scope of AD research by providing new animal models exhibiting neurodegenerative processes relevant to AD neuropathology. Examination of different species of aged animals including the rapidly advancing transgenic mouse models revealed very limited AD-like pathology. Most other animal models have single event expression such as extracellular Abeta deposition, intraneuronal neurofilamentous aggregation of proteins akin to neurofibrillary tangles, oxidative stress or apoptosis. To date, there are no paradigms of any animal in which all the features of AD were evident. However, the intravenous injection of Al-maltolate into aged New zealand white rabbits results in conditions which mimics a number of neuropathological, biochemical and behavioral changes observed in AD. Such neurodegenerative effects include the formation of intraneuronal neurofilamentous aggregates that are tau positive, immunopositivity of Abeta, presence of redox active iron, oxidative stress and apoptosis, adds credence to the value of this animal model system. The use of this animal model should not be confused with the ongoing controversy regarding the possible role of Al in the neuropathogenesis, a debate which by no means has been concluded. Above all this animal model involving neuropathology induced by Al-maltolate provides a new information in understanding the mechanism of neurodegeneration.

The influence of developmental period of aluminum exposure on synaptic plasticity in the adult rat dentate gyrus in vivo

Previous studies from our group have demonstrated that chronic aluminum exposure from parturition throughout life impairs both long-term potentiation (LTP) and long-term depression (LTD) of the excitatory postsynaptic potential (EPSP) slope and reduces the population spike (PS) amplitude in the rat dentate gyrus in vivo. The present study sought to extend these findings by evaluating the developmental periods critical for aluminum-induced impairment of synaptic plasticity. Rats were exposed to aluminum (gestational, lactational and postlactational) through drinking 0.3% aluminum chloride in water over different developmental intervals: (1) prenatal exposure; (2) beginning from birth and terminating at weaning; (3) beginning at weaning throughout life; (4) beginning at birth and continuing throughout life. As adults (postnatal day 80-100), field potentials were measured in the dentate gyrus of hippocampus in response to stimulation applied to the lateral perforant path. The results showed: (1) Prenatal aluminum exposure had no effect on the magnitude of LTP as measured by the EPSP slope and LTD as measured for the PS amplitude, while it had a small effect on the magnitude of LTP as measured for the PS amplitude and LTD as measured by the EPSP slope. (2) Lactational, postlactational and throughout life exposure to aluminum impaired both LTP and LTD of the EPSP slope and PS amplitude, except that LTD of PS amplitude was not significantly changed in animals postlactationally exposed. (3) Aluminum exposure from parturition throughout life caused the greatest impairment of the range of synaptic plasticity, while prenatal aluminum exposure caused the least. From these results we conclude that the lactational period was the most susceptible to aluminum-induced impairment of synaptic plasticity and that chronic aluminum exposure from parturition throughout life is extremely disruptive to synaptic plasticity and should be avoided.

No spatial working memory deficit in beta-amyloid-exposed rats. A longitudinal study

Two experiments are described assessing whether long-term intraventricular or intrahippocampal administration of beta-amyloid protein 1-40 (beta A1-40) affects spatial working memory in rats monitored in a longitudinal study using the open-field water maze. A delayed matching-to-position procedure (DMTP) was employed in which platform locations were semi-randomly altered between days but were kept constant over the four trials on each day. Intertrial intervals (ITIs) were either 30 s or 1 h between Trials 1 and 2 (all other intervals = 30 s), with Trial 2 performance being an index for spatial working memory. Animals were trained before and tested repeatedly at various intervals after application of various compounds (see below) in five successive test sessions (TSs). In Experiment 1, beta A1-40 was applied after a challenge with long-term oral exposure to aluminium (Al; as 0.1% sulfate in drinking water). This in itself did not affect spatial working memory at any delay, despite of the more than 6 months of intake. beta A1-40 administered alone via intracerebroventricular (icv) minipumps (20 micrograms in 250 microliters) led to a small increase in latencies to find the platform, which recovered to control levels 3 months after minipumps were exhausted. Application of beta A1-40 in Al-exposed animals led to a subtle and progressive decline in working memory. This deterioration was reversed by the nootropic compound nefiracetam, which had no effect on the Al only group. In Experiment 2, well-trained rats were bilaterally implanted with intra-hippocampal minipumps containing beta A1-40 or reverse sequence beta A40-1. This did not impair spatial working memory in the DMTP task, measured either directly after minipumps were exhausted, or 2 weeks later. When intraperitoneally (i.p.) injected with a low concentration of the muscarinic antagonist scopolamine (0.2 mg/kg), a dose that was not effective alone, animals in the beta A1-40 group were amnesic. These data suggest that intra-hippocampal beta A1-40 administration alters cholinergic transmission, but these alterations may be mild and thus do not lead to obvious working memory deficits in a DMTP task in well-trained animals.

Passage of peptides across the blood-brain barrier: pathophysiological perspectives

Blood-borne peptides are capable of affecting the central nervous system (CNS) despite being separated from the CNS by the blood-brain barrier (BBB), a monolayer comprised of brain endothelial and ependymal cells. Blood-borne peptides can directly affect the CNS after they cross the BBB by nonsaturable and saturable transport mechanisms. The ability of peptides to cross the BBB to a meaningful degree suggests that the BBB may act as a modulatory pathway in the exchange of informational molecules between the brain and the peripheral circulation. The permeability of the BBB to peptides is a regulatory process affected by developmental, physiological, and pathological events. This regulation sets the stage for the relation between peptides and the BBB to be involved in pathophysiological events. For example, some of the classic actions of melanocortins on the CNS are explained by their abilities to cross the BBB, whereas aspects of feeding and alcohol-related behaviors are associated with the passage of other specific peptides across the BBB. The BBB should no longer be considered a static barrier but should be recognized as a regulatory interface controlling the exchange of informational molecules, such as peptides, between the blood and CNS.

In vitro exposure to aluminum does not alter long-term potentiation or glutamate release in rat hippocampal slices

Aluminum has been reported to inhibit long-term potentiation (LTP) following in vivo administration and decrease glutamate release following in vitro exposure. Because glutamate release is critical for synaptic transmission and the development and maintenance of LTP in the hippocampus, we examined the effects of aluminum chloride (AlCl3) on depolarization-induced glutamate release and LTP in rat hippocampal slices. The effects of AlCl3 on [14C]glutamate release were examined by incubation of slices in depolarizing (56 mM)K+ buffer solution in the absence or presence of 2 mM CaCl2. After 15 min depolarization, AlCl3 (100-1000 microM) did not significantly affect Ca(2+)-dependent [14C]glutamate release from slices, whereas a known Ca2+ channel blocker (100 microM CdCl2) decreased Ca(2+)-dependent [14C]glutamate release by approximately 50%. In contrast to a previous report, acute exposure to AlCl3 was without effect on depolarization-dependent glutamate release. LTP of the population spike (PS) in CA1 of hippocampus was induced by the delivery of stimulus trains to the stratum radiatum. LTP of the PS was observed in both control slices and slices bathed in solution containing 100 microM AlCl3. Neither the magnitude nor longevity (measured up to 1 h posttrain) of LTP distinguished control from aluminum-exposed slices. The lack of sensitivity in rat to the encephalopathic changes induced by aluminum, or methodological differences in exposure conditions may account for the lack of effect of aluminum on in vitro LTP in rat hippocampus.

Impairment of motor coordination in mice after ingestion of aluminum chloride

The mechanisms of aluminum (Al) neurotoxicity is of increasing interest. Al compounds are known to produce neurological and behavioral abnormalities in some mammalian species. The present study was designed to determine the effects of Al chloride on the skilled motor performance in mice on the rota-rod treadmill. Al chloride, depending on the duration of treatment, produced an impairment of the motor coordination ability in mice.

Effects of postnatal aluminum exposure on biological parameters in the rat plasma

Young rats were treated by gastric intubation with aluminum chloride (100 mg Al/kg/day) and aluminum lactate (100 and 200 mg Al/kg/day) from postnatal days 5 to 14. This treatment lead to a reduction in body weight. The plasma concentrations of total proteins and albumin decreased whereas the alpha 1 globulins increased in the treated rats. The aluminum concentrations in plasma and hepatic homogenates increased particularly at 200 mg Al lactate. The reduction in average body weight could be attributed to various causes: a decreased food consumption, a transient undernutrition, a reduction of the protein synthesis in the liver. The increase of the plasma concentration of the alpha 1 globulins revealed an inflammation process.

Studies of aluminum neurobehavioral toxicity in the intact mammal

1. Aluminum (Al) has been implicated in neurotoxic syndromes in several conditions, including Alzheimer's disease (AD). The developmental stage of the mammalian brain most susceptible to Al was determined in rabbits systematically exposed to Al during the prenatal, postnatal, or second month or for 1 month as adults or as aged subjects. Eyeblink reflex classical conditioning showed an Al-induced learning deficit only in the adult and aged rabbits. 2. 4-Aminopyridine, which was reported to improve learning in AD subjects, attenuated the Al-induced learning deficit. 3. Conditioned eyeblink acquisition is slower in AD subjects than controls, supporting the Al-loaded rabbit as a model of some AD effects. 4. To determine if the Al-loaded rabbit modeled the AD cholinergic deficit, acetylcholine (Ach) overflow was measured in rabbit hippocampus using microdialysis. Aluminum pretreatment reduced basal and potassium-stimulated Ach overflow compared to controls. 5. Acetylcholine overflow increased as control rabbits acquired the conditioned eyeblink reflex, then subsequently decreased, although conditioned eyeblink performance continued. In contrast, Al-loaded rabbits showed a delay in conditioned eyeblink acquisition and greatly attenuated Ach overflow. The Al-induced attenuation of Ach overflow may contribute to the Al-induced learning deficit. 6. Brain Al entry was studied using microdialysis of blood, brain, and lateral ventricle. Aluminum rapidly entered the brain and lateral ventricle. Frontal cortical Al was greater than lateral ventricular Al, suggesting that Al primarily enters the brain through the cerebral microvasculature. 7. The brain/blood Al ratio was always significantly less than 1. This ratio was influenced by the Al form administered, brain site and animal species. Thus, there appears to be an active process moving Al out of brain extracellular fluid (ECF). 8. Brain and blood dialysate Ach concentrations were not different after cyanide addition to the dialysate, supporting the conclusion that an active process moves Al out of brain ECF.

Neurotoxic effect of enteral aluminium

Long Evans rats were treated for 90 days with water-soluble, insoluble or chelated aluminium compounds. The daily treatments given were as follows: controls, NaCl (100 mg/kg body weight) plus citric acid (30 mg/kg); AlCl3 (30 or 100 mg/kg); Al(OH)3 (100 mg/kg) plus citric acid (30 mg/kg); Al(OH)3 (300 mg/kg). Their learning ability was determined in the labyrinth test at day 90, and the choline-acetyltransferase, acetylcholinesterase activity and aluminium content of the brains were measured. Soluble and chelated aluminium compounds seriously worsened the learning ability, and the aluminium content of the brain was elevated. Acetylcholinesterase activity increased and choline-acetyltransferase activity decreased, resulting in a diminished cholinergic activity, which is a characteristic of Alzheimer's disease.

Effects of postnatal aluminum exposure on choline acetyltransferase activity and learning abilities in the rat

Young rats were treated by gastric intubation with aluminum lactate (0, 100, and 200 mg Al/kg/day) from postnatal days 5 to 14 to determine the treatment's influence on brain choline acetyltransferase activity and learning abilities. The results indicated that aluminum concentrations in the cerebral areas increased in parallel to plasma aluminum at the dose of 200 mg. In the same case, choline acetyltransferase activity was reduced. At postnatal days 50 and 100, the treated rats did not show alterations in their learning abilities in the 2 tests which are based on different motivations (avoidance of an aversive light or alimentary motivation) and different ways of achievement (pressing on a lever or running in a maze). A low reduction in the general activity, particularly in the radial maze test, was only observed in rats treated with 200 mg Al/kg/day.

Environmental effects of aluminium

Aluminium (Al), when present in high concentrations, has for long been recognised as a toxic agent to aquatic freshwater organisms,i.e. downstream industrial point sources of Al-rich process water. Today the environmental effects of aluminium are mainly a result of acidic precipitation; acidification of catchments leads to increased Al- concentrations in soil solution and freshwaters. Large parts of both the aquatic and terrestrial ecosystems are affected.In the aquatic environment, aluminium acts as a toxic agent on gill-breathing animals such as fish and invertebrates, by causing loss of plasma- and haemolymph ions leading to osmoregulatory failure. In fish, the inorganic (labile) monomeric species of aluminium reduce the activities of gill enzymes important in the active uptake of ions. Aluminium seems also to accumulate in freshwater invertebrates. Dietary organically complexed aluminium, maybe in synergistic effects with other contaminants, may easily be absorbed and interfere with important metabolic processes in mammals and birds.The mycorrhiza and fine root systems of terrestrial plants are adversely affected by high levels of inorganic monomeric aluminium. As in the animals, aluminium seems to have its primary effect on enzyme systems important for the uptake of nutrients. Aluminium can accumulate in plants. Aluminium contaminated invertebrates and plants might thus be a link for aluminium to enter into terrestrial food chains.

New evidence for an active role of aluminum in Alzheimer's disease

Application of molecular biological techniques and sensitive elemental analysis have produced new evidence implicating aluminum as an important factor in down regulation of neuronal protein metabolism. Aluminum in Alzheimer's disease may act by electrostatically crosslinking proteins, particularly the methionine containing histone H1(0), and DNA. The consequence of such crosslinking is reduced transcription of at least one neuron specific gene, the low molecular weight component of neurofilaments. In the superior temporal gyrus in Alzheimer's disease, down regulation of this gene occurs in approximately 86% of surviving neurons and, therefore, aluminum must be considered as having an active role in the pathogenesis. Epidemiological studies are reviewed that independently support the hypothesis that environmental aluminum is a significant risk factor. Preliminary evidence also suggests that a disorder in phosphorylation may be an important initiating factor.

Neurobehavioral effects in offspring of mice given excess aluminum in diet during gestation and lactation

Aluminum (Al) as Al lactate in a purified diet (25, 500 or 1000 micrograms Al/g diet) was fed to Swiss-Webster mice from conception through weaning. Weights, food intake and toxic signs were recorded at regular intervals and pregnancy outcome evaluated. Pups were assessed for growth, neurobehavioral development and toxic signs prior to weaning. Offspring were also evaluated with a multi-item neurobehavioral test battery immediately after weaning and again after a 2-week period during which they were all fed control (25 micrograms/g Al) diet. No maternal or reproductive toxicity was detected and there were no group differences in pup mortality, growth, toxic signs, or neurobehavioral development prior to weaning, with the exception of poor performance in a climbing test in the 1000 micrograms Al/g diet group. Parameters significantly affected by Al in the postweaning neurobehavioral testing were foot splay, forelimb and hindlimb grip strengths, and thermal sensitivity. Negative geotaxis was inconsistently affected and startle responses were not affected. These results show that maternal dietary exposure to excess Al during gestation and lactation which do not produce maternal toxicity can result in persistent neurobehavioral deficits in weanling mice.

Developmental alternations in offspring of female rats orally intoxicated by aluminum chloride or lactate during gestation

The oral treatment of pregnant rats by aluminum chloride or lactate at various doses was applied from day 1 to day 21 of gestation to determine its influence on mortality, weight evolution, and neuromotor maturation of their pups. No effect of treatment on litter size was detected, but an increased mortality appeared during the first week: treatment by aluminum lactate was less active than was an equivalent treatment by aluminum chloride. Weight was transitorily delayed, but the reversal of this effect could be attributed to the decrease of litter size. The neuromotor maturation of surviving pups treated with the two aluminum salts showed an important impairment during the first 2 weeks of postnatal life.

Aluminum produces age related behavioral toxicity in the rabbit

Two- to 3.4-year-old, retired breeder, rabbits received repeated aluminum (Al) lactate or sodium (Na) lactate injections. All six rabbits receiving twenty 400 mumol Al/kg SC injections died, demonstrating much higher mortality than previously seen in younger rabbits. Subsequent rabbits receiving Al were dosed with 200 mumole/kg injections. Aluminum injections inhibited body weight gain. Renal function, as measured by creatinine clearance, in these rabbits was inferior to younger rabbits, perhaps contributing to the Al induced toxicity. Renal function decreased during Al injections suggesting a nephrotoxic effect of Al. Rabbits were tested for their ability to acquire, retain and extinguish a classically conditioned reflex, nictitating membrane extension. Rabbits which received Al acquired and retained the conditioned response less well than Na lactate injected rabbits. Impaired acquisition was evidenced by lower percent conditioned responses, more trials to 1 to 10 consecutive conditioned responses and longer conditioned response latencies. Aluminum injections produced significant elevations in tissue Al concentration in frontal gray and hippocampal brain as well as most peripheral tissues studied. Aluminum induced behavioral toxicity is greater in adult and aged rabbits than in young rabbits. Aged rabbits are more susceptible to Al induced mortality than adult or young rabbits.

Aluminum-induced neurotoxicity: alterations in membrane function at the blood-brain barrier

Aluminum is established as a neurotoxin, although the basis for its toxicity is unknown. It recently has been shown to alter the function of the blood-brain barrier (BBB), which regulates exchanges between the central nervous system (CNS) and peripheral circulation. The BBB owes its unique properties to the integrity of the cell membranes that comprise it. Aluminum affects some of the membrane-like functions of the BBB. It increases the rate of transmembrane diffusion and selectively changes saturable transport systems without disrupting the integrity of the membranes or altering CNS hemodynamics. Such alterations in the access to the brain of nutrients, hormones, toxins, and drugs could be the basis of CNS dysfunction. Aluminum is capable of altering membrane function at the BBB; many of its effects on the CNS as well as peripheral tissues can be explained by its actions as a membrane toxin.

Chronic, oral aluminum administration to rats: cognition and cholinergic parameters

Administration of aluminum sulfate in the drinking water of male Sprague-Dawley rats for thirty days resulted in an impairment of both consolidation and extinction of a passive avoidance task. No impairment of performance was observed on an active avoidance task, radial arm maze or open field activity measure. Biochemical analysis indicated a slight (less than 10%) but significant increase in hippocampal muscarinic receptor number after aluminum treatment as determined by tritiated quinuclidinyl benzilate (3H-QNB) binding. No changes were found in choline acetyltransferase (ChAT) activity, phosphoinositide hydrolysis, 3H-QNB binding in the cortex or tritiated pirenzepine (3H-PZ) binding in the hippocampus or cortex. These results indicate that cholinergic degeneration was not the cause of the observed cognitive impairments.

Age-related disruption of classical conditioning: a model systems approach to memory disorders

The model systems approach to the neurobiology of memory involves studying a well characterized learned response in a relatively simple and well controlled preparation. The best characterized mammalian model system is classical conditioning of the rabbit's eyeblink response. Using this preparation, significant progress has been made toward understanding the neurobiological systems and mechanisms involved in elaboration of the conditioned response. Using a well characterized model system such as classical eyeblink conditioning, it should be possible to both characterize the changes in learning and memory that accompany aging and to investigate their neural substrates. Our strategy for using the conditioned eyeblink preparation for studying age-related memory deficits is four-fold and includes investigating conditioning deficits in: (1) humans across the life span, (2) rabbits across the life span, (3) Alzheimer's disease patients, and (4) rabbits with aluminum-induced neurofibrillary degeneration. In this paper, we present exemplary data from each of these lines of research. If similar deficits occur in each of these groups, it may be possible to begin to form hypotheses about the neurobiology of age-related memory disorders.

Aluminum and Alzheimer's disease: perspectives for a cytoskeletal mechanism

A considerable volume of literature has accumulated concerning the association of aluminum with Alzheimer's disease. The pathogenic mechanisms resulting in Alzheimer's disease remain unknown, but recent investigations have focused on cytoskeletal abnormalities as perhaps the key lesion in Alzheimer's disease and related neurological disorders. The diversity of neuronal functions that are dependent on cytoskeletal integrity suggests that subtle effects on polymerization, assembly, transcription, or processing of cytoskeletal elements may have significant and far-reaching neurological effects. That aluminum may participate in the development of neuropathological lesions characteristic of Alzheimer's disease is suggested by evidence that aluminum is a potent cytoskeletal toxin, produces cognitive deficits in laboratory animals, and can be detected within abnormal neurons isolated from brain tissue from Alzheimer's disease patients. In this review, a critical look will be taken at the enigmatic role aluminum has played in Alzheimer's disease research, the possibility of its pathogenicity, and its use as a tool for the investigation of cytoskeletal changes that may result in the biochemical and, ultimately, clinical manifestations of Alzheimer's disease.

Aluminum and Alzheimer's disease

There is now substantial evidence indicating that an accumulation of aluminum occurs in grey matter in diseases associated with Alzheimer neurofibrillary degeneration. Four principle sites of aluminum accumulation have been identified in Alzheimer's disease: DNA containing structures of the nucleus, the protein moieties of neurofibrillary tangles, the amyloid cores of senile plaques and cerebral ferritin. Consideration of the extensive information now available on the toxic effects of aluminum in these four loci strengthens the hypothesis that aluminum could be important in the pathogenesis of this neurodegenerative process. The evidence, however, does not support an etiological role for aluminum in Alzheimer's disease. The primary pathogenic events responsible for Alzheimer's disease are presumed to have affected the genetically determined barriers to aluminum resulting in increased amounts of this toxic element to vulnerable target sites.

Neurotoxic cations induce membrane rigidification and membrane fusion at micromolar concentrations

The effect of the neurotoxic cations aluminum, cadmium and manganese on membranes was examined in sonicated unilamellar vesicles containing phosphatidylserine and compared to the effect of Ca2+. Fusion of membranes was monitored by assessing the resonance energy transfer between N-(7-nitrobenz-2-oxa-1,3-diazol-4-y)phosphatidylethanolamine and N-(lissamine-rhodamine B-sulfonyl)phosphatidylethanolamine. Self-quenching of high concentrations of carboxyfluorescein in liposomes was used to demonstrate the release of molecules entrapped in liposomes to compare the kinetics of leakage and intermixing of lipid. Rigidification of membranes was evaluated by monitoring the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene embedded in membranes containing phosphatidylserine and dipalmitoylphosphatidylcholine. Cation-induced lipid intermixing of vesicles membranes and release of dye from the vesicles occurred in the same concentration range. With aluminum, these effects were observed with concentrations less than 25 microM. Significant rigidification of vesicle membranes was apparent with less than 25 microM of Al3+. Similar effects could only be observed with concentrations of Cd2+ and Mn2+ at least one order of magnitude higher (200 and 400 microM, respectively).

Neurobehavioral development following aluminum administration in infant rabbits

Aluminum (Al) is known to be a neurotoxic agent in some species, inducing neurofibrillary tangles, dendritic atrophy, and behavioral deterioration, and has been implicated as a possible agent in human Alzheimer's disease and dialysis dementia. This study was conducted to assess the neurotoxic effects of Al in infant rabbits, and to compare the effects to those previously observed to follow exposure in the adult animal. Aluminum tartrate (2 microM) or physiologic saline was injected into the right lateral ventricle of 2-day-old (day P3) New Zealand white rabbits. The animals were trained in a step-down active avoidance task on P12 and retested 1 day later. They were killed on P20, and their hippocampal CA1 pyramidal cells examined for neurofibrillary tangles or prepared with the rapid Golgi stain for an examination of dendritic development. Additional animals were similarly infused with 1 or 3 microM Al for qualitative and some quantitative observations. No overt neurologic signs were observed in the 1- or 2-microM groups, however, most of the 3-microM group died between P10 and P20. Although there were no significant differences between the 2-microM and control animals on either learning or retention of the active avoidance task, deficits in retention of the task were observed in the 3-microM group. Neurofibrillary tangles in CA1 pyramidal cells were observed with dosages of 1 microM and higher. In the 2-microM group, the pattern of dendritic arborization in CA1 pyramidal cells was consistent with that expected for cells retarded in their development. These results have implications in terms of developmental differences in the neurobehavioral effects of Al.

Permeability of the blood-brain barrier to neuropeptides: the case for penetration

Evidence that peptides can cross the blood-brain barrier (BBB) is reviewed. Penetration is suggested by the observations that blood levels correlate with cerebrospinal fluid levels for many peptides and that peripheral administration of peptides results in effects on the CNS. Passage is confirmed by experiments involving administration of a peptide (immunoactive or radioactive) in one compartment and identification of its appearance in the other, supported by such methods as selective labeling, cross-reactivity with highly specific antibodies, and chromatography. The degree of passage varies among peptides and their analogs. The major route of passage is probably by a non-competitive, non-saturable mechanism, wih the physicochemical characteristics of the peptide (e.g. lipophilicity, charge, molecular weight, and protein binding) determining the degree of passage. A competitive transport mechanism also exists for some peptides. Penetration of the BBB via large pores or by pinocytosis does not appear to be of major importance for peptides. Permeability of the BBB to peptides, but not to the larger iodinated albumin, is affected by intraperitoneal administration of aluminum, apparently by an increase in the permeability of the membrane to lipophilic materials.

The aluminum-induced increase in blood-brain barrier permeability to delta-sleep-inducing peptide occurs throughout the brain and is independent of phosphorus and acetylcholinesterase levels

The effect of aluminum on levels of inorganic phosphorus and acetylcholinesterase in blood and brain and on permeability of the blood-brain barrier (BBB) in different regions of the brain to the neuropeptide delta-sleep-inducing peptide (DSIP) was studied in adult rats. Aluminum (100 mg/kg) significantly increased the permeability of the BBB to intracarotid 125I-N-Tyr-DSIP so that levels of radioactivity in whole brain were 45% higher than in control animals. The pattern of regional distribution of radioactivity in the brain was, however, unaffected, demonstrating that the affect of aluminum occurs throughout the BBB. Aluminum also significantly decreased inorganic phosphorus levels in the serum by 19%, but this effect did not correlate with BBB permeability to DSIP. Aluminum did not decrease brain levels of phosphorus despite the drop in blood levels of phosphorus nor affect brain or blood levels of acetylcholinesterase. Experiments with radioactive 32P reinforced the finding that blood but not brain levels of phosphorus are reliably affected by aluminum. The lack of correlation between changes in BBB permeability and decreased levels of inorganic phosphorus in the blood suggests that the effect of aluminum may not be mediated by its effects on phosphorus metabolism. Also, the change in BBB permeability after administration of aluminum does not appear to depend on changes in brain cholinergic activity but does occur throughout the brain.

The effects of aluminum loading on selected tissue calcium and magnesium concentrations in rats

Considerable evidence implicates elevated brain aluminum (Al) concentration in the pathogenesis of several forms of central nervous system dysfunction seen particularly among dialysis patients. In animals Al intoxication also leads to cerebral dysfunction. Since increased brain calcium (Ca) concentration has been associated with similar disturbances of cerebral function, this study was initiated to examine the effects of increased Al concentration on Ca and magnesium (Mg) concentrations in brain and other selected tissues. Daily intraperitoneal injection of Al (2.7 mg) for 10 d resulted in a significant increase in brain, liver, spleen, bone, and heart Al concentrations when compared to controls receiving saline injection. In brain, liver, and spleen, but not heart, Ca concentration was significantly higher in Al-treated rats than controls. In brain there was a significant correlation between Ca and Al concentration. Total plasma Ca concentration was not significantly different between the groups. Al loading had no significant effect on tissue Mg concentration. These results indicate that Al affects selected tissue Ca concentrations which ultimately may be involved in Al organ toxicity.

Liver, kidney, and central nervous system toxicity of aluminum given intraperitoneally to rats: a multiple-dose subchronic study using aluminum nitrilotriacetate

In the first test, aluminum nitrilotriacetate (Al-NTA), aluminum chloride, aluminum potassium sulfate, or saline was injected ip, employing male Wistar rats. Each group consisted of ten rats. Al was given in a dose of 5 mg Al/kg body wt/day, for 14 days. Only those rats given Al-NTA showed morphological damage of the liver and kidney. Damages included diffuse midzonal coagulation necrosis of hepatocytes and acute proximal tubular necrosis of the kidney at Day 4. Seven of ten rats given Al-NTA died within 5 days. The second test was performed in metabolic cages. Al-NTA, in a dose of 1.5 to 2.0 mg Al/kg body wt/day, and NTA, of an equivalent dose, were injected ip for 54 days. Midzonal coagulation necrosis and some regenerative changes were observed in the hepatic parenchyma at Day 8. At the end of the study, complete regeneration occurred in the liver. Biochemical tests at Days 6, 13, and 28 showed high amounts of GOT, GPT, LDH, gamma-GTP, and ALP. Necrosis of proximal tubular cells of the kidney and some regeneration was noted at Day 8. Metabolic acidosis was demonstrated at Days 6, 13, and 28. Moreover, from Day 38 on, atrophy of the nerve cells of the cerebrum and demyelination of the brain stem were observed. Control rats given NTA did not exhibit any organ damage. It is concluded that a relatively small dose of Al can produce toxicosis when given with certain metal chelators.

Synaptic density in chronic animals with experimental neurofibrillary changes

Synaptic density was quantitated in the cerebral cortex and subiculum of rabbits with experimental neurofibrillary changes. Animals were subjected to subcutaneous injection of aluminum tartrate for 90 days, and synapses stained with ethanolic phosphotungstic acid were analyzed in animals killed 100, 200, or 300 days postinjection with aluminum tartrate. A significant difference was found in synaptic density between animals injected with aluminum tartrate and their age-matched controls. This difference was a result of a low synaptic density present in animals killed 200 or 300 days postinjection of aluminum tartrate. In contrast, animals killed 100 days postinjection revealed the same synaptic density as their control. The data suggest that the synaptic depopulation associated with experimental neurofibrillary changes is a gradual process, and such changes are demonstrable only long after the initial appearance of neurofibrillary changes.

Cytochemical study on the effect of aluminum on neuronal Golgi apparatus and lysosomes

Ultracytochemical reactions for enzymatic markers were applied to study the effect of aluminum on some cell organelles of neurons in the Ammon cortex and spinal cord in rabbits. The results showed that aluminum caused an appearance of secondary lysosomes and an increase in the number of lysosomes. The latter finding was endorsed by statistical analysis of Ammon neurons using a two-sided t-test. Concomitantly, decrease of the intensity of the reaction for thiamine pyrophosphatase (TPPase) and nucleoside diphosphatase (NDPase) in the Golgi apparatus was found. The reaction for NDPase in the endoplasmic reticulum remained unchanged. Cytochemical reactions for alkaline phosphatase and Mg2+-activated adenosine triphosphatase in the plasmalemma of neurons were negative both in control and in aluminum-treated animals. Our data point to the activation of the system of intracellular digestion and suppression of the enzymatic activities (NDPase, TPPase) of the Golgi apparatus in CNS neurons of rabbits treated with aluminum.

High affinity uptake of GABA and glycine by rabbits with aluminum-induced neurofibrillary changes

The high affinity uptake of GABA and glycine by synaptosomal preparations of rabbit hippocampus and spinal cord has been characterized. The high affinity uptake by such preparations from rabbits in which chronic neurofibrillary changes had been induced with aluminum chloride was measured and found to be reduced. The reduction was the greatest when the number of neurons affected was the greatest. These results suggest that normal neurotransmitter function is considerably disturbed in neurons affected with neurofibrillary changes.

Chronic model of neurofibrillary changes induced in mature rabbits by metallic aluminum

A slurry of aluminum powder injected into the brains of mature rabbits produced neurofibrillary changes in neurons of spinal cord and cerebrum similar to those produced by aluminum chloride, and with similar topography and rates of formation. The major difference observed with this preparation was that many rabbits survived several weeks or months before having any obvious seizures, compared to 2 to 3 weeks with aluminum chloride, and some survived with no obvious symptoms, apparently indefinitely (12 months being the longest time before sacrifice). This chronic animal model of neurofibrillary changes, induced in a mature nervous system, will allow better investigations of alterations in the biochemistry, pathology, behavior and cognition which may occur.