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

Animal Model of Aluminum-Induced Alzheimer's Disease

Lack of a satisfactory animal model for Alzheimer's disease (AD) has limited the reach progress of the pathogenesis of the disease and of therapeutic agents aiming to important pathophysiological points. In this chapter, we analyzed the research status of animal model of aluminum-induced Alzheimer's disease. Compared with other animal models, Al-maltolate-treated aged rabbits is a more reliable and efficient system in sharing a common mechanism with the development of neurodegeneration in Alzheimer's disease.

Molecular characterization and measurement of Alzheimer's disease pathology: implications for genetic and environmental aetiology

The neuropathological changes seen in Alzheimer's disease represent an interaction between the ageing process in which normal intellectual function is retained, and changes which are specifically associated with severe cognitive deterioration. Molecular analysis of these changes has tended to emphasize the distinction between neurofibrillary pathology, which is intracellular and highly correlated with cognitive deterioration, and the changes associated with the deposition of extracellular amyloid, which appears to be widespread in normal ageing. Extracellular amyloid deposits consist of fibrils composed of a short 42 amino acid peptide (beta/A4) derived by abnormal proteolysis from a much larger precursor molecule (APP). The recent demonstration of a mutation associated with APP in rare cases with familial dementia, neurofibrillary pathology in the hippocampus and atypical cortical Lewy body pathology raises the possibility that abnormal processing of APP could be linked directly with neurofibrillary pathology. Neurofibrillary tangles and neuritic plaques are sites of dense accumulation of pathological paired helical filaments (PHFs) which are composed in part of an antigenically modified form of the microtubule-associated protein tau. The average brain tissue content of PHFs measured biochemically does not increase in the course of normal ageing but increases 10-fold relative to age-matched controls in patients with Alzheimer's disease. There is also a substantial (three-fold) disease-related decline in normal soluble tau protein relative to age-matched controls. This intracellular redistribution of a protein essential for microtubule stability in cortico-cortical association circuits may play an important part in the molecular pathogenesis of dementia in Alzheimer's disease. The role of abnormal proteolysis of APP in this process remains to be elucidated. Immunohistochemical studies on renal dialysis cases have failed to detect evidence of neurofibrillary pathology related to aluminium accumulation in brain tissue. Nevertheless it needs to be seen whether more sensitive biochemical assays of neurofibrillary pathology can demonstrate evidence of an association with aluminium.

Aluminium and the pathogenesis of Alzheimer's disease: a summary of evidence

Known risk factors for Alzheimer's disease (AD) are few and insufficient knowledge is available to recommend steps to reduce AD in our ageing populations. Although not 'the cause', considerable evidence implicates human ingestion of aluminium as a possible risk factor for the expression of dementia of the Alzheimer type. A recent epidemiological study in Ontario relating the incidence of AD to aluminium in drinking water strongly supports this conclusion. To test further the hypothesis that aluminium may play a role in the pathogenesis of AD we conducted a clinical trial employing the trivalent metal ion binding compound, desferrioxamine. The design was a two-year randomized trial with behavioural assessments blinded to study assignment. Sixty-three patients with probable AD were selected who were living at home and were under 74 years. Forty-eight signed an informed consent and completed all initial testing. The main outcome measure was a video-recorded home-behavioural assessment of measures of skills of daily living. The principal outcome was that the mean slope for performance of the skills of daily living for the group without treatment was -1.72% maximum score/month, compared to -0.87% maximum score/month for the group treated with desferrioxamine (P = 0.038). Considerable evidence supports the hypothesis that aluminium has an active role in the pathogenesis of AD.

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.

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.

Decrease of glial fibrillary acidic protein in rat frontal cortex following aluminum treatment

Aluminum lactate was injected either intraperitoneally or stereotactically into the lateral cerebral ventricles of rats. Rats were killed at various times after treatment, and frontal cortex, hippocampus, and striatum were dissected out. Microtiter plate-based sandwich ELISA and immunohistochemistry were used to measure the glial fibrillary acidic protein (GFAP) concentration. GFAP levels were significantly decreased in frontal cortex 7 days after a single lateral ventricular injection of aluminum lactate and 14 days following systemic treatment. In contrast, neither hippocampus nor striatum exhibited any significant changes in the content of this astrocytic intermediate filament protein after aluminum treatment. Levels of a predominantly astroglial enzyme, glutamine synthetase, were also selectively reduced in the frontal cortex following intraventricular injection of aluminum. This depression exhibited a regional and temporal specificity similar to that found for GFAP. These results suggest a selective and progressive diminution of astrocytic responsivity in frontal cortex following either systemic or intraventricular aluminum dosing. The depression of GFAP levels reported here, which was found in the rat cerebral cortex 7-14 days after aluminum treatment in a species that does not form neurofilamentous aggregates, may reflect extended impairment of astrocytic function and suggests that these cells may be the primary targets of aluminum neurotoxicity.

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.

Reversibility of neurofilamentous inclusion formation following repeated sublethal intracisternal inoculums of AlCl3 in New Zealand white rabbits

In this report, we describe the clinical, topographical and immunohistochemical characteristics of neurofilament (NF) inclusion formation induced by the intracisternal inoculation of young adult New Zealand white rabbits at 28-day intervals with 100 micrograms AlCl3 over the course of 267 days. The ability to recover following cessation of aluminum exposure has also been assessed. The extent of neurofilamentous inclusion formation was proportionate to the cumulative amount of AlCl3 inoculated and initially consisted of fusiform axonal distention in the ventral spinal cord at day 51 following the initial inoculum. Spinal motor neuron perikaryal inclusions and discrete axonal spheroids were observed at day 107 and supraspinal neurofilamentous pathology by day 156. Perikaryal inclusions were immunoreactive to antibodies recognizing both poorly phosphorylated (SMI 32) and more highly phosphorylated high molecular weight NF (NFH). In contrast, axonal spheroids were intensely immunoreactive at all stages with antibodies recognizing highly phosphorylated NFH and an age-dependent NFH phosphorylation state (SMI 34) with only faint SMI 32 immunoreactivity. Immunoreactivity to an antibody recognizing ubiquitin-protein conjugates did not appear until day 156, whereas inclusions were not immunoreactive to antibodies recognizing either phosphatase-dependent or -independent microtubule-associated protein tau at any stage. Upon withdrawal from further AlCl3 exposure after intervals of 51, 107 or 156 days following the initial inoculum, clinical recovery ensued in all rabbits. In all but the most severely affected rabbits, perikaryal neurofilamentous inclusions resolved. However, axonal spheroids continued to be prominent. These studies demonstrate that the repetitive intracisternal inoculation of AlCl3 in New Zealand white rabbits induces a reversible process of neurofilamentous inclusion formation that preferentially affects motor neurons, and in which recovery will occur in those inclusions containing an admixture of both poorly and highly phosphorylated NFH.

Aluminium contamination via assisted leaching from metallic aluminium utensils at neutral pH

Fluoride ion in trace concentrations is found to leach metallic aluminium from utensils even at neutral pH, releasing aluminium hydroxide which is readily soluble in dilute acids. The levels of leaching at different F(-) concentrations are given and compared with leaching levels with equivalent concentrations of Cl(-). It is suggested that consumption of water boiled in aluminium utensils may contribute to cumulative aluminium toxicity.

Aluminium maltol-induced neurocytoskeletal changes in fetal rabbit midbrain in matrix culture

We have developed a neuronal culture system to evaluate the neurotoxic effects of aluminium maltol on fetal rabbit midbrain sections containing the oculomotor nucleus. Cultures were treated with 5, 7, 9, 11, 13 and 15 mumol/l aluminium maltol or 39 and 45 mumol/l maltol (molal equivalents to 13 and 15 mumol/l aluminium maltol). Control cultures were maintained in nutrient medium alone. Silver-positive neuritic swellings and occasional perikaryal neurofibrillary tangles were observed in cultures treated with 11, 13 and 15 mumol/l aluminium maltol. The number of tangles (involved neurons) produced in aluminium maltol treated cultures were counted and compared to (untreated) controls. We observed a total of 3, 7 and 7% of involved neurons following treatment with 11, 13 and 15 mumol/l aluminium maltol respectively, and none in the control group. By immunohistochemistry, neurofibrillary tangles were immunoreactive with MAbs to phosphorylated (SMI-31), non-phosphorylated, phosphorylation dependent (SMI-32) and phosphorylation independent (SMI-33) epitopes of the high (-H) and middle (-M) molecular weight neurofilament subunits (NF-H/M). By contrast these lesions were nonreactive with MAbs recognizing tau, MAP2 or different beta-tubulin isotypes. The perikaryal tangles consisted of focal accumulations of 10 nm straight filaments by electron microscopy. These findings are in agreement with previous data from rabbit in vivo studies after the administration of aluminium maltol intravenously (Bertholf et al., 1989) or intraventricularly (Katsetos et al., 1990). Using this in vitro system, aluminium-induced neurofibrillary tangles can be consistently produced, and changes in the distribution of neurofilament proteins evaluated. These studies may aid in the assessment of the possible role of aluminium in the aetiology of human neurodegenerative disorders.

Neuronal cytoskeletal lesions induced in the CNS by intraventricular and intravenous aluminium maltol in rabbits

The antigenicity of neuronal cytoskeletal lesions was studied immunohistochemically in adult New Zealand white rabbits after intraventricular (subacute) and intravenous (chronic) administration of a water-soluble aluminium compound, aluminium (Al) maltol. After short-term intraventricular administration, rabbits developed widespread neurofibrillary degeneration (NFD) involving pyramidal neurons of the isocortex and allocortex, projection neurons of the diencephalon, and nerve cells of the brain stem and spinal cord. There was a predilection for motor neuron involvement and for the infratentorial portions of the neuraxis. Perikarya and proximal neurites were especially affected. Bundles of 10 nm filaments were frequently present. Three of the animals treated intravenously for 12 weeks or longer displayed NFD in the oculomotor complex and in the pyramidal neurons of the occipital isocortex. Following either mode of administration, the affected neurons exhibited immunostaining with a panel of monoclonal antibodies (MAbs) against phosphorylated (SMI-31), non-phosphorylated/phosphatase-sensitive (SMI-32), and dephosphorylation-independent (SMI-33) epitopes of high and middle molecular weight neurofilament (NF) protein subunits. They were non-reactive with MAbs to microtubule-associated protein 2 and the class III neuron-associated beta-tubulin isotype. Our findings indicate that intraventricular Al maltol produces similar, but more widespread degeneration of projection-type neurons than the less water-soluble Al compounds as reported by others. The NFD lesions are compared with those of senile dementia of the Alzheimer type (SDAT) and motor neuron disease.

Aluminum neurotoxicity in mammals

Although aluminum comprises a large percentage of the Earth's crust, it is excluded from body tissues, and especially from the central nervous system. When aluminum is experimentally introduced to the central nervous system, several neurotoxic effects are observed:i.e. neurofibrillary changes, behavioral and cognitive deficits and enzymatic and neurotransmitter changes, as well as certain types of epileptic seizures.The localization of relatively high levels of aluminum in Alzheimer disease, Guamanian amyotrophic lateral sclerosis and Parkinsonism-dementia has led to the implication of aluminum as a pathogenic factor in these diseases. Recent studies have shown that microtubule-associated proteins are part of the paired helical filaments which make up the intraneuronal neurofibrillary tangle. Other studies have identified the protein making the vascular and neuritic (senile) plaque amyloid and located the gene responsible for this protein to chromosome 21.Our electron microprobe analysis studies have not found the levels of aluminum or silicon in either the neurofibrillary tangles or amyloid cores reported elsewhere, nor have the levels of aluminum been elevated in approximately one half of the tangles and plaque cores examined to date.

Polynucleotide cross-linking by aluminum

The observations that there was an increased concentration of Al in the brains of Alzheimer's, Guam-Parkinson, and amyotrophic lateral sclerosis disease patients and that there was an apparent localization of the Al in chromatin led to a study of the interaction of Al(III) with DNA. We have previously shown that Al cross-links calf thymus DNA at low pH (S. J. Karlik, G. L. Eichhorn, P. N. Lewis, and D. R. Crapper, Biochemistry 19, 5991 [1980]). Extended studies indicate that cross-linking occurs in DNAs of all base ratios, including polydAdT and polydGdC. Since Al cross-links prevent renaturation in polydAdT, the decrease in the amount of polymer renatured in the presence of Al becomes a quantitative appraisal of the extent of cross-linking. Saturation of cross-linking occurs at a 0.4 ratio of Al to nucleotide phosphate, indicating that potentially 80% of the base pairs are Al bound. Cross-links are broken at elevated pH and by EDTA.

Effects of aluminium chloride on cultured cells from rat brain hemispheres

Neurofilamentous tangles have been induced by aluminium chloride in rat brain neurons cultivated on astroglial feeder layers. Monoclonal antibodies to neurofilaments were found to stain these aluminium-induced tangles. Immunostaining of these structures with anti-paired helical filament serum was always negative, though good staining of neuronal perikarya was achieved. This observation supports the hypothesis that aluminium-induced tangles are made up of neurofilament proteins. These tangles appear to be distinct immunochemically from Alzheimer-paired helical filaments.

Aluminium contamination from fluoride assisted dissolution of metallic aluminium

Trace amounts (microg g(-1) quantities) of fluoride ion are found to catalyse the dissolution of metallic aluminium in very slightly acidic or alkaline aqueous media. Possibly hazardous levels of aluminium could get leached from cooking utensils if fluoridated water or fluoride rich foodstuffs are used. The fluoride assisted corrosion of aluminium is most dramatic in oxalic, tartaric acids or sodium bicarbonate. Carbon dioxide also corrodes aluminium in the presence of the fluoride ion, generating colloidal hydrated aluminium oxide which is readily soluble in dilute organic and mineral acids.

Aluminum-induced decreases in choline acetyltransferase, tyrosine hydroxylase, and glutamate decarboxylase in selected regions of rabbit brain

The neuropathological and neurochemical effects of intracisternally administered aluminum-powder suspensions were studied in adult rabbits. The right half of each brain was fixed for neuropathological examination, and neurotransmitter-synthesizing enzyme activities were measured in homogenates of structures dissected from the left half of each brain. The neuropathological changes associated with aluminum-induced encephalomyelopathy, including neurofibrillary degeneration, were observed in several regions of the central nervous system of the aluminum-treated rabbits. The striatum was consistently free of changes. Decreases in choline acetyltransferase and tyrosine hydroxylase activities of more than 30% were observed in the striatum of animals within 14-21 d and at longer times after aluminum injection. The decrease in striatal choline acetyltransferase activity appears to be unrelated to pathological changes in the striatal cholinergic neurons. The decrease in tyrosine hydroxylase activity in the striatum may be unrelated to neuropathological changes in dopaminergic cell bodies in the midbrain. Significant decreases in glutamate decarboxylase activity in the cerebellum may be related to cell losses in this region, whereas choline acetyltransferase activity deficits in the whole hippocampus remain unexplained.

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.

An immunocytochemical comparison of cytoskeletal proteins in aluminum-induced and Alzheimer-type neurofibrillary tangles

Exposure of the central nervous system (CNS) of rabbits to aluminum salts produces a progressive encephalopathy. Examination of CNS structures discloses widespread perikaryal neurofibrillary tangle (NFTs) formation. The aluminum-induced NFTs consist of collections of normal neurofilaments, and differ ultrastructurally and in their solubility characteristics from Alzheimer-type NFTs, the latter being composed of largely insoluble paired helical filaments. The present study compares NFTs found in the rabbit to those of Alzheimer's disease, using monoclonal antibodies (SMI 31, SMI 32) that recognize phosphorylated and non-phosphorylated determinants respectively in normal neurofilaments, and an antiserum raised against purified microtubules. Paraffin-embedded sections were stained by the avidin-biotin immunocytochemical method. Intense staining of aluminum-induced NFTs was found after processing with SMI 31 and SMI 32, while no staining of non-tangled perikarya of control rabbits or of Alzheimer-type NFTs was seen. Antimicrotubule anti-serum gave weak, nonfocal staining in the aluminum-treated and control rabbits, while Alzheimer-type NFTs were stained intensely. These results show that phosphorylated and non-phosphorylated neurofilaments accumulate in aluminum-induced NFTs, thus complementing the previously demonstrated specific slowing of the axonal transport of neurofilaments in aluminum intoxication. Further, they suggest that the presence of microtubular proteins may be necessary for altered neurofilaments to take on a paired helical configuration.

Ventral root axonopathy and its relation to the neurofibrillary degeneration of lower motor neurons in aluminum-induced encephalomyelopathy

The injection of metallic aluminum (Al) into the cerebrospinal fluid of adult rabbits induces neurofibrillary degeneration of lower motor neurons. We studied the ventral roots and the corresponding motor neurons of Al-treated animals to clarify the modality and extent of reaction of the axon in relation to the severity of perikaryonal involvement. Moreover, the involvement of dorsal root ganglion cells was compared to that of lower motor neurons. Rabbits received 0.15 ml of a 1% Al slurry intracisternally and were perfused through the heart with aldehydes at 14-62 days after injection. Spinal cords and roots were embedded in Epon and examined morphologically and by morphometric techniques. An axonopathy was observed in the ventral roots, characterized by neurofilamentous axonal swellings and myelin attenuation in several size classes of axons. Results obtained from axons traced in serial sections indicate that there may be a unifocal or a multifocal axonopathy. Dorsal root ganglion cells showed milder changes by comparison with motor neurons and their axons in the ventral roots. The most severe axonopathy was associated both with an incidence of 66-81% of motor neurons showing neurofibrillary degeneration and with a rapidly progressing motor weakness. These findings are related in the discussion section to the pathological expression of human neurological disorders in which the lower motor neurons are selective targets.

Dendritic alterations in chronic animals with experimental neurofibrillary changes

Dendritic changes were quantitated in the cerebral cortex and subiculum of rabbits injected with aluminum tartrate for 90 days (5 days/week) at 100, 200, and 300 days after the last injection of aluminum. Both apical and basal dendrites of the cerebral cortex and subiculum responded similarly to aluminum tartrate. The dendrites were fewer and shorter in the animals examined at 200 and 300 days postinjection of aluminum tartrate. Such dendritic changes were more prominent at longer postinjection times and in dendrites that were more peripheral from the cell body. Aluminum-induced changes in apical dendrites were more prominent in the subiculum than in the cerebral cortex. Aluminum-induced changes in basal dendrites, however, were more prominent in the cerebral cortex than in the subiculum. The results suggest a time delay between the initial accumulation of neurofibrillary changes and the subsequent loss of peripheral dendritic branches, which appears to be long-lasting.

Histochemical localization of aluminum in the rabbit CNS

Aluminum was observed in the nucleolus, interchromatin granules, rough endoplasmic reticulum, free ribosomes, euchromatin, and the heterochromatin of the neuron. The association of aluminum with the first four r-RNA-containing cellular components and with the last two DNA-containing chromatins suggests the association of aluminum with the nucleic acids. The aluminum may interfere with the normal mechanism of the protein synthesis of r-RNA and of the transcription or gene modulation of DNA. Aluminum was also observed in the astrocytic process and in the nuclei of endothelial cells, pericytes, and the muscle cells of the blood vessels. The detection of aluminum in the pyrimidal cells of the cerebral cortex and hippocampus and in the spinal cord neurons, was observed 1 h after i.v. injection, indicating a rapid entry of aluminum from the injection site through the blood-brain barrier (BBB) to the neurons. Using Morin stain, pyramidal neurons of the cerebral cortex and hippocampus, motoneurons of spinal cord, ganglion cells, and bipolar cells of retina and Purkinje cells of cerebellum, exhibited yellow fluorescence, with peak intensity at 560 nm. Tangles were observed in these six types of neurons. The granule cells of hippocampus and cerebellum and the photoreceptors of the retina exhibited green fluorescence with the peak intensity at 490-500 nm. Tangles were not observed in these three types of neurons.

Intranuclear aluminum accumulation in chronic animals with experimental neurofibrillary changes

Young New Zealand white rabbits (1.5 kg body weight) subjected to daily subcutaneous injection of aluminum tartrate (7.7 mg/kg body weight) developed neurofibrillary tangles (NFTs) in specific areas of the central nervous system. The NFTs were initially observed in the spinal cord and brain stem. The hippocampus was the last region to show NFTs. Animals neither died nor showed any neurologic signs. Their growth pattern during and following the aluminum injection was comparable to that of controls. Energy-dispersive X-ray spectrometry detected aluminum within the nucleus of a high percentage of NFT-bearing neurons in the spinal cord and hippocampus. Aluminum was not detected in NFT-free neurons. These findings suggest the association of intranuclear aluminum with NFTs induced experimentally in the chronic animals.

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.

Aluminum-induced neurofibrillary changes in axons and dendrites

We examined the chronic effect of aluminum on the rabbit central nervous system (CNS) and documented the occurrence of axonal swellings (spheroids) and dendritic thickening in spinal cord neurons in addition to the accumulation of neurofibrillary material in the perikaryon. The axonal swellings always occurred at the first heminode, and the neurofilaments appeared disorganized, whereas in dendrites the neurofilaments generally retained their longitudinal arrangements. Although neurofibrillary tangles were present in cortical neurons, no axonal swellings were observed. Thickening of segments of apical dendrites proximal to the cell body affected by neurofibrillary changes was present. The axonal swellings resembled those observed in IDPN intoxication, and in amyotrophic lateral sclerosis, and may be useful as a model for studying these diseases.

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.