Aluminum ingestion and behavior in the Long-Evans rat

Evaluation of 28-day repeated oral dose toxicity of aluminum chloride in rats

The present study investigated the potential adverse effects of aluminum chloride (AlCl₃) following a 4-week repeated oral administration in Sprague-Dawley rats. The test article was administered once daily by gavage to male and female rats at dose levels of 0, 100, 300, and 900 mg/kg/day for 4 weeks. After administration of AlCl₃ at 900 mg/kg/day, treatment-related systemic toxicity manifested as significant increases in salivation incidence, neutrophil percentage, reticulocytes, serum triglyceride, adrenal gland and liver weights, and single-hepatocyte necrosis, as well as significant decreases in body weight gain, food intake, hemoglobin, mean corpuscular hemoglobin, mean corpuscular hemoglobin concentration (MCHC), lymphocyte percentage, serum total protein and albumin, and thymus weight in male rats; and significant increases in salivation incidence, serum triglyceride, and liver weight, as well as a significant decrease in lymphocyte percentage in female rats. At 300 mg/kg/day, a significant decrease in MCHC was found in male rats, but not in female rats. However, this finding was not toxicologically significant because the reduction was minimal and was not accompanied by changes in any other parameters. No treatment-related effects were observed in the 100 mg/kg/day group of both genders. Under the experimental conditions of this study, the target organs of AlCl₃ were determined to be the blood, liver, and thymus in rats. The no-observed-adverse-effect level was found to be 300 mg/kg/day in rats of both genders.

The Effect of Aluminum Exposure on Reproductive Ability in the Bank Vole (Myodes glareolus)

Human impact on the environment is steadily increasing the amounts of aluminum in the ecosystems. This element accumulates in plants and water, potentially exposing herbivores to its harmful effect. In heavily polluted sites, a decrease in the density of small rodent populations has been observed. This decline may be caused by many factors, including decreased fertility. The aim of the presented research was to determine how aluminum, administered at concentrations similar to those recorded in industrial districts (Al I = 3 mg/l, Al II = 200 mg/l), affects the reproductive abilities of small rodents. As the indicators of reproductive abilities, body weight, weight of the testes and accessory sex glands of males, and uterus weight of females were estimated. In females, the number of matured follicles (types 6, 7, and 8) was analyzed, while in males, the quantity and quality (matured, viable, swollen, motile, head abnormalities) of epididymal sperm cells were assessed. Moreover, the development of testes, measured by spermatogenic index, was determined. The model species was the bank vole. Our results have proven that aluminum impairs adult individuals' reproductive abilities by decreasing the quality and quantity of sperm cells and by causing morphologically abnormal development of the gonads. However, no difference in male organometric parameters was found, and only in females treated with 3 mg/l Al, the uterus weight was higher than control. No differences were found in the total number of matured follicles. These results suggest that the decline in rodent numbers in industrial districts is due, at least in part, to poorer males' reproductive abilities, resulting from exposure to aluminum contamination.

Learning and Memory: Considerations for Toxicology

The goal of this article is to outline a strategy for assessing chemical-induced dysfunction of learning and memory in laboratory animals. Toward that end, several questions are raised, including if tests of learning and memory should be included in a primary screening effort, what considerations should guide the selection of particular test methods, and experimental designs. Examples are provided demonstrating that tests of learning and memory can be simple and cost-effective, yet still provide meaningful data on the specificity of effects and on the neural mechanisms involved in chemically induced neurotoxicity.

Possible peripheral markers for chronic aluminium toxicity in Wistar rats

This investigation gives detailed analysis of peripheral marker enzymes as well as neurobehavioral tests following chronic aluminium (Al) exposure (10 mg/kg b.w. for 12 weeks intragastrically). We observed a significant decrease in the levels of serum cholinesterase after toxicity. The enzymatic activity of cytochrome oxidase (CO), the terminal enzyme of the electron transport chain, was significantly diminished and that of glucose-6-phosphate dehydrogenase (G-6-PD) was significantly enhanced. Neuromuscular co-ordination was assessed using motor and memory function tests. Deficits were observed suggesting a probable model for chronic Al neurotoxicity.

Understanding Aspects of Aluminum Exposure in Alzheimer's Disease Development

Aluminum is a ubiquitously abundant nonessential element. Aluminum has been associated with neurodegenerative diseases such as Alzheimer's disease (AD), amyotrophic lateral sclerosis, and dialysis encephalopathy. Many continue to regard aluminum as controversial although increasing evidence supports the implications of aluminum in the pathogenesis of AD. Aluminum causes the accumulation of tau protein and Aβ protein in the brain of experimental animals. Aluminum induces neuronal apoptosis in vivo and in vitro, either by endoplasmic stress from the unfolded protein response, by mitochondrial dysfunction, or a combination of them. Some, people who are exposed chronically to aluminum, either from through water and/or food, have not shown any AD pathology, apparently because their gastrointestinal barrier is more effective. This article is written keeping in mind mechanisms of action of aluminum neurotoxicity with respect to AD.

Are there negative CNS impacts of aluminum adjuvants used in vaccines and immunotherapy?

In spite of a common view that aluminum (Al) salts are inert and therefore harmless as vaccine adjuvants or in immunotherapy, the reality is quite different. In the following article we briefly review the literature on Al neurotoxicity and the use of Al salts as vaccine adjuvants and consider not only direct toxic actions on the nervous system, but also the potential impact for triggering autoimmunity. Autoimmune and inflammatory responses affecting the CNS appear to underlie some forms of neurological disease, including developmental disorders. Al has been demonstrated to impact the CNS at every level, including by changing gene expression. These outcomes should raise concerns about the increasing use of Al salts as vaccine adjuvants and for the application as more general immune stimulants.

Neurofilament phosphorylation and disruption: A possible mechanism of chronic aluminium toxicity in Wistar rats

The present study was designed to investigate the possible effects of chronic aluminium exposure on neurofilament phosphorylation and its subsequent disruption in various regions of the rat brain. An intra-gastric dose of aluminium (10mg/kg bw for 12 weeks) resulted in a marked enhancement of Ca2+/CaM dependent protein kinase activity as compared to cAMP dependent protein kinase. The levels of phosphoprotein phosphatase were found to be significantly depleted only in the cerebral cortex. After in vitro phosphorylation using [32gamma-P] ATP, various proteins were resolved on one-dimensional 8% SDS-PAGE, stained with Coomassie Blue and autoradiographed. The amount of 32P-incorporated was quantified using ADOPE PHOTOSHOP (7.0). The 200 kDa neurofilament protein was identified using immunoblotting. Finally, the extent of phosphorylation induced neurofilamentous damage was assessed using immunocytochemical studies. The cytoskeletal proteins were found to be aggregated and disrupted in all the three neuronal regions following 12 weeks of aluminium treatment. This study lends further support to the possible role of aluminium as a potent neurotoxic agent and in the etiopathogenisis of various neurodegenerative diseases.

Dietary protein restriction causes modification in aluminum-induced alteration in glutamate and GABA system of rat brain

BACKGROUND

Alteration of glutamate and gamma-aminobutyrate system have been reported to be associated with neurodegenerative disorders and have been postulated to be involved in aluminum-induced neurotoxicity as well. Aluminum, an well known and commonly exposed neurotoxin, was found to alter glutamate and gamma-aminobutyrate levels as well as activities of associated enzymes with regional specificity. Protein malnutrition also reported to alter glutamate level and some of its metabolic enzymes. Thus the region-wise study of levels of brain glutamate and gamma-aminobutyrate system in protein adequacy and inadequacy may be worthwhile to understand the mechanism of aluminum-induced neurotoxicity.

RESULTS

Protein restriction does not have any significant impact on regional aluminum and gamma-aminobutyrate contents of rat brain. Significant interaction of dietary protein restriction and aluminum intoxication to alter regional brain glutamate level was observed in the tested brain regions except cerebellum. Alteration in glutamate alpha-decarboxylase and gamma-aminobutyrate transaminase activities were found to be significantly influenced by interaction of aluminum intoxication and dietary protein restriction in all the tested brain regions. In case of regional brain succinic semialdehyde content, this interaction was significant only in cerebrum and thalamic area.

CONCLUSION

The alterations of regional brain glutamate and gamma-aminobutyrate levels by aluminum are region specific as well as dependent on dietary protein intake. The impact of aluminum exposure on the metabolism of these amino acid neurotransmitters are also influenced by dietary protein level. Thus, modification of dietary protein level or manipulation of the brain amino acid homeostasis by any other means may be an useful tool to find out a path to restrict amino acid neurotransmitter alterations in aluminum-associated neurodisorders.

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.

Response of regional brain glutamate transaminases of rat to aluminum in protein malnutrition

BACKGROUND

The mechanism of aluminum-induced neurotoxicity is not clear. The involvement of glutamate in the aluminium-induced neurocomplications has been suggested. Brain glutamate levels also found to be altered in protein malnutrition. Alterations in glutamate levels as well as glutamate-alpha-decarboxylase in different regions of rat brain has been reported in response to aluminum exposure. Thus the study of glutamate metabolising enzymes in different brain regions of rats maintained on either normal or restricted protein diet may be of importance for understanding the neurotoxicity properties of aluminium.

RESULTS

Dietary protein restrictions does not have an significant impact on regional aluminum content of the brain. The interaction of aluminum intoxication and protein restriction is significant in the thalamic area and the midbrain-hippocampal region in cases of glutamate oxaloacetate transaminase. In the case of glutamate pyruvate transaminase, this interaction is significant only in thalamic area.

CONCLUSION

The metabolism of amino acids, as indicated by activities of specific transaminases, of brain is altered in response to aluminum exposure. These alterations are region specific and are dependent on dietary protein intake or manipulation of the brain amino acid homeostasis.

Long-term study of chronic oral aluminum exposure and spatial working memory in rats

The authors report an effort to advance animal models that mimic the cognitive decline of Alzheimer's disease. Rats were trained and repeatedly tested in a spatial delayed matching-to-position paradigm in the water maze, with the location of the submerged platform changing between, but not within, days. After Trial 1 (random search) and intertrial intervals of 30 s or 1 hr, memory was tested in Trial 2. Young rats quickly acquired this task and were repeatedly tested after different intervals over 7 months, with a slight increase in performance toward the end of testing, but no difference in latencies between delays. Oral long-term treatment of 1 group with 0.1% aluminum caused no delay-dependent working memory deficit. This testing protocol may enable between- and within-subject long-term assessment of spatial working memory before and after drug treatment and may prove useful in animal models of progressive cognitive decline.

Differential responses of certain brain phosphoesterases to aluminium in dietary protein adequacy and inadequacy

The aluminium-induced neurotoxic consequences include, among other factors, dephosphorylation, phosphorylation as well as hyperphosphorylation of specific macromolecules. Accordingly, activities of phosphoesterases were measured in different regions of rat brain, maintained with either adequate or inadequate protein diet, following aluminium exposure. Male Wistar rats weighing 80-100 g were treated with aluminium chloride at a dose of 15% of the LD50 for 4 weeks. In different regions of the brain of aluminium-exposed rats, significant variation in both phosphomonoesterase and phosphodiesterase activities have been recorded. These alterations were found to be varied when the rats were subjected to dietary protein insufficiency. These findings demonstrate the specificity of aluminium on different phosphoesterases. These regional variations may be attributed to the accumulated level of aluminium or may be due to cellular localization of these enzymes and linked to whether the enzymes are compartmentalized with different aluminium hydration species.

Behavioral effects of aluminum in mice: influence of restraint stress

The influence of restraint stress on potential aluminum (Al)-induced behavioral changes was assessed in CD-1 mice. Three groups of adult mice were given 0, 300 and 600 mg Al/kg body weight per day in drinking water for 2 weeks. One-half of the animals in each group were concurrently subjected to restraint stress during 1 h per day throughout the study. After cessation of treatment, open-field activity, active avoidance learning, and motor resistance and coordination of the animals were evaluated. At the end of the behavioral testing period, mice were killed and Al concentrations were determined in a number of tissues. There were no remarkable effects of Al, restraint stress or their combined administration on either open-field activity or on the number of avoidances in an automatic reflex conditioner. However, a lower motor resistance and coordination in a rotarod were observed following exposure to Al at 600 mg/kg/day, restraint alone or concurrent administration of Al (300 and 600 mg/kg/day) plus restraint stress. The levels of Al in whole brain and cerebellum were significantly enhanced in mice exposed to Al plus restraint. Although the present results scarcely show Al-induced neurobehavioral effects, the influence of restraint stress on Al levels in whole brain and cerebellum can be the basis for further studies on the potential role of this element in certain neurological disorders.

Effects of vanadium on activity and learning in rats

The effects of vanadate administration on activity and learning were assessed in rats. Four groups of adult male rats were given by gavage 0, 4.1, 8.2, and 16.4 mg/kg/day of sodium metavanadate for eight consecutive weeks. Three weeks after the cessation of the treatment, general motor activity of all animals was measured in an open-field. Rats were also tested for two-way shock avoidance learning in an automatic reflex conditioner. At the end of the testing period, rats were killed and vanadium concentration was determined in a number of tissues. Vanadium exposure caused an observable but not significant effect on body weight gain, while a persistent presence of vanadium was observed in all tissues measured. The results of the behavioral testing show that oral vanadate administration resulted in significant reductions in both general activity and learning.

Neurobehavioral alteration in rodents following developmental exposure to aluminum

Aluminum (Al) is one of the most abundant metals in the earth's crust, and humans can be exposed to it from several sources. It is present in food, water, pharmaceutical compounds, and in the environment, e.g., as a result of acid rain leaching it from the soil. Exposure to Al has recently been implicated in a number of human pathologies, but it has not yet been definitely proved that it plays a major causal role in any of them. In this paper we review the effects of developmental exposure of laboratory animals to Al salts as a model for human pathological conditions. The data presented show behavioral and neurochemical changes in the offspring of AL-exposed mouse dams during gestation, which include alterations in the pattern of ultrasonic vocalizations and a marked reduction in central nervous system (CNS) choline acetyltransferase activity. Prenatal Al also affects CNS cholinergic functions under Nerve Growth Factor (NGF) control, as shown by increased central NGF levels and impaired performances in a maze learning task in young-adult mice. The need for more detailed studies to evaluate the risks for humans associated with developmental exposure to Al, as well as the importance of using more than one strain of laboratory animal in the experimental design, is emphasized.

Effects of aluminum exposure on behavioral parameters in the rat

Adult rats were treated by intraperitoneal injection of aluminum gluconate for 3 months. Rats were submitted to the radial maze test to determine the influence of chronic aluminum intoxication on cognitive and noncognitive behavioral processes. Both learning abilities (working memory and reference memory) and rapidity (time spent to respond and to master a trial) were analyzed. Aluminum concentration was evaluated in the brain, serum, and liver to assess aluminum body burden. While hippocampus and neocortex showed a significant increase in aluminum concentration, aluminum treatment did never affect the animal's performance during cue learning or when the insert cues were removed. The only behavioral difference observed was a decrease in rapidity: both the total time to finish a trial and the latency to make the first choice were lengthened in aluminum-intoxicated rats.

Intraneuronal aluminum potentiates iron-induced oxidative stress in cultured rat hippocampal neurons

Aluminum can facilitate Fe-mediated oxidative injury, which may contribute to Al neurotoxicity. It has been reported that Al potentiates Fe-induced oxidative stress in cultured granule cells, suggesting a mechanism for Al facilitation of Fe-mediated oxidative injury. However, the relationship of intracellular Al concentration to Fe-induced oxidative stress has not been reported. In the present study, neuronal oxidative stress and survival were investigated. Embryo rat hippocampal neuron cultures were treated with Al2(SO4)3 and/or FeSO4. An ionophore, A23187, was utilized to facilitate cellular Al uptake. Intraneuronal Al concentration was ascertained by laser microprobe mass spectrometry (LMMS). Neuronal oxidative stress was measured by confocal laser scanning microscopy, using 2,7-dichlorofluorescin diacetate (DCFH-DA) as a probe. The study showed that neuronal Al uptake was facilitated by the ionophore and that an increase of intraneuronal Al concentration potentiated Fe-induced oxidative stress and neuronal death. The results indicate that Al potentiation of Fe-induced oxidative stress might contribute to Al facilitation of oxidative injury, and thus to Al 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.

Effects of dietary aluminum excess and manganese deficiency on neurobehavioral endpoints in adult mice

Studies in mice have suggested that both dietary Al excess and dietary Mn deficiency promote oxidative tissue damage. To determine if these factors can interact to produce functional nervous system damage, female mice (N = 10-12 per group) were fed diets with control or low Mn (35 or 3 micrograms Mn/g diet) and/or control or high Al (25 or 1000 micrograms Al/g diet, Al as Al lactate) content for a 90-day period. No overt signs of neurotoxicity were observed in any group. Excess Al produced a threefold Al accumulation in both liver and brain, a slight acceleration of growth, decreased motor activity, decreased grip strength, and decreased startle responsiveness. Manganese deprivation led to liver, brain, and femur Mn depletion and reduced liver MnSOD activity but no neurobehavioral changes. No interactive effects between Al excess and Mn deficiency were observed. Neither Al excess nor Mn deficiency altered brain or liver lipid peroxidation measures. This study suggests that (1) subchronic dietary Al at doses of 1000 micrograms Al/g diet produces elevated brain Al and altered neurobehavioral indices in adult mice; (2) brain lipid peroxidation is not altered by this treatment; (3) dietary Mn deficiency does not influence Al neurotoxicity in adult mice.

Effects of aluminum ingestion on spontaneous motor activity of mice

Aluminum (Al) as aluminum lactate in a purified diet was fed to adult female Swiss-Webster mice over a six week period. Comparison groups were: controls (CON), 25 micrograms Al/g diet; low Al (LO), 500 micrograms Al/g diet; high Al (HI), 1000 micrograms Al/g diet; and pair fed (PF) 25 micrograms Al/g diet pair fed to HI group. Weights, food intake and toxic signs were recorded at 3-day intervals and activity levels were measured during a 24-hr session during week 5 using an automated apparatus. Food intake was not reduced overall in Al-treated groups but they demonstrated a cyclic pattern of food intake. Mean weight gain over the 6-week period in the HI (0.5 g) and PF(0.1 g) groups was somewhat less than that in the CON (2.3 g) and LO (2.0 g) groups. No neurotoxic signs were recorded in any group, but a dose dependent increase in localized fur loss was seen. Overall activity level was 20% lower in HI than CON groups, with vertical movement more affected than horizontal movement. HI mice were less active during the diurnal period of peak activity than CON mice and their activity periods were also somewhat shorter (130 vs. 200 min). Activity of LO and PF mice did not differ significantly from controls, although PF activity levels were more variable. These data demonstrate that short term feeding of aluminum at levels within an order of magnitude of estimated human intake can influence neurobehavioral function as indexed by motor activity.

Comparison of the effects of central and peripheral aluminum administration on regional 2-deoxy-D-glucose incorporation in the rat brain

Intracerebroventricular (ICV) Injection of aluminum tartrate (ALT 205.7 mcg) in the rat induces a progressive encephalopathy characterized by neurobehavioral derangements, by the slowing of the background rhythm of the quantitative electroencephalogram and by learning and memory deficits. The condition, lethal within about 35 days, is associated with a reduced ability of cerebral synaptosomes to incorporate radiolabeled 2-Deoxy-D-glucose (2DG) in vitro. The present study surveyed and compared the in vivo regional cerebral glucose uptake (rCGlu) capacity of rats injected with ALT 7 or 14 days previously either by the ICV or intraperitoneal (120 mg/Kg) routes. ICV injection produces transient rCGlu depression in caudate-putamen, geniculate bodies and periaquaeductal gray, resolving by day 14. Thalamic nuclei exhibit depressed rCGlu by the 7th day undergoing further depression by day 14. The rCGlu of occipitoparietal cortices, normal at day 7, was increased by day 14. In contrast, peripheral aluminum administration produced transient rCGlu depression in olfactory bulbs, frontal and occipitoparietal cortices, nucleus accumbens and cerebellum, and transiently increased rCGlu in the geniculate nuclei. These effects, present by day 7, had resolved by day 14 when rCGlu had increased in the previously normal pontine nuclei and decreased in the previously normal hippocampus. Neither treatment changed rCGlu in the septal nuclei, globus pallidus, amygdala, olfactory cortex, substantia nigra, superior or inferior colliculi or the medullary nuclei. The pattern of anomalies in cerebral 2DG incorporation most probably indexes the deranged glucoregulatory and metabolic demands of these brain areas in the aluminum intoxicated state.

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.