Modulation of 14C‐labeled glucose metabolism by zinc during aluminium induced neurodegeneration

Aluminium (Al) is one of the most prominent metals in the environment and is responsible for causing several neurological disorders, including Alzheimer's disease. On the other hand, zinc (Zn) is an essential micronutrient that is involved in regulating brain development and function. The present study investigates the protective potential of Zn in the uptake of ¹⁴C‐labeled amino acids and glucose and their turnover in rat brain slices during Al intoxication. Male Sprague Dawley rats (140–160 g) were divided into four different groups: normal control, Al treated (100 mg/kg body weight/day via oral gavage), Zn treated (227 mg/liter in drinking water), and Al + Zn treated. Radiorespirometric assay revealed an increase in glucose turnover after Al exposure that was attenuated after Zn treatment. Furthermore, the uptake of ¹⁴C‐labeled glucose was increased after Al treatment but was appreciably decreased upon Zn supplementation. In addition, the uptakes of ¹⁴C‐lysine, ¹⁴C‐leucine, and ¹⁴C‐aspartic acid were also found to be elevated following Al exposure but were decreased after Zn treatment. Al treatment also caused alterations in the neurohistoarchitecture of the brain, which were improved after Zn coadministration. Therefore, the present study suggests that Zn provides protection against Al‐induced neurotoxicity by regulating glucose and amino acid uptake in rats, indicating that Zn could be a potential candidate for the treatment of various neurodegenerative disorders. © 2015 Wiley Periodicals, Inc.     

Lipid peroxidation and aluminium effects on the cholinergic system in nerve terminals

In the present study, we analyzed how aluminium and oxidative stress induced by ascorbate/Fe²⁺ affect the mechanisms related with the cholinergic system in a crude synaptosomal fraction isolated from rat brain. [³H]Choline uptake, [³H]acetylcholine release, membrane potential and Na⁺/K⁺-ATPase activity were determined in the presence or in the absence of aluminium in control conditions and in the presence of ascorbate (0.8 mM)/Fe²⁺ (2.5 μM). The extent of lipid peroxidation was measured by quantifying thiobarbituric acid reactive substances (TBARS). Under oxidizing conditions aluminium increased the formation of TBARS by about 30 %, but was without effect when the synaptosomal preparation was incubated in the absence of oxidants. Additionally, aluminium potentiated the inhibition of the high-affinity [³H]choline uptake observed following lipid peroxidation and had the same effect on the Na⁺/K⁺-ATPase activity. [³H]Acetylcholine release induced by 4-aminopyridine, and membrane potential were not significantly affected under oxidizing conditions, either in the absence or in the presence of aluminium. We can conclude that aluminium, by potentiating lipid peroxidation, affects the uptake of choline in nerve endings. This effect, occurring during brain oxidative injury, might contribute to the cholinergic dysfunction and neuronal cell degeneration known to occur in Alzheimer’s disease.     

The REACH registration process: A case study of metallic aluminium,aluminium oxide and aluminium hydroxide

The European Union’s REACH Regulation requires determination of potential health and environmental effects of chemicals in commerce. The present case study examines the application of REACH guidance for health hazard assessments of three high production volume (HPV) aluminium (Al) substances: metallic aluminium, aluminium oxide, and aluminium hydroxide. Among the potential adverse health consequences of aluminium exposure, neurotoxicity is one of the most sensitive targets of Al toxicity and the most critical endpoint. This case study illustrates integration of data from multiple lines of evidence into REACH weight of evidence evaluations. This case study then explains how those results support regulatory decisions on classification and labelling. Challenges in the REACH appraisal of Al compounds include speciation, solubility and bioavailability, application of assessment factors, read-across rationale and differences with existing regulatory standards. Lessons learned from the present case study relate to identification and evaluation of toxicologic and epidemiologic data; assessing data relevance and reliability; development of derived no-effect levels (DNELs); addressing data gaps and preparation of chemical safety reports.     

Aluminum citrate uptake by immortalized brain endothelial cells: implications for its blood-brain barrier transport

The objective was to further test the hypothesis that aluminum (Al) citrate transport across the blood–brain barrier is mediated by a monocarboxylate transporter (MCT). Speciation calculations showed that Al citrates were the predominant Al species under the conditions employed. Al citrate did not inhibit lactate uptake and was not taken up by the rat erythrocyte, suggesting it does not serve as an effective substrate for either MCT1 or the anion exchanger. Studies were conducted with b.End5 cells derived from mouse brain endothelial cells to identify the properties of the carrier(s) mediating Al citrate transport. Western blot analysis of b.End5 cells showed expression of the transferrin receptor and MCT1, but not MCT2 or MCT4. Uptake of Al citrate was 70% faster than citrate. Citrate and Al citrate uptake were sodium independent. Citrate uptake increased at pH 6.9 compared to 7.4, whereas Al citrate uptake did not. Al citrate uptake was reduced by inhibitors of mitochondrial respiration and oxidative phosphorylation, suggesting ATP dependence, but not by ouabain, suggesting no role for Na/K-ATPase. Uptake was not affected by -ketoglutarate or malonate, substrates for the dicarboxylate carrier. Many substrates and inhibitors of MCT1 and organic anion transporters reduced Al citrate uptake into b.End5 cells. BSP and fluorescein, organic anion transporter substrates/inhibitors, inhibited Al citrate uptake. We conclude that Al citrate transport across the blood–brain barrier is carrier-mediated, involving either an uncharacterized MCT isoform expressed in the brain such as MCT7 or MCT8 and/or one of the many members of the organic anion transporting protein family, some of which are known to be expressed at the blood–brain barrier.     

Differential toxicity of novel aluminium compounds in hippocampal culture

The dependence of aluminium (Al) toxicity on its chemical form has been implicated in previous studies, but the complex chemistry of Al in solutions of biological preparations has hampered a reliable assessment. Here, we assessed the toxicity of select and pure Al(III) citrate compounds, well-characterized at physiological pH, and compared it with Al from standard solution (in HCl). Cell death rates of neurones and glia were established in hippocampal cultures following 3h incubations in a HEPES-buffered solution and 24h incubations in full culture medium. Overall, Al toxicity was found to vary considerably between compounds, with duration of exposure, medium type, and cell type as factors. While Al (from atomic absorption standard solution) induced the highest levels of cell death, AlCit1, ((NH(4))(5)[Al(C(6)H(4)O(7))(2)].2H(2)O) was the most toxic citrate compound, and affected viability of neurones more than glia (viability at 500 microM/3h-neurones: 40%; glia: 60%). AlCit2 (K(4)[Al(C(6)H(4)O(7))(C(6)H(5)O(7))].4H(2)O) did not show any toxicity after 3h, but severe toxicity after 24h in both cell types (viability at 500 microM/24h-neurones: 50%, glia: 30%). AlCit3 ((NH(4))(5)[Al(3)(C(6)H(4)O(7))(3)(OH)(H(2)O)].(NO(3)).6H(2)O), exhibited a cell type specific toxicity profile, and only affected neuronal viability at both time points (neuronal viability at 500 microM/3h: 20%). The medium type and presence of serum (FBS) was also found to contribute to the toxicity pattern, with serum providing partial protection. Since the Al(III) compounds introduced here are assumed to form in vivo, our data raise further awareness for the toxicity of Al(III) in general, and for the importance of Al speciation and cell type specific actions in its toxicity.     

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.     

Neurofibrillary degeneration of nerve cells after intracerebral injection of aluminium cream

Summary Intracerebral administration of aluminium cream (aluminium hydroxide) in rabbits resulted in the development of pathological EEG, convulsive seizures, paresis of the extremities and neuronal changes consisted in a focal clearings in the cytoplasm filled by neurofibrillary tangles. In principle, the topography of the neurofibrillary changes was the same as that observed byKlatzo, Winiewski andStreicher in rabbits after injection of aluminium phosphate.

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Zusammenfassung Intracerebrale Applikation von Aluminiumpaste (Aluminiumoxyd) bei Kaninchen führte zum Auftreten von pathologischen EEG-Veränderungen, Krampf-anfällen, Extremitätenparesen sowie von Nervenzellveränderungen in Form fokaler Cytoplasmaaufhellungen, die von verplumpten Neurofibrillen erfüllt sind. Die Topographie der neurofibrillären Veränderungen entsprach grundsätzlich den Beobachtungen vonKlatzo, Winiewski u.Streicher an Kaninchen nach Injektion von Aluminiumphosphat.

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This work was supported by grand PL 480, agreement No. 227706 sponsored by the United States Public Health Service.     

Studies of anti-Xa activity in human plasma II: The role of lipoproteins

The major plasma inhibitor of Factor Xa is thought to be anti-thrombin III (At III). However, adsorption of plasma by aluminium hydroxide (A1(OH)₃) increases its rate of neutralisation 7–8 fold, and this ‘fast-acting’ anti-Xa activity has been shown to be independent of At III. Gel filtration of plasma indicated that the anti-Xa activity after Al(0H)₃ adsorption was located largely in the high molecular weight (> 200,000) fractions, which contain most of the plasma lipoproteins. Purified lipoproteins of very low-density (VLDL), low-density (LDL) and high density (HDL) were prepared by ultracentrifugation and their anti-Xa activities measured before and after adsorption by Al(OH)₃. Both LDL and HDL had significant anti-Xa activities by clotting and amidolytic assays. Al(OH)₃ adsorption of LDL and HDL gave a marked increase in anti-Xa clotting activity and a decrease in amidolytic activity. Incubation of the adsorbed lipoproteins with phospholipase enzymes destroyed the anti-Xa activity, and prior incubation of Factor Xa with Ca⁺⁺ and phospholipid protected it against inactivation, indicating that the anti-Xa activity of the adsorbed lipoproteins is mediated via binding of Xa to phospholipid in the lipoproteins. These results indicate that lipoproteins, especially LDL and HDL, are responsible for the increased anti-Xa activity of plasma after Al(OH)₃ adsorption. These lipoproteins appear to contain high affinity phospholipid binding sites for Xa which are revealed by Al(OH)₃ adsorption.     

The effect of aluminium on NTPDase and 5′-nucleotidase activities from rat synaptosomes and platelets

Aluminium (Al), a neurotoxic compound, has been investigated in a large number of studies both in vivo and in vitro. In this study, we investigated the effect in vivo of long-term exposure to Al on NTPDase (nucleoside triphosphate diphosphohydrolase) and 5'-nucleotidase activities in the synaptosomes (obtained from the cerebral cortex and hippocampus) and platelets of rats. Here, we investigated a possible role of platelets as peripheral markers in rats. Rats were loaded by gavage with AlCl(3) 50 mg/(kg day), 5 days per week, totalizing 60 administrations. The animals were divided into four groups: (1) control (C), (2) 50 mg/kg of citrate solution (Ci), (3) 50 mg/kg of Al plus citrate (Al+Ci) solution and (4) 50 mg/kg of Al (Al). ATP hydrolysis was increased in the synaptosomes from the cerebral cortex by 42.9% for Al+Ci and 39.39% for Al, when compared to their respective control (p<0.05). ADP hydrolysis was increased by 13.15% for both Al and Al+Ci, and AMP hydrolysis increased by 32.7% for Al and 27.25% for Al+Ci (p<0.05). In hippocampal synaptosomes, the hydrolysis of ATP, ADP and AMP, was increased by 58.5%, 28.5% and 25.92%, respectively, for Al (p<0.05) and 36.7%, 22.5% and 37.64% for Al+Ci, both when compared to their respective controls. ATP, ADP and AMP hydrolysis, in platelets, was increased by 172.3%, 188.52% and 92.1%, respectively in Al+Ci, and 317.9%, 342.8% and 177.9%, respectively, for Al, when compared to their respective controls (p<0.05). Together, these results indicate that Al increases NTPDase and 5'-nucleotidase activities, in synaptosomal fractions and platelets. Thus, we suggest that platelets could be sensitive peripheral markers of Al toxicity of the central nervous system.     

Uptake and release of calcium by rat brain synaptosomes

Rat brain synaptosomes, prepared by discontinuous Ficoll density gradient centrifugation, accumulated ⁴⁵Ca during brief incubations in modified Krebs-Ringer media. Uptake of ⁴⁵Ca was increased by 5 mM glutamate and 50 mM KCl, conditions that depolarize nerve cells; uptake of ²²Na was also increased by these agents. With 0.2 mM diphenylhydantoin, the increased ⁴⁵Ca uptake due to KCl was diminished, whereas that due to glutamate was less affected; conversely, with 0.15 μM tetrodotoxin the increased ⁴⁵Ca uptake due to glutamate was diminished, whereas that due to KCl was less affected. Both diphenylhydantoin and tetrodotoxin diminished the augmented uptake of ²²Na due to KCl and glutamate; thus the increased uptake of ⁴⁵Ca under depolarizing conditions may be dissociated from the increased influx of sodium. Ruthenium red decreased the uptake of ⁴⁵Ca under all conditions, as did procaine and the lanthanide Pr³⁺. Neither 5 mM lutamate nor 50 mM KCl increased ⁴⁵Ca uptake by brain mitochondria under comparable experimental conditions, whereas ATP increased the uptake by mitochondria but not that by these synaptosomes. Altering the sodium gradient by equimolar substitution of lithium or choline for sodium in the medium increased ⁴⁵Ca uptake, whereas ²²Na uptake was decreased. Inhibiting the sodium pump by ouabain or strophanthidin also increased ⁴⁵Ca uptake, and increased ²²Na uptake as well. The increased uptake of ⁴⁵Ca induced by ouabain was inhibited by diphenylhydantoin and tetrodotoxin. Measurements of the total calcium content showed that conditions producing an increased uptake of ⁴⁵Ca also produced a net uptake of calcium, rather than merely accelerating a ⁴⁵Ca⁴⁰Ca exchange. Experiments measuring the loss of previously accumulated ⁴⁵Ca showed that directly decreasing the sodium gradient or inhibiting the sodium pump slowed the loss of ⁴⁵Ca. These data are considered in terms of calcium influx through ‘leak’ pathways and gated channels (sensitive to membrane depolarization) and of net efflux dependent on a coupled sodium-calcium exchange mechanism.     

A comparison of sodium-dependent glutamate binding with high-affinity glutamate uptake in rat striatum

The specific sodium-dependent binding of [³H]glutamate to membranes of the rat striatum was examined and a comparison made with high affinity glutamate uptake. In the presence of sodium, [³H]glutamate binding was saturable and of high affinity. No binding could be detected in the absence of sodium. Removal of the cortical afferents to the striatum resulted in a parallel decrease in Na⁺-dependent glutamate binding and in high-affinity glutamate uptake. After the injection of the neurotoxin kainic acid into the striatum, the density of Na⁺-dependent glutamate binding sites was reduced by 40%, while high-affinity uptake showed no significant decrease. Drugs which inhibit high-affinity uptake were also effective at inhibiting Na⁺-dependent binding. The results suggest that about half the Na⁺-dependent glutamate binding sites in the striatum represent high-affinity uptake sites on the corticostriatal terminals. The remainder of the binding sites are located on striatal neurons and may also be uptake sites.     

Effects of complexed iron and aluminium on brain calcium.

Ferric lactate increases Ca(2+)-uptake by Ehrlich carcinoma ascites cells as well as in vitro and in vivo Ca(2+)-uptake by the liver. Iron and aluminium are increased in the substantia nigra of patients with Parkinson's disease and aluminium is suspected to be involved in the pathophysiology of Alzheimer's disease. This study was conducted to determine if there is any relationship between iron and aluminium uptake and a possible calcium influx into brain tissue. Groups of Swiss mice were injected in the tail vein with 100 microliters of 0.05 M ferric lactate plus 2 microCi45CaCl2, or 100 microliters of 0.05 M aluminium lactate plus 2 microCi45CaCl2, or 100 microliters of saline plus 2 microCi45CaCl2. Twenty-four hr later they were sacrificed by decapitation. Samples of blood and the total brain were weighed and ashed. The ashes were dissolved and the solution transferred to counting vials evaporated to dryness. A scintillation solution was added to the vials and the radioactivity was counted. To accurately assess brain uptake in each animal the value of brain specific activity was related to blood specific activity. When compared to those of control animals, these values gave the 24 hr increase of 45Ca-uptake by brain of ferric lactate or aluminium lactate-treated animals. A significant increase of 45Ca-uptake was observed for ferric lactate (136% of control value, p less than 0.005), which is more important for aluminium lactate (163% of control value, p less than 0.001). The nature of the complexed metal-brain tissue interaction is not known, several mechanisms are discussed.     

Neuroprotective effect of Allium cepa L. in aluminium chloride induced neurotoxicity

The present study was envisaged to investigate the neuroprotective potential of Allium cepa (A. cepa) in aluminium chloride induced neurotoxicity. Aluminium chloride (50 mg/kg/day) was administered orally in mice supplemented with different doses of A. cepa hydroethanolic extract for a period of 60 days. Various behavioural, biochemical and histopathological parameters were estimated in aluminium exposed animals. Chronic aluminium administration resulted in significant motor incoordination and memory deficits, which were also endorsed biochemically as there was increased oxidative stress as well as elevated acetylcholinesterase (AChE) and aluminium levels in the brain. Supplementation with A. cepa in aluminium exposed animals significantly improved muscle coordination and memory deficits as well as reduced oxidative stress, AChE and decreased abnormal aluminium deposition in the brain. Histopathologically, there was marked deterioration visualized as decreased vacuolated cytoplasm as well as decreased pyramidal cells in the hippocampal area of mice brain which were found to be reversed with A. cepa supplementation. Administration of BADGE (PPARγ antagonist) in aluminium exposed animals reversed the neuroprotective potential of A. cepa as assessed with various behavioural, biochemical, neurochemical and histopathological estimations. In conclusion, finding of this study suggested significant neuroprotective potential of A. cepa in aluminium induced neurotoxicity. Further, the role of PPARγ receptor agonism has also been suggested as a putative neuroprotective mechanism of A. cepa, which needs further studies for confirmation.     

Aluminium incorporation into the brain of rat fetuses and sucklings

Aluminium is highly neurotoxic and inhibits prenatal and postnatal development of the brain in humans and experimental animals. However, the incorporation of aluminium into the brain of fetuses and sucklings during gestation and lactation has not been well clarified because aluminium lacks a suitable isotope for a tracer experiment. In this study, we used 26Al (a radioisotope of aluminium with a half-life of 716,000 years) as a tracer, and measured 26Al incorporation into the brain of rat fetuses and sucklings by using accelerator mass spectrometry. 26Al (26AlCl3) was subcutaneously injected into pregnant rats and lactating rats. By day 21 of gestation, considerable amounts of the 26Al injected into the pregnant rats had been transferred to the brain and nuclear fraction (brain cell nuclei) of the rat fetuses. From day 5 to day 20 postpartum, the amounts of 26Al measured in the brain of suckling rats increased significantly. On day 20 postpartum, 26Al was found in the nuclear fraction isolated from the brain of suckling rats. It is concluded that 26Al subcutaneously injected into pregnant rats and/or lactating rats was incorporated into the brain and nuclear fraction (brain cell nuclei) of fetuses and sucklings through the transplacental passage and/or maternal milk.     

Sodium dependence of the nerve growth factor — regulated hexose uptake in chick embryo ganglionic cells

Embryonic dorsal root ganglionic cells, when incubated in vitro in the absence of nerve growth factor (NGF) undergo a general metabolic degeneration which is preceded by certain changes in permeation properties. Previous studies demonstrated that NGF can rapidly modulate permeation properties which regulate the availability to the cell of an important energy source, glucose. Hexose uptake was determined by measuring the ability of the cells to accumulate [³H]labelled 2-deoxy-d-glucose. The work reported here shows that the NGF-dependent portion (about one-third) of the total specific hexose uptake was also dependent on the presence of Na⁺, with the apparent uptake constant (K_t) for deoxyglucose varying inversely with an external Na⁺ concentration of 70–140 mM; V_max was unaffected in this range. Preincubation of ganglionic cells with 10 mM ouabain for 15–60 min, followed by a pulse with [³H]-deoxyglucose, also resulted in 50–95% reduction of the NGF-sensitive uptake. A similar pretreatment of cells with veratridine gave a 25–50% reduction in uptake. The NGF-controlled hexose uptake was also energy dependent, being diminished 50–95% after a 30–90 min preincubation with 2 mM 2,4-dinitrophenol. Uptake activities for other substrates (α-aminoisobutyric acid, uridine) which exhibited NGF regulation were likewise Na⁺-sensitive. These results indicate that availability of major energy substrates to NGF-dependent dorsal root ganglionic neurons is controlled by sodium gradients across their membranes. It is conceivable that NGF provides for maintenance and development of its target neurons by acting on such sodium gradients and, consequently, regulating the intake of essential nutrients.     

Ion dependency of uptake and release of GABA and (RS)-nipecotic acid studied in cultured mouse brain cortex neurons

The influence of sodium ions on GABA uptake into neurons cultured from cerebral cortex was investigated at sodium concentrations ranging from 16 to 151 mM. Sodium did not affect the K_m for GABA uptake but the uptake rates as a function of the sodium concentration was sigmoid at all GABA concentrations studied (1-200 μM). Hill plots of these curves exhibited straight lines with slopes of 1.7-2.1, suggesting that the coupling ratio between sodium and GABA is at least 2. (RS)-Nipecotic acid, a GABA analogue, was transported with high affinity (K_m 8.0 ± 2.1 μM) like GABA, but the V_max for nipecotic acid was lower than found for GABA (0.664 ± 2 0.035 versus 0.955 ± 2 0.059 nmol × min^?1 × mg^?1), suggesting a microheterogeneity of the GABA transport sites. Neurons loaded with the respective vitiated compounds exhibited a pronounced K⁺-stimulated, calcium-dependent release of both GABA and nipecotic acid indicating that these cultured cells have developed functionally active GABA-ergic synapses.     

Partial reversal of aluminium-induced neurofibrillary degeneration by desferrioxamine in adult male rabbits

J. Savory, M. M. Herman, R. T. Erasmus, J. C. Boyd and M. R. Wills (1994) Neuropathology and Applied Neurobiology 20, 31–37 Partial reversal of aluminium–induced neurofibrillary degeneration by desferrioxamine in adult male rabbits Desferrioxamine, a chelating agent with a high affinity for aluminium, has been reported to slow the clinical progression of dementia associated with Alzheimer's disease [4], We report here the effects of desferrioxamine treatment on aluminium–induced neurofibrillary degeneration in rabbits. Adult male New Zealand white rabbits received a single injection of aluminium–maltolate into the lateral cerebral ventricle. Three days later, one group of rabbits was treated with intramuscular injections of desferrioxamine twice daily; a second group received saline instead of desferrioxamine. Both groups were sacrificed 4 or 5 days following initiation of desferrioxamine or saline treatment. Minimal neurofibrillary degeneration was found in two of six desferrioxamine–treated rabbits, while all six rabbits treated with saline showed extensive neurofibrillary degeneration, particularly in the ventral horn of the lower spinal cord. Quantitation of the neurofibrillary degeneration in ventral horn neurons of lumbar cord revealed 30% to be affected in saline–treated animals compared to zero affected neurons following desferrioxamine treatment. When sacrificed just 3 days after aluminium treatment, 50% of the rabbits already revealed neurofibrillary degeneration, corresponding to the timepoint when desferrioxamine treatment was begun in the above animals; on quantitation, 7.5% of ventral lumbar cord neurons were involved. These findings indicate a partial reversal of aluminium–induced neurodegeneration by desferrioxamine. Delaying desferrioxamine treatment to 6 days after aluminium administration prevented any reversal of the aluminium effect; all animals had abundant neurofibrillary degeneration as well as a striking basophilic spicular deposit of calcium and argyrophilic material in the leptomeninges, lateral ventricles and brain parenchyma adjacent to these areas. Pre–treatment of rabbits with desferrioxamine did not provide the expected protective effect against aluminium–induced neurofibrillary degeneration. No pathological effects were observed when saline or desferrioxamine were given alone, without aluminium     

Astrocytes restrict discharge duration and neuronal sodium loads during recurrent network activity

Influx of sodium ions into active neurons is a highly energy‐expensive process which must be strictly limited. Astrocytes could play an important role herein because they take up glutamate and potassium from the extracellular space, thereby dampening neuronal excitation. Here, we performed sodium imaging in mouse hippocampal slices combined with field potential and whole‐cell patch‐clamp recordings and measurement of extracellular potassium ([K⁺]_o). Network activity was induced by Mg²⁺‐free, bicuculline‐containing saline, during which neurons showed recurring epileptiform bursting, accompanied by transient increases in [K⁺]_o and astrocyte depolarizations. During bursts, neurons displayed sodium increases by up to 22 mM. Astrocyte sodium concentration increased by up to 8.5 mM, which could be followed by an undershoot below baseline. Network sodium oscillations were dependent on action potentials and activation of ionotropic glutamate receptors. Inhibition of glutamate uptake caused acceleration, followed by cessation of electrical activity, irreversible sodium increases, and swelling of neurons. The gliotoxin NaFAc (sodium‐fluoroacetate) resulted in elevation of astrocyte sodium concentration and reduced glial uptake of glutamate and potassium uptake through Na⁺/K⁺‐ATPase. Moreover, NaFAc extended epileptiform bursts, caused elevation of neuronal sodium, and dramatically prolonged accompanying sodium signals, most likely because of the decreased clearance of glutamate and potassium by astrocytes. Our experiments establish that recurrent neuronal bursting evokes sodium transients in neurons and astrocytes and confirm the essential role of glutamate transporters for network activity. They suggest that astrocytes restrict discharge duration and show that an intact astrocyte metabolism is critical for the neurons' capacity to recover from sodium loads during synchronized activity. GLIA 2015;63:936–957     

Manganese Flux Across the Blood–Brain Barrier

Manganese (Mn) is essential for brain growth and metabolism, but in excess can be a neurotoxicant. The chemical form (species) of Mn influences its kinetics and toxicity. Significant Mn species entering the brain are the Mn²⁺ ion and Mn citrate which, along with Mn transferrin, enter the brain by carrier-mediated processes. Although the divalent metal transporter (DMT-1) was suggested to be a candidate for brain Mn uptake, brain Mn influx was not different in Belgrade rats, which do not express functional DMT-1, compared to controls. Brain Mn influx was not sodium dependent or dependent on ATP hydrolysis, but was reduced by mitochondrial energy inhibitors. Mn and Fe do not appear to compete for brain uptake. Brain Mn uptake appears to be mediated by a Ca uptake mechanism, thought to not be a p-type ATPase, but a store-operated calcium channel. Efflux of Mn from the brain was found to be slower than markers used as membrane impermeable reference compounds, suggesting diffusion mediates brain Mn efflux. Owing to carrier-mediated brain Mn influx and diffusion-mediated efflux, slow brain Mn clearance and brain Mn accumulation with repeated excess exposure would be predicted, and have been reported. This may render the brain susceptible to Mn-induced neurotoxicity from excessive Mn exposure.     

Saturable uptake of [I] -triiodothyronine at the basolateral (blood) and apical (cerebrospinal fluid) sides of the isolated perfused sheep choroid plexus

The uptake of ¹²⁵I-labelled -triiodothyronine (T₃) was measured on the blood side of the isolated perfused choroid plexus of the sheep using steady-state and single-circulation paired tracer techniques. The steady-stake uptake of T₃ was 33.5% (perfussion fluid protein content was 0.05 g·dl⁻¹) which could be reduced to 9.4% in the presence of 500 μM unlabelled T₃ showing partial saturation. The CSF to blood steady-state [¹²⁵I]T₃ measurements gave plasma/CSF ratio, R%, of 24.6 ± 4.8% which was reduced to 9.8 ± 2.1% in the presence of 500 μM unlabelled T₃ in the mock CSF. The transport of T₃ across the blood face of the choroid plexus and the CSF to blood transport, failed to show sodium dependence. Using the single circulation paired tracer technique, the initial uptake in less than 60 s, U_max of [¹²⁵I]T₃ was 50.4 ± 3.9% relative to the extracellular marker [³H] -mannitol. However, when 250 μM unlabelled T₃ was present, U_max was reduced by 66%, although further significant inhibition at higher concentrations was not observed. Uptake of T₃ at the blood side of the choroid plexus was partially saturated in the presence of unlabelled reverse T₃ and DT₃, suggesting little uptake stereospecificity. Unlabelled thyroxine (T₄) and the amino acid analogues cycloleucine (aminocyclopentane-1-carboxylic acid) and BCH (β-2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid) each reduced [¹²⁵I]T₃ uptake significantly, but not to the same degree as T₃ stereoisomers. The neutral amino acids alanine and phenylalanine, had no effect on uptake. The [¹²⁵I]T₃ unidirectional flux was calculated from U_max vlues and the resultant kinetic curve could be resolved into two components; a non-saturable process with a slope of 1.2 ml·min⁻¹·g⁻¹, and a saturable process with K_m = 66 ± 22 μM and V_max = 0.44 ± 0.11 μmol·min⁻¹·g⁻¹. These data suggest that [¹²⁵I]T₃ uptake at the blood face of the choroid plexus, is mediated by both saturable and non-saturable uptake processes, which lack stereospecificity, sodium dependence, and exhibit cross competition both with T₄ and the large neutral amino acid analogues, cycloleucine and BCH. Transport from CSF was also partially saturable, did not exhibit sodium dependence.