Aluminum chelation by 3-hydroxypyridin-4-ones in the rat demonstrated by microdialysis

The ability and site of the metal-chelating 3-hydroxypyridin-4-ones (HPs) to mobilize aluminum (Al) was assessed in Al-loaded rats using microdialysis. Four HPs with greatly varying lipophilicity were studied. One week after Al loading, microdialysis probes were implanted in the liver, a jugular vein, and the frontal cortex. An HP was given iv followed by continuous microdialysis for 5 h. Al concentrations in dialysates from the liver increased rapidly and were consistently greater than from blood, suggesting that liver was a primary site of Al chelation. Brain dialysate Al concentrations remained low, suggesting little Al chelation in the brain and little distribution of the Al HP complex into the brain. Al concentrations were determined in the main organs/tissues of a separate group of Al-loaded rats, and the percentage of the total Al body burden in each organ/tissue was calculated. The skeletal system and liver had 57 and 28% of the Al body burden, consistent with the liver as a primary site of Al chelation. The HPs chelate extravascular Al and have been shown by others to be orally active. They warrant further investigation as Al chelators.     

Aluminum enhances iron uptake and expression of neurofibrillary tangle protein in neuroblastoma cells

Aluminum (Al) and iron (Fe) have been implicated as playing a toxic role in the pathologic lesions of Alzheimer's disease. In the following report we describe the uptake and toxicity of Al, the effect of Al on Fe uptake, and the expression of neurofibrillary tangle (NFT) protein in murine neuroblastoma cells (Neuro 2A). Significant cell Al uptake and inhibition of cell growth were seen in Neuro 2A cells at 24, 48, 72, and 96 h after plating in medium containing Al transferrin (Al-Tf) and Al citrate. Al-loaded Neuro 2A cells showed increased rates of 59Fe and 125I-Tf uptake and total cellular Fe content at 24, 48, 72, and 96 h after plating compared with control cultures. Significant increases in NFT protein staining were detected in Al-exposed cells at 72 and 96 h in culture compared with controls. The intensity of NFT staining in Al-loaded cells was directly proportional to the time in culture. There was no difference in malonyldialdehyde levels measured in control versus Al-loaded Neuro 2A cells. These results suggest that the accumulation of Al in Neuro 2A cells resulted in increased uptake of Fe, inhibition of cell growth, and expression of NFT protein, partially mimicking the pathological hallmarks of Alzheimer's disease. This model system may also be applicable for Al-induced dialysis dementia, because the Al concentrations at which cell toxicity occurred can be found in dialysis patients.     

Dissimilar Aluminum and Gallium Permeation of the Blood-Brain Barrier Demonstrated by In Vivo Microdialysis

Aluminum (Al) and gallium (Ga) permeations of the blood-brain barrier (BBB) were assessed in rats. Unbound extracellular Al and Ga concentrations were ascertained at the two potential sites of BBB permeation, cerebral capillaries and choroid plexuses, by implantation of microdialysis probes in the frontal cortex and lateral ventricle, respectively. A microdialysis probe implanted in the jugular vein revealed unbound blood Al or Ga concentrations. Al or 67Ga citrate was administered via the femoral vein. Peak Al and Ga concentrations were seen within the first 10 min at all three sites. Area under the curve (concentration vs. time to final sample) values were calculated using RSTRIP. Within-rat overall frontal cortical/blood and lateral ventricular/blood ratios [brain/blood ratios (oBBRs)] were calculated from area under the curve values. Aluminum frontal cortical oBBRs were significantly higher than those for the lateral ventricle. Ga oBBRs were not significantly different between the two sites. Al and Ga oBBRs were significantly different in the lateral ventricle. These results suggest that the primary site of A1 permeation across the BBB is at cerebral capillaries, whereas Ga permeation across the BBB does not significantly differ between cerebral capillaries and choroid plexuses. The use of Ga as a model to study Al pharmacokinetics may not be appropriate in the elucidation of the site or mechanism of Al entry into the brain.     

13C enrichment of extracellular neurotransmitter glutamate in rat brain--combined mass spectrometry and NMR studies of neurotransmitter turnover and uptake into glia in vivo.

13C-enrichment analysis of glutamate in the extracellular fluid (GLU(ECF): 2-3 microM) by gas-chromatography/mass-spectrometry (GCMS) was combined with in vivo NMR observation of whole-brain GLU (approximately10 mM) to study neurotransmitter uptake. Brain GLU C5 was 13C-enriched by intravenous [2,5-13C]glucose infusion. GLU(ECF) was collected by microdialysis from the cortico-striatal region of awake rats. The 13C-enrichment of basal dialysate GLU C5 during 0.75-1.25 hr of infusion was 0.263 +/- 0.01, very close to the enrichment of whole-brain GLU C5. The result strongly suggests that dialysate GLU consists predominantly of neurotransmitter GLU. For selective 13C-enrichment of neurotransmitter GLU, the whole-brain 13C-enrichment was followed by [12C]glucose infusion to chase 13C from the small glial GLU pool. This leaves [5-13C]GLU mainly in the large neuronal metabolic pool and the vesicular neurotransmitter pool. The uptake of synaptic [5-13C]GLU(ECF) into glia and metabolism to glutamine (GLN) were monitored in vivo by NMR observation of [5-13C,15N]GLN formed during 15NH4Ac infusion. The rate of GLN synthesis, derived from neurotransmitter GLU(ECF) (which provided 80-90% of the substrate) was 6.4 +/- 0.44 micromol/g/hr. Hence, the observed rate represents a reasonable estimate for the rate of glial uptake of GLU(ECF), a process that is crucial for protecting the brain from GLU excitotoxicity.     

Vasopressin analog delays extinction of classically conditioned bradycardia

Albino rabbits were subjected to Pavlovian (classical) conditioning and extinction of concomitant heart rate and eyeblink responses. Sixty minutes before each of three extinction sessions animals were treated with 5 or 20 μg/kg of deamino-dicarba-arginine-8-vasopressin or saline. Vasopressin treatment delayed extinction of bradycardiac conditioned responses but did not affect concomitant eyeblink conditioned responses. It was concluded that classically conditioned autonomic responses may be useful tools for studying the effects of peptides on learning.     

Aluminum induced oxidative events and its relation to inflammation: a role for the metal in Alzheimer's disease.

Aluminum (Al) is a simple trivalent cation incapable of redox changes. The toxicity of the metal has been the subject of much controversy in the past few decades. Although it has been generally believed that the metal is innocuous to human health, a causal role for Al has been established in dialysis dementia (Alfrey et al., 1976), osteomalacia (Bushinsky et al., 1995) and microcytic anemia without iron deficiency (Touam et al., 1983). Aluminum has also been implicated in Alzheimer's disease (AD) although a direct causal role has not been determined. The exact mechanism of Al toxicity is not known. However, there are several lines of evidence that show the metal's capacity to exacerbate oxidative events. The present review is intended to propose a coherent pathway linking Al-induced oxidative events to Alzheimer's disease. The preliminary segment is an introduction to reactive oxygen species and their potential involvement in the pathogenesis of AD and the generation of an inflammatory response. Evidence on the relation between AD and inflammatory processes is also presented. The epidemiological and clinical evidence of Al neurotoxicity is summarized in the second section of the review. Finally, a hypothesis indicating that aluminum can exacerbate AD by activating ROS generation and initiation of an inflammatory cascade is presented.     

Aβ(42) induced MRI changes in aged rabbit brain resembles AD brain

Alzheimer’s disease is the most common form of dementia and is structurally characterized by brain atrophy and loss of brain volume. Aβ is one of the widely accepted causative factors of AD. Aβ deposition is positively correlated with brain atrophy in AD. In the present study, structural brain imaging techniques such as Magnetic Resonance Imaging (MRI) were used to measure neuroanatomical alterations in Alzheimer’s disease brain. MRI is a non-invasive method to study brain structure. The objective of the present study was to elucidate the role of Aβ on brain structure in the aged rabbit brain. Among 20 aged rabbits, one batch (n = 10) rabbits was injected chronically with Aβ(1-42) and another batch (n = 10) with saline. The MRI was conducted before Aβ(1-42)/saline injection and after 45 days of Aβ(1-42)/saline injection. All the aged rabbits underwent MRI analysis and were euthanized after 45 days. The MRI results showed a significant reduction in thickness of frontal lobe, hippocampus, midbrain, temporal lobe and increases in the lateral ventricle volume. We also conducted an MRI study on AD (n = 10) and normal (n = 10) cases and analyzed for the thicknesses of frontal lobe, hippocampus, midbrain, temporal lobe and lateral ventricle lobe. We found significant reductions in thickness of the frontal lobe and the hippocampus. However, no significant reduction in the thickness of midbrain, temporal lobe or increase in the lateral ventricle volume was observed compared to normal. Correlations in brain atrophy changes between rabbit brain and human AD brain were found for frontal lobe and hippocampal regions. In contrast, other regions such as midbrain, temporal lobe, and lateral ventricles were not correlated with rabbit brain atrophy changes in the corresponding regions. The relevance of these changes in AD is discussed.     

Citrate exudation from white lupin induced by phosphorus deficiency differs from that induced by aluminum

Both phosphorus (P) deficiency and aluminum (Al) toxicity induce root exudation of carboxylates, but the relationship between these two effects is not fully understood. Here, carboxylate exudation induced by Al in Lupinus albus (white lupin) was characterized and compared with that induced by P deficiency. Aluminum treatments were applied to whole root systems or selected root zones of plants with limited (1 microM) or sufficient (50 microM) P supply. Aluminum stimulated citrate efflux after 1-2 h; this response was not mimicked by a similar trivalent cation, La(3+). P deficiency triggered citrate release from mature cluster roots, whereas Al stimulated citrate exudation from the 5- to 10-mm subapical root zones of lateral roots and from mature and senescent cluster roots. Al-induced citrate exudation was inhibited by P limitation at the seedling stage, but was stimulated at later growth stages. Citrate exudation was sensitive to anion-channel blockers. Al treatments did not affect primary root elongation, but inhibited the elongation of lateral roots. The data demonstrate differential patterns of citrate exudation in L. albus, depending on root zone, developmental stage, P nutritional status and Al stress. These findings are discussed in terms of possible functions and underlying mechanisms.     

Cerebellar-Dependent Associative Learning Is Preserved in Duchenne Muscular Dystrophy: A Study Using Delay Eyeblink Conditioning

ObjectiveBesides progressive muscle weakness cognitive deficits have been reported in patients with Duchenne muscular dystrophy (DMD). Cerebellar dysfunction has been proposed to explain cognitive deficits at least in part. In animal models of DMD disturbed Purkinje cell function has been shown following loss of dystrophin. Furthermore there is increasing evidence that the lateral cerebellum contributes to cognitive processing. In the present study cerebellar-dependent delay eyeblink conditioning, a form of associative learning, was used to assess cerebellar function in DMD children.MethodsDelay eyeblink conditioning was examined in eight genetically defined male patients with DMD and in ten age-matched control subjects. Acquisition, timing and extinction of conditioned eyeblink responses (CR) were assessed during a single conditioning session.ResultsBoth groups showed a significant increase of CRs during the course of learning (block effect p < 0.001). CR acquisition was not impaired in DMD patients (mean total CR incidence 37.4 ± 17.6%) as compared to control subjects (36.2 ± 17.3%; group effect p = 0.89; group by block effect p = 0.38; ANOVA with repeated measures). In addition, CR timing and extinction was not different from controls.ConclusionsDelay eyeblink conditioning was preserved in the present DMD patients. Because eyeblink conditioning depends on the integrity of the intermediate cerebellum, this older part of the cerebellum may be relatively preserved in DMD. The present findings agree with animal model data showing that the newer, lateral cerebellum is primarily affected in DMD.     

Effect of regular electrical stimulation of the septum on defensive conditioning

A conditioned defensive reflex to photic stimulation was produced in rabbits in computer-controlled experiments during regular electrical stimulation of the septum. During reflex formation spectral-correlation analysis was undertaken of sensomotor and visual cortical potentials and hippocampal potentials. In each rabbit the reflex to light was produced during septal stimulation at a definite frequency (2, 4, 7, and 9 Hz). Regular electrical stimulation of the septum at frequencies of 7 and 9 Hz accelerated conditioning whereas stimulation at a frequency of 2 Hz prevented formation of the temporary connection (the reflex appeared at the 35th combination). By changing the frequency of electrical stimulation of the septum, the speed of learning can thus be influenced. It is suggested that the role of the septum is to set a definite level of synchronization of brain processes at the optimal value for conduction of excitation from its afferent to its effector system.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 3, pp. 239–244, May–June, 1978.     

Nitric oxide exacerbates Al-induced inhibition of root elongation in rice bean by affecting cell wall and plasma membrane properties

Aluminum (Al) toxicity is one of the most widespread problems for crop production on acid soils, and nitric oxide (NO) is a key signaling molecule involved in the mediation of various biotic and abiotic stresses in plants. Here we found that exogenous application of the NO donor sodium nitroprusside (SNP) exacerbated the inhibition of Al-induced root growth in rice bean [Vigna umbellata (Thunb.) Ohwi & Ohashi ‘Jiangnan’, Fabaceae]. This was accompanied by an increased accumulation of Al in the root apex. However, Al treatments had no effect on endogenous NO concentrations in root apices. These results indicate that a change in NO concentration is not the cause of Al-induced root growth inhibition and the adverse effect of SNP on Al-induced root growth inhibition should result from increased Al accumulation. Al could significantly induce citrate efflux but SNP had no effects on citrate efflux either in the absence or presence of Al. On the other hand, SNP pretreatment significantly increased Al-induced malondialdehyde accumulation and Evans Blue staining, indicating an intensification of the disruption of plasma membrane integrity. Furthermore, SNP pretreatment also caused greater induction of pectin methylesterase activity by Al, which could be the cause of the increased Al accumulation. Taken together, it is concluded that NO exacerbates Al-induced root growth inhibition by affecting cell wall and plasma membrane properties.     

Hippocampal State-Dependent Behavioral Reflex to an Identical Sensory Input in Rats

We examined the local field potential of the hippocampus to monitor brain states during a conditional discrimination task, in order to elucidate the relationship between ongoing brain states and a conditioned motor reflex. Five 10-week-old Wistar/ST male rats underwent a serial feature positive conditional discrimination task in eyeblink conditioning using a preceding light stimulus as a conditional cue for reinforced trials. In this task, a 2-s light stimulus signaled that the following 350-ms tone (conditioned stimulus) was reinforced with a co-terminating 100-ms periorbital electrical shock. The interval between the end of conditional cue and the onset of the conditioned stimulus was 4±1 s. The conditioned stimulus was not reinforced when the light was not presented. Animals successfully utilized the light stimulus as a conditional cue to drive differential responses to the identical conditioned stimulus. We found that presentation of the conditional cue elicited hippocampal theta oscillations, which persisted during the interval of conditional cue and the conditioned stimulus. Moreover, expression of the conditioned response to the tone (conditioned stimulus) was correlated with the appearance of theta oscillations immediately before the conditioned stimulus. These data support hippocampal involvement in the network underlying a conditional discrimination task in eyeblink conditioning. They also suggest that the preceding hippocampal activity can determine information processing of the tone stimulus in the cerebellum and its associated circuits.     

小麦根系对铝毒的反应及其与根细胞壁组分和细胞壁对铝的吸附-解吸性能的关系

研究了小麦根系对铝毒的反应与不同根段细胞壁的组分及细胞壁对铝的吸附解吸性能的关系。结果表明,30μmol/LAlCl3可迅速抑制根系伸长,在铝处理30h时其根长仅为对照的30.2%;小麦根系相对伸长率随着铝浓度的提高而急剧降低,30μmol/LAlCl3处理24h对根系伸长的抑制率高达70.9%。小麦根系中距根尖0~10mm根段的铝含量和细胞壁中果胶糖醛酸含量明显高于距根尖10~20mm根段;距根尖0~10mm根段细胞壁对铝的吸附量明显大于距根尖10~20mm根段,而前者吸附态铝的解吸率低于后者;铝浓度从10μmol/L提高到20μmol/L时细胞壁对铝的吸附量增加,但对铝的解吸没有明显影响。采用1.0mol/LNH3·H2O对细胞壁预处理2h降低果胶甲基酯化程度后,铝吸附量降低了20.9%,但对铝解吸率没有影响。由此可见,小麦根尖是铝毒的主要位点,细胞壁果胶含量和果胶甲基酯化程度对小麦不同根段细胞壁对铝的吸附、积累具有重要作用,铝与细胞壁的结合是根系对铝毒胁迫反应的重要原因。     

Neuron activities of the motor cortex during conditioned eye blink reflex in rabbits (author's transl)]

Effects of the tone (CS) on neurons of the motor cortex were investigated in naive, pseudoconditioned, and conditioned rabbits. Conditioning to eye blink reflex was made by a combination of CS and air puff (US). Effects of electrical stimulation of the subcortical structures were also observed on the cortical neurons associated with the conditioned reflex. The results were as follows. (1) Proportion of neurons which significantly increased the firing rate in response to the CS, type E, was higher in the conditioned group than in other two groups. On the other hand, no group difference was found in the proportion of neurons which significantly decreased the firing rate to the stimulus, type I. (2) Most of the type E neurons in the conditioned rabbits began to fire at latencies of about 50 to 100 msec after the CS, preceding about 200 msec to the appearance of the peripheral conditioned responses (EMG). (3) Most of the type E neurons in the conditioned animals were more easily affected by stimulation of the medial geniculate body and the brain stem reticular formation. Based on the results mentioned above, it is concluded that in the rabbits conditioned to the eye blink reflex, excitability of neurons in the motor cortex is enhanced by the tone (CS), and by electrical stimulation to the medial geniculate body and the brain stem reticular formation.     

Level of neuroactive steroids in the brain, and gender-related differences in formation and decrease of conditioned reflex in rats

We investigated gender-related differences in dynamics of the brain sexual steroids during learning and the decrease of conditioned reflex in the modeling experiment. It was revealed that, before training to conditioned reflexes, females manifested a greater anxiety than males. Significant differences between males and females in formation of the conditioned reflex of passive avoidance were not revealed, whereas the conditioned response decrease were by 2-3 days faster in male rats than in females. It was revealed that there was an increase of testosterone content in various structures of the brain, especially in hippocampus and frontal cortex with its constant level in the blood plasma in learning conditioned response of passive avoidance in male adult rats. Also an increased estradiol concentration was found in females' amygdale, while increased value of estradiol was detected in hippocampus and the singular cortex in decrease of the conditioned response of passive avoidance. In blood plasma, the testosterone level was not changed, and the estradiol concentration was reduced significantly after the decreased conditioned reflex. Different dynamics of changes in the levels of sex steroids in the brain and the blood plasma can indicate a probability of their formation in nervous tissue. The correlation analysis confirms the conception about selective involvement of the brain's testosterone and estradiol in the specific structures in realization ofthe learning and memory processes in adult male and female rats.     

Effects of arginine-vasopressin and ACTH 4-10 on acquisition of active avoidance response in rats with alcohol pretreatment in prenatal and adult age

Alcohol administration in drinking water to mother rats during gestation resulted in a permanent learning deficit of the offspring when behavioural reactions were tested in active avoidance conditioned reflex situation in adult age. A similar deficit of learning capacity was observed in adult rats following alcohol administration for two weeks; the acquisition of active avoidance response was tested later. Administration of arginine-vasopressin and ACTH 4-10 during behavioural test led to a significant improvement of learning ability of the animals pretreated with alcohol. The observations indicate that the ethanol-induced deficit of learning capacity involves peptidergic mechanisms and the behavioural manifestations following chronic alcohol treatment are not irreversible processes.     

Classical eyeblink conditioning during acute hypobaric hypoxia is improved in acclimatized mice and involves Fos expression in selected brain areas.

This work attempts to evaluate the cognitive aspects of the acclimatization ability of mice submitted to simulated altitude. Critical altitudes were detected by evaluating open field activity, combined or not with object recognition tasks, at different acute simulated altitudes. Results showed impaired cognitive abilities at approximately 3,733 m and above. To evaluate acclimatization capabilities, mice submitted to hypobaric hypoxia at approximately 5,000 m for 1 wk were tested for learning and memory performances with classical eyeblink conditioning at the same altitude or at land altitude. Results showed total acclimatization in mice conditioned at approximately 5,000 m but no improved performance in those conditioned at land altitudes compared with controls. Selected brain sites of conditioned animals were analyzed by immunohistochemistry to detect expression of the protein product of the protooncogene c-fos (Fos) in relation to both motor learning processes and hypobaric conditions. In the nucleus of the solitary tract, a higher expression of Fos was found in the acute hypobaric conditioned animals than in control conditioned and nonconditioned animals. Similar patterns between groups were found in the other brain areas, mainly in the piriform cortex and area 1 of the cingulate cortex and in the hippocampus. Differences between hemispheres were detected only in acute hypobaric animals. The present results show that acclimatization to high altitude prevents the impairment of classical eyeblink conditioning evoked by hypobaric hypoxic conditions but does not improve this task when acquired under land conditions, although it could diminish the activation requirements for its performance.     

铝诱导植物程序性细胞死亡信号转导的研究进展

铝是制约酸性土壤上作物生产的主要因素。铝诱导氧化胁迫产生大量活性氧/一氧化氮,引起胞质钙超载,通过线粒体信号转导途径激发相关凋亡基因,从而引起细胞主动死亡,以减轻铝对植物的进一步毒害。本文综述了铝诱导程序性细胞死亡的信号分子、相关基因以及信号转导途径,对未来的研究方向提出了展望,为深入研究植物铝毒害机理和耐铝机制提供参考。     

High Selenium Yeast mitigates aluminum-induced cerebral inflammation by increasing oxidative stress and blocking NO production

High Selenium Yeast (SeY) serves many important roles with respect to the maintenance of normal nervous system functioning. Studies have reported the nerve inflammation induced by Aluminum (Al) was associated with the increase of mortality. However, in-depth studies are required to verify the hypothesized neuro-protective efficacy of SeY against Al-induced cerebral damage through modulation of the inflammatory response. Here, mice were treated with SeY (0.1 mg/kg) and/or Al (10 mg/kg) by oral gavage for 28 days. Inflammation was assessed by histopathological examination and expression of biomarkers for inflammation. Furthermore, the oxidation–reduction levels and the NO production were assessed using diagnostic kits and RT-PCR. The data indicated that SeY significantly protected cerebrum against Al-induced pathological changes, in addition to the disordered expression of biomarkers of inflammation, the imbalance of oxidation–reduction, and the increase of NO production. Therefore, the chemoprotective potential of SeY against Al-induced cerebral inflammation via restore the levels of oxidation–reduction and the generation of NO was demonstrated.