Lead as an inductor of some morphological and functional changes in synaptosomes from rat brain

Neurobehavioral deficits, histoarchitectural alterations, parvalbumin neuronal damage and glial activation in the brain of male Wistar rat exposed to Landfill leachate

Concerns about inappropriate disposal of waste into unsanitary municipal solid waste landfills around the world have been on the increase, and this poses a public health challenge due to leachate production. The neurotoxic effect of Gwagwalada landfill leachate (GLL) was investigated in male adult Wistar rats. Rats were exposed to a 10% concentration of GLL for 21 days. The control group received tap water for the same period of the experiment. Our results showed that neurobehavior, absolute body and brain weights and brain histomorphology as well as parvalbumin interneurons were severely altered, with consequent astrogliosis and microgliosis after 21 days of administrating GLL. Specifically, there was severe loss and shrinkage of Purkinje cells, with their nucleus, and severe diffused vacuolations of the white matter tract of GLL-exposed rat brains. There was severe cell loss in the granular layer of the cerebellum resulting in a reduced thickness of the layer. Also, there was severe loss of dendritic arborization of the Purkinje cells in GLL-exposed rat brains, and damage as well as reduced populations of parvalbumin-containing fast-spiking GABAergic interneurons in various regions of the brain. In conclusion, data from the present study demonstrated the detrimental effects of Gwagwalada landfill leachate on the brain which may be implicated in neuropsychological conditions.

Neuroecotoxicology: Effects of environmental heavy metal exposure on the brain of African giant rats and the contribution of vanadium to the neuropathology

Increased exploitation of minerals has led to pollution of confined environments as documented in Nigeria Niger Delta. Information on the effects on brain of such exposure is limited. Due to its exploratory activities, the African giant rat (Cricetomys gambianus) (AGR) provides a unique model for neuroecotoxicological research to determine levels of animal and human exposure to different pollutants. This study aims to unravel neuropathological features of AGR sampled from three agro-ecological zones of Nigeria. Fifteen AGR were sampled according to previously determined data on heavy metal exposure: high vanadium, high lead, and low metals. Eighteen AGR were collected from low metal zone and divided into two groups. Control group received vehicle while SMV exposed group received 3 mg/kg sodium metavanadate (SMV) intraperitoneally for 14days. Brain immunohistochemical analyses were conducted, and ultrastructural changes were studied in experimentally exposed group. Results showed significant loss of tyrosin hydroxylase, parvalbumin, orexin-A and melanin concentration hormone containing neuronal populations in brains obtained from high vanadium and high lead zones and in experimentally intoxicated SMV groups. Similarly, significant decrease numbers of dendritic arborations; extracellular matrix density, perineuronal nets; astrocytes and microglia activations are documented in same groups. Ultrastructural studies revealed mass denudation, cilia loss, disintegration of ependymal layer and intense destructions of myelin sheaths in SMV exposed group. These are the first "neuroecotoxicological" findings in distinct neuronal cells. The implications of these findings are highly relevant for human population living in these areas, not only in Nigeria but also in similarly polluted areas elsewhere in the world.

Lead Modulates trans- and cis-Expression Quantitative Trait Loci (eQTLs) in Drosophila melanogaster Heads

Lead exposure has long been one of the most important topics in global public health because it is a potent developmental neurotoxin. Here, an eQTL analysis, which is the genome-wide association analysis of genetic variants with gene expression, was performed. In this analysis, the male heads of 79 Drosophila melanogaster inbred lines from Drosophila Synthetic Population Resource (DSPR) were treated with or without developmental exposure, from hatching to adults, to 250 μM lead acetate [Pb(C₂H₃O₂)₂]. The goal was to identify genomic intervals that influence the gene-expression response to lead. After detecting 1798 cis-eQTLs and performing an initial trans-eQTL analysis, we focused our analysis on lead-sensitive "trans-eQTL hotspots," defined as genomic regions that are associated with a cluster of genes in a lead-dependent manner. We noticed that the genes associated with one of the 14 detected trans-eQTL hotspots, Chr 2L: 6,250,000 could be roughly divided into two groups based on their differential expression profile patterns and different categories of function. This trans-eQTL hotspot validates one identified in a previous study using different recombinant inbred lines. The expression of all the associated genes in the trans-eQTL hotspot was visualized with hierarchical clustering analysis. Besides the overall expression profile patterns, the heatmap displayed the segregation of differential parental genetic contributions. This suggested that trans-regulatory regions with different genetic contributions from the parental lines have significantly different expression changes after lead exposure. We believe this study confirms our earlier study, and provides important insights to unravel the genetic variation in lead susceptibility in Drosophila model.

Perinatal exposure to lead induces morphological, ultrastructural and molecular alterations in the hippocampus

The aim of this paper is to examine if pre- and neonatal exposure to lead (Pb) may intensify or inhibit apoptosis or necroptosis in the developing rat brain. Pregnant experimental females received 0.1% lead acetate (PbAc) in drinking water from the first day of gestation until weaning of the offspring; the control group received distilled water. During the feeding of pups, mothers from the experimental group were still receiving PbAc. Pups were weaned at postnatal day 21 and the young rats of both groups then received only distilled water until postnatal day 28. This treatment protocol resulted in a concentration of Pb in rat offspring whole blood (Pb-B) below the threshold of 10 μg/dL, considered safe for humans.We studied Casp-3 activity and expression, AIF nuclear translocation, DNA fragmentation, as well as Bax, Bcl-2 mRNA and protein expression as well as BDNF concentration in selected structures of the rat brain: forebrain cortex (FC), cerebellum (C) and hippocampus (H). The microscopic examinations showed alterations in hippocampal neurons.Our data shows that pre- and neonatal exposure of rats to Pb, leading to Pb-B below 10 μg/dL, can decrease the number of hippocampus neurons, occurring concomitantly with ultrastructural alterations in this region. We observed no morphological or molecular features of severe apoptosis or necrosis (no active Casp-3 and AIF translocation to nucleus) in young brains, despite the reduced levels of BDNF. The potential protective factor against apoptosis was probably the decreased Bax/Bcl-2 ratio, which requires further investigation. Our findings contribute to further understanding of the mechanisms underlying Pb neurotoxicity and cognition impairment in a Pb-exposed developing brain.

Evaluation of pteridine metabolism in battery workers chronically exposed to lead

Occupationally-exposed lead affects the neuromuscular junction and might cause disturbances in the locomotor activity. This study was undertaken to evaluate pteridine metabolism, in which neurotransmitters are synthesized in battery workers. Urinary neopterin, biopterin and creatinine were measured using high performance liquid chromatography. Serum neopterin concentrations were detected by enzyme-linked immunoassay. Blood dihydropteridine reductase (DHPR) activities and deltaaminolevulinic acid (delta-ALA) were measured spectrophotometrically. Blood and urinary lead were detected by atomic absorption spectroscopy. Significantly increased blood and urinary lead levels, urinary neopterin, biopterin and delta-ALA were found in workers, while DHPR activities were indifferent compared to control group. Urinary creatinine decreased. This is the first study to demonstrate that increased activity of the pteridine pathway results in the accumulation of the neurotransmitters that may be responsible for the neurological disorders.

Effects on the central and peripheral nervous activity in rats elicited by acute administration of lead, mercury and manganese, and their combinations

Adult male Wistar rats were treated with inorganic lead, mercury and manganese, and their double combinations, in acute application. The aim was to study the effects on spontaneous and stimulus-evoked cortical, and evoked peripheral, nervous activity, to detect any interaction of the metals and any correlation between the changes caused in the spontaneous and stimulus-evoked electrical activity of the primary somatosensory cortical area, and the compound action potential of the tail nerve. In the frequency distribution of the spontaneous cortical activity, a shift to lower frequencies was seen. The cortical responses evoked by whisker or tail stimulation showed an increase of the peak-to-peak amplitude and peak latency on administration of the metals and metal combinations. With the metal combinations, synergism was observed. Correlations found between alterations of the spontaneous and evoked, or between cortical and peripheral, activity were evaluated in terms of mechanism. According to the results, combined exposure to the three heavy metals studied might lead to synergistic action, indicating an increased health risk in settings with exposure to several heavy metals.

Zinc and Calcium Reduce Lead Induced Perturbations in the Aminergic System of Developing Brain

Since alterations in monoamines and monoamine oxidase (MAO) have been postulated to play a role in toxic effects of lead (Pb) on the central nervous system, we have examined the protective effects of calcium (Ca2+) and zinc (Zn2+) supplementation on Pb-induced perturbations in the levels of monoamines and the activity of MAO. Swiss albino mice were lactationally exposed to low (0.2%) and high (1%) levels of Pb-acetate via drinking water of the mother. Pb-exposure commenced on postnatal day (PND) 1, continued up to PND 21 and stopped at weaning. Ca2+ or Zn2+ (0.02% in 0.2% Pb-water or 0.1% in 1% Pb-water) was supplemented separately to the mother up to PND 21. The levels of monoamines (epinephrine, norepinephrine, dopamine and serotonin) and the activity of MAO in the brain regions such as hippocampus, cortex, cerebellum and medulla of young (1 month old) and adult (3 month old) mice were determined in the synaptosomal fractions. The synaptosomal monoamines though increased with low level (0.2%) Pb-exposure, significantly decreased with high level (1%) Pb-exposure in all the brain regions in both the age groups. In general, the young mice seem to be more vulnerable to Pb-neurotoxicity. Ca2+ or Zn2+ supplementation significantly reversed the Pb-induced perturbations both in the levels of monoamines and in the activity of MAO. However, the recovery in monoamine levels and MAO activity was more pronounced with Ca2+ supplementation as compared to Zn2+. These results provide evidence that dietary Ca2+ and/or Zn2+ provide protection against Pb-induced neurotoxic effects.

Effect of acute administration of certain heavy metals and their combinations on the spontaneous and evoked cortical activity in rats

The aim of this study was to see the effect of acutely administered inorganic lead, mercury, manganese, and their combinations, on the electrical activity in the somatosensory system of rats. Male Wistar rats were anaesthetised with urethane, the head was fixed in a stereotaxic frame and the left hemisphere was exposed. Weak electric shocks to the whiskers and the tail served as stimuli. Spontaneous and stimulus-evoked activity was recorded from the primary projection area of the whiskers and the tail. After an hour of control recording, one of the following was given to the rat i.p.: 1000mg/kg Pb(2+), 7mg/kg Hg(2+), 50mg/kg Mn(2+), 500mg/kg Pb(2+)+25mg/kg Mn(2+), or 500mg/kg Pb(2+)+3.5mg/kg Hg(2+). Lead caused a massive increase in the cortical response amplitude, starting immediately after administration and developing in the next 40-50min. Latency showed a minimal increase. The spontaneous activity was moderately shifted to lower frequencies. The effect of Hg(2+) on the response amplitude and on the ECoG was similar but stronger than that of Pb(2+). The effect of Mn(2+) on the evoked activity was marked but less strong than with Pb(2+). The ECoG shift was moderate. With Hg(2+) and Mn(2+), the response amplitude showed first a decrease than an increase. The effect of the Pb(2+)+Mn(2+) combination on the activities was not additive but the correlation between the alteration of the ECoG and the evoked potential was stronger than with any of the metals alone. With Pb(2+)+Hg(2+), the effect of Pb(2+) dominated on the evoked and that of Hg(2+) on the spontaneous activity. In the peripheral nerve, action potential amplitude and conduction velocity were decreased. These alterations of the spontaneous and stimulus-evoked cortical activity probably reflected a specific action of the heavy metals on the nervous activity.

Effect of lead exposure on dopaminergic transmission in the rat brain

Lead is a neurotoxicant with known behavioral and neurochemical effects. In this study we attempted to relate the behavioral effects of lead to neurotransmission. Oral administration of 1000 ppm of lead acetate to young rats for 30 days caused a reduction in locomotor activity and stereotypic exploratory behavior during a 20 min testing period. This locomotor hypoactivity induced by lead was accompanied by a reduction in stereotypic behavior (sniffing, lickings, biting and grooming). These outcomes suggested that lead might interfere with catecholaminergic and particularly dopaminergic neurotransmission. Therefore, we examined the effect of the lead acetate on the uptake of dopamine in striatal synaptosomal preparations. The collected data showed a clear inhibition of the uptake of 3H-DA with an IC50 of 3.5 x 10(-5)M. This inhibition of the uptake of dopamine suggests that the behavioral effects of lead may be involved in dopaminergic neurotransmission.

Lead neurotoxicity in children: basic mechanisms and clinical correlates

Lead has been recognized as a poison for millennia and has been the focus of public health regulation in much of the developed world for the better part of the past century. The nature of regulation has evolved in response to increasing information provided by vigorous scientific investigation of lead's effects. In recognition of the particular sensitivity of the developing brain to lead's pernicious effects, much of this legislation has been addressed to the prevention of childhood lead poisoning. The present review discusses the current state of knowledge concerning the effects of lead on the cognitive development of children. Addressed are the reasons for the child's exquisite sensitivity, the behavioural effects of lead, how these effects are best measured, and the long-term outlook for the poisoned child. Of particular importance are the accumulating data suggesting that there are toxicological effects with behavioural concomitants at exceedingly low levels of exposure. In addition, there is also evidence that certain genetic and environmental factors can increase the detrimental effects of lead on neural development, thereby rendering certain children more vulnerable to lead neurotoxicity. The public health implications of these findings are discussed.

Lead intoxication during intrauterine life and lactation but not during adulthood reduces nucleus accumbens dopamine release as studied by brain microdialysis

Environmentally relevant levels of lead (Pb) have been demonstrated to have a neurotoxic action, especially on children. In this study, Long-Evans rats were continuously exposed to Pb acetate in drinking water from early gestational days (2-6) or from 28 days of age. At the 13th week of age, the functional activity of the nucleus accumbens (NAC) dopaminergic system was studied by means of transversal microdialysis. Neither Pb treatment regimen modified dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) extracellular concentrations, with respect to control rats. However, neuronal depolarisation, induced by perfusion with 60 mM KCl, increased extracellular DA levels to a significantly minor degree in rats exposed to Pb during the intrauterine life, with respect to both control and adult Pb treated rats. The in utero treated rats also responded with a lower DA release to amphetamine (1 mg/kg ip) administration. On the other hand, no difference in NAC DA level was found amongst treatment groups in response to different concentrations of the D(2)-D(3) dopaminergic agonist quinpirole, locally administered by means of inverse dialysis. These data indicate a preferential impairment of NAC DA synthesis and/or release in rats exposed to Pb acetate during their intrauterine life.

Chronic lead intoxication affects the myelin membrane status in the central nervous system of adult rats

The aim of the experiments presented here was to discern whether prolonged consumption of leaden water, which imitates an environmental exposure, affects the structure of myelin in the central nervous system of adult rats and whether the observed morphological destruction is reflected in biophysical and/or biochemical changes. The results indicated that during chronic lead (Pb) intoxication, the Pb level of the myelin fraction increases significantly. Electron microscopy studies show that myelin in control experiments is built up of ordered layers, whereas in a Pb-intoxicated sample, this order is destroyed in large areas of all preparations. Morphological disturbances in Pb-intoxicated in vivo myelin were reflected by changes in myelin membrane fluidity measured by spectrofluorometry and electron paramagnetic resonance (EPR). Prolonged Pb toxicity also caused significant changes in the morphological structure of oligodendrocytes, an increase of phosphatidylethanolamine, and decrease of protein SH group levels. Simultaneously, we found that the protein and total phospholipid content and levels of phosphatidylinositol, sphingomyelin, phosphatidyloserine, cholesterol, and the pattern of total myelin protein obtained by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) in Pb-intoxicated myelin did not change compared to control values. Also, Pb intoxication did not induce peroxidation by itself and did not accelerate peroxidation produced by iron (Fe) in brain myelin.

Does lead provoke the peroxidation process in rat brain synaptosomes?

Up to now there has been no information concerning the effect of lead on the peroxidation process in brain nerve endings. We have examined whether lead acetate (in chronic and acute models of toxicity in vivo and in vitro) affected the level of free radicals in synaptosomes obtained from rat brain. Simultaneously, we have checked the effect of peroxidation of Pb2+ on brain homogenates and microsomal fraction. Our results indicated that the lead level in synaptosomal fraction obtained from lead-treated rats was much higher than in controls. We did not observe induction of spontaneous and Fe(3+)-dependent peroxidation either in synaptosomes or in homogenates and brain microsomes after chronic and acute lead administration to the rats. Lead itself also did not enhance both processes when added in vitro to the control brain synaptosomes in micromolar concentrations. The lack of the lead effect on the peroxidation process in subcellular fractions of brain was rather surprising, because lead is known to be the accelerator of Fe(3+)-dependent peroxidation processes in liver. Additionally, livers from rats under the same toxicity conditions were examined. We have found that lead did not provoke spontaneous peroxidation in liver, but contrary to brain fractions, it drastically increased iron-dependent peroxidation in liver homogenates and microsomes. The lack of the effect of lead on inducing peroxidation processes in brain is probably the consequence of the brain having stronger protective mechanisms against its toxicity than the liver.