Neonatal lead exposure impairs development of rodent barrel field cortex

Unveiling the Health Ramifications of Lead Poisoning: A Narrative Review

The presence of lead (Pb) in children's toys and paint is a significant global public health concern. Numerous studies conducted worldwide have measured lead concentrations in these products. This article aims to examine the research findings and shed light on the implications for human health, including legal consequences and public awareness. Despite regulations on lead levels in polyvinyl chloride (PVC) paints and children's toys in many countries, several reviewed documents indicate that these products often contain substantial amounts of lead, frequently surpassing legal limits. Particularly high levels of lead in paints have been found in countries such as China, Thailand, and Brazil. It is crucial to raise awareness among parents by educating them about this issue and empowering them to take proactive measures to protect their children from lead poisoning associated with toys and colored paints. There is also global support for eliminating lead pigments and regulating the amount of lead in PVC toys.

Manganese-doped hydroxyapatite as an effective adsorbent for the removal of Pb(II) and Cd(II)

The water polluted by lead(Pb(II)) and cadmium(Cd(II)) seriously endangers ecological safety and needs to be solved urgently. Because of the relatively low adsorption rate of pure hydroxyapatite for heavy metals, a series of manganese-doped hydroxyapatites (MnHAPs) were prepared by using manganese, a common impurity in hydroxyapatite, as a doping element to improve the adsorption performance. The structural and functional groups of the materials with different Mn/(Ca +Mn) molar ratios (0%, 5%, 10%, 20%, and 30%) were investigated by scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), X-Ray diffraction (XRD), Raman spectrometer and Fourier transform infrared spectroscopy (FTIR) characterization. The presence of manganese influenced the formation and growth of hydroxyapatite crystals, resulting in lattice distortion and a large number of lattice defects in materials. Among them, manganese-doped hydroxyapatite with a Mn/(Ca +Mn) molar ratio of 10% (MnHAP-10) could most effectively remove Pb(II) and Cd(II), with the adsorption capacity of 1806.09 mg g^-1 for Pb(II) at pH = 5 and 176.88 mg g^-1 for Cd(II) at pH = 5.5. Then the adsorption behavior and mechanism were further researched systemically. It was concluded that the immobilization of Pb(II) by MnHAP-10 was mainly through dissolution precipitation and ion exchange, while Cd(II) was adsorbed by ion exchange and electrostatic interaction. In conclusion, MnHAP-10 has the potential to be applied as an effective adsorbent for the removal of Pb(II) and Cd(II) pollution.

Preventive Effect of Limosilactobacillus fermentum SCHY34 on Lead Acetate-Induced Neurological Damage in SD Rats

Lead poisoning caused by lead pollution seriously affects people's health. Lactic acid bacteria has been shown to be useful for biological scavenging of lead. In this experiment, Sprague-Dawley (SD) rats were treated with 200 mg/L of lead acetate solution daily to induce chronic lead poisoning, and oral Limosilactobacillus fermentum (L. fermentum) SCHY34 to study its mitigation effects and mechanisms on rat neurotoxicity. The L. fermentum SCHY34 showed competent results on in vitro survival rate and the lead ion adsorption rate. Animal experiments showed that L. fermentum SCHY34 maintained the morphology of rat liver, kidney, and hippocampi, reduced the accumulation of lead in the blood, liver, kidney, and brain tissue. Further, L. fermentum SCHY34 alleviated the lead-induced decline in spatial memory and response capacity of SD rats, and also regulated the secretion of neurotransmitters and related enzyme activities in the brain tissue of rats, such as glutamate (Glu), monoamine oxidase (MAO), acetylcholinesterase (AchE), cyclic adenosine monophosphate (cAMP), and adenylate cyclase (AC). In addition, the expression of genes related to cognitive capacity, antioxidation, and anti-apoptotic in rat brain tissues were increased L. fermentum SCHY34 treatment, such as brain-derived neurotrophic factor (BDNF), c-fos, c-jun, superoxide dismutase (SOD)1/2, Nuclear factor erythroid 2-related factor 2 (Nrf2), and B-cell lymphoma 2 (Bcl-2), and so on. L. fermentum SCHY34 showed a great biological scavenging and potential effect on alleviating the toxicity of lead ions.

Lead-Induced Motor Dysfunction Is Associated with Oxidative Stress, Proteome Modulation, and Neurodegeneration in Motor Cortex of Rats

Lead (Pb) is a toxic metal with great neurotoxic potential. The aim of this study was to investigate the effects of a long-term Pb intoxication on the global proteomic profile, oxidative biochemistry and neuronal density in motor cortex of adult rats, and the possible outcomes related to motor functions. For this, Wistar rats received for 55 days a dose of 50 mg/Kg of Pb acetate by intragastric gavage. Then, the motor abilities were evaluated by open field and inclined plane tests. To investigate the possible oxidative biochemistry modulation, the levels of pro-oxidant parameters as lipid peroxidation and nitrites were evaluated. The global proteomic profile was evaluated by ultraefficiency liquid chromatography system coupled with mass spectrometry (UPLC/MS) followed by bioinformatic analysis. Moreover, it was evaluated the mature neuron density by anti-NeuN immunostaining. The statistical analysis was performed through Student's t-test, considering p < 0.05. We observed oxidative stress triggering by the increase in malonaldehyde and nitrite levels in motor cortex. In the proteomic analysis, the motor cortex presented alterations in proteins associated with neural functioning, morphological organization, and neurodegenerative features. In addition, it was observed a decrease in the number of mature neurons. These findings, associated with previous evidences observed in spinal cord, cerebellum, and hippocampus under the same Pb administration protocol, corroborate with the motor deficits in the rats towards Pb. Thus, we conclude that the long-term administration to Pb in young Wistar rats triggers impairments at several organizational levels, such as biochemical and morphological, which resulted in poor motor performance.

The Role of Nrf2 on the Cognitive Dysfunction of High-fat Diet Mice Following Lead Exposure

Lead (Pb) exposure can induce the severe deleterious damage on the central nervous system (CNS). High-fat diet also has been suggested that it had some adverse effects on learning and memory, cognitive function, but there is lack of study on Pb and high-fat diet co-exposure on the CNS damage. In this study, the goal was to explore the effect of Pb on the cognitive function of mice with high-fat diet and to investigate whether Nrf2 signaling pathway acts in the cerebral cortex. C57BL/6J mice were randomly divided into control, high-fat diet, Pb (drinking water with 250 mg/L lead acetate), and high-fat diet with Pb (drinking water with 250 mg/L lead acetate) co-exposure groups for 12 weeks. Experiment data showed that learn memory and exploration ability of mice obviously decreased in Pb and high-fat diet, and reactive oxygen species (ROS) increased; then, the protein expressions of Nrf2, heme oxygenase-1, NADP(H):dehydrogenase quinone 1, and superoxide dismutase 2 were lower significantly compared with those in the control group. This study suggested that down-expressed Nrf2 signaling pathway possibly related to the cognitive dysfunction induced by Pb and high-fat diet co-exposure.

Locus coeruleus spiking differently correlates with S1 cortex activity and pupil diameter in a tactile detection task

We examined the relationships between activity in the locus coeruleus (LC), activity in the primary somatosensory cortex (S1), and pupil diameter in mice performing a tactile detection task. While LC spiking consistently preceded S1 membrane potential depolarization and pupil dilation, the correlation between S1 and pupil was more heterogeneous. Furthermore, the relationships between LC, S1, and pupil varied on timescales of sub-seconds to seconds within trials. Our data suggest that pupil diameter can be dissociated from LC spiking and cannot be used as a stationary index of LC activity.

Auditory Training Reverses Lead (Pb)-Toxicity-Induced Changes in Sound-Azimuth Selectivity of Cortical Neurons

Lead (Pb) causes significant adverse effects on the developing brain, resulting in cognitive and learning disabilities in children. The process by which lead produces these negative changes is largely unknown. The fact that children with these syndromes also show deficits in central auditory processing, however, indicates a speculative but disturbing relationship between lead-exposure, impaired auditory processing, and behavioral dysfunction. Here we studied in rats the changes in cortical spatial tuning impacted by early lead-exposure and their potential restoration to normal by auditory training. We found animals that were exposed to lead early in life displayed significant behavioral impairments compared with naïve controls while conducting the sound-azimuth discrimination task. Lead-exposure also degraded the sound-azimuth selectivity of neurons in the primary auditory cortex. Subsequent sound-azimuth discrimination training, however, restored to nearly normal the lead-degraded cortical azimuth selectivity. This reversal of cortical spatial fidelity was paralleled by changes in cortical expression of certain excitatory and inhibitory neurotransmitter receptor subunits. These results in a rodent model demonstrate the persisting neurotoxic effects of early lead-exposure on behavioral and cortical neuronal processing of spatial information of sound. They also indicate that attention-demanding auditory training may remediate lead-induced cortical neurological deficits even after these deficits have occurred.

Arsenic aggravated reproductive toxicity in male rats exposed to lead during the perinatal period

The aim of this study was to assess the reproductive toxic effects of arsenic on adult Wistar rats exposed to lead during the perinatal period. The pregnant rats were allowed ad libitum access to tap water containing 819 mg of lead (Pb) per L or without Pb from conception until weaning. Litter size, survival rate and developmental milestones of the pups delivered by Pb exposed dams were comparable to those of the control rats. Conversely, the pups exposed to Pb during the perinatal period exhibited significant delay in cliff avoidance, negative geotaxis, surface righting reflex, ascending wire mesh and testis descent. The control and perinatal Pb-exposed male rats were maintained on tap water containing 2.3 mg of arsenite (As) per L or without arsenite from the pubertal period (post-natal day 55) to adulthood (post-natal day 115) and assessed for reproductive end points. The results revealed that the (1) relative weights of the testis, epididymis, seminiferous tubules and ventral prostate; (2) daily sperm production; (3) epididymal sperm density and (4) numbers of motile, viable, and HOS tail swelled sperm declined significantly in the rats exposed to either Pb or As. The activity levels of testicular 3β- and 17β-hydroxysteroid dehydrogenases were also significantly decreased in the experimental rats. Significant elevation in the levels of reactive oxygen species and lipid peroxidation in association with reduced activities of antioxidant enzymes in the testis and different epididymal regions was recorded in the experimental rats. In the fertility study, although each male in the control and experimental groups produced a copulatory plug and impregnated a female, the mean conception time significantly increased in the experimental groups. The mean number of implantations decreased significantly in the females mated with the experimental males. Moreover, the results of the present study also indicate that reproductive alterations were more deteriorated in the Pb-exposed rats treated with arsenic when compared to individual exposures. In conclusion, the data clearly suggest that reproductive toxicity in male rats exposed to Pb during the perinatal period is exacerbated by As treatment during the pubertal period.

Dysfunction of cortical synapse-specific mitochondria in developing rats exposed to lead and its amelioration by ascorbate supplementation

BACKGROUND

Lead (Pb) is a widespread environmental neurotoxin and its exposure even in minute quantities can lead to compromised neuronal functions. A developing brain is particularly vulnerable to Pb mediated toxicity and early-life exposure leads to permanent alterations in brain development and neuronal signaling and plasticity, culminating into cognitive and behavioral dysfunctions and elevated risk of neuropsychiatric disorders later in life. Nevertheless, the underlying biochemical mechanisms have not been completely discerned.

METHODS

Because of their ability to fulfill high energy needs and to act as calcium buffers in events of high intensity neuronal activity as well as their adaptive regulatory capability to match the requirements of the dynamicity of synaptic signaling, synapse-specific or synaptic mitochondria (SM) are critical for synaptic development, function and plasticity. Our aim for the present study hence was to characterize the effects of early-life Pb exposure on the functions of SM of prepubertal rats. For this purpose, employing a chronic model of Pb neurotoxicity, we exposed rat pups perinatally and postnatally to Pb and used a plethora of colorimetric and fluorometric assays for assessing redox and bioenergetic properties of SM. In addition, taking advantage of its ability as an antioxidant and as a metal chelator, we employed ascorbic acid (vitamin C) supplementation as an ameliorative therapeutic strategy against Pb-induced neurotoxicity and dysfunction of SM.

RESULTS

Our results suggest that early-life exposure to Pb leads to elevated oxidative stress in cortical SM with consequent compromises in its energy metabolism activity. Ascorbate supplementation resulted in significant recovery of Pb-induced oxidative stress and functional compromise of SM.

CONCLUSION

Alterations in redox status and bioenergetic properties of SM could potentially contribute to the synaptic dysfunction observed in events of Pb neurotoxicity. Additionally, our study provides evidence for suitability of ascorbate as a significant ameliorative agent in tacking Pb neurotoxicity.

Conflicts of Interest in Biomedical Research Harm Children With and Without Disabilities

Children have been exposed to unjustifiable risks that in some cases amount to research abuse. Powerful, financially interconnected stakeholders control all facets of research, including the approval process. Physician investigators, their academic institutions, and institutional review boards (IRBs) all come under the influence of funding sponsors, whose interests conflict with the best interest of children. Children cannot rely on IRBs or on any of the existing research oversight agencies to protect them, for research too often takes inordinate risks in the name of the greater good.

The association between blood lead level and clinical mental disorders in fifty thousand lead-exposed male workers

BACKGROUND

While there has been research into the relationship between blood lead (BPb) level and mental disorders, there have been few investigations that use clinically diagnosed mental disorders in the adult population with a retrospective cohort study design. Hence, our study investigated the association between BPb level and risk of clinically diagnosed mental disorders.

METHODS

The data of male workers exposed to lead (Pb; n=54,788) were collected from annual Pb associated medical check-ups from 2000 to 2004 in Korea. The workers' hospital admission histories due to mental disorders (International Classification of Diseases, 10th revision, F00-F99) were used to identify clinically diagnosed mental disorders. After merging the data, the hazard ratio (HR) with a 95% confidence interval (95% CI) was calculated by survival analysis using the Cox proportional hazards model according to the quartile level of BPb (1st quartile<4.10 μg/dl, 2nd quartile<6.04 μg/dl, 3rd quartile<10.00 μg/dl, and 4th quartile≥10 μg/dl).

RESULTS

In a total of 54,788 workers, there were 223 admission cases of mental disorders (F00-F99) during the follow-up period. The HR (95% CI) of total mental and behavioral disorders (F00-F99) was 1.63 (1.12-2.39) in the 4th quartile group compared to the HR of the 1st quartile group after adjusting for age. The HR (95% CI) of the 4th quartile group was 2.59 (1.15-5.82) for mood (affective) disorders (F30-F39).

LIMITATION

The hospital admission data, not outpatient data, were used for current study while almost affective disorder treated at outpatient clinic level.

CONCLUSION

Our study highlighted that Pb exposure can cause clinical mental disorders that require hospital admission in adult male workers. Our relatively large sample size strengthens the evidence of the association between BPb level and risk of clinically diagnosed mental disorders.

The role of Nrf2 in protection against Pb-induced oxidative stress and apoptosis in SH-SY5Y cells

Lead exerts severe adverse effects on the nervous system in which oxidative stress might mediate impairments. In this study, we focused on Nrf2, which has been identified to significantly influence the protection of a cellular system against many xenobiotic compounds. We found that PbAc exhibited neurotoxicity mainly through oxidant-based processes and could be inhibited by NAC and DPI in SH-SY5Y cells. As a defense response, Nrf2 was activated when exposed to PbAc, thereby inducing a rapid increase in Nrf2 nuclear accumulation, as well as Nrf2-ARE binding activities in a ROS-dependent manner. Analysis of Nrf2-regulated gene expression and protein showed that PbAc could induce the mRNA transcription of HO-1, GSTα1, GCLM, GCLC, and NQO1, as well as the protein expression of HO-1 and γ-GCS. The responses of these genes to PbAc were regulated by Nrf2. Silencing Nrf2 expression in SH-SY5Y cells inhibited PbAc-induced gene transcription and protein expression. Overexpression of Nrf2 led to decreased ROS production and cell apoptosis, as well as increased cell viability under PbAc exposure. These results indicated that the Nrf2-ARE system exhibited a protective role in Pb-induced neurotoxicity, providing potential therapeutic strategies for the prevention and treatment of Pb-related diseases.

Perceptual Training Restores Impaired Cortical Temporal Processing Due to Lead Exposure

Low-level lead exposure is a risk factor for cognitive and learning disabilities in children and has been specifically associated with deficits in auditory temporal processing that impair aural language and reading abilities. Here, we show that rats exposed to low levels of lead in early life display a significant behavioral impairment in an auditory temporal rate discrimination task. Lead exposure also results in a degradation of the neuronal repetition-rate following capacity and response synchronization in primary auditory cortex. A modified go/no-go repetition-rate discrimination task applied in adult animals for ∼50 days nearly restores to normal these lead-induced deficits in cortical temporal fidelity. Cortical expressions of parvalbumin, brain-derived neurotrophic factor, and NMDA receptor subunits NR2a and NR2b, which are down-regulated in lead-exposed animals, are also partially reversed with training. These studies in an animal model identify the primary auditory cortex as a novel target for low-level lead exposure and demonstrate that perceptual training can ameliorate lead-induced deficits in cortical discrimination between sound sequences.

Role of the mitochondrial Ca²⁺ uniporter in Pb²⁺-induced oxidative stress in human neuroblastoma cells

Lead (Pb(2+)) has been shown to induce cellular oxidative stress, which is linked to changes in intracellular calcium (Ca(2+)) concentration. The mitochondrial Ca(2+) uniporter (MCU) participates in the maintenance of Ca(2+) homeostasis in neurons, but its role in Pb(2+)-induced oxidative stress is unclear. To address this question, oxidative stress was induced in human neuroblastoma SH-SY5Y cells and in newborn rats by Pb(2+) treatment. The results showed that the production of reactive oxygen species is increased in cells upon treatment with Pb(2+) in a dose-dependent manner, while glutathione and MCU expression were reduced. Moreover, neuronal nitric oxide synthase protein expression was elevated in rats exposed to Pb(2+) during gestation, while MCU expression was decreased. Application of the MCU activator spermine or MCU overexpression reversed Pb(2+)-induced oxidative stress and inhibition of mitochondrial Ca(2+) uptake, while the MCU inhibitor Ru360 and MCU knockdown potentiated the effects of Pb(2+). These results indicate that the MCU mediates the Pb(2+)-induced oxidative stress response in neurons through the regulation of mitochondrial Ca(2+) influx.

Taurine mitigates cognitive impairment induced by chronic co-exposure of male Wistar rats to chlorpyrifos and lead acetate

Organophosphate pesticides and heavy metals are ubiquitous environmental pollutants and neurotoxicants. We investigated the effects of taurine (an antioxidant; TA) on oxidative stress and cognition in male Wistar rats co-treated with chlorpyrifos (an organophosphate pesticide; CPF) and lead acetate (heavy metal; LA). The Wistar rats were divided into 5 groups of 10 rats each. The first two groups were administered with distilled water and soya oil respectively. The remaining three groups were administered with taurine (TA), 50 mg/kg body weight, CPF+LA group [CPF (4.25 mg/kg, 1/20 LD₅₀] and LA (233.25 mg/kg, 1/20 LD₅₀) and TA+CPF+LA group [TA (50 mg/kg), CPF (4.25 mg/kg) and LA (233.25 mg/kg)]. The xenobiotics were administered once daily by oral gavage for 16 weeks. The results showed reductions in the activities of brain antioxidant enzymes and acetylcholinesterase, increased lipoperoxidation and histopathological alterations of the cerebral cortex in the CPF+LA group. However, TA mitigated perturbations in the activities of the antioxidant enzymes and acetylcholinesterase, counteracted oxidative stress and brain lipoperoxidation and attenuated neuronal degeneration induced by joint CPF and LA-induced neurotoxicity. The results suggested that TA is neuroprotective following chronic co-exposure of rats to CPF and LA.

Effects of chronic and acute lead treatments on the biophysical properties of erythrocyte membranes, and a comparison with model membranes

Rat erythrocytes, or erythrocyte membrane ghosts, have been subjected to either chronic (drinking water containing 15 mM lead acetate for 3 months) or acute (10⁻⁹–10⁻²M lead acetate for 1 h) Pb²⁺ treatments and subsequent changes in membrane properties have been measured. Pb²⁺ concentration in chronically treated rat plasma was 1.8 μM, which is one order of magnitude above normal values. Membrane permeability, or hemolysis, was increased in both cases. A comparative study using liposomes, in the form of large unilamellar vesicles, also indicated an increase in membrane permeability. Membrane microviscosity, or acyl chain molecular order, measured as DPH fluorescence polarization, showed an increased order in the acute treatments, at least below 700 μM Pb²⁺, and a similar increase in chronically treated rats. The correlation between acute and chronic treatments, and between cell and model membranes, suggests that the present observations may be relevant in the pathogenesis of lead intoxication in humans.

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The biophysical effects of lead on model and biomembranes have been examined.

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There is a positive correlation between acute and chronic treatments.

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Acute responses require lead doses 2–3 orders of magnitude higher than in chronic treatments.

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Lead increases membrane permeability, or hemolysis.

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Lead increases membrane microviscosity, or acyl chain molecular order.

Effects of chronic lead intoxication on rat serotoninergic system and anxiety behavior

Chronic lead exposure has been shown to produce behavioral disturbances in human and animal models. These disturbances are associated with alterations in monoaminergic neurotransmission in the central nervous system (CNS), some of which have been attributed to serotonin (5-HT). This study was undertaken to investigate the chronic effects of lead exposure on the serotoninergic system in the dorsal raphe nucleus (DRN) and the consequences of its toxicity on rat behavior. Adult male Wistar rats were chronically exposed for 3 months to 0.5% lead acetate in drinking water. The serotoninergic system was evaluated using immunohistochemistry and the anxiety behavior was assessed by the light/dark box test. The results show that chronic lead exposure induces a significant increase of blood and brain lead levels in treated rats compared with controls. The density of the immunoreactive serotoninergic cell bodies was significantly higher in treated rats in all parts of the DRN. Assessment of animal behavior using the light/dark box test showed that lead-treated rats spent significantly more time in the light chamber compared with controls (P=0.001). These findings suggest that lead exposure may possibly induce increased anxiety as a consequence of changes in neuronal 5-HT content in the DRN.

Exploring potential sources of differential vulnerability and susceptibility in risk from environmental hazards to expand the scope of risk assessment

Genetic factors, other exposures, individual disease states and allostatic load, psychosocial stress, and socioeconomic position all have the potential to modify the response to environmental exposures. Moreover, many of these modifiers covary with the exposure, leading to much higher risks in some subgroups. These are not theoretical concerns; rather, all these patterns have already been demonstrated in studies of the effects of lead and air pollution. However, recent regulatory impact assessments for these exposures have generally not incorporated these findings. Therefore, differential risk and vulnerability is a critically important but neglected area within risk assessment, and should be incorporated in the future.

Chronic lead intoxication affects glial and neural systems and induces hypoactivity in adult rat

Lead is an environmental toxin and its effects are principally manifested in the brain. Glial and neuronal changes have been described during development following chronic or acute lead intoxication, however, little is known about the effects of chronic lead intoxication in adults. In this study we evaluated immunohistochemically the glial and dopaminergic systems in adult male Wistar rats. 0.5% (v/v) lead acetate in drinking water was administrated chronically over a 3-month period. Hypertrophic immunoreactive astrocytes were observed in the frontal cortex and other brain structures of the treated animals. Analysis of the astroglial features showed increased number of astrocyte cell bodies and processes in treated rats, an increase confirmed by Western blot. Particular distribution of glial fibrillary acidic protein immunoreactivity was observed within the blood vessel walls in which dense immunoreactive glial processes emanate from astrocytes. Glial changes in the frontal cortex were concomitant with reduced tyrosine hydroxylase immunoreactive neuronal processes, which seem to occur as a consequence of significantly reduced dopaminergic neurons within the nucleus of origin in the substantia nigra. These glial and neuronal changes following lead intoxication may affect animal behavior as evidenced by reduced locomotor activity in an open field test. These findings demonstrate that chronic lead exposure induces astroglial changes, which may compromise neuronal function and consequently animal behavior.

Decreased expression of the voltage-dependent anion channel in differentiated PC-12 and SH-SY5Y cells following low-level Pb exposure

Lead (Pb) has been shown to disrupt cellular energy metabolism, which may underlie the learning deficits and cognitive dysfunctions associated with environmental Pb exposure. The voltage-dependent anion channel (VDAC) plays a central role in regulating energy metabolism in neurons by maintaining cellular ATP levels and regulating calcium buffering, and studies have shown that VDAC expression is associated with learning in mice. In this study, we examined the effect of 5 and 10microM Pb on VDAC expression in vitro in order to determine whether Pb alters VDAC expression levels in neuronal cell lines. PC-12 and SH-SY5Y cells were used since they differentiate to resemble primary neuronal cells. VDAC expression levels were significantly decreased 48 h after exposure to Pb in both cell lines. In contrast, exposure to 24 h of hypoxia failed to produce a decrease in VDAC, suggesting that decreased VDAC expression is not a general cellular stress response but is a result of Pb exposure. This decreased VDAC expression was also correlated with a corresponding decrease in cellular ATP levels. Real-time reverse transcription-polymerase chain reaction demonstrated a significant decrease in messenger RNA levels for the VDAC1 isoform, indicating that Pb reduces transcription of VDAC1. These results demonstrate that exposure to 5 and 10microM Pb reduces VDAC transcription and expression and is associated with reduced cellular ATP levels.

Chronic low-level lead exposure affects the monoaminergic system in the mouse superior olivary complex

Low-level lead (Pb) exposure is associated with behavioral and cognitive dysfunction, but it is not clear how Pb produces these behavioral changes. Pb has been shown to alter auditory temporal processing in both humans and animals. Auditory temporal processing occurs in the superior olivary complex (SOC) in the brainstem, where it is an important component in sound detection in noisy environments and in selective auditory attention. The SOC receives a serotonergic innervation from the dorsal raphe, and serotonin has been implicated in auditory temporal processing within the brainstem and inferior colliculus. Because Pb exposure modulates auditory temporal processing, the serotonergic system is a potential target for Pb. The current study was undertaken to determine whether developmental Pb exposure preferentially changes the serotonergic system within the SOC. Pb-treated mice were exposed to no Pb, very low Pb (0.01 mM), or low Pb (0.1 mM) throughout gestation and through 21 days postnatally. Brainstem sections from control and Pb-exposed mice were immunostained for the vesicular monoamine transporter 2 (VMAT2), serotonin (5-HT), and dopamine-beta-hydroxylase (DbetaH; a marker for norepinephrine) in order to elucidate the effect of Pb on monoaminergic input into the SOC. Sections were also immunolabeled with antibodies to vesicular glutamate transporter 1 (VGLUT1), vesicular gamma-aminobutyric acid (GABA) transporter (VGAT), and vesicular acetylcholine transporter (VAChT) to determine whether Pb exposure alters the glutaminergic, GABAergic, or cholinergic systems. Pb exposure caused a significant decrease in VMAT2, 5-HT, and DbetaH expression, whereas VGLUT1, VGAT, and VAChT showed no change. These results provide evidence that Pb exposure during development alters normal monoaminergic expression in the auditory brainstem.

Prenatal exposure to benzo(a)pyrene impairs later-life cortical neuronal function

Prenatal exposure to environmental contaminants, such as benzo(a)pyrene [B(a)P] has been shown to impair brain development. The overarching hypothesis of our work is that glutamate receptor subunit expression is crucial for cortical evoked responses and that prenatal B(a)P exposure modulates the temporal developmental expression of glutamatergic receptor subunits in the somatosensory cortex. To characterize prenatal B(a)P exposure on the development of cortical function, pregnant Long Evans rats were exposed to low-level B(a)P (300 microg/kg BW) by oral gavage on gestational days 14-17. At this exposure dose, there was no significant effect of B(a)P on (1) the number of pups born per litter, (2) the pre-weaning growth curves and (3) initial and final brain to body weight ratios. Control and B(a)P-exposed offspring were profiled for B(a)P metabolites in plasma and whole brain during the pre-weaning period. No detectable levels of metabolites were found in the control offspring. However, a time-dependent decrease in total metabolite concentration was observed in B(a)P-exposed offspring. On PND100-120, cerebrocortical mRNA expression was determined for the glutamatergic NMDA receptor subunit (NR2B) in control and B(a)P-exposed offspring. Neural activity was also recorded from neurons in primary somatic sensory (barrel) cortex. Semiquantitative PCR from B(a)P-exposed offspring revealed a significant 50% reduction in NR2B mRNA expression in B(a)P-exposed offspring relative to controls. Recordings from B(a)P-exposed offspring revealed that N-methyl-d-aspartate (NMDA) receptor-dependent neuronal activity in barrel cortex evoked by whisker stimulation was also significantly reduced (70%) as compared to controls. Analysis showed that the greatest deficit in cortical neuronal responses occurred in the shorter latency epochs from 5 to 20 ms post-stimulus. The results suggest that in utero exposure to benzo(a)pyrene results in diminished mRNA expression of the NMDA NR2B receptor subunit to result in late life deficits in cortical neuronal activity in the offspring. The findings from this study lead to a strong prediction that in utero exposure to benzo(a)pyrene at a time when synapses are first formed and adjusted in strength by activity in the sensory pathways will produce a strong negative effect on brain function in offspring progeny.

GAP-43 is critical for normal targeting of thalamocortical and corticothalamic, but not trigeminothalamic axons in the whisker barrel system

Mice lacking the growth-associated protein GAP-43 (KO) show disrupted cortical topography and no barrels. Whisker-related patterns of cells are normal in the KO brainstem trigeminal complex (BSTC), while the pattern in KO ventrobasal thalamus (VB) is somewhat compromised. To better understand the basis for VB and cortical abnormalities, we used small placements of DiI to trace axonal projections between BSTC, VB, and barrel cortex in wildtype (WT) and GAP-43 KO mice. The trigeminothalamic (TT) pathway consists of axons from cells in the Nucleus Prinicipalis that project to the contralateral VB thalamus. DiI-labeled KO TT axons crossed the midline from BSTC and projected to contralateral VB normally, consistent with normal BSTC cytoarchitecture. By contrast, the KO thalamocortical axons (TCA) projection was highly abnormal. KO TCAs showed delays of 1-2 days in initial ingrowth to cortex. Postnatally, KO TCAs showed multiple pathfinding errors near intermediate targets, and were abnormally fasciculated within the internal capsule (IC). Interestingly, most individually labeled KO TCAs terminated in deep layers instead of in layer IV as in WT. This misprojection is consistent with birthdating analysis in KO mice, which revealed that neurons normally destined for layer IV remain in deep cortical layers. Early outgrowth of KO corticofugal (CF) axons was similar for both genotypes. However, at P7 KO CF fibers remained bundled as they entered the IC, and exhibited few terminal branches in VB. Thus, the establishment of axonal projections between thalamus and cortex are disrupted in GAP-43 KO mice.

Very low lead exposures and children's neurodevelopment

PURPOSE OF REVIEW

We remain far from achieving the goal of eliminating lead-associated neurodevelopmental morbidities in children. New evidence regarding the blood lead levels at which morbidities occur have led to calls for the Centers for Disease Control and Prevention to reduce the current screening guideline of 10 microg/dl. The review evaluates the basis for these calls.

RECENT FINDINGS

Adverse outcomes, such as reduced intelligence quotient and academic deficits, occur at levels below 10 microg/dl. Some studies suggest that the rate of decline in performance is greater at levels below 10 microg/dl than above 10 microg/dl, although a plausible mechanism has not been identified. Increased exposure is also associated with neuropsychiatric disorders such as attention deficit hyperactivity disorder and antisocial behavior. Functional imaging studies are beginning to provide insight into the neural substrate of lead's neurodevelopmental effects. Current protocols for chelation therapy appear ineffective in preventing such effects, although environmental enrichment might do so.

SUMMARY

No level of lead exposure appears to be 'safe' and even the current 'low' levels of exposure in children are associated with neurodevelopmental deficits. Primary prevention of exposure provides the best hope of mitigating the impact of this preventable disease.

Late neurodevelopmental effects of early exposures to chemical contaminants: reducing uncertainty in epidemiological studies

Early exposures to environmental chemicals are reliably associated with late neurotoxicities in children. However, substantial scatter of observations exists around the estimated dose-effect relationships. This variability has many potential sources, one of which is interindividual differences in susceptibility. Such differences imply that the long-term impacts of exposure will not the same for all individuals, but will vary depending on a variety of factors that might either aggravate or mitigate contaminant effects. These include co-exposures, genetic polymorphisms and characteristics of the social environment. The context dependence of contaminant effects has implications both for study designs and analytical approaches. In addition, a systems approach to understanding the associations among contaminant exposures, covariates and health outcomes is necessary.

Lead neurotoxicity in children: decomposing the variability in dose-effect relationships

BACKGROUND

Enormous progress has been made in recent decades in our understanding of lead neurotoxicology in children, but an important obstacle to additional progress is the striking variability that is evident in any plot of a lead biomarker versus a health endpoint.

METHODS

In this article, three potential sources of variability are identified: (1) errors or imprecision in characterizing dose (and/or outcome); (2) incomplete characterization of endpoint variance attributable to factors other than lead; and (3) inter-individual differences in susceptibility to lead neurotoxicity.

RESULTS

Strategies are suggested for reducing the variability contributed by these sources, including the development of validated PBPK models and biomarkers of early biological effects; the development of more comprehensive models of outcome variance and, specifically, the application of multi-level models that incorporate supra-individual and supra-family risk factors; and the use of study designs that permit assessments of the effect modifying influence of contextual factors on the form and severity of neurotoxicity.

CONCLUSION

Decomposing the variability in the distribution of observed scores around the best-fit lines that describe the dose-effect relationships for lead neurotoxicity in children is a major research need.

Developmental potential in the first 5 years for children in developing countries

Many children younger than 5 years in developing countries are exposed to multiple risks, including poverty, malnutrition, poor health, and unstimulating home environments, which detrimentally affect their cognitive, motor, and social-emotional development. There are few national statistics on the development of young children in developing countries. We therefore identified two factors with available worldwide data--the prevalence of early childhood stunting and the number of people living in absolute poverty--to use as indicators of poor development. We show that both indicators are closely associated with poor cognitive and educational performance in children and use them to estimate that over 200 million children under 5 years are not fulfilling their developmental potential. Most of these children live in south Asia and sub-Saharan Africa. These disadvantaged children are likely to do poorly in school and subsequently have low incomes, high fertility, and provide poor care for their children, thus contributing to the intergenerational transmission of poverty.

Biological markers of fetal lead exposure at each stage of pregnancy

It has been suggested that plasma lead (Pb) represents the fraction of circulating Pb that crosses the placenta. Whole-blood Pb levels, the conventional method for measuring circulating Pb, may not adequately reflect plasma Pb levels. The objective of this study was to assess the relationship between whole-blood and plasma Pb in a cohort of pregnant women. A group of 237 pregnant women, recruited in Mexico City from 1997 to 1999, was studied. whole-blood and plasma lead concentrations were evaluated at 12, 24, and 34 wk of gestation by inductively coupled plasma-mass spectrometry. Data were analyzed using a mixed-effects regression model. An exponential relationship was found between plasma and whole-blood Pb levels and significant modification of the association by stage of pregnancy. The association was stronger in the second trimester relative to the first, and it further increased in the third trimester. The model predicts increased plasma Pb levels for a given whole-blood Pb value as pregnancy advances for whole-blood Pb levels greater than approximately 110 microg/L, but not for blood Pb levels less than 100 microg/L. These findings could be due to physiologic changes during pregnancy, such as decreasing hematocrit, saturation of red cell Pb binding capacity, and increased bone resorption or intestinal absorption. Collectively, these data suggest that at elevated maternal blood Pb levels the developing fetus may be at greater risk of Pb exposure from increased maternal plasma Pb than otherwise predicted from whole-blood Pb levels.

Gestational 2,3,7,8-tetrachlorodibenzo-p-dioxin exposure effects on sensory cortex function

Gestational exposure to environmental contaminants such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) poses a significant threat to normal growth and differentiation of the developing brain. To characterize the impact of gestational TCDD exposure on subsequent cortical function, pregnant Long Evans rats were exposed to a single acute dose (100 or 700ng/kg b.w. via gavage) on gestational day 15. This dosing regimen had no significant effect on birth index. After the TCDD-exposed animals were born and reached maturity, neural activity was recorded under urethane anesthesia from neurons in primary somatic sensory cortex. Spontaneous activity was reduced by approximately 50% in barrel cortex compared to corn oil vehicle controls. The magnitude of neuronal response to sensory (whisker) stimuli also was significantly reduced, and responses did not achieve control levels at any stimulus intensity. The greatest deficit was in the short latency component of the cortical responses. These decrements in cortical responsiveness were present in young F1 generation TCDD-exposed animals and persisted for up to 180 days. Because glutamate receptors are crucial to the evoked responses and show developmental regulation, selected iontotropic glutamate receptor subunits (NMDA NR2A+NR2B and GluR1) were profiled for RNA levels in the cortex of F1 generation rats. The expression of NR2B (NMDA receptor) and GluR1 (AMPA receptor) subunits was significantly reduced in the TCDD-exposed F1 generation animals compared to vehicle controls. The results indicate that gestational TCDD exposure results in cortical deficits that are paralled by diminished expression of certain NMDA and AMPA receptor subunits at a time when synapses are being formed for the first time in cortex.

Modulation of ERK1/2 and p38(MAPK) by lead in the cerebellum of Brazilian catfish Rhamdia quelen

Lead (Pb2+) is a neurotoxic trace metal, widespread in aquatic environment that can change physiologic, biochemical and behavioral parameters in diverse fish species. Chemical exposure may drive modulation of mitogen-activated protein kinases (MAPKs) that are a family of highly conserved enzymes which comprise ubiquitous groups of signaling proteins playing critical regulatory roles in cell physiology. Extracellular signal-regulated kinases (ERK1/2) and p38(MAPK) control complex programs such as gene expression, embryogenesis, cell differentiation, cell proliferation, cell death and synaptic plasticity. Little information is available about MAPKs in aquatic organisms and their modulation by trace metals. The aim of this work was to determine the modulation of ERK1/2 and p38(MAPK) phosphorylation by Pb2+ in vivo and in vitro, in cerebellar slices of the catfish, Rhamdia quelen. In the in vitro model, slices were incubated for 3 h with lead acetate (1-10 microM). In the in vivo studies, the animals were exposed for 2 days to lead acetate (1 mg L(-1)). ERK1/2 and p38(MAPK) (total and phosphorylated forms) were immunodetected in cerebellar slices by Western blotting. Pb2+ added in vitro at 5 and 10 microM increased significantly the phosphorylation of both MAPKs. The in vivo exposed animals also showed a significant increase of ERK1/2 and p38(MAPK) phosphorylation without changes in the total content of the enzymes. In conclusion, the present work indicates that it is possible to evaluate the ERK1/2 and p38(MAPK) activation in the central nervous system (CNS) of a freshwater fish largely distributed in South America. Moreover, Pb2+, an important environmental pollutant may activate in vitro and in vivo ERK1/2 and p38(MAPK) enzymes. These findings are important considering the functional and ecologic implications associated to Pb2+ exposure of a freshwater fish species, such as R. quelen, and the roles of ERK1/2 and p38(MAPK) in the control of brain development, neuroplasticity and cell death.

Oxidative stress in mouse brain exposed to lead

This study was carried out to investigate effects of developmental Pb-exposure on antioxidant enzyme activities of mice brain. BALB dams were exposed to 600 p.p.m. of Pb-acetate in drinking water during pregnancy and lactation. Pb-exposure presented significant increase of plasma and brain Pb and 5-aminolevulinic acid (ALA) concentrations of weaned pups. In Pb-exposed 21-day-old pups, activities of superoxide dismutase, glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Re) decreased significantly in hypothalamus, corpora quadrigemina and corpus striatum compared with Na-exposed pups. Regarding 70-day-old pups, Pb-exposure had different effects on antioxidant enzymes of the three brain regions. The activities of GSH-Px and GSH-Re in corpora quadrigemina and GSH-Re in hypothalamus of Pb-exposure group did not decrease significantly. That meant that the lead employed might make occurrence of long-term effect on the antioxidant enzymes possible. The result also implied a correlation between ALA and oxidative stress in mice brain. Based on these results, it seemed that oxidative stress because of decreased antioxidant function, induced by significant accumulation of ALA, might be the main mechanism involved in mice brain neurotoxicity induced by developmental Pb-exposure.

Prenatal alcohol exposure (PAE) reduces the size of the forepaw representation in forepaw barrel subfield (FBS) cortex in neonatal rats: relationship between periphery and central representation

Prenatal alcohol exposure (PAE) alters limb development that may lead to structural and functional abnormalities of the limb reported in children diagnosed with Fetal Alcohol Spectrum Disorder. To determine whether PAE alters the central representation of the forelimb we used the rodent barrel cortex as our model system where it was possible to visualize and quantitatively measure the size of the forepaw representation in the forepaw barrel subfield (FBS) in first somatosensory cortex. In the present study, we examined the effects of PAE on pattern and size of the forepaw and forepaw representation in FBS in neonatal rats at gestational day 32 that corresponds to postnatal day 9. Pregnant Sprague-Dawley rats were chronically intubated with binge doses of ethanol (6 g/kg) from gestational day 1 through gestational day 20. The offspring of the ethanol treated dams comprised the ethanol (EtOH) group. The effect of PAE on the EtOH group was compared with a nutritional-controlled pairfed (PF) group and a normal chowfed (CF) group. The ventral (glabrous) surface area of the forepaw digits, length of digit 2 through digit 5, and the corresponding glabrous forepaw digit representations in the FBS were measured and compared between treatment groups. In rats exposed to in utero alcohol, the sizes of the overall glabrous forepaw and forepaw digits were significantly reduced in EtOH pups compared to CF and PF pups; overall glabrous forepaw area was 11% smaller than CF controls. Glabrous digit lengths were also smaller in EtOH rats compared to CF controls and significantly smaller in digit 2 through digit 4. The glabrous digit representation in FBS was 18% smaller in the EtOH group when compared to the CF treatment. However, PAE did not produce malformations in the forepaw or alter the pattern of the forepaw representation in FBS; instead, PAE significantly reduced both body and brain weights compared to controls. Unexpectedly, little or no correlation was observed between the size of the glabrous forepaw compared to the size of the glabrous forepaw representation in the FBS for any of the treatment groups. The present findings of PAE-related alterations in sensory periphery and the central cortical representation may underlie deficits in sensorimotor integration reported among children with Fetal Alcohol Spectrum Disorder.

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.

Lead neurotoxicity: From exposure to molecular effects

The effects of lead (Pb(2+)) on human health have been recognized since antiquity. However, it was not until the 1970s that seminal epidemiological studies provided evidence on the effects of Pb(2+) intoxication on cognitive function in children. During the last two decades, advances in behavioral, cellular and molecular neuroscience have provided the necessary experimental tools to begin deciphering the many and complex effects of Pb(2+) on neuronal processes and cell types that are essential for synaptic plasticity and learning and memory in the mammalian brain. In this review, we concentrate our efforts on the effects of Pb(2+) on glutamatergic synapses and specifically on the accumulating evidence that the N-methyl-D-aspartate type of excitatory amino acid receptor (NMDAR) is a direct target for Pb(2+) effects in the brain. Our working hypothesis is that disruption of the ontogenetically defined pattern of NMDAR subunit expression and NMDAR-mediated calcium signaling in glutamatergic synapses is a principal mechanism for Pb(2+)-induced deficits in synaptic plasticity and in learning and memory documented in animal models of Pb(2+) neurotoxicity. We provide an introductory overview of the magnitude of the problem of Pb(2+) exposure to bring forth the reality that childhood Pb(2+) intoxication remains a major public health problem not only in the United States but worldwide. Finally, the latest research offers some hope that the devastating effects of childhood Pb(2+) intoxication in a child's ability to learn may be reversible if the appropriate stimulatory environment is provided.

Lead Exposure and (n-3) Fatty Acid Deficiency during Rat Neonatal Development Affect Subsequent Spatial Task Performance and Olfactory Discrimination

Docosahexaenoic acid [22:6(n-3), DHA] is important for optimal infant central nervous system development, and lead (Pb) exposure during development can produce neurological deficits. Long-Evans strain rats were fed either an (n-3) deficient [(n-3) Def] diet to produce brain DHA deficiency, or an adequate [(n-3) Adq] diet through 2 generations. At the birth of the 2nd generation, the dams were subdivided into 4 groups and supplied drinking water containing either 5.27 mmol/L (Pb) or sodium (Na) acetate until weaning. Rats were killed at 3 wk (weaning) and 11 wk (maturity) for brain Pb and fatty acid analysis. Spatial task and olfactory-cued behavioral assessments were initiated at 9 wk. Rats in the (n-3) Def group had a 79% lower concentration of brain DHA compared with the (n-3) Adq group with no effect of Pb exposure. At weaning, Pb concentrations were 7.17 +/- 0.47 nmol Pb/g of brain (wet weight) in the (n-3) Adq-Pb group and 6.49 +/- 0.63 nmol Pb/g of brain (wet weight) in the (n-3) Def-Pb group. At maturity, the brains contained 1.30 +/- 0.22 and 1.07 +/- 0.12 nmol Pb/g (wet weight), respectively. In behavioral testing, significant effects of both Pb and DHA deficiency were observed in the Morris water maze probe trial and in 2-odor olfactory discrimination acquisition and olfactory-based reversal learning tasks. Both lactational Pb exposure and (n-3) fatty acid deficiency led to behavioral deficits with additive effects observed only in the acquisition of 2-odor discriminations.

Prenatal alcohol exposure alters the size, but not the pattern, of the whisker representation in neonatal rat barrel cortex

Maternal alcohol exposure results in a variety of neurodevelopmental abnormalities that include cognitive and sensorimotor dysfunctions that often persist into adulthood. Many reports of central nervous system disturbances associated within a clinical diagnosis of fetal alcohol syndrome point toward disturbances in central information processing. In this study, we used the rat barrel field cortex as a model system to examine the effects of prenatal alcohol exposure (PAE) on the organization and size of the large whisker representation in layer IV of the posteromedial barrel subfield (PMBSF) in somatosensory cortex. Pregnant rats (Sprague-Dawley) were intragastrically gavaged daily with alcohol doses (6 gm/kg body weight) from gestational day 1 to day 20 in a chronic binge pattern which produced blood alcohol levels ranging between 260 mg/dl and 324 mg/dl. Chow-fed (CF), pair-fed (PF), and cross-foster (XF) groups served as normal, nutritionally matched, and maternal controls, respectively, for the ethanol-exposed (EtOH) treatment group. All pups were examined on gestational day 32 corresponding approximately to postnatal day 9. EtOH and control group pups were weighed, anesthetized, and perfused. Brains were removed and weighed, with and without cerebellum and olfactory bulbs, and the neocortex was removed and weighed. Cortices were then flattened, sectioned tangentially, and stained with a metabolic marker-cytochrome oxidase-to reveal the barrel field. A subset of 27 cortical barrels, associated with the representation of the large whisker pad, was selected to examine in detail. The major results were: (i) the total barrel field area comprising the PMBSF was significantly reduced in EtOH (by 17%) and XF (by 16%) pups compared with CF pups, (ii) the sizes of individual barrels within the PMBSF were also significantly reduced in EtOH (16%) and XF (18%) pups, (iii) the septal region between barrels was also significantly reduced in EtOH (18%) and XF (12%) pups, (iv) anteriorly located barrels underwent greater reduction in size relative to the posteriorly located barrels, (v) body weights were also significantly reduced in EtOH (21%) and XF (27%) pups, (vi) total brain weight [with and without (forebrain) cerebellum/olfactory bulbs] and cortical weights were also significantly reduced in EtOH (total brain weight 15%, forebrain weight 16%, cortical weight 15%) and XF (18%, 19%, 20%) pups, and in contrast (vi) neither the overall barrel field pattern nor the pattern of individual barrels in the PMBSF was altered. These findings suggest that PAE reduces body and brain weight as well as the central cortical representation of the whisker pad, while leaving the overall barrel field pattern unperturbed. While these results might appear to support a miniaturization hypothesis (smaller PMBSF, smaller brain, smaller body weight), PAE also shows regional vulnerability within the PMBSF whereby anteriorly located barrels are most affected.

The effects of meso-2,3-dimercaptosuccinic acid and oligomeric procyanidins on acute lead neurotoxicity in rat hippocampus

Oxidative stress is considered to be a mechanism involved in lead neurotoxicity. Apoptosis is also thought to relate to lead neurotoxicity. The present study, focused on the hippocampus, was designed to investigate the two possible mechanisms involved in lead neurotoxicity and the potential protective effects of 2,3-dimercaptosuccinic acid (DMSA) and oligomeric procyanidins (OPC). It was proved that reactive oxygen species and oxidative damage were implicated in the induction of apoptosis induced by lead in the hippocampus. Administration of DMSA attenuated the oxidative stress and apoptosis in addition to having strong chelating and lead-removing capacity. OPC alone had antioxidant protective effects in the hippocampus but no removing capacity for lead in vivo despite showing higher affinity and stronger chelating ability for Pb(2+) than DMSA in vitro. It is suggested that OPC chelates Pb(2+) but does not discharge it from the body and even accumulates Pb(2+) in some organs. At the same time, a reasonable deduction can also be made that the complex of OPC-Pb(2+) prevents or at least weakens the neurotoxicity of Pb(2+). Whether this complex displays toxicity over a long time span should be studied further.

Reductions in blood lead overestimate reductions in brain lead following repeated succimer regimens in a rodent model of childhood lead exposure

Although many studies have demonstrated the efficacy of succimer chelation in reducing blood and brain lead levels, the relative efficacy of the drug in the two tissues is less well understood. This issue is important because blood lead levels after chelation are used clinically to estimate reductions in the brain, the most critical organ in considering lead-induced neurotoxicity. The present study was designed to further investigate this issue, using multiple chelation regimens. Long-Evans rats were exposed to one of three lead exposure regimens from birth until postnatal day 40, followed by treatment with succimer (one or two 3-week regimens) or vehicle. The results indicated that one succimer regimen was significantly superior to vehicle treatment in lowering lead levels in both blood and brain across the entire 8-week follow-up period. Similarly, a second succimer regimen offered significant additional benefit relative to one regimen for both blood and brain across the 4-week follow-up period. However, several findings revealed that succimer-induced reductions in brain lead lagged behind reductions in blood lead and were generally smaller in magnitude. Furthermore, a rebound was detected in blood, but not brain, lead levels after both succimer regimens. Given the results of this study, we urge caution in using blood lead as a surrogate for brain lead levels, particularly during and immediately after chelation treatment when reductions in blood lead levels overestimate reductions in brain lead levels. The present results suggest that, in clinical use, succimer treatment may need to extend beyond the point at which blood lead levels have dropped to an "acceptable" target value in order to effectively reduce brain lead levels and minimize neurotoxicity.

Clinical disorders of brain plasticity

Clinical disorders of brain plasticity are common in the practice of child neurology. Children have an enhanced capacity for brain plasticity compared to adults as demonstrated by their superior ability to learn a second language or their capacity to recover from brain injuries or radical surgery such as hemispherectomy for epilepsy. Basic mechanisms that support plasticity during development include persistence of neurogenesis in some parts of the brain, elimination of neurons through apoptosis or programmed cell death, postnatal proliferation and pruning of synapses, and activity-dependent refinement of neuronal connections. Brain plasticity in children can be divided into four types: adaptive plasticity that enhances skill development or recovery from brain injury; impaired plasticity associated with cognitive impairment; excessive plasticity leading to maladaptive brain circuits; and plasticity that becomes the brain's 'Achilles' Heel' because makes it vulnerable to injury. A broad group of pediatric neurologic disorders can be understood in terms of their impact on fundamental mechanisms for brain plasticity. These include neurofibromatosis, tuberous sclerosis, Fragile X syndrome, other inherited forms of mental retardation, cretinism, Coffin-Lowry syndrome, lead poisoning, Rett syndrome, epilepsy, hypoxic-ischemic encephalopathy and cerebral palsy.

Lead Poisoning

Understanding of lead toxicity has advanced substantially over the past three decades, and focus has shifted from high-dose effects in clinically symptomatic individuals to the consequences of exposure at lower doses that cause no symptoms, particularly in children and fetuses. The availability of more sensitive analytic methods has made it possible to measure lead at much lower concentrations. This advance, along with more refined epidemiological techniques and better outcome measures, has lowered the least observable effect level until it approaches zero. As a consequence, the segment of the population who are diagnosed with exposure to toxic levels has expanded. At the same time, environmental efforts, most importantly the removal of lead from gasoline, have dramatically reduced the amount of lead in the biosphere. The remaining major source of lead is older housing stock. Although the cost of lead paint abatement is measured in billions of dollars, the monetized benefits of such a Herculean task have been shown to far outweigh the costs.