Pre- and postnatal lead exposure affects the serotonergic system in the immature rat brain

Protective effects of Nigella sativa L. seed extract on lead induced neurotoxicity during development and early life in mouse models

Lead (Pb), a ubiquitous heavy metal and a known neurotoxicant, produces adverse effects on the brain via increased production of reactive oxygen species (ROS) and causes oxidative stress. In this study we examined the neuroprotective effects of the ethanolic extract of Nigella sativa L. seeds on Pb induced oxidative stress in the developing brain of mice. Mouse pups were exposed to low (0.1%) and high (0.2%) doses of Pb from the first day of pregnancy through their mothers (via drinking water) and lactation until post-natal day (PND) 21. The mRNA expression levels of superoxide dismutase (SOD1), peroxiredoxin (Prdx6), amyloid precursor protein (APP) common, APP695 and APP770 were examined in the cortex and hippocampus of the mouse brain excised on PND 21 by semi-quantitative RT-PCR. The free radical scavenging activity of ethanolic Nigella sativa L. extract was assessed by DPPH assay. The results showed that Pb exposure caused a significant decrease in the expression of SOD1, Prdx6 and APP695 and an increase in APP770 in both cortex and hippocampus in a dose dependent manner as compared to the control group. The expression of APP common remained unaltered. Histological assessment of the cortex and hippocampus demonstrated a decrease in the neuronal number and Nissl bodies. The administration of 250 and 500 mg kg-1 ethanolic Nigella sativa L. extract reversed the adverse effects by significantly increasing the expression of SOD1, Prdx6 and APP695 and decreasing the expression of APP770 in both the regions. These results strongly suggest that Nigella sativa L. supplementation greatly improves Pb-induced neurotoxicity in early life and provides neuroprotective and antioxidant potentials.

Calcium and zinc supplementation protects lead (Pb)-induced perturbations in antioxidant enzymes and lipid peroxidation in developing mouse brain

Several studies have implicated oxidative stress as one of the important mechanisms of toxic effects of lead (Pb). In the present study we tested the beneficial effects of calcium (Ca2+) and zinc (Zn2+) in protecting the Pb-induced oxidative stress in the brains of developing and adult mice. Mice were lactationally exposed to 0.2% Pb and supplemented with either calcium (Ca2+) or zinc (Zn2+) and the mitochondrial antioxidant enzymes [superoxide dismutase (SOD), xanthine oxidase (XO) and catalase (CAT)] and lipid peroxidation (LP) were analyzed in cortex, hippocampus, cerebellum and medulla of brains excised on postnatal day (PND) 14, 21, 28 and 3 months. The levels of free radicals were measured using direct Electron Paramagnetic Resonance (EPR) spectroscopy. Exposure to Pb resulted a significant decrease in the activities of SOD, XO and CAT while the LP levels were significantly increased in different brain regions. Evaluation of EPR signals and g-values showed abundant accumulation of free radicals in different regions of the brain following Pb exposure. Interestingly the supplementation with Ca2+ or Zn2+ reversed the Pb-induced effects on antioxidant enzymes, LP and free radical formation; however Zn2+ supplementation appeared to be more protective. These findings strongly support that zinc and calcium supplementation significantly protect the Pb-induced oxidative stress, a major contributing factor to neurotoxicity.

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.

Developmental lead exposure impairs contextual fear conditioning and reduces adult hippocampal neurogenesis in the rat brain

The effects of developmental lead exposure on the emotional reactivity, contextual fear conditioning and neurogenesis in the dentate gyrus of 60-80 days-old rats were studied. Wistar rat pups were exposed to 0.2% lead acetate via their dams' drinking water from postnatal day (PND) 1 to PND 21 and directly via drinking water from weaning until PND 30. At PND 60 and 80 the level of anxiety and contextual fear conditioning were studied, respectively. At PND 80 all animals received injections of BrdU to determine the effects of Pb on the generation of new cells in the dentate gyrus of hippocampus and on their survival and differentiation patterns. The results of the present study demonstrate that developmental lead exposure induces persistent increase in the level of anxiety and inhibition of contextual fear conditioning. Developmental lead exposure reduced generation of new cells in the dentate gyrus and altered the pattern of differentiation of BrdU-positive cells into mature neurons. A lower proportion of BrdU-positive cells co-expressed with the marker for mature neurons, calbindin. In contrast, the proportions of young not fully differentiated neurons and proportions of astroglial cells, generated from newly born cells, were increased in lead-exposed animals. Our results demonstrate that developmental lead exposure induces persistent inhibition of neurogenesis and alters the pattern of differentiation of newly born cells in the dentate gyrus of rat hippocampus, which could, at least partly, contribute to behavioral and cognitive impairments observed in adulthood.

Developmental lead exposure induces depressive-like behavior in female rats

The involvement of neurotoxicants in the etiology of emotional pathologies is becoming an issue in neurotoxicology. Lead (Pb) exposure during childhood has been associated with increased impulsivity, aggressivity, and delinquency. Considering the paucity of experimental studies investigating the involvement of developmental Pb exposure in emotional disorders, our objective was to investigate whether Pb exposure during pregnancy and/or lactation could be related to depressive symptoms in adult male and female rats. Wistar dams received 10 mg of Pb, as Pb acetate, or 13.4 mg of Na acetate, by gavage, daily, during pregnancy and lactation. By cross-fostering at the time of birth, pups were either exposed to Pb or Na acetate during pregnancy only, lactation only, or during both pregnancy and lactation. At 70 days of age, animals were submitted to the open-field test followed by the forced swimming test. Pb levels were measured in the blood of dams (weaning) and pups (after behavioral evaluation). The results demonstrated that exposure to Pb during both pregnancy and lactation induced, in males, an increased emotionality state detected in the open-field test, and in females, depressive-like behavior detected in the forced swimming test. These alterations were observed at residual blood Pb levels (i.e., around 5 microg/dL).

Bone lead levels in adjudicated delinquents. A case control study

BACKGROUND

Lead exposure shares many risk factors with delinquent behavior, and bone lead levels are related to self-reports of delinquent acts. No data exist as to whether lead exposure is higher in arrested delinquents. The goal of this study is to evaluate the association between lead exposure, as reflected in bone lead levels, and adjudicated delinquency.

METHODS

This is a case-control study of 194 youths aged 12-18, arrested and adjudicated as delinquent by the Juvenile Court of Allegheny County, PA and 146 nondelinquent controls from high schools in the city of Pittsburgh. Bone lead was measured by K-line X-ray fluorescence (XRF) spectroscopy of tibia. Logistic regression was used to model the association between delinquent status and bone lead concentration. Covariates entered into the model were race, parent education and occupation, presence of two parental figures in the home, number of children in the home and neighborhood crime rate. Separate regression analyses were also conducted after stratification on race.

RESULTS

Cases had significantly higher mean concentrations of lead in their bones than controls (11.0+/-32.7 vs. 1.5+/-32.1 ppm). This was true for both Whites and African Americans. The unadjusted odds ratio for a lead level > or =25 vs. <25 ppm was 1.9 (95% CL: 1.1-3.2). After adjustment for covariates and interactions and removal of noninfluential covariates, adjudicated delinquents were four times more likely to have bone lead concentrations >25 ppm than controls (OR=4.0, 95% CL: 1.4-11.1).

CONCLUSION

Elevated body lead burdens, measured by bone lead concentrations, are associated with elevated risk for adjudicated delinquency.

Effects of maternal lead administration on monoaminergic, GABAergic and glutamatergic systems

The effects of perinatal exposure to lead (300 mg/l) on the development of monoaminergic and aminoacidergic systems were evaluated in the striatum, cerebral cortex (Cx), dorsal hippocampus (d-Hipp) and basal-medial hypothalamus. Maternal exposure to lead produced regional alterations in monoamine content, with increases in dopamine and serotonin or their metabolites. Further, decreased glutamate levels were seen in all brain regions studied, while GABA content decreased only in the Cx. Together, these results show that lead causes alterations to neurotransmitter systems during development. These may be related to lead-induced neurobehavioral impairment.

Behavioral responses to ethanol in rats perinatally exposed to low lead levels

Wistar rats were exposed to 220 ppm of lead (Pb) in the drinking water from conception to the end of the nursing period (postnatal day 25). Maternal blood Pb levels at this time were 25 microg/dl. Male offspring were tested at the age of 35 or 70 days. We studied the anxiolytic response to 0.5-2.0 g/kg ethanol in an elevated plus maze test and preference for increasing ethanol solutions (2%, 4%, and 6%, v/v) in a free-choice paradigm; we also determined basal blood levels of corticosterone. Results demonstrated that, at 35 days of age, experimental rats were hypersensitive to the anxiolytic effect of ethanol and showed greater voluntary intake of this drug. In addition, 35-day-old Pb-treated rats exhibited higher basal levels of corticosterone as compared with those of controls. These differences disappeared at 70 days. Our findings are discussed in terms of either Pb-induced alterations in the development of the CNS or higher levels of corticosterone in experimental animals. Possible Pb-ethanol effects interactions are also considered.

Neurodevelopmental evaluation of 9-month-old infants exposed to low levels of lead in utero: involvement of monoamine neurotransmitters

The objective of this work is to investigate the neurotoxicty of low-level lead exposure in utero on infants and the possible involvement of dopaminergic and serotonergic neurotransmitters. The correlation analysis for cord blood lead level, the concentrations of dopamine metabolite homovanillic acid (HVA) and serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) in cord plasma and the neurodevelopmental scales of infants were conducted on 244 9-month-old children. Both score of sociability subscale and 5-HIAA concentration were correlated with cord blood lead level. The sociability score was negatively correlated with the concentration of HVA, whereas both the coordination score and the global score were negatively correlated with the concentration of 5-HIAA. With partial correlation analysis, after taking HVA into account, the significant negative correlation between the sociability score and the cord blood lead level that existed in the linear correlation analysis disappeared, and the score of global scale correlated negatively with lead level in cord blood. When taking 5-HIAA into account, the scores of all the neurodevelopmental subscales except the language subscale were significantly negatively correlated with lead level in cord blood. The results indicated that low-level lead exposure in utero could produce a neurotoxic effect on the developing serotonergic system in infants. The neurotoxicity of low-level lead exposure in utero may affect the sociability of infants. Serotonergic activity was shown to have a potential effect on neurodevelopmental assessment. It may interfere with the association between low-level lead exposure in utero and other neurodevelopmental performances of 9-month-old children.

Central lead administration induces natriuretic and kaliuretic effects in rats

The aim of the present experiments was to discern whether central acute lead injections affect brain control of renal function. Adult Wistar male rats received third-ventricle injections of lead acetate in three different doses (0.03, 0.3, and 3.0 nmol/rat). Lead acetate induced a significant increase in renal excretion of sodium and potassium. Pretreatment with losartan, a selective angiotensin II AT1 receptor antagonist (10.8 nmol/rat into the third ventricle 10 min before central lead injection), inhibits lead-induced natriuretic and kaliuretic effects. In addition, pretreatment with gadolinium, a calcium-channel blocker (0.3 nmol/rat into the third ventricle 20 min before central lead administration), reversed the increase in renal excretion of sodium and potassium provoked by central lead administration. Taken together, the data presented here suggest that lead injected into the third ventricle increases renal excretion of sodium and potassium by a mechanism that depends on the functional integrity of central angiotensin II AT1 receptors and calcium channels.

Effects of lead-arsenic combined exposure on central monoaminergic systems

Lead acetate (116 mg/kg/day), arsenic (11 or 13.8 mg/kg/day as sodium arsenite), a lead-arsenic mixture or vehicle were administered to adult mice through gastric intubation during 14 days. Then, the regional content of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3,4 dihydroxyphenyl-acetic acid (DOPAC), 5-hydroxyindole-3-acetic acid (5-HIAA), arsenic, and lead were quantified. Compared with the accumulation after single element exposures, the mixture elicited a higher accumulation of lead and a lower arsenic accumulation in the brain. Compared to controls, lead induced only an augmentation of DOPAC (200%) in the hypothalamus. By contrast, the mixture provoked increases of DOPAC in the hypothalamus (250%), DA and 5-HIAA in the striatum (67 and 187%, respectively) and NE decreased in the hypothalamus (45%). Although these alterations were similar to those produced by arsenic alone, the mixture provoked a 38% decrease of NE in the hippocampus and increases of 5-HT in midbrain and frontal cortex (100 and 90%, respectively) over control values, alterations that were not elicited by either metal alone. These results demonstrate an interaction arsenic/lead on the central monoaminergic systems of the adult mouse.

Acute effect of intracerebroventricular administration of lead on the drinking behavior of rats induced by dehydration or central cholinergic and angiotensinergic stimulation

In the present paper, the acute effect of third ventricle injections of lead acetate (5, 10, 100, 1000 ng/rat) on the drinking behavior of adult, male, Wistar rats was investigated. Lead generates a prompt and significant reduction in water intake induced by three different circumstances: dehydration (14 h of water deprivation) and after carbachol (2 micrograms/rat, ICV) or angiotensin II (10 ng/rat, ICV) administration. These results show that lead may produce very fast actions in the central nervous system and suggest that inhibition of water intake by lead may depend on impairment of central cholinergic and/or angiotensinergic functions.