Developmental lead exposure in rats: is a behavioral sequel extended at F2 generation?

Anxiety, aggression, reward sensitivity, and forebrain dopamine receptor expression in a laboratory rat model of early-life disadvantage

Despite early-life disadvantage (ELD) in humans being a highly heterogenous construct, it consistently predicts negative neurobehavioral outcomes. The numerous environmental contributors and neural mechanisms underlying ELD remain unclear, though. We used a laboratory rat model to evaluate the effects of limited resources and/or heavy metal exposure on mothers and their adult male and female offspring. Dams and litters were chronically exposed to restricted (1-cm deep) or ample (4-cm deep) home cage bedding postpartum, with or without lead acetate (0.1%) in their drinking water from insemination through 1-week postweaning. Restricted-bedding mothers showed more pup-directed behaviors and behavioral fragmentation, while lead-exposed mothers showed more nestbuilding. Restricted bedding-raised male offspring showed higher anxiety and aggression. Either restricted bedding or lead exposure impaired goal-directed performance in a reinforcer devaluation task in females, whereas restricted bedding alone disrupted it in males. Lead exposure, but not limited bedding, also reduced sucrose reward sensitivity in a progressive ratio task in females. D1 and D2 receptor mRNA in the medial prefrontal cortex and nucleus accumbens (NAc) were each affected by the early-life treatments and differently between the sexes. Most notably, adult males (but not females) exposed to both early-life treatments had greatly increased D1 receptor mRNA in the NAc core. These results illuminate neural mechanisms through which ELD threatens neurobehavioral development and highlight forebrain dopamine as a factor.

Boswellia serrata suppress fipronil-induced neuronal necrosis and neurobehavioral alterations via promoted inhibition of oxidative/inflammatory/apoptotic pathways

Boswellic acid (BA) is a pentacyclic terpenoid derived from the gum-resin of Boswellia serrate. It is known for its strong antioxidant, anti-inflammatory, and anticancer properties. It has improved spatial learning and provides neuroprotection against trimethyltin-induced memory impairment. The aim of this study is to evaluate the possible neuroprotective activity of B. serrata extract (BSE) containing BA against fipronil (FPN)-induced neurobehavioral toxicity in Wister male albino rats. Sixty male rats were allocated equally into six groups. The first group served as control; the second and third groups received BSE at two different oral doses (250 or 500 mg/kg body weight [BW], respectively). The fourth group was orally intoxicated with FPN (20 mg/kg BW), whereas the fifth and sixth groups served as preventive groups and co-treated with FPN (20 mg/kg BW) and BSE (250 or 500 mg/kg BW, respectively). The experiment was conducted over 8 weeks period. Results revealed that co-treatment with BSE led to significant (p > 0.05) dose-dependent reduction in malondialdehyde (MDA), nitric oxide (NO), interleukin-6 (IL6), tumor necrosis factors-alpha (TNF-α), nuclear factor Kappa-B (NF-κB), Cyclooxegenase-2 (COX-2), prostaglandin E2 (PGE2), serotonin, and acetylcholine (ACh). Conversely, significant (p > 0.05) up regulation of catalase (CAT), glutathione peroxidase (GSH-Px), gamma-aminobutyric acid (GABA), and acetylcholine esterase (AChE) has reported in BSE-co-treated groups. In addition, significant (p > 0.05) promotion in neurobehaviours, histopathologic imaging of the cerebral, cerebellar, and hippocampal regions, and immunohistochemical expression of caspase-3 and glial fibrillary acidic protein (GFAP) were also reported in the BSE-treated groups in a dose-dependent manner. In conclusion, BSE (500 mg/kg BW) is a natural, promising neuroprotective agent that can mitigate FPN-induced neurobehavioral toxicity via the suppression of oxidative, inflammatory, and apoptotic pathways and relieve neuronal necrosis and astrogliosis.

Forced swimming stress increases natatory activity of lead-exposed mice

Recent evidence points to the relationship between lead toxicity and the function of the hypothalamic-pituitary-adrenal axis, which suggests that lead exposure could influence how an individual cope with stress. Here we test this hypothesis by investigating the behavioral effects of lead exposure in mice during the forced swimming test (FST), a parading in which animals are exposed to a stressful situation and environment. Swiss mice received either 180 ppm or 540 ppm of lead acetate (Pb) in their ad-lib water supply for 60-90 days, starting at postnatal day 30. Control (Ctrl) mice drank tap water. At the end of the exposure period, mice were submitted to a 5-min session of FST or to an open-field session of the same duration. Data from naïve animals showed that corticosterone levels were higher for animals tested in the FST compared to animals tested in the open-field. Blood-lead levels (BLL) in Pb-exposed mice ranged from 14.3 to 106.9 µg/dL. No differences were observed in spontaneous locomotion between Ctrl and Pb-exposed groups in the open-field. However, in the FST, Pb-treated mice displayed higher swimming activity than Ctrl ones and this effect was observed even for animals with BLL higher than 20 µg/dL. Furthermore, significant differences in brain glutathione levels, used as an indicator of led toxicity, were only observed for BLL higher than 40 µg/dL. Overall, these findings suggest that swimming activity in the FST is a good indicator of lead toxicity and confirm our prediction that lead toxicity influences behavioral responses associated to stress.

Developmental exposure to Pb2+ induces transgenerational changes to zebrafish brain transcriptome

Lead (Pb2+) is a major public health hazard for urban children, with profound and well-characterized developmental and behavioral implications across the lifespan. The ability of early Pb2+ exposure to induce epigenetic changes is well-established, suggesting that Pb2+-induced neurobehavioral deficits may be heritable across generations. Understanding the long-term and multigenerational repercussions of lead exposure is crucial for clarifying both the genotypic alterations behind these behavioral outcomes and the potential mechanism of heritability. To study this, zebrafish (Danio rerio) embryos (<2 h post fertilization; EK strain) were exposed for 24 h to waterborne Pb2+ at a concentration of 10 μM. This exposed F0 generation was raised to adulthood and spawned to produce the F1 generation, which was subsequently spawned to produce the F2 generation. Previous avoidance conditioning studies determined that a 10 μM Pb2+ dose resulted in learning impairments persisting through the F2 generation. RNA was extracted from control- and 10 μM Pb2+-lineage F2 brains, (n = 10 for each group), sequenced, and transcript expression was quantified utilizing Quant-Seq. 648 genes were differentially expressed in the brains of F2 lead-lineage fish versus F2 control-lineage fish. Pathway analysis revealed altered genes in processes including synaptic function and plasticity, neurogenesis, endocrine homeostasis, and epigenetic modification, all of which are implicated in lead-induced neurobehavioral deficits and/or their inheritance. These data will inform future investigations to elucidate the mechanism of adult-onset and transgenerational health effects of developmental lead exposure.

Avaliação neurocomportamental e níveis de acetilcolinesterase cerebral em ratos expostos subcronicamente ao fipronil

RESUMO O fipronil é um inseticida de toxicidade seletiva amplamente empregado na agricultura e na medicina veterinária. Porém, há relatos de efeitos neurotóxicos dessa substância, que geram prejuízos para vertebrados. Avaliou-se a atividade locomotora, a coordenação motora e a atividade da enzima acetilcolinesterase cerebral em ratos expostos ao fipronil. Ratos Wistar machos adultos (n=15) receberam fipronil em dose de 30mg/kg, por via oral, durante 15 dias; o grupo controle (n=15) foi tratado com solução fisiológica, por via oral, no mesmo período. No 16° dia de experimentação, os animais foram submetidos aos testes de arena de campo aberto e hole board. No 17° dia, foram anestesiados e eutanasiados, procedendo-se à coleta de órgãos, e posteriormente foi feita a avaliação da AChE cerebral. A exposição ao fipronil não provocou alterações significativas sobre a coordenação motora e a atividade locomotora, porém gerou inibição significativa da atividade da acetilcolinesterase cerebral. Esses achados sugerem que o fipronil pode provocar efeitos neurotóxicos em curto prazo, os quais podem ser exacerbados caso a exposição seja prolongada.

Developmental manganese, lead, and barren cage exposure have adverse long-term neurocognitive, behavioral and monoamine effects in Sprague-Dawley rats

Developmental stress, including low socioeconomic status (SES), can induce dysregulation of the hypothalamic-pituitary-adrenal axis and result in long-term changes in stress reactivity. Children in lower SES households experience more stress and are more likely to be exposed to environmental neurotoxins such as lead (Pb) and manganese (Mn) than children in higher SES households. Co-exposure to stress, Pb, and Mn during early development may increase the risk of central nervous system dysfunction compared with unexposed children. To investigate the potential interaction of these factors, Sprague-Dawley rats were bred, and litters born in-house were culled on postnatal day (P)1 to 6 males and 6 females. One male and female within each litter were assigned to one of the following groups: 0 (vehicle), 10 mg/kg Pb, 100 mg/kg Mn, or 10 mg/kg Pb + 100 mg/kg Mn (PbMn), water gavage, and handled only from P4-28 with half the litters reared in cages with standard bedding (29 litters) and half with no bedding (Barren; 27 litters). Mn and PbMn groups had decreased anxiety, reduced acoustic startle, initial open-field hypoactivity, increased activity following (+)-methamphetamine, deficits in egocentric learning in the Cincinnati water maze (CWM), and deficits in latent inhibition conditioning. Pb increased anxiety and reduced open-field activity. Barren-reared rats had decreased anxiety, CWM deficits, increased startle, and initial open-field hyperactivity. Mn, PbMn, Pb Barren-reared groups had impaired Morris water maze performance. Pb altered neostriatal serotonin and norepinephrine, Mn increased hippocampal serotonin in males, Mn + Barren-rearing increased neostriatal serotonin, and Barren-rearing decreased neostriatal dopamine in males. At the doses used here, most effects were in the Mn and PbMn groups. Few interactions between Mn, Pb, and rearing stress were found, indicating that the interaction of these three variables is not as impactful as hypothesized.

Disturbed sensorimotor and electrophysiological patterns in lead intoxicated rats during development are restored by curcumin I

Lead poisoning is one of the most significant health problem of environmental origin. It is known to cause different damages in the central and peripheral nervous system which could be represented by several neurophysiological and behavioral symptoms. In this study we firstly investigated the effect of lead prenatal exposure in rats to (3g/L), from neonatal to young age, on the motor/sensory performances, excitability of the spinal cord and gaits during development. Then we evaluated neuroprotective effects of curcumin I (Cur I) against lead neurotoxicity, by means of grasping and cliff avoidance tests to reveal the impairment of the sensorimotor functions in neonatal rats exposed prenatally to lead. In addition, extracellular recordings of motor output in spinal cord revealed an hyper-excitability of spinal networks in lead treated rats. The frequency of induced fictive locomotion was also increased in treated rats. At the young age, rats exhibited an impaired locomotor gait. All those abnormalities were attenuated by Cur I treatment at a dose of 16g/kg. Based on our finding, Cur I has shown features of a potent chemical compound able to restore the neuronal and the relative locomotor behaviors disturbances induced by lead intoxication. Therefore, this chemical can be recommended as a new therapeutic trial against lead induced neurotoxicity.

Effects of Regular Treadmill Exercise on a DNA Oxidative-Damage Marker and Total Antioxidant Capacity in Rat Hippocampal Tissue

Background and Purpose

Regular exercise can result in changes in the levels of oxidative stress in the hippocampus; however, little attention has been paid to physical-activity-induced neuronal protection to exposure to lead compounds. This study investigated the effects of regular treadmill exercise on a DNA oxidative-damage marker [8-hydroxy-2'-deoxyguanosine (8-OHdG)] and the total antioxidant capacity (TAC) of hippocampal tissue in lead-acetate exposed rats.

Methods

This study investigated the effects of 8 weeks of regular treadmill exercise on 8-OHdG and the TAC of hippocampal tissue in lead-acetate-exposed rats. Wistar rats were randomly divided into four groups: baseline, sham (control), lead, and exercise+lead. The exercise program involved running on a treadmill with increasing intensity five times a week for 8 weeks. Animals in the lead and exercise+lead groups received lead acetate at 20 mg/kg body weight intraperitoneally three times weekly for 8 weeks. Animals in the sham group received solvent (ethyl oleate) at 30 mg/kg body weight three times weekly for 8 weeks. TAC and 8-OHdG were measured by spectrophotometric and ELISA techniques, respectively. Data were analyzed by ANOVA and Tukey's post-hoc test with a significance cutoff of p≤0.05.

Results

The level of 8-OHdG and the TAC were significantly higher and lower, respectively, in the lead group than in the baseline and sham groups (p<0.01). However, the 8-OHdG level and TAC value in hippocampal tissue were significantly decreased and increased, respectively, in the exercise+lead group relative to the lead group (p<0.05).

Conclusions

The TAC of hippocampal tissue may be directly associated with neural protection mechanisms of exercise following lead acetate injection, and the beneficial effects of regular exercise in preventing hippocampal neuronal damage could be due to decreased hippocampal oxidative stress such as reflected by a lower 8-OHdG level and increased TAC.

Developmental effects of parental exposure to soil contaminated with urban metals

Soil is a highly complex material, and because of rapid population growth, intense industrial activity and petrochemical development, it has suffered from contamination with substances of various origins. These environmental contaminants may have detrimental effects on human health, particularly during development. Due to the ability to transmit contaminants to the fetus, evaluating the effects of exposure of pregnant women on the psychomotor development of their offspring is of particular interest. Therefore, this study aimed to investigate the effects of exposure of female rats to an urban soil influenced by the dispersion of air contaminants during periods of pre-pregnancy, pregnancy and lactation on offspring development. Using physiological, behavioral and hematological parameters, deleterious effects on offspring were assessed. In behavioral parameters, parental exposure during pregnancy and lactation resulted in no significant differences in the evaluated parameters when compared to the control group. In contrast, pups from the pre-pregnancy group displayed decreased locomotor and exploratory activity in addition to increased levels of anxiety. Furthermore, offspring of rats exposed to contaminated urban soil during pre-pregnancy demonstrated significant changes in weight gain and development length and a reduction in the number of platelets compared to controls. Significantly, pups born to mothers exposed to contaminated urban soil during the pregnancy displayed changes in birth weight, weight gain during the growth, development length, incisor eruption and opening of the ears in addition to a reduction in their physical performance and a change in the number of lymphocytes. These results clearly show the negative influence of parental exposure to contaminated urban soil on the general development of the rats during the periods studied. These data indicate that developing organisms are highly sensitive to external factors. Further, they demonstrate the utility of these various biomarkers for identifying and displaying toxic effects of exposure to contaminated soils.

"Permethrin chronic exposure alters motor coordination in rats: effect of calcium supplementation and amlodipine"

Recently was observed that pyrethroids decrease motor coordination and that calcium channels can be important targets for this effect. To contribute with this observation, this work studied the motor coordination and exploration (using hole-board apparatus), and locomotion (using open-field apparatus) of rats exposed to following treatments: permethrin (PM), PM plus calcium gluconate (CG) and PM plus amlodipine (AML). The results obtained show that CG or AML alone not changed the motor coordination while PM decreases it. CG kept the effect of permethrin; AML, however, decreased the values of permethrin to the control. Locomotor activity and exploration, which could confound results of motor coordination, were not modified by treatments. The concentration of PM in brain tissue was increased by the CG and AML. The neurosomatic index (weight brain/body weight) was increased by the PM and PM+CG. In conclusion, the combined results here obtained indicates that the calcium ion and the channels in which it is involved can be important targets for the toxic effect of pyrethroid insecticide permethrin on motor nerve activity of rats.

Ingestion of Mn and Pb by rats during and after pregnancy alters iron metabolism and behavior in offspring

Manganese (Mn) and lead (Pb) exposures during developmental period can impair development by direct neurotoxicity or through interaction with iron metabolism. Therefore, we examined the effects of maternal ingestion of Mn or Pb in drinking water during gestation and lactation on iron metabolism as well as behavior in their offspring. Pregnant dams were given distilled water, 4.79mg/ml Mn, or 2.84mg/ml Pb in drinking water during gestation and lactation. Pups were studied at time of weaning for (59)Fe absorption from the gut, duodenal divalent metal transporter 1 (DMT1) expression, hematological parameters, and anxiety-related behavior using an Elevated Plus Maze (EPM) test. Metal-exposed pups had lower body weights and elevated blood and brain concentrations of the respective metal. Pb-exposed pups had lower hematocrits and higher blood Zn protoporphyrin levels. In contrast, Mn exposed pups had normal hematological parameters but significantly reduced Zn protoporphyrin. Pharmacokinetic studies using (59)Fe showed that intestinal absorption in metal-exposed pups was not different from controls, nor was it correlated with duodenal DMT1 expression. However, intravenously injected (59)Fe was cleared more slowly in Pb-exposed pups resulting in higher plasma levels. The overall tissue uptake of (59)Fe was lower in Mn-exposed and lower in the brain in Pb-exposed pups. The EPM test demonstrated that Mn-exposed, but not Pb-exposed, pups had lower anxiety-related behavior compared to controls. We conclude that gestational and lactational exposures to Mn or Pb differentially alter Fe metabolism and anxiety-related behavior. The data suggest that perturbation in Fe metabolism may contribute to the pathophysiologic consequences of Mn and Pb exposure during early development.

Therapeutic and pathogenetic animal models for Dolichos pruriens

The therapeutic and pathogenetic effects of Dolichos pruriens were evaluated using experimental models in rats. In the therapeutic experiment Wistar rats were housed in a heated environment (25+/-3 degrees C) to induce itch, and treated with ascending potencies D. pruriens (6 cH, 9 cH, 12 cH and 30 cH), each for 10 days. The positive control group received vehicle (ethanol 30% in water). The negative control group received no treatment and were kept at a standard temperature. In the pathogenetic experiment, all animals were kept at a temperature of 20+/-3 degrees C and treated for 30 consecutive days with D. pruriens 6 or 30 cH, or ethanol vehicle, or no treatment. The experiments were performed blind. The statistical analysis used Bartlett's test, followed by ANOVA/Tuckey-Krammer or Kruskal-Wallis/Dunn. The results point to the existence of therapeutic effects, with inhibition of the itching, skin lesions and fur thinning produced by heat, more evident in later observations, with the 9 12, and 30 cH potencies (Kruskal-Wallis/Dunn; P=0.001). No changes were observed in the other parameters, such as open field activity and laterality of the itching. In the pathogenetic experiment, no changes were observed in any parameters examined. We conclude that the proposed experimental model demonstrates the therapeutic effect of D. pruriens, but not its pathogenetic effects.

Reward and anxiety in genetic animal models of childhood depression

One of the most important criteria for major depressive disorder in adults and in children and adolescents as well, is the loss of interest in or pleasure from typically enjoyable experiences or activities: anhedonia. Anxiety is frequently co-morbid with depression. We examined reward and anxiety in genetic animal models of childhood depression. Two different "depressed" lines were studied: the Flinders Sensitive Line (FSL) and their controls, Sprague-Dawley (SD) rats and the Wistar Kyoto (WKY) line and their controls, Wistar rats. Recently, we found that prepubertal rats (about 35 days old) from these lines exhibited increased immobility in the swim test, and abnormal social play observed after 24-h isolation. We hypothesized that FSL and WKY prepubertal rats will further show anhedonia in two different behavioral assays: the conditioned place preference test (CPP), examining the rewarding aspect of social interaction and the saccharin preference test. Behavior in the open field paradigm and freezing behavior in the CPP apparatus were also used as measures of anxiety. WKY, but not FSL prepubertal rats, consumed less of the saccharin solution compared to their control line. FSL, and WKY prepubertal rats found social interaction to be rewarding to a similar extent as their control lines, in the CPP test. Only the WKY rats showed anxiety in behavior in the open field and freezing behavior in the CPP paradigm. The results suggest that WKY prepubertal rats are anxious and sensitive to stress-induced anhedonia, while FSL prepubertal rats exhibit none of these symptoms.

Motor behavior and brain enzymatic changes after acute lead intoxication on different strains of mice

Lead is a nonphysiological metal that has been implicated in toxic processes that affect several organ systems in humans and other animals. Although the brain generally has stronger protective mechanisms against toxic substances than other organs have, exposure to lead results in several neurophysiological and behavioral symptoms. The administration of a single injection (i.p.) of lead acetate in mice is a model of acute Pb2 + toxicity. In the present study, this model was used to explore the magnitude of the effect of different doses, time intervals and mice strains on several biobehavioral parameters. We investigated the effects of acute lead acetate administration on body and brain weight, brain lead acetate accumulation and specially, spontaneous locomotion and brain catalase activity. Lead acetate was injected i.p. in outbred (Swiss or CD1) and inbred (BALB/c, C57BL/J6 or DBA/2) mice at doses of 0, 50, 100, 150 or 200 mg/kg. At different time intervals following this acute treatment, several biochemical, physiological and behavioral responses were recorded. Results indicated that acute lead acetate has deleterious dose-dependent effects on brain and body weight. The effect on body weight in the present study was transient, although lead acetate was detected in neural tissues for several days after administration. Spontaneous locomotor activity only was reduced up until 24 hours. The effect of lead on body weight was strain-dependent, with Swiss mice showing greater resistance compared to the other strains. Total brain catalase activity in lead-pretreated Swiss mice showed a significant induction. This enzymatic upregulation could provide a protective mechanism for oxidative stress in these mice.

Lead and spatial vs. cued open field performance

Male Fischer 344 rats received chronic exposure to either water containing 250 ppm lead or tap water. On the first day of the study, rats were allowed to habituate to a 1-m(2) open field arena with a rectilinear grid pattern of food wells on the floor for a 2-min session. On the following 7 days, half the rats were trained (four trials per day, 2-4-min intertrial interval) to find a food location based on extra-maze spatial cues and the other half were trained to find a food location based on a discrete intra-maze cue placed over the baited food well. While lead did not appear to significantly affect motor activity during the habituation phase, lead-exposed spatially trained rats exhibited superior acquisition and performance of the food-rewarded task compared to their controls and their cue-trained lead-exposed and counterparts. Furthermore, by the last day of training, Day 7, lead significantly reduced the relative amount of time spent on the periphery of the maze in spatially and cued-trained rats.

Effect of mercuric chloride and lead acetate treatment during the second stage of rapid post-natal brain growth on the behavioral response to chlorpromazine and on delta-ALA-D activity in weaning rats

During the early post-natal period the brain is extremely sensitive to external agents. In the present study, we examined the effects of the treatment with lead acetate (3.5 or 7.0 mg/kg) and mercuric chloride (2.5 or 5.0 mg/kg) during the early post-natal period (day 8-12) on the behavioral response to chlorpromazine (CPZ) of 22-day-old rats. The effects of these metals on the sulfhydryl-containing enzyme delta-aminolevulinate dehydratase (delta-ALA-D) were also investigated. Mercuric chloride (2.5 mg/kg) did not affect brain enzyme activity, but caused a significant stimulation of renal delta-ALA-D of 24-day-old rats (27%), while animals treated with 5 mg/kg HgCl(2) showed a small but significant inhibition of cerebral (10%) and renal delta-ALA-D activity (15%). Lead acetate (3.5 or 7 mg/kg) treatment did not affect renal or cerebral delta-ALA-D. Mercuric chloride treatment (5 mg/kg) changed the pattern of open-field activity and the CPZ-induced catalepsy. However, since the undernutrition that accompanied the metal treatment also caused changes in CPZ-induced catalepsy, the effect of mercury on catalepsy could not be clearly established. Lead acetate treatment (7 mg/kg) changed the pattern of open-field motor activity and abolished the decrease in activity observed in control rats. The cataleptic response of animals to CPZ was also affected by lead acetate treatment (7 mg/kg). The increase in activity is compatible with the hyperactivity described in animals exposed to lead for long periods. Thus, the present study suggests that a short exposure to lead or mercury during suckling (second stage of rapid post-natal brain growth) caused permanent changes in locomotor activity that can be interpreted as hyperactivity. Additionally, the behavioral response to CPZ was affected by metal treatment indicating an alteration in the dopaminergic system.