Effects of prenatal exposure to deltamethrin on forced swimming behavior, motor activity, and striatal dopamine levels in male and female rats

Maternal exposure to deltamethrin during pregnancy and lactation impairs neurodevelopment of male offspring

Deltamethrin (DM) is a highly effective and widely used pyrethroid pesticide. It is an environmental factor affecting public and occupational health and exerts direct toxic effects on the central nervous system. As the major target organs for neurotoxicity of DM, the hippocampus and the cerebellum are critical to the learning and motor function. Pregnant Wistar rats were randomly divided into four groups and gavaged at doses of 0, 1, 4or 10 mg/kg/d DM from gestational day (GD) 0 to postnatal day (PN) 21. The PC12 cells were selected to further verify the regulatory mechanisms of DM on the neurodevelopmental injury. We found that maternal exposure to DM caused learning, memory and motor dysfunction in male offspring. Maternal exposure to DM induced the decrease in the density of hippocampal dendritic spines in male offspring through the reduced expression of M1 mAchRs, which in turn reduced the mediated AKT/mTOR signaling pathway, contributing to the inhibition of dynamic changes of GluA1. Meanwhile, DM exposure inhibited the BDNF/TrkB signaling pathway, thereby reducing phosphorylation of stathmin and impairing cerebellar purkinje cell dendrite growth and development. Taken together, maternal exposure to DM during pregnancy and lactation could impair neurodevelopment of male offspring.

Systematic evaluation of the toxicological effects of deltamethrin exposure in zebrafish larvae

Deltamethrin (DM) is a widely used pesticide and has been generally detected in aquatic systems. To systematically investigate the toxic effects, zebrafish embryos were treated with various concentrations of DM for 120h. The LC₅₀ was determined to be 102 μg L^-1. Lethal concentrations of DM induced severe morphological defects in the surviving individuals. Under non-lethal concentrations, DM suppressed the development of neurons in the larvae, which was associated with the reduction in locomotor activity. DM exposure induced cardiovascular toxicity, including suppressed growth of blood vessels and enhanced heart rates. DM also disrupted the development of bones in the larvae. Moreover, liver degeneration, apoptosis and oxidative stress were observed in the larvae treated with DM. Correspondingly, the transcriptional levels of the genes related to the toxic effects were altered by DM. In conclusion, the results obtained in this study provided evidence that DM showed multiple toxic effects on aquatic organisms.

Antioxidant/protective effects of carob pod (Ceratonia siliqua L.) water extract against deltamethrin-induced oxidative stress/toxicity in zebrafish larvae

In our study, the antioxidant capacity of carob pods water extract (CPWE) against deltamethrin (DM)-induced oxidative stress, a widely used pesticide around the world, was investigated in vitro and in vivo in a zebrafish model. The in vitro antioxidant capacity of the obtained extract was evaluated with different methods using trolox, BHA and BHT standard antioxidants. For in vivo experiments, 4hpf zebrafish embryos were exposed to 10 ppb and 25 ppb DM for 120 h and the larvae were treated with 1-10 and 100 ppm CPWE for 4 h at 72th hours. According to the results obtained, it has been determined that the exposure of zebrafish to DM during the developmental period causes important body malformations, decrease in survival rate, reduction in eye size, shortening in body length and decrease in locomotor activity in the dark period. In addition, according to the results of whole-mount staining, it was determined that DM caused a significant increase in the amount of free oxygen radicals and apoptotic cells. It was also confirmed by metabolome analysis that CPWE application for 4 h reduced DM-induced toxicity and oxidative stress. As a result, it can be said that CPWE has an important antioxidant capacity in eliminating DM-induced oxidative stress.

Effects of pyrethroids on the cerebellum and related mechanisms: a narrative review

Pyrethroids (PYRs) are a group of synthetic organic chemicals that mimic natural pyrethrins. Due to their low toxicity and persistence in mammals, they are widely used today. PYRs exhibit higher lipophilicity than other insecticides, which allows them to easily penetrate the blood-brain barrier and directly induce toxic effects on the central nervous system. Several studies have shown that the cerebellum appears to be one of the regions with the largest changes in biomarkers. The cerebellum, which is extremely responsive to PYRs, functions as a crucial region for storing motor learning memories. Exposure to low doses of various types of PYRs during rat development resulted in diverse long-term effects on motor activity and coordination functions. Reduced motor activity may result from developmental exposure to PYRs in rats, as indicated by delayed cerebellar morphogenesis and maturation. PYRs also caused adverse histopathological and biochemical changes in the cerebellum of mothers and their offspring. By some studies, PYRs may affect granule cells and Purkinje cells, causing damage to cerebellar structures. Destruction of cerebellar structures and morphological defects in Purkinje cells are known to be directly related to functional impairment of motor coordination. Although numerous data support that PYRs cause damage to cerebellar structures, function and development, the mechanisms are not completely understood and require further in-depth studies. This paper reviews the available evidence on the relationship between the use of PYRs and cerebellar damage and discusses the mechanisms of PYRs.

Developmental deltamethrin: Sex-specific hippocampal effects in Sprague Dawley rats

Pyrethroid pesticides are widely used and can cause long-term effects after early exposure. Epidemiological and animal studies reveal associations between pyrethroid exposure and altered cognition following prenatal and/or neonatal exposure. However, little is known about the cellular effects of such exposure. Sprague Dawley rats were gavaged with 0 or 1.0 mg/kg deltamethrin (DLM), a Type II pyrethroid, in corn oil (dose volume 5 mL/kg) once per day from postnatal day (P) 3-20 and assessed shortly after dosing ended or as adults. No effects of DLM exposure were found on striatal dopaminergic markers, nor on AMPA receptor subunits or on NMDA-NR1. However, DLM increased NMDA-NR2A and decreased NMDA-NR2B levels in the hippocampus, in males but not females. Additionally, adult hippocampal CA1 long-term potentiation was increased in DLM-treated males but not females. Potassium stimulated extracellular glutamate release in the hippocampus was not affected using in vivo microdialysis. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) showed increased apoptotic cells in the dentate gyrus of male rats, in the absence of changes in cleaved caspase-3 at P21. Proinflammatory cytokines interferon gamma trended up in striatum, interleukin-1β trended down in nucleus accumbens, IL-13 trended up in hippocampus, and keratinocyte chemoattractant/human growth-regulated oncogene (KC/GRO or CXCL1) was significantly increased in the hippocampus in male DLM-treated rats on P20. The data point to the developing hippocampus as a susceptible region to DLM-induced adverse effects.

Influence of perinatal deltamethrin exposure at distinct developmental stages on motor activity, learning and memory

BACKGROUND

Perinatal exposure to deltamethrin (DM) causes attention-deficit/ hyperactivity disorder-like behaviors. However, the vulnerable time window to DM exposure and the possible mechanism are obscure. We aimed to identify the critical window(s) at perinatal stages for DM exposure and the possible mechanism.

METHOD

Pregnant mice were exposed to DM (0.5 mg/kg) at three different prenatal stages [gestational day (GD) 0-5, 6-15 and 16-birth (16-B)] and early postnatal stage (PD 0-10). Locomotor activity, learning and memory were evaluated using open field and Y-maze test, respectively. Nissl staining and western blots were used to examine the neuronal loss and the protein expression, respectively.

RESULTS

Perinatal exposures to DM had no effect on reproductive and growth index of offspring. However, mice receiving DM exposure during GD 16-B displayed significantly higher mortality suggesting GD 16-B is the most vulnerable time window to DM exposure. Prenatal but not early postnatal DM exposure impaired locomotor activity, learning and memory, and caused neuron loss in the dentate gyrus of male offspring. However, neither prenatal nor postnatal DM exposure affected mouse behavior of female offspring. Prenatal DM exposures decreased the protein levels of NR2A and NR2B in both hippocampi and cerebral cortices of male offspring. However, female mice receiving DM exposure at GD 16-B but not other stages displayed increased expression levels of NR2A and NR2B in hippocampi.

CONCLUSION

Prenatal but not early postnatal DM exposure impairs the neuron development in male but not female mice. Altered NMDA receptor expression may correlate to DM-induced behavioral deficits.

Developmental pyrethroid exposure and age influence phenotypes in a Chd8 haploinsufficient autism mouse model

Hundreds of genes have been associated with autism spectrum disorder (ASD), including loss-of-function mutations in chromodomain helicase DNA binding protein 8 (Chd8). Environmental factors also are implicated in autism risk and have the potential to exacerbate phenotypes in genetically sensitized backgrounds. Here we investigate transcriptional and behavioral phenotypes in a Chd8 haploinsufficient (Chd8V986*/+) mouse line exposed to the pesticide deltamethrin (DM) from conception to postnatal day 22. Vehicle-exposed Chd8V986*/+ mice displayed ASD-associated phenotypes, including anxiety-like behavior and altered sociability, replicating a previous study with this mouse line. A core set of genes was altered in Chd8V986*/+ mice at multiple ages, including Usp11, Wars2, Crlf2, and Eglf6, and proximity ligation data indicated direct binding of CHD8 to the 5' region of these genes. Moreover, oligodendrocyte and neurodegenerative transcriptional phenotypes were apparent in 12 and 18 month old Chd8V986*/+ mice. Following DM exposure, the mutant mice displayed an exacerbated phenotype in the elevated plus maze, and genes associated with vascular endothelial cells were downregulated in the cerebral cortex of older Chd8V986*/+ animals. Our study reveals a gene x environment interaction with a Chd8 haploinsufficient mouse line and points to the importance of investigating phenotypes in ASD animal models across the lifespan.

The association of prenatal and childhood pyrethroid pesticide exposure with school-age ADHD traits

BACKGROUND

Pyrethroid insecticides are commonly used in residential settings, and their use has increased rapidly. Although research has been scarce, they have been reported to be associated with impaired neurodevelopment. Moreover, susceptible exposure windows and the long-term effects of pyrethroids have not been investigated. We examined the association between pyrethroid exposure and attention-deficit/hyperactivity disorder (ADHD) symptoms over time, with exposure windows spanning from the prenatal period to school-age.

METHODS

Using 524 mother-child pairs, we measured urinary concentrations of 3-phenoxybenzoic acid (3-PBA), a major pyrethroid metabolite, and asked parents to fill-out the ADHD Rating Scale IV (ARS). We used Poisson regression to identify the susceptible periods of pyrethroid exposure, by correlating various 3-PBA exposure windows (prenatal, ages 2, 4, 6 and 8) with ADHD symptoms at ages 6 and 8.

RESULTS

Doubling of prenatal and age 2 3-PBA concentrations was associated with increased ADHD symptoms at age 6 (2.7% change, 95% confidence interval [CI]: 0.3, 5.2; 5.2% change [95% CI: 0.5, 10.2], respectively). The 3-PBA concentrations at age 4 and age 6 were linked with ADHD symptoms at age 8 (2.7% change [95% CI: 0.3, 5.3]; 3.3% change [95% CI: 0.2, 6.4], respectively). There were no clear sex-specific patterns in association.

DISCUSSION

Both prenatal and early-childhood exposure to 3-PBA were found to be associated with ADHD symptoms. Exposure during pregnancy, and at ages 2 to 6 were found to be susceptible periods for pyrethroid neurotoxicity at ages 6 and 8.

Review of rodent models of attention deficit hyperactivity disorder

Attention deficit hyperactivity disorder (ADHD) is a polygenic neurodevelopmental disorder that affects 8-12 % of children and >4 % of adults. Environmental factors are believed to interact with genetic predispositions to increase susceptibility to ADHD. No existing rodent model captures all aspects of ADHD, but several show promise. The main genetic models are the spontaneous hypertensive rat, dopamine transporter knock-out (KO) mice, dopamine receptor subtype KO mice, Snap-25 KO mice, guanylyl cyclase-c KO mice, and latrophilin-3 KO mice and rats. Environmental factors thought to contribute to ADHD include ethanol, nicotine, PCBs, lead (Pb), ionizing irradiation, 6-hydroxydopamine, neonatal hypoxia, some pesticides, and organic pollutants. Model validation criteria are outlined, and current genetic models evaluated against these criteria. Future research should explore induced multiple gene KOs given that ADHD is polygenic and epigenetic contributions. Furthermore, genetic models should be combined with environmental agents to test for interactions.

Effects of pyrethroids on brain development and behavior: Deltamethrin

Deltamethrin (DLM) is a Type II pyrethroid pesticide widely used in agriculture, homes, public spaces, and medicine. Epidemiological studies report that increased pyrethroid exposure during development is associated with neurobehavioral disorders. This raises concern about the safety of these chemicals for children. Few animal studies have explored the long-term effects of developmental exposure to DLM on the brain. Here we review the CNS effects of pyrethroids, with emphasis on DLM. Current data on behavioral and cognitive effects after developmental exposure are emphasized. Although, the acute mechanisms of action of DLM are known, how these translate to long-term effects is only beginning to be understood. But existing data clearly show there are lasting effects on locomotor activity, acoustic startle, learning and memory, apoptosis, and dopamine in mice and rats after early exposure. The most consistent neurochemical findings are reductions in the dopamine transporter and the dopamine D1 receptor. The data show that DLM is developmentally neurotoxic but more research on its mechanisms of long-term effects is needed.

Pyrethroid based pesticides - chemical and biological aspects

Human and animal welfare primarily depends on the availability of food and surrounding environment. Over a century and half, the quest to identify agents that can enhance food production and protection from vector borne diseases resulted in the identification and use of a variety of pesticides, of which the pyrethroid based ones emerged as the best choice. Pesticides while improved the quality of life, on the other hand caused enormous health risks. Because of their percolation into drinking water and food chain and usage in domestic settings, humans unintentionally get exposed to the pesticides on a daily basis. The health hazards of almost all known pesticides at a variety of doses and exposure times are reported. This review provides a comprehensive summation on the historical, epidemiological, chemical and biological (physiological, biochemical and molecular) aspects of pyrethroid based insecticides. An overview of the available knowledge suggests that the synthetic pyrethroids vary in their chemical and toxic nature and pose health hazards that range from simple nausea to cancers. Despite large number of reports, studies that focused on identifying the health hazards using doses that are equivalent or relevant to human exposure are lacking. It is high time such studies are conducted to provide concrete evidence on the hazards of consuming pesticide contaminated food. Policy decisions to decrease the residual levels of pesticides in agricultural products and also to encourage organic farming is suggested.

Ambient Pyrethroid Pesticide Exposures in Adult Life and Depression in Older Residents of California's Central Valley

Pyrethroid pesticide exposures may be associated with the onset of depression in later life via disruption of dopaminergic, serotonergic, and neurological functioning. We sought to investigate the association between living near agricultural pyrethroid pesticide applications and depression measures in central California, using two waves (PEG 1&2, total N = 1,654) of a case control study of Parkinson’s disease (PD). At enrollment, participants self-reported history of use of depression medications and dates of MD-diagnosed depression and anxiety. Participants also completed a Geriatric Depression Scale-Short Form upon enrollment. We used the California Pesticide Use Registry to assign estimated ambient pyrethroid pesticide exposures at participant’s home addresses over the 5 years before the index date (date of outcome, or an age-matched year for participants without the outcome). We used logistic and linear regression to evaluate associations between living near any pyrethroid applications over the 5-year index period and measures of depression and anxiety. We also evaluated modification by study wave and PD status. We observed associations of pyrethroids with depression, depression medications, and anxiety (adjusted odds ratio [aOR] depression = 1.54, 95% confidence interval [CI] 1.14, 2.07; aOR depression medications = 1.68, 95% CI 1.25, 2.25; aOR anxiety = 1.60, 95% CI 1.17, 2.18). However, we observed no associations with mild/moderate depressive symptoms according to the GDS score at enrollment (aOR = 1.04, 95% CI 0.77, 1.42). We did not observe a consistent modification of the pyrethroid-depression associations by study wave and PD status. Ambient pyrethroid pesticide exposures may be associated with measures of depression in later life.

Effect of long-term treatment with a mixture of pyrethroids on the expression of genes that govern male germ cell production in rats

Humans are exposed to pyrethroid-based pesticides through agricultural produce. In this study, male Wistar rats were orally treated for 9 to 12 months with a mixture of pyrethroids that is equivalent to one-fifth (high dose; HD) or one-twenty fifth (low dose; LD) of the amount of pyrethroids present in the cereals and rice consumed by an average Indian. In rats treated for 9 months, the spermatogenesis-associated genes Abp, Ar, Cd9, Dax1, Dazap1, Ddx3y, Gdnf, Gfra1, Grth, Inhb, Ovol1, P1, Plzf, Pygo2, Scf, Tgfb1, Tp1, Tp2, and Vim1 were downregulated in both LD and HD groups. In rats treated for 12 months Gdnf, Hsf2, Inhb, Tgfb1, Thy1, and Ybx2 expression was downregulated in both LD and HD groups. Steroidogenesis-associated genes 17-β-Hsd, Gata4, Hmgcr, Hmgcs1, Pde4b, and Tspo gene expression were reduced in both LD- and HD-treated groups treated for 9 months. In 12-month-treated rats, Creb1 expression decreased in both LD and HD groups. The epigenetic reprogramming-associated genes, Dnmt1, Dnmt3a, Dnmt3b, Hdac10, Hp1bp3, Kat3a Kat3b, Mch2ta, Ncoa7, and Sirt1 were downregulated in both HD and LD groups of 9-months-treated rats. In rats treated for 12 months, Hdac10, Mch2ta, Ncoa7, and Sirt1 messenger RNA levels decreased in both the HD and LD groups. Thus, we demonstrate that long-term exposure to a mixture of pyrethroids caused aberrations in the transcriptome of factors involved in sperm production and development.

Residential pyrethroid insecticide use, urinary 3-phenoxybenzoic acid levels, and attention-deficit/hyperactivity disorder-like symptoms in preschool-age children: The Environment and Development of Children study

Previous animal studies have reported that pyrethroids can cause dopamine system abnormalities and attention-deficit/hyperactivity disorder (ADHD) phenotypes. However, epidemiological studies investigating the associations between pyrethroid exposure and ADHD are limited. We aimed to investigate the association between pyrethroid exposure and ADHD-like symptoms among preschool-age children. We used data from 385 children at 4 years of age participating in the Environment and Development of Children (EDC) study. We evaluated pyrethroid exposure through questionnaires and urinary 3-phenoxybenzoic acid (3-PBA) concentrations. We assessed ADHD-like symptoms using the Korean ADHD rating scale (K-ARS). We conducted negative binomial regressions to evaluate the associations between pyrethroid exposure and ADHD-like symptoms. Residential use of insecticide adhesive (β = 0.42, 95% CI: 0.11, 0.74) and insecticide spray (β = 0.33, 95% CI: 0.08, 0.59) was associated with an increase in log-transformed creatinine-adjusted urinary 3-PBA concentrations. Residential insecticide adhesive use was associated with a 51.6% increase in K-ARS scores (95% confidence interval [CI]: 6.3, 116.1) among boys, when compared with non-users. When compared with creatinine-adjusted 3-PBA levels <0.50 μg/g creatinine, creatinine-adjusted 3-PBA levels ≥3.80 μg/g creatinine were associated with a 58% increase in K-ARS scores (95% CI: 0.1, 150.5) among boys. We found associations of residential pyrethroid insecticide use and urinary 3-PBA concentrations with K-ARS scores among preschool-age boys. Since the present study explored cross-sectional associations in preschool-age children, the possibility of reverse causality cannot be dismissed. Further studies implementing a cohort study design are warranted.

Deltamethrin Exposure Daily From Postnatal Day 3-20 in Sprague-Dawley Rats Causes Long-term Cognitive and Behavioral Deficits

Pyrethroids are synthetic insecticides that act acutely on voltage gated sodium channels to prolong channel opening and depolarization. Epidemiological studies find that exposure to pyrethroids are associated with neurological and developmental abnormalities in children. The long-term effects of type II pyrethroids, such as deltamethrin (DLM), on development have received little attention. We exposed Sprague-Dawley rats to DLM by gavage at doses of 0, 0.25, 0.5, and 1.0 mg/kg/day from postnatal day (P) 3-20 in a split-litter design. Following behavioral testing as adults, monoamine levels, release, and mRNA were assessed via high performance liquid chromatography, microdialysis, and qPCR, respectively. Long-term potentiation (LTP) was assessed at P25-35. Developmental DLM exposure resulted in deficits in allocentric and egocentric learning and memory, increased startle reactivity, reduced conditioned contextual freezing, and attenuated MK-801 induced hyperactivity compared with controls. Startle and egocentric learning were preferentially affected in males. Deltamethrin-treated rats exhibited increased CA1 hippocampal LTP, decreased extracellular dopamine release by microdialysis, reduced dopamine D1 receptor mRNA expression in neostriatum, and decreased norepinephrine levels in the hippocampus. The data indicate that neonatal DLM exposure has adverse long-term effects on learning, memory, startle, glutamatergic function, LTP, and norepinephrine.

Social behavior effects of diphenyl dimethyl bicarboxylate (DDB) in the sensory contact model

Sensory contact model (SCM) permits the evolution of diverse psychopathological states by the repeated antagonistic interactions between male mice. Biphenyl dimethyl dicarboxylate (DDB) is used as a hepatoprotective agent. The present work aimed to study the possible effects of DDB on social behavior developed by SCM by studying its effects on the transformation process to aggressive and submissive behaviors. Besides, measuring behavioral changes using the open field test (OFT) and the elevated plus maze test (EPM), neurochemical parameters [serotonin (5HT), norepqinephrine (NE), and dopamine(DA)], and immunological changes (total leucocyte count, differential leucocytic count, and evaluation of bone marrow lymphocytes count and viability assessment). Adult male Swiss mice were used; DDB was given in a dose of 100 mg/kg by oral gavage daily for 2 weeks from the fifth day to the last day of the SCM. The present study concluded that administration of DDB to the SCM involved animals was shown to be associated with significant positive impacts on the behavior of depressed partner in the SCM which were manifested by decreased latency and increased ambulation and rearing in OFT, increased number of entry in the open arm/total no of entries in EPM. This was associated with changes in brain levels of neurotransmitters which were manifested by increased NE and decreased DA, as well as the examined immunity related parameters which were manifested by increased total leucocyte count, bone marrow lymphocytes, and monocytes. So DDB can be used as a supportive antidepressant agent in patients with liver impairment and should be avoided in aggressive ones. However, more randomized controlled trials should be carried out to ascertain these effects.

Prenatal Deltamethrin Exposure-Induced Cognitive Impairment in Offspring Is Ameliorated by Memantine Through NMDAR/BDNF Signaling in Hippocampus

Background: Pyrethroids have been widely used in residential and agricultural areas. However, little is known about the effects of prenatal exposure to deltamethrin on cognition in early development of offspring. In this study, the effects of prenatal exposure to deltamethrin on learning and memory abilities, N-methyl-D-aspartate receptor (NMDAR) subunits, brain derived neurotrophic factor (BDNF), Tyrosine kinase B (TrkB) receptor, and phosphorylated cAMP response element binding protein (pCREB) in the hippocampus of offspring rats were investigated.

Experimental Approaches: Groups each of six female SD rats, as F0-generation, were administered with deltamethrin (0, 0.54, 1.35, and 2.7, 9 mg/kg), or memantine (10 mg/kg), or co-administered with deltamethrin (9 mg/kg) and memantine (10 mg/kg) daily by gavage during pregnancy. The learning and memory ability was evaluated using Morris water maze (MWM) task on postnatal day 21. The expression of NMDAR (GluN1, GluN2A, and GluN2B), BDNF, pTrkB/TrkB, and pCREB/CREB in hippocampus were assessed with western blotting.

Results: Prenatal exposure to a relatively low dose of deltamethrin (2.7, 1.35, and 0.54 mg/kg) had no impact on learning and memory abilities or the expression of NMDAR, BDNF, pTrkB, and pCREB in the hippocampus of the exposed offspring. The group treated with 9 mg/kg deltamethrin showed impaired cognitive abilities and decreased expression levels of GluN1, GluN2A, GluN2B, BDNF, pCREB/CREB, and pTrkB/TrkB in the hippocampus. However, the declined cognitive ability were ameliorated by memantine treatment with increased GluN1, GluN2A, GluN2B, BDNF, pCREB/CREB, and pTrkB/TrkB expression in the hippocampus.

Conclusion and Implications: Prenatal exposure to a relatively high does of deltamethrin (9 mg/kg) alters cognition in offsprings and that this cognitive dysfunction can be ameliorated by memantine treatment. Moreover, NMDAR/BDNF signaling may be associated with the effects of prenatal exposure to deltamethrin on cognitive ability in offspring.

Prenatal exposure to lambda-cyhalothrin alters brain dopaminergic signaling in developing rats

The present study is focused to decipher the molecular mechanisms associated with dopaminergic alterations in corpus striatum of developing rats exposed prenatally to lambda-cyhalothrin (LCT), a new generation type II synthetic pyrethroid. There was no significant change in the mRNA and protein expression of DA-D1 receptors at any of the doses of LCT (0.5, 1 and 3mg/kg body weight) in corpus striatum of developing rats exposed prenatally to LCT on PD22 and PD45. Prenatal exposure to LCT (1 and 3mg/kg body weight) resulted to decrease the levels of mRNA and protein of DA-D2 receptors in corpus stratum of developing rats on PD22 as compared to controls. Decrease in the binding of 3H-Spiperone in corpus striatum, known to label DA-D2 receptors was also distinct in developing rats on PD22. These rats also exhibited decrease in the expression of proteins - TH, DAT and VMAT2 involved in pre-dopaminergic signaling. Further, decrease in the expression of DARPP-32 and pCREB associated with increased expression of PP1α was evident in developing rats on PD22 as compared to controls. Interestingly, a trend of recovery in the expression of these proteins was observed in developing rats exposed to LCT at moderate dose (1.0mg/kg body weight) while alteration in the expression of these proteins continued to persist in those exposed at high dose (3.0mg/kg body weight) on PD45 as compared to respective controls. No significant change in the expression of any of these proteins was observed in corpus striatum of developing rats prenatally exposed to LCT at low dose (0.5mg/kg body weight) on PD22 and PD45 as compared to respective controls. The results provide interesting evidence that alterations in dopaminergic signaling on LCT exposure are due to selective changes in DA-D2 receptors in corpus striatum of developing rats. Further, these changes could be attributed to impairment in spontaneous motor activity on LCT exposure in developing rats.

Developmental neurotoxicity of succeeding generations of insecticides

Insecticides are by design toxic. They must be toxic to effectively kill target species of insects. Unfortunately, they also have off-target toxic effects that can harm other species, including humans. Developmental neurotoxicity is one of the most prominent off-target toxic risks of insecticides. Over the past seven decades several classes of insecticides have been developed, each with their own mechanisms of effect and toxic side effects. This review covers the developmental neurotoxicity of the succeeding generations of insecticides including organochlorines, organophosphates, pyrethroids, carbamates and neonicotinoids. The goal of new insecticide development is to more effectively kill target species with fewer toxic side effects on non-target species. From the experience with the developmental neurotoxicity caused by the generations of insecticides developed in the past advice is offered how to proceed with future insecticide development to decrease neurotoxic risk.

Neurodevelopmental consequences of gestational and lactational exposure to pyrethroids in rats

Indiscriminate use of pyrethroids has raised serious health related concerns, especially about their effects on children. The present study was designed to assess the developmental neurotoxicity of two pyrethroids; bifenthrin (BIF) and β-cyfluthrin (CYF) administered at 1/15 of LD₅₀ in rats. Pregnant females were exposed to the test compounds orally throughout gestation and lactation periods. Neonates were weighed and sexed at birth and were observed for any gross abnormality. Growth, viability and weaning indices were calculated during the lactation period. Exposure to both the compounds did not alter the physical developmental parameters viz. eye opening, pinna detachment, and fur appearance. CYF significantly impaired growth and survivability of pups. Behavioral endpoints assessed in neonates (surface righting, pivoting, and negative geotaxis reflex) as well as adults (motor activity and motor coordination) exhibited marked effect of CYF treatment. Administration of BIF to pregnant dams impaired pivoting in neonates. Decreased locomotion in the open-field and impaired rota-rod performance were also witnessed in BIF-exposed animals. Enhanced oxidative stress was seen in corpus striatum, cerebellum, and hippocampus regions of the brain; reduced catalase, superoxide dismutase, and glutathione peroxidase activities were measured in BIF and CYF treated weanlings. Acetylcholinesterase activity was also found to be lowered following administration of both compounds at PND 21. The present results suggest that exposure to pyrethroids during critical periods of growth can induce long term effects on the behavior of animals. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 1761-1770, 2016.

Immunohistochemical Changes in the Mouse Striatum Induced by the Pyrethroid Insecticide Permethrin

Epidemiological studies have linked insecticide exposure and Parkinson's disease. In addition, some insecticides produce damage or physiological disruption within the dopaminergic nigrostriatal pathway of non-humans. This study employed immunohistochemical analysis in striatum of the C57BL/6 mouse to clarify tissue changes suggested by previous pharmacological studies of the pyrethroid insecticide permethrin. Dopamine transporter, tyrosine hydroxylase, and glial fibrillary acidic protein immunoreactivities were examined in caudate-putamen to distinguish changes in amount of dopamine transporter immunoreactive protein from degeneration or other damage to dopaminergic neuropil. Weight-matched pairs of pesticide-treated and vehicle-control mice were dosed and sacrificed on the same days. Permethrin at 0.8, 1.5 and 3.0 mg/kg were the low doses and at 200 mg/kg the high dose. Brains from matched pairs of mice were processed on the same slides using the avidin-biotin technique. Four fields were morphometrically located in each of the serial sections of caudateputamen, digitally photographed, and immunopositive image pixels were counted and compared between members of matched pairs of permethrin-treated and vehicle-control mice. For low doses, only 3.0 mg/kg produced a significant decrease in dopamine transporter immunostaining. The high dose of permethrin did not produce a significant change in dopamine transporter or tyrosine hydroxylase immunostaining, but resulted in a significant increase in glial fibrillary acidic protein immunostaining. These data suggest that a low dose of permethrin can reduce the amount of dopamine transporter immunoreactive protein in the caudate-putamen. They also suggest that previously reported reductions in dopamine uptake of striatal synaptosomes of high-dose mice may be due to nondegenerative tissue damage within this region as opposed to reductions of dopamine transporter protein or death of nigrostriatal terminals. These data provide further evidence that insecticides can affect the primary neurodegenerative substrate of Parkinson's disease.

Propentofylline treatment on open field behavior in rats with focal ethidium bromide-induced demyelination in the ventral surface of the brainstem

Propentofylline (PPF) is a xanthine derivative with pharmacological effects that are distinct from those of classic methylxanthines. It depresses the activation of microglial cells and astrocytes, which is associated with neuronal damage during neural inflammation and hypoxia. Our previous studies showed that PPF improved remyelination following gliotoxic lesions that were induced by ethidium bromide (EB). In the present study, the long-term effects of PPF on open field behavior in rats with EB-induced focal demyelination were examined. The effects of PPF were first evaluated in naive rats that were not subjected to EB lesions. Behavior in the beam walking test was also evaluated during chronic PPF treatment because impairments in motor coordination can interfere with behavior in the open field. The results showed that PPF treatment in unlesioned rats decreased general activity and caused motor impairment in the beam walking test. Gliotoxic EB injections increased general activity in rats that were treated with PPF compared with rats that received saline solution. Motor incoordination was also attenuated in PPF-treated rats. These results indicate that PPF reversed the effects of EB lesions on behavior in the open field and beam walking test.

Laboratory Rodent Diets Contain Toxic Levels of Environmental Contaminants: Implications for Regulatory Tests

The quality of diets in rodent feeding trials is crucial. We describe the contamination with environmental pollutants of 13 laboratory rodent diets from 5 continents. Measurements were performed using accredited methodologies. All diets were contaminated with pesticides (1-6 out of 262 measured), heavy metals (2-3 out of 4, mostly lead and cadmium), PCDD/Fs (1-13 out of 17) and PCBs (5-15 out of 18). Out of 22 GMOs tested for, Roundup-tolerant GMOs were the most frequently detected, constituting up to 48% of the diet. The main pesticide detected was Roundup, with residues of glyphosate and AMPA in 9 of the 13 diets, up to 370 ppb. The levels correlated with the amount of Roundup-tolerant GMOs. Toxic effects of these pollutants on liver, neurodevelopment, and reproduction are documented. The sum of the hazard quotients of the pollutants in the diets (an estimator of risk with a threshold of 1) varied from 15.8 to 40.5. Thus the chronic consumption of these diets can be considered at risk. Efforts toward safer diets will improve the reliability of toxicity tests in biomedical research and regulatory toxicology.

Association of pyrethroid pesticide exposure with attention-deficit/hyperactivity disorder in a nationally representative sample of U.S. children

BACKGROUND

Pyrethroid pesticides cause abnormalities in the dopamine system and produce an ADHD phenotype in animal models, with effects accentuated in males versus females. However, data regarding behavioral effects of pyrethroid exposure in children is limited. We examined the association between pyrethroid pesticide exposure and ADHD in a nationally representative sample of US children, and tested whether this association differs by sex.

METHODS

Data are from 8-15 year old participants (N = 687) in the 2001-2002 National Health and Nutrition Examination Survey. Exposure was assessed using concurrent urinary levels of the pyrethroid metabolite 3-phenoxybenzoic acid (3-PBA). ADHD was defined by either meeting Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition criteria on the Diagnostic Interview Schedule for Children (DISC) or caregiver report of a prior diagnosis. ADHD symptom counts were determined via the DISC. Multivariable logistic regression examined the link between pyrethroid exposure and ADHD, and poisson regression investigated the link between exposure and ADHD symptom counts.

RESULTS

Children with urinary 3-PBA above the limit of detection (LOD) were twice as likely to have ADHD compared with those below the LOD (adjusted odds ratio [aOR] 2.42; 95 % confidence interval [CI] 1.06, 5.57). Hyperactive-impulsive symptoms increased by 50 % for every 10-fold increase in 3-PBA levels (adjusted count ratio 1.50; 95 % CI 1.03, 2.19); effects on inattention were not significant. We observed possible sex-specific effects: pyrethroid biomarkers were associated with increased odds of an ADHD diagnosis and number of ADHD symptoms for boys but not girls.

CONCLUSIONS

We found an association between increasing pyrethroid pesticide exposure and ADHD which may be stronger for hyperactive-impulsive symptoms compared to inattention and in boys compared to girls. Given the growing use of pyrethroid pesticides, these results may be of considerable public health import.

Developmental Deltamethrin Exposure Causes Persistent Changes in Dopaminergic Gene Expression, Neurochemistry, and Locomotor Activity in Zebrafish

Pyrethroids are commonly used insecticides that are considered to pose little risk to human health. However, there is an increasing concern that children are more susceptible to the adverse effects of pesticides. We used the zebrafish model to test the hypothesis that developmental exposure to low doses of the pyrethroid deltamethrin results in persistent alterations in dopaminergic gene expression, neurochemistry, and locomotor activity. Zebrafish embryos were treated with deltamethrin (0.25-0.50 μg/l), at concentrations below the LOAEL, during the embryonic period [3-72 h postfertilization (hpf)], after which transferred to fresh water until the larval stage (2-weeks postfertilization). Deltamethrin exposure resulted in decreased transcript levels of the D1 dopamine (DA) receptor (drd1) and increased levels of tyrosine hydroxylase at 72 hpf. The reduction in drd1 transcripts persisted to the larval stage and was associated with decreased D2 dopamine receptor transcripts. Larval fish, exposed developmentally to deltamethrin, had increased levels of homovanillic acid, a DA metabolite. Since the DA system is involved in locomotor activity, we measured the swim activity of larval fish following a transition to darkness. Developmental exposure to deltamethrin significantly increased larval swim activity which was attenuated by concomitant knockdown of the DA transporter. Acute exposure to methylphenidate, a DA transporter inhibitor, increased swim activity in control larva, while reducing swim activity in larva developmentally exposed to deltamethrin. Developmental exposure to deltamethrin causes locomotor deficits in larval zebrafish, which is likely mediated by dopaminergic dysfunction. This highlights the need to understand the persistent effects of low-dose neurotoxicant exposure during development.

The neurotoxicity of organochlorine and pyrethroid pesticides

Organochlorine and pyrethroid compounds represent an old and a new class, respectively, of insecticides. Organochlorines such as DDT, dieldrin, or chlordecone, have been banned, primarily because of environmental issues. DDT is still used in certain countries to fight malaria-bearing mosquitoes, while lindane still finds some limited used against head lice. In contrast, pyrethroids find widespread use because of their efficacy, low environmental persistence, and relatively low mammalian toxicity. Like all insecticides, organochlorines and pyrethroids target the nervous system of insects and of nontarget species. All pyrethroids and DDT interact with the sodium channel; by keeping it open longer, they increase the likelihood of action potentials developing, thus creating a condition of hyperexcitability, whose main clinical sign is tremors. Most other organochlorines (except chlordecone), as well as certain (type II) pyrethroids, block the chloride channels of the GABA-A receptor, and cause seizures. Evidence of an association between exposure to organochlorine and pyrethroid insecticides and neurodegenerative diseases (e.g., Parkinson's disease) is weak, at best.

Pyrethroid pesticide exposure and parental report of learning disability and attention deficit/hyperactivity disorder in U.S. children: NHANES 1999-2002

BACKGROUND

Use of pyrethroid insecticides has increased dramatically over the past decade; however, data on their potential health effects, particularly on children, are limited.

OBJECTIVE

We examined the cross-sectional association between postnatal pyrethroid exposure and parental report of learning disability (LD) and attention deficit/hyperactivity disorder (ADHD) in children 6-15 years of age.

METHODS

Using logistic regression, we estimated associations of urinary metabolites of pyrethroid insecticides with parent-reported LD, ADHD, and both LD and ADHD in 1,659-1,680 children participating in the National Health and Nutrition Examination Survey (1999-2002).

RESULTS

The prevalence rates of parent-reported LD, ADHD, and both LD and ADHD were 12.7%, 10.0%, and 5.4%, respectively. Metabolite detection frequencies for 3-PBA [3-phenoxybenzoic acid], cis-DCCA [cis-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid], and trans-DCCA [trans-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acid] were 77.1%, 35.6%, and 33.9%, respectively. The geometric mean 3-PBA concentration was 0.32 μg/L (median = 0.31 μg/L; interquartile rage = 0.10-0.89 μg/L). cis- and trans-DCCA 75th-percentile concentrations were 0.21 μg/L and 0.68 μg/L, respectively. Log10-transformed 3-PBA concentrations were associated with adjusted odds ratios (ORs) of 1.18 (95% CI: 0.92, 1.51) for parent-reported LD, 1.16 (95% CI: 0.85, 1.58) for ADHD, and 1.45 (95% CI: 0.92, 2.27) for both LD and ADHD. Adjusted ORs remained nonsignificant and decreased after controlling for creatinine and other environmental chemicals previously linked to altered neurodevelopment. Similarly, no significant associations were observed for cis- and trans-DCCA.

CONCLUSIONS

Postnatal pyrethroid exposure was not associated with parental report of LD and/or ADHD. Given the widespread and increasing use of pyrethroids, future research should evaluate exposures at current levels, particularly during critical windows of brain development.

Evaluation of changes in monoamine levels and apoptosis induced by cyfluthrin in rats

The aim of this study was to evaluate monoamine and mitochondrial cytochrome c levels and lipid peroxidation in adult male rats treated with cyfluthrin (14 mg kg⁻¹dose; approximately 1/10 of the LD₅₀value) for 14 days. This study also examined cyfluthrin induced-apoptosisviathe signaling proteins Bcl-2, caspase-9 and caspase-3, and possible anti-apoptotic effects of Alfa-basic crystallin.

Urinary metabolites of organophosphate and pyrethroid pesticides and behavioral problems in Canadian children

BACKGROUND

Exposure to organophosphate pesticides has been associated with neurobehavioral deficits in children, although data on low levels of exposure experienced by the general population are sparse. Pyrethroids are insecticides rapidly gaining popularity, and epidemiological evidence on their potential effects is lacking.

OBJECTIVE

We examined the association between exposure to organophosphate and pyrethroid pesticides, indicated by urinary metabolites, and parentally reported behavioral problems in children.

METHODS

We used data on children 6-11 years of age from the Canadian Health Measures Survey (2007-2009). We used logistic regressions to estimate odds ratios (ORs) for high scores on the Strengths and Difficulties Questionnaire (SDQ), which may indicate behavioral problems, in association with concentrations of pyrethroid and organophosphate metabolites in the urine of 779 children, adjusting for covariates (sex, age, race/ethnicity, income, parental education, blood lead levels, maternal smoking during pregnancy, and others).

RESULTS

At least one urinary metabolite for organophosphates was detected in 91% of children, and for pyrethroids in 97% of children. Organophosphate metabolites were not significantly associated with high SDQ scores. The pyrethroid metabolite cis-DCCA [3-(2,2-dichlorovinyl)-2,2-dimethylycyclopropane carboxylic acid] was significantly associated with high scores for total difficulties on the SDQ (OR for a 10-fold increase = 2.0; 95% CI: 1.1, 3.6), and there was a nonsignificant association with trans-DCCA (OR = 1.6; 95% CI: 0.9, 3.0).

CONCLUSION

In contrast with previous studies, we did not observe an association between exposure to organophosphate pesticides and behavioral scores in children. However, some pyrethroid urinary metabolites were associated with a high level of parent-reported behavioral problems. Longitudinal studies should be conducted on the potential risks of pyrethroids.

Involvement of dopaminergic and serotonergic systems in the neurobehavioral toxicity of lambda-cyhalothrin in developing rats

In view of extensive uses of lambda-cyhalothrin, a new generation type II synthetic pyrethroid, human exposure is quite imminent. The present study has therefore been carried out to investigate effect of lambda-cyhalothrin on brain dopaminergic and serotonergic systems and functional alterations associated with them. Post-lactational exposure to lambda-cyhalothrin (1.0 mg/kg or 3.0 mg/kg body weight, p.o.) from PD22 to PD49 caused a significant decrease in the motor activity and rota-rod performance in rats on PD50 as compared to controls. Decrease in motor activity in lambda-cyhalothrin treated rats was found to persist 15 days after withdrawal of exposure on PD65 while a trend of recovery in rota-rod performance was observed. A decrease in the binding of ³H-Spiperone, known to label dopamine-D2 receptors in corpus striatum associated with decreased expression of tyrosine hydroxylase (TH)-immunoreactivity and TH protein was observed in lambda-cyhalothrin treated rats on PD50 and PD65 compared to controls. Increase in the binding of ³H-Ketanserin, known to label serotonin-2A receptors in frontal cortex was observed in lambda-cyhalothrin exposed rats on PD50 and PD65 as compared to respective controls. The changes were more marked in rats exposed to lambda-cyhalothrin at a higher dose (3.0 mg/kg) and persisted even 15 days after withdrawal of exposure. The results exhibit vulnerability of developing rats to lambda-cyhalothrin and suggest that striatal dopaminergic system is a target of lambda-cyhalothrin. Involvement of serotonin-2A receptors in the neurotoxicity of lambda-cyhalothrin is also suggested. The results further indicate that neurobehavioral changes may be more intense in case exposure to lambda-cyhalothrin continues.

Veterinary Pesticides

Veterinary pesticides are used to treat a range of parasitic conditions in companion and farm animals. These products are based on a number of different compounds with different modes of action and different spectra of toxicity. The older agents include the synthetic pyrethroids and organophosphorus compounds, while the newer examples include, for example, representatives of the insect growth promoters, the neonicotinoids, and the oxadiazones. For many of these compounds, toxicity is associated with their pharmacological activity or mode of action. Thus the synthetic pyrethroids and the organophosphorus compounds exert neurotoxic effects. For others, toxicity may be associated with mechanisms that are independent of their mode of action. When used according to the manufacturer's instructions, these products are generally safe and efficacious. However, accidental contamination and misuse can lead to toxicity in operators and treated animals. These compounds are important in the treatment of parasitic disease in animals and their regulation and uses are based on favourable risk-benefit outcomes.

Neurochemical changes following a single dose of polybrominated diphenyl ether 47 in mice

Polybrominated diphenyl ethers (PBDEs) are commonly used as commercial flame retardants in a variety of products, including plastics and textiles. Previous studies in our laboratory, and in the literature, showed that exposure to a specific PBDE congener (PBDE 47) during a critical period of brain development may lead to developmental delays and hyperactivity in adulthood. To date, the underlying causes of these behavioral alterations are unknown, although in vitro studies linked PBDEs with potential alterations in neurotransmitter levels, particularly acetylcholine (ACh) and dopamine (DA). Alterations in DA function have also been noted in cases of hyperactivity in rodents and humans. The current study examined monoamine levels in male mice acutely exposed to corn oil vehicle or PBDE 47 (1, 10, or 30 mg/kg) on postnatal day (PND) 10. Animals were sacrificed on PND 15, PND 20, and in adulthood (131-159 days old). The cortex, striatum, and cerebellum were isolated and analyzed by high-performance liquid chromatography to determine the concentration of monoamines within each brain region. A statistically significant increase in DA levels was seen within the cortex, regardless of age, but only in the 10-mg/kg PBDE treatment group. While these effects did not show a monotonic dose response, we previously reported hyperactivity in littermates in the same dose group, but not at the lower or higher dose. Thus, early developmental exposure to PBDE 47 alters the levels of cortical DA in male mice, which may correlate with behavioral observations in littermates.

Developmental neurotoxicity of pyrethroid insecticides in zebrafish embryos

Pyrethroid insecticides are one of the most commonly used residential and agricultural insecticides. Based on the increased use of pyrethroids and recent studies showing that pregnant women and children are exposed to pyrethroids, there are concerns over the potential for developmental neurotoxicity. However, there have been relatively few studies on the developmental neurotoxicity of pyrethroids. In this study, we sought to investigate the developmental toxicity of six common pyrethroids, three type I compounds (permethrin, resmethrin, and bifenthrin) and three type II compounds (deltamethrin, cypermethrin, and lambda-cyhalothrin), and to determine whether zebrafish embryos may be an appropriate model for studying the developmental neurotoxicity of pyrethroids. Exposure of zebrafish embryos to pyrethroids caused a dose-dependent increase in mortality and pericardial edema, with type II compounds being the most potent. At doses approaching the LC(50), permethrin and deltamethrin caused craniofacial abnormalities. These findings are consistent with mammalian studies demonstrating that pyrethroids are mildly teratogenic at very high doses. However, at lower doses, body axis curvature and spasms were observed, which were reminiscent of the classic syndromes observed with pyrethroid toxicity. Treatment with diazepam ameliorated the spasms, while treatment with the sodium channel antagonist MS-222 ameliorated both spasms and body curvature, suggesting that pyrethroid-induced neurotoxicity is similar in zebrafish and mammals. Taken in concert, these data suggest that zebrafish may be an appropriate alternative model to study the mechanism(s) responsible for the developmental neurotoxicity of pyrethroid insecticides and aid in identification of compounds that should be further tested in mammalian systems.

Potential developmental neurotoxicity of pesticides used in Europe

Pesticides used in agriculture are designed to protect crops against unwanted species, such as weeds, insects, and fungus. Many compounds target the nervous system of insect pests. Because of the similarity in brain biochemistry, such pesticides may also be neurotoxic to humans. Concerns have been raised that the developing brain may be particularly vulnerable to adverse effects of neurotoxic pesticides. Current requirements for safety testing do not include developmental neurotoxicity. We therefore undertook a systematic evaluation of published evidence on neurotoxicity of pesticides in current use, with specific emphasis on risks during early development. Epidemiologic studies show associations with neurodevelopmental deficits, but mainly deal with mixed exposures to pesticides. Laboratory experimental studies using model compounds suggest that many pesticides currently used in Europe--including organophosphates, carbamates, pyrethroids, ethylenebisdithiocarbamates, and chlorophenoxy herbicides--can cause neurodevelopmental toxicity. Adverse effects on brain development can be severe and irreversible. Prevention should therefore be a public health priority. The occurrence of residues in food and other types of human exposures should be prevented with regard to the pesticide groups that are known to be neurotoxic. For other substances, given their widespread use and the unique vulnerability of the developing brain, the general lack of data on developmental neurotoxicity calls for investment in targeted research. While awaiting more definite evidence, existing uncertainties should be considered in light of the need for precautionary action to protect brain development.

Vanadium exposure through lactation produces behavioral alterations and CNS myelin deficit in neonatal rats

The current study was performed to assess the vanadium(V)-induced developmental toxicity in sucklings of Wistar rats. Dams of treated litters were intraperitoneally injected with 3 mg NaVO(3)/kg body weight/day during 12 days starting on postnatal day (PND) 10. Surface righting reflex, negative geotaxy and hindlimb support tests were performed on pups every 48 h, from 8th to 18th PND. Open field test was performed on the 21st PND. On 22nd PND, some animals were transcardially perfusion-fixed and their brains were removed and cut with a cryostat. Brain sections were processed for myelin histochemistry and for anti-myelin basic protein immunohistochemistry. Delay in eye opening and decreased muscular strength and locomotion were observed in V-exposed pups of both sexes. A decreased myelin staining in corpus callosum and cerebellum in these pups was also observed. Results suggest that vanadium exposure through lactation would induce neurotoxicity in rat developing CNS.

Dopaminergic system modulation, behavioral changes, and oxidative stress after neonatal administration of pyrethroids

Pyrethroids are a class of insecticides involved in different neurological disorders. They cross the blood-brain barrier and exert their effect on dopaminergic system, contributing to the burden of oxidative stress in Parkinson's disease through several pathways. The aim of the present study was to evaluate the effect of neonatal exposition to permethrin and cypermethrin (1/10 of DL(50)) in rats from the eighth to the fifteenth day of life. Open-field studies showed increased spontaneous locomotor activity in the groups treated with permethrin and the one treated with cypermethrin, while a higher number of center entries and time spent in the center was observed for the cypermethrin-treated group. Lower dopamine and higher homovanillic acid levels were measured in the striatum from both treated groups. A reduction of blood glutathione peroxidase content was measured, while no change in blood superoxide dismutase was observed. Carbonyl group formation increased in striatum, but not in erythrocytes. Lipid peroxidation occurred in erythrocytes, but not in striatum. No changes in fluidity at different depths of plasma membrane were measured in striatum or erythrocytes. The activation of monocyte NADPH oxidase by phorbol esters (PMA) shows that superoxide anion production was reduced in the pyrethroid-treated groups compared to the control group. Our studies suggest that neonatal exposition to permethrin or cypermethrin induces long-lasting effects after developmental exposure giving changes in open-field behaviors, striatal monoamine level, and increased oxidative stress. Although the action of pyrethroids on various target cells is different, a preferential interaction with the extracellular side of plasma membrane proteins can be observed.

Long lasting effects of prenatal exposure to deltamethrin on cerebral and hepatic cytochrome P450s and behavioral activity in rat offspring

Prenatal exposure to different doses (0.25, or 0.5 or 1.0 mg/kg corresponding to 1/320 th or 1/160 th or 1/80 th of LD50) of deltamethrin to the pregnant Wistar rats from gestation day 5 to 21 were found to produce a dose dependent increase in the activity of cytochrome P450 (CYP) dependent 7-ethoxyresorufin-O-deethylase (EROD), 7-pentoxyresorufin-O-dealkylase (PROD) and N-nitrosodimethylamine demethylase (NDMA-D) in brain and liver of offspring postnatally at 3 weeks. The increase in the activity of cytochrome P450 monooxygenases was found to be associated with the increase in the mRNA and protein expression of xenobiotic metabolizing CYP1A, 2B and 2E1 isoenzymes in the brain and liver of offspring. Dose-dependent alterations in the parameters of spontaneous locomotor activity in the offspring postnatally at 3 weeks have indicated that increase in cytochrome P450 activity may lead to the accumulation of deltamethrin and its metabolites to the levels that may be sufficient to alter the behavioral activity of the offspring. Interestingly, the inductive effect on cerebral and hepatic cytochrome P450s was found to persist postnatally up to 6 weeks in the offspring at the relatively higher doses (0.5 and 1.0 mg/kg) of deltamethrin and up to 9 weeks at the highest dose (1.0 mg/kg), though the magnitude of induction was less than that observed at 3 weeks. Alterations in the parameters of spontaneous locomotor activity in the offspring postnatally at 6 and 9 weeks, though significant only in the offspring at 3 and 6 weeks of age, have further indicated that due to the reduced activity of the cytochrome P450s during the ontogeny, the pyrethroid or its metabolites accumulating in the brain may not be cleared from the brain, thereby leading to the persistence in the increase in the expression of cerebral and hepatic cytochrome P450s in the offspring postnatally up to 9 weeks. The data suggests that low dose prenatal exposure to pyrethroids has the potential to produce long lasting effects on the expression of xenobiotic metabolizing cytochrome P450s in brain and liver of the offspring.

A reassessment of the neurotoxicity of pyrethroid insecticides

The pyrethroids are a widely used class of insecticides to which there is significant human exposure. They are however generally regarded as safe to man, and there have been few reports of human fatalities. Their acute toxicity is dominated by pharmacological actions upon the central nervous system (CNS), predominantly mediated by prolongation of the kinetics of voltage-gated sodium channels, although other mechanisms operate. This review summarizes our present understanding of such actions and the pharmacological options to antagonize them. One significant problem is the very clear heterogeneity of pyrethroid sensitivity that is seen across sodium channel subtypes; however, the distribution and function of these across the central nervous system are poorly characterized. The review also provides an overview of recent studies that suggest additional effects of pyrethroids: developmental neurotoxicity, the production of neuronal death, and action mediated via pyrethroid metabolites. The evidence for these is at present equivocal, but all 3 carry important implications for human health.

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).

Reproductive evaluation of two pesticides combined (deltamethrin and endosulfan) in female rats

Data from in vitro studies suggest that the pesticides deltamethrin (D) and endosulfan (E) exert estrogen-like effects. There is concern that interaction between weakly estrogenic compounds can increase their estrogenic potency. The aim of the present study was to determine estrogenic activity in an animal model and the possible female reproductive adverse effects of these pesticides combined. Wistar rats received daily (po), from day 6 of pregnancy to day 21 of lactation, deltamethrin and endosulfan concomitantly: D: 2.0 mg/kg+E: 1.5 mg/kg, or D: 3.0 mg/kg+E: 2.0 mg/kg, or D: 4.0 mg/kg+E: 3.0mg/kg. Some offspring also were exposed directly after weaning. Maternal and reproductive outcome data were assessed. An uterotrophic assay to screen in vivo estrogenic activity of D+E was also performed. A group of female offspring was analyzed for vaginal opening (VO), first estrus, estrous cycle regularity, and weights of the uterus and ovaries. No signs of maternal toxicity were detected. Results from the uterotrophic assay indicate absence of in vivo estrogenic activity of D+E. No significant variations in reproductive endpoints of females were observed. These results suggest that administration of D+E does not pose a reproductive hazard to female rats exposed during critical periods of development, indicating that the combination does not exert estrogen-like effects in vivo or is not delivered to target organs.

Developmental neurotoxicity of pyrethroid insecticides: critical review and future research needs

Pyrethroid insecticides have been used for more than 40 years and account for 25% of the worldwide insecticide market. Although their acute neurotoxicity to adults has been well characterized, information regarding the potential developmental neurotoxicity of this class of compounds is limited. There is a large age dependence to the acute toxicity of pyrethroids in which neonatal rats are at least an order of magnitude more sensitive than adults to two pyrethroids. There is no information on age-dependent toxicity for most pyrethroids. In the present review we examine the scientific data related to potential for age-dependent and developmental neurotoxicity of pyrethroids. As a basis for understanding this neurotoxicity, we discuss the heterogeneity and ontogeny of voltage-sensitive sodium channels, a primary neuronal target of pyrethroids. We also summarize 22 studies of the developmental neurotoxicity of pyrethroids and review the strengths and limitations of these studies. These studies examined numerous end points, with changes in motor activity and muscarinic acetylcholine receptor density the most common. Many of the developmental neurotoxicity studies suffer from inadequate study design, problematic statistical analyses, use of formulated products, and/or inadequate controls. These factors confound interpretation of results. To better understand the potential for developmental exposure to pyrethroids to cause neurotoxicity, additional, well-designed and well-executed developmental neurotoxicity studies are needed. These studies should employ state-of-the-science methods to promote a greater understanding of the mode of action of pyrethroids in the developing nervous system.

The effect of electroconvulsive shock seizures on behaviour induced by dopaminergic agonists and on immobility in the Porsolt test

Male, Wistar rats were given a course of eight electroconvulsive shock seizures (ECS group) or matched handling (control group). They were then tested for locomotion and rearing (7 days post-ECS), for grooming and yawning (9 days post-ECS), and for immobility in the Porsolt test (7, 14 and 21 days post-ECS). Seven days post-seizure, the ECS group showed significantly more locomotion following intraperitoneal administration of apomorphine (0.2 mg/kg), but not following injections of amphetamine (1 mg/kg). Drug-induced rearing was not different in the ECS and control animals. Nine days post-seizure, the ECS group showed significantly more grooming induced by the D-1 dopamine receptor agonist, SKF 38393 (1 mg/kg), but no difference in the yawning induced by the D-2 dopamine receptor agonist, quinpirole (0.05 mg/kg). In the Porsolt test, immobility was decreased in the ECS animals at 7 and 14, but not at 21 days post-ECS. It is concluded that ECS increases activity in the dopaminergic systems of the rat brain for at least 1-2 weeks post-seizure. The beneficial effects of electroconvulsive therapy (ECT) may relate to these dopaminergic alterations.