Effects of repeated oral postnatal exposure to chlorpyrifos on open-field behavior in juvenile rats

Environmental exposure to chlorpyrifos during gestation, APOE polymorphism and the risk on autistic-like behaviors

Autism spectrum disorder (ASD) encompasses several neurodevelopmental conditions characterized by communication and social impairment, as well as repetitive patterns of behavior. However, it can co-occur with other mental conditions such as anxiety. The massive use of chlorpyrifos (CPF) has been linked to the increased prevalence of developmental disorders. Likewise, ASD has also been closely linked to a wide variety of genetic factors. The aims of the present investigation are to study how gestational CPF exposure and APOE polymorphism affects communication skills, early development and mid-term anxiety-like behaviors, as well as, changes in gene expression related to the cholinergic system. C57BL/6J and humanized apoE3 and apoE4 homozygous mice were exposed to 0 or 1 mg/kg/day of CPF through the diet, from gestational day (GD) 12-18. In addition, a group of C57BL/6J females were injected subcutaneously with 300 mg/kg/day of valproic acid (VPA) on GD 12 and 13. This group was used as a positive control for studying some core and associated autism-like behaviors. Communication skills by means of ultrasonic vocalizations and physical/motor development were assessed during the preweaning period, whereas locomotor activity, anxiety-like behaviors and the gene expression of cholinergic elements were evaluated during adolescence. Our results showed that C57BL/6J mice prenatally exposed to CPF or VPA showed a decrease in body weight and a delay in eye opening. Communication and anxiety behavior were affected differently depending on treatment, while gene expression was altered by sex and treatment. In addition, none of the parameters evaluated in apoE transgenic mice exposed to CPF were affected, but there were differences between genotypes. Therefore, we suggest that prenatal CPF exposure and VPA produce divergent effects on communication and anxiety.

Grape seed alleviates lindane-induced oxidative stress and improves growth performance, caecal fermentation and antioxidant capacity in growing rabbits

This study evaluated the protective effect of grape seed on performance, caecal characteristics, blood metabolites and liver antioxidant status in lindane-treated rabbits. Four-week-old New Zealand White rabbits (n = 96) with an initial body weight of 0.750 ± 0.23 g were randomly divided into four groups (n = 24). One group was the control received only corn oil orally, while group L were received lindane daily via gavage in corn oil (4 mg/kg BW; 1/50 LD₅₀ for oral dose), group GS was treated with 50 g grape seed /kg diet, and group LGS treated with a combination of both L and GS for 98 days. Results revealed that final body weight (FBW), average daily gain (ADG), dry matter intake and feed efficiency (FE) were similar between GS and control groups, and achieved the highest FBW and ADG, and the best FE. Caecum pH of the L group increased, while the caecum pH of the GS group decreased sharply. There was a significant increase in the concentration of total VFA, acetic acid, propionic acid and NH₃ -N in the GS group, but butyric acid level decreased. GS treatment resulted in a significant increase in the concentrations of total protein, albumin and AChE. GPx, GST, CAT and SOD activity decreased, but TBARS activity significantly increased in the group L, while GS caused a significant elevation of antioxidant activity in the liver. These results confirm that the antioxidant compounds present in grape seed can alleviate the oxidative stress caused by lindane-induced hepatotoxicity and could be a useful supplement to maintain health and improve performance in rabbits.

3-Indolepropionic acid upturned male reproductive function by reducing oxido-inflammatory responses and apoptosis along the hypothalamic-pituitary-gonadal axis of adult rats exposed to chlorpyrifos

We examined the effect of 3-Indolepropionic acid (3-IPA), an antioxidant on the organophosphorus pesticide chlorpyrifos (CPF)-induced reproductive toxicity in rats. The five experimental rat cohorts were treated per os for 14 consecutive days as follows: Control (Corn oil 2 mL/kg body weight), CPF alone (5 mg/kg), 3-IPA alone (40 mg/kg) and the co-treated rat cohorts (CPF:5 mg/kg + 3-IPA: 20 or 40 mg/kg). Biomarkers of testicular and epididymal function, oxidative stress, myeloperoxidase (MPO) activity and the levels of nitric oxide (NO), reactive oxygen and nitrogen (RONS) species and lipid peroxidation (LPO) were assessed. Also, tumour necrosis factor-alpha (TNF-α), Bcl-2-associated X (Bax) and B cell lymphoma 2 (Bcl-2) proteins were estimated, and tissue histology was microscopically examined. CPF alone significantly (p < 0.05) increased biomarkers of reproductive toxicities were averted in rats co-treated 3-IPA. Decreases in antioxidants and increases in lipid peroxidation and reactive oxygen and nitrogen species were lessened (p < 0.05) in CPF and 3-IPA co-treated rats. CPF mediated increases in TNF-α, NO, Bax, and MPO activity was reduced (p < 0.05) in the epididymis, testes, and hypothalamus of rats co-treated with 3-IPA. In addition, Bcl-2 expression was increased in rats co-treated with 3-IPA dose-dependently. Histopathological examination revealed severe lesions induced by CPF were prevented in rats co-treated with 3-IPA. Our findings demonstrate that exogenous 3-IPA reduced CPF-induced oxidative stress, inflammation, and apoptosis in the epididymis and testes of male rats.

Biodistribution, cardiac and neurobehavioral assessments, and neurotransmitter quantification in juvenile rats following oral administration of aluminum oxide nanoparticles

Little is known about the uptake, biodistribution, and biological responses of nanoparticles (NPs) and their toxicity in developing animals. Here, male and female juvenile Sprague-Dawley rats received four consecutive daily doses of 10 mg/kg Al₂ O₃ NP (diameter: 24 nm [transmission electron microscope], hydrodynamic diameter: 148 nm) or vehicle control (water) by gavage between postnatal days (PNDs) 17-20. Basic neurobehavioral and cardiac assessments were performed on PND 20. Animals were sacrificed on PND 21, and selected tissues were collected, weighed, and processed for histopathology or neurotransmitter analysis. The biodistribution of Al₂ O₃ NP in tissue sections of the intestine, liver, spleen, kidney, and lymph nodes were evaluated using enhanced dark-field microscopy (EDM) and hyperspectral imaging (HSI). Liver-to-body weight ratio was significantly increased for male pups administered Al₂ O₃ NP compared with control. HSI suggested that Al₂ O₃ NP was more abundant in the duodenum and ileum tissue of the female pups compared with the male pups, whereas the abundance of NP was similar for males and females in the other tissues. The abundance of NP was higher in the liver compared with spleen, lymph nodes, and kidney. Homovanillic acid and norepinephrine concentrations in brain were significantly decreased following Al₂ O₃ NP administration in female and male pups, whereas 5-hydroxyindoleacetic acid was significantly increased in male pups. EDM/HSI indicates intestinal uptake of Al₂ O₃ NP following oral administration. Al₂ O₃ NP altered neurotransmitter/metabolite concentrations in juvenile rats' brain tissues. Together, these data suggest that orally administered Al₂ O₃ NP interferes with the brain biochemistry in both female and male pups.

Gestational and perinatal exposure to diazinon causes long-lasting neurobehavioral consequences in the rat

Diazinon is a widely-used organophosphate pesticide. Pulsatile exposure to diazinon during neonatal development has previously been shown cause long-term neurobehavioral impairments in rats. However, the effects of chronic low concentration exposures during perinatal development remain unclear. This experiment evaluated such effects in Sprague-Dawley rats by implanting osmotic pumps in breeder females prior to conception (N = 13-15 litters per condition) which then delivered chronic, zero order kinetic low-level infusions of 0, 114 or 228 ug/day of diazinon throughout pregnancy. One male and one female from each litter was assessed with a battery of behavioral tests that continued from four weeks of age into adulthood. Litter was used as the unit of variance for the analysis of variance test of significance, with sex as a within litter factor. Diazinon treatment condition was the between subjects factor and time or sessions were repeated measures. Chronic diazinon exposure from pre-mating until the neonatal period caused a significant (p < 0.05) increase in percent of time spent on the open arms of the elevated plus maze, an index of risk-taking behavior. Gestational and lactational diazinon exposure also caused a significant (p < 0.05) degree of hyperactivity in the Figure-8 apparatus during adolescence, specifically affecting the early part of the hour-long test session. This effect had dissipated by the time the rats reached adulthood. Diazinon exposure also caused a significant impairment in novel object recognition, a test of cognitive function. Offspring exposed to 228 ug/day diazinon (p < 0.05) showed significantly less preference for the novel vs. familiar object than controls during the first five minutes of the novel object recognition test.

Diphenyl diselenide abrogates brain oxidative injury and neurobehavioural deficits associated with pesticide chlorpyrifos exposure in rats

Exposure to pesticide chlorpyrifos (CPF) is associated with neurodevelopmental toxicity both in humans and animals. Diphenyl diselenide (DPDS) is a simple synthetic organoselenium well reported to possess antioxidant, anti-inflammatory and neuroprotective effects. However, there is paucity of information on the beneficial effects of DPDS on CPF-mediated brain injury and neurobehavioural deficits. The present study investigated the neuroprotective mechanism of DPDS in rats sub-chronically treated with CPF alone at 5 mg/kg body weight or orally co-treated with DPDS at 2.5 and 5 mg/kg body weight for 35 consecutive days. Endpoint analyses using video-tracking software in a novel environment revealed that co-treatment with DPDS significantly (p < 0.05) protected against CPF-mediated locomotor and motor deficits precisely the decrease in maximum speed, total distance travelled, body rotation, absolute turn angle, forelimb grip strength as well as the increase in negative geotaxis and incidence of fecal pellets. The enhancement in the neurobehavioral activities of rats co-treated with DPDS was verified by track plot analyses. Besides, DPDS assuaged CPF-induced decrease in acetylcholinesterase and antioxidant enzymes activities and the increase in myeloperoxidase activity and lipid peroxidation level in the mid-brain, cerebral cortex and cerebellum of the rats. Histologically, DPDS co-treatment abrogated CPF-mediated neuronal degeneration in the cerebral cortex, dentate gyrus and cornu ammonis3 in the treated rats. In conclusion, the neuroprotective mechanisms of DPDS is related to the prevention of oxidative stress, enhancement of redox status and acetylcholinesterase activity in brain regions of the rats. DPDS may be a promising chemotherapeutic agent against brain injury resulting from CPF exposure.

Developmental neurotoxicity in the progeny after maternal gavage with chlorpyrifos

Today, developmental intellectual disorders affect one out of six children in industrialised countries. Intensively used in agriculture, the neurotoxicant pesticide chlorpyrifos (CPF) is known for its environmental persistence and bioaccumulation. Its role has not yet been established in the aetiology of intellectual impairments. Here we assessed whether maternal ingestion of low CPF dose in rats could impair the cerebral function of their progeny. Rat dams received daily CPF exposures (1 mg/kg, per os) during gestation and lactation. Behaviours relevant to mental retardation were measured in the surface righting, negative geotaxis and grip strength at post-natal days (PND) 3 and 7. Open field tests were performed at PND 16, 18 and 20. Fear conditioning was assessed at PND 34. Startle inhibition was tested at PND 31 and 60. According to the results, the progeny of CPF-treated dams showed slower negative geotaxis as neonates, lower novelty exploration as juveniles and faster startle reflex as adolescents and adults. This data suggests that developmental CPF relevant to human exposure may impair novelty-related activity and sensori-motor functions, thus adaptability to the environment. This data supports the hypothesis that CPF may contribute to behavioural disorders including acquisition retardation and consequences as an adult.

Developmental neurotoxicity of the organophosphorus insecticide chlorpyrifos: from clinical findings to preclinical models and potential mechanisms

Organophosphorus (OP) insecticides are pest-control agents heavily used worldwide. Unfortunately, they are also well known for the toxic effects that they can trigger in humans. Clinical manifestations of an acute exposure of humans to OP insecticides include a well-defined cholinergic crisis that develops as a result of the irreversible inhibition of acetylcholinesterase (AChE), the enzyme that hydrolyzes the neurotransmitter acetylcholine (ACh). Prolonged exposures to levels of OP insecticides that are insufficient to trigger signs of acute intoxication, which are hereafter referred to as subacute exposures, have also been associated with neurological deficits. In particular, epidemiological studies have reported statistically significant correlations between prenatal subacute exposures to OP insecticides, including chlorpyrifos, and neurological deficits that range from cognitive impairments to tremors in childhood. The primary objectives of this article are: (i) to address the short- and long-term neurological issues that have been associated with acute and subacute exposures of humans to OP insecticides, especially early in life (ii) to discuss the translational relevance of animal models of developmental exposure to OP insecticides, and (iii) to review mechanisms that are likely to contribute to the developmental neurotoxicity of OP insecticides. Most of the discussion will be focused on chlorpyrifos, the top-selling OP insecticide in the United States and throughout the world. These points are critical for the identification and development of safe and effective interventions to counter and/or prevent the neurotoxic effects of these chemicals in the developing brain. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Spatial learning impairment in prepubertal guinea pigs prenatally exposed to the organophosphorus pesticide chlorpyrifos: Toxicological implications

Exposure of the developing brain to chlorpyrifos (CPF), an organophosphorus (OP) pesticide used extensively in agriculture worldwide, has been associated with increased prevalence of cognitive deficits in children, particularly boys. The present study was designed to test the hypothesis that cognitive deficits induced by prenatal exposure to sub-acute doses of CPF can be reproduced in precocial small species. To address this hypothesis, pregnant guinea pigs were injected daily with CPF (25mg/kg,s.c.) or vehicle (peanut oil) for 10days starting on presumed gestation day (GD) 53-55. Offspring were born around GD 65, weaned on postnatal day (PND) 20, and subjected to behavioral tests starting around PND 30. On the day of birth, butyrylcholinesterase (BuChE), an OP bioscavenger used as a biomarker of OP exposures, and acetylcholinesterase (AChE), a major molecular target of OP compounds, were significantly inhibited in the blood of CPF-exposed offspring. In their brains, BuChE, but not AChE, was significantly inhibited. Prenatal CPF exposure had no significant effect on locomotor activity or on locomotor habituation, a form of non-associative memory assessed in open fields. Spatial navigation in the Morris water maze (MWM) was found to be sexually dimorphic among guinea pigs, with males outperforming females. Prenatal CPF exposure impaired spatial learning more significantly among male than female guinea pigs and, consequently, reduced the sexual dimorphism of the task. The results presented here, which strongly support the test hypothesis, reveal that the guinea pig is a valuable animal model for preclinical assessment of the developmental neurotoxicity of OP pesticides. These findings are far reaching as they lay the groundwork for future studies aimed at identifying therapeutic interventions to treat and/or prevent the neurotoxic effects of CPF in the developing brain.

On the effect of minocycline on the depressive-like behavior of mice repeatedly exposed to malathion: interaction between nitric oxide and cholinergic system

This study was performed to investigate the antidepressant-like effect of minocycline in mice exposed to organophosphate pesticide malathion and possible involvement of nitric oxide/cGMP pathway in this paradigm. Mice were administered specific doses of malathion once daily for 7 consecutive days. After induction of depression, different doses of minocycline were daily injected alone or combined with non-specific NOS inhibitor, L-NAME, specific inducible NOS inhibitor, AG, NO precursor, L-arginine, and PDE5I, sildenafil. After locomotion assessment in open-field test, immobility times were recorded in the FST and TST. Moreover, hippocampal nitrite concentrations and acetylcholinesterase activity were measured. The results showed that repeated exposure to malathion induces depressive-like behavior at dose of 250 mg/kg. Minocycline (160 mg/kg) significantly reduced immobility times in FST and TST (P < 0.001). Combination of sub-effective doses of minocycline (80 mg/kg) with either L-NAME (3 mg/kg) or AG (25 mg/kg) significantly exerted a robust antidepressant-like effect in FST and TST (P < 0.001). Furthermore, minocycline at the same dose which has antidepressant-like effect, significantly reduced hippocampal nitrite concentration. The investigation indicates the essential role for NO/cGMP pathway in malathion-induced depressive-like behavior and antidepressant-like effect of minocycline. Moreover, the interaction between nitrergic and cholinergic systems are suggested to be involved in malathion-induced depression.

Developmental neurotoxicity of monocrotophos and lead is linked to thyroid disruption

Aim:

A role of thyroid disruption in developmental neurotoxicity of monocrotophos (MCP) and lead is studied.

Materials and Methods:

A total of 24 female rats after conception were randomized into four groups of six each and treated as follows: Group I - Sham was administered distilled water orally. Group II - A positive control was administered methyl methimazole at 0.02% orally in drinking water. Group III - MCP orally at 0.3 mg/kg and Group IV - Lead acetate at 0.2% orally in drinking water. The drug was administered from gestation day 3 through post-natal day 21 in all the groups. Acetylcholinesterase (AChE) inhibition, thyroid profile (thyroid stimulating hormone, T₃ and T₄), neurodevelopment (brain wet weights, DNA, RNA and protein), and neurobehavioral (elevated plus maze, photoactometry, and Morris water maze) parameters were assessed in pups. A histopathology of thyroid of dams and brain of progeny was conducted.

Results:

Inhibition of AChE was <20%. Thyroid profile decreased in the treatment groups. Neurodevelopmental and neurobehavioral parameters did not reveal any significant changes. Thyroid architecture was affected significantly with MCP and lead. Cortical layers too were affected. The three layers of cerebellum either had abnormal arrangement or decreased cellularity in all treated groups relating to thyroid disruption.

Conclusion:

MCP and lead might have affected the development of cerebrum and cerebellum via thyroid disruption leading to developmental neurotoxicity.

Pesticide exposure and neurodevelopmental outcomes: review of the epidemiologic and animal studies

Assessment of whether pesticide exposure is associated with neurodevelopmental outcomes in children can best be addressed with a systematic review of both the human and animal peer-reviewed literature. This review analyzed epidemiologic studies testing the hypothesis that exposure to pesticides during pregnancy and/or early childhood is associated with neurodevelopmental outcomes in children. Studies that directly queried pesticide exposure (e.g., via questionnaire or interview) or measured pesticide or metabolite levels in biological specimens from study participants (e.g., blood, urine, etc.) or their immediate environment (e.g., personal air monitoring, home dust samples, etc.) were eligible for inclusion. Consistency, strength of association, and dose response were key elements of the framework utilized for evaluating epidemiologic studies. As a whole, the epidemiologic studies did not strongly implicate any particular pesticide as being causally related to adverse neurodevelopmental outcomes in infants and children. A few associations were unique for a health outcome and specific pesticide, and alternative hypotheses could not be ruled out. Our survey of the in vivo peer-reviewed published mammalian literature focused on effects of the specific active ingredient of pesticides on functional neurodevelopmental endpoints (i.e., behavior, neuropharmacology and neuropathology). In most cases, effects were noted at dose levels within the same order of magnitude or higher compared to the point of departure used for chronic risk assessments in the United States. Thus, although the published animal studies may have characterized potential neurodevelopmental outcomes using endpoints not required by guideline studies, the effects were generally observed at or above effect levels measured in repeated-dose toxicology studies submitted to the U.S. Environmental Protection Agency (EPA). Suggestions for improved exposure assessment in epidemiology studies and more effective and tiered approaches in animal testing are discussed.

Chlorpyrifos and neurodevelopmental effects: a literature review and expert elicitation on research and policy

BACKGROUND

Organophosphate pesticides are widely used on food crops grown in the EU. While they have been banned from indoor use in the US for a decade due to adverse health effects, they are still the most prevalent pesticides in the EU, with Chlorpyrifos (CPF) being the most commonly applied. It has been suggested CPF affects neurodevelopment even at levels below toxicity guidelines. Younger individuals may be more susceptible than adults due to biological factors and exposure settings.

METHODS

A literature review was undertaken to assess the evidence for CPF contributing to neurodevelopmental disorders in infants and children. Other literature was consulted in order to formulate a causal chain diagram showing the origins, uptake, and neurological effects of animal and human exposure to CPF.The causal chain diagram and a questionnaire were distributed online to scientific experts who had published in relevant areas of research. They were asked to assess their confidence levels on whether CPF does in fact contribute to adverse neurodevelopment outcomes and rate their confidence in the scientific evidence. A second questionnaire queried experts as to which kind of policy action they consider justifiable based on current knowledge. In a special workshop session at the EuroTox congress in Dresden in 2009 the results of both questionnaires were further discussed with invited experts, as a basis for a policy brief with main messages for policy makers and stakeholders.

RESULTS

Most experts who responded to the first questionnaire felt that there was already enough evidence to support a ban on indoor uses of CPF in the EU. However, most felt additional research is still required in several areas. The responses from the first questionnaire were used to formulate the second questionnaire addressing the feasibility of government action. In turn, these expert participants were invited to attend a special session at the EuroTox congress in Dresden in 2009.

CONCLUSIONS

Some of the evidence that CPF contributes to neurodevelopmental disorders is still disputed among experts, and the overall sense is that further research and public awareness are warranted. There have been campaigns in North America making the potential exposure concerns known, but such information is not widely known in the EU. The ability of government action to produce change is strongly felt in some quarters while others believe better knowledge of consumer use trends would have a greater impact.

Evaluation of epidemiology and animal data for risk assessment: chlorpyrifos developmental neurobehavioral outcomes

Developmental neurobehavioral outcomes attributed to exposure to chlorpyrifos (CPF) obtained from epidemiologic and animal studies published before June 2010 were reviewed for risk assessment purposes. For epidemiological studies, this review considered (1) overall strength of study design, (2) specificity of CPF exposure biomarkers, (3) potential for bias, and (4) Hill guidelines for causal inference. In the case of animal studies, this review focused on evaluating the consistency of outcomes for developmental neurobehavioral endpoints from in vivo mammalian studies that exposed dams and/or offspring to CPF prior to weaning. Developmental neuropharmacologic and neuropathologic outcomes were also evaluated. Experimental design and methods were examined as part of the weight of evidence. There was insufficient evidence that human developmental exposures to CPF produce adverse neurobehavioral effects in infants and children across different cohort studies that may be relevant to CPF exposure. In animals, few behavioral parameters were affected following gestational exposures to 1 mg/kg-d but were not consistently reported by different laboratories. For postnatal exposures, behavioral effects found in more than one study at 1 mg/kg-d were decreased errors on a radial arm maze in female rats and increased errors in males dosed subcutaneously from postnatal day (PND) 1 to 4. A similar finding was seen in rats exposed orally from PND 1 to 21 with incremental dose levels of 1, 2, and 4 mg/kg-d, but not in rats dosed with constant dose level of 1 mg/kg-d. Neurodevelopmental behavioral, pharmacological, and morphologic effects occurred at doses that produced significant brain or red blood cell acetylcholinesterase inhibition in dams or offspring.

CHLORPYRIFOS INCREASES THE LEVELS OF HIPPOCAMPAL NMDA RECEPTOR SUBUNITS NR2A AND NR2B IN JUVENILE AND ADULT RATS

The present study investigated the effect of chlorpyrifos on NMDA receptor subunits NR2A and NR2B in juvenile and adult rats. Chlorpyrifos was administered with the dose of 40 and 70 mg/kg to juvenile and adult rats, respectively. Chlorpyrifos significantly inhibited the AChE activity in juvenile and adult rats (p < .05). NR2A and NR2B levels significantly increased in juvenile and adult rats by chlorpyrifos application (p < .05). Increased NR2A and NR2B levels may reflect increased glutaminergic activity, consequently neuronal damage. In the case of neuronal damage, learning and memory could be affected negatively even though NR2A and NR2B increased.

Long-term effects on hypothalamic neuropeptides after developmental exposure to chlorpyrifos in mice

BACKGROUND

Increasing evidence from animal and human studies indicates that chlorpyrifos (CPF), similar to other organophosphorus insecticides still widely used, is a developmental neurotoxicant. Developmental exposure to CPF in rodents induces sex-dimorphic behavioral changes at adulthood, including social and agonistic responses, which suggests that CPF may interfere with maturation of neuroendocrine mechanisms.

OBJECTIVES

We assessed the hypothesis that CPF affects the levels of neurohypophyseal hormones acting as modulators of social behavior in mammals, such as oxytocin (OT), arginine vasopressin (AVP), and prolactin (PRL).

METHODS

Pregnant female mice were orally administered with either vehicle (peanut oil) or 3 or 6 mg/kg CPF on gestational day (GD) 15 to GD18, and offspring were treated subcutaneously with either vehicle or 1 or 3 mg/kg CPF on postnatal days (PNDs) 11 to PND14. Dose levels were chosen to avoid systemic toxicity and inhibition of brain acetylcholinesterase. Offspring were sacrificed at 5 months of age, and expression of OT, AVP, and PRL was analyzed in the hypothalamus by Western blot or enzyme-linked immunosorbent assay (ELISA) analysis.

RESULTS

Both male and female mice showed dose-related enhancement of OT expression, with males presenting the more intense effect. AVP expression was significantly reduced in male mice at the higher prenatal and postnatal dose. We observed no significant effect on PRL expression in either sex. Overall, outcomes were mainly attributable to fetal exposure, whereas postnatal doses appeared to potentiate the prenatal effects.

CONCLUSIONS

Our data indicate that developmental exposure to CPF may permanently interfere with specific key signaling proteins of the hypothalamic peptidergic system, with time-, dose-, and sex-related effects still evident at adulthood.

Effect of different administration paradigms on cholinesterase inhibition following repeated chlorpyrifos exposure in late preweanling rats

Chlorpyrifos (CPS) is widely used in agricultural settings and residue analysis has suggested that children in agricultural communities are at risk of exposure. This has resulted in a large amount of literature investigating the potential for CPS-induced developmental neurotoxic effects. Two developmental routes of administration of CPS are orally in corn oil at a rate of 0.5 ml/kg and subcutaneously in dimethyl sulfoxide (DMSO) at a rate of 1.0 ml/kg. For comparison between these methods, rat pups were exposed daily from days 10 to 16 to CPS (5 mg/kg) either orally dissolved in corn oil or subcutaneously dissolved in DMSO, both at rates of either 0.5 or 1.0 ml/kg. A representative vehicle/route group was present for each treatment. Both the low and high volume CPS in DMSO subcutaneous groups were lower than that of the low and high volume CPS in oil oral groups. At 4 h following the final administration, serum carboxylesterase was inhibited > 90% with all treatments. For cholinesterase activity in the cerebellum, medulla-pons, forebrain, and hindbrain, and serum, inhibition in the CPS-oil groups was similar and inhibition in the CPS-DMSO groups was similar. However, significantly greater inhibition was present in the high volume CPS-DMSO group as compared to the CPS-oil groups. Inhibition in the low volume CPS-DMSO group was generally between that in the CPS-oil groups and the high volume CPS-DMSO group. These data suggest that using DMSO as a vehicle for CPS may alter the level of brain ChE inhibition.

Mobile Phone Radiation and the Developing Brain: Behavioral and Morphological Effects in Juvenile Rats

The increasing use of mobile phones by children and teenagers has raised concerns about their safety. Addressing such concerns is difficult, because no data are available on possible effects from long-term exposure to radiofrequency (RF) fields during the development of the nervous system. Possible morphological and functional changes were evaluated in the central nervous system of young male Wistar rats exposed to 900 MHz mobile phone signal for 2 h/day on 5 days/week. After 5 weeks of exposure at whole-body average specific energy absorption rates of 0.3 or 3.0 W/kg or sham exposure, six rats per group were examined histologically, and the remaining 18 rats per group were subjected to behavioral tests. No degenerative changes, dying neurons, or effects on the leakage of the blood-brain barrier were detected. No group differences were observed in the open-field test, plus maze test or acoustic startle response tests. In the water maze test, however, significantly improved learning (P = 0.012) and memory (P = 0.01) were detected in rats exposed to RF fields. The results do not indicate a serious threat to the developing brain from mobile phone radiation at intensities relevant to human exposure. However, the interesting finding of improved learning and memory warrants further studies.

Developmental exposure to pesticides zineb and/or endosulfan renders the nigrostriatal dopamine system more susceptible to these environmental chemicals later in life

Several epidemiological studies have suggested a role for environmental pesticide exposures in idiopathic Parkinson's disease. The purpose of this study was to test the hypothesis that exposure to pesticides such as endosulfan and/or zineb during critical periods of postnatal development could result in neuronal dysfunction and enhance the impact of these pesticides during exposure as adults. C57BL/6 mice, exposed daily to each of the pesticides or their mixtures from postnatal days 5 to 19, exhibited insignificant changes in striatal dopamine, acetylcholinesterase and alpha-synuclein levels. However, mice exposed to these pesticides as juveniles and re-exposed at 8 months of age had significantly altered striatum and brain cortex neurotransmitter levels. Thus, mice re-exposed during adulthood to zineb, endosulfan and their mixtures showed a significantly depleted striatal dopamine levels, to 22, 16 and 35% of control, respectively. Acetylcholinesterase activity in the cerebral cortex was significantly increased in all pesticide treated groups (rho< or =0.05) upon repeated exposure, and pesticide mixture treatment also significantly increased levels of normal and aggregated alpha-synuclein. Collectively, these findings support our hypothesis that exposure to pesticides such as endosulfan and zineb during critical periods of postnatal development contributes to neurotransmitter changes upon re-challenge in adulthood.

Exposure to organophosphates reduces the expression of neurotrophic factors in neonatal rat brain regions: similarities and differences in the effects of chlorpyrifos and diazinon on the fibroblast growth factor superfamily

BACKGROUND

The fibroblast growth factor (FGF) superfamily of neurotrophic factors plays critical roles in neural cell development, brain assembly, and recovery from neuronal injury.

OBJECTIVES

We administered two organophosphate pesticides, chlorpyrifos and diazinon, to neonatal rats on postnatal days 1-4, using doses below the threshold for systemic toxicity or growth impairment, and spanning the threshold for barely detectable cholinesterase inhibition: 1 mg/kg/day chlorpyrifos and 1 or 2 mg/kg/day diazinon.

METHODS

Using microarrays, we then examined the regional expression of mRNAs encoding the FGFs and their receptors (FGFRs) in the forebrain and brain stem.

RESULTS

Chlorpyrifos and diazinon both markedly suppressed fgf20 expression in the forebrain and fgf2 in the brain stem, while elevating brain stem fgfr4 and evoking a small deficit in brain stem fgf22. However, they differed in that the effects on fgf2 and fgfr4 were significantly larger for diazinon, and the two agents also showed dissimilar, smaller effects on fgf11, fgf14, and fgfr1.

CONCLUSIONS

The fact that there are similarities but also notable disparities in the responses to chlorpyrifos and diazinon, and that robust effects were seen even at doses that do not inhibit cholinesterase, supports the idea that organophosphates differ in their propensity to elicit developmental neurotoxicity, unrelated to their anticholinesterase activity. Effects on neurotrophic factors provide a mechanistic link between organophosphate injury to developing neurons and the eventual, adverse neurodevelopmental outcomes.

An age-dependent physiologically based pharmacokinetic/pharmacodynamic model for the organophosphorus insecticide chlorpyrifos in the preweanling rat

Juvenile rats are more susceptible than adults to the acute toxicity of organophosphorus insecticides like chlorpyrifos (CPF). Age- and dose-dependent differences in metabolism may be responsible. Of importance are CYP450 activation and detoxification of CPF to chlorpyrifos-oxon (CPF-oxon) and trichloropyridinol (TCP), as well as B-esterase (B-est) and PON-1 (A-esterase) detoxification of CPF-oxon to TCP. In the current study, a physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) model incorporating age-dependent changes in CYP450, PON-1, and tissue B-est levels for rats was developed. In this model, age was used as a dependent function to estimate body weight which was then used to allometrically scale both metabolism and tissue cholinesterase (ChE) levels. In addition, age-dependent changes in brain, liver, and fat volumes and brain blood flow were obtained from the literature and used in the simulations. Model simulations suggest that preweanling rats are particularly sensitive to CPF toxicity, with levels of CPF-oxon in blood and brain disproportionately increasing, relative to the response in adult rats. This age-dependent nonlinear increase in CPF-oxon concentration may potentially result from both the depletion of nontarget B-est and a lower PON-1 metabolic capacity in younger animals. The PBPK/PD model behaves consistently with the general understanding of CPF toxicity, pharmacokinetics, and tissue ChE inhibition in neonatal and adult rats. Hence, this model represents an important starting point for developing a computational model to assess the neurotoxic potential of environmentally relevant organophosphate exposures in infants and children.

Developmental neurotoxicity of organophosphorous pesticides: fetal and neonatal exposure to chlorpyrifos alters sex-specific behaviors at adulthood in mice

Developmental exposure to the organophosphorous insecticide chlorpyrifos (CPF) induces long-term effects on brain and behavior in laboratory rodents. We evaluated in adult mice the behavioral effects of either fetal and/or neonatal CPF exposure at doses not inhibiting fetal and neonatal brain cholinesterase. CPF (3 or 6 mg/kg) was given by oral treatment to pregnant females on gestational days 15-18 and offspring were treated sc (1 or 3 mg/kg) on postnatal days (PNDs) 11-14. Serum and brain acetylcholinesterase (AChE) activity was evaluated at birth and 24 h from termination of postnatal treatments. On PND 70, male mice were assessed for spontaneous motor activity in an open-field test and in a socioagonistic encounter with an unfamiliar conspecific. Virgin females underwent a maternal induction test following presentation of foster pups. Both sexes were subjected to a plus-maze test to evaluate exploration and anxiety levels. Gestational and postnatal CPF exposure (higher doses) affected motor activity in the open field and enhanced synergically agonistic behavior. Postnatal CPF exposure increased maternal responsiveness toward pups in females. Mice of both sexes exposed to postnatal CPF showed reduced anxiety response in the plus-maze, an effect greater in females. Altogether, developmental exposure to CPF at doses that do not cause brain AChE inhibition induces long-term alterations in sex-specific behavior patterns of the mouse species. Late neonatal exposure on PNDs 11-14 was the most effective in causing behavioral changes. These findings support the hypothesis that developmental CPF may represent a risk factor for increased vulnerability to neurodevelopmental disorders in humans.

Age-dependent pharmacokinetic and pharmacodynamic response in preweanling rats following oral exposure to the organophosphorus insecticide chlorpyrifos

Previous studies have indicated that juvenile rats are more susceptible than adults to the acute toxicity from exposure to the organophosphorus insecticide chlorpyrifos (CPF) and age-dependent differences in metabolism and sensitivity to cholinesterase (ChE) inhibition may be responsible. Metabolism involves CYP450 activation and detoxification of CPF to CPF-oxon and 3,5,6-trichloro-2-pyridinol (TCP), as well as cholinesterase (acetyl- and butyrylcholinesterase), carboxylesterase (CaE), and A-esterase (PON-1) detoxification of CPF-oxon to TCP. The pharmacokinetics of CPF, TCP, and the extent of blood (plasma/RBC), and brain ChE inhibition in rats were determined on postnatal days (PND)-5, -12, and -17 following oral gavage administration of 1 and 10mg CPF/kg of body weight. As has been seen in adult animals, for all preweanling ages the blood TCP exceeded the CPF concentration, and within each age group there was no evidence of non-linear kinetics over the dose range evaluated. Consistent with previous results, younger animals demonstrated a greater sensitivity to ChE inhibition as evident by the age-dependent inhibition of plasma, RBC, and brain ChE. The brain may be particularly sensitive in younger animals (i.e. PND-5) due to substantially lower levels of ChE activity relative to later preweanling stages and adults. Of particular importance was the observation that even in rats as young as PND-5, the CYP450 metabolic capacity was adequate to metabolize CPF to both TCP and CPF-oxon based on the detection of TCP in blood and extensive ChE inhibition (biomarker of CPF-oxon) at all ages. In addition, the increase in the blood TCP concentration ( approximately 3-fold) in PND-17 rats relative to the response in the younger rats, are consistent with an increase in CYP450 metabolic capacity with age. This is the first reported study that evaluated both the pharmacokinetics of the parent pesticide, the major metabolite, and the extent of ChE inhibition as a function of preweanling age. The results suggest that in the preweanling rat, CPF was rapidly absorbed and metabolized, and the extent of metabolism and ChE inhibition was age-dependent.

[Mosquito bites allergy, which prevention?]

Mosquito bites may induce allergic reactions in children. Usually underestimated, these reactions are often cutaneous and difficult to distinguish from non-specific histaminic phenomena. Recently, the identification of major allergens in mosquito saliva has allowed the achievement of recombinant allergens, which should facilitate the diagnosis and treatment of allergic reactions. Preventive cares must be performed in all children with large reactions, allergic or even non-allergic. Prevention consists in cutaneous protection, the use of repellents (with special attention to their toxicity), and antihistamines. A practical sheet for patient is provided.

Behavioral effects and ChE measures after acute and repeated administration of malathion in rats

Organophosphorus compounds such as malathion are environmental contaminants that may evoke neurobehavioral responses including anxiety and depression. In this study, after a functional observational battery, rats were tested in an open field and temperature test to better define doses used in subsequent experiments. Then, we investigated the effects of acute and repeated treatment with malathion on elevated plus-maze and forced-swim test, which are validated animal models to observe for anxiety- and depressive-related behaviors, respectively. We found that both acute and repeated malathion administration induced anxiogenic and depressive-like responses at doses that affected neither locomotion nor systemic temperature. Biochemical assays demonstrated inhibition of cholinesterase activity by these effective doses.

Alterations in central nervous system serotonergic and dopaminergic synaptic activity in adulthood after prenatal or neonatal chlorpyrifos exposure

Exposure to chlorpyrifos (CPF) alters neuronal development of serotonin (5HT) and dopamine systems, and we recently found long-term alterations in behaviors related to 5HT function. To characterize the synaptic mechanisms underlying these effects, we exposed developing rats to CPF regimens below the threshold for systemic toxicity, in three treatment windows: gestational days (GD) 17-20, postnatal days (PN) 1-4, or PN11-14. In early adulthood (PN60), we assessed basal neurotransmitter content and synaptic activity (turnover) in brain regions containing the major 5HT and dopamine projections. CPF exposure on GD17-20 or PN1-4 evoked long-term increases in 5HT turnover across multiple regions; the effects were not secondary to changes in neurotransmitter content, which was unaffected or even decreased. When the treatment window was shifted to PN11-14, there were no long-term effects. Dopamine turnover also showed significant increases after CPF exposure on GD17-20, but only when the dose was raised above the threshold for overt toxicity; however, hippocampal dopamine content was profoundly subnormal after exposures below or above the acute, toxic threshold, suggesting outright neurotoxicity. These results indicate that, in a critical developmental period, apparently nontoxic exposures to CPF produce lasting activation of 5HT systems in association with 5HT-associated behavioral anomalies.

Pesticides and children

Prevention and control of damage to health, crops, and property by insects, fungi, and noxious weeds are the major goals of pesticide applications. As with use of any biologically active agent, pesticides have unwanted side-effects. In this review, we will examine the thesis that adverse pesticide effects are more likely to occur in children who are at special developmental and behavioral risk. Children's exposures to pesticides in the rural and urban settings and differences in their exposure patterns are discussed. The relative frequency of pesticide poisoning in children is examined. In this connection, most reported acute pesticide poisonings occur in children younger than age 5. The possible epidemiological relationships between parental pesticide use or exposure and the risk of adverse reproductive outcomes and childhood cancer are discussed. The level of consensus among these studies is examined. Current concerns regarding neurobehavioral toxicity and endocrine disruption in juxtaposition to the relative paucity of toxicant mechanism-based studies of children are explored.

Morphologic effects of subtoxic neonatal chlorpyrifos exposure in developing rat brain: regionally selective alterations in neurons and glia

The widely used organophosphate insecticide, chlorpyrifos (CPF), elicits neurobehavioral teratogenesis with exposure windows ranging from the embryonic neural tube stage through postnatal development. To explore the morphologic changes occurring in late-stage exposure, newborn rats were given 5 mg/kg of CPF s.c. daily on postnatal days (PN) 11-14, a regimen that is devoid of systemic toxicity, but that elicits long-term cognitive impairment. On PN15 and 20, we examined the septal nucleus, striatum and somatosensory cortex. Across all three regions, CPF elicited a significant decrease in the number of glial cells. Superimposed on this basic pattern, there were region-specific alterations in the number and type of neurons, and neuronal perikaryal dimensions. In the septal nucleus, the CPF group exhibited an increase in the number of neurons on PN20, representing a delay in the normal maturational decline; there was a parallel decrease in the glial/neuronal ratio. In the striatum, the number of neurons per unit area was reduced in the CPF group, accompanied by perikaryal hypertrophy, as evidenced by an increase in the average neuronal cell diameter. In the somatosensory cortex, the distribution of cell sizes indicated a decrease in the proportion of small, nonpyramidal cells. Thus, there are subtle morphological changes in the juvenile rat brain after neonatal CPF exposure that are detectable with quantitative analysis and that correlate with later emergence of behavioral alterations. Furthermore, the current findings support the hypothesis that CPF interferes with gliogenesis, a relatively late event in brain development; accordingly, the vulnerable period for adverse effects of CPF is likely to extend into childhood or adolescence.

Developmental exposure to chlorpyrifos alters reactivity to environmental and social cues in adolescent mice

Neonatal mice were treated daily on postnatal days (pnds) 1 through 4 or 11 through 14 with the organophosphate pesticide chlorpyrifos (CPF), at doses (1 or 3 mg/kg) that do not evoke systemic toxicity. Brain acetylcholinesterase (AChE) activity was evaluated within 24 h from termination of treatments. Pups treated on pnds 1-4 underwent ultrasonic vocalization tests (pnds 5, 8, and 11) and a homing test (orientation to home nest material, pnd 10). Pups in both treatment schedules were then assessed for locomotor activity (pnd 25), novelty-seeking response (pnd 35), social interactions with an unfamiliar conspecific (pnd 45), and passive avoidance learning (pnd 60). AChE activity was reduced by 25% after CPF 1-4 but not after CPF 11-14 treatment. CPF selectively affected only the G(4) (tetramer) molecular isoform of AChE. Behavioral analysis showed that early CPF treatment failed to affect neonatal behaviors. Locomotor activity on pnd 25 was increased in 11-14 CPF-treated mice at both doses, and CPF-treated animals in both treatment schedules were more active when exposed to environmental novelty in the novelty-seeking test. All CPF-treated mice displayed more agonistic responses, and such effect was more marked in male mice exposed to the low CPF dose on pnds 11-14. Passive avoidance learning was not affected by CPF. These data indicate that developmental exposure to CPF induces long-term behavioral alterations in the mouse species and support the involvement of neural systems in addition to the cholinergic system in the delayed behavioral toxicity of CPF.

Effects of gestational exposure to chlorpyrifos on postnatal central and peripheral cholinergic neurochemistry

The effects of gestational exposure to the commonly used organophosphorus insecticide chlorpyrifos (O,O-diethyl O-[3,5,6-trichloro-2-pyridinyl]phosphorothioate) on postnatal central and peripheral cholinergic neurochemistry were investigated. Pregnant rats were orally dosed daily with chlorpyrifos (0, 3, 5, or 7 mg/kg) in corn oil from gestation day 6 to 20. Pups were sacrificed on postnatal days 1, 3, 6, 9, and 12 for the determination of brain, heart, lung, and serum cholinesterase, and brain choline acetyltransferase activities, along with liver carboxylesterase activity. Exposure to chlorpyrifos did not produce signs of overt toxicity to the dams or developing offspring. Cholinesterase activities were inhibited in a dose-related manner, with brain cholin-esterase inhibition of about 26%, 32%, and 45% on postnatal day 1. Inhibition of brain cholineste-rase persisted in all treatment groups until postnatal day 6 and in the medium and high-dosage groups through postnatal day 9. Liver carboxylesterase activity was also inhibited in a dose-related manner, with a recovery profile parallel to that of brain cholinesterase. Choline acetyltransferase activity was decreased by about 13% in the high-dosage group on postnatal days 9 and 12. These results indicate that gestational exposure to chlorpyrifos results in relatively persistent inhibition of brain cholinesterase and a delayed depression of choline acetyltransferase at a time when brain cholinesterase activity had returned to control levels in the high-dosage group.

Chlorpyrifos exposure of developing zebrafish: effects on survival and long-term effects on response latency and spatial discrimination

Chlorpyrifos (CPF) is a widely used insecticide, which has been shown to interfere with neurobehavioral development. Rat models have been key in demonstrating that prenatal CPF exposure causes choice accuracy deficits and motor alterations, which persist into adulthood. Complementary nonmammalian models can be useful in determining the molecular mechanisms underlying the persisting behavioral effects of developmental CPF exposure. Zebrafish with their clear chorion and extensive developmental information base provide an excellent model for assessment of molecular processes of toxicant impacted neurodevelopment. To facilitate the use of the zebrafish model and to compare it to the more typical rodent models, the behavioral phenotype of CPF toxicity in zebrafish must be well characterized. Our laboratory has developed methods for assessing spatial discrimination learning in zebrafish, which can differentiate response latency from choice accuracy in a three chambered fish tank. Low and high doses of CPF (10 and 100 ng/ml on days 1-5 postfertilization) both had significant persisting effects on both spatial discrimination and response latency over 18 weeks of testing. The high, but not the low dose, significantly accelerated mortality rates of the fish during the study from 20-38 weeks of age. Developmental exposure to either 10 or 100 ng/ml of CPF caused significant spatial discrimination impairments in zebrafish when they were adults. The impairment caused by 10 ng/ml was seen during early but not later testing, while the impairment caused by 100 ng/ml became more pronounced with continued testing. The higher dose caused a more pervasive impairment. The 10 and 100 ng/ml doses had opposite effects on response latency. The low 10 ng/ml dose significantly slowed response latency, while the high 100 ng/ml dose significant increased response latency. Both of these effects diminished with continued testing. CPF exposure during early development caused clear behavioral impairments, which lasted throughout adulthood in zebrafish. The molecular mechanisms by which early developmental CPF exposure produces these behavioral impairments expressed in adulthood can now be studied in the zebrafish model.

Variables influencing the toxic response to organophosphates in humans

Concerns and doubts associated with the predictable health effects in humans following exposure to xenobiotics is primarily due to the failure to consider the variables influencing the toxic response in each instance. Lack of correlation between laboratory data, animal experiments and clinical findings in man associated with exposure to organophosphates (OPs) is an example. We have reviewed the literature to identify the variables that need to be considered following exposure to OPs. These include factors related to the OP (physico-chemical properties, solvents, impurities), duration and routes of exposure, and factors related to the individual(s) exposed. Individual variables include variations in metabolic, sequestration and excretory processes and health status (age, gender, environmental factors, concurrent medications, cholinergic status). The assessment of ill-health following exposure is critical to the development and compliance with guidelines and to the adoption of the best instrumentation. We have suggested a schematic assessment that needs to be applied for each exposure associated with organophosphates and provided the reasons for the development of this format. Exposure to xenobiotics through the environment, occupation or following therapy is an unavoidable aspect of modern life. Application of the principles discussed to each xenobiotic exposure is necessary to provide accurate and adequate information to advance the prevention or minimising toxicity.

Prenatal chlorpyrifos exposure in rats causes persistent behavioral alterations

Use of chlorpyrifos (CPF) has been curtailed due to its developmental neurotoxicity. In rats, postnatal CPF administration produces lasting changes in cognitive performance, but less information is available about the effects of prenatal exposure. We administered CPF to pregnant rats on gestational days (GD) 17-20, a peak period of neurogenesis, using doses (1 or 5 mg/kg/day) below the threshold for fetal growth impairment. We then evaluated performance in the T-maze, Figure-8 apparatus and 16-arm radial maze, beginning in adolescence and continuing into adulthood. CPF elicited initial locomotor hyperactivity in the T-maze. Females showed slower habituation in the Fig. 8 maze; no effects were seen in males. In the radial-arm maze, females showed impaired choice accuracy for both working and reference memory and again, males were unaffected. Despite the deficits, all animals eventually learned the maze with continued training. At that point, we challenged them with the muscarinic antagonist, scopolamine, to determine the dependence of behavioral performance on cholinergic function. Whereas control females showed impairment with scopolamine, CPF-exposed females did not, implying that the delayed acquisition of the task had been accomplished through alternative mechanisms. The differences were specific to muscarinic circuits, as control and CPF groups responded similarly to the nicotinic antagonist, mecamylamine. Surprisingly, adverse effects of CPF were greater in the group receiving 1 mg/kg as compared to 5 mg/kg. Promotional effects of acetylcholine (ACh) on cell differentiation may thus help to offset CPF-induced developmental damage that occurs through other noncholinergic mechanisms. Our results indicate that late prenatal exposure to CPF induces long-term changes in cognitive performance that are distinctly gender-selective. Additional defects may be revealed by similar strategies that subject the animals to acute challenges, thus, uncovering the adaptive mechanisms that maintain basal performance.

Functional alterations in CNS catecholamine systems in adolescence and adulthood after neonatal chlorpyrifos exposure

Chlorpyrifos (CPF), one of the most widely used pesticides, is a neurobehavioral teratogen in animals. We administered CPF to neonatal rats on postnatal days (PN) 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), regimens devoid of overt systemic toxicity. We then examined the impact on catecholaminergic systems in adolescence (PN30) and adulthood (PN60), assessing basal neurotransmitter content and transmitter utilization rates (turnover) in brain regions comprising the major noradrenergic and dopaminergic projections. Although CPF had only sporadic effects on basal norepinephrine and dopamine content, it profoundly suppressed norepinephrine turnover across multiple regions, indicative of net reductions in presynaptic activity. Dopamine turnover showed less consistent effects, with subnormal turnover in some regions and activation in others. We also evaluated whether CPF exposure altered the ability of catecholamine systems to respond to acute cholinergic stimulation, elicited by administration of a single challenge dose of nicotine. In the normal brain, nicotine increases the utilization of norepinephrine and dopamine. With only a few exceptions, animals receiving neonatal CPF exposure showed lasting desensitization of the nicotine response; not only was the activation by nicotine blunted in the CPF group, but in some regions the nicotine response was reversed, eliciting a reduction in transmitter turnover. These results indicate that neonatal CPF exposure produces widespread deficiencies in catecholaminergic synaptic function that persist into adulthood, and that are best revealed by dynamic measures of synaptic activity and responsiveness, as opposed to static markers like basal transmitter levels. The effects seen here are likely to contribute to alterations in behavioral performance that persist or emerge long after the termination of CPF exposure.

Appraisal of risks from nonoccupational exposure to chlorpyrifos

The toxicological database for chlorpyrifos indicates that humans are not more sensitive than laboratory animals to the toxic effects. Although an oral dose of 1 mg/kg-day resulted in measurable levels of chlorpyrifos in the blood, daily dosing at this level from 9 days to 2 years did not affect brain acetylcholinesterase activity (AChE) in laboratory animals. Developmental toxicity did not occur at doses below maternal toxicity. Most nonoccupational illnesses resulting from entry into areas treated with chlorpyrifos likely stem from odor, rather than the ability of the organophosphate to inhibit AChE. Based on biological monitoring studies, chronic aggregate nonoccupational exposures to chlorpyrifos ranged from 0.0002 mg/kg-day (adults) to 0.0005 mg/kg-day (infants and small children)-1 order of magnitude less than exposures estimated by standard procedures. Other biological monitoring data indicated that cumulative exposure to all organophosphate pesticides ranged from 0.0003 mg/kg-day (adults) to 0.003 mg/kg-day (children). Considering all these factors, the risks of aggregate, nonoccupational exposure to chlorpyrifos have been overstated by more than a 1000-fold.

Persistent behavioral consequences of neonatal chlorpyrifos exposure in rats

Chlorpyrifos (CPF) is a widely used insecticides which has been shown to alter brain cell development. The current project was conducted to determine whether there are persistent behavioral effects of early [1 mg/kg/day postnatal days (PNDs) 1-4] or late (5 mg/kg/day PNDs 11-14) postnatal CPF exposure in rats. We tested spontaneous alternation in a T-maze, locomotor activity in the Figure-8 apparatus and learning in the 16-arm radial maze, throughout adolescence and into adulthood. Exposure during either neonatal period elicited significant long-term effects on cognitive behavior. In the radial-arm maze, as has been seen previously, control male performed more accurately than control females. Early postnatal CPF exposure reversed this effect. With exposure on PNDs 1-4, females in the CPF group showed a reduction in working and reference memory errors in the radial maze, reducing their error rate to that seen in control males; in contrast, CPF-exposed males exhibited an increase in errors during the initial stages of training. When animals were exposed on PNDs 11-14 and then tested in adolescence and adulthood, males showed a significant slowing of response latency in the T-maze and the rate of habituation in the Figure-8 apparatus was slowed in both sexes. When females were challenged acutely with the muscarinic antagonist, scopolamine, they did not show reference memory impairment, whereas controls did; these results suggest that adaptations occur after CPF exposure that lead to loss of muscarinic cholinergic control of reference memory. No such changes were seen with a nicotinic cholinergic antagonist (mecamylamine). These results indicate that early neonatal exposure to CPF induces long-term changes in cognitive performance that, in keeping with the neurochemical changes seen previously, are distinctly gender-selective. Additional defects may be revealed by similar strategies that subject the animals to acute challenges, thus uncovering the adaptive mechanisms that maintain basal performance.