Neurological effects of acute exposure to caffeine and organophosphates in mice.

Organophosphate (OP) pesticides are commonly known for their neurotoxicity. In the current experiments, two OPs used agriculturally, chlorpyrifos and dimethoate, were separately adminis- tered with centrally acting caffeine that is known to affect the pharmacological action of other substances. The aim of this study was to determine whether the combination of OP and caffeine may influence their neurotoxic potential. For this purpose, some neurobehavioral effects of this concomitant exposure were assessed in adult Swiss mice. All substances were given intra- peritoneally (i.p.) as single injections. In the passive avoidance task, chlorpyrifos (100 mg/kg) administered together with caffeine (40 mg/kg) significantly impaired acquisition. In the rota-rod test, the addition of caffeine at doses of 20 and 40 mg/kg, induced motor coordination impairment in chlorpyrifos (100 mg/kg)-treated mice. Neurobehavioral impairments were not observed for caffeine, chlorpyrifos and dimethoate (50 mg/kg) given separately as well as for the combina- tion of dimethoate and caffeine. Chlorpyrifos (100 mg/kg) alone and in combination with caffeine (40 mg/kg) significantly reduced acetylcholinesterase (AChE) activity. The current study shows that concomitant exposure to caffeine and chlorpyrifos can cause neurotoxic effects in mice despite the absence of these effects when caffeine and chlorpyrifos are administered alone. How- ever, the possible mechanisms involved need further investigations.

Primary Adrenal Lymphoma: Two Case Series From China.

Objective: Primary adrenal lymphoma (PAL) is a rare form of adrenal mass. We summarize our experience in its clinical presentation, biochemical indexes, radiological features, pathological information, therapy regimens, and outcomes. Methods: This was an institutional review board-approved retrospective review of medical records and surgical pathology specimens of patients with a diagnosis of PAL at the Chinese People's Liberation Army General Hospital and the First Affiliate Hospital of Xiamen University between July 2007 and July 2017. Results: Twenty-six patients were identified. The mean age at presentation was 60.84 ± 13.14 years with a male-to-female ratio of 2.25:1 (18:8). The most common presenting symptoms were loss of appetite (65%, 17/26), weight loss (62%, 16/26), abdominal pain (58%, 15/26), and fatigue (58%, 15/26). The levels of lactate dehydrogenase (75%, 15/20), ß2-microglobulin (100%, 10/10), C-reactive protein (82%, 14/17), and ferritin (88%, 7/8) and the erythrocyte sedimentation rate (83%, 10/12) were elevated. Bilateral involvement was seen in 21 of 26 patients (81%); 12 of 19 evaluated patients with bilateral lesions (63%) were confirmed to have adrenal insufficiency. On computed tomography (CT), the mean tumor diameter was 7.31 ± 3.35 cm and the median Hounsfield density was 37.0 HU (range: 31.0-45.0 HU); 67% (10/15) and 27% (4/15) of lesions presented with mild and moderate enhancement after injection of contrast medium. 18F-fluorodeoxyglucose positron emission tomography (FDG PET)-CT revealed not only an adrenal tumor but also extra-adrenal lesions. Diffuse large B-cell lymphoma (DLBCL) was the most common phenotype (92%, 24/26). Ninety-two percent (24/26) of patients received chemotherapy while 8% (2/26) received unilateral adrenalectomy plus chemotherapy. The prognosis of PAL was poor, with a general survival time of 7.20 ± 5.18 months. Conclusion: PAL is a rare disease. The clinical characteristics of PAL include loss of appetite and weight loss. Endocrine evaluation should be performed to determine whether patients have adrenal insufficiency, especially patients with bilateral lesions. FDG-PET appears to be more accurate than other imaging modalities in revealing extra-adrenal sites. Better therapy is required to improve the poor prognosis of PAL.

Western corn rootworm pyrethroid resistance confirmed by aerial application simulations of commercial insecticides.

The western corn rootworm (Diabrotica virgifera virgifera LeConte) (WCR) is a major insect pest of corn (Zea mays L.) in the United States (US) and is highly adaptable to multiple management tactics. A low level of WCR field-evolved resistance to pyrethroid insecticides has been confirmed in the US western Corn Belt by laboratory dose-response bioassays. Further investigation has identified detoxification enzymes as a potential part of the WCR resistance mechanism, which could affect the performance of insecticides that are structurally related to pyrethroids, such as organophosphates. Thus, the responses of pyrethroid-resistant and -susceptible WCR populations to the commonly used pyrethroid bifenthrin and organophosphate dimethoate were compared in active ingredient bioassays. Results revealed a relatively low level of WCR resistance to both active ingredients. Therefore, a simulated aerial application bioassay technique was developed to evaluate how the estimated resistance levels would affect performance of registered rates of formulated products. The simulated aerial application technique confirmed pyrethroid resistance to formulated rates of bifenthrin whereas formulated dimethoate provided optimal control. Results suggest that the relationship between levels of resistance observed in dose-response bioassays and actual efficacy of formulated product needs to be further explored to understand the practical implications of resistance.

Sub-lethal effects of dimethoate alone and in combination with cadmium on biochemical parameters in freshwater snail, Galba truncatula.

The objective of the present study was to evaluate the influence of the organophosphorus pesticide dimethoate and cadmium on biochemical parameters of a freshwater snail, Galba truncatula, in laboratory conditions. In 14 days, snails were exposed to 0, 100, 200, and 400 µg L-1 of dimethoate and 0.0 and 1000 µg L-1 of cadmium chloride. The results evidenced that dimethoate induces oxidative stress and alters biochemical parameters in freshwater snails. Cadmium also induced significant changes in biochemical parameters. The combination of the dimethoate and cadmium markedly increased the effects on G. truncatula. Dimethoate and cadmium mixture caused a decrease in Acetylcholinesterase (AChE), and Glucose-6-phosphate dehydrogenase (G6PDH) activities, glycogen, and total antioxidant capacity (TAN) levels, and increased aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), glutathione peroxidase (GPx), and catalase (CAT) activities, and malondialdehyde (MDA) level in exposed snails. The increased toxicity and bioaccumulation of cadmium after the exposure to the highest concentration of dimethoate indicates a synergistic effect leading to a reduced performance of the detoxification system in the snail. Dimethoate contributed to the bioconcentration of cadmium in snails and increased its toxic effects evidenced in biomarkers of oxidative stress and cell damage.

Biotic and abiotic factors investigated in two Drosophila species - evidence of both negative and positive effects of interactions on performance.

Multiple environmental factors acting in concert can interact and strongly influence population fitness and ecosystem composition. Studies investigating interactions usually involve only two environmental factors; most frequently a chemical and another abiotic factor such as a stressful temperature. Here we investigate the effects of three environmental factors: temperature, an insecticide (dimethoate) and interspecific co-occurrence. We expose two naturally co-occurring species of Drosophila (D. hydei and D. melanogaster) to the different environments during development and examine the consequences on several performance measures. Results are highly species and trait specific with evidence of two- and three-way interactions in approximately 30% of all cases, suggesting that additive effects of combined environmental factors are most common, and that interactions are not universal. To provide more informative descriptions of complex interactions we implemented re-conceptualised definitions of synergism and antagonism. We found approximately equal proportions of synergistic and antagonistic interactions in both species, however the effects of interactions on performance differed between the two. Furthermore, we found negative impacts on performance in only 60% of interactions, thus our study also reveals a high proportion of cases with positive effects of interactions.

Effects of dimethoate in male mice reproductive parameters.

The aim of the current study was to investigate the ability of dimethoate (DMT) to induce reprotoxicity in male mice. The dose (20 mg/kg/day) was given orally for 30 days. A significant decrease in sperm count, motility and viability and a significant increase of morphologically abnormal spermatozoa percent in DMT treated mice was observed. Testicular Acetylcholinesterase (AChE) and Butyrylcholinesterase (BChE) activities were inhibited. Also, a significant increase in lipid peroxidation level and a significant decrease in the activities of antioxidant enzymes were observed in testis of DMT mice. In addition, gene expression of glutathione peroxidase 4 (GPx4) was quantified in RNA samples extracted from the testis by real-time reverse transcription-polymerase chain reaction (RT-PCR). Compared with control, mRNA expression of GPx4 was slightly decreased after DMT-exposure.

Study the effect of insecticide dimethoate on photosynthetic pigments and photosynthetic activity of pigeon pea: Laser-induced chlorophyll fluorescence spectroscopy.

Pigeon pea is one of the most important legume crops in India and dimethoate is a widely used insecticide in various crop plants. We studied the effect of dimethoate on growth and photosynthetic activity of pigeon pea plants over a short and long term exposure. Plant growth parameters, photosynthetic pigment content and chlorophyll fluorescence response of pigeon pea (Cajanus cajan L.) plants treated with various concentrations of the insecticide dimethoate (10, 20, 40 and 80 ppm) have been compared for 30 days at regular intervals of 10 days each. Laser induced chlorophyll fluorescence spectra and fluorescence-induction kinetics (FIK) curve of dimethoate treated pigeon pea plants were recorded after 10, 20 and 30 days of treatment. Fluorescence intensity ratio at the two fluorescence maxima (F685/F730) was calculated by evaluating curve-fitted parameters. The variable chlorophyll fluorescence decrease ratio (Rfd) was determined from the FIK curves. Our study revealed that after 10 days of treatment, 10 ppm of dimethoate showed stimulatory response whereas 20, 40 and 80 ppm of dimethoate showed inhibitory response for growth and photosynthetic activity of pigeon pea plants, but after 20 and 30 days of treatment all the tested concentrations of dimethoate became inhibitory. This study clearly shows that dimethoate is highly toxic to the pigeon pea plant, even at very low concentration (10 ppm), if used for a prolonged duration. Our study may thus be helpful in determining the optimal dose of dimethoate in agricultural practices.

Additive effects of predator cues and dimethoate on different levels of biological organisation in the non-biting midge Chironomus riparius.

The combined effects of a pesticide and predation risk on sublethal endpoints in the midge Chironomus riparius were investigated using a combination of predator-release kairomones from common carp (Cyprinus carpio) and alarm substances from conspecifics together with the pesticide dimethoate. Midge larvae were exposed for 30 days to three sublethal dimethoate concentrations (0.01, 0.1 and 0.25 mg L(-1)) in the presence or absence of predator cues. Sublethal endpoints were analysed at different levels of biological organisation. Available energy reserves, enzyme biomarkers, feeding rate and life history endpoints were investigated. Three endpoints were significantly affected by the two highest dimethoate concentrations, i.e. AChE activity, age at emergence and emergence success, with a significant decrease in response after exposure to 0.25, 0.1 and 0.01 mg L(-1) dimethoate, respectively. Four sublethal endpoints were significantly affected by predator stress: Total protein content, GST activity and biomass decreased only in the presence of the predation risk, while AChE activity further decreased significantly in the presence of predation cues and effects on AChE of combined exposure were additive. From this study we can conclude that sublethal life history characteristics should be included in ecotoxicity testing as well as natural environmental stressors such as predator stress, which might act additively with pollutants on fitness related endpoints.

[Impacts that dimethoate inhibited the benchmark dose of acetylcholinesterase based on experimental designs].

OBJECTIVE: To obtain the impacts of experimental design on benchmark dose (BMD), and the result was applied to test the computer simulation by software Slob (optimal method to calculate the BMD: for a certain sample capacity, to add the experimental groups by reducing the amount of animals in each group) , consequently, this method can be widely used in the future. METHODS: Eighty adult female SD rats were ig given dimethoate 0.5, 1, 2, 4, 8, 16 and 32 mg/kg for 21 d, respectively. Rats were sacrificed, and acetylcholinesterase (AChE) activity in the hippocampus, cerebral cortex and serum of rats was determined after dimethoate was ig given to rats for 21 d. And then, the software package PROAST28.1 was applied to calculate the BMD. The four does groups of 10 animals (4 x 10 design) and 8 x 5 design were selected from 8 x 10 design to study the impacts of experimental design on BMD. RESULTS: Comparing with the normal control, the significant decline of AChE in hippocampus was observed in 2, 4, 8, 16 and 32 mg/kg groups (P < 0.05), whereas the significant decrease was obtained in 0.5, 1, 2, 4, 8, 16 and 32 mg/kg groups (P < 0.05). Taking the 8 x 10 design as the standard, the confidence interval of BMD calculated by both of 4 x 10 design and 8 x 5 design covered the BMD by 8 x 10 design. And also, confidence interval of BMD, calculated by design scheme 1, 2, 3, 4 and 6 of 4 x 10 design, wider than that of 8 x 5 design, but its scheme 5 narrower than 8 x 5 design. CONCLUSION: To add experimental groups in a certain sample capacity was the optimal method to calculate BMD, but was not the common toxicity experimental design (e. g. set four groups including control, low-dose, moderate-dose, high-dose group).

Metabonomics analysis of urine and plasma from rats given long-term and low-dose dimethoate by ultra-performance liquid chromatography-mass spectrometry.

This study assessed the effects of long-term, low-dose dimethoate administration to rats by ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Dimethoate (0.04, 0.12, and 0.36 mg/kg body weight/day) was administered daily to male Wistar rats through their drinking water for 24 weeks. Significant changes in serum clinical chemistry were observed in the middle- and high-dose groups. UPLC-MS revealed evident separate clustering among the different dose groups using global metabolic profiling by supervised partial least squares-discriminant analysis. Metabonomic analysis showed alterations in a number of metabolites (12 from urine and 13 from plasma), such as L-tyrosine, dimethylthiophosphate (DMTP), dimethyldithiophosphate (DMDTP), citric acid, uric acid, suberic acid, glycylproline, allantoin, isovalerylglutamic acid and kinds of lipids. The results suggest that long-term, low-dose exposure to dimethoate can cause disturbances in liver function, antioxidant and nervous systems, as well as the metabolisms of lipids, glucose, fatty acids, amino acids, and collagen in rats. DMTP and DMDTP, which had the most significant changes among all other studied biomarkers, were considered as early, sensitive biomarkers of exposure to dimethoate. The other aforementioned proposed toxicity biomarkers in metabonomic analysis may be useful in the risk assessment of the toxic effects of dimethoate. Metabonomics as a systems toxicology approach was able to provide comprehensive information on the dynamic process of dimethoate induced toxicity. In addition, the results indicate that metabonomic approach could detect systemic toxic effects at an earlier stage compared to clinical chemistry. The combination of metabonomics and clinical chemistry made the toxicity of dimethoate on rats more comprehensive.

Activity of selected antioxidative enzymes in rats exposed to dimethoate and pyrantel tartrate.

This study presents the results of research concerning the effect of single and combined application of pyrantel tartrate and dimethoate on selected antioxidative enzymes: catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx), in rat erythrocytes. Pyrantel tartrate was applied twice, at a dose of 85 mg/kg bw at a two week interval, i.e. on day 14 and 28 of the experiment, orally, in a water solution with a stomach tube. Dimethoate was administered with drinking water for 28 days at a dose of 25 mg/kg bw/day. It was found that pyrantel tartrate caused only small changes in the activity of the antioxidative enzymes under analysis. Subchronic exposure of rats to dimethoate caused a significant increase in the activity of CAT, SOD and GPx in erythrocytes, indicating the existence of strong oxidative stress. In combined intoxication, no significant effects of administering pyrantel tartrate on the activity of CAT, SOD and GPx was found in animals poisoned with dimethoate. The profile of changes was similar to that observed in rats exposed only to the organophosphorus insecticide. This may indicate a lack of interaction between the compounds used in the experiment.

Changes of drug metabolizing enzymes in the liver of male sheep exposed to either cypermethrin or dimethoate.

Xenobiotics such as insecticides are metabolized to more or less toxic metabolites by drug-metabolizing enzymes including cytochrome P450 (Cyp P450), cytochrome b5 (Cyp b5), NADPH-cytochrome c reductase (Cyt.c R), N-nitrosdimethylamine-N-demethylase I (NDMA-dI), glutathione (GSH), glutathione s-transferase (GST), and glutathione reductase (GR). Therefore, the present study showed the influence of oral administration of cypermethrin (6 and 12 mg/kg/day) and dimethoate (1.6 and 3.2 mg/kg/day) for 63 consecutive days on the activities of the above mentioned enzymes in the livers of male sheep. Low and high-treatments of sheep with cypermethrin significantly increased the levels of Cyp P450 by 56% and 98%, Cyp b5 by 65% and 80%, GSH by 68% and 74%, and Cyt.c R by 67% and 98%, respectively in a dose-dependent manner. However, low dose of cypermethrin increased the activities of GST and GR by 56% and 91% respectively. In addition, low and high dose-treatments with dimethoate increased the hepatic contents of Cyp P450 by 27% and 40%, GSH by 259% and 132%, whereas NDMA-dI decreased by 27 and 55% respectively, and no change in the content of Cyp b5 and the activity of Cyt.c-R at any given dose of this compound. It is concluded that exposure to cypermethrin and dimethoate significantly changed the hepatic activity of phases I & II drugmetabolizing enzymes in sheep, and these changes are mainly dependent on the administred dose, and also on the type of the tested insecticides. Also, such changes should be considered when therapeutic drugs administered to people exposed to such insecticides.

A role for solvents in the toxicity of agricultural organophosphorus pesticides.

Organophosphorus (OP) insecticide self-poisoning is responsible for about one-quarter of global suicides. Treatment focuses on the fact that OP compounds inhibit acetylcholinesterase (AChE); however, AChE-reactivating drugs do not benefit poisoned humans. We therefore studied the role of solvent coformulants in OP toxicity in a novel minipig model of agricultural OP poisoning. Gottingen minipigs were orally poisoned with clinically relevant doses of agricultural emulsifiable concentrate (EC) dimethoate, dimethoate active ingredient (AI) alone, or solvents. Cardiorespiratory physiology and neuromuscular (NMJ) function, blood AChE activity, and arterial lactate concentration were monitored for 12h to assess poisoning severity. Poisoning with agricultural dimethoate EC40, but not saline, caused respiratory arrest within 30 min, severe distributive shock and NMJ dysfunction, that was similar to human poisoning. Mean arterial lactate rose to 15.6 [SD 2.8] mM in poisoned pigs compared to 1.4 [0.4] in controls. Moderate toxicity resulted from poisoning with dimethoate AI alone, or the major solvent cyclohexanone. Combining dimethoate with cyclohexanone reproduced severe poisoning characteristic of agricultural dimethoate EC poisoning. A formulation without cyclohexanone showed less mammalian toxicity. These results indicate that solvents play a crucial role in dimethoate toxicity. Regulatory assessment of pesticide toxicity should include solvents as well as the AIs which currently dominate the assessment. Reformulation of OP insecticides to ensure that the agricultural product has lower mammalian toxicity could result in fewer deaths after suicidal ingestion and rapidly reduce global suicide rates.

Protective effects of Danshensu on liver injury induced by omethoate in rats.

This study was to evaluate the protective effects of Danshensu on liver injury induced by omethoate in Sprague Dawley rats. The acute omethoate poisoning model was established by administrating subcutaneously with omethoate at a single dose of 60 mg/kg. Danshensu treatment markedly inhibited the increases of aspartate aminotransferase, alanine aminotransferase, cyclooxygenase-2, tumor necrosis factor-alpha, thromboxane B(2), and thromboxane B(2)/6-keto-PGF1alpha ratio induced by omethoate. The histopathological examination further confirmed that administration with Denshensu ameliorated liver injury. The results demonstrated that Danshensu possesses protective action on hepatic injury induced by omethoate and the pharmacological mechanism was related to the anti-inflammatory effect and circulation improvement of Danshensu, at least in part.

Study of the toxic effects of an insecticide and copper sulphate on chicken embryos.

The toxic effects of the BI 58 EC insecticide (38% dimethoate) applied alone or in combination with copper sulphate were studied on chicken embryo in the early phase of development. The test materials were injected in 0.1-0.1 ml volume into the air chamber of eggs on the first day of incubation. Subsequently, on days 2 and 3 of incubation permanent preparations were made from the embryo in order to study the early developmental stage. Embryos fixed on slides and stained with osmium tetroxide solution were studied under light microscope. According to the result of the statistical evaluation, to sum up, we can say that the simultaneous administration of the test materials did not result in a significant increase in the embryo mortality, but after the combined administration the rate of embryonic mortality markedly increased. As a result of combined administrations the developmental anomalies included the apperance of a blood ring, poor development or absence of somites, the retarted development of the vascular system, the head and the body, irregular differentiation of the brain vesicles. Summarising the findings, it can be established that the insecticide treatment combined with heavy metal resulted in enhanced embryotoxicity in the case of both combinations, which was primarily manifested in an increased embryonic mortality rate.

Analysis and integration of developmental neurotoxicity and ancillary data into risk assessment: a case study of dimethoate.

Dimethoate is an organophosphate (OP) pesticide used to control a wide variety of insects on agricultural crops and ornamentals. To ensure that dimethoate is used safely, it is important to determine exposure levels that protect against adverse effects at all life stages, including the developing fetus, infant, and child. Based on an analysis of a developmental neurotoxicity (DNT) study, a cholinesterase (ChE) sensitivity study, a cross-fostering study, and several single- and multigenerational reproductive toxicity studies, two potential critical endpoints for dimethoate were identified: brain ChE inhibition (ChEI) in adult females, and pup mortality. An initial evaluation concluded that pup mortality was a preferable endpoint, based on an increased number of pup deaths born to dams dosed with > or =3 mg/kg dimethoate via oral gavage. Closer examination, however, revealed that the pup deaths were clustered in a small number of litters in which the dams providing postnatal care exhibited maternal care deficits. When the data were analyzed using the dam as the unit of statistical significance, a significant increase in the average litter proportion of pup deaths was observed only when the dams were dosed postnatally with 6 mg/kg dimethoate while they were raising the pups. Gestational exposure (i.e., during pregnancy only) to 6 mg/kg dimethoate exerted no effect on pup survival. This leads to the conclusion that it is postnatal exposure of the nursing dams that is associated with pup mortality. Furthermore, a previous benchmark dose (BMD) meta-analysis approach revealed that BMDL(10) for adult females (the lower 95% bound of the dose resulting in a 10% reduction in the parameter of interest) for ChEI was > 3-fold lower than the BMDL(10) for pup mortality (0.19 and 0.68 mg/kg, respectively). Overall, this study underscores the importance of using the dam as the unit of statistical significance when assessing data collected in the perinatal period, and it is concluded that adult brain ChEI is the correct critical endpoint for assessing risk of dimethoate toxicity.

Developmental toxicity of orally administered technical dimethoate in rats.

BACKGROUND: Dimethoate (O,O-dimethyl-S-(N-methylcarbamoyl-methyl) phosphorodithioate), an organophosphate insecticide, was examined for its potential to produce developmental toxicity in rats after oral administration. METHODS: Pregnant Fischer 344 rats were given sublethal doses of 0 (corn oil), 7, 15, and 28 mg/kg/day dimethoate by gavage on gestation days (GD) 6-15. Maternal effects in 15 and 28 mg/kg/day dose groups included cholinergic signs such as tremors, diarrhea, weakness, and salivation, and depression in the maternal and fetal brain acetylcholinesterase (AChE) activities. Other maternal toxicity that included reduction in body weight and feed consumption was observed only in the treated group of 28 mg/kg/day. No maternal toxicity was apparent in the 7 mg/kg/day dose group. RESULTS: Maternal exposure to dimethoate during organogenesis significantly affected the number of live fetuses, early resorption, and mean fetal weight in the 28 mg/kg/day dose group. No external, visceral, and skeletal abnormalities were observed in any of the treated groups compared to the control. CONCLUSIONS: On the basis of the present results dimethoate can produce clinical signs of toxicity and significant inhibition of the maternal and fetal AChE activities in dose groups of 15 and 28 mg/kg/day and showed fetotoxicity without teratogenic effects at 28 mg/kg/day.

Stimulus frequency dependence of the central and peripheral somatosensory evoked activity in rats treated with various pesticides.

Rats were treated with a combination of insecticide agents in different timing schemes. In acute administration, 1/5 LD50 of the three insecticides: dimethoate, propoxur and cypermethrin, or their combination, was given once by gavage. In the developmental model, female rats received oral doses of 1/25 LD50 of the above insecticides in combination in three timing schemes including pregnancy and lactation. Responses in the somatosensory cortex and in the tail nerve, evoked by peripheral electric stimulation, were recorded in acute preparation under urethane anesthesia. It was tested whether the parameters of the cortical and peripheral evoked response are dependent on the frequency and whether this dependence is different in control and treated animals. The latency increase of the cortical responses with increasing stimulation frequency was significantly stronger in rats treated acutely with cypermethrin and the combination, and in rats receiving the combination during both intra- and extrauterine development. On the duration, the effects were less clear. Frequency dependent increase of the tail nerve action potential latency was significantly intensified by cypermethrin, and the amplitude decrease, by cypermethrin and dimethoate. Fatigue of this response during a stimulation series was also altered by the insecticides. Frequency dependence and fatigue possibly reflect the actual state of the nervous system and may have the potency to be developed to functional biomarkers.

Use of benchmark dose and meta-analysis to determine the most sensitive endpoint for risk assessment for dimethoate.

A meta-analysis of several rat toxicity studies for dimethoate was conducted to determine the most sensitive endpoint for use in risk assessment. The analysis was motivated by a recent developmental neurotoxicity (DNT) study, which identified the same no observed adverse effect level (NOAEL) for pup mortality and cholinesterase inhibition. The pup mortality NOAEL was lower than that determined in a range-finding study for the DNT and other reproduction studies, and was highly influenced by a single total litter loss in the middle dose group, which made interpretation difficult. First, a meta-analysis was conducted of four recent studies by gavage dosing with very similar designs, including the DNT. Benchmark dose (BMD) modeling was used to determine the appropriate point of departure for regulatory purposes, the lower limit of the BMD for a 5% incidence for pup mortality (BMDL(5)) and the lower limit of a 10% inhibition of brain cholinesterase (BMDL(10)*), the asterisk denotes that the BMD is based on continuous response variable as opposed to an incidence level. For pup mortality, the BMDL(5) for post-natal days (PND) 1-4 was 0.64 mg/kg/day. For cholinesterase inhibition, the lowest BMDL(10)* was 0.19 mg/kg/day for the dams at gestation day 20. These results show that the regulatory point-of-departure for cholinesterase inhibition is more than threefold lower than pup mortality. Thus, risk assessments protecting against cholinesterase inhibition are likely to also be protective of pup mortality. In addition, cholinesterase inhibition and pup mortality were evaluated in two 2-generation reproduction studies by dietary exposure. Also, cholinesterase inhibition was evaluated in a 28-day dietary study. Dietary exposure is more relevant than gavage exposures for many human risk assessment scenarios. There was no consistent pup mortality at the highest doses of the two 2-generation dietary studies (6.0 and 6.5mg/kg/day). The average BMD(10)s for brain cholinesterase inhibition for the 2-generation studies was 0.65 mg/kg/day, with a range of 0.49--0.96 mg/kg/day. This suggests that cholinesterase inhibition is at least a 10-fold more sensitive endpoint than pup mortality for dietary exposures. For the 28-day dietary study, the BMD(10) for brain cholinesterase inhibition was 1.1mg/kg/day for males and 0.70 mg/kg/day for females. The exposure duration in the 28-day dietary study is closest to the durations in the gavage studies. Compared to the dams in the gavage studies, which had a BMDL(10) of 0.19 mg/kg/day, the animals were more than threefold more sensitive to cholinesterase inhibition by gavage compared to dietary exposure.

Dimethoate effects on thyroid function in suckling rats.

The aim of our work is to study dimethoate effects on thyroid function given in drinking water (40 mg/kg body weight, equivalent to 0.2 g/L) to mothers from day zero until the 10th day after delivery. Pups and their mothers were sacrificed on day ten after parturition. Compared to a control group, dimethoate-treated pups showed a 48% decrease in body weight which could be attributed to a defect in thyroid hormones. Indeed, after treatment by dimethoate, plasma rates of free T4 and T3 decreased by 56% and 40% in the young and by 27% and 15% in dams respectively. We can attribute the reduction in plasma thyroxine and triiodothyronine rates to a decrease in thyroid iodine levels (-75%) in the young and (-24%) in their mothers. The decrease in production of thyroid hormones after dimethoate treatment affect thyroid stimulating hormone (TSH) levels. In fact, plasma TSH levels were multiplied in dimethoate-treated group by factors of 2.31 in dams and 1.96 in their offspring. These biochemical modifications confirmed the histological thyroid aspects of pups and dams. In fact, in dimethoate-treated rats, some thyroid follicles of pups presented vesicular cavities without colloid; others contained colloid. However in dams, thyroid follicles presented cubical epithelial cells which surrounded empty vesicular cavities.