Time course of biochemical and behavioural effects of a single high dose of chlorpyrifos

Pesticide and trace element bioaccumulation in wild owls in Brazil

Owls are outstanding environmental quality bioindicators due to their position at the top of the food chain and susceptibility to pollutant accumulation. Exposure to chemical contaminants is often a risk for these animals. Moreover, studies addressing the bioaccumulation of trace elements and pesticide residues in tropical nocturnal raptor species are scarce. We analyzed the 26 organs (heart, liver, and kidney) of Tyto furcata (n=3), Megascops spp. (n=5), Pulsatrix koeniswaldiana (n=1), and Asio stygius (n=1) carcasses, collected from June 2018 to May 2019 in the Southern region of Brazil. The original vegetation consisted of areas of Araucaria forests and grassy-woody steppes with gallery forests, which were greatly modified by the introduction of agriculture. In four animals and eight organs, the pesticides abamectin, atrazine, chlorpyrifos-ethyl, and diurom were analyzed through high-performance liquid chromatography coupled with a mass detector. In six animals and eighteen organs, the trace elements cadmium, lead, chromium, and nickel were identified via atomic absorption spectrophotometry. Chlorpyrifos-ethyl was detected in the livers of the genus Megascops. Chromium was found at high concentrations in all matrices analyzed for this trace element. Moreover, P. koeniswaldiana presented lead levels indicative of high exposure. The bioaccumulation of these toxics in owls described here can impact the population levels of these species, impact on its ecological function, and consequently unbalance the ecosystem. Moreover, owls are considered bioindicators; therefore, the occurrence of bioaccumulation indirectly gives us information about the quality of the environment.

Microbiota and organophosphates

Organophosphates (OPs) are important toxic compounds commonly used for a variety of purposes in agriculture, industry and household settings. Consumption of these compounds affects several central nervous system functions. Some of the most recognised consequences of organophosphate pesticide exposure in humans include neonatal developmental abnormalities, endocrine disruption, neurodegeneration, neuroinflammation and cancer. In addition, neurobehavioral and emotional deficits following OP exposure have been reported. It would be of great value to discover a therapeutic strategy which produces a protective effect against these neurotoxic compounds. Moreover, a growing body of preclinical data suggests that the microbiota may affect metabolism and neurotoxic outcomes through exposure to OPs. The human gut is colonised by a broad variety of microorganisms. This huge number of bacteria and other microorganisms which survive by colonising the gastrointestinal tract is defined as "gut microbiota". The gut microbiome plays a profound role in metabolic processing, energy production, immune and cognitive development and homeostasis. The effects are not only localized in the gut, but also influence many other organs, such as the brain through the microbiome-gut-brain axis. Therefore, given the gut microbiota's key role in host homeostasis, this microbiota may be altered or modified temporarily by factors such as antibiotics, diet and toxins such as pesticides. The aim of this review is to examine scientific articles concerning the impact of microbiota in OP toxicity. Studies focussed on the possible contribution the microbiota has on variable host pharmacokinetic responses such as absorption and biotransformation of xenobiotics will be evaluated. Microbiome manipulation by antibiotic or probiotic administration and faecal transplantation are experimental approaches recently proposed as treatments for several diseases. Finally, microbiota manipulation as a possible therapeutic strategy in order to reduce OP toxicity will be discussed.

Anxiolytic activity of paraoxon is associated with alterations in rat brain glutamatergic system

Exposure to organophosphate (OP) compounds leads to behavioral alterations. To determine whether paraoxon has effects on anxiety, anxiety-like behaviors were assessed in paraoxon-exposed rats. Protein expression of glutamate transporters has also been measured in hippocampus and prefrontal cortex. Three doses of paraoxon (0.3, 0.7, or 1 mg/kg) or corn oil (vehicle) were intraperitoneally injected to adult male rats. At 14 or 28 days after exposure, behavioral tests were done using elevated plus-maze (EPM) or open field tests. Thereafter, animals were sacrificed and both hippocampi and prefrontal cortices were extracted for cholinesterase assay and western blotting. Animals treated with convulsive doses of paraoxon (0.7 and 1 mg/kg) showed an increase in percentage of time spent in open arms and percentage of open arm entries in the EPM. In the open field test, an increase in the time spent in central area was observed in rats treated with the same doses of paraoxon. These effects of paraoxon were independent of any changes in locomotor activity. There was an increase in both astrocytic glutamate transporter proteins (GLAST and GLT-1) in the hippocampus of animals treated with 0.7 and 1 mg/kg of paraoxon. In the prefrontal cortex, protein levels of the GLAST and GLT-1 increased in 0.7 and decreased in 1 mg/kg groups. Only a significant decrease in EAAC1 protein was observed in the prefrontal cortex at 14 days following exposure to 1 mg/kg of paraoxon. Collectively, this study showed that exposure to convulsive doses of paraoxon induced anxiolytic-like behaviors in both behavioral tests. This effect may be attributed to alterations of glutamate transporter proteins in the rat hippocampus and prefrontal cortex.

Screening of organic pollutants in pet hair samples and the significance of environmental factors

Organic pollutants (OPs) represent a wide range of chemicals that are potentially harmful for human and wildlife health. Many of these pollutants have been identified as endocrine disruptors that can alter hormonal balance producing adverse biological effects such as neurotoxicity, reproductive disorders, carcinogenicity and hepatotoxicity. For years, hair has been selected as a non-invasive source to assess levels of animal contamination. In the present study, a multiclass screening method for determining about 60 organic pollutants in pet hair was designed and validated for qualitative and quantitative purposes. Concentrations from different classes of organochlorine, and organophosphate pesticides (OCPs, and OPPs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (NDL-PCBs and DL-PCBs), polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs) were identified in the selected pet hair samples from Ourense (NW, Spain). We detected most of these pollutants in the selected hair pets. The mean concentrations found ranged from 89 to 6556ng/g for OPEs, from 8.6 to 1031ng/g for PAHs, from 8.6 to 256ng/g for PBDEs, from 29 to 184ng/g for OPPs, from 0.29 to 139 for OCPs, from 0.30 to 59ng/g for NDL-PCBs and from 1.2 to 14ng/g for DL-PCBs. To our knowledge, this is the first study to document the presence of OPs in pets from North-West Spain and it could provide baseline information for future monitoring of OPs in the area.

Protective effects of dietary omega-3 fatty acid supplementation on organophosphate poisoning

In this study, we aimed to study the possible preventive effect of docosahexaenoic acid (DHA), a dietary omega-3 fatty acid, on toxicity caused by chlorpyrifos (CPF). Six groups of Sprague Dawley rats (200-250 g) consisting of equal numbers of males and females (n = 8) were assigned to study. The rats were orally given for 5 days. The control group was administered pure olive oil, which was the vehicle for CPF. The CPF challenge groups were administered oral physiological saline, pure olive oil, or DHA (50, 100 and 400 mg/kg dosages) for 5 days. The animals were weighed on the sixth day and then administered CPF (279 mg/kg, subcutaneously). The rats were weighed again 24 h following CPF administration. The body temperatures and locomotor activities of the rats were also measured. Blood samples, brain and liver tissues were collected for biochemical, histopathological and immunohistochemical examinations. A comparison with the control group demonstrated that CPF administration increased malondialdehyde (MDA) levels in blood, brain and liver, while it reduced catalase (CAT), superoxide dismutase (SOD) and glutathione peroxidase (GPx) concentrations ( p < 0.05-0.001). Advanced oxidation protein products (AOPPs) increased only in the brain ( p < 0.001). DHA reduced these changes in MDA and AOPP values ( p < 0.05-0.001), while it increased CAT, SOD and GPx concentrations ( p < 0.05-0.001). Similarly, DHA prevented the decreases in body weight, body temperature and locomotor activities caused by CPF at 100 mg/kg and 400 mg/kg dosages ( p < 0.05-0.001). Similar to the physiological and biochemical changes, the histopathological damage scores, which increased with CPF ( p < 0.05-0.01), decreased at all three dosages of DHA ( p < 0.05-0.01). Our findings suggest that DHA, by supporting the antioxidant mechanism, reduces toxicity caused by CPF.

Analysis of neurobehavioural data by chemometric methods in ecotoxicological studies

Incorporation of chemometric tools in behavioural data management workflows allows for the early identification of most relevant endpoints complementarily to statistical confirmatory approaches. In this work, the effects of two model neurotoxicants, chlorpyrifos (CPF) and nicotine, exposures on behavioural profiles of adult zebrafish at three different times (2, 6 and 24h) were evaluated using open field test (OFT) paradigm experiments. Two chemometric methods like Principal Component Analysis (PCA) and Analysis of Variance-Simultaneous Component Analysis (ASCA) have been used to interpret the changes observed in the obtained behavioural data. A decreased of the locomotor activity, an anxiolytic effect and an altered exploratory behaviour were the most affected behavioural endpoints in the CPF exposures. However, an increase of the locomotor activity and an anxiogenic effect were observed in the nicotine exposures. Finally, an excellent correlation between the ASCA results and the results obtained using traditional statistical procedures for both compounds were encountered.

Methamidophos, an Organophosphorus Insecticide, Induces Pro-aggressive Behaviour in Mice

Although evidence indicates that exposure to organophosphorus (OP) pesticides induces neurobehavioral disorders, little is known about the effects of OP on aggressive behaviour. Our study investigated the effects of repeated exposure to an OP pesticide, methamidophos, on the isolation-induced aggressive behaviour in mice. Forty seven male mice were individually housed for a month. Socially isolated animals were then confronted with a standard non-isolated opponent for 15 min (pre-treatment trial), and the latency and frequency of aggressive and general exploratory behaviours were recorded. Based on the presence of attack behaviour in the pre-treatment trial, mice were classified as isolation-induced aggressive and non-aggressive. All mice were then treated for 7 days with methamidophos (3.5 mg/kg/day, n = 22, intraperitoneal (i.p.)) or saline (1 mL/kg/day, control group, n = 25, i.p.), and a second trial was performed. Repeated exposure to methamidophos induced attack behaviour in non-aggressive mice. The treatment with methamidophos also decreased plasma butyrylcholinesterase and brain acetylcholinesterase activity. These results suggest that methamidophos has a pro-aggressive effect on socially isolated mice.

Zebrafish is a predictive model for identifying compounds that protect against brain toxicity in severe acute organophosphorus intoxication

Acute organophosphorus (OP) intoxication is a worldwide clinical and public health problem. In addition to cholinergic crisis, neurodegeneration and brain damage are hallmarks of the severe form of this toxidrome. Recently, we generated a chemical model of severe acute OP intoxication in zebrafish that is characterized by altered head morphology and brain degeneration. The pathophysiological pathways resulting in brain toxicity in this model are similar to those described in humans. The aim of this study was to assess the predictive power of this zebrafish model by testing the effect of a panel of drugs that provide protection in mammalian models. The selected drugs included “standard therapy” drugs (atropine and pralidoxime), reversible acetylcholinesterase inhibitors (huperzine A, galantamine, physostigmine and pyridostigmine), N-methyl-d-aspartate (NMDA) receptor antagonists (MK-801 and memantine), dual-function NMDA receptor and acetylcholine receptor antagonists (caramiphen and benactyzine) and anti-inflammatory drugs (dexamethasone and ibuprofen). The effects of these drugs on zebrafish survival and the prevalence of abnormal head morphology in the larvae exposed to 4 µM chlorpyrifos oxon [1 × median lethal concentration (LC₅₀)] were determined. Moreover, the neuroprotective effects of pralidoxime, memantine, caramiphen and dexamethasone at the gross morphological level were confirmed by histopathological and transcriptional analyses. Our results demonstrated that the zebrafish model for severe acute OP intoxication has a high predictive value and can be used to identify new compounds that provide neuroprotection against severe acute OP intoxication.

Exposure to Gulf War Illness chemicals induces functional muscarinic receptor maladaptations in muscle nociceptors

Chronic pain is a component of the multisymptom disease known as Gulf War Illness (GWI). There is evidence that pain symptoms could have been a consequence of prolonged and/or excessive exposure to anticholinesterases and other GW chemicals. We previously reported that rats exposed, for 8 weeks, to a mixture of anticholinesterases (pyridostigmine bromide, chlorpyrifos) and a Nav (voltage activated Na(+) channel) deactivation-inhibiting pyrethroid, permethrin, exhibited a behavior pattern that was consistent with a delayed myalgia. This myalgia-like behavior was accompanied by persistent changes to Kv (voltage activated K(+)) channel physiology in muscle nociceptors (Kv7, KDR). In the present study, we examined how exposure to the above agents altered the reactivity of Kv channels to a muscarinic receptor (mAChR) agonist (oxotremorine-M). Comparisons between muscle nociceptors harvested from vehicle and GW chemical-exposed rats revealed that mAChR suppression of Kv7 activity was enhanced in exposed rats. Yet in these same muscle nociceptors, a Stromatoxin-insensitive component of the KDR (voltage activated delayed rectifier K(+) channel) exhibited decreased sensitivity to activation of mAChR. We have previously shown that a unique mAChR-induced depolarization and burst discharge (MDBD) was exaggerated in muscle nociceptors of rats exposed to GW chemicals. We now provide evidence that both muscle and vascular nociceptors of naïve rats exhibit MDBD. Examination of the molecular basis of the MDBD in naïve animals revealed that while the mAChR depolarization was independent of Kv7, the action potential burst was modulated by Kv7 status. mAChR depolarizations were shown to be dependent, in part, on TRPA1. We argue that dysfunction of the MDBD could be a functional convergence point for maladapted ion channels and receptors consequent to exposure to GW chemicals.

Low-level repeated exposure to diazinon and chlorpyrifos decrease anxiety-like behaviour in adult male rats as assessed by marble burying behaviour

Occupational exposure to organophosphate (OPs) pesticides is reported to increase in the risk of developing anxiety and depression. Preclinical studies using OP levels, which inhibit acetylcholinesterase activity, support the clinical observations, but little is known of the effects of exposure below this threshold. We examined the effects of low level OP exposure on behaviours and neurochemistry associated with affective disorders. Adult rats were administered either diazinon (1 mg/kg i.p.) which is present in sheep dip and flea collars, chlorpyrifos (1 mg/kg i.p.) which is present in crop sprays, or vehicle for 5 days. OP exposure did not affect acetylcholinesterase activity (blood, cerebellum, caudate putamen, hippocampus, prefrontal cortex), anhedonia-like behaviour (sucrose preference), working memory (novel object recognition), locomotor activity or anxiety-like behaviour in the open field arena. In contrast OP exposure attenuated marble burying behaviour, an ethological measure of anxiety. The diazinon-induced reduction in marble burying persisted after exposure cessation. In comparison to vehicle, dopamine levels were lowered by chlorpyrifos, but not diazinon. 5-HT levels and turnover were unaffected by OP exposure. However, 5-HT transporter expression was reduced by diazinon suggesting subtle changes in 5-HT transmission. These data indicate exposure to occupational and domestic OPs, below the threshold to inhibit acetylcholinesterase, can subtly alter behaviour and neurochemistry.

Effect of monocrotophos, an organophosphorus insecticide, on the striatal dopaminergic system in a mouse model of Parkinson’s disease

Our earlier study had shown that low concentrations of monocrotophos (MCP) elicited dopaminergic features of Parkinson’s disease (PD) in the nematode Caenorhabditis elegans. In the present study, the effect of low doses of MCP on the striatal dopaminergic neurons was investigated using the mouse model system. MCP was initially screened for its ability to cause any neurobehavioral deficits and alterations in the dopaminergic system in Swiss albino mice, aged 8 weeks and weighing 25–30 g, with repeated doses at 0.3 and 0.6 mg/kg body weight (b.w.)/day for 7 days and 30 days. Mice were treated with four intraperitoneal injections for every 2 h with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) at the dosage of 14 mg/kg b.w. MCP was administered to these mice at the above-mentioned doses for 7 days. Mice administered with MCP alone revealed a significant ( p < 0.05) reduction in the dopamine (DA) content at both 7 and 30 days and showed a significant ( p < 0.05) increase in neurobehavioral deficits. Interestingly, when MCP was administered for 7 days to MPTP-treated mice, further significant decrease in both DA content and increase in neurobehavioral deficits were apparent. The extent of reactive oxygen species and lipid peroxidation were markedly increased, while the ratio of reduced to oxidized glutathione levels were significantly decreased ( p < 0.05) in the treated mice as compared to the control. Significant histopathological alterations and a marked reduction in the number of tyrosine hydroxylase positive cells were evident in striatum of mice treated with higher doses of MCP. These changes were comparable to that seen in mice treated with MPTP and post-administered lower doses of MCP. Our findings suggest that MCP per se has the propensity to induce pathological changes in the dopaminergic neurons as well as augment the degeneration in a compromised nigrostriatal system such as that in PD.

Neurologic dysfunction and genotoxicity induced by low levels of chlorpyrifos

Chlorpyrifos (CPF) is an organophosphorus cholinesterase inhibitor widely used as an insecticide. Neuro and genotoxicity of this agent were evaluated following daily subcutaneous injections at 0.1, 1 and 10mg/kg or its vehicle to laboratory rats during one week, at the end of which somatosensory evoked potentials (SEP) and power spectrum of the electroencephalogram (EEGp) were recorded under urethane anesthesia. In another group of conscious animals, auditory startle reflex (ASR) was evaluated followed, after euthanasia, with measurements of plasma B-esterases, and genotoxicity with the alkaline comet assay (ACA) at the same CPF doses. The results indicated a CPF dose related inhibition of B-esterases. Enhanced inhibition of the ASR by a subthreshold pre-pulse was observed at all doses and ACA showed a significant higher DNA damage than vehicle controls in animals exposed to 10mg/kg CPF. A trend to higher frequencies of EEGp and an increase in amplitude of the first negative wave of the SEP were found at all doses. The first positive wave of the SEP decreased at the CPF dose of 10mg/kg. In summary, a shift to higher EEG frequencies and alterations of somatosensory and auditory input to the central nervous system were sensitive manifestations of CPF toxicity, associated with depression of B-esterases. The changes in electrical activity of the cerebral cortex and DNA damage observed at doses that do not elicit overt toxicity may be useful in the detection of CPF exposure before clinical signs appear.

Time course of serum S100B protein and neuron-specific enolase levels of a single dose of chlorpyrifos in rats

Organophosphate (OP) compounds are a large class of chemicals, many of which are used as pesticides. It is suggested that OPs specifically affect glia and neurons. Effects of acute exposure to chlorpyrifos (CPF), which is a common organophosphorus pesticide used worldwide, on neuron-specific enolase (NSE) and S100B levels in rat blood during 7 days were assessed. Rats were evaluated either before (0 hr) or 2, 12, 24, 48 and 168 hr (7 days) after injection of CPF (279 mg/kg, s.c.) or vehicle (peanut oil, 2 ml/kg, s.c.) for clinical signs of toxicity. Immediately after the evaluation of toxicity, blood samples were taken for biochemical assays. CPF administration produced decreases in body-weight and temperature, which were observed for first time at 12 hr after CPF administration and continued for 168 hr (p < 0.05-0.001). Serum S100B and NSE levels were acutely increased 2 hr after CPF administration and remained high at 12 hr (p < 0.01-0.001). NSE and S100B levels were not different in either CPF or vehicle groups at following time points. Serum butyrylcholinesterase (EC 3.1.1.8; BuChE) activity was dramatically reduced at 2 hr after CPF and remained low at each time points during 7 days (p < 0.01-0.001). Our results suggest that the usefulness of serum levels of these glia- and neuron-specific marker proteins in assessing OP toxicity, specifically CPF-induced toxicity.

Repeated exposure to chlorpyrifos alters the performance of adolescent male rats in animal models of depression and anxiety

Chlorpyrifos (CPF) is a broad spectrum, highly effective organophosphorus (OP) pesticide that has been largely used worldwide. Over the past decades, numerous studies have assessed the potential neurotoxic effects of either acute or chronic exposure to CPF on developing brain. Despite being an acetylcholinersterase inhibitor, the effects of CPF are not only confined to cholinergic system, but are involved in a wide variety of neurotransmitter systems, especially the serotonin (5-HT) system, which leads to long-lasting changes in 5-HT-related emotional behaviors. In our present study, 4-week-old adolescent male Sprague-Dawley rats were repeatedly exposed to CPF at daily doses of 10, 20, 40, 80, and 160 mg/kg/day (s.c., 7 days), and then subjected to a battery of emotional behavioral tests that related to serotonergic function in order to determine CPF effects in adolescent rats. Results in behavioral tests demonstrated CPF significantly increased the entries to and time spent in the open arms in the elevated plus-maze test at the dose of 40-160 mg/kg, the number of shocks in the Vogel's conflict test at the dose of 20-160 mg/kg, and significantly decreased the latency to feed in the novelty-suppressed feeding test in both dose range. Interestingly, in the forced swimming test, at the dose of 10mg/kg, CPF significantly increased the immobility time, whereas it significantly decreased the immobility time at the dose of 160 mg/kg. Our data suggest that repeated exposure to CPF elicits alterations of the emotional behaviors related to serotonergic nervous system in adolescent male rats. However, the underlying mechanism needs further investigations.

Impulsivity as long-term sequelae after chlorpyrifos intoxication: time course and individual differences

Chlorpyrifos (CPF) is a common organophosphate (OP) insecticide that has been widely used in agriculture as a pesticide. The primary mechanism of acute toxic action of OPs is initiated by acetylcholinesterase (AChE) inhibition. However, non-AChE targets have also been proposed as alternative that contributes to the acute lethal action and side effects of short or long-term exposure. Recently, we have found that a single dose of 250 mg/kg CPF produces acceleration in acquisition on schedule-induced polydipsia (SIP) procedure 6 months after its administration. Moreover, CPF animals show a higher level of impulsivity in a delay-discounting task 1 year after acute administration, and these effects are potentiated when animals are divided into high (HD) and low (LD) drinkers in SIP. In the present study, rats were injected with a subcutaneous (sc) dose of 250 mg/kg of CPF, and 10 weeks later its effect on delay-discounting task was evaluated. Consequently, these animals were evaluated based on SIP, and divided into two populations (HD and LD) according to their rates of drinking in this task. One year after OP administration, these animals were re-evaluated in a delay-discounting task. Results revealed that the CPF-administered rats prefer immediate reward and show a more impulsive choice, 10 weeks after CPF administration. Furthermore, 1 year after it administration, only animals treated with CPF that are high drinkers on SIP are more impulsive than the rest of the groups Therefore, these data suggest that some individuals are more sensitive to OP intoxication than the others, at least in terms of durability of sequelae.

Behavioral and biochemical effects of neonicotinoid thiamethoxam on the cholinergic system in rats

Thiamethoxam is a neonicotinoid insecticide, a group of pesticides that acts selectively on insect nicotinic acetylcholine receptors (nAChRs), with only a little action on mammalian nAChRs. Nevertheless, the selectivity of neonicotinoids for the insect nAChRs may change when these substances are metabolized. Therefore, we aimed to determine the potential effects of thiamethoxam on mammalian brain, testing the performance in the open field and elevated plus-maze of rats exposed to this insecticide and, in order to establish the neurochemical endpoints, we measured the acetylcholinesterase activity in different brain regions (hippocampus, striatum and cortex) and the high-affinity choline uptake (HACU) in synaptosomes from rat hippocampus. Treated animals received thiamethoxam (25, 50 or 100mg/kg) for 7 consecutive days. The results showed that treatment with thiamethoxam induced an increase in the anxiety behavior at two doses (50 or 100mg/kg). Moreover, there was a significant decrease in both HACU and acetylcholinesterase activity. Our hypothesis is that thiamethoxam (or its metabolites) could be acting on the central rats nAChRs. This would produce an alteration on the cholinergic transmission, modulating the anxiety behavior, acetylcholinesterase levels and HACU.

Acute high dose of chlorpyrifos alters performance of rats in the elevated plus-maze and the elevated T-maze

Chlorpyrifos (CPF) is a broad spectrum organophosphate (OP) pesticide widely used in agriculture, industry and household. Several animal studies indicate emotional disturbances after CPF exposure, although the results are sometimes puzzling. Thus, both anxiolytic and anxiogenic effects of CPF have been reported in different animal models of anxiety [Sánchez-Amate MC, Flores P, Sánchez-Santed F. Effects of chlorpyrifos in the plus-maze model of anxiety. Behav Pharmacol 2001;12:285-92; Sánchez-Amate MC, Dávila E, Cañadas F, Flores P, Sánchez-Santed F. Chlorpyrifos shares stimulus properties with pentilenetetrazol as evaluated by and operant drug discrimination task. Neurotoxicology 2002;23:795-803; López-Crespo G, Carvajal F, Flores P, Sánchez-Santed F, Sánchez-Amate MC. Time-course of biochemical and behavioural effects of a single high dose of chlorpyrifos. Neurotoxicology 2007;28:541-7]. On the other hand, other behavioural effects of CPF are time-dependent [López-Crespo G, Carvajal F, Flores P, Sánchez-Santed F, Sánchez-Amate MC. Time-course of biochemical and behavioural effects of a single high dose of chlorpyrifos. Neurotoxicology 2007;28:541-7], raising the question that the effects of CPF could be task and post-administration time dependent. To test this hypothesis, three groups of rats were treated with a single high dose of CPF (250 mg/kg); one of the groups was tested on day 5 on the elevated plus-maze, to complete our previous study on day 2 [Sánchez-Amate MC, Flores P, Sánchez-Santed F. Effects of chlorpyrifos in the plus-maze model of anxiety. Behav Pharmacol 2001;12:285-92]. The remaining groups were tested on the elevated T-maze on days 2 and 5. CPF produced an increased open arm activity on the elevated plus-maze on day 5, an increased escape latency on the elevated T-maze on day 2 and an impaired inhibitory avoidance on day 5. Data are discussed taking together all studies carried out in our laboratory, confirming that CPF effects on emotional behaviour are dependent on both task contingencies and post-administration time.

Long-term monoamine changes in the striatum and nucleus accumbens after acute chlorpyrifos exposure

This study examined the time-course effects (2, 7, 14 and 30 days) of acute chlorpyrifos (CPF) intoxication (250 mg/kg, s.c.) on monoamine systems and acetylcholinesterase (AChE) activity in the striatum and nucleus accumbens of adult male rats. We show that CPF produced significant long-term inhibition of AChE activity in the striatum and nucleus accumbens. In the striatum, CPF intoxication resulted in changes in dopamine (DA) metabolism after 2 days and changes in serotonin (5-HT) turnover after 7 and 15 days. Significant decreases in monoamine content including norepinephrine (NE), DA, 5-HT and their metabolites were found in the nucleus accumbens 30 days after CPF intoxication. These results suggest that acute exposure to CPF induces long-term changes in the monoamine systems (NE, DA and 5-HT) in adult animals. The lack of correlation between regional AChE activity and neurochemical outcomes points to independent mechanisms.