Neuropathy target esterase in mouse whole blood as a biomarker of exposure to neuropathic organophosphorus compounds

The adult hen is the standard animal model for testing organophosphorus (OP) compounds for organophosphorus compound‐induced delayed neurotoxicity (OPIDN). Recently, we developed a mouse model for biochemical assessment of the neuropathic potential of OP compounds based on brain neuropathy target esterase (NTE) and acetylcholinesterase (AChE) inhibition. We carried out the present work to further develop the mouse model by testing the hypothesis that whole blood NTE inhibition could be used as a biochemical marker for exposure to neuropathic OP compounds. Because brain NTE and AChE inhibition are biomarkers of OPIDN and acute cholinergic toxicity, respectively, we compared NTE and AChE 20‐min IC₅₀ values as well as ED₅₀ values 1 h after single intraperitoneal (i.p.) injections of increasing doses of two neuropathic OP compounds that differed in acute toxicity potency. We found good agreement between the brain and blood for in vitro sensitivity of each enzyme as well for the ratios IC₅₀(AChE)/IC₅₀(NTE). Both OP compounds inhibited AChE and NTE in the mouse brain and blood dose‐dependently, and brain and blood inhibitions in vivo were well correlated for each enzyme. For both OP compounds, the ratio ED₅₀(AChE)/ED₅₀(NTE) in blood corresponded to that in the brain despite the somewhat higher sensitivity of blood enzymes. Thus, our results indicate that mouse blood NTE could serve as a biomarker of exposure to neuropathic OP compounds. Moreover, the data suggest that relative inhibition of blood NTE and AChE provide a way to assess the likelihood that OP compound exposure in a susceptible species would produce cholinergic and/or delayed neuropathic effects. Copyright © 2016 John Wiley & Sons, Ltd.     

In vitro age-related differences in rats to organophosphates

The mechanism of toxic action for organophosphates (OPs) is the persistent inhibition of acetylcholinesterase (AChE) resulting in accumulation of acetylcholine and subsequent hyperstimulation of the nervous system. Organophosphates display a wide range of acute toxicities. Differences in the OP's chemistries results in differences in the compound's metabolism and toxicity. Acute toxicities of OPs appear to be principally dependent on compound specific efficiencies of detoxication, and less dependent upon efficiencies of bioactivation and sensitivity of AChE. Serine esterases, such as carboxylesterase (CaE) and butyrylcholinesterase (BChE), play a prominent role in OP detoxication. Organophosphates can stoichiometrically inhibit these enzymes, removing OPs from circulation thus providing protection for the target enzyme, AChE. This in vitro study investigated age-related sensitivity of AChE, BChE and CaE to twelve structurally different OPs in rat tissues. Sensitivity of esterases to these OPs was assessed by inhibitory concentration 50s (IC₅₀s). The OPs displayed a wide range of inhibitory potency toward AChE with IC₅₀s in the low nM-μM range with no differences among ages; however, the CaE IC₅₀s generally increased with age reflecting greater protection in adults. These results suggest age-related differences in acute toxicities of OPs in mammals are primarily a result of their detoxication capacities.     

Further studies toward a mouse model for biochemical assessment of neuropathic potential of organophosphorus compounds

Inhibition and aging of neuropathy target esterase (NTE) by neuropathic organophosphorus (OP) compounds triggers OP compound‐induced delayed neuropathy (OPIDN), whereas inhibition of acetylcholinesterase (AChE) produces cholinergic toxicity. The neuropathic potential of an OP compound is defined by its relative inhibitory potency toward NTE vs. AChE assessed by enzyme assays following dosing in vivo or after incubations of direct‐acting compounds or active metabolites with enzymes in vitro. The standard animal model of OPIDN is the adult hen, but its large size and high husbandry costs make this species a burdensome model for assessing neuropathic potential. Although the mouse does not readily exhibit clinical signs of OPIDN, it displays axonal lesions and expresses brain AChE and NTE. Therefore, the present research was performed as a further test of the hypothesis that inhibition of mouse brain AChE and NTE could be used to assess neuropathic potential using mouse brain preparations in vitro or employing mouse brain assays following dosing of OP compounds in vivo. Excellent correlations were obtained for inhibition kinetics in vitro of mouse brain enzymes vs. hen brain and human recombinant enzymes. Furthermore, inhibition of mouse brain AChE and NTE after dosing with OP compounds afforded ED₅₀ ratios that agreed with relative inhibitory potencies assessed in vitro. Taken together, results with mouse brain enzymes demonstrated consistent correspondence between in vitro and in vivo predictors of neuropathic potential, thus adding to previous studies supporting the validity of a mouse model for biochemical assessment of the ability of OP compounds to produce OPIDN. Copyright © 2014 John Wiley & Sons, Ltd.     

The specificity of carboxylesterase protection against the toxicity of organophosphorus compounds.

The ability of endogenous carboxylesterase (CaE) to protect against the lethal effects of a variety of organophosphorus (OP) compounds was examined in rats. The in vivo protection provided by endogenous CaE was measured by the difference in the LD50 values of OP compounds in control rats and rats whose CaE activity had been inhibited by sc injection with 2 mg/kg of 2-(O-cresyl)-4H-1,3,2-benzodioxaphosphorin-2-oxide. Endogenous CaE provided significant protection against the in vivo toxicity of soman, sarin, tabun, and paraoxon, but not against dichlorvos, diisopropyl fluorophosphate, or ethoxymethyl-S-[2-(diisopropylamino)ethyl] thiophosphonate (VX). The relationship between the in vivo CaE protection against OP compounds and their relative reactivities with CaE and acetylcholinesterase (AChE) was evaluated by measuring the in vitro bimolecular rate constants (ki) for inhibition of plasma CaE and brain AChE. Except for VX, ki values for CaE inhibition varied less than 10-fold while ki values for AChE inhibition varied 10(5)-fold. The degree of in vivo inhibition of CaE by equitoxic doses of the OP compounds increased as the CaE/AChE ki ratio increased. However, the protective ratio of the LD50 values in control vs CaE-inhibited rats decreased as the CaE/AChE ki ratio increased. This inverse relationship between in vivo CaE protection and relative in vitro reactivity for CaE suggested that CaE detoxication is more important for highly toxic OP compounds (i.e., compounds with high AChE ki values and low LD50 values) than for less toxic compounds.     

Tissue-Specific Effects of Chlorpyrifos on Carboxylesterase and Cholinesterase Activity in Adult Rats: An in Vitro and in Vivo Comparison

Organophosphate (OP) pesticides can bind to carboxylesterase(CaE), which may lower the concentration of OPs at the targetsite enzyme, acetylcholinesterase (ChE). It is unclear fromthe literature whether it is the CaE's affinity for the OP and/orthe number of CaE molecules which is the dominant factor indetermining the protective potential of CaE. We undertook adetailed, in vitro and in vivo survey of both CaE and ChE toascertain if in vitro sensitivity of CaE and ChE predicted thepattern of inhibition seen after in vivo dosing with chlorpyrifos(CPF; 80 mg/ kg, p.o.) in male or female adult Long-Evans rats.For the brain, the in vitro sensitivity to CPF-oxon did predictthe in vivo patterns of inhibition: In vitro, brain ChE wasapproximately 25 times more sensitive to the active metabolite,CPF-oxon, than brain CaE, and in vivo brain ChE was more inhibitedthan brain CaE. In contrast, the in vitro sensitivity of plasmaChE and CaE did not correlate well with the in vivo patternof inhibition: In vitro, plasma ChE was approximately 6.5 timesless sensitive to CPF-oxon than plasma CaE, but in vivo, plasmaChE was more inhibited than CaE. In order to understand therole of CaE in protecting the brain ChE from inhibition by CPF-oxonin vitro, adult rat striatal tissue was incubated in the presenceand absence of adult rat liver tissue and IC₅₀S of CPF-oxonwere determined. The increase in the striatal CPF-oxon IC₅₀value noted for ChE in the presence of liver suggested thatCaE was binding the CPF-oxon and limiting its access to ChE.Male liver CaE, which has the same affinity for binding CPF-oxonas female liver CaE but has twice as many binding sites, causeda greater increase in the striatal CPF-oxon IC₅₀ than femaleliver, suggesting that the number of binding sites does playa role in the detoxification potential of a tissue. In summary,we found that (1) there are tissue and gender-related differencesfor basal ChE and CaE activity; (2) the in vitro sensitivityof CaE or ChE to CPF-oxon is highly tissue-specific; (3) thepattern of ChE and CaE inhibition after in vivo dosing withCPF is not necessarily predictable from the in vitro IC₅₀ forthese same enzymes, and (4) the number of CaE molecules mayplay a role in modifying the toxicity of CPF.     

Oxidative stress biomarkers in Cyprinus carpio exposed to commercial herbicide bispyribac‐sodium

Cyprinus carpio were exposed under field conditions to 20.87 µg l^?1 of commercial herbicide bispyribac‐sodium (Nominee®, SC), during 7, 21 and 72 days. Enzymatic parameters such as catalase (CAT), glutathione S‐transferase (GST) and acetylcholinesterase (AChE) activities, as well as thiobarbituric acid‐reactive substances (TBARS) and protein carbonyl contents were studied in different tissues. After 7 days of exposure, GST activity decreased. At the same period, brain AChE activity increased, but a reduction of activity was observed in muscle tissue. Brain TBARS levels increased at 7 days. After 21 days of exposure liver CAT levels and muscle AChE activities decreased. In the same period, liver protein carbonyl and muscle TBARS increased. After 72 days of exposure in the field, AChE activity was reduced in both brain and muscle. Protein carbonyl contents in liver and brain TBARS levels increased. Muscle AChE activity, TBARS and protein carbonyl can be used as biomarkers of exposure to the herbicide bispyribac‐sodium. This study demonstrates effects of exposure to bispyribac‐sodium under rice field conditions on oxidative stress parameters in tissues of Cyprinus carpio. Copyright © 2010 John Wiley & Sons, Ltd.     

Function of plasma and microsomal enzymes in soman toxicity

Such organophosphorous (OP) nerve agents as sarin (isopropyl methylphosphonofluoridate) and soman (pinacolyl methylphosphonofluoridate) are effective inhibitors of acetylcholinesterases (AChE), butyrylcholinesterases (BChE) and carboxylesterases (CaE). The acute toxicity of these compounds in mammals is known to be mediated through inhibition of AChEs, which leads to increased acetylcholine (ACh) levels. The aim of this study was to compare the significance of the plasma CaEs, microsomal CaEs and CYP450 enzymes in detoxification of soman with and without physostigmine treatment. The mice received physostigmine (0.1 mg/kg body wt) intravenously (i.v.) 10 min prior to the intraperitoneal (i.p.) injection of soman (0.400-0.650 mg/kg body wt in olive oil). To avoid possible signs of poisoning, the animals received atropine sulfate (37.5 mg/kg body wt in saline) subcutaneously (s.c.) immediately after the soman administration. In the present study, the inhibitory effect of soman was greater in plasma CaE than in hepatic microsomal CaE fraction. In addition, soman or the combination of soman-physostigmine had no remarkable effect on the microsomal CaE or P4502B activities. In spite of this, however, the microsomal CaEs might offer more protection against multiple LD50s of soman.     

Responses of AChE and GST activities to insecticide coexposure in Carassius auratus

Organophosphates and carbamates are widely used pesticides and play an important role in global agriculture. The misuse of these compounds has caused environmental problems and has had a negative impact on wildlife. In this study, the in vivo effects of commercial chlorpyrifos and isoprocarb on acetylcholinesterase (AChE) and glutathione S‐transferase (GST) activities in goldfish (Carassius auratus) were investigated. Muscle and brain AChE activity was significantly inhibited by chlorpyrifos and isoprocarb (alone and in combination) after 2, 5, 10, and 15 days of exposure, and obvious concentration‐response and time‐response relationships were obtained. Gill GST activity was significantly inhibited by chlorpyrifos and isoprocarb (single compounds and in combination), however, concentration dependence and time dependence were not apparent. The joint effect of chlorpyrifos/isoprocarb was additive with regard to AChE activity inhibition and was antagonistic with regard to GST activity inhibition. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.     

Oxime-mediated in vitro reactivation kinetic analysis of organophosphates-inhibited human and electric eel acetylcholinesterase

Organophosphate (OP)-based pesticides and nerve agents are highly toxic compounds which interrupt the catalytic mechanism of acetylcholinesterase (AChE) by phosphorylating the hydroxyl moiety of serine residue. The inhibited enzyme can be reactivated by the nucleophilic action of oxime reactivators. To analyze the effect of different AChE sources on reactivation efficacy of reactivators, several in vivo studies have carried out using variety of AChE sources like pig, rat and monkey. Investigations on species differences provide a better insight for the development of new reactivators. Hence, present study was mainly targeted on comparative analysis of the reactivation of electric eel and human AChE inhibited by different OP. A series of butene-linked bis-pyridinium mono oximes which vary in functional groups present at the second pyridinium ring have been examined against sarin, VX, tabun and ethyl-paraoxon-poisoned AChE. In case of tabun-inhibited AChEs, tested oximes were better than reference oximes. For VX-poisoned human AChE, reactivator K251 (k_r2;1.51?mM?^??^1?min?^??¹) showed good reactivation efficacy with standard oximes. Studies stipulated that butene-linked oximes consisting of different functional moieties are good reactivators and found to have better efficacy to reactivate nerve agent-inhibited human AChE in comparison to eel AChE.     

Acute toxicity of apple snail Pomacea canaliculata’s eggs on Rhinella arenarum tadpoles

The effect of the crude homogenate of snail Pomacea canaliculata’s eggs (CHSE) exposition on Rhinella arenarum tadpoles was investigated. Exposure to 10?g CHSE/L treatment produced 95% tadpole mortality, whereas the median lethal concentration (48-h LC₅₀) was 4.35?g/L. Moreover, CHSE inhibited significantly the activities of acetylcholinesterase (AChE) and glutathione-S-transferase (GST) with respect to control tadpoles, and modified tadpoles swimming behavior. Together all these evidences indicate that eggs of snail P. canaliculata have a neurotoxic effect on tadpoles limiting survival at low concentrations and short time exposition.     

In vitro Reactivating Effects of Standard and Newly Developed Oximes on Malaoxon‐Inhibited Mouse Brain Acetylcholinesterase

Abstract: Malathion is an organophosphate (OP) pesticide whose toxicity depends on its bioactivation to malaoxon. Human malathion poisoning has been treated with oximes (mainly pralidoxime) in an attempt to reactivate OP‐inhibited acetylcholinesterase (AChE). However, pralidoxime has shown unsatisfactory therapeutic effects in malathion poisoning and its routine use has been questioned. In this study, we evaluated the in vitro potency of standards and newly developed oximes in reactivating malaoxon‐inhibited AChE derived from mouse brain supernatants. Malaoxon displayed a concentration‐dependent inhibitory effect on mouse brain AChE (IC₅₀ = 2.36 μM), and pralidoxime caused a modest reactivating effect (30% of reactivation at 600 μM). Obidoxime and trimedoxime, as well as K047 and K075, displayed higher reactivating effects (from 55% to 70% of reactivation at 600 μM) when compared with pralidoxime. The results show that obidoxime, trimedoxime, K074 and K075 present higher reactivating effects on malaoxon‐inhibited AChE under in vitro conditions when compared with pralidoxime. Taking into account the unsatisfactory effects of pralidoxime as antidotal treatment in malathion poisonings, the present results suggest that obidoxime, trimedoxime, K074 and K075 might be interesting therapeutic strategies to reactivate malaoxon‐inhibited AChE in malathion poisonings.     

Evaluation of spatial and temporal changes in biomarker responses in the common carp (Cyprinus carpio L.) for biomonitoring the Meriç Delta, Turkey

The aim of this study is to examine the activity of several biomarkers in carp, Cyprinus carpio L., to determine their response to xenobiotics, such as organochlorine pesticides (OCPs), in the Meriç Delta. Fish were collected from contaminated sites and from areas regarded as relatively less contaminated in four sampling periods. Hepatic glutathione S-transferase (GST), carboxylesterase (CaE), lactate dehydrogenase, aspartate aminotransferase, and acid phosphatase activities were measured as biomarkers in the fish. For all fish, the condition factor and hepatosomatic index, were calculated to determine the condition of the fish. The results of this study indicated that the mean GST activity showed an increase in fish from the Meriç-Ergene junction site and a decrease in Enez site with respect to fish from Meriç site. Furthermore, the study shows that spatial and temporal changes of biomarkers such as GST and CaE might be useful for the assessment of environmental contamination in the Meriç Delta.     

B-esterase determination and organophosphate insecticide inhibitory effects in JEG-3 trophoblasts

The placenta and trophoblasts express several B-esterases. This family includes acethylcholinesterase (AChE), carboxylesterase (CES) and butyrylcholinesterase (BChE), which are important targets of organophosphate insecticide (OP) toxicity. To better understand OP effects on trophoblasts, B-esterase basal activity and kinetic behavior were studied in JEG-3 choriocarcinoma cell cultures. Effects of the OP azinphos-methyl (Am) and chlorpyrifos (Cp) on cellular enzyme activity were also evaluated.JEG-3 cells showed measurable activity levels of AChE and CES, while BChE was undetected. Recorded Km for AChE and CES were 0.33 and 0.26 mM respectively. Native gel electrophoresis and RT-PCR analysis demonstrated CES1 and CES2 isoform expression. Cells exposed for 4 and 24 h to the OP Am or Cp, showed a differential CES and AChE inhibition profiles. Am inhibited CES and AChE at 4 h treatment while Cp showed the highest inhibition profile at 24 h. Interestingly, both insecticides differentially affected CES1 and CES2 activities.Results demonstrated that JEG-3 trophoblasts express AChE, CES1 and CES2. B-esterase enzymes were inhibited by in vitro OP exposure, indicating that JEG-3 cells metabolization capabilities include phase I enzymes, able to bioactivate OP. In addition, since CES enzymes are important for medicinal drug activation/deactivation, OP exposure may interfere with trophoblast CES metabolization, probably being relevant in a co-exposure scenario during pregnancy.     

Overview of the toxic effects of titanium dioxide nanoparticles in blood,liver, muscles,and brain of a Neotropical detritivorous fish

The toxicity of titanium dioxide nanoparticles (TiO₂‐NP) in the blood, liver, muscle, and brain of a Neotropical detritivorous fish, Prochilodus lineatus, was tested. Juvenile fish were exposed to 0, 1, 5, 10, and 50 mg L^?1 of TiO₂‐NP for 48 hours (acute exposure) or 14 days (subchronic exposure) to evaluate changes in hematology, red blood cell (RBC) genotoxicity/mutagenicity, liver function (reactive oxygen species (ROS) production, antioxidant responses, detoxification, and histopathology), acetylcholinesterase (AChE) activity in muscles and brain, and Ti bioaccumulation. TiO₂‐NP did not cause genetic damage to RBC, but acutely decreased white blood cells (WBC) and increased monocytes. Subchronically, RBC decreased, mean cell volume and hemoglobin increased, and WBC and lymphocytes decreased. Therefore, NP has the potential to affect immune system and increase energy expenditure, reducing the fish's ability to avoid predator and to resist pathogens. In the liver, acute exposure decreased ROS and increased glutathione (GSH) content, while subchronic exposure decreased superoxide dismutase activity and increased glutathione‐S‐transferase (GST) activity and GSH content. GSH and GST seem to play an essential role in metabolizing NP and ROS, likely increasing hepatocytes' metabolic rate, which may be the cause of observed cell hypertrophy, disarrangement of hepatic cords and degenerative morphological alterations. Although most studies indicate that the kidney is responsible for metabolizing and/or eliminating TiO₂‐NP, this study shows that the liver also has a main role in these processes. Nevertheless, Ti still accumulated in the liver, muscle, and brain and decreased muscular AChE activity after acute exposure, showing neurotoxic potential. More studies are needed to better understand the biochemical pathways TiO₂‐NP are metabolized and how its bioaccumulation may affect fish homeostasis and survival in the environment.     

Sublethal effects of pesticide mixtures on selected biomarkers of Carassius auratus

In the present study, the in vivo effects of commercial propoxur alone and in combination with isoprocarb and chlorpyrifos on acetylcholinesterase and glutathione S-transferases activities in goldfish (Carassius auratus) were investigated. Brain and muscle AChE activity was significantly inhibited (88% and 85% at most, respectively) by propoxur after 5 d of exposure at concentrations between 141 and 2263 μg/L, bell-shaped concentration–response curves were obtained. In most cases, time dependence was apparent. Under insecticide mixture exposure (binary mixture propoxur/isoprocarb and ternary mixture propoxur/isoprocarb/chlorpyrifos), the inhibition of AChE activity was significant in all cases and linear concentration–response relationships were observed. Propoxur (alone and in combination) significantly inhibited gill GST activity, and both mixtures also induced significant inhibition of liver GST activity. However, concentration and time dependence were not apparent. AChE is likely to be more informative than GST and seems to be a good biomarker to diagnose exposure to anticholinesterase pesticides in wild populations of this species.     

Phoxim‐induced damages of Bombyx mori larval midgut and titanium dioxide nanoparticles protective role under phoxim‐induced toxicity

Phoxim (O,O‐diethyl O‐(alpha‐cyanobenzylideneamino) phosphorothioate) is a powerful organophosphorus pesticide with high potential for Bombyx mori larvae of silkworm exposure. However, it is possible that during the phoxim metabolism, there is generation of reactive oxygen species (ROS) and phoxim may produce oxidative stress and neurotoxicity in an intoxicated silkworm. Titanium dioxide nanoparticles (TiO₂ NPs) pretreatment has been demonstrated to increase antioxidant capacity and acetylcholinesterase (AChE) activity in organisms. This study was, therefore, undertaken to determine phoxim‐induced oxidative stress and neurotoxicity to determine whether phoxim intoxication alters the antioxidant system and AChE activity in the B. mori larval midgut, and to determine whether TiO₂ NPs pretreatment attenuates phoxim‐induced toxicity. The findings suggested that phoxim exposure decreased survival of B. mori larvae, increased malondialdehyde (MDA), carbonyl and 8‐OHdG levels, and ROS accumulation in the midgut. Furthermore, phoxim significantly decreased the activities of AChE, superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione‐S‐transferase (GST), and levels of ascorbic acid (AsA), reduced glutathione (GSH), and thiol in the midgut. TiO₂ pretreatment, however, could increase AChE activity, and remove ROS via activating SOD, CAT, APX, GR, and GST, and accelerating AsA–GSH cycle, thus attenuated lipid, protein, and DNA peroxidation and improve B. mori larval survival under phoxim‐induced toxicity. Moreover, this experimental system would help nanomaterials to be applied in the sericulture. © 2013 Wiley Periodicals, Inc. Environ Toxicol 29: 1355–1366, 2014.     

Pollution biomarkers in the spiny lizard (Sceloporus spp.) from two suburban populations of Monterrey, Mexico

Environmental pollution may severely impact reptile species in urbanized areas. The magnitude of the impact is analyzed in the present study using lizard tail tips for the quantitative evaluation of enzymatic biomarkers of pollution. Spiny lizards (Sceloporus serrifer and S. torquatus) were collected from two suburban localities in the Monterrey metropolitan area, Mexico: Chipinque Ecological Park, a natural protected area, and El Carmen Industrial Park (IP), a highly polluted site. Different enzymes were used as biomarkers including: acetylcholinesterase (AChE), butyrylcholinesterase (BChE), carboxylesterase (CaE), alkaline phosphatase (ALP), acid phosphatase (ACP), superoxide dismutase (SOD) and glutathione S-transferase (GST). The levels of AChE, BChE and ACP activity were not significantly different between localities. AChE and BChE, commonly used as biomarkers of neurotoxic polluting agents (e.g. organophosphate pesticides) do not appear to be affecting the populations from the study locations. In contrast, the levels of CaE, GST, ALP and SOD were significantly different between the localities. These biomarkers are regularly associated with oxidative stress and processes of detoxification, and generally indicate pollution caused by heavy metals or hydrocarbons, which are common in industrial sites. The data resulting from the analysis of these biomarkers indicate that these polluting agents are affecting the populations of Sceloporus in IP. The present work validates the possibility of conducting additional ecotoxicological studies using biomarkers in combination with a nondestructive sampling technique in species of spiny lizards that are abundant in many North America areas.     

Cholinesterase activities and behavioral changes in Hypsiboas pulchellus (Anura: Hylidae) tadpoles exposed to glufosinate ammonium herbicide

In this study, amphibian tadpoles of Hypsiboas pulchellus were exposed to herbicide Liberty^®, which contains glufosinate ammonium (GLA), for 48 h to the following concentrations: 0 (control), 3.55, 4.74, 6.32, 8.43, 11.25, 15, 20, 26.6, and 35.5 mg GLA L^?1. Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activities, as well as swimming capabilities (swimming speed and mean distance) were measured in tadpoles whose concentrations displayed survival rates >85 %. Our results reveal that sublethal concentrations of GLA significantly inhibited both AChE and BChE activities in tadpoles with respect to the control, showing a concentration-dependent inhibitory effect. The highest inhibition percentages of AChE (50.86 %) and BChE (53.02 %) were registered in tadpoles exposed to 15 mg GLA L^?1. At this concentration, a significant increase of the swimming speed and mean distance were found in exposed tadpoles with respect to the control, as well as a negative and significant correlation between swimming speed and BChE activity, thus suggesting that this enzyme inhibition is related to an increase in swimming speed. Therefore, exposure of tadpoles to GLA in the wild at concentrations similar to those tested here may have adverse consequences at population level because neurotransmission and swimming performance are essential for tadpole performance and survival.